Mechanism of release of heavy metals in solidified/stabilized bodies of fly ash piperazine chelating agents

Heavy metals in fly ash from municipal solid waste incineration are major environmental hazard, and their solidification/stabilization have become the primary problem in fly ash treatment and disposal. Portland cement is commonly used to treat waste incineration fly ash. In order to reduce energy consumption and improve product efficiency, the ability of a new macromolecular organic chelator, sodium piperazine-N,N'-bis-dithiocarboxylate (TS300), to solidify heavy metals in fly ash in concert with different amounts of cement (30%, 40%) was investigated. The effects of TS300 on the leaching concentration, chemical morphological changes, and microstructure of the target heavy metals Zn, Cd, Cr, Pb, and Ni were investigated. The results showed that TS300 co-cement could effectively immobilize the heavy metals in fly ash and reduce the leaching concentration by more than 60%. The chemical morphology of heavy metals Cr, Cd, Pb and Ni moved to a more stable direction overall after solidification. With the rise of TS300 and cement addition, curing block crystal composition, acid resistance strength, and pore density increased. The curing block with 40% addition of ordinary silicate cement and 8% addition of TS300 had the lowest heavy metal leaching concentration and the best curing effect. In summary, investigating the effect and mechanism of TS300 co-cement solidification/stabilization of heavy metals could analyze the effect of cement synergistic agents in curing and stabilizing fly ash heavy metals, reduce the environmental risk of landfill leachate, and provide new ideas for the subsequent research and development of fly ash heavy metal chelating agents.