A significant source of copper losses from pyrometallurgical copper extraction is attributed to dissolved and entrained copper in discarded slag. Entrained copper can be recovered via pyrometallurgical slag cleaning in a settling furnace, where the slag viscosity and copper droplet size distribution (CDSD) are critical parameters. Reduced copper losses suggest improved raw material efficiency, and the slag becomes a more environmentally safe byproduct. In this study, iron silicate slags from a smelting furnace are industrially CaO modified in a fuming furnace to contain a CaO content between 8 and 18 wt.%. The viscosity of slags with and without CaO modifications is evaluated in the temperature range from 1423 to 1723 K. The influences of the CaO modifications on the CDSD, slag matrix copper content, and total copper content were determined. The results show that the slag viscosity decreases with increasing CaO concentrations in the slag. In addition, the copper content decreases in the slag phase, and the CDSD shifts to contain relatively larger droplets. The effect of CaO slag modification reveals a linear relationship between the overall copper recovery and viscosity, which increased from 63 to 88% when the viscosity in the respective batch was 0.51 and 0.25 Pa·s.

One of the most significant sources of copper losses from pyrometallurgical copper extraction is attributed to dissolved and entrained copper in the discarded slag. The entrained copper can be recovered via pyrometallurgical slag cleaning in a settling furnace. Reduced copper losses mean increased smelter profits by improved raw material efficiency, and, in addition, the slag will become a more environmentally safe by-product. One way to increase the copper recovery during the settling process is to modify the slag to improve the properties that decrease copper solubility and slag viscosity. In this study, iron silicate slag was modified using CaCO3 on an industrial scale to evaluate its effect on the settling process. More specifically, the changes in settling were related to the modifications and measurements of slag viscosity and copper droplet size distributions in the slag. The trial was evaluated by comparing the copper content in different batches, the size distribution of copper-containing droplets using automated scanning electron microscopy, and performing rheological studies using a high-temperature rheometer. The results showed that increasing the CaO content of the slag by modification with CaCO3 has a positive effect on the settling process and is thus a possible method to improve the industrial settling process of valuable metals in slag.

Viscosity is a critical parameter during metal extraction, influencing the settling of valuabledroplets, slag handling, and mass transfer. The viscosity of oxide melts can be measured withhigh-temperature rheometers. During such measurements, interactions between the crucible andthe oxide system can change the chemical composition, melt structure, and thus the viscosity.For increased reliability of viscosity measurements, the influence of crucible and spindlematerials on viscosity must be studied. In this study, the viscosity of a syntheticFeOx–SiO2–Al2O3 melt was measured using the rotating spindle technique and three differentcrucible and spindle materials (Mo, Fe, and Ni) to determine the interactions with the melt andthe influence on viscosity. The interaction was evaluated by comparing the post-experimentalchemical analyses, the Fe/Fe2+/Fe3+ content, visual observations, and using scanning electronmicroscopy–energy dispersive spectroscopy (SEM–EDS). The results showed that all thecrucibles partially dissolved into the melt, affecting the melt structure, composition, and, thus,the viscosities. The viscosity data obtained using the Mo setup interacted the least with the melt,was the most stable, and with the best reproducibility.

