Silver ion-catalyzed ammonium persulfate oxidation enhances low-temperature sulfuric acid curing and water leaching of valuable metals in copper slag: Experimental and mechanistic analysis

Copper slag (CS) contains high-value metals (Fe, Co, Cu, and Zn), but traditional mineral processing has high energy consumption and poor cost-effectiveness. To tackle such problems, the present research puts forward an innovative method where Ag + -catalyzed ammonium persulfate (APS) oxidation enhances low-temperature H₂SO₄ curing and water leaching of valuable metals in CS. Process mineralogy analysis, thermodynamic evaluation, single-variable experiments, and a range of characterization methods were employed to elucidate the CS features, verify process feasibility, evaluate metal leaching rates, and reveal Ag⁺'s leaching enhancement mechanism. Results show that 96.59 % Fe, 90.36 % Co, 95.12 % Cu, and 94.28 % Zn were leached from CS. Compared with the traditional H 2 SO 4 curing process, their leaching rates increased by 3.85 %, 6.58 %, 19 %, and 6.16 %, respectively. Meanwhile, the curing temperature decreased from 200 °C to 80 °C (120 °C reduction), and H₂SO₄ consumption fell by 10 %. Mechanistic analysis reveals that Ag⁺ enhances leaching through two pathways: First, it catalyzes APS decomposition to generate ·SO₄⁻ with high oxidizing activity. These radicals significantly accelerate the oxidation of sulfide minerals and low-valence iron-based minerals, driving reactions to more thorough completion and promoting formation of more water-soluble metal sulfates. Second, Ag⁺ transforms the cured slag's microstructure from initial dense, smooth state to crisscrossing crack network extending into particle interiors. This evolution not only provides channels for inward diffusion of H 2 SO 4 and APS (facilitating deep oxidation) but also creates favorable conditions for outward migration of water-soluble metal sulfates into the leachate. This method offers a low-energy, sustainable approach for large-scale CS utilization.