Dye Adsorption by Leather Waste: Mechanism Diffusion, Nature Studies, and Thermodynamic Data

Tannery solid waste (leather) is a possible adsorbent of dye contaminants in wastewater. In this paper the nature and mechanisms of dyes adsorption by chromium-tanned leather waste (CTLW) are proposed and discussed on the basis of isotherms, adsorption kinetics, and thermodynamics of three dyes: Red 357, Black 210, and Yellow 194 in aqueous solutions. Langmuir, Brunauer-Emmett-Teller (BET) and Henry isotherm models were used to fit the adsorption equilibrium data, respectively. The kinetic data were evaluated using boundary layer mass transfer and intraparticle diffusion models. The boundary layer mass transfer coefficient was in the order of 10(-6) and 10(-5) m.min(-1) for the three studied dyes. However, the intraparticle diffusion were of the order of 10(-8) and 10(-11) m(2).min(-1) for the Red 357 and Black 210 dyes, respectively, demonstrating that intraparticle diffusion is the predominant mass transfer mechanism of these dyes. The values of Delta H, Delta S, Delta G, and E-a suggest that adsorption is spontaneous, exothermic, and chemical in nature. The chemical nature is also confirmed by Fourier transform infrared (FT-IR) analysis.