Due to increased copper production and the associated environmental consequences, copper production processes need to be improved, considering the impact of their byproducts, among others slag. This study investigated the leaching of individual constituents of iron silicate slag from a copper smelter. This was done by characterising granulated samples of its constituents – glass, matte, speiss – to determine their leaching contribution. It was observed that leaching in distilled and deionised water without pH regulation achieved various natural pH for the constituents. At natural pH, glass (Cu, Zn) and speiss (Ni, Sb) contributed to leaching. Static pH titrations showed the increased leaching of Zn, Cu, Ni, As, and Sb with decreasing pH. The results showed that, an iron silicate slag consisting of glass, matte and speiss, contributes to leaching as follows: matte – Cu and Ni, speiss – Cu, Ni, As, and Sb. Zn leaching is similar among the constituents.En raison de l’augmentation de la production de cuivre et des conséquences environnementales associées, on a besoin d’améliorer les processus de production du cuivre, tenant compte de l’impact de leurs sous-produits, parmi lesquels les scories. Cette étude a examiné la lixiviation des constituants individuels des scories de silicate de fer provenant d’une fonderie de cuivre. Ceci a été accompli en caractérisant les échantillons granulés de ses constituants –verre, matte, smaltite–pour déterminer leur contribution à la lixiviation. On a observé que la lixiviation dans de l’eau distillée et désionisée sans régulation du pH atteignait divers pH naturels pour les constituants. Au pH naturel, le verre (Cu, Zn) et la smaltite (Ni, Sb) contribuaient à la lixiviation. Les titrages de pH statique ont montré une augmentation de la lixiviation du Zn, Cu, Ni, As et Sb avec une diminution du pH. Les résultats ont montré que les scories de silicate de fer composées de verre, de matte et de smaltite contribuent à la lixiviation comme suit: matte–Cu et Ni, smaltite–Cu, Ni, As et Sb. La lixiviation du Zn est similaire parmi les constituants.

The increased demand for Li-ion batteries has prompted the scientific community to improve recycling routes in order to reuse the valuable materials in batteries. After their end-of-life, the batteries are collected, discharged, and mechanically disintegrated, generating plastic and metallic streams that are recycled directly; this leaves behind a small particle size fraction known as black mass (BM). BM is composed mainly of graphite and Li-metal complex oxides. Pyrometallurgy is a route known for recycling of BM, in which identifying the BM’s behavior at high temperatures is essential. In this study, two types of BM are characterized in two fractions of 150–700 µm and smaller than 150 µm. The thermal behavior of the BM is studied with thermal analysis techniques. The analyses demonstrate that the mineralogical and morphological properties of the two fractions do not significantly differ, while the amounts of C and organic materials might vary. When the BM was thermally treated, the binders decomposed until a temperature of 500 ℃ was reached, where the volatilization of hydrocarbons was observed, although F mostly persisted in the BM. The Li-metal oxide was partially reduced to lower oxides and Li carbonate at ⁓ 600 ℃, and the main mass loss was caused by carbothermic reduction immediately thereafter. As the products of this process, metallic Co and Ni phases were formed, and part of the graphite remained unreacted. Regarding the Li behavior, it was observed that in the presence of Al, AlLiO2 is the most likely composition to form, and it changes to LiF by increasing the F concentration in the composition.

During primary copper sulfide smelting and converting, one of the main copper losses is to the slag, which decreases the overall copper recovery. To decrease the copper losses, which are mechanically entrained or dissolved, a slag cleaning route can be used. At the Boliden Rönnskär smelter in Sweden, the slag from the smelting furnace is treated under reducing conditions in a fuming furnace and then tapped into an electric settling furnace where the copper is separated from the slag under the action of gravity. A trial was conducted in the settling furnace at the Rönnskär smelter to increase the knowledge of the copper content in slag and how the process parameters temperature and settling time influence the final slag copper content. The slag was also modified with CaO, to enhance the slag properties for an increased settling velocity and thus decreased copper content. The trial was evaluated by collecting multiple samples of the ingoing and outgoing slag and then compare the slag copper content in the samples. The results showed that the copper content increased with increasing temperature and decreased when the slag was modified with CaO, both parameters had a more pronounced effect compared to the settling time. The slag was also characterized showing that copper was associated with spinels and bubbles, which hinders the settling.

Granulated iron silicate slag, a by-product of pyrometallurgical copper extraction, has excellent properties for construction applications. Slag modification with CaO enhances the application properties regarding pozzolanic reactivity, potentially extending slag use in the future. The slags’ short-term leaching behavior has already been investigated with promising results, while the long-term leaching effects are less studied. Therefore, this study aims to determine the long-term leaching effects on CaO-modified iron silicate slags. The CaO-modifications were conducted during full-scale slag treatment operation. The slags were characterized and leached, and the remaining slags were investigated regarding the formation of secondary phases. The long-term leaching of main and trace elements was determined over 30 days using a dynamic leaching method corresponding to an extended time period. The leaching tests showed increased leaching of the main slag elements (Si, Ca). Zn and Cu showed peak leaching after four days of leaching, and the leaching of As and Sb decreased with the increasing CaO content in the samples. After dynamic leaching, secondary phases formed on the Cu-containing inclusions on the sample surfaces. Independent of the CaO content, the leaching of Cu was increased when subjected to external acidic and oxidating conditions using static pH titration at pH 5 in dilute nitric acid.

