The determination of plathum, palladium and rhodium in autocatalyst. An

exploration of sample preparation techniques for the rapid sequential multi-

elementai ICP-MS analysis

br Mark Payette

Submitted to tbe Department of Cbemishy and Biochcmisty

in partial fiifilment of the requirements for the degree

or Master of Science in Chemistry

Laurentian University

Sudbury, Ont.

lune, 1997

O Mark Payeîte, June, 1997

The author has gnaaed a non- exclusive Licence allowing the National Li'brary of Canada to reproduce, loan, distri'bute or sel1 copies of this thesis in microform, paper or electronic formats.

The author retains ownership of the copyright in this thesis. Neaher the thesis nor substantial exîracts h m it

reproduced without the author's

L'autem a accordé une licence non

Bibliothèqye nationale du Canada de re~foduire, fêter, distnam ou venûre des copies de cette thèse sous la forme & microfiche/i%n, de reproduction sur papier ou sur f m t électroniquee.

L'auteur conserve la propriété du &oit d'auiem qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être miprimes ou autrement reprodinits sans son

The project was to d m l o p a fa and irisxpaisive mabod to eil'ièctively d e t h e

the concentration of platinum, pailadiwn and rbodium in new and used crushed automob'ie

catalytic converters. INCO Ltd., Sudbury Division, Copper Clift: Chrimio. is the iargest

North American autocatalyst r e q d a . The prias paid for the used cataiyst units depend

on the content of the platinum group eiements (PGEs). The buyer's r e a h are compand

with the sdlers results (Ledoux Co.) and if necessary, the resuits obtawd by a referee

laboratory. Enoneous r d t s can becorne a t n w l y costly for the company and therefore

the detennination of platinun, palladium, and rhodium concentration in autocatalyst is of

PreKmly INCO Ltd., Sudbury his ion uses a nickel d d e preconcentration of

the PGEs followed by tellurium coprecipitation. Oace the telluriurn coprecipitate is

dissolved, the samples are thm anaiyzed on both en inductively couple plrisma optical

emission spectrometer (ICP-OES) and an atomic absorption spectrometer (AAS). The

results reported are f?om duplicated aoaiysis which are monitored by the use of sample of

a Certified Reference MaterÎal (NIST 2556 and 2557).

Fue assay preconcentration is a very effective method of removing the PGEs h m

the interferhg mat* that may affect the ICP-OES and AAS r d t s . Unfortunately, tthis

technique requires a dedicated analyst about 38 man hours to perform a single analysis

fiom stm to finish. Thaefore other fmer, and e q d y precise and accurate methods are

king explored. Sincc the ma& of dissolved autocatdyst affects the ICPSES and AAS

results, it was decideci to try the inductively coupleci plasma mass spectrometcy (IB-MS).

With this instrument, ma& affects are minimized and possie interferences can be

prediaed prior to sample anaiysis. This instrument aiso offirs the possibüity of paforming

a fm semiquantitative d y s i s on the sample which wül S o m the d y s t of possible

interferences. Since mat* interferences are no longer of great SiBaificance, samp1e

preparation techniques other than f ~ e a s s ~ y have bem învestigated in this snidy, including

acid dissolution, microwaveasisted digestion and alkali fùsion.

Of the three methods listed above, aikali fusion wu the only method that muid

effectively dissolve the supponiag autocatalyst matrix. As a r d t , the extraction of

platinum, palladium, and rhodium was IarBJy incteased (-100 % for aii PGEs) as

cornparrd to the dyt ica i results nom both &d dissolution and microwaveassisted

digestion. On the other b d , acid dissolution and microwaveassisted digestion were able

to effectively extract platinum and pailaâiwn (> 98%) but d d wt be used to extract

rhodium (- gû?!). It is belîeved that rhodium f o m an undissolvaô1e oxide with the d d

dissolution and microwave-assisted digestion sample preparation techniques thus affecting

the analytical detemination of the spscies. Using a correction fiutor for the rhodnim

element could e m e the use of the acîd dissolution and rnicrowaveassisted digestion

techniques thus providing for a much cleaner dissolved sample for ICP-MS andysis.

Acknowledgments

There have been a host of individuals who have been essential to the completion of

this research project and to each of you 1 am t d y tlilinknil for your patience, kindness and

helpfilness.

To begin with I wouid like to thank Inco Limiteci for pamitting me to use th&

facilities for my research. Without such support many snidents would not have the

opportunity to do graduate research degnes. 1 speak for al1 those students who in some

way have been touched by the kindness of Iaco Limited and other companies like Inco

Ltd..

1 would also like to thank Zbig Waszczylo for his guidance and profound

knowledge of chemistry, Dave Maskery for bis insight and impeccable memory, Phil

Gougeon for his extra tirne, Carmen for his ICP analysis, Dennis and John for their insight,

and al1 those who have directly or indirectly s i e d my grad studies. There are also many

other individuais h m hco Ltd. Central Process Technology Laboratory that L would like

to thank. For those aot listed here, and you know who you are, 1 am very much indebted

to you and 1 thank you from the bottom of my heart.

Lastly I would like to thPnk Dr. J. Bo&, Dr. N. BeIzüe, and Dr. F. Smith for

accepting me as a graduate student, and aiso ali Laurentian Chemistry Faculty for allowing

me to pursue my cûeam.

Mark Payette

Acknowledgment s

Table of contents

Table of Figures

Table of Tables

Chapter 1 Introdudion

1.1 The history, occurrence and importance of platinum group element s

1.2 Autocatalyst composition and chmcterization

1.3 Two-way and three-way catalytic systems

1.4 Analytical methods for the determination of the PGE

1.4.1 The fire Assay pre-concentration method

1.4.2 Acid dissolution techniques on used autocatalyst

1 -4.3 The microwave assisted dissolution technique and autocatalyst samples

i .4.4 The alkaline fusion techaique for used autocatalyst

1.5 Analytical methods for PGE determination in catalytic

converters

1.5.1 Introduction

1 -5.2 Spectrophotorneük (Colorimetric) methods

1.5 -3 GravUnetrîc analysis

1.5.4 X-Ray fluorescence @RF) spectroscopy

1.5.5 Neutron activation anaiysis (NU) 20

1 -5.6 Atomic absorption spectroscopy (AU) 22

1.5.7 Emission speztroscopy (ICP-OES) 24

1.5.8 Inductively coupled plasma mass spectroscopy (ICP-MS) 25

1.6 Purpose and scope of this project 27

Chapter 2 Experîmental Procedures for Autocatalyst Quantification

2.1 Sample pre-treatment

2.1.1 Sample preparation

2.1.2 Sarnple calcination

2.1.3 Sample weighing

2.2 Test Method #1 : Acid dissolution method prior to ICP-MS analysis

2.3 Test Method #2 : Microwave-assisteci dissolution

2.4 Test Method #3 : Zirconium fusion of autocatalyst samples

2.5 Final sarnple preparation step prior to ICP-MS utilizing isotope dilution and interna1 standard techniques

2.6 ICP-MS analysis (Optional Parameters)

2.7 instrumental caiibration and interkence removal

2.8 Selection of intemal standard

2.9 Isotope preparation

Chapter 3 Results and Discussion

3.1 Assessrnent of ma& interferences

3.2 Test Method #1 : Acid dissolution of autocatalyst ssmpls

3.2.1 Introduction

3.2.2 Autocatalyst type affects on acid dissoiution

3.2.4 The effect of leaching time in open beaker digestions

3.2.5 Studying the various acid cornbitions

3.3 Test Method $2 : Microwave-assisted digestion of autocatdyst samples

3.3.1 Introduction

3.3.2 Effect of varying the microwave digestion time

3.3.3 Effect of the addition of HF to the microwave samples

3.4 Test Method #3 : Sodium peroxide fusion of samples

3 -4.1 Introduction

3 -4.2 Problems arising from alkali ma& composition

3 -4.3 Problems due to interna1 standard selection

3 -4.4 Sample drying prior to dissolution

3 -4.5 Effects of sample Ne and qumtity offlux

3.4.6 Automated fluxing

3.5 Sample fision rmlts and discussion

3 .S. 1 Test rnethod #3A : Discussion of remlts ftom mass match4

internai standards.

vii

3 .S.2 Test method 3B: Discussion on nailts &om isotope diiution internai standards

Chapter 4 Conclusion

References

Appendut A Detailed üst of methods and their steps

Appendix B Asset Fies for ICP-MS analysis

Appendk C Seaii-quantitative analysis r d t s of Autocatalyst

Table of Figures

Figure 1.1 Dia- of the two types of automobile catalytic converters.

The fimt (top picture) is the pellet type catalytic converter while

the second (bottom pichue) is the monolithic type cataiytic

converter.

Figure 1.2 Flow-Chart illustrating the recychg pathway of new and used catalytic convertas.

Figure 3.1 The effect of eutocatalyst type on the extracfion of PGEs in new and spent catalyst ushg an aqua regia dissolution to sample dryneu.

Figure 3.2 The percent extraction of PGEs in aushed autocatalyst (NET 2557) and using aqua regi'a over a 4 hour period.

Figure 3.3 PGE recoveries from a variety of acid combinations in open-beaker digestions of MST 2557 (Honeycomb).

Figure 3.4 Calcination r d t s from LECO and water analysis of NIST 2557 (honeycomb) autocatalyst.

Figure 3.5 Calcination nsults from LECO and water analysis of NIST 2556 (Pellet) autocatalyst.

Figure 3.6 Effea ofvarying sample weight on PGE extraction on dned autocataiyst samples(2 Hours @ 500°C) (NIST 2556 Pellet)

Figure 3.7 Effect ofvarying sample weight on PGE d o n on dried autocatalyst sarnples(2 Hom @ 5ûû°C) (NIST 2556 Honeycomb)

Figure 3.8 E f f i of varyiag flux weight on PGE d o n on dried autocatalyst 80 samples(2 Hours @ 50°C) (NiST 2556 Peliet)

Figure 3.9 Effect of varying flux weight on PGE d o n on dried autocatalyst 81 samples(2 Hours @ 500°C) (NIST 2557 Honeycomb)

Table of Tables

Table 1.1 Platinun metals and their neighbors in the periodic table

Table 1.2 Pirysical properties of the platiaum group elements.

Table 1.3 The typical content of autocatalyst Cm Mg).

Table 1.4 Matrix composition (non-certified results) as reported by National

Institute of Standards and Technology În Gaithersbug, MD (1993)

Table 2.1 Operathg conditions for the microwave digestion of a - O. 1 O gm catalyst ample.

Table 2.2 Operational parameters used on ICP-MS for the anaiysis of

sodium peroxide fiision samples

Table 2.3 Spectral removal of possible Merences fiom Cu, Y, Sr, and Pb.

Table 2.4 Relative abundance of natural isotopes used in this project.

Table 3.1 The percent extraction of PGEs in crushed autocatalyst (NET 2557) and using aqua regia over a 4 hour period.

Table 3.2 Efféct of varying the microwave digestion time on SRM 2556 (Pellet)

and SRM 2557 (honeycomb) while digesting with aqua regia and HF.

Table 3.3 Effect of adding HF to the microwave digestion for samples of SRM 2556 (pellet) and SRM 2557 (honeycomb)

Table 3 -4 Perceni difference for MST 2556 somples dissohred using microwave dissolution and not treated with HF,

Table 3.5 Percent Werence for NIST 2556 samples disrolved using microwave dissolution treated with HF.

Table 3.6 Percent differeuce for MST 2557 samples dissolvecl

using microwave dissolution and not a a e d with HF.

Table 3.7 Percent Werence for MST 2557 saxnples dissolved ushg microwave dissolution treated with HF.

Table 3.8 Repeatability of microwave resutts for MST 2556 and 2557 samples wiîhout HF.

Table 3.9 Repeatability of microwave redts for MST 2556 and 2557 samples with HF.

Table 3.10 Cornparison of ICP-MS nsults validating the addition of 2 mL of concentrated HCl to the aspirated sample to help improve the accufacy of PGE determination and remove the bias.

Table 3.1 1 Percent merence of ICP-MS results using Ntheniurn and thallium intemal standards.

Table 3.12 Precision of ICP-MS results using nithenium and thallium intemal standards.

Table 3.13 Percent difference of ICP-MS results using indium and indium intemal standards.

Table 3.14 Precision of ICP-MS m u h s ushg iridium and indaun intanal

standards.

Table 3.15 Wata concentration of previoudy dned and d y z e d a u t d f i c

samples.

Table 3.16 ICP-MS results fiom wet and dried NIST samples

Table 3.17 Relative error involved with hand &ion of standard reference materials

Table 3.1 8 Percent Ilifference involved with the automatic fision of standard rderence rnatezials

Table 3.19 Repeatabiliîy associated with hand fusion of autocatalyst

Table 3.20 Repeatabüity associated with the automatic fusion of autocataiyst

Table 3.2 1 ICP-MS results for Pt determination compared with nickel sulfide fire-assay and phosphoric acidffire assay.

Table 3.22 ICP-MS results for Pd d e t e m i d o n compand with the nickel alfide 91 fire-assay results and the phosphoric acidlfire-assay results.

Table 3.23 ICP-MS results for Rh detemûnation compared to the nickel sulfide fie-assay results and the phosphoric acid/fire-assay results.

Table 3.24 Percent difference of ICP-MS results using ptlgg and ~ d ' ~ isotopes and indium intemai standards

Table 3.25 Precision of ICP-MS results using and ~ d ' " isotopes and

indium internai standards.

Chapter 1 Introduction

1.1 THE HISTORY, OCCURRENCE AM) IMPORTANCE OF PLATINUM GROUP ELEMENTS

The platinum group elanents (PGE) wasi*st of platinuni, palladium, rhodium,

iridium, osmium, and mthenium and of these metals generdy occut together in nature

(Vines, 1941). They are best known for their s p d c traits. Generally al1 PGE elements

are very rare, heavy, white to grayish-white in color, highly resistant to corrosion, and

bave high melting temperatures (Bugbee, 198 1).

The first known people to recognize platinum as a separate elernent were the Re-

Columbian Indians of Enrador who worked the metai into most of their native jewelry.

The £ k t reference to the metal was in a commentary by Julius Caesar Scaliger published

in 1557 after sending a sample to Spain with a letter saying that the metal wouid not melt

by fire or by any Spanish art known (MacDonald and Hunt, 1982). It was not until 1735

that the alluvial platinum h m Spanish New Granada (now Columbia) was regularly

coileaed and sent to Europe for refhing and fabrication (MacDonald and Hunt, 1982).

The next piatinum deposit to corne into production was in the Ural mountains in

Northern Russia in 1824. This platinum was to be the first water-borne grains of platinum

found to be interlaced with a gold deposits. At the the, the Ural mountains were rnined

for gold but at a later date platinum was aiso extmcted. Unfortunately, the Russian

revolution intemipted the much d e d platinwn supply. As a r d t of the Russian

revohrtion, other platinum containhg ore bodies were required to Satie the growing

demand for the PGE metals. Swn after, pktinum was found by Merensky in South A f b ,

in what is now named the Merensky r d This new deposit helped to bll the plaîinum

demand. In 1930, Canada dm joined in the -011 and rehhg of platinum. This

platinum was a byproduct of the copper-nickeI'deposits found in the Sudbury district of

Canada and it was mined and r&ed by Inco Limited and Falconbridge Limited. To this

date, oniy Canada, Russia, South Afnca and Cohnnbia refbe and seif platinum metals.

The piatinum m a s include the elements in groups 8,9, and 10 of the 2d and îd

transition periods. Their position within the paiodic table as well as th& local neighbors

can be seen in Table 1.1 (Lide, 1991). Some of the reiated physicai properties to the POE

metals are üsted in Table 1.2 (Cabri, 198 1).

The industrial utüuetion of the platinum metais is continually expanding which

increases the demand for the already scarce metals (Cowley and Matthey, 1996). Thy an

mostly used in the automobile, petroieum, medical, and chemicai industries but as well

have many rninor industriai uses. The largest danand for plaîinum, paîldium md rhodium

is in the automobile industry (Cowley and Matthey, 1996). These three met& are used in

the automobile catalyst convaters for the conversion of toxic exhaust gases f?om

automobiles into non-poUuting gases.

Table 1.1 PIatinum metals and theu neigbbors in the periodic table

Atomic Number

Elernent

Atomic Weight

Atomic Nwnber

Element

Atomic Weight

Group 11 Group 6

24

Cr

52.0

Atornic Number

Element

Atomic Weight

Group 7

25

Mn

54.9

42

Mo

95.9

43

Tc

98.9

74

W

183.8

75

Re

186.2

Table 1.2 Physical prope!rties of the platinun group elements.

Note:

a) HCP = hexagonal cl&-packed

FCC = fii-tered cubic

HCP

3030

5027

8.7

22.5

129.3

9.50

300670

B!

FCC

1555

3140

8.33

12.0

244.3

10.5

404~

1.278

1.373

117

172

. 1

Latrice stnicnire'

Mclting point, OC I

Boiling point, OC

First ionization potemiai, ev L

Dcnsity a i 20°C, ~gm.~* W3 1

Specitïc heat ai O°C, JKS'F' 1

Resistivity microhman I

Hardness, anneaiecl, VHN

C d n t radius, A

Atomicradius,A(12-foldCoordinotion)

Modulus of elanicity in tension, lcNms* lad I

Tcosile men@, annealeû, kNmm2* 10-~

FCC

2454

4130

9

22.4

128.4

3.30

2001210

Rn

HCP

2334

3900

7,364

12.2

230.5

7.60

200-350

1.241

1336

416

4%

FCC

1768.4

3827

8

21.45

131.2

10.6

-2

Rb

FCC

1%7

3727

7.46

12.4

26.4

4.51

100-102

1.247

1.342

3 16

688 L

1.2 AUTOCATALYST COMPOSIT~ON AND CWRACTEREATION

Automobile cataiysts are essdally comprised of a d b t o r y olride canier on

which two or more pncious metais are dispersed in very low concentrations. T w o types

of carriers (or substrates) are wmmonly used. The monoiithic (or honeycomb) type whose

body comprises cordierite (2Mg0.2A12a.SSi&) with a su& coating (1% by weight

of cordierite) of predorninantly y-Ai& to provide a hi@ mufiace area film on which the

PGE is dispersed. The bead type catalyst is comprised of individual W s (either 3.2 mm

spheres or 3.2mm x 6.3mm cylinders) made of y-Al2@ (Mîshra, 1993 ). The PGE loading

and weight of autocatdyst is dependent on the size and make of the automobile. nie ratio

of Pt, Pd, and Rh also varies widely. Typicaiiy the content of the POE is shown in Table

1.3 (Mishra, 1993 ).

