Slag Foaming Research Articles

Effect of Temperature on CH4/CO Carburization Process of Hydrogen‐Based Direct Reduced Iron Pellets

Cementite (Fe3C) has a high combined‐carbon content, which not only increases the carbon content but also provides a heat source and shortens the smelting time. Besides, the CO generated by carbon oxidation can stir the molten pool. It is beneficial to the formation of foaming slag and the removal of inclusions. To study the formation behavior of cementite and surface‐deposited carbon during the carburizing process of hydrogen‐reduction pellets under different conditions, the effects of temperature and carburizing gas composition on the carburizing rate of hydrogen‐reduction pellets are studied. The results show that the carburization rate of CH4 gas is proportional to the carburization temperature. The carburization rate of CO gas is inversely proportional to the temperature, and almost no carburization occurs at 900 °C. The contents of cementite and deposited carbon in different weight gain samples are compared by X‐ray diffraction (XRD) refinement and high‐pressure air gun injection. The analysis revealed that CH4 gas is easier to form deposited carbon in the later stage of carburizing at 900 °C. It provides a theoretical basis for the control of the carburization behavior of hydrogen‐based pellets.

Evaluation of Biochar and Coke Blends for Slag Foaming Applications in Electric Arc Furnace Steelmaking

Evaluation of Biochar and Coke Blends for Slag Foaming Applications in Electric Arc Furnace Steelmaking

Attenuation of sound signals in foams for the basic oxygen furnace using physical modelling techniques

The control of slag foaming is important for optimising basic oxygen furnace (BOF) performance. Acoustics systems monitoring wide frequency bandwidths have been applied to BOF monitoring for the purpose of understanding slag foam height and density but there is limited information about their accuracy and repeatability. Improved understanding of the fundamental behaviour of sound in slag foam could help resolve these issues. In this cold physical model study using, aqueous foams generated in a cylindrical vessel were used to study the attenuation of sound in large samples of foam. Sound pulses over the range of 201 to 1801 Hz were transmitted through varying aqueous foam heights of 100 to 250 mm and acoustic signals detected via a measurement microphone were analysed. The results indicated aqueous foams consisting of smaller bubbles in the range of 0.4 to 0.75 mm with visibly thicker outer films displayed a stronger correlation between the attenuated sound and the stationary foam heights. It was also observed that frequencies above 1009 Hz were more sensitive in terms of their attenuation in varying foam heights and the time-dependant drainage of bubbles compared to lower frequencies. These frequencies were generally higher than those used for industrial slag foam monitoring systems.

Influence of Carbon Material Properties on Slag‐Foaming Dynamics in Electric Arc Furnaces: A Review

In this article, the impact of conventional carbon sources, alongside potential carbon bio‐sources, on slag‐foaming behavior is investigated. It highlights the complex relationship between these carbon sources and their properties, such as fixed carbon (FC), volatile matters (VMs), mineral composition in ash, reactivity, and wetting, which ultimately influence the slag foaming efficiency. The challenges associated with biochar and the significant differences in foaming behavior are addressed. For biochar to achieve effective slag foaming, it is essential that it contains an FC of at least 60 wt% and ash of less than 5 wt%. Though less impactful than CO generation from iron (II) oxide reduction, VMs from carbon sources, especially with high‐VM biochar, show secondary effects on reaction courses. The disadvantages associated with the high reactivity of biochar can be overcome by improving its physicomechanical and physicochemical properties. Despite the potential of biochar–coke mixtures to benefit slag foaming without enhancing biochar properties directly, challenges such as biochar floatation on the liquid slag surface and rapid burn‐off exist. Biocoke offers foaming results comparable to those of conventional sources. Despite the benefits of biocoke over other carbon sources, the review underscores its relatively unexplored status in the context of slag‐foaming applications.

