Key Takeaways & Executive Findings
- •• • The composite membrane achieved a theoretical maximum Cr(VI) adsorption capacity of 471.970 mg·g−1 (Langmuir model), significantly outperforming many conventional adsorbents and demonstrating high efficacy for chromium removal. • • Optimal adsorption occurred at pH 2, with equilibrium reached in approximately 73 h; the process followed pseudo-second-order kinetics and Langmuir isotherm, indicating chemisorption and monolayer coverage. • • Thermodynamic analysis confirmed the adsorption was spontaneous and endothermic, implying that increasing temperature enhances adsorption performance, which is beneficial for industrial applications involving warm effluents. • • After three adsorption-desorption cycles, the membrane maintained structural stability with a moderate reduction in capacity, highlighting its potential for regeneration and reuse in practical wastewater treatment.
Abstract
A novel slag-based carbon powder-sodium alginate composite membrane was fabricated by incorporating purified slag-derived carbon powder into a sodium alginate matrix, followed by dual crosslinking with polyethyleneimine and glutaraldehyde. The membrane was designed to achieve waste-to-treat-waste objectives, enhance the resource value of industrial slag, and provide an efficient, regenerable adsorbent for Cr(VI) removal from water. Adsorption performance was systematically evaluated. Optimal adsorption occurred at pH 2, with elevated temperature and initial Cr(VI) concentration favoring uptake; equilibrium was reached at approximately 73 h. The adsorption kinetics followed a pseudo-second-order model, and isotherm data fitted the Langmuir model, yielding a theoretical maximum adsorption capacity of 471.970 mg·g−1. Thermodynamic analysis indicated a spontaneous, endothermic process. In simulated wastewater containing multiple metal ions, competitive effects moderately reduced adsorption capacity. After three adsorption-desorption cycles, the membrane retained good structural stability despite a decline in capacity. Characterization via SEM-EDS, FTIR, and XPS revealed a porous structure and the involvement of functional groups such as –COOH and –NH2, with partial reduction of Cr(VI) to Cr(III). The adsorption mechanism was attributed to synergistic electrostatic interaction, chemical coordination, and redox reactions.
1. Introduction
Hexavalent chromium (Cr(VI)) is a highly toxic and mobile heavy metal pollutant commonly found in industrial effluents from mining, electroplating, and tanning operations. Conventional treatment methods such as chemical precipitation, ion exchange, and membrane filtration suffer from drawbacks including secondary sludge generation, high operational costs, and membrane fouling. Adsorption is recognized as a promising alternative due to its simplicity, high efficiency, and low secondary pollution. However, the development of cost-effective adsorbents with high capacity and selectivity remains a challenge.
This study addresses this bottleneck by valorizing industrial slag—a solid waste from aluminum electrolysis—into a high-purity carbon powder (95.67% carbon) and incorporating it into a sodium alginate matrix. The resulting composite membrane, crosslinked with polyethyleneimine and glutaraldehyde, integrates the high surface area of carbon with the abundant functional groups of alginate, thereby enhancing active sites for Cr(VI) adsorption and reduction. This approach not only provides an efficient adsorbent but also contributes to waste resource utilization, aligning with circular economy principles.
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CHEN Qiuyi, ZHANG Zhe, HUO Qiang, MO Yuanyuan, JU (2026). Preparation of Slag-Based Carbon Powder-Sodium Alginate Composite Membrane and Its Efficient Adsorption of Cr(VI) from Aqueous Solutions. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202512057
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Frequently Asked Questions
What is the maximum adsorption capacity of the composite membrane for Cr(VI) under optimal conditions?
The theoretical maximum adsorption capacity is 471.970 mg·g−1, as determined by the Langmuir isotherm model at pH 2 and 25 °C.
How does the adsorption performance vary with pH and temperature?
Adsorption is optimal at pH 2, with capacity increasing with temperature, indicating an endothermic process. The adsorption follows pseudo-second-order kinetics, suggesting chemisorption.
What is the mechanism of Cr(VI) removal by the composite membrane?
The removal mechanism involves electrostatic interaction between Cr(VI) anions and protonated amine groups, chemical coordination with carboxyl/hydroxyl groups, and partial reduction of Cr(VI) to less toxic Cr(III), as confirmed by XPS analysis.
Can the membrane be regenerated and reused?
Yes, the membrane can be regenerated through desorption. After three adsorption-desorption cycles, it retains good structural stability, though adsorption capacity decreases moderately, indicating potential for multiple uses.
How does the membrane perform in the presence of competing metal ions?
In simulated wastewater containing multiple metal ions, competitive effects reduce adsorption capacity to some extent, but the membrane still exhibits significant selectivity for Cr(VI), making it applicable to complex effluents.
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