Desulfurization from Bauxite Water Slurry (BWS) Electrolysis
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GENERALLY speaking, high-sulfur bauxite accounted for about 11 pct of bauxite resources in China,[1] and the sulfur content of which is more than 0.7 pct.[2] Due to the high aluminum–silicon ratio, high-sulfur bauxite was fit for alumina production process using Bayer’s process after desulfurization.[3] And the application of high-sulfur bauxite will relieve the pressure of increased costs of high-grade bauxite. But there are still many problems in the application of high-sulfur bauxite, such as the corrosion of equipment, the increase of alkali consumption, and the decline of alumina dissolution ratio.[4] It was noted that lots of sulfur-containing compounds resulted in scab during the mother solution flash process, which influenced the heat transfer efficiency, increasing the cost of alumina production.[5] At present, there are some methods for the use of high-sulfur bauxite as follows. The sulfur and Al phases in bauxite were separated by flotation method, achieving solid–solid separation.[5] The sulfur phase was oxidized into SO2 through the pre-oxidation roasting, realizing the gas–solid separation.[6] S2 was oxidized into SO42 during the leaching process, which was fixed in the red mud by adding sulfur-fixing compounds, such as lime or barium salt desulfurization, realizing the liquid–solid XUZHONG GONG and MINGYONG WANG, Associate Professors, LAN GE, SIYUAN ZHUANG, and LIHUI REN, Masters, ZHI WANG, Professor, and YUHUA WANG, Master, Engineer, are with the National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P.R. China. Contact e-mail: [email protected] Manuscript submitted February 13, 2015. Article published online September 18, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
separation. However, these methods all have limitations, such as low desulfurization efficiency, high cost, and high risk for environmental pollution.[7] Fossil fuel electrolysis desulfurization had some advantages, such as mild condition and high desulfurization ratio.[8,9] The inorganic and organic sulfur was removed together, and inorganic sulfur removal ratio could reach 100 pct under 373 K (100 C).[10,11] In general, electrolysis desulfurization is a kind of sulfur-containing compound oxidation process using oxidant from water electrolysis, during which SO42 was produced and then the solid ore was separated, realizing the removal of sulfur. In the coal water slurry electrolysis process, due to the formation of organic compounds,[12,13] electrode surface was covered, resulting in the electrode deactivation. However, there was no such problem for the inorganic mineral electrolysis. The sulfur-containing phase in high-sulfur bauxite was mainly pyrite, which was about 94 to 96 pct of the total sulfur content,[14] and it could be removed more easily by electrolysis. In addition, due to high conductivity of leaching solution, the bauxite dissolution environment was more suita
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