Kinetics and isotherms of leather dye adsorption by tannery solid waste

► Adsorptions of three leather dyes by chromium- and vegetable-tanned leather waste were investigated. ► pH and sorbent effect on the adsorption and isotherm and kinetics were obtained. ► Acid medium and chromium-tanned leather were the optimum pH and sorbent. ► Unconventional isotherms, type BET and Henry, were observed for two dyes. ► Kinetic behaviors suggest chemical nature to the three adsorbed dyes in chromium-tanned leather. In this work, the potential for reuse of industrial wastes of vegetal and chromium tanned leather as an adsorbent has been proposed to be an efficient and economical alternative in removal of tannery dyes from aqueous solutions. Wastewater samples from a leather wet finishing process were characterized. Synthetic aqueous solutions in the range of wastewater dye concentrations were produced and the adsorption pH values of two types of leather waste (chromium- and vegetable-tanned) were analyzed. The adsorption isotherms and kinetics of the dyes Acid Yellow No. 194, Acid Red No. 357 and Acid Black No. 210 were obtained for chromium-tanned waste at the optimal adsorption pH (between 2 and 3). For the adsorption of the YELLOW 194, RED 357 and BLACK 210 dyes, the isotherms showed C1, H2 and H3 shapes and could be represented by the Henry, Langmuir and BET models, respectively. The kinetics of the three dyes showed behaviors similar to the Elovich model, suggesting that the adsorption had a chemical nature. The kinetics of YELLOW 194 were represented by pseudo-first and pseudo-second order models, while the RED 357 adsorption kinetics were represented by a pseudo-second order model. Moreover, YELLOW 194 adsorption was controlled by diffusion into the boundary layer, whereas the RED 357 and BLACK 210 adsorptions were controlled by diffusion into adsorbent particles.