Iron-rich Slag Research Articles

Capabilities and limitations of Pb, Sr and Fe isotopic analysis of iron-rich slags: a case study on the medieval port at Hoeke (Belgium).

In this work, an analytical approach was developed for Pb, Sr, and Fe isotopic analysis of archaeological samples recovered from an iron work site by using multi-collector inductively coupled plasma - mass spectrometry (MC-ICP-MS). The sample types include slag, coal, clay and hammer scales, all obtained from an archaeological site at Hoeke (Belgium). Despite the wide concentration range of the target elements present in the samples and some sample manipulations necessarily performed outside of a clean laboratory facility, the analytical procedure yielded accurate and precise results for QA/QC standards while blank levels were negligible. Preliminary results concerning Pb, Sr and Fe isotope ratio variations in archaeological materials associated with iron working processes are provided. The samples revealed high variability in metal isotopic compositions, with the 208Pb/207Pb ratio ranging from 2.4261 to 2.4824, the 87Sr/86Sr ratio from 0.7100 to 0.7220, and δ 56Fe values from -0.34 to +0.08‰, which was tentatively attributed to the mixing of materials during the iron production process or variability within the source material. Also, contamination introduced by coal and furnace/hearth lining material could have contributed to the wide range of isotopic compositions observed. Because of the absence of information and data for primary ore samples to compare with, the provenance of the materials could not be established. The present study highlights the challenges in interpreting archaeological data, particularly in terms of the isotopic variability observed. It underscores the necessity of integrating analysis data with historical and archaeological knowledge. Further research, involving detailed analysis of these source materials combined with robust historical evidence, is essential to validate hypotheses concerning the origin of iron.

3D printing of an iron-rich slag based hybrid mortar. A durable, sustainable and cost-competitive product?

Automation through 3D printing can be a possible technological breakthrough in construction. However, the carbon footprint is not necessarily reduced as the print formulations consist of more ordinary Portland cement (OPC) compared to conventional high-performance mortar. In this study, a hybrid mortar with minor amount of OPC and mainly Fe-rich, low-Ca slag is used for printing several structures, followed by a profound study on the durability properties of the printed material. The hybrid mortar outperformed the benchmark with respect to its compressive strength (80.5 ± 4.3 MPa versus 52.4 ± 1.7 MPa) and drying shrinkage (0.8 mm/m versus 1.3 mm/m). The capillary pores present in the printed hybrid resulted in a lower freeze-thaw resistance. Leaching tests showed that the hybrid binder immobilized heavy metals. The hybrid mortar has a CO2 impact between 164 kg CO2/m3 and 548 kg CO2/m3, and costs range from 129 to 193 euro/m3. This study showed that the hybrid mortar can offer a suitable alternative to 3D-printable OPC-mortars.

Synergistic effects and mechanism of the ternary flux system Fe2O3-CaO-MgO on the coal ash slag fluidity

Basic oxides are usually widespread in low-rank coals and cause many ash-related problems in gasification applications. In this paper, the synergistic effects of the ternary flux system of Fe2O3-CaO-MgO in lowering the ash fusion temperature and improving the viscosity-temperature characteristics were verified by testing the properties of samples with different Fe2O3/(CaO + MgO) ratios. The flow temperatures and temperatures of the critical viscosity decreased and then increased with the decrease of Fe2O3/(CaO + MgO) ratio and reached the lowest point when the iron oxide and alkaline earth metal oxide (CaO, MgO) contents were close to each other. From the perspective of mineral transformation, the formation of low melting point ferroan spinel and the eutectic between anorthite and ferroan spinel are the main mechanisms of synergism. No severe crystallization was observed in the iron-rich slags because Fe2+ could reduce the crystallization tendency. As CaO and MgO dominated the basic oxides, a CaO/MgO ratio of 4:6 effectively limited the crystallization and lower the temperature of critical viscosity (TCV). Thus, when regulating the coal ash fluidity, the content of iron oxide and the ratio between CaO and MgO should be consciously balanced to meet the requirements of the gasifier for slag removal.

