The recovery of zinc from solution obtained by thedissolution of zinc from sphalerite with ammoniacalsolutions at elevated temperatures and pressures

Item Type text; Thesis-Reproduction (electronic)

Authors Ammon, Robert Leroy, 1930-

Publisher The University of Arizona.

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THE REOQVERX OF Z W FROM SOLUTION OITAMSB BX THEDISSOLUTION OP ZING FROM SPHALERITE WITH A M Q m G A LSOLUTIONS AT ELEVATED TEMPERATURES AI® PRESSURES

' ’ ■ ' ' bX " . -Robert Lo Ammon .

A ■ Thesis .Snbmitted to the Faculty of the DEPARTMENT OF'MINING'AND METALLURGICAL-'ENGINEERING

In Partial Fulfillment of the Requirements For the Degree of - MASTER OF SOlENOm' '

In the Graduate O.ollege - - UNIVERSITY OF ARIZONA.

19 5 9

d:::,';’>C.vV ;.

v .■; :r J.- • . V

STATEMENT BY AUTHORThis thesis has been submitted in partial fulfillment of

requirements for the advanced degree of Master of Science at the University of Arizona under a cooperative agreement between the University of Arizona and the United States Bureau of Mines. The cooperative agreement provides that the privilege of publishing all or part of the text has been granted to the United States Bureau of Mines. The thesis is deposited in the University of Arizona Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgement of the source is made. Requests for permission for extended quotations from or reproduction of this manuscript in part or in whole may be granted jointly by the Dean of the Graduate College and the United States Bureau of Mines when in their judgment the proposed use of the material is in the interests of scholarship. The author hereby accepts the conditions of publication as stated above.

SIGNED:

APPROVAL BY THESIS DIRECTORThis thesis has been approved on the date shown below:

T. G.Chapman Director of Thesis

' D a t e f '

w m m & m w M M T

The author 'c-Jishes to express his thanks to Dro T^ G0 Chapmanof the College of Mines,, and to Hr0 Carl^Rampacek of the UnitedStates Bureau of Mines for their assistance and. constructive criticismduring the preparation of the thesis and the conduct of the expert”mental work described herein. Appreciation is also expressed to

" -t-.r ' t ■ ■ - tv":::lf o :B6..:Sd; Stiles 'of the; United States Bureau of "Mines .for his. aid ■in chemical analysisg and to others who have given, aid and advice0

'r. > * ' " . 4. ■

Table ef Contents

I - ,■■■.. Introduction - -

Page

Purification and Electrolysis of Zinc Sulfate.' S O X H f b X O Z l S , v*=f '' e= «=a w , . "» «=• oa, ear r=a cat «=at =. F=tt cs» #3 «s

'Purification.and Electrolysis of Ammoniacal Zine Solutions *=* ** ™ ^ ^ —■ w, «• = ™ “ ** —. ^ «=* ^ ^ Sf

7-8

Production of Zinc Oridey^ ,« '« # a #. ■ - Production of Zinc Dust' * ^ «

' '-v Object of Experimental Work =-«*=-” « « «,«» ; -■ vQ ■ 'II Materialss Equipment and Analytical Procedures « «* « ** 9 '

Description of Concentrate ~ « « « « . » » «i «.«.» «.v 9 ;- '■ •; Description of Equipment «- « « » >» « « » » m « w « w 10

■ . ; The Antoclaye * «=•■ m. m-'m-m «■'■:■•=#'w-.." «=* «> = « ««» ti « «. 10■ ■ ''; '''' - ' / The Still '* “ ™ ™ ™ O ^ 'tea m #9 pa llj.

Eumaces »• * * ^ ™ ^ ■= e* *«» ^ ## .fs* ■ ««*; «= 1^■ : The' 'Electrolytic Apparatus '«=» *< » ;*■ «# « « » ■« ■ *'w * 16 ■

Ohemrcal Analyses ^ ^ ■*=* ^ ^ /=# «=* h M *» ^ IS 1III ■' Erperxmental Work .* = * ^ ^ ^ «• =■ >= ,*=• . <=■ « *=» «> •=» •* .»» »» 18

Procedure for the Determiriatlon of Time andDegree of Agitation * » '■»» .« « !» !«._« *« <*» —' _»»/« « «' 18'

■ ;: ; ' P' v.:: Determination of ' Time'/SmdvBegree ' of, Agitation *' **;. ' 20 '. ' Improved Design of Autoclave to Secure , ; _

: . Better Gontact of : .Reactants >= ~ » ■= » » ^ • 21i

Chapter PageDetermination of a Satisfactory Washing ; \ ■tPechniQtxe ^ ™ ^ ^ *=’ = .■ w ^ <m «== = =* ^ ™ w . e* ^

Residues Washed '•with Various Quantities of Water ® 23. Residues Washed with Various Quantities of 10 Per Cent Aipionia. Solution « = ~ » - 2h

The Recovery of Zinc by Distillation of Ammonia : 25• Purification Of Pregnant Solution « « ■«. 25

f:: Precipifatidn of' Basie • Zinc Sulfate » •=. ■». « 26; V Calcination of Basie Zinc Sulfate » *». « « «.' « = ; 27.i .Reduction of the Calcined Zinc Salt with Hydrogen 28 'The Recovery of Ammonia from Pregnant Solution ‘hy Distiliation «; « w «=» -#» m * * ' <=» >» »» «*_.*»■ » , 29

• Recovery' .of Ammonia During the Purging and ' .. . .■ ' Filtering.■ deration «'•*« C « w «.« « « « .«• '« ' 29

^ #8*| **■-■«* ' WRetention Of Ammonia in 'Washed Residue.. , Distillation of Ammonia from Purified .. :

Pregnant Solution w '«'«: «=■ « « #» « «» 1= m =>. - 31Recovery of Zinc from Ammoniacal Zinc : ■ w . 'Solution by Electrolysis »»>» » u ^ -_<« «, ■=. «.->»■- « 32

Purification of Zinc SdlUtion hy Cementation #» >* •: 32/ ' - .:Preli,minary:-Electrolysis'' « „=.«. .» « 33.v: Electrolysis of Zinc leach Solution * « «-(«. « *« . 3U. Repurification of leach Solution by theAddition of 'Ferric. Sulfate ~ »' » » «*• • “ ■' . .■ 35Repurif ic at ion of Leach Solution by the Additiondf Ferrous.Sulfate;, and Oxidation ,*=* « » . 36

w ' w *=* . W ' 38Bibliography1;;; ■; . - : f v ... : ... ■ .. . fCbnclusions and Reeoimraendations ^

List of Tables

luTEiber .. " \: ■ Page,;' L;. ' - The'Effect of Mashing the Leached. Kesidues with

Various Q-uantitles of Water - - '•» = » -.-= :™;..V •2 The Effect, of. Washing the Leached Residues tilth

Various Quantities of 10 Per s Cent Ammonia Solution « 2)4.3 Sulfur Content of Calcined. Basle Zinc Sulfate 2?U Betention of Ammonia in Residues When Washed With . ' r-

■ Varying Quantities of Water ~ - - ** *' » - «'■«# - . 305'; ' Purifleatlon of' Zinc Solutioh.fhr .Eleotrolysi® by . ■ ; ;

. .■ Ceiaentafxon w ^ m «« w ^ m => *»» «= ■*» = -=* == « ^ , 33

;ffigur©;- ' : V v :;v i : ■ a

,Jllu.@trations

X ;^:v: - :v . ■ v ^AB:SBB"bl<Bd' AuSogi-WB W ^ ■***-, '**■■*». :m'-** w W w. W' M ^ « / -.ll ;;Shafts Bearlmgj)-. amd Packlmg Glaiid :Parr .Series Presswe Eeaotor ** = % 12

■■■

' / : ' : ' ' PjcttoeS v V

"Pletmre - , : ' : / ' . .;1 The Ammonia Distillation Apparatus

, 2; ' . The Electrolytic Apparatus w « « «- fay ■ ■ W fay csi ^

Page1515

- V;

- . ' ■ : ■ ■ : A ;

¥

THE BEGOrai OF ZHO FH0M SGIiOTXOH vOBTiOKED BY THE: - lESStitoTKE c r ^ S G 'lS C E S B IS M H 1 W W AMHOmOAL .SOLUTIONS AT,ElJFAtBD TEMPERATURES AND ERASURES .

. ,, CHAPTER I ^ INTRODUCTION , : ': : ; . .

