Fayalite Slag Research Articles

The effect of slag variability in the attempted manufacture of AYF (alite-ye'elimite-ferrite) cement clinker at both laboratory and pilot scale

The production of AYF (alite-ye'elimite-ferrite) clinker was tested at laboratory and semi-industrial scale using by-products from the metallurgical industry: AOD slag; ladle slag; and fayalitic slag. Alite could be produced with ye'elimite using fluorine originating from AOD (argon oxygen decarburisation) slag as a mineraliser. After a successful laboratory demonstration, the clinker production was scaled to a semi-industrial trial. It was discovered that the reason for the absence of alite formation in a semi-industrial demonstration was that the AOD slag from the specific batch did not perform the designed mineralisation effect for alite formation. This study demonstrates that alite-ye'elimite can be produced at 1260 °C at laboratory scale by using fluorine mineralisation originating from an industrial by-product – in this case, AOD slag. However, the utilisation of by-products for delicate reactions requires detailed determination of the properties of the slag, as the variability from the same source yields different clinker chemistries and mineral phases.

Behavior of Tantalum in a Fe-Dominated Synthetic Fayalitic Slag System—Phase Analysis and Incorporation

Pyrometallurgical processes produce slags that may contain valuable elements because of their high oxygen affinity. However, the concentration is extremely low, which causes losses. In fact, these elements, for example, tantalum and rare earth elements, are less than 1% recycled. To return such technologically important elements to the material cycle, pyrometallurgically is used to enrich them in the simplest possible compounds within the slag, which have favorable properties for recovery (morphology, crystal size, magnetic properties), allowing further mechanical separation. The purpose of modification of the slag system is to obtain engineered artificial minerals” (EnAM), a process in which targeted minerals with high element concentration are formed. In this article, this approach is investigated using tantalum-rich fayalitic slag, since this slag is commonly found in the industry for the pyrometallurgical treatment of waste electric and electronic equipment. Synthetic fayalitic slags in reducing environment under different cooling rates were produced with Ta addition. The characterization of the produced samples was carried out using powder X-ray diffraction (PXRD) and electron probe microanalysis (EPMA). Additionally, the speciation of Fe and Ta was accessible through X-ray absorption near-edge structure (XANES) spectroscopy. EPMA also provided a semiquantitative assessment of the Ta distribution in these individual compounds. In these slags, tantalum accumulated in perovskite-like oxidic and silicate compounds as well as in magnetic iron oxides. The enrichment factor is highest in tantalite/perovskite-type oxides (FexTayO6, CaxFeyTazO3) with up to 60 wt.% Ta and ‘tantalomagnetite’ (FeII(FeIII(2-5/3x)Tax)O4) with a maximum of ~30 wt.% Ta (only fast cooling). This is followed by a perovskite-like silicon containing oxide (XYO3) with 12–15 wt.% Ta (only slow cooling), and a hedenbergite-like compound (XYZ2O6) with a varying content of 0.3–7 wt.%. The Ta concentration in pure Fe, Fe(1-x)O, hercynitic spinel and hematite is negligible. Despite the very low phase fraction, the most promising EnAM compound is nevertheless perovskite-like tantalum oxide, as the highest enrichment factor was obtained. Tantalum-rich magnetite-like oxides also could be promising.

Development of Self-Compacting Geopolymer Concrete Using Fayalite Slag Aggregates

Because of its high cement consumption, which limits its use in concrete construction, self-compacting concrete requires a higher cement content and various admixtures. Therefore, it is prudent to explore alternative options to minimize environmental impacts while creating environmentally friendly self-compacting concrete. This study examines the use of fly ash (FA) and ultrafine slag (UFS) in self-compacting geopolymer concrete (SGC), supplemented with fayalite slag aggregates (FSA). These aggregates, in varying quantities up to 60%, were used instead of traditional sand. The rheological properties and compressive strength of SGC were investigated. The analysis revealed that the addition of FSA improved the flowability of SGC. Notably, using a combination comprising 60% FSA, the largest slump measurement of 683.5 mm was achieved. Substituting up to 20% of FSA generally improved the properties of SGC at all ages. After one year, the mixture containing 20% FSA outperformed other compositions, with a maximum compressive strength of 49.38 MPa.

