Elemental and mineralogical composition of metal-bearing neutralisation sludges, and zinc speciation – A review

Zinc (Zn) in sludges from neutralisation of acidic emissions is a potential environmental pollutant and an element interest for recovery. Findings regarding the elemental mineralogical composition such wastes were aggregated literature examined together better understanding management options, with focus on Zn. Zn concentrations ranged 0.006%–22% 46 acid mine drainage sludges, 0.009%–43% 72 metal-finishing 0.024%–11.5% 32 pyrometallurgical 1.71–55.7% 14 production sludges. The main characterization technique was X-ray diffraction, which found dominant minerals to be calcite, gypsum, quartz, iron oxides, but could not identify considerable proportions amorphous phases. More than 60 mineral phases observed. Crystalline compounds identified included hydroxides, sulfates, sulfides, metallic Zn; spinel, olivine carbonate dominated may also present crystalline low concentration, solid solution, and/or phases, characterised more detail using other techniques. Overall, it concluded that occurs high includes have mobility. recovery seems feasible would enable disposal less harmful residual.