Arsenic-contaminated sulfuric acid solutions are produced in large quantities as by-product during pyrometallurgical processing of sulfide minerals. Options for re-using such acid solutions are increased if the arsenic is removed and recovered as a product. The performances of tributyl phosphate and a mixture of 6 wt-% 1,2-octanediol in 2-ethylhexanol were studied in liquid-liquid extraction of arsenic from an industrial solution containing 10.4 M H2SO4. It was found that, due to the complex phase equilibria, a process design based on conventional batch equilibrium data did not describe the countercurrent processes accurately. A countercurrent flowsheet utilizing undiluted tributyl phosphate was investigated by pseudo-countercurrent extractions. 83.7 % extraction of arsenic and 31.4 % coextraction of H2SO4 was obtained in three-stage countercurrent extraction operated at a solvent-to-feed ratio of 0.79. Two-stage countercurrent scrubbing with pure water at O/A = 4.03 back-extracted 83.6 % of H2SO4 and 24.9 % of arsenic. 100 % and 89.7 % back-extraction was achieved in four-stage stripping at O/A = 2.01 for H2SO4 and arsenic, respectively. The effects of varying the flowsheet and operating parameters on separation efficiency are discussed.

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A novel solvent extraction scheme was developed for the processing of Co-rich lithium-ion battery (LIB) leachate to a Ni–Co–Mn (NCM) sulfate mixture that can be directly used in the precursor synthesis of LIB cathodes. Conventional hydrometallurgical recycling of spent LIBs usually aims at separation of Li, Ni, Co, and Mn into pure fractions, which is simplified here. Operating pH and the number of extraction stages for each separation were evaluated from batch equilibrium experiments. Two continuous countercurrent extractions with bis(2-ethylhexyl) hydrogen phosphate (D2EHPA) and one with Cyanex 272 were studied in bench-scale mixer-settler equipment, and a Ni–Co–Mn solution with n(Ni):n(Co) = 14.16 and n(Ni):n(Mn) = 8.06 was obtained. The Ni:Co:Mn molar ratio in the NCM mixture can be adjusted to, for example, 8:1:1 using a Co-rich raffinate from the same process, and no additional transition metal salts are required for tuning the composition. Stripping raffinate containing 102.7 g L−1 Co at 99.8% relative purity was obtained from Cyanex 272 extraction. The main benefit of the process concept is that the solvent extraction separations can be operated with less stringent requirements than when producing pure metal salts.

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