Adsorption Mechanisms for Chromium Removal in Aqueous Systems

Chromium contamination in water, primarily in its hexavalent form (Cr(VI)), poses a significant threat to ecosystems and human health. Adsorption has emerged as a versatile, cost-effective approach to capture and immobilise chromium species from effluents. The process relies on the physicochemical interaction between metal ions and solid surfaces, encompassing electrostatic attraction, pore filling, redox transformation and specific surface complexation. Materials such as biochars, activated carbons and magnetic composites exhibit high surface areas and tailored functional groups that facilitate both the reduction of Cr(VI) to the less toxic trivalent state (Cr(III)) and subsequent retention on the adsorbent matrix. Operational parameters—including pH, adsorbent dosage, contact time and ionic strength—critically influence adsorption capacity and kinetics. At low pH, protonated surfaces favour uptake of anionic Cr(VI) species, while oxygen-containing moieties (e.g. hydroxyl, carbonyl) serve both as electron donors for reductive conversion and as binding sites for resultant Cr(III). The balance of adsorption and redox reactions underpins the removal efficiency and reusability of the sorbent, making this hybrid mechanism particularly appealing for wastewater treatment and resource recovery.

Research from Nature Portfolio

Researchers have developed a magnetic biochar derived from agricultural waste that integrates iron oxides (Fe₂O₃/Fe₃O₄) onto a porous carbon scaffold. The point of zero charge of the composite lies around pH 6.2, optimising removal of Cr(VI) under acid conditions. Adsorption follows pseudo-second-order kinetics and fits a Langmuir monolayer model, indicating chemisorption predominance. Mechanistically, Cr(VI) anions are attracted to positively charged sites and partially reduced at the biochar surface, yielding Cr(III) that is then immobilised through surface complexation and pore entrapment. Even after multiple regeneration cycles, the material retains over 80 % of its initial capacity, demonstrating promise for scalable water remediation.

Adsorption Mechanisms for Chromium Removal in Aqueous Systems publication trend

The graph below shows the total number of articles in adsorption mechanisms for chromium removal in aqueous systems across all publications each year (not limited to Nature Index journals).

Technical terms

Adsorbent: A solid substrate designed to capture dissolved species from liquid via surface interactions.

Hexavalent chromium (Cr(VI)): A highly soluble and toxic form of chromium that exists as oxyanions in aqueous media.

Langmuir isotherm: A model describing monolayer adsorption on a homogeneous surface with finite binding sites.

Pseudo-second-order kinetics: A rate equation implying that chemisorption is the rate-limiting step, dependent on the availability of sorption sites.

Surface complexation: The formation of coordinate bonds between metal ions and functional groups on the adsorbent surface.

References

1. Removal of aqueous Cr(VI) by magnetic biochar derived from bagasse. Scientific Reports (2020).
2. Tofukasu-derived biochar with interconnected and hierarchical pores for high efficient removal of Cr (VI). Biochar (2023).
3. Utilizing Sida Acuta leaves for low-cost adsorption of chromium (VI) heavy metal with activated charcoal. Journal of Hazardous Materials Advances (2023).
4. Efficient Removal of Cr(VI) from Water by Biochar and Activated Carbon Prepared through Hydrothermal Carbonization and Pyrolysis: Adsorption-Coupled Reduction Mechanism. Water (2019).