Removal and recovery of arsenic from concentrated sulfuric acid by solvent extraction

Abstract

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.