Study of the Dissolution Behavior of Muscovite in Stone Coal by Oxygen Pressure Acid Leaching
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INTRODUCTION
STONE coal is a particular vanadium-bearing siliceous shale in China, which mainly formed before the middle Devonian Epoch. Stone coal contains inorganic and organic components, and the content of inorganic is much higher than that of organic materials, which is similar to coal.[1,2] The grade of V2O5 is usually lower than 1 pct and the components are complex. The vanadium in stone coal mainly exists of the crystal lattice of muscovite and illite where V(III) replaces Al(III) as isomorphism.[3,4] For extracting vanadium from stone coal, it is essential to break down the structure of muscovite and illite in stone coal. At present, there are two main categories: (1) transforming V(III) into V(IV) or V(V) via roasting; and (2) directly disintegrating the crystal lattice of muscovite and illite via leaching.[5–7] In recent years, the direct acid leaching process has been getting increased attention, which has resulted in the development of the atmospheric pressure acid leaching process[8–10] and the oxygen pressure acid leaching process.[11–13] The atmospheric pressure acid leaching process usually needs to add fluoride (like HF, NAN-NAN XUE, Doctoral Candidate, and TAO LIU and JING HUANG, Associate Professors, are with the School of Resource and Environmental Engineering, Wuhan University of Science and Technology, Wuhan 430081, China, and also with the Hubei Provincial Engineering Technology Research Center of High efficient Cleaning Utilization for Shale Vanadium Resource, Wuhan 430081, China. YI-MIN ZHANG, Professor and Dean, is with the School of Resource and Environmental Engineering, Wuhan University of Science and Technology, and also Director with the Hubei Provincial Engineering Technology Research Center of High efficient Cleaning Utilization for Shale Vanadium Resource. Contact e-mail: [email protected] Manuscript submitted February 25, 2015. Article published online December 17, 2015. 694—VOLUME 47B, FEBRUARY 2016
NaF, NH4F, and CaF2) or oxidant (like NaClO and MnO2) to leach vanadium efficiently.[14–16] The oxygen pressure acid leaching process introduces a pressure field to raise temperature and shorten time. It does not produce air pollution brought by the traditional roasting-leaching process, and there is no need to add the fluoride or oxidant during the whole leaching process. Deng et al.[17] found that under the conditions of leaching time of 3 to 4 hours, a temperature of 423 K (150 °C), H2SO4 consumption of 25 to 30 pct, liquid-to-solid ratio of 1.2 mL/g, the particle size less than 0.074 mm, FeSO4 addition of 3 to 5 pct, and oxygen pressure of 1.2 MPa, the vanadium recovery can be more than 92 pct by the method of two-step pressure acid leaching. Fan et al.[18] also demonstrated that with the increase of FeSO4 addition, the recovery of SiO2 was improved in the first leaching stage, but it decreased in the second leaching stage. However, its maximum recovery only attained 0.75 pct. That is, the SiO2 was difficult to leach. Oxygen pressure acid leaching is a process of solid-liquid-gas three-phase
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