Leaching potential of stabilized fly ash from the incineration of municipal solid waste with a new polymer

The presence of toxic metals in municipal solid waste incineration fly ash is of great concern due to their leaching potential in landfills. To prevent groundwater or soil contamination caused by metal leaching from fly ash, recently the Chinese government began to require that the leachate concentrations of toxic metals not only satisfied the GB 16889-2008 criteria prior to landfilling but also introduced a series of measures to monitor the groundwater quality in the landfill site and its adjacent areas (GB/T 18772-2017). The stringent hazardous waste measures for pollution control on landfill sites of municipal solid waste demand the development of more efficient chemical stabilizers. To this end, a novel type of chemical stabilizer, a dithiocarboxylate functionalized polymer (TEM_CSSNa) was fabricated. Its efficiency for stabilizing toxic metals was evaluated at different dosages over a range of pH values. To compare with traditional stabilizers, sodium sulfide (Na₂S) and thiourea (Tu) were also studied. The results showed that TEM_CSSNa-stabilized fly ash could satisfy the criteria at a dosage of only 3%, while those for Na₂S and Tu were around 10%. In addition, this new polymer retained its stabilizing efficiency over a broad pH range. After TEM_CSSNa stabilization treatment, approximately 40-65% of the metals existed in the residual fraction, whereas only 35-55% were converted to the residual fraction using Na₂S and Tu stabilization. The formation of a geochemically stable phase reduced the mobility of toxic metals and therefore diminished their leaching potential in landfills.