Study on pollutant solidification mechanisms in red mud-based cementitious materials enhanced by chitosan, ultrafine quartz powder, and attapulgite

The rapid growth of the construction sector has increased the demand for environmentally friendly and sustainable building materials. The utilization of industrial solid waste for producing cementitious materials has emerged as a key research focus in infrastructure development. Red mud, a byproduct of the aluminum industry, presents a promising solution for mitigating environmental pollution and promoting resource recycling in construction. However, its high alkalinity and heavy metal content pose risks of soil salinization and water contamination. This study addresses these challenges by incorporating chitosan, ultrafine quartz powder, and attapulgite into red mud-based cementitious materials. The effects on mechanical strength, pollutant stabilization, and microstructural characteristics are systematically evaluated. A Box–Behnken design is employed to develop predictive models for 28d compressive strength, sodium ion retention, and heavy metal immobilization. Advanced characterization techniques—including SEM–EDS, XRD, FTIR, MIP, and XPS—are used to investigate the underlying solidification mechanisms and the role of composite additives. Additionally, pseudo-first-order and pseudo-second-order kinetic models are applied to analyze the adsorption behavior of sodium and heavy metal ions. pH measurements confirm that the modified materials significantly reduce leachate alkalinity. Overall, this research contributes to the advancement of sustainable construction materials by enhancing the performance and environmental safety of red mud-based systems, thereby promoting the eco-friendly reuse of industrial waste in civil engineering applications.