Application of ultrafine bubbles for enhanced carbonation of municipal solid waste incineration ash during direct aqueous carbonation

Abstract

Municipal solid waste incineration fly ash was selected as the alkaline Ca-bearing solid waste, and a series of direct aqueous carbonation experiments using 10% CO2 gas were conducted to showcase the capability of ultrafine bubbles (UFBs) in enhancing carbonation efficiency. Results from the experiments, conducted using a one-pass water flow system, revealed that carbonation without UFBs increased the CO2 content of the ash from 59 to 200 mgCO2/g (an increase of 141 mgCO2/g), while the presence of UFBs elevated it to 237 mgCO2/g (an increase of 178 mgCO2/g). Consequently, the introduction of UFBs led to a 26% increase in CO2 content in ash [(178−141) / 141]. This improvement was primarily attributed to the enhanced carbonation efficiency for particles ≥ 46 µm. The positive impact of UFBs was more evident (62% increase in CO2 content in ash) in experiments using a water circulation system, where carbonation proceeded at a faster rate compared to the one-pass water flow system. In terms of the mechanism, X-ray diffraction and scanning electron microscopy analyses indicated that UFBs facilitated the removal of CaCO3 deposition, which inhibited Ca(OH)2 dissolution. To the best of our knowledge, this study is the first to demonstrate the favorable influence of UFBs on fly ash carbonation efficiency.