3,5,6-三氯-2-吡啶醇在紫色土中的吸附特征与参数估计

Adsorption Characteristics and Its Parameters Estimation of 3,5,6-trichloro-2-pyridinol in Purple Soil

通过批量平衡实验和土柱实验获得了3,5,6-三氯-2-吡啶醇(简称TCP)在紫色土土壤中的吸附特征,并应用模型对上述吸附过程进行模拟。其中,吸附动力学参数通过准一阶、准二阶动力学方程、Elovich模型和粒子扩散模型反演;等温吸附参数应用Freundlic、Langmuir和Linear模型反演;土柱实验中的吸附参数基于Thomas与YoonNelson模型反演。结果表明:TCP在紫色土中的吸附动力学过程包含快速的表面物理吸附和慢速的内部化学扩散2个阶段,且粒子扩散模型表现最好。等温吸附过程可以通过Freundlic模型描述(R^2=0.94),获得的吸附容量常数K_f为0.79 mL/g,吸附水平较小说明TCP在紫色土中具有较大的迁移风险。TCP在土柱中达到平衡需要的时间约为1 215 min,土壤对TCP的吸附率为10.65%。Thomas与Yoon-Nelson模型能够较好地模拟TCP在紫色土中的动态吸附曲线(R^2≥0.84),获得的平衡浓度q0为0.008 6 mg/g。

The adsorption parameters of pesticide are one of the most important factors to determine its destination and pollution in the soil and water. However,these parameters varied substantially in different environments even though tested by the same soil samples. 3,5,6-trichloro-2-pyrdionl（ TCP） is the main degradation product of pesticide chlorpyrifos and herbicide triclopyr,and it exhibits anti-degradation ability,high water solubility and high migration capability,which would lead to the soil and water pollution easily. This situation might be exacerbated in purple soil distributing regions because of the low organic matter content and large pores with high water conductivity of the soil. In order to provide more accurate data,the adsorption behaviors of TCP in purple soil were explored on the basis of three environments： isothermal adsorption and kinetic adsorption by bath equilibrium experiment,and soil column experiment by breakthrough curves. Then the parameters of these adsorption processes were simulated by their corresponding models. As for kinetic adsorption,the performance of four models was tested,which were pseudo-first-order,pseudo-second-order,Elovich,and intraparticle diffusion model,respectively; isothermal adsorption was fitted by Freundlic,Langmuir and Linear models; and the adsorption in soil column experiment was simulated by Thomas and Yoon-Nelson models. By comparing the performance of these methods,the appropriate models were identified,and the adsorption parameters in different environments were obtained through inversion simulation. The main conclusions were as follows： the kinetic adsorption of TCP in purple soil included two stages： both rapid physical adsorption on the surface and slow chemical diffusion inside,and intraparticle diffusion model performed the best with determination coefficient R^2 of 0. 99,implying the diffusion had important effect on the kinetic adsorption; as for isothermal adsorption,Freundilic model performed the best（ with R^2 of 0. 94）,and the inversion simulated parameter of Kfwas 0. 79 mL/g,which indicated a high risk of transportation in soil;in the soil column experiment,the equilibrium time was 1 215 min for breakthrough curve of TCP,and the adsorption rate was 10. 65%. The dynamic adsorption curves can be well simulated by Thomas and Yoon-Nelson models（ R^2≥0. 84）,from which the equilibrium concentration was obtained： q0 equaled to0. 008 6 mg/g. Therefore,this study identified the appropriate model to describe the adsorptions of TCP in purple soil in different environments,and the corresponding parameters were obtained by inversion simulation. These results were able to provide useful references for predicting the destination of TCP in purple soil,as well as other easy transporting pollutants.