Effects and mechanisms of amendments on remediation of cadmium contaminated acid paddy soils

A field experiment was conducted to study Cd immobilization in Cd contaminated soils. The study analyzed the remediation effects of lime (L), fused calcium magnesium phosphate (P), sepiolite (S), humic acid (H) and mixed lime amendments (LP, LS and LH) on Cd bioavailability in a Cd contaminated acid paddy soils. The results indicate that amendments significantly change the proportion of Cd forms in contaminated soils. Except for H, the other 3 amendments lower acid extractable fraction of Cd, while increasing oxidation fraction and residual Cd. The 4 amendments reduce the 0.1 mol·L^-1 NaNO₃ and 0.01 mol·L^-1 CaCl₂ extracted Cd by 26%~97%. The order of reduction is LS > S > LP > P > L > LH > H. The content of Cd in the aboveground parts of rice decreases by 6%~49% under amendment application. Amendment increasing soil pH is the main factor influencing soil Cd immobilization. In conclusion therefore, sepiolite could be a suitable amendment of Cd contaminated acid paddy soils. However, humic acid is not so suitable for remediating Cd contaminated acid paddy soils.