Studies on the System Hydrochloric Acid-Water-Tri-n-Butyl Phosphate

Abstract

This study is intended to determine the species formed in the heterogeneous equilibrium between aqueous hydrochloric acid and tributyl phosphate and to clarify the mechanism of extraction. In addition to the conventional distribution measurement of hydrochloric acid and water, physico-chemical measurements of volume-change, density and viscosity were carried out with the equilibrated organic phases. Infra-red absorption spectra were also measured. It was found that the major extracting species is [TBP·H₂O] at the equilibrated acid concentration in aqueous phase below 2.0M. Above 2.0M, two other species were found to exist as a result of solute-solvent interactions in the system studied ; the one formed at lower acid concentration has the general formula [(TBP)₂·H₃O⁺·(y+1)H₂O···Cl⁻] (y was determined as 3.5) and the another formed at higher acid concentration has the formula [TBP·H₃O⁺·2H₂O···Cl⁻]. With Redlich-Kister equations on the equilibrium distribution in two components system, the activities and activity coefficients of two species [TBP·H₂O] and [(TBP)2·H₃O|++·4.5(H₂O)···C1⁻] and the equilibrium constant of the two species in organic phase at lower acid concentration were determined.