BOF Slag Research Articles

Effect of Carbonation Degree on Mineral Composition, Microstructure, and Cementitious Properties of BOF Slag

Effect of Carbonation Degree on Mineral Composition, Microstructure, and Cementitious Properties of BOF Slag

Clinker-Free Cement Manufactured with Metallurgical Slags

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.

Mechanical, Rheological, and Microstructural Study of Ternary Alkali-Activated Pastes Using BOF Slag, Metakaolin, and Glass Powder as Precursors

Mechanical, Rheological, and Microstructural Study of Ternary Alkali-Activated Pastes Using BOF Slag, Metakaolin, and Glass Powder as Precursors

Metallurgical slag used for efficient growth of Chlorella pyrenoidosa to achieve CO2 conversion to biodiesel

AbstractMetallurgical slag such as solid waste generated in the steel industry carries environmental pollution risks, but it is rich in nutrients required by microalgae. Metallurgical slag used for carbon capture and biomass energy conversion has multiple benefits: (i) reduction and harmless treatment of metallurgical solid waste, (ii) assisting in carbon neutrality by efficient carbon fixation, and (iii) production of biodiesel from CO2. In this study, AOD, BOF, BFS, HVS, and VTS slag were applied to culture Chlorella pyrenoidosa (C. pyrenoidosa) with the regulation of growth, carbon fixation, and lipid synthesis. An excellent fixed amount of CO2 with 94.59 mg is obtained from C. pyrenoidosa biomass at BOF slag added (mass ratio of CO2 captured/microalgae/slag with 1.99/1.00/10.53) since high Ca/Mg mass ratio of 419 (8.38 mg/L Ca and 0.02 mg/L Mg), no Cr and low concentration of Al (0.04 mg/L) contribute to regulating antioxidant enzyme activity (SOD and POD) to resist ROS and improving PEPC activity to reduce carbon flux toward lipid to promote biomass synthesis. Both metal concentrations from Ca (5.86 mg/L), Mg (0.05 mg/L), Al (0.42 mg/L), and Cr (0.006 mg/L) and suitable pH (10.53) in AOD leaching solution at solid/liquid ratio of 0.5 g/L change carbon flow toward efficient lipid synthesis (47.07 wt%) by continuously providing raw materials and energy by regulating ACC, ME, and PEPC activities. High value‐added biodiesel with high concentrations of C16 and C18 methyl esters from lipid of C. pyrenoidosa is achieved, following other ecological and economic benefits including 197 mg CO2 captured and 2198 mg AOD applied with harmless. In this study, C. pyrenoidosa is cultured with elements from metallurgical slag solid waste, which promotes C. pyrenoidosa efficient carbon fixation to assist in carbon neutrality, and provides guidance for CO2 conversion to high‐value‐added products with low cost.

Accelerated carbonation and stabilization of BOF slag: data fitting relationship between particle size and CO2 sequestration

Carbonation of BOF slag offers a promising solution to reduce f-CaO content and simultaneously capture CO2. This study investigated the influence of particle size on f-CaO consumption and CO2 sequestration of BOF slag while exploring the kinetics of the carbonation process. Under optimum conditions, the finest particle size achieved f-CaO consumption and CO2 sequestration values reaching 99.72% and 5.57%, respectively; whereas the largest particle size exhibited values of 97.89% and 3.4%, respectively. The shrinking core model accurately described the carbonation process with internal diffusion identified as the rate-limiting step for the whole process. The transition point between two rate-limiting steps was determined along with an established equation between particle size, CO2 sequestration and time. The XRD patterns and SEM images illustrated morphological changes in slag before and after carbonation. These findings can provide crucial insights for optimizing the carbonation process and facilitating its utilization as cementitious materials.

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.

A Study on the Production of Low-heat Cement Using Non-carbonate Raw Materials with 5% Substitution of Limestone

This study aims to produce low heat cement by substituting limestone, the main raw material of cement, with non-carbonate raw materials for 2050 carbon neutrality. The use of non-carbonate raw materials can reduce CO<sub>2</sub> generated by the calcination of limestone and reduce the amount of energy required for the calcination. The non-carbonate materials reviewed in this study are BOF slag, KR slag, and blast furnace slag with a CaO content of more than 40%. Compared to limestone, non-carbonate materials have lower grindability and higher Fe<sub>2</sub>O<sub>3</sub> and Al<sub>2</sub>O<sub>3</sub> content, which limits their ability to substitute limestone. By applying the chemical composition of non-carbonate raw materials and applying a low heat cement modulus to calculate the clinker raw material mixture, it was possible to calculate a raw material mixture that substitutes 5% limestone. The raw materials were mixed in the laboratory, fired to produce clinker, and mixed grinding of the fired clinker and gypsum to produce low-heat cement. The chemical and physical properties of the cement produced using the non-carbonate raw materials were evaluated and found to meet the KS standard. In the future, the use of non-carbonate raw materials to substitute limestone is expected to contribute significantly to the reduction of CO<sub>2</sub> emissions in the cement industry.

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.

Fly Ash and BOF Slag as Sustainable Precursors for Engineered Geopolymer Composite (EGC) mixes: A Strength Optimization Study

Fly Ash and BOF Slag as Sustainable Precursors for Engineered Geopolymer Composite (EGC) mixes: A Strength Optimization Study

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.

