Adsorption Characteristic of Cd on Loess Soil Affected by Humic Acid

Vibration-centrifuge method was used to study adsorption characteristic of Cd on loess soil affected by humic acid.The results showed that the adsorption of Cd on loess soils fitted well with Freundlich isothermal equation no matter with or without humic acid,and the adsorption quantity of Cd increased from 29.22 mmol·kg-1 to 31.39 mmol·kg-1 by adding 10 mL 55 mg·L-1 humic acid solution at 25 ℃.The adsorption capacity of Cd reduced with increasing of environmental temperature,indicating that adsorption of Cd was an excergic process,meanwhile,the adsorption standard free energy changed fromΔG1θ=-0.888 5 kJ·mol-1 to ΔG2θ=-0.949 7 kJ·mol-1 at presence of humic acid.The adsorption kinetics of Cd best fitted with Evolich kinetics equation,and then was double constant equation,but at presence of humic acid,it changed to double constant equation.The adsorption speed of Cd was faster than that without humic acid.The adsorption capability of Cd increased with humic acid concentration and the solution pH increasing.The adsorption quantity of Cd was higher at low pH.