土壤性质对单一及复合污染下外源镉稳定化过程的影响

Effects of Soil Properties on the Stabilization Process of Cadmium in Cd Alone and Cd-Pb Contaminated Soils

通过对11个性质差异较大的土壤进行室内培养(土壤水分65%～70%WHC,温度25℃),观测了镉(Cd)单一和镉-铅(Cd-Pb)复合污染360 d内有效Cd含量随时间的变化,利用动力学模型对其稳定化过程进行模拟,并采用相关和逐步回归分析讨论了土壤理化性质对外源Cd稳定化过程的影响.结果表明,不同土壤中有效态Cd含量均在培养开始的15 d内迅速下降,随后变化减缓,培养60 d后基本达到平衡,其稳定化过程可用二级动力学方程、一阶指数衰减函数进行模拟.Pb的存在提高了Cd的有效性.模型的动力学参数稳定化平衡含量和表观速率常数可用来表征Cd的稳定化过程.土壤性质对这2个关键参数有显著影响,高pH值和高阳离子交换量(CEC)对Cd平衡含量有极显著的抑制作用,且pH值的直接抑制作用最大;土壤质地影响Cd的稳定化速率常数,在黏粒含量少、砂粒含量多的土壤中Cd能够更快达到平衡.

In order to clarify the effects of soil properties on the stabilization process of the cadmium （Cd）added, 11 different soils were collected and incubated under a moisture content of 65% -70% at 25℃. The changes of available Cd contents with incubation time （ in 360 days） in Cd and Cd-Pb contaminated treatments were determined. The stabilization process was simulated using dynamic equations. The results showed that after 1.0 mg.kg-1 Cd or 500 mg.kg-1 Pb ＋ 1.0 mg.kg-1 Cd were added into the soil, the available Cd content decreased rapidly during the first 15 days, and then the decreasing rate slowed down, with an equilibrium content reached after 60 days＇ incubation. In Cd-Pb contaminated soils, the presence of Pb increased the content of available Cd. The stabilization process of Cd could be well described by the second-order equation and the first order exponential decay; meanwhile, dynamic parameters including equilibrium content and stabilization velocity were used to characterize the stabilization process of Cd. These two key dynamic parameters were significantly affected by soil properties. Correlation analysis and stepwise regression suggested that high pH and high cation exchange capacity （CEC） significantly retarded the availability of Cd. High pH had the paramount effect on the equilibrium content. The stabilization velocity of Cd was influenced by the soil texture. It took shorter time for Cd to get stabilized in sandy soil than in the clay.