Activated biochar with iron-loading and its application in removing Cr (VI) from aqueous solution

New biochar-based materials were synthesized via iron salt loading on biochar (derived from bamboo and poplar) or activated biochar and were used for Cr (VI) removal from aqueous solution. Surface morphology structure characterizations revealed that KOH-activated biochar possessed a large surface area and porosity with uniform distribution of iron particles on the biochar's surface. In particular, X-ray diffraction (XRD) patterns indicated that biochar originating from poplar were rich in CaCO3, which led iron salts to load more uniformly. The comparison adsorption experiments were investigated, including the effects of the initial Cr (VI) concentration, contact time and initial pH value on the Cr (VI) removal. The highest Cr (VI) adsorption capacity (25.68 mg/g) appeared on iron-loaded activated biochar (Fe/PBC-ND), which surpassed the capacity for iron-unloaded activated biochar (PBC-ND, 5.4 mg/g) and was accompanied by an increase in removal efficiency from 12% to 56%. The kinetic data and isotherm data of iron-loaded activated biochar (Fe/PBC-ND) fit well with the Elovich model and Freundlich model, which implies that the adsorption process had higher activation energy. The Cr (VI) adsorption through an iron-loaded activated biochar mechanism had synergistic effects of chemical and physical reactions, including electrostatic attraction, reduction, co-precipitation and pore accommodation according to Fourier Transform Infra-Red (FTIR), X-ray photoelectron spectroscopy (XPS) and XRD analysis. Therefore, the iron loading and KOH-activated method could potentially broaden the application of biomass-derived adsorbents for practical treatment of Cr (VI)-containing wastewater.