Liquid-liquid extraction of titanium(IV) from hydrochloric acid solutions by 2-ethylhexyl 2-ethylhexyl-phosphonic acid

The extraction of titanium(IV) from hydrochloric acid solutions by 2-ethylhexyl 2-ethylhexyl phosphonic acid (EHEHPA) in kerosene has been investigated under different conditions. The organic extracts were examined by infrared spectrophotometry. From the results, it is found that the extraction of titanium(IV) at low aqueous acidity ([HCl] less than or equal to 2 mol dm(-3)) is governed by a cation-exchange reaction and at higher aqueous acidity ([HCl] greater than or equal to 2 mol dm(-3)) by a solvating reaction. At low acidity, a monomeric species is formed when the EHEHPA is present in excess, while the extraction at higher titanium concentration proceeds in a reaction involving the formation of a polymeric species. From the extraction study under non-equilibrium conditions, it is confirmed that the extraction at low aqueous acidity is governed by an S(N)1 mechanism.