A critical evaluation of methods applicableto the determination of cyanides

by C. POHLANDT*, Chem., Dip., E. A. jONES*, B.Sc., and A. F. LEE*, Ph.D.

SYNOPSISA literature survey of methods suitable for the determination of cyanides in process streams and effluents is presen-

ted. Of the large number of methods published, 92 are examined in detail, emphasis being placed on the selectivityof the methods, i.e. the extent to which they enable one to distinguish between ionic cyanide and metal-cyanide com-plexes. Methods designed for the determination of 'total cyanide' (i.e. ionic cyanide as well as coordinated cyanide)are evaluated critically. Other aspects of the methods are also considered, such as sensitivity, accuracy, speed, andfreedom from interferences. .

SAMEVATTING'n Literatuuroorsig oor metodes wat geskik is vir die bepaling van sianiede in prosesstrome en uitvloeisels word

aangebied. Van die groot aantal gepubliseerde metodes, word 92 in besonderhede ondersoek met die klem op dieselektiwiteit van die metodes, d.w.s. in watter mate hulle 'n mens in staat stel om tussen ioniese sianied en metaal-sainiedkomplekse te onderskei. Metodes wat ontwerp is vir die bepaling van 'totalesianied' (d.w.s. ioniese sianied engekoordineerde sianied) word krities geevalueer. Ander aspekte van die metodes soos sensitiwiteit, akkuraatheid,spoed en afwesigheid van steurings, word ook in oenskou geneem.

Introduction

The accurate determination of cyanides in wastewaters and process streams presents difficult analytiealproblems. In such solutions, depending on the pH value,cyanides occur as molecular acid (HCN), as cyanide ions(CN-), and as metal complexes of widely varying stabi-lity. Because of the extreme toxicity of hydrogen cyanideand ionic cyanide, accurate and sensitive methods ofdetermination are required for the monitoring of wastewater. If the environment is to be protected from pollu-tion, one must ensure that the cyanide content of naturalwaters does not exceed 0,025 p.p.m. Depending on theirstability constant, complexed metal cyanides vary intoxicity. The ionization of such complexes due to changesin pH or to photo-decomposition caused by sunlight canresult in the formation of molecular hydrogen cyanide.Even complexes as stable as the cyanoferrates can thusbecome toxic to marine life, and 0,4 p.p.m. has beendetermined as the maximum permissible level in freshwatersl.

In the analysis of waters, ionic cyanide and potentiallyionizable metal cyanides are often determined togetherbecause of their toxicity. The chlorination of an alkalinesolution containing these compounds results in theformation of cyanogen chloride and subsequently, as theresult of hydrolysis, harmless cyanate ions. This proce-dure finds an application in the treatment of industrialwaste waters and in analytical procedures for the deter-mination of cyanides. Since only ionizable species areoxidized by chlorine, this method differentiates betweenthe cyanides that are amenable to chlorination and thetotal cyanide present in a sample2. The latter is there-fore a measure of the ionizable and non-ionizable cyanidespecies present. The distillation of two samples is re-quired, one of which will be chlorinated and the otherunchlorinated. After distillation, both absorption solu-

* Council for Mineral Technology (Mintek), Private Bag X3015,Randburg 2125, Transvaal.

«;) 1983.

tions are analysed for cyanide. The difference in theresults obtained is the amount of cyanide amenable tochlorination. For the control of pollution, this differen-tiation between the cyanides that are amenable to chlori-nation and the total cyanide present in a sample isgenerally satisfactory. However, there is no clear-cutdivision between ionizable and non-ionizable compounds,and the ionization of complex cyanides of, for example,nickel, cobalt, silver, and gold, depends largely on thetime, temperature, and amount of chlorine used in theoxidation step.

Frequently, the terms simple and complexed are usedto differentiate between various cyanide compounds. Theformer term describes cyanides that are readilyconverted to hydrogen cyanide after acidification to apH value lower than 4. The term complexed is applied tocyanide compounds that require digestion, heating, orother severe methods of decomposition to liberate hydro-gen cyanide. This differentiation can be useful withrespect to the total cyanide content of a sample; however,it gives little information about the types of speciesactually present.

In this paper, cyanide compounds are classified asfree cyanides (i.e. molecular acid and ionic cyanide) orcomplexed metal cyanides. The complexed metal cya-nides can be further classified as weakly complexed cya-nides or as strongly complexed cyanides. (The lattergroup consists of the very stable hexacyanoferrates andhexacyanocobaltate). The term total cyanide is used forall cyanide, i.e. free as well as coordinated cyanide, presentin a sample. The concentration of free cyanide in a solu-tion depends on the pH value of the solution and on itscontent of heavy metals capable of forming cyanidecomplexes. In alkaline hydroxide solutions (i.e. 0,1 Msodium hydroxide), the free cyanide is completelyionized and stable metal-cyanide complexes are formed.In neutral or acid solutions, the free cyanide is onlyweakly ionized, and the formation and partial evolutionof hydrogen cyanide are favoured. Weakly complexedmetal cyanides decompose at pH values lower than 4,

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JANUARY 1983 11

with the evolution of hydrogen cyanide. Strong metal-cyanide complexes are usually unaffected at room tem-perature, but partial decomposition can occur with in-creasing temperature and acid content. Furthermore,the metals released upon decomposition react with un-decomposed, strongly complexed metal cyanides to forminsoluble heavy-metal double salts, viz Cu3[Fe(CN) 6]

2'KFe[Fe(CN)6] or (UO2)2[Fe(CN)6]' Obviously, a systemcontaining hydrogen cyanide or complexed cyanideprecipitates, or both, is unstable, which malms analysisdifficult. Sample solutions are stabilized by the additionof sodium hydroxide until the pH value is greater than11 to prevent losses of volatile hydrogen cyanide. Theaddition of sodium hydroxide to metal-cyanide precipi-tates results in decomposition and the formation ofmetal hydroxides.

In addition to the analysis of process streams andwaste waters, it might also be necessary for the cyanidecontent of the resins and pulps used in a process to bedetermined. It appears that all complexed metal cyanidesare retained on anion-exchange resins from alkalinesolution. The acidification of a solution prior to ion ex-change would therefore result in decomposition of theweakly complexed cyanides, as described above, where-as strongly complexed metal cyanides, i.e. those of iron(Il), iron(III), and cobalt(III), would be expected to beretained on the resin. Also, precipitation mightoccur within the resin network owing to the reac-tion between the released heavy-metal ions and thestrongly complexed metal cyanides. This reaction mightresult in the gradual 'poisoning' of the anion-exchangeresin, i.e. the resin would losc its efficiency. For effectivecontrol of a hydrometallurgical process and accuratedetermination of the cyanides, the kinds of metal com-plexes present, as well as their relative stability con-stants, must be known.

