High-Temperature Volatilization Mechanism of Stibnite in Nitrogen-Oxygen Atmospheres

The volatilization of stibnite (Sb₂S₃) in nitrogen and mixtures of nitrogen-oxygen was investigated in the temperature range 973 K to 1423 K (700 °C to 1150 °C). The overall volatilization reaction study was carried out using a thermogravimetric analysis technique under various gas flow rates. The results indicated that in an inert atmosphere, stibnite can be volatilized most efficiently as Sb₂S₃(g) with a linear rate up to about 1173 K (900 °C). At temperatures above 1223 K (950 °C), stibnite decomposes to antimony and sulfur gas, impairing the antimony volatilization. For linear behavior in nitrogen gas, kinetic constants were determined, and an activation energy of 134 kJ/mol was calculated for the volatilization reaction. However, in the presence of oxygen, antimony can be volatilized efficiently as valentinite (Sb₂O₃) at low oxygen concentrations (approximately 1 to 5 pct) at approximately 1173 K to 1223 K (900 °C to 950 °C); otherwise, at higher partial pressures of oxygen, the volatilization of antimony is limited by the formation of nonvolatile cervantite (SbO₂). In highly oxidizing atmospheres, a high vaporization of antimony could be achieved only at temperatures higher than 1423 K (1150 °C) where cervantite becomes unstable and decomposes into SbO(g) and 0.5O₂(g).