Preparation of lightweight aggregates via co-sintering MSWI fly ash and waste CRT with potential for heavy metals and chlorine recovery.

Abstract

Municipal solid waste incineration fly ash (MSWI FA) poses great resource utilization challenges due to contained high concentration of heavy metals (HMs) and chlorine (Cl). In this study, lightweight aggregates (LWAs) were produced using FA and waste cathode ray tubes (CRT). The influences of sintering temperature and phosphates addition on HMs and Cl volatilization, pore structure and mineral phase evolution were investigated. When the mass ratio of FA to CRT was 7:3 and sintering temperature ranged from 1150 to 1200 °C, the removal efficiencies of lead (Pb), zinc (Zn) and cadmium (Cd) all exceeded 90%, whereas that of copper (Cu) surpassed 65%. The secondary fly ash (SFA) is rich in Cl and HMs, endowing it with promising potential for resource recovery. Phosphates had a negligible effect on the volatilization of HMs at high temperatures; however, they suppressed chlorine release via the formation of chlorapatite. As Ca3(PO4)2 dosage increased from 0 to 10%, Cl removal rates decreased from 95.86% to 85.28%, but the water-soluble Cl content in sintered products remained lower than 2%. The incorporation of CRT facilitated sintering at reduced temperatures. With SiN employed as a foaming agent, the total porosity rose markedly as the sintering temperature elevated, reaching at the maximum value of 68.67% under the FA:CRT mass ratio of 7:3 at 1200 °C. Environmental risk assessment verified that the sintered LWAs present low ecological risk.