Equilibrium, kinetic and thermodynamic studies on the adsorption of atrazine in soils of the water fluctuation zone in the Three-Gorges Reservoir

Abstract

Background: Environmental behavior of pesticide in soils is a key current research focus. Studying the adsorption characteristics of pesticides in soils as a parameter for evaluating the risk of groundwater pollution by pesticides is commonly applied in agriculture. Results: To provide a theoretical basis for environment risk assessment and pollution remediation, the thermodynamics and kinetics of the equilibrium of atrazine adsorption in the Three-Gorges Reservoir area were assessed and analyzed via batch experiments. Results showed that the sorption of atrazine was an exothermic and spontaneous process at temperatures of 298–318 K. Atrazine was more easily adsorbed by soils at concentrations of 0–30 mg L−1, with low-temperature adsorption being more effective than high-temperature adsorption. The adsorption of atrazine to the two assessed soils was well fitted by the Freundlich and Langmuir models. The adsorption kinetics of atrazine in soils were consistent with the quasi-second-order kinetic model and intraparticle diffusion was found not to be the only control step. The monolayer adsorption occurred with non-uniform energy distribution on the soil surface, indicating that the adsorption of atrazine by the two kinds of soil was controlled by internal diffusion surface adsorption and liquid film diffusion, leading to the complexity of its adsorption kinetics. The values of standard free energy ΔrGm0 < 0, indicated that the adsorption of atrazine in soils was spontaneous and dominated by physical adsorption. Changes in standard enthalpy (ΔrHm0) indicated that the adsorption was exothermic. Conclusions: Atrazine exhibited a weak adsorption capacity in both soils, indicating it is highly mobile in the soil–water environment and can easily cause groundwater pollution. Therefore, much attention should be paid to the environmental behavior of pesticide soil moisture fluctuations, potentially leading to the broad transfer and spread of pollution.