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The durability problems in Portland cement are related to decalcification of C–S–H; alkali-activated composites are proposed as alternative, focusing on acid exposure and resistance. They were prepared from recycled materials, basic oxygen furnace carbonated and desulfurization slags. The standard material is 100% metakaolin geopolymer compared to slag-based alkali-activated materials (AAMs) with and without reinforcement of fibers (basalt, and cellulose), added in 4 wt%. The acidic environments are H2SO4, HCl, and HNO3N = 2.14 (10, 7.5, and 12.5 wt%, respectively). The chemical resistance is improved by the addition of basalt fibers. The decrease in weight loss is 48% in HNO3 and 47% in HCl for AAM-Bas sample, while for AAM-Cell it is 9% in HCl and 34% in HNO3. The compressive strength of the AAM and AAM-Bas samples remains constant after HCl attack, while this acid attacks cellulose samples, which are stable in HNO3 and have a compressive strength of 10 MPa. [ABSTRACT FROM AUTHOR]

To develop more sustainable purification and recovery processes, it is critical to accurately determine inorganic impurities of natural graphite (NG) and valuable elements present in low concentrations in steelmaking slag. This study applied three microwave-assisted acid digestion methods for basic oxygen furnace (BOF) slag, NG, and NG ash. Nitric acid (HNO3), hydrochloric acid (HCl), and hydrogen fluoride (HF) were used in method 1. In method 2, method 1 was followed by microwave-assisted boric acid (H3BO3) digestion. In method 3, acids (HNO3, HCl, HF, and H3BO3) were added simultaneously. Concentrations were measured using inductively coupled plasma–optical emission spectrometry. Analytical performance was evaluated using spiking recovery tests (NG) and certified reference (slag) material (CRM). Spiking recoveries for Al, Ca, Fe, K, Mg, Na, and Si were between 5% and 116% (method 1) and 94%–116% (methods 2 and 3). CRM recoveries for Al, Ca, Fe, Mg, Mn, P, Si, Ti, and V were between 2% and 102% (method 1) and 92%–103% (methods 2 and 3). The unsuitability of method 1 was evident due to the low recoveries. Methods 2 and 3 digested Ca- and Si-containing BOF slag completely without visible residue. The sufficient recoveries verified the adequacy of the methods. The suitability of method 3 probably depended on the phases of samples, as quartz was not completely digested from the NG. Method 2 completely digested the inorganic material of NG, and the spiking test showed no loss of volatile silicon compounds. These methods have not been published for NG or NG ash and validated for slag before. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the effective use of a mixture of steel sludge (S1) and slag (S2) from the converter process of steel production for the production of cement mortars. Metallurgical waste used in the research, which is currently deposited in waste landfills and heaps near plants, posing a threat to groundwater (possibility of leaching metal ions present in the waste), was used as a substitute for natural sand in the range of 0–20% by weight of cement (each). The obtained test results and their numerical analysis made it possible to determine the conditions for replacing part of the sand in cement mortars with a mixture of sludge and slag from a basic oxygen furnace (BOF) and to determine the effects of such modification. For the numerical analysis, a full quadratic Response Surface Model (RSM) was utilized for two controlled factors. This model was subsequently optimized through backward stepwise regression, ensuring the inclusion of only statistically significant components and verifying the consistency of residual distribution with the normal distribution (tested via Ryan-Joiner's test, p > 0.1). The designated material models are helpful in designing ecological cement mortars using difficult-to-recycle waste (i.e., sludge and converter slag), which is important for a circular economy. Mortars modified with a mixture of metallurgical waste (up to 20% each) are characterized by a slightly lower consistency, compressive and flexural strength, and water absorption. However, they show a lower decrease in mechanical strength after the freezing–thawing process (frost resistance) compared to control mortars. Mortars modified with metallurgical waste do not have a negative impact on the environment in terms of leaching heavy metal ions. The use of a mixture of sludge and steel slag in the amount of 40% (slag/sludge in a 20/20 ratio) allows you to save 200 kg of sand when producing 1 m3 of cement mortar (cost reduction by approx. EUR 5.1/Mg) and will also reduce the costs of the environmental fee for depositing waste. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag is an industrial waste produced from steel-making. It can be utilized as building material, but its high content of free CaO (f-CaO) causes volume expansion of materials and limits its utilization. However, carbonation of BOF slag can decrease the f-CaO content, improve stability, and reduce carbon emissions. This study investigated the influence of temperature, pressure, liquid to solid, reaction time, and stirring pattern on f-CaO consumption and CO2 sequestration, which reached a maximum f-CaO consumption and CO2 sequestration of 99.58% and 5.12% (51.2 g CO2/Kg BOF slag), respectively, under optimum conditions. According to the results of the XRD patterns of carbonated slag, no peaks of CaO were detected, the peaks of Ca2Fe2O5 and Ca2SiO4 were slightly reduced, and new peaks of CaCO3 were detected. The reaction process has been described by a shrinking core model revealing that the diffusion of reactants through the product layer was the rate-limiting step for carbonation. The kinetic equation for CO2 sequestration was derived as: InK = − 2132.83·T−1–9.1543. This approach presents a green, cost-effective, and rapid method for enhancing steel slag utilization while capturing and storing CO2. The method proposed in this paper holds significant potential for wider adoption. [ABSTRACT FROM AUTHOR]

The study of alkali-activated materials as a replacement for portland cement has been growing in recent years due to the sustainable nature of these materials. Nevertheless, ternary alkali-activated pastes using waste glass as a precursor have been insufficiently studied concerning their rheological, mechanical, and microstructural properties. In addition, there is a lack of research studying alkali-activated mixtures using basic oxygen furnace (BOF) slag and glass waste as precursors. Therefore, this paper aims to study the effect of glass powder (GP) content as a precursor, the effect of the activator ratio in alkali-activated ternary pastes of BOF slag, metakaolin (MK), and GP, and the influence of the Na2SiO3/NaOH ratio on its mixtures. The activator solutions of NaOH and Na2SiO3/NaOH were used in the production of the pastes. The liquid/solid ratio was kept fixed at 0.6 and the molarity of the NaOH solution was fixed at 12 M, seeking to analyze the impact of the Na2SiO3/NaOH ratio, with adopted values of 0.75, 1.5, and 2.5. We also aimed to study the impact of the glass content in the mixture for the values of 10%, 20%, and 25%, replacing the BOF slag. The workability by the minislump test, rheology, compressive strength for 1 and 28 days, and microstructural parameters were analyzed. ANOVA was performed to determine the significance of variables in the workability and compressive strength parameters. Pastes with the highest activator ratio (Na2SiO3/NaOH=2.5) produced better compressive strength (34.74 to 36.11 MPa) and lower minislump spreads (90 to 98 mm) compared with the mixtures with Na2SiO3/NaOH=1.5 and 0.75, besides indicating a denser microstructure, linked to higher production of aluminosilicate gels. Higher GP contents generated pastes with lower mechanical performance (16.7 MPa for Na2SiO3/NaOH=0.75) and microstructural qualities, albeit with better workability (124-mm minislump spread). [ABSTRACT FROM AUTHOR]