Go Do Van Arsdalex in summarizingg as of 19535 the potentialof hyd:rometaU.iar.gieal methods, stated that the standards of' pyrityset hy'ednsmmers of metals have steadily increased over the yearsywhereasj the grade and purity of available Ores have steadilydecreased^ Furthermore, if these trends continue, greater and.greater reliance must be placed on those processes that producemetal products of a higher degree of purity» Hydrometallurgieal■processes are,: adapted to produee metal products of the desiredpurities^ ■ ' , • ' :

During recent years in experimental, pilot plant and eem*mercial Operations, the treatment Of ores by hydrometallurgisal■ ■ ■ : / { . ' . ; ■ ■■methods has rapidly increased in importance owing to the utilisation of higher temperatures and pressures for the dissolution of certain

: metals from orest? V : \ / ' . , '';'V , ; 'f; Ln ;lSli.,' thb/Southeriesters,, Experimental Station of thet '

United States Bureau of lines '.star|@4 a 'long' range research project

10- . Fan Arsdale, G0 D»a Hydrometallurgy of Base Metalss leGratft*Hill Book Company, Inc. y.New. York, 1953, p0 336o

dealing tilth the dissolution of metals from minerals and concentrates at elevated temperatures and pressures^ From 195U to 1958a the disso^ 'lutiorn.' &£:■■ hopper from copper minerals-and:'ores, in, acid, pulps was •: • ■ ■

.«■ , .;k v :studied-hy J0 T: Momasohj* Jo Oi/frerbergj,*3 Eo S® K i r b y § 0 R0 Hanson^ and f o' Ap 'losso . , ■

, In 1957s dissolution of zinc from sphalerite uas studied by Mo H0 Stanczyko^ Stanozyk^s experimental work showed that sphalerites in both,aoid and basic pulpss could be oxidized and dissolved with / ■the extraction of a high .percentage of the zinc' content0 -; fhe1 important conclusions of the - .experiment al work were g, in ' abstract, f ©rag/ as follows t

Ihen ammonia was used as a solvent in the presence of oxygens the dissolution of zinc amounted, to 9?o9 P©r cent using a modified Parr autoclaveg an addition of 2o56 poxmds of ammonia per pound of

2® / ' Mommsoug ,J> f <> g . The, Rissolmtion of Ghalcopyrite at Elevated :Tej^eratures , and Pressures^ .IhesiSg University of Arizonag;, 1955®: ' ,:3a ,.; Tverbergg-Jp The dissolution of Ohalcopyrite ' at' Elevated: ■Temperatures and Pressuresg"Part "llg Thesiss University of krizonas 19564=, - Kirbyg R0 S®s The Dissolution of Ghalcopyrite and Ghaleociteat Elevated Temperatures and PressureSg Thesisg University of Arizonas

■ 5o, . Hansons G0 R0g The Dissolution of Copper from Mixed CopperOres- at Elevated Temperatures and Pressures0 Thesiss University of Kriz.aEg'^WTr” ™ - ™ - ™ — ~ ... ;;: 6o .. ; MosSg T«..A® g' The Dissolution:' of Copper from Bornite.g Covelliteg and .Copper Concentrates at llevated''-Temperatures ■ and Pressures^', Thesis g University: of Arizona s' 1 8» . v-t, y.,: :y j , .:yy.-y,y.- 'V7s Stanc'zykg' Mp' Heg The Dissolution of ‘Zinc, from Sphalerite at ' ■■■Elevated. Temperatures, and'Pressuresa. Thesisg .University of Arizonag 1958

zirie3 an oxygen /partial presstare of 100 pounds per square inch gauge, a temperature of 200 degrees Centigrades a pulp density of 5 per cent of solids, a digestion period of one hour, and an impeller peripheral■ : .;; : o ■; ::: ■ . ■ " ;speed of 6^^*^ feet per Mimateer

- When ammonium carbonate uas .used as a solvent in the presenceof oscygen, the liberation of carbon dioxide), resulting from the reac­tions g produced ■unduly high pressures and resulted in the rupture of the safety valve6 The use of ammonium carbonate was discontinued • due to the hazard of encountering pressures in excess of 1,200 pounds per square incho^

The use of sulphuric acid and ferric sulfate generated by the reaction between pyrite and oxygen ...resulted in the dissolution ' of per teeht ef the zinc ■from sphalerite in a modified Parr autoclave with the' addition: ef ©0i8^’ pound of pyrite per pound 'ef t sphalerite, a pulp density of 5 per cent of solidsr, an' oxygen partial pressure of 100 pounds, per square inch gauge, a temperature of ,200 degrees Centigrade, an impeller peripheral speed ©f 6k!?o!? feet per minute, and a digestion period of one hour0'

The substitution of sulfuric aeid,: for the reagehis.generated from pyrite and oxygen, dissolved 96,3k per cent of the zinc in a modified Parr autoclave using an addition of 0=, 25 pound, of sulfuric, ■ • aeid per pound- .of-Sphalerite, an oxygen partial.pressure of 100 pounds .per square inch gauge, a pulp density'of 5. per cent of solids, an

impeller peripheral speed of 6h$o5> feet per minute;, a digestion period of one horn’s, and a temperature of 200 degrees Oentigradeo : PURIFICATION AMD ELECTROLYSIS OF ZBTC S W A T E SOLUTIOMS •

The possibility ofVrecovering zine from its solutions by electrolysis has been knomn for approximately 80 yearsg but commercial use Was .not made of this knowledge until 191i|.j, when Anaconda Copper Miming Company and;' Oemsblidated' Minimg' and , SmeIting; 0,oa|)dliy;of,Canada began to develop electrolytiG processes independently for zince, From these investigations^ - use of the process has spread all ever the world.

Current practice in the recovery of sine from acid solutions was briefly abstracted from the literature on the subject as followss Impurities found in acid leach solutions are mainly silicas aluminum^ irong, arseniCg antimony^: cepperg cadmium^ cobalts and, minor amounts ■

\ ■' ,’T'I ' ' v • ; ' - ■ - - , /.. ■ . . . * ' •, ■■ '' of home; others<," ■■ ■ :Th@se:■ :impnriileS /are,. reBioved in;:two ..groups :by ■ .separate procedures*. The first group comprised; of ironi silica„ 'aluminum^ arsenic 9 antimonyc, germanium^ and tin is ■■ remered by oxida*»! , 'r: , \ • ' " ' ■: ' - % ■tion with manganese dioxide followed by neutralising the acidity .with an excess of roasted, ore at times aided by the addition of lime?*

12 - . rock and burned lime,, . The second groups namelys copper5 eadmiums' ' 1 .■ ' •' ' • '>v ■■ ' . ...Mi v 7 : - - /' ' .cobalts and nickel is removed by treating the neutralised and filtered

10o Van Arsdaie, op. cit0i, pp0 18-19«llo : ; Ibidg P. 123o ■ :; v i : ; ; ■'12. Haywardg Co' Do, Van Nostrand Co.g

EoS An Outline of Metallurgical Practices 3rd ed» Incog New I or kg p o 2L^T" ", ■ .... .

leach solution with ssine dusts The mechanism involves a simple inter** '■' : ■' ' Y/ 't ''/ ' " V' vchange;of imptirity with the sine0 ■ '

■ All plants use prececltares fundamentally the same 5 the principal differences are in the acidity of the electrolyte^ the sine content of the solhtfand- the 'currentdensity useda t4- vlhe . sine is ' deposited. . • on the cathode t-iith the regeneration of sulfuric acido Aluminum is •used for cathodes mhile east or rolled^sheet lead is used for anodes in all plantso^ .; : -•/ „' • ■: .•/

: ' PURIFIGAT10M AMD ELECTROLYSIS OF AMOMIACAL Z1MC S0LUTI0MS '' .f: / :: f A-;'heareh -of: the' (literature did/ not.' reveal - any ..plants' 'uhi#.:,, • : ■ used, arnioniacal solutions for the extraction of sine from its; ores»The only information available concerning the use of ammoniaeal sdl=» rants for the recovery of sine from ores was obtained from the expert** mental work of inve stigators» The findings of some- of the invest!^ .gators' werh- hriefly -as"'followsf ' Ho'Eo'-'liawreacet0; stated' that in the ......treatment of zinc calcines where ammonia or ammonium^carbonate •was used as the solvents the residues contained the leads iron5, precious , metals j antimony s lime and' insolubles» Cadmium., copper % and . lessef amounts of other metals were dissolved with the zinc and were removed^by. eemestat£bh.;with'serap;;>:sinco ■ '■ ■.:' ‘ f :

13.0 Van Arsdale , opo cite3 p0 19o . ' ' . ;v'.ll).o Haprards op0 cit0 j,, p6 2 2o ' ." v 1 ; .V .. ;I5q - ■: f 'Van' Arsdale s , op .0 oit*'$ p6 ;126o.' '' • i'- ' ’ - . t ... ; ..v-I60 ‘ faw@noea.: H6 M0 s Recent Developments in Ammonia Leaching for fine Gfes.3 School of Mines and Metallu:rgy9 University of. Missouri - Bulletin^ Vol» 10s Ho® ■3£i-lay,19272.fP'o ..3o •' /■ ;. •

T0. Oaupfeell'*' stated, that the electrodeposition of zinc from aimnoniaoal solutions presented some unusual significant aspects# The normal single electrode potential, of zinc is -<0ey6 voltP yet zinc ■ is deposited"from' aramoniacalcarbonate solutions at a minimum potential of »1011 volts although the ei,hydrogen' overvoltageM on zinc at low current densities is »0®72 volt#; The explanation of this apparent abnormality lies in the

extremely lew hydrogen ion concentration of aramoniacal solutions a ' ■ Obviously^ in such solutions^ the potential required to liberate hydrogen cathodically must be greater than that necessary for the deposition of zinc# As the hydrogen ion concentration decreases^ the hydrogen overvoltage increases;-andg thus it is possible to deposit .' zinc cathodically at potentialsranging from »1#11 to ■ »1C15 volts#

. . In such experimental work aluminum was commonly used as the cathode with.stainless.steel as the anode# The reactions as given by Oamphell were as followss ;\ V ■ . ■ ■■ ,

V " At -'the cathodes ■ ' ' ; V.V' ' / ■ y: ZnClH.)4* = 2 e * \lm t h M ' ' '/ ■ . ' ;.«?. b : .. 3 ,. ,

. ' v - At the anode t , , - . - . .

