Abstract <p>The direct return of copper smelting and refining slag (CRS) to the furnace poses a challenge, as it can negatively impact the productivity and final quality of copper products; pyrolusite has also not been fully utilized owing to its high cost of reduction and significant associated pollution. To improve the situation, pyrolusite and CRS were separately taken as the oxidizing and reducing agents to achieve coleaching and clean, efficient recycling of valuable metals in the two materials under atmospheric pressure acid-leaching conditions. The thermodynamic database in HSC Chemistry software was used for computation and modeling of Cu–H₂O, Mn–H₂O, and Cu–Mn–H₂O systems and the corresponding potential–pH (<i>E</i>–pH) diagrams were plotted. Thermodynamic analysis shows that the solution activity and temperature significantly affect the thermodynamic behavior of ions. Enhancing ionic activity allows the stabilizing zones of Cu²⁺ and Mn²⁺ to shift towards low pH values; while the temperature rise significantly shrinks the costabilizing zone of the two, with greater shrinkage of the stabilizing zone of Cu²⁺, indicative of better dissolution stability of Mn²⁺ at high temperatures. Thermodynamic analysis provides theoretical guidance for the selective leaching and separation in Cu and manganese (Mn) hydrometallurgy. The results of subsequent leaching experiments provide valid evidence for the reliability of <i>E</i>–pH diagrams plotted using thermodynamic prediction.</p> Graphical Abstract <p></p>