In the complex world of soil and water chemistry, certain minerals act like microscopic sponges, soaking up pollutants and keeping our environment safe. Among the most dangerous of these pollutants is hexavalent chromium, Cr(VI), a highly toxic and mobile substance often found at industrial and mining sites. Now, a groundbreaking study published in Carbon Research has identified the specific "superstar" minerals that are best at neutralizing this threat while simultaneously locking away organic carbon.
The research, led by Professor Bin Dong from Tongji University, focuses on the interaction between dissolved organic matter (DOM) and various iron (oxyhydr)oxides. The team discovered that low-crystallinity minerals, specifically ferrihydrite, are far more effective at managing chromium than their more "perfect" crystalline cousins like goethite and hematite. This work represents a major collaborative effort centered at the College of Environmental Science and Engineering at Tongji University and the Shanghai Institute of Pollution Control and Ecological Security, with support from the YANGTZE Eco-Environment Engineering Research Center and Guilin University of Technology. "Nature has a built-in filtration system, but not all minerals are created equal," says Professor Bin Dong. "By understanding the molecular handshake between organic matter and iron minerals, we can design smarter, nature-based solutions to clean up heavily contaminated mine soils while helping the planet store more carbon."
The "Ferrihydrite" Advantage:
The study utilized ultra-high-resolution mass spectrometry (FT-ICR MS) and advanced electron microscopy to watch these chemical reactions in real-time. The findings were striking:
- Surface Power: Unlike other minerals where reactions happen in the surrounding water, ferrihydrite pulls both the organic matter and the toxic chromium onto its surface. This "surface-first" approach creates a much faster and more stable cleanup process.
- Molecular Traps: Ferrihydrite uses a diverse toolkit of chemical bonds—including electrostatic adsorption, ligand exchange, and even "lattice doping"—to pin chromium and carbon in place.
- Double Benefit: This process doesn't just immobilize the toxic Cr(VI); it also sequesters carbon. By binding organic carbon to the mineral surface, it prevents that carbon from being released back into the atmosphere as CO2.
- Real-World Success: The team didn't just stay in the lab. Leaching experiments on actual contaminated mine soil confirmed that using organic matter alongside in situ iron minerals effectively "locks down" the chromium, preventing it from washing away into groundwater.
Implications for a Greener Future
The discovery of how these low-crystallinity iron minerals function provides a new blueprint for environmental remediation. Instead of relying on energy-intensive chemical treatments, engineers can now look toward synergetic strategies that use natural organic matter and specific iron minerals to heal damaged landscapes. By improving our understanding of the geochemical cycling of iron, chromium, and carbon, the team at Tongji University is paving the way for technologies that solve two problems at once: cleaning up toxic legacies and fighting climate change through carbon sequestration.
Corresponding Author:
Bin Dong
College of Environmental Science and Engineering, Tongji University, Shanghai, China.
Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai, China.
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Journal reference: Lin, C., Dong, B. & Xu, Z. Effect of low-crystallinity Fe (Oxyhydr)oxides on dissolved organic matter-mediated Cr(VI) reductive immobilization and concurrent carbon sequestration. Carbon Res. 5, 8 (2026).
https://doi.org/10.1007/s44246-025-00242-4
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About Carbon Research
The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.
