Solvent Extraction Research and Development, Japan, Vol. 22, No 2, 135 – 146 (2015)

Extraction and Purification of Copper from a Nigerian Chalcopyrite Ore Leach Liquor

by Dithizone in Kerosene

Alafara A. BABA,1*

Kuranga I. AYINLA,1,2*

Folahan A. ADEKOLA,1 Malay K. GHOSH,

3

Pradeep C. ROUT3 and Amos I. AMBO

4

1Department of Industrial Chemistry, University of Ilorin, P. M. B. 1515,

Ilorin–240003, Nigeria. 2Department of Chemistry, Institute of Basic and Applied Sciences,

Kwara State Polytechnic, P. M. B. 1375, Ilorin, Nigeria. 3Hydro & Electrometallurgy Department, CSIR-Institute of Minerals and Materials Technology,

Bhubaneswar-751013, India. 4Department of Chemistry, Faculty of Natural & Applied Sciences,

Nasarawa State University, P.M.B. 1022, Keffi, Nigeria.

(Received June 12, 2014, Accepted July 31, 2014)

The extraction and purification of copper by dithizone in kerosene from an aqueous chloride chalcopyrite

leach liquor containing 934.44 mg/L Cu, 2326.73 mg/L Fe, 92.14 mg/L Mn, 0.65 mg/L Mg, 0.22 mg/L Ca,

0.076 mg/L Sn and 0.011 mg/L Pb was investigated. The effects of extractant concentration and pH of

aqueous media on the total copper extraction were studied. The results of fundamental studies on solvent

extraction of synthetic solutions of Cu(II) showed that metal ion extraction increased with increasing pH

and extractant concentration. The leach liquor purification was firstly done by total precipitation of iron and

manganese using Ca(OH)2 and H2O2 as oxidizer at pH 3.58 and 4.25, respectively. An extraction efficiency

of 97.3% total copper was obtained by 0.2 mol/L dithizone in kerosene at 25±2 oC within 30 minutes at pH

5.0. A 0.1 mol/L HCl solution was found to be adequate for the stripping of about 98.3% Cu from the

loaded organic phase. The stripped copper solution was recovered as copper oxide (Tenorite, CuO : 05-

0667) via precipitation with sodium hydroxide followed by calcination at 600 oC for 120 minutes. Finally,

an operational scheme summarizing the extraction procedure to obtain a high grade copper compound was

presented.

1. Introduction

Copper, the 25th

most abundant element in the earth’s crust is found primarily in the form of

chalcopyrite (CuFeS2) with many diverse applications in thermal conductors, electrical conductors,

building materials and as important constituents of various metal alloys [1]. However, the continuous

depletion of high-grade ores has attracted the attention of scientists and technologists towards the treatment

of complex and/or low-grade ores for metal recovery. The low grade chalcopyrite ore may contain iron,

zinc, cadmium, lead, magnesium and calcium along with copper as impurities and these must be

appropriately treated to obtain high grade metal values [2, 3].

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Due to increasing demand for high purity metals, concerns over environmental issues and continuous

depletion of high grade ores which has resulted in the treatment of ores of lower grade and greater

complexity, solvent extraction has thus become an important hydrometallurgical tool [4-6]. Compared to

pyrometallurgical options, the hydrometallurgical extraction of metals including copper from ore resources

has come about for economic, environmental and technical reasons [7, 8].

In hydrometallurgical options, metal values are generally recovered from leach liquors using leaching,

precipitation, solvent extraction and electro-winning techniques. However, the processing of leach solutions

containing different concentrations of some foreign metals such as iron, zinc and manganese along with

copper together with a high acid concentration is very complex and separation of the metals using various

techniques such as precipitation, adsorption, solvent extraction, etc. are required for optimal purification of

the copper leach solution [8, 9].

