Heavy metal solidification and CO2 sequestration from MSWI fly ash by calcium carbonate oligomer regulation

Abstract

The efficiencies of heavy metals (HMs) solidification and CO2 sequestration from current municipal solid waste incineration fly ash (MSWI FA) carbonation technology are low, and the reaction conditions are complicated. A novel MSWI FA carbonation treatment, which was carried out under room temperature and pressure and controlled by calcium carbonate oligomers, is proposed. Through orthogonal tests, the reaction time (t), temperature (T), CO2 flow rate (V), magnetic stirring rate (W), and liquid-solid ratio (L) of the MSWI FA carbonation treatment were investigated. The results showed that the five influential factors were W>T>L>t>V, and the optimal parameters were 60 min, 20 °C, 200 ml min−1, 600 rpm and 10 L kg−1 (the carbonation efficiency (CE) was 13.8%). When alkaline additives (NaHCO3 or NaOH) were added, the CE increased to 16.5% and 15.1%, respectively, due to the increase of CO32− ions in the solution. The leaching concentrations of Zn, Pb, Cu, and Ni were greatly reduced in the treated samples, and the solidification efficiency reached to 99.1%, 100.0%, 91.3%, and 95.6%, respectively, because they were converted to carbonates and were adsorbed and wrapped by calcium carbonate polymer. The pores on the surface of the treated sample were reduced, and the particle sizes increased. The pH of the leachate of the treated samples decreased to 9.0–11.5 due to the carbonation reaction. This study provides an effective MSWI FA treatment method that has a highly efficient use of HMs and the potential for CO2 sequestration and resource utilization.