Thesis
Interactions between antimony and schwertmannite: sorption, coprecipitation, and controls on antimony mobility
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2025
DOI:
https://doi.org/10.25918/thesis.524
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Abstract
Schwertmannite is a poorly crystalline Fe(III) oxyhydroxysulfate mineral commonly found in acid mine drainage (AMD). In AMD environments, antimony (Sb) is a significant contaminant released through the oxidative dissolution of Sb-rich sulfide ores. Schwertmannite strongly affects geochemical cycling of Sb. Nonetheless, the mechanisms of Sb uptake and the impact of schwertmannite transformation on Sb mobility are not well characterised. This thesis investigates (1) the coprecipitation of schwertmannite with Sb(V) across environmentally relevant concentrations, (2) the sorptive behaviour of Sb(V) on pre-existing schwertmannite, and (3) the transformation of Sb(V)-bearing schwertmannite under acidic, sulfate-rich conditions typical of AMD.
Coprecipitation experiments show that Sb(V) substitutes for Fe(III) in schwertmannite via partial heterovalent substitution, up to ≈ 8 mol%, confirmed by Sb K-edge EXAFS analyses showing edge-sharing and double-corner-sharing linkages between SbV(O,OH)6 and FeIII(O,OH)6 octahedra. Elevated Sb(V) concentrations (Sb/Fe ≥ 0.06) inhibited schwertmannite precipitation. Structural incorporation enhanced the mineral’s resistance to ligand-promoted dissolution, suggesting that Sb(V)-bearing schwertmannite may serve as a long-term sink for Sb in AMD settings.
Sorption experiments reveal that aqueous Sb(V) uptake by pre-existing schwertmannite proceeds mainly through structural incorporation rather than surface adsorption. Also, ligand- promoted dissolution tests indicate incongruent Sb–Fe release, showing Sb(V) retention within the near-surface structure of schwertmannite. This highlights schwertmannite’s potential as an effective reactive barrier for Sb(V) immobilisation.
Transformation experiments conducted at 60 °C under strongly acidic (pH ≈ 2–3), sulfate-rich conditions show that schwertmannite transforms predominantly to jarosite at pH ≈ 2 and to goethite at pH ≈ 3. The onset of transformation, marked by schwertmannite dissolution outpacing secondary mineral formation, temporarily releases Sb(V) into solution. Antimony is subsequently re-incorporated into newly formed jarosite and goethite through partial Sb(V)-for-Fe(III) substitution.
Overall, this research demonstrates that schwertmannite effectively immobilises Sb(V) through structural incorporation but that its transformation can transiently trigger Sb(V) mobility before re-sequestration into the structure of secondary minerals. These findings improve the mechanistic understanding of Sb retention and mobilisation in AMD environments and provide a scientific basis for designing passive remediation systems aimed at reducing Sb contamination in impacted ecosystems.
Details
- Title
- Interactions between antimony and schwertmannite: sorption, coprecipitation, and controls on antimony mobility
- Creators
- Mohammad Rastegari
- Contributors
- Edward D Burton (Supervisor) - Southern Cross UniversityScott G Johnston (Supervisor) - Southern Cross UniversityNiloofar Karimian (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- 169
- Identifiers
- 991013321027902368
- Copyright
- © Mohammad Rastegari 2025
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis