INTEGRATED SYNCHROTRON APPROACHES TO CHARACTERISE ORGANIC MATTER-IRON PHASES RELEVANT TO PASSIVE MINE WASTE REMEDIATION SYSTEMS
Bibliographic record
Abstract
The work presented in this thesis used synchrotron X-ray scattering and X-ray absorption spectroscopy (XAS) techniques to characterize samples relevant to mine waste systems. Passive remediation systems such as permeable reactive barriers and constructed wetlands aim for long-term contaminant immobilization. Contaminant removal is achieved through mechanisms such as precipitation in sulfide phases and/or sorption onto iron oxyhydroxides. These processes occur in the presence of various dissolved organic compounds such as tannins that are released in natural environments through organic matter degradation. Research on tannin influences on mineral precipitation is necessary to better understand contaminant immobilization processes. This thesis aims to examine the role tannins (using tannic acid as the model compound) play during iron oxyhydroxide and iron sulfide precipitation. Tannic acid was found to favour formation of crystalline phases when present during ferrihydrite and mackinawite precipitation. The presence of tannic acid during ferrihydrite synthesis favoured the formation of lepidocrocite and goethite as tannic acid concentration increased. The presence of tannic acid during mackinawite synthesis favoured formation of greigite, however increasing tannic acid concentration also led to ferrihydrite precipitation . Tannic acid is redox sensitive and in the presence of redox sensitive metals such as Fe, it can change the system’s chemistry. During ferrihydrite synthesis, tannic acid reduced Fe(III) to Fe(II) even under aerobic conditions. The tannic-acid generated Fe(II) might have catalyzed the transformation of early formed ferrihydrite to lepidocrocite and goethite or they might have formed through oxidation of the produced Fe(II). During mackinawite synthesis, tannic acid catalyzed oxidation of Fe(II) to Fe(III) and S(-II) and S0; changing the system’s chemical conditions to favour greigite and ferrihydrite precipitation. This project suggests that the presence of tannic acid as well other redox sensitive tannin compounds may be important in passive remediation systems since they influence redox conditions and promote the formation of a mixture of crystalline and poorly crystalline phases at initial stages of iron oxyhydroxide and iron sulfide precipitation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".