Composition and Cr- and Fe-speciation of dust generated during ferrochrome production in a DC arc furnace
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Bibliographic record
Abstract
A potential hazard associated with ferrochrome production is the unintentional generation of Cr(VI) in the off-gas dusts produced during smelting. Cr(VI) is a well-known environmental toxin and genotoxic carcinogen. Although Cr(VI) has been identified in baghouse dusts associated with submerged-arc furnaces, its occurrence in DC-arc-furnace dusts has not been previously investigated. In this study, we report the bulk composition and phase make-up, as well as the surface and bulk speciation of Cr and Fe of dusts generated during smelting of chromite ore under basic slag conditions in a pilot-scale DC arc smelter. Dusts are captured from both within the DC furnace as well as along the off-gas handling stream, after passing through the afterburner. The dusts primarily comprise feed material (chromite, flux, reductant), aerosolized slag, and glassy spherules, interpreted as off-gas condensates. Dusts collected from within the furnace, known as freeboard dusts, are dominated by feed materials, with elevated amounts of flux (lime) and lesser amounts of slag and spherules. In contrast, spherules dominate dusts collected along the off-gas handling stream by dust separators that capture the increasingly fine-grained fraction of dust, with the highest proportion of spherules occurring in baghouse dusts. Chromite is the primary host of Cr in all dust samples, whereas the spherules have low Cr contents. Cr(VI) was identified by X-ray photoelectron spectroscopy in the surfaces of dust collected from all parts of the smelter system considered, including from the furnace freeboard, despite the overall reducing conditions present therein. Cr(VI) concentrations are sufficiently high in dusts collected from the off-gas handling stream (post-afterburner, cyclone, and baghouse) to be detected in the bulk dust samples by X-ray absorption spectroscopy. The higher concentration of Cr(VI) in the finer-grained off-gas dusts, especially the baghouse dusts, is consistent with the increased abundance of spherules, the major Cr(VI)-hosting phase, in these samples. Fe is similarly more oxidized in dusts collected down the off-gas handling stream compared to dusts collected from within the furnace, which are dominated by Fe(II). Fe(III) hosted by FeOOH is predominate in dusts collected from all locations along the off-gas handling stream. These results demonstrate that there is sufficient oxygen ingress and sufficiently high temperatures in the closed DC furnace for Cr(VI) to be generated in the freeboard off-gas dusts. Cr(VI) is associated with the finest grained fraction of dusts, underlining the importance of ensuring the continual improvement of dust-capture systems, especially in terms of their ability to target increasingly finer fractions of dust.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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 it