Cadmium and lead remediation using magnetic oak wood and oak bark fast pyrolysis bio-chars

Abstract

Magnetic oak wood biochar (MOWBC) and magnetic oak bark biochar (MOBBC) were obtained from oak wood and oak bark biochars made by fast pyrolysis during bio-oil production. These were investigated as potential green adsorbents for cadmium and lead remediation from water. Biochars were obtained from fast pyrolysis at 400 and 450°C in an auger-fed reactor and then magnetized by mixing aqueous biochar suspensions with aqueous Fe3+/Fe2+ solutions, followed by treatment with NaOH. The compositions and surface chemistries of these magnetic biochars were examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), energy-dispersive X-ray spectroscopy (EDXRF), BET surface area (SBET), energy-dispersive-X-ray-fluorescence analysis (EDXRF), point of zero charge (pHPZC), density and magnetic moment determinations. The SBET of the magnetic oak wood and bark chars were 6.1 and 8.8m2g−1, respectively.Batch sorption studies were performed at 25–45°C, pHs of 2–7 and different solid-to-liquid ratios. Maximum lead and cadmium removal occurred at pH 4–5. Sorption isotherms over a concentration range of 1–100mg/L exhibited increasing metal ion removal as temperature went up with both magnetic wood and bark biochars. Sorption performances at 25, 35 and 45°C were evaluated using the Freundlich, Langmuir, Redlich–Peterson, Toth, Sips, Radke and Prausnitz and Koble–Corrigan adsorption isotherm models. Kinetic data were better fitted by second order kinetic model. Lead and cadmium were successfully remediated from water using magnetic biochar. These magnetic biochars remediated Pb2+ and Cd2+ better than their corresponding nonmagnetic biochars previously reported, adsorbing more metal ions than expected based on their SBET values. They were easily manipulated by low external magnetic fields, permitting their easy separation from the aqueous-phase. Magnetic filtration requires no gradient and therefore no separation system fouling occurs, allowing convenient adsorbent cleaning, recycle or replacement from contaminated water.