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Valorization of slag from metallurgical processes becomes ever more important as a measure to reduce the environmental impact of metal production operations. To this end, the slag composition has to be changed so that the expected technical and environmental requirements of potential end-users can be met. This paper provides a thermodynamic analysis of the copper flash smelting process which was done based on calculation with the FactSage thermodynamic software package. The purpose was to understand the effect of operational parameters on slag chemistry and elemental partitioning in the process. The results of the thermodynamic analysis are used to understand the content changes of impurities considered as harmful to the environment in the slag. Laws and standards regulating the influence of pollutants were analyzed to understand the impact of content changes on application of slag in different markets. A further important aspect is to increase Cu recovery to the matte as recovering more copper is the major economic driver. The study confirms that an increase in the matte grade and temperature lead to higher partitioning of Pb, Zn, and As to the slag. With increasing matte grade, the volatilization of these elements decreases, and with higher operating temperature solubility of Cu and S in slag will increase. The increase of the Fe/SiO2 ratio maximizes the distribution coefficient (wt.% in matte/wt.% in slag ratio) of Pb and reduces the distribution coefficient of As to the slag. Using the current evaluation, the sensitivity of slag quality and metal recovery on operating parameters and slag marketability is estimated. By example of two fictitious smelters it is shown how conditions in existing smelters can be modified to improve the slag marketability and Cu recovery. It is demonstrated that a suitable compromise between slag quality for improved saleability, metal recovery, and optimal operation of the metallurgical process needs to be identified and implemented.

The oxidation balance is arguably one of the most important parameters during pyrometallurgical processes. In many cases, iron is the most abundant multivalent element present in silicate slags. Within these molten oxide mixtures, the oxygen balance is dominated by the relative fractions of Fe3+ and Fe2+ present. Measuring the concentration of ferrous and ferric iron in quenched slags can provide useful information about the oxidation state of the liquid slag at the moment of freezing. These measurements are not always straightforward, especially in lead-rich slags, as present in modern secondary smelting processes. Building on previous work, this article aims towards a practical and reliable methodology for determining the Fe3+ concentration in lead-rich silicate slags using continuous wave electron paramagnetic resonance (CW-EPR). The method is demonstrated for different Fe3+/ $$\Sigma $$ Fe ratios and a basic model is proposed that relates the slag composition to the EPR spectrum, optimized for a high-lead ternary PbO–SiO2–Fe2O3 slag.

The valorization of Basic Oxygen Furnace (BOF) slag is important as the global annual production of this slag amounts to about 200 million tonnes. Al2O3 can be added to modify the composition and mineralogy of the slag. Al2O3 dissolution can provide long term volumetric stability to the solidified slag and tailor its microstructure/mineralogy for high-added value non-binder applications e.g., aggregates. To ensure the effectiveness of this modification, a fast dissolution of the additives is required. In this study, the dissolution of alumina particles in molten BOF slag between 1500 °C and 1600 °C was experimentally investigated. The alumina particles dissolve indirectly in the BOF slag. A continuous layer of CaAl4O7 (CA2) and CaAl2O4 (CA) solids are formed at the alumina/slag interface. Its thickness remains between 3 and 7 µm. The dissolution process starts rapidly wherein the initial particle diameter is reduced from 1092 µm to almost half within 60 seconds after particle addition. The dissolution rate however then drops rapidly due to the formation of an alumina enriched zone around the dissolving particle. The diffusion coefficient of Al2O3 in liquid slag varies from 1.5 × 10−3 mm2/s at 1600 °C to 9.8 × 10−5 mm2/s at 1500 °C. The activation energy of the Al2O3 dissolution process is determined to be 751 ± 54 kJ mol−1 under the present experimental conditions. Clustering of dissolving particles is observed between 1550 °C and 1500 °C, which has an adverse effect on the dissolution rate.

The pursuit of low-CO2 technologies has led to a surge in research on alternative cementitious materials, of which alkali-activated materials are a large family. In recent years alkali-activated materials have expanded to encompass Fe-rich precursors in addition to the more commonly employed aluminosilicate precursors. The formation mechanism of alkali-activated materials from two Fe-rich synthetic slags has been assessed by employing in-situ X-ray total scattering and subsequent pair distribution function analysis. The evolution of the local atom-atom correlations reveals three reaction stages. After the dissolution of Fe-silicate clusters from the slag, a binder phase is formed with Fe in both Fe2+ and Fe3+ oxidation states. The Fe2+ state is present in the form of trioctahedral layers, similar to those in Fe(OH)2, while the Fe3+ is likely located in the polymerized silicate network. Exposure to air causes the Fe2+ species to transition to the Fe3+ state.

Basic oxygen furnace (BOF) steel slag is a major waste of the steelmaking industry. Utilization of BOF slag contributes to the sustainability of the steel industry by alleviating its environmental impact. Vitrification during cooling is an effective method to promote the cementitious activity of slags with the aim to apply slags in high value-added applications. In the present study, an Al2O3- and SiO2-modified BOF slag was water granulated at a pilot scale. The amorphous and mineral fractions were measured quantitatively. The critical cooling rate to vitrify the modified slag was calculated through the Time-Temperature-Transformation diagrams constructed using in situ confocal scanning laser microscopy. To provide an insight into the crystallization behavior during the granulation process, a mathematical model was developed. The model was validated by comparing the amorphous fraction obtained from experiments with that from simulation. Temperature profiles of the slag particles with varied sizes were calculated with the aid of COMSOL Multiphysics software. The effect of particle size on the vitrified fraction was discussed in detail and the temperature gradient from surface to center of the particle was identified. The results provide novel fundamental understanding of the vitrification process regarding to the slag valorization, which will help the industrial implementation of granulation for pollution remediation and other engineered environmental systems such as chemical industry and pharmaceutical industry. ispartof: Metallurgical and Materials Transactions B - Process Metallurgy and Materials Processing Science vol:50 issue:3 pages:1260-1268 status: published