Co-modification of BOF Slag and Copper Slag to Recover Valuable Metals by Carbothermal Reduction

Co-modification of BOF Slag and Copper Slag to Recover Valuable Metals by Carbothermal Reduction

Citric Acid Leaching of Industrial BOF Slags

About 800,000 t of BOF slag are generated per year during the steel production process by Austrian steel plants of voestalpine. Austrian legislative authorities restrict the use as recycling construction material in road building to the bituminous binder course, which additionally includes a lifetime responsibility of the producer for possible future contaminants that currently have not been considered.Alternative routines of recycling of BOF slag are thus addressed in a project of K1-MET within the COMET funding program of the Austrian Research Promotion Agency (FFG), financed by the Austrian government and industry. Selective leaching processes are investigated by the Chair of Mineral Processing, Montanuniversität Leoben to recover the iron bearing oxides contained in the slag (i.e. magnesio wuestite, Ca- and Mg ferrites) with the lowest amount of phosphorous possible, which is contained in larnite (dicalciumsilicate) only.Common mineral processing methods obtained only poor results due to intergrowth conditions. Selective leaching of P containing larnite by citric acid may provide an alternative.Systematic tests for optimum leaching conditions concerning optimum mass ratio of agent to industrial slag, volume of eluate, leaching time, leaching temperature, and pH were performed. As the acid consumption is comparatively high, a special effort was spent on the regeneration of citric acid.

Thermodynamics and Kinetics on Hot State Modification of BOF Slag by Adding SiO2

Thermodynamics and Kinetics on Hot State Modification of BOF Slag by Adding SiO2

Recovery of phosphorus from steelmaking slag and phosphate tailings by a collaborative processing method

To efficiently recover phosphorus from industrial solid wastes, the collaborative processing of P-bearing steelmaking slag and phosphate tailings was proposed. Steelmaking slag and phosphate tailings were remelted to make P enrich in a specific mineral phase and then selective leaching was adopted to separate the P-concentrating mineral phase. The P-concentrating leachate can be used to recover calcium phosphate by chemical precipitation. It shows that the P was mainly concentrated in the dicalcium silicate after remelting of steelmaking slag and phosphate tailings and it could be selectively leached. When the mass ratio of the original BOF slag to phosphate tailings was 7:3, the mixed slag with basicity of 2.3 was obtained. The dissolution efficiency of P from this mixed slag reached 89.2% whereas Fe was barely leached at pH 1. The residue containing 68.6% FetO and 15.6% MgO can be reused in the metallurgical process. When the pH of leachate was adjusted to 7, more than 89.3% of phosphate ions precipitated in the form of calcium phosphate, and the obtained precipitate containing 28.8% CaO, 19.8% P2O5, and 47.2% SiO2, could be a potential P-Si fertilizer. The total recovery ratio of P from mixed slag was approximately 80% and other components could be reused in steel plants, achieving the comprehensive utilization of steelmaking slag and phosphate tailings.

Improving the efficiency of steelmaking slag processing at PJSC “MMK”

This paper assesses the efficiency of metallurgical slag processing at PJSC “MMK” in LLC “Slagservice”, which indicates the need to improve it in terms of increasing the degree of extraction of iron from slag. Proposals for improving the existing technology of steelmaking slag processing and the development of new technologies have been developed. An assessment of the efficiency of the metallurgical slag recycling at LLC “Slakservice” in 2019 is given. Ways to improve the efficiency of steelmaking slag processing in the conditions of existing production are presented. The description of the experimental setup for testing the basic principles of the proposed technology is given. The method of metallurgical slag processing was used in laboratory conditions, it corresponds to the existing technology of metallurgical slag processing in LLC “Slakservice”, including slag crushing, classification by size, metal separation by screening and magnetic separation.It is established that the method of separation of slag-metal conglomerate can be used in industrial conditions. The method of assessing the efficiency of metallurgical slag processing through the degree of extraction of metal-containing components from the slag was used for processing the results. A method of improving the existing technology of steelmaking slag processing is proposed, which includes increasing the content of metallic iron in the current converter slag by means of liquid-phase reduction of iron oxides using coal. The method of increasing the content of metallic iron in the current BOF slag in slag bowls using movable reactors is proposed. This method makes it possible to increase the content of metallic iron in the current BOF slag by about two times, which contributes to increasing the efficiency of magnetic separation at the stage of secondary slag processing.

Tiempo de configuración y propiedades mecánicas de cementos de ceniza / escoria activados con álcali curados a temperatura ambiente

El objetivo de este trabajo es investigar el comportamiento del estado fresco y endurecido de las pastas cementosas activadas con álcali obtenidas de la mezcla de cenizas de fondo/escoria BOF y cenizas volantes/escoria BOF. Para el propósito, se evaluaron las propiedades en el fresco y estado endurecido. Se produjeron diez pastas en dos sistemas separados, cuyas proporciones entre cenizas y escoria BOF fueron 100: 0, 75:25, 50:50, 25:75 y 0: 100 (cenizas volantes o cenizas de fondo: escoria BOF). En general, la adición de escoria de acero BOF actúa acelerando los tiempos de configuración, a temperatura ambiente de curado. Además, las curvas tensión-deformación demostraron que las cenizas pesadas y la escoria de acero BOF favorecen el comportamiento dúctil en tensión axial. Además, la adición de escoria BOF puede influir en las propiedades en estado fresco y endurecido. Por tanto, es factible utilizar escoria de acero combinada con ceniza de carbón en mezclas binarias alcalinas activadas.

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

Mineral Carbonation of Basic Oxygen Furnace Slags

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.

Effect of BOF Slag Modification on the Dissolution Behavior of Phosphorus from Practical Dephosphorization Slag

Effect of BOF Slag Modification on the Dissolution Behavior of Phosphorus from Practical Dephosphorization Slag