Separation and recovery of vanadium and iron from oxalic-acid-based shale leachate by coextraction and stepwise stripping

Abstract

Iron is the main element that affects the purification and enrichment of vanadium solutions. In traditional solvent extraction, only the vanadium is recovered and the iron is lost. Thus, the separation and recovery of vanadium and iron from an oxalic-acid-based shale leachate by coextraction and stepwise stripping was investigated. The results showed that vanadium and iron were selectively separated and recovered by coextraction and stepwise stripping. In the coextraction, 98.60% and 99.64% of the vanadium and iron, respectively, were coextracted after six-stage countercurrent extraction using Aliquat 336. The coextraction mechanism was determined to be an anion exchange reaction between the anionic complexes of vanadium and iron and Aliquat 336. In the selective stripping of vanadium, 99.35% of the vanadium and only 0.32% of the iron were stripped after four-stage countercurrent stripping using HCl, and the vanadium-to-iron separation factor was as high as 47956. The selective stripping mechanism was that the anionic complexes of iron and oxalate were transformed into [FeCl4]– in HCl solution, and the [FeCl4]– was extracted again by Aliquat 336. In the stripping of iron, 99.62% of the iron was stripped by NaOH, forming a Fe(OH)3 precipitate with a purity of 98.5%. Compared to direct chemical precipitation and traditional solvent extraction, this process has fewer steps and is more efficient. Furthermore, vanadium and iron can be separated and recovered simultaneously, and the comprehensive utilization of resources is improved.