Removal of Reactive Blue 221 by Kaolinite from Aqueous Solutions

The adsorption behavior of reactive blue 221 (RB221) on kaolinite was investigated by batch tests. The experiments were performed by employing a spectrophotometer to measure the concentration of RB221 before and after adsorption. The effects of various parameters such as initial solution pH, ionic strength, temperature, and acid activation were determined. The adsorption process reached equilibrium within 3 h. The adsorbed amount of RB221 increased with increasing ionic strength, temperature, and acid activation, but it decreased with increasing pH. Langmuir and Freundlich isotherms were applied to fit the equilibrium data to identify the best isotherm to describe the RB221 adsorption. The data were best described by the Langmuir isotherm. The isosteric heat of adsorption indicated the endothermic nature of RB221 adsorption on kaolinite. It was concluded that reactive blue 221 physically adsorbs on kaolinite. The value of the dimensionless separation factor (R-L) suggests that kaolinite can be used for the removal of reactive blue 221 from aqueous solutions. The experimental results were applied to a batch design. As a result, kaolinite could be used for the removal of dyes from aqueous solutions.