Thermal treatment of municipal solid waste incineration fly ash and nanofiltration membrane concentrate co-processing: Speciation of chromium and its leachability

The thermal treatment of municipal solid waste incineration fly ash (MSWI FA) has raised serious concerns due to the increasing leaching concentration of Cr, and Cl severely limits the reuse and utilization of MSWI FA. A nanofiltration membrane concentrate (NF-MC) is utilized in this study to leach the MSWI FA to remove Cl and the fate of Cr in the leaching MSWI FA by NF-MC (L-MSWI FA) is investigated. The results showed that Cl in the MSWI FA was effectively removed at a removal rate greater than 95%. After the thermal treatment of the proportion of the MSWI FA based on the L-MSWI FA (P-MSWI FA), it was revealed that Cr primarily as Cr2O3 hexagonally shaped flake-like crystallites, was oxidated first to Cr(VI), and the leaching concentration reached the maximum (1.17±0.05 mg/L) at 800°C. Cr(VI) was then reduced, and the chemical valence of Cr between Cr(III) and Cr(VI) confirmed that the leachability of the Cr-containing materials rose after the thermal treatment. In addition, it was believed that Cr(VI) was reduced when the temperature was greater than 1000°C. The results of this study provide theoretical guidance for controlling the enhancement of Cr leachability during the thermal treatment process.