Study on the reduction of chlorine and heavy metals in municipal solid waste incineration fly ash by organic acid and microwave treatment and the variation of environmental risk of heavy metals

Municipal solid waste incineration (MSWI) fly ash usually needs to undergo dechlorination or heavy metal stabiliza-tion pretreatment for further treatment, recycling or disposal. In this paper, the removal effect of chlorine in fly ash by water washing, lactic acid, citric acid and microwave treatment was studied, and XANES was used to analyze chlo-rine chemical form in fly ash. In addition, the heavy metals in fly ash were also checked. The results indicated that dou-ble washing and triple washing could remove 88.0 % and 95.5 % of chlorine from fly ash respectively. The double water washing + microwave/organic acid could remove about 96.6 % of chlorine, and 42.9 % and 47.2 % of insol-uble chloride respectively. The microwave treatment could maximize the stabilization of heavy metals with a BI value of 39.1 %, 0.11 %, 1.65 %, 15.4 % and 3.98 % for Cd, Cr, Cu, Pb and Zn. The elution of heavy metals by citric acid was obvious. Double water washing + citric acid removed 87.0 % of Cd, 17.2 % of Cr, 11.9 % of Cu, 39.6 % of Pb and 43.6 % of Zn, but the environmental risk of Cu and Cr increased about 2-3 % after the treatment. The results of this study provide guidance for the pretreatment of fly ash before resource utilization.

Automated summary

This study investigated the removal effect of chlorine in municipal solid waste incineration (MSWI) fly ash through water washing, lactic acid, citric acid, and microwave treatment. XANES analysis was used to determine the chemical form of chlorine in fly ash, and heavy metals in fly ash were also examined. The results showed that double washing and triple washing could remove 88.0% and 95.5% of chlorine, respectively. The combination of double water washing with microwave or organic acid could remove about 96.6% of chlorine and a significant amount of insoluble chloride. Microwave treatment effectively stabilized heavy metals, while citric acid eluted heavy metals. The findings of this study provide guidance for pretreating fly ash before resource utilization.