Reaction Mechanism and Technical Application of Metallic Bismuth Extraction from Bismuthinite Concentrate by Low-Temperature Alkaline Smelting

Traditional bismuthinite concentrate precipitation smelting has problems of low recovery of valuable metals (e.g., Bi, Cu, Mo, and Ag), high fuel consumption, and high cost of SO2 flue gas treatment. Therefore, in this study, an eco-friendly alkaline smelting process was proposed to extract metallic bismuth and recover valuable metals. The phase equilibrium composition of the Bi2S3-Na2CO3-C system was revealed by thermodynamic simulations at different temperatures and reductant contents. Based on reaction product characterizations and thermodynamic simulations, the following reaction mechanism and suitable bismuth extraction path were confirmed: Bi2S3 first reacted with Na2CO3 to form Bi2O3 and Na2S, and the intermediate (Bi2O3) was then reduced to metallic Bi by both C and CO. Under optimized conditions (Wbismuthinite/WNa2CO3/Wcoke = 200:300:20, 900 °C, 150 min), up to 96.56% Bi, 75.07% Pb, and 85.11% Ag were enriched in crude bismuth, respectively, while 93.57% Cu, 70.23% Fe, 96.63% Mo, and 94.34% W entered the salt slag. More than 99.9% W and Mo were recovered as Na2WO4 and Na2MoO4, respectively, from the salt slag by water leaching. In the leaching residue, chalcopyrite, pyrite, and elemental sulfur could be recovered by flotation.