Equilibrium, Isotherm and Kinetic Adsorption Studies of Direct Blue 71 onto Raw Kaolin

Background: Nowadays, the development of new materials is emergent that can be used in the adsorption process to remove dyes from the aquatic environment. Therefore, in this study, the performance of raw Kaolin as a low cost adsorbent was evaluated in removing Direct Blue 71 (DB71) dye from aqueous solutions. Methods: For investigating the adsorption, various parameters were optimized and data were adjusted to four isotherm models: Freundlich, Dubinin–Radushkevich, Langmuir and Temkin, in order to determine the one presenting the best adjustment to the experimental data. Moreover, the kinetics study for adsorption was evaluated using diffusion, pseudo-first-order kinetic and pseudo-second-order kinetic models. Results: The results revealed that at the DB71 concentration of 10 mg/L, adsorbent dose of 2.5 g/L, and contact time of 75 min, the DB71 removal reached 98.5%. Adsorption data fitted best into the Langmuir and D-R adsorption isotherms. The maximum monolayer adsorption capacity was 36.41 mg/g. The pseudo second order kinetics best described the kinetics of the adsorption system. Conclusion: It was revealed that Kaolin could be applied for DB71 dye removal from solution samples with the adsorption capacity of 36.41 mg/g and thus could be used as a low-cost and effective adsorbent.