In entrained flow gasifiers, the production of oxidic slag accompanies the gasification process. This slag forms a layer on the refractory walls, flows downwards gravitationally, and is collected in a water quench. Hence, the slag flow must be constant, since a slag blockage represents a worst-case-scenario. Crystallization of the slag increases slag viscosity, subsequently leading to a possible slag blockage. Therefore, crystallization processes in oxidic slags need to be understood and hence investigated. In this study, three artificial, coal ash related oxidic slag systems were analyzed on their crystallization behavior. Therefore, their melt behavior was investigated via hot-stage microscopy and differential thermal analysis (DTA). Additional thermochemical calculations were performed to predict crystallized phases. Subsequently, quenching experiments were conducted to generate supercooled crystallization in the slag samples. These samples were analyzed afterward via X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the morphologies of crystals were characterized/described. In-situ observations on crystallization growth were performed by using a confocal laser scanning microscope (CLSM). Finally, crystallized phases were compared with results obtained from thermochemical calculations, and the impact of kinetics on the distributed phases was discussed. The knowledge on the crystallization behavior of various phases can be transferred to other slag systems and can improve general crystallization predictions made by thermochemical calculations.

Basic oxygen furnace (BOF) steel slag is a main byproduct that is produced during the converter steelmaking process. The volume instability and fast crystallization of BOF slag limits its added-value application. This article aims to understand the effect of Al2O3 on the mineralogical modification and crystallization kinetics of a high basicity BOF steel slag. Continuous cooling transformation and time–temperature–transformation curves were constructed to determine the crystallization characteristics of BOF slag. The critical cooling rate to vitrify the slag was experimentally obtained. The crystallization sequence was clarified by integrating in situ and post-mortem observations with thermodynamic calculations. The results suggest that the addition of Al2O3 can effectively remove free lime, decrease the melting point, and improve the glass formation ability of the high basicity BOF slag. Undercooling the slag is enhanced by increasing the cooling rate and/or adding Al2O3. By steering the addition of Al2O3 and the cooling rate, BOF slag can be modified to obtain a more amorphous phase, presenting an enhanced potential to be a binder for added-value applications.

Valorization of basic oxygen furnace (BOF) slag is of significant importance for mitigation of the steel production’s environmental impact. The present work aims to investigate the influence of SiO₂ addition and oxygen partial pressure on the mineralogical modification of a typical industrial BOF slag. The slag basicity (mass ratio of CaO/SiO₂) was varied from 1.8 to 4.4 by mixing specific amounts of SiO₂ with the master BOF slag. The original and modified slags were remelted and solidified under argon or air atmosphere followed by slow cooling. The experimental observations were then compared with the results of thermodynamic modeling to achieve a thorough understanding. With decreasing the basicity, free lime was eliminated, as it forms dicalcium silicate (Ca₂SiO₄). With increasing oxygen partial pressure, wustite was oxidized to hematite, which combined with free lime to form calcium aluminoferrite (C₂AF). The effects of SiO₂ addition and oxygen partial pressure were finally evaluated with respect to the energy consumption for the BOF slag valorization. The modified slag is suitable as a precursor for construction applications as binders. ispartof: Metallurgical and Materials Transactions B - Process Metallurgy and Materials Processing Science vol:50 issue:1 pages:210-218 status: published

Due to the scarcity of Sb reserves and the challenging recovery of Sb from waste plastics, it is of great significance to recover Sb from metallurgical residues. A comprehensive characterization of Sb-containing metallurgical residues is essential to develop efficient and clean technologies to recover Sb and other associated metals. This paper reports a complete characterization of three typical Sb-containing metallurgical residues, namely crude antimony trioxide, lead softening slag, and antimony slag. The particle size distribution, chemical composition, morphology, mineralogical composition, and thermal transitions of these residues were determined. The phase equilibria in the antimony slag at 1000 °C were experimentally studied to figure out the Sb distribution within different phases. Feasible Sb recovery technologies were proposed and critically discussed based on the characterization results.

Both primary and secondary copper productions encounter a limitation in the process efficiency due to droplet losses in slags. One of the causes for the mechanical entrainment of these droplets is their interaction with solid spinel particles, hindering the sedimentation of the copper droplets. Previous experiments with synthetic slags provided insights into this interaction and yielded two possible mechanisms: separately formed droplets and particles become attached to one another due to fierce agitation of the slag and metal phases; or the spinel particles and metal droplets form as the result of a chemical reaction together with a new droplet or alongside a droplet that was already present in the system. This experimental study aims to investigate the hypothesis of the formation of copper droplets sticking to spinel particles due to a chemical reaction further. A slag that is initially free from Cu droplets was prepared. After creating controlled conditions to induce the chemical reaction, the formation of sticking droplets was observed. The results from this experiment therefore confirm the previously proposed reactive mechanism. ispartof: Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science vol:48 issue:5 pages:2459-2468 status: published

The slag samples taken from landfill, which originated from different metallurgical processes, have been characterized in this study. The slags were categorized as electric arc furnace (EAF) slag, argon oxygen decarburization/metal refining process slag and vacuum oxygen decarburization slag based on chromium content and basicity. EAF slags have higher potential in metal recovery than the other two slags due to its higher iron and chromium contents. The size of the iron-chromium-nickel alloy particles varies from a few μm up to several cm. The recoveries of large metal particles and metal-spinel aggregates have potential to make the metal recovery from landfilled slags economically viable.

BOF steel slag is a main by-product in steelmaking. The valorization of BOF slag is good for the industry and the environment. In the present study, the carbo-thermic reduction of BOF slag has been investigated, the reduction of Fe and P containing phases (i. e. oxide and compounds) is discussed, and the effects of Al2O3 additions on the reduction process are described. XRD and EPMA have been applied for characterizing the slag. We conclude that, by controlling the test conditions, it is possible to purify the recovered Fe.

