Rapid determination of copper in copper ores

T. It. RAO, B. V. RAO and S. L. N. ACHARYULU

LOW grade copper ores and copper ores in asso-ciation with considerable quantities of other ele-ments such as iron, lead, zinc and vanadium,

require a separational step wherein copper is gene-rally separated as sulphide either with sodium thio-sulfate' or with thioacetamide.2 In these methods, theprecipitated copper sulfide is ignited to cupric oxide,dissolved in dilute nitric acid and titrated iodometri-cally. In a recent method' wet oxidation of precipi-tated copper sulfide is effected with nitric acid andtitrated with disodium ethylene diamine tetra-acetate(EDTA). The authors' work on the beneficiation oflow grade copper ores and extraction of copper fromthese ores has necessitated developing a rapid andaccurate method for the determination of copper. Aseparational step wherein cupric ion could be precipita-ted as cuprous oxide has been introduced to avoidignition of copper sulfide to cupric oxide, which is timeconsuming.

This paper presents a method for the rapid andaccurate determination of copper ores and concen-trates. Copper is separated as cuprous oxide withascorbic acid in dilute acetic acid medium. The preci-pitated cuprous oxide is dissolved in dilute nitric acidand titrated iodometrically or alternatively with EDTAusing murexide or pyrocatechol violet as indicator.This method is quite rapid and accurate and yieldsresults which are comparable with those obtained byelectro-gravimetric method.4

Reagents

0.05 N sodium thiosulfate solution was preparedby dissolving 12.5 grams of sodium thiosulfate(A.R., B.D.H.) in 1000 ml distilled water andstandardised with standard potassium dichromatesolution.'

0.05 M EDTA solution was prepared by dissolving18613 gm reagent grade disodium ethylenediaminetetra-acetate dihydrate in 1000 nil distilled water andstandardised against nearly neutralised zinc chloridesolution prepared from a known weight A.R. zincpellets."

Messrs T. H. Rao. B. V. Rao, S. L. N. Acharyulu, DefenceMetallurgical Research Laboratory, Hyderabad.

SYNOPSIS

A rapid and accurate method for the estimation ofcopper in high and loin grade copper ores and concen-trates is described. After the decomposition in the usualmanner with acids, copper is separated by precipita-tion as cuprous o .vide with ascorbic acid in dilute aceticacid medium . The cuprous oxide is dissolved in nitricacid and titrated iodometrically or alternatively withED TA using either nvrocatechol violet or murexide asindicator . The results are comparable to those obtainedhi' electrogravimetric method.

Standard copper solution

2 gm electrolytic copper was dissolved in 10 ml con-centrated nitric acid and the solution was heated tilloxides of nitrogen ceased to evolve. The solution wascooled and transferred to 1000 nil volumetric flask,diluted to mark with distilled water.

Ascorbic acid (Merck) was employedfor cuprous oxide precipitation.

as a reagent

Determination of copper

A known volume (containing 25- 100 mg.) of coppersolution was transferred to a 250 ml beaker, renderedammoniacal with I : 4 ammonia and acidified with 1 : 4acetic acid. Ascorbic acid (I gm) was added and thesolution was boiled. The precipitated cuprous oxidewas filtered through filter pulp and washed with hotwater. Cuprous oxide was dissolved in warm I : i nitricacid and washed with 2% nitric acid. The solution andthe washings were collected in a conical flask. Urea(2 gm) was added and the solution was boiled. Aftercooling the solution, ammonia was added to removefree mineral acid. The solution was acidified with aceticacid and cooled to room temperature. I gm potassiumiodide was added. The liberated iodine was titratedwith standard sodium thiosulfate solution using 1%starch solution as indicator.

Alternatively, the solution and the washings werediluted to 100 ml , 2 to 3 drops of aqueous solutionof murexide followed by small volumes of ammoniumchloride--ammonia buffer (pH 10) to give yellowishgreen color were added. This solution was titrated with0.05 M EDTA to a violet-blue end point.

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Rau et a!.: Rapid determination of copper in copper ores

TABLE I Amount of copper in mg

TakenFound ( bythiosulfate ) 0' Error

Found(by EDTA) ;o Error

25.0 24 .8 5 0.60 24.87 0'52

5010 49.77 0.46 4982 0'36

75.0 74.73 0.36 74 - 75 0'33

100'0 99'54 0*46 99'75 0'25

TABLE: II Determination of copper in ores and concentrates

Per cent copper found

byTHIO

byEDTA

by electro-gravimetry

* Ore concentrate 23.71 23' 83 23'87

tOre sample A 4.69 4' 62 4'64

B 4.19 4*16 4.12

C 1.07 1110 1'12

Alternatively, the solution and the washings werediluted to 100 ml : 0.5 gm ammonium nitrate, 4-5drops of 0-1 per cent aqueous solution of pyrocatecholviolet indicator were added. The acidity of the solutionwas adjusted with 0 - 5 M ammonia until the blue colorof the copper pyrocatechol violet complex just appears.2 gm sodium acetate was added and the solution wastitrated against 0.05 M EDTA solution to a sharpyellowish-green end point.

