One-pot synthesis of a magnetic Zn/iron-based sludge/biochar composite for aqueous Cr(VI) adsorption

Using the traditional Chinese medicine residual (TCMR) as biomass, and the iron-based waterworks sludge (IBWS) and Zinc chloride (ZnCl2) as modified materials, this study synthesized IBWS/ZnCl2/TCMR-derived biochar composite ([email protected]) in one-pot technique for aqueous Cr(VI) adsorption. Batch experiments of Cr(VI) adsorption were carried out with the [email protected] as an adsorbent. The pH research revealed that acidic conditions (pH < pHzpc) were in favor of Cr(VI) adsorption, with the highest removal observed at pH 2. The maximum adsorption capacity of [email protected] was about 27.04 mg/g at 35 °C. Based on the examination of kinetics, isotherm, the adsorption process by [email protected] was consistent with the equation of pseudo-second-order and the Langmuir model, which had a monolayer adsorption nature. Anions have negative effects on Cr(VI) reduction by [email protected], the negative effects order followed Cl−< SO42−< PO43−, which were positive correlated with the concentration and the charge of anions. Potential removal mechanism was investigated with various characterization techniques, indicating that the major mechanisms of Cr(VI) adsorption by [email protected] were physical and chemical adsorption, including the reaction of Cr(VI) to Cr(III). IBWS was calcined to impart magnetism of composite, and ZnCl2 generated magnetic zinc ferrite (ZnFe 2O4) while activating the composite, endowing the composite with enhanced Cr(VI) adsorption capability and stronger magnetism. Therefore, [email protected] appears to be a viable material for removing Cr(VI) in wastewater.