Removal of hexavalent chromium from aqueous solutions by sorption with activated carbon. Review

Abstract

The article considers sources of hexavalent chromium in the environment, its toxicity, methods of removal, main adsorbents used for Cr(VI) removal, obtaining of carbon sorbents using different raw materials. The interpretation of the mechanism of Cr(VI) removal is given. Chromium is widely used in many industries, which results in the generation of a large amount of hazardous waste - wastewater from steel, metalworking, electroplating, tanning, automotive, paint, paper-pulp and textile plants. Chromium is one of the most dangerous inorganic pollutants because of its carcinogenic effects on biological species. In aquatic environments, chromium usually exists in the trivalent Cr(III) or hexavalent Cr(VI) state. Hexavalent chromium ions in aqueous media are highly toxic even in small amounts, and their removal from solution poses a serious wastewater treatment problem. Methods such as adsorption ion exchange, membrane separation, coagulation, chemical precipitation, extraction and electrochemical separation can remove hexavalent chromium from wastewater. Adsorption is considered to be the most efficient, economically feasible, environmentally sustainable and technologically promising process. Among adsorbents of different nature, activated carbon is the most widely used. Wood is the most common source of activated carbon but given the importance of wood in maintaining the ecosystem, alternative sources of activated carbon production are being sought. Activated carbon is produced from various materials by high temperature carbonization. Activated carbon materials have high specific surface area and developed porous structure. The micropores in activated carbon account for the physical adsorption of chromium ions. The presence of functional groups containing O and N in activated carbon affects the chemical structure and the process of chemical sorption.