海泡石对典型水稻土镉吸附能力的影响

Effect of Sepiolite on Sorption of Cd by Typical Paddy Soils

通过吸附解吸实验研究了添加海泡石后典型水稻土对Cd的吸附解吸特性及其对吸附溶液pH值变化的响应。结果表明,Freundlich方程可以较好地拟合红黄泥、黄泥田和红沙泥3种典型水稻土对Cd的等温吸附过程（R2〉0.962）。在溶液初始Cd浓度相同的情况下,添加海泡石可使3种水稻土对Cd的吸附量增加20%以上,增强土壤对Cd的吸附强度,有效降低吸附Cd的解吸率,其效果随海泡石添加量的增大而增强。3种水稻土吸附Cd的解吸率均高于70%,而且都随吸附量的增加而上升。溶液的pH值是影响土壤吸附Cd的一个重要因素,在低pH值的条件下（pH〈4）,随着溶液pH值的降低,土壤对Cd的吸附量迅速降低,当溶液pH值高于5时,pH值的变化对吸附量的影响较小。在溶液初始pH值2-8范围内,添加海泡石均能有效提高3种水稻土对Cd的吸附能力。

The adsorption-desorption of cadmium（Cd） by clay minerals or soils have been extensively studied, however, the effect of the application of sepiolite on Cd adsorption-desorption in soils remains poorly understood. The aim.of this study was therefore to investigate Cd sorption and desorption by 3 typical paddy soils pretreated with sepiolite through a batch equilibration method. Our results indicated that the sorption amount of Cd on each tested soil increased with the Cd equilibrium concentration, after adding cadmium ion ranged from 0 to 20 mg· L^-1, but did not reach a maximum. Freundlich equations were fitted well （R^2〉 0.962） to all the sorption experimental results. Sepiolite not only enhanced Cd adsorption, but also increased the retention of Cd by the three soils. At the same initial Cd concentrations, sepiolite added at 5 and 10 mg·kg^-1 increased the adsorption amount by 17%-34% and 25%-60%, and decreased the release percentage by t.4%-13.6% and 10.3%-25.0%, respectively, as compared with the controls. Solution initial pH was also an important factor affecting the adsorption of Cd in soil. The enhancement of Cd sorption caused by the solution initial pH increase was apparent with the pH ranged from 2 to 4, but the effect was minimal with the pH ranged from 5 to 8. Moreover, addition of sepiolite obviously increased the sorption amount of Cd by the 3 soils with the pH ranged from 2 to 8. These results provide support for the feasibility of sepiolite used as amendment for the immobilization of Cd in paddy soil.