不同磷酸盐下红壤对镉离子的吸附-解吸特征

Effect of Different Phosphate on Adsorption-Desorption of Cadmium in Red Soil

采用等温吸附法研究了红壤对镉离子的吸附特性,分析加入不同形态的磷酸二氢盐(磷酸二氢铵、磷酸二氢钾和磷酸二氢钙)对镉离子吸附-解吸特征的影响。结果表明,在加入镉浓度0～20mg·L-1范围内,红壤对镉离子的吸附量随平衡液中镉离子浓度的升高而增加,吸附等温线符合Freundlich方程。土壤吸附镉离子后,在磷添加浓度为0～160mg·L-1下,土壤对镉离子的等温吸附仍然符合Freundlich方程(R2>0.94),但磷酸盐对镉离子吸附具有明显影响;磷酸二氢钙使镉离子的最大吸附量降低了2.5%～7.9%,使镉离子的吸附率降低10%～20%,而磷酸二氢铵和磷酸二氢钾对镉离子的吸附特征无明显影响。随加入磷量的增加,3种磷酸盐下镉离子解吸量和解吸率均显著降低,解吸量降幅为15.8%～27.8%,解吸率降低了3.7%～9.5%;但在低镉时磷酸二氢钙对红壤镉离子的解吸率显著高于磷酸二氢铵和磷酸二氢钾。由于Ca2+与Cd2+之间存在较强的竞争吸附,使得磷酸二氢钙对红壤镉离子吸附-解吸的影响大于磷酸二氢铵和磷酸二氢钾。

The characteristics of cadmium adsorption and the effects of different kinds of phosphate （ NH4H2PO4, KH2PO4, Ca（H2PO4）2） on the adsorption-desorption of cadmium in red soil were investigated by a batch experiment. The results showed that the adsorption amount of cadmium increased with the concentration of cadmium in the equilibrium solution under the range of initial concentration of cadmium from 0 to 20 mg.L^-1. The relationship between the adsorption amount of cadmium and the concentration of cadmium in the equilibrium solution could be described by the Freundlich equation. After the red soil adsorbed cadmium, the adsorption isotherms of cadmium in red soil could also be described by the Freundlich equation （R^2〉0.94） in the presence of phosphate from 0 to 160 mg.L^-1. But the added phosphate markedly affected on the adsorption of cadmium. The maximum amount of adsorbed cadmium by the red soil decreased by 2.5%-7.9% after adding Ca（ H2PO4）2. The adsorption percentage of cadmium substantially declined by 10%-20% with the increasing concentration of Ca（ H2PO4）2. Whereas, NH4H2PO4 and KH2PO4 didn＇t influence on the adsorption amount of cadmium in red soil. The desorption amount and desorption rate of cadmium from the red soil significantly decreased by 15.8%-27.8% and 3.7%-9.5% with the increasing concentration of phosphates. The desorption rate of cadmium by Ca（H2PO4）2 was higher than NH4H2PO4 and KH2PO4 when the cadmium adsorption was lower. Ca（ H2PO4）2 had more significant effect on adsorption-desorption of cadmium in red soil than NH4H2PO4 and KH2PO4 because of competitive adsorption between Ca^2＋ and Cd^2＋.