Study on the adsorption behavior of atrazine onto loess soil in northwest China

Batch experiments were performed to understand the sorption kinetics and thermodynamics of atrazine (ATZ) onto loess soil. Meanwhile, the effects of the systemic temperature, pH value and the initial concentration of ATZ were also investigated for the adsorption of ATZ onto loess soil. The results indicate that the adsorption kinetic of ATZ onto loess soil could be better described by the pseudo-second-order model, and the boundary layer control and intraparticle diffusion were both involved in the adsorption kinetic process. The adsorption thermodynamics of ATZ onto loess soil were linear, and were fitted well with the Henry model (R²>0.90). Thermodynamic parameter analysis showed that Gibbs free energy (ΔG^θ) and Entropy (ΔH^θ) were less than zero, while Enthalpy (ΔS^θ) was greater than zero, which tended to prove the spontaneous nature of the adsorption process, the endothermic nature of the adsorption and the increased randomness at the solid-solution interface due to the adsorption of ATZ. The average adsorption free energy E was between 0.86-1.30 kJ/mol when the temperature increased from 25 to 45℃. This indicated that adsorption was dominated by physical adsorption. The adsorption capacity of ATZ tended to decrease with the increase of pH value between 2 and 10. When the initial concentration of ATZ increased from 2.5 to 10.0 mg/L, the adsorption capacity of ATZ increased from 0.0825 to 0.6210 mg/g. The results indicate that the adsorption rate of ATZ onto loess involved a surface adsorption, diffusion within the particles and external film diffusion mechanism. The adsorption processes of ATZ onto loess were mainly affected by the hydrophobic effect of soil organic distribution.