Basic Oxygen Furnace Slag Research Articles

Effect of gypsum on the hydration of fused cement clinker from basic oxygen furnace slag

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.

High Efficacy Two-Stage Metal Treatment Incorporating Basic Oxygen Furnace Slag and Microbiological Sulfate Reduction.

Lignocellulosic sulfate-reducing biochemical reactors (SRBRs) can be implemented as passive treatment for mining-influenced water (MIW) mitigating the potentially deleterious effects of MIW acidic pH, and high concentrations of metal(loid)s and SO42-. In this study, a novel two-stage treatment for MIW was designed, where basic oxygen furnace slag (slag stage) and microbial SO42- reduction (SRBR stage) were incorporated in series. The SRBRs contained spent brewing grains or sugarcane bagasse as sources of lignocellulose. The slag reactor removed >99% of the metal(loid) concentration present in the MIW (130 ± 40 mg L-1) and increased MIW pH from 2.6 ± 0.2 to 12 ± 0.3. The alkaline effluent pH of the slag reactor was mitigated by remixing slag effluent with acidic MIW before SRBR treatment. The SRBR stage removed the bulk of SO42- from MIW, additional metal(loid)s, and yielded a circumneutral effluent pH. Cadmium, copper, and zinc showed high removal rates in SRBRs (≥96%) and likely precipitated as sulfide minerals. The microbial communities developed in SRBRs were enriched in hydrolytic, fermentative, and sulfate-reducing taxa. However, the SRBRs developed distinct community compositions due to the different lignocellulose sources employed. Overall, this study underscores the potential of a two-stage treatment employing steel slag and SRBRs for full-scale implementation at mining sites.

Utilizing mineral sequestration technology for enhanced performance of concrete containing basic oxygen furnace slag

Basic oxygen furnace slag (BOFS) is a widely available by product of the steel-making industry that poses high interest for scientists in various fields. The carbon capture potential of BOFS is proven to be high. However, its further uses are actively investigated. BOFS is particularly attractive as a construction material due to its hydraulic reactivity and good strength, making it suitable for use as binding material and aggregate in concrete. However, it has a major drawback - unstable compounds that lead to material deterioration caused by volumetric expansion. Most of the research in the field focuses on the processing of BOFS in laboratory or industrial settings to eliminate the expensive products inside the slag and make it more durable. The suitability of using mineral sequestration technology instead of artificially accelerated carbonation has not yet been studied well. This research aimed to identify the main properties of the mortar mixes containing BOFS that underwent mineral sequestration over a long period to assess the technology’s feasibility. The correlation with quantitative data from thermogravimetric analysis (TGA) was also identified. Based on test results, the correlation between aging conditions and CO2 uptake was established, indicating that stockpiled and wet/dry cycle conditions were the most optimal aging methods for BOFS to achieve the highest carbonation (4.15-5.15%), hence the maximum stabilization degree of aggregates.

Leaching Characteristics of Heavy Metals from Asphalt Mixture with Basic Oxygen Furnace Slag as Aggregate

Abstract Basic oxygen furnace (BOF) slag, which has good mechanical properties, can be recycled as pavement materials. However, BOF slag contains several kinds of heavy metals. Batch leaching tests are usually conducted to investigate the leaching characteristics of asphalt mixture with BOF slag, which has a few limitations. In this article, the leaching characteristics of heavy metals were investigated through the column leaching test device self-designed in the laboratory. The factors that influence the leaching of heavy metals were evaluated. The experimental results indicate that high-basicity BOF slag that has high content of free calcium oxide (f-CaO) can effectively inhibit the leaching of heavy metals from asphalt mixture. Copper and nickel have no leaching risk in neutral and weakly acidic conditions. However, zinc and lead in asphalt mixture with medium-basicity BOF slag have a risk of causing environmental implication in long-term leaching process. Moreover, covering of asphalt inhibits the leaching of f-CaO and hinders the contact between heavy metals and the leachant at the same time. The conclusions of this article provide a theoretical basis for the green application of BOF slag as an asphalt pavement material.

