An environmentally-friendly process for recovering, solidifying As and preparing bronze material from tin-bearing middling

Abstract

Tin-bearing middling, a hazardous solid waste produced during beneficiation of tin deposits and tin-bearing tailings, presents a serious environmental pollution risk due to high levels of As. This paper aims to explore an environmentally friendly technology to reduce toxic substances and prepare a high value-added bronze material from tin-bearing middling. The co-process for tin-bearing middling, anthracite, and copper is first proposed at 1073–1123 K. Variables like temperature, amount of added anthracite, and holding time were optimized. Those results showed that 95.56% Sn and 92.79% As were recovered; levels of Fe in the residue reached 73.52 wt%. During roasting, SnO2 in the tin-bearing middling was initially transformed into SnO(g), then into an Fe–Sn spinel (Fe3-xSnxO4) and Ca2SnO4, and finally a Cu–Sn alloy. Generation of the Fe–Sn spinel came primarily from substitution of Fe2+ by Sn2+, but small amounts of Sn4+ replaced Fe3+ in Fe3O4. Meanwhile, FeAsS and FeAsO4 were initially transformed into As4(g) and then solidified as a Cu–As alloy. Interestingly, the residual As existed as Fe–As alloy, but As leaching levels did not exceed 0.02 mg/L. After initial treatment, the Cu alloy can be prepared for bronze. Meanwhile, subsequent volatilization and solidification of As resulted in a significant reduction of arsenic-bearing waste that minimizes environmental risk.