Table 1.3 The typical content of autocatalyst (in pg/g).

Bead (2-Way) 350 150 - Bead (3-Way) 850 300 60

Honeycomb (2-Way) 900 300 - Honeycomb (3-Way) 1100 300 100

The catalyst wiil sometimes contain other proprietary components such as nickel

oxide (NiO) and cerium oxide (CeO) to help stabilkhg the bigh surdice area of Aiz03.

The spent autocataîyst also contciins various types of impurities. Lead, Manganese,

Carbon, Sulfiir and Phosphonis are picked up Born p w h e and oil additives. Süica, bon,

and Chromium are picked up h m the d d g operation. The pcesence of these

elements mua be taken into rccount when devishg anaiytical rnethods since they wül play

a large role in the deteInhaîion of the PGE dements. Table 1.4 below üsts the non-

certifieci results of the m a t x composition of both standard derence rnatds (SRMs). It

is estimateci that in 1985.50 percent of dl catalytc converters w a e recycled.

Table 1.4 MatrUt composition (non-certified results) as reportai by National Iristinite of

Standards and Technology in Gaithersburg, MD (1993)

Element Concentration, Method

wt % (mgKg x lo4) of analysis

SRM 2556 SRM 2557

(Pellet) (Honeycomb)

AIuminum (Al)

Barium (Ba)

Calcium (Ca)

Cenum (Ce)

Iron (Fe)

Lanthanum (La)

Magnesium (Mg)

Nickel (Ni)

Silicon (Si)

XRF, INAq ICP-MS

XRF, ICP-MS

XRF, ICP-MS

XRF, INAq ICP-MS

XRF, INAA, ICP-MS

XRIF, INAq ICP-MS

??

XIRF

XRF, ICP-MS

Element Concentration, mf lg Method of Aaalysis

Barium (Ba) 100 NIA XRF, ICP-MS

Cadmium (Cd) N/A 44 XRF

Zinc (Zn) 600 IO00 ;WF, INAq ICP-MS

Zirconium (Zr) 300 300 XRF

As mentioned earlier, the automobile industry is the p h u y indu- that uses

Platinum, Palladium, and Rhodium in automobile d y s t s . The purpose of the utdyst is

to convert toxk exhust gases h m fbel oornbustion into a non-toxk and less pobthg

form. In 1975, aii North Amencan vehicles were required by Law to be fitted with catalytic

converters foiiowing environmental pmblems cesuithg bom 'automobile use in large U.S.

dies (Brown et al., 1991). Similar actions have now been taken in lapan, Europe and also

Mexico. A large amount of platinum, palladium and rhodium is used annually in the United

States and Canada for this purpose, representing a major source of consumption for these

elements.

The old cataiytk converters were peIIet fom 2-way catalytic converters. These

catalytic converters contained d quantities of platinum and palladium and were used

for the oxidation of the hydrocarbons (HC) and carbon monoxide gas. Both hydrocarbon

and carbon monoxide are dangerous gases but the oxidized forms Ca or HB are

acceptable pon combustion by-products. The conversion of the gases is show in the

unbalanced reactions (1) and (2).

2c0+o2 PtSd P 2 C a (Acceptable gases) (1)

HC + 0 2 PtJd CO2 + HzO (Acceptable gases) (2)

With the advent of the Clean Air Act in 1985, it was requind that engine emissions

drop by 35% for hydrocarbon and carbon monoxide and also 60% for NOK. Therefore the

two-way converters were no longer &ectve. As a result of the Clean Air Act, rhodium

was now required for the reduction of NOx into the Iess toxic N2 gas as seen with the

unbalanced ceaction (3).

NO + 2 CO --k, N2 + 2 C a (acceptable gases) (3)

The 3-way catalytic converters have dm changed in fom The PGEs are now

deposited omto a honeycomb sûucture composeci of cordierite. A diagram of the two fonn

of catalytic convertas can be seen in fip 1.1. Ali automotive companies now use the

three-way catalyîic converters and mat the autocataiytic honeymmb ma& with a 0.2%

platinum, palladium and Rhodium solution.

Various wmpanies purcbase quantities of these used autocatalysts for the recovery

of these platinum group metais. Figure 1.2 is a flow chart iiiustrating the recycling of

catalytic converters. Due to contractual obligations, analytical results are of parmount

importance since they dictate the purchase valw of the recyclable matenals.

Figure 1.1 Diagram of the two types of automobite caîaiytic convatas. The th (top

picture) is the peuet type catalytic converter whüe the second (bottom

pi-) is the monoüthic type d y t i c converter.

Figure 1.2 Flow-Chart iiiustrating the recyciing pathway of used catalytic converters.

Con

Catalyst Manufacturer

Production Swap

Junk Yard Big Collector

Swap Yard Small Collector

Auto Crusher ,

1.4 ANALYTICAL METHODS FOR THE DETERMINATION OF THE E E

Most instrumentai techniques listeû below require the amples to be dissolved or

undago some type of sample hancihg pnor to instnunental adysis. For PGE

daermination, the most popuiar technique iwoIves a sample pre-concentration aep

foiiowed by instrumental detemination of POE oonentrstions. The most cornmon and

widely used pre-concentration technique is the ciassical fireassay technique @ugbee,

1981, Smith, 1987). Fire-assayhg is a highly sensitive pre-concentration mahod for

plathum, paiiadiwn and rhodium detemination. A brief account of the hassay

procedure is given in section 1.4.1.

There are some reports of alternative methods to fie-assay for sample preparation

in autocatalyst analysis. Beary and Padsen (1995) of the National Institute of Standards

and Technology (NIST) used a hot chîorine Carius Tube dissoiution method in the

certification of SRM 2557 (monolith), and SRM 2556 @elle$). This was followed by

isotope dilution inductively coupled plasma mass spectrometq (ID-ICP-MS)

determination of Platinum and Palladium and an intemal standard ICP-MS determination

of Rhodium. This dissolution method does not readily lend itseif to routine application, so

other techniques were explored. The dissolutioa techniques investigated in this work focus

on a hot plate atid dissolution technique, microwaveassisted dissolution technique, and

the sodium paoxide fusion technique. Each of these dissolution techniques will be briefly

discussed.

1.4.1 THE FIRE ASSAY PRE-CONCENTRATION METHOD

Procedures to perfonn a basic fire assay were published by Vannoccio Biringuccio

in the sDaeaah cenhiry. In most cases, it is used as a methoci of qumtitative analysis of an

ore - that is, to detemine the amounts of gold, silver, and 0th- vehies in ore in the ounce

per ton range. Fie assay is dso appropriaîe for samples that are inhomogeneous in nature

wbich therefore rquire large sample size to ensure quantitative rapresentative r d t s . The

material for analysis is nised in a ttrnaca with a flux mixture. The method is applied t d y

principally to the detamination of PGEs. Sihw. gold, tin, coppa, and merauy in ores

may alsa be detennined by fireassay m&ods. In each instance, an doy phase tbat

contains the dissolved anaiyte is produceci. The d o y phase is then dissoived and anaiyzed

using a variety of chemical or instrumental techniques to establish q d a t i v e l y the

andyte content.

The collector that is used for the alloy phase plays a large role in the quantitative

detennination of PGEs. nie most popular coilectors are sîlver and lead or a combination

of the two. In 1975, Steele reportcd that 92 % of all platinun concentration

determinations for the South Afncan Ore Certification program used lead as the cokctor

in their fire assay (Steele et al., 1975). Lead comb'ied with silver as a fire assay coilector

has dso been used for the isolation of platinun, palladium and rhodium (Beamish, 1966).

Unfominately neither of these colîectors proved effective as an isolator for rhodium. Ti

(Sn) has also been used as a fie assay collector for PGE with disappointhg results (Faye

1965). In 1992, Tuwati used gold as a collector for the isolation of platinum, palladium

and rhodium fiom autocatalyst (Tuwati, 1992). He reported a collection of 99+ % of the

platinum and palladium and 99% of the rhodium. A disadvantage of his tezhnique is the

relative high cost of gold as a collector. In addition to the above mahoâs, fie-assaying

procedures using nickel sulfide have been widely used (Robert, 1971). In 1987, Date et

al., also studied the use of nickel suffide as a collector for POE in geological samples pnor

to ICP-MS analysis (Date, Davk, et Cheung, 1987). Keyworth (1982) descnied a detded

listing of cost, loss, operating ranges, seprational losses of PGEs while using various

collectors. The nickel &de tire assay pre-concentration technique for the determinafion

of PGEs in used autocatalyst and 0 t h samples foliowed by ICP-OES and AAS analysis is

comidered one of the most precise and accurate methods avaiIabk for PGE

determinations.

The 4 amount of PGEs tbrt stay in the da$ during tâe nickel &de Mon step

are anaiyzed through a lead bead wliection procedure and a h a i meastarement is done by

ICP. The results ofthe lead b e d analysis are then added to the nickel sulfide r d t s .

1.4.2 ACID DlSSOLunoN TECHNIQUES ON USED AUTOCATALYST

Noble m d s wae thus designated because of their relatively high resistance to

anack by chemical agents. Single minerai &d attack on properly aatlealed noble m d s

shows little effect on the metals. Van Loon (1977) reported thgt wen a quantitative attack

with aqua regia showed littie e&ct on a platinum wh. Howewer, it has ben show that

hely divided palladium metallic residue was completely dissoived ushg hot HCI.

Therefore the degree of division, degree of compaction, metallurgical histoory and the

presence of hnpurities will play a large rok in sample dissolution. Thae exist a number of

prefened approaches for metals decomposition but the choiw of one of these is dependent

on the partidar metal as well as the factors listed above.

Aqua regia is the most commonly used combination. This consists of 3 parts

hydrochloric acid and 1 part nitric acid. It is thought to contain unstable mixture of Eiee

chlorine, nitrosyl chioride (NOCI), NO, gases and âee HCI and H N 0 3 . Its &cacîty is

attributed to the oxidïzing power of fiee C ~ I O M ~ in aqueous solution as wefl as the

complexing power of the chloride ion Accordhg the American Standard Materials (MM-

1994), aqua regia wiil dissolve platinum and palladium quite readily if they are fhely

devided. Unfortunately, qua regia also oxidizes rhodium thus forming an insoluble

rhodium oxide @ha). Strong and Murray-Smith (1974) used aqua regia to dissolve

geological samples for the detemimation of gold. Aqua regia has been mixed with other

acids to increase geological sample dissolution. Gowing and Potts (1991) examined how

aqua regia dissolveci geological samples for the determination of gold and PGE's. They

reported 100 % dissolution of gold and palladium, 18 % dissolution of platiwm and

rhodium, and littie attraction of the remahhg PGE's. Kuo-Yrng et crl. (1993) anaiipted

various acid combinations for the dissolution of PGE's in an eutomobile catalyst. AU but

two acid combïitions werc ineffiective extractors for rhodium while aii provided

quantitative extraction of phtinum, aad p d d à i m The two acid combinations were a

HClE@OJH& combination and the second was a H&)/HCVHZSOr/H2& combomtionR

1.4.3 TEE MCROWAVE ASSISTED DISSOLUTION TECHNIQUE AND

AUTOCATALYST SAMPLES

The micr~wave~assisted sample prepmtion technique is r a p i e becoming a widely

used analyticai tedmique due to its ability to quickly d idve inwutable geological

matrices consisting of refhctory materials which are normaily resistant to acid attack. The

introduction of microwave assisteci pressure dissotution has been a mjor advance in

geochemicd Pnalyois and it is now regarded as a substitute for acid dissolution, pressure

bomb dissolution, Carius tube dissolution and alkali fusion dissolution for geological

samples. The principle is simple. A sample is weighed and placed into a PTFE vessel.

Acids are then addecl and the mixture is then agitated to promote thorough ming. Once

the initial reactions are complete, the vessel is d e d . The seal contains a membrane that is

mptured if the pressure within the vessel becornes too hi*. The vessels are then put into a

carousel that can hold twelve PTFE vessds and placed into the microwave oven. The

contents are irradiatecl with microwave mergy and the contents of the vessel are quickly

heated. At the same tirne, the pressure withîn the vessei rises. This aliows the acid attack

on the samples to take place at considerably higher temperatures which inmeases its

Several references exists which cover the applicab'ity of this technique to

geological samples. Kokot et al. (1992) have thoroughly d e d the applicab'rlity of

microwave dissolution to various samples as weii as various acid combinations and

microwave programming. Ginepro et aL (1996) have used the microwave oven for the

daennination of heavy metals in seâiments using miaowave desorption and Tessier

sequential extemai oxidation of metai aquatic sediments. Yi and Msswida (1995) and

Beary a al. (1994) both studied the use of microwave dissolution and isotope dilution

ICP-MS to the anaiysis of PGEs in gwlogid samples. Nowinski and Hodge (1994)

studied the applicability of rniaowave dissolution of ore samp1es for gold and platinm

group metals prior to ICP-MS anaiysis. Totluid a al., (1995) have wmpued microwave

dissolution results to o h dissolution techniques u s d for geologid ample aailysis.

Sample dissolution via the rnicrowave has ais0 k e n extensiveiy miewed by Smith and

Anenault (1996).

There appear to be no reports in the literature of the microwave dissolution

technique appiied to the analysis of autocataiyst samples.

1.4.4 THE ALKALINE FUSION TECIINIQUE FOR USED AUTOCATALYST

There exist a large number of matenals that are resistant to the strongest hot

mineral acid attacks. Even using a combination of concentrated hot mineral acids has

proved inefG6Ctive for the dissolution of these matenals. Among these matenals is

cordierite which is the supporthg matrix used in the production of honeycomb automobile

catalya. Unlike the Y-alumlliia used in the pelle$ fom of the autocatalyst, wbich is readily

dissolved using concentmted hydrofluonc acid, cordiente is artremely resistant to mineral

acid anack. Therefore altemative techniques are required for sample decomposition.

Alkali fbsion is one technique that can be used. This meîhod rquires the sample to be

finely ground and mixed with an acidic or basic flux. The proporiion of sarnple to aux

varies fiom 1 :2 to 1 5 0 and the sample and flux are bseû in various types of crucible. The

choice of crucible is dependent on the flux chosen as descrihi by Anderson (1987). The

crucible, sample and flw are then heated into a clear melt and cooled. Next the samples

are dissolved in a concentrated mineral acid combination und then diluted for instrumental

analysis. For our purpose, the flux chosai was the basic sodium peroxide flux which is one

of two fluxes capable of disso1ving cordierite. The extrane oxidizing nature of the sodium

peroxide flw required the utili2ation of a zirconium crucible as d e s c r i i by Anderson

(1 987).

The use of an elkali hion to digest Uwluble residues prior to PGE detemination

has been used with varying degree of sucass. Brown and Biges (1994), Hodge et al.

(1986)' SenGupta (1989) and SenGupta and moire (1989) have all used aIkali fusion to

dissolve geological amples prior to Pa's and Au determination. Totland et ai. (1995)

studied and comparexi resuhs from an aikali hion on refmence materials to those of

mimwave dissolution of the saxne samples. In most cases, Plkali &sion gave excellent

sensitivity, and results compareci extmnely w d mth the certifieci vaiues. Enzweiler et al.

(1995) studied the applicability of aikali fwion for the determination of PGE's in

geological samples. There appears to be no published reports covering the use of all<ali

fiision to the daennination of PGEs in autocatalyst.

Alkali fusion provides a means of dissolvhg autocatslyst samples but does not

provided the abiüty to separate the PGEs fiom the supporting maaix. Its applicability to

AAS and ICP-OES requires caution to avoid various interferences of extemal elements

found within the samples' supporting rnatrUr. On the other han& fused samples and@

by ICP-MS do not d e r Eoom the sarne spectral interferenas that affect the ICP-OES and

AAS and can therefore be used to detamine PGEs in dissolved alkali fused samples. One

problem with the use of ICP-MS analysis for dissolved alkali fised samples arises from

salt fomtion. The sarnple solution contains high sodium and chloride concentrations

which can lead to salt formation. Salt can plug the ICP/mass spectrometer interface so

sample solutions require considerable dilution prior to sample anaiysis.

1.5 ~ ~ A L Y T I c A L METHODS FOR PGE DETERMINATION IN CATALYTIC

CONVERTERS

Platinum group elements are present in most esrth-dace materials at trace

concentrations. The PGEs play an extremely important role in seversil major industries.

Therefore, the ability to d e t h e these elanente is important for researchers linked to

PGE utiiization. A variety of anaiytical methods have been appüed to POE analysis in

various samp1e types. These methods inchide spectrophotometric (colorimetrîc),

gravimetric and titrimetric detenninations, x-ray fluorescent spectrosopy m), neutron activation analysis (NAA), atomic absorption spectroscopy (AAS), emission spectroscopy

(ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).

1.5.2 SPECTROPHOTOMETRIC (COLORIMETRIC) METHODS

Spectrophotometric methods were the mainstay of trace maals analysis pnor to

the introduction of modem instrumental techniques. Spectrophotometry is a mature and

inexpensive method for analyzing PGEs. It is ohn considered to be one of the best

methods for analyzing PGEs. It is carried out by way of absorbance measurements d e r

the appropnate reagents are added to develop a chatactezistic d o r . Depending on the

sample composition, several steps may be required More quantitative analysis can take

place. An example of the spectrophotometrîc detennination of platinun, palladium and

rhodium is as fol ows.

Platinum is quantifieci using a concentrated HCI solution with the subsequent

addition of tin 0 chlonde. The quantitative absorbance of the platinum chlonde is

measured at 403 nm. The sensitivity for this platinun determination is 0.03 ppm whüe

using a 10 g sample (Wagner, 1955). Another specaophotometric determination for

platinwn determination requires the use of gnitrosodimethyianaiine (Yoe rnd Kirkland,

1954). In this case, the smsitivity was 0.0029 pg and a working d i of 0.015ppm

was found while using a lm ceil. The optimum range for platinun detennination ranges

between 0.7 to 2.4 ppm and the precisioa for this technique ranges ôetween 1.4 and 3.û%.

