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: In order 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 298–318K. 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 were 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 <0, indicated that the adsorption of atrazine in soils was spontaneous and dominated by physical adsorption. Changes in standard enthalpy ( ) indicated that the adsorption was exothermic. Conclusion: 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.

Optimization of Cr (VI) removal from aqueous solution with activated carbon derived from Eichhornia crassipes under response surface methodology

“…The intraparticle diffusion model indicates the diffusion mechanism. According to Yu et al [86], in the qt vs t 0.5 graph, if the regression line passes through the origin, the intraparticle diffusion process of Cr (VI) is the only rate control step. Moreover, if the regression line did not pass through the origin, the intragranular diffusion process of Cr (VI) is not the only rate control step.…”

“…As shown in Table 8, the value of C is different from zero, which means the regression line did not pass through the origin. This indicates that extragranular diffusion processes such as surface adsorption and liquid film diffusion may affect the boundary layer control and adsorption rate [86].…”