Effect of Mechanical Activation Treatment on the Recovery of Vanadium from Converter Slag
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NADIUM is an important alloying agent in the manufacture of steels and alloys. The attributes of high tensile strength, fatigue resistance, and hardness provide good properties in Ni/V, Cr/V, and Fe/V alloys.[1] The compound, vanadium pentoxide is also used as a catalyst in the production of sulfuric acid and maleic anhydride.[2] The common grade of vanadium is usually less than 2 pct by weight in the host rock, such as phosphate rock, titaniferous magnetite, and uraniferous sandstone. The direct extraction of vanadium from these minerals is uneconomical.[3] Consequently, vanadium is typically recovered as a by-product or co-product of certain processes. For example, vanadium slag is one by-product of the blast furnace–basic oxygen furnace (BF-BOF) process performed on vanadium titaniferous magnetic ores.[2] Commercially, the extraction of vanadium from vanadium slag is typically conducted by sodium salt roasting–water leaching, which entails roasting the
JUNYI XIANG, XUEWEI LV, and CHENGUANG BAI are with the School of Materials Science and Engineering, Chongqing University, No. 174 Shazheng Street, Shapingba District, Chongqing 400044, China. Contact e-mail: [email protected] QINGYUN HUANG is with the School of Materials and Metallurgical Engineering, Chongqing University of Science and Technology, Chongqing 401331, China. Manuscript submitted August 9, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
vanadium slag with sodium salts (NaCl or NaCO3) followed by leaching with water.[4,5] However, this process seriously affects the environment because of the emission of corrosive gases, including HCl, Cl2, and SO2.[6] Calcification roasting–acid leaching is a clean alternative to the conventional sodium salt roasting–water leaching process.[7,8] Unlike sodium roasting–water leaching, vanadium slag roasted with calcium salt (CaO or CaCO3) transforms into the acid-soluble calcium vanadate.[9] However, the calcification roasting process also entails the problems of easy sinter ring formation in the kiln and a relatively low leaching rate under the same roasting processes.[6,10] Therefore, it is desirable to achieve a high vanadium leaching ratio and to minimize the sinter ring problem. In recent decades, many investigations were performed to obtain the optimum conditions for improving the leaching efficiency of vanadium. The formation of acid-soluble calcium vanadate during roasting is the critical in increasing the efficiency of the subsequent leaching process.[9,11] The main roasting parameters are the Ca/V mole ratio, roasting temperature, and holding time. Many studies indicated that the optimal Ca/V mole ratio was approximately 1:1, or the stoichiometric ratio needed to generate Ca2V2O7. Adding either too much or too little calcium can negatively affect the leaching efficiency.[9,12,13] The optimal roasting temperature was in the range of 1073 K to 1473 K (800 C to 1200 C) depending on the natural properties of the slags and the calcium content.[14,15] The leaching parameters, including acidity, type of acid, particle size
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