Extraction of phosphoric acid with long-chain tertiary amines—II: Extraction from potassium hydrogen phosphate and various acid solutions

Abstract

The extraction of phosphoric acid from its aqueous solutions containing various proportions of potassium hydrogen phosphates with the long-chain tertiary amine Alamine 336 in toluene was studied at 25°C. Also measured was the exchange of phosphate anions with the anions of strong mineral acids (chloride, bromide and sulfate) between aqueous acid solutions and those of Alamine 336 in toluene at 25 and 40°C. The extraction of phosphoric acid was previously found to increase with the activity of undissociated acid a H 3PO 4 . It therefore decreased on replacement of H 3PO 4 with KH 2PO 4 due to reversal of the acid dissociation and to formation of the dimeric species H 5P 2O 8 − in the aqueous phase, and conforms to the previously proposed model with the inclusion of this aqueous species. The relative affinities of the anions for the tertiary substituted ammonium cation increase in the order: H 2PO 4 −<HSO 4 −<Cl −<Br −.