Currently used methods of determination are oftenslow and subject to interferences. For example, the sen-sitive pyridine-pyrazolone colorimetric method describedby Epstein3, which is also recommended in a modifiedform in a 'standard' method2, requires distillation toseparate the cyanide from the interfering substances. Themethod is time-consuming, does not permit very stablemetal-cyanide complexes to be determined, and doesnot allow cyanide to be quantitatively recovered in con-centrations below 0,1 p.p.m.4. Similar observations havebeen made about other methods, and it has been pointedout that, with most of these, ionic cyanide cannot bedistinguished quantitatively from metal-cyanide com-plexes5.

It was decided that a comprehensive literature surveyshould be undertaken, the aim being to select and torecommend procedures for the fast, accurate, and preciseanalysis of ionic cyanide in the presence of complexedcyanides, and vice versa. The study on the determinationof complexed cyanides would include the determinationof hexacyanoferrates and hexacyanocobaltates, as wellas methods that enable one to distinguish between indivi-dual metal-cyanide complexes-a further advantage inthe control of hydro metallurgical processes.

12

Decomposition of Complexed Metal Cyanides

Most methods for the determination of the totalamount of cyanide present in a sample involve treatmentwith acid to convert the cyanide species to hydrogencyanide, followed by distillation. Important aspects ofthe distillation step are the elimination of interferencesand the decomposition of stable metal-cyanide com-plexes. Among the ions commonly found in waters andeffluents, sulphide and thiocyanates are responsible forthe most serious interferences.

Sulphide distils with hydrogen cyanide and can havean adverse effect on subsequent methods of determina-tion. Its removal, prior to distillation, involves filtrationof the precipitates obtained with cadmium nitrate2 orlead carbonate6, or by its reduction with sodium hydro-gen sulphite4. Sulphide can also result from the decom-position of thiocyanate or of thiocyanate complexeswhen conventional reflux distillation procedures are used.This is particularly the case when a metal salt such asmercuric chloride or cuprous chloride is added as a cata-lyst to accelerate the decomposition of complexed metal-cyanides4. In a 'standard method'2, the addition of mag-nesium chloride instead of cuprous chloride is recommen-ded if the concentration of thiocyanate exceeds 5 mg/I.The relatively harsh conditions required to dissociatecomplexed metal-cyanides are therefore likely to produceadditional interferences.

Current methods of decomposition require boilingunder reflux for at least one hour. Although this lengthof time is generally adequate, the complexes of iron,copper, mercury, and cobalt require longer treatmenttimes because of their stability, and decomposition oftendoes not continue to completion. Procedures that havebeen developed to cope with the analysis of these com-plexes involve ligand exchange or irradiation with ultra-violet light to displace the coordinated cyanide. Duringreflux distillation, ligand exchange by a mixture of twocomponents, 1,2-hydroxy-3,5-benzene disulphonic acid(Tiron) and tetraethylenepentamine (TEP), resulted inthe complete recovery of ionic cyanide from Cu+, Ni2+,Hg2+, Fe2+, Fe3+, and Cd2+ complexes 7, only cyanidepresent as hexacyanocobaltate not being recovered. Thismethod is faster than conventional distillation methods.Also, because of the mild conditions employed (a pHvalue of 4,5 adjusted with hydrochloric acid), many inter-ferences, notably those from sulphide and thiocyanate,are eliminated.

Kruse and Mellon8 have reported ligand exchange bythe addition of the sodium salt of ethylenediaminetetra-acetic acid (EDTA) followed by distillation in thepresence of phosphoric acid. Complete recoveries ofcyanide ions were obtained from the complexes of iron,copper, nickel, cadmium, chromium, and manganese,and the recovery of cyanide from its cobalt complex was90 per cent. The cyanide complexes of thallium, silver,and mercury were not considered, and interferencesfrom species other than cyanides were not discussed.This method has the disadvantage that the distillationmust be continued until the phosphoric acid is concen-trated and becomes syrupy. .

More recently, ligand exchange by the addition of

JANUARY 1983 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

1

,-\

~

t

!'-'

,-

~'-

t

IliJII1

t

EDTA was advocated for the recovery of cyanide fromiron and cobalt complexes9,1O. This information is avail-able to the present authors only in abstract form, andno further details are available.

The use of ultraviolet irradiation for the decompositionof metal-cyanide complexes has been investigated4,1l,12.The decomposition, even of cobalticyanides, is achievedin a matter of minutes by irradiation with ultravioletlight, of a sample that has been slightly acidified withphosphoric acid. For ultraviolet irradiation, a mercurylamp of 100 to 400 Wand a special quartz cell that canbe completely filled with sample solution are required.Because it is rapid, this method lends itself readily toautomation4. However, ultraviolet irradiation also resultsin the decomposition of thiocyanate to form sulphideand cyanide, and one must take special precautions toprevent this interference.

Preconcentration of Cyanide Compounds

Since the preconcentration of cyanides by distillationis unsatisfactory in many respects, attempts have beenmade to use solvent extraction or ion-exchange proce-dures instead. For example, Wronski13 successfully usedtributyltin in trichloroethylene to extract and precon-centrate small amounts of ionic cyanide from solutionsat pH values from 7 to 10. Cyanide was recovered fromthe organic phase by the use of a four-stage strippingcycle. This method has the advantage that thiocyanate,complexed metal-cyanides, and sulphide are either notextracted or not stripped. However, it is not clearwhether mildly complexed metal-cyanides like[Zn(CN) 4]2- remain stable under the conditions em-ployed.

A potentially useful method involves the extractionand preconcentration of cyanide compounds by the useof quaternary amines, followed by back-extraction witha sodium hydroxide solution 14.

The concentration of metal-cyanide complexes on astrongly basic ion exchanger, followed by the stepwiseelution of pairs of these complexes, has been reported byBurstall et al.15, who found difficulty in eluting severalof the adsorbed cyanide complexes. The method istedious, and requires major changes to make it suitablefor analytical purposes.

The adsorption of ionic and some complexed cyanideson a strongly basic ion exchanger followed by the on-column release of hydrocyanic acid with sulphuric acidwas employed by Gilathl6, who achieved complete reco-veries of cyanide bound to zinc, cadmium, copper, andsilver. Although this procedure requires only 20 minutes,it is apparent that the complexes of iron, cobalt, andmercury would resist decomposition, and that incompleterecoveries of cyanide would be obtained in the presenceof these metals.

Tritrimetric Methods

An excellent review of visual titrimetric methods hasbeen published by Bark and Higsonl7. It appears thatthe earliest method for the determination of cyanidewas reported in 1~51 by Liebigl8. This method is basedon the development of turbidity due to silver cyanidethat forms as a result ofthe reaction between the cyanide

and a silver nitrate solution. A similar method, based onturbidity due to the presence of silver iodide in thepresence of ammonia with potassium iodide as the indi-cator, has been reported by Denigesl9. Various modifica-tions to these argentometric procedures have been sug-gested. The American Public Health Association2 recom-mends a modified Liebig18 method in which p-dimethyl-benzyledene rhodanine is used as the indicator2O for thedetermination of concentrations of cyanide higher than1 mg/I.

