Immobilisation Of Heavy Metals In Hazardous Waste Incineration Residue Using Glass-ceramic

Hazardous waste incineration residue（HWIR）is a kind of industrial waste produced in the process of disposing of various hazardous wastes by incineration.HWIR is classified as HW18（the eighth category of hazardous waste）in the China National Hazardous Wastes List（2021）due to the presence of heavy metals（e.g.Zn,Cu,and Cr）.The heavy metals may enter the human body through different ways and seriously endanger human health and life safety.In this paper,the HWIR from an environmental protection corporation in China was taken as the research project.Based on the result of the physical and chemical properties analysis,a 100%HWIR was used to prepare SiO₂–Al₂O₃–Fe₂O₃–CaO glass-ceramic samples.The results showed that Zn,Cu,and Cr present in HWIR were effectively immobilised through the melting–sintering process,which provided a new method for the HWIR disposal.The main conclusions were as follows:1)The appearance of HWIR was dark brown with glass luster.HWIR was weak alkalinity and low water content.There was no obvious crystal phase in HWIR.The contents of Zn,Cu,and Cr in the HWIR were all high.In addition,HWIR is also rich in SiO₂,Fe₂O₃,Al₂O₃ and CaO.2)The optimal heat treatments for SiO₂–Al₂O₃–Fe₂O₃–CaO glass-ceramic preparation were the crystallization temperature of 1080°C,the crystallization time of 1h,the nucleation temperature of 760°C and the nucleation time of 1 h.The glass-ceramics formed under optimal conditions exhibited a superior compressive strength of 204.84 MPa,volume density of 2.80 g/cm³,and water absorption of 1.20%.The samples also exhibited an excellent chemical resistance and the mass losses of the samples soaked in the extremely acidic and alkaline environment for 5 days were all less than 0.05%.In addition,the samples also performed a good crystallinity.The haematite（Fe₂O₃）could be formed first and then the pseudobrookite（Fe₂Ti O₅）and anorthite（Ca（Al₂Si₂O₈））were formed in the sintering process.The three types of crystals coexist and were uniformly embedded in the amorphous glassy matrix.3)The heavy metals Zn,Cu,and Cr could be effectively immobilised using SiO₂–Al₂O₃–Fe₂O₃–CaO glass-ceramic samples.Compared with the raw HWIR sample,the leaching concentrations of Zn,Cu,and Cr from the prepared glass-ceramic samples decreased significantly,and their immobilisation efficiencies exceeded 99%.The glass-ceramics had the dual effects of physical sealing and chemical stability on Zn,Cu and Cr and the ion exchange in the amorphous glassy matrix and iron-rich crystalline phases（chemical stability）were the main immobilisation mechanisms of Zn,Cu,and Cr.