It is important to note that several works in this area of study have been geared towards the use of

certain extracting agents such as ACORGA 5397 [10], which is widely use to treat pregnant sulphuric acid

leach solution commercially. LIX reagents will extract copper from chloride solutions in the Cuprex

Process [11] and ammoniacal solution can be treated by some other LIX reagents such as LIX 54, 842, 860

[12, 13]. Despite slow extraction kinetics, dithizone as an extractant, is characterized with good physical

properties in terms of phase separation, low aqueous solubility and chemical stability as compared to the

LIX and ACORGA reagents [14,15]. However, the use of dithizone (Figure 1) with kerosene as extractant

has not been well utilized especially for copper extraction. Therefore, due to the ease of interaction with

metal ions such as copper to form neutral complex species [16], it is important to consider this extractant as

a viable alternative for the hydrometallurgical treatment of a chalcopyrite leach liquor of Nigerian origin by

solvent extraction. The detailed characterization and kinetic data of this ore have been recently reported

[17].

Figure 1. Chemical structure of dithizone.

2. Experimental

2.1 Reagents

Liquid – liquid extraction experiments were carried out using leachate from the leaching of 10 g/L

chalcopyrite ore by a 2 mol/L HCl solution at 80 oC for 120 minutes for which the highest dissolution

efficiency was recorded in our recent study [17]. The composition of the leachate at the above conditions,

determine by using an ALPHA-4 Atomic Absorption Spectrophotometer (AAS) gave: 934.44 mg/L Cu,

2326.73 mg/L Fe, 92.14 mg/L Mn, 0.65 mg/L Mg, 0.22 mg/L Ca and 0.076 mg/L Sn and 0.011 mg/L Pb.

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Dithizone (95 % purity, BDH product); bis (2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, 85-

90 % purity, Cytec – France) and 8-hydroxyquinoline (99 % purity, BDH product) extractants were used as

received. Commercial kerosene (diluent) obtained from Olak Filling Station, Ilorin, Kwara State, Nigeria

was re-distilled before use. The aqueous solutions of different molarities (CuCl2.2H2O, FeCl3.6H2O,

MnCl2.2H2O, for example) used in the liquid-liquid extraction investigations were accordingly prepared by

dilution with de-ionized water. All salts and acids were of analytical grade. No modifier was used in these

experiments because problems with respect to phase separation or third phase formation were not observed

[3].

2.2 Methods

To ascertain the extraction performance, preliminary extraction trials were initially carried out with the

aforementioned extractants under different conditions, and the results of the preliminary trials confirmed

that dithizone in kerosene was a good candidate among the three extractants. Thus, the performance of the

studied extractants under these conditions: 0.2 mol/L, 25 ± 2 °C, 30 minutes extraction time followed the

order: dithizone ˃ Cyanex 272 ˃ 8-hydroxyquinoline. The percent extraction at optimal conditions from the

initial 1000 mg/L Cu2+

were found to be 78.5 %, 62.7 % and 57.2 %, respectively [8].

Consequently, the experimental method adopted for this study comprised preliminary work aimed at

establishing conditions for the optimal extraction of total copper from a synthetic Cu(II) solution. This was

carried out using dithizone as the extractant and subsequently applying these conditions to the recovery and

beneficiation of pure copper as copper oxide from the chalcopyrite leachate. Prior to obtaining a pure

copper solution from the chalcopyrite pregnant solution, it is desirable to remove major impurities such as

iron, manganese and other trace metals present in the solution. Hence, the following procedures were

adopted in the processing of the leach liquor:

2.2.1 Total iron precipitation

The composition of the leach liquor revealed iron as the major impurity which needed to be removed

to achieve high copper metal values. Consequently, the leach liquor, initially at 25 2 °C, was heated to a

temperature of 90 °C for 15 minutes. After cooling, the solution pH was then raised to 3.58, by slow

addition of Ca(OH)2 using a graduated pipette. At this pH, all the iron was removed as goethite (FeOOH),

according to the following stochiometry [18]:

Fe3+

+ 3OH- → FeOOH + H2O (1)

