BOF Slag Research Articles

Development of Lightweight Construction Blocks by Alkaline Activation of Bof Slag

Development of Lightweight Construction Blocks by Alkaline Activation of Bof Slag

Thermodynamics and Industrial Trial on Increasing the Carbon Content at the BOF Endpoint to Produce Ultra-Low Carbon IF Steel by BOF-RH-CSP Process

Abstract Thermodynamic analysis was performed to obtain the relation between the carbon content at the BOF endpoint and the dissolved oxygen content in liquid steel and the (FeO + MnO) content in the slag with the help of thermodynamic calculation software FactSage. It finds that both the [O] and (FeO + MnO) content increase with decreasing the carbon content at the BOF endpoint and the increasing rate is larger when the carbon content is lower. In addition, in the case of the higher temperature at the BOF endpoint the [O] in liquid steel increase and the (FeO + MnO) in the slag increase as well. The consumption of O2 for decarbonization at the BOF endpoint is much more than that in RH degasser since the majority of the blowing O2 at the BOF endpoint will produce FeO into the slag, thus it increase the metal loss and deteriorate the steel cleanness during the consequent refining process. As a result, the carbon content at the BOF endpoint should be properly increased within the RH decarbonization ability. At last, industrial trials were carried out and confirmed that total oxygen consumption decrease obviously and the (FeO + MnO) of final BOF slag decline as well with increasing carbon content at BOF endpoint from 0.042% to 0.081%. In addition, it almost does not slow down the RH process and the carbon content in final steel all met the demand of the ultra-low carbon steel. In addition, mechanical properties of IF steel with higher carbon content at the endpoint of BOF are almost all more superior to those of heat with lower carbon content at BOF endpoint.

Estimation of application efficiency of “Flumag M” magnesia flux in agglomeration and BF production.

To decrease viscosity of BF slag and improve its desulfurization ability during hot metal production a magnesia oxide is used, which is introduced into a blast furnace, as a rule, within iron ore sinter, as well as in the form of a fluxing additive. Dolomite, sometimes iron ore materials with increased magnesia content (for example, Kovdor concentrate, raw or roasted Bakal siderite) as well as magnesia-contained wastes, most often BOF slag, are usually used as a main source of magnesia oxide during iron ore sinter production. Brucite, which is widely used abroad, mainly in Japan during iron ore sinter production, is a very prospective magnesia flux. However, brucite was never used in sinter production in Russia. Main parameters and efficiency of its application were obtained under Japan raw materials conditions. However sinter chemical and mineral compositions at Russian and Japanese sinter plants considerably differ. In this connection studies on influence of the magnesia flux “Flumag M”, which is identical by its composition to brucite, on the process parameters of sinter burden sintering and pellets production were carried out. The estimation of application efficiency of “Flumag M” magnesia flux was made during typical sintering of NLMK sinter burden. It was determined, that partial and complete substitution of dolomite by the “Flumag M” magnesia flux in the NLMK sinter burden results in an increase of specific productivity of sintering process by 10–20% (comparative) and the sinter strength by 3–5% (comparative) correspondently. Laboratory experiments on “Flumag M” magnesia flux application, carried out in STI NITU “MISiS”, showed, that raw pellets with magnesia flux additives have higher compressive strength comparing with the pellets having dolomite additives. Impact strength and abrasion strength of roasted pellets is higher, comparing with those with dolomite. Optimal content of “Flumag M” flux in the pellets burden is 2%. The application of “Flumag M” magnesia flux enables to remove burden from the burden and increase strength of roasted pellets.

Effects of Alkali Activation and CO2 Curing on the Hydraulic Reactivity and Carbon Storage Capacity of BOF Slag in View of Its Use in Concrete

This work investigates the sequential application of alkali activation and CO2 curing to BOF steel slag as a technique for improving its hydraulic reactivity for use in concrete, while also exploiting its potential as a carbon sink. Activation with either a sodium hydroxide/sodium-silicate or a sodium hydroxide/sodium carbonate solution was first evaluated in a preliminary calorimetric study for selecting the solution compositions leading to the formation of early stage hydration products. The pastes produced with the selected solutions were then cured either in a humidity chamber or in a carbonation chamber (at 20 or 50 °C) for up to 28 days, in order to assess long term reaction products. Mineralogical and thermal analysis showed the formation of a C–S–H like phase, specifically in the samples activated by the sodium hydroxide/sodium-silicate solution, whereas significant occurrence of gaylussite was noticed in the samples activated with the sodium hydroxide/sodium carbonate solution. A maximum CO2 uptake of 6% by wt, due to calcium carbonate formation, was observed in the latter samples, whereas a 5% value was achieved in the former ones. The compressive strength of the mortars prepared with sodium hydroxide/sodium silicate and cured in the carbonation chamber at 50 °C was above 2 MPa, while it was lower for the other samples, particularly those activated with sodium hydroxide/sodium carbonate. Alkali activation employing sodium hydroxide/sodium silicate solutions followed by CO2 curing at relatively high temperature (i.e. 50 °C) resulted a promising treatment for BOF slag valorization in the manufacturing of concrete for non structural applications.

