Solvent Extraction Separation of Co(II) from Synthetic Leaching Sulfate Solution of Nickel Laterite Ore with High Magnesium Content

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1 Materials Transactions, Vol. 52, No. 6 (2) pp. 2 to 25 #2 The Japan Institute of Metals Solvent Extraction Separation of (II) from Synthetic Leaching Sulfate Solution of ckel Laterite Ore with High Magnesium ntent Manseung Lee ; *, Sangbae Kim 2, Youngyoon Choi 2 and Jonggwee Chae Department of Advanced Materials Science & Engineering, Mokpo National University, Chonnam , Korea 2 Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, Daejeon 35-35, Korea Leaching of nickel garnierite ore with sulfuric acid resulted in a mixed sulfate solution of (II) and (II) with high magnesium content. In order to find an optimum condition to separate cobalt, solvent extraction experiments have been performed from the synthetic leaching sulfate solution with the following composition: (II) ¼ :8 g/l, (II) ¼ 4:4 g/l, (II) ¼ 32:2 g/l. The effects of extraction variables on the separation of (II) from nickel and magnesium were investigated by using D2EHPA, PC88A, Cyanex272, and Alamine336. Saponifiaction degree of cationic extractants, extractant concentration, and volume ratio were changed. In our experimental range, extraction of nickel was negligible. Among the cationic extractants tested in this study, the highest separation factor between (II) and (II) was obtained with saponified Cyanex272. Alamine336 in the presence of Cl 2 extracted only (II), while the extraction percentage of (II) was nearly zero. [doi:.232/matertrans.m227] (Received January 8, 2; Accepted March 4, 2; Published May 25, 2) Keywords: (II), (II), (II), solvent extraction, separation. Introduction Laterite oxide ores are divided into three distinct zones with the depth from the surface: the limonitic, the saprolitic and the garnieritic layer. ) Hydrometallurgical methods for processing nickel laterite ores include acid leaching at atmospheric pressure, high pressure acid leaching(hpal) and microwave heating. 2 4) Recent research has been focused on developing hydrometallurgical processes which can treat all types of laterite ores irrespective of magnesium content. In AMAX process, the fine limonitic ores were treated by HPAL and the free acid from HPAL was utilized in leaching garnierite ore at atmospheric pressure. ) Treatment method for acid leaching solution of laterite ore can be classified into mixed sulphide or hydroxide precipitation, direct recovery by solvent extraction or ion exchange. 5,6) Numerous studies have been reported on the separation of (II) and (II) by solvent extraction. 7 ) In acidic solution, most extractants have a selectivity for (II) over (II), while some extractants have a higher selectivity for (II) in ammoniacal solution. ) Mixed extractants containing versatic, hydroxyoxime and TBP could extract most of cobalt and nickel from the laterite leach solution. 5) Although versatic acid is very selective for (II) and (II) over (II), the disadvantage of versatic acid is that its solubility to aqueous is high. 5) Use of Cyanex272 and Cyanex3 was found to be effective in separating cobalt from sulfate solution with the following composition (II) ¼ :6 g/l, (II) ¼ 5: g/l, and (II) ¼ 5: g/l. 2) Leaching of garnierite ore at 8 C with g/l sulfuric acid resulted in a solution with the following composition: (II) ¼ 32:2 g/l, iron ¼ 3:5 g/l, (II) ¼ 4:4 g/l, and (II) ¼ :8 g/l. 3) Since the concentration ratio of (II) to (II) was nearly 4 in the above laterite leach solution, mass action effect of magnesium on the extraction and separation of the metal ions is expected. In order to find an *rresponding author, mslee@mokpo.ac.kr optimum condition to separate cobalt from the synthetic sulfate leach solution, solvent extraction experiments have been performed employing D2EHPA, PC88A, Cyanex272, and Alamine336. Effect of certain parameters, such as concentration and saponification degree of cationic extractants, and volume ratio of the two phases, on the extraction percentage of the metals was investigated. 