Immobilization mechanism of Ca(H₂PO₄)₂-modified attapulgite on multiple heavy metals in mining soils: Speciation...

This study developed a novel stabilization material, termed CaP@A, by modifying attapulgite with calcium dihydrogen phosphate (Ca(H₂PO₄₄)₂) for the remediation of heavy metal-contaminated soil. The results demonstrated that CaP@A effectively immobilized a range of heavy metals (Cd, Pb, Zn, Cu, Ni, Cr). At a 4 % application rate, the immobilization efficiencies for Cd and Pb reached 53.85 % and 44.36 %, respectively. Furthermore, the treatment promoted the transformation of acid-soluble fractions into more stable residual forms, thereby significantly reducing the bioavailability and mobility of the metals. Mechanistic investigations revealed that the immobilization occurred primarily through adsorption, precipitation, and ion exchange. However, the efficiency declined when the Ca(H₂PO₄)₂ content exceeded 20 %, which can be attributed to pore blockage and saturation of active sites, indicating an optimal phosphate loading threshold. This study confirms the potential of CaP@A as an effective remediation material and provides crucial theoretical guidance for optimizing its practical application.