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Antimony Retention by Iron (oxyhydr)oxide Minerals: From Atomic-Scale Mechanisms to the Selectivity of Commonly-Applied Extraction Procedures
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Antimony Retention by Iron (oxyhydr)oxide Minerals: From Atomic-Scale Mechanisms to the Selectivity of Commonly-Applied Extraction Procedures

Mona Hosseinpour Moghaddam
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2025
DOI:
https://doi.org/10.25918/thesis.555
Appears in  Recent Southern Cross PhD Theses
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Hosseinpour Moghaddam M PhD 20259.07 MBDownloadView
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Abstract

Antimony (Sb) Fe(III) (oxyhydr)oxides Sorption and coprecipitation Synchrotron spectroscopy Sequential extraction
Antimony (Sb) is a toxic and carcinogenic metalloid that has been recognised as a priority pollutant for more than four decades by both the United States Environmental Protection Agency and the European Union. Increasing production and consumption of this technologically critical element have led to elevated releases of Sb into the environment, raising concerns regarding associated human and ecological health risks. Consequently, a thorough understanding of the processes that control Sb mobility, fate, and bioavailability in the environment is required to improve predictions of its behaviour and support effective risk assessment and remediation strategies. In near-surface environments, Fe(III) (oxyhydr)oxide minerals are abundant hosts for Sb(V), the dominant Sb species under oxic conditions. Although the importance of Fe(III) (oxyhydr)oxides in controlling Sb behaviour is widely recognised, uncertainties remain regarding how specific minerals interact with Sb(V). This study used synchrotron-based X-ray absorption spectroscopy to investigate the atomic-scale retention mechanisms governing Sb(V) sorption and coprecipitation with selected Fe(III) (oxyhydr)oxide minerals, including ferrihydrite, lepidocrocite, goethite and feroxyhyte. The study also evaluated the selectivity of commonly used extraction methods for quantifying Sb(V) associated with these minerals, including single-step extraction with 1 M HCl and the sequential extraction schemes of Wenzel et al. and the Community Bureau of Reference (BCR). Retention of Sb(V) by ferrihydrite was dominated by structural incorporation rather than surface complexation, with EXAFS spectroscopy revealing edge-sharing and double-corner-sharing linkages between SbO₆ and FeO₆ octahedra. These linkages partially stabilised ferrihydrite against proton-promoted dissolution. The BCR extraction scheme substantially underestimated ferrihydrite-bound Sb(V), while the Wenzel scheme recovered most sorbed and coprecipitated Sb(V) in fractions targeting poorly crystalline hydrous oxides. For lepidocrocite, coprecipitation involved substitution of Sb(V) for Fe(III) within the mineral structure, whereas sorption occurred through surface SbO₆–FeO₆ linkages. Sorption enhanced preferential Sb release relative to Fe during acid dissolution, while coprecipitation produced congruent dissolution behaviour. Sequential extraction schemes again showed limitations in accurately identifying Sb retention pathways. In goethite, coprecipitation led to structural incorporation of Sb(V), rendering it largely inaccessible to extraction procedures, whereas surface adsorption produced greater extractability. Both the Wenzel and BCR schemes underestimated the potential for Sb(V) desorption from the goethite surface. Finally, interactions between Sb(V) and feroxyhyte showed strong binding through both sorption and coprecipitation mechanisms. These pathways resulted in negligible Sb release under ligand-exchange conditions, highlighting feroxyhyte’s strong potential to immobilise Sb(V) in natural systems. Overall, these findings provide new insight into Sb retention mechanisms in Fe(III) (oxyhydr)oxide minerals and demonstrate that commonly used extraction procedures may misrepresent Sb associations in environmental materials. Careful consideration of mineral-specific retention mechanisms is therefore essential for accurately interpreting extraction data and assessing Sb mobility in contaminated environments.

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