Hydrothermal sulfidation and floatation treatment of heavy-metal-containing sludge for recovery and stabilization

► Hydrothermal sulfidation-floatation was applied to treat the heavy-metal-containing sludge. ► 72.67% of Pb and 88.74% of Zn in sludge can be converted to PbS and ZnS. ► Synthetic ZnS had a lower selectively floatability than PbS and CuS. ► The recovery of ZnS can increased to 72.8% after crystal modification in hydrothermal condition. ► After sulfidation-floatation treatment, the heavy metal remaining in the tailings was stable.