Steel slag is a significant environmental liability generated by pyrometallurgical processes. Residue generation, such as granulated blast furnace slag and basic oxygen slag (BOF), is intrinsic in steel production. Blast furnace slag, generated in the carbothermal reduction of iron ore, is almost entirely used as a supplementary cement material in Portland cement. BOF slag, produced in the conversion of pig iron into steel in a basic oxygen converter, is still not consolidated or valued for reuse. This research proposes the reuse and valorization of BOF slag combined with blast furnace slag in clinker-free cement production. Cement formulations were produced with different slag and gypsum contents, ranging from 80 to 90% blast furnace slag, 10 to 20% gypsum, and 10 to 15% BOF slag. All formulations were evaluated for compressive strength at ages of 3, 7, 14, 28, 91, and 180 days of curing. At the initial ages, the cement formulations exhibited high resistance. On the 3rd day, the cement formulations reached up to 10 MPa, and on the 7th day, 40 MPa. At late ages, the best-performing formulation, ECO2, showed, after 28 days of hydration, a compressive strength greater than 50 MPa, and at 180 days, a compressive strength greater than 80 MPa. It was possible to understand that BOF slag acts in cement alkaline activation with pH increase, more or less actively due to the presence of lime, portlandite, and calcite. [ABSTRACT FROM AUTHOR]

To realize efficient P removal and resource utilization of steelmaking slag, a synthetic slag with appropriate basicity was produced by co-processing the practical dephosphorization slag and basic oxygen furnace slag. The selective leaching behavior and dissolution kinetics of P were investigated. The results indicated that the P dissolution efficiency and reaction rate were significantly influenced by the variety in stirring rate and pH. However, the decreasing solid/liquid ratio and particle size can significantly enhance the reaction rate, while exerting a slight impact on the P dissolution efficiency. The leaching temperature had less influence on both P dissolution efficiency and reaction rate. Under the optimal leaching conditions, the leaching reaction of the P-condensed phase primarily occurred within the initial 3 min, and, finally, the P dissolution efficiency reached 87.5%, with an extremely low dissolved amount of Fe. After leaching, the Fe-rich residue consisted of massive Fe2O3, MgO, and MnO, with only 0.32% P2O5. This residue can be used as a raw material or flux in steel plants. Furthermore, it was found that the selective leaching of P was controlled by diffusion through the product layer, with the apparent activation energy of 5.80 kJ/mol. The empirical equation has been established. [ABSTRACT FROM AUTHOR]

Engineered geopolymer composites (EGC) have emerged as a more environmentally friendly alternative to conventional engineered cementitious composites (ECC). These composites offer high mechanical and durability features. However, there is a lack of research on EGC, particularly with basic oxygen furnace (BOF) slag as a precursor and iron ore tailings (IOT) as a partial replacement to fine aggregate. Despite their effectiveness as industrial waste products in conventional concrete, this study aimed to determine the optimal compositions of fly ash (FA), steel fibres (SF), and IOT by varying their percentages. Overall, 150 mix combinations were tested, including six binder combinations, five combinations of fine aggregates, and five percentage variations in SF. Finally, one optimum mix was selected for each binder combination, based on the ultimate compressive strength values corresponding to the six optimal mixes. The compressive strengths of all the mixes were evaluated at both 7 and 28 days of curing, involving three replicate samples after oven curing (initial 24 h) followed by subsequent ambient curing until their respective ages. The highest observed compressive strength after 28 days was 41.77 MPa for 50 mm cubes. This strength was achieved with a composition of 60% FA, 1.5% SF, and 45% IOT. An increase in IOT percentage led to a nearly linear increase in strength, while the strength peaked at 1.5% for steel fibres. The addition of BOF slag significantly enhanced the compressive strength compared to mixes with full FA. A 40% fly ash replacement with BOF slag resulted in an average strength that was 39% higher than the combination with 100% fly ash. However, the strength growth decreased after a 10% replacement. Analysis of variance was conducted using the design of experiments methodology to determine the significance of the parameters and their interactions. All three independent parameters were found to be statistically significant, while their interactions were not. Utilizing Taguchi's analysis method with the L25 orthogonal array, it was concluded that IOT percentage was the most influential parameter. [ABSTRACT FROM AUTHOR]

The rotation speed of the basic oxygen furnace (BOF) and the shape of the tapping hole have an important influence on the amount of slag carryover during the tapping process. The CFD fluid simulation software Fluent is used to analyze the flow field of the 210 t BOF rotation tapping process. The results revealed that the amount of slag carryover in the early stage is the largest when the tapping hole inclination angle is 0° and the rotation speed is 1.0 r/min. The flow field analysis shows that this is caused by the fluctuation of molten steel and slag, which makes the slag flow into the tapping hole again. The case of a rotation speed of 1.2 r/min shows the least amount of slag carryover. By comparing the three kinds of tapping holes, it can be known that a reduction in the tapping hole diameter brought a decrease in yield loss and a decrease in amount of slag carryover. As the height of molten steel decreases, the shear stress on the tapping hole decreases. The increase in the diameter of the tapping hole increases the shear stress, which in turn increases the wear of the refractory material. [ABSTRACT FROM AUTHOR]

Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn. [ABSTRACT FROM AUTHOR]

In this study, a portable spectral analysis instrument based on spontaneous emission spectroscopy (SES) was developed for the in situ, non-intrusive, and quantitative measurement of gaseous Na inside ZD coal-fired boilers, which is mainly applied for predicting slagging in furnaces. This technology is needed urgently because the problem of fouling and slagging caused by high alkali metals in ZD coal restricts the rational utilization of this coal. The relative extended uncertainty for the measurement of gaseous Na concentration is Urel = 10%, k = 2, which indicates that measurement data are reliable under working conditions. It was found that there is a clear linear relationship between the concentration of gaseous Na and fouling in high-alkali coal boilers. Therefore, a fast and efficient method for predicting the slagging and fouling of high-alkali coal boilers can be established by using this in situ online real-time optical measurement. [ABSTRACT FROM AUTHOR]

For the soil in an area which has been repeatedly chosen as one of the 10 most polluted places in the world, stabilization of Pb and Zn was assessed in batch, incubation, and column experiments. Single and combined amendment of scrap-recycling slag (Slag-R), charcoal, coal ash, hydrated lime, and basic oxygen furnace (BOF) slag were applied for the stabilization. Notably, the combined amendment of Slag-R and hydrated lime exhibited superior stabilization efficiencies than the individual use of all stabilizing agents and combined use of charcoal and hydrated lime. The combined amendment of Slag-R and hydrated lime decreased Pb levels by 92–99% and Zn levels by 63–88% in the incubation experiments and by 75% and 89–93%, respectively, in the column experiments. In particular, the combined amendment showed a synergistic effect for Pb stabilization because a higher pH enhanced sorption onto the slag and because sorption onto Fe (hydr)oxides of the sorbent possibly helped to remove Pb. Zinc had a relatively lower sorption tendency, so it was mainly controlled by the pH increase from hydrated lime. Although the addition of hydrated lime was very effective in stabilizing high concentrations of Pb and Zn, the dosage should be controlled carefully because excessively high pH redissolves Pb and Zn as anions. [ABSTRACT FROM AUTHOR]

Slag, a by-product of the iron and steelmaking industry, has been identified as an alternative construction material; however, there are currently limited engineering reuse applications for some slags. Steel slag coarse aggregates (>6 mm) has been successfully used in the asphalt mix for the surface course in pavement constructions; nonetheless, the construction applications of finer slag particles (<6 mm) are limited due to their expansive properties when hydrated. Therefore, this research aims to investigate the potential of using granulated blast furnace slag (GBFS) in controlling the swelling of fine particles of fresh basic oxygen furnace slag (BOFS). A series of laboratory tests were conducted to evaluate the engineering properties, swelling, and shear behavior of BOFS-GBFS mixtures to identify controlling factors and governing mechanisms of swelling, followed by acceptable mix proportions for potential use in pavement applications. Both accelerated swell tests and long-term swell consolidation tests demonstrated an exponential reduction in the hydration-induced expansion of BOFS with the addition of GBFS. For example, up to 77% of the swelling reduction was observed by replacing 30% of BOFS particles with GBFS. In contrast, the peak deviatoric stress of BOFS was reduced linearly with an increase in GBFS content, causing a 15% reduction of friction angle with a 30% addition of GBFS content. Optical microscopy and micro-computed tomography (CT) analysis revealed the bond formed between BOFS-GBFS particles due to the chemical reaction between the free lime in BOFS with silica and alumina in GBFS in the presence of water. The overall laboratory results were summarized by developing a design chart in which the optimal mix of GBFS to BOFS lies between 25% and 30%, volumetric swelling is less than 1%, and the peak friction angle is about 43°. [ABSTRACT FROM AUTHOR]

