Methylene blue adsorption by the waste of Abu-Tartour phosphate rock

Phosphate rock (PR) is an abundant ore and represents the basic raw material for the phosphatic fertilizer industry. Prior to industrial processing, PR is concentrated by grinding-and-screening to separate a fine fraction that is very poor in P2O5. This fine fraction is a solid waste and represents a disposal problem. The present study shows that the fine fraction of ground-and-screened Abu-Tartour PR can be used as an adsorbent for the removal of methylene blue dye from aqueous solutions. The amount of dye adsorbed was found to vary with initial methylene blue concentration and contact time. Raising the temperature enhances the rate of adsorption but has no effect on the adsorption capacity at equilibrium. The adsorption equilibrium data were found to fit the Langmuir isotherm, indicating monolayer adsorption on a homogeneous surface. The Elovich model can be used to predict the adsorption kinetics at ambient temperatures especially when the initial concentration of MB is relatively high, while Ho's model deviates from the data as the initial concentration increases. However, as the temperature increases and MB concentration decreases, Ho's model fits the data better than the Elovich model. On studying the mechanism of adsorption, the results showed that the overall rate of dye uptake is controlled by intraparticle diffusion. The multilinear plots of intraparticle diffusion were modeled by piecewise linear regression and related to pore-size distribution of the adsorbent. (C) 2010 Elsevier Inc. All rights reserved.