Efficient extraction and separation of vanadium and chromium in high chromium vanadium slag by sodium salt roasting-(NH4)2SO4 leaching

Abstract

A novelty process based on sodium salt roasting-(NH4)2SO4 leaching was proposed to extract vanadium and chromium in high chromium vanadium slag (HCVS). V2O5 and Cr2O3 was then prepared. The effects of roasting and leaching conditions on vanadium and chromium extraction behavior were studied systematically and completely. Vanadium precipitation conditions and chromium reduction conditions were optimized further. 94.6% vanadium and 96.5% chromium were extracted when HCVS and Na2CO3 were mixed in the molar ratio of n(Na2CO3)/n(V2O3+Cr2O3) of 2.5, then leached in 30g/L (NH4)2SO4 solution. 94.8% vanadium was precipitated as ammonium polyvanadate (APV) just by adjusting the leaching liquid pH at 4.5, almost all chromium was remained in liquid, achieving the efficient separation of vanadium and chromium. Chromium was then recovered by reduction and precipitation. More than 99% chromium was reduced when Na2S2O5 was added in m(Na2S2O5)/m[Cr(VI)] above 3. By roasting the deposits of vanadium and chromium respectively, 91.49% V2O5 and 89.89% Cr2O3 were obtained. The supernatant after vanadium and chromium extraction containing NH4+ could be recycled as the new leaching medium with some new (NH4)2SO4 added, which greatly reduced the discharge of ammonia-nitrogen wastewater and made the whole process more environmentally friendly.