Basic oxygen furnace (BOF) steel slag is a main byproduct in steelmaking, and its valorization is therefore of considerable interest, from a metal-recovery perspective and from a residue-utilization perspective. In the present study, the carbothermic reduction of BOF slag was investigated systematically. The reductions of Fe- and P-containing phases (i.e., oxide and compounds) are discussed. Effects of Al2O3 and SiO2 additions on the solidification microstructure and mineralogy associated with the reduction processes were also investigated. The formation and growth of the extracted metallic phase are discussed, and the mineralogy of the residue slag is determined. We conclude that by controlling the additions under a rapid cooling condition, it is possible to extract metallic iron as high-grade metal and simultaneously to utilize the remaining slag for construction applications.

The environmental impact of inorganic polymer mortars from non-ferrous slag was assessed and compared to ordinary Portland cement (OPC) mortar based on a load bearing capacity of 10 MN of bricks of 0.1 m high. Two strategies to minimize the environmental impact of inorganic polymers were pursued. Activating solutions with a lower alkali content (H 2O/Na 2O = 16, 24, 32, 40, 48; constant SiO 2/Na 2O = 1.6) were investigated while keeping the water/slag mass ratio of the inorganic polymer mortar mix constant. Another synthesis route considered the complete replacement of the activating solution by maize ashes. These were blended with the slag in different ash/slag mass ratios (0.2, 0.4, 0.6) before adding water, producing a so-called “one-part” inorganic polymer. A sensitivity analysis showed that the effect of compressive strength and transport distance is extensive. Because of this considerable transport distance dependence, several cities in Flanders were selected to perform a detailed LCA study. The optimal scores of the environmental impact were observed for Mol, the location of the sand supplier, and accounted for 23% with respect to OPC for the samples with the activating solution with a ratio of H 2O/Na 2O = 24 and 17% for an ash/slag ratio of 0.2.

Crystallization tendency and the state of oxidic slags are important influencing factors for slag viscosity and therefore slag tapping. During the gasification process slag is constantly produced and flows down the gasifier walls until it is intercepted and stored for further treatment or a possible valorisation. The kinds of fuel used for gasification lead to different kinds of slag composition likewise. Slag viscosity is strongly influenced by the composition of the slag and the temperature. However, the process of crystallization represents another major influencing factor. Slag crystallization is also affected by several parameters, whose effects need to be considered in experimental studies. This study investigated the impact of the sample state, the chosen crucible material, and the oxygen partial pressure on the crystallization of a Fe-rich oxidic slag in the confocal laser scanning microscope (CLSM) experiment. Using sample powder may lead to heterogeneous nucleation and crystallization during heating due to heterogeneous melting of the compounds. The selection of crucible material is crucial to prevent alloy formation of Fe-species with Pt-crucibles under reducing atmosphere. Finally, the partial pressure of oxygen influences the crystallization tendency as well as the morphology of the crystallized phases. These parameters impede the reproducibility of results as well as the comparison with results deriving from other experiments like sample quenching. This contribution provides an enhanced understanding of the stated parameter effects on the experimental investigation of oxidic slags using the CLSM setup and yields advice to prevent experimental influence on the results.

Belonging to the family of alternative cementitious materials, inorganic polymers are rising in importance because of the drive to decrease CO2 emissions of concrete production. A synthetic Fe-rich slag resembling industrial copper or lead slags, was mixed with a sodium silicate activating solution. 57Fe Mossbauer spectra analyses indicate that the oxidation reactions are taking place simultaneously with the polymerization reactions. The slag contains Fe2+ states and a small amount of Fe3+. During polymerization a new octahedral Fe2+ state is formed, while oxidation is manifested through the appearance of an additional Fe3+ state. The reactions continue after setting, lowering the relative contributions of the slag in the Mossbauer and FTIR spectra of the samples. The Na+/Fe3+ molar ratio in the mixture that makes up the binder after 28 days is approximately 1, suggesting the participation of tetrahedral Fe3+ in the silicate framework, charge balanced by Na+.

© 2019, The Minerals, Metals & Materials Society and ASM International. The influence of the Al 2 O 3 level in CaO-SiO 2 -MgO-Al 2 O 3 (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was investigated through static refractory finger corrosion tests. The tests were performed at 1620 °C under Ar atmosphere, using slags with Al 2 O 3 contents of 5, 10, and 20 wt pct, respectively. The results indicate that the formation of 2CaO·SiO 2 at the slag/refractory interface was suppressed by increasing the Al 2 O 3 content to 20 wt pct, thereby changing the corrosion mechanism from an indirect dissolution to a direct dissolution of CaO and MgO from the refractories. The increased solubility limit of MgO by the Al 2 O 3 -rich CSMA slags results in an overall higher corrosion rate of the MgO-doloma refractory. ispartof: METALLURGICAL AND MATERIALS TRANSACTIONS B-PROCESS METALLURGY AND MATERIALS PROCESSING SCIENCE vol:50 issue:4 pages:1822-1829 status: published

Microstructure tailoring of metallurgical slags allows the production of alternative construction binders with customized properties. In this study, the variations of rheology and strength of alkali-activated basic-oxygen-furnace (BOF) slags are quantified. Two modifications of BOF slag were created adding amounts of alumina and silica at high temperature (>1250 °C). The additions, defined by thermodynamic modeling, lowered the liquidus temperature facilitating the generation of amorphous when the slag was fast cooled. The first modification (SAT1) incorporated 5 wt% silica and 11 wt% alumina, while the second (SAT2) included around 13 wt% alumina. Both modifications generated a hybrid microstructure composed of cementitious and non-cementitious crystalline phases and an amorphous fraction. During alkali activation using NaOH solutions of 0.25 M, rheological measurements on fresh paste using SAT2 registered plastic viscosity values 2.3 times higher than those of SAT1. The compressive strength after 28 days for the binder developed from SAT2 slag was 10–30% stronger than the one from SAT1. These binders showed similar crystalline reaction products but compositional differences in the amorphous gel correlated to the initial slag modification. The detected differences in the binder properties are significant enough to justify BOF-slag engineering as a way to deliver customized precursors for alkali activation. ispartof: CEMENT & CONCRETE COMPOSITES vol:97 issue:March 2019 pages:143-153 status: Published online

