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The current study outlines the electrochemical recovery of tellurium from a metallurgical plant waste fraction, namely Doré slag. In the precious metals plant, tellurium is enriched to the TROF (Tilting, Rotating Oxy Fuel) furnace slag and is therefore considered to be a lost resource-although the slag itself still contains a recoverable amount of tellurium. To recover Te, the slag is first leached in aqua regia, to produce multimetal pregnant leach solution (PLS) with 421 ppm of Te and dominating dissolved elements Na, Ba, Bi, Cu, As, B, Fe and Pb (in the range of 1.4-6.4 g dm −3), as well as trace elements at the ppb to ppm scale. The exposure of slag to chloride-rich solution enables the formation of cuprous chloride complex and consequently, a decrease in the reduction potential of elemental copper. This allows improved selectivity in electrochemical recovery of Te. The results suggest that electrowinning (EW) is a preferred Te recovery method at concentrations above 300 ppm, whereas at lower concentrations EDRR is favoured. The purity of recovered tellurium is investigated with SEM-EDS (scanning electron microscope-energy dispersion spectroscopy). Based on the study, a new, combined two-stage electrochemical recovery process of tellurium from Doré slag PLS is proposed: EW followed by EDRR.

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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