Separation of iron impurity during vanadium acid leaching from black shale by yavapaiite-precipitating method

During oxygen pressure acid leaching to release vanadium from black shale, a large amount of Fe is also leached, which is detrimental to the following purification and enrichment processes. To suppressed the Fe leaching, this study attempts to clarify the precise conditions for yavapaiite (KFe(SO4)(2)) formation and apply the above-mentioned strategy to oxygen pressure acid leaching process of black shale. When the acid concentration was 10-20 vol%, a maximum Fe precipitation efficiency of approximately 81% could be achieved in the K2SO4 center dot Fe-2(SO4)(3)center dot H2SO4 solution system under the following conditions: temperature, 190 degrees C or higher; Fe3+ concentration, 0.40-0.60 mol/L; potassium to iron molar ratio, 2.0-2.5; time, 4-5 h. X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy analyses showed that yavapaiite could be formed when the H2SO4 concentration and temperature reached 10 vol% and 150 degrees C, respectively. Adjusting the K+ concentration in the leaching solution was demonstrated to an effective method to generate yavapaiite during the oxygen pressure acid leaching for black shale. The migration of Fe can be inferred as pyrite to Fe3+ to krausite/yavapaiite and finally to yavapaiite.