不同比例钾钙锌共存对土壤镉吸附的影响

Effect of coexistence of potassium, calcium and zinc on the cadmium adsorption in lateritic red soils

采用等温平衡法,测定了锌、钾、钙两两共存下赤红壤镉的吸附量,应用Freundlich方程分析了土壤镉的吸附特征,并计算了镉的分配系数(KdCd)。结果表明,用Freundlich吸附等温方程拟合土壤镉的吸附特征具有很好的相关性。与单钠体系相比,钙钾、钙锌及锌钾共存均使赤红壤吸附镉的能力减弱,赤红壤的总吸附容量(Kf值)分别降低了56.5%、96.73%和91.3%。不同离子两两共存下改变土壤吸附镉能力的程度不同,钙钾共存的Kf值明显高于钙锌、钾锌共存,对Kf值的影响程度的次序为:锌钾≈钙锌,钙钾。钙锌、钾共存时,增加吸附体系中锌质量浓度将明显降低镉的分配系数(KdCd值),共存离子中锌含量与KdCd值呈明显负相关。钙锌、钾锌以不同比例与镉共存时,锌含量高低是制约KdCd值大小的主要因子。

Batch adsorption experiments were conducted to investigate the effects of coexistence of potassium, calcium, and zinc on adsorption of cadmium in lateritic red soils. Freundlich adsorption model was chosen for analysis adsorption characteristics of cadmium. At the same time, the distribution coefficient of Cd was calculated using this model as well. The results showed that the adsorption data of Cd fitted very well to the Freundlich model （P〈0.01）. Compared with the Na^＋ existing system, co-existing binary cations of Ca^2＋, K^＋ and Zn^2＋ can decrease the adsorption capacity of cadmium in lateritic red soils, and total adsorption capacity （ Kf value ）decreased 56.5%（Ca^2＋ - K^＋）, 96.73%（Ca^2＋ - Zn^2＋）, and 91.3%（Zn^2＋ - K^＋）, respectively. In addition, with co-existing binary cations of Ca^2＋, K^＋ and Zn^2＋, adsorption of Cd reduced with the sequence of K^＋ - Zn^2＋ ≈Ca^2＋ -Zn^2＋ 〉 Ca^2＋ - K^＋. When Ca and Zn or K and Zn coexist with Cd in various ratios, increasing Zn level can lead to significant decrease of Cd distribution coefficients. A negative correlation was observed between distribution coefficients and Zn concentration among Ca2＋-Zn2＋ and Zn2^-K＋ co-existing system. The level of Zn was the major factor regulating Cd distribution coefficients when Ca and Zn or K and Zn coexist with Cd in various ratios.