Abstract

This study presents the mass transfer mechanism of Cr(VI) during the adsorption on used black tea leaves (UBTLs) as a low cost biosorbent. Batch adsorption experiments were conducted in acidic media with different particle sizes of UBTLs and Cr(VI) concentrations, and the results were verified with different transport models to elucidate the mass transfer mechanism. Scanning electron microscope (SEM) and X-ray microanalysis (EDX) of adsorbed UBTLs were also carried out to search the mechanism. From the view point of transport modeling and SEM analysis, the effect of particle size and the concentration of Cr(VI) on the adsorption of Cr(VI) on the UBTLs suggest that the initial rapid step of adsorption is reaction-controlled dominated by the attraction of negative Cr(VI) species with the protonated UBTLs surface in acidic media, and the following slow step is intraparticle-diffusion-controlled which consisted of the high deposition of adsorbed species at the cavities on the surface. The overall mass transfer gradually shifts from the reaction controlled to the diffusion controlled with increasing of the initial concentration Cr(VI) in solution.

Key words: Hexavalent chromium, used black tea leaves, adsorption, SEM and EDX, mass transfer mechanism.