Objective  The effects of sepiolite (H), bentonite (P), calcium magnesium phosphate fertilizer (G) and phosphate rock powder (L) on cadmium (Cd) pollution in acidic farmland soils with 0.3 mg kg⁻¹, 1.0 mg kg⁻¹ and 1.5 mg kg⁻¹ Cd levels were studied .

  Methods  The experiment was simulated by indoor culture.Samples were taken at 10 d, 20 d and 30 d after culture with the single purified agent, and samples were taken at 30 d after culture with the compound passivating agent. Then, soil pH and available cadmium content were measured to evaluate the effect of passivating agent.

  Result  The pH values in the three Cd contaminated soils increased with H and G passivators (P < 0.05), while the pH values did not change significantly with P and L passivators. Compared with CK, the effective Cd content in 0.3 mg kg⁻¹ Cd contaminated soil with four passivators was decreased, but the difference was not significant (P > 0.05). In soil with 1.0 mg kg⁻¹ Cd addition, the effective Cd contents of H and G passivating agents decreased significantly, but the effective Cd contents of P and L passivating agents did not change significantly (P > 0.05). In addition, 2%H + 1%G passivators reduced soil available Cd by 52.73%, with the best effect. In 1.5 mg kg⁻¹ Cd contaminated soil, the effective Cd contents were significantly decreased by H and G passivator alone, while the effective Cd contents were not significantly decreased by P and L passivator alone (P > 0.05). However, the effective Cd content in soil treated by 1.5% H + 1% G passivators combined was reduced by 56.45%, showing a good effect.

  Conclusion  it is recommended that the 2% H + 1% G and 1.5 H + 1% G passivating agents were used to passivate 1.0 mg kg⁻¹ and 1.5 mg kg⁻¹ Cd contaminated soils.