Enhanced leaching and separation of gold and copper from gold-containing copper-based waste

• The theory of ion morphology change in leaching of Au (III), Cu (II) and Ag (I) chlorides was established. • A HCl-NaCl-NaClO 3 system achieved 98.89% Au and 99.33% Cu leaching with negligible Ag dissolution. • Gold leaching follows a chemically controlled Avrami model (Ea=65.85 kJ/mol), while copper leaching is diffusion-controlled (Ea=8.22 kJ/mol). • The chlorination leaching of gold-containing copper-based waste follows the ' multi-step oxidation-catalytic synergy ' mechanism. To address toxic substances and ammonia-nitrogen wastewater from cyanidation/aqua regia-based recovery of gold-bearing copper-based electrical contact scrap, Chlorination-oxidation enhanced leaching was proposed by using an HCl-NaCl-NaClO 3 system in this study. Combined with thermodynamic calculations, optimization of leaching process parameters, and leaching kinetic studies, the mechanisms of the selective leaching of Au and Cu as well as the inhibition of Ag dissolution was clarified, resolving the ambiguities regarding Au-Ag separation in copper-rich systems. Au and Cu leaching efficiencies reach 98.89% and 99.33% with optimized leaching system (3 mol/L HCl + 60 g/L NaCl) at L/S of 50 and 40°C for 5 h, respectively, while Ag is almost not leached due to the formation of a dense AgCl passivation film. Cu leaching is liquid film diffusion-controlled (Ea = 8.22 kJ/mol), and Au leaching follows the Avrami model (Ea = 65.85 kJ/mol) governed by interfacial reactions. Thermodynamic analysis and E-pH diagrams (Au-Cu-Cl- H 2 O, and Au-Ag-Cl- H 2 O) confirm that weakly acidic to acidic conditions (pH = -2 to 5.892) and high potential (E = 0.99075 to 2.0 V) favor stable AuCl 4 - and CuCl 2 . The process follows a "multi-step oxidation-catalytic synergy" mechanism: NaClO 3 reacts with HCl to generate Cl₂, which preferentially oxidizes Cu to CuCl 2 , and Cu 2+ catalyzes AuCl 4 - formation.