Sustainable use of waste glass sand and waste glass powder in alkali-activated slag foam concretes: Physico-mechanical, thermal insulation and durability characteristics

In many countries, the safe removal of the massive volume of waste glass has emerged as a major environmental priority. However, the manufacture of concrete pollutes the environment with greenhouse gasses and consumes vast amounts of natural resources. As a result, the construction industry has recently been paying more and more attention to reusing glass waste to produce environmentally friendly building materials. This work aims to manufacture environmentally friendly alkali-activated foam concrete (AAFC) by examining the combined effects of waste glass powder (GP) and waste glass sand (GS) as partial substitutes for granulated blast-furnace slag (GBFS) and river sand (RS) respectively. The present study involved the experimentation of AAFC mixtures with GP contents of 0 and 10 % as a replacement for GBFS and GS contents of 0, 25, 50 and 100 % as a replacement for RS. Eight AAFC mixtures with fixed alkaline solution-to-binder (A/B) ratio of 0.5 were fabricated and cured at 80 °C for 24 h. The effects of different GS and GP contents on the oven dry density, flowability, water absorption, porosity, sorptivity, thermal conductivity, compressive strength, flexural strength, high temperature resistance and hydrochloric acid (HCI) resistance of AAFC mixtures were evaluated. Microstructure of the mixtures was analyzed by SEM and EDS. The findings indicated that the AAFC mixture with 50 % GS exhibited the best mechanical properties with a compressive strength of 3.48 MPa, representing a 71.4 % increase over the reference mixture. The mixture with 50 %GS also exhibited the lowest sorptivity regardless of GP content. Thermal conductivity enhanced by 4.6 and 7.0 % by replacing RS with 50 % GS at 0 and 10 % GP content. Replacing RS with GS and GBFS with GP increased the high temperature and acid resistance of the AAFC mixtures and the best high temperature and acid resistance were obtained for the mixtures containing 100 %GS and 10 %GP.

Biochar as a slag foaming agent in EAF – A novel experimental setup

Slag foaming practice is employed widely in electric arc furnace steelmaking to improve the energy efficiency, protect the furnace structures and reduce noise pollution. Slag foaming is typically launched by injecting fossil-based carbonaceous material (e.g. coke dust) into the melt. In this study, a novel laboratory-scale experimental setup was used for studying the substitution of fossil carbon by biochar as slag foaming agent. The setup was equipped with an injection device for feeding carbon and a camera system for observing the foaming phenomenon and recording the process. A set of experiments was conducted for studying the foaming in slag-carbon systems using two carbonaceous materials: 1) coke dust was used as a reference material and 2) a high-quality biochar was used as a possible replacement. In the experiments, sufficient foaming was achieved with both of the carbonaceous materials. The biochar produced almost equal foaming behavior as coke dust. The results indicate that biochar could be used to substitute carbon for slag foaming in the EAF.

Laboratory Scale Evaluation of the Slag Foaming Behavior

Due to the ambitious climate targets of the European Union, one can expect that the electric arc furnace (EAF) will gain greater importance in the future of steelmaking. Since slag foaming is a decisive factor in an efficient process, understanding this phenomenon is essential when applying hydrogen-based direct reduced iron (DRI). Therefore, a method was developed to check different slag compositions concerning their foaming behavior. Slag samples are melted, and a carbon carrier is added. After a selected reaction time, the crucible is quenched in liquid nitrogen, superficially freezing the state while foaming. Afterward, it is halved, providing metallographic examination and height measurement possibilities. Three slags were tested, MgO-saturated EAF slag, MgO-unsaturated EAF slag, and electrical Smelter-like slag. Digital and scanning electron microscopy with energy dispersive x-ray spectroscopy are used to compare the slags and evaluate the method. The Smelter slag shows no foamability, unaffected by the FeO content. Contrary, good foamability can be observed for EAF slags.

