Adsorption of cobalt(II) ions from aqueous solutions by palygorskite

A study on the removal of cobalt ions from aqueous solutions by palygorskite was conducted under batch conditions. The effect of time, pH of the dispersion, ionic strength, temperature and initial metal concentration on the adsorption of Co2+ onto palygorskite was investigated. The adsorption of Co2+ was a fast process that followed the pseudo-second-order kinetics. This process could be described by the Langmuir model and gave a maximum Co2+ adsorption capacity of 8.88 mg/g at 35 °C. The adsorption was dependent on pH and was influenced by the ionic strength. The adsorption mechanism primarily involved inner-sphere complexation, with minor contributions of the exchange of structural Mg2+ ions. Palygorskite could be completely regenerated with Na2CO3 and continued to exhibit excellent Co2+ adsorption even after three consecutive cycles.