Ionic speciation and volumetric properties modeling of the ternary system CuCl2 – HCl – H2O from 273.15 to 373.15 K and at 101.3 kPa using the Pitzer equations

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^–, ${\mathrm{CuCl}}_2^0$, 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.