- ' I ; ' .

: In the work of Campbell which investigated, only the possibility of recovering zinc from ammoniadal solutionss a current efficiency ®f ;

I?# ' - Campbell^ Paj, The Electrolysis, of Ammoniacal Bine Carbonate 'Solutions s ; Transaction American 'Electrochemical SbeieTy^ Toi7~b~6g "TZ-•. ppi# swi?;: ■ ■ ■ ■ ■ " ; -1 ' ' ' ■ '■■■■■ ' ' ' -

86„6 per cent was obtained with a power consumption of lak5 Kilowatt hours of ;zia©*: '.. Gamphell was of the. opinion that, these .va,ln@©could have.been, improved if better electrical eontaet between the electrodes and buss bar had been, devised.c. .

Oampbell also gave the following reaction for the regeneration .of the solvents' . ...... ' . ''.v y - . % -

OH^ : i'HgGQg: : h m ^ + ; 5 Hg0 : ' t (M|-)2;:; ;: f : 2Since Campbell used synthetic: solutions of high puritys information concerning* the purity of zinc deposited from commercial solutions was not obtaimed^. ' . ■ '

. , mimfios: m:.2bic: ceibe ■ . ■. t'' ’ "■' '; ' 2lne: :@2dLd®: is now - produced pyr ometallurgically by several;; ' t,

. methods^ - .Probably the oldest is the so-called French process in. - .which sine vapor9- derived from distilling metallic .zinc* is oxidized by air to .produce' an oxide of high. purity0 A second method^ :knoTO. as .the--IfetMerill ■ preeess ntiliz@.s;.h coal and oxide %ore or roasted sphalerite which.i® heated on a• grate by combustion . of part of the coal* Reducing conditions produce a zinc vapor which is reoxidized above the fuel bed resulting in a finely divided ■ oxide* ■ la. the Waelz process' lowwgrade ores, slagss or. retort, . . ■ t residues are* treated in a rotary kiln and the zinc collected as impure .oxide, which requires further treatment by other methods to •■ ,, ■ . . pj; produce a' product of high purityQ•

■ m20^21c.

Hayward* opa oxtoa pa 2-58«.ibid, ;p0.25?0■ Th-id.

■ PRODUCTION OF ZHC DUST ' 'One of the more important methods for the production, of zinc

powder consists of blowing compressed air across a stream of molten zinco The zinc is atomized and the fineness of the dust is controlledby variation in. air pressure^ size of the stream of zinc, design and:. '■ ■ : ' V ■ ' : . .■ V ; . ■ ' 22location;,of the nozzle with respect to the stream of zince ' .: ; V ' ' : :C®JE0Ti?l QP experii^ tal iork - . : ' : :

The experimental work described in this thesis was undertaken to determine the possibilities of recevering zinc by electrolysis and hydrogen reduction- from a composite solution which resulted from the ■ treatment; of' sphalerite ■ with an aumoniacal .solvent and oxygen at : . , elevated temperatures and pressures^ It was also;, an objective’ to ., detennine the feasibility of producing high purity zinc salts from the leach solution^ It was a further object to determine the feasibility of recovering the ammonia from the leached residue and leach solution by distillation^

22o 5 Bray3 J0 L0il Non-Ferrous Production Metallurgy John Wiley and Sons,a’ Ine»s New Iork7 l9G7» '

• M p m n . v .

MAfEEIAISs BeyiPffiHT. AMD AMALITIGAL PEOGEDUEES

; , Description of Concentrate. A gine sulfide flotation concentrate which uas obtained from

the Iron King %ne ' Yavapai Gonnty^ Ariadna -was employed for the:..."work' ooncemtrAW ' , drled im air amd/-

■was nots. at any time5, subjected to the external application’of heat© A ,partial chemical analysis of a representative sample gave the following resultsg . ir;. . ; ■

■Constituent;i-Z3nd;: .■ Sulfur v Iron: :;A . ■ ’’lead ■: -Copper' Cadmium Arsenics Selenium

Percentage

6qU3 v1*23 ’’QJt.20,120o260o30

: - : A screen'analysis' of the concentrate yielded results as/ .-Ar : ■%'' -.;' A ,::: ■" A ; ■

\ A ;; . , .’v ■' Percentage • : ; A*d£Q 4- 200 mesh 1*39«200 f 270 mesh : ” 2&8S«=.270 * 325 mesh . ■ :■ 3 06$^325: me sh 4--- 20 microns .1 02*39*20 microns . ’: v : 39<r70; . ,100*00'■ ; ■■■

!23q .... : ■ Stanczykj opa citej, p0 13v.9

k tniHeraloglcai aaaljsts of ■ tlae 'aiimias' 200»isesli aad plas 20«mieron fraction - made by M0 H0 Sfane^yk revealed that Rthe c* once ni­trate t-?as principally composed of sphalerite and appreciable amounts of pyrlte , dolomite and galena0 The concentrate also contained sporadic grains of quartserieiteg chaleoeite and covellite» The sphalerite rangedfin color from, dark reddish brown t© amber .and' -. numerous sphalerite particles were interlocked with grains■of pyrite and galenao It was estimated that over 90 per cent of the sphalerite was free from inclusions0M ■ ' . ,

. Description of Equipment'' ' ... ;■ . The'tetoelave : /v . ' ' •' f ' . The autoclave used iiifthe experimehtai "work was an''iii##ller\ type pressure; reactor .f designed by J® Q0 - Tverberg^ and. modified . by members of the experimental staff of the United States Bureau of MineSo Deferring to Figures X and 2, the autoclave consisted, of a head assembly^ a reaction chamber of two«‘liter capacity made of 316 stainless steelg. a set' of. locking. collars to1secure the head: . assembly to the reaction chamber, and other accessory equipment0 ■.

The head assembly contained the impeller^ impeller shafts bearing assembly's, packing glanda thermocouple wellp and an .arrange­ment for circulating water to cool the impeller packing gland0

The reaction chamber was of cylindrical design with a forty- five: degree. bevel, at the junction of the sides and bottom^ .•;Th®;; chamber comtaimed.a gas-inlet Valves a valve'for bleeding gases from

Tverbergs Jo '0oS op® cit1°

11V

Compression nut —

Cooling waterPackingValves

Valve

Impeller shaft

Reaction chamber

Thermocouple wellImpeller

Figure 1. Assembled Autoclave (Scale 1:3)

12

Hub and Bearing Assembly

y''1-- Compression Nut

•Packing Gland

Water Cooling Ducts

Figure 2. Shaft, Bearing, and Packing Gland Assembly, Parr Series 4511 Pressure Reactor

'til©:boito> a pressure relief valve to protect the equipment in the ' v.' event of excessive pressure^ and a gauge for measuring the pressure0

Other modifications adopted to improve agitation and the suspension of solids in the pulp were id enlarge the diameter of the impeller from two to ',t#o:' and ::threpwquarter inches^' %ith the blades , remaining pitched to give a downward actiono A stainless steel accessory impeller shaft support2 which was added to prevent the impeller as it rotated from striking the thermocouple wells served as-h :baffI#, for increased agitatibm^ : 1 ' ’

. ' :fhe packing element used to obtain a pressure seal around the impeller shaft was an asbestos material impregnated with oil and graphite<, The. seal was prepared by .winding short lengths of the material around the impeller shaft and eompressing•the element. ■ between the packing gland by means of a vise» Alternate high com­pression and additions•of the impregnated asbestos material yielded service at pressures that sometimes exceeded 800 pounds per square ineh:i,or: wellXover ' 200 : hours Xdf operations ^ ! : . ' •

The accessory equipment used in the operation of the autoclave included a 110«volts 1/12 horsepowers variable speedy alternating current motor| a ls pO0*swatt electrical heating units and a rheostat - for - controlling the heating imit» The heating unit was . cylindrical^: in shape and designed to accommodate the reaction chamber of the autoclaveo The heating unit supported the electric motor which

Stanczykj, dps cits'j, 'ps 20o

' revolted /bhe impe3J.er shafi: *y aaans'of an- endless belt# - The revolm« tiofts per mintet.e of the Impeller was. ascertained by means of, a Stewart=»¥arner hand taohdto.eter0 . The temperature of the reaction chamber m s measured by: means of a Ghromel«Arm?iel thermocouple and a Model teeds and Northrup portable potentiometers •: . ' v ' : The Still

