Extraction of sulphuric acid by methyl diphenyl phosphate and tributyl phosphate

The extraction equilibria in the sulphuric acid–methyl diphenyl phosphate–water and sulphuric acid–tributyl phosphate–water systems were investigated. The activities of methyl diphenyi phosphate and tributyl phosphate were calculated in the range of aqueous 0–10M-H2SO4, with the aid of the Gibbs–Duhem relationship. The experimental data found are consistent with the formation of the [H(H2O)3(MePh2PO4)4+][HSO4–] complex with the equilibrium constant K= 2 × 10–3(mol/kg MePh2PO4)–1. At higher acid concentrations complete miscibility of MePh2PO4and H2SO4 is observed. At low concentrations of H2SO4, the acid is extracted by tributyl phosphate in the form of H2SO4(H2O)6(Bu3PO4)3 with K= 20 (mol/kg Bu3Po4)–3. Some summarizing remarks on the extraction of HNO3, HCl, and H2SO4 by MePh2PO4 and Bu3PO4 are also given.