Thermodynamic model for synergistic solvent extraction of mineral acids by tris(2-ethylhexyl)amine and 1-octanol

Abstract

Recovery of excess acid after leaching is essential in circular hydrometallurgical processes, because it reduces reagent consumption and generates less waste. Solvent extraction can be used for acid recovery from aqueous solutions. This study presents a thermodynamic model for the synergistic solvent extraction of H₂SO₄, HCl, and methanesulphonic acid (MSA) using tris(2-ethylhexyl)amine (TEHA) and 1-octanol in n-dodecane. The model is developed using the mixed-solvent electrolyte (MSE) framework of OLI Systems, integrating an extensive set of own experimental data and literature data. It captures both individual and synergistic extraction behaviours and accurately calculates equilibrium properties such as acid distribution, water uptake by the solvent, volume change during extraction, and organic phase mass density at room and elevated temperatures. Validation with H₂SO₄ recovery from NiSO₄ solutions confirms its predictive capabilities for industrially relevant conditions. This work offers a robust tool for designing acid recovery processes through solvent extraction and gives mechanistic insights into the studied extractant systems.