2. Experimental Synthetic sulfate solution containing (II), (II), and (II) was prepared by dissolving reagent grade SO 4, SO 4, and SO 4 in doubly distilled water. The concentration of each metal in the synthetic solution was 4.4 g/l (II),.8 g/l (II), and 32.2 g/l (II). Solution ph was adjusted to the desired value by adding a small amount of dilute sulfuric or NaOH solution to the synthetic solution. Industrial grade D2EHPA, PC88A (Mobil Chemical), and Alamine336 (gnis.) was purchased and was used without further purification. Cyanex272 was kindly supplied by the Korea branch of Cytec company. Toluene was used as a diluent for extractants. Saponification of cationic extractants was done by adding stoichiometric amount of concentrated NaOH solution to each extractant in toluene. The resulting mixture of extractant and NaOH solution was stirred for 24 h. Alamine336 was used without any pretreatment. Volume ratio of organic to aqueous phase was varied from unity to five by keeping the volume of the aqueous phase at 2 ml. Necessary volume of aqueous and organic phase was placed in a separatory funnel and shaken for an hour at ambient temperature with a Wrist Action Shaker. The mixture was allowed to settle for 24 h and then the aqueous phase was separated from the organic phase. Solution ph was measured using a ph meter (Fisher Accumet ph model 62). Since the concentration of (II) and (II) in the synthetic solution was very high, measuring the concentration of these metals in the raffinate after

2 22 M. Lee, S. Kim, Y. Choi and J. Chae Cyanex272 concentration, / kmol/m 3 Table Extraction results obtained by various mixtures of extractants at equal volume ratio of organic to aqueous from the synthetic solution ph of 6. Extractant (%) (%) (%) D2EHPA PC88A Cyanex TBP...2 Alamine D2EHPA + TBP..4.8 D2EHPA + TOPO D2EHPA + Alamine PC88A + TBP PC88A + TOPO.4.. PC88A + Alamine Cyanex272 + TBP...6 Cyanex272 + TOPO..6.4 Cyanex272 + Alamine Fig. Effect of Cyanex272 concentration on the extraction of (II), (II) and (II) from the synthetic solution of ph 6 at equal volume ratio of organic to aqueous. extraction would result in great error in the measured values. Therefore, extraction percentage of (II) and (II) was obtained by determining the concentration of metals extracted into organic phase. For this purpose, the metals in the loaded organic were stripped with 2. kmol/m 3 sulfuric acid solution and then the concentration of the metals in the stripped solution was measured using ICP-AES (Spectrflame, EOP). 3. Results and Discussion 3. Solvent extraction by D2EHPA, PC88A, and Cyanex272 and their mixtures balt is separated from nickel sulfate solution by using dialkylphosphorus extractants. The basicity of these extractants increases with the decrease in the distance of the alkyl chain from the central phosphorus atom, from the phosphoric acid(d2ehpa) to the phosphonic acid(pc88a) to the phosphinic acid(cyanex272). ) This results in the increase of the separation factor between cobalt and nickel from phosphoric acid to phosphinic acid. ) We have performed preliminary experiments on the extraction of the metals from the synthetic sulfate solutions by using D2EHPA, PC88A, and Cyanex272 in the ph range of 4 to 7. Figure shows the extraction data by Cyanex272 from the sulfate solution of ph 6. In these experiments, the concentration of Cyanex272 was varied from. to.7 kmol/m 3 and the volume ratio of the two phases was unity. Although the extraction percentage of (II) was the highest among the three metal ions, it was below % in our experimental range. The reason why the extraction percentage of the metals was low was due to the exchange of hydrogen ions during extraction reaction. It was reported that Aliquat 336 had a selectivity for (II) over (II) from mixed sulfate solutions in the ph range of 5 to 7. 4) In order to investigate the possibility of extracting only cobalt from the synthetic solution by extractant mixture, Alamine336, TBP and TOPO were mixed with each of D2EHPA, PC88A, and Cyanex272. In these experiments, the concentration of all the extractants was fixed at.5 kmol/m 3. The results are shown in Table. This table indicates that adding TBP or Alamie336 to our cationic extractants had a negligible effect on the extraction of the three metals compared to the results obtained by the individual cationic extractant. 