SOLVENT EXTRACTION OF NICKEL AND COBALT FROM CALDAG LATERIT LEACH SOLUTIONS USING VERSATIC 10 AND CYANEX 272 Sait Kursunoglu, PhD (Abdullah Gul University) Zela Tanlega Ichlas, M.Phil. (Curtin University, WA School of Mines) Don Ibana, Assoc. Prof. (Curtin University, WA School of Mines) Muammer Kaya, Prof. (Eskisehir Osmangazi University)

Nıckel and Cobalt extractıon processes Processing of nickel laterite is divided into three main catagories depending on the downstream route Mixed Hydroxide Precipitation (MHP), Cawse Operation (WA) Mixed Sulfid Precipitation (MSP), Murrin Murrin Operation (WA) Direct Solvent Extraction (DSX), Bulong Operation (WA), Goro (New Caledonia) Synergestic Solvent Extraction (SSX), which is gained attention for selective separation of nickel and cobalt from impruties such as manganese, calcium and magnesium. However, SSX has not been applied for industrial applications up until now.

The aım of thıs study The use of two SX steps using Versatic 10 and Cyanex 272 in the first and second steps, respectively, to carry out SX of the nickel and cobalt from a partially neutralised atmospheric leach solution of Caldag laterite nickel ores is the main porpous of this investigation. The second aim is to present a flowsheet to generate two separate streams of nickel and cobalt electrolytes that are sufficiently pure for electrowinning of each metal. The use of this configuration instead of the reverse, which was practiced in Bulong, has been suggested by Donegan (2006) as it has the potential to minimize reagent costs by reducing ammonia and acid consumptions and reducing Cyanex 272 inventory, which is much more expensive than Versatic 10. Although this configuration has been investigated by Tsakiridis and Agatzini (2004) to separate nickel and cobalt from magnesium and calcium, the behaviour of manganese which is the most difficult impurity to be removed in this system, has not been reported.

MATERIALS: Caldag laterıte leach solutıon Table 1 Typical composition of synthetic feed solution. MATERIALS: Caldag laterıte leach solutıon Synthetic sulfate solutions that simulate those produced in Caldag Nickel, following the partial neutralisation step to remove iron from the leach solution by limestone addition, was prepared by dissolving analytical grade salts of NiSO4.6H2O, CoSO4.7H2O, MnSO4.H2O, MgSO4.7H2O and chloride of CaCl2.2H2O in deionised water. Versatic 10 (Industrial Grade), Cyanex 272 (Industrial Grade), TBP (≥99% purity) as a modifier and ShellSol 2046 (Industrial Grade) as a dilluent were used. Table 1. Elemental composition of partially neutralised leach solution. Element Ni Co Mn Ca Mg Concentration (mg/L) pH: 4.5 4100 240 1600 530 8750

Method: experımental 1 M H2SO4 and 5M NaOH were used for pH arrangment. Fıgure 1. Experımental set-up. Overhead Motor Organic Phase Thermometer Hot Plate Aqueous Phase Water Bath Glass Platform Impeller

RESULTS AND DISCUSSION Metal extraction with Versatic 10 Solvent extraction experiments were carried out with VersaticTM 10 concentrations of 10% and 20% (v/v%) and 5% TBP (v/v%) in ShellSol® 2046 as a dilluent. The organic system containing 20% VersaticTM 10 and 5% TBP was selected as the best composition at an A/O ratio of unity and 40 °C. Using this system, 98% of nickel, 98% of cobalt and 94% of manganese were extracted at pH 7.26 in a single contact whereas 65% of calcium and 12% of magnesium were co-extracted. (in the next slide) The following metal extraction order was obtained: Ni2+> Co2+> Mn2+> Ca2+> Mg2+ which is consistent with the findings of Preston (1985) and Cheng (2006). (in the next slide)

Extraction pH isotherms Figure 2. Extraction of metals with VersaticTM 10 a) 20% VersaticTM 10 + 5% TBP; b) 10% VersaticTM 10 + 5% TBP; 40 °C; A/O 1:1.

Thırd phase formatıon and local precıpıtatıon Figure 3. Third phase formation and local precipitation at pH 6.5 (Condition: 5% VersaticTM 10 + 5% TBP; 40 °C; A/O 1:1). Figure 4. Third phase formation and local precipitation after pH 7 (Condition: 10% VersaticTM 10 without TBP; 40°C; A/O 1:1).

