Porous biochar derived from waste distiller's grains for hexavalent chromium removal: Adsorption performance and mechanism

The liquor industry produces more than 50 million tons of waste distiller's grains every year, which is not properly utilized. In this work, we used distiller's grains as the raw materials to fabricate sustainable biochar adsorbents with the hierarchical pore structure for the removal of Cr(VI) from aqueous solution. The biochar adsorbents prepared by different activators were characterized and used for Cr(VI) adsorption by batch adsorption experiments. Both adsorption kinetics and thermodynamics are also carried out to clarify the structure-activity relationship for the removal of Cr(VI) by biochar, and the experimental results suggested that the adsorption process of Cr(VI) was multilayer and physical-chemical synergistic adsorption. Notably, biochar KOH-AC featured the maximum Cr(VI) adsorption capability with up to 144.5 mg·g−1, better than those biochar adsorbents reported in the literature. Further mechanism studies indicated that the adsorption of Cr(VI) was attributed to a synergistic effect of electrostatic interaction and reduction adsorption. This study provides a promising strategy for the resource utilization of distiller's grains, and biochar prepared can be used as a sustainable adsorbent for the purification of chromium-containing wastewater.