Normal pressure transforming kaolinite-rich soil into sodalite for Cd-contaminated soil remediation

Cadmium (Cd) soil contamination poses a particularly acute threat to public health. While synthetic zeolites have shown promise in immobilizing Cd, their widespread application is hindered by high material costs, energy-intensive synthesis, and reliance on high-pressure reactors. To date, no study has reported the successful transformation of natural kaolinite-rich soil into sodalite zeolite under normal pressure conditions. This study bridges that critical gap by developing a novel, low-cost, and energy-efficient route to synthesize sodalite from kaolinite-rich soil using only a household electric cooker at ambient pressure. Superior to the conventional high-pressure hydrothermal route, it offers significant advantages in terms of material costs, equipment expenses, synthesis efficiency, and energy consumption. Remarkably, this soil-derived sodalite demonstrates exceptional Cd-contaminated soil remediation efficacy. With only 0.3 % sodalite additions (w/w), the proportion of exchangeable Cd species in the soil decreases from 43.2 % to 22.6 %, converting into Fe-Mn oxide-bound and residual forms, effectively diminishing Cd's mobility. Mechanistic investigations reveal that Cd 2+ is primarily locked into the framework of sodalite through ion exchange reactions and partially captured on the surface via chemisorption effects. In the state of Cd adsorption saturation, the contribution ratios of ion exchange and chemisorption by sodalite are approximately 78.7% and 21.3%, respectively. Overall, this study develops an innovative normal-pressure sodalite synthesis route using natural soil and further reveals the huge potential of soil resources for zeolite synthesis and contaminated soil remediation.