Conversion of Sulfur by Wet Oxidation in the Bayer Process
- PDF / 832,396 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 72 Downloads / 186 Views
INTRODUCTION
ALUMINA is the raw material used in aluminum reduction, mostly produced by the Bayer process. Throughout this process, bauxite (as well as any other bauxite components) is dissolved in alkali solution at certain temperatures under pressure. The solution is clarified by filtering off the solid impurities, then Al(OH)3 is produced after precipitating the supersaturated sodium aluminate solution. Next, Al(OH)3 is calcined at 1253 K (980 °C) and decomposed to alumina. Alongside the rapid development of the alumina industry, bauxite resources are growing scarcer every day. Trends throughout recent years suggest that highsulfur bauxite will soon dominate alumina production practices, which poses a serious problem. China possesses over 800 million tons of diasporic high-sulfur bauxite, mainly in Guizhou, Chongqing, and Yuxi provinces; bauxite that is highly valuable, provided that effective methods of removing its sulfur are made available. The most common sulfur-bearing minerals in highsulfur bauxite are pyrite and its isomers (marcasite and melnikovite) and sulfates such as CaSO4.[1] During the Bayer process of alumina production, the sulfur in highsulfur bauxite first goes into the solution in the form of S2, and then the S2 is gradually oxidized into various forms of S2O32, SO32, and SO42. The most notable ZHANWEI LIU, Associate Professor, and WENHUI MA, Professor, are with the Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, P.R. China, and also with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province/The National Engineering Laboratory for Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, Yunnan, P.R. China. Contact e-mail: [email protected] and [email protected] WANGXING LI and ZHONGLIN YIN, Professors, and GUOBAO WU, Senior Engineer, are with the Zhengzhou Research Institute of CHALCO, Zhengzhou 450041, Henan, P.R. China. Manuscript submitted January 3, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
negative effects of sulfur’s presence in the Bayer process are as follows:[2] (1) Na2S2O3 can react with Fe to form Na2S, Na2SO3, and Fe(OH)2, which destroy the oxide film of steel and accelerate the corrosion of equipment, posing a rather significant safety risk. (2) Na2S can react with Fe2O3, and Na2S2 can react with Fe(OH)2 to form Na2[FeS2(OH)2]Æ2H2O, and Na2[FeS2(OH)2]Æ2H2O, which is much more soluble in sodium aluminate solution. This increases the iron content in alumina products, deteriorating the quality of the products. (3) When the content of Na2SO4 in spent liquor is high enough, it can precipitate in the form of Na2CO3Æ2Na2SO4; the double salt can then scale the inside digester and evaporator, creating problems during evaporation which impact industrial production. (4) The sulfur in the Bayer process converts to Na2SO4 eventually, increasing alkali consumption. Relatively few research projects have investigated the conversion of sulfur in th
Data Loading...
