Investigation of Kinetics and Isotherm Models for the Acid Orange 95 Adsorption from Aqueous Solution onto Natural Minerals

Adsorption of Acid Orange 95 (AO 95) from aqueous solution onto natural bentonite, zeolite, and sepiolite was studied, and the effects of the parameters like pH, contact time, temperature, and lab concentration of dye were investigated. The AO 95 adsorption onto A bentonite, sepiolite, and zeolite was favorable at pH 1.5. It was found that temperature does not affect the adsorbed amount of dye significantly. Among the adsorbents, the highest adsorption capacity is that of bentonite. The pseudo-first-order and pseudo-second-order models were employed to analyze the experimental kinetic data. The adsorption experimental equilibrium data were analyzed with two- (Langmuir, Freundlich, Dubinin-Radushkevich, Harkins-Jura, Temkin, and Jovanovic) and with three- or four-parameter models (Redlich-Peterson, Radke-Prausnitz, Toth, Sips, and Fritz-Schliinder). Both linear and nonlinear regression methods were applied to calculate the kinetic and isotherm parameters, and the nonlinear regression was found as a more suitable method. Regarding to the results of the nonlinear analysis, the rates of adsorption conformed to the pseudo-first-order kinetics, and the most suitable adsorption models were found to be the Toth, Harkins-Jura, and Freundlich isotherms for sepiolite, bentonite, and zeolite, respectively.