Magnetic biochar was made from peanut hull biomass using iron chloride in a simplified aqueous phase
approach and pyrolysis at alternative peak temperatures (450e650 C). Magnetic biochar showed an
extreme capacity for adsorption of hexavalent chromium Cr (VI) from aqueous solution, which was 1e2
orders of magnitude higher compared to standard (non-magnetic) biochar from the same feedstock.
Adsorption increased with pyrolysis temperature peaking at 77,542 mg kg1 in the sample pyrolysed at
650 C. In contrast to magnetic biochar, the low adsorption capacity of standard biochar decreased with
increasing pyrolysis temperature. The fine particle size of magnetic biochar and low aqueous pH were
also important for adsorption. Surfaces of products from batch adsorption experiments were characterized
by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, X-ray
photoelectron spectroscopy and vibrating sample magnetometer. This revealed that g-Fe2O3 was crucial
to the properties (adsorbance and magnetism) of magnetic biochar. The removal mechanism was the Cr
(VI) electrostatic attracted on protonated eOH on g-Fe2O3 surface and it could be desorbed by alkaline
solution. Findings suggest that pyrolysis has potential to create effective, magnetically recoverable adsorbents
relevant to environmental application.