From dangerous wastes to green construction materials, as thermally stable-radiation blocker, in presence of meso-porous magnesia and alumina

The nominal objective behind this study is to recycle iron-rich slag (GGBFS) and lead-rich glass waste (LRGW) as industrial solid wastes in the presence of meso-porous magnesia or alumina to produce sustainable, eco-friendly, and high-performance binding materials. Four NaOH-activated composites (AACs) pastes have been prepared: Pure alkali-activated slag (AAS), AAS-20%LRGW, AAS-20%LRGW-3% meso-porous MgO, and AAS-20%LRGW-3% meso-porous Al2O3. After the hardening process, the compressive strength was measured at 1, 7 and 28-days of normal curing (high humidity at 25 °C). Thermal stability test for all AACs, after 28-days, was conducted at 250, 500 and 750 °C. Two different radio-active isotopes (Cs-137 and Co-60) were used, as gamma radiation sources, to investigate the attenuation performance of all prepared AACs. The results confirmed that, among the four composites, AAS-20%LRGW-3% meso-porous MgO composite pastes possessed the highest compressive strength (29.3 MPa), highest thermal stability (25 MPa, 18.2 MPa and 10 MPa at 250 °C, 500 °C and 750 °C, respectively). Moreover, this composite has the highest gamma radiation shielding performance, whatever the intensity of the gamma-ray or firing temperature. At cesium isotope, it was found that the μ values were 0.199 ± 0.003, 0.197 ± 0.003, 0.194 ± 0.005 and 0.188 ± 0.005 cm−1 at 25, 250, 500 and 750 °C, respectively. This efficiency is attributed to the role of meso-porous MgO; it has a high surface area (8891 cm2/g), high adsorption capacity (2.042 cm3/g), and low average pore diameter (37.17 nm); these textural characteristics helped much in the generation of additional hydrates/binding phases such as calcium-silicate-hydrates (CSHs), calcium-aluminate-hydrates (CAHs), calcium-alumino-silicate hydrates (CASHs as gehlenite or hydrogarnet), hydrotalcite, magnesium silicate hydrates (MSHs) as well as sodium-alumino-silicate-hydrates (NASHs) and lead silicates (Pb3SiO5). All these phases were detected via XRD, TGA/DTG as well as SEM/EDX techniques. Moreover, the inclusion of meso-porous MgO enhanced the immobilization of hazardous lead according to the obtained data from the toxicity characteristics leaching procedure (TCLP). Hence, we recommend using AAS-20%LRGW-3%MgO composite as gamma-radiation blocker in medical fields and concrete landfills containing dangerous radioactive wastes.

Iron-rich slag addition in ternary binders of Portland cement, aluminate cement and calcium sulfate

The growing demand for sustainability in the recent decades has driven the exploration for new supplementary cementitious materials (SCM) such as the non-ferrous metallurgy (NFM) slags. In this study, the hydration of an iron-rich NFM slag incorporated in CAC-PC‑calcium sulfate ternary binders was investigated. The dimensional stability of mortars demonstrated the contribution of the slag addition in mitigating excessive expansion while maintaining an acceptable mechanical strength over 180 days. The degree of slag hydration estimated with X-ray Computed Tomography (XCT) support the activating effect of the PC, while isothermal calorimetry, XRD, TGA and ATR-FTIR were used to delineate the evolution of the phase assemblage. Finally, TEM-EDS revealed the incorporation of Fe in hydrate gels grouped into two clusters according to a Ca-Al-Si ternary diagram: (1) Al-rich gels in the formulation with no PC; and (2) intermixed hydrate gels associated with Ca, Al and Si in the formulations with PC.

