New Bioadsorbent Derived from Winemaking Waste Cluster Stalks: Application to the Removal of Toxic Cr(VI) from Liquid Effluents

Abstract

A winemaking waste was used as a precursor of activated carbon used for the removal of hazardous Cr(VI) from solutions. The preparation process consisted of a hydrothermal process and a chemical activation of the resulting product, with KOH. The adsorption results show that the adsorption of Cr(VI) on the obtained activated carbon is strongly dependent on the stirring speed applied to the carbon/solution mixture, pH of the solution, and temperature. The equilibrium isotherm was well fitted to the Langmuir Type-II equation, whereas the kinetic can be described by the pseudo-second-order kinetic model. Thermodynamic studies revealed that Cr(VI) adsorption was an exothermic and spontaneous process. Finally, desorption experiments showed that Cr(VI) was effectively desorbed using hydrazine sulfate solutions, and, at the same time, the element was reduced to the less hazardous Cr(III) oxidation state.