不同分层土壤对锌的吸附解吸特性

Adsorption and Desorption Characteristics of Zinc in Different Layered Soils

为探究重金属锌在不同分层土壤中的吸附解吸特性,了解锌在分层土壤中的迁移规律,试验通过批量平衡试验,分析了锌在4个分层土壤(耕作层、犁底层、心土层、母质层)中的吸附解吸行为。结果表明:各分层土壤对锌的吸附动力学过程包括快速吸附、慢速吸附、吸附平衡3个阶段,准二级动力学方程对吸附过程的拟合效果优于准一级动力学方程,Langmuir方程能更好的拟合4种分层黑土对锌的等温吸附过程,4种土壤分层对锌的吸附能力由大到小的顺序为耕作层、犁底层、心土层、母质层,是因为随着土壤深度的增加,土壤有机质质量分数逐渐减小,4种分层土壤对锌的吸附能力逐渐降低。吸附热力学试验表明,随着温度的升高,各分层土壤对锌的吸附量均逐渐增大,ΔG<0(ΔG为吉布斯自由能的变化),ΔH>0(ΔH是标准焓变),ΔS>0(ΔS是标准熵变)说明了4个分层土壤对锌的吸附过程为自发、吸热、无序的过程。Zn的解吸量与吸附量呈正比,最大解吸量随着剖面深度的增加而减小,且均存在滞后效应。N、P质量浓度的增加,可以提高土壤固定Zn的能力,减小Zn对土壤农作物、地下水的重金属危害。

To explore the adsorption and desorption characteristics,the migration rule of zinc(Zn)in different soil layers.We studied the adsorption and desorption behavior of Zn in four soil layers(cultivated layer,plow pan layer,subsoil layer and parent material layer)by batch equilibriummethod.The results show three stages of desorption kinetics process of Zn in soil,which are fast adsorption,slow adsorption and adsorption equilibrium.The quasi-second order kinetic equation can better fit the adsorption processthan quasi first-order kinetics equation.Langmuir equation fits better in isothermal adsorption process in four layers of mollisols.The adsorption capacity of Znin descendingorderin four soil layersis cultivated layer,plow pan layer,subsoil layer and parent material layer which is caused by the adsorption capacity of soil to Zn gradually decreases with soil organic matter content gradually decreases with the increase of depth.The results of adsorption thermodynamics test shows the adsorption amount of Zn in each soil layer gradually increases with the increase of temperature.ΔG<0(ΔG is the change of Gibbs free energy),ΔH>0(ΔH is the standard enthalpy change),ΔS>0(ΔS is the standard entropy change)indicates the adsorption process of Zn in four soil layers is spontaneous,endothermic and disordered.The amount of Zn desorption is proportional to the amount of adsorption,the maximum desorption amount decreases with the increase of the depth of the profile,and there is a hysteresis effect.The increase in the mass concentration of N and P can improve the ability of soil to fix Zn and reduce the heavy metal harm of Zn to soil crops and groundwater.