Hydration of blended cement with high volume iron-rich slag from non-ferrous metallurgy

The hydration of blended cements with up to 70 wt% iron-rich slag was investigated. Isothermal calorimetry revealed a retarding effect of the slag on Portland cement hydration during the first day, while from 2 days onwards the reaction extent of C3S, C3A and C4AF increased. The slag reacted to 20–30% after 150 days resulting in AFm phases, as well as a new phase with a layered double hydroxide structure with (Mg + Fe)/Al around 3. Fe was also detected in the C-S-H phase of the blended cements, whereas no clear increase of Fe(III)-containing hydrates was observed. The Ca/Si atomic ratio of C-(A)-S-H in the blended cements decreased with increasing slag content, while the Al/Ca ratio increased only slightly. This study elucidated the fate of iron in cements blended with iron-rich slags and showed the suitability of the latter as SCM with a reactivity similar to the one of siliceous fly ash.

Alkali-activated geopolymers based on iron-rich slag from copper industry

In the present study geopolymers were prepared using fayalite slag (iron-silicate fines) from copper producing plant (Aurubis Bulgaria AD). The influence of the different concentrations of alkali activator on properties and structure was examined. The prepared geopolymers were characterized by maximal compressive strength of about 27 MPa. The microstructural examination revealed that only small amount of the precursor reacted, but certain amount of ferric iron (Fe3+) participate in the structure of newly formed geopolymer gel.

Understanding dissolution characteristics of steel slag for resource recovery

Steel slags are generally alkaline with a high calcium content and are viewed as a potential feedstock for carbon dioxide sequestration and utilization, mostly through aqueous mineral carbonation routes. For recovery of multiple metals such as Ca, Fe, Mg, and Si, and generation of value-added products by dissolution and precipitation reactions in aqueous media, enhancing the metal selectivity and extraction efficiency are important. However, there is limited understanding of independent parameters that influence these important characteristics. In this work, a systematic attempt was made to correlate these key dissolution characteristics of basic oxygen furnace slag in acidic media with its mineralogical and physical characteristics, the changes in aqueous chemistry, and the role of potential secondary precipitates. The findings from this study substantiate that steel slag is a potential feedstock because of the calcium being mainly present as orthosilicates, which were found to leach congruently without forming a leached layer that might hinder calcium extraction. The leaching of Fe(II) from the slag is the main source of impurity and its slow oxidation-precipitation leads to a pH plateau at the end of the dissolution step. Oxidation-precipitation of Fe(II) is controlled by hydroxyl concentration in the aqueous solution, which necessitates a pH-swing step by addition of a base after dissolution. Use of surface complexing agents, such as sodium molybdate, can significantly reduce iron impurity in the leachate and obtain an iron-rich slag residue for recycle to iron and steel industry.

METALLURGICAL WASTE VALORIZATION FOR FABRICATING GLASS-CERAMICS MATERIALS

The valorization of a metallurgical waste (i.e., an iron-rich slag) as raw material for the fabrication of high hardness glass-ceramics using differential thermal analysis, X-ray diffraction, X-ray fluorescence and scanning electron microscopy was investigated. The melting of the slag was aided by the addition of waste glass cullet (WGC) and the vitrification field of this system was investigated. The non-isothermal crystallization kinetics of the parent glass with the highest slag content was studied by DTA and crystallization of the parent glasses led to of pyroxenic crystalline phases, suggesting the application of the obtained glass-ceramics as building materials. Environmental benefits such as the reduction in the consumption of virgin raw materials and the elimination or reduction of CO2 and SO2 emissions due to absence of carbonates and sulphates in the batch composition make it an interesting alternative for the application of this technology.

Unraveling the nano-structure of a glassy CaO-FeO-SiO2 slag by molecular dynamics simulations

Non-ferrous metallurgy slags are gaining significant interest as a resource in the production of alternative low-energy cementitious materials. Their atomistic structures, however, are still not fully understood due to their glassy nature. In the work presented herein, a comprehensive description of the nano-structure of a CaO-FeO-SiO2 slag was obtained by using molecular dynamic simulations in conjunction with previously obtained experimental data from X-ray and neutron pair distribution function studies. Iron was predominately 4- and 5-fold coordinated with oxygen, forming polyhedra in tetrahedral and pyramidal/triangular bipyramidal configuration. The [FeOx] polyhedra were corner-shared to the silica tetrahedra, while the higher coordinated fractions (x = 5 or 6) seemed to prefer to be next to each other, sharing edges. Ca was mostly surrounded by 6 or 7 oxygens in polyhedra that are predominantly edge-sharing with other units. The obtained results fit the experimental data well and as such provide an accurate and realistic picture of the iron-rich slag structure.