Decarburization of Pig Iron in Synthetic BOF Converter Slag

The paper presents a study on the decarburization of pig iron droplets in synthetic BOF slag. The effects of droplet size and slag composition were studied. The results show evidently that the deca ...

Geotechnical Properties and Application of Lime Modified Phosphogypsum Waste

Residual deposits of Phosphogypsum are readily available in large quantities in South Africa and currently are landfilled or pumped into the sea, as there are limitations to engineering applications due to the radionuclides content. In this study, mild acid treated residual phosphogypsum was stabilized with Lime Fly Ash (LFA) binder, and the geotechnical properties and changes in phosphogypsum radioactivity were evaluated. Part of the LFA binder were replaced with basic oxygen slag (BOG) and the properties of the LFA-BOG composite were also evaluated. Citric acid as a reducing reagent was effective in reducing the radionuclides in the residual phosphogypsum and stabilization of acid treated phosphogypsum with lime fly ash (LFA) improved the Unconfined Compression Strength (UCS). In particular composites containing 50 % PG mobilized UCS of 1.08 MPa and optimum replacement of 30 % of the LFA with BOF slag further improved the strength to 3.2 MPa. The final composites met the requirements of South African Roads (TRH4, 1996) specification and have equivalent strength values as C1-C4 materials and fit criteria for subbbase in terms of strength durability, and are also applicable for masonry bricks production in accordance with SANS 1215.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18232

Use of BOF slag and blast furnace dust in asphalt concrete: an alternative for the construction of pavements

El auge de la construcción de grandes obras de ingeniería ha impulsado la demanda por acero, lo que ha generado un incremento en la producción de residuos siderúrgicos, una situación que causa problemas ambientales debido a la acumulación y no disposición adecuada de estos subproductos. El uso de materiales reciclados en diferentes procesos debe estar enfocado hacia el desarrollo sostenible y la protección del medio ambiente. Este trabajo se desarrolló con el objetivo de estudiar el uso de la escoria de horno al oxigeno (BOF) y el polvo de alto horno (AH) para fabricar mezclas asfálticas en caliente para pavimentos como una alternativa para mitigar los problemas ambientales derivados de la acumulación de residuos siderúrgicos y de la explotación de materiales no renovables, como la grava y la arena. Para lograr el objetivo, se analizaron tres tipos de mezclas asfálticas, una mezcla con materiales convencionales (control) y dos mezclas sustituyendo parcial y totalmente el agregado grueso por BOF y el agregado fino por polvo de AH. El diseño de las mezclas se realizó con la metodología Ramcodes, la cual se basa en el principio del polígono de vacíos. Se realizaron ensayos para evaluar las características físicas y la susceptibilidad al agua y deformación plástica de cada tipo de mezcla. Los resultados de este estudio indican que es factible el uso de los residuos siderúrgicos analizados para reemplazar parcialmente los agregados convencionales en la pavimentación de carreteras.

Experimental investigation on BOF slag oxidation in air

ABSTRACTBasic oxygen furnace (BOF) slag contains a significant amount of iron-containing species, which is considered to be iron resources and therefore need to be recovered. In this work, the oxidation behaviour of BOF slag under air (at selected oxidation temperatures and holding time) was investigated to explore the potential of transforming non-magnetic wustite in the BOF slag into magnetic spinel, which may subsequently be recovered by magnetic separation. The experimental results show that the iron-containing spices in the BOF slag can be oxidised into magnetic spinel phases in the investigated temperature range of 1000–1150°C and thereafter be recovered by magnetic separation. The formation of these phases is closely related to the oxidation temperatures and holding time: a higher oxidation temperature and longer holding time lead to a larger amount of formed magnetic species; however, the amount of formed magnetic species decreases at elevated temperature (>1050°C) and with extended holding time (>40 min).

