Liquid-liquid extraction of tungsten(VI) from hydrochloric acid solutions by neutral organophosphorus compounds and high molecular weight amines

Abstract

The extraction of tungsten(VI) from hydrochloric acid solutions by neutral organophosphorus compounds (tributyl phosphate, TBP, and trioctyl phosphine oxide, TOPO), and high molecular weight amines (trioctylamine, TOA, R 3N, and trioctylmethylammonium chloride, TOMAC, R 3R′NCl) in benzene was investigated in the presence of tartaric acid under various conditions. As a result, it was found that the extraction efficiency for tungsten(VI) of TBP, TOPO, TOA and TOMAC is in the order TOPO ⪢ TOMAC > TOA > TBP. The extraction efficiencies are lowered by increasing the amount of tartaric acid, although the presence of tartaric acid prevents the precipitation of tungsten salts. The distribution coefficients for TBP, TOPO, TOA and TOMAC rise steeply as the aqueous acidity is increased to a maximum at initial hydrochloric acid concentrations of 9–9.5, 6–6.5, 7–8 and 8 mol dm −3, respectively, and then falls at higher acidity. Based on the above, the equilibrium equations for the extraction of tungsten(VI) from hydrochloric acid solutions by TBP, TOPO, TOA and TOMAC are proposed as follows: WO 2Cl 2(a) + 2TBP(o) ⇌ WO 2Cl 2·2TBP(o) WO 2Cl 2(a) + 2TOPO(o) ⇌ WO 2Cl 2·2TOPO(o) WO 2Cl 2(a) + R 3NHCl(o) ⇌ R 3NHWO 2Cl 3(o) and: WO 2Cl 3(a) + R 3R′NCl(o) ⇌ R 3R′NWO 2Cl 3(o) + Cl −(a) where (a) and (o) represent aqueous and organic phases, respectively. These equations were confirmed by infrared spectra.