Performance and mechanism of Cr(VI) removal by sludge-based biochar loaded with zero-valent iron

In this work, sludge-based biochar was prepared from municipal sludge as raw material and coupled with zero-valent iron to obtain sludge-based biochar loaded with zero-valent iron (ZVI@SBC) for treating Cr(VI)-containing wastewater. Batch adsorption experiments were carried out to investigate the effects of adsorbent dosage, solution pH, adsorption time, adsorption temperature and pollutant concentration on the Cr(VI) removal by ZVI@SBC, and the potential mechanism of Cr(VI) removal by ZVI@SBC was investigated by characterization techniques. The optimum values of Cr(VI) removal efficiency and adsorption capacity by ZVI@SBC were achieved at the dosage of 25 mg. The Cr(VI) removal performance by ZVI@SBC existed strongly pH-dependent. Moreover, increasing the adsorption temperature promoted the Cr(VI) removal by ZVI@SBC. Notably, the Cr(VI) removal by ZVI@SBC was consistent with the pseudo second order kinetic model and the Langmuir model. The adsorption experiments showed that the maximum Cr(VI) adsorption capacity by ZVI@SBC was 150.83 mg/g at initial Cr(VI) concentration of 50–150 mg/L and adsorption temperature of 298 K. The Cr(VI) removal process by ZVI@SBC was homogeneous and chemical adsorption. The removal mechanism of Cr(VI) by ZVI@SBC was a complex process involving adsorption-reduction of Cr(VI) and release-adsorption of Cr(III). This work demonstrated that the sludge-based biochar loaded with zero-valent iron hold a better removal ability for Cr(VI) wastewater and provided a reference for the removal of Cr(VI) wastewater.