Batch and column sorption of arsenic onto iron-impregnated biochar synthesized through hydrolysis

Iron (Fe)-impregnated biochar, prepared through a novel method that directly hydrolyzes iron salt onto hickory biochar, was investigated for its performance as a low-cost arsenic (As) sorbent. Although iron impregnation decreased the specific surface areas of the biochar, the impregnated biochar showed much better sorption of aqueous As (maximum sorption capacity of 2.16 mg g⁻¹) than the pristine biochar (no/little As sorption capacity). Scanning electron microscope equipped with an energy dispersive spectrometer and X-ray diffraction analysis indicated the presence of crystalline Fe hydroxide in the impregnated biochar but no crystal forms of arsenic were found in the post-sorption biochar samples. However, large shifts in the binding energy of Fe₂p, As₃d, O₁s and C₁s region on the following As sorption indicated a change in chemical speciation from As(V) to As(III) and Fe(II) to Fe(III) and strong As interaction with oxygen-containing function groups of the Fe-impregnated biochar. These findings suggest that the As sorption on the Fe-impregnated biochar is mainly controlled by the chemisorption mechanism. Columns packed with Fe-impregnated biochar showed good As retention, and was regenerated with 0.05 mol L⁻¹ NaHCO₃ solution. These findings indicate that Fe-impregnated biochar can be used as a low-cost filter material to remove arsenic from aqueous solutions.