Abstract: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 R2 of 0.99, implying the diffusion had important effect on the kinetic adsorption;as for isothermal adsorption, Freundilic model performed the best (with R2 of 0.94), and the inversion simulated parameter of Kf was 0.79mL/g, which indicated a high risk of transportation in soil;in the soil column experiment, the equilibrium time was 1215 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 (R2≥0.84), from which the equilibrium concentration was obtained: q0 equaled to 0.0086mg/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.
