Phosphorus adsorption efficiency and characteristic analysis of basic oxygen furnace slag

Basic oxygen furnace slag (BOFS) is a high-volume waste resulting from the production of steel from pig iron. Due to its high free lime content, BOFS is difficult to recycle and/or include into conventional cement systems. Alkali-activation technology offers a pathway to transform industrial wastes such as BOFS into low-carbon cements. Alternative precursors for cement systems are needed as the reliance on commonly used materials like ground granulated blast furnace slag (GGBFS) is becoming unsustainable due to decreasing availability. This study investigates alkali-activated cements incorporating 20 and 30 wt.% of naturally weathered BOFS as a replacement for GGBFS, in both sodium silicate- and sodium carbonate-activated systems. A fraction of BOFS subject to mechanical activation is compared against the untreated BOFS in the 20 wt.% systems. It is observed that in naturally weathered BOFS, a significant portion of the free-lime is found to convert to portlandite, which accelerates alkali-activation kinetics. In sodium silicate-activated systems, the high pH of the activator results in incomplete reaction of the portlandite present in BOFS. The sodium carbonate-activated system shows near complete conversion of portlandite, causing an acceleration in the kinetics of reaction, setting, and hardening. These findings confirm the viability of sodium carbonate activated GGBFS-based systems with only a minor loss in strength properties. BOFS can be utilised as a valuable cement additive for the production of sustainable alkali-activated cements utilising sodium carbonate as a less carbon-intensive activator solution than the more commonly used sodium silicate. Mechanical activation of BOFS offers further optimisation potential for alkali-activation.

The mineral carbon sequestration capacity of basic oxygen furnace (BOF) slag offers great potential to absorb carbon dioxide (CO2) from landfill emissions. The BOF slag is highly alkaline and rich in calcium (Ca) containing minerals that can react with the CO2 to form stable carbonates. This property of BOF slag makes it appealing for use in CO2 sequestration from landfill gas. In a previous study, CO2 and CH4 removal from the landfill gas was investigated by performing batch and column experiments with BOF slag under different moisture and synthetic landfill gas exposure conditions. The study showed two stage CO2 removal mechanism: (1) initial rapid CO2 removal, which was attributed to the carbonation of free lime (CaO) and portlandite [(Ca(OH)2)], and (2) long-term relatively slower CO2 removal, which was attributed to be the gradual leaching of Ca2+ from minerals (calcium-silicates) present in the BOF slag. Realising that the particle size could be an important factor affecting total CO2 sequestration capacity, this study investigates the effect of gradation on the CO2 sequestration capacity of the BOF slag under simulated landfill gas conditions. Batch and column experiments were performed with BOF slag using three gradations: (1) coarse (D50 = 3.05 mm), (2) original (D50 = 0.47 mm), and (3) fine (D50 = 0.094 mm). The respective CO2 sequestration potentials attained were 255 mg g-1, 155 mg g-1, and 66 mg g-1. The highest CO2 sequestration capacity of fine BOF slag was attributed to the availability of calcium containing minerals on the slag particle surface owing to the highest surface area and shortest leaching path for the Ca2+ from the inner core of the slag particles.

The purpose of this study was to recycle basic oxygen furnace (BOF) slag in the production of autoclaved aerated concrete (AAC), and to examine the influence on the properties of AAC products. The magnetic substances in the BOF slag accounted for about 15 wt.% and the magnetic proportion increased as the particle size decreased. The nonmagnetic portion of the BOF slag was acquired by a magnetic separation process and its major constituents were Ca (~42 wt.% as CaO) and Si (~35 wt.% as SiO2), which are the essential elements of AAC. When using the BOF slag for AAC production, the bulk density and compressive strength of the specimens decreased as the amount of slag increased. The results of the performance analysis revealed that at appropriate water–solids ratios, using 15 wt.% or less of the BOF slag was beneficial to the properties of the AAC products. In general, it should be feasible to recycle the BOF slag in the production of AAC. However, the foreign elements introduced by the BOF slag can alter the formation and structure of hydrates, including tobermorite, and thus affect the properties of the AAC product, a potential issue that needs to be addressed.

