Extraction of hydrochloric acid with binary mixtures of tertiary amine and organophosphorus acid and analysis of the interaction between the constituents of these mixtures

•Extraction of HCl by binary mixture of amine and acidic extractant was investigated.•The interaction between different acidic extractants and amine was discussed.•Acid extraction decreased with increasing the acidity of acidic extractant.•Stronger acidic extractant forms an amine salt with tertiary amine.•Mixture containing weak acidic extractant performed weak interaction.

Binary mixtures of tertiary amine and acidic extractant showed synergism on the extraction of metals from a weak acid solution but there is uncertainty in identifying the solvent extraction reaction. The nature of interaction between the extractants in the binary mixture affects synergism in extraction reaction. In order to correlate the interaction with the physical properties of each extractant in the binary mixture, extraction of HCl from dilute solution in the absence/presence of rare earth elements (REEs) has been investigated. The extraction order of HCl and REEs was: Cyanex 272 + Alamine 336 > PC88A + Alamine 336 > D2EHPA > Alamine 336. The interaction between strong acidic extractant (D2EHPA) and Alamine 336 was strong enough to form an amine salt which took part in the reaction. In the binary mixture of weak acidic extractant (Cyanex 272 and PC88A) and Alamine 336, each extractant took part in the reaction independently.