Isotherm, kinetic, and thermodynamic studies on the adsorption behavior of malachite green dye onto montmorillonite clay

Systematic batch mode studies of adsorption of malachite green (MG) on montmorillonite clay were carried out as a function of process parameters which include pH, adsorbent dosage, agitation speed, ionic strength, initial MG concentration, and temperature. Montmorillonite was found to have excellent adsorption capacity. Equilibrium adsorption isotherms were measured for the single-component system, and the experimental data were analyzed by using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm equations. It was found that the Langmuir equation appears to fit the equilibrium data. The monolayer (maximum) adsorption capacity (q(m)) was found to be 262.494 mg g(-1) for montmorillonite. The experimental kinetic data were analyzed using the first-order, second-order, Elovich, and intraparticle kinetic models and the second-order kinetic model described the adsorption kinetics accurately for MG. Thermodynamic activation parameters such as Delta G*, Delta S*, and Delta H* of the adsorption of MG on montmorillonite were also calculated.