[目的]为探究贵州黄壤对污染毒性较强的铅(Pb)和镉(Cd)元素的吸附特征及吸附机制，针对性地为农业土壤重金属Pb、Cd污染防治提供理论依据。[方法]以贵州省不同位点玄武岩母质黄壤为研究对象，根据1-site/2-p Ka广义复合表面络合模型(SCM)理论的相关公式，结合黄壤理化性质测定实验、电位滴定实验和Pb、Cd的吸附边实验，获得黄壤表面酸碱性质参数即模型参数，然后利用1-site/2-p Ka SCM模拟黄壤表面3种活性位点形态分布情况以及不同pH下的Pb、Cd吸附行为，探讨黄壤对Pb、Cd的吸附特征及吸附机理，进行相关性分析，解析影响黄壤对Pb、Cd吸附的因素。[结果]根据SCM理论相关公式，计算获得4个黄壤样品的电荷零点pHpzc，SCM分别为5。040、5。549、7。984、4。297，表面位点浓度(Hs)分别为0。137，0。183，0。181，0。308 mol/kg，表面位点密度(Ds)分别为4。519，2。571，2。122，3。664 sit/nm2;通过SCM模拟了不同pH条件下黄壤表面≡SOH2+、≡SOH、≡SO-形态的变化，并初步解释了Pb、Cd在黄壤表面的吸附机理，同时拟合了不同pH下Pb、Cd在黄壤表面的吸附行为(相关系数R≥0。96)，说明SCM适用于描述黄壤表面Pb、Cd的吸附特征。吸附边实验表明Pb、Cd初始浓度以及土壤环境的pH均会影响Pb、Cd在黄壤表面的吸附行为，且Pb、Cd在黄壤表面的吸附存在差异;黄壤对Pb的吸附能力大于Cd，不仅源于Pb具有更小的水合离子半径和更大的水解常数，且由SCM计算络合平衡常数lg KSOPb大于lg KSOCd，表明Pb在黄壤表面形成的络合物比黄壤Cd的络合物稳定。相关性分析表明黄壤Hs主要受铁铝氧化物和有机质的影响，pH对黄壤pHpzc及lg KSOCd、lg KSOPb有重要影响。[结论]1-site/2-p Ka SCM对于准确描述贵州玄武岩母质黄壤表面Pb、Cd吸附特征及解释Pb、Cd的吸附机制具有很好的适用性，可为重金属在农业土壤中的迁移转化行为研究提供参考。
Adsorption behavior and surface complexation models of plumbum and cadmium in basalt yellow soil
[Objective]This study aims to to understand the adsorption characteristics and mechanisms of Plumbum(Pb)and cadmium(Cd)elements,which have strong pollution toxicity,in Guizhou yellow soil,thus providing theoretical basis for the prevention and control of heavy metal Pb and Cd pollution in agricultural soil.[Method]Basalt parent yellow soil from different sites in Guizhou Province was selected as the research object.According to the relevant formulas of the 1-site/2-p Ka Generalized Complex Surface Complexation Model(SCM)theory,combined with soil physicochemical property determination experiments,potentiometric titration experiments,and Pb and Cd adsorption edge experiments,the surface acid-base property parameters,namely model parameters,of yellow soil were obtained.Then,using the 1-site/2-p Ka SCM,the morphological distribution of three active sites on the yellow soil surface and the adsorption behavior of Pb and Cd at different pH levels were simulated to explore the adsorption characteristics and mechanisms of Pb and Cd by yellow soil.Correlation analysis was conducted to analyze factors influencing the adsorption of Pb and Cd by yellow soil.[Result]According to the relevant formulas of the SCM theory,the charge zero pHpzc,SCM of the four yellow soil samples were obtained as 5.040,5.549,7.984,and 4.297,respectively.The surface site concentrations(Hs)were 0.137,0.183,0.181,and 0.308 mol/kg,and the surface site densities(Ds)were 4.519,2.571,2.122,and 3.664 sit/nm2,respectively.Changes in the forms of ≡SOH2+,≡SOH,and ≡SO-on the yellow soil surface under different pH conditions were simulated by SCM,and the adsorption mechanisms of Pb and Cd on the yellow soil surface were preliminarily explained.The adsorption behavior of Pb and Cd on the yellow soil surface was fitted at different pH levels(correlation coefficient R≥0.96),indicating that SCM was suitable for describing the adsorption characteristics of Pb and Cd on the yellow soil surface.Adsorption edge experiments showed that the initial concentrations of Pb、Cd and the pH of the soil environment both affect the adsorption behavior of Pb and Cd on the yellow soil surface,and there are differences in the adsorption of Pb and Cd on the yellow soil surface;The adsorption capacity of yellow soil for Pb was greater than that for Cd,which was not only due to Pb having a smaller hydrated ion radius and a larger hydrolysis constant,but also because the calculated complexation equilibrium constant lg KSOPb was greater than lg KSOCd,indicating that the complex formed by Pb on the yellow soil surface was more stable than that formed by Cd.The correlation analysis indicated that Hs in yellow soil was primarily influenced by iron-aluminum oxides and organic matter.pH had a significant impact on pHpzc and lg KSOCd,as well as lg KSOPb in yellow soil.[Conclusion]The 1-site/2-p Ka SCM is highly applicable for accurately describing the adsorption characteristics of Pb and Cd on the surface of basalt parent yellow soil in Guizhou Province and explaining the adsorption mechanisms of Pb and Cd,.It could provide reference for the study of the migration and transformation of heavy metals in agricultural soil.
万方数据
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