Modeling of adsorption isotherms and kinetics of Remazol Red RB adsorption from aqueous solution by modified clay

The adsorption of an anionic dye Remazol Red RB, from aqueous solution on modified clay was investigated at 298, 313, and 333 K. Different parameters that influence the adsorption process such as contact time, initial dye concentration, solution pH, and temperature were systematically studied. Adsorption capacity increased with increasing of temperature, initial dye concentration, and pH. The value of zeta potential decreased with increasing of pH. Experimental adsorption data were modeled by different equilibrium isotherms such as Langmuir, Freundlich, Temkin, Dubinin-Radushkevich (D-R), Brunauer-Emmett-Teller (BET), Halsey, Harkins-Jura, Smith, and Henderson isotherms. The adsorption process followed the Langmuir isotherm model with high coefficients of correlation (R-2 > 0.99) at different temperatures. The pseudo-second-order kinetic model fitted well in correlation to the experimental results. Activation energy of the adsorption process (Ea) was found to be 34.49 kJ mol(-1) and 40.27 kJ mol(-1) for initial dye concentrations of 75 and 150 mg/L, respectively-by using the Arrhenius equation, indicating the strong electrostatic interactions between the adsorbent and dye. Thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic in nature.