低分子量有机酸影响可变电荷土壤吸附铜的机制

采用平衡实验法研究了水杨酸和邻苯二甲酸对砖红壤吸附铜的影响,并通过吸附铜的解吸实验探讨了有机酸对铜吸附的影响机制.结果表明,有机酸可以增加土壤对铜的吸附量,与对照相比,有机酸体系中吸附的铜的解吸量高.有机酸对铜吸附的影响随体系pH值的增加而增大,约在pH4.3(水杨酸体系)或pH4.5(邻苯二甲酸体系)达最大,然后逐渐减小.土壤对有机酸的吸附量越高,有机酸对铜吸附的影响程度越大.有机酸可以通过形成表面三元络合物和改变土壤的表面电荷2种机制影响土壤对铜的吸附.水杨酸体系中铜的解吸增量与吸附增量的百分比在76%～89%之间,说明水杨酸主要是通过增加土壤表面的净负电荷量来增加铜的静电吸附量.

Mechanisms of low molecular weight organic acids affecting Cu adsorption by variable charge soils

The influence of salicylic and phthalic acids on Cu adsorption by laterite was studied adopting equilibrium test technique, and the affecting mechanisms of organic acids on Cu adsorption were tested and explored through the desorption of adsorbed Cu. Organic acids could increase the Cu adsorption amount of soil and the desorption amount of Cu adsorbed in organic acids system was higher than that in control system. The influence of organic acid on Cu adsorption increased with the increase of pH value in the system and reached the maximum about pH4.3 (salicylic acid system) and 4.5 (phthalic acid system); and then decreased gradually. The higher the amount of organic acids adsorbed, the larger the influence degree of the Cu adsorption by organic acids. Organic acids could influence Cu adsorption by soil through two mechanisms: the formation of soil-organic acid-cation surface ternary complex compound and the change of surface charge of soil. In salicylic acid system, the percentage of the increment in the Cu desorption to that in the Cu adsorption was in the range of 76% to 89%, showing that salicylic acid increase electrostatic adsorption amount of Cu mainly through the increase of net negative charge amount of soil surface.