Experiment and Simulation on Adsorption of 3,5,6-Trichloro-2-Pyridinol in Typical Farmland of Purple Soil, Southwestern China

Abstract

ABSTRACTThe adsorption behaviors of 3,5,6-trichloro-2-pyridinol (TCP) are explored by experiment and simulation on typical farmland of purple soil in southwestern China. Samples are collected from three farmlands with seasonal crop rotation of wheat-corn, rice-rape and vegetables respectively, and isothermal adsorption, breakthrough curves (BTCs) of packed and intact soil column experiments are tested. Adsorption parameters are also obtained by inversion simulation of appropriate model. The results reveal that the adsorption varies substantially in different farmlands and environmental conditions. Isothermal adsorption displays a decrease trend from the soil with crop of wheat-corn to rice-rape, then vegetables, and the main influencing factor is content of clay and silt. Langmuir model fits the isothermal adsorption best (R2 = 0.99), and the estimated adsorption capacity (qm) of soil is 2.73, 1.19 and 0.55 mg/g, corresponding to the sample from farmland of wheat-corn, rice-rape and vegetable, respectively. However, the adsorbed amount by unit mass is almost the same in packed columns because of the incomplete interaction between TCP and soil, accounting for 0.59–3.24% of qm. In intact soil columns, the adsorption on TCP decreases further, 0.13–1.15% of qm. Thomas model fits TCP's adsorption well in packed soil columns (R2 ≥ 0.97) but poorly in intact soil because of the preferential flow, and the fact that the more intensive the preferential flow, the poorer is the performance of the model.