重金属吸附对紫色土表面电荷性质的影响

Effect of Heavy Metal Adsorption on the Surface Charge Properties of Purplish Soils

在实验室条件下,研究了Pb、Cu、Zn、Cd在3种紫色土中的吸附特征,并采用恒流置换法测定重金属吸附饱和后3种紫色土表面电荷总量、表面电位、电荷密度。结果表明:(1)一定pH条件下在同种土壤上的吸附能力大小依次是Pb2+>Cu2+>Cd2+、Zn2(2)3种紫色土在一定pH条件下对同种重金属离子的吸附强度依次是石灰性紫色土>中性紫色土>酸性紫色土,与其表面电荷密度的大小相一致;(3)Pb2+、Cu2+在3种紫色土表面以电性吸附和专性吸附的方式共存,其专性吸附的比例分别约为40%、25%、20%,并导致表面电位降低了约0.05V(近30%),表面电荷总量以及表面电荷密度降低了20%￣40%;(4)Zn2+、Cd2+在土壤表面上绝大多数发生电性吸附,对紫色土表面电荷性质没有显著的影响。

All the physical and chemical properties of soil are ascribed to surface charge of soil particles. Many processes in the soil system are influenced by surface charge. Some researches available hold that some chemical process, such as heavy metal contamination, especially, lead or copper contamination, will have a deeply influence on the surface charge properties. The changes of surface charge properties may results in the change of soil quality. Therefore to understand the extent of such changes carries weight in predicting soil quality degradation and restoring contaminated soils. In this paper, the adsorption characteristics of heavy metals （including Pb^2＋, Cu^2＋, Cd^2＋, Zn^2＋） on the acidic, neutral and calcareous purplish soils was studies, the effect of heavy metal adsorption on the surface charge quantity, surface potential and surface charge density of soils were conducted. The experimental results show that： （1） at certain pH, the adsorption strength of heavy metal on every soils is Pb^2＋〉 Cu^2＋〉 Cd^2＋ Zn^2＋, （2） at certain pH, the quantity of every heavy metal adsorpted by soils is calcareous purplish soils〉 neutral〉 acidic, which is in line with the surface charge density, （3） Pb^2＋,Cu^2＋ adsorption, which include electrical adsorption as well as specific adsorption, each accounted for about 40%,25%,20%, significantly changed the surface charge properties： Surface potential decreased 0.05 V, decreased about 30%,surface charge density decreased 20%～40%. However, Zn^2＋. Cd^2＋ adsorption, which belonged to electrical adsorption, result in few change of the surface charge properties.