The c o l d solution shows absorbrma maxima a 550 and 525 nm, the latter being used

for the absorbance measurement. The color is due to two diffamt comp1exes, one bang

Pt[(CH&N.C~O]~Cl2.

Many reagents can be used for the spectrometric detemination of patladium

concentration. The most promising of these is 2,2-dipyridUieketoxime which was

developed by Holland and Bozic (196%). Palladium reacts with the reagent to fom a water

insoluble chelated complex whkh can be readily extracteci by the use of chloroform at a

pH of 4-5. Beer's Law is followed oves a concentration range between 0.5 to 10 ppm with

the maximum at 410 nm being used for analyticai quantification of palladium. hie to the

possibility of interferences, ethylene diaxnine tetracetic acid (EDTA) is used to mask

nickel, copper, iron, and cobalt.

To determine the rhodium concentration by spectrometry, one d d use a 1-to-1

mixture of 1,44iphenylcarbazide and 1,4-diphenylcarbazone. This mixture would react

with the dominant rhodium @I) salts to fom a purple complex of unknown structure

(Ayres and Johnson, 1960). The optimum range is 0.3 to 1.5 ppm while using a lm

optical path and the optimum wavelength for absorbame measurement is 565 am. The

color is developed in a perchloric acid m e b of pH 3.0. Reported imerfkrences are Ir,

Fe, Co, Ni Pb, and Cu. Both the acidity and concentration are criticai.

These methods are often quite difncult to carry out successfûliy, with a variety of

criticai factors. Some of these are pH, reagent concentration, time, temperature, order of

mixing reagents, stab'iiity, masking of interférences, organic solvents and salt

concentrations. However, under favorable conditions, the colorimetric methods offer good

seositivity in the microgram range (Beamish 1965).

1.5.3 G R A ~ C ANALYSIS

Gtavimetn0c methods have hktoncally played a large role in the daetmination of

PGE metals; but due to their relative costs (manpower, and time), many iaboratork~ have

opted for the more rapid instrumental anaiyticai methods. As a resuit, there has been a

generai move away h m the relatively slow but extremely accurate precr*pitation methods.

Nevertheless, gravimetic methods sti l l play an important role as the final arbita of

quantitative composition, in the appropriate concentration range (> 1% PGE).

Generally, platinwn group met& do not occur aione in samples. Therefore when

exploring gravimetric methods, one must employ severai isolation steps for the final

concentration detedat ion of aii PGEs. The foiiowing will demonstrate how isolation

and gravimetric analysis can help to d e t e d e the concentration of platinum in a platinum,

palladium and rhodium mamire in a chlorinateci solution. The first step involves the

addition of sodium bromate pnor to boiling foUowed by solution neutraliuition (pH = 7.0).

This aep causes the precipitation of palladium and rhodium as hydrated dioxides thus

leaving platinum in solution done. The next step involves the bubbling of hydrogen suifide

(&S) gas into the platinum containhg solution. This r d t s in the formation of a black

plathum sulfide precipitate. The platinum sulfde is then separated and heated to 750°C

leavhg the Pt metd for quantitative anaiysis (Güchrist and Wichers, 1935). Mooiman

(1993) has reviewed the various published techniques for noble metal extraction by use of

organic solvents in dilute solution. De a al. (1970) also wver many dserent solvent

extractions for noble metals in theù book

The use of x-ray fluorescmce specaoscopy is often the favored method due

to t s speed and also because of its abi1it.y to anaîyze simples non-destructively. The main

19

drawback to this method is b ladr of sedivity for the PGE m a s where it is limited to

samples with milligram or higher concentrations and the neeâ for simiiar standards that

closely match the matri.< of the samples. XRF can be used to anaiyze !amples with no

prior pre-concentration steps. One such example is Giauque a al. (1977) who apptied

XRF to the detemination of 40 elernents including PGEs in various sample matrices.

Many methods have been developed for the x-ray fluorescence anaiysis of noble metaIs,

after separation and pre-concentration of the elements has been achieved. Predominaat

among these is lead bead fire assay pre-concentration of aoble metals foilowed by a

tlattening and annealing of the bead which is then piaceâ into the ample holda and is

anaiyzed for PGE concentrations. Tnere are dso reports of PGE analysis on impregnated

fiiter paper containing the pre-concentrateci noble met& (MacNevin & Hakkita, 1957).

Neutron Activation Analysis (NAA) has played a major role in establishg the

geochemical data base for PGE in rocks. The main reason for this is that NAA is very

sensitive towards PGE's and it can avoid most of the contamination problems typical of

wet chemical analysis in the ppb range. For example, NAA is dc ient ly sensitive to

measure the six PGEs in moa un-aiineralized ultramafic rock on samples of 100 mg or

less without any type of pre-concentration of the metais (Cabri, 1981). The acairacy

obtained h m this anaîysis is typically 11 5%. In practice, rhodium is not detemiiwd due

to its derivative's short haElif'e (4.4 minutes). Otherwise, activation techniques are

probably unqualled for the detemination ofsubmicrograin traces ofmost maals. Using a

flux of 5x10~' neutrodcm2.q neutron activation is at least one order of -tude more

sensitive for most platinum group elements then the ks t spectrophotometric method.

With this flux, the sample absorbs the neutron to fom artificial short-We radionuclides . The radioactive spectnim of the radionuclides, once fomeâ, are memureci and interpreted

in ternis of guantity of the various elements present.

For used automobile cataiyst, there exist no pubüshed reference methods focusing

on NAA d y s i s , but thae are a iixnited number of publications which review the

application of NAA on PGE anaiysis for geological samples. Crocket et al., (1968). De

Wet et ai., (1971), Gijbeis and Hoste (1971). Millard and Bartel (1971), Nadkami and

Momson (1974). Gilbert et al., (1977) and Hofnnaa a al. (1978) have (in pubfished on

NAA d y s i s for PGEs in rock and ore samplos. GjWs and Hoste (1971), Crocket

(1968), Gjbels and Govaens (1973) have al- mviewed the application of NAA analysis

to the PGEs. In their researches, they have presented two separete methods of NAA for

the detennination of PGEs. The first method is Radionuclides Neutron Activation Analysis

(RNAA) which requires no prior sampIe preparation. The second is Instnimental Neutron

Activation Analysis @UA) and requires some sort of prior sample preparatioa such as

Radionuclide Neutron Activation Analysis (RNAA) has been extensively applied to

geological studies of un-mineralized rocks. It hes proven highly effaaive for Pd and In but

is somewhat less usefùl to Os, Ir, and Pt and totally ineffectve for Rh (Cabri, 1981, De

Soete et al., 1972). Crocket et al., (1968) developed an RNAA method for the analysis of

Ru. Pd, Os, Ir, Pt, and Au in geological sarnples. Small arnounts of sarnples (100-200 mg)

where first mixed with non-radioactive carriers of those elernents and irradiated (Crocket

et al., 1968). The results reported by Crocket et al. showed RNAA's inability to

efktively d e t e d e Pt, Os, Ir. Nadkami and Momson (1974) also stuclied the use of

RNAA for the detennination of Au, Ru, Pd, Os, Ir, and Pt in gedogicai materials while

ushg a Strafion N.M.R @olycyclc-NBL47) ion exchange resin. Again, the results

indicate a Wted abiiity to eîZ&vely m a u r e Ir, and Os. There are o t k reports

descnig RNAA analysis of geologicai samples, but MM report good results for

platinun, and rhodium which suggests that RNAA may not be appropriate when analyzing

automobile catalytic converters.

Instrumental neutron activation anaiysis (INA) is the second method. This

method generaîiy requires a p r e - c o n d o n step prior to quantitative analysis of various

materiais. It has proven higbiy efEective for the PGE determination in &de beMag

rocks. Turkstra et el. (1970) were able to deterxnine Rh, Pd, Au, Pt, Ir, and Ag in fused

ores, concentrated mattes and lead fie-assay beads via INAA. In thgr research, th- were

able to quantitatively measure Ir, Pt, and Au in South A£ncan ores, and hi&

concentrations (15-500 ppm.) Rh, Pd, Ag, Ir, Pt and Au in mattes. Lead firr-assay beads

nom the South African ores allowed for the high concentration determinations of Rh, Pd,

Ag, Ir, Pt and Au. H o h et al., (1978) demonstratecl tbat INAA could show supaior

accuracy and precision than most dyt icai methods present in 1978, exclucihg ICP-MS.

There are no reports of INAA for the anaiysis of autocatalyst sarnples.

The only major disadvantage of NAA techniques are the instrumental costs,

availability of suitable irradiation sources, and the tirne requued for dyti*cai analysis. It

has also proven to be ineffeaive in determinhg platinum and rhodium quantitatively

(RNAA) and also lacks sensitivity (INAA) for all three PGEs in autocatalyst.

1 S.6 ATOMIC ABSORPTION SPECTROSCOPY (AAS)

Atomic absorption spemoscopy (AM) is the measurement of the absorption of

opticai radiation by atoms in their gaseous state. The phenornenon of light absorption by

liquids and crystals dates to the 18" century. It was not for many years that the maiytical

applications and instrumentation became avdable to perform empirîd anaiyticai

determinations In 1963, Walsh and Haussman (1963) developed a method for the analysis

of PGE's by AAS. This is considered to be one of the major landmarks in noble metal

analyticd cherni-. Although not enthusiastically received in North Awrica until 1964,

the technique was ixnmediately investigated for noble metai analyses partidarly by

Austraiian and South Afncan researchers. At the present tirne atomic absorption

spectroscopy is the most widdy u d detemimion tool for these metais. The basic

hctionality AAS is quite simple. A dissolved somple is aspirated h o a hot flme where it

is atomited. Upon atomization, the atoms absorb the characteristic iight emitted fiom a

holiow cathode lamp WCL) and the difference between the incident light and the

absorbeci light is subtracted and used to empiricaiîy quanti@ the concentration of the

element wncerned.

The depressive intetzlementd interferences orperienced in aiomic absorption

qectroscopy in the determination of noble metals are more cornplex than for most other

elements and therefore serious problems have Mm (Janssen and Urnland, 1970).

Fortunately there exist extensive interfîmnce studies that propose a wide variety of

remedies to help in the analysis of PGEs. The d e s t remedy is to use releasing agents to

block extemal inter-elemental interfierences wiih the noble metals. One mch case is the use

of vanadium to help in determining Pt, Pâ, Rh, Ru and Au in geologicai sample~.

The second possibiiity to overcoming the depressive inter-elemental interfierences

is through the separation of the noble maals tiom their interfering mat& This approach

has attained the greatest popularity for noble metals determination. Neo-classical fire assay

is by far the most widely used sepadonal technique. Mer sepmtion, a releasing agent is

added to block noble metals fiom interfering with one another. Le HouiXer and De Blois

(1986) used silver to collect Pt, Pd, and Rh îrom geological samples foilowed by an

alkaline cyanide solution dissolution Vanadium was used to correct for eIemental

interferences. The remlts were promising with the exception of Rh which is aot properly

coiiected by silver. Schnepfe and Grimaldi (1969) used gold to wUect Pt, Pd and Rh ftom

a geologicai semple followed by an aqua regia dissolution. They fomd tbat wpper sulfate

can enhance the Pt sensitivity by as much as 5W and that lanthanum chlonde could also

be used to prevent Rh interferences with Pt. In thQr research they showed that PGE

extraction fiom the AAS anaîysis samples showed an excellent correlation to

spectrochemical and chernicd results. The copper and Lanthanum combination has also

been shown to eüminate Pt, Pd, and Rh interferkg with one another.

As with 1 AAS work, noble metais also d e r Born problems associated with

elemental determinations. These problems are : Doppler and pressure h e broadening,

resonance broadenuig, limitations imposed by the absorption cocfncient of transition that

gives rise to the particular line u d (flame temperature innuences it), interferences due to

inwmplete isolation of the emitted opticai h e , and the dependence of sensitivity on

opticai path length and other events in the flame. The background due to absorption by

molecular species also poses problems (Koirtyohann and Pickett, 1966).

This technique requires a srnail amount of the solutioa to pass into a plssma where

it is not ody atomired but also energized to emit al1 possible spectral lines through

electronic excitation. The intensity of the spectral lines is proportional to the concentration

of the species in solution. This provides one large advantage over atomic absorption

qectroscopy in that it pennits simuhaneous multi-element d y s i s over a large linear

dynarnic range of concentrations.

There are a lirnited number of literature reports involving the use of ICP for the

anaiysis of Pt and Pd in geological samples. Brown and Biggs (1984) applied ICP to the

analysis of Pt and Pd in geological samples. They used an ion exchange chromatography

step as a possible aiternative to the lengthy fie-assay procedure. Their research looked at

both high and low grade materials. The low grade materials were concenmted by nickel

sulfide fie assay. Extensive interference midies were perfonned and the accufacy of the

method was estimated using sample materials previously anaiyzed by AAS. The detection

bits for Pt at 265.9 nm, Pd at 340.5 nrn and Rh ot 343 -5 nm were O. 1, 0.03 and 0.03

pB/mL respectively (Wemyss and Scott, 1978). Aberwmbia (1982) investigated the

possibility of using ICP-OES for the determination of Pt, Pd, and Au in geoiogical

samples. His research showed that the Pt band at 265.9 mn showed signifiant problems

due to interferences by Mo, Ni Cu, V, Si, Mn, Fe and Mg. As a result of these problems,

samples with low Pt lewls were suôjected to lead fire-assay prior to ICP anaiysis. Richard

Brown (1982) descriied extensively the use of ICP-OES for the anaiysis of various sampte

matrices for precîous metais. He examineci how dissolveâ sdds affected the extractions,

how silver could be used as an intemal standard for the precious metais, how matrix

dements can cause spectral interferences with certain noble metals and how ICP-OES

f i a g a reeree values on the geological suaples. Rao and Bridger (1982) examine

the possibiity of pefiorrning a dina detemination of process soiution with both high

dissolved solids and SiBnificant amounts of PGEs. Their research look at torch

assemblies, alum interfaaices on Pt, as weli as possible spectral overlaps with the Pt üaes.

Inductively coupled plasma mass spectroscopy (ICP-MS) is a =Iy new technique

for elemental and isotopic anaiysis. The technique combines the characteristics of the ICP

for atornization and ionizing injected material with the sensitivity of m a s spectrornetry

(sensitivity limit 0.03-0.22 ng w'). There are two distinct advantages to ICP-MS

analysis. Fudy, the spectra are very simple and inter-elemental interferences are largely

absent. Secondly, the technique provides for the sequential analysis of both elemental and

isotopic ratios, the latter previously being restricted to thermal ionization mass

spectroscopy (TI-MS). As a M e r refinement to this method, isotope dilution techniques

may be employed.

Sample preparation is the critical step in the trace analysis procedure; fiequently, it

is responsible for establishing the lower detection limits of an d y s i s through its influence

on the analytical blank This is panicularly important in ICP-MS as the technique requires

that the sample be in liquid form with the total amount of dissolved solvents being less

then 0.1 %. The least popuiar method for sample preparation is alkalllie fision foiîowed by

acid dissolution due to introduction of additional extenial eiementai interfaences aot

found in the initial ssmple matrix. Wet-digestion m*hoâs are often employed but they

require close attention by the a d y s t to avoid unintentional bohg over or evaporation of

the sample to dryness. Thuq a more rapid and e f f i v e digestion method for trace metal

analysis hes been sought. Microwave assisteci sample dissohttion may be the answer for

fast, clean sample preparation. AU of these are discussed in this th&

Inductively coupled plasma mass spectroscopy has beai widely used for the

detemination of PGEs in geological sample due to the iarge danand for these noble

metals. Date and Oray (1989) descriibe the many advantages of ICP-MS for gcolo@d

samples and d e m i e ais0 vPiaus sample prepantion techniques. Pary et al., (1995)

describe the appücability of ICP-MS for the determination of PGEs and gold on various

sample matrices in geological sarnples, biological samples, botanid samples, and water

samples. Their paper looked at the detection Mts in each of the sampIe types while u&g

various digestion methods and ample preparation methods and tt provides many

refemices for additionel information on ICP-MS anaîysis for noble metals and gold. Piotr

Nowinski (1994) looked at the applicab'ity of using a microwave oven for the digestion of

geological samples foliowed by ICP-MS and Totland et d (1995) looked at an aikali

fusion and microwave assisted preparation procedure for the deternllnation of POE and

Au in geological matenals. Their results were genedly in agreement with the reference

results but showed a tendency to bias on the high side.

Isotope Dilution ICP-MS (D-ICP-MS) has also been extensively applied to noble

metals detemination in geological samples. This method can provide the analyst with up

to a ten-fold increase in accuracy in PGE determination in various sample types. Cattenck

et al. (1995) used isotope dilution ICP-MS or ID-MS for the determination of various

metals in various types of matrices with exallent results. Nowllisky and Hodge (1994)

and Enzweiler et al., (1995) studied the appücability ofvarious digestion techniques in the

detemination of PGEs and Au in geologicai samples folowed by ID-ICP-MS. Nowinsky

and Hodge (1994) showed that microwave assisteci dissolution of samples foUowed by ID-

ICP-MS is a viable methods for geologid samples -sis whik Enzwda et al., (1995)

showed that ID-ICP-MS of a peroxide nised and teiiurium coprecipitated sample also

gave acceptable results. Yi and Massuda (1995) paformed a sequentid determination of

Ru, Pd, Ir, and Pt et ultratrace l d s by ID-MS on various geologid samples. Their

method proved to be quite reiiable in cornparison with otha dyt ical techniques. Beary

et ai., (1994) explorecl different sample pnpatation approaches for isotope dilution ICP-

MS of c e d e d materiais. Their paper helped to dsveiop the sensitivity, prcision and

accuracy reqWred for autocatalytic PGE detenninatiom et Inco Limited, Sudbury

Division.

