Reaction Behaviors of Associated Minerals in Molten Salt Smelting of Stibnite and Kilogram-Class Trials

Abstract

The molten salt metallurgy of Sb, which involves the smelting of stibnite in a binary NaCl-Na2CO3 salt with sulfur-fixing and the addition of a reductant, has been proposed as a clean method for Sb extraction. However, the reacting behaviors of the minerals associated with stibnite (Sb2S3) during the smelting are still unclear, and industrial tests have not been conducted. This study investigated the behaviors of PbS, FeS2, SiO2, and CaCO3, which are the main minerals associated with stibnite, during reducing smelting by using the NaCl-Na2CO3 molten salt. The results showed that PbS could react with Na2CO3 to generate metallic Pb at 950 °C. FeS2 and SiO2 formed stable NaFeS2 and Na2SiO3 with the molten salt at a high temperature, respectively. CaCO3 formed an unstable intermediate product of Na2Ca(CO3)2 at 675 °C and decomposed with increasing temperature. Kilogram-class trials were also performed using 50 kg of concentrate and more than 300 kg of mixture material, and the results showed that the direct recovery rate of Sb and Au reached maximum values of 93.22% and 92.06% at temperature 920 °C in eutectic Na2CO3-NaCl molten salt, respectively, while the total sulfur-fixing ratio reached 99.49%. Thus, the associated minerals consumed the molten salt, and the feasibility of molten salt smelting was verified by this kilogram-class pilot experiment.