蛭石在非缓冲与缓冲体系中的Zn~(2+)、Cd~(2+)吸附行为研究

探讨了蛭石分别在非缓冲体系与缓冲体系中的Zn2+、Cd2+吸附行为,比较了2个体系中Zn2+、Cd2+的平衡吸附量(qe),qe与平衡液相离子浓度(ce)、qe与ce和吸附剂浓度(W0)之比(ce/W0)的对应关系。结果表明,在非缓冲体系与缓冲体系中,在3个W0水平上,Zn2+、Cd2+都具有其独立的qe—ce等温吸附曲线,而qe与ce/W0具有良好的相关性,在3个W0水平上的qe—ce/W0等温吸附曲线基本拟合在一起,即在qe—ce/W0等温吸附曲线中均基本消除了吸附剂浓度效应;加入缓冲溶液的传统方法并不能消除W0对离子吸附效果的影响;缓冲体系中,大量的其他阳离子参与Zn2+、Cd2+的竞争吸附,从而使得Zn2+、Cd2+的qe相对降低;缓冲体系的qe—ce、qe—ce/W0等温吸附曲线与非缓冲体系相比,线性形式更为明显,缓冲体系的qe—ce/W0等温吸附曲线中,qe与ce/W0的对应关系没有非缓冲体系中的好。

Adsorption of Zn~(2+) and Cd~(2+) on vermiculite in buffer and non-buffer systems

Experiments of Zn~(2+) and Cd~(2+) adsorptions by three concentration level of vermiculitein in buffer and non-buffer solutions were conducted to compare the adsorption behavior of Zn~(2+) and Cd~(2+) in two systems. Two types of adsorption isotherms were established by index of absorption quantity (q_e ), equilibrium concentration (c_e) and ratio of q_e to the concentration of adsorbent (W_0). The results showed that the adsorption of Zn~(2+) and Cd~(2+) at three level of W_0 had independent q_e-c_e adsorption isotherm both in buffer and in non-buffer solutions. The q_e was well correlated with c_e/W_0, and the q_e-c_e/W_0 adsorption isotherms obtained at three W_0 level coincided with each other. The absorption quantity of aim ions was relative low in buffer solutions for the competition of other cations; the q_e-c_e and q_e-c_e/W_0 adsorption isotherm in buffer solutions presented more obvious liner form than that in non-buffer solutions, while the correspondence of q_e and c_e/W_0 in non-buffer solutions was better than that in buffer solutions. The present findings suggest that the method of containing buffer solution to eliminate the adsorbent effect was not advisable.