Titrimetric methods involving the electrochemicaldetection of the end-point are widely used, and arediscussed in detail later.

Generally, titrimetric procedures are employed for thedetermination of larger quantities of cyanide in the ab-sence of weakly complexed metal cyanides and otherinterferences.

Colorimetric Methods

From the review of methods available for the deter-mination of small amounts of ionic cyanide, it is apparentthat colorimetric methods are suitable for amounts suchas 0,1 to 1 p.p.m. Few of the methods are specific forcyanide, and there is interference owing to the presenceof sulphur, thiocyanate, thiosulphate, and certainmetals21-39.

For the detection and determination of small amountsof cyanide in effluents, Aldridge's method4O-42 is recom-mended. This method is an example of the K6nig synthe-sis, in which cyanogen bromide or chloride reacts withpyridine and an aromatic amine to form a dye. Aldridgereacted cyanide with an excess of bromine, removing theexcess of bromine with arsenous acid solution andallowing the cyanogen bromide to react with a pyridine-benzidine reagent. The K6nig reaction is used in thedetermination of ionic cyanide. In the presence of thio-cyanate, ferrocyanide, and ferricyanide, and sodium andcalcium chlorides, a distillation under reduced pressureis recommended after complex cyanides have been'fixed' with zinc acetate solution3,43,44. However, the useof carcinogenic benzidine is hazardous, and other inves-tigators used a variety of coupling agents3,17,21,22,44-51.

The most successful of these methods is the variationproposed by Epstein3, which involves the oxidation ofcyanide to cyanogen chloride with chloramine-To Thecyanogen chloride is then reacted with pyridine con-taining pyrazolones, and the blue colour produced ismeasured at 630 nm. This method is sensitive, andcan be used in acid, neutral, or slightly alkaline media.A modification of Epstein's method in which amore stable reagent, pyridine-barbituric acid, is em-ployed, is currently recommended by the AmericanPublic Health Association2.

It must be borne in mind that, with methods based onthe K6nig synthesis, all ionizable cyanide compoundscan be determined, i.e. those amenable to brominationor chlorination. With these methods, one is thereforeunable to distinguish between cyanide ions, weakly com-plexed metal-cyanides, or thiocyanate. To eliminateinterferences from compounds other than cyanides, adistillation step prior to colorimetric determinations isrecommended. Also, the distillation step must be devised

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JANUARY 1983 13

in such a way that even the most stable cyanide com-plexes, i.e. those of mercury(II), ITon(II), iron(III), andcobalt(III), are dissociated to evolve hydrogen cyanide.Only then does the colorimetric measurement of the ioniccyanide in the absorption solution give an accurate valueofthe 'total' cyanide present in the sample.

Electrochemical Methods of Determination

Potentiometric ProceduresThe potentiometric determination of cyanide with

silver nitrate was first reported in 1922, and early proce-dures up to 1962 have been reviewed by Bark andHigsonl7. The most widely used indicator electrode isthe silver rod or billet, although gold, mercury, andamalgam electrodes have been used occasionally52. Thetheory of the argentometric titration of cyanide in theabsence and presence of ammonia was given by Ricci53.In theory and practice, two points of inflexion are ob-tained in the potentiometric titration curve, the firstbeing due to the formation of a soluble silver complex,and the second to the appearance of insoluble silver(I)cyanide:

Ag+ + 2CN- = [Ag(CN)2]-

Ag+ + [Ag(CN) 2]- = Ag [Ag(CNhJ.

The second inflexion therefore corresponds to thesecond (permanent) turbidity of the normal Liebig18titration and to the end-point given by Deniges in hismodificationl9, where ammonia and iodide ions are addedas indicator. The change in slope of the first potentio-metric inflexion is about ten times greater than that ofthe second and, because of this and the fact that it is lesssusceptible to interferences, it is normally used in prac-tical applications. As in the Denig�s titration, thepresence of excess ammonia distorts the slope of thesecond potentiometric inflexion19 but does not changethe first or second equivalence points, since the forma-tion constants of the ammonia complexes of silver aremuch lower than those of the corresponding cyanidecomplexes.

When metal ions are added to a cyanide solution,complexes are formed. If the stability constants forthese complexes are higher than that for the silver-cyanide complex [Ag(CN) 2]-' an amount of ionic cyanideproportional to the concentration of metal ions presentwill be removed from solution, and there will be a reduc-tion in the silver nitrate titre. Under normal analyticalconditions, the cyanozincate(II) ion [Zn(CN) 4]2- reportsas ionic cyanide in argentometric titrations. In poten-tiometric titrations, the equivalence point for zinc cya-nide slightly precedes that for [Ag(CN) 2]-' but zinc con-centrations of up to 0,1 gjl can be tolerated before thesilver-cyanide complex is distorted during the titrationof a 1 per cent solution of sodium cyanide with 1,0 Nsilver nitrate 54. In the presence of a complexing agent,the hexacyanoferrate(II) ion gives an inflexion curve thatfalls between those for silver in argentometric titrations,and does not interfere with the first potentiometricequivalence point 55. In alkaline 52 (including ammonia-cal54) solutions, iron(II) - and iron(III)-cyanide com-plexes interfere. Under ordinary analytical conditions

in thc absence of strong complexing agents, nickel andcopper also interfere 54. Some discrimination against thecyanide complexes of copper can be obtained by use ofthe second argentometric inflexion point in the presenceof sodium thiosulphate56.

In addition to silver nitrate, which is more commonlyemployed, mercuric chloride(I), iodine(I), and nickel(II)ions57, and brominc58 have been used as titrants forcyanide.

Amperometric ProceduresAmperometric titrations are preferred for low concen-

trations of cyanide and for automated procedures. Thcamperometric titration of cyanide is equal in accuracyand precision to the visual Deniges method, and can bcemployed for more-dilute samplcs59. Shinozuka andStock6O found that the amperometric titration of cyanidewith silver nitrate in 0,1 M sodium hydroxide gave lowresults, and they substituted 0,1 M sodium sulphite forthe sodium hydroxide. For amperometric titrations,rotating or vibrating61 platinum electrodes are preferred,with dilute silver nitrate solution as the titrant. Howevcr,titrations have been donc with iodine solution. For thedetermination of very low concentrations of cyanide, theanodic current that is generated at a polarized silver orgold electrode has been measured direct62-64. This currentis proportional to the cyanide concentration:

~

Ag + 2 CN-

Au + 4 CN-

--+ [Ag (CN)2]- + e,

--+ [Au (CN) 4]- + 3e.

The approach has been made the basis of two sophisti-cated analytical methods involving flow injection 6,11.

