Abstract
This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe3O4. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe3O4 on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.
Highlights
Chromium (Cr) is a common groundwater contaminant at hazardous sites, which could be released from intense anthropogenic activities, including chemical synthesis, mining, dyeing, metallurgy and wood preserving industries [1,2]
The representative diffraction peaks at the positions of 35.2◦, 41.5◦, 50.6◦, 67.4◦ and 74.4◦ matched well with the standard PDF card of Fe3 O4 (PDF#75-1610). Such diffraction peaks were quantified by the previous study of synthesised magnetic biochar by zero-valent iron through co-pyrolysis method [24]
The results confirmed that Fe3 O4 was successfully doped onto the biochar material
Summary
Chromium (Cr) is a common groundwater contaminant at hazardous sites, which could be released from intense anthropogenic activities, including chemical synthesis, mining, dyeing, metallurgy and wood preserving industries [1,2]. Cr(VI) is highly mobile in water, which could cause an acutely toxic and carcinogenic effect to humans, animals, plants and microorganisms [4,5]. Cr(III), by contrast, is less toxic and could precipitate in the aquifer in the form of oxides or hydroxides with poor migration ability [6]. Cr(VI) in the groundwater is difficult to be naturally converted into Cr(III) because of the lack of electron donors, such as carbon sources [8]. Given the long-term storage characteristic, the technique development on effective Cr(VI) removal from polluted groundwater has become urgently important
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