Separation and recovery of iron impurities from a complex oxalic acid solution containing vanadium by K3Fe(C2O4)3•3H2O crystallization

Vanadium and iron have been effectively separated from the acid leachate of vanadium-bearing shale by solvent extraction or ion exchange; however, in these methods, the iron was not recovered, and the comprehensive utilization rates of the resources were low. In this paper, the recovery of iron impurities from a complex oxalic acid solution containing vanadium via the crystallization of K3Fe(C2O4)(3)center dot 3H(2)O was investigated. Using the optimum conditions, 90.7% of the Fe was recovered, and only 1.4% of the V and 5.0% of the Al were lost. The concentration of Fe decreased from 5366 mg/L before crystallization to 500 mg/L after crystallization. The crystallized product was then further purified by recrystallization to obtain K3Fe(C2O4)(3)center dot 3H(2)O in 99.0% purity, which was characterized using FT-IR, XRD, and SEM. Based on the speciation of vanadium and iron in the oxalic acid system, the mechanism by which the iron impurities were recovered was determined. The mechanism consisted of five main steps: complexation, oxidization, coordination, nucleation, and crystal growth. The recovery of iron impurities from a complex oxalic acid solution containing vanadium via the crystallization of K3Fe (C2O4)(3)center dot 3H(2)O is a novel and efficient method, and this process provides a new direction for the comprehensive utilization of vanadium resources.