Extracting Vanadium over Iron from Direct Acid Leaching Solution of V-bearing Steel Slag by Solvent Extraction with Tertiary Amine TOA

Solvent extraction of direct acid leaching solution of vanadium-bearing steel slag with tertiary amine TOA, was carried out, and the effects of the main factors on extraction of vanadium over iron were investigated. Meanwhile, the structure-activity relationship of TOA and the solution chemical behavior of extracting vanadiumover iron were analyzed. Through a 4-stage countercurrent extraction under the following optimum conditions: TOA concentration of 15 vol.%, initial aqueous phase pH of 1.8~1.9, phase ratio (A/O) of 3, and extraction time of 3 min, the extraction of vanadium over iron was well achieved, and vanadium extraction rate reached 98% whereas iron was barely extracted. N atom of TOA has a lone pair of electrons and can be an electron contributor, TOA acidified by H₂SO₄ to convert to [(C₈H₁₇)₃NH]₂SO₄, can achieve extraction through anion-exchange reaction.Through oxidation by H₂O₂, V(Ⅳ) in aqueous phasewas oxidized to V(Ⅴ). Through neutralization by NH₃·H₂O to increase aqueous phase pH, VO₂⁺ was converted to various forms of anions. When vanadium was in the specific form of [H₂V₁₀O₂₈]^4-, a higher extraction rate could be obtained. Vanadium could exist in form of [H₂V₁₀O₂₈]^4- within a wide pH range of 1.2~2.4. As the pH increased within this pH range, the concentration of [H₂V₁₀O₂₈]^4- and the dissociation of HSO₄^- also increased, which improved extraction rate. However, Fe(III) would be precipitated by hydrolysis at pH > 1.9, which would prevent the two phases from separating and cause a coprecipitation loss of vanadium.When pH < 2.0, Fe (Ⅲ) existed in the form of Fe³⁺ and could not be extracted by TOA, so the purpose of extracting vanadium over iron was realized.