Calcium dissolution-induced porosity increase in cement-solidified MSWIFA: Implications for heavy metal leaching behavior

Calcium dissolution in cement-solidified municipal solid waste incineration fly ash (MSWIFA) presents a potential risk to the long-term environmental safety of waste management, primarily by increasing porosity and thereby enhancing heavy metal leaching. This paper proposes a coupled theoretical-numerical leaching model for copper (Cu) and lead (Pb), explicitly integrating calcium dissolution dynamics. The theoretical framework incorporates a calcium mass balance equation, with dissolution kinetics governed by porosity, diffusion coefficients, and calcium concentration gradients within the cement matrix. A three-dimensional numerical model was developed and experimentally validated, yielding three key findings: (1) Calcium dissolution increases porosity of cement-solidified MSWIFA, which in turn enhances heavy metal leaching through improved diffusion efficiency; (2) this effect intensifies with higher leachable calcium content; and (3) although the observed increase in leaching caused by calcium dissolution is relatively small (＜5 %), the cumulative impact over time may pose significant environmental risks. This study provides a predictive tool for assessing the leaching behavior of cement-solidified MSWIFA, supporting risk-informed decision-making in its management.