黄土–粉土混合土对Pb(Ⅱ)的静平衡和动态吸附特性

Adsorption characteristics of loess-modified natural silt towards Pb(II): equilibrium and kinetic tests

竖向防污屏障是防止地下水土污染的主要屏障。天然土是屏障最主要的材料来源。以天然粉土为母土,黄土为添加剂,以重金属Pb(Ⅱ)作为污染物的代表,通过粉土–黄土混合土对Pb(Ⅱ)的静平衡吸附和动态吸附试验研究黄土作为添加剂对天然粉土的改良效果。试验考虑了黄土添加量、溶液pH值、反应时间以及重金属初始浓度等对吸附的影响。结果表明添加黄土可以有效改善天然粉土的吸附效果,混合土对Pb(Ⅱ)的吸附容量随黄土添加量的增加线性增长,添加20%黄土的混合土的吸附容量达天然粉土的2倍;添加黄土可减少混合土对重金属的吸附时间,在相同时间内减少迁移量。通过扫描电镜和XRD等手段揭示了黄土对Pb(Ⅱ)的吸附主要是方解石与Pb(Ⅱ)发生界面沉淀作用生成白铅矿;粉土对Pb(Ⅱ)的吸附主要是长石等矿物棱角处经风化水解形成的–OH基团对Pb(Ⅱ)的阳离子交换作用。黄土由于高方解石含量在对Pb(Ⅱ)的吸附方面表现突出,可以作为一种添加剂加入天然土层中,以增强屏障对重金属的吸附阻滞效果,减少环境污染。

Vertical wall is one of the barriers used to prevent contamination of subsurface soil and groundwater. Natural soil is the main resource of the barrier materials. Loess is added to a natural silt to enhance its adsorption capability. Lead is chosen to represent the contaminants. Equilibrium and kinetic adsorption tests are carried out to investigate the effects of loess on the adsorption characteristics of the mixed soils. The effects of loess proportion, initial solute pH value, shaking time and initial solute on the adsorption capability of mixed soils are considered. The maximum adsorption capacity of the mixed soils increases linearly with the increase of the amount of the loess. The adsorption capacity of the mixed soils amended with 20% loess can be two times greater than that of the natural soil. Compared with that of the natural silt, the adsorption time of Pb（Ⅱ） can also be reduced for the loess-modified soil. Using the electron spectroscope and X-ray diffraction, it is illustrated that the high adsorption capability of loess is due to the surface precipitation of calcite with lead. The adsorption of lead on silty soil is ascribed to cation exchanging process. It is indicated that loess can be used as an additive to increase the adsorption ability of the natural soil and then to reduce the risk to the environment pollution regarding heavy metals due to high content of calcite and high adsorption capability of lead.