Polarographic and Voltammetric ProceduresIonic cyanide depolarizes the dropping mercury

electrode to give an anodic wave as follows:

Hg + 2 CN- ~~ Hg (CN)2 + 2e.

This wave is well developed in 0,1 M sodium hydroxide,and starts at about -0,45 V versus the saturatcdcalomel electrode. Two early procedures65,66, in whichsimple direct-current (d.c.) polarography was used, werebased on this reaction. The advent of sensitive modernwaveforms, such as differential-pulse polarography, haspermitted the determination67 of cyanide in concentra-tions down to 1,5 /Lg/l. Furthermore, by the use of phase-sensitive, alternating-current (a.c.) polarography andcomplex-forming electrolytes, metal ions such as chro-mium, copper, nickel, zinc, cadmium, and iron as well asionic cyanidc, can bc determincd68. An alternativeapproach for low concentrations of cyanide is the use ofanodic-stripping voltammetry, in which the cyanideis deposited as insoluble copper cyanide on the surface ofthe electrode and subsequently stripped 69.

Applications Involving Ion-selective ElectrodesAlthough these procedures are basically potentio-

metric, these applications are dealt with separately herebecause of the different structure of the sensor. Of thehalide-membrane electrodes, cyanide-selective mem-branes based on silver iodide (Corning 476127) or a mix-ture of silver iodide and silver sulphide (Orion Research94 - 06) are most commonly used 70-82. For both of these,

14 JANUARY 1983 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

some form of ion-exchange reaction takes place at thcboundary phases ofthe membrane layer 73:

I

2CN- + AgIsolid ~~ Ag(CN)2 - + r-

CN + AgII' d ~ AgCN + I-.

so I

The electrode responds primarily to the liberated iodideIOn,

As the electrode responds only to the dissociated ioniccyanide (CN-), the effect of pH on electrode re-sponse can be predicted from a log diagram of thehydrocyanic acid-ionic cyanide dissociation system,Theoretically, the optimum range of pH for the electrodeis between 12 and 13, but it can be used at a pH value aslow as 7 (provided that the solution is carefully buffered),probably as a result of the reaction 76

AgII ' d + 2HCN -~ Ag(CN)2- + 2H+ + r-

SOl ~-

In the presence of metal-cyano complexes, those com-plexes with a stability constant lower than that of silver(I)-cyanide, e,g, the complexes of zinc and cadmium,also give an electrode response and report as ioniccyanide.

In analytical applications, the cyanide-selective elec-trode can be used as follows:

(1) in the direct determination of ionic cyanide insolution, where it gives a true Nernstian responseover the concentration range 10-1 to 10-5 M, or

(2) as an indicator electrode in the titrimetric deter-mination of cyanide.

Indirect Methods Involving Atomic-AbsorptionSpectrophotometry

The two general indirect methods for the determina-tion of cyanide involve the following:

(a) the formation of an insoluble precipitate and thedetermination of the metal in the precipitate or ofthe excess metal ion in solution, and

(b) the formation of a stoichiometric complex, sepa-ration of the complex by extraction, and deter-mination ofthe metal in the complexl,83-87,

Worthy of note with respect to speed, sensitivity, andspecificity are the methods described by Jungreis andAin85 and Ramseyer and Janauerl. The former is specificfor ionic cyanide, and is based on the formation of asoluble silver-cyanide complex as a result of contactwith metallic silver. The latter is specific for the hexa-cyanoferrates. Although very sensitive, this method iscomparatively slow owing to the separation step invol-ved. Both methods are relatively free from interferences.

-j

Automated Techniques

Automated methods for the determination of cyanidesare generally very fast and sensitive.Flow Analysis

Technicon Auto-Analyzer equipment was used forthese analyses4,6,l1,88. Often a distillation step is incor-porated that not only eliminates interferences but sepa-rates the cyanides from particulate matter. The cyanidesare determined by colorimetric or amperometric mea-surement with detection limits that can be as low as 0,5 to

1,0 fLg of cyanide per litre. The speed of flow analysis isremarkable and, depending on the conditions employed,sampling rates that vary from 10 to 100 samples per hourcan be achieved, Flow analysis differentiates only betweensimple and complexed cyanides. The term simple refersto ionic cyanides as well as to ionizable metal-cyanidecomplexes that are determined together. The additionaldetermination of strong metal-cyanide complexes canbe achieved only by the inclusion of irradiation withultraviolet light to decompose them,

Gaseous hydrogen cyanide has been separated fromother cyanide species by diffusion in Conway micro-diffusion cells prior to flow analysis6, but this procedureis extremely time-consuming, taking from 3 to 5 hours89.Gas Chromatography

Nota et al.12 developed a very simple and sensitivemethod for the determination of trace amounts ofiron(II)-, iron(III)-, and cobalt(III)-complexed cya-nides. After the complexed cyanides have been brokendown by irradiation with ultraviolet light, cyanogenbromide is formed

(CN- + Br2 -+ CNBr + Br-)

and is separated by gas chromatography. Ionic cyanidcand thiocyanate are converted by hypochlorite into cya-nogen chlorides, which are stable under ultraviolet light.Ions commonly found in waste waters (such as Fe3+,CU2+, and Zn2+) and potential cyanide-forming materials(such as cyanate, glycine, urea, sulphides, and sulphites)do not interfere, The sensitivity is at nanogram level.Ion Chromatography

This technique9O is specific for ionic cyanide, andremarkably free from interferences. It is based on theseparation of ionic cyanide from metal-cyanide com-plexes and other anions, including sulphide and thio-cyanate, on pellicular anion-exchange resins. Ampero-metric measurement after separation allows ionic cya-nide to be detected at concentrations of a few micro-grams per litre,

Analysis of Solids

The determination of cyanide in solid substances israrely described in the literature. One method91, whichis applicable to the analysis of stable metal-cyanidecomplexes, employs fusion with sulphur and a mixtureof potassium chloride and potassium carbonate to formthiocyanate. The latter is determined colorimetrically,and the cyanide content calculated. Cyanide is recoveredfrom all metal-cyanide compounds, including the hexa-cyanoferrates and hexacyanocobaltates.

The method recommended by the American PublicHealth Association2 for the determination of cyanide insolid wastes involves leaching of the sample withdistilled water. Insoluble cyanides in a solid sample aredetermined as usual by distillation. Insoluble ironcyanides can be leached from solid waste by beingstirred with caustic soda for 12 to 16 hours.

Discussion and Recommendations

From this survey of 92 potentially useful proceduresfor the determination of cyanide, it is apparent that mostof them are ideally suited to the analysis of samples

tJOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JANUARY 1983 15

('ontaining only ionic cyanide and no interfering substan-ces. The choice of procedure would then depend only onthe concentration of cyanide in the sample solution. Forexample, titrimetric methods are suitable for the deter-mination of concentrations of ionic cyanide above 1 mg/l,procedures involving the use of cyanide-selective elec-trodes cover the range from 0,05 to 10 mg/l, and withcolorimetric methods one is able to detect concentrationsas low as 20 fLg/l.

