Extraction of nitric acid and hydrochloric acid by methyl diphenyl phosphate

Abstract

The extraction of HNO₃ and HCl by methyl diphenyl phosphate is compared with the corresponding systems involving tributyl phosphate. The activity of methyl diphenyl phosphate was calculated over the range of aqueous 0–14M-HNO₃ and 0–9M-HCl by use of the Gibbs–Duhem relationship. Nitric acid is extracted primarily in the form of the undissociated complex HNO₃,H₂O,MePh₂PO₄, while the hydrochloric acid complex HCl,2H₂O,2MePh₂PO₄ is partly dissociated in the organic phase. The equilibrium constants for complex formation were estimated to be K= 0·4 (mol/kg MePh₂PO₄)^–1 and 9 × 10^–4 for HNO₃ and HCl, respectively. In both cases the standard reaction entropy is the dominating term in the standard change of free energy ΔG°.