Ludwigite is a multi-element coexisting iron ore. Through the sinter pot experiment, the effect of ludwigite on the metallurgical properties of the sinter is studied, and its action mechanism is revealed combined with X-ray diffraction (XRD) analysis. The appropriate amount of ludwigite is obtained on the evaluation mechanism of softening and melting properties of the sinter, which provides theoretical guidance for practical production. The results show that with the increase of the amount of ludwigite, the yield, vertical sintering speed, and drum index in the metallurgical properties of the sinter show a gradual downward trend, and the low-temperature reduction pulverization index RDI+3.15 shows a gradual upward trend. The addition of ludwigite is conducive to the formation of calcium ferrite and promotes the activity of MgO. The addition of excessive ludwigite will lead to the formation of Mg2B2O5 and Ca3B2O6, Slag phase is formed. With the increase of the proportion of ludwigite, the melting range of the sinter is slightly widened, and the permeability is improved first and then reduced. Under this ore blending condition, ludwigite resources can be added and used in sintering batching, and the proportion shall not exceed 6%. [ABSTRACT FROM AUTHOR]

Due to the presence of free lime (FL) in slag and its lack of reaction with concrete components, concrete containing slag reduces strength. Pozzolanic Portland cement (PPC) in the presence of moisture and normal heat during chemical reactions with lime (calcium hydroxide) generates stable calcium silicates that have adhesion properties. By using PPC instead of Portland cement type I in roller compacted concrete (RCC) containing basic oxygen furnace slag (BOFS), it is possible to determine the mechanical properties of RCC due to the reaction between the FL in BOFS and PPC. Therefore, this study aims to investigate the effect of PPC on the mechanical properties of RCC containing BOFS. For this purpose, specimens are made with various cement content values (225-400 kg/m3), various BOFS content values (0-50%) and with the optimum moisture. The properties examined in this paper are compressive strength, indirect tensile strength, and static modulus of elasticity tests. The results show that the use of PPC is effective in compensating the negative impact of using BOFS and providing the minimum specified mechanical properties. Also, the proportion of consumption of PPC with BOFS value is determined for the possibility of maximum reaction between FL and pozzolan in cement. [ABSTRACT FROM AUTHOR]

The study presented in the paper evaluated the properties of pavement quality concrete (PQC) containing coarse aggregates made from aged and unaged basic oxygen furnace (BOF) slag. Workability, air content, strength, drying shrinkage, expansion, abrasion resistance and expansive potential of PQC were evaluated. Air content and workability of fresh slag concrete increased marginally. Compressive and flexural strength of the concrete containing aggregates of aged and unaged slag was observed to be less than the strength of normal concrete. The reduction in strength of concrete containing aged slag aggregates was more as compared to the concrete containing unaged slag aggregates due to the presence of a dusty coating around the aged aggregates. The drying shrinkage of the concrete increased with the content of steel slag aggregates. The abrasion resistance of the slag concrete was found to be better than the abrasion resistance of conventional concrete. Deterioration of slag concrete was not observed due to normal water curing up to 90 days. However, accelerated aging of concrete in water at 70°C resulted in the localised cracking and eruptions due to expansion. The study showed that, aged as well as unaged slag aggregates may be used for the preparation of concrete mixtures of required properties for road construction. [ABSTRACT FROM AUTHOR]

An industrial by‐product of the steel industry called basic oxygen furnace (BOF) slag has recently undergone extensive research for high‐end applications outside of road load and landfill. In contrast to the Bogue methodology used with regular Portland cement, BOF slag lacks a quick and straightforward quantitative phase analysis procedure that would allow it to be employed as a high‐end raw material. The main phases of BOF slag (C2S, C2(A,F), Ff, RO‐Phase, and f‐C) can be calculated using the method presented in this paper based on chemical composition. [ABSTRACT FROM AUTHOR]

The steel industry produces the most widely used metal on earth. The main challenge of the industry for the next decade is the steel production transformation process. The CO2 intensive blast furnace/basic oxygen furnace (BOF) route will be substituted by a combination of a Direct Reduced Iron plant (based on natural gas, at later stage on "green" hydrogen) with an Electric Arc Furnace (EAF) or a Submerged Arc Furnace (SAF), heated with renewable energy. Thus, the well‐known latent hydraulic granulated blast furnace slag (GBS) being successfully used in cement and concrete for more than 140 years will vanish step by step. GBS is used as a supplementary cementitious material (SCM) not only, but in particular, due to its clinker reduction and from there its CO2 reduction potential for the cement and concrete production. Whereas the DRI process itself does not generate any slag, EAF and SAF will do. These slags will be very different. Moreover, the new EAF slags will be also different compared to today's scrap based EAF slag. However, specific slag/metal ratios, resulting slag volumes, chemical and mineralogical compositions and physical properties of the new slags are yet unknown. Thus, also their cementitious and environmental properties are still unknown. Different running projects aim mainly to create slags being similar to GBS. The main objective is to provide the cement and concrete industry furthermore with a (latent) hydraulic SCM. [ABSTRACT FROM AUTHOR]

In the production of cast iron, slag is a reaction product from the process steps such as melting, spheroidization and inoculation elements combined with oxygen and sulfur. The slag is a mixture of oxides and sulfides that often appears on the surface of the molten iron, where it can be removed or, in the worst case, carried into the mold during casting causing slag defects. It is accepted that slag is a part of the cast iron process by most foundries, and it is given little attention as long as it is manageable. However, some slag compositions have a more negative effect on the production and are less appreciated by the foundry operators than others. In this context, two different slag samples from an 80-ton holding furnace were collected to study their compositions and give a plausible explanation for their different behavior. They were referred to as "Good" and "Bad" slag samples by the operators. The "Bad" slag also caused more slag defects in the castings. The slags were evaluated by X-ray fluorescence spectroscopy and combustion techniques to measure the total concentrations of oxygen and sulfur. This information was used as input parameters for thermodynamics calculations, using the CALPHAD method, to evaluate the equilibrium phases of the slag samples and their behavior as a function of temperature. The results show that the "Good" slag has a higher solid content than the "Bad" slag. This might be associated with an easier removal from the molten iron by the operators than a more liquid content slag. Furthermore, there may be less slag entering the mold with higher solids, and thus, the "Good" slag has fewer casting defects. [ABSTRACT FROM AUTHOR]