Understanding the leaching behavior of inorganic polymers made of iron rich slags

Abstract This study investigates the leaching of main and trace elements from inorganic polymers made with an iron rich, fumed, > 90% amorphous slag. Different inorganic polymer binders were synthesized, varying the amount of the activating solution and the silica over sodium oxide ratio from 1.6, to 1.8, to 2.0, with constant water content of ±63%. Cascade and column leaching tests were performed in combination with geochemical speciation modeling (Visual MINTEQ) with the aim to understand the speciation of the elements in the inorganic polymer and their leaching behaviour as a function of pH. This would allow to identify the elements which would be the major issue with respect to leaching when the slag will be used in a construction material. The formed inorganic polymer was able to immobilize cationic elements such as barium, copper, magnesium, manganese, and zinc, in the pH range 7–12.5 due to adsorption. Elements such as antimony, arsenic, phosphorus, molybdenum, and vanadium were easily leached out in column and cascade leaching tests, because they most likely occurred as anions in the pore solution. Lead, chromium, and titanium were immobilized in the binder or in crystalline phases in the pH range 3.5–12.5. The study shows that there are multiple factors that affect leaching, the most important of which is shown to be the nature (cationic or anionic) of the elements and the morphology of the matrix. Anions that are present as trace elements (

Physicochemical Properties of the Molten Iron-Rich Slags Related to the Copper Recovery

The properties of a molten slag play an important role in the separation of the slag from the matte during copper smelting. In this study, the viscosity, electrical conductivity, density, and surface tension of molten FeOt-SiO2-CaO-based slags were measured, and the effects of the common constituents, such as CaO, Fe3O4, and Cu2O, on various properties were investigated. The primary phases in the molten slags which are suitable for the copper recovery process were obtained, and they mainly correspond to fayalite and tridymite. The comparison of the static settling properties of molten industrial copper slag before and after modification is also discussed.

Functional glass-ceramic foams from ‘inorganic gel casting’ and sintering of glass/slag mixtures

Abstract The here described investigation was essentially aimed at exploring the chemical stabilization and reutilization of iron-rich slag from copper metallurgy, by the manufacturing of glass-ceramic foams. The foams were developed according to a new method, recently reported for pure recycled soda-lime glass. Mixtures of soda-lime glass/slag powders (with slag content ranging from 10 to 30 wt%), suspended in alkaline aqueous solution, underwent progressive low temperature (80 °C) hardening, owing to the formation of hydrated calcium silicate compounds (C S H). Before complete setting, an extensive foaming could be achieved by vigorous mechanical stirring, with the help of a surfactant. After foaming, glass/slag mixtures could be sintered at 800–1000 °C; the mutual interaction caused an extensive crystallization, with precipitation of Ca Fe silicates and iron oxides (hematite and magnetite), promoting the mechanical properties (up to 4.4 MPa, with a porosity of about 80%). Leaching test confirmed the stabilization of pollutants, from the slag, in the final ceramics. Owing to the separation of iron oxides, particularly magnetite, the newly obtained foams exhibited a ferrimagnetic behavior, that could be exploited in electromagnetic shielding applications.

Rapid Separation of Copper Phase and Iron-Rich Phase From Copper Slag at Low Temperature in a Super-Gravity Field

A novel approach for quickly separating a metal copper phase and iron-rich phase from copper slag at low temperature is proposed based on a super-gravity method. The morphology and mineral evolution of the copper slag with increasing temperature were studied using in situ high-temperature confocal laser scanning microscopy and ex situ scanning electron microscopy and X-ray diffraction methods. Fe3O4 particles dispersed among the copper slag were transformed into FeO by adding an appropriate amount of carbon as a reducing agent, forming the slag melt with SiO2 at low temperature and assisting separation of the copper phase from the slag. Consequently, in a super-gravity field, the metallic copper and copper matte were concentrated as the copper phase along the super-gravity direction, whereas the iron-rich slag migrated in the opposite direction and was quickly separated from the copper phase. Increasing the gravity coefficient (G) significantly enhanced the separation efficiency. After super-gravity separation at G = 1000 and 1473 K (1200 °C) for 3 minutes, the mass fraction of Cu in the separated copper phase reached 86.11 wt pct, while that in the separated iron-rich phase was reduced to 0.105 wt pct. The recovery ratio of Cu in the copper phase was as high as up to 97.47 pct.