Thus, total iron precipitation was carried out by dropwise addition of hydrogen peroxide (H2O2), 9 %

v/v to maintain the pH at 3.58 until the colour of the slurry changed from cream to permanent brown

indicating total iron removal. The Ca(OH)2 slurry was stirred for a period of 10 minutes and then filtered

[19]. The residue was washed with de-ionized water several times, dried at 110 °C for 3 hours and was

analyzed by X-ray diffraction (XRD). The pure copper solution (after adjusting the pH to 4.25 to totally

remove manganese and other impurities) was subsequently used for the solvent extraction studies at pH 5.0.

2.2.2 Extraction of copper by dithizone

Batch experiments were accordingly carried out at room temperature (25 2 °C) by equilibrating

equal volumes of 25 ml of predetermined concentrations of dithizone in kerosene with 25 ml of the leachate

and shaking the mixture using a Gallenkemp orbital shaker (AMPS) for 30 minutes (time enough to reach

equilibrium as verified in preliminary tests) [8]. The pH was controlled by addition of small quantities of

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Ca(OH)2 and H2O2 solutions. After equilibration and phase separation, the concentration of the copper left

in the aqueous phase was analysed using AAS. The concentration of metal ion in the organic phase was

calculated from the difference between its concentration in the aqueous phase before and after extraction.

The percent of total copper extracted was quantitatively calculated. The effects of the extractant

concentration and the pH of the aqueous media on copper extraction were evaluated [3, 7, 10, 20].

2.2.3 Copper salt production

Copper and its salts such as copper oxide are important products with wide applications in the

chemical and other allied industries. To this end, the extracted/stripped product containing pure copper

obtained from the solvent extraction step (involving precipitation and stripping for the enrichment of

copper) was beneficiated to obtain a high grade copper salt as follows: an appropriate volume of pure

copper solution was treated using excess potassium hydroxide (KOH) solution. The precipitate so obtained

was then calcined for 2 hours using a Carbonite ELF 11/14B model muffle furnace at temperatures between

550 °C and 600 °C. The resulting product after calcination was further subjected to XRD analysis to

confirm the varietie(s) of copper compound formed.

2.3 Extraction efficiency

In all extraction experiments, the ratio of total Cu2+

extracted into the organic phase to its

concentration in the aqueous phase, the extraction distribution ratio, D is given by [9]:

aq

org

Cu

CuD

2

2

(2)

The percentage of total copper extracted (%E) is then calculated from the relation:

org

aq

V

VD

DE

100% (3)

3. Results and discussion

3.1 Fundamental studies with a synthetic Cu2+

solution:

3.1.1 Effect of dithizone concentration on a synthetic Cu2+

solution

To ascertain the effect of dithizone on copper extraction from a 1000 mg/L synthetic copper solution,

the concentration of dithizone in kerosene was varied in the range of 0.01 – 0.5 mol/L. The results showed

that the extraction of copper increased with increasing dithizone concentration as shown in Figure 2.

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Figure 2. Plot of percentage of copper extracted versus dithizone concentration.

Experimental Conditions:Dithizone Concentration = 0.01 – 0.5 mol/L, Temperature = 252 °C, Contact

time = 30 min, [Cu2+

]initial = 1000 mg/L, pHinitial = 1.0.

Figure 2 shows that the percentage of copper extracted increased from 39.5 to 78.5 % as the dithizone

concentration increased from 0.01 – 0.2 mol/L. With a further increase above 0.2 mol/L, the percentage

extraction apparently decreased to 75.2 % with 0.5 mol/L dithizone. The possible gradual decrease in

extraction yield might be due to precipitation phenomena [7]. Therefore, 0.2 mol/L dithizone in kerosene,

which gave the highest extraction yield, was selected for further studies. The plot of log D versus log

[dithizone] gave a straight line with the slope of 1.73, approximately 2, indicating the association of 2

moles of extractant per mole of metal ion (Figure 3).