Unfortunately, unless they are synthetic, samplesrarely eontain only ionic cyanide. Complex samples, e.g.industrial effluents, contain mixtures of gaseous and ioniccyanidc, metal-cyanide complexes of varying stability,and a variety of interfering substances. Irrespective ofthese, there are very few methods that one can use todistinguish between ionic cyanide and weakly complexedmetal-cyanides in such samples. It appears that, forthe selective determination of ionic cyanide in thepresence of metal-cyanide complexes, the followingmethods arc the most useful with respect to speed, sen-sitivity, accuracy, and the elimination of interferences:

(1) an indirect method involving atomic-absorptionspectrophotometry, which is based on the forma-tion of [Ag(CN)2]- as the result of contact withsilver wire having a large surface area85, and

(2) ion chromatography 9°, based on the separationby ion exchange of ionic cyanide from metal-cyanide complexes and other anions.

None of the methods inspected can be used success-fully in the selective determination of cyanide in coor-dination complexes with metals in the presence of ioniccyanide and other interfering substances. It is thereforecommon practice for a two-step analytical approach tobe used, viz dissociation and separation of all the cyanidespecies by distillation procedures, followed by determina-tion of the liberated cyanide in an adsorption liquid. Thelatter step can be carried out by the use of any of theprocedures discussed earlier because of the absence ofinterfering substances. The total amount of cyanidedetermined minus the amount of ionic cyanide deter-mined by a different method would then give the con-centration of cyanide that is complexed with metal ions.However, distillation procedures are unsatisfactory inmany respects, as was pointed out earlier.

The most serious interferences are caused by sulphide,thiocyanate, and thiocyanate complexes. It has beenshown4 that 30 per cent of the thiocyanate present (atthe 100 fLg/llevel) decomposed to cyanide and sulphidewhen a 'standard' distillation procedure2 was used. Sul-phide can interfere in subsequent determinations in twoways. Firstly, the detector, for instance a cyanide selec-tive electrode, also responds to sulphide ions, and a posi-tive interference results. Secondly, the sulphide ions areair oxidized to polysulphides that react with the cyanidepresent to form thiocyanate, which results in a negativeinterference. The tendency of thiocyanates to decomposeduring distillation is aggravated by the severe conditionsnecessary for the decomposition of stable metal-cyanidecomplexes. For example, the reflux distillation procedureat low pH, which is recommended by the U.S. Environ-mental Protection Agency (EPA)92, has been shown to be

subject to serious interferences from sulphide and thio-eyanates 7. This is also true for the 'standard' methodrecommended by the American Public Health Associa-tion2, as was pointed out earlier. It has also been shownthat, in the absence of sulphide and thiocyanatcs, theEP A method gives excellent recoveries of cyanide fromall metal complexes except [Co(CN 6)]3--at concentrationsgreater than 20 fLg/l. The method recommended by theAmerican Public Health Association2 apparently doesnot give reliable results at levels around 100 fLg/l beeausethere is incomplete absorption of hydrocyanic acid4.

The ligand-displacement method of Ingcrsoll et al. 7

appears to be the only distillation procedure in which nointerferences from sulphide and thi~_)Cyanates occur. Thisis achieved by the use of a moderate pH value of 4,5,which allows lead acetate to be added direct into thedistillation flask. The lead sulphide precipitate is stableunder the conditions chosen, and an excess of lead guardsagainst sulphide that might be generated from the thio-cyanate. This procedure gives complete recoveries ofcyanide from all metal complexes except [Co(CN) 6]3-and needs a distillation time of only half-an-hour ascompared with at least an hour required by conventionalprocedures. It is unfortunate that the cyanide cannot bereleased from the hexacyanocobaltate by use of the dis-tillation procedures discussed here. However, an approxi-mate measurement of the amount of cyanide bound tocobalt can possibly be obtained from determination ofthe metal by atomic-absorption spectrophotometry.

of

Distillation methods are relatively time-consumingand inadequate for the routine analysis of large numbersof samples. If a high sampling rate and high sensitivityare required, an automated technique such as flowanalysis should be considered. With this type of analysis,concentrations of ionic cyanide of 1 fLg/l can be detected,and the total amount of cyanide present in a sample canbe determined by the irradiation of metal complexeswith ultraviolet light. Irradiation with ultraviolet lightis by far the fastest and most effective means of decom-posing all metal-cyanide complexes, including[Co(CN) 6]3-. However, thiocyanate is unfortunately alsodecomposed by ultraviolet light, and gives a positiveinterference. At present there appears to be no simplesolution to the general problem of intereference by thio-cyanate. In its absence, there should be a decrease inanalysis time if irradiation with ultraviolet light is com-bined with manual distillation procedures. It is also feltthat the combination of the ion-chromatography proce-dure9°, which was recommended for the determinationof ionic cyanide, and irradiation with ultraviolet lightcould give a fast and sensitive method for the determina-tion of total cyanide.

Methods concerned with the determination of indivi-dual metal-cyanide complexes are rare. Usually two orthree metal complexes are determined simultaneouslyas, for example, the hcxacyanoferrates87. It appearsthat individual metal-cyanide complexes could be iden-tified by the use of ion-exchange or solvent-extractionseparations followed by determination of the metalspresent by atomic-absorption spectrophotometry.

~

16 JANUARY 1983 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

"

J

For the determination of cyanide in solid samples likepulps, the 'standard' procedure discussed earlier can beused. The analysis of resins should follow similar lines;i.e. leaching with water or sodium hydroxide solutionfor free and simple cyanides, and distillation procedures(possibly in the presence of EDTA) for complexed metal-cyanides. It appears that analysis involving resins re-quires moderate sequestering agents so that interferencesfrom the decomposition of the resin itself can be avoided.

Conclusions

It appears that most titrimetrie, colorimetric, and elec-trochemical methods (including potentiometry and theuse of cyanide-selective electrodes) for the determinationof ionic cyanide are liable to interference from ionizablemetal-cyanide complexes, e.g. [Zn(CN) 4]2-. Thesemethods can therefore be employed only if such complexesare known to be absent. Potentially accurate methods forthe determination of ionic cyanide include ion chroma-tography (because of its ability to effect separations) andindirect atomic-absorption spectrophotometry based onthe selective formation of [Ag(CN)2r.

Similarly, nom of the methods mentioned gives areliable result for the 'total' amount of cyanide presentin a sample. T1:c decomposition of stable complexes andthe separation from interfering substances by distillationis therefore necessary. However, most distillation proce-dures cannot effect the decomposition of all the metal-cyanide complexes, and they suffer from interferences.The most useful distillation procedure appears to be theligand-displacement technique of lngersoll et al.7. Withthis method, interference from sulphide and thiocyanatecan be avoided, and all the ionic and coordinatedcyanide-except cyanide from [Co(CN) 6]3--presentin asample can be distilled out.