Preface to the Proceedings of the 5th European Academic Symposium on EAF Steelmaking

The European Academic Symposium on EAF Steelmaking (EASES) is a series of events targeted at researchers and doctoral candidates working with different aspects of electric arc furnace (EAF) steelmaking. Previously, four events were organised in 2015, 2016, 2018, and 2021 in Aachen, Germany. The 5th European Academic Symposium on EAF Steelmaking (EASES 2023) was organised jointly by the RWTH Aachen University (Department for Industrial Furnaces and Heat Engineering) and University of Oulu (Process Metallurgy Research Unit) and held at the University of Oulu in Oulu, Finland on 5-7 June 2023. A total of 29 presentations were held at the event, out of which 13 featured an accompanying full paper. After the symposium, the authors of the full papers were invited to submit their manuscripts to be included in the proceedings. The proceedings consist of a total of 12 peer-reviewed papers published in the IOP Conference Series: Materials Science and Engineering. Based on the presentations, the development of modelling and monitoring tools for process optimization, the use of biochar to replace fossil carbon for slag foaming, and the use of hydrogen as an alternative burner fuel were identified as current hot topics. In the future, the importance of the EAF process is expected to increase further due to the increasing availability of scrap and plans for ore-based production routes based on hydrogen direct reduction.

Biocoke Thermochemical Properties for Foamy Slag Formations in Electric Arc Furnace Steelmaking

This paper is devoted to studying the thermochemical properties of carbon sources (laboratory-scale conventional coke, biocoke with 5 wt.%, and 10 wt.% wood pellet additions) and the influence of these properties on foamy slag formations at 1600 °C. Thermogravimetric analysis (TGA) conducted under air unveiled differences in mass loss among carbon sources, showing an increasing order of coke < biocoke with 5 wt.% wood pellets < biocoke with 10 wt.% wood pellets. The Coats–Redfern method was used to calculate and reveal distinct activation energies among these carbon sources. Slag foaming tests performed using biocoke samples resulted in stable foam formation, indicating the potential for biocoke as a carbon source to replace those conventionally used for this process. Slag foaming characters for biocoke with 5 wt.% wood pellets were improved more than coke. Using biocoke with 10 wt.% wood pellets was marginally worse than coke. On the one hand, for biocoke with 5 wt.% wood pellets, due to increased reactivity, the foaming time was reduced, but it was sufficient and optimal for slag foaming. Conversely, biocoke with 10 wt.% wood pellets reduced foaming time, proving insufficient and limiting the continuity of the foaming. This study highlights that thermochemical properties play a significant role, but comprehensive assessment should consider multiple parameters when evaluating the suitability of unconventional carbon sources for slag foaming applications.

Investigation of the Impact of Biochar Application on Foaming Slags with Varied Compositions in Electric Arc Furnace-Based Steel Production

This paper investigates the influence of biochar, either as an individual component or in combination with high-temperature coke, on the slag foaming behavior. High-temperature coke serves as a reference. Three scenarios were considered to study the slag foaming behavior, each characterized by different slag chemical compositions. The results indicate that biochar can promote steady foaming for specific slags when the basicity (CaO/SiO2) falls within a range of 1.2 to 3.4. Experimental findings also reveal that stable foaming can be achieved when a mixture containing biochar and coke with a ratio of 1:1 is employed, with a minimum slag basicity of 1.0 and FeO content of 25 wt.%. The foaming range obtained using different FeO contents (15 wt.% to 40 wt.%) in the mixture surpasses the range observed with the individual application of coke or biochar. The X-ray diffraction (XRD) analysis showed that unrelated to the carbon source applied, the general pattern was that the phases larnite (Ca2SiO4) or dicalcium silicate were detected for slag foams with high basicity. Monticellite (CaMgSiO4) and magnesium iron oxide (Fe2MgO4) were predominant in slag foam samples, with the highest MgO content. The presence of monticellite and merwinite (Ca3MgSi2O8) occurred in samples with the lowest basicity. Eventually, the application of the mixture of coke and biochar showed the potential to obtain stable foaming across a wide range of slag compositions.