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Figure 3. Plot of logD versus log[dithizone]; Experimental Conditions: Same as for Figure 2.

3.1.2 Effect of equilibrium pH

To study the effect of pH on the extraction of copper from its aqueous solution by 0.2 mol/L dithizone

in kerosene, experiments were carried out in the equilibrium pH range of 1-6 at room temperature (25

2 °C). The result of this investigation is shown in Figure 4.

Figure 4. Effect of equilibrium pH on the amount of copper extracted by 0.2 mol/L dithizone in kerosene.

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The results in Figure 4 at a phase contact time of 30 minutes indicate that the extraction of copper from the

aqueous phase by the extractant (dithizone) in kerosene is pH dependent. Hence, the extraction of copper

increases with increasing equilibrium pH from 1-6. As is observed, copper extraction increases from 78.5 –

92.6 %. It is important to note that the extraction at pH 5 was 92.6 % and becomes practically constant as

the same degree of extraction was achieved at pH 6. Therefore, the optimum pH was set at 5 and selected

for further use. The plot of logD versus log[H+] in Figure 5 gave a straight line with a slope of 1.66 which

could be assumed to be 2 for copper extraction and this indicates the association of 2 moles of extractant in

the extracted metal species. Thus, the extraction equilibrium equation involved in the extraction of

copper(II) ion (Cu2+

) from the aqueous phase by dithizone, H2Dz in kerosene is consistent with the

following stoichiometry:

Cu2+

+ 2H2Dz Cu(HDz)2 + 2H+ (4)

and the equilibrium constant, Kex is expressed as:

Kex = [Cu(HDz)2]org [H+]

2aq (5)

[Cu2+

]aq [H2Dz]2org

By substituting the distribution ratio, DCu, equation (5) becomes:

Kex = DCu[H+]

2aq (6)

[H2Dz]2equil.

Therefore, log DCu = log Kex -2pH + 2log[H2Dz]equil. (7)

Figure 5. Plot of log D vs log [H+].

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3.2 Leach liquor purification studies

3.2.1 Total iron removal

The total iron present in the chalcopyrite leachate was separated from copper by adjusting the pH of

the solution from its initial pH value of 1.0 to 3.58 at room temperature (25 2 °C) using lime powder,

Ca(OH)2 and 9 %(v/v) hydrogen peroxide as an oxidizing agent. The resulting solution after precipitation

followed by filtration was analysed by AAS and the results are summarized in Table 1. The residual brown

solid obtained during precipitation after drying and analysis by XRD is identified as goethite (FeOOH: 29-

0713).

Table 1. Results of total iron removal by precipitation.

Metal ions Concentration before

iron removal (mg/L)

Concentration after iron removal (mg/L)

at pH 3.58 at pH 4.25

Cu2+

(aq) 936.44 883.21 877.43

Fe3+

(aq) 2326.73 0.37 0.18

Mn2+

(aq) 92.14 78.14 0.93

Mg2+

(aq) 0.65 0.32 < 0.10

Ca2+

(aq) 0.22 0.19 0.0

Sn2+

(aq) 0.076 0.061 < 0.10

Pb2+

(aq) 0.11 0.10 < 0.10

3.2.2 Solvent extraction of copper by dithizone

The resulting solution after total iron precipitation followed by manganese removal at pH 4.25

contains pure copper. This purified solution adjusted to pH 5.0 was extracted by 0.2 mol/L dithizone in

kerosene for 30 minutes. The result of the extraction process showed that 93.6 % of the copper was

extracted by 0.2 mol/L dithizone in a single stage (n=1) extraction. However, extraction results for n =2, 3,

4 and 5 are 94.8, 95.9, 96.5 and 96.3 %, respectively. These affirmed that about 97% total copper extraction

would be possible in four concurrent stages.

