Solutions to hazardous wastes issues in the leather industry: adsorption of Chromium iii and vi from leather industry wastewaters using activated carbons produced from leather industry solid wastes

This study presents the use of an innovative material to tackle hazardous wastes in the leather industry. Activated carbons produced from Leather industry waste (LIW) were used to adsorb (Cr) III and (VI), which are found in leather wastewater. Two physical and chemical activation processes were used in this study. In physical activation, carbonization and activation with CO2 were carried out consecutively without intermediate cooling at 700 °C with a residence time of 30 min. In the chemical activation, the LIW was impregnated with a KOH solution in a KOH/LIW ratio of 4/1 w/w. Carbonization was conducted in nitrogen, using two carbonization temperatures, 500 and 700 °C, for 30 min. All activated carbons had Cr (III) adsorption greater than 95%. The experimental data was analysed using Langmuir and Freundlich isotherms). Cr (III) and Cr (VI) adsorption kinetics studies were also carried out based on the Pseudo-first order, Pseudo-second order, Elovich and Intraparticular Diffusion models. The Langmuir and Temkin Isotherm models presented the best fit for Cr (III) adsorption, while the DRK Isotherm models fitted the experimental data for Cr (VI). The thermodynamic parameters of Cr (III) and Cr (VI) adsorption were also determined. A Cr (III) and Cr (VI) adsorption mechanism is proposed using activated carbons from gravel as adsorbent. The production of activated carbon from LIW and its application for the removal of chromium present in the liquid residues of the leather industries can present a potential for the reduction of treatment costs and the application of a circular economy.