Fernández-González and 5 co-authors, reported in mid-2021 that copper slag is presently considered a waste in copper pyrometallurgy despite the significant quantities of iron (>40 wt. %) and copper (1 to 2 wt. %). On the other hand, solar energy, when properly concentrated, offers great potential in high-temperature processes. Therefore, concentrated solar power (CSP) could be used in the treatment of copper slag to transform fayalite into magnetite and copper sulfides and oxides into copper nodules.
The results showed that fayalite was partially decomposed into magnetite and silica. Moreover, copper nodules (65–85 wt. % Cu) were identified in the treated samples, while the initial slag, analyzed by X-ray diffraction, X-ray fluorescence, and SEM-EDX, did not show the presence of metallic copper.
Finally, the treated copper slag was crushed and grinded down to 40 µm, and two fractions were obtained by magnetic separation. The magnetic fraction (85%) was mainly comprised of magnetite, while the non-magnetic fraction (15%) had 5–10 wt. % Cu. Considering the experimental results, 7.5–18 kg Cu/t slag might be recovered from the slag. A preliminary economic analysis, considering the current copper price, indicates that only the recovery of copper could represent a significant economic benefit (>30 €/t slag). Therefore, CSP might be a potential candidate for the treatment of copper slag to recover copper and iron.
The authors concluded that slags from copper metallurgy are a residue/by-product of great interest due to the high quantity of iron (>40 wt. %), but also due to the copper content (1–2 wt. %). Conventional recovery of copper from copper slags involves electric furnaces and additions of carbon and pyrite, being energetically intensive and giving as a result slag with 1–2 wt. % in optimal conditions. The copper in the slag is usually matte (Cu2S·FeS) or an oxide associated with the other oxides of the slag. The problem of electric furnaces is the energy consumption.
Concentrated solar power (CSP) could be an alternative in the treatment of copper slags due to the great potential in high-temperature processes, such as those involved in most metallurgical processes. The utilization of CSP in the treatment of copper slags was proposed in this manuscript. Thermal decomposition of fayalite is thermodynamically favorable at the temperatures and conditions involved in the process. The presence of an oxidizing environment leads to the decomposition of the fayalite but the reduction of copper oxide to metallic copper requires reductant conditions. Both processes compete with each other, as different conditions are required, so searching for a situation where the maximum quantities of both phases are recovered should be considered.
The results indicated that fayalite was partially decomposed during the experiments into magnetite and silica because the slag became magnetic after the treatment and the magnetite content significantly increased. However, the fayalite decomposition was not complete since it was still detected in the treated samples. Moreover, copper nodules (65–85 wt. % Cu) were identified in the treated samples, while the initial slag, analyzed by X-ray diffraction, X-ray fluorescence, and SEM-EDX, did not show the presence of metallic copper.
Finally, samples of treated slag were crushed and grinded down to 40 µm with the aim of separating the iron and copper. Two fractions were obtained by magnetic separation: a magnetic fraction (85%), mainly comprised of iron as magnetite; and a nonmagnetic fraction (15%) that was a copper concentrate with 5–10 wt. % Cu. Considering the experimental results, 7.5–18 kg Cu/t slag might be recovered from the slag.
A preliminary economic analysis, considering the current copper price, indicated that only the recovery of copper could represent a significant economic benefit (>30 €/t slag). Therefore, CSP might be a potential candidate for the treatment of copper slags to recover copper and iron, although further research is still required to think about the scalation of the process up to the industrial level.
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