Synergistic Passivation and Resistance Mechanism of Calcium-iron-phosphorus Materials on Cd and Cu Contaminated Soil

To address the dual challenges of heavy metal pollution and soil acidification prevalent in southern China, this study investigates the synergistic immobilization effects and resistance mechanisms of combined applications of calcium-based alkaline materials with phosphorus and iron-based materials on heavy metals in contaminated soils. Cd and Cu contaminated soils were targeted, with calcium carbonate (Ca), disodium hydrogen phosphate (P), and zero-valent iron (Fe) used as amendments. Soil incubation experiments and acid rain leaching experiments were conducted. Results show that the Ca, Fe, and P contained materials significantly reduced the bioavailability of Cd and Cu in the soil, with the Ca-P-Fe combination exhibiting the optimal performance. This combination significantly minimized the active fractions of Cd and Cu by increasing the soil pH and Fe_a content. Range analysis indicated that Fe in Ca-P-Fe combination was most effective in controlling ECA-Cd activity, while Ca was most effective for ECA-Cu. Under long-term acid rain stress (simulating 25~100 years), the Ca-P-Fe combination remiained effective in immobilizing the bioavailability of Cd and Cu, with ECA-Cd and ECA-Cu decreasing by 25.65% and 14.78%, and soil pH increasing by 2.58. These findings validiate that the Ca-P-Fe combination exerts significant synergistic immobilization effects on Cd and Cu contaminated soils and maintains stable immobilization performance under long-term acid rain stress.