Copper Sulfation from Enargite Roasting Using Coal and Fayalite Slag Mixture

In this work, the roasting of an enargite mix was carried out in oxidative conditions. The temperature range of the study was 773–973 K. The mixture had a 4:6:6 molar ratio of enargite, magnetite and coal, respectively. The roasting was made in an open atmosphere. The time was 1 h for each isothermal test. The effect of temperature and weight loss were studied. The results indicate that the temperature affects the products. At 773–873 K, the copper phases were sulfates. When the temperature was increased to 973 K, all the present phases were oxidized, and no arsenic phase was encountered in the XRDs. Therefore, this process is an excellent alternative for roasting copper concentrates with enargite, removing arsenic in the gas phase and generating a calcine that could then go to lixiviation to finally recover the copper through electrowinning.

Experimental Study and Thermodynamic Modelling of Equilibrium Distributions of Ni, Sn and Zn Between Slag and Black Copper for E-Scrap Recycling Applications

The recycling of waste electronic and electrical equipment (WEEE) and other secondary copper-containing materials through the "black copper" process relies on the selective distribution of metals among the gas, slag, and copper-rich liquid phase. This distribution is controlled by the effective oxidation/reduction potential, often expressed in terms of oxygen partial pressure. Separation of Ni and Sn presents a certain challenge in recycling though black copper route due to similar distribution coefficients over a wide range of oxygen partial pressures and possibly can be improved by optimizing the slag chemistry. This study provides experimental information on the distribution of Ni, Sn, and Zn between fayalite slags or calcium ferrite slags and copper-rich metal at 1250°C. The study uses high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA) techniques along with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for selected measurements of low concentrations. The oxygen partial pressure is controlled by the CO/CO2/Ar gas flow or by measuring the concentration of copper oxide in the slag. The effect of slag composition in terms of Fe/SiO2 or Fe/CaO ratio is studied by using different holding materials, such as silica (SiO2) ampoule, solid spinel (Fe3O4), wüstite (FeO), or dicalcium ferrite (Ca2Fe2O5). The experimental results are compared with literature data and used to optimize thermodynamic models for FactSage® software. The results demonstrate an opportunity for more effective separation of Ni and Sn using at oxidizing stage by using calcium ferrite slag promoting the formation of Sn4+.

A preliminary appraisal for utilizing abandoned industrial side streams as alternatives to cement within radiation protection applications

Recently, there has been arising a severe alert regarding climate crisis all over the world. As industrial production capacities have been soaring every passing day, the primary sources of the earth's crust have been depleting like there is no tomorrow. Sustainable and greener suggestions should be followed to overcome the upcoming catastrophic climate change. With this motivation, cement material, whose influence on global warming is excessive, has been studied to be replaced by alternative material systems in different application areas, and radiation shielding applications may be regarded as one of these emerging fields. In this study, the authors were motivated to replace ordinary Portland cement (OPC) with alternative side streams (SS) that have accumulated in nature without any benefits. First, the high-quantity SS were determined and presented as follows: fly ash (FA), blast furnace slag (BFS), red mud (RM), electric arc furnace slag (EAFS), fayalite slag (FS), rice husk ash (RHA), silica fume (SF), ferrochrome slag (FS), and copper mining tailings (CMT). Each side stream's average chemical compositions were obtained, and their theoretical density values were calculated. After that, the theoretical radiation shielding properties were assessed using Phy-X/PSD software within the 0.15–15 MeV photon energy range. Some essential parameters such as linear attenuation coefficient (LAC), half-value layer (HVL), effective atomic number (Zeff), radiation protection efficiency (RPE), and build-up factors (EBF and EABF) paved the way for comparing SS with OPC material. The results for radiation protection demonstrated that high-density-oxide-containing SS like RM, FS, and EAFS could replace OPC material with a good performance. Owing to this replacement, the authors strongly believe that the future can be sustained in a more secure environment without OPC material, but with SS in radiation shielding applications.