In both primary and secondary copper production, copper losses in slags are a decisive factor confining the process efficiency. An important cause for mechanical entrainment of metal droplets in slags is their attachment to solid spinel particles present in the slag phase, hindering sedimentation. To further optimize the production process, it is important to gain insights in the fundamental mechanisms governing this attachment. In the present study, the influence of the spinel composition on the attachment of copper droplets is investigated. First, the attachment is studied in an industrially relevant synthetic PbO–CaO–SiO2–Cu2O–Al2O3–FeO–ZnO slag system. Second, the wetting of copper on two spinel substrates (ZnFe2O4 and MgAl2O4) has been studied in the absence of a slag system, by sessile-drop experiments. Based on the results of both types of experiments, a clear influence of the spinel composition on the sticking behavior of copper droplets is noted. These observations might be transferred to industrial processes to adapt processing parameters to diminish copper losses in industrial slags.

Bauxite residue (red mud) with a high alumina content requires large amounts of fluxes during smelting, which increases the overall process cost, the energy consumption during smelting, and the acid consumption during slag leaching and decreases the throughput of bauxite residue in the smelting phase. Therefore, alumina was removed (or recovered) from bauxite residue by alkali roasting prior to smelting. The sample after alumina removal could be smelted at 1500 °C without the need of adding any flux to obtain a clear slag–metal separation. After smelting, the slag was leached with acids (HCl, H2SO4, or HNO3). The recovery yields of the rare-earth elements (REEs), except scandium, drastically decreased in the low-alumina slags, compared to the original bauxite residue. These poorer recovery yields are due to the formation of a perovskite (CaTiO3) phase, which binds REEs except scandium. CaTiO3 is a stable phase and does not dissolve in acids under normal conditions. Therefore, slag was quenched to suppress the CaTiO3 formation. The REEs and titanium could also be dissolved in acidic solutions at 25 °C by quenching the molten slag. Removal of alumina from bauxite residue by alkali roasting with sodium carbonate requires high temperatures (>900 °C). Therefore, sodium carbonate was replaced with sodium hydroxide to decrease the energy consumption by decreasing the roasting temperature (

An important cause for the mechanical entrainment of copper droplets in slags during primary and secondary copper production is their interaction with solid spinel particles, hindering the sedimentation of the copper droplets. In the present study, the interactions between the three phases involved (slag–Cu droplets–spinel solids) were investigated using an adapted sessile drop experiment, combined with detailed microstructural investigation of the interaction zone. An industrially relevant synthetic PbO-CaO-SiO2-Cu2O-Al2O3-FeO-ZnO slag system, a MgAl2O4 spinel particle, and pure copper were examined with electron microscopy after their brief interaction at 1523 K (1250 °C). Based on the experimental results, a mechanism depending on the interlinked dissolved Cu and oxygen contents within the slag is proposed to describe the origin of the phenomenon of sticking Cu alloy droplets. In addition, the oxygen potential gradient across the phases (i.e., liquid Cu, slag, and spinel) appears to affect the Cu entrainment, as deduced from a microstructural analysis.

Used direct-bonded magnesia–chromite refractory bricks from a secondary Cu smelter were collected to characterize the degradation occurring during application. Based on this post-mortem analysis, lab scale experiments were designed using the direct-bonded refractory type and a fused grain magnesia–chromite refractory. Firstly, the infiltration behavior of a Cu–CuxO and a Cu–CuxO–PbO mixture was investigated. Secondly, the influence of temperature and the prior infiltration of a Cu–CuxO mixture on the infiltration of the ZnO containing fayalite slag was determined. The combination of the post-mortem study and the lab scale tests allowed a more comprehensive understanding of the evolution of the refractory microstructure during degradation. Likewise, it allowed to evaluate how certain parameters, such as temperature and refractory type, affect the infiltration and degradation behavior. As a consequence, conclusions can be drawn about measures to minimize refractory wear in copper smelter linings.

The corrosion behavior of MgO in iron-saturated ZnO-rich fayalite (ZFS) slags having various FeO/SiO2 ratio and CaO/SiO2 ratio was investigated using MgO crucible tests for 12 h at 1200°C. The FeO/SiO2 and CaO/SiO2 ratios in the ZFS slags were varied from 1.0 to 2.2, and from 0.04 to 0.32, respectively. In all of the tests, it was observed that MgO dissolves into ZFS slags and that (Zn,Fe,Mg)2SiO4 olivine and (Zn,Fe,Mg)O solid solution are formed at the crucible/slag interface. The MgO dissolution decreased with the FeO/SiO2 ratio up to a value of 1.7 and then slightly increased, whereas it continuously increased with the CaO/SiO2 ratio. There is no obvious relationship between the amount of olivine and the FeO/SiO2 ratio or CaO/SiO2 ratio. In comparison, the formation of (Zn,Fe,Mg)O solid solution is enhanced by increasing the FeO/SiO2 ratio or CaO/SiO2 ratio in ZFS slags. The results suggest that MgO corrosion is the lowest for FeO/SiO2 and CaO/SiO2 ratios around 1.7 and 0, respectively.

A ZnO-containing fayalite-based slag can be formed in copper smelting from secondary raw materials and its high viscosity is a common issue that hinders slag tapping. In this work, the crystallization behavior of the industrial slag was observed in situ by confocal laser scanning microscopy. Solid precipitation was found to be the major cause of the poor slag fluidity. The phase relations in the industrial slag system ZnO-“FeO”-SiO2-Al2O3-CaO (CaO/SiO2 = 0.05, Al2O3/SiO2 = 0.15) were investigated by quenching the samples after reaching equilibrium at 1423 K (1150 °C) under iron saturation. The equilibrium composition of the phases was determined with electron probe micro-analysis. The effect of individual components, such as FeO, ZnO, and CaO on the phase equilibrium of the slag system has been quantitatively studied. The relation between the solid-phase fraction and the chemical composition of the slag has been revealed. Suggestions to modify the slag composition toward low viscosity are provided.

