Improving immobilization efficiency and mechanism analysis of sodium hexametaphosphate on MgO-based cementitious material solidified MSWI FA

MgO-based cementitious material (MCM) is a potential green substitute for solidifying municipal solid waste incineration fly ash (MSWI FA). Sodium hexametaphosphate (SHMP), a commonly used dispersant, has a great influence on the hydration process of MCM-MSWI FA blends. In this study, the effect of different SHMP additions on the performance of the MCM-MSWI FA (3:7 in mass ratio) blends was investigated. The compressive strength and leaching toxicity of the blends were measured, and the structural evolution was analyzed by XRD, FTIR, TG/DTG, and SEM. These tests revealed that the addition of SHMP could significantly optimize the effect of MCM solidifying MSWI FA since SHMP could promote the dispersion of hydration products in the blends. The blends containing more than 1% SHMP exhibited immobilization efficiencies higher than 97.5% for heavy metals (Cd, Pb, and Zn) after curing for 28 days. Collectively, this work demonstrates the indispensable role of SHMP in the application of MCM solidifying MSWI FA, providing theoretical support for practical engineering.