Investigation on preparation and compressive strength model of steel slag foam concrete

Investigation on preparation and compressive strength model of steel slag foam concrete

Preparation of Steel Slag Foam Concrete and Fractal Model for Their Thermal Conductivity

The innovation of structural forms and the increase in the energy-saving requirements of buildings have led to higher requirements regarding the application conditions of steel slag foam concrete (SSFC) to ensure that the SSFC has a lower thermal conductivity and sufficient compressive strength, which has become the primary research object. Through a comprehensive consideration of 7 d compressive strength and thermal conductivity, the recommend mix ratio of SSFC was as follows: maximum SS size = 1.18 mm, water–cement ratio = 0.45, replacement rate of SS = 20–30%. Moreover, a theoretical formula was derived to determine thermal conductivity versus porosity based on fractal theory. The measured values of the foam concrete found elsewhere corroborate the fractal relationship regarding thermal conductivity versus porosity. This fractal relationship offers a straightforward and scientifically sound way to forecast the thermal conductivity of SSFC.

Compressive strength, pore structure, and hydration products of slag foam concrete under sulfate and chloride environment

In this study, blast furnace slag (BFS) was used instead of partial complex Portland cement (PC) to produce slag foam concrete (SFC), aiming to improve the ion attack resistance and compressive strength of nature foam concrete (NFC). The behavior of compressive strength, pore structure, hydration products, and microstructure of SFC in salt environments (5% Na2SO4, 5% NaCl, 5% Na2SO4+5% NaCl) was investigated. The findings indicate that the negative effect on the compressive strength of sulfate is mitigated by chlorine. In NFC, the loss of compressive strength in the Na2SO4, Na2SO4+NaCl, and NaCl solution at 120 days is 18.06%, 12.28%, and 3.58%, respectively. The optimization of SFC by the addition of BFS first increases with the amount of replaced cement until the positive effect of BFS is overshadowed by its negative effect when the amount replaced reaches 50%. And the salt erosion resistance of SFC with 30% of cement replacement is the best of all mixtures with KSO42- and KSO42-+Cl- of 0.89 and 0.94 respectively. In the beginning, the SO42- and Cl- promote the production of more ettringite (AFt) in the SFC, which results in the filling of the original cracks and a reduction in pore volume. The opposite situation gradually occurs in SFC owing to the expansion of the AFt, as salt curing continues. The content of hydration products varies according to the amount of BFS added, and a decrease in Ca(OH)2 and an increase in the gel are observed in SFC with 30% −50% of cement replacement compared to NFC.

Evaluation of Slag Foaming Behavior Using Renewable Carbon Sources in Electric Arc Furnace-Based Steel Production

The influence of different carbon sources, including anthracite, calcined petroleum coke, three samples of high-temperature coke, biochar, and a mixture of 50 wt.% biochar and 50 wt.% coke, on slag foaming behavior was studied. The slag’s composition was set to FeO-CaO-Al2O3-MgO-SiO2, and the temperature for slag foaming was 1600 °C. The effect of the carbon sources was evaluated using foaming characteristics (foam height, foam volume, relative foaming height, and gas fraction), X-ray diffraction (XRD), chemical analysis of the slag foams, Mossbauer spectroscopy, observation by scanning electron microscope (SEM), and energy-dispersive spectroscopy (EDS) mapping. Different foaming phenomena were found among conventional sources, biochar as a single source, and the mixture of coke and biochar. Biochar showed the most inferior foaming characteristics compared to the other studied carbon sources. Nevertheless, the slag foaming process was improved and showed slag foaming characteristics similar to results obtained using conventional carbon sources when the mixture of 50 wt.% coke and 50 wt.% biochar was used. The XRD analysis revealed a difference between the top and bottom of the slag foams. In almost all cases, a maghemite crystalline phase was detected at the top of the slag foams, indicating oxidation; metallic iron was found at the bottom. Furthermore, a difference in the slag foam (mixture of coke and biochar) was found in the presence of such crystalline phases as magnesium iron oxide (Fe2MgO4) and magnetite (Mg0.4Fe2.96O4). Notwithstanding the carbon source applied, a layer between the foam slag and the crucible wall was found in many samples. Based on the SEM/EDS and XRD results, it was assumed this layer consists of gehlenite (Ca2(Al(AlSi)O7) and two spinels: magnesium aluminate (MgAl2O4) and magnesium iron oxide (Fe2MgO4).