■ - . A pot”type still (Picture l) tfas utilized for the recovery ' of -ammonia- and the precipitation of the zine.oxide^sulfate. salt from the leach solution0 The still consisted; of a steam generator $ dis»

..tilling pots and collecting systeitio • .• The steam generator x-ias composed of a 2 5,000 milliliter • ;

Srlemmeyer flask containing boiling,stones.and-,set- on a portable •hot plate o The mouth of - the flask m s closed nith a trao hole rubber stopper containing a glass tube which was exposed to the atmosphere

-. at one ..end;;and- submerged; .under the boiling water' at the other$ thus - acting as a safety valve0 The other hole contained a glass tube which conducted the steam to the pot#

. The distilling pot was made up of a;ig000 milliliter beaker f closed with "a large two^hole rubber stopper B Steam entered, the still through the stem of a. glass !!T!! and passed down through a -wing of the !!T?! which extended, through the stopper and. into the leach solution# The other wing of the W * joint contained a stainless steel rod

• 'sealed by means.of a rubber tube arid extending down through both• wings of the RTH and into the solution in the stillc The precipi- tate which formed during the operation and which tended to impair

Picture 2. The Electrolytic Apparatus

the passage!: of steam into the solutioa. was 'removed by manipulation of the stainless steel rod0 The second hole in the stopper contained a • glass'tribe thromgh which steam and ammonia passed to the collecting, '■system*. ■ .■/.■: . ■ , /■.':■ ■■. T,

The collecting.system consisted of a standard water-cooled condensing thbe with an Srlemoeyer flask used as the. receiver <>

% / : ■ ■ " ' :■'■' ■' ; -■ . .. .

Residues were dried in a Precision Scientific Company drying oven9 Type 1262s which was maintained at approximately 100 degrees Centigradee ■ v - ■ “ . : ' ■' ' ■

Zinc salts were'calcined in a #evi«Puty*( Electric Furnaces Type RBT»56lOs controlled by a Brown Electric PyrometerQ

i: tube furnace5 Type 77 manufactured by the Electric Heating Apparatus GoBf>any .-was also employed for the calcination and the 'hydrogen reduction -of zinc ■ saltSo.. ■ - - :

...,■■-:'. ' * The Eleetrolytio Apparatus'■■ ■■■' . ... . .(Picture 2) " \

A. Mellaphoae. industrial Rectifier ,,. Type Hl50 ?0s was used to convert 220-volt9 single phase9 alternating current to the desired .direct current voltage^ A .square- glass battery jar with two stain# less steel anodes and.an aluminum cathode constituted the electrolytic

. . ' Chemical Analyses ■ :. " ‘ ' '.The 'chemical analyses of materials and products with the .

exception of the analyses- for - ammonia and ammonium salts„ were made .

by De £0 Muraeke amd fi@ A6 Stiles of the staff of the United States Bureau of Hi&ess . . , ' ■ ' : '

Amonia was detenriined by titrating Tilth standard hydrochloric aoid with,'methyl red as. the indicator*- Ammonium' salts were determined by the Kjeldahl method as'-outllned by Kolthoff and Sandell^^^ ;' %

26o Kolthoffd I0 Mop and Sandells Eo Bea Textbook of QuantitativeInorganic Analysis s 3rd ed0 3 The Macmillan Comp any 9 MewJ'orkg ppffl 536^37

; ' ; , /■ ' CHAPTER U X ' ' -• a ./.v \ \ r -: . V ;■ a ';

Eo' H0 Btanozyk^' demonstraied that 97oO per cent of the zinc, contained in a charge of sphalerite could be dissolved in a period of 60 MriuteS'.nith::an impeller peripheral speed of 65ko5 feet.'per minute a ratio of 2o56 pounds of ammonia per pound of contained zinc s a pulp density.of 10 per cent of solids^ a partial pressure of oxygen ' .'of 100 pounds per square imcMg'/amd a temperature of 200' degrees Centigradeo . The conditions as described nere for. the production of approximately $00 milliliters of solution using a.modified Parr

: autoclave of one liter, capacity^:. . " '/{A-' • - a - .; In order to utilize the two^-liter capacity of the modified

Tverberg autoclave to the best advantages it was necessary to deter**' mine the time and degree of agitation required for the. production of approximately one liter of solution with a satisfactory dissolution of zinc while maintaining the pulp density,, partial pressure of oxygeBj,' ammoniawsine ratios and temperature as determined by Stanczyke

V ''Procedure for'the Determination of Time

and Degree of AgitationA'charge of 111?1 grams of zinc concentrate was put into

the autoclave with ammonium hydroxide to constitute a ratio of

Stanczykj opG cit03 p0 it6c:;v . i s

2o$6 pounds of amnonia per 'pound ©f'Ooataiaei aine■as# staffieient ' water to make a pulp density of 10o0 per cent of solids« The autoclave was then-assembled and:the reaction chamber was purged three oonsee=> ntlwe, times by introdtieing oxgrgen: th a-pressure of $0 pounds per : . v PaparW;:ikeli:'.and: th@B:' diseharging the oxygen, to the atmbsptore® / " t . ;

The charge -.was then heated to. a- te®perature of .185 degrees Centigradeg after Tfhieh5 oxygen was added to bring the partial pres-* sure of oxygen in the reaction chamber upto 100 pounds per square .incho, -;:.Agitation.of the ■charge was initiated;and':coBtiBued;fdr...30 or-t 60 minutesat IgOOQ or 23000 resolutions per minute which was equal to a peripheral speed of 63ho3 or 1^30960 feet per minute respectively.The exothermic nature of the reaction caused the temperature to.:v.v:-v:p::.yv ::L ■ . ::r,; V y ; - : -V "-t:;.'' increase :.tp;- 200 degrees Centigrade in a period , of approximately three • . minuteso The temperature was. maintained at 200 degrees Centigrade by manually adjusting the rheostat which controlled the heatere During the reaction the oxygen partial pressure was maintained at 100 'pounds, per: square incho At the end of the time: periods the : agitation was halted andj as a result : .the reaction rate was decreased, to a point where it was considered, to have essentially stoppedo

The autoclave was then removed from the heater and placed in- a pooling tank into which cold water was.elrculatedo A thirty-minute , period was required to cool:the charge from 200 'degrees Centigrade, to room temperatureo After cooling the charge9 the waste gases.were expelled to the atmospheres The autoclave was then disassembled and the' charge was- 'transferred: from the reaction chamber to a vacuum . filter for separation of the solids from, the solution o' Water containing.

:;v.- : r.', . 20ammonia WS" nsed/io wa'sh the residue which remained in the reaction . bomb onto the filter0 ; The volumes of the/leach liquor and wash water ' were measured and samples were taken for analyses» The residue was then dried in as oven at 100 degrees Centigrade^ weighed^ and assayedP ■, : ; The ©xte^btidns given .'in- the/fpllowing text. have been calcu«lated on the basis of subtracting the zinc in the residues from the. total zinc in the chargee /Oonparisons of the extractions based on this method a si compared with the extractions based on the total sine - minus,the zinc in the solution showed an agreement within one per cent/ determination of Time and Degree of Agitation

The object of these tests.was to determine the time and the ■degree of agitation necessary for the production of approximately one liter'of solution with satisfactory zinc dissolution using theconditions:as described .in. the experimental procedure 0 The results •of four tests:.were as foiJLowsi / ■ /

Time 5, Minutes

■.'/:"/:■ Peripheral Impeller Speed,; ' Feet per Minute '

\ Extraction 5 ' Per Cent.

. 30 1 \ 2To9. 60 -v : \ '"/ ' ' , • ' : . :'/ ■■ ■ - , ’ 37o2, /30' / • .13O9»0 - ■ ■/.:,'i . : k20k.60 v/vA- ; :: l309mO ' 95 o 9

interpretation of Results. Increasing the volume of the charge undoubtedly affected the

conditions required for the satisfactory dissolution of the zinc in the charge o. Stanesyks in producing a volume of 500 milliliters j, obtained a dissolution of 97oO per cent of:the zinc in 60 minutes ■ using 'an impelieh peripheral ;.;isp©ed of 65)4=5 feet per minute,»/, The .•

result of 9509 per cent extraction of the zinc in 60 minutes using .an impeller peripheral speed of ls309o0 feet per minute eoirpared '. favorably, #lth the result, obtained by Stanczyko 'The; increase in peripheral speed necessitated by the increase in volume of the charge indicated the importance of proper agitation^' ■ ' ' Improved Design ;of -iutoclaye to' Secure,; v' . . Better Contact - of Reactants

: ' '" I' In order to increase - the dissolution of the zinc in thecharge 3 a study tras made to determine if the degree of agitation inthe autoclave could be' improvedc . ,