A large amount of furnace slag is produced from steelmaking every year. The resultant by‐products will severely damage the natural environment and ecosystems if not treated properly. Businesses worldwide have thus been striving for slag recycling and solving various complex problems. In this study, basic oxygen furnace slag (BOFS) was regarded as an adsorbent to adsorb phosphate in water. In addition to a physical–chemical property analysis of the by‐products, the present study explored the performance of basic oxygen furnace slag in adsorbing phosphorous (P) with different size settings, and observed the surface structure of fused basic oxygen furnace slag.The results revealed that free‐state Ca accounts for the majority in basic oxygen furnace slag content, demonstrating the removal of nearly all phosphorous in water. The results of Fourier‐transform infrared spectroscopy (FT‐IR) on basic oxygen furnace slag with >200 mesh size revealed complex wave crests at the fingerprint region (570–980 cm−1). The result signifies that the basic oxygen furnace slag samples comprise strong Si─O and O─Si─O bonds within silicate minerals. Moreover, basic oxygen furnace slag samples with a particle size >200 mesh contain very high content of lime (CaO) (reaching 49.5%). This property fully demonstrates that basic oxygen furnace slag samples in a small particle size were more active as an aggregate. This study found that the Langmuir adsorption isotherm model (R2 = 0.997) is slightly better than the Freundlich adsorption isotherm model (R2 = 0.984), which shows that the process in which basic oxygen furnace slag adsorbs P is monolayer adsorption, and the adsorption energy is more uniformly distributed among BOFS samples. This study also found that basic oxygen furnace slag samples melted at 1200°C can effectively encapsulate some heavy metal pollutants and form stable glassy slag. The change proved that a fused basic oxygen furnace slag sample could effectively encapsulate heavy metal pollutants and formed glassy‐state slag with high stability. This mechanism would reduce the likelihood of heavy metal leaching when basic oxygen furnace slag serves as a subgrade aggregate, permeable material, or concrete aggregate in the future. [ABSTRACT FROM AUTHOR]

The prediction of equilibrium components for chemical reactions is a considerable section in the metallurgical industry. According to the ion and molecule coexistence theory (IMCT), a modified mass action concentration model based on a thermodynamic database is proposed in this paper, which complys with the law of mass conservation and can be applied in the batching process for Al-Ti-Ca-oxide system that originates from SHS (Self-propagating High-temperature Synthesis) metallurgy. The trend for slag and alloy component under different batching conditions are in good agreement with experiment, while the difference between the theoretical calculation and experiment can be attributed to the deviation from the thermodynamic equilibrium. The modified mass action concentration model with melts and slag can be used to predict the composition and content of the system when equilibrium is achieved at a certain temperature under a specific material ratio, which is conducive to reducing the cost of the experiment and predicting the operability of the actual process. Moreover, it is believed that this thermodynamic insight may has certain application prospects in these metallurgical procedure based on the equilibrium process. [ABSTRACT FROM AUTHOR]

The gradual increase in industrial wastes allowed the utilization of these wastes in different areas. Steel slag, one of the industrial wastes, is formed during the reduction of molten crude iron to molten crude steel in basic oxygen furnaces or scrap to molten crude steel in electric arc furnaces and induction furnaces. Removal, storage, or disposal of steel slag is an important environmental and economic problem. Steel slag offers opportunities to be used as an alternative material in various areas and contributes to the national economies through recycling. This research provides information about the studies and application examples on the use of steel slag as a soil amendment and mineral fertilizer in the world. This usage allows reducing the consumption of natural resources and providing great agricultural, environmental, and economic gain by minimizing the negative environmental effects of steel slag. [ABSTRACT FROM AUTHOR]

The blast furnace and basic oxygen furnace (BF-BOF) is still the main process used for the production of iron and steel in China. With the approach of the "dual carbon" target, the iron and steel industry needs to transform and upgrade to "green" and "low-carbon" practices. At present, the low-carbon hydrogen metallurgy technology route based on hydrogen instead of carbon is mainly adopted at home and abroad, and the domestic route is mainly based on oxygen-rich BFs and hydrogen-based shaft furnaces (SFs). It promotes the transformation of the traditional BF to hydrogen-rich, oxygen-rich, and carbon-recycled (Hy-O-CR) technology. A new ironmaking system and method for a reduction smelting furnace (RSF) with Hy-O-CR is presented in this paper. The ironmaking system includes nine sets of equipment, such as an RSF, gas dust collector, dryer, CO2 separator, electrolytic water device, blower, heat exchanger, storage tank of reduction gas, and chimney. From top to bottom, the RSF includes an indirect reduction zone, a soft melting dripping zone, and a coke combustion zone. The ironmaking methods include coke and ore mixed charging, injection of the mixed reduction gas composed of electrolytic green hydrogen and circulating gas from the furnace gas into the indirect reduction zone, injection of oxygen into the coke combustion zone, CO2 recovery of the furnace top gas, and slag and iron treatment. By redesigning the size of the furnace type and optimizing the parameters, the metallization rate of the indirect reduction zone can be as high as 85–95%, and the carbon consumption per ton of hot metal can be greatly reduced. By using oxygen to recycle the reduction gas produced by its reactor, the process achieves the goal of reducing CO2 emissions by more than 50%, thus realizing green and low-carbon metallurgy. [ABSTRACT FROM AUTHOR]

Before using basic oxygen furnace slag (BOFS) in any engineering application, it is important to determine its properties. The chemical composition, mineralogy, and physical properties of BOF slag are subject to large fluctuations as a result of different raw additives, different compositions of the molten iron used for producing the steel, oxygen stirring of a molten pool, uneven temperature fields, and other complex physical conditions. Thus, in this research, the engineering properties of BOF slag aggregates with different ages were identified, and then the feasibility of BOF slag aggregates in mortar application was investigated. It was found that stockpiled BOFS was harder than fresh BOF slag, which had lower aggregate crushing values and lower LA abrasion values. Also, stockpiled BOFS showed less expansion than fresh BOF slag regardless of water and 1 M NaOH solution immersion. The chemical reaction between f-CaO, f-MgO, and water due to weathering in the field extremely reduced the expansion of BOFS submerged in water. BOFS may contain reactive silica, which causes an alkali–silica reaction (ASR). Stockpiled BOFS (100%, 75%, 50%, 25%) used as a mineral filler in asphalt concrete mix brought about low tensile strength at break up (crack), low compressive strength at +50 °C, poor cohesion, and residual porosity. However, these parameters were partially improved with the use of a thermostable adhesive additive for road bitumen based on polyphosphoric acid esters. The comprehensive assessment in this study indicates that while some mixtures meet the specified criteria for certain properties, there are challenges, particularly regarding crack resistance and cohesion, that need to be addressed to fully align with the standard. Adjustments to the mixture proportions, the exploration of alternative additives, and the use of different types of fillers may be necessary to achieve the desired properties, especially in terms of crack resistance and cohesion. [ABSTRACT FROM AUTHOR]

The influence of V2O5 on the phosphorus partition between liquid crude steel and heterogenous basic oxygen furnace (BOF) slag with CaO/SiO2 = 4.2 was investigated at a temperature of 1600 °C in a middle frequency induction furnace. Thereby the phosphorus transfer from "steel to slag" as well as from "slag to steel" was studied over a holding time of 60 minutes. The measured results were shown as phosphorus partition and phosphorus capacity and compared with the experimental values from the literature. It was found that V2O5 in highly basic BOF slags decreases phosphorus partition and phosphorus capacity. In addition, the resulting slags were investigated using a scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

Basic oxygen furnace slag is considered a potential material for the replacement of natural aggregate in Portland cement concrete due to its similar physical characteristics. Therefore, in the present work, the slag was analyzed by Nitrogen sorption porosimetry, elemental analysis, mineralogical analysis, and volume stability. On the other hand, concrete mixtures were manufactured with basic oxygen furnace (BOF) slag aggregates and characterized mechanically and morphologically. The results showed superior compressive strength due to interfacial improvements in the slag aggregate. Statistically, there was no differentiation between the reference concrete and the slag concrete mixtures for tensile strength. Additionally, due to the porosity and low stiffness presented by the slag, the concrete elastic modulus showed a slight decrease. The replacement of sand with BOF slag as fine aggregate in Portland cement concrete presents itself as a sustainable alternative for the elimination and valorization of this environmental liability. [ABSTRACT FROM AUTHOR]