Because of its speed in decomposing cyanide com-plexes, irradiation with ultraviolet light warrants furtherattention. A combination of this method with the separa-tion, by ion chromatography, of interfering species mightresult in a fast method for the determination of totalcyanide.

Acknowledgement

This paper is published by permission of the Councifor Mineral Technology.

1.References

RAMSEYER, G. 0., and JANUAER, G. E. Selective separa-tions by reactive ion exchange. Part 11. Preconcentrationand determination of complex iron cyanides in waters.Analyt. Ghim. Acta, vo1. 77. 1975. pp. 133 - 143.PUBLIC HEALTH ASSOCIATION, AMERICAN WATER ASSOCIA-TION, AND WATER POLLUTION CONTROL FEDERATION.Standard methods for the examination of water and wastewater. 14th edition. New York, American Public HealthAssociation, American Water Association, and WaterPollution Control Federation, 1975. p. 361.EpSTEIN, J. Estimation of micro quantities of cyanide.Ind. Engng Ghem., vo1. 19. 1947. pp. 272 - 274.GOULDEN, P. D., et al. Determination of nanogram quanti-ties of simple and complex cyanides in water. Analyt. Ghem.,vo1. 44. 1972. pp. 1845 - 1850.BAHENSKY, V. Determination of free and bound cyanides.Ghem. Abstr., vo1. 75. no. 67279q. 1971.PIHLAR, B., et al. Amperometric determination of cyanideby use of a flow-through electrode. Talanta, vo1. 26. 1979.pp. 805 - 810.

2.

3.

4.

~15.

6.

7. INGERSOLL,D., et al. Ligand displacement method for thedetermination of total cyanide. Analyt. Ghem., vo1. 53. 1981.pp. 2254 - 2258.KRUSE, J. M., and MELLoN, M. G. Colorimetric determina-tion of cyanide and thiocyanate. Analyt. Ghem., vo1. 25.1953. pp. 446 - 450.KOSHIMIZU, T. Practical application of the ion-electrodemethod. VI. Effect of EDTA on decomposition of metalcyanide complexes. Eisei Kagaku, vo1. 20. 1974. p. 328.CHEN, F. R., et al. Comparison of decomposition rates ofsome complex cyanides in various pretreatments. Ghem.Abstr., vo1. 92, no. 64413u. 1980.PIHLAR, B., and KOSTA, L. Determination of cyanides bycontinuous distillation and flow analysis with cylindricalamperometric electrodes. Analyt. Ghim. Acta, vo1. 114. 1980.pp. 275 - 281.NOTA, G., et al. Determination of complex cyanides inwaters by gas chromatography. J. Ghramat., vo1. 123. 1976.pp. 411- 413.WRONSKI, M. Preconcentration of'cyanide from water byextraction with tributyltin hydroxide. Talanta, vo1. 28.1981. pp. 255 - 256.MOORE, F. L., and GROENIER, W. S. Removal and recoveryof cyanide and zinc from electroplating wastes by solventextraction. Ghem. Abstr., vo1. 86, no. 95408b. 1977.BURSTALL,F. H., et al. Ion exchange process for recoveryof gold from cyanide solution. Ind. Engng Ghem., vo1. 45.1953. pp. 1648 - 1658.GILATH, 1. Breakdown of alkaline complex cyanide by ionexchange. Analyt. Ghem., vo1. 49.1977. pp. 516 - 517.BARK, L. S., and HIGSON, H. G. A review of methodsavailable for the detection and determination of smallamounts of cyanide. Analyst, Land., vo1. 88. 1963. pp.751 - 760.LIEBIG, J. von. Annalen., vo1. 77. 1851. p. 102 andJ. Ghem.Soc., vo1. 4. 1852. p. 219 (Cited in ref. 1)DeNIGes, G. Ann. Ghim. Phys., vo1. 6. 1895. p. 381. (Citedin ref. 1).RYAN, J. A., and CULSHAW,G. W. The use of p-dimethylaminobenzyledene rhodanine as an indicator for the volu-metric determination of cyanides. Analyst. Land., vo1. 69.1944. p. 370.DAGNALL,R. M., et al. Analytical chemistry of ternarycomplexes. V. Indirect spectrophotometric determination ofcyanides. Talanta, vo1. 15. 1968. pp. 107 - 110.DEGUCHI, M., and SAKAI, K. Indirect spectrophotometricdetermination of cyanide ion with bromopyrogallol red.Ghem. Abstr., vo1. 74, no. 49366r. 1971.BUHL, F., and KANIA, K. Application of the silver-I, 10-phenanthroline-eosin ion-association complex for the deter-mination of cyanide. Ghem. Abstr., vo1. 92, no. 1O3676d.1980.KEIL, R. New highly selective spectrophotometric deter-mination of cyanide by destroying the platinum-3, 4-dia-mino-benzoic acid complex Fresenius Z. Analyt. Ghem.,vo1. 275. 1975. pp. 265 - 268.FUJINUMA, H., et al. Spectrophotometric determination ofcyanide ion with O-cresolphthalin. Ghem. Abstr., vo1. 85,no. 86649h. 1976.MORI, 1., et al. Spectrophotometric determination of copper(II) and cyanide with o-hydroxyhydroquinonephthalein.Ghem. Abstr., vo1. 88, no. 83097e. 1978.FUJINUMA, H., and ITSUKI, K. Use of organic solvents forthe determination of cyanide ions with pheno-phthalein.Ghem. Abstr., vo1. 88, no. 98647f. 1978.YASHIKI, M. Spectrophotometric determination of cyanideion using a mercury(II) thiothenoyltrifluoroacetone com-plex. Ghem. Abstr., vo1. 75, no. 147406u. 1971.TANAKA,Y. Spectrophotometric determination of cyanideusing mercuric complex of p-dimethylaminobenzylidene-rhodanine. Ghem. Abstr., vo1. 77, no. 121848f. 1972.CLYDE, D. D., and WARNER, M. A. Spectrophotometricdetermination of cyanide by use of aqueous potassiumiodide and mercury(II) iodide. Analyst, Land., vo1. 103.1978. pp. 648 - 651.HINZE, W. L., and HUMPHREY, R. E. Mercuric iodate as ananalytical reagent. Spectrophotometric determination ofcertain anions by an amplication procedure employing thelinear starch iodide system. Analyt. Ghem., vo1. 45. 1973.pp. 385 - 388.VERMA, Y., et al. Spectrophotometric determination of cya-nide ions through ligand exchange reaction in solution.Analyt. Abstr., vo1. 38, no. IB67. 1980.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JANUARY 1983 17