A charge of one liter of pulp of 10 per cent, of solids, was. introduced into a glass beaker which approximated- the dimensions - of the reaction chambero The iiipeller from the autoclave was inserted into the pulp at the same level it occupied in the autoclave» The.speed of the impeller was initiated at 15000 revolutions per minute or a peripheral speed of. 65Uo5 feet per minute9 and increased' to - 2^000 resolutions per minute, or lP309o0 feet;per minuted At 1?O00 revolutions per minute a; deep vortex extended down through the center of the pulp to the impeller with the pulp revolving in the chamber in the same direction as the'impeller at' a rapid speedo . Increasing the speed to 2,000 revolutions per minute succeeded only to increase the rate at Which the pulp revolved in the beaker with little pro* . bability that the contacts, between the gas, liquid, and solid phases

. were-- Improvedo In order to overcome this condition, an impeller oftwo and three-fourths inches in diameter was'1 substituted- for the original two and one-half inch diameter, impeller,, . Further testing

showed that the larger impeller was: more effective in putting the gas phase in contact with the solid and liquid phases when it was located approximately one and one«half inches above the position of the original impeller0 In addition, a baffle'of 316 stainless steel . sheet, was,constructed to fit on the thermocouple well and extend to' the impeller shaft just above the impeller0

To determine the affect of these modifications, a quantitative test was conducted'in the autoclave, using the procedure, as'described. Vim the:.:dete'min.atibn;pf ''titae: hnd rdegree: of agitation with the same, .conditions as in the previous tests with a time of 60 minutes and an impeller speed of 2,000 revolutions per minute or a peripheral.

■ - v - , ' ' .. : , • ,, ' ' ' ■ - ' ; ' . ' 'speed of IpUUO feet per minute0 The dissolution of zinc in this test amounted to 98oO' per cent as compared with a dissolution of ; 95<»9 'per cent' without the modifications. as described <,' ' . . . ■ V'V

, • Determination Of a .Satisfactory■ ' . ¥ashing"Teehniqu-e

Two series of tests were conducted to determine the affects of various limited quantities of water and ammonia solution on the extraction of soluble' simo .-frotn the leached residues■ In producing one liter of ‘pregnant solution by the method; described ''in the deter® , mination of time and degree of agitation, only a small quantity of leached residue was made available for the experimental work on 1washingo This condition necessitated that for each test in Which ' the quantity of wash solution,, was varied, a complete cycle of , '.operation including: dissplution was' necessaryo' •Operating' conditions. were maintained, constant at 2056 pounds- of ammonia per pound, of contained zinc, at- a temperature of 200 degrees Centigrade, a .

partial pressure of oxygen of 100 pounds per square inch* a time period of 6b toizmtes* a pulp density of 10 per cent of solids* and an impeller peripheralspieed of lsUliO feet per -minute o The operating procedure ■ described in the deterniination of time and degree of agitation was used with the-'exception of the procedure involving the transferring of- leached residues from the autoclave to the filter0 :For .these tests* the residues were washed onto the filter with pregnant leach solution so that the washing -media could be added to the residue;on . the filtero . "Residues Washed with Various Quantities of Water. ' These tests were conducted to determine the feasibility o f J ..washing the leached residues with-'wateri>: ; fhe; quahtity of, .water was- varied from QoS to h parts per part of dry residue0 The washing was done by the displacement method in increments of 0o5 parts per . part of dry residue© The results are given in Table 10 . ;V '

fable lo The .Effect of Washing .the. leached'Residues, with, VariousQuantities of: Water

" Quantity of .Water* ' : -■ . ■'Parts per Part of Dry Residue ,, ;

Extraction*"'! = - ', Per Sent

<;> ■■ ■■ 0o$ ' ' W8»2 ' - ■■■-■ >' ; \ . IcO ' :■■■ ■- ' . , - -■ - ' 'i- ;':' .' 98,5,0; : - , - . :

- - 2.0

-«• Pased on the total zinc in the original charge of sphalerite^ -

•Interpretation of Results\ Washing with ,0„5 part of water per 'part: of residue, produced

an extraction of ?8 0 2 per cent :of the zinc© Washing with additional

vquantities of water did. not improve the extraction uithia the experi»' mental error. Using a smaller quantity of water was not attempted V since' 5 .part of■'water'1 per part :.of residue was the minimum, quantity, -t which would completely cover the leached residue and insure proper

. contact of the wash water with the residue0 " .j Residues Washed with. Various Quantities of 10 Per Cent Ammonia Solution

The object of. this series of ‘tests was to determine the affect of varying quantities of 10 per cent, ammonia solution on the extraction of soluble ainc. from the leached, residues0 The washing was done, by the displacement method in increments Of 0®5 part per part of dry ' residue with the- total quantity of solution varying from 0o5' to U parts per part of dry residues The results are given in Table 20

Table 2» The Effect of Washing the leached Residues with Various.. I - Quantities of 10 Per Cent Ammonia Solution«

Quantity of Ammonia Solutions Parts per Part of Dry Residue

' ;■ • ' Extraction^. ■ '.' . ‘ ■ ' Per Cent'

. ' ' . 95°8 ■ '■■■■. 1 f loO V ■; ; .Tf. .1 f ■ . 96a. v. :;:v■ " ' ■ 2o0 . , . 97*5 ■'

• ' koO : V ; ... ' .

* Based on the total zinc in the original; charge of sphalerite

.'t'. / Interpretation of Results ; " f1 . . • ^The. extraction., of zinc from the leached residues increased

from 95<=>8 to 97=5 per cent, as the quantity of wash, solution was increased from 0^5 to 2 parts Of solution'per part of dry 'residue0

: V .■■■. V.,.,' -vIncreasing, the quantity of wash Solution to h parts per part of dry residue did not improve the exfcraetlbno . A comparison of the results

obtained by cashing With water and ammonia solmtion showed that washing with water produced a higher extraction^ 9802per eent$msed less’; solutions (hjj pari per part of dry residue^ .than the,, . ammonia solution which required 2 parts of solution per. part of • dry residue to produce a 91 <& per cent extractiono It is possible ;that the,lack of ions in the water encouraged the removal,of . soluble zinc ffom the residue.during the washing processD . '

In the leaching operation from which a residue of 19 grams was produced, for every liter of pregnant solution^ the quantity of .pregnant solution that remained In the .residue.' after filtering .was quite smell* This fact was realized when 95oO per cent of the zinc "charged to the autoclave appeared in the pregnant solution in the form'of soluble zinc without washingo' ' The: of: %inc by .Distillation "of Ammonia ; -r., The object of this experiment,al' work was to determine the

feasibility of recovering zinc from purified pregnant solution by distilling the ammonia and precipitating, the zinc as a basic sine" sulfateo • The production of metallic zinc by reduction of the cal­cined basic zinc sulfate with hydrogen was also investigated^■ Purification of Pregnant Solution .

. Before attempting.the recovery of the zinc from the pregnant ,'Solutipnj,'' it was neeesMry to purify the leach liquor in" order to ■: reduqe contamination of the zinc product by undesirable elements and compounds .

, Beeause of the; high pH of the solution during dissolution, /theAhdneeh^htion nf;metals vsueh, as iron, and lead in th®. pregnant /'

solution remained. .low9:Howevers metals in the concentrate such, as; ; copper which formed; amines along with zinc were present in the leach solution* Coppers cadmium,, and other metals less active than zinc were removed from the pregnant solution hy - cementation and agitation vwith'.ehemicallj pure izinc*The following..data', give the eoncentra4 ' ■ tions of several elements and compounds in the'unpurified leach solution as coisp.ared with the concentrations in the solution afterthe purification operatieno ''1,4: ; ’:" ■ ; ■ '1 v,; ied- 'Eea:ehlSolutlonav ■ -Purified ieaeh; Soluti0na,■ . v': . Grams per Liter - : : , Grams, per Liter . ..Zinc . ' ' - - 6lo2 - 65oUCopper 1*85 0*005lead - : . ' . • 0*18 ■ - " 4. 0*1&Iron y ■ 0*001 'v,. : - . ' --‘Mil': Cadmium - ' . 0*052 . :.. ' 0*017Sulfate; Ion ' 109*37 ' 120*90: Anteonia 87o3-' - ' 85*9 - -

* t ' '4 ' ; >■ *# 10*5 in the purified, and unpurified leach solutions* Precipitation of Basic Zinc Sulfate , .■' V' ;:v- Awaonia was'removed- from'.the purified pregnant solution ' ;... . '■by the passage of steam through the"liquor* The stilX3 .described on ; page 1U and pictured on page 15, was used for this operation* The resulting lowering of the pH of the-solution caused-the zinc to be precipitated, as hydrated basic. zinc sulfate^ - At a pH value of' 7*5, it was found that 97oh per cent of the zinc in the original solution had been precipitated* Chemical analysis of the basic zinc sulfate was as. follows::: . . ; ' ‘

' . ■'Cosastitiments.. . 1 _ • V ; . /Fer'tient': • 2 ± I i e ; v , b$ak

. Sulfate Ion . ' 26o2Water . "' 20@7 . -

■ Silica ■ Oo02Oopper' ; , - 0o 002

; . , RpOg ..Group ; V - 1 0o03" Oalclw Oxide. . ; ; ' V / - ' - OoOls.

