Efficient recovery of valuable elements from oxygen-rich alkaline leaching solution of chrome-vanadium slag using selective crystallization separation process

Abstract

A method for separating vanadium (V) and chromium (Cr) was studied to effectively process the alkaline leaching solution (ALS) obtained during the oxygen-rich leaching of V-Cr slag based on the sub-molten salt vanadium chromium co-extraction production process. The cooling crystallization experiments showed that with the conditions of OH^– concentration of 8.75 mol/L, final temperature of 40℃, etc., the yield of vanadate reached over 63 %, indicating that Na₃VO₄ could be separated effectively by cooling crystallization in the low alkalinity region. Na₃VO₄ was further recovered as V₂O₅ product with a purity of 98.58 %. To address the low recovery efficiency of Na₂CrO₄ in previous studies, a novel approach of evaporation concentration combined with KOH addition was proposed. This method utilized double salt reaction crystallization to generate K₃Na(CrO₄)₂ with lower solubility, thereby facilitating efficient separation and recovery of chromium. With the conditions of 16.25 mol/L OH^–, n (KOH)/n (NaOH) = 0.3, etc., the yield of chromate increased from 20 % to over 88 %. K₃Na(CrO₄)₂ was eventually recovered as Cr₂O₃ by reduction precipitation with a purity of 98.67 %. The entire process successfully achieved separation and recovery of vanadium and chromium in the ALS, producing qualified vanadium chromium products with almost no wastewater discharge, providing a new strategy for the resource utilization of the ALS.