Evaluation of the Cooling and Pavement Performance of Basic Oxygen Furnace Slag Used in Asphalt Mixture

Basic oxygen furnace slag (BOF) is widely used in road construction, but there is a lack of characteristics in different asphalt mixtures. This study investigates the properties of hot-mixed asphalt (HMA), containing stone mastic asphalt (SMA), porous asphalt (PA), and dense-graded BOF as a partial substitution for natural aggregates. The purpose of this study is to evaluate various BOF slag contents in the asphalt mixtures that would affect the cooling behavior after compaction. Asphalt mixture specimens contained 0%, 20%, 40% and 60% BOF slag, respectively, as coarse aggregate. Test results showed that BOF slag has a lipophilic property, so that it can be adsorbed by asphalt cement, thereby reducing the cost of asphalt. The stability value of all the asphalt mixtures increases with the proportion of BOF slag replacement. In addition, the voids in the mineral aggregate (VMA) value variable exhibited significant differences among asphalt mixtures, and could determine the deviation of the cooling trend of asphalt mixtures. Furthermore, it was found that the cooling procedure of the BOF slag used in dense-graded asphalt mixture takes about 100 min, and that the temperature tends to be moderate; however, it took about 120 min of cooling the SMA and PA mixture with BOF slag. In addition, the distribution of voids of the dense asphalt mixture was not uniform. This would result in various locations of inconsistent thermal energy temperature on asphalt mixtures.

Reducing environmental impacts: The use of basic oxygen furnace slag in portland cement

The technological process of clinkerization is responsible for a high consumption of energy and the release of carbon dioxide (CO2) to the environment. It is estimated that the cement industry generates, for every tonne of cement produced, around 0.7–1 tonne of CO2, in order to be responsible for 5% of CO2 global emission, while in Brazil, this corresponds to 1.4%. This study reused the basic oxygen furnace slag, submitted to different cooling processes, for the partial replacement of clinker. Formulations of CPIII portland cement were prepared with substitution of 5.4% by weight of clinker by basic oxygen slag with 53 and 71% amorphous phase. The compressive strength was evaluated at ages 3, 7, 28 and 91 days, determined setting times, hot and cold expansibility. The addition of basic oxygen furnace slag, regardless of the crystallinity degree, provided the cement gains in the initial and final mechanical strength. By adding slag with 71% amorphous phase, the cement presented 29 and 40.4 MPa of compressive strength after 7 and 28 days, respectively; while with the addition of slag with 53% amorphous phase, the cement strength exhibited 31.9 MPa after 7 days and 41.4 MPa after 28 days. The use of BOF slag, as a partial clinker substitute, allows it to reduce pollutant emissions and to achieve a higher energy efficiency without affecting the cement physical-chemical properties.

Erratum for “Environmental Impact Assessment and Total Cost Analysis of BOF and BSSF Slag in Asphalt Concrete” by Shih-Huang Chen, Tyas Wahyu Pramesthi, Putri Adhitana Paramitha, and Chia-Chen Wu

Erratum for “Environmental Impact Assessment and Total Cost Analysis of BOF and BSSF Slag in Asphalt Concrete” by Shih-Huang Chen, Tyas Wahyu Pramesthi, Putri Adhitana Paramitha, and Chia-Chen Wu

Chromium Stability in Steel Slags

Chromium is an essential element in steelmaking industry. Steel slag inevitably contains some chromium and there is a risk of Cr emission from slag to the environment, however, in which form the emission of the element occurs and whether it is a hexavalent Cr is a concern. To investigate the conditions of hexavalent chromium formation in steel slags and its migration to the atmosphere, an estimation of Cr oxide's stabilities is carried out in this paper. Factsage 7.1 is applied to analyze the thermodynamic properties of Cr oxides with respect to the Cr6+ formation. An Ellingham diagram and standard Gibbs free energy change are proposed. Stability diagrams for BOF, EAF, and LF slag systems with various compositions are derived. Slag basicity is indicated as an influencing factor for Cr containing phase formation. Based on thermodynamic calculations Cr3+ phases are determined to be dominant for the given slags and no hexavalent Cr phases are found in the real multicomponent slag systems.

Metal Recovery from BOF Steel Slag by Carbo-thermic Reduction

BOF steel slag is a main by-product in steelmaking. The valorization of BOF slag is good for the industry and the environment. In the present study, the carbo-thermic reduction of BOF slag has been investigated, the reduction of Fe and P containing phases (i. e. oxide and compounds) is discussed, and the effects of Al2O3 additions on the reduction process are described. XRD and EPMA have been applied for characterizing the slag. We conclude that, by controlling the test conditions, it is possible to purify the recovered Fe.

