Effect of SiO2, Al2O3 and CaO on characteristics of lightweight aggregates produced from MSWI bottom ash sludge (MSWI-BAS)

Abstract

For the utilization of municipal solid waste incineration bottom ash sludge (MSWI-BAS), the production of lightweight aggregates (LWA) was carried out using it as raw materials. SiO2, Al2O3 and CaO were the major oxides in MSWI-BAS, so their effect on characteristics of LWA was investigated to optimize the process. Results showed that the increase in SiO2 content from 25% to 40% caused the good growth of the structure with Si and O as the skeleton, leading to LWA with increased compressive strength and particle density from 0.5 to 6.18 MPa and from 755 to 1268 kg/m3 respectively, and reduced 1 h water absorption from 50% to 14%. Lower strength LWA with more pores and amorphous phases were obtained at 20% ≤ Al2O3 ≤ 30% because excessive Al2O3 inhibited the crystallization inside the products. Dramatic changes occurred when CaO increased from 21% to 22% with compressive strength and particle density from 8.82 to 2.02 MPa and from 1300 to 862 kg/m3 respectively, and 1 h water absorption from 4% to 36%, indicating that more CO2 was produced. This attempt to utilize MSWI-BAS can produce high-performance LWA that meets the sustainability philosophy and reduces the cost of waste treatment and lightweight aggregates production.