In basic oxygen furnace double slag process, the slag shows a coexisting state of both liquid and solid. In order to study the effect of multi-phase slag on dephosphorization, heat experiments were conducted in this study, and the multi-phase slag was analyzed with the method of SEM-EDS. The results show that the mass fraction and size of solid solution increase with increasing basicity and decreasing FetO concentration. The distribution of P2O5 (LP2O5) between the solid solution and liquid phase increases with the T.Fe content in the liquid phase. While the increase of CaO content in liquid phase shows the opposite effect. A higher CaO content in liquid phase brought a decrease in γP2O5. The increase of T.Fe content in liquid slag has no notable effect on γP2O5 of dephosphorization slag, but increases γP2O5 of decarburization slag. The partition ratio of phosphorus between slag and steel (LP) increases with the increase of basicity, for conditions of FetO content in dephosphorization slag less than 25%. In the case of basicity of 3.0, LP reaches a maximum at FetO = 15%. When the basicity is 3.5 and 4.0, LP value is the largest at FetO of 15% or 20%. [ABSTRACT FROM AUTHOR]

Open-graded asphalt friction course (OGAFC) is an asphalt course constructed over a dense-graded and impermeable surface to allow quick drainage of surface water runoff and enable reduction of hydroplaning and splash and spray. OGAFC mixtures demand high-quality aggregates to perform the intended functions while transferring traffic loads to the underlying layer. Steel slag is a byproduct generated during steel production, and large quantities are unutilized in steel-producing countries, including India. This study evaluated the mechanical performance properties of OGAFC mixtures using basic oxygen furnace (BOF) steel slag as replacement for coarse aggregates at percentages of 0%, 25%, 50%, 75%, and 100%. OGAFC mixtures with two types of modified asphalt binders and five percentage replacements of coarse natural aggregates with BOF steel slag were fabricated. The mechanical performance of the OGAFC mixtures was evaluated in terms of rutting resistance (dynamic creep test and Hamburg wheel tracking device test), cracking potential (indirect tensile strength, cracking tolerance index, and semicircular bending test), fatigue life (indirect tensile fatigue test), and modulus properties (indirect tensile stiffness modulus and resilient modulus). The test results indicated that the use of BOF steel slag not only improved the performance of OGAFC mixtures in terms of rutting resistance, cracking potential, and modulus properties, but also increased the fatigue life of the OGAFC mixes. OGAFC mixes up to 100% BOF steel slag content exhibited superior performance compared with the mixtures with natural aggregates. [ABSTRACT FROM AUTHOR]

The annual output of steelmaking slag has exceeded 150 million tons. Mass accumulations of slag damage the environment and hinder sustainable development. Preparing cementing materials in the powder form is a promising solution for the large-scale utilization of slag. Our study focused on the effects of MgO and P2O5 on the grindability, soundness, and cementitious activity of steelmaking slags. Experimental results showed that by increasing the P2O5 content in basic oxygen furnace slag from 0.5% to 3%, the free CaO content, grindability index, and early strength decreased from 6.82% to 5.35%, 0.78 to 0.72, and 29.3 MPa to 21.0 MPa, respectively, and the later strength increased from 42.8 MPa to 46.5 MPa. For electric arc furnace slag, the free CaO content, grindability index, and early and later strengths decreased from 4.0% to 1.9%, 0.75 to ~ 0.6, 29.5 MPa to 23.6 MPa, and 31.2 MPa to 27.5 MPa, respectively. The increase in the MgO content insignificantly influenced the grindability of the slag, but led to a deterioration in the soundness and cementitious characteristics of the slag powders. These results provide guidance for optimizing the chemical composition of steel slag during steelmaking to improve its use in cementing materials and thereby alleviate slag pollution and carbon dioxide emissions caused by cement production. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of using steel fibers and steel shavings in roller-compacted concrete containing coarse basic oxygen furnace slag aggregate was investigated in order to improve its mechanical properties and to produce an electrically conductive and environment-friendly concrete. For this purpose, various samples containing 0.4, 0.7, and 1% of steel fiber and 3, 5, and 7% of steel shaving were fabricated. The compressive strength, indirect tensile strength, electrical resistance, and specific density tests were conducted on the samples. The results demonstrated the positive effect of steel fiber and the destructive effect of steel shaving on the compressive and tensile strengths of RCC containing BOFS. The results of the electrical resistance test showed a more positive effect of steel shaving than steel fiber in the conductivity of RCC samples. Regarding the specific gravity results, the natural aggregate replacement with BOFS as well as steel fiber and steel shaving resulted in an increase in the specific gravity of the mixtures. Utilizing the both steel fiber and steel shaving can compensate the unfavorable properties on the RCC containing BOFS. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the utilization possibilities of steel slags, basic oxygen furnace (BOF) and electric arc furnace (EAF) slags, as backfill material in coastal structures. Within the scope of the study, physical, mechanical and chemical properties of the steel slags were investigated and their potential to create environmental risks were evaluated. The results showed that soundness loss and filler content ratio were below the limit values for steel slags to be used as backfill material. It was determined that the density, porosity, water absorption and Los Angeles abrasion ratios of steel slags were generally higher than natural aggregates. In order to reach the California Bearing Ratio (CBR) limit (> 25%), the maximum particle size of the steel slag was reduced to 25 mm. In this particle size, CBR of the slag samples generally gave better results compared to the natural aggregate (38%), except for Kardemir and Asil samples. In addition, the concentration values of heavy metals (Cu, Cd, Cr, Pb, Ni, Zn, Hg and As) were below the limit values specified in the regulation. It is suggested that EAF slags should be aged for at least 6 months and BOF slags for at least 24 months in open air conditions before being used as backfill material in coastal structures after the maximum particle size is reduced to 25 mm. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace slag (BOFS) is a waste material generated during the steelmaking process and has the potential to harm both the environment and living organisms when disposed of in a landfill. However, the cementitious properties of BOFS might help in utilizing this waste as an alternative material in alkali-activated systems. Therefore, in this study, BOFS and blast furnace slag were activated with varying dosages of NaOH, and the fresh, physical, mechanical, and microstructural properties were determined along with statistical analysis to reach the optimal mix design. The test results showed that an increase in BOFS content decreased compressive and flexural strengths, whereas it slightly increased the water absorption and permeable pores of the tested mortar samples. On the contrary, the increase in NaOH molarity resulted in a denser microstructure, reduced water absorption and permeable pores, and improved mechanical properties. Statistically significant relationships were obtained through response surface methodology with optimal mix proportions, namely, (i) 24.61% BOFS and 7.74 M and (ii) 20.00% BOFS and 8.90 M, which maximize the BOFS content with lower molarity and improve the mechanical properties with lower water absorption and porosity, respectively. The proposed methodology maximizes the utilization of waste BOFS in alkali-activated systems and may promote environmental and economic benefits. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag is the main co-product in the steelmaking process, its recycling within the iron and steel enterprises is crucial for the industry to ensure greater sustainability. According to the composition characteristics of BOF slag, a method of separating and recovering iron resources by regulating the composition of BOF slag with silica as an additive at high temperature was proposed. In this study, the growth of iron-containing phase during oxidative modification of BOF slag was in-situ observed by ultra-high-temperature confocal scanning laser microscope, and the phase transformation and mineral structure evolution were analyzed by chemical analysis, X-ray diffraction and field emission scanning electron microscopy. The results demonstrated that the increase of oxidation temperature effectively promoted the transformation of iron oxides to (Mg,Fe2+)O·Fe 2 O 3 , but too high temperature could lead to the increase of iron-containing melilite phase and reduce the iron recovery. In the oxidative modification process, the appropriate holding time and cooling mode facilitated the growth and development of (Mg,Fe2+)O·Fe 2 O 3 particles, which was conducive to the separation and recovery of iron resources. After BOF slag was oxidized at 1300 ℃ for 240 min and cooled in the furnace (1 ℃/min), the grade of magnetic slag obtained by magnetic separation had a grade of 40.26%, a recovery of 70.95%, and a P and S content of 0.042 and 0.456, respectively, which may be used as an important supplement to the raw materials for sintering. The regulated secondary slag may be used to diversify into higher value-added production. Therefore, the systematic research and development of oxidative modification-crushing-magnetic separation technology may promote the efficient utilization of BOF slag components and heat energy. [ABSTRACT FROM AUTHOR]

