Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags
The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu<sup>1+</sup>Fe<sup>3+</su...
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| Format: | Article |
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MDPI AG
2023-10-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/13/11/1374 |
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| author | Hassan Gezzaz Cristiana L. Ciobanu Nigel J. Cook Kathy Ehrig Ashley Slattery Benjamin Wade Jie Yao |
| author_facet | Hassan Gezzaz Cristiana L. Ciobanu Nigel J. Cook Kathy Ehrig Ashley Slattery Benjamin Wade Jie Yao |
| author_sort | Hassan Gezzaz |
| collection | DOAJ |
| description | The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu<sup>1+</sup>Fe<sup>3+</sup>O<sub>2</sub>) from a spinel solid solution (magnetite, Fe<sub>3</sub>O<sub>4</sub>) and understand why cuprospinel (CuFe<sub>2</sub>O<sub>4</sub>) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe<sup>2+</sup><sub>6.89</sub>Cu<sup>2+</sup><sub>0.86</sub>Co<sub>0.13</sub>Mg<sub>0.15</sub>Si<sub>0.02</sub>)<sub>8.05</sub> (Fe<sup>3+</sup><sub>15.52</sub>Al<sub>0.41</sub>Ti<sub>0.01</sub>Cr<sub>0.01</sub>)<sub>15.95</sub>O<sub>32</sub>, and (Cu<sup>1+</sup><sub>0.993</sub>Co<sub>0.002</sub>Mg<sub>0.002</sub>)<sub>0.997</sub>(Fe<sup>3+</sup><sub>0.957</sub>Al<sub>0.027</sub>Ti<sub>0.005</sub>Si<sub>0.004</sub>)<sub>0.993</sub>O<sub>2</sub>, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling. |
| first_indexed | 2024-03-09T16:35:39Z |
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| id | doaj.art-d404faf1e6c2412487098ea7209ce345 |
| institution | Directory Open Access Journal |
| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-09T16:35:39Z |
| publishDate | 2023-10-01 |
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| spelling | doaj.art-d404faf1e6c2412487098ea7209ce3452023-11-24T14:57:27ZengMDPI AGMinerals2075-163X2023-10-011311137410.3390/min13111374Copper-Bearing Magnetite and Delafossite in Copper Smelter SlagsHassan Gezzaz0Cristiana L. Ciobanu1Nigel J. Cook2Kathy Ehrig3Ashley Slattery4Benjamin Wade5Jie Yao6School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, AustraliaSchool of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, AustraliaSchool of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, AustraliaSchool of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, AustraliaAdelaide Microscopy, The University of Adelaide, Adelaide, SA 5005, AustraliaAdelaide Microscopy, The University of Adelaide, Adelaide, SA 5005, AustraliaSchool of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, AustraliaThe cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu<sup>1+</sup>Fe<sup>3+</sup>O<sub>2</sub>) from a spinel solid solution (magnetite, Fe<sub>3</sub>O<sub>4</sub>) and understand why cuprospinel (CuFe<sub>2</sub>O<sub>4</sub>) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe<sup>2+</sup><sub>6.89</sub>Cu<sup>2+</sup><sub>0.86</sub>Co<sub>0.13</sub>Mg<sub>0.15</sub>Si<sub>0.02</sub>)<sub>8.05</sub> (Fe<sup>3+</sup><sub>15.52</sub>Al<sub>0.41</sub>Ti<sub>0.01</sub>Cr<sub>0.01</sub>)<sub>15.95</sub>O<sub>32</sub>, and (Cu<sup>1+</sup><sub>0.993</sub>Co<sub>0.002</sub>Mg<sub>0.002</sub>)<sub>0.997</sub>(Fe<sup>3+</sup><sub>0.957</sub>Al<sub>0.027</sub>Ti<sub>0.005</sub>Si<sub>0.004</sub>)<sub>0.993</sub>O<sub>2</sub>, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling.https://www.mdpi.com/2075-163X/13/11/1374magnetitedelafossitesmelter slagsOlympic DamHAADF STEM imagingcooling history |
| spellingShingle | Hassan Gezzaz Cristiana L. Ciobanu Nigel J. Cook Kathy Ehrig Ashley Slattery Benjamin Wade Jie Yao Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags Minerals magnetite delafossite smelter slags Olympic Dam HAADF STEM imaging cooling history |
| title | Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags |
| title_full | Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags |
| title_fullStr | Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags |
| title_full_unstemmed | Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags |
| title_short | Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags |
| title_sort | copper bearing magnetite and delafossite in copper smelter slags |
| topic | magnetite delafossite smelter slags Olympic Dam HAADF STEM imaging cooling history |
| url | https://www.mdpi.com/2075-163X/13/11/1374 |
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