To determine the effect of ZnO in ZnO-containing fayalite (ZFS) slags on the degradation of magnesia-chromite refractories, the corrosion behaviour of a direct-bonded magnesia-chromite refractory was studied by rotating refractory finger tests at 1200 °C under reducing atmosphere. In addition, MgO crucible tests at these conditions were performed to investigate in particular the effect of ZnO on the slag/MgO interaction. The dissolution of MgO from periclase into the ZFS slags is not enhanced by increasing the ZnO content in the slags. (Fe,Mg,Zn)2SiO4 olivine and (Fe,Mg,Zn)O solid solution are the only two products in the slag/MgO interfacial reactions, even when the ZnO content in the ZFS slag reaches 16.7 wt%. The diffusion of ZnO into the chromite grains to form the (Fe,Mg,Zn)(Fe,Al,Cr)2O4 spinel was favoured with increasing the ZnO content in ZFS slags.

The corrosion behavior of alumina-silica (Al 2 O 3 –SiO 2 ) refractories by liquid carbon steel was studied. This was performed by a refractory crucible test in a vacuum induction furnace at 1520–1545 °C under reducing atmosphere. The results indicate that Mn, Si and a minor amount of Fe in the steel were oxidized at steel/refractory interface, combing with refractory components to form a MnO–SiO 2 –Al 2 O 3 –based slag. This slag was liquid at the testing temperature, and infiltrated along the open-pore network and the grain boundaries into the Al 2 O 3 –SiO 2 refractories. Both Al 2 O 3 –rich and Al 2 O 3 –SiO 2 aggregates in the refractories dissolved into the infiltrating slag. As a result, the refractories were structurally weakened and residual Al 2 O 3 –rich and Al 2 O 3 –SiO 2 aggregates in the hot face of the refractories were washed away into the liquid steel, affecting steel quality.

The present study focuses on the in-situ analysis of slags from secondary copper production by means of laser-induced breakdown spectroscopy (LIBS) in order to improve the process efficiency and the end product quality. Synthetic slag samples, simulating secondary copper production slags, were melted in a laboratory induction furnace and were analyzed using LIBS. SiO2 and FeO were the major components and Al2O3, ZnO and CuO were introduced in the synthetic slag as minor components with concentrations below 10 wt%. The solidified samples were analyzed by means of X-ray wavelength dispersive spectroscopy in an electron probe micro analyzer (WDS-EPMA) and the obtained elemental composition was used as reference for the construction of calibration curves for the elements of interest, i.e. Si, Fe, Al, Zn and Cu. The quality of these calibration models was evaluated by the coefficient of correlation (R2). The accuracy was estimated by means of the prediction error percentage obtained from cross-validation of the calibration curves as well as by external validation using samples originating from industry. The last samples were melted under the same conditions as those of the laboratory prepared samples, and LIBS spectra were collected from the free surface of their melts. Furthermore, the solidified industrial samples were analyzed by WDS-EPMA and the determined concentrations were compared with the ones obtained using LIBS. Results were obtained for SiO2, FeO, ZnO and CuO with the accuracies better than 13.5%, which are considered as satisfactory. The quantification of Al2O3 was significantly influenced by self-absorption. The limits of detection (LOD) of the elements with respect to their oxides, i.e. SiO2, FeO, Al2O3, ZnO and CuO, were estimated as 1.5 wt%, 1.0 wt%, 0.097 wt%, 0.15 wt% and 0.012 wt%, respectively, which are appropriate for the targeted application.

Fe-rich inorganic polymers are rising in importance because of their low CO2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeOx-SiO2 slag is investigated in more detail using 57Fe Mossbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe2+ state in the binder transforms to Fe3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the inorganic polymer powder, the Mossbauer spectra remain stable until 400–500 °C. At 400 °C the Fe2+ in the slag starts to be oxidized, showing the formation of new Fe3+ components. ispartof: Journal of Non-Crystalline Solids vol:526 status: published

© 2018, The Minerals, Metals & Materials Society and ASM International. The viscosity of basic oxygen furnace slag modified by the addition of Al2O3, SiO2, and Na2O was measured via a rotational-type rheometer. The experiment was performed under both continuous cooling condition (5 °C/min) at a constant rotational speed (30 rpm) and isothermal condition at various rotational speeds (between 2 and 120 rpm). The present work suggests that during cooling from liquid to solid, the slag successively undergoes Newtonian regime, shear thinning (time depedent) and thixotropy with a time-dependent apparent yield stress. The corresponding slag microstructure is (1) a fully liquid or partially liquid slag with negligible crystal–crystal interaction in the Newtonian regime, (2) a liquid slag with crystal aggregates/clusters in the shear thinning regime and (3) a skeletal solid network in the regime of thixotropy with a certain level of apparent yield stress. ispartof: METALLURGICAL AND MATERIALS TRANSACTIONS B-PROCESS METALLURGY AND MATERIALS PROCESSING SCIENCE vol:49 issue:5 pages:2649-2657 status: published

Ladle metallurgy (LM) slag is generated during the refining process step in stainless steel making. In view of its very fine particle size, due to the transformation of β- to γ-C 2 S, and the Cr content, the slag is challenging in terms of handling and disposal and is used in only few applications. The current work explores the utilisation of the LM's fine fraction in Ordinary Portland Cement (OPC) clinker production. Three sets of samples containing LM slag, in 0 wt% (OPC – reference), 6 wt% (OPC6) and 14 wt% (OPC14), were investigated. The sintering temperature was 1450 °C with 40 min soaking time. The clinkers containing LM slag, showed a slight increase in C 3 S and a decrease in C 3 A and C 4 AF. The formation of the C 3 S initiated at a lower temperature probably due to the presence of F and C 2 S. Longer setting times were found for OPC6 and OPC14. The compressive strength results were found to be comparable at 2 d (22–25 MPa), 7 d (36–38 MPa) and 28 d (44 MPa) of curing, falling into 42.5R CEM I category. The emission of kgCO 2 /t of clinker during production, is estimated to decrease at least 12% for OPC14. A processing step for the pre-treatment of the slag is also presented, aiming to reduce the initial Cr content.

