Wei, et al (2024) Removal mechanism of Pb(II) from soil by biochar-supported nanoscale zero-valent iron composite materials. Royal Society of Chemistry. https://doi.org/10.1039/D4RA03357D

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As industrial activities continue to expand, heavy metal pollution, particularly lead contamination, has become a significant environmental concern. Lead, often released from battery manufacturing, metal smelting, and other industrial processes, can infiltrate soil and groundwater, posing severe health risks and environmental hazards. Traditional methods for lead removal are often costly and inefficient, prompting researchers to explore more sustainable and effective alternatives. One promising solution involves the use of biochar-supported nanoscale zero-valent iron (BC-nZVI) composites.

BC-nZVI composites are created by integrating biochar with nanoscale zero-valent iron (nZVI). Biochar, derived from the pyrolysis of biomass such as rice husks, is known for its porous structure and large surface area, making it an excellent adsorbent for contaminants. By loading nZVI onto biochar, researchers can enhance its adsorptive capacity and reactivity, providing an efficient means to remove heavy metals from contaminated environments.

The synthesis of BC-nZVI involves a rheological phase reaction, where ferrous chloride (FeCl2) and rice husk biochar are mixed and reacted under controlled conditions. This process results in the formation of a composite material with nZVI particles uniformly dispersed on the biochar surface, creating a sheet-like structure. Advanced characterization techniques such as High-Resolution Transmission Electron Microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR) are employed to analyze the physical and chemical properties of the BC-nZVI composites.

Extensive experiments have demonstrated the effectiveness of BC-nZVI in removing lead (Pb(II)) from contaminated soil and water. The composite material’s performance is influenced by several factors, including pH, temperature, soil-water ratio, and the initial concentration of lead ions.

Key Findings:

Optimal Conditions for Lead Removal: The best lead removal efficiency is achieved at a pH of 6, a temperature of 20°C, and a soil-water ratio of 1:5. Under these conditions, BC-nZVI can reduce the lead concentration from 30 mg/L to trace levels within 120 minutes.

Adsorption Mechanisms: The adsorption process follows a quasi-second-order kinetic model and the Langmuir isotherm model, indicating that lead removal is primarily driven by chemical adsorption. The thermodynamic analysis suggests that the adsorption process is spontaneous and involves surface complexation, reduction, and co-precipitation mechanisms.

Temperature and Soil-Water Ratio Effects: Increasing the temperature enhances the removal efficiency of Pb(II), likely due to the increased reactivity and mobility of lead ions at higher temperatures. A higher soil-water ratio facilitates better lead extraction and adsorption, with the optimal ratio being 4:10.

Magnetic Recovery: The magnetic properties of BC-nZVI enable easy separation and recovery from treated soil using an external magnetic field, enhancing its reusability and cost-effectiveness.

Environmental and Practical Implications

BC-nZVI composites offer a sustainable and cost-effective solution for addressing heavy metal pollution, particularly lead contamination. By utilizing agricultural waste (rice husks) and integrating it with nZVI, this approach not only mitigates environmental pollution but also promotes the reuse of waste materials. The magnetic properties of BC-nZVI further enhance its practicality, allowing for efficient recovery and reuse in multiple treatment cycles.

The development and application of BC-nZVI composites represent a significant advancement in environmental remediation technologies. This innovative material combines the high adsorptive capacity of biochar with the reactivity of nZVI, providing an effective means to tackle lead contamination in soil and water. With further research and optimization, BC-nZVI composites could become a standard tool in the fight against heavy metal pollution, contributing to cleaner and safer environments.