As one of the by-products in the steel industry, granulated blast furnace slag (GBFS) is widely used as an aggregate or a pozzolanic material (a partial replacement for Portland cement) in the concrete mixture after the crushing or grinding process. However, using a basic oxygen furnace slag (BOFS) as a cementitious material is limited because of its inherent shortcomings such as low cementing property and undesirable expansion characteristics due to free lime. To overcome BOFS’s these properties, the BOFS was ground, blended with the ground granulated blast furnace slag (GGBFS), and used as a pozzolanic material in this research. A total of five mortar mixtures were developed, including ordinary Portland cement (OPC) as a control group, two binary mixtures, and two ternary blended mixtures with 50% cement replacements by GGBFS and BOFS by weight percentages. Properties of these mixtures were evaluated according to ASTM C 989 and C 311 standard specifications that include compressive strength, alkali-silica reaction (ASR), and sulfate resistance tests. Moreover, basic material characterization of GGBFS and BOFSs was investigated by X-ray diffraction (XRD), chemical composition analysis (XRF), and particle size distribution (PSD). The test result shows that the blended mixture with 15% BOFS and 35% GGBFS satisfied the strength activity index and good ASR and sulfate resistance.

Mechanism for alkaline leachate reduction through calcium carbonate precipitation on basic oxygen furnace slag by different carbonate sources: Application of NaHCO3 and CO2 gas

To investigate the advantageous effects of incorporating industrial solid waste basic oxygen furnace (BOF) slag on the mechanical characteristics of warm-mixed rubber asphalt (WMRA) and hot-mixed rubber asphalt (HMRA) mixture, varying proportions of BOF slag were substituted for limestone coarse aggregates (0%, 25%, 50%, and 75%). Additionally, a 1.5% dosage of Sasobit warm-mixed modifier was introduced to prepare the rubber asphalt. Subsequent to preparation, both static mechanical tests (including Marshall and indirect tensile tests) and dynamic mechanical tests (including dynamic creep and elastic modulus tests) were conducted to evaluate the influence of BOF slag on the mechanical behavior of WMRA and HMRA mixtures across different substitution levels. Following testing, a two-way analysis of variance (ANOVA) was employed to dissect the impact of BOF slag content and Sasobit warm-mixed modifier on the static and dynamic mechanical properties of the rubber asphalt mixtures. The findings reveal that BOF slag exhibits commendable engineering aggregate properties, enabling substantial substitution of coarse aggregates in both HMRA and WMRA mixtures. As the proportion of BOF slag increases, it enhances the resistance of asphalt mixtures to permanent deformation and cracking under static and dynamic loading conditions, while broadening the range of elastic deformation for both WMRA and HMRA mixtures subjected to repeated loading. Moreover, a synergistic enhancement in the resistance of rubber asphalt mixtures to dynamic load-induced deformation is observed when employing both BOF slag and Sasobit warm-mixed modifier. The findings offer valuable insights for enhancing the performance of WMRA and HMRA mixtures, as well as broadening the utilization of BOF slag and waste rubber.

Impact of basic oxygen furnace slag on the hydration microstructure, mechanical properties, and carbon emissions of supersulfated cement

Effect of basic oxygen furnace slag type on carbon dioxide sequestration from landfill gas emissions

Abstract. Basic Oxygen Furnace Slag (BOFS), a by-product of steelmaking, offers an environmentally friendly alternative to natural coarse aggregates (NCA) in concrete. In South Africa alone, over a million tons of BOFS is produced annually, however, the low utilisation rate of the by-product often leads to growing landfills of the material. The low utilisation rate is primarily due to the free lime content of BOFS, which causes volume instability of the BOFS due to the larger calcium hydroxide crystal which forms during the hydration process and thus limits the potential applications for use. This study explores whether the incorporation of supplementary cementitious materials (SCMs), namely ground granulated blast furnace slag (GGBS) and Metakaolin (MK), may improve the volume stability of concrete made with BOFS as an aggregate but reacting with the BOFS hydration products. Concrete mixes were prepared with 0%, 50%, and 100% volumetric replacement of NCA by BOFS. Furthermore, ordinary portland cement was partially replaced with 60% GGBS in some mixes and 15% MK in others. The compressive strength test was used to assess potential reactivity between BOFS and SCMs, while prism expansion tests evaluated the impact on volume stability and the concrete microstructure was assessed by microcrack analysis method. Results show that BOFS aggregates react with SCMs, due to the difference in the rate of compressive strength gain of the BOFS mixes, relative to those with NCA. Furthermore, including SCMs improved the overall volume stability of concrete made with BOFS, though microcracks were more prevalent. This suggests that while macro-scale stability improved, microstructural issues remain.