Ranking of Injection Biochar for Slag Foaming Applications in Steelmaking

The electric arc furnace (EAF) has the potential to significantly contribute to the decarbonization of the iron and steel industry. However, during EAF steelmaking, carbon still needs to be injected into the molten slag to initiate slag foaming, which is beneficial to the energy efficiency and protection of the furnace. To move away from fossil carbon, biocarbon has gained attention as an injection carbon agent. In this study, two biochar candidates were added to the molten slag layer of an induction furnace for steel melting, to simulate EAF steelmaking conditions. The resultant slag foaming height was measured, and a ranking in comparison to two fossil carbon candidates was developed. The results indicate that the injection biochar sample, in the form of a bio-briquette, has a considerable degree of slag foaming capacity. More work is ongoing to develop a standardized testing methodology of ranking various injection biochar candidates for their suitability and qualification for use on a larger scale.

The effect of the addition of alumina on the viscosity, surface tension, and foaming efficiency of 2.5(CaO/SiO2)-xAl2O3-yFeO-MgO melts

Viscosity and surface tension strongly influence the efficiency of slag foam in metallurgical processes. An excellent foaming slag preserves heat and lowers the cost of smelting in an electric furnace. In this study, we investigated the viscosity, surface tension, and foaming efficiency of a 2.5CaO/SiO2-xAl2O3-yFeO-MgO slag. We also investigated the different valence oxygen ions by X-ray photoelectron spectroscopy (XPS). The results showed that with a gradual increase in the content of Al2O3, the viscosity initially increased and then decreased, and the changes in surface tension followed a similar pattern. The change in viscosity was caused by the increase in the degree of polymerization of the slag, which was determined by the competitive relationship between polymerization and the reduction in the stability of the overall network structure. Adding a small amount of Al2O3 to the slag slightly increased the number of Al–O–Al structures, whereas adding a large amount of the Al2O3 led to the formation of low-strength Al–O–Si structures, which reduced the stability of the network structure, thus reducing the viscosity. Because the surface tension is related to the concentration of non-bridging oxygens (NBOs), when the NBO content increased, the instability of the surface structure caused an increase in energy, thus increasing the surface tension. In addition, the CaO–SiO2–5MgO-xAl2O3-yFeO five-element oxide in this study had the lowest surface tension at the same NBO concentration, which positively contributed to slag foaming. Finally, When the Al2O3 content in the system increased from 5.1 to 15.7 wt%, the foaming efficiency increased from 24.2 to 69.2 (minute‧centimeters), an increase of 286%.

Utilization of Renewable Carbon in Electric Arc Furnace-Based Steel Production: Comparative Evaluation of Properties of Conventional and Non-Conventional Carbon-Bearing Sources

Conventional (anthracite, calcined petroleum coke, and coke) and non-conventional (biochar, and biocokes (3 wt.% torrefied wood, and 3 wt.% petroleum coke + 3 wt.% charcoal)) carbon-bearing sources have been studied for their use in electric arc furnace (EAF)-based steel production. Commonly, for the use of carbon sources in EAFs, one of the important properties is the content of fixed carbon, the release of volatiles as well as the elemental composition of inorganics. The properties of six carbon sources were analyzed by determining the proximate analysis, X-ray fluorescence analysis (XRF), coke reactivity index (CRI), and strength after reaction with CO2 (CSR), Brunauer–Emmett–Teller (BET) specific surface area and Barrett–Joyner–Halenda (BJH) pore size and volume analysis, ash chemical analysis, optical and scanning microscopy, Raman spectroscopy and X-ray diffraction (XRD) analysis. The results indicate biocoke as a promising option to replace conventional carbon-bearing sources. In the sample set, the fixed carbon, volatiles, and ash content of the biocokes were similar despite the total difference in additives. Additionally, the use of additives did not significantly affect the biocoke reactivity indices, but slightly decreased the strength after the reaction with CO2. Carbon-bearing sources have been characterized in terms of their structural properties. XRD analysis revealed that the amount of disordered carbon increased in the order: coke < calcined petroleum coke ~ biocoke (3 wt.% torrefied wood) < biocoke (3 wt.% petroleum coke + 3 wt.% charcoal) < biochar. The results obtained on the physical, chemical, and structural properties of carbon sources are the basis for further research on the behavior of slag foaming.