This study evaluates commercially available magnesia–chromite, magnesia–carbon and magnesia–doloma bricks for their use in a Vacuum Oxygen Decarburisation ladle. The corrosion behaviour of these bricks by stainless steelmaking slags is, therefore, investigated through crucible tests in a vacuum induction furnace at elevated temperatures (1650 and 1750 °C) and low oxygen partial pressures (5.3 and 3.0×10 −11 atm). The results reveal that magnesia–carbon bricks are severely corroded due to the high dissolution of MgO, while magnesia–chromite and magnesia–doloma refractories exhibit an excellent corrosion resistance. The MgO enrichment in the slag is believed to be the reason of the low wear rate of the MgO–doloma refractories. Rebonded and direct-bonded MgO–chromite refractories show similar corrosion resistance against the slags because of the ‘secondary chromite inactivation’. Decreasing the slag basicity enhances the dissolution of MgO into the slag, thereby increasing the corrosion of the magnesia-based refractories.

Crystalline argon oxygen decarburization slag, in powdery form, was investigated for its hydration potential by alkali activation and curing at 80 degrees C. Na-silicate and K-silicate of the same modulus were used as activators. Isothermal calorimetry at 80 degrees C indicated exothermic reactions in the slag pastes. When the slag mortars were cured under steam at 80 degrees C appreciable gain in compressive strength was measured. This was attributed to C-S-H which was detected in TG, FTIR, and Si-29 NMR analyses. Upon hydration at 90d, the amount of crystalline phases decreased, whereas the XRD amorphous content in the slag increased. Electron microscopy showed the formation of different morphologies of reaction products depending on the alkaline activator employed. Presence of reaction rims around the crystalline phases with a major presence of Ca, Si, and O in the reacted matrix was observed in elemental maps.

To investigate the densification of porous alumina plugs, hydrogen measurements, using the Hydris probe system, were performed in molten steel with different oxygen levels at around 1600 °C. The oxygen contents in molten steel were controlled by Al and Fe-Si alloy additions to 664, 296, 92, 51 and 2.5 ppm, respectively. High oxygen levels (> = 92 ppm) in molten steel were found to favor the infiltration of steel into porous alumina plug. The infiltrating steel interacts with SiO2-containing phases and Al2O3 inside the plug, forming liquid FeOnAl2O3-SiO2 slag and FeAl2O4 (hercynite). These newly formed phases, along with the infiltrating steel fill the porous structure of the alumina plugs. As a result, severe densification was observed inside the alumina plugs in contact with molten steel containing high oxygen levels. In comparison, no densification occurred in the plugs contacting with the steel having low oxygen contents of 51 and 2.5 ppm. ispartof: Journal of the European Ceramic Society vol:38 issue:6 pages:2662-2670 status: published

The interaction between a supersonic oxygen jet and liquid metal is a dominant factor affecting transport phenomena during the converter process. A systematic description of the interaction is of significant importance for a quantitative understanding of the transport phenomena. In this paper, cold model experiments and the corresponding numerical simulations were carried out to investigate the gas-slag-metal interaction inside an 80 t BOF converter. The effects of the operation parameters, such as inlet pressure, slag thickness and slag viscosity on the multiphase interaction have been studied. It has been found that the cavity profile is closely related to the operational conditions. The cavity depth increases with an increase in oxygen inlet pressure, whereas the cavity width is much less affected. The cavity profile is also clearly influenced by the thickness of the slag layer. The influence of slag viscosity on cavity profile is not significant under the present simulation conditions.

Valorization of slag from metallurgical industrial processes becomes ever more important as this may help optimizing and reducing the use of natural resources such as rock and sand. In view of this objective, metallurgical processes have to be analyzed in order to modify the slag composition so that it will meet the expected requirements of potential users of these resources. This paper gives the results of a thermodynamic analysis of the flash smelting process to understand the impact of operational parameters on slag chemistry and elemental partitioning in the process. It is shown that an increase of the matte grade and temperature leads to higher deportment of Pb, Zn and As to the slag. With increasing matte grade the volatilization of these elements decreases. Furthermore, the results indicate an increasing solubility of Cu and S in slag at higher temperatures.

In Europe, 50% of the copper originates from recycling. High-Cu containing scraps are regularly rich in impurities like Fe, Ni, Sn and Pb. Many high-Cu containing scraps are fed directly into anode-furnace casting installations or furnaces with limited refining capability. The impurities levels of the anodes produced in these processes should however remain acceptable for further electro-refining.The distribution of Sn between copper and slag has been investigated for conditions relevant to copper converting. Unlike previous studies, this work focuses on the behavior of Sn relevant to fire refining conditions, which are essential for anode refineries.In this study, liquid Cu–1Sn and CuOx–FeOy–SiO2 slag, with CaO additions, were equilibrated at 1300 °C in vacuum sealed SiO2 ampoules. After metal–slag equilibration, the samples were quenched in water. The composition of the slag and Cu metal was investigated with Electron Probe X-ray Microanalysis. The distribution coefficients of Sn between slag and Cu metal were determined as a function of slag composition.

