Effective separation of V(IV) and Fe(III) from sulfuric acid solution by solvent extraction with P507 and N235

A selective and highly effective method is proposed for the extraction and separation of V(IV) and Fe(III) using the trioctyl tertiary amine (N235) and 2-ethylhexyl hydrogen-2-ethylhexylphosphonate (P507). Various solvent extractants for extracting and separating V(IV) and Fe(III) have been studied; P507 and N235 appear to be the most active solvent extractants offering high extraction efficiency and separation factor. The effect of pH, composition and concentration of extractant mixture on the extraction efficiency and separation factor was investigated using the general conditions of 1:1 (v/v) organic to aqueous ratio and 0.2 g/L and 0.5 g/L of V(IV) and Fe(III), respectively. Results showed that the maximum separation factor was 31, and the extraction efficiencies of Fe(III) and V(IV) were 89.4% and 15.3%, respectively, under the conditions of initial solution pH of 1.2, VP507:VN235 of 1:2 and total extractant concentration of 30% (v/v). The hydrogen bond (N-H+···O=P) between P507 and N235 was generated upon mixing, which produced the P507 monomer as indicated by the slope analysis, software simulation, and Fourier transform infrared (FT-IR) spectral analysis. The monomer of P507 can heighten the extraction efficiency, as well as effectively weaken the stability of vanadium containing extraction complex. In addition, the extraction complexes [2(R3NH···OP(O)R2)VO]2+ and [3(R3NH···OP(O)R2)Fe]3+ were formed by a cation exchange process. The mixed extraction system extracted and separated V(IV) and Fe(III) more effectively than that by pure P507 or N235.