The basic oxygen furnace slag is a major waste by-product generated from steel-producing plants. It possesses excellent characteristics and can be used as a natural aggregate. Chemically, the basic oxygen furnace slag encloses free CaO and free MgO, which is the main reason for the expansion crisis since these free oxides of alkaline earth metals react with water to form their hydroxide yields. The objective of the present research study is to stabilize the basic oxygen furnace slag by using innovative geopolymer technology, as their matrix contains a vast quantity of free silicon, which can react with free CaO and free MgO to form stable silicate compounds resulting in the prevention of the basic oxygen furnace slag expansion predicament. Lab-scale and ready-mixed plant pilot-scale experimental findings revealed that the compressive strength of fine basic oxygen furnace slag-based geopolymer mortar can achieve a compressive strength of 30–40 MPa after 28 days, and increased compressive strength, as well as the expansion, can be controlled less than 0.5% after ASTM C151 autoclave testing. Several pilot-scale cubic meters basic oxygen furnace slag-based geopolymer concrete blocks were developed in a ready-mixed plant. The compressive strength and autoclave expansion test results demonstrated that geopolymer technology does not merely stabilize the basic oxygen furnace slag production issue totally, but also turns the slags into value-added products.

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.

Newer urban soils, frequently composed of several types of anthropogenic materials, may contain basic oxygen furnace (BOF) slag, which is a steel industry byproduct and considered a potential alternative material for road construction. An understanding of the flow and solute transfer processes through urban soils thus requires hydraulic characterization of these materials. The BEST (Beerkan Estimation of Soil Transfer Parameters) algorithm serves to estimate the full set of unsaturated soil properties by means of conducting an inverse analysis of Beerkan water infiltration data. This study aimed at characterizing unsaturated hydraulic properties of the BOF slag and its evolution during a 1‐yr period through water infiltration experiments and use of an adapted BEST method for inverse analysis. Results indicate the evolution with time of BOF slag hydraulic parameters due to their physicochemical changes when exposed to rainfall events. Moreover, the findings of this study highlight the initial spatial variability of hydrodynamic characteristics, which after a certain period shifts to mostly homogeneous behavior. This study has contributed to the hydrodynamic characterization of BOF slag by providing hydraulic conductivity and water retention curves, as required for modeling water and thus solute transfer processes vs. time, which is relevant to BOF slag reuse and environmental considerations.

Tempering and modification of basic oxygen furnace slag with blast furnace slag: mineral phase transformations and cementitious material enrichment mechanisms.

Decreasing ore grades and an increasing consumption of metals has led to a shortage of important primary raw materials. Therefore, the urban mining of different deposits and anthropogenic stocks is of increasing interest. Basic oxygen furnace (BOF) slag is produced in huge quantities with the so-called Linz-Donawitz process and contains up to 5.2, 0.9, 0.1, and 0.07% of Mn, Al, Cr, and V, respectively. In the present study, sulfur-oxidizing Acidithiobacillus thiooxidans and iron- and sulfur-oxidizing Acidithiobacillus ferridurans were applied in batch and stirred tank experiments to investigate the biological extraction of metals from BOF slag. In the batch experiments, up to 96.6, 52.8, 41.6, and 29.3% of Cr, Al, Mn, and V, respectively, were recovered. The stirred tank experiments, with increasing slag concentrations from 10 to 75 g/L, resulted in higher extraction efficiencies for A. ferridurans and lower acid consumption. Selective metal precipitation was performed at pH values ranging between 2.5 and 5.0 to study the recovery of Mn, Al, Cr, and V from the biolixiviant. Selective precipitation of V and Cr was achieved at pH 4.0 from A. thiooxidans biolixiviant, while Fe and V could be selectively recovered from A. ferridurans biolixiviant at pH 3.0. This work revealed the potential of BOF slag as an artificial ore for urban mining and demonstrated that combining bioleaching and selective precipitation is an effective method for sustainable metal recovery.

Steel slag, a kind of industrial waste, has been considered applying in road construction as aggregate based on abundant indoor tests. The permanent deformation performance of asphalt mixture with Basic Oxygen Furnace (BOF) slag is evaluated by test with UTM-25 and simulation with equations at different temperatures and various stress levels in this study. Results show that the permanent deformation behavior of BOF base asphalt mixture is relatively sensitive to temperature and it can be perfectly modeled with proper equations, otherwise, strain per load cycle of specimen is responsible for mixture failure instead of accumulated permanent strain.