Na2O induced stable heavy metal silicates phase transformation and glass network depolymerization

Abstract

The pollution of heavy metals and chlorine salts widely exists in solid/hazardous waste, while the stable heavy metal silicates limit the heavy metals removal. This work proposed mechanism of Na2O induced stable heavy metal silicates phase transformation and glass network depolymerization to promote heavy metals chlorination volatilization. Medical waste incineration slag (MWI S) containing heavy metal silicates was used as typical sample. Compared with the control, Cu and Zn volatilization efficiencies sharply increased from 77.54% to 92.22% and 18.70% to 93.82% at 3% Na2CO3, 1200 °C, 40 min. It showed that Na2O successfully induced phase transformation from stable Zn2SiO4 and CuSiO3 to ZnO and CuO easy to react with chloride by destroying the Si–O of Zn–O–Si and Cu–O–Si, respectively. Meanwhile, Na2O effectively destructed Si–O bond to depolymerize the glass network, resulting in the percentage of Q0 and Q1 increase from 25.14% to 38.29%, reducing melt viscosity and improvement of volatilization environment to form bigger bubbles. Medical waste incineration fly ash (MWI FA) was applied as Na source to further verify that the mechanism was significantly enhance Cu and Zn volatilization efficiencies. This study provided new method to reduce heavy metal residues in glass products prepared by melting treatment of solid/hazardous wastes.