A novel process for silver enrichment from Kaldo smelting slag of copper anode slime by reduction smelting and vacuum metallurgy

Abstract

Silver in Kaldo smelting slag of copper anode slime is diffuse and hard to be enriched. In this study, a novel process consisting of reduction smelting and vacuum metallurgy was developed to enrich Ag in Kaldo smelting slag of copper anode slime through laboratory and scale-up experiments. Pb, Bi and Ag in the slag were first enriched in Pb–Bi–Ag alloy by reduction smelting. Results show that when the reduction smelting was conducted for 40min under 1350 °C with the addition of reductant, limestone and iron powder accounting respectively for 10%, 20% and 26% of the raw feed, the recovery of Pb, Bi and Ag was 95.12%, 98.13% and 99.11%, respectively. After the reduction smelting, Ag was separated from Pb and Bi by vacuum distillation based on their difference in vapor pressure. Results show that Pb and Bi in Pb–Bi–Ag alloy were removed under the pressure of 3Pa, distillation temperature of 1000 °C and distillation duration of 2 h. After the vaccum metallurgy process, Ag enrichment ratio is above 9. The scale-up experiment shows that Ag recovery is higher than 98%, and more than 97% of Pb and Bi form Pb–Bi alloy product, which further proves that this novel process is simple but efficient for silver enrichment and separation from Pb and Bi in Kaldo smelting slag of copper anode slime.