The extraction of mineral acids by the phosphine oxide Cyanex 923

The distribution equilibria of mineral acids: H2SO4, H3PO4, HCl, HClO4 and HNO3 between aqueous solutions and organic solutions of the phosphine oxide Cyanex 923 in toluene or decane are described. Partition studies have shown that the organic diluent only slightly influences the acid extraction. The extraction mechanism can be related to the solvation of the acid and formation of the L . H(m)(+)X(m-) (m = 1, 2, or 3) species in the organic phase, where L is the extractant: only in the case of initial high HNO3 concentrations is the formation of the L .(HNO3)(2) species apparent in this phase. The effect of temperature on the acid extraction is also evaluated.