Isotherm and Kinetic Adsorption of Malachite Green Using Low-Cost Adsorbent of Coal Fly Ash

In this study, isotherm and kinetic adsorption of malachite green (MG) using coal fly ash (CFA) as the adsorbent was investigated. This study aimed to examine the character of CFA analyzed by Atomic Absorption Spectrophotometry (AAS), Fourier-Transformed Infra-Red (FTIR), and X-Ray Diffraction (XRD) analysis. In addition, the adsorption of MG on CFA was also studied, including the effect of solution pH, adsorbent mass, contact time, and concentration of malachite green on the adsorption process. From the experimental data, the kinetic parameters isotherms and energy of the adsorption were determined. Kinetic study showed that the kinetic adsorption of MG on CFA fit well the Ho and McKay’s pseudo-second-order, with an adsorption rate constant (k2) of 0.0377 g mg-1 min-1. Furthermore, the Langmuir isotherm model was the most suitable model to describe adsorption. Changes in the standard Gibbs free energy calculated from equilibrium constant (KL) at room temperature (303 K) showed that the adsorption process occurred spontaneously through chemical interaction (chemisorption) and most probably formed a monolayer on the surface of the adsorbent.