As a result of the analytical data provided fiom the authors above, both the h t d

standard and isotope dilution ICP-MS techniques were gcplored for the daennination of

PGEs in used outocatalyst. It is hoped that one of these techniques can provide EghS

accurate, sensitive and precise resuîts as rquired for the determination of PGEs in useâ

autocatalyst while elirninirting soma of the interferences with ICP-MS as seen in Evans and

Giglio's (1 993) research paper.

1 -6 PURPOSE AND SCOPE OF THIS PROJECT

The ah of this project was to develop a simple, fast and sensitive method for the

determination of platinum, palladium and rhodium content withui usd automobile

cataîyst. A well emblished method involves a combination of nickel suifide fie-assay pre-

concentration foliowed by another pre-concentration step using lead on the nickel suifide

slag (Appendix A). The PGEs collected fiorn both techniques are dissolvecl ushg

concentrated mineral acids, then sarnples are d y z e d both by ICP-AES and AAS. The

results are combined and reponed. The fie-assay is a highly accurate method and well

developed technique, but the pre-concentration steps are time consuming, costly, and very

labor intensive.

The three methods exploreci in this study are: (1) concentmted a h d acid

dissolution, (2) microwave assisteci dissolution, and (3) Zirconium cniaile sodium

peroxide fùsion M e r the automobile catalyst samples are dissolveci, the arialysis is

pafonned using a Perkin-Elmer Elan 6000 ICP-MS and the resuits an compareci to the

classical methods: Nickel sulfide coiiestion and ICP and AAS finish (ha Limited) and the

Ledoux A-1 method consisting of an acici digestion plus fire assay digestion method with

ICP finish.

CEAPTER 2 EXPERIMENTAL PROCEDURES FOR AUTOCATALYST QUANTIFICATION

In this project, thne sample preparation methods were explorecl as possiile

replacement for the present Nickel-SuEde fire-assay technique. These three methods w m

concentrated acid digestion on a hot-plate, microwave assistai digestion, and alkaii fusion.

The basic procedure in dl three techniques foilowed the same steps. First the samples

were dried and cmoled. Next a hown amount was weighed into an appropriate vessd

The samples were digested ushg one of the three methods. Following sample trament,

the samples were ali dissolved accordingiy and fïnaliy pnpared for sample d y s i s on the

Inductively Coupled Mass Spectrometry (ICP-MS) instniment. Each of these methods will

be descnbed individuaiiy below.

Prior to sarnple dissolution using one of the three methods descllied above, (acid

dissolution, or microwave assisted dissolution, or dkaii fision) the autocaîalytic samples

were ail pre-treated in the sarne way. The fint step was to cmsh the samples which is

elaborated in section 2.1.1, then al samples were dried as outlined in section 2.1.2, Finally

the samples were weighed ushg one of two methods listed in section 2.1.3 and then

dissolved ushg one of the three studied methods.

The samples used throughout this work were &&y pulverized (-200 mesh or 75

pm) and thoroughiy mixed. Two catincd amples wae used as conaol monitors. The first

standard reférace material (SRM) is SRM 2556 which is the pellet fom of the

autocataiyst and the second is SRM 2557 which is the honeycomb fonn Sampk

composition for both standards can be oan in Appendot C. The standards are pnpared in

the same fmhion as nonnd autocatalyst samples.

The autocatalyst like many other semples arrive in the damp or wet state.

Anderson (1987) descn'bed how wet samples can affect the accuracy of the resdts in a

negative way. Therdore, fiom an atialytid point of view, this means that the samples

contain potentially large amounts of water associated to them which ~ u l d give rise to

unwanted quantitative analytical mors. As a redt, samples were calcined in a

temperature controlled Cole Palmer muflle b a c e for 2 hours at 500°C prior to sample

analysis for platinum palladium and rhodium. This removes unwanted water associated

with the samples and carbon which c m also cause anaiytical problems. Calcination in this

manner is the accepted way to dry autocataiyst samples Peary and Paulsen, 1996, Beary

et al., 1994).

Sample wcjghing was pafonneâ foilowhg Anderson's (1987) technique. Two

Merent methods of sample weighiDg were uwd in tbis pmject, the choice of method

king dependent on the type of Mettk balance that was used. Gaie*, for ail alkali

fùsions, the samples were diredy weigùed into the zirconium auables. Sample weighg

for both microwave dissolution and acid dissolutio~~ involved the use of a weighing plate.

Samples were added to the plate atta the baiance was tard Then the sample was

transfured to the digestion vessels and the weigbing plate was once again weiaed to

ensure accurate results. Great care was taken with di weightings.

2.2 TEST METHOD #1: ACID DISSOLUTION METHOD USING

BEAKEM~OTPLATE

Acid dissolution provides an easy way of dissolvtig most materials (Anderson,

1987). The choice of digestion vesse1 for acid dissolution is dependent on the nature of the

acid. AU dissolutions which useci hydrofluoric acid (HF) were carriecl out in Tefion

beakers due to the ability of HF to dissolve Borosüicete glass. ûthdse , aii other acid

dissolutions were perfonned ushg Boros3cate gkssware. A 0.25 g sample of catalyst was

weighed using the Mettler 100 or 166 electronic balance as descn'bed in section 2.1.3. The

weighed samples were traasferred to the proper digestion vessels and the vessets were

washed d o m with a miall mount ofdeionwd water (DI) to ensure that al1 the cataiysî

sample would be in contact with the acids. Then a 45 mL concentrateâ hydrochloric and a

15 mL portion of concentrateci nitric acid was added (3:1 qua regk solution). Other

acids, aich as hydrofluoric aci4 sulfiuic Md, and percblonc ad, wae then added to the

aqua regia mixture to belp dissoive rhoàium Î f it was repuireci* After the addition of the

last acid, the contents of the beakers w a e thorougbhl mhed and placed onto a hotplate.

The simples once placecl on the hot plate wouid nmaia there d dl the a i d s had

evaporated. The beakers were then removed and aüowed to cool. Once coold, a 10 mL

aliquot of D.I. water was added followed by the addition of 50 mL of comentrated

hydrochioric acid. The contents wae thomugbly mixed aad the sunples were re-beated

for a couple of minutes. ûnce the solution was clear, the dUsohnd srmples wae moved

fiom the hot plate and cooled d o m Mer cooling the contents of the beakas were

emptied imo a 500 mL glas vo1umetnc fîask. The sample beal<er was repeatedly wmhd

with D.I. water and the wasbings were transfensd to the 500 mL volurnetric flask. DI.

water was added to just below the 500 mL. The fiasks were thai aansferred to a coobg

bath for 20 minutes. M e r cooling for 20 mimites, the samples were removed fom the

coolhg bath and allowed to accliudze to room temperature. At tbis point the s ~ p l t s

were dissolveci to the 500 mL m k e r and the vesse1 were placed on an automatic agitation

plate for proper solution -g. Atta about 5 minutes, a 50 mL aüquot was p h a d into a

50 mL Falcon tube as the stock solution for fbture ICP-MS dysis. These Falcon tubes

permittecl the samples to be stored for up to 2 months with no ample degraâation or salt

precipitation.

The samples were digested with the Hoyd RMS-150 electronidy oontrolied

microwave digestion unit. Sample weights mged between 0.100 to 0.200 gm of used

automobiie atalyst or refierence mataîals. The sa~~ples were weighed (section 2.1.3) in a

plastic weighing dish and then acinsfaed to the 120 mL Tefion iiiicrowave digesti0on

vessel. The weighing dish was thai raweighed as d e s c f l i in sedon 2.1.3. A 20 gm

aliquot of aqua regia (3:l HCVHNCh) was then added to the digestion vessei and in some

cases a 1 mL aliquot of HF was also added te maease the -*on of rhodium. The

31

microwave carousel can hold 12 vessels and most runs iSvoIved 11 srmples and 1 ftagent

blank. AU analyses were pafomed whüe using ail 12 vessels as the microwave oven

power was calibraed on this basis. Af?er the addition of the acids (qua regia or a c p

regia + hydrofluoric acid) the catalyst samples were mked and aliowed to react at room

temperature momentady (until any visible reaction had subsideâ). The vesseis were then

capped with a 120 PSI rupture membrane and placed into the microwave carousel. The

oven was operateci at d m u m powa for 10 to 20 minutes (se Table 2.1 below). Mer

the power was tumed O& the ve~sels were Ieft in the microwave for 15-20 niinutes and

then cooled in a cold water bath. Once the vessels had co01ed Suflscientiy, they were then

removed and carefully vented in a fUme hood.

With the vessels vented and cooled, the contents were anptied into a 200 m .

voIumetric flask. The Teflon microwave vesse1 was repeatedly washed with DI water and

the washings were transferred to the volumetric flask. Additional DI water was added to

just below the 200 mL. Since the solution was still warm, the volumetric flask and its

contents were transferred to the cooüng bath for 20 minutes. A f k coohg, the flasks

were placed on the counter top and la to acclimatize to room temperature. The solution

was diluted to the 200 mL mark and then mixeci using a magnetic stirring bar and an

automatic stirring plate. A 50 mL portion of the flask was ttansferred to a 50 rnL Falcon

tube for storage. Stored samples remained in soIutîon for severai months with no sarnple

precipitation. This was the concentrat4 stock sohition for that the finai ICP-MS analysis.

Table 2.1 Operating conditions for the microwave digestion of a - 0.10 g (~1tocatalyst

sample.

Microwave Power Output 500 W

Microwave Power Duration thne : 10-20 minutes

Maximum Pressure 120 psi

Estimated Temperature 180 - 2OO0C

Volume of Digestion solvent : 20 mL aqua regîa (withlwithout HF)

2.4 TEST METHOD #3 : ALKALI FUSION OF AüTûCATALYST SAMPLES

A 0.25 g portion of the dried autocataiya sample was weighed into a dned

zirconium crucible. The weight was recorded and then a 2.5 g portion of sodium peroxide

flux was added. The samples w m thoroughly mixeci With the Cole P a m r automatic

agitator for 3-5 Mnutes. The autocatalyst and flux were then fised on a LEC0 FX-503

automatic fluxer for 3 minutes. The automatic fluer was u d to aisure that d sampies

were fused in the exact same way. The mass was allowed to cooi., then the cruaile was

tranderred to a 250 mL Teflon beaker and 100 mL of distilled and deionized water was

added to the vessel. During the addition of water, cace was taken to avoid sample loss

through sputtering. The addition of 50 mL of concentrated hydrochloric foiiowed by 50

mL of concentrated nitric acid took place only affa alî reactions were complete. Care was

again taken when adding the concentrated hydrocbionc acid to avoid sputiaiDg of the

sarnples. The addition of concentrated niüic acid posed no problems in temis of sputtering

as the reaction continued at a much gentier me. The samples were trderred to a 500

mL glas volumetric flask d e r the bubbluig had ceased. The auOble rad Tdon beaker

wae repeatedly washed with D.I. water and the washings wae also tradiared to the

mL fiask. Mer the Ûansfer of the mixture to the voluxnetri*~ flask, the mixture wts düuted

to just below the 500 mL tnarker with DJ. -ter. The flasks were then W i e d to a

coobg bath for 20 minutes. Atta cooling for 20 minutes, the samples wae removed fiom

the coolhg bath and allowed to acclimatk to rom temperature. At this point the

solution was made up to the 500 mL mark and thm transferred to an automatic agitation

plate for proper solution mixing. After about 5 minutes, a 50 mL aliquot was pl& hto a

50 mL Falcon tube for fiihire ICP-MS analysis. These Falcon tubes permitted the samples

to be stored for up to 2 months with no sample degradation or salt prexipitation. The

stock solution, so obtained, was diluted as appropriate pnor to ICP-MS analysis, as

describeci in m ' o n 2.5.

2 .S FINAL+ SAMPLE PREPARATlON STEP PRIOR TO ICP-MS UTILIZING ISOTOPIC

DILUTiON AND INTERNAI, STANDARD TECHMQüES

From the 50 mL concentrated stock solutions stored in the Falcon tubes, a 1 rnL

portion of sample was combined with 3 mL of concentrated hydrochloric acid and 1 rnL of

intemal standard into a 50 mL Falcon Tube. Dependhg on the type of ICP-MS analysis,

one could also add 1 mL of ~ t ' ~ / ~ d ' " isotope interna1 standard as wel as a 1 rnL spike

(containhg known concentrations of Pt, Pd, and Rh) to repliate samples. Each one of

these components was added to the 50 rnL Falcon Tube and diluted to the 50 mL mark

with D.I. water. Once all the components wat nWed in, then the samples were

thoroughly mixed and they were now r d y for introduction into the Perlrin Elmer Elan

6000 ICP-MS. The placement of these samples was done accordhg to a prepared asset

fiSe as s a n in Appendix B. The operatiord parameters for the ICP-MS are listed in Table

2.2.

It should be noted h t the nnel Mmpk p r e p d o n was only p a f o d

immediately pnor to ICP-MS anaiysis and îhat di samples were thoroughly mixed.

2.6 ICP-MS ANALYSIS (OPERATIONAL P-)

Before the analysis of the dissolveci PGEs in solution, a sampie file was generated

using the weights transcnied fkom section 2.1.3 iato a PC software package. An example

is given in Appendk B. The sample file sewed as a ternplate for the Elan 6000 ICP-MS

software package. The samples were then loaded accordhg to the sequence üsted in the

sample file and then analyzed on the P a h Elmer Elan 6000 ICP-MS foMng the

operational parameters listed in Table 2.2 below.

Table 2.2 Operational Parameters useâ on the ICP-MS for the Analysis of

Sodium Peroxide Fusion Sampks

RF forward power :

Argon Gas Flow (Nebuber):

Analog Stage :

Sample Cone :

Skimmer Cone :

Nebuliter Type :

Solution Uptake :

Peak Scan Parameters :

Reading Replicates :

Discriminator Threshold :

Number of Scans :

Sample Sweep :

Mass Spectrometer :

Detector :

Ion Lens Setting :

1,oOO Watts

1 .O2 Umin

-2,300 Volts

Nickel with a 0.1 5 mm orifice

Nickel with O. 1 O mm orifice

Cyclonic Spray Chamber

15 Urnin

Peak Hopping

1

55 mV0lts

3

40 seconds

Quad Mass Spectrometer

Dual Detector

6.2 Volts

The detection b i t for the ICP-MS htmment for dl elements in the periodic table

can be seen in APPENDIX C.

Since the ICP-MS calibration w e is iinear through to zero* a single d % d o n

solution was used for the caliiration of the instrument. This single ulIbration soiution was

composed of -4 pfi Rhodium, - 20 pfi of palladium and - 40 CcglL of platinum which

was mixed with the indium and iridium intemal standard. The caiibration solution was

rnonitored using an indium and iridium internai standard prepared from purchased

Certifieci Spectral Standards.

Mer the calibration of the ICP-MS with the PGE calibrating solution, the n a t

step is to calibrate for the removal of possible intederences. Such interferences can affect

the determination of the three PGEs and are rernoved rnathematically usïng the corrections

Iisted in Table 2.3. Using three solutions of hown concentrations of rnercury, th, lead,

strontium, copper, yttrium and H u m . , the intensities for each of these element are

measured for the blank solutions and inputted into the ICP-MS software. When the

samples are analyzed, the intensities of the species imrolved in the molecular ion

interferences are measured. Once measured, they are psssed through the mathematid

f o d a e listed in Table 2.3 and then removed fiom the s p d c PGEs in solutions. The

removal of these Uaerrence is imporîant for the high accuracy and precise determination

of platinum, palladium and rhodium,

Table 2.3 Spectral removal of possiie interfierences from Cu, Y, Sr, and Pb.

The ICP-MS software WU moaitor the copper, strontium, yttrium, and hafhîum for

possible isobaric and double charged spectral interfierences of platinum, palladium, and

rhodium. Copper combined with the argon gas in the piasma gas f o m a copper argide

(~uAr+*) which isobaricaily intetferes with rhodium and pallaâium dements dependiag on

which copper isotope is present. Strontium comb*med with oxygen f o m a strontium

oxide which iwbacically interferes with rhodium and palladium. Yttrium oxide formed

within the ICP torch will also isobaricafiy interfiere with palladiwn, Double charged lead

204 wül intetfere with the monoisotopic rhodaim 104 species and Wum pre!sent within

the zirconium nuciales forms a Wum oxide speck that interfères with platinun 195.

F M y , th 1 18 will interfere with indium which is used as intemal standard and mercury

Unares lightiy with the detetmitllltion of I d . W~th the d g up of these iaterference

removals tiom the sample, the d y s i s of autocataiytic snmples can now p r d .

2.8 SELECTION OF INTERIVAL STANDARD

The choice of intemal standards for the determination of Pt, Pd, and Rh in n m and

used automobile catalyst is dependent on the element. The determination of Pt, Pd and Rh

in new and used automobile catalya CM use a wide variety of internai standards.

Therefore each element is discussed separately.

The analysis of platinum can be doue either through isotope dilution (Sa Table

2.4) or through the utiiization of intemal standards. For this research, the intemal standard

hlg3 was used at first. This is chemicaily dissirnilar to Pt but close in rmw. Another

possible choice was Tlm' but it was obsewed to drift on the ICP-MS and to affect the

detefmination of platinum, so it was not used. The final choice was to use a platinum

isotope. The choice of isotope was largely dependent on its avaüability as weil as its

natural abundance within the catalyst. A semiquantitative -5s of fused catalyst (sa

Appendix A) showed that Pt1% was almost nonexistent and therefote was chosen as our

isotope interna1 standard. The isotope was p u r c M âom Oak Ridge National

Laboratory as a metai powder containhg 95.3 1% of ptm abmdant. The method for the

dissolution of this metal powder is giwn in section 2.9.

Palladium not behg mononuclidic in nature caild also be d y z e d through either

isotope dilution (See Table 2.4) or with an intemai standard The interna1 standard chosen

was inNs which is chemidy metent fiom Pd but it is relatively dose in mass. Another

possible choice for interna1 standard was RU"' but this element showed miwr

irregularities during Jnrnple d y s i s and was therefore not used. Internai standards

provideci excellent dy t i c a l resuits but it was believed that isotope dilution muid provide

additional sensitivity, accmcy and precision to the detemidon of palladium, Tûaefbre

the isotope diution ICP-MS detemination of pallnAium was attempted. ~ d ' ~ was ody

found in trace amounts in a semiquantitative analysis of the fused outomobite cataiyst as

seen in AppendUr A and was *&ore chosen. As a result, the isotope was purchased

from Oak Ridge Natiod Moratory as a metal powder which wntained 94.Wh of the

isotope. The dissolution procedure for tbis metai was simüar to that of the Ptlm isotope

(section 2.9).

