Liquid-Liquid Extraction of Vanadium(IV) with Trioctylamine from Aqueous Oxalic Acid Solution

Abstract

Extraction behavior of vanadium (IV) from aqueous oxalic acid solution with trioctylamine (TOA) in benzene was investigated to determine the composition of a complex involved in the extraction. The stoichiometry of the complex was determined by either the mole ratio method, the continuous variation method and the slope ratio method. Mole ratios of [Oxalate/V(IV)], [TOA/V(IV)] and [Oxalate/TOA] in the organic phase were found to be 2.0, 2.0 and 1.0, respectively, at a constant mole ratio 2.3 for [Oxalate/V(IV)] in the aqueous phase. The effect of hydrogen ion concentration on the distribution ratio (D) of vanadium (IV) was also examined. A slope of the plots of log D vs. pH of the aqueous phase was about -2.0 at the equilibrium. These results suggest that the oxalato-vanadium (IV) species is associated with two molecules of R₃NH⁺. With respect to the effect of TOA concentration, the plots of log D vs. log[R₃N]_(o) yield a slope of about 2.0. Based on these observations we come to a conclusion that the extracted vanadium (IV) species in the organic phase predominantry consists of (R₃NH)₂VO(C₂O₄)₂.