The surface properties of the copper loaded organic solutions and the compounds formed were studied

using a Shimadzu H400F Fourier transform infrared (FT-IR) spectrometer. The spectra were obtained in the

range 400 to 4000 cm-1

running 100 scans at a resolution of 4cm-1

using the KBr disc technique. Metal-

organic complex formation, bond breaking during leaching and solvent extraction processes often give rise

to the appearance of oxides, sulphates, sulphides and oxysulphates. Their characteristic peaks occur in the

ranges 400 – 2000 cm-1

[21]. Hence, the FT-IR spectrum depicted in Figure 6A-C shows that the extraction

mechanism occurs via metal-organic complexation. Comparing Figures 6A and B (before and after metal

complexation with dithizone, respectively), a distinct peak at 669.32 cm-1

indicates the metal-extractant

bonding which was absent in Figure 6C. This was in agreement with the fact that the metal was completely

stripped with the regeneration of the extractant [22].

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Figure 6. FT-IR spectral pattern of: (A) The extractant (0.2 mol/L dithizone in kerosene); (B) Copper

loaded organic at optimal condition; (C) The organic phase after metal stripping by 0.1 mol/L HCl

solution.

B

A

C

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3.3 Beneficiation studies

3.3.1 Stripping of copper from the dithizone extract by 0.1 mol/L HCl solution

The copper loaded organic phase was stripped with 0.1 mol/L HCl solution. The result of the stripping

investigation showed that 98.3 % was recovered from the organic phase. The FT-IR of the organic phase

after stripping is shown in Figure 6C. The result shows the disappearance of the CuO peaks, especially at

669.32 cm-1

. Also, Figure 6C is very similar to that for dithizone in kerosene (Figure 6A, main extractant),

and thus indicates a high level of copper recovery from the extractant.

Furthermore, the stripped aqueous solution was further treated by adding potassium hydroxide pellets

and the precipitate so produced was calcined. The black crystal solid formed is identified by XRD to be

copper oxide with a few traces of Fukuchilite (Figure 7). The melting point of the high grade copper oxide

formed was measured and compared to the industrial standard* as 12930C and 1326

0C*, respectively. This

product could be utilized as a pigment in ceramics, cuprammonium hydroxide solution for rayon, p-type

semi-conductor and other industrial applications.

Figure 7. X-ray diffraction pattern of the product formed after calcinations for 2 hours.

(1) CuO {05-0667}; (2) Cu3Fe8S2 (Fukuchilite) {17-0137}. The Joint Committee on Powder

Diffraction Standard (JCPDS) file numbers for peak attributions are in the brackets.

3.3.2 Operational scheme

The operational hydrometallurgical scheme summarizing the procedures for the treatment of a

Nigerian chalcopyrite ore for copper extraction and its beneficiation as copper oxide is depicted in Figure 8.

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Fe, Mn discarded

Chalcopyrite leaching

Precipitation pH 3.58 and 4.25

Copper Solvent ExtractionpH 5.0

De-Extraction

Precipitation followed by Calcination

SS

L

Chalcopyrite ore

SGrinding

Pulverization

SS

LLeach residue

Ca(OH)2

H2O2Oxidizer

Iron residue

0.1M HCl

Copper compound

Figure 8. A hydrometallurgical processing flow chart for treating a Nigerian chalcopyrite ore.

4. Conclusion

The extraction of copper from an aqueous chalcopyrite leach liquor by dithizone in kerosene for the

production of high grade copper oxide was investigated. The results of the preliminary trials with synthetic

copper solutions with the extractant showed that the extraction of copper (II) increased with increasing pH

and extractant concentration. The established conditions were optimized and used for the treatment of the

chalcopyrite leach liquor. After total iron precipitation at pH 3.58, followed by total manganese and other

impurities removal at pH 4.25, the efficiency of copper extraction by 0.2 mol/L dithizone in kerosene

reached 93.6 % in a single stage at 25 2 °C within 30 minutes at pH 5.0. Furthermore, 98.3 % of the

copper loaded organic phase was successfully stripped with 0.1 mol/L HCl solution. Copper was recovered

from the strip liquor as pure copper oxide (Tenorite, CuO: 05-0667) by precipitation with potassium

hydroxide followed by calcination at about 600 °C for 120 minutes. Finally, the operational

hydrometallurgical scheme summarizing the leaching, solvent extraction and precipitation operations for

the extraction of pure copper and the production of high grade copper oxide was presented.

