From natural adsorption to targeted immobilization: Efficacy and mechanisms of clay minerals in remediating soil heavy metals

• Natural clay minerals can effectively reduce the content of available heavy metals in the soil and reduce their accumulation in crops. • The mechanism by which modified clay minerals fix heavy metal ions and cations was investigated. • Modified clay minerals are beneficial for achieving targeted passivation of heavy metals. • The key factors affecting the immobilization efficiency of heavy metals in soil were summarized. Heavy metals (HMs) pollution in soil poses a serious threat to agricultural production, food safety, and human health, making relevant remediation research of great practical significance. Therefore, it is of great significance to pay attention to the remediation of soil HMs pollution. Clay minerals (CMs) as an economical and efficient green remediation material, they have been widely used in soil remediation. We systematically summarized the methods, effects and mechanisms of CMs and modified clay minerals (MCMs) on the immobilization of typical HMs in soil. Studies have shown that raw clay minerals can effectively immobilize heavy metal cations, while modification treatments that increase their specific surface area, number of functional groups, and heavy metal precipitant content can significantly improve the immobilization efficiency. Modified clay materials mainly immobilize heavy metal anions through reduction precipitation and electrostatic adsorption mechanisms. Soil pH, organic matter content, moisture conditions, coexisting ions, and material application rate are key environmental factors affecting fixation effectiveness. This article also summarizes the characterization techniques and latest trends used to elucidate the fixation mechanisms of clay-based materials. Overall, this study constructs a “structure-functionalization-targeted immobilization” framework for clay mineral remediation and critically assesses the shortcomings of current research in understanding long-term environmental behavior and ecological risks. Our research provides a fundamental understanding of the changes in heavy metal bioavailability in contaminated soils mediated by CMs and their modified materials, the mechanisms involved, and their subsequent impacts.