Utilization of air granulated basic oxygen furnace slag as a binder in belite calcium sulfoaluminate cement: A sustainable alternative

Basic oxygen furnace (BOF) slag negatively impacts ordinary Portland cement performance when replacement levels exceed 5%. This necessitates the exploration of alternative applications for the slag. Simultaneously, a high-volume slag utilization is desired to benefit slag recycling as supplementary cementitious materials. Therefore, this study aims to optimize the air granulated BOF slag substitution potential in belite calcium sulfoaluminate cement by investigating the hydration products in standard mortar. The reactivity of the novel binder is correlated with workability, and mechanical performance by thermal, mineralogical, and microstructure analysis. Consequently, the 10–30% replacement delays the final setting time by inhibiting the ettringite formation leading to a decrease in mechanical performance till 28 days. At later ages (28–180 days), the 30–50% substitution exhibited the synergy in mechanical performance, which is attributed to the hydrogarnet, calcium silicate hydrate, and strätlingite formation. Moreover, all the mortar samples exhibited heavy metals’ leaching and drying shrinkage below the permissible limit.

Swelling Behavior of Basic Oxygen Furnace Slag and Granulated Blast Furnace Slag Mixtures: A Laboratory Investigation

Swelling Behavior of Basic Oxygen Furnace Slag and Granulated Blast Furnace Slag Mixtures: A Laboratory Investigation

Synthesis and Evaluation of Geopolymer Mixtures Containing Chronologically Aged Basic Oxygen Furnace Slags

Applying industrial by-products as a substitution for conventional construction materials (natural resources) is a superior solution for the environment in terms of waste management and reduction in greenhouse emissions and for the construction industry in terms of cost and expenditure. Applying basic oxygen furnace slag (BOFS), one of the metallurgical industry by-products, as a construction material can be a high-potential and promising idea. However, the utilization of BOFS in construction applications is considerably limited because of its inherent characteristics leading to volumetric expansion behavior caused by the chemical reaction between free lime (f-CaO) and water. This study used geopolymer technology to stabilize the expansive behavior of chronologically aged BOFS aggregates. The compressive strength, expansion behavior, and drying shrinkage characteristics of a normal ordinary Portland cement (OPC) mixture and a geopolymer mixture containing siliceous river sand and chronologically aged BOFS aggregates were investigated. The test results showed that the compressive strength of geopolymer mixtures containing chronologically aged BOFS aggregate achieved 64.02 MPa, and the expansion behavior of geopolymer mixtures was improved compared with normal OPC mixtures containing the same BOFS aggregates, reaching 0.02% and 0.44%, respectively. However, due to the air-curing method, geopolymer mixtures had higher drying shrinkage values than normal OPC mixtures. Therefore, further studies should be conducted to investigate how to control the drying shrinkage of geopolymer mixtures containing chronologically aged BOFS aggregate.

Synergistic effect from combined use of scrap-recycling slag and hydrated lime to stabilize Pb and Zn in highly contaminated soil.

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.

Synergistic treatment of blast furnace slag and basic oxygen furnace slag for efficient recovery of iron: Phase transformation and oxidation mechanisms

In light of the steel industry's rapid advancements, the availability of high-quality mineral resources is diminishing. Therefore, the recovery of iron from BOF slag is of great significance to the sustainability development. Considering the compositional characteristics of BOF slag, the transformation of the iron-containing phase into (Mn,Mg)yFe3-yO4 is the key step. Thus, a novel process for recovering iron resources by synergistic treatment of blast furnace slag (BFS) and BOF slag was proposed. This research employed FactSage thermodynamic simulation, XRD, SEM-EDS, XPS, and EPMA to analysis the impact of BFS addition (10–50 %), cooling methods (from water-cooling to furnace-cooling), and temperature (1400–1600 °C) on phase transformation and the RO oxidation mechanism, and the conditions of (Mn,Mg)yFe3-yO4 generation and enrichment was obtained. The results show that at BFS addition of 30 %, reaction temperature 1400 °C and furnace-cooling, the iron-containing phase (Ca2Fe2O5 and RO) was almost completely transformed into (Mn,Mg)yFe3-yO4. The oxidation mechanism of RO was formation of (Mn,Mg)yFe3-yO4 by cation diffusion. Under optimal conditions, the iron recovery rate and the grade reached 65.74 % and 32.07 %, respectively, which can be used as raw material for ironmaking. Meanwhile, the main phase of the tailing slag was β-Ca2SiO4, without f-CaO, which has the potential to be used in the cement and concrete industries with the advantages of both low cost and eco-friendly. Therefore, the process with green, efficient and low cost was provided, which is a feasible idea for the comprehensive utilization of industrial solid waste.

A Bogue approach applied to BOF slag

AbstractAn 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.