Finally, for the daennination of the mononuclidic Rh there are three possible

intemal standards. The first involves the use of ~ d ' ~ which is one mass unit removed fiam

pdl*' and chemically similar to the Rh. The second is with ~ t ' " which is again chemicaily

similar to Rh but has a large mass difference and W y there is In'" which is chemically

different from rhodium but close in mass and naturally absent in autocataiyst. Of these,

h l 1 ' was chosen as the intemal standard for rhodium determination.

Table 2.4 Relative abundance of naturai isotopes used in this project.

Element

Ru

Ru

Ru

Rh

f d

Pd

Pd

Ir

Ir

Pt

Pt

Pt

Pt

In

In

Measured Mass

99

101

102

1 O3

10s

106

108

191

193

194

195

196

198

113

115

Relative abundance

12.72

The pdlM (94.000? abundant) and ~ t " (95.31% abtsndant) were purchased fkom

Oak Ridge National Laboratory as a metd powders. The powden were dissolveci in

concentrateci aqua regia on a hot-plate and then once cooled they were storeâ in a 2moK

ultra-pure HCl solution. The concentration of the two isotopes w e n deternwied with an

ICP-OES analysis which was then comlated to ICP-MS detenninations. The

concentration of the isotopes is continuously king moaitored during sample d y s i s on

the ICP-MS and th& concentrations are tabuiated using specincally dmloped software.

package developed at INCO Ltd., Sudbury Division.

Chapter 3 Results and Discussion

The use of nickel sulfide fie aswy collection for Pt, Pd and Rh in the pte-

concentration of autocatalyst sampfes is a highly accurate procedure but it is dm time

consuming, labor intensive, dependent on the anaiyst laboratory skül level, and is subject

to experimental e m due to the large amount of sarnple handliag (Beamish, 1966). Ii

addition to the above, fie assay pre-concentration generally r e e s a large amount of

acid to be used for sample preparation. As a result, this project loob for altemative

sample preparation methods that could be used for the simultaneous determination of Pt,

Pd and Rh in both new and used autocataiyst. This new method would be used in

combination with a Perkin-Elma Elan 6000 ICP-MS for highly accurate, precise and

sensitive analytical determinations of the PGEs. The ICP-MS provides many advantages in

that the analyst can predict possible interences, its provides a broad iinear dyaamic

range, sample analysis are rapid and not hindend with emission peak oveilaps and the

instrument is fully autornated.

Many sample dissolution methods are available but the method chosen should be

low cost, relatively simple, and highly accurate. The methods considered in this project

were: hot plate acid dissolution, microwave assisteci dissolution, and zirconium aucible

alkali frisions. These will be seen in section 3.2 (Acid dissolution), section 3.3 (Microwave

assisted dissolution), and sections 3.4-3.5 ftsion) respedively. Prior to

explorhg each dissolution method and its results, a look at possible problems that could

aEkct the ICP-MS results is warranted.

3.1 ASSESSMENT OF MATIUX INTERFERENCES

In an effort to provide the best conditiong and analyticai resuits for the recovery of

PGE's, most autocatalytic samples d y z e d on the ICP-MS were andyzed dong with

certifiai standard reference matenCaIs (SR-) autocatalytic samples (NIST 2556 @dl&),

NIST 2557 (honeycomb)). In addition to using d e d materiais, catain ~ m p l e ~ were

spiked with a known concentration of Pt, Pd, and Rh solution and recoveries for each

element were caiculated to assess the vaiidity of the analyticai resuits. F i d y , the use of

isotopes as interna1 standards wouid a b provide with extremeiy sensitive d y t i d

results.

The ICP mass spectrometer is a non-specific ionization source, and as such mat&

interferences and other sources of instrumentai error were of concem during sample

dys i s . There exists thtee possible sources ofanaiyticai error that can aéct the ICP-MS

results. The first two mors are fkom interferences &sing Born either molecular ions

ancilor doubly charged ions present within the prepared solution. Both of these two

interferences are readily identified by the anaiyst and are easiiy c o r r d for. The third

source of error is due to the drifthg of the ICP-MS over a period of tirne. Generaiiy this

last source of error affects the rnid-rnass measurements of several elements and it is vey

dficult to identify. The last source of error can be correcteci for but it generdy requires

special software development.

Molecular ion interferences (isobaric interferences) affect aU PGEs in autocatalyst

in varying degrees. For Pt, there was no sigaificant elemental isobaric intaference other

than a stight interference fiom Ht"*0" and @780'6Hf with the ultra-trace levels of

hafhium originating fiom the zirconium crucible. pdlW also suffers nom isobiuic

interferences fiom various isotopes of strontium and oxygen as shown with S~~'O'? But

again strontium is found in trace concentration and poses very M e problems in Pd

determinations W'03 on the other hand is isobaridy interfered by copper argîdes such as 63 4û Cu Ar which is present in trace to ultra-trace lewel in the dissolved samples. The wpper

@des will also interfére with Pd but h&ium, copper, and strontium show M e or no

affects on the anaiytical results Born the ICP-MS. A saniquantitative d y s i s (Appendix

B) of fûsed samples showed that the PGEs consists of hudred of thousands of counts per

second whiie the isobaric intafaing species account for hundreds of counts per second.

Through the Elan 6000 ICP-MS software, these dernents were cali'brated using specially

prepared interference solutions and subtracted fiom the PGE anaiytical r d t s

automatidiy pnor to reporthg of the resuits.

The second possible interfirence originated fion double charged @es such as

lead. Pt is unaffected by this type of interference but Pd and Rh are affected to m g

extents. The extent of the interference is dependent on operational conditions as well as

the presence of the doubly charged Iead species. If lead is present in detectable amounts,

doubly charged ions kom the percent level of Pb in the sample will produce an

interference at n/z 104 (M'Pb'2) with ~ d ' ~ and also at n/t 103 fkom ?b+* with Rh.

Doubly charged interferences are dso monitored within this project through the ELAN

6000 ICP-MS sohare and for specially prepared celibrating interference solutions.

Therefore, interference fiom lead is virtually eliminated for the PGE analytical nsults.

The last source of error is due to instrumental driffing which generally affkcts the

measunment of heavy elerneats. Udortunately, tbis type of error is vey diacult to

identiQ and requires specïaliy developed software. As a result, software was developed to

correct for the instrumental driAing and all resuits are reported after a drift conecti*on

cakulation. This drift correction eliminates this source of emr during ICP-MS analysis of

PGEs but it is propnetary and therefore the mathematical details are not covered in this

thesis.

3.2 TEST METHoD # 1 : ACID DISSOLUTION OF AUTOCATALYST SAMPLES

The fkst method of autocatalyst sample dissolution requires the use of

concentrated acids to digest the samples on a hotplate. There are many factors that can

affect the extraction of Pt group met& fiom the autocatalytic matrix Among these

factors are the type of autocatalyst, the sample particle size, the leaching tirne, and the

various acid combinations. AU of these fàctors play a role in PGE recoveries so each will

be discussed in detail.

The supporting matrix win affect the rmvery of PGEs in new and used

autocatalyst. Wu a al. (1993) briefly disaissed how recoveries fiom acîd dissolutions

were affected by mat& composition type. Presentiy there are a nwtlber of supporting

matrices for the PGEs in autocatalyst and these fiill essentiaiiy into two classes. These two

classes of catalyst are the monolithic and the peiîet types. The fist type has the PGEs

sprayed onto a cordiente m a t h while in the second the PGEs onto a y-silica substrate. A

cornparison of an aqua regia dissolution (3: 1 HCVHN03) on the two types of NIST

sarnples (NIST 2556 -pellet and NIST 2557 -Monolith) is shown in Figure 3.1.

Figure 3.1 The effect of autocatalyst type on the extmtion of PGEs in new and spent catalyst using an aqua regia disso1ution to sample dryaess.

It is apparent that the aqua rea digestion gives >85% recovery in di instances,

regardless of the matrix type. This is probably b s e the PGEs fom a Surface coaîing

and are not an integrai part of the matrix itself. However, thae are signifiant diffefences

in the recoveries fiom the two types of ~IW&S. The y - a l d a in the pelleîs is pdally

soluble in aqua regia whereiu the cordierite of the honeycomb type catalyst is impervious

to acid attack. Thus the dEerence in solubility of the two matrix components is most

likely to be the cause for the bata recoveries âom the pellets.

3.2.3 EFFECT OF SAMPLE PARTICLE SIZE

Sampie size can play a sigdlcant role in the extraction of noble metals. Anderson

(1987) described how the padcle size of noble metal samples af!f'iected acid dissolution

results. Since aii samples in this project were prepmed in the same fmhion, the sample size

should be the same in ali cases. Generally, ali the autocatalytic samples were pulverized to

75 pm or -200 mesh and to prevent larger particles fiom entering into the sarnpk bettle,

al1 the crushed samples were thoroughly sifted. The particles that were larger than 75

or -200 mesh are trapped in the sieve and cannot p a s through. But in cases where the

sample sire may vary, it should be appreciated that sarnple size can affect the percent

extraction of that particular element (Ferry et al. 1995).

3 2.4 THE EFFECT OF LEACHING TIME IN OPEN BEAKER DIGESTIONS

Peny et al. (1995) describeci how extraction times affect PGE recoveries âom

various sample matrices. Their results indicate that extraction time can have a major

influence, and so a study ofthis &kt was &ed out using the autocatdyst samples with

aqua regia digestion. The percent of extraction for a range of digestion times was

measured using the dried and d e d MST 2557. Each of the seven acid combations

used an aqua regia (3:1 HCVHNa) mixture but additional acids were added to improve

the recoveries of the PGEs. Atta mcasured t h e intervals, the sarnples were removed

Born the hotplate, cooled and then diluted to 500mL. The d t s of this study are shown

Figure 3.2 and Table 3.1 .

Figure 3.2 The percent extraction of PGEs in cnashed autocatalyst (NIST 2557) and using aqw regia over a 4 hour period.

Percent Extraction (%)

1 1.5 2 2.5 3 3.5 4

Digestion Time (Houn)

Table 3.1 The percent dos of PGEs kt d e d autocatalyst (MST 2557) and using aqua regia over a 4 hour period.

From the results above it can be seen that there was no improvement in the

extraction of Pt and Pd when extending the dissoIution t h e 6om 1 hour to 4 hours. There

was an improvement with Rh where &er 1 hou, only 82.00! of Rh was extracted while

after 4 houn 90.2% Rh was actracted. Acid dissolution does not effectvely extract ail

PGEs like the alkaü fiinon technique cm. Several attempts w m made to improve the Rh

extraction but for wet acid dissolution 90.2% was the best rwvery ochieved.

3.2.5 STUDMNG THE VARIOUS ACID COMBINATIONS

A study of the various acid combinations on the spent autocatalyst samples was

performed to explore the possibility of improving the rmveries of Pt, Pd and Rh. Seven

different acid combinations were tried. The results of these experiments are shown in

Figure 3.3.

Figure 3.3 PGE ncoveries fkom a variety of acid coaibUiation~ in opai-begkm -

digestions ofNIST 2557 (Honeycomb).

Percent Extraction (%)

Sample #

Note: Sarnple #

1) HCI+HN03 (3 : 1)

Rhodium Palladium

From the figure above, it is obsmd that none of the various acid combinatiom

was able to extract 1W/o of Pt, Pd and Rh from the autocatalyst. The five acid

wmbination (#7) using 15 mL hydrochloric iiaâ, 5 mL nitric aci4 2 mL bydrofluonc acid,

10 mL perchioric acid, and 5 mL of 1:1 suifùric acid showed the best recoveries of the

PGEs ( 97% of Pt and Pd and 91 % Rh). Ail other acid combination showed infaor

extraction results to this acid combination. Thus it appears that open-beaker digestion is

not a satisfactory option for the dissolution of spait autocatalyst samples.

3.3 TEST METHOD #2 : MICROWAVE-ASSISTED DIGESTION OF AUTOCATALYST SAMPLES

A study was carried out to check whether the dissolution of the autocatalyst

semples would be improved when using the microwave-assisted digestion technique.

Autocatalyst samples were digested using various digestion times and two Werent acid

combinations. The variation of digestion tirne was midieci to sa if Rh could be fiilly

extnicted while the use of aqua regia and aqua regia with HF was studied due to the

improved Rh extraction resuIts when digested via the hot-plate technique. A bnef

discussion of these midies are as follows. A 0.15 g autocatalyst samples of reference

matenals was used in each study since it yielded the highest POE recoveh.

3.3.2 EFFECT OF VARMNG THE MICROWAVE DIGESTION TIME

The e f f i of varying rnicrowave digestion time was studied on the two different

certified reference catalyst sarnples. The resuhs obtained with two different dissolution

times are shown in Table 3.2 as compand to their cemfied values.

Table 3.2 Effect of varying the miaowave digestion thne on S R , 2556 (Peuet) and

SRM 2557 (honeycomb) wbile digesting with aqua regia and HF mixnue.

Platinurn Palladium Rhodium

SRM 2556 d u e s in ppm values in ppm values in ppm (pellet type) (% recovery) (% recovery) (% recovexy)

certified values 697.4 * 2.3 326.0 f 1.6 51.2 I 0.5

Found (ICP-MS) 715.2 * 2.8 328.5 k 1.9 46.3 * 0.9 10 minutes (1 02 -6%) (100.8%) (90.5%)

Fould (ICP-MS) 71 1.9 I 2.4 327.0 I 2.1 46.6 i 0.7 20 minutes (102.1%) (100.3%) (9 1 .O%)

SRM 2557 values in ppm values in ppm values in ppm (honeycomb type) (% recovery) (% recovery) (% recovery)

certified values 1131 i 11 233.2 î 1.9 135.1 * 1.9

Found (ICP-MS) 1125.9 f 9.8 231.5 * 2.1 121.9 i 1.7 10 minutes (99.6%) (99.3%) (90.3%)

Found (ICP-MS) 1128.6 & 8.8 233.9 * 2.0 126.4 i 1.5 20 minutes (99.8%) (100.3%) (94.0%)

Results are expressed in pprn and based on dry weight (500°C for 2 houn). Average of

triplicate results.

In this investigation, the previously drieâ autocataiytic samp1es were digested witb

an aqua wgia mixture for eïther 10 or 20 minutes. The qua regia combination gave

exdent open-beaka r d t s which were comparable to d other rcid combinations used

in the open-beaka hot-plate digestion studies. The microwave oven was set to identical

power setting for each of the digested autocataîytic samples. The cornpuison of the

microwave results for the two NIST samples a f k Mefent dissolution time showed that

an increase in dissolution time wiii not increase the extraction of the Pt, Pd and Rh. The

results do show a slight but bignifiant improvement which can be amibuted to

Uistnimental drifting of the ICP-MS. It has ken obsecved tbat independent of the

dissolution time chosen, Pt and Pd are weli extracted through microwave dissolution. On

the other hand, Rh shows poor recoveries via miaowave dissolution evai afta varying

the digestion time. The poor Rh extractions could be due to two re8~011~. The fist reason

might be related to the oxidation of the Rh to Rh oxide (RhZ&) which is largely insoluble

in almost al1 acid combinations. The second possibility for poor Rh recoveries is probably

due to the inwmplete digestion autocatalyst samples. Therefore, digesting the samples for

20 minutes could correct for some low PGE results and was therefore chosen for all

samples.

Pt and Pd resuits were acceptable, but Rh results were wnsistently low. If this

method is employed, a correction fâctor needs to be appiied to the Rh recovery values.

3.3.3 EFFEC~ OF THE ADDlTION OF HF TO THE MICROWAVE SAMPLES

It has been observed that with the addition of conceatrated HF to samples

dissolved via the open-beaker acid digestion technique, the percentage of Rh recovered

was increased significantly. Thus a series of experiments were made in which HF was

added to the r d o n mDmûe composeci of the sample an qua regia in microwave-

assisted digestions. The resuits are given in Tables 3.3.

Table 3.3 Wect of adding HF to the microwave digestion for amples of SRM 2556

(Pellet) and SRM 2557 (honeycomb).

Platinum Palladium Rhodium

SRM 2556 (pellet type)

certified values

Found (ICP-MS) Aqua regia with

no HF Found (ICP-MS) Aqua regia with

0.5 mL HF F O U ~ (ICP-MS) Aqua regia with

1.0mLHF

values in ppm (% recovery)

values in ppm (% recovexy)

values in ppm (% recovery)

SRM 2557 values in ppm values in ppm values in ppm (honeycomb type) (% recovery) (% recovery) (% recovery)

cedec i values 1131 Il1 233.2 * 1.9 135.1 k 1.9

Found (ICP-MS) 1096.9 î 3.1 225.6 f 2.5 114.8 f 1.7 Aqua regia with (97 .O%) (96 -7%) (85.0%)

no HF Found (ICP-MS) 1125.9 k 2.8 231.5 î2.1 121.9f 1.7 Aqua regia with (99.6%) (99.3%) (90.3%)

0.5 mL HF Found (ICP-MS) 1128.6 î 1.8 233.9 * 2.0 126.4 I 1.5 Aqua regia with (99.8%) (100.3%) (94.0%)

1.0 mL HF

Results are expresseci in ppm and based on dry weight (500°C for 2 hours). Average of aipticate resuits.

From the resuits in Tables 3.3, it can be seen that samples treated with HF and

aqua regia (3 : 1 HCVWNa) showed betta Rh recoveries than those treated with just qua

regia. Sarnples treated with HF showed Rh fecoveries of 91 to 94% and up wbile those

with or@ aqua regia showed Rh recoveries ranging around 78 to 85%. Therefore it cui be

concluded that HF does help in the extraction of Rh.

Another advantage of using HF m the miaowave dissoIutioa is that the r d t s

fiom the samples treated with HF showed a better p&sion and accuracy over the

samples treated with only aqua regïa. The cornparison of the percent difference for NIST

25 56 samples treated and not treated w*th HF caa be seen in tables 3.4 and 3.5 below.

