High-Temperature Volatilization Mechanism of Stibnite in Nitrogen-Oxygen Atmospheres
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IN the production of copper by smelting/converting technology, antimony is one of the deleterious elements that undergo vaporization side reactions. It is commonly understood that in the roasting or smelting of copper concentrates, antimony distributes along the various phases in the pyrometallurgical process, and depending on the operating conditions, an important fraction of antimony volatilizes; thus, antimony elimination through the gas phase is viewed as a technique to eliminate this element.[1] Although the pyrometallurgical methods dominate the production of antimony from sulfides, mainly from stibnite (Sb2S3), little has been reported on the rate of oxidation/volatilization of this mineral. Vartiainen et al.[2] conducted a thermodynamics analysis on the vapor pressures of antimony and arsenic in sulfidic concentrates for the conditions of a copper flash smelting furnace. They also studied the behavior of antimony in a laboratory vertical laminar flow furnace using two copper concentrates containing 4.25 pct Sb and 13.8 pct Sb for a residence time of 0.3 seconds. From that study, they concluded that the removal of antimony was a function of the oxygen concentration and a function of the preheating temperature of the reaction gas. The most favorable conditions
RAFAEL PADILLA, Professor, GUSTAVO RAMI´REZ, Student, and MARIA C. RUIZ, Professor, are with the Department of Metallurgical Engineering, University of Concepcio´n, Edmundo Larenas 285, 4070374 Concepcion, Chile. Contact e-mail: rpadilla@ udec.cl Manuscript submitted March 23, 2010. Article published online September 2, 2010. 1284—VOLUME 41B, DECEMBER 2010
for antimony removal were at the highest preheating temperature of 1373 K (1100 °C) and 2 pct O2. They concluded that an adequate model for a flash smelting process should include the oxidation and decomposition kinetics of the impurity minerals and their vaporization. For the oxidation of synthetic Sb2S3, Zivkovic et al.[3] performed a nonisothermal study on the reaction of Sb2S3 in air in the range of 473 K to 1073 K (200 °C to 800 °C) and reported that the oxidation proceeded according to the following: 2Sb2 S3 þ 9O2 ¼ 2Sb2 O3 þ 6SO2 ðgÞ
½1
Sb2 O3 þ 1=2O2 ¼ 2SbO2
½2
Recently, Hua et al.[4] studied the volatilization of Sb2S3 in a steam atmosphere in the range of 923 K to 1123 K (650 °C to 850 °C), and they proposed a complex gas phase reaction mechanism for the vaporization of Sb2S3, concluding that Sb2S3 could be oxidized to Sb2O3 and metallic Sb by water vapor at elevated temperatures when the Sb2O3 and Sb are removed constantly from the gas phase by condensation. In regard to the volatilization of antimony in nitrogen, Komorova et al.[5] studied the vaporization of synthetic Sb2S3 and synthetic sulphosalts ((CuAg)12 Sb4S13, AgSbS3, and CuPbSbS3 among others) with the transportation method. For the vaporization of Sb2S3 in the temperature range 873 K to 1097 K (600 °C to 824 °C), they concluded that the condensate was antimony trisulfide and that evaporation of antimony from sulphosalts occu
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