Use of kaolinite as adsorbent: Equilibrium, dynamics and thermodynamic studies on the adsorption of Rhodamine B from aqueous solution

The adsorption efficiency of kaolinite for Rhodamine B (RhB) removal from aqueous solution is reported. The optimized conditions for adsorption were evaluated as: initial concentration of RhB (90 mg/L), agitation time (80 min), adsorbent dose (3 g/L), pH (7), and temperature (303 K). The adsorption data were evaluated using Langmuir, Temkin, Freundlich, Flory–Huggins and Dubinin–Kaganer–Radushkevich isothermal models, but high correlation coefficients (R2) confirmed the validity of Langmuir isotherm, with monolayer adsorption capacity (qm) equal to 46.08 mg/g (83%). The kinetic data agreed well with pseudo-second order model with rate constants (K2) in the range 0.568–4.69 × 10− 3 g/mg min. Diffusion studies indicated that intra-particle diffusion is not the sole rate-controlling factor. The thermodynamic parameters indicated that adsorption of RhB onto kaolinite was spontaneous, endothermic, and the entropy increased during adsorption. The study revealed that kaolinite can be utilized as an efficient low-cost adsorbent for decolorization of wastewater containing RhB dye.