Mechanism of phase transformation in the preparation of porous glass from high-sulfur coal gangue and fly ash
High-sulfur coal gangue is used as the primary raw material,and in conjunction with municipal solid waste incineration(MSWI)fly ash,porous glass has been produced.The process not only immobilizes heavy metals such as Pb,Cd,Zn,Cr,Cu,and Mn found in the MSWI fly ash but also achieves the harmless disposal and resource utilization of multiple solid and hazardous wastes.This study employs two strategies address the challenge of balancing lightweight and high strength in porous glass.Firstly,by adjusting the atmosphere to create a weakly reducing environment,the premature reaction of residual carbon is hindered,allowing the residual carbon in the high-sulfur coal gangue to react with Fe2O3 at temperatures above 1 000 ℃ to generate CO2 gas.Thereby the foaming of the melt can be promoted,reducing the bulk density of the porous glass from 900 kg/m3 to 300 kg/m3.Secondly,by adding kaolin to the raw material mixture,the primary crystalline phase of the porous glass walls shifts from feldspar to mullite.The unique interlocking structure of mullite crystals imparts higher strength,enhancing the strength of the porous glass by 80％when the bulk density is at 500 kg/m3.Toxicity leaching tests on the porous glass indicate that the leaching concentrations of various heavy metals are far below the specified standards(5.0 mg/L).The leaching concentration of Pb in the porous glass is reduced to 1.1X10-2 mg/L,and the concentrations of other heavy metals also show a significant downward trend.The results show that porous glass has a good fixation effect on multi-element heavy metals.
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