Holistic valorization of fayalitic slag to pig iron and glass fibers

A valorization process for fayalitic copper slags is presented. A primary copper slag is reduced via carbothermic reduction thus creating a pig iron phase and a secondary copper slag, which is used for glass fiber production. The carbothermic reduction is carried out with graphite pellets or carbon fibers as an alternative reduction agent in crucibles within a furnace using inductive heating. The experiments are prepared and evaluated using FactSage 8.1. Carbon is used with an excess of 10% of the calculated value. The effect of temperature variation and turbulence on the carbothermic reduction process are studied. Glass fiber drawing is realized manually after remelting the secondary copper slag. The threshold for successful glass fiber production lays at a FeOx content below 10 wt%. The produced pig iron phase as well as the resulting glass fibers are characterized, while their industrial applicability is discussed.

Establishment of a Hydrometallurgical Scheme for the Recovery of Copper, Nickel, and Cobalt from Smelter Slag and Its Economic Evaluation

In pursuit of carbon neutrality, the demand for metals that are necessary for the development of clean energy technologies is rapidly increasing. Metallurgical waste, such as slag, presents a promising secondary source of these key metals. This research aims to develop an eco-friendly hydrometallurgical process to recover Cu, Ni, and Co from discarded copper/nickel slag. High-pressure acid leaching (HPAL) was used to selectively leach Ni, Cu, and Co from the fayalite slag, yielding high leaching efficiencies of 99.9%, 89.4%, and 99.9%, respectively, with low Fe and Si tenors to the pregnant leach solution (PLS). The solvent extraction (SX) technique utilizing LIX 984N was used to selectively extract and enrich copper from the dilute PLS to about 23 g/L Cu with a very low Fe concentration of 0.05 g/L. Potassium amyl xanthate (PAX) solution was used to form Ni and Co xanthate complexes from the raffinate solution. Nickel was selectively recovered using ammonia solution, while the cobalt xanthate complex was thermally decomposed and recovered as cobalt oxide solids of about 25 wt.% Co. A comprehensive process flowsheet is presented. Furthermore, to realize the real application of the developed slag cleaning process, a preliminary economic evaluation was performed.

Enhancing the thermal stability of alkali-activated Fe-rich fayalite slag-based mortars by incorporating ladle and blast furnace slags: Physical, mechanical and structural changes

A proper and detailed understanding of the thermal stability of Fe-rich fayalite slag-based alkali-activated materials (AAMs) is important due to their potential use in refractory and fire-resistant applications. Here, fayalite slag (FS) was used as the main precursor for AAMs. The effects of incorporating ladle slag (LS) or blast furnace slag (BFS) and different temperature exposures up to 1000 °C were investigated through visual observation, compressive strength, ultrasonic pulse velocity (UPV), thermal conductivity, x-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope coupled with electron probe microanalyzer (SEM-EPMA). The experimental results indicated that the incorporation of LS or BFS as additional calcium and aluminum sources positively affected the high-temperature behavior of blended mortars, which exhibited a reduction in voids, cracks, and thermal shrinkage while having higher residual strength and thermal stability than solely FS-based AAMs. This was mainly due to the differences in mineralogical transformation and the phases formed. Interestingly, the joint effect of elevated temperature exposure and the addition of LS or BFS enhanced the formation of more stable crystalline phases and densified the structure of blended mortars at 1000 °C.

