Separation and recovery of vanadium and aluminum from oxalic acid leachate of shale by solvent extraction with Aliquat 336

The solvent extraction of vanadium has been widely studied in inorganic acid systems; but less in organic acid systems. In this study, the separation and recovery of vanadium and aluminum from oxalic acid leachate of shale by solvent extraction with Aliquat 336 was investigated. The results indicated that 99.06% of vanadium was extracted and only 7.95% of aluminum was co-extracted in a counter-current extraction comprising five stages under the optimal conditions; the separation factor (beta) of vanadium and aluminum was 1221. 99.32% of vanadium stripped by 8 mol/L HCl in a counter-current stripping comprising four stages, and V2O5 with a purity of 98.4% was obtained by ammonium precipitation method from the stripped vanadium solution. The speciation and extraction mechanism of vanadium were revealed. Vanadium mainly existed as a complex anion, VO (C2O4)(2)(2-), and aluminum mainly existed in the forms of Al(C2O4)(2)(-) and Al(C2O4)(3)(3-) in the oxalic acid leachate of shale. The extraction mechanism of vanadium by Aliquat 336 was an anionic exchange mechanism, and the structure of the extractable complex for vanadium could be determined as [(R4N)(2)center dot VO(C2O4)(2)]. A process flowsheet for the separation and recovery of vanadium and aluminum from the oxalic acid leachate of shale using solvent extraction was developed, which has the advantages of rapid extraction speed and without adjusting the initial pH of solution.