References

1) S. K. Sahu, B. D. Pandey, V. Kumar, Miner. Proces. Techn., 542–549 (2007).

2) A. O. Adebayo, K. Sarangi, Chem. Biochem. Eng. Q., 25, 309 – 316 (2011).

- 145 -

3) D. P. Mantuano, G. Dorella, R. C. A., Elias, M. B. Mansur, J. Power Sources, 159, 1510-1518 (2006).

4) T. Hosseini, N. Mostoufi, M. Daneshpayeh, F. Rashchi, Hydrometallurgy, 105, 277-283 (2011).

5) A.A. Baba, F. A. Adekola, R. B. Bale, J. Hazardous Mater., 171, 838-844 (2009).

6) G. Owusu, Hydrometallurgy, 47, 205-215 (1998).

7) A. A. Baba, F. A. Adekola,.Hydrometallurgy, 109, 187–193 (2011).

8) K .I. Ayinla, Dissolution kinetics and solvent extraction of copper from chalcopyrite ore in acidic

media, [M.Sc. Thesis], Department of Chemistry, University of Ilorin, Ilorin, Nigeria.

9) K..Sarangi, P. K. Parhi, E. Pradhan, A. K. Palai, K. C. Nathsarma, K. H. Park, Sep. Purf. Technol., 55,

44-49 (2007).

10) K. El-amari, E. Jdid, P. Blazy, Physicochem. Probl. Process., 49, 329–339 (2013).

11) Z. Stevanavic, M. Antonijevic, R. Jonovic, L.J. Avramovic, R. Markovic, M. Bugarin, V. Trujiv, J.

Mining and Metall., 45B, 45–47 (2009).

12) V. Stefanova, P. Illev, W. Mroz, B. Stefanov, J. University Chem. Technol. Biotechnol., 45, 99 (2010).

13) D. Veeratana, H. Y. Sohu, Miner. Eng., 1, 821 (1998).

14) A.O. Adebayo, K. Sarangi, Chem. Biochem. Eng. Q., 25(3), 309-316 (2011).

15) R. B. Sudderth, G. A. Kordosky. Some practical considerations in the evaluation and selection of

solvent extraction reagents, chemical reagents in the mineral processing industry, Malhotra, Rigg,

S.M.E. (Eds.) Littleton Colorado, 181-196 (1986).

16) I. T. Urasa, S. F. Macha, W. El-Maaty, J. Chromatographic Sci.,35, 519-524 (1997).

17) A. A. Baba, K. I. Ayinla, F. A. Adekola, R. B., Bale, M. K., Ghosh, A. G.. F. Alabi, A. R. Sheik, I. O.

Folorunso, Int. J. Miner. Metall. Mater., 20, 1021-1028 (2013).

18) A. V. Ropenak, Hematite - the solution to a disposal problem an example from the zinc industry. In: J.

E. Dutrizac and A. J. Morhemius (ed), Iron control in hydrometallurgy, Ellis Horwood, Chichester,

U.K, 730–741 (1986).

19) G. Kordosky, M. Virnig, B. Boley, Tsinghina. Sci. Technol.,11, 160-164 (2006).

20) K. Ochromowicz, T. Chmielewski, Physicochem. Probl. Process.,49, 357-367 (2012).

21) A. I. Boldyrev, Infra-red spectra of minerals, 2, 101-120 (1976).

22) V. C. Farmer, The infra-red spectra of minerals, Monograph 4, Mineralogical Society, London, 4

(1974), p. 12-20.

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