Blast furnace–basic oxygen furnace (BF–BOF) process is the predominant method for smelting vanadium titano-magnetite (VTM) in China. Hydrogen-rich (H2-rich) gas injection in BF is considered as an important way to reduce CO2 emission under the background of low carbon metallurgy. In this paper, the softening–melting behaviors of VTM sinter in H2–rich gases were investigated by the method of determination of its reduction softening drippinger performance under load. The experimental results indicated that the permeability of VTM sinter during the softening–melting process was improved by increasing the H2 content of the reducing gases. The maximum pressure drop of the burden decreased gradually from 29.76 kPa to 19.97 kPa, and the total characteristic value (representing the comprehensive softening–melting property) also decreased obviously from 2357.52 kPa·°C to 630.94 kPa·°C with the increase in H2 content. The softening interval of the samples was widened, while the melting–dripping interval increased firstly and then decreased. In that case, the position of the melting–dripping zone in BF would move downwards, which was beneficial to smelting smoothly. The thermodynamic analysis indicated that Ti- and Fe-bearing phases were more difficult to be reduced than iron oxides, and H2-rich gas is beneficial to the reduction of that kind of oxides. Titano-magnetite will be reduced stepwise to form Fe2TiO4, and then in the order of FeTiO3→TiO2→Ti(C,N). Wustite (FeO) was an important component during the slag-forming process, whose content increased firstly and then decreased. Perovskite and silicate were the main phases in the dripping slag samples. [ABSTRACT FROM AUTHOR]

Keeping recycling and the circular economy in mind, this study explores the reduction in emission of a highly optimized, commercially employed friction material formulation through the addition of metallurgical slags from a basic oxygen furnace in varying quantities from 6 to 38 wt%. The various compositions were paired with a pearlitic grey cast iron counterface and tested on a pin on disc tribometer. The friction coefficient and pin wear increased with the slag addition but were still within the permissible limit when compared to the original formulation. Specimens with higher slag content observed extremely compacted and extended secondary contact plateaus, which also recorded significant slag presence. The extended plateaus detached in the form of chunks from the mating surfaces, which settled on the equipment hardware and restricted the production of airborne particles. From an industrial symbiosis perspective, the addition of metallurgical slags proved to be a promising way of obtaining green friction materials with reduced emissions. [ABSTRACT FROM AUTHOR]

Steel slag (SS) is a secondary material from steelmaking production with little commercial value. Its volumetric expansion and low reactivity limit the use of SS in Portland cement (PC)-based materials. This study investigated the potential use of basic oxygen furnace (BOF) slag as a single precursor in alkali-activated matrices (AAMs). Six AAM pastes were assessed by changing the silica modulus (0.75, 1.50 and 2.22) and the sodium concentration (4% or 6% Na2O—wt. SS). The early hydration was assessed using isothermal calorimetry (IC), followed by the assessment of the mechanical performance (compressive strength), apparent porosity, and structure and microstructure characterization (X-ray diffraction, thermogravimetric analysis and scanning electron microscopy). The results indicated that although the BOF slag may be considered a low-reactivity material, the alkaline environment effectively dissolved important crystalline phases to produce hydrates (reaction products). An optimized combination of activator sources was achieved with 4% Na2O and a silica modulus of 1.50–2.22, with a compressive strength up to 20 MPa, a significant amount of reaction products (C-S-H/C-A-S-H gels), and low initial and cumulative heat release. Those properties will help to promote SS recycling use in future engineering projects that do not require high-strength materials. [ABSTRACT FROM AUTHOR]

Mineral carbonation is a method in carbon capture and utilization (CCU) in which carbon dioxide reacts with natural or synthetic mineral phases to form carbonates. In this study, BOF slag consisting of alite, Ca3SiO5, belite, Ca2SiO4, melilite, (Ca,Na)2(Mg,Al)[4][Si2O7], brownmillerite, Ca(Fe,Al)2O5, calcium ferrite, Ca2FeO4 and Ca-, Mg- and Mn-bearing wuestite, (Mg,Ca,Mn,Fe)O, was crushed into different particle size fractions and exposed over various durations (1 d, 3 d, 9 d, 14 d, 24 d) at a grate to 120 °C hot off-gas with a CO2 content of 25%. However, the total inorganic carbon (TIC) content never increases above the detection limit of 0.5% throughout the experimental duration. The determination of the carbonation depth using phenolphthalein does not reveal a homogeneous carbonation front, but an irregular carbonation. This observation was confirmed by microprobe analyses using elemental mapping. The solubility of the slag increases with increasing carbonation, e.g., the leachability of sulfate increases from 7.8 to 8270 mg/kg dry matter (DM), and of calcium from 940 to 3860 mg/kg DM. The leaching of environmentally relevant element varies: the leachable concentration of molybdenum increases from 0.017 mg/kg DM to 0.089 mg/kg DM, that of chromium remains constant (ca. 0.05 mg/kg DM) whereas that of vanadium decreases from 1.1 to 0.45 mg/kg. In summary, the chosen carbonation technology must be improved to enhance carbonate yield. [ABSTRACT FROM AUTHOR]

Control of carryover slag is essential during transfer of liquid steel from basic oxygen furnace to ladle to maintain preferred steel cleanliness. Carryover slag is oxidising in nature and its higher amount will lead to higher refractory wear rate, low alloy recovery and increased secondary steelmaking treatment time. Measuring the amount of carryover slag is essential for evaluating current tapping practices and implementing necessary precautions when needed. In the present study, a kinetic process model has been developed using FactSage macro processing code. Steel lollipop and slag samples were collected between tapping start and onset of ladle refining process for a medium carbon aluminium killed grade. Liquid steel-slag interaction, flux addition to slag, various metallic additions to steel and refractory dissolution to slag were taken into account in the model. Multiple simulations were performed with varying amounts of carryover slag and composition of steel and slag of initial samples from the ladle furnace were equated with the predicted values from FactSage kinetic model to determine the carryover slag amount. Apart from predicting the carryover slag amount, this model can be useful to understand the effect of tapping parameters on variations in liquid steel and slag chemistry during tapping. [ABSTRACT FROM AUTHOR]

[Display omitted] • BOF slag is an environmental friendly alkalinizing agent for sludge stabilization. • Class A biosolid from sludge was achieved for doses of 4.50gBOF/gTSS 0. • Low C, N and P solubilizations, thus cheapening management cost of liquid fraction. • Low heavy metal mobilizations from sludge and BOF slag during the treatment. This study assessed, for the first time ever, the use of basic oxygen furnace (BOF) slag as alkalinizing material during the sludge conditioning, as an environmentally-friendly alternative to CaO and other conventional alkalis. Its effects on the dewatering, solubilisation and stabilization of sewage sludge were studied, testing increasing dosages of BOF from 0 to 6 gBOF/gTSS 0 at room temperature and under constant mechanical agitation was evaluated. Results revealed that the addition of BOF slag to sewage sludge produced similar degrees of solubilisation to those obtained using lime, reaching a maximum of 34% of total COD for 3.00 gBOF/gTSS 0. The use of BOF slag also involved a low solubilisation of either nitrogen, carbon or phosphorous, a negligible mobilization of heavy metals and a positive effect on its biological hygienisation. A Class A biosolid for doses of 4.50gBOF/gTSS 0 or higher was achieved, which can be applied directly to the soil for agricultural purposes in accordance with current legislation. [ABSTRACT FROM AUTHOR]

