•The effect of P2O5 incorporated in slag on the hydration characteristics of cement-slag system.•The migration of phosphorus ions into cement matrix.•The P/Si atomic ratio of the C-S-H gel phase.
...This paper presents the influence of P2O5 incorporated in slag on the hydration characteristics of cement-slag system. It was found that the gradual addition of phosphorus oxide in slag did not change overall mineralogy of the hydration products. Except hydration retardation in the dormant stage, chemically bound water and portlandite contents, hydration degree of slag, and pore structure at all investigated ages were similar among cement-slag pastes with different P2O5 percentages. Furthermore, significantly higher amount of monosulfate was observed as the P2O5 content in slag increased. In addition, a higher Al/Si atomic ratio was measured in the C-S(A)-H gel phase formed in the cement matrix. However, similar Ca/Si atomic ratio of C-S(A)-H gel phase and Mg/Al atomic ratio of hydrotalcite-like phase were determined in all slag pastes, irrespective of the addition of P2O5. In contrast to magnesium ion which was retained within the original slag boundary, phosphorus ions could migrate into cement matrix. Therefore, P/Si atomic ratio of the C-S-H gel phase increased with the increasing phosphorus oxide content in slag, reaching up to ∼0.08.
•The hydration of commercial slag and synthetic slag with similar physical and chemical properties.•The role of sulfur species in slag on the hydration process of slag cement.
The effect of slag of ...different origins (synthetic slag produced in the laboratory and commercial slag collected from different steel factories) with comparable chemical composition, amorphous content and particle size distribution, on the hydration characteristics of slag cement was investigated. In order to study the effect of sulfur in slag, a model cement paste of a C3S-slag blend was also produced. It was found that origin of slag has very little impact on the hydration process of cement-slag system. Synthetic slag shows a comparable compressive strength gain to commercial slag at 1 day, and from then on, a lower compressive strength is reached by it compared with that of commercial slag until 28 days. The sulfur in slag starts to participate in reaction after 1 day and it dominates the rate of heat release in calorimetric measurement, consistent with the result of compressive strength test. It significantly affects the elemental composition of the cementitious matrix at 7 days, and higher Al/Si and S/Ca ratios can be detected in cement-commercial slag blend at 7 days. The sulfur is involved in the formation of AFm-phase, such as calcium monosulfoaluminate, and the thermodynamic modelling shows that upon the gradual incorporation of sulfur in slag, calcium monosulfoaluminate precipitates continuously with the consumption of strätlingite and portlandite. The conclusion obtained in the paper provides a basis to understand the role of sulfur in slag on the hydration process of slag cement
The expected shortage of Li due to the strong increase in electromobility is an important issue for the recovery of Li from spent Li-ion batteries. One approach is pyrometallurgical processing, ...during which ignoble elements such as Li, Al and Mn enter the slag system. The engineered artificial mineral (EnAM) strategy aims to efficiently recover critical elements. This study focuses on stabilizing Li-manganates in a synthetic slag and investigates the relationship between Mnsup.4+ and Mg and Al in relation to phase formation. Therefore, three synthetic slags (Li, Mg, Al, Si, Ca, Mn, O) were synthesized. In addition to LiMnsup.3+Osub.2, Lisub.2Mnsup.4+Osub.3 was also stabilized. Both phases crystallized in a Ca-silicate-rich matrix. In the structures of Lisub.2MnOsub.3 and LiMnOsub.2, Li and Mn can substitute each other in certain proportions. As long as a mix of Mnsup.2+ and Mnsup.3+ is present in the slag, spinels form through the addition of Mg and/or Al.