SCRUBBING OF LOADED ORGANIC PHASE The loaded organic solutions were subjected to a scrubbing step with acidified water at pH 5.6 and 5.8, and A/O of unity. The pH of the deionised water was adjusted with sulphuric acid. More than 90% of magnesium was scrubbed out after three scrubbing stages at pH 5.6 while only 16% Ca was removed from the loaded organic solutions. It was found that nickel, cobalt and manganese were more stable in the organic phase than magnesium and calcium. Less than 3% of nickel, cobalt and manganese were removed from the loaded organic phase. Table 2. Effect of pH on the three-stage scrubbing of the metals using acidified water at 40 °c and A/O 1:1. pH Scrubbing Metal in aqueous phase, % Metal in organic phase, % Ni Co Mn Ca Mg 5.6 0.3 1.9 2.1 15.7 90.1 99.7 98.1 97.9 84.3 9.9 5.8 0.4 1.0 2.2 13.9 82.1 99.6 99.0 97.8 86.1 17.9

STRIPPING OF THE LOADED ORGANIC PHASE Stripping of the metals from loaded organic solution following the scrubbing tests were performed using acidified water at pH 0.5, 0.75, 1.0, 2.0 and 3.0, and A/O of unity. Figure 5 shows that at a pH of 0.75, nickel, cobalt, manganese, magnesium and calcium can be stripped completely from the organic phase. The stripping percentage of the nickel, cobalt, manganese and calcium significantly decreased with the increasing pH while magnesium decreased only slightly. Figure 5. Stripping pH isotherms using acidified water.

Metal extraction with Cyanex 272 The loaded strip solution was subjected to solvent extraction tests using Cyanex® 272 with concentration of 15% and 5% and also with the addition of 5% TBP as phase modifier. Based on the data, the organic system containing 15% Cyanex® 272 and 5% TBP was determined to be the best system for the selective extraction of cobalt and manganese, leaving most of the nickel, magnesium and calcium in the raffinate. The pH isotherms of manganese and cobalt shifted towards lower pH when the concentration of Cyanex® 272 increased. (in the next slide) Cobalt and manganese were almost completely extracted by 15% Cyanex® 272 and 5% TBP at pH 4.83 in a single contact, while approximately 2% Ni was co-extracted from the aqueous phase.(in the next slide)

Extraction pH isotherms Figure 6. Extraction of metals with Cyanex®272 a) 15% Cyanex® 272 + 5% TBP; b) 5% Cyanex® 272 + 5% TBP; 40 °C; A/O 1:1.

SCRUBBING OF THE LOADED ORGANIC PHASE WITH COBALT SALT SOLUTION The loaded organic phase for the scrubbing test was prepared by loading the organic solution using 15% Cyanex® 272 and 5% TBP in ShellSol® 2046 at an A/O ratio of unity and pH 5.0 by which 96% of Co, 98% of Mn, 41% of Mg, 40% of Ca and 3% of Ni were extracted from the aqueous phase. The scrubbing tests were carried out at an A/O ratio of unity as well. The co-extracted nickel, manganese, calcium and magnesium were contacted with a cobalt salt solution containing 20 g/l of cobalt. The cobalt in the aqueous solution displaced nickel, manganese, calcium and magnesium from the loaded organic. The displacement mechanism is illustrated by Eq.1 (Ritcey, 2006). Nickel, magnesium and calcium were completely scrubbed out from the loaded organic solution after two stages scrubbing test whereas scrubbing efficiencies were as high as 93% for manganese. (𝐶 16 𝐻 35 𝑂 2 𝑃)(𝑁𝑖, 𝑀𝑛, 𝐶𝑎, 𝑀𝑔)+ 𝐶𝑜𝑆𝑂 4 ⇋ (𝐶 16 𝐻 35 𝑂 2 𝑃)𝐶𝑜 + (𝑁𝑖, 𝑀𝑛, 𝐶𝑎, 𝑀𝑔)𝑆𝑂 4 (Eq,1)

Figure 7. Extraction of cobalt at pH 5 Figure 7. Extraction of cobalt at pH 5.0 (Condition: 15% Cyanex® 272 + 5% TBP, 40 °C, A/O 1:1). Figure 8. Scrubbing of loaded organic with cobalt salt solution containing 20 g/l of cobalt.

Figure 9. Stripping pH isotherms using acidified water. STRIPPING OF THE LOADED ORGANIC PHASE The loaded organic scrub solution was subjected to stripping with acidified water at pH 0.75, 1.0 and 1.5, and A/O of unity. As can be seen from Figure 9, complete stripping of cobalt and manganese were achieved at pH of 1.0. Figure 10 shows the stripped organic solutions which were observed to be as clear as the fresh ones. Figure 9. Stripping pH isotherms using acidified water. Figure 10. Stripping of loaded organic solution.

PROPOSED FLOWSHEET FOR THE EXTRACTION AND SEPARATION OF NICKEL AND COBALT FROM CALDAG LATERITE LEACH SOLUTIONS Figure 10. Proposed SX flow sheet for the extraction of nickel and cobalt from Caldag laterite leach solutions (Kursunoglu, 2016).

Conclusions A two-sequential solvent extraction circuits allows nickel and cobalt separation. 94% Ni and 91% Co are totally separated from the feed solution. 20 g/l of cobalt salt solution is effective to remove co-extracted impurities. The first bench scale solvent extraction flowsheet is proposed for Caldag laterite leach solution.

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