.-.V'lagnesitim; Oxide . ■ .:71 ;: \ '" . ■ ' ' 0q08The depleted solution remaining after distillation contained

Q09 grams per liter of zinco After filtratieri the depleted solutionwas evaporated and produced a crystallized salt which contained all . the zinc, .as, a.'Sulfate or .' Galcinatioh of Basic- Zinc Sulfate::.8alt' % -' ' :_ . -, - : V' ' - V: ; /.. ' -' '. . -

In: order to produce a. zinc "oxide fre.e.-frem. sulfur for the1 " . ' "■ , , : l' " . V ; ' % 7 - " .'. -y ' ■ : y; 'reduction, step9 it x-jas necessary to ealcine the zinc salt in orderto drive off the undesirable sulfur which was- lit. the salt, in the 'form of, a'sulfateo A series of ealeinations was ebhdueted at various temperatures for several time periods to determine a pro­cedure for the elimination of sulfur0 The results are given in Table 3o : ' - ' 1

Table.y3o. Sulfur Content of-Calcined .Basic Zinc Sulfate 0

Temperature ,' y,;' Sulfur'Content's’Per..Cent' '.

One Hour Two Hours . Three Hours;700°C ■10075 ■ , m •800% 9o6h m . ' w ' - '900°d r 2,65* ' 3o50* 0ol6 •

1000% 0d09 0o09 0o07• 1100% 0o06 . OdOh 0o03 7

1200% : : r . ■■ 7 0d02v'. 0d02 0.02 :::.1306%yy;:y 1 y . ; 0o02 ■- :77%0'C3-:'’- T, ■■ - ' ' . 70*03.* Values inconsistentd /

. . ' ' , Interpretation of He suits ■.r : ' ' " r v ': v ' : ; V :"7 : ; - " v v7\ : - 7' ' " ' r - : "■. There suits indicated that temperature was more important

than time la the eliminatioa of sulfur0 • Maximum sulfur elimination • was attained t hen the salt:was calcined for one hour at 1,200 degrees Centigradeo ' : .. ..;7 7f; .

Washing the calcined salt produced in one -hour at 1,000 degree® Centigradh with water failed to lower the sulfur content which indi* cated that the sulfur was in an insoluble forma

Calcining the salt at 1,000 degrees Centigrade for one hour ■ with the passage -of a slight -current, of air over - the salt was also' ' ineffective;;la . reducing: :the: sulfur content®..;; ; ':7 ■ v ;, • ;1Reduction of the Calcined Zinc Salt with Hydrogen ;

Since the reduction: pf sine oxide by carbon at temperatures above the boiling point, of'zinc was a well-known process, it was .; desirable to determine if . the zinc. Oxide., produced by the calcination Of basic zinc sulfate for one hour at 1,200 degrees Centigrade, could be reduced by hydrogen at a temperature below the melting point of ■

, zinco- • : . • ■ . 7 ■ ■ ' . ' . 7 ',7 A- five^gram sample was placed in a' tube furnace and heated

to UOO degrees .Centigrade, with. the. passage-:' of . a current■’ of hydrogen-, ' 7 over the, salt sufficient to produce a two«inch flams upon leaving the tubeo After a period of one hour, there was no visible sign of reductioiio • 7. , ' , i 7 . -. -

Reduction was'then attempted at.700 and 900 degrees Centigrade,7 ,77- 7.7 ' 7-,'""■'7.7- ■'.':',7;v ■ 7 ' : ■ 7 :- which''weie' Above the melting point but below the boiling point of zincoIn both cases zinc oxide was' reduced and the volatilized, zinc condensed

on the cool wall of' the tube0 At ;?00 degrees Centigrade the reduction •of 7Go0 per cent of the zinc oxide required minutes and produced metallic ssine of 95 J4 per cent puritje At 900 degrees Centigrade' reduction was essentially completed at 10 minutes Bifh the production of metailic. zinc *ieii w s -97=1 per cent pure0 Volatilization of. the reduced zinc below its boiling point was possible.due to the ' \ passage of the hydrogen-which carried the zihe yapor away and pre- ■ vented the establishment of equilibrium vapor pressure®. • i; , An attempt tb.-'redtio /the zlnc, 0x1 1®' at a temperature of ' • . .' 200 degrees:Centigrade and a pressure• of 300 pounds per square inch r of hydrogen in: the autoclaye with a continuous passage of hydrogen was unsuccessfulo ' ; ; ' ' % - ' • : "

\ The Recovery of Ammonia. from Pregnant ■., . ' • : /• -Solution by Distillation . • i ,, -. • •. '1-

The ob ject of this :study was to determine the possibility of recovering ammonia while precipitating the zinc from the pregnant solution by the distillation of the ammonia« To satisfy the operating condition of 2 0 56 pounds of ammonia per 'bound; of'Contained zinc,, • 151 grams of ammonia iri: .the form of ammonium hydroxide s the zinc con- eentrate^ and enough water to. make a .pulp density of 10 per cent of • solids were 'charged to the - autoclave<, ... .' . : , "" -Recovery of Ammonia During the Purging,:.and. Filtering Operation .

After the autoclave was charged and;, assembled^; and before the dissolution operation, the reaction chamber was purged to eliminate undesirable nitrogen® During the purging, it was.found that 0*2 gram of'-.ammonia was removed with the. purged 'gases® •

;ln, o^der ioss^gv^fier dissolution^ a .eonsiderable quantity o£ excess free amaonia -was removed, from -the'pregnant solution before;disassembly of the'antoclave. This was

. accomplished by attaching a hose connected to a source of reduced.y 'pressure, to " the. autoclave and passing the: •withdrawa' gases ' through ■.;

cold water xvhieh dissolved the ammonia in the gasesQ ' This procedureaccounted for the recovery of 62ol grams of ammonia0 An additional 0o6 gram was recovered by the same method during the filtering oper­ation which'iaade a total recovery of 62,9 grams or Ulo8 per cent of the ammonia charged to the autoclave by the method described^ Retention of Ammonia in the .Washed Residues .' . . '

Since the washing procedure which utilized water as the washing medium produced the better' results,, experimental work: was . conducted to determine the quantity of ammonia retained by the,residues when they were washed with varying quantities' of. watero The ,results' are given in Table i|-o -

Table i|*. ' -Retention of Ammonia in Residues iJhen Washed with Varying . Quantities uf Waterq ' . ' ' . .

V";; ' - Quantity :bf Retained Ammonia ./ '--'■. .iQuantity ’ of 'Wate%; - \ : y y :'. bbs0 per. Ton of

Parts per,. Part of Dry,,Residue Grams Per Geaf^: Becdvered. Zlnoc-- , OoO ■ ' . Oo73 0olt8

'f .: .'-: : ' . ' " -A,: ;''0»3S:: ''v,' :' ■-S25 I' -■-i3:o3.: v: l6r . -' ' : I' - O o H - QoiO .. A 2S0: OoOB o0o5 ,2*8' UoO At:/' ■ . ' OoOU ■■ ' 0003 lok

the total ammonia - @%rged. to the awtoelavey

. . V. ; of . y ; / .'The recovery of retained ammonia apparently did not present

a problem since the quantity lias reduced to 0o03 per cents based on •the original charge, when: wash water was used at the rate of b parts per part of dry residue» Apparently, the retained ammonia was not adsorbed, but was contained in the solution that remained in the residue\ after. filtratim, ‘ and:xwas'- .therefore .recoverable ;by''vdihplace":! men to '• • .'l • -;;• •; . - \ ;''v ■■' ■.Distillation of Ammonia from Purified Pregnant Solution .... . z-1 Ammonia was removed from the purified, .pregnant solution 'bythe passage of steam through the solution during precipitation of the. basic sine sulfateo ' i .. • .:

' .. .■ f.. The 'Steam distillatibn recovered 53»2 grams of ammonia with 23 o 2 grams remaining in the zinc^depleted.solution as ammonium sulfate® ■ All of this combined:ammonia was recovered by the addition of 1E>0 per cent of the theoretically required calcium oxide and further distillation® ■ ; C:- ' - ; . '. , ■' : ' ' The precipitated: %inc sulfate when separated from the zinc**

depleted solution by filtration, retained .ii,a3: grams- of ammonia 0 Mashing the precipitated salt with waterp recovered l*b'grams of

: ammoii a'.with; the'- remaihing ' 2 o9 grams. 'apparently.' adsorhed. by: the:; ba sic sine sulfate® ' ”' :V ■ u" .. '

- ' :: The 5362: grams of ammonia recovered during distillation,» plus the. 23*2 grams recovered during redistillation, plus the l®b / grams recovered by washing the precipitated zinc sulfate resulted in a recovery of •77®9 grams of free ammonia or 31®5 per cent of the

ammonia in the original charge0 The per cent along tilth theUlo8 per cent, previously recovered by purging, reducing the pressure,and filtering, made a grand total recovery of 93o3 per cent of theammonia charged to the' autoplaveo. The' remaining 60f per cent wasassumed to have been lost during handling of the solution.and byadsorption^ , . -i iy t : ’

. An alternate'method was used to recover ammonia from the zinc«depleted solution in the form of ammonium sulfate. It consisted inthe evaporation of the zinc*>depleted solution %ith the productiph ofa crystallized salt • 'which contained all. the ammonia as ammoniumsulfate. The salt contained 23=3 per cent of ammonia and 10$ percent.of tine. ;; . . , ; ■U;-: I- .