In the present work, synthetic slags (FeO-SiO2-CaO-P2O5-Al2O3-TiO2-V2O5 system) mimicking the composition of the slag inclusions of Ipanema were solidified at different cooling rates. FactSage ...software was used to calculate the slag’s phase equilibria from 500ºC to 1600°C to guide the microstructural characterisation. The samples solidified with slower cooling rates featured wüstite dendrites and a eutectic-like matrix, with intradendritic (Al,V,Ti)-containing iron spinel precipitates in the wüstite. The rapidly solidified slag showed refined wüstite dendrites surrounded by a Fe-O-Si-Ca-containing amorphous single-phase matrix without intradendritic (Al,V,Ti)-containing iron spinel precipitation. The comparison of the calculated phase diagram with the as-cast microstructures showed a few discrepancies. For instance, the FactSage’s database must be updated to consider the simultaneous solubility of Al, V and Ti in the thermodynamic description of the spinel phases, such as FToxid-SP-V, FToxid-SPINA, FToxid-TiSp and (FeO)2(TiO2)(s). Finally, the intradendritic precipitation of (Al,V,Ti)-containing iron spinel phases in the wüstite of the slag inclusions indicated that an Ipanema’s iron artefact was exposed to high service temperatures between 750 and 1050ºC.
Recycling ladle furnace (LF) slag helps in sustainable steel making and reduces steel production costs. This paper focuses on recycling Si/Mn/Al-killed LF slag as a replacement for CaO-Al
2
O
3
...-based synthetic slag for treating high carbon Si/Mn-killed steels. Characterization of different types of LF slag was carried out to identify chemical composition and mineralogical phases. Industrial trials were carried out by recycling LF slag along with lime and calcined bauxite as additives. The effect of recycled LF slag on the kinetics of desulphurization and other process parameters was studied and compared with regular practice. It was observed that LF slag can be recycled successfully as a replacement for CaO-Al
2
O
3
-based synthetic slag at an industrial scale.
Novel SiO2-CaO-CaF2-R2O-MgO based synthetic slags (R2O represents alkali metal oxides) with varied binary basicity values were used with oxygen injection to refine silicon melts and remove Fe from ...metallurgical-grade silicon. Silicon samples and slags at the silicon-slag interfaces were obtained during refinement. The compositions of the silicon samples were analyzed, and the quenched slag samples and mild cooling slags from the final crucible were inspected using scanning electron microscopy and energy dispersive X-ray spectroscopy. After 15 min of refinement, the Fe removal rate ranged from 52.3 to 60.1 wt%. During the refining process, the Fe-concentrated phase formed within the silicon droplets and was then transferred to the silicon-slag interfaces and wetted with slags. The Fe-concentrated phase at the silicon-slag interface can dissolve directly in the slags. It can also be transferred into the slag phase in the form of droplets, which can be affected by the binary basicity of the slags. Ti removal demonstrated a similar mechanism. Fe-bearing crystals were not detected in the quenched slag samples obtained during refinement, while complex Fe-bearing phases were detected in the final slag. This study demonstrates Fe removal from metallurgical-grade Si using slag refining methods and reveals the removal mechanism during the refinement.
Currently, steel production through induction furnace is nearly 30% of the total steel production in the world. However, steel produced through induction furnace routes contains high sulphur (0.06 to ...0.1 wt %) which is not acceptable for the structural steels. Therefore, it is imperative to develop the synthetic slag for the desulphurisation of the steel in the induction furnace. The slag properties such as sulphide capacity, sulphur partition ratio, viscosity, liquidus temperature, the solubility of components, basicity are considered to design synthetic slag for desulphurisation of the steel in the induction furnace. Developed synthetic slag is consisted of 20-30 wt% SiO
2
, 5-20 wt% Al
2
O
3
, 40-60 wt% CaO, 5-10 wt% MgO. The evaluation of synthetic slag is performed in the induction furnace for desulphurisation of plain carbon and alloy steel. The maximum degree of desulphurisation is 84% with the addition of 2-3 wt% synthetic slag for Al killed steel while 32% for non-killed steel is achieved. The desulphurisation time to achieve the sulphur level (0.03-0.04) is 10 minutes using developed synthetic slag (2-3 wt% liquid metal). Sulphur partition and sulphide capacity of synthetic slag increase with the basicity of the developed synthetic slag.
