Comparison of the efficiency of metal recovery from wet- and dry-discharged municipal solid waste incineration bottom ash by air table sorting and milling

Abstract

Separating high-density fractions from municipal solid waste incineration bottom ash (BA) is a promising approach for collecting metal resources and harmful elements. Herein, the efficiency of the recovery of metals (Cu, Zn, Au, Ag, and Pb) in the high-density fractions of two air-dried BAs discharged from wet-based systems (WBA), was compared with that of two BAs discharged from dry-based systems (DBA). WBAs and DBAs (<8 mm) were sorted using sieving, magnetic separation, milling, and air table sorting techniques. Newton’s separation efficiency was used to evaluate three scenarios that combined various sorting processes. WBA contained high-density fractions (D1, 2.73–3.63 g/cm3) with a density similar to that of D1 in DBA (2.68–3.67 g/cm3), but the surface of the particles was covered by more minerals. When D1, and the metal particles were recovered after the milling of the low-density fractions, the overall separation efficiency in WBA (0.30–0.40) was lower than that in DBA (0.49) because of the lower separation efficiency for Zn and Pb compared to that for the other target metals. In contrast, no significant difference was recorded in the separation efficiency for Cu, Au, and Ag between WBA and DBA. D1 (18000–132000 mg-Cu/kg) and metal particles (29900–199800 mg-Cu/kg) in both WBA and DBA recorded abundant Cu contents. Moreover, the Au content in some D1 was similar to that found in natural ores. The elemental contents and separation efficiency results indicated that D1 and metal particles should be collected from both WBA and DBA.