3.2 Solvent extraction by saponified D2EHPA, PC88A, and Cyanex272 In order to increase the extraction percentage of (II) from the solution, use of saponified extractants was tried. First, the saponification degree of each extractant was kept at 3% and the extraction experiments were done from the synthetic solution of ph 5 and 6. In these experiments, the concentration of D2EHPA, PC88A, and Cyanex272 was kept at.3 kmol/m 3 and the volume ratio of organic to aqueous phase was varied from unity to five. Figures 2, 3, and 4 show the variation in the extraction percentage of the three metals with volume ratio by saponified extractants. of nickel by saponified D2EHPA, PC88A, and Cyanex272 was nearly zero in our experimental range. In the solvent extraction by D2EHPA, extraction percentage of (II) was much higher than that of (II), which agreed well with the reported data on the extraction order of these three metals by D2EHPA. ) Volume ratio affected little the extraction percentage of (II), while extraction percentage of (II) increased with increasing volume ratio of organic to aqueous. The data in Fig. 2 imply that (II) can be separated from the synthetic solution by using saponified D2EHPA. However, the high concentration of in the solution makes it uneconomical to extract (II). In the extraction with saponified PC88A and Cyanex272, extraction percentage of (II) by Cyanex272 was higher

3 Solvent Extraction Separation of (II) from Synthetic Leaching Sulfate Solution of ckel Laterite Ore Volume ratio(o/a) Fig. 2 Effect of volume ratio of organic to aqueous on the extraction of metals by 3% saponified.3 kmol/m 3 D2EHPA from the synthetic solution of ph 5 and 6. Fig. 4 Effect of volume ratio of organic to aqueous on the extraction of metals by 3% saponifed.3 kmol/m 3 Cyanex272 from the synthetic solution of ph 5 and Separation factor (D /D ) D2EHPA PC88A Cyanex272 Volume ratio(o/a) Fig. 3 Effect of volume ratio of organic to aqueous on the extraction of metals by 3% saponifed.3 kmol/m 3 PC88A from the synthetic solution of ph 5 and 6. than that by PC88A, whereas the reverse was true for (II). of (II) rapidly increased with volume ratio of the two phases. The increase in the extraction percentage of (II) with volume ratio by PC88A was similar to that by Cyanex272. Separation factor between (II) and (II) at various extraction conditions are represented in Fig. 5. The highest separation factor between (II) and (II) was obtained by using saponified Cyanex272. In the case of saponified Fig. 5 Variation of the separation factor between and by 3% saponified extractants from the synthetic solution of ph 5. Cyanex272, separation factor increased rapidly with the increase of volume ratio of the two phases, while there was little change in the separation factor with volume ratio in the case of saponifed PC88A. In order to investigate the effect of Cyanex272 concentration, the concentration of saponified Cyanex272 was varied from. to.3 kmol/m 3. In these experiments, the saponification degree was kept at 3% and the results are shown in Fig. 6. The extraction percentage of nickel was nearly zero. The increase in the extraction percentage of

4 24 M. Lee, S. Kim, Y. Choi and J. Chae 8 (II) (II) Cyanex272 (kmol/m 3 ) Saponification percentage Fig. 6 Effect of 3% saponified Cyanex272 concentration on the extraction of (II) and (II) from the synthetic solution of ph 5 at several volume ratio of organic to aqueous. Fig. 8 Effect of saponification degree on the extraction of metals from the synthetic solution of ph 5 at equal volume ratio of aqueous to organic by.2 kmol/m 3 Cyanex272. Separation factor (D /D ) Cyanex272 (kmol/m 3 )..2.3 When volume ratio of organic to aqueous was higher than 2, there was not much difference in the separation factor between (II) and (II) with volume ratio. Figure 8 shows the effect of saponification degree of Cyanex 272 on the extraction of the metals from the synthetic solution of ph 5. In these experiments, the concentration of Cyanex272 was fixed at.2 kmol/m 3 and the volume ratio of both phases was unity. In the case of (II), the extraction percentage was linearly increased with an increase in the saponification degree up to 2% and then remained constant with further increase of saponifiaction degree. Extraction percentage of (II) was nearly zero in our experimental range, while extraction percentage of (II) was slightly higher than that of (II). Fig. 7 Effect of 3% saponified Cyanex272 concentration on the separation factor between and from the synthetic solution of ph 5 at several volume ratio. (II) with Cyanex272 concentration and volume ratio was more pronounced than that of (II). Since the concentration of (II) was much higher than that of (II) in the synthetic solution, a slight increase in the extraction percentage of (II) indicates that large amount of (II) is extracted into Cyanex272. Figure 7 shows the variation in the separation factor between (II) and (II) with Cyanex272 concentration