镉在黑土和棕壤中吸附行为比较研究

Adsorption behavior of cadmium in phaeozem and burozem.

比较研究了重金属镉在黑土和棕壤中的吸附热力学和动力学行为.结果表明,在实验设定的浓度范围内,黑土和棕壤对Cd2+吸附量随溶液中Cd2+浓度的增加而增加.黑土对Cd2+的吸附固定能力明显强于棕壤.在平衡液浓度为20mg.kg-1时,黑土对Cd2+的吸附量为1485.2mg.kg-1、棕壤为700.6mg.kg-1.两种土壤对Cd2+的吸附等温线与Langmuir、Freundlich和Henry方程均有较好的拟合性,而Temkin方程不适合用来描述Cd2+在两种土壤中的等温吸附.根据Langmuir的拟合结果,Cd2+在黑土和棕壤中的最大吸附量分别可达5939.3和2790mg.kg-1.黑土较高的吸附能力与其高的有机质含量和粘粒含量有关.黑土和棕壤中Cd2+的吸附是一个快速反应过程,2min内能达到平衡吸附量的90%,15～30min左右达到吸附平衡.一级动力学方程是拟合Cd2+在黑土和棕壤中吸附动力学过程的最优方程,其次为Elovich方程和双常数方程.随着初始浓度的增加,Cd2+在土壤中的吸附速率也不断增大.随着吸附量的增大和反应时间的延长,吸附速率不断下降.在较低的初始浓度下,Cd2+在黑土中的下降趋势要快于棕壤.

The study on the thermodynamics and kinetics of Cd^2＋ adsorption in phaeozem and burozem showed that within the test range, Cd^2＋ adsorption was increased with its increasing initial concentration, and phaeozem had a much higher Cd^2＋ adsorption capacity than burozem. When the Cd^2＋ concentration in adsorption equilibrium was 20 mg·kg^-1, the amount of adsorbed Cd^2＋ was 1 485.2 mg·kg^-1in phaeozem, but 700.6 mg·kg^-1 in burozem. The adsorption isotherm of Cd^2＋ in the two soils could significantly conform to Langmuir, Freundlich and Henry equations, while Temkin equation was not applicable to describe the isothermal adsorption process of Cd^2＋ in phaeozem and burozem. The maximum adsorption of Cd^2＋ in phaeozem and burozem was 5 939.3 and 2 790mg·kg^-1, respectively, according to Langmuir formulation. The Cd^2＋ adsorption in test soils was a rapid reaction, with 90 % of Cd^2＋ adsorption in the first 2 min and reached equilibrium in 15- 30 min. First-order dynamic equation was the optimal model to describe the kinetics of Cd^2＋ adsorption, while the other models in point were Elovich and Two-constant equations. The adsorption rate of Cd^2＋ in test soils was increased with its increasing initial concentration, but decreased with its increasing adsorbed amount. Under low concentratiohs of Cd^2＋ , the decrease of its adsorption rate with time was more quickly in phaeozem than in burozem.