Steam washing for MSWI-FA treatment

This study investigates steam washing (SW) as an innovative pretreatment for municipal solid waste incineration fly ash (MSWI-FA) dechlorination, useful for a more effective stabilization in cementitious matrix. By using a detailed analytical approach (XRPD, XRF, ICP-MS, IRMS, SEM) and geochemical modeling, great focus is dedicated on pollutant leaching reduction and changes in ash physicochemical characteristics as a function of exposure time. The research demonstrates that SW removes up to 70 % cadmium, 17 % zinc, and 10 % lead, primarily by dissolving the soluble and carbonate/hydroxide fractions and promoting the reprecipitation and adsorption of heavy metals into more stable compounds. Chloride, sulfate, and heavy metal leaching are reduced by 85 %, 50 %, and 90 %, respectively, with even short treatment time (8 min) performing better than conventional water washing at a liquid-to-solid ratio of 2. However, antimony leaching remains above regulatory thresholds, controlled by soluble Ca-antimonate phases, thus requiring supplementary tailored treatments. Further optimization of the energy recovery during the exposure and a comprehensive life-cycle assessments to evaluate its long-term environmental and economic impact, may contribute significantly to propose SW as a sustainable strategy for MSWI-FA treatment and valorization.