Carbonation of Steel Slag: Testing of the Wet Route in a Pilot-scale Reactor

This work reports the first results of an on-going activity aimed at the scale up of the wet-route carbonation of steel slag for storing CO2 and generating a product with valorization potential. Two batches of Basic Oxygen Furnace slag (BOF1 and BOF2) collected at different times from a steelmaking plant downstream iron recovery were used to perform the tests in a pilot-scale rotary kiln unit part of ENEA's research infrastructure. The tests were carried out at ambient (25°C- 37°C) and enhanced temperature (45°C-53°C), under a 40-47% CO2 flow, at atmospheric pressure for a reaction time of 30min. In each experiment around 1000-1500g of BOF slag was employed. The residues were humidified in order to achieve a liquid to solid ratio of 0.17 l/kg. This value was selected on the basis of the results of preliminary lab-scale static and dynamic experiments that are also presented in this paper. The product collected at the end of each test was cured at controlled conditions (T=25°C e RH=100%) for 28 days and then characterized in terms of particle size, CO2 uptake and environmental behavior. The mean diameter (D50) of the obtained product was around 1mm for the tests performed at room temperature and slightly lower for the test performed at 50°C, i.e. around twice the size of the starting material. The CO2 uptake measured for samples collected immediately after the tests was quite similar (4-6% wt.), whereas after curing a 50% increase was observed for all BOF1 slag samples, while only a slight increase was observed for BOF2 slag. These results are significantly higher than the ones of the lab-scale tests. The leaching behavior of the product appeared also to be significantly affected by the treatment performed in the pilot plant.

Formation of Spinel Phases in Oxidized BOF Slag under Different Cooling Conditions

To enhance utilization of wastes generated from steelmaking, a BOF slag sample from Ning Steel group in China is treated by oxidizing at 1500 °C for 30 min and then cooled by different methods. The treated samples are characterized, in combination with calculations using FactSage 6.4. XRD results show that iron oxides in BOF slag are converted largely by the oxidation to spinel phases, Fe3O4 and MgFe2O4, which also eliminates free CaO and MgO. EDS analyses show Fe element existing in di‐calcium silicate and glass phase, which are Fe3+ ions formed by oxidation. An incorporation of Fe3+ ions into crystal structures has stabilized high temperature polymorph of C2S, β‐C2S, and α’‐C2S, in the treated slag samples. Fe3+ ions may also act as a network former to facilitate glass formation. This may make it possible for the glass and α’‐C2S phase to complement each other, leading to a higher hydraulicity, while the BOF slag, after the spinel separation, is blended in cements. Some suggestions are proposed, based on the present and early studies, to enhance hydraulicity for the BOF slag, as well as grain sizes of spinel phases, which may result in economic and environmental benefits for steel and cement industries.

Crystallization behavior of melted BOF slag during non-isothermal constant cooling process

The current research aims to elucidate the crystallization mechanism of the melted BOF slag in the constant cooling process for its effective recycling. Firstly, the DSC measurement of the BOF slag was performed in non-isothermal condition of constant cooling from the melt. The XRD and EDS analyses of the slag were carried out to observe the inner structure during crystallization. The observations confirmed that the cooling rate did not affect the crystallization mechanism of the melted BOF slag. However, it could influence the change in the size and shape of the crystalline phases, because the cooling rate is correlated to the holding time in the certain temperature range for the generation of the specific phases. From this research, it is expected to control the phase morphology in BOF slag by adjusting the cooling process for its valuable utilization.

Study on the treatment of BOF slag to replace fine aggregate in concrete

Excessive free lime in the BOF slag will react with water and causes serious expansion, and thus, results in its reutilization difficulty. In this study, scrubbing attrition and chelating reagent treatment were used to remove free lime from BOF slag. After removing free lime, the BOF slag was used as fine aggregate for making cement mortar. Under different curing periods, the specimens were characterized for their physical and mechanical properties, ultrasound conduction velocity, and volume expansion. By reducing free-calcium oxide through attrition and chelating processes, the expansion rate of specimen can be reduced to 0.16%. The compressive strength and flexural strength of cement mortars prepared with BOF slag can reach 45.4MPa and 7.1MPa, respectively. The test results suggested that the scrubbing and chelating treatments can effectively remove free-calcium oxide and improve expansion and strength development of concrete mortar.

Environmental Impact Assessment and Total Cost Analysis of BOF and BSSF Slag in Asphalt Concrete

Abstract Dense grade asphalt concrete (DGAC), a popular surface material in Taiwan, allows for the design of the new recycling materials to reduce the use of natural aggregate. Basic oxygen-furnace...

Experimental study on slag splashing of an 80 t combined blown converter

Physical modelling of slag splashing practice of an 80 t combined blown converter was conducted in this paper. Through measuring the mass flux of splashed slag, the effect of different operating parameters on slag splashing was investigated. By means of variance analysis, the influence significance of different operating parameters on slag splashing was obtained, and the optimal combination of operating parameters were acquired as follows: lance height 600 mm, top gas flowrate 18000 Nm3 h−1, four nozzles lance, bottom nozzle configuration D4, bottom gas flowrate 100 Nm3 h−1, and amount of remained slag 10%. In addition, the relation between the agitation energy of top blow and mass flux of splashed slag was discussed, and the estimation model for mass flux of splashed slag during BOF slag splashing practice was proposed through data analysis.

Identification of Fe-Containing Phase in Oxidation Process of BOF Slag

In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg + replace the Fe2+ of magnetite crystal to form spinel.