Municipal solid waste incineration fly ash exposed to carbonation and acid rain corrosion scenarios: Release behavior, environmental risk, and dissolution mechanism of toxic metals

• Published in: The Science of the total environment Vol. 744; p. 140857
• Main Authors: Li, Weihua, Sun, Yingjie, Xin, Mingxue, Bian, Rongxing, Wang, Huawei, Wang, Ya-nan, Hu, Zhanbo, Linh, Ho Nhut, Zhang, Dalei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.11.2020
• Subjects: Acid rain; carbonates; carbonation; cement; CO2-saturated water; corrosion; environment; Environmental risk; fly ash; Mechanism; municipal solid waste; Municipal solid waste incineration fly ash; phosphoric acid; risk; Toxic metal leaching; toxicity; waste incineration; Mn; CA-FA; SAR; Acid rain; STI; CLAmax; Mechanism; PA-FA; PTM(s); PC-FA; T; S/S; V; Municipal solid waste incineration fly ash; OPTIsta; ESDP; Toxic metal leaching; MSWI; OPTImax; T1; T2; CO2-saturated water; TM(s); CSW; F1; F2; F3; Environmental risk; F4; F5; R-FA; OPTI; RAC; FA
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.140857

This study investigated the leaching behavior, environmental risk, and dissolution mechanism of toxic metals (TMs) in solidified/stabilized municipal solid waste incineration fly ash (MSWI FA) exposed to alternative “carbonation + acid rain corrosion” disposal scenarios. The content of TMs (mg/kg) showed a trend of Zn (12,187.10 ± 168.60) > Pb (3374.43 ± 66.12) > Cu (1055.14 ± 32.52) > Cr (127.95 ± 8.12) > Cd (119.05 ± 6.26) > Ni (49.50 ± 3.20). Initial leaching of CO2-saturated water (CSW) and replacement of simulated acid rain (SAR) increased the environmental risk of leached TMs. The results of “average release rate” (mg/(kg·d)) of TMs indicated that Zn (0.8307)/Cu (0.0278)/Cd (0.0109) and Cu (0.0581)/Cr (0.001176)/Ni (0.004339) in phosphoric acid stabilized FA and Pb (0.0753)/Cr (0.001921)/Ni (0.00111) and Pb (0.0656)/Zn (1.0560)/Cd (0.0050) in Portland cement solidified FA were the key “problem TMs” during carbonation and acid rain corrosion, respectively. CSW leaching increased the independent environmental risk of most TMs in residual FA (especially Zn/Cd) due to the increased carbonate-bound fraction. Compared with independent carbonation, alternative “carbonation + acid rain corrosion” contributed to a higher comprehensive environmental risk for TMs in residual FA. CSW leaching system was an indirect carbonation based on CO2-water and FA matrix, in which “nucleation and dissolution” of carbonates and “immobilization and dissolution” of TMs coexisted. The dissolution mechanism of TMs was mainly controlled by reaction equilibrium of nucleation and dissolution of carbonates containing TMs. Dissolution and nucleation were the dominant mechanism in the early and later periods of CSW leaching, respectively. Carbonate layer dissolution, H+ corrosion/displacement, and counter-ion effect (SO42− > NO3− > Cl−) were the main mechanisms affecting TM dissolution during SAR leaching. [Display omitted] •Initial leaching of CSW and SAR increased the leaching risk of most TMs.•CSW leaching increased the independent risk of most TMs in residual FA.•CSW + SAR leaching led to higher comprehensive risk for residual FA than CSW leaching.•Carbonates dissolution promoted higher TM leaching in early CSW leaching.•Carbonates dissolution, H+ corrosion and counter-ion effect occurred in SAR leaching.