Table 3.4 Percent difference for NIST 2556 samples dissolved using microwave dissolution and not treated with HF.

Note: Results presented above are the average of triplicate results.

NIST 2556

NIST Value MicrowaveACP-MS

DEerence Percent Merence compared to

NIST

. d g Rh

51.2=t0.5 3 9 . W .O -2 1.3

- 28.32

Pt 697 .4*2.3 695.5h9.1

+1.9 + 0.28

Pd 326k1.6

33025.4 4.2

- 1.29

Table 3.5 Pacent Merence for NIST 2556 sampIes dissoIved using microwave dissolution treated witb HF.

NIST 1 ~ g / g 1 2556

MST Value

NIST 1 1 1 1 Percent merence compared to

Note: Results presented above are the average of triplicate results.

When cornparhg the results fkom the hvo tables above, it cm be obsmed that the

addition of HF does help to improve the PGE relative percent error. At the m e time, it

also helps in the recovery of Pt (99.7% without HF compared to 99.9% with HF) and Rh

(779% without HF compared to 87.9% with HF) but it shows a negative effect 4 t h Pd

(101.00h without HF compared to 99.7% with HF). Unfortunately, the recovery of Rh is

still too low and therefore requires a correction. Although HF helped in the further

extraction of Rh but stiü does not solve the low recovery problem.

Rh 51.2M.5

Pt 697.4*2.3

- 0.12

Unlike the NIST 2556 (Pellet) autocatalyst sample, the NIST 2557 autocatalyst

samples shows a slightiy dbierent results. These results can be seen in Table 3.6 and Table

3.7 below.

Pd 326I1.6

- 0.3 1 - 12.11

Table 3.6 Percent diffecence for NIST 2557 samples dissolved

using microwave dissolution and not treated with HF.

Note: Results presented above are the average of tripiicate nsults.

NIST 2557

NIST Value Microwave/ICP-MS .

Merence . Percent ciifference compared to

Table 3.7 Percent dEerence for NIST 2557 samples dissolved using microwave dissolution treated with HF.

MST

dg ,

t NIST Value 1131k11 233.2k1.9 135.111 .9

Merence +6.2 -0.8 -1 1.7 Percent difference c o m p d to + 0.55 - 0.36 - 8.66

NIST

Rh 135.1*1.9 1 14.8*5.2 -20.3 - 15.0

Pt 1131kl l

1096.9I13.9 -35 ,O + 1.30

Note: Results presented above are the average of triplkate results.

Pd 233211.9 225.6I3.7

-7.6 - 3.30

As seen in the two tables above, HF is useful for improving the percent relative

error for the MST 2557 autocatalyst ssmples. While improving the acwracy, it also helps

with the recovery of Pt (97.M without HF wmpared to 100.6% witb HF), Pd (96.7%

without HF compared to 99.7% with HF), and Rh (85.W wiîhout HF compared to

91 .O0! with HF). Therefore HF plays a major role in the extraction of & Pd and Rh in

used autocatalyst samples. Unfortunately, the r d t s for Rh extraction are di too low

and therefore require a correction.

In addition to helping improve the m c y of the microwave dissolution nwilts,

HF has alw improved the repeatability of the microwave digestion technique. This is

obsemd when compaMg the r d t s in Table 3.8 and Table 3.9 below.

Table 3.8 Repeatabidity of microwave resuits for NIST 2556 and 2557 semples without HF.

A Results reported with a 95% confidence intefval.

-

le ment SRM 2557 (Monolith)

Pt Pd Rh

SRM 2556 (Pellet) Pt Pd Rh

- n

12 12 12

12 12 12

Mean @g@

1096-9 225.6 114.8

695.5 330.0 39.9

- SD

13.9 3-7 5.2

9.1 5.4 3 .O

RSD % A

2.5 3.3 9 .O

2 -6 3 -3 15.1

Table 3 -9 Repeatabüity of microwave results for NIST 2556 a d 2557 samples with

A Results reported with a 95% confidence interval.

Samples treated with HF and then digested via the rnicrowave have shown

excellent repeatability. The repeatability of these samples was calculated at about half of

the repeatability of those samples no treated with HF which indicates that HF is beneficial

to both the accuracy as seen, but also the precision of PGE dissolution h m the two types

of sample matrices (Honeycornb and Peiiet). As a result of these hdings, HF was added

to all subsequun samples to aid in the PGE dissolution. Unfortuaately, because of the very

Iow Rh recoveries, microwave assiaed dissolution was not explored in any great detail.

To improve Rh recoveries, two Limitations of this technique and instrumentation need to

be changed. The first limitation is due to the temperature and pressure required for sample

dissolution. The present rnicrowave apparatus can only go to 120 PSI which is not high

enough to digest the samples aad Rh properly. The second limitaîion to microwave

assisted dissolution is its inabiliîy to M y dissolve the cordierite and y-aluminia which

could pose as a possible problem for the ICP-MS hardware. SampIe w o n could

prevent such hardware problems but it is not required since the cordierite and y-aluminia

1 .2 1 .1 ,

1.3

1.1 1.1 2.9

- SD

13.2 2.6 1.6

3.8 1.8 0.7

Mean

1137.2 232.4 123 .4

696.6 325.0 45 .O

Element SRM 2557 (Monoiith)

Pt I

Pd Rh

SRM 2556 (Pellet) Pt Pd Rh

- n

6 6 6

6 6 6

precipitate to the bottom of the JO mL Falcon Tube and thus are not trpnsférred to the

final aspirated solution.

The first method explorecl in this project was sodium peroxide fusion of dned

autocatalyst. This method provides the analyst with a f'kt and labor sahg analfical

method for prepuing autocatalyst samples prior to ICP-MS d y s i s . But, d e s s the

method is properly developed, fùsion prepsration d l not provide accurate and pr-

analytical results. There are five areas of possible conceni when preparing samples by

alkali fusion. The first problem is due to rnatrix interférences fiom interferhg species in

the dissolved matrix or the matrix itseif while the second problem is fiom the choice of

intemal standards used with the ICP-MS for accurate and precise PGE daennination.

Samples that have not been prevhusly dned and therefore have water bound to them c m

also be a major concem for PGE detemination in new and used autocatalyst samples. The

problem of choosing proper sample weight and flux weight is also important in the

determination of Pt, Pd and Rh. The f i d problem deals with how the samples are fused.

Since each of these plays an extremely important role in quantitative analysis of

autocatalyst by fision preparation, each will be discussed in detail.

3.4.2 PROBLEMS ARISING FROM ALKALI MATRIX COMPOSïïiON

Sodium peroxide alkali tiision is by fiu the best method for dissolving the

autocatalyst samples. It is one of few dissolution rnahoâs that can effectively dissolve the

honeycomb's cordiente ma& as discussed by Totland et al., (1995). Udortunately, the

use of sodium combined 6th concentrateci hydrochlonc acid does provide for the

possiûiility of forrning salts within the ICP-MS instrumentation and dso in the dissolved

samples. Sdt formation prevents the proper detection of PGEs în successive samples

thereby affècting the dyt icel r d t s . To avoid possible salt formation problems, the

present samples were diluteci with deionid -ter Usng extrane care and caltirateci

glassware. Due to the excellent sensitivity of the ICP-MS, this is a possible solution to

preventing salt forniaton but not for most other anaiytical instnunents. This is why ICP-

MS is the desirecl instrument for PGE Bnalysis in used autocataiytic sarnpla. This dilution

kctor has proven very effective and no further exploration into sample dilution bas been

attempted.

Along with interferences resulting fiom salt formation, another fkctor affecting the

analytical results is the concentration of acids within asphted samples. Initially analyzed

samples contained 0.4% (vlv) dissolved acid and the Pt, Pd and Rh results were mostly

biased low. Several attempts were made to correct for the analytical bias but none were

successful. The problem was later solved when a 2-3 mL aliquot of concentrated

hydrochloric acid was added to the aspirated sample. It was established that due to the

initiaiiy Iow concentration of acid within the aspirated samples, the Pt was precipitathg as

Pt chloride species. With the addition of concentrated hydrochloric acid, the Pt could no

longer precipitate and the bias was no longer apparent. The results âom the addition of 2

rnL of HCI to the aspirated samples can be seen in Table 3.10 below.

Table 3.10 Compan*son of ICP-MS resulto vaiidnting the addition of 2 IL of concentrated HCI to the aspirated sample to help improve the acairacy of PGE detennination and remove the bias.

1 SRM 2557 (Hontycomb) ( /g

SRM 2556 (Pcllct)

A) NIST certified results. B) Aspirated Sample results with no prior addition of concentrated HCI. C) Aspirated samples redts with concentrated HCl added (2-3 d)

From the table above, it is apparent that the addition of 2 to 3 mL of conantrated

HCI to the aspirated solution helped in improving the determination of Pt, Pd and Rh. For

the MST 2557 autocataiytic sample, the ICP-MS resuhs with no hydrochloric acid added

had 99.7 f 0.8 % extraction for Pt, 99.0 f 0.6 % for Pd and 99.5 f 0.4% for Rh. The

simples with hydrochioric acid added to the aspirated samples showed a 100 f 0.8 %

extraction for Pt, 99.3 k 0.5 % for Pd, and 100 f 0.3 % for Rh. Thdore it is observed

that hydrochloric acid did help in the determination of the PGEs for the howycomb type

catalyst since there was 0.33 f 0.1 % irnprovement for Pt and Pd and 0.70 f 0.1 %

improvement for Rh.

For the NIST 2556 autocatalytic ample, sampfes not treated with hydrochloric

acid saw a 99.7 f 0.9 % extraction of Pt, 99.1 M.6 % -*on of Pd, and 98.6 f 0.5 %

extraction of Rh. Samples treated with hydrochloric acid pnor to aspiration showed

extraction of 99.9 f 0.7% for Pt, 99.5 I 0.5 % for P4 and 99.2 I 0.4 % for Rh. Thae

was a 0.3 f 0.1 % improvement for Pt and Pd and a 0.6 f 0.1 % improvement for Rh.

Thus, the addition of hydrochloric acid dso helps in the determination of Pt, Pd, and Rh in

pellet type autocatalyst samples.

The addition of 2-3 mL of concentrated hydrochioric acid does help improve the

ICP-MS results for the three PGEs in autocatalyst but shows little 8 k c t on improving the

instrumental precision. Due to the improvement in PGE results, al1 subsequent aspirated

samples were spiked with a 2-3 mL addition of concentrated hydrochloric a d pnor to

sample analysis on the ICP-MS.

3 -4.3 PROBLEMS DUE TO INTERNAL STANDARD SELECTIûN

The selection of an internai standard plays a vital role in the determination of Pt,

Pd and Rh in new and used autocatalyst. Two types of internal standards were tried. The

first type included elements not found withh the dissolved niatrix but whose m a s closely

matched those of Pt, Pd and Rh. The second type of internal standards were isotopes of

the elements Pt and Pd. Rhodium is monoisotopic and therâore required the first type of

internai standard for moaitoring. A brief discussion of these two types of internal

standards foiiows.

As mention& the first type of interd standards were used because they were not

present in the sample solutions and they were closely matched in ~MSS to the PGEs. In this

case four elements were chosen as internal standards and these were Indium and llullium

for Pt and Iridium aad Ruthenium for Rh, Pd. The dection of these initial four standards

was due to their relatively close masses to the PGE elements. It was found that the use of

two of these intemai standards failed to produce satisfactory nsults. Thallium and

Ruthenium

Table 3.11.

3.12.

Table 3.1 1

both gave inconsistent resuits when used as intemai standards as shown in

The precision associateci with these two intemai standards is shown in Table

Percent ciifference of ICP-MS results using ruthenium and thallium interna1 standards.

N S T Value 1 1131.0*11 1 23321.9 1 135.1*1.9

SRM 2557 Pt 1 Pd 1 Rh

FusioriICP-MS DBerence

Percent difference compared to NIST

NIST Value FusionnCP-MS

The results in Table 3.1 1 above show that Rutheniium and Thallium give good

PGE determinations but slightly outside acceptable range. Generaily, fireassay &'bit a

1.0 % relative error. nie average relative percent error for the MST 2557 samples was

found to be 1.04 % for Pt and an average of 2.0% for both Pd and Rh. As for the MST

2556 sample, Pt had a 0.72 % relative enor and Pd and Rh showed an average 1.2 %

relative error. Therefore, fiom the data presented above, it can be concludeci that Ru is not

an acceptable intemal standard for the determination of Pd and Rh. Thallium still is an

1 142.8*1 1 +11.80 +l .O4

-

Difference Relative Error (%) compared

to NiST

697.4*2.3 692.46.3

230.5I3.2 -2 -70 -1.16

-5.00 -0.72

131.311.4 -3 -80 -2.81

326*1.6 323.1G.4

51.2M.5 50 AM.6

-2.90 -0.89

-0.80 -1 -56

acceptable interna1 standard for the determination of Pt but shows the same =tic nature

of Ru. This erratic behavior is rsadüy seen in Table 3.12 below.

Table 3.12 Precision of ICP-MS resuits using Nthenium and thallium intenial standards.

Element 1 - n 1 Mean hg@ 1 - SD / RSD NA 1 SRM 2557 (Monolith) 1 1 1 1

SRM 2556 (Pellet)

A Precision based on a 95% confidence interval

The target precision for this study was < 2%. For both the Ru and Ti internai

standards, the precision is found to be above this target. This is largely due to the erratic

behavior of the intemal standards and as a result of this erratic behavior, Ru and Tl

possibly can not be possibly used as internal standards for the detemination of Pt, Pd, and

Rh. Therefore a more suitable set of internal standards is required.

Since nithenhm and thallium gave unacceptable results when used as interna1

standards, other elements were tried as interd standards. The second set consisted of

iridium and indium, also not presait in the dissohred autocatalyst samples. The general

accuacy and precision associated with the use of indium and iridium as intenial standards

can be seen in Tables 3.13 and 3.14 below,

Table 3.13 Percent merence of ICP-MS resuits using iridium and indium intenial standards.

SRM

SRM Mid&! 2556 Pt Pd Rh

MST Value 697.4*2.3 32611.6 51.2a.5

Aikali Fusion/ICP-MS 696.515.9 324.512.0 50.8&0.5

DEerence -0.90 -1.50 -0.40 ,

Percent Merence compared to -0.13 -0.46 -0.78 NIST

The relative percent errors associated with the use of indium and indium as

internai standards are found to be weii below the 1% k t for Pt, Pd, and Rh

determinations in autocatalyst. The recovenes for each of the PGEs are also much better

then those of Ru and Ti interna1 standards. Since indium and iridium show good relative

percent errors as compared to the certifieci results, the precision of these two standards is

shown in Table 3.14.

Rh u

135.111.9

135.811.6

+0.70

+OS2

Pd

233.2I1.9

231.6~1.7

-1.60

-0.69

2557 I

NIST Value

Aîkali FusionfICP-MS

Merence

Percent merence compared to

Pt

1131.0111

1131.3I6.8

+0.30

+0.03

Table 3.14 Precision o f ICP-MS r d t s using indium and indium k t d standards.

RSD % A Element

A Precision based on a 2a or 95% confidence interval

1

SRM 2556 (Pellet)

From the results above, the precision associated with the determination of Pt, Pd

and Rh are below the 2% limit . The relative standard deviations associateci with the use of

indium and iridium are well within acceptable lisnits and are even lower then those

reported by NIST (Beary and Paulsen, 1996). Therefore, indium and indium seem to be

the appropnate choice as intemal standards for Pt, Pd and Rh determination for new and

used autocatalyn samples.

- a

1131.36.3

SRM 2557 (Monohth)

Pt

I

1

The next set of internal standards tested not ody matched the Pt and Pd through

mass but also chemicaliy. Isotope dilution ICP-MS is considend to be the most accurate

and sensitive anaiytical method available for PGE determinations (Beary et al., 1994). The

accuracy and sensitivity for isotope dilution is better then that of NAA with Pt, Pd, and Rh

determinations. Rh is monoisotopic and therefore required the first type of internal

standard. Iridium was used to detemine Rh by ICP-MS. The isotopes were dissolved

16

Mean (-&&

6.8

- SD

1.2

ushg ultra-pure nitric and hydrochloric acid (Aldrich) over a hot-plate and were dihited

with D.I. water. The acid concentrations of the disdohted stock solution of isotopes were

closely matched to those of dissdved autcsataiyst to ensure totai compatiiüity between

the two samples and elimlliate ma& effects. One problem with the use of this second set

of intemal standarâs was that the software needed to be developed and the method only

became available at the end of this project, so fw resuits were obtained.

3.4.4 SAMPLE DRYING PRIOR TO DISSOLUTION

The autocataiyst, although previously drkd arrives at the laboratory in a wet or

darnp state and must therefore be dried (Anderson, 1987). Once the samples are dried,

they should be then stored in a d e s i ~ o r to prevent them fiom picking up water fkom the

atmosphere. In this project, the samples were âried by the method used by MST in the

certification of autocatalyst materiais (Beary et al., 1994). In the NIST dryiag process, the

sarnples are dried at 500°C for 2 houn and then cooled in a desiccator. This elhinates

both carbon and water fiom within the certined MST 2557 (honeycomb) and NIST 2556

(Pellet) samples. (See Figures 3.4 and 3.5)

Figure 3.4 Calcination redts fiom LEC0 and water anaiysis of MST 2557 (honeycomb) autocataiyst.

Figure 3.5 Calcination results from LEC0 and water d y s i s of NIST 2556 (Peuet) autocatalyst.

+ Percent Water ----#----. Perceni Carbon -+-- Percent SiiWr

The water content of several autocatdyst samples prevïouely analyzsd by firr assay

can be found in Table 3.15 below. The samples are used to validate the rllraü fision

preparation technique.

Table 3.15 Water concentration of prwiously dned and analyzed autocataiytic samples.

Sample Sample Smple Dry Sample Percent Number ID Added Wei@ water '

(#) (BI (BI (%)

4 S24350) 2,0743 2.0078 3.21 i 1.01 5 5247 1 (M) 2.0126 1.9926 0.99 I 1.05 6 S2427(P) 2,1515 2.0666 3.95 I 1.11 7 S 2 4 6 0 0 2.2097 2.1856 1.09 I 1.03

0 is the monolithic autocatdyst fom.

