Analysis and comparison of mass transfer phenomena related to Cu2+ sorption by hydroxyapatite and zeolite

Zeolite and hydroxyapatite (HAP) are well-known sorbent materials, with high capacities for removal of toxic heavy metals. In this study, the influence of process parameters onto kinetics of Cu2+ sorption by zeolite and HAP was analyzed and compared. The effects of Cu2+ concentration, sorbent mass and agitation speed were explored for both materials, as well as the effect of zeolite particle size. Using single resistance mass transfer models, the values of volumetric mass transfer coefficient (k(f)a) and effective diffusion coefficient (D-eff) were defined. The obtained results showed that the sorption onto HAP was governed only by pore diffusion, since the film diffusion and surface saturation occurred within the first few minutes of the reaction. Using zeolite, sorption was governed by film diffusion during the first 10 min, followed by diffusion inside the pores. The resistance of releasing cations counter diffusion was negligible in the fluid film, but it was considerable in sorbent pores. (C) 2013 Elsevier B.V. All rights reserved