and volume ratio. The highest separation factor was obtained with 3% saponified.2 kmol/m 3 Cyanex Solvent extraction by Alamine336 balt ion has a strong tendency to form complexes with chloride ion, while nickel is not willing to form complexes with chloride ion. ) The difference in the tendency to form chloride complexes between (II) and (II) has been utilized in the solvent extraction separation of the two metals from chloride solution. ) Adding chloride ions to the sulfate solution would lead to the formation of cobalt anionic species and then separation of (II) from (II) and (II) would be possible by using anionic extractants. In order to test this possibility, certain amount of Cl 2 was added to the synthetic solution of ph 5 and the resulting solution was extracted by.2 kmol/m 3 Alamine336 diluted in toluene. Figure 9 shows that extraction percentage of cobalt linearly increased with the increase of Cl 2 concentration up to.6 kmol/m 3. In the absence of Cl 2, extraction percentage of cobalt was nearly zero, while adding Cl 2 to the synthetic solution had a favorable effect on the extraction of cobalt. In these experiments, the

5 Solvent Extraction Separation of (II) from Synthetic Leaching Sulfate Solution of ckel Laterite Ore three metals were investigated. Mixing cationic extractant with TBP or Alamine336 had no pronounced effect on the extraction of the three metals in the ph range of 4 to 7. Saponified D2EHPA extracted (II), while the extraction percentage of (II) and (II) was nearly zero. Saponification of PC88A and Cyanex272 increased the extraction percentage of (II) and (II). Although the extraction percentage of (II) was low compared to that of (II), the amount of (II) extracted into organic phase was comparable due to the high concentration of (II) in the synthetic solution. Adding Cl 2 to the synthetic sulfate solution and then use of Alamine336 led to the extraction of only cobalt into organic, leaving (II) and (II) in the aqueous solution. Acknowledgments Cl 2 concentration, / kmol/m 3 This research was supported by the General Research Project of the Korea Institute of Geoscience and Mineral Resources(KIGAM) funded by the Ministry of Knowledge Economy of Korea. Fig. 9 Effect of adding Cl 2 to the synthetic sulfate solution of ph 5 on the extraction of metals by.2 kmol/m 3 Alamine336. extraction percentage of (II) and (II) was nearly zero. Therefore, it can be concluded that Alamine336 was superior to the cationic extractants tested in this study in separating cobalt from nickel and magnesium sulfate solution. However, the highest extraction percentage of (II) by.2 kmol/m 3 Aalmine336 was only 2% and the amount of cobalt extracted into Almine336 depends on the concentration of chloride ion added to the sulfate solution. This was verified in our experiments in which increase of the volume ratio(o/a) up to 5 affected little the extraction percentage of (II). Further study is needed to increase the extraction percentage of cobalt by adding the least amount of Cl 2 to the solution. 4. nclusions Solvent extraction experiments have been performed to find an optimum condition to separate (II) from the synthetic sulfate solution with the following composition: (II) ¼ :8 g/l, (II) ¼ 4:4 g/l, (II) ¼ 32:2 g/l. D2EHPA, PC88A, Cyanex272, and Alamine336 were used and the effect of extraction conditions on the separation of the REFERENCES ) A. R. Burkin: Critical reports on applied chemistry Vol. 7 Extractive metallurgy of nickel, (John Wiley & Sons, NY, 987) pp ) D. Georgiou and V. G. Papangelakis: Hydrometallurgy 49 (998) ) Y. Xu, Y. Xie, L. Yan and R. Yang: Hydrometallurgy 8 (25) ) R. G. McDonald and B. I. Whittington: Hydrometallurgy 9 (28) ) C. Y. Cheng, G. Boddy, W. Zhang, M. Godfrey, D. J. Robinson, Y. Pranolo, Z. Zhu and W. Wang: Hydrometallurgy 4 (2) ) Z. Zainol and M. J. col: Hydrometallurgy 96 (29) ) B. K. Tait: Hydrometallurgy 32 (993) ) N. B. Devi, K. C. Nathsama and V. Chakravortty: Hydrometallurgy 49 (998) ) N. V. Thakur: Hydrometallurgy 48 (998) ) J. Rydberg, M. x, C. Musikas and G. R. Choppin (ed.): Solvent Extraction Principles and Practice, (Marcel Dekker, Inc., NY 24) pp ) M. Aguilar and J. L. rtina (ed.): Solvent Extraction and Liquid membranes: Fundamentals and Applications in New Materials, (CRC Press. NY, 28) pp ) P. E. Tsakiridis and S. L. Agatzini: Hydrometallurgy 72 (24) ) M. S. Lee, S. B. Kim, Y. Y. Choi and J. G. Chae: Korean J. Metals Mater. 48 (2) ) A. A. Nayl: J. Hazardous Mater. 73 (2)