(P) is the pellet autocatdyst fom. a Al1 water results are reported averages of tripiicate dys is . Water was determined ushg

the weight Merence method.

As with the certified standards, the results in Table 3.15 show that the monoIithrtc

type of autocatalyst generally contain around 1% bound water whaeas the pellet fom of

catalyst general contains anywhere fiom 24% bowd water. Although the concentration

of b o n d water is quite mail, Ï t does play a large rote in the d y t i c a l resuits on the 1 8 -

MS. This is seen when cornparhg the wet and dried ICP-MS results ofNIST 2556 (Pellet)

and NIST 2557 (honeycomb) as seen in Table 3.16 below.

Table 3.16 ICP-MS results fiom wet and dned NIST samples

SRM 2557 (Honeycomb) SRM 2556 (Pellet)

Pt - - Pd - Eé Rh - Pt Rh -

A 1131*11 233.211.9 13s.la1.9 697.4k2.3 326I1.6 51.2*0.5

B 1118.6f8.8 230.9f1.9 133.8I1.8 683.3k6.4 317.1f2.2 50.2f0.8

c 1130.8I6.8 233.2f1.7 135.111.6 697.1f5.9 326.1f2.0 51.2f0.5 I l I I I I I I A NIST Certifieci Results

B Wet sample ICP-MS results

C Dned samples for 2 hours at 500°C and analyzed by ICP-MS

These results illustrate the importance of a dryin~calcination step in the sample

preparation process.

3.4.5 EFFECTS OF SAMPLE SIZE AND QUANTITY OF FLUX

A series of experiments were carrieci out to investigate how a variation in

the sample and flux weights would affect the recovery of Pt, Pd and Rh from used

autocatalyst. The sample Ne is particularly important when dealing with PGE-containhg

samples, as the metals are often unevenly distributecl so the Iarger the sample, the more

homogeneous and representativc the resulrs wiii be. To find the smallest ample size for

effective analysis, the standard refereace materiais MST 2556 (pellet) and MST 2557

(honeycomb) were fuseci ushg various weights ranging between 0.1 g to 0.5 g. AU these

samples were fised with 2.5 g of sodium peroxide foilowing the mahod listed in section

2.2. The resuits fiom NIST 2556 (Pellet) and MST 2557 (Honeycomb) can be seen in

Figures 3.6 and 3.7.

Figure 3.6 Effect of varying m p l e weight on POE extradon on dned autocatalyst samples(2 Hours @ 50o0C) (NIST 2556 Petlet)

Percent Extraction of Anaïyte (%)

Wei@ Of Autocatalyst Sample (gm)

Figure 3.7 EEect of varying sample wught on PGE d o n on dried eutocatalyst samples(2 Hours @ 500°C) (NIST 2557 Honeycomb)

Percent extraction of analyte (%)

Weight of autocatalyst sample (gm)

From the results in Fi~ufes 3.6 and 3.7, it was obseved thaî the minhum weight

required for effèctive autocataîyst saxnple fisions was about 0.25 g for NIST 2556 (100

percent extraction ofPt, Pd and 99.3 % Rh) and MST 2557 (100 percent aarsction of Pt,

Pd, and Rh) whüe ushg 2.5 g sodium peroxide aikali fim. It was ais0 observeci that larger

samples do not fise es well, p d I y because there was inainiCient hvr amilable. The

r d t s for the NIST 2557 samples compared weli to those of MST 2556. Consequently, a

0.25 g autocatalyst sample size is used for the remainder of this study.

Along with varying the sample weight, it is dso important to observe how the

amount of flux affects analytical renilts. Using the standard reference materials MST 2556

(pellet) and NIST 2557 (honeycomb), a 0.25 g autocatalyst sample was tUsed using

various sodium peroxide weights. The flux weights ranged between 1 to Sg additions. The

samples were nised using the method iisted in section 2.2. The results are shown in

Figures 3.8 (NIST 2556 - Pellet) and 3.9 (NIST 2557 - Honeycomb).

Figure 3.8 Effect of vwng flw waght on PGE extraction on dned autocatdyst samples(2 Hours @ 500°C) (NIST 2556 Pellet)

Percent Extraction (%)

Sodium Peroxide Wei@ (gm)

Figure 3.9 Effect of vaiying flw< weight on PGE extraction on dried autocatalyst samples(2 Hours @ 5ûû"C) (NïST 2557 Honeycomb)

Percent Extraction (%)

Weight Sodium Peroxide (gm)

The resuits seen in Figures 3.8 and 3.9 show aimost identicai results. For NIST

2556 (Pella) samples, the extradon of 99.6 % Pt, 99.2 % of Pd, and 99.8 % of Rh was

achieved. NIST 2557 (Honeycomb) r d t e d in extradons of 99.3 % of Pt, 99.3 % of Pd,

and 100.0 % of Rh. Thadore, the results indicate that a 2.5 g of fiwt is d c i e n t for use

with a 0.25 g sample, so this was used for these studies.

Since an automatic fluxer was available, some experiments were carrieci out to

compare results using this method with the slower manu81 fluxing method. It was

anticipated that the automatic fluxer would show a greater wnsistency of results. These

resuIts are shown in Tables 3.17 and 3.18.

Table 3.17 Relative error involved with hand fbsion of standard reference materials

SRM s 2 557(Honeycomb) Pt Pd Rh

NIST Value 1131 233.2 135.1

Merence +9 .9 -2 -7 -1.1 Relative error (%) compared to +0.87 -1.17 -0.80

NIST ~ SRM

2556 (Pellet) 1 1 I NIST Value 1 697.4 1 326 1 51.2

1 Relative enor (%) compared to 1 -1 -76 1 -7.1 1 1 -5 -45 1 NIST 1 1 1

Table 3.18 Relative error involveci with the automatic fision of standard reference materials

SRM 2557(Honeycomb)

NIST Value Alkali Fusion/ICP-MS

A comparison of the two tables above shows that a smaller relative percent error

DifEerence 1 +0.30

Alkali Fusion/ICP-MS Difference

Relative error (%) compared to NIST

compared to NIST is achieved when usîng the autornatic fiuxer for ail PGEs. The

Rh 135,111.9 135.8k1.6

. Pt

1 131.W11 1131.36.8

-1 -60 -0.69 Relative emor (%) compared to

NiST

improved results on more noticeable with the MST 2556 (Pellet) samples than those of

Pd 233.2*1,9 231.&1,7

+0.70 +OS2 +0.03

SRM 2556 (Pellet) NIST Value

696.515.9 -0.90 -0.13

NIST 2557 (Honeycomb) sarnples. A comparison ofthe repeatability of each of these two

sample preparation methods may provide for additionaf information. The repeatabiiity for

324.5*2.0 -1.50 -0.46

the two methods of fision are seen in Tables 3.19 and 3 -20 below.

Rh 5 1.2a.5

Pt 697.4~2.3

50.8G.5 -0.40 -0.78

Pd 326*1.6

Table 3.19 Repeatabüity associated with hand fision of autocatalyst

Element 1 - n 1 Mean (u& 1 - SD l

a Results reported on a 95% confidence interval.

%RSD a

SRM 2556 (Pellet) Pt Pd

Table 3.20 Repeatability associated with the automatic fusion of autocatalyst

16 16

a Resuits reporteci on a 95% confideme interval.

685.1 302.8

1131.3 23 1.6

SD -

6.8 1.7 1.6

0.5 2.0 5.9

Rh

SRM 2556 (Pellet) Pt Pd Rh

15.8 26.7

RSD % '

1.2 1.5 2.4

. 1.9 1.3 1.7

4.6 1 17.6

15

16 16 15

135.8

696.5 324.5 50.8

From the resuits in the pmcision tables above, it is observed that the automatic

fùsion of autocatalyst samples d a s provide for a Mer mahod of sarnple prepmtion

The method repeatabiiity for automatic fùsions are much betta thai those of manuai hand

fisions since automatc sample fùsion treats all samples equally thus eliminating the

possiiüay of randorn errors d a t e d with the inaaual Rision of samples. Such errors are

due to the improper sample agitation wbich varies W e e n samples, the various flux

temperatures due to the changing cnicible location over the fiame, and sample spülage,

loss, or sputtering due to overheating. As a result of the findings above, ail samples were

fiised using a LEC0 automatic fluer.

3.5 SMLE FUSION RESULTS AND DISCUSSION

The deternination o f Pt, Pd and Rh in both NIST and routine production samples

relied h e d y on the ability of ICP-MS to provide highly acairate and precise

determinations of the PGEs in the new and used autoatalyst sampies. An examination of

the reailts suggests that they are clearly dependent on the choice of internal standard used

to monitor each of the PGEs. Since two types of internal standard were used in this

project, it is important to compare the d y t i c a l results from each of these two types of

intemal standard. The firsî type of intemai standard included elements not present in the

dissolved autocatalyst mat& but that closely matched the mass of either Pt, Pd or Rh and

is discussed in Test Method 3G The second set of intenial standards was made of

isotopes of Pt and Pd. The use of this isotope düution technique is expected to give

excelient resuits since the standards match tk analyte elements in both mass and chernical

properties (Beary and Paulsen, 1996). This technique cannot be used for monoisotopic

elements such as Rh, so a cornVition of the two internai standards was required where

Rh detenninations were needed. The second method is seen in Test Method #3B. An

exploration of the results fkom the two test rnethods foiIows.

3.5.1 TEST METHOD #3A : DISCUSSION OF RESULTS FROM MASS MATCHED

INTERNAL STANDARDS.

Two sets of internai standards were d e d . The first set consisted of

Ruthenium for Pd and Rh detenninatiom and Thallium for Pt determinatiom wbile the

second type consisted of Indium for Pd and Rh determinations and Iridium for Pt

detenninations. The R f l combinations gave poor resuits and so was not used m e r .

Indium and iridium wexe selected as the internal standards for PGE analysis on the ICP-

MS. The accuracy and precision of the tesuIts for the two NIST samples d y z b d with

indium and iridium as internal standards can be seen in Tables 3.13 and 3.14.

The results pre~nted in the two tables above show no bias with good recoverks

and repeatabilities. Thus the choice of indium aad iridium as internai standards proved

effective. As a result, 24 separate and previously anaiyzed autocatdyst samples were

selected and analyzed for PGE determination using this alkali fusion dissolution technique

followed by ICP-MS analysis. The results fkom both the nickel suifide fue assay method

and Ledoux's (A-1) acid dissolution and fire assay method (see Appendix) are compared

with the resuhs fiom thîs project.

The platinum redts are considered first. Table 3.21 presents results obtained for

Pt analyses using this test method dong with correspondiig results obtained using the

rnethods dedbed in Appendix B. The last two columns give the percent difference in

result between the test method and the standard methods employed nickel ailfide

collection and acid dissolutionlfire ssay cokction.

Table 3.21 ICP-MS resuhs for Pt detemidon compared with nickel sulfide fin-assay and phosphoric acid/fire assay.

Sample NiS Fire Phosphoric ICP-MS % Diffaaice % Merence Assay A acidfire-

as=Y = # c1d8 dg CiB/g to NiS Mahod to Acid/Fiue

Assay Method

2427 583.89 603.09 585.10 0.2 1 -2.98 2428 922.64 925.04 922.46 -0.02 -0.28 2435 420.00 424.12 417.41 -0.62 -1.58 2443 885.95 893.15 886.37 0.05 -0.76 2445 463.89 570.18 570.56 22.99 0.07 2460 870.86 869.84 864.08 -0.78 -0.66 247 1 921.95 913.04 915.42 -0.71 0.26 2475 663.78 686.06 679, t 7 2.32 -1.00 2484 845.49 882.86 872.80 3 .23 -1.14 2493 705.95 696.0 1 707.89 0.27 1.71

2495* 914.99 915.09 895.70 -2.1 1 2.12 2502 655.55 650.06 644.34 -1.71 -0.88 2970 937.38 1002.18 937.54 0.02 -6.45 2935 798.18 889.04 802.19 0.50 -9.77 295 1 852.35 911.32 851.94 -0.05 -6.52 2912 934.23 934.29 934.9 1 0.07 0.07 2962 913.04 976.12 976.51 6.95 0.04 298 1 856.12 915.09 914.37 6.80 -0.08 303 1 663.78 658.98 666.1 1 0.3 5 1 .O8 3048 677.83 673 .O3 673 -93 -0.58 0.13 3007 692.92 689.83 694.72 0.26 0.71 3004 643.90 629.83 643.16 -0.12 2.12 3025 717.61 739.89 718.3 1 O. 10 -2.92 3016 656.20 665.15 665.5 1 1.42 0.05

A Anaiysis done with Nickel sulfide fue assa, and teiiuriurn CO-praipitation folowed by ICP-OES and AAS spectd analysis. Results an of tripliate assays. Anaiytical r d t s reporteci from phosphoric acid dissolution plus h a s s a y digestion combinations foliowed by ICP-OES specnal dys is .

ICP-MS redts fiom alkaü fused samples foilowed by anaiysis on a Perkin Elmer Elan 6000 ICP-MS using Indium and Iridium intemal standards. Results are an average of quintupla assays.

A doser examination of the resuits in the tabk shows tbat in plmost every instant

the test method is close (within 1%) to one or both of the standard rnethods. The

exception is #2495 which is about 2% lower then both of the results. Howeva, the nickel

suifide and phosphoric acid/fkassay resuhs themsebes difib by more tban 2% for

samples #'s 2427,2445,2970,2935,2951,2962,2981, and 3004. From this perspective,

a 2% Merence in one nsult suggests the method compares f o d y with the standard

method.

The average precision for quintuplet a~says d a t e d with these 24 values was

found to be 1.13% on a 95% coufidence interval. A Students t-Test was pedormed to

measure signincant difference between the test mahod resuits to those of the nickel

sulfide and phosphoric acidlfireassay methods. A cornparison of the test method r d t s

and the nickel suifide results found a 1 ta 1 of 1.763. A compatison of the test method

results to the acidlfire-assay method resulted in a 1 ta 1 of 2.057. The t23,01325 was found to

be 2.069 (Khazanie, 1990). These values show that there are no significant dierences

between the test method of the student method and the nickel sulfide and phosphonc

acid/fire-assay standard methods at the 95% confidence level. This is also true for the 99%

confidence interval (t23,0.0025 = 2.807).

The palladium test results are considered next (Table 3.22) using this test method

dong with corresponding results obtained using the nickel s a d e and phosphonc

adfire-assay standard methods descri'bed in Appendix B. The lest two columns give the

percent difference in result between the test method and the standard methods employed

by the nickel suIfide method (column 5) and the acidlfire-assay method (column 6).

Table 3.22 ICP-MS r d t s for Pd determination c o m p d with the nickei sulfide fire-assay r d t s and the phosphoric ricidiire-assay iesults.

Sample NiS Fire- Phosphori ICP-MS % Merence % Diffefetlce Assay A cacidJfire-

assay # ~ d 6 ~ d 8 pg/g to NiS Method to AcidFie

Assay Method

A Anaiysis done with Nickel sulade fire assay and tciiuriurn co-precipîtation foUowed by ICP-OES and AAS spectral 81181ysiis. Resuits are of tripiicate assays. Anaiyiical resuits reporteci âorn phosphorîc acid dissoIuti011 plus fie-assay digestion combinations foiioweâ by ICP-OES spearal anaiysis. ICP-MS resuhs h m alkali fùsed samples fdowed by d y s i s on a P e r h Elwr Elan 6000 ICP-MS using Indium and Iridium i n t d standards. Resuits are an average of quintuplet assays.

A closer examination of the Pd results in the table shows that in almost mry

instant the test method is close (witbin 1%) tto one or both of the standard methods. The

exception is #2495 which is about 2% bigha then both the nickel d i d e and phosphoric

acid/fire-assay results. Unfortunately, even aAa repeated alkali fùsions and ICP-MS

analysis, the Pd results never came close to either the nickel d d e nor the acid/fire-asay

resuhs. As a result, the sample is beüeve to be mothm prepared autocatalyst mple,

therefore it was removed nom our sample populations by using the Dkon & Dean outliner

test (1951).

The average precision for quintuplet assays associated with these 24 values was

found to be 1.09% on a 95% confidence inteoral. A Students t-Test was performed to

measure sisnificant diierence between the test method results to those of the nickel

sulfide and phosphoric acidlfire-assay results. A cornparison of the test method results and

the nickel suffide results found a 1 ta 1 of 1.521. A cornparison of the test method results to

acidfire-assay method resulted in a 1 t 1 of 0.021. The ta, 0.m was found to be 2.069

(Khazanie, 1990). These values show that there are no signifiant ciiffierences baween the

test method of the student method and the nickel sulnde and the phosphonc acidfireassay

standard methods at the 95% confidence Ievel. This is also tnie for the 99% confidence

intervai (t23.0.0025 = 2.807).

The rhodium results are now considerd. These results are given in Table 3.23

dong with conesponding resuits obtained ushg the nickel sulnde and phosphonc acidlfire

assay standard methods described in Appendix B. The lest two columns give the percent

dEerence in result between the test method and the other two standard methods.

Table 3.23 ICP-MS r d t s for Rh detaaiiaation compareci to the nickel d d e fire-assay redts and the phosphoric acid/hassay resuits.

Sample NiS Fire- Phosphoric ICP-MS % Mefence K Difference AssayA acidlfire

assay # ~dE5 pgig to NiS Method to AciWie

Assay Method

Mysis done with Nickel sulfide fbe assay and teIIUnun CO-precipitation followed by ICP-OES and AAS s p d anaiysis. Resufts are of triplïcate assays. M y t i c a i results reported from phosphoric acid dissolution plus fireassay digestion combinations foliowed by ICP-OES spearal analysis. ICP-MS resuits âom alkali fùsed samp1es followed by d y s i s on a Pakin Elmer Elan 6000 ICP-MS using indium and Iridium intenial standards. R d t s are an average of .

quintupkt assays.

A doser examination of the Rh d t s in the table shows that in aimost m r y

instant the test method is close (within 1%) to one or both of the standard methods.

