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.
Highlights
Sb is mainly used for manufacturing alloys, semiconductor optoelectronic devices, and Sb compounds [1,2]
The results showed that PbS could participate in reduction reactions with Na2 CO3, and carbon and metallic Pb were obtained after 700 ◦ C, with the production rate of Pb reaching 96.55% at 950 ◦ C
SiO2 was converted to Na2 SiO3 after 850 ◦ C, and CaCO3 form the unstable compound Na2 Ca(CO3 )2 with the molten salt, which consumed a portion of the molten salt
Summary
Sb is mainly used for manufacturing alloys, semiconductor optoelectronic devices, and Sb compounds [1,2]. Padilla [14,15] researched the carbon reduction of stibnite to produce Sb oxide and metallic Sb using CaO as a sulfur-fixing agent. This method solved the problem of SO2 flue gas pollution in the traditional process. Our team investigated the molten salt smelting of stibnite in the laboratory, and the Sb generation rate and sulfur-fixing rate were both higher than 90% [22,23] This new method is a low-carbon and environmentally friendly process. A kilogram-class pilot test was performed in a rotary furnace to further verify the feasibility of the process
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