Selective solvent extraction of nickel and cobalt from a Ni lateritic sulfuric solution using synergism caused by LIX860N-IC and Versatic 10

Abstract

This work investigated the efficiency of the LIX860N-IC + Versatic 10 synergistic system (pH range 2–6, 40 °C) to treat an aqueous sulphate solution containing Ca, Co, Cu, Mg, Mn, Ni, and Zn, which mimics a liquor obtained by the sulfation-roasting-leaching process applied to a lateritic Brazilian Ni ore, after precipitation of Fe, Al, and Cr. Almost complete extraction of Cu was observed at pH 2 (1 stage, A/O = 1:1), while a rise in the selectivity of Ni/(Mn + Zn) and Co/(Mn + Zn) was identified at pH 2–6 and pH > 5, respectively. By varying both extractant concentrations, an organic phase containing 0.4 M LIX860N-IC + 0.4 M Versatic 10 was selected to obtain high Ni and Co extractions with low Mn and Zn extractions. At the studied pH range, antagonism occurred for Ca, Cu, and Mg extractions, while synergism was found for Ni and Zn extractions. For Co and Mn, such an effect was pH dependent: antagonism at pH 2–5 and below 4.5, respectively, otherwise synergism was identified. The stoichiometry of Co and Ni extractions with the LIX860N-IC + Versatic 10 system were obtained by data fitting supported by statistical analysis. Ni and Co were complete and selectively extracted together (>99.9 %) at pH 4.5 (2 stages, A/O = 1:1.1) with low extractions of Mn (3.3 %) and Zn (20 %), leaving Ca and Mg in the raffinate. In the sequence, while Zn was completely scrubbed off from the loaded organic using a scrub solution containing 3.5 g/L Ni and 0.2 g/L Co at pH 4.5 (1 stage, O/A ≤ 15), Mn scrubbing efficiency achieved from 85.6 % to 97.8 % at an O/A ratio ranging from 5 to 25, which can be attributed to possible Mn oxidation in the extract. Finally, Ni was completely stripped out (3 stages, A/O = 10:1), using a synthetic Ni spent electrolyte (50 g/L Ni + 1 M H2SO4), while Co stripping increased from 70 % in the first stage to 75.4 % in the second, and to only 76 % in the third stage, indicating that Co oxidation might have occurred in the loaded organic solution. The remaining Co in the extract was stripped out with 5 M HCl (2 stages, A/O = 1:1). Consequently, to avoid Mn and Co oxidations in the loaded organic solution, the solvent extraction circuit with LIX860N-IC + Versatic 10 requires an operation under an inert atmosphere.