Adsorption characteristics of Cd(II) from aqueous solution onto activated palygorskite

A series of activated palygorskites were prepared by acid treatment and heat treatment, and the activated samples were applied as adsorbents for the removal of Cd(II) from aqueous solutions. The effects of various experimental parameters were investigated using a batch adsorption technique. Results showed that the adsorption capacity of the acid-treated palygorskite for Cd(II) increased with the increase of the concentration of initial Cd(II) solution, contact time and pH of initial suspension. It was found that the adsorption capacity of activated palygorskite increased with increasing the HCl concentration and calcination temperature, and the maximum adsorption capacity of acid-treated and heat-treated palygorskites for Cd(II) was obtained with 12 mol/L HCl and at about 300 °C. The adsorption isotherms of activated palygorskites for Cd(II) could be described by both Langmuir and Freundlich equations, and the Freundlich model is better to represent the adsorption process. The final pH values of the solution in all adsorption experiment were also measured. In addition, the interactions at the clay–water interface and the Cd(II) adsorption mechanisms onto the activated palygorskites were discussed.