Linz‐Donawintz (LD) slag is a solid waste produced during the basic oxygen furnace process of steel making and is more often disposed of on nearby land causing a disturbance in vegetation and human health. Hence, judicial management of LD slag is a need for an hour. For this purpose, the usability of LD slags as a reinforcement material in epoxy composites was investigated in the present work. In this investigation, the physical properties (density, void content, water absorption rate), mechanical properties (tensile properties, flexural properties, compressive strength, hardness), and tribological properties (sliding wear behavior) are reported. From the experimental investigation, it is found that the density, void content, and water intake capacity increase with LD slag loading. The maximum voids present in the composite is 1.92% for epoxy/40 wt. % LD slag composite. Similarly, maximum water uptake of only 0.6% is observed for composite with maximum filler content and for maximum immersion time. Further, it is observed that the strength of composite under tensile and flexural loading was compromised slightly. At 40 wt. % of LD slag, the measured tensile and flexural strength are 20.8 MPa and 28.78 MPa respectively. The strength of composites under compressive loading increases with filler content and reaches a maximum of 108 MPa for epoxy/40 wt. % LD slag composite. The high hardness of filler assists in increasing the hardness of the composites. The hardness of neat epoxy is Shore‐D number 75 which increases to Shore‐D number 84. With increased hardness, ultimately the specific wear rate under dry sliding conditions reduces. Taguchi's L25 orthogonal array having four factors, each at five different levels is implemented to conduct the sliding wear tests. A forecast model is built on an artificial neural network (ANN) which successfully envisages the sliding wear performance of the composite under investigation inside and outside the experimental domain. [ABSTRACT FROM AUTHOR]

The control of slag foam that is produced during the Basic Oxygen Furnace (BOF) process has been the subject of significant research. The behaviour of slag foams is complex. Hence, the control of slag foam in the dynamic process of the BOF is challenging. Acoustic analysis of the BOF is one of the most promising methods for the indirect measurement of slag foam height. This paper reviews different studies on the fundamental behaviour of acoustics in liquid foams and various acoustic studies related to determining the slag foam height during the BOF process. Studies on the BOF have been carried out using both cold water models and plant trials, where acoustic measurements taken directly from the process were analysed. These studies showed that the attenuation of sound through liquid foam was influenced mainly by factors such as viscosity, bubble size, and foam height. Current systems are said to be 70 to 87 per cent accurate in detecting and/or predicting slopping events in the BOF, though there is a lack of systematic data in the literature to fully quantify this accuracy. There have been various attempts to combine sound with vibration and image signals to improve the prediction of slopping events in BOFs. The review substantiates the lack of accuracy of the current systems in determining the slag foam height using acoustic analysis and the need to address fundamental questions about the behaviour of sound in dynamic foam, its reliance on different factors, and the relatability of comparing cold model data to industrial data. [ABSTRACT FROM AUTHOR]

Steel slag is an industrial by product of steel manufacturing processes and has been widely utilized within civil and construction materials for road materials and environmental remediation in countries like Japan, USA, and European Union nations. However, the current utilization of steel slag in Vietnam is very low mainly because of lack of quality control of slag treatment and chances for reuse of treated steel slag. This paper presents the up to date steel slag production status in Vietnam through the extensive survey and sampling at seven large steel factories. The paper also highlights the environmental and quality control issues of these steel slags to use as road construction aggregates by assessing the heavy metals concentration in the leachate. The basic oxygen furnace (BOF) and electric arc furnace (EAF) slag samples were collected to evaluate leaching properties of metals leached from the slags. The two standardized batch leaching tests of steel slag roadbed material in Japan (JIS K 0058-1) and toxicity characteristics leaching procedure (TCLP—EPA method 1311) were performed to the evaluated the hazardous metals. The results of the leaching test show that almost all of the concentration of the metals in the leached solution does not exceed the National Standard for Industrial Wastewater Discharge (QCVN 40-2011). The pH and parameters such as total chromium, nickel, copper, lead, arsenic, and manganese differ from the two test methods. The acidic conditions employed in the EPA 1311 were not representative of condition excepted during slag reuse in road constructions because in the operation condition of the road, acidic liquid is absent. The leaching test results confirmed that JIS test which uses deionized water with gentle mixing prevents the slag sample from size degradation is suitable for the environmental assessment of steel slag use for roadbed material. This research suggests that the adjustment of pH value prior to disposal or reuse as base materials and official guideline should be promulgate by the authorities to ensure the leachate meet the surface water quality standard. [ABSTRACT FROM AUTHOR]

The modification of basic oxygen furnace (BOF) slag by adding silica can improve the properties of BOF slag for applications in the cement industry. The rapid dissolution of silica is essential to hot slag modification. In this work, the dissolution behavior of silica in the molten CaO–SiO2–Fe2O3–MgO–MnO system as synthetic BOF slag was investigated by using the traditional rotating cylinder technique. Effects of rotation speed, temperature, immersion time, and slag basicity on the silica dissolution were studied. Scanning electron microscopy equipped with energy dispersive spectrometer (SEM‐EDS) and FactSage simulations were employed to reveal the dissolution mechanism. It was found that the dissolution of the silica rod was affected by both the thermodynamic driving force and the slag viscosity. The silica dissolution rate in molten CaO–SiO2–Fe2O3–MgO–MnO slag increased with increasing the rotation speed and temperature, but first increased and then decreased when decreasing the slag basicity from 2.5 to 1.5. A linear correlation between the logarithm of the dissolution rate and the logarithm of cylinder periphery velocity with a slope of 0.44 was observed, indicating the mass transfer within the boundary layer as the dissolution rate determining step. A direct dissolution way was found during the dissolution of silica in molten CaO–SiO2–Fe2O3–MgO–MnO slag. [ABSTRACT FROM AUTHOR]

Friction properties of open graded asphalt friction course (OGAFC) mixtures play an essential role in ensuring traffic safety, especially under wet weather conditions. This study evaluated the friction characteristics of basic oxygen furnace (BOF) and electric-arc furnace (EAF) steel slag aggregate incorporated OGAFC mixes. Nine sets of OGAFC mixes were fabricated using five percentage replacements (0%, 25%, 50%, 75%, and 100%) of the coarse natural aggregate fraction by BOF and EAF steel slags. The effect of modified binder type (polymer and crumb-rubber modified) on the frictional characteristics of OGAFC mixes was also examined. The principal friction test devices used were the British pendulum tester and dynamic friction tester. Multiple friction performance aspects were studied: (1) effect of surface condition (dry, wet, and ponding) on the measured friction coefficient; (2) separate evaluation of adhesion and hysteresis friction components; (3) variation of friction coefficient with varying slip speeds, and (4) friction performance later in the OGAFC service life using artificially polished aggregates, and comparison of the performance with unpolished aggregates. Results revealed that the use of steel slags in OGAFC mixes considerably enhanced the frictional characteristics and that the skid resistance of OGAFC-BOF mixes was better than that of OGAFC-EAF mixes. Frictional resistance of the mixes was found to increase with an increase in steel slag content. OGAFC mixes comprising polished steel slag aggregates also showed promising results with the increment in steel slag content. The findings also indicated that OGAFC-CRMB mixes perform better than OGAFC-PMB mixes. [ABSTRACT FROM AUTHOR]