An experimental investigation of the precipitation behavior of the Dy2O3 containing slag during cooling was carried out in this work. The slag with composition 45 wt% SiO2—49 wt% CaO—6 wt% Dy2O3 was equilibrated at 1673, 1773 and 1873 K for 24 h in an argon atmosphere, and then quenched in water to determine the phase relations. The composition and microstructure of the equilibrated phases of the systems were determined by EPMA/WDS. The precipitation behavior of the REEs containing phases during cooling was studied by using an in-situ confocal scanning laser microscope (CLSM) observation technique combined with an infrared imaging furnace heating (IIF). Data resulting from this work aims to support further investigation on separation of rare earths from metallurgical slags.

Steel reoxidation in the tundish has a significant influence on the steel cleanliness and therefore on the mechanical properties of the final product. In the present work, the steel reoxidation by two types of gunning mass (GM), viz. magnesia- and alumina-based GM, and two types of tundish slag, viz. lime–alumina–silica and lime–alumina slags, has been investigated. The evolution of the steel composition during the test was analyzed and predicted based on thermodynamic and kinetic considerations. The calculated steel composition agrees well with measured values, when assuming the mass transfer in slag phase limits the reoxidation reactions. The oxidation capacity of the gunning mass and tundish slag is quantified by calculating the oxygen amount supplied from the GM and the slag to the steel phase. It was found that compared to alumina GM, magnesia GM exhibits a stronger oxidation capacity due to its higher content of reducible oxides (10 wt pct SiO2 + 6 wt pct FeO). Compared to lime–alumina–silica tundish slag, lime–alumina slag (with more FeO + MnO contents) provides more oxygen to the molten steel in the present experimental conditions and consequently shows a stronger oxidation capacity.

The binding properties of continuous casting stainless steel slag were studied when activated by a combination of Na silicate and 5 M NaOH as well as K silicate and 5 M KOH at steam curing temperatures of 60, 70, 80, 90, 100 and 110 °C. The slag mortars developed moderate compressive strength (∼5 MPa) at 60 °C which initially increased moderately and then steeply (>30 MPa) at higher curing temperatures. The porosity of K activated mortars was lower than for Na activated mortars. Thermal and ATR-FTIR analysis showed the formation of C–S–H type of reaction products for both activators at all temperatures, while the formation of brucite was promoted at higher curing temperatures. A much denser hydrated matrix with a better bonding with aggregates was formed at higher curing temperatures. Heavy metal leaching from the slag was dependent on its type and curing temperature of samples.

During gasification of refuse derived fuel (RDF) to produce syngas in a system in which a melt is also produced, the gasified organic fraction of the RDF is in contact with the molten inorganic fraction, i.e. a slag. Examples of such systems are plasma gasifiers, in which crude syngas is further cracked in a plasma converter. Depending on the degree of gas–slag interaction, their compositions may vary and influence the valorisation potential of both resources. To evaluate the influence of this interaction, a pseudo-kinetic model was developed based on local thermodynamic equilibrium between the gas phase and part of the slag phase. The interaction level was accounted for by varying the amount of the slag that equilibrates with the gas. The valorisation potential of the resulting gas and slag phases was evaluated in terms of the heat of combustion and the mineralogy after cooling, respectively. Engineering of the slag composition was made through lime-rich addition. The influence of waste compositi...

The aim of this work was to investigate the binding potential of non-hydraulic, crystalline continuous casting stainless steel slag, which is a by-product from stainless steel production, by alkali activation with sodium hydroxide and potassium hydroxide. Calorimetric analysis of the activated slag showed low cumulative heat evolution at 20°C. Slag mortars did not harden at this temperature. Considerable enhancements in heat evolution and hardening were observed at 80°C. The resulting hydrated slag showed the formation of calcium silicate hydrate type reaction products and brucite in thermogravimetric analysis. X-ray diffraction analysis showed a reduction in the amount of γ-dicalcium silicate and periclase. Elemental mapping showed the presence of calcium, silicon and minor amounts of magnesium in the hydrated phase. An optimum activator dosage of 7·5M of sodium hydroxide or potassium hydroxide was found to generate the highest amount of reaction products and compressive strength.

One of the main factors limiting the lining lifetime in pyrometallurgical smelters is continuous refractory oxides dissolution in the slag bath. The overall wear is accelerated when the slag infiltrates the porous brick and the dissolution thus occurs in a larger part of the lining. This work investigates the possibility of preventing deep infiltration by sealing off the pores with newly formed phases. Static finger tests at constant temperature (1200 °C) were performed in contact with a synthetic non-ferrous PbO–SiO 2 –MgO slag, showing the formation of forsterite (Mg 2 SiO 4 ) throughout the refractory sample by the reaction between SiO 2 (slag) and MgO (refractory). This phase grows with time, eventually sealing off the pores near the interface with the bath. The phase grows too slow to prevent full infiltration of the refractory but creates an equilibrium state in the sealed off part of the sample, ceasing the chemical corrosion in that part of the sample.

The chemical dissolution of lime particles in molten CaO–Al2O3–SiO2-based slags was observed by using a confocal scanning laser microscope (CSLM) in a temperature range from 1450 to 1600 °C. The dissolution behavior was found to be largely dependent on temperature and slag chemistry. A considerable increase in the dissolution rate was observed at elevated temperatures. The in situ observations revealed that the dissolution process in the slags containing MgO was controlled by chemical reactions at the interface. For slags without MgO, the dissolution could be divided into three stages when an interfacial reaction (IR) layer formed at the interface. The dissolution was limited by chemical reactions during the early stage, a mixed control of product layer and boundary layer diffusion during the intermediate stage, and boundary layer diffusion control in the final stage. The IR layer formed during dissolution at the interface between the lime particles, and the liquid slag free of MgO was clearly a kinetic b...