Effect of Impurities on Spinel Precipitation Behavior in Molten Fayalite Slag

The effects of alumina (Al2O3) and magnesia (MgO) impurities on the precipitation of spinels such as magnetite (Fe3O4) due to the oxidation of fayalite (Fe2SiO4) slag in copper smelters were investigated. Molten fayalite slag was oxidized in alumina, magnesia, and quartz sample boats, and spinel precipitation behaviors were compared. The inclusion of Al2O3 and MgO as impurities promoted the precipitation and growth of spinel crystals. It was assumed that this effect was attributed to the rapid formation of hercynite at the interface between the alumina sample boat and slag, growth of spinel due to the substitution of Al and Fe(III) in hercynite, and the solid solution of Mg in spinels. However, as the experiments with quartz sample boats were conducted unavoidably with SiO2 saturated slag, the possibility of suppression of solute diffusion due to increased viscosity and decreased FeO activity in the slag cannot be ignored. Therefore, it is considered that the effects of Al2O3 and MgO on spinel precipitation must be further investigated.

The Effect of Clay Minerals on Fayalite Slag Structure and Refractory Brick Wear during Copper Smelting

Metallic copper production via the pyrometallurgical route is hindered due to the increased presence of gangue in the clay minerals in copper sulfide concentrates and its unpredictable effect on this operation. In this study, the relationship between smelting copper slag composition, including the clay components and the refractory brick wear, was investigated in experimental laboratory tests. Synthetic fayalite slags doped with 2, 5, or 8 wt% high-purity kaolinite or montmorillonite were introduced into magnesia chromite refractory crucibles and melted in an electrical furnace under the controlled partial pressure of oxygen (10−8 atm) for 12 h at temperatures of 1250 and 1300 °C. After the experimental time, the crucibles were quenched in water, and the obtained samples were analyzed using the XRD, SEM, and ICP techniques. According to the results, at 1300 °C the presence of montmorillonite in the fayalite-based slag promoted infiltration through the refractory brick and increased the dissolution of the magnesia component from the hot face. In the case of the kaolinite, the infiltration was even higher, but the magnesia dissolution was delayed.

Recycling high volume Fe-rich fayalite slag in blended alkali-activated materials: Effect of ladle and blast furnace slags on the fresh and hardened state properties

The valorization of Fe-rich fayalite slag (FS) as a precursor for alkali-activated materials (AAMs) is hampered by its low reactivity at ambient temperature. Here, FS was blended with waste-based reactive co-binders such as ladle slag (LS) and blast furnace slag (BFS) to improve the fresh and hardened state properties of the AAMs for potential construction applications. The results showed that the incorporation of LS and BFS as an additional source of Ca and Al accelerated the reaction kinetics and influenced the binder gel type and formation mechanism. In all the mixes, Fe, Si and Na are present in the evolving binder gel. In addition to these elements, the binder gel of the blended formulations is also rich in higher quantities of Ca and Al and showed possible formation of C-A-S-H and C-(N)-A-S-H together with the development of andradite, a calcium ferrosilicate hydrate phase formed from chemical interaction between FS and co-binders; it indicates that both FS and co-binder participated in the binder gel formation. Furthermore, the nucleating and filling effects of co-binders improved the workability, ultrasonic pulse velocity and mechanical properties; this also densified the structure and lowered the water absorption and permeable porosity of the blended mortars. The compressive strength of blended mortars was above 20 MPa, thus satisfying the strength requirements of building materials according to ASTM C62. The results of this study emphasize the reuse potential of FS with other waste streams in producing eco-friendly AAMs, which can have a wide range of construction applications.

