Fig 1 - uploaded by Inge Bellemans
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Phase diagram for a system containing iron, aluminium, silicon and copper at a partial pressure of oxygen of 10 −8 atm. The coloured region (2) in the diagram shows where alloy, slag and spinel are in equilibrium within the system. Region (1) corresponds to the compositions where alloy and slag are in equilibrium with each other. The thick line in region (2) indicates the compositions where the liquid slag contains about 10 wt% of solid spinel particles.
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This study investigates the origin of the attachment of metal droplets to solid spinel particles in liquid slags. Previous research hinted a reactive origin: the spinel particles form by a chemical reaction together with a new droplet or alongside a droplet that was already present in the system. In this study, a smelting experiment was used to inv...
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Citations
... should preferably be operated above 1524 K to avoid solid precipitation and, thus, a more viscous slag. Solid particles in the slag can hinder settling, as they can attach to copper droplets, forming a copper-solid entity with a lower average density than the copper phase [4,[45][46][47]. The lower density of the copper-solid entity results in accumulation above the settled copper phase in a settling furnace. ...
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.
Graphical Abstract
... That is typical to sulfide mattes which are extremely difficult to quench into glassy form. Some physically entrained copper matte droplets were observed in the slag, and they were aggregated to the edges of the spinel crystals (Bellemans et al. 2018a(Bellemans et al. , 2018bDe Wilde et al. 2016a, 2016b, as shown in Fig. 5(d). The concentrations of trace metals in matte, slag, and spinel with standard deviations (±1σ) are shown in Table 5. Fig. 6(a) shows that the concentration of silver dissolved in all mattes equilibrated with spinel-saturated iron silicate slags kept almost constant over the entire matte grade range studied, fluctuating around 1 wt%. ...
The distribution behavior of trace metals between copper matte and spinel-saturated iron silicate slags was investigated at 1250 • C and pSO2 of 0.25 atm at low silica concentrations. The experiments were conducted in magnetite (Fe3O4) spinel crucibles in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature equilibration-quenching technique. The concentrations of trace elements in matte, spinel, and slag were quantified by electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The trace metals (Ag, Ni, Co, and Sn) in all phases and their distribution coefficients were calculated as a function of matte grade. Results show that silver and nickel can be effectively recovered into matte, whereas cobalt and tin are predominantly deported into slag and gas phases, respectively. These results augment the fundamental thermodynamic data of trace metal distributions in copper smelting processes at low-silica fluxing practices.
... Settling processes can also be hindered by the attachment of copper to solid phases, as suggested in experimental studies by Bellemans et al. and De Wilde et al. [27][28][29][30]. Copper attached to spinels has a lower density than the underlying copper phase and thus cannot settle completely [29]. ...
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.
... This contribution, known as boundary fluorescence or secondary fluorescence (SF) near phase boundaries, may be a significant source of error when analysing for a trace/minor element in a phase next to another phase containing the element of interest. For example, in studies of the interaction between Cu-Ag alloy droplets and spinel particles in slag, Bellemans et al. [132,133] found that the attached droplets have a higher fraction of Fe than the non-attached droplets, which is the result of secondary fluorescence effects. ...
Electron probe microanalysis (EPMA) is a microanalytical technique widely used for the characterization of materials. Since its development in the 1950s, different instrumental and analytical developments have been made with the aim of improving the capabilities of the technique. EPMA has utilized crystal diffractors with gas detectors (wavelength-dispersive spectrometers, WDS) and/or solid-state detectors (energy-dispersive spectrometers, EDS) to measure characteristic X-rays produced by an electron beam. In this review, we give an overview of the most significant methodological developments of EPMA that have occurred in the last three decades, including the incorporation of large area diffractors, field-emission guns, high-spectral resolution X-ray grating spectrometers, silicon drift detectors, as well as more powerful Monte Carlo simulations, which have opened a wide range of new possibilities for the characterization of materials using EPMA. The capabilities of the technique are illustrated by a selection of representative applications of EPMA to materials science and engineering, chosen to show the current merits and limitations of the technique. Given the lack of coverage in previous reviews of the excellent capabilities of EPMA for measurements of thin films and coatings, that topic is covered in detail. We finally provide ideas for new research opportunities using EPMA.
