Equilibrium and Kinetics of Methylene Blue Sorption onto Clay-Carbonate Diatomite

Surface characteristics of the clay-carbonate diatomite and its adsorption properties with respect to methylene blue (MB) were investigated. The equilibrium isotherms were modeled by the Langmuir, Freundlich, and Dubinin–Radushkevich equations. The Langmuir model more adequately described the experimental data with a correlation coefficient of 0.9783 and a maximum adsorption capacity of 112.8 mg/g. The separation factor was 0.143, indicating the favorability of the sorption process. The treatment of the experimental kinetic data showed that the pseudo second order model better describes the kinetic curves of the MB sorption. Intraparticle diffusion does not control the MB sorption rate, and film diffusion is the main contributor to the rate limitation. The activation energy for sorption, calculated using the Dubinin–Radushkevich model, was 17.4 kJ/mol, indicating the predominance of physical sorption. The results show that this sorbent can be used for the purposes of water purification from organic pollutants.