Mechanical Properties and Microscopic Mechanism of Basic Oxygen Furnace (BOF) Slag-Treated Clay Subgrades

Civil engineering faces a substantial challenge when dealing with soft and compressible clayey soils. Conventional soil stabilization techniques involving ordinary Portland cement (OPC) result in notable CO2 emissions. This study explores the utilization of basic oxygen furnace (BOF) slag, a by-product of steel production, for strengthening kaolin clay. This research investigates the influence of BOF slag particle size, BOF slag content, and the use of activators such as lime and ground granulated blast-furnace slag (GGBFS) on the stabilization of kaolin clay. The strength development is assessed through unconfined compressive strength (UCS) test, bender element (BE) test, and scanning electron microscopy (SEM). The findings reveal that higher BOF content and extended curing periods enhance soil strength, and lime and GGBFS effectively augment the stabilizing properties of BOF slag. Stabilizing kaolin clay with a 30% BOF/GGBFS mixture in a 50/50 ratio with 1% lime and curing for 7 days yielded a compressive strength of 753 kPa, meeting the Federal Highway Administration’s requirement for lime-treated soil. These combined measures contribute to developing a more robust and stable material with enhanced geotechnical properties.

Elemental Concentrations of Natural Graphite and Steelmaking Slag: Development of Microwave-Assisted Acid Digestion

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.

A Bogue approach applied to basic oxygen furnace slag

Basic oxygen furnace (BOF) slag is an industrial by-product of the steel industry and has recently been investigated intensively for high-end applications other than road load and land fill. However, to be applied as a high-end raw material BOF slag lacks a quick and simple quantitative phase analysis method compared to the Bogue approach applied to ordinary Portland cement. This study presents a method to calculate the main phases of BOF slag (C2S, C2(A,F), magnetite (Ff), RO-Phase and f-C) based on chemical composition. A quantitative model assessment was performed in order to further improve the model and two approaches were used to validate the Bogue BOF slag model. One approach compared the calculated chemical composition of phases with real data the second one evaluated whether the Bogue BOF slag model gives comparable quantitative model assessment measures compared to the classical cement Bogue approach. Both approaches validated the proposed final model.

Metal Deportment in Complex Secondary Raw Materials: The Case of Vanadium in Basic Oxygen Furnace Slags

With the increasing demand for metalliferous and mineral raw materials and the consequent depletion of the global natural resource base, the possible utilization of secondary raw material sources is receiving more and more attention. In the present study, we present results from a detailed vanadium deportment study of three basic oxygen furnace slag (BOS) samples known to containing elevated bulk concentrations of vanadium. Complementary analytical methods that were used to quantify the abundance and composition of V-containing phases include SEM-based automated mineralogy, X-ray fluorescence analysis, and X-ray powder diffraction as well as electron probe microanalysis. The vanadium deportment was quantified using Monte-Carlo simulations of the data obtained from automated mineralogy and electron microprobe analysis. The total V concentrations identified by XRF are between 1.7 and 2.2 wt.% V. The most important hosts of vanadium are larnite-, brownmillerite- and portlandite-solid solutions. In two samples Ca carbonates also significantly contribute to the V deportment, while wuestite, lime, and native iron do not contribute significantly to the vanadium deportment. A thorough consistency check identifies considerable uncertainties in the density of the V-bearing phases as the most likely reason to explain remaining discrepancies between measured and calculated V values.

Physical, mechanical, chemical, and environmental characterization of stockpiled BOF slag as railway ballast material

Crushed stone from natural sources is commonly used as ballast in railways. The material is a good ballast, but its extraction is destructive. Therefore, this study characterizes basic oxygen furnace (BOF) slag as an alternative material for railway ballast in Kazakhstan with respect to physical, mechanical, chemical and environmental properties. The characterized BOF slags are of two types (top and bottom) with 10 years minimum age. Grain size distribution, specific gravity, absorption capacity, flakiness, lightweight particles, and 3D image analysis for forms and angularity were used for physical characterization. These BOF slags were found to have high specific gravity and a predominantly spherical shape, with larger particles displaying lower sphericity and greater angularity than smaller ones. The mechanical characterization of the BOF slag were carried out using various methods, including LA abrasion, Micro-Deval, aggregate crushing value, aggregate impact value, volumetric expansion, and fouling. BOF slag aggregates demonstrated exceptional strength with good resistance to fragmentation, crushing, surface abrasion, and sudden loading. The expansion rate is considerably lower than the standard limit, and the fouling rate is better than limestone and similar to granite. X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were all used for chemical characterization. Both BOF slags contain CaO and Fe2O3 with a high peak of SiO2 and portlandite, which suggests that most of the free lime has undergone hydration due to the natural aging of the BOF slag. Regarding the environmental characterization, the tests employed were organic impurity, freeze and thaw, and sodium-based soundness. No organic impurity was observed in the BOF slag, and the BOF slag demonstrated good resistance to weathering and degradation. The characteristics of the investigated BOF slag obtained from laboratory testing were analyzed to confirm its performance for implementation in railway ballast in compliance with the specific requirements, primarily the GOST standard, which is commonly employed in Russia and former Soviet republics, including Kazakhstan. As a result, both BOF slags demonstrated total compliance with the specifications, and the possibility of using stockpiled BOF slag for railway ballast material in Kazakhstan was established.