Study on novel steel slag foam concrete pore structure and bp neural network prediction model

In this paper, a new type of steel slag foamed concrete was prepared. Its pore structure was analyzed by MATLAB image processing technique, and the influence of steel slag on the compressive strength of foamed concrete was investigated. In addition, a BP neural network prediction model for the pore structure of foam concrete was established. The research results show that when the content of steel slag is 30%, the pore structure of steel slag foamed concrete is appropriate. The compressive strength of steel slag foamed concrete increases with the decrease of the density and the proportion of irregular pores. With the density remaining unchanged, the compressive strength of foamed concrete increases with the increase of the ratio of round and small pores. The prediction errors of the BP neural network model in the average pore diameter and average pore roundness factor were less than 8.5% and 5%, respectively.This research can provide a theoretical basis for the production of steel slag foam concrete.

Matte-slag separation behavior as a function of iron phase reduction in copper slag

The Isa smelting furnace discharges the matte and slag in the same tapping hole. As a result, an electric furnace needs to clean the slag. In the present study, the copper slag cleaning in an electric furnace, particularly the separation of the matte from the slag during the reduction process, was investigated. For Fe3O4 to FeO, the foaming slag in the melt disappeared when the Fe3O4 content was less than 10%. With the formation of the metallic iron, the foaming slag formed again, hindering the sedimentation of the matte. When the anthracite dosage increased to 2.61%, the copper content in the slag increased to 9.46%. The microstructure of the slag and the existence of the metallic iron found in the slag were analyzed in detail. The results obtained in this study provide a theoretical basis for the reasonable control of the transformation of Fe3O4 during the copper slag cleaning.

Influence of surfactant on foam generation and stabilization in cement slurry

Modern civil engineering and industrial buildings use foamed cement because of its low heat conductivity and light weight.Despite their high performance, foamed cement products manufactured solely from cement might be prohibitively expensive for commercial entities. Thus, chemically foaming cement is important. This paper compiles and reviewsthe foamed cement preparation, mostly used physical and chemical foaming processes. Physical foaming creates foamed cement by mixing foam into a slurry. Physical foaming methods are inefficient and energy-intensive. Chemical foaming involves adding a foaming ingredient to cement slurry. Foaming agents like surfactants react to create bubbles that expand the slurry. Surfactants in the liquid solution promote a bubble by spontaneously cicatrizing holes caused by external perturbations. These chemicals stabilize foams and bubbles for minutes to hours. Oil and gas well cementing uses Self-generated nitrogen foam cement (SNFC) with a high-efficiency foam stabilizer. Three surfactants produced cement pastes with and without MWCNT. A viscosity-modifying agent (VMA) in an aqueous cement paste dispersion can change its rheology. Sodium dodecyl sulfate (SDS) and CaCl2 increase nanosilica (NS) fluidity for pumping cement-based grout. FSCGM is used for coal mine infill grouting. Foamed sulfoaluminate cement-based grouting material (FSCGM) makes firefighting CO2 foam. Cement-hollow glass microballoon syntactic foams have greater compressive strength than neat cement at equal densities. Polydentatephosphonate-modified polymers and ester-type polycarboxylate superplasticizers create many cement mortar bubbles (PCE-1). Calcium ions stabilize polymer bubbles. Aqueous epoxy resin is added to cement slurries to reduce plastic viscosity and boost heat conductivity to make high-porosity cement foams (HPCF). Foamed cement bubble stability is highest at particle wetting angle π/2. SDS in silica suspension adjusts this angle. Ti-extraction blast furnace slag (TEBFS) foam with 20–40% sulfoaluminate cement (SAC) makes foamed cement.