Removal of cadmium from aqueous solution by magnetic biochar: adsorption characteristics and mechanism

Abstract Experiments were conducted to investigate the potential for the efficient resource utilization of waste cow manure and corn straw in an agricultural ecosystem. In this study, magnetic biochar of cow manure and straw was synthesized by co-precipitation method, and cadmium was removed by adsorption in aqueous solution. Several physicochemical characterization techniques were applied, including scanning electron microscopy, Brunauer-Emmett-Teller (BET), Zeta potential analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy. The effects of pH value, magnetic biochar content, kinetics and isotherm on the adsorption of cadmium were investigated. The physicochemical characterizations revealed that the physical and chemical properties of the magnetic biochar were substantially changed compared to the unmodified biochar. The results showed that the surface of biochar became rough, the number of oxygen-containing functional groups increased, and the specific surface area increased. The results of adsorption experiments show that the adsorption capacity is affected by pH, magnetic biochar addition, cadmium concentration and adsorption time. The adsorption kinetics and isothermal adsorption experiments showed that the Cd adsorption processes of the cow manure and corn straw magnetic biochars were consistent with the Freundlich model and quasi-second-order kinetic model. The results of this study also showed that Cd adsorption effect of cow manure magnetic biochar was found to be more effective than that of corn straw magnetic biochar. In conclusion, the magnetic biochar of cow dung is an effective adsorbent for the absorption of cadmium in wastewater.