- I ’ Recovefy of %ino from Ammoniacal Zinc ,Solution by Electrolysis

The object of this investigatioh was to determine thepossibility of recovering zinc from the purified pregnant solutionby electrolysiss V' > '. i ' "V; V:’Purification of line Solutidn by Cementation •--------------------------------------■ --------------:— ----------------------:------------— .

The experimental work involving the purification of thepregnant solution comprised three cycles with the addition of ■■ • : ' ' , " • ’ ■ . ■ : ■ -v :• ■ .'• • ■ ' :. •" . ' ' , :chemically pure:granulated zinc followed by agitation and flltra«

'■ ::: : ^ f '■''l If'-:tion=; One,cycle of this method of purification, as described on\ l ': ••vu. 'i. ■ : ■ ■ .. • ,, ■ _• . ■

page; 2$, was used, prior to the recovery of zinc as a basic zinc ,sulfateo In the purification of the solution prior to electrolysis, three cycles were, used to reduce the copper and lead concentrations0 The results of the purification steps are given in Table 3=

: Table $<, Purification of Wine Solution for Electrolysis by tiementationo v; / ' .,

' OonstituentalOriginal Solution Grams . per Liter

Solution after Cementatimr v r , . Grams per litert : '-" .Stage. 1, : -Stag@'';2':'/: 'Stage 3

Zinc , .-i 71,70 71,65 77,8$Ammonia ' ' lllol: : - ,109^8 I0%8 : 100*1Sulfate Ion ' 109o61 109,11 109,39 109o62Sopper . ‘ : Oo37 . ; : 0*037 <0oQ05 40*003Cadmium v v ■ ,• 0o058 . v ' : : 0,013 . 0, 009 0,006-lead ' ■. ; •. 0,170 0,020 0^020 0,007#gmesium 0xide' • 0o202. . 'v: :©,219 J . 0*210' . 0*700Calcium Cxide". : ■ ;:7' v . 0,066 v"' " 'v ' " 0o05l ' ' ©*©377 ■:: . 0*072•Silica • - S e W : Ocioo ©o081 0e060EgOj Group. 0ol3^ ©,109 OolEL OoOlOSelehium v. ■ ; 0*013 '0,013 . 0,013 Go OilArsenic OoOll ■ 0,012

• " . ' ", »>-•' ' ■„ ' •. 0*013 0,011

Preliminary:Electrolysis ':VAn eleGtrolytie eellc, pictured, on page and described on

page ‘162 composed of a battery jarg anodes of 316 stainless steel, and a cathode: of;sheet aluminum were used f© conduct a.preliminary electrolytic test utilizing a synthetic solution which approximated, the composition of the sine leach solution in zincs ammonia9 and sulfate ion concentrations 0 The purpose of the qualitative prelim^

tInary: test:,## to-detersi# -the' voltage necessary for'; electrolysis at a spacing of one inch between anode and cathode and the.approxi™mate current'effieieney that could be expected 0

Since-information was hot available concerning the 'decompo«■ .'sition voltage of sine -amihe'' sulfate ■' in',solution^ Va voltage ' of Pop was used3 which was above the theoretical decomposition voltage of .203^ for zih© sulfate.'solution0'0 , 1 - • .

Pbo, v : ?an: Ahs;dale 3. £#ita > po 12%

v '" :v To aid in the deposition of fine-grained zines agitation ras nsodf aid; gtam; 'arable was: added ;te the solution at the' rate of. two tparts- per 2 s000 parts of eontained zinco^^ .i

Electrolysis of the synthetic solution for a three«hour period at a cathode ourrent density of approximately 8o5 amperes per square . foot,) a voltage of Stf) for.- a' 'spaoing ,of - one inch between electrodes ' produced a bright^ firiBs and fine-grained; deposit of zinc„ The computed current efficiency was; 7oo0 per cento Electrolysis of Zinc teach Solution , / : /: ,The'':Conditipns: which produced a: satisfactory depositioh of zinc from the synthetic solution were utilized in the electrolysis of zinc'froa a thrice purified pregnant. solutipn0

The initially deposited zinc was bright and adhered to the cathodes,'-:but .after one hours a dark - spongy scale appeared on theV ' ■ ' deposited zinc and began to spread slowly across the surface of the Zinc deposito The metallic zinc became, corrugated and began to crumbleo „■ ;

■ A search of■the literature revealed that a similar condition - was caused on zinc deposited from acid solutions by the presence of arsenic in the solutionf^^ A cheim.cal. analysis of the purified pregnant solution showed the presence of 0o0lU gram per liter of ;arsehib; and' TOe#ll gram per liter of seleniunio . The addition of 'V . . ■

29a Ibids po 127» ' ' : ; .306 , ; Mantelly .-0o -1* gImdustrial Wectroohemistry^; McGrraw^ill. .Eook 0onpaByg: Inc»y lew'TorEPpT™^?^^:X.-v" . .v :

an equivalent quantity of arsenic to the pure synthetie solution before eledtrqlysis . prod.ueed . a zinq deposit x-iith the characteristic.' spongy scale -and corrugation similar to that deposited from purified leach solutiono ' ' .Bepurification of leach.Solution by the Addition of Ferric Sulfate

•v'!s/;,aoiLd processes, 'arsenic content -was reduced from the r solution prior , to electrolysis by precipitation along'.with .ferric, hydroxide An attempt was made to utilize this mechanism of coprecipitation for the removal of arsenic and selenium from the zinc leach ammoniacal solution» Unlike acid solutions where the . Iron was present as ferric ' ion .'and, the pH was raised to cause precip* itations ferric iron was added to the aramoniaeal pregnant liquor of high pHy 10o5s in the form of a solution of ferric sulfate0 ;., ' ■ , .Five .'grams - of''ferric, sulfate in an. aqueous solution •were .’added to 80Q milliliters of zinc leach solution producing one liter of solution after dilution,. The resulting solution which contained OoQlh gram of arsenic and Q00078 gram of selenium per liter was - subjected to electrolysis under the initial conditions: .as:pre^ , viously described o. It'Was noted that although the. arsenic content was not changed with the ferric sulfate addition, the: selenium ;centetit was decreased frpm 0e011 to 0*0078 gram per litero The . resulting''.zinc: deposit' displayed:, the .same' unsatisfactory eharae» . teristics as before which indicated that the impurity or impurities " which eaused the difficulty had not been sufficiently removed . from the solution* i.. '. -i.' :

31 o Mantells op* cit6, pp* 35l"352o

Eepurif$.dation of Leach Solution by the Addition of Ferrous Sulfate and Oxidation - .\ : ; • An additional: methods x-jhieh was proposed by Garl Eampaeek of.:the United States Bureau of 'Minebj comprised the coprecipitation of the arsenic and selenium tJith the iron by ’ the addition of ferrous sulfate and oxidizing the ferrous iron to the ferric state followed ' by,preoipita# ''''' ;'.t ■■ ' ' ■ A

. An aqueous solution, containing 5> grams of ferrous; sulfate was added to 800 milliliters of previously purified leach solution making: on#' iiter of solution upon dilutiorio : Air was. bubbled' through ' the solution:for two hoursa after’which the precipitated- ferric hydroxide was separated, by filtratibno The 'resulting solution indicated that the arsenic content was reduced from OcOlh to 6d0087 gram per liter and that .the selenium,;content was. reduced from 0oOil to GoOO^li gram per litere Electrolysis of the resulting solution proved suoeessful in that the zinc deposit 'was- bright^ firm9. fine-­grained j, and free ;fr©m"spongyi:black. scales and ' cdfrugatidnso-' -: ': ■ :V:

The successful:electrolysis was, conducted for 17co? hours during which 1805 grams of zinc were deposited from the solution at a . calculatedvcurrent: efficiency; of 55 per cents Although the char­acter of the deposit was sounds sprouting occurred at the edges , of the cathode where the current density was high due to the geometry ■of the;-surface. The- problem of sprouting wap resolved by placing three,Incite strips along the- edges of the cathode thus preventing ' ■ the solution from coming In contact Tilth edges of. high current

■ .i ', ; ■ :■

With the production of a zinc leach solution which could be satisiadtdrily electrolyzed for more than 17 hours5 another problem presented itself in the form of a fine powdery zinc deposit on the cathode.in areas where 'the,solution was possibly not, well agitated0 .The ■ deposition of the" powdered-'zinc''was;believed to have been partly respdhsible for the. low current' effieiency0 ■. , Mantell has suggested that the .control of temperaturea •current :,#hsltyi agitation, viscosity of solutions metal ion 'concern# trations pHp and additives were necessary for the elimination of undesired deposition characteristicso"' y : y ... • ' y . '

