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

Abstract

It is intended in this study on the system H₂SO₄-H₂O-TBP to determine the species formed in the equilibrated organic phase and to clarify the extracting mechanism of aqueous sulphuric acid into organic phase. As in the previous report published in this Memoir, physico-chemical measurements of volumeswelling, density, viscosity and electrical conductivity were carried out with the equlibrated organic phase in addition to the conventional distribution measurement of sulphuric acid and water. It was found that the extracting species is [TBP·Hᴏ] at the equilibrated acid concentration in aqueos phase below 2.0M and that three other species were found to exist above 2.0M ; the one formed at lower acid concentration has the general formula [(TBP)₃·H₃O⁺(x+2)H₂O···HSO₄⁻], (x was determined as 2.5), the one formed at medium acid concentration is [TBP·H₃O+(x+2y/3)H₂O···HSO₄-] (y was determined as 0.25), and the one formed at higher acid concentration is [TBP·2{H₃O+(x+5y-3/6)H₂O···HSO₄}] They dissociate partly. The activities and activity coefficients of the two species [TBP·H₂O] and [(TBP)₃·H₃O⁺4.5H₂O···HSO₄⁻] stable at lower acid concentration and the equilibrium constant between them were determined with Redlich-Kister equations.