~

33. PRANITIS, P. A. F., and STOLMAN,A. Spectrophotometricdetermination of cyanide in biological materials. Ohem.Abstr., vol. 88, no. 6991Of. 1978.FOWLER, E. W., et al. The colorimetric determination ofcyanide in solution from gold cyanidation plants. J ohannes-burg, National Institute for Metallurgy, Report 323. 1968.SCHILT, A. A. Colorimetric determination of cyanide. Tris(1,10-phenanthroline)-iron(II) ion as a selective and sen-sitive reagent. Analyt. Ohem., vol. 30. 1958. pp. 1409 - 1411.BAROLO,P., et al. Determination of total cyanide in wastewater without preliminary distillation. Analyt. Abstr., vol.37, no. 4H61. 1979.HnRo, K. and YAMAMOTO,Y. A new spectrophotometricdetermination of cyanide by solvent extraction as tris-(1,10-phenanthroline)-iron(II)-thiocyanate. Analyt. Lett.,vol. 6. 1973. pp. 761 - 767.ROBERTS, R. F., and WILSON, R. H. The determination offerrocyanide and related compounds in commercial sodiumchloride. Analyst, Land., vol. 93. 1968. pp. 237 - 243.GALIK, A., and VOPRAVILOVA,J. Extraction of prussianblue into chloroform in the presence of ajatin. Talanta,vol. 21. 1974. pp. 307 - 310.ALDRIDGE, W. N. A new method for the estimation ofmicro quantities of cyanide and thiocyanate. Analyst, Land.,vol. 69. 1944 pp. 262 - 265.ALDRIDGE, W. N. The estimation of micro quantities ofcyanide and thiocyanate. Analyst, Land., vol. 70. 1945.pp. 474 - 475.TAo, J., and JEN, Y. Cyanide-containing sediments anddetermination of free cyanides in waste waters. Ohem.Abstr., vol. 92. no. 99352a. 1980.ROBERTS, R. F., and JACKSON, B. The determination ofsmall amounts of cyanide in the presence of ferro-cyanideby distillation under reduced pressure. Analyst, Land.,vol. 96. 1971. pp. 209 - 212.LAMBERT,J. L., et al. Stable reagents for the colorimetricdetermination of cyanide by modified Konig reactions.Analyt. Ohem., vol. 47. 1975. pp. 916 - 918.FROLOV, L. F., et al. Automatic monitoring of purificationof cyanide containing effluents. Ohem. Abstr., vol. 90, no.156520p. 1979. . . .LINCK, R. ComposItion and method for determmmg cya-nide. Ohem. Abstr., vol. 86, no. 50288w. 1977.GRONINGSSON,K. Dicarboxidine y,yl-(4,4-diamino- 3,31-biphenlylene-dioxy) dibutyric acid as a reagent for thespectrophotometric determination of cyanide and chlorine.Analyst, Land., vol. 104. 1979. pp. 367 - 370.NAGASHIMA,S. Spectrophotometric determination of cya-nide with sodium isonictinate and sodium barbiturate.Analyt. Ohim. Acta, vol. 99. 1978. pp. 197 - 201.NAKAMURA,E., et al. Spectrophotometric determination ofcyanide ion with isonictonic acid-pyrazolone. Ohem. Abstr.,vol. 90, no. 10967n. 1979.IsHn, K., et al. Spectrophotometric determination of cya-nide ion with isonicotinic acid-pyrazolone. Ohem. Abstr.,vol. 79, no. 111398m. 1973.MONTGOMERY,H. A. C., et al. Determination of free cya-nide in river water by a solvent-extraction method. Analyst,Land., vol. 94. 1969. pp. 284 - 291.GREGORY, J. N., and HUGHAN, R. R. Analysis of silverplating solutions. Analyt. Ohem., vol. 17. 1945. pp. 109-113.RICCI, J. E. Titration curve for the argentometric determi-nation of cyanide. Analyt. Ohem., vol. 25. 1953. pp. 1650-1656.LEE, A. F. The effect of copper, iron, nickel and zinc on theargentometric determination of cyanide. Johannesburg,Anglo American Research Laboratories, Project No. R/9,Report no. 212. 1976.ASPLUND, J. Titration of cyanide and hexacyanoferrate(II)with silver nitrate. I. Calculation of titration curves forpotentiometric titration. II. Determina~ion of sodi',lmcyanide and sodium hexacyanoferrate(II) m a complexmgagent. Talanta, vol. 25.1978. pp. 137 -146.INGLEs, J. C. Continuous automatic cyanide titration incopper-bearing gold mill leach liquors. Ottawa, Depart-ment of Energy, Mines and Resources, Mines Branch,Research Report R212. 1969.AMIN, M., et al. Potentiometric titration methods for freeand complexed cyanides. Ohem Abstr., vol. 87, no. 177036p.1977.GOWDA, B. T., and MAHADEVAPPA,D. S. A direct methodof estimating cyanide ion in metal salts and complexes bymeans of chloramine T, dichloramine T and lead tetra.acetate. Talanta, vol. 24. 1977. pp. 325 - 326.

