| Title | Composition and Cr- and Fe- speciation of dust generated during ferrochrome production in a DC arc furnace |
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| Author | Berryman, E J ;
Paktunc, D; Kingston, D; Beukes, J P |
| Source | Cleaner Engineering and Technology vol. 6, 100386, 2022 p. 1-12, https://doi.org/10.1016/j.clet.2021.100386  Open Access |
| Image |  |
| Year | 2022 |
| Alt Series | Natural Resources Canada, Contribution Series 20210630 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | engineering geology; Science and Technology; chromium; chromium geochemistry; chromite; smelting |
| Illustrations | tables; schematic diagrams; figures; element distribution diagrams; plots; spectra |
| Program | CanmetMINING - Green Mining Innovation-Processing Chromite |
| Released | 2021 12 30 |
| 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. |
| Summary | (Plain Language Summary, not published)
A potential hazard associated with ferrochrome production is the unintentional generation of Cr(VI) in dusts produced during smelting. Cr(VI) is a
well-known environmental toxin and genotoxic carcinogen. Although Cr(VI) has been identified in dusts associated with one type of furnace, namely submerged-arc furnaces, its occurrence in dusts generated in DC arc furnaces has not been previously
investigated. In this study, we address this knowledge gap by characterizing in detail dusts generated during smelting of chromite ore in a pilot-scale DC arc smelter. Cr(VI) was identified on the surfaces of the dust particles collected from all
parts of the smelter system, including dusts collected from inside the furnace. Fine grained glassy spherules are the major Cr(VI)-hosting phase in the dust samples. Overall Cr(VI) contents of the dusts were low. Only the most spherule-rich samples,
the fine-grained dusts collected from the baghouse, contained sufficient Cr(VI) to be detected by bulk techniques. Iron was similarly more oxidized in the finer grained dust samples, as indicated by the predominance of Fe(III)-bearing FeOOH. The
findings of this study underline the importance of ensuring the continual improvement of dust-capture systems, especially in terms of their ability to target increasingly finer fractions of dust. |
| GEOSCAN ID | 329581 |
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