Fast Assessment of Total Iron Contents in Steelmaking Slags by Means of Water Displacement Test for Recycling of the Iron in the Ironmaking and Steelmaking Process

Steelmaking slags are usually processed to recover iron for recycling in the ironmaking and steelmaking process which replaces high-cost purchased steel scrap and iron ores. It is crucial to quickly determine the total iron content in an iron-bearing slag product for prompt and accurate quality control of the slag product. The water displacement test has been widely adopted in the slag processing industry as an industrial method to quickly assess the total iron contents in iron-rich slag products. However, this industrial method is often misused, and serious disparities exist between total iron contents evaluated using water displacement densities and by chemical analysis. Such disparities have resulted in the generation of great amounts of non-recyclable “iron-rich” steelmaking slag products with actual low levels of iron. In this research, we aimed to resolve this disparity. A total of 40 steelmaking slag samples were tested for water displacement densities and were chemically analyzed for total iron contents. The total iron contents in the slag samples were also evaluated using the measured water displacement densities with assumed parameters from two references. The research results suggest that the current industrial method for evaluating the total iron contents in the steelmaking slag products via the water displacement test cannot deliver precise but rather approximate results. Using assumed parameters from one reference to evaluate the total iron contents in the tested slag samples, the maximum error is about 12% and the average error is about 5%. While using assumed parameters from the other reference to evaluate the total iron contents in the tested samples, the maximum error is about 19% and the average error is about 10%. In order to decrease the evaluation error, a formula relating the total iron contents in the steelmaking slag samples via chemical analysis to the water displacement densities of the samples was developed by data fitting. Compared to the current industrial method of assessing the total iron contents in steelmaking slags via water displacement densities with assumed parameters from the references, the best fit formula gives the least error. Therefore, in order to quickly evaluate the total iron contents in a steelmaking slag product, a correlation formula between the total iron contents measured via chemical analysis and the water displacement densities should be developed in the first place. The formula then can be used to quickly determine the total iron content in the slag product with measured water displacement densities of the product for quality control when the product is being produced. Procedures were proposed in this paper for correctly measuring water displacement densities of slag samples and for correctly preparing the slag samples for chemical analysis.

Application of Electromagnetic Field Theory in the Study of Iron-Rich Slag Resistance Mechanism of Low Carbon MgO-C Refractories

Electromagnetic field (EMF) can promote the reaction between the Fe/Mn ion in slag and MgO-C refractories to form Mn-doped MgFe2O4 spinel. In order to further study the morphology and characteristics of Mn-doped MgFe2O4 spinel, the experiments were respectively carried out in medium-frequency induction furnace and resistance furnace. MgO-C refractories containing 6 wt.% carbon and iron-rich slag containing 53.62 wt.% Fe2O3 were used. The results show that the penetration layer in the slag line under EMF is obvious and the reduced Fe from FexO is distributed homogeneously in this layer. However in the resistance furnace having no EMF, there is not MgFe2O4 spinel but MgAl2O4 spinel formed. The iron content in Mn-doped MgFe2O4 spinels decrease dramatically from the erosion layer to penetration layer, while the manganese content in the spinel remains unchangeable.

