Key Takeaways & Executive Findings
- •• • Iron-based magnetic biochar (MBC-Fe) achieves high adsorption capacities for heavy metals; for instance, Pb(II) adsorption capacity reaches up to 200 mg/g (Zhao et al., 2019), enabling efficient removal from wastewater with easy magnetic separation. • • The introduction of iron increases specific surface area and pore volume by up to 30% compared to pristine biochar, enhancing active sites for metal binding and improving adsorption kinetics. • • MBC-Fe exhibits fast adsorption kinetics, reaching equilibrium within 2 hours for Cd(II) removal (Tan et al., 2017), which is critical for industrial continuous-flow treatment systems. • • Magnetic separation efficiency of MBC-Fe exceeds 95% under external magnetic field, allowing >90% recovery and reuse over multiple cycles, reducing operational costs in wastewater treatment.
Abstract
Biomass is the only renewable carbon resource with huge reserves and wide sources, and it is green and environmentally friendly. Under the background of 'dual carbon', the clean and efficient utilization of biomass has received increasing attention. Preparation of biochar from biomass is one of the main methods to use biomass efficiently. Biochar surfaces possess porous and aromatic structures, which exhibit good fixation effects on heavy metals in wastewater. However, biochar has shortcomings such as difficulty in recovery and non-reusability. The introduction of iron into biochar can not only enrich surface functional groups, develop pore structure, and increase specific surface area, but also endow magnetic properties, facilitating solid-liquid separation after adsorption. This paper reviews the preparation methods of iron-based magnetic biochar (MBC-Fe), summarizes the effects of different iron sources on its characteristics, and illustrates the adsorption performance and mechanisms of MBC-Fe for typical heavy metals in water. Finally, applications of MBC-Fe in the removal of heavy metal ions from wastewater are concluded, and future utilization potential in other fields is proposed. The review highlights that MBC-Fe exhibits high adsorption capacities, e.g., for Pb(II) and Cd(II), with rapid kinetics and easy separation, making it a promising adsorbent for wastewater treatment.
1. Introduction
Heavy metal contamination in wastewater poses severe environmental and health risks, with 2022 national emissions reaching 48.1 tons in China. Conventional treatment methods such as chemical precipitation and electrochemical processes suffer from high energy consumption, secondary sludge generation, and incomplete removal at low concentrations. Adsorption using biochar derived from biomass offers a sustainable and cost-effective alternative, but pristine biochar faces limitations in recovery and reusability, hindering its practical application.
Iron-based magnetic biochar (MBC-Fe) addresses these bottlenecks by integrating iron oxides or zero-valent iron into the carbon matrix, imparting magnetic properties for facile separation and enhancing surface reactivity. This review systematically examines preparation methods, iron source effects, and adsorption mechanisms, providing a comprehensive framework for optimizing MBC-Fe synthesis and deployment in wastewater treatment. The experimental data from cited studies demonstrate significant improvements in adsorption capacity and kinetics, positioning MBC-Fe as a viable technology for scalable heavy metal remediation.
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GUO Yaxin, XUE Mukun, CHEN Yunxiao, DONG Xiaoyun, PENG Hao, WANG Baofeng (2026). Research Progress on the Preparation of Iron-Based Magnetic Biochar and Its Adsorption Performance for Heavy Metals in Wastewater. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2024122001
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Frequently Asked Questions
What are the main preparation methods for iron-based magnetic biochar, and how do they influence adsorption performance?
Common methods include pyrolysis of biomass with iron salts, co-precipitation, and impregnation followed by pyrolysis. Pyrolysis temperature and iron loading significantly affect surface area and magnetic properties. For example, higher pyrolysis temperatures (e.g., 600°C) increase surface area but may reduce oxygen functional groups, impacting adsorption capacity. Optimal conditions typically yield adsorption capacities of 100-200 mg/g for Pb(II) and Cd(II).
How does the choice of iron source (e.g., FeCl3, FeSO4, zero-valent iron) affect the characteristics and adsorption efficiency of MBC-Fe?
Iron sources influence the formation of magnetic phases (e.g., Fe3O4, γ-Fe2O3) and the distribution of iron nanoparticles. FeCl3 often results in uniform dispersion and higher surface area, while zero-valent iron can enhance reduction of Cr(VI) to Cr(III). Adsorption capacities vary: for Cd(II), rice straw-derived magnetic biochar using FeCl3 achieved 45 mg/g, whereas Fe-Mn binary oxide-biochar reached 80 mg/g, indicating that composite oxides may offer synergistic effects.
What are the primary adsorption mechanisms of heavy metals onto iron-based magnetic biochar?
Mechanisms include electrostatic attraction, ion exchange, surface complexation with oxygen-containing groups, and precipitation. For Pb(II), surface complexation and precipitation as Pb(OH)2 dominate. For Cr(VI), reduction to Cr(III) by zero-valent iron followed by adsorption is key. The presence of iron oxides also facilitates inner-sphere complexation, enhancing binding strength.
Can iron-based magnetic biochar be regenerated and reused, and what is the associated cost-effectiveness?
Yes, MBC-Fe can be regenerated using dilute acid or alkali solutions. For example, desorption efficiency of Pb(II) using 0.1 M HCl exceeds 90%, and the adsorbent retains >80% capacity after five cycles. This reusability, combined with magnetic recovery, reduces overall treatment costs compared to non-magnetic adsorbents, making it economically viable for industrial applications.
What are the scalability challenges for industrial application of iron-based magnetic biochar?
Scalability challenges include uniform iron loading on large biomass batches, controlling pyrolysis conditions to ensure consistent quality, and managing iron leaching under acidic conditions. However, pilot-scale studies using agricultural residues (e.g., rice straw) have demonstrated reproducible adsorption capacities, and the use of low-cost iron salts (e.g., FeCl3) keeps material costs low. Further optimization of reactor design and process parameters is needed to achieve continuous operation.
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