Durability of alkali-activated Fe-rich fayalite slag-based mortars subjected to different environmental conditions

Fe-rich alkali activated materials (AAMs) require detailed understanding of their durability prior to their real-life application in the construction industry. Three mixes were formulated with fayalite slag (FS) as the main precursor. The effect of incorporation of ladle slag (LS) or blast furnace slag (BFS) on the shrinkage and exposure to physical and chemical attacks representing environmental conditions in cold and tropical regions (acidic solution at room temperature and in freeze-thaw, combined sodium sulfate and sodium chloride solution at room temperature and in freeze-thaw, freeze-thaw in water and dry-wet cycles) was investigated via visual observation, mass loss, compressive strength, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS). Experimental results show the considerable role of incorporated LS and BFS in modifying the gels formed and controlling material degradation of blended AAMs after exposure. In contrast, sole FS-based samples were completely degraded particularly those exposed to freeze-thaw in water, acid, and combined sodium sulfate and sodium chloride solution, indicating their vulnerability to frost and chemical attacks.

Origin of Historical Ba-Rich Slags Related to Pb-Ag Production from Jihlava Ore District (Czech Republic)

The aim of this study was to characterize historical slags which originated during silver production from the Jihlava ore district, Czech Republic. The area was among the head producers of silver within the Lands of the Czech Crown in 13th–14th centuries. The mined ores had complex composition, being formed mostly by pyrite, sphalerite, galena, chalcopyrite, and accessory silver-rich minerals such as silver-bearing tetrahedrite (freibergite) or pyrargyrite, with gangue represented by quartz and Mn-rich carbonates or baryte. Large volumes of slags with contrasting composition were generated during the Pb-Ag production. Altogether, two main types of slags were identified in the district. The first type is characterized by high BaO contents (up to 34.5 wt.%) and dominancy of glass, minor quartz, and accessory amounts of Ba-rich feldspar (up to 93 mol.% of Cls), metal-rich inclusions, Ba-Pb sulphates and only rare pyroxene, wollastonite and melilite. The composition of the second group belongs to fayalitic slags containing glass, Fe-rich olivine, accessory pyroxene, feldspar, quartz, and inclusions of various metallic phases. Fluxes were derived from gangue (quartz, carbonates, baryte) or local host rocks for both types of slag. The calculated viscosity indexes reflect (with minor exceptions) medium-to-high effectivity of metal separation. Smelting temperatures were estimated from a series of ternary plots; however, more reliable estimates for both types of slags were obtained only from experimental determination of melting temperature and calculations using bulk/glass compositions (~1100–1200 °C).

The Effect of Zn Content and Granulation Temperature on Zn Leaching in an Fe-Saturated (FeXZn(1−X))2SiO4 System

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.

CFD Modeling of the Melting Behavior of a Fayalitic Slag

The melting behavior of a fayalitic slag was investigated with computational fluid dynamics and validated with experimental data. A heating microscope was employed to perform a typical ash melting behavior (AMB) test, in order to gain information about the melting behavior of the slag. The numerical approach is based on using the volume of fluid (VOF) method, in order to track the interface between the slag and the gas phases, and on the enthalpy–porosity model, in order to simulate the slag as a phase change material (PCM). The combined VOF-PCM model was therefore applied to perform a parameter study on the mushy zone constant A_{rm mushy}, which enters the equations of the enthalpy–porosity sub-model and is an a priori unknown. The goal of the investigation was to determine the correct value for A_{rm mushy}, by comparing the numerical results to the AMB test.

Assessment of Metallurgical Slags as Solar Heat Absorber Particles

The use of ceramic solid particle technology in TES-integrated CSP plants offers a high solar-to-electricity ratio and enhanced storage densities, thanks to their high operational temperatures and wide temperature ranges. Metallurgical slags with composition similar to that of the state-of-art bauxite particles can be used as a sustainable and economical secondary raw material to prepare solid particles. In this study, the as-received state and the high-temperature phase and microstructural changes of two fayalite slags from copper and lead production were elucidated by XRD and SEM/EDS methods in a comparative manner. Solid particles were prepared from slags by the oil dropping method, with subsequent heat treatment. Solar-thermal-application-related functional properties of slag particles, such as heat capacity, absorptance, and thermophysical properties, were evaluated by differential scanning calorimetry (DSC), spectrophotometer, heating microscope, and high-temperature compressive tests, respectively. Owing to the formation of more stable Fe-rich phase components and less amount of glassy phase, copper slag is found to be a more promising secondary resource than lead slag in terms of material and functional properties.

