岩溶区石灰性土壤对Cd^2＋吸附的解吸特性及滞后效应

Desorption characteristics and hysteresis of adsorbed cadmium in calcareous soils on karst area

采用一次平衡法对Cd^(2+)在岩溶区典型石灰性土壤(棕色石灰土和黑色石灰土)中的解吸特性及滞后效应进行研究.结果表明,Cd^(2+)在两种石灰性土壤中的解吸量及解吸率均随初始Cd^(2+)浓度和吸附量的增加而增大,解吸量与吸附量呈极显著二次幂函数关系;Cd^(2+)于两种土壤中的解吸率均较小,分别为4.64%—28.93%(棕色石灰土)和2.27%—10.02%(黑色石灰土),显然黑色石灰土对Cd^(2+)的固持性较好.Linear模型是描述Cd^(2+)在2种石灰性土壤中解吸等温模型的最佳方程.Cd^(2+)吸附-解吸等温线不重合,解吸等温线明显滞后于吸附等温线,表明滞后效应的存在.基于Freundlich系数、Cd^(2+)分配系数及吸附量与解吸量间的差异3种方法计算滞后指数,计算结果表明,石灰土中Cd^(2+)初始浓度越高则解吸滞后程度越大,且黑色石灰土中Cd^(2+)的滞后程度略高于棕色石灰土.

Cadmium desorption characteristics and hysteresis by calcareous soils on karst area were investigated in batch sorption experiments. The results showed that the amount and rate of Cd^2＋desorption increased with the initial concentration of cadmium and the amount of adsorbed Cd in the two calcareous soils. The relationship between amount of desorbed Cd^2＋and sorbed Cd^2＋was significantly quadratic power function. The quantity of Cd^2＋desorbed from the soils after three desorption runs was small,varying between 4. 64% to 28. 93% for Brown rendzina,and 2. 27% to10.02% for Rendizina.Obviously the latter had higher retention for Cadmium. Both Cd^2＋desorption isotherms were adequately described by Linear equation.In particular,there was an apparent sorptiondesorption hysteresis of Cd^2＋in soils. The extent of hysteresis was quantified based on the Freundlich exponent,the Cd^2＋distribution coefficient,and the differences obtained from sorption and desorption amount of Cd^2＋. The results revealed that hysteresis indices significantly increased as the amount of Cd^2＋in the systems increased.Higher hysteretic degree was obtained for Rendizina.