The viscosity of steel slag plays a pivotal role in steelmaking, impacting various aspects of the steelmaking operation and product quality. This paper introduces a novel approach for predicting the viscosity of turndown slag from a basic oxygen furnace using a stacking regression model. The stacking model in this approach incorporates four base models: multiple linear regression (LR), random forest (RF), k-nearest neighbour (KNN) and AdaBoost (ADB), while random forest is selected as a meta-model. The selection of meta-models is done through a systematic framework provided for identifying suitable meta-models in a stacking model. Similarly, the framework also demonstrated the workflow for constructing and evaluating a series of stacking models with different configurations. On the evaluation of 20 stacking models (including two and three-layers), the optimal configuration is found to be LR + KNN with R2 value of 0.993 and the shortest training time. Additionally, a correlation analysis of slag viscosity with composition and temperature is done, which will help the operators of steel melting shops in optimize the steelmaking process based on the required slag viscosity. Ultimately, this study emphasizes the efficacy of optimal-configured stacking regression models in industrial applications, achieving both maximum accuracy and minimal computational time. [ABSTRACT FROM AUTHOR]

The effect of slag composition on the cleanliness of Al-Ti deoxidized interstitial-free steel produced via basic oxygen furnace (BOF)-ladle furnace (LF)-Ruhrstahl-Heraeus (RH)-continuous casting (CC) process was investigated by the systematic samplings and analyses for four heats in a steel plant in China. Oxygen/nitrogen analyzer, automatic scanning electron microscope, field-emission scanning electron microscope, and energy spectroscopy analysis were used to analyze the variations of number, size, type, and morphology of inclusions in molten steel from RH to tundish, and X-ray fluorescence was used to analyze the slag composition. The relationship between slag composition and inclusion characteristics in molten steel was investigated. The effect of slag composition on the oxygen mass transfer from the slag–metal interface to liquid steel was also studied through a theoretical calculation. The results showed that the cleanliness of molten steel was greatly affected by the slag composition. The deterioration of steel cleanliness was mainly arisen from a serious reoxidation of molten steel by oxidizing components like (T.Fe + MnO) in top slag during RH refining process. A weak ability to absorb inclusions of top slag with high CaO/Al2O3 and CaO/SiO2 mass ratios was confirmed from the inclusions analyses. The size and number of Al2O3 inclusion clusters were larger, and Ti content in Al2O3-TiO x inclusions was higher from RH to tundish in the case of serious reoxidation. The reduction of FeO content and keeping the CaO/Al2O3 and CaO/SiO2 ratios at about 1.6 and 4–7, respectively, in top slag during RH refining process was beneficial to minimize the reoxidation of Al and Ti and increase the inclusion absorption ability of top slag. [ABSTRACT FROM AUTHOR]

Carbonation treatment is one of the most promising methods to improve the volume stability of basic oxygen furnace (BOF) slag, but the reasons for the reduced activity of heavily carbonated BOF slag have been rarely investigated. This study prepared carbonated BOF slag under the condition of CO 2 concentration at 99 % and pressure at 3.0 MPa, and evaluated its activity through various methods. The mechanism behind activity inhibition was revealed. Results showed that the maximum CO 2 sequestration of BOF slag was 13.4 % within 3 h. Highly carbonated BOF slag exhibits lower hydration activity than uncarbonated slag, with a 15.9 % decrease in strength activity index and a 61.0 % reduction in cumulative hydration heat release. After carbonation treatment, a 1–5μm thick CaCO 3 barrier layer accumulates on the surface of BOF slag, affecting slag hydration even with accelerated hydration. This barrier layer inhibits the efflux of internal calcium ions and can persist long-term during the hydration without being affected. Furthermore, carbonation treatment increased the leaching risk of heavy metal ions, particularly Mn, by 175-fold. • Highly carbonated BOF slag has lower hydration activity compared to uncarbonated slag. • A CaCO 3 barrier layer forms on the surface of carbonated BOF slag, impacting hydration. • The barrier layer inhibits the leaching of calcium ions. • Alkalinity decrease in carbonated BOF slag increases leaching risk of heavy metal ions. [ABSTRACT FROM AUTHOR]

This study investigated the effectiveness of tartaric acid treatment in inhibiting the expansive behaviour of basic oxygen furnace (BOF) steel slag, aiming to optimize its utilization as a sustainable replacement for natural coarse aggregate in concrete. Tartaric acid-treated steel slag (TTSS) and non-tartaric acid-treated steel slag (NTSS) were comprehensively characterized for particle size and shape properties, physical and mechanical behaviour, and durability aspects including MgO stability factor and iron unsoundness. Chemical, morphological, mineralogical, and microstructural analyses were conducted using XRF, SEM-EDS, XRD, FT-IR, and optical microscopy, elucidating the impact of tartaric acid treatment. Compressive strength tests were then performed with TTSS incorporation levels of 30 %, 40 %, 50 %, and 0 % as reference batch (RB). As a result, TTSS showed 7.44 % and 10.92 % better physical and mechanical properties than NTSS respectively. Whereas on durability aspects, TTSS depicts 40 % better results on iron unsoundness and 36.43 % higher water absorption over NTSS. Furthermore, a maximum compressive strength of 44 MPa was achieved with a significant improvement of 15.80 % from RB. Additionally, TTSS aggregate-based cement concrete exhibited a denser microstructure and improved performance. This work highlights the potential of BOF steel slag as an aggregate resource, contributing to a circular economy and mitigating the environmental burdens associated with traditional aggregate production. [Display omitted] • Treated steel slag aggregate significantly improves the volumetric stability. • Steel slag tartaric treatment showed better or comparable key aggregate properties. • Achieved 50 % replacement of conventional aggregate with the treated aggregate. • Sustainable and eco-friendly approach towards steel slag solid waste management. [ABSTRACT FROM AUTHOR]

• The physical transformation of slag particles with residue carbon was in-situ observed. • The distributions of carbon and ash in slags determine the transformation features. • Carbon residue can wrap the molten phase, maintaining the original particle morphology. • The carbon-thermal reactions increase the refractory phase and thus the flow temperature. The ash residue after gasification in the coal gasifier contains a certain proportion of residual carbon, which exerts a significant effect on the slag properties such as sintering, melting, and flow within the furnace. The residues discharged outside the gasifier retain the distribution patterns of ash and residual carbon under gasification conditions. This study selected coarse and fine residues generated from an entrained-flow gasifier and investigated the transformation of slags with different carbon contents during heating process. The obtained ash residues underwent characterization to determine the modes of the compositions occurrence. Subsequently, ash residues with different carbon contents were observed for the sintering-melting processes with a high-temperature confocal scanning laser microscope (CSLM). With the aid of FactSage, the physicochemical transformation of slag particles was determined. The impact of residual carbon on particle characteristics manifests in both physical structure and chemical reactions. On one hand, residue residual carbon can act as a skeleton during the melting process, causing the molten phase to enter the pores of porous carbon, intensifying particle shrinkage. After the inorganic components melt, the liquid encapsulated by carbon retains the original particle shape. On the other hand, the carbon can react with the inorganic ash components. If the carbon content is less than 6%, a new Fe x Si with a high ash melting point can be formed. As the carbon content increases, the carbon reacts with the Si to form SiC. This implies a reduction in the liquid content. Therefore, the flow temperature is greatly delayed by an increase in carbon content above 14%. [ABSTRACT FROM AUTHOR]