Evaluation of properties of energy-efficient geopolymer cellular concrete containing basic oxygen furnace slag aggregate

In north-western Kazakhstan, there is a higher demand for energy-efficient construction materials such as cellular concrete in the construction industry due to severe weather conditions. Moreover, construction industries in Kazakhstan are looking into developing new construction materials utilizing industrial by-products. Unlike blast furnace slag (BFS), utilization of basic oxygen furnace slag (BOFS) is limited due to its chemical composition and volumetric instability mainly caused by f-CaO and f-MgO. This study developed a total of nine energy-efficient geopolymer mixtures (3-normal geopolymer mixture and 6-geopolymer cellular concrete). Mix design variables included a partial substitution of river sand (RS) with BOFS aggregate (0%, 50%, and 100%) and three different percentages of a foaming agent (0%, 25%, and 50%). The properties of geopolymer mixtures were evaluated in terms of compressive strength, hardened density, expansion behavior, and thermal conductivity. Test results presented that replacing RS with 50% BOFS aggregates decreased compressive strength, while replacing sand with 100% BOFS aggregate led to increasing the strength regardless of the geopolymer mixture type. Geopolymer cellular concrete had lower compressive strength and thermal conductivity compared to the normal geopolymer mixture due to a higher porous cellularity structure and satisfied the threshold value of expansion due to converting f-CaO and f-MgO to CaSiO3 and MgSiO3 and absorbing the expansion stress by cellular structure.

Geopolymer as a key material to utilize basic oxygen furnace slag (BOFS) as an aggregate

Geopolymer as a key material to utilize basic oxygen furnace slag (BOFS) as an aggregate

Exploring public risk perception and its impact on the acceptance of basic oxygen furnace slags used in artificial reefs

The issue of sea desertification has gradually emerged, and some scientists believe that it is caused by a decrease in the concentration of iron ions in seawater. Based on practical experience in Japan and South Korea, it has been found that the components of calcium, iron, phosphorus, and silicon in slag (Basic oxygen furnace slag, BOF slag) can provide nutrients needed for algae growth. Making artificial reefs from slag can be beneficial for raising overall marine productivity. The annual output of slag in Taiwan is about 1.6 million tons. In line with the circular economy policy, utilizing slag in artificial reefs to improve the marine environment is being promoted, which also achieves policy objectives. This study investigates the concept of risk perception on public acceptance of the policy to transfer slag into artificial reef construction. Finally, the research suggests that by utilizing scientific communication to enhance knowledge transfer, and leveraging mainstream and emerging social media as channels of communication between the public and decision-makers, citizen participation and information disclosure can be promoted, which would be beneficial for public acceptance of utilizing slag in the marine environment.

Motion and dispersion characteristics of graphite particles in a bottom-blown converter for molten slag reduction

In order to improve the recovery of iron resource in molten basic oxygen furnace (BOF) slag through carbothermal reduction, bottom blowing argon gas is used to promote the mixing efficiency between molten slag and graphite particles in the converter. In the present work, computational fluid dynamic-discrete particle model (CFD-DPM) method coupled with the reduction kinetic model of FeO in molten slag by graphite particle is employed to simulate the multiphase system composed of molten slag, graphite particle and argon gas. The motion and dispersion characteristics of graphite particles in a bottom-blown converter were mainly investigated, and the decrease of graphite particle diameter caused by the reduction reaction was considered. A particle dispersion index was also proposed to evaluate the distribution uniformity of graphite particles in the molten slag. In addition, the effects of initial particle diameter and bottom tuyere arrangement on the dispersion characteristics of graphite particles were further discussed. The results show that the proportion of large-sized particles is higher in the inactive-flow zone and the motion trajectory of graphite particles can be divided into two regimes. Graphite particles with an initial diameter of 5 mm and the converter with six bottom-blown tuyeres are more conducive to the homo-dispersion of graphite particles.

Characterizing Chronologically Aged Basic Oxygen Furnace Slags as Aggregates and Their Use in Asphalt Concrete Mix as Filler

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.