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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.

A Cu-rich complex sulpfide concentrate (containing Sb as sulphosalts and gudmundite, and As as arsenopyrite) is roasted in Nitrogen atmosphere carrying traces of oxygen (pO2≈10-5.3bar). In situ measurements through QMS indicated that the volatilized species are mainly elemental sulfur, S2(g), and gaseous sulfur oxides. Sb- and As-bearing volatilized species could not be detected, owing to their low concentrations in the gas phase. Characterization studies through XRD and SEM-EDS confirmed that the condensates collected at room temperature during the roasting experiments comprised of (1) cyclo-octa sulfur, S8(s) and polysulfur oxides, Sn−xOx(s); (2) amorphous trisulfides of Sb and As; (3) and cubic crystalline trioxides of Sb and As. The solid phases in the condensate were found to be fine-sized (sub-micronic) and widely intermixed. Consequently, quantification of the solid phases in the condensates through direct measurement techniques like QEMSCAN was not possible. A novel approach of partial quantification of solid phases in the condensate through a stochastic model-based calculation approach is also presented. The model results suggested the occurrence of vapor-phase complexation of sulfides of Sb and As in the gas phase. Additional attributes of the volatilized species could be determined through a thermodynamic equilibrium calculation showing that the formation of the complex oxides, As4−nSbnO6(g), would be negligible compared to that of the complex sulfides, As4−nSbnS6(g).

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.Graphical Abstract

Four different Cu-rich polymetallic concentrates (additionally comprising Zn, Pb and impurity elements As, Sb) from various deposits in Sweden are examined, in particular for the sintering tendency during roasting in inert atmosphere. Experiments performed in a laboratory-scale roasting setup between 200 °C and 700 °C in intervals of 100 °C revealed that significant sintering initiates from 500 °C for all four concentrates. Two sintering mechanisms are determined from the examination of the sintered calcines: (1) solid-state assimilation of Cu-, Zn- and Fe-bearing main sulphide minerals to form a high-temperature solid solution, the iss phase belonging to the Cu-Fe-Zn-S system; (2) low-melting liquid phase formation due to partial melting of galena facilitated by the presence of impurity-bearing minerals, mainly the arsenopyrite and Sb sulphosalts such as tetrahedrite. Galena also forms a melt below 700 °C with the iss phase. Therefore, the presence of galena in polymetallic concentrates generally increases the susceptibility to early sintering. These experiments in inert atmosphere facilitate a fundamental study with practical relevance to the roasting in low oxidation potential environments, favourable for volatilization of impurity elements such as As and Sb.

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.

During the pyrometallurgical extraction of copper, a significant fraction of this metal is lost with discard slag, which decreases profits and overall copper recovery. These copper losses can be reduced by using a settling furnace, in which suspended droplets containing copper separate from slag under the influence of gravity. An industrial trial was conducted in a settling furnace to increase the knowledge of the effect of temperature and settling time on the copper content of slag, and thus enhance the settling process to increase copper recovery. Slag samples were collected from four sample points: the ingoing and outgoing slag stream, within the furnace during settling, and the granulated slag. The chemical composition of the slag samples was analyzed and compared between batches with different temperatures and settling times. The appearance of copper and its associated phases were analyzed using a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector (SEM-EDS). The results indicated that the outgoing slag copper content increased with an increase in temperature, and it was also concluded to be influenced by the attachment of copper to spinels and gas bubbles. The results indicate that regulating the settling furnace temperature to a lower interval could increase copper recovery.

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Despite the fact that H 2 and H 2 O are always present in the gas atmosphere of a blast furnace shaft, their role in the solution-loss reactions of coke has not been thoroughly examined. This study focuses on how H 2 and H 2 O affect the reaction behavior and whether a strong correlation can be found between reactivity in the conditions of the CRI test (Coke Reactivity Index) and various simulated blast furnace shaft gas atmospheres. Partial replacement of CO/CO 2 with H 2 /H 2 O was found to significantly increase the reactivity of all seven coke grades at 1373 K (1100 °C). H 2 and H 2 O, however, did not have a significant effect on the threshold temperature of gasification. The reactivity increasing effect was found to be temperature dependent and clearly at its highest at 1373 K (1100 °C). Mathematical models were used to calculate activation energies for the gasification, which were notably lower for H 2 O gasification compared to CO 2 indicating the higher reactivity of H 2 O. The reactivity results in gas atmospheres with CO 2 as the sole gasifying component did not directly correlate with reactivity results in gases also including H 2 O, which suggests that the widely used CRI test is not entirely accurate for estimating coke reactivity in the blast furnace.

The presence of halogens has an adverse effect on the zinc extraction process through electrowinning, the last phase of the RLE (Roasting, Leaching and Electrowinning) zinc extraction route. Fluoride (F−) may be present as calcium fluoride (CaF2) and this is, for example, the case in double leached Waelz oxide (DLWO). Efficient removal of F− from primary and secondary raw materials for zinc extraction results in a simplified process and increases flexibility in the selection of raw materials. Understanding of the solubility behavior of pure CaF2 can give valuable information on treatment for maximized halogen removal. Dissolution of CaF2 was studied with the addition of sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3). Dissolution studies were combined with thermodynamic calculations to understand the solubility behavior of CaF2 under different conditions. Results from the experiments and the thermodynamic calculations show that Na2CO3 and NaHCO3 have similar behavior if the pH is controlled at the same value. The available carbonate (CO32−) ion in the system limits the concentration of calcium (Ca2+) ion by precipitation of CaCO3, which enhances the dissolution of CaF2. At higher temperatures and pH, calcite, vaterite, and aragonite were formed and co-precipitation of CaF2 along with calcium carbonate (CaCO3) was observed. At lower temperatures and lower pH levels, only calcite and vaterite were formed and a coating by CaCO3 on CaF2 was found to hinder complete dissolution reaction. The results of this study indicate that the temperature along with the reagents used for the dissolution tests have a significant impact on the CaCO3 polymorph mixture (calcite, vaterite and aragonite) formation.

Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect on electrowinning for zinc production. Knowledge of the characteristics of DLWO, and especially on how a fluoride mineral might exist, can contribute to further improvement of the selective leaching for the removal of fluoride. In this study, DLWO was characterized using analytical techniques, such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), 19F liquid-state nuclear magnetic resonance (19F LS NMR), X-ray powder diffraction analysis (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and 19F solid-state nuclear magnetic resonance (19F SS NMR). This study showed that DLWO mainly consisted of zincite (ZnO), cerussite (PbCO3) and a spinel containing zinc, iron and manganese. The fluoride mineral identified was calcium fluoride (CaF2). In SEM analysis, fluorine was found in larger grains together with calcium and oxygen, which was possibly calcium carbonate.