Hydroxyl group-mediated cadmium immobilization on zeolites by soil organic matter

Waste-derived zeolite efficiently removes Cd across various pH conditions. • pH conditions drive the shift in Cd removal mechanisms on zeolite. • Hydroxyl groups in soil dissolved organic matter enhance Cd fixation on zeolite. • Sustainable strategy integrates waste reuse with remediation. Soil dissolved organic matter (DOM), which is ubiquitously released during remediation of heavy metal-contaminated soil-water systems, exerts significant yet underexplored influence on heavy metal fate. Here, we systematically investigated the effect of soil DOM on cadmium (Cd) adsorption using industrial waste-synthesized zeolites, which showed high adsorption efficiency across pH 3.0–7.0. More importantly, adsorption-desorption experiments confirmed that soil DOM selectively enhanced Cd immobilization on zeolites through its functional groups. By integrating EEM-PARAFAC, FT-ICR-MS, and 2D-FTIR-COS analyses, we further identified the dominant soil DOM components and specific functional groups responsible for the immobilization. In soil DOM-free systems, Cd adsorption was primarily governed by Si/Al O bonds, whereas in soil DOM-amended systems, Cd retention was jointly controlled by zeolite surface sites and DOM-derived oxygen-containing functional groups, forming a stable zeolite-soil DOM-Cd ternary system, in which hydroxyl groups ( OH) played a dominant role in promoting Cd immobilization. This work provides new molecular-level insights into the critical role of soil DOM in enhancing heavy metal immobilization and offers a scientific basis for developing effective remediation strategies using waste-derived zeolites for treating Cd contaminated wastewater. Download: Download high-res image (145KB) Download: Download full-size image