外源镉在几种典型农耕土壤中的稳定化特征

采用室内培养的方法,研究了重金属镉(Cd)在水稻土(渗育型)、黄壤、酸性紫色土、中性紫色土和石灰性紫色土5种典型农耕土壤中的稳定化过程,探讨Cd进入土壤后其有效态含量在180 d内随时间的变化特征,并利用动力学模型进行模拟,通过相关性分析,定量化描述土壤理化性质对Cd稳定化过程的影响。结果表明:有效态Cd在培养15 d内迅速下降,随后缓慢降低,外源Cd添加量≤2 mg·kg-1时,30 d后基本达到平衡,外源Cd添加量≥5 mg·kg-1时,60 d后才趋于稳定;平衡后,水稻土、黄壤及酸性紫色土中有效态Cd含量占加入总量的52.6%~66.7%,中性紫色土和石灰性紫色土中占33.6%~46.5%。5种动力学方程中,以二级动力学方程模拟外源Cd的稳定化效果最好,以该方程拟合所得的稳定化平衡含量和表观速率常数可用来表征Cd进入土壤后的稳定化过程。相关性分析表明,Cd在土壤中的稳定化过程与土壤性质密切相关,表现为p H值、CEC和有机质含量较高的土壤中有效态Cd含量较低,高p H值、高CEC和高有机质含量对平衡时的Cd含量有显著抑制作用,且以p H对Cd稳定化速率和平衡含量的影响最大。

Stabilization characteristics of cadmium in some typical agricultural soils

A incubation experiment in laboratory was conducted to study the stabilization processes of cadmium(Cd) in five typical agricultural soils, including paddy soil, yellow soil, acid purplish soil, neutral purplish soil and calcareous purplish soil, which were obtained in Sichuan Province. The changes of available Cd with the increasing incubation time to 180 days was determined, and simulated by dynamic equations. Correlation analysis was also made to investigate the effects of soil properties on the stabilization process of Cd in soils. The results showed that the available Cd decreased rapidly during the first 15 days, then slowly decreased. Little change was observed for the available Cd with increasing time to 30 days, when soil Cd concentration was not more than 2 mg·kg^-1, and with increasing time to 60 days when soil Cd concentration was not less than 5 mg·kg^-1. Finally, the available Cd concentration in paddy soil, yellow soil and acid purplish soil accounted 52.6%~66.7% of the total Cd in soil. For the neutral purplish soil and calcareous purplish soil, the available Cd accounted 33.6%~46.5% of the total Cd in soil. Besides, the stabilization process of Cd in soils could be well described by the second-order equation among five dynamic equations. The dynamic parameters, including equilibrium content and stabilization velocity, could be used to describe the stabilization process of Cd in soils. Furthermore, correlation analysis indicated that the stabilization process of Cd in soils was closely related to soil properties. Lower available Cd was observed in soils with higher pH, CEC and OM content. Higher pH, CEC and OM in soils had significant inhibition effect on the Cd content in soils. In especial, the pH of soils presented the greatest effect on the equilibrium content and stabilization velocity of Cd.