A Cu-rich polymetallic complex concentrate produced at the Garpenberg Mines of Boliden Mineral AB, Sweden is investigated. Roasting at 700 °C in N₂ leads to extensive liquid formation. The calcine obtained after cooling down to the room temperature is found to be severely sintered, entrapping numerous melt nuggets. This work focuses on analyzing redistribution of the minor (Ag) and trace elements consequent to the roasting treatment. Advanced micro-analytical techniques such as quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), laser-ablation inductively coupled plasma-mass spectrometry (ICP-MS) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) are used in conjunction for detailed characterization of the initial concentrate and the roasted calcine, especially the melt nuggets (which symbolizes the phases which were molten at 700 °C). The minor element—Ag is primarily in the silver-antimonide and tetrahedrite mineral phases in the initial concentrate. Ag separates out of tetrahedrite when the later interacts with galena to form a liquid phase. Furthermore, Mn, Cd, Tl and Hg are the relevant trace elements in the Garpenberg concentrate. Sphalerite is the major host of Mn, Cd and Hg. Tl is mainly in galena. Consequent to liquid formations at 700 °C, the trace elements redistribute and tend to segregate in low-melting phase-fractions. Statistical methods such as correlation matrices and clustering analysis are used effectively in evaluating the data from laser-ablation ICP-MS measurements on sulphide samples.

The zinc in the fayalite slag of copper smelters, in which Zn-containing raw materials are used, is mainly found to be in oxidic phases, such as glassy iron silicate. During the slag water granulation process, the molten slag is heated, whereby the granulated slag achieves varying granulation temperatures. Therefore, in this study, we aimed to characterize and assess the leaching behavior of a synthesized Fe-saturated (FeX,Zn(1−X))2SiO4 system to understand the dependance of the zinc leaching behavior on the parameters of the ZnO content (1–10 wt.%) and granulation temperature (1300 or 1400 °C). It was found that the Zn leaching increased with the increasing Zn content and granulation temperature, using both batch and static pH leaching methods. Zn leaching was further increased at pH 5 using diluted nitric acid under oxidation conditions. Among the oxides in the samples—fayalite, spinel, and glass—glass was found to contribute to Zn leaching, owing to its weathering during pH-titration.

Four different Cu-rich polymetallic concentrates are tested for volatilization of Sb and As during laboratory-scale roasting. The experiments are performed between 200 °C and 700 °C, at intervals of 100 °C and in an inert atmosphere. Sb volatilization is much less (maximum approximately 45 pct) than As volatilization (maximum approximately 95 pct) in these conditions at 700 °C. As volatilization is however limited from the concentrate having As mainly in a tetrahedrite solid solution ((Cu,Ag,Fe,Zn)12(Sb,As)4S13). Sb and As retained in the roasted calcine are found in the low-melting liquid phase, formed at approximately 500 °C. This melt phase gets enlarged and enriched in Sb with an increase in temperature. However, there is noticeable As volatilization from this melt phase with the temperature approaching 700 °C. Furthermore, there is an early and relatively high Sb volatilization from the concentrate having Sb substantially as gudmundite. Micron-scale elemental redistribution in gudmundite in the 350 °C roasted calcine confirms its transformation at this temperature. Other Sb minerals did not undergo any detectable transformation at this temperature, suggesting that the significant Sb volatilization starting between 300 °C and 400 °C was primarily from gudmundite. This benign attribute of gudmundite featured in this work in the context of roasting should also be relevant from the geometallurgical perspective during concentrate production, where concentrates bearing Sb are considered substandard for further Cu extraction irrespective of the Sb mineralogy.