... This contribution, known as boundary fluorescence or secondary fluorescence (SF) near phase boundaries, may be a significant source of error when analysing for a trace/minor element in a phase next to another phase containing the element of interest. For example, in studies of the interaction between Cu-Ag alloy droplets and spinel particles in slag, Bellemans et al. [132,133] found that the attached droplets have a higher fraction of Fe than the non-attached droplets, which is the result of secondary fluorescence effects. ...
Electron probe microanalysis (EPMA) is a microanalytical technique widely used for the characterization of materials. Since its development in the 1950s, different instrumental and analytical developments have been made with the aim of improving the capabilities of the technique. EPMA has utilized crystal diffractors with gas detectors (wavelength-dispersive spectrometers, WDS) and/or solid-state detectors (energy-dispersive spectrometers, EDS) to measure characteristic X-rays produced by an electron beam. In this review, we give an overview of the most significant methodological developments of EPMA that have occurred in the last three decades, including the incorporation of large area diffractors, field-emission guns, high-spectral resolution X-ray grating spectrometers, silicon drift detectors, as well as more powerful Monte Carlo simulations, which have opened a wide range of new possibilities for the characterization of materials using EPMA. The capabilities of the technique are illustrated by a selection of representative applications of EPMA to materials science and engineering, chosen to show the current merits and limitations of the technique. Given the lack of coverage in previous reviews of the excellent capabilities of EPMA for measurements of thin films and coatings, that topic is covered in detail. We finally provide ideas for new research opportunities using EPMA.
... The second example of fundamental research is shown in the paper by Bellemans et al. [2] who studied a particular case of metal losses in liquid slag. They considered that the adherence of metal droplets to solid particles can cause inadequate sedimentation behavior, which was experimentally studied by evaluating the Cu droplets and their attachment to spinel particles in a Fe-Si-Al-O-based system. ...
Operation of slags and their valorisation are one major topic in the metallurgical industry. Different phases within the slag have influences on the slag properties, which requires fundamental knowledge on the system to consider effective measures to reach the individual optimisation targets. Solid phases like spinels in slags have an impact on viscosity, resulting in operational issues, increased metal losses and other effects in daily operation. In this document an overview on spinel-containing slags of the non-ferrous metallurgical processes is given, with focus on operation in liquid state. It shows a summary of the current state of experimental and modelling work in this field done by different research groups. The importance of studies on thermodynamic properties and phase diagrams to solve practical operational issues is outlined.
The goal of this work is to accurately measure the viscosity of an industrial secondary copper smelting slag. Established literature commonly performed such measurements in non-inert labware, such as alumina. Despite the fact that the dissolution of alumina into the slag was addressed as a source for errors, a comprehensive analysis of how this interaction affects the measurement reliability is hitherto lacking. Furthermore, the type of dissolution (direct or indirect) will influence the interaction kinetics. This work aims to verify a possible relation between the dissolution and viscosity measurement reliability. For this purpose, the infiltration depth during and time stability of four different slag PbO-SiO2-CaO-Al2O3-ZnO-Fe2O3 viscosity measurements were analyzed. Both in-situ viscosity measurements and post mortem SEM images of the interface were therefore analyzed. It was observed that a multiphase interfacial layer was formed upon alumina dissolution. This layer consisted of a spinel intermediate layer and an enclosed interfacial slag. EDX measurements confirmed the difference between the latter layer’s composition and the bulk slag. Samples with a high interfacial slag viscosity yielded a dense spinel layer. As a result, alumina dissolved indirectly and more reliable viscosity measurements were obtained that were more stable over time. While samples with a low interfacial slag viscosity yielded a discontinuous spinel layer and therefore alumina could dissolve fast into the bulk slag, resulting in more unreliable viscosity measurements that varied over time.
