Experimental study and modeling of basic dye sorption by diatomaceous clay

This paper presents a study on the adsorption of basic dye, methylene blue, from an aqueous solution onto diatomaceous earth (diatomite). The effect of initial dye concentrations, adsorbent particle size and concentration, and agitation speed on adsorption was investigated. Adsorption isotherms obtained at different solutions temperatures revealed an irreversible adsorption with a capacity of 42 mmol dye/100 g diatomite reached within 10 min. This value slightly increases with increasing the solution temperature. A proposed correlation to describe the irreversible adsorption isotherm was introduced, which resulted in a better fit to the experimental data than that of Langmuirʹs and Freundlichʹs. Two simplified kinetics models, pseudo-first order and pseudo-second order, were tested to investigate the adsorption mechanisms. It was found that the kinetics of adsorption of methylene blue onto the surface of diatomite at different operating condition are best described by the pseudo-first-order model.