Abstract

This work develops a thermodynamic model for ionic speciation and volumetric properties of the ternary system CuCl2 – HCl – H2O from 273.15 to 373.15 K and at 101.3 kPa, a system relevant to chalcopyrite leaching in chloride media and hydrogen production via the copper–chlorine thermochemical cycle. The Pitzer equations were used to estimate water activities, CuCl2·2H2O(cr) solubilities, and densities, calibrated using published experimental data. The speciation model includes Cu2+, H+, CuCl+, Cl–, CuCl20, and HCl0, showing reasonable species distribution results as a function of temperature and total concentration. Based on volume of mixing calculations at 298.15 K, CuCl2 acts as a structure breaker of water, while HCl behaves as a structure maker. New Pitzer parameters and the solubility product constant of CuCl2·2H2O(cr) are provided as temperature–dependent functions. The model demonstrates high accuracy in reproducing experimental data and offers insights into the physicochemical behavior of concentrated CuCl2 + HCl + H2O solutions. © 2025 Elsevier Ltd