Efficient recovery of valuable metals from electroplating sludge smelting soot via a combined alkali roasting and acid-free aluminum salts leaching methods

Abstract

Electroplating sludge smelting soot (ESSS), contains high-grade value metals (such as Zn, Sn, Pb, precious metals Au and Pt) and large amounts of harmful elements Br and S, which could potentially cause valuable resources wastage and environmental pollution, therefore requires responsible recycling. An efficient and eco-friendly process for the cascade recovery of Zn, Sn, Pb, and precious metals Au and Pt from ESSS was proposed, combining NaOH roasting and acid-free aluminum salts leaching. Optimal NaOH roasting conditions achieved high extraction efficiencies for Zn, Sn, and Pb, which were then separated via water leaching. A novel Al(NO₃)₃ + AlCl₃ leaching system was developed to recover Au and Pt from the enriched residue. By optimizing the NaOH roasting conditions and the Al(NO₃)₃ + AlCl₃ leaching conditions, the decomposition and conversion of 99.91 % Zn, 99.56 % Sn, and 98.72 % Pb in ESSS were achieved, simultaneously accomplishing the leaching of 87.89 % Au and 100 % Pt. Mechanisms of NaOH roasting and Al(NO₃)₃ + AlCl₃ leaching were elucidated using XRD, SEM, ICP, XRF, and DFT calculations. Leaching kinetics of Au and Pt were also studied. Finally, Au and Pt were efficiently recovered from the leaching solution by lead powder replacement. This study provides a feasible and promising solution for the green and efficient recovery of valuable metals from ESSS.