Determination of copper in ores andconcentrates

2 gnu copper ore or 0'5 gm concentrate was weighed intoa 500 ml conical beaker. 20 nil of mixed concentratedhydro-chloric, sulfuric and nitric acids (1 : I : I) wasadded and gently heated until the digestion was com-plete. 5 nil of concentrated sulfuric acid was addedand the heating was continued till sulfur trioxide fumeswere evolved. The contents were cooled to room tem-perature. 100 150 nil water was added and the solutionwas gently heated till all the salts formed were dissol-ved. The solution was filtered and the residue waswashed with 5 sulfuric acid and subsequently withhot water. The filtrate and the washings were collectedinto a 400 nil beaker. Citric acid or tartaric acid(5 gm) was added to complex Fe (III; and neutralisedwith ammonica. The solution was rendered slightlyacidic with I : 4 acetic acid and heated gently. 2_ gmascorbic acid was added and the solution was thenboiled. The cuprous oxide thus precipitated was filteredthrough filter pulp and washed with 20,, acetic acidand hot water. The washed precipitate was dissolvedin minimum quantity of warn I : I nitric acid andwashing was effected with hot 2°; nitric acid. Thesolution was allowed to cool and was made tip to250 ml in a standard volumetric flask. Aliquots of thecopper solution were taken and the copper was deter-mined iodometrically. Alternatively, copper solutionwas titrated with 0'05 M EDTA using pyrocatecholviolet or murexide as indicator.

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*Mysore ore.tA, B and C are the hand picked ore samples obtained fromKhetri, Kalihan and Agnigundala.

Results

Typical results for the determination of copper inpure copper solutions by the above mentioned proce-dure are given in Table 1. The results are reproducibleand accurate to within about 0.5 per cent. Variousore samples from Khetri, Kalihan and Agnigundalamines (hand picked and sampled) and ore concentratefrom Mysore ore were analysed for copper and theresults are presented in Table II. An aliquot ofsample solution before the precipitation of cuprousoxide was taken and the percentage of copper wasdetermined by electro-gravi metric method. In Table lIresults obtained with the proposed method are com-pared with values obtained by electro-gravimetric method.

Acknowledgement

The authors wi.h to express their grateful thanks toShri M. Subralimaniam for his assistance in the work.

References

I. Scott. W. W.: Standard methods of chemical analysis, Vol.1, Technical Press Limited, London, 5th Ed . pp. 369-371.

2. Flaschka, H. and Jkoblzcvich, H. : Anal Chim. Acta. 4,482, 1950.

3. Stiles, R. E. and Munneke, D. L.: Rep. Invest. U. S. BurMines RI 6852 (1966), Anal. Ahstr. 5282, Vol. 14 (1967).

4. Charles Cooper, W. : Treatise on Analytical Chemistry,Interscience Publishers , New York, 1961, Part 11 , Vol. 111,pp. 33.

5. Vogel, A. 1. : A text hook of quantitative inorganic analysis,The English language Book Society, 3rd Ed. pp. 350-51.

6. Vogel, A. I.: A text book of quantitative inorganic analysis,The English language Book Society, 3rd Ed. pp. 433.

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Rao el al.: Rapid determination of copper in copper ores

Discussions

Mr M. Totlani (Bhabha Atomic Research Centre,Bombay) : Can this method be used in the case ofconcentrates , which in addition to Cu, also containNi, Co, Mo and Fe?

Mr S. L. N. Acharyulu (Author) : The method proposedcan be applied for the determination of copper in thecase of concentrates containing nickel, cobalt, molyb-denum and iron, because :

(a) ascorbic acid has no reducing action on nickel(ii) and cobalt (ii)

(b) ascorbic acid reduces molybdenum (vi) to molyb-denum (v) only, and

(c) iron (iii) complexed with citrate does not interfere.

Dr Sharma (Khetri Copper Project) : I would requestthe author to explain the advantages of his methodover the short iodide process. In our works we areanalysing about 100 samples by three analyses withtwo attendants for every eight-hour shift. In the methoddescribed by the author what would be the time andnumber of men required for analysing 100 samples pereight-hour shift?

Mr S. L. N. Acharyulu (Author): As the short iodideprocess does not involve a separational step, it is rapid butdoes not yield accurate results. The proposed methodis more advantageous when accurate analysis is re-quired. These two methods cannot, therefore, be com-pared in terms of time requirements.

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