59. LAITENIN, H. A., et al. Amperometric titration of cyanidewith silver nitrate using a rotating platinum electrode.Analyt. Ohem., vol. 18. 1946. pp. 574 - 575.SHINOZUKA,P., and STOCK,J. T. Voltammetry and ampero-metric titrimetry of cyanide at the rotating platinum micro-electrode. Analyt. Ohem., vol. 34. 1962. pp. 926 - 928.KOGAN, L. A., et al. Amperometric method for determiningcyanides in the waste water of coal tar chemical plants.Ohem. Abstr., vol. 73, no. 28610e. 1970.Du, R. I., et al. Amperometric titration of hydrocyanicacid with iodine. Ind. Lab., vol. 45. 1979. pp. 1086 -1088.MCCLOSKEY,J. A. Direct amperometry of cyanide at ex-treme dilution. Analyt. Ohem., vol. 33. 1961. pp. 1842 -1843.STRAFELDA,F., and BENESOVA, J. Amperometric analyzerof cyanide solutions. Ohem. Abstr., vol. 73, no. 137093j. 1970.JURA, W. H. Shielded dropping mercury electrode forpolarographic analyses of flowing solutions. Determinationof cyanide ion. Analyt. Ohem., vol. 26.1954. pp. 1121-1123.KARCHMER,J. H., and WALKER, M. T. Polarographic deter-mination of free cyanide in the presence of sulphides.Analyt. Ohem., vol. 27. 1955. pp. 32 - 41.WISSER, K. Trace determination of cyanide by the differen-tial pulse polarographic technique. Fresenius Z. Analyt.Ohem., vol. 286. 1977. pp. 351 - 354.MARECHAL,A., et al. Polarographic determination of lowlevels of cyanide and metals in efluents from electroplatingplants. Analusis, vol. 9. 1981. pp. 333 - 335.BERGE, H., and JEROSCHEWSKI, P. Inverse voltammetricdetermination of cyanide ion from the hanging mercury drop.Fresenius Z. Analyt. Ohem., vol. 228. 1967. pp. 9 - 15.GERCHMAN,L. L., and RECHNITZ, G. A. Potentiometrictitration of cyanide using the cation-sensitive glass electrodeas indicator. Fresenius Z. Analyt. Ohem., vol. 230. 1967.pp. 265 - 271.ToTH, K., and PUNGOR, K Determination of cyanides withion selective membrane electrodes. Analyt. Ohim. Acta,vol. 51. 1970. pp. 221 - 230.FLEET, B., and VaN STORP, H. The determination of lowlevels of cyanide ion using a silver responsive ion selectiveelectrode. Analyt. Lett., vol. 4. 1971. pp. 425 - 435.FLEET, B., and VaN STORP, H. Analytical evaluation of acyanide ion selective membrane electrode under flow-stream conditions. Analyt. Ohem., vol. 43. 1971. pp. 1575-1581.FRANT, M. S. Application of specific ion electrodes to elec-troplating analyses. Plating, 1971. p. 686.FRANT, M. S., et al. An electrode indicator technique formeasuring low levels of cyanide. Analyt. Ohem., vol. 44.1972. pp. 2227 - 2230.MASCINI, M. Influence of pH on the response of a cyanideion selective membrane electrode. Analyt. Ohem., vol. 45.1973. pp. 614 - 615.HIGASHIVRA,M., et al. Determination of cyanide in wastewaters containing cyanocomplexes with ion selectiveelectrode. Ohem. Abstr., vol. 80, no. 63623c. 1974.LAPATNICK,L. N. Application of ion selective electrodes tothe analysis of silver plating baths. Analyt. Ohim. Acta,vol. 72. 1974. pp. 430 - 433.HOFTON, M. Continuous determination of free cyanide inefluents using silver ion electrode. Environ. Sci. Technol.,vol. 10. 1976. pp. 277 - 280.SEKERKA, I., and LEcHNER, J. F. Potentiometric determi-nation of low levels of simple and total cyanides. Water Res.,vol. 10. 1976. pp. 479 - 483.NAKAHARA,K. Determination of cyanide ions in thepresence of sulphur cempounds. Ohem. Abstr., vol 89. no.84311a. 1978.GOEDECKE, R., et al. Continuous monitoring and controof the detoxification of cyanide containing waste water withhydrogen peroxide. Ohem. Abstr., vol. 93, no. 173127v. 1980.DANcHIK, R. S., and BOLTZ, D. F. Indirect atomic absorp-tion spectrometric methods for the determination of cya-nide. Analyt. Ohim. Acta, vol. 49. 1970. pp. 567 - 569.KIRKBRIGHT,G. F., and JOHNSON,H. N. Application ofindirect methods in analysis by atomic-absorption spec-trometry. Talanta, vol. 20. 1973. pp. 433 - 451.JUNGREIS, K, and AIN, F. Determination of cyanide in thep.p.b. range by atomic absorption spectrometry. Analyt.Ohim. Acta, vol. 88. 1977. pp. 191 - 192.MONTEIL, A. Determination of cyanate in effluents by directatomic-absorption spectrometry. Analusis, vol. 7. 1979.pp. 69 - 72.

..

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

18

60.

61.

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

JANUARY 1983 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY

1\

87. GRIEVE, S., and SYTY, A. Determination of cyanide byconversion to ammonia and ultraviolet absorption spectro-metry in the gas phase. Analyt. Ohem., vol. 53. 1981. pp.1711 - 1712.CASAPIERI, P., et al. The determination of cyanide ions inwaters and effluents by an Auto-Analyzer procedure. Ana-lyt. Ohim. Acta, vol. 49.1970. pp. 188 -192.KRUSE, J. M., and THIBAULT, L. E. Determination of freecyanide in ferro and ferricyanides. Analyt. Ohem., vol. 45.

88.

89.

AB'MEC '83

-t An international conference on Mines Transport willbe held in Stanhope Bretby, England, from 27th Juneto 2nd July, 1983. An exhibition of related British equip-ment will be staged in Swadlincote (five minutes distancefrom Bretby).

The conference and exhibition are sponsored by theAssociation of British Mining Equipment Companies(ABMEC) and organized on their behalf by Mining Indus-try Promotions Ltd.

Transport has been chosen as the theme of this eventas relating to all aspects of mining, because it can beshown that very considerable improvements in produc-tivity can be achieved by comparatively modest invest-ment in this field.

Current practice and future df"Telopments will bereviewed by invited speakers from the United Kingdomand from overseas; and papers will cover mineral,

Analytical chemistry

Edinburgh is the site of the SAC 83 International Con-ference and Exhibition on Analytical Chemistry, orga-nized by the Analytical Division of the Royal Society ofChemistry (RSC), formerly the Society for AnalyticalChemistry - hence the term SAC.

The well-known SAC Conferences take place trien-nially. The scientific programme will be organized aroundplenary, invited, and contributed papers and posterscovering the whole field of analytical chemistry. Inaddition, there will be specialist symposia on particularanalytical themes organized by RSC Groups and otherassociated bodies. The programme will also include a

-;

90.1973. pp. 2260 - 2261.DIONEX. Electrochemical detector, operator's manualU.S.A., the Company, Publication no. 035555. Feb. 1981.TOBIA, S. K., et al. Determination of cyanide ion in cyano-complexes. Analyst, Lond., vol. 99. 1974. pp. 544 - 546.

ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY.Methods for chemical analysis of waters and wastes. Cincin-nati, the Laboratory, 1978. (Cited in ref. 5).

91.

92.

materials, and personnel transport in both undergroundand surface mining operations.

The programme of the conference will be arranged toensure that delegates have ample opportunity to visitthe exhibition, and special buses will operate over theshort distance between conference and exhibition. Theexhibition will offer the delegates opportunity to see thelatest developments from British manufacturers ofequipment referred to in the papers, and will attractmany visitors from home and overseas in addition toconference delegates.

Those interested to have further information shouldcontact Richard West, ABMEC '83 Conference andExhibition, Mining Industry Promotions Ltd, P.O. Box53, Rickmansworth, Herts, WD3 2AG, U.K. Tel:0923 778311, Telex: 296689 WESTEX G.

series of workshops where research workers can demon-strate new apparatus and techniques, and an extensiveexhibition of commercial and scientific equipment andbooks.

An innovation at SAC 83, which is to be held from 17thto 23rd July, 1983, will be a set of update courses con-vened by international authorities on topical subjects.

Further details are obtainable from Miss P. E.Hutchinson, Secretary of the Analytical Division, RoyalSociety of Chemistry, Burlington House, London WIVOBN, U.K.

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY JANUARY 1983 19