Influence of pretreatments on accelerated dry carbonation of MSWI fly ash under medium temperatures

Abstract The dry gas-solid carbonation of municipal solid waste incineration fly ash was investigated in order to attain harmless treatments. The main composition of fly ash was Ca-containing compounds, which could react with CO2 to produce carbonate for solidification, alleviating the pollution of heavy metals and soluble chlorides originated from fly ash. The accelerated carbonation tests were conducted under medium temperatures (350 oC to 550 oC) in the fixed-bed experimental system. Moreover, the effects of pretreatment involving calcination and water-washing on carbonation were studied. The composition, phase content and structure of fly ash were determined using quantitative X-ray diffraction (QXRD) and scanning electron microscope (SEM). Additionally, the leaching characteristics of Cu, Zn, Pb, Cr, Cd, and Ni were investigated. The results revealed that pretreatments influenced mass gain during carbonation. The mass gain of calcined fly ash increased with the increasing temperature, whereas the mass gain of raw fly ash and washed fly ash decreased after 400 oC. The QXRD calculation indicated that CaClOH did not decompose completely at 600 oC. The CaCO3 content of carbonated washed fly ash reached the maximum of 88% at 550 oC. In addition, raw fly ash and washed fly ash could be carbonated completely at 350 oC, whereas calcined fly ash required 400 oC. The leaching characteristics analysis showed that pretreatments would increase the leaching concentration of heavy metals (except Pb). However, the leaching concentration of Cu, Pb and Cr decreased obviously after carbonation. For fly ash in this study, carbonation at 400 oC-450 oC can meet the requirements. The study provides useful information for the research and applications of dry carbonation of MSWI fly ash.