Extraction and Purification of Copper from a Nigerian Chalcopyrite Ore Leach Liquor by Dithizone in Kerosene. Ilorin , Nigeria.

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1 Solvent Extraction Research and Development, Japan, Vol. 22, No 2, (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. ROUT 3 and Amos I. AMBO 4 1 Department of Industrial Chemistry, University of Ilorin, P. M. B. 1515, Ilorin , Nigeria. 2 Department of Chemistry, Institute of Basic and Applied Sciences, Kwara State Polytechnic, P. M. B. 1375, Ilorin, Nigeria. 3 Hydro & Electrometallurgy Department, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar , India. 4 Department 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 mg/l Cu, mg/l Fe, mg/l Mn, 0.65 mg/l Mg, 0.22 mg/l Ca, mg/l Sn and 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 H 2 O 2 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 o C 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 : ) via precipitation with sodium hydroxide followed by calcination at 600 o C for 120 minutes. Finally, an operational scheme summarizing the extraction procedure to obtain a high grade copper compound was presented. 1. Introduction Copper, the 25 th most abundant element in the earth s crust is found primarily in the form of chalcopyrite (CuFeS 2 ) 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]

2 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 o C 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: mg/l Cu, mg/l Fe, mg/l Mn, 0.65 mg/l Mg, 0.22 mg/l Ca and mg/l Sn and mg/l Pb

3 Dithizone (95 % purity, BDH product); bis (2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, % 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 (CuCl 2.2H 2 O, FeCl 3.6H 2 O, MnCl 2.2H 2 O, 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 hydroxyquinoline. The percent extraction at optimal conditions from the initial 1000 mg/l Cu 2+ 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: 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]: Fe OH - FeOOH + H 2 O (1) Thus, total iron precipitation was carried out by dropwise addition of hydrogen peroxide (H 2 O 2 ), 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 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

4 Ca(OH) 2 and H 2 O 2 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] 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 Cu 2+ extracted into the organic phase to its concentration in the aqueous phase, the extraction distribution ratio, D is given by [9]: D Cu 2 org 2 Cu aq The percentage of total copper extracted (%E) is then calculated from the relation: 100D % E (3) V aq D Vorg (2) 3. Results and discussion 3.1 Fundamental studies with a synthetic Cu 2+ solution: Effect of dithizone concentration on a synthetic Cu 2+ 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 mol/l. The results showed that the extraction of copper increased with increasing dithizone concentration as shown in Figure

5 Figure 2. Plot of percentage of copper extracted versus dithizone concentration. Experimental Conditions:Dithizone Concentration = mol/l, Temperature = 25 2 C, Contact time = 30 min, [Cu 2+ ] initial = 1000 mg/l, ph initial = 1.0. Figure 2 shows that the percentage of copper extracted increased from 39.5 to 78.5 % as the dithizone concentration increased from 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)

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

7 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 %. 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 (Cu 2+ ) from the aqueous phase by dithizone, H 2 Dz in kerosene is consistent with the following stoichiometry: Cu H 2 Dz Cu(HDz) 2 + 2H + (4) and the equilibrium constant, K ex is expressed as: K ex = [Cu(HDz) 2 ] org [H + ] 2 aq (5) [Cu 2+ ] aq [H 2 Dz] 2 org By substituting the distribution ratio, D Cu, equation (5) becomes: Kex = D Cu [H + ] 2 aq (6) [H 2 Dz] 2 equil. Therefore, log D Cu = log K ex -2pH + 2log[H 2 Dz] equil. (7) Figure 5. Plot of log D vs log [H + ]

8 3.2 Leach liquor purification studies 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: ). Table 1. Results of total iron removal by precipitation. Metal ions Concentration before Concentration after iron removal (mg/l) iron removal (mg/l) at ph 3.58 at ph 4.25 Cu 2+ (aq) Fe 3+ (aq) Mn 2+ (aq) Mg 2+ (aq) < 0.10 Ca 2+ (aq) Sn 2+ (aq) < 0.10 Pb 2+ (aq) < 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. Metalorganic 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 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 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]

9 C B A 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

10 3.3 Beneficiation studies 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 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 C and C*, 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 { }; (2) Cu 3 Fe 8 S 2 (Fukuchilite) { }. The Joint Committee on Powder Diffraction Standard (JCPDS) file numbers for peak attributions are in the brackets 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

11 Chalcopyrite ore S Grinding Pulverization Chalcopyrite leaching Leach residue S L Fe, Mn discarded Precipitation ph 3.58 and 4.25 Ca(OH) 2 Oxidizer H 2 O 2 Iron residue S L Copper Solvent Extraction ph 5.0 De-Extraction 0.1M HCl Precipitation followed by Calcination 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: ) 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., (2007). 2) A. O. Adebayo, K. Sarangi, Chem. Biochem. Eng. Q., 25, (2011)

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http://www.e-journals.net ISSN: 0973-4945; CODEN ECJHAO E- Chemistry 2011, 8(S1), S434-S438 Recovery of Copper, Nickel and Zinc from Sulfate Solutions by Solvent Extraction Using LIX 984N VAISHNAVI SRIDHAR