Abstract Synthetic slag has been added during BOF tapping in order to modify the physicochemical properties of resulting slag with the aim of assessing the influence on inclusion density, composition ...and size distribution. Viscosities and activities of slag oxides were calculated by FactSage 7.2, using the FToxid database and Viscosity module. All heats were treated under vacuum in an RH degasser for 15 minutes. A comparative analysis of top slags with two levels of FeO+MnO (> 10% and ≤ 10%) was carried out. The higher level of FeO+MnO led to almost thrice more inclusion than the lower level. Top slags after treatment with synthetic slag brought the best result of inclusions features thanks to their higher CaO activity, lower viscosity and lower activity of Al2O3. These heats presented smaller inclusions and lower initial inclusion density at ladle arrival at RH. Based on these evidences, top slags with synthetic slags added during the tapping and FeO+MnO content ≤ 10% conferred the best condition in steel cleanliness.
The purpose of the article is to study the kinetics of the process of desulfurization of steel in steel casting ladles during the release of steel from the steelmaking unit and during its stay in the ...ladle when refining liquid limestone-alumina slag (CaO + Al2O3) or solid slag forming. It is known that successful desulfurization depends on the chemical composition of the slag, the time of its formation in the ladle, the oxidation of the metal, the conditions of mixing steel in the ladle, additional technological operations, ladle processing. To study the kinetics of the process of desulfurization, industrial studies were carried out in the oxygen-converter shop of PJSC “Azovstal Iron and Steel Works” with the melting of 17Г1СУ steel in 350-ton converters for different metal processing options in steel casting ladles. A total of 1456 smelts were carried out, of which 460 – when treated with synthetic slag (SS), 271 – when treated with solid slag-forming mixture (SSFM), 630 – when used together with SS and SSFM and 94 – without treatment of SS and SSFM. In the treatment of steel in the ladle there were used synthetic slag composition,%: CaO – 47-52; Al2O3 – 32-39, SiO2 – 3-7, MgO – 10-14, MnO + FeO up to 1.5, TiO2 – 4-6, S – up to 0.035 and solid slag-forming mixture (fractions up to 5 mm), consisting of 76–78 % lime containing up to 0.05 % sulfur and 22–24 % fluor-spar – up to 0.1 % sulfur. Mathematical processing of experimental and comparative smelts produced by the method of multiple correlation revealed the influence of each of the factors of the converter process (the basicity of slag B, the specific consumption of lime qlime and fluor-spar qf.s., cast iron temperature), as well as the basicity of converter slag falling into the ladle when draining metal from the converter, its sulfur content (S)s, the specific flow rate of the SS and the SSFM on the sulfur content of the finished metal, which is described by the corresponding equations and is characterized by certain graphic dependencies. Comparative analysis of the desulfurization efficiency of different options in comparison with the variant when the metal was not treated in any way, showed that the amount of sulfur recovered from the metal in the processing of its solid slag-forming mixture, synthetic slag, together slag and mixture increased in 1.36, 2.1 and 2.46 times, respectively. The method of correlation analysis revealed that the specific amount of sulfur recovered when applying solid slag-forming mixture is 14 times higher than when using synthetic slag (with their separate application).
In this paper, the effect of MgO, BaO, Na 2 O and SrO addition to a pre-melted CaO-Al2O3 -Si 2 O synthetic slag on sulfur removal from plain carbon steel was studied under the same experimental ...conditions. The slags were pre-melted at 1400°C in an electric resistant furnace and desulfurization experiments were carried out in a high frequency induction furnace. The results showed that the optimum reaction time for desulfurization was 15 min. It was found that while SrO addition to the ternary slag enhances the sulfur removal capability, MgO, Na 2O and BaO additions reduce desulfurization efficiency of the ternary slag. Moreover, it was observed that restricting access to oxygen from the atmosphere by using a covered crucible, could increase desulfurization efficiency of the slag by more than two fold
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