This work aimed to assess the possibility of stabilising argon oxygen decarburisation (AOD) stainless steel slag with CaO/SiO2 ~ 1.6, by using a secondary alumina by-product (~75 wt% Al₂O₃, referred herein as SA, found under the name ‘‘Valoxy®’’) and reduced levels of B₂O₃. Two groups of samples were synthesised: one reference group with AOD slag and 0.26, 0.16, 0.10 and 0.05 wt% of B₂O₃ and one with equivalent compositions but to which 5 wt% of SA is added. Experimentally, the slags were produced in a platinum crucible in a resistance furnace, heated with 5 °C/min until 1,640 °C, equilibrated for 1 h, followed by slow cooling to room temperature. The mineralogical composition was analysed by QXRD whereas the micro-hardness was measured through a Vickers indentation test. The microchemistry and morphology were analysed by EPMA–WDS. Analysis indicated that AOD was successfully stabilised by 5 wt% SA and 0.10 wt% B₂O₃, whereas for 0.05 wt% B₂O₃, volumetric expansion occurred over time. In terms of mineralogy, the use of SA promoted the formation of spinel instead of gehlenite. Electron microscopy revealed a more dense morphology in the samples with SA when compared to the reference ones. Elemental maps indicated that Cr predominantly participates in the spinel phase. Vickers tests showed a slight increase in hardness in the samples with SA. In conclusion, the addition of SA resulted in substantially different microstructures that appear to be promising in terms of chemical and mechanical stability. However, in terms of volumes the required addition levels for effective stabilisation are substantial compared to B2O3 additions. ispartof: Waste and Biomass Valorization vol:5 issue:3 pages:343-353 status: published

This work is focused on exploring various cold and hot stage treatment paths of stainless steel slag as a tool to improve its hydraulic properties. At a cold stage, mechanical and chemical activation was applied on industrial stainless steel slag; and it was found that both activation methods effectively improve the reactivity of the studied slag. In addition, the detailed investigation of hydration on two major phases, γ – C2S and merwinite, revealed that their hydration resulted in the formation of C – S – H gel, typically formed during the hydration of OPC. Regarding the hot stage treatment, the combination of the chemistry modification with the addition of fly ash at 30 wt. % and fast cooling by means of water quenching resulted in a complete amorphisation of the material. Ultimately, the produced material possessing similar properties to granulated blast furnace slag could be used as a latent hydraulic material in blended cements.

The dissolution of solid lime particles into liquid slags at high temperatures was evaluated by means of confocal scanning laser microscopy. An additional solid layer around the lime particle was observed at the intermediate stage of the dissolution into CaOAl2O3SiO2 slags. The dissolution rate was decelerated due to the existence of the additional layer and the dissolution profile could be clearly distinguished into three stages, that is, an early, intermediate, and late stage. By adding 10 wt % MgO, this layer could be effectively eliminated and the slope of the whole dissolution profile kept relatively constant. The dissolution path and mechanisms were subsequently evaluated by incorporating thermodynamic calculations. Both direct and indirect dissolutions could be distinguished. It was realized that the decrease in composition range for solid precipitating after adding MgO could significantly reduce the interfacial reaction (IR) layer formation. Post-mortem analyses on quenched samples were further carried out to confirm the theoretical calculations. It was found that the solid layer in slags without MgO was (CaO)2·SiO2 and (CaO)3·SiO2 which is in line with the thermodynamic calculations. However, only (CaO)2·SiO2 was noticed in slags with MgO which both (CaO)2·SiO2 and MgO phases should be present according to the calculations. The nonequilibrium during dissolution may play an important role on phase transformation and MgO particles in much smaller quantity may have dissolved into (CaO)2·SiO2 phase. The diffusion of CaO in both slags with and without MgO was additionally investigated. The local CaO concentration distributions from the direct dissolution phase to the slag bulk could be well fitted with the theoretical model proposed via Fick's second law. As a result, the local diffusion coefficient in the dissolution region was obtained and the effect of MgO addition on diffusion could be assessed. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2907–2916, 2013

article i nfo Slags from non-ferrous metallurgy are Fe rich, with Si as a minor constituent, and with low levels of Al. Due to variations in the slag cooling practice, they can exist as semi-amorphous or as crystalline solids. Considering that both higher Al in the slag and a higher cooling rate during solidification would have an impact on the availability of Al and ultimately on the formation of linkages in the inorganic polymer, we study the micro- structure and reactivity of a Fe and Al rich slag cooled in different ways. Results show that high cooling rates lead to a predominantly amorphous material. For lower cooling rates the content of amorphous phase varies from 52 wt.% to 12 wt.%. Spinel is the primary phase precipitating, whereas, for the lowest cooling rate investigated, pyroxenes form as well. Dissolution tests in a 10 M NaOH solution for 96 h reveal that approx. 54 wt.% of Al and 33 wt.% of Si of the total content become available for the highly amorphous slag. On the contrary, the dissolved Al and Si are below 5 wt.% when slag pot cooling is applied. The above strongly influence the resulting inorganic polymers with the ones originating from the amorphous slag being superior in mechanical properties.

The aim of this work was to investigate the hydraulic behaviour of a stainless steel converter slag after changing its chemical composition and cooling path. The target slag was designed to resemble ground granulated blast-furnace slag (GGBFS). A synthetic slag with a chemical composition close to stainless steel converter slags was mixed with 22, 30 and 38 wt% fly ash (FA) from lignite combustion, heated up to 1550°C and then granulated by quenching in water; the solidified new slags were named FA22, FA30 and FA38 respectively. Quantitative X-ray diffraction on FA22 revealed that the amorphous phase was approximately 40 wt%, the rest being bredigite and merwinite. For FA addition of 30 wt% or more, the amorphous phase reached almost 100 wt%. The resulting slags showed significant hydraulic activity when mixed with sodium-based activators, with C-S-H, hydrotalcite and hydrogarnet being the main hydration products formed. The calorimetric behaviour and the mechanical properties of blended cements with 30 wt% FA30 and FA38 were comparable to a blended cement with GGBFS. Assuming that FA addition will take place during the liquid state of the slag, the proposed process can result in a new hydraulic binder.