Investigation of the adsorption kinetics of methylene blue onto cotton wastes

Cotton stalk (CS), cotton waste (CW), and cotton dust (CD), which are cotton wastes, were used as adsorbents to study the adsorption kinetics of methylene blue from aqueous solution. Kinetics of the batch adsorption experiment was investigated according to the pseudo-first order, the pseudo-second order, and the intraparticle diffusion models used commonly in the literature. The effects of the initial concentration, solution pH, and temperature on kinetic parameters (adsorption rate constant, initial adsorption rate, equilibrium adsorption capacity, etc.) were studied. The results showed that the adsorption process was well fitted to the pseudo-second order model for all adsorbents. The activation energy (Ea) of the adsorption process was determined by using the pseudo-second-order rate constants by means of Arrhenius’ equation. The values of Ea were estimated as 7.05, 10.89, and 35.72 kJ mol −1 for CS, CW, and CD, respectively. From the results, it was understood that the adsorption process was controlled by an intraparticle diffusion mechanism as well as both an activated process and a physical adsorption process.