There are t h e exceptions whkb are #'s 2435, 2445, and 2495 which are respectively 27

%, 2.5%, and 9.2 % lower or higha than both the other two method nsults. However,

the nickel sulnde and phosphoric acid/&easay resuhs themseives mer by more than

50% for sample 2445 and more than 9.2 % for samples 2427,2428, and 2443. For a 2.5%

variation, the foUowing INCO and Ledoux samples that vary by more than 2.5% are 2427,

2428, 2443, 2475, 2493, 2502, 2935, 3004, and 3031. From this perspective, a 2.5%

diffmnce in one result suggests the rnethod cornpans f o d y with the standard method.

As for the other hHO samples, 2495 and 2435, even &er repeated alkali fiisions and ICP-

MS analysis, the Rh results never came close to either the nickel suifide nor the a c i d / h

assay results. As a result, the samples are believed to be another pnpared autocatalyst

sarnple but due to the disappearance of the original sample container, this will never be

confimed. As a result, the sample were removed fiom Our sarnple populations by using

the Dixon & Dean outliner test (1% 1).

The average precision for quïntuplet assays associated with these 24 values was

found to be 1.23% on a 95% confidence interval. A Students t-Test was performed to

measure significant difference between the test method results to those of the nickel

suifide and phosphoric acid/fireassay resuits. A cornparison of the test method results and

the nickel sulfide method results found a 1 ta 1 of 0.1 1. A cornparison oftbetest method

results to phosphoric acid/fireassay method resuited in a 1 h 1 of 0.17. The tu, 0.025 was

found to be 2.069 (Kbazanie, 1990). These values show that there are no signifiant

ciifferences between the test method of the student method and the other two standard

methods at the 95% confidence level. Tbis is also m e for the 99% coddence interval

(t23,O.oOZS = 2-807)-

The results presented above indicate that the f int test method @vas acceptable

redts and could be used to replace the nmeat standard nickel sulfide method. Test

method #3B is now considered.

3.5.2 TEST METHOD 3B: DISCUSSION ON RESULTS FROM ISOTOPE DïLüTïON W R N A L STANDARDS

Before the isotope dilution studies could be tested, it was necessary to develop the

required software for the instrument. This method will look at the results achieved with

the NIST autocatalyst samples. The percent difference associated wîth the m a s matched

indium and indium standards is seen in the Table 3.13 while those using the ushg ~ t ' *

and ~ d ' ~ isotopes and Iridium interna1 standards are seen in Table 3.24.

Table 3.24 Percent difference of ICP-MS results using ~ t ' * and pdlW isotopes and indium internai standards

NIST Value 1 1131.0*11 1 233.211.9 1 135.111.9

Percent Merence compared 1 -0.07 1 -1.35 1 -0.96

SRM

NIST Value 1 697.4k2.3 1 32611.6 1 51.2I0.5

Percent merence compared to -0.65 NIST 1 1 1 +Os8

Table 3.24 shows that isotope dilution shows no bias and provides excelient

results. The relative error of this method compareci to the MST fesults is under the one

percent imposed INCO limit for PGE deteminations in autocatalyst for most uialytes

(except NlST 2557 - Pd (1.35%)). The isotope dution resuits are a h closely match

those listed in Table 3.13 for the In and Ir intemal standards. As a result, this test method

muid be explored even fiutha.

Indium and iridium provide excelient d e s and at the same time really good

instrumentai precision. The precision rissociated with the use of these two internai

standards is seen in Tables 3.14 and 3.25 below.

Table 3.25 Precision of ICP-MS results ushg ~ t ' ~ and ~ d ' " isotopes and

indium intenial standards.

Element 1 - n l ~ e a n (u&l - SD 1 RSD%* SRM 2557 (Monolith) 1 1 1 1 1

SRM 2556 (Pellet) 1 1 1 1

A Precision redts (%MD) are reportecl on a 95% confidence interval for aii

of the 8 independently determined ICP-MS r d t s .

A cornparison of the pre'sion for the two test rnethoâs shows thaî isotope dilution

can provide for a more p h s e determination of PGEs in MST 2557 (honepmb)

autocataiyst samples than ushg the i n ~ u i d i u m intemal standards. On the other han4

the indiumiidium internai standards provide for a better precision detemhations of

PGEs in MST 2556 (pellet) autoataiyst samples. With fbrther n f i n e n t of the isotope

dilution method, the method may be worth deveioping. It provides for both good 8ccu~cy

and precision.

Chapter 4 Conclusion

Three test methods were studied for the dissolution of autoccitalyst saxnples pnor

to ICP-MS anaiysis. These thme m*hods were open besker acid digestions, microwave-

assisted digestion, and allrali nision fhious. Of these three methods, two methods (acid

digestion and microwaveassisted digestion) were not able to M y dissolve the

autocatalyst snatrix and the third method (alkali hion) was the oniy m e h d capable of

dissolving the autocatalyst matrix. Both acid dissolution a . miaowave digestion wuld

effeaively extract Pt (>97% acid dissolution and >99% microwave dissolution) and Pd

(>97% acid dissolution and >99% microwaw dissolution) but would require a correction

factor to report Rh (>91% acid dissolution and H(r/o rnicrowave dissolution)

concentrations. Alcali tùsion was able to dissolve the matrix and extract all PGEs in the

autocatalyst samples (-10M Pt and Pd, and Rh). When dyzing the îùsed samples two

types of intemal standards can be used. The first is mass-matched intenial standards and

the second is isotope dilution intemal standards. Although much of this project fonised on

the development of the mas-matched intenial standard technique, both interna1 standards

could be readily used to effhvely analyze trace PGE concentrations afker sample fusion.

As a result of the alkali fbsion r d t s , a fiist, simple, sensitive and cost4èctive

method was developed for the analysis of PGEs in autocatalyst.

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0

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Appendix A Autocatalyst

The nickel sulnde dieaion of the PGE was adapted fiom the method ofRobert et

al. (1 97 1). Cumntly, Inco Ltd. staff use this method for the determination of PGE in

autocatalyst and other samples foiiowed by AA or 1 8 . This method was carried out as

well in our present work for the cornparison of accuracy 4th our proposed method. The

procedure Uivolves the foilowing steps:

1. The components of the fusion mixture ( shown in Table Al) were added to a 40g

clay cnicible.

Table-Al Fire assay flux for nickel suifide coilection

2. A O. 1 Assay ton (2.9174g) of the autocatalyst sample was weighed out in a

weighing dish, and transferred to the loaded cruciile.

Inaredient

Borax

Sodium carbonate

Silica

Nickel

S u b r Powder

Wei@ (@

60

30

15

18

9

The mixture was caretiilly stimd with a spahili until it was thoroughly mixeci.

The crucible was placed in an electric fiiniace and heatd at 980 OC for 90 minutes.

After the fiision was complete, the auaile was removed fiom the fimace and the

fusion melt was quickly poured into a mold, wvered with a kat resistant lid and

allowed to cool domi to room temperature.

The nickel suEde (-27g) button containhg the PGE's was sepmted from the

slag. The slag was saved in the original pot and manalyzed for any losses of

PGE's in the NiS fusion step. This subsequeat analysis was cMied out by a lead-

collection analysis fire asssy.

The button was transferred to a 1000-mL beaker, 6 0 0 rnL of cunc. HCl were

added and the mixture left overnight on a hot plate at low heat to dissolve the

button. When the dissolution of the button was complete, the beaker was removed

fiom the heat and aliowed to cool slightly.

15 mL of tellurium tetrachloride (TeCL) were added, and the mixture was boiled

for 5 minutes. 4 0 m . of starnous chloride (SnCI*) were added &er allowing the

mixture to cool slighîiy.

The solution was placed back on the hot plate and boiled for another 10 minutes.

Note: The purpose of the addition oftelluriun tetrachloride and starmous chloride was to

ensure wmplete removal of pS Pd, and Rh h m solutio~

9. The manire was then filtered through a Whatman glas fibers filter grade F and the

tiltrate discarded. The watch glass, beaker, and @ter fiinne1 were washed with

(vh) K I .

10. The filter contaking the PGEis was transfened back into the origmal beaker,

DO mL of HCl and 4 0 mL of HNO, were addeâ, and tbm the m*xture was Wied

for 1 hou.

1 1. The solution was then fdtaed through a Whatman glas microfibre fïiter paper and

then the beaker and filter holder were Msed with 50% (vhr) HC1.

12. The filtrate was placed back on the hot plate, and heated to dryness over low

heat on a padded hot plate.

13. 25 mL of conc. HCI and 5 mL of conc. HN03 were added to the residue, and the

mixture was heated gentiy until the POE'S were completely dissolved.

14. The solution was transferred to a 100 rnL volumetric flask and diluted to the mark

with deionized water and mixed well. The solution was then anaiyzed for Pt, Pd,

and Rh by ARL 34000 ICP.

15. The PGE's lost to the slag in the MS fiision step were recoverd through a Pb

collection, cupellation to 100mg Pb bead, and digestion with aqua regia. Final

measurement was done by ICP-OES.

The Ledoux mahod is a combination of acid dissolution and fireassay. The

method layout for this thesis orighates fiom a fjur dating to Aprii 19, 1989. The mcthod

can use either or both AAS or ICP or DCP. The proadure involves the foliowing steps:

1. Four portions of the sample (100 me&) weighing between 8 and 15 gm are a a n s f d to a

800 mL beakers, The samples are weighed to the nearest 0.1 mg and dried at 125OC.

2. To the @et sarnples m the 800 mL beaker, 35 mL HISOh 35 mC H a and 50 mL of water

are added and the solution is heated to a slight boil over one hour period when decomposition

should be completed.

3. To the monolith samples in 800 mL in tdon beakers, add 50 mL of H20.75 mL ofHF, and

15 mL ofH2S04. Evaporates to fumes of H2S04. To the salts in the 800 mL g l a s , and

respective teflon beakers, add about 100 rnL of water, about 100 mL of HCl and 50 mL of

brornine water. Boil to a minimum of 1 hour to convert rhodium to the chloride form.

4. Dilute to 400 rnL, add about 5 g of sodium thiosuIfate, heat to boiling, and just keep at boiling

point for 2 hours.

5 . Allow to settle for minimum of 3 hours. Filter and wash thoroughly with cold 1% HCl.

6. Wash precipitate back into original 800 mL beaker, pour hot dilute (1:2) aqua regia through

paper, boil and filter into reserve filtrate nom the previous step.

7. Any residue srnd in the case of pellet, larger in the case of monoliths is treated as foilows:

A) Pellets: Fume paper with HNO3 and HCI04 to dryness. Treat with aqua regia and combine

with the rnain solutions.

B) Monolith: Ignite in a scarifier, scorify in presence of about 25 mL of Au and cupel. Dhsolve

aqua regia and check on plasma or AAS for ntaineâ Pt. Pd and/or Rh.

8. Evaporate the aqua regia solution wntaining the bullr of Pt, Pd, and Rh, and t r d e r to

200mL volumetnc flasks. Take fkom each flask a 15 mL aüquot with dry pipet and check the

approxhate Pt, Pd, and the exact Rh content by AAS. Clean the pipet with water, and

combine with the main solution.

9. Palladium present : Transfer to sepraratory bels and extract the pdladium by repeated

treatments witb chlorofonn and sodium dirnethyl glyoxime soluti~ns~

IO. Evaporate the chloroform phase soiutions to byness. Add small moullfs of nitric and

perchloric acids and again evaporate to dryness. Dissolve in a fiw mL ofaqua regiLa, transfer

to 100 mL volumetrk fiasks and determitle Pd by AAS or DCP. T d e r the aqueous phase

(Pd removed) to 600 mL beakers.

11. Evaporate to 100 mL, add 25 mL of nitric aciâ, 10 mL of percbloric acid and 5 mL SuKiinc

acid. Evaporate to dryness. Evaporate twice to dryness, with the intm*ttent addition of s m d

amounts of HCI. Dissolve residue in 50 mL of 3-% (VN) HCl and transfer to volumetric

flasks of proper size. (Maximum for 200 g, 10 mg of Pt).

12. Repare standards by dissolvhg pure Pt, to cover the range of Pt determination, in aqua regia

Add appropriate amounts of Rh chlorine solution nitric acid-free. (See previous AAS

determination).

13. Dilute to approhtely 800/0 of the volume of the flasks with 300/. HCl. Add 30 mL. 28%

stannous chloride (VN) in 1 : 1 HCI. Six milümeter ofthe SnClz solution per 200 mL.

14. Compare the Pt content of the smaples and standards by Merenta! spectrometry.

15. In the absence of Pd, omit the DMG chloroform extraction, but otherwise following the

procedure as written.

ANALYST: MP Simple FUtniw - R:UcP-MSUri970127.SAM 04-16-1997 03:07:0 1

Po6 SPU ID SPLE DESC WEIOHT VOLUME

ANALYST : MP 04-16-1997 03 :07:0 1

POS SPLE ID SPLE DESC WElQHT VOLUME

Original Data File: 3MTUlzr.ntr Analyzed On: Monday, 3anuaiy 27,1997 15:54.09 Anatyred In: mgMg

9 TO: MP Analyreci By: MP

SAMPLE IDENT. Rh Pd Pt #Drift i Standard Drift 1

tinse RINSE #DR!FT 1 R1NSE mhnk 2435FU-1 2435FU-2 2435FU-3 2435FU-4 2435FU-5 2493FU-1 2493FU-2 2493FU-3 2493FU-4 2493FU-5 2471 FU-1 2471 FU-2 2471 FU-3 2471 FU4 2471 FU-5 S2556-1 S2557-2 2427FU-1 2427F U-2 2427FU-3 2427FU4 2427FU-5 246OFU-1 2460FU-2 246.OFU-3 246ûFU-4 246OFU-5 2495FU-1 2495FU-2 2495FU-3 2495FU-4 2495FU-5 2428FU-1 2428FU-2 2428FU-3 2428FU-4 2428FU-5 2475FU-1 2475FU-2 2475FU-3 2475FU-4 2475FU-5 2502FU-1 2502FU-2 2502FU-3

ritme rime Standard check rime Sample Bbnk Dry Dry Dry Dry Dsr Dry Dry Dry Dty Dsr Dry Dry Dry Dry Dry 2556-1 2557-2 Dry Dry Dry Dry Dry Dry Dly Dry Dry Dly Dry Dry Diy Dw Dly Dry Dry Dry Dry Dry Dry Dry Dry Diy Diy Dry Dry Diy

2502FU-5 #Drift 1 rime RINSE #DRIFT 1 RINSE #Blank 2484FU-1 2404FU-2 2484FU-3 2484FU-4 2484FU-5 244SFU-1 2445FU-2 2445ÇU-3 2445FU-4 2445FU-5 2443FU-1 2443FU-2 2443FU-3 2443FU-4 2443fU-5 S2556-1 S2556-2 S2556-1 +SPK S2557-1 S2557-2 #Drift l

Sample ID: sample blank Sample Datemme: Wednesday. November 1 3.1 996 I3:42:3l Sample Desciption: sample blank Solution Type: Sample Blank File: Number of Replkates: 1 Peak Processing Mode: Average Signal Profile Proœssing Mode: Average Dual Detector Mode: Dual Dead Time (ns): 70

Sample File: Method File: C:\elandata\Method\TotaIQuant.mth Dataset File: C:\elandata\DatasehTotalQuant Analysis\sample blank.028 Tuning File: defauktun Optimization File: default.dac Response File: C:\elandata\System\cunent.rsp

Analyte Intensities

Analyte H He Li Be B C N O F Ne Na Mg Al Si P S CI Ar K Ca SC Ti v Cr Mn Fe Co

Concent ration lntensity lntensity Units Not Measured Not Measured

0.00427 2.00 0.00000 0*00 1.31 570 346.00

2258.04093 21 1257.00 147870028.08100 1 19971 7.00

Not Measurd 9131 173.00

57.00 46.52578 371 59 ,O0 1 7.1 5930 41 78.00 71 30577 20276.00

266.55234 11 1713.00 65.23790 2909.00

35iï952.07515 52379444.00 31 3571 85.61 098 22û35723.00

69220341 35.00 1647.201 42 618002.00 563,09956 32501 7.00 21.27708 1OS51.00 0.00000 0.00

792.88298 323374.00 56.91 161 23762.00 1.97555 1071 .ûû

4978.26787 2442899.00 1,08519 456.00

TotalQuant Equations

Analyte Equation

AA HyQide GFAA Jbhsion MS 1.50 0.02 1.50 0.003

3 ~ ~ 1 ~ l l t FIQnt Hg ICP ICP- AA Hw& GFAA J3hh hdS

Mo 45 0.08 0.003

AU detection iimits are given in micrognims per lits and were detamined using elcmcntal standards in dilute aqueous solution Al1 detcction limits are based on a 98% conGdaice lcvcl(3 standard deviations). Atomic absorption (Mode1 5 100) and ICP mission (Plasma 2000) dctection Wts wcre &termineci using

instrumental peramctas optimi7Ldfbr the individual clcm~lt ICP anission dctccticm Iimits obtained dMng muitieiem~lt auaiyscs wiii typidy bc within a k t o r of 2 of the values s h o w

Cold vapor mercury dctecticm limits wat dctamid with a M l 0 0 or FIAS400flow injection systan with amaigamation accemq. The detection limit without an amaigamation acmsoxy is 0.2 iigII, with a

holow cathode b p , 0.05 lia with a Systan 2 eicciro&lcss dbchqc lamp. (Thc Hg detaction limit with tfitdcdi~~tedFIMS-100mFIMS~maciaydyzasis<O.O1OPGlLwithoutrinamd~ti~1

accessory and < O.ûûf lig1L with an amaIgdon acœsoxy .) HvQide deteftion lgaits wcre dctamuacd USinganMHS-IO MaciayDIydridt qswm.

Graphite W AA deteciion limits were d c t c d d ushg 50-ILL sample volmes, a L'vov platfarm and fiill STPFcooditiolls(ModelS100FC with5100~7riarisnF~Moda)eaModcl4100ZL). Graphite

~dctectimlimitscanbtfiPthcraihwirnlbythrwofnp1icateinjccti0ll~. ICP-MS detection limits were detamincd ushg an ELAN 5000. Lettas foITowing an ICP-MS deîection fimit

value der to the use of a less abundant mass for the detanmation as foiiows: a- (213, bCa 44, d - Fe 54, d-Ni60,e-S34,f-SeaL,

1 14