Glyphosate adsorption by ferric supported active carbon

Ferric supported active carbon was prepared by impregnation-calcination method and the characteristics of its surface were investigated by scanning electron magnification (SEM), and both adsorption isotherm and adsorption kinetics of Fe-AC were studied. The effects of different factors on the adsorption process were also studied. Freundlich equation fitted well to supported ferric active carbon adsorption isotherm, the maximum adsorption capacity was 5.8 mmol/g; and the adsorption kinetics was fitted well by Lagergren equation, so adsorption rate constant can be calculated out 0.088 min^-1 that can decrease with the temperature increase. According to Kannan & Sundaram internal diffusion model, the internal diffusion constant was higher than 10 mg·min^-1/2/g, which decreased with the temperature increase. Due to the ionization form of glyphosate and the change of Fe-AC surface characteristics, the adsorption capacity of glyphosate decreased when the pH of solution increased. Antagonistic effect caused the adsorption capacity decrease of Fe-AC due to the existence of NaCl, and when the concentration of NaCl reached 4 g/L, salting-out effect became dominant, which increased the adsorption capacity slightly. Because of the steric hindrance of glyphosate and the complex formation between phosphate and supported ferric active carbon surface, the Fe-AC adsorption capacity decreased continuously while the concentration of phosphate increase.