Mineralogy and glass content of Fe‐rich fayalite slag size fractions and their effect on alkali activation and leaching of heavy metals

AbstractFayalite slag (FS) is an Fe‐rich nonferrous metallurgy (CaO‐MgO‐) FeOx‐SiO2 slag originating from nickel or copper manufacturing processes, which currently is disposed to landfills or used in low‐value applications. This study investigates the mineralogy and glass content of certain sized fractions of FS and how it influences the reactivity, mechanical, and microstructural properties of the alkali‐activated materials produced. Water‐quenched granular FS was sieved into two size fractions: namely, a fine fraction (FF) with a particle size range of 0–0.5 mm and a coarse fraction (CF) with a particle size range of 1.5–2 mm. It was then milled to a similar median particle size of 10 μm to be used as a binder precursor. The reaction kinetics of each fraction was determined via thermal analysis microcalorimeter, and the microstructural evolution and chemical composition of the binder were studied using a scanning electron microscope coupled with an energy dispersive X‐ray spectroscopy. The environmental leaching behavior of both fractions before and after alkali activation was assessed according to the EN 12457‐2 standard. The results showed that both fractions consisted of fayalite, magnetite crystalline phases, and MgO‐SiO2‐FeOx (‐CaO‐Al2O3) glass phase. However, FF had a higher glass content (63 wt.%) in comparison to CF (39 wt.%), and, consequently, FF was more reactive under alkali activation, as evidenced by faster reaction kinetics, faster strength development, and improved microstructural properties. Alkali‐activated samples had differences in the chemical compositions of their binder gels at early stages, though later, their binders became increasingly homogenous and consisted of an Na‐K‐Fe‐Si gel with Mg, Ca, and Al as minor constituents in both samples. Additionally, the leaching behavior of potentially toxic metals and substances from precursors and alkali‐activated samples prepared was below the limits set for paved structures as specified by Finnish legislation.

Equilibrium Distributions of Pb, Bi, and Ag between Fayalite Slag and Copper-Rich Metal, Calcium Ferrite Slag and Copper-Rich Metal. Thermodynamic Assessment and Experimental Study at 1250 °C

Rising concentrations of impurities are expected at copper fire-refining stage due to lower availability of high-quality copper concentrates and due to increasing recycling of electronics and other secondary materials in primary copper smelting. Extra steps involving the removal of impurities from copper into the slag phase may provide a solution, but better understanding of thermochemistry is needed to evaluate the feasibility of changes in the process. In the present study, the distribution coefficients of Pb, Bi, and Ag between the fayalite or calcium ferrite slags and copper-based metal at 1250 °C were measured experimentally, using high-temperature equilibration, rapid quenching, and electron probe X-ray microanalysis (EPMA). The experiments were undertaken in a closed system using a modified substrate support technique, at relatively high oxidizing conditions typical for copper refining. The improved substrate technique enables the measurement of distributions coefficients for slags in equilibrium with solid spinel (Fe3O4) or dicalcium ferrite (Ca2Fe2O5). Experimental results of the present study and the literature data were analyzed together using thermodynamic modeling. As a result, thermodynamic database has been developed and used to predict the effects of oxygen partial pressure, wt% Cu in slag, temperature, and Fe/SiO2 and Fe/CaO in slags on the distribution coefficients of Pb, Bi, and Ag for the fayalite and calcium ferrite slag systems.

Development of Sustainable Alkali-Activated Mortars Using Fe-Rich Fayalitic Slag as the Sole Solid Precursor

Graphical AbstractDevelopment of sustainable alkali-activated mortars using Fe-rich fayalitic slag as the sole solid precursor.