Incomplete Sulfide Oxidation in Oxygen-Depleted Mine Waste Systems and Consequences for Aqueous Sulfur Speciation
Bibliographic record
Abstract
The oxidative dissolution of sulfide minerals in mine wastes can lead to oxygen depletion and redox gradients, impacting the mobility of redox-sensitive solutes, especially in heterogeneous tailings systems. However, the controls of these gradients on sulfide reactivity and sulfur (S) mobilization are not well-understood, posing challenges to long-term drainage quality assessments. This research explored the weathering of pyrite, Fe-rich sphalerite, and S-bearing mineralogy in controlled conditions (6<pH<9, ambient vs. sub-oxic) and at three legacy tailings in Ontario and two in Nova Scotia, Canada. Findings indicate oxidation rates of pyrite (up to 10-10 mol m-2 s-1) were higher than sphalerite (up to 10-11 mol m-2 s-1) and, in both minerals, decreased by two orders of magnitude under sub-oxic (<50 ppm O2) conditions. Secondary S-bearing mineral precipitation mainly involved elemental S, without the notable presence of sulfate- or thiosulfate-salts above 0.01 wt. %. In experiments, sulfate was the primary aqueous S species, but significant amounts of thiosulfate, tetrathionate, and sulfite were also present, consistent with known sulfide oxidation pathways. Notably, pyrite weathering produced fewer incompletely oxidized S than sphalerite under similar conditions. Samples from three legacy tailings in Cobalt, Ontario, revealed up to 3.5 wt. % sulfide minerals, predominantly chalcopyrite and cobaltite/gersdorffite, with sulfate dominating dissolved S. However, significant fractions of thiosulfate and tetrathionate were also detected. Tailings from Nova Scotia showed higher sulfide mineral content but smaller intermediate S fractions, mostly thiosulfate and sulfite. Across all sites, surface waters exhibited lower total and intermediate-S levels than tailings porewaters, with redox conditions primarily influencing aqueous S speciation. Only marginal correlations were observed between intermediate S species, dissolved Fe levels, and tailings mineralogy, implying a subdued influence of the latter on S speciation. This research highlights the complexities of S oxidation and its control by various factors, including redox conditions and mineralogy, in controlled environments and tailings systems. A wide range of intermediate S species can be produced even under low-reactivity conditions, emphasizing the need to incorporate these insights into mine waste management strategies and long-term water quality predictions.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".