Selective Recovery of Valuable Metals (Se, Te, Cu) from the Selenium Distillation Residue by Sulfuric Acid Oxidative Leaching

Selenium distillation residue (SDR), inevitably generated in the treatment of refining selenium by vacuum distillation of crude selenium, is a kind of solid residue with low utilization yet massive recycling value. It contains a diverse and complicated component of selenide, telluride, and high-level precious metals. In this study, oxidative acid leaching at atmospheric pressure is adopted to systematically treat SDR to separate selenium, tellurium, copper, and effectively enrich gold and silver. The leaching method in H2SO4-H2O2 mixed solution under an oxygen atmosphere was employed to investigate the effects of H2SO4 concentration, H2O2 concentration, oxygen flow rate, liquid-solid ratio, and leaching time on the recovery of Se, Te, and Cu. Under the optimal conditions, the recoveries of Se, Te, and Cu, respectively, achieved 87.96%, 87.02%, and 98.82% while Au, Ag, and Pb were enriched in the leaching residue, the contents were 0.42%, 16.5%, and 24.27%, respectively. Thermodynamic analysis indicated that insoluble Cu2Se could be oxidized to soluble H2SeO3 in the pH range of - 1.5 to 0, and the potential 0.83 V. XRD and EPMA results outline that CuSe, AgSe, CuTe, and AgTe exist in leaching residue resulting in incomplete leaching of Se, Te, and Cu. Besides, the existence of core-shell grain of AgCl@AgSe is another main reason for the incomplete leaching of selenium. Oxygen partial pressure can enhance mass transfer by diffusion and open the envelope phase. The leaching percentages of Se, Te, and Cu at 0.5 MPa are measured as 93.97%, 99.83%, and 97.42%, respectively.

Automated summary

This study adopted oxidative acid leaching at atmospheric pressure to systematically treat selenium distillation residue (SDR) and successfully separated selenium, tellurium, and copper, while enriching gold and silver. Under optimal conditions, the recoveries of Se, Te, and Cu were high, but incomplete leaching of selenium was due to the presence of CuSe, AgSe, and AgCl@AgSe in the residue. Oxygen partial pressure enhanced the leaching effect.