Ultrasonic-Persulfate Synergetic Unlocking the Efficient Extraction of Targeted Zn, In, and Ge in Zinc Slag: From Experimental Evaluation to DFT Study

Zinc smelting dust (ZSD), a hazardous solid waste rich in strategic (In, Ge) and heavy metals (Zn and Pb), is crucial for mitigating environmental risks and alleviating resource constraints through their recovery. To address the bottleneck of low leaching efficiency and unclear mechanisms caused by the isomorphic substitution of In/Ge in sphalerite (ZnS), this study proposes a novel ultrasound-assisted sodium persulfate (Na2S2O8) oxidation leaching (USL) process and reveals its atomic-level enhancement mechanisms through cross-scale experimental and simulation studies. Under optimized conditions (Na2S2O8/ZSD mass ratio of 0.35 g/g, 600 W, 2.0 mol/L H2SO4, liquid-to-solid volume mass ratio of 8:1 mL/g, 80 °C, 40 min), the leaching efficiencies of Zn, In, and Ge reached 99.20, 93.41, and 93.50%, respectively, representing improvements of 7.20–8.52% over conventional processes (91.98, 86.30, and 84.89%). Integrated density functional theory simulations and multiscale characterizations unveiled atomic-scale synergistic mechanisms: coadsorption models of In–Cu and Ge–Cu doped systems exhibited the lowest adsorption energies (−5.63 and −6.15 eV), indicating that the simultaneous action of H2SO4 and oxidants significantly enhances metal leaching. The coadsorption of H2SO4/S2O82– triggered H → S and Zn → O charge transfer, weakening Zn–S bonds on the ZnS(110) surface. This synergy reduced the leaching activation energy from 8.20 to 16.31 kJ/mol to 3.97–7.67 kJ/mol, achieving a reduction of 43.64–60.93%. Ultrasonic cavitation enhanced the process through dual effects: (1) microjet-induced physical destruction of passivation layers (surface roughness Ra increased from 1.66 to 159.00 nm); and (2) localized hotspots driving S2O82– decomposition, promoting sulfur phase evolution (S2–→ S0/SO42–). This work provides an atomic–mesoscopic–macroscopic cross-scale strategy for the green recovery of strategic metals from hazardous solid wastes.