Mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes from stone coal

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Rare Met. (2013) 32(1):57–62 DOI 10.1007/s12598-013-0013-5

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Mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes from stone coal Fei Wang, Yi-Min Zhang*, Jing Huang, Tao Liu, Yi Wang, Xiao Yang, Jie Zhao

Received: 22 February 2012 / Revised: 11 June 2012 / Accepted: 15 June 2012 / Published online: 21 February 2013 Ó The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2013

Abstract The mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes were researched by comparing the blank extraction with the extraction with calcium fluoride as aid-leaching reagent. The leaching experiments were carried out under the conditions of 95 °C, 6 h, 1.5 mlg-1, 15 vol % H2SO4, and 5 % calcium fluoride (mass ratio of CaF2 to stone coal). The concentrations of hydrogen ion were adjusted from initial 1.82 and 4.79 molL-1 to the pH of 1.80 ± 0.05 by 200 gL-1 lime milk, respectively. The solvent extraction experiments were carried out under the organic phase using 15 vol% D2EHPA, 5 vol% TBP, and 80 vol% sulfonated kerosene and O/A phase ratio of 1/4. The leaching rate of vanadium and six-stage countercurrent solvent extraction rate of vanadium can be remarkably improved from 66.71 to 92.97 % and 81.15 to 98.81 %, respectively, when calcium fluoride was added as aid-leaching reagent. In the leaching process, fluorine can enhance the breakage of the structure of vanadium-bearing minerals. Meanwhile, fluoride ion can combine with iron ion to generate acid-insoluble iron fluoride hydrate (Fe2F57H2O) and consume all ferric ions and a portion of ferrous ions. In adjusting pH value process, the massive impurities are decreased to form KAlSO4 and FeAlF5. In solvent extraction process, fluorine can prevent the formation of ferric hydroxide colloids and eliminate the formed unstable ferric hydroxide colloids and the silicon-containing colloids to promote the sufficient contact between the aqueous phase and the organic phase and the sufficient reaction.

F. Wang, Y.-M. Zhang*, J. Huang, T. Liu, Y. Wang, X. Yang, J. Zhao College of Resources and Environmental Engineering, Wuhan University of Science and Technology, Wuhan 430081, China e-mail: [email protected]; [email protected]

Keywords Vanadium; Stone coal; Aid-leaching reagent; Calcium fluoride; Mechanisms

1 Introduction Vanadium is an important byproduct that is used almost exclusively in ferrous and nonferrous alloys due to its physical properties such as high tensile strength, hardness, and fatigue resistance [1]. In China, the gross reserves of vanadium in stone coal, which is an important vanadiumbearing resource and is also called black shale, are 118 million tons in terms of V2O5, and this accounts for more than 87 % of the domestic reserves of vanadium [2]. However, the amount of V2O5 extracted from stone coal only accounts for 30–40 % of total V2O5 output of China in 2010, which is not commensurate with the reserves of vanadium in stone coal in China. Hence, th

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