Thermodynamic evaluation and properties of refractory materials for steel ladle purging plugs in the system Al2O3-MgO-CaO

The influence of iron oxide in the phase relationships of Al2O3-MgO-CaO and Al2O3-MgO purging plug refractory material has been studied by the thermodynamic analysis tool FactSage. Results showed that the system without CaO to be advantageous on the onset temperature of liquid phase, and on the liquid content at defined chemical composition and temperature. Therefore, CaO negatively influences the iron-rich slag resistance of the purging plug material. Analysis of used purging plugs proved the thermodynamic results. They showed that spinel solid solution and calcium hexaluminate as stable phases were formed in the reaction with iron oxide slag.Corundum-spinel castables with and without calcium aluminate cement were investigated in the laboratory to compare the relevant technical properties. In the cement bonded castable, the curing and drying strength are increased by increasing the cement content. However high cement addition requires higher water demand, which results in higher open porosity and a lower hot modulus of rupture (HMoR). In the CaO-free, no-cement castable with hydratable alumina binder, the water demand is slightly higher when compared to the ultra-low cement castable. However, the curing and drying strength are still slightly higher for the no-cement castable. As there is no significant difference in HMoR with various hydratable alumina binder additions, low dosage of such binder in the range of two to four percent is normally recommended to avoid excessive water addition. Cement bonded castables (with CaO) show some advantages to the no-cement castable (non-CaO) regarding HMoR, however the no-cement castable could have advantages regarding the iron-rich slag resistance and thermal shock resistance.

Slagging and Fouling Characteristics of HRSG for Ferrosilicon Electric Furnaces

The slagging and fouling characteristics of the heat recovery steam generator (HRSG) for ferrosilicon electric furnaces are discussed in this paper. Three ash samples were taken from the HRSG of a ferrosilicon furnace in Ningxia Province, China, which suffered from serious slagging and fouling. X-ray fluorescence (XRF), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the ash samples. The results show that low melting point salt Na2SO4 and composite salts Na (AlSi3O8) and 3K2SO4·CaSO4 deposit on the superheater tube walls in aerosol form and solidify to form the initial slag layer. With the continuous deposition of the low melting point compounds, more and more ash particles in the flue gas adhere to the slag surface to form a thicker slag. Low melting point composite salt NaO·Al2O3·SiO2 is absorbed on the evaporator tube walls in aerosol form. With the deposition of NaO·Al2O3·SiO2, more and more ash particles are absorbed to form the fouling. Since there is less space between pin-finned tubes, the large iron-rich slag particles are easily deposited on tube walls and fin surfaces, which is advantageous to the fouling process. There are large quantities of superfine ash particles in the flue gas that easily adhere to other particles or tube walls, which facilitates the slagging and fouling process.

Magnetic Glass Ceramics by Sintering of Borosilicate Glass and Inorganic Waste.

Ceramics and glass ceramics based on industrial waste have been widely recognized as competitive products for building applications; however, there is a great potential for such materials with novel functionalities. In this paper, we discuss the development of magnetic sintered glass ceramics based on two iron-rich slags, coming from non-ferrous metallurgy and recycled borosilicate glass. The substantial viscous flow of the glass led to dense products for rapid treatments at relatively low temperatures (900–1000 °C), whereas glass/slag interactions resulted in the formation of magnetite crystals, providing ferrimagnetism. Such behavior could be exploited for applying the obtained glass ceramics as induction heating plates, according to preliminary tests (showing the rapid heating of selected samples, even above 200 °C). The chemical durability and safety of the obtained glass ceramics were assessed by both leaching tests and cytotoxicity tests.

‘Slag_Fun’ – A New Tool for Archaeometallurgy: Development of an Analytical (P)ED-XRF Method for Iron-Rich Materials

This paper describes the development of a new analytical tool for bulk chemical analysis of iron-rich archaeometallurgical remains by Polarising Energy Dispersive X-ray Fluorescence ((P)ED-XRF). Prompted by the ongoing archaeological and archaeometric analyses of early first millennium BC iron smelting and smithing finds from Tell Hammeh (az-Zarqa), Jordan, the creation of this tool has already benefited several studies on iron-rich slag, of widely varying provenance as well as age (Anguilano 2002; Chirikure 2002; Ige and Rehren 2003; Stanway 2003). Following an explanation of the archaeological background and importance of the Hammeh finds, the paper describes the technical foundations of XRF analysis and the design, development and application of the slag_fun calibration method.