. Unfortunately, it was necessary to stop'further experimental work at this pointo If additional work is planned involving the electrolysis of zinc f fpm' ammoniacal solution, the writer- suggests that more detailed work be conducted on the removal of impurities and control of operating conditions than whs possible for thisthesisc

■;;.'3Bo ■; ''i 'Manteil, op^ 'clt,,'. pp„ 211™2220y

: i

" ’ Conolttsloas .lo ■ In order to obtain leach solution for the experimental work involving the recovery of sine .from -sndh solutions, it was necessary to produce leach solution of one liter per test, whereas3 all

" , previous ,pr##u###''molutloh- -of :## milliliter# per test. - &

the- dissolution of aim from Iron.ling sphalerite concentrate in '■ the modified two-liter capacity autoclave designed by Jo C. Trerbergs

,, :iserea6lai the puasetity of soluMea f m s @90 eilliiiters to one liter required an increase in the time of dissolution from 30 minutes to

" 'v: - one hour -aad as taorotoe- 1m: the impeller peripheral speed from ’. t@ lg% 0 f#et/pe# - - - ' :. ■■■■■ %. -

' 2* A comparison of the results obtained when the leached. ■ resldflse ssre washed - with water and tt per esat srnmonih eolutios shewed -W*t isshisg iritii water: predaced ;8 higher extraction- of soluble sine from the residue 0 98 .2 per cent 5 and used less wash solution5 0og port per part of dry residue3 than the ammonia

- : aolutlom -#l@h, require# two parts .of wash' soiutiss, to prodw#.- a ■'- 9 7 per cent extraction® ' ' -

I®, . The aamoniacal sine leach solution was purified prior tothe recovery of. Bln# as basis sins; sulfate by the aiditloavof

'' graBstiiltS:viiziq for .the,:pre©5$>iSaii3,0b . :Q£,'eo|per$.. lead* ■ ca<^um# ■' and.,;. ■ possibly minor amounts ef other metalso}4.o In the recovery of zinc from the purified leach solution afterone stage of cementation by the distillation of ammonia3 97oU per,eeat of the zinc lias precipitated.as basle zirio sulfate nhen the solution reached a pH value of 7=5 ;V -5=' ■ The ealoination of the .basic zinc -sulfate for one - hour at1^200 degrees Centigrade produced a .zinc oxide xiith a sulfur content of 0o02.per .eento ' . \6;0 ; , The recovery of zinc as basic ' zinc sulfate and the caleinationof the basic .hinc siilfate for the productidn: of zinc oxide ■ showed promises but additional work on a larger scale would be necessary for a final evaluation of the possibilities of such a methods to , The reduction of the zinc - o#de,'with hyd at a temperaturejust below the melting pointbfzinc was unsuecessfulo At tempera- tures of 700 and 900 degrees Centigrades hox»ever s reduction of zinc

@xidei\took.%ladhi und'ialthough:^• the rate of reduction and. volitallzation of:zincs by observations ■increased as the temperature was raised«80 : , 1 . The production of metallic. zihC;by. .the precipitation of basic zinc ■sulfates its calcinations and reduction of the calcine with hydrogen showed some promises but further.works on a quantitativebasiss would be necessary for a more - definite' dqmel#8iqn.o ■:%’ • '- The recovery of ammonia amounted, to 93=3 per cent by theoperations of purgings the reducing Of pressure in the aut©clave

' v " ■' ' _■ . ' ' ' : ■ ' iv, ' . ' ' ■■ ■ ' : , ' '

; ■ •■UW/of.Arizona:Ubrnw'

before disassembly and during filterings the washing of the basie, zinc snlfateand the leached residuesa and the further distilling ';of the alnu depieied uqlxitiuih®;'''' ' : 'y'k'/y10o When the quantity of wash water was increased to It, 0 parts per part of dry residues the loss ofammonia by the residue decreased from OaltB Pdf cent Of the ammonia charged to the autoclaves or 2 $ 0 $

pounds per ton of recovered %inca to a value of 0o03 per /eents" or. " :-\lsi!. potmds: per ton of: recoyered aine0 :y. ■ .' • 'H o : The ammoniacal zinc leach solution was purified prior to. ;electfdlysiS;;-in two stages. The object of the first stage was to reduce or eliminate copper. fead's;- Cadmiums";' possibly minor .. amounts of other metals with three cycles of granulated sine addi­tions o The object of the second stage was to reduce or eliminate impurities such as arsenica.seleniums and. other interferring ... impurities by the addition, of ferrous sulfates oxidation of the ferrous,, irons and coprecipitation of; arsenic,, seleniums and ironG . 120 ■ The electrolysis of a synthetic solution for a period of.'thredv houre: prqduoed'h^bfight^ firms •;and ''fine<*grained deposit of . ,/ zinc with a current efficiency.of 76 per ceht@ ; .13o The electrolysis of the leach solution after the first stage of purification produced a zinc ' deposit with spongys•black scalds and corrugations* ’ ' , " ' . ' ^lU* llectrolysis of the leach solution after the second stage of purification was successful in producing a. zinc deposit of comparable

quality: to that, produced 'by the electrolysis of the synthetic solution ' Although the character of the deposit was 'sound* electrolysis for an iS^hour period resulted in a powdery deposit I

. RecormendatioRS ::

, '1/ - -fhe'.writer believes that the progress attained in the elec«-» trolysis of ammonia cal 1 zinc leach solution justifies further experl* mental work* and., therefore* adds the following suggestions that might 'he of helps : ..'V; ’ .■ , : ": n . : i : , : I . ^ ■ ■v:,;:."- :la ; . • The use of higher' pulp densities for the production of leachsolutiohs in the autoclave should be investigated to increase the. coneentratiob of dissolved sine in the solution®2e : ;. A more detailed study of the affects and removal of iffipuri**

. ties 'shpuld be oonduotedo y:3o The Use of a. oiroulating solution in the electrolytic cellshould be investigated*ho The affects of temperature* voltage* electrode spacing*additives and depletion of•electrolyte on current and power efficiency

, 'A ’

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•Brayji Jo Lo s Non-Ferrous Production Metallurgy John Wiley aad Boms^, Imq0^ 'lew.. Jork3 19U7o : . '

' Ga3^Mells To - P.,. The Electrolysis of Ammoniacal Zinc Carbonate : . Solutions s TraHsaetion American Electrochemical Societyj, . ''Vol,: 9^V ' ' ' ^ .r ;v : , ./ " V';: '.K :; Hanson^ Go- B0 s The Dissolution of Copper from Mixed popper

' : Ores at 'Elevated Temperatures and Pressures,, ThesisUniversity ' of Arizona^ 1957o, 1'. \ , ' y :’V : . .. ": ::Haywardj Go Boj An Outline of Metallurgieal Practice3rd edc> Do Van losti’and Go’rrpanjra lheoS Me%-P Yorkg 1952® ‘ :Kirbys Bo Go3 The Dlssoluiioh of Ghaleopyrlte and. Ghalcoeite

:■ at Blevated Temperatures and Pressures s Thesis3 University of , Arizona^ \ ',y. -

6s ' : ' Kolthoff s lo Mo fl and - Sandell3 Eo, :B0 s Textbook- of Quantitative Inorganic Analysiss 3rd ed02 The Macmillan Company, Men Yorko ■

■ • : 7b; ; i- Dawrences Hs Mo^ Becent Developments. in Ammonia Leaching for . Zinc Gres9 School of Mines and Metallurgy? University ofp v Miesourl lulletin's:f6l.*vl©# Hoy::3s::May^lt27tv180 1 lantells Co Lo^ Industrial ElectrochsTaistrys McGrap-Hill Book :

' : Companys InCa,s :leif lorks

9s : ;; :MoMnsony Js;' Tes The Dissolution ,of Ghaleopyrlte at Elevated •. • Temperatures and~Pressures3 Thesiss ■ University of Arizonas 1955

/■: 10s: ■<;; 'Mosss, T0 A0 9 The Dissolution of Copper from Borhlte, Govellitea and Copper Goneentrates:at Blevated Temperatures and Pressures3

.' 1 • Thesis s University ;df. Arizona ™l|5H» ,, ; : : ■ ■ . .lle ' Stanczyka, M0 HQ 3 The Dissolution of Zinc from Sphalerite at' -;

: Elevated Temperatures and Pressures,, Thesis 9 University of .: ■:' ; AriiEai l95Er^™~^": — ™-y™r ^

12t ' - Tverbergs J0. 0»a The Dissolution of Chaleopyrite at Elevated • : Temperatures and Pressures Part 11$ Thesis s University of : •/

; , ' /1' Arizdnag 1956^0.:;' , / -; ; .'P ;13o ' : Van Aradale^, G0 D0 s Hydrometallurgy of Base Metals g. McGram«

M Hill Book Gompanys Inco , Neu Torlc3 1953o ■ P