The immobilization mechanism of lime on Cu and Cd in paddy soil in short/long term
Lime is widely used in the remediation of acid polluted soil in southern China due to its affordability,accessibility,and eco-friendly characteristics.This study aimed to expand the immobilization effects and mecha-nisms of lime on Cu and Cd in both the short and long term.Lime was used as amendments to investigate the activity changes of Cu and Cd in soil,the speciation distributions and transformations of Cu and Cd in soil and colloids,combined with the speciation distribution characteristics of in-situ iron oxides.The results showed that compared with the control group (CK),the contents of Cu and Cd extracted from CaCl2 (CaCl2-Cu and CaCl2-Cd) were de-creased by 96.49% and 55.43% respectively under short-term incubation (SL),however,there was no significant difference under long-term incubation (LL,12 years).The contents of Cu and Cd extracted from HCl (HCl-Cu and HCl-Cd) were consistent with those in CaCl2 extraction state.The transformation results of Cu and Cd in soil and colloid showed the contents of amorphous iron oxides increased by 2.72% and 8.10%,respectively,and the reducible Fe-Mn oxides bond Cu and Cd in soil by 5.43% and 3.65%;the amorphous iron oxide bond Cu and Cd in the colloid by 13.77% and 4.25%,correspondingly under short-term incubation conditions (SL).During 12 years' incubation,the trend of the ratio of crystalline iron oxides content to amorphous iron oxides content decreased first and then in-creased,and finally had no significant difference with the CK,which was consistent with the immobile effects of soil Cu and Cd.In summary,lime could effectively reduce the bioavailability of Cu and Cd in soil in the short-term,but there was no obvious immobile effect after 12 years.And it was the amorphous iron oxides that bound heavy metals,which were the important immobile forms in soil immobilization.This study has important guiding significance to promote the application of Cu and Cd control technology in acid contaminated soil in southern China.
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