Separation of aluminium(III) and gallium(III) by extraction from alkaline solutions with trioctylmethylammonium chloride and tartaric acid

Abstract

The separation of trivalent aluminium and gallium by extraction from sodium hydroxide solutions in the presence of tartrate ion was investigated using trioctylmethylammonium chloride (TOMAC). When the simultaneous extraction of aluminium and gallium was carried out from alkaline solutions containing tartrate at a molar concentration ratio of [Tar^2-]/([Al]+[Ga])=8, the separation factor(S_f) increased with aqueous pH, but at [Tar^2-]/([Al]+[Ga])≤5 it decreased with increase in aqueous pH. The distribution ratios of aluminium in the simultaneous extraction exceeded that in the individual extraction of aluminium while for gallium, these ratios decreased. This enhancement in selectivity for aluminium may arise from an exchange reaction between an aluminium species in an aqueous phase and an extracted gallium in an organic phase. The separation factor (Y=S_f) is related to the molar concentration ratio of aluminium and gallium (X=[Al]/[Ga]) as Y=A exp{-B×(X-9.38)²}+C, where A, B and C are variables that vary according to aqueous pH, and were determined by the least squares method.