Ternary Slag Research Articles

Influence of magnesite/limestone addition on the hydration characteristics of ternary slag cement systems

To explore the potential of magnesite adopted as supplementary cementitious material (SCM) in cement industry, the authors of this paper investigated the hydration characteristics of ternary slag cement mixtures containing magnesite or limestone. All cement pastes were formulated with a water-to-binder ratio of 0.4, and a total of 50 % substitution level was applied across the blends, with varying slag and magnesite/limestone contents. Experimental results confirmed that adding limestone to slag cement can promote the hydration of cement clinker through the nucleation effect, while not for magnesite addition. As the substitution ratio of magnesite increased, there was a notable increase in both the critical pore diameter and cumulative pore volume, leading to a continuous decrease in the compressive strength of cement pastes. Compared to limestone-containing blends, the incorporation of magnesite was more beneficial to the compressive strength at 7 and 28 days. Additionally, limestone facilitated the precipitation of hemi- and mono-carboaluminate, whereas no hemicarbonate was observed in mixtures containing magnesite. The addition of magnesite promoted the formation of hydrotalcite-like phase, and the quantitative analysis revealed that the dissolution of magnesite primarily occurred in the first 7 days. The authors believed that the results obtained in this paper proposed new perspectives on utilizing magnesite as SCM in cement industry.

Effects of Oxygen Partial Pressure and slag Basicity on the Behavioral Characteristics of Ni in Slag Drying Smelting

This study was intended to investigate the effects of basicity and oxygen partial pressure on the distribution behavior of Ni in the nickel smelting process using nickel oxide ore, the raw material of nickel, among natural ores. Experiments were conducted in a vertical tube furnace using Fe-Ni metal and FeO-MgO-SiO2 ternary slag, which simulated the composition of natural ore. An equilibrium experiment was conducted to observe the distribution ratio of Ni, and thermodynamic data required for this experiment was calculated through Factsage. As a result, it was found that as the oxygen partial pressure increased, the Ni content in the slag increased linearly. The Ni content in the slag increased as the basicity moved away from 0.60.

Thermal Reactivation of Hydrated Cement Paste: Properties and Impact on Cement Hydration.

In this research, the properties and cementitious performance of thermally activated cement pastes (referred to as DCPs) are investigated. Hydrated pastes prepared from Portland cement and slag blended cement were subjected to different thermal treatments: 350 °C for 2 h, 550 °C for 2 h, 550 °C for 24 h and 750 °C for 2 h. The properties and the reactivity as SCM of the DCPs were characterised as well as their effect on the mechanical performance and hydration of new blended cements incorporating the DCPs as supplementary cementitious materials (SCMs). It was observed that the temperature and duration of the thermal treatment increased the grindability and BET specific surface area of the DCP, as well as the formation of C2S phases and the reactivity as SCM. In contrast, the mechanical strength results for the blended cements indicated that thermal treatment at 350 °C for 2 h provided better performance. The hydration study results showed that highly reactive DCP interfered with the early hydration of the main clinker phases in Portland cement, leading to early setting and slow strength gain. The effect on blended cement hydration was most marked for binary Portland cement-DCP blends. In contrast, in the case of ternary slag cement-DCP blends the use of reactive DCP as SCM enabled to significantly increase early age strength.

Combined silicon refining for boron removal and Si-Kerf recycling using K2O-CaO-SiO2 slags

It is crucial for the photovoltaic (PV) industry to establish a circular materials flow for more sustainable solar silicon production. In the present work, a series of K2O-SiO2 and K2O-CaO-SiO2 slags were examined for the combination of silicon purification and Si-kerf waste recycling. The study revealed that the predominant mass transfer mechanism and the variation in slag composition during refining are due to the silicothermic reduction of K2O. The boron removal degree reached levels above 80% in most of tests, with boron gasification as potassium metaborate confirmed as an important mechanism for boron removal, especially in slags with high K2O content. In the case of ternary slags, the results indicated that an increase in CaO enhances boron partitioning in slag phase and a high K2O content also led to boron accumulation in the slag phase due to rapid reaction kinetics in the early stage of refining. The distinct behaviours of calcium and postassium ions in the slag phase were revealed by molecular dynamics simulations. It was found that potassium ions preferentially modify bridging oxygen, while calcium ions contribute more to depolymerizing the tectosilicate network and generating more non-bridging oxygens, which may further aid in the boron stabilization in slag phase. The oxidation layer of Si-kerf was removed successfully and enabled the coalescence of the silicon nanoparticles into the Si melt. Additionally, the presence of SiC clusters in the slag phase was also observed, indicating effective removal of SiC and the feasibility of Si-kerf waste recycling.

Properties of Fluorine-Free Steelmaking Flux Prepared Using Red Mud

The basic oxygen steelmaking process is based on the CaO-FeO-SiO2 ternary slag system, characterized by a high melting point and low lime dissolution rate, often becoming one of the key factors limiting the efficiency of the converter. The bulk solid waste red mud, produced by the Bayer alumina process and rich in Fe2O3/Al2O3/Na2O, significantly reduces the melting point of the steelmaking slag system and enhances the efficiency of lime dissolution. This study utilized red mud as the main raw material to prepare a fluoride-free flux. An in situ online observation system was used to measure the melting point of the flux and the dissolution rate of lime in the flux. The results indicate that the melting point of the red mud-based flux is below 1200 °C, and under the same conditions, the lime dissolution rate is 10 to 15 times higher than when this flux is not used. Experiments in a 10 kg induction furnace show that using this flux, the dephosphorization rate under conditions without oxygen blowing is close to 40%, far higher than the rate achieved using CaF2. Under oxygen-blowing conditions, the dephosphorization rate using the red mud-based flux is comparable to that of CaF2, and significantly higher than without any flux, especially under high [C] content conditions. The data show that the red mud-based flux has the potential to be widely used as a fluoride-free flux in the steelmaking process.

Prediction of component activities in the ternary molten slags containing titanium oxide by pseudo-multicomponent approach of MIVM

Based on the molecular interaction volume model (MIVM) and the coexistence theory model (CTM), the component activities were predicted in the ternary slags FeO-MnO-SiO2, FeO-MnO-TiO2, MnO-SiO2-TiO2 and FeO-SiO2-TiO2. In com parison with the experiment data, the total average relative errors of the predicted value by pseudo-multicomponent approach of MIVM were 16%, the total average standard deviations were 0.062. On the other hand, the total average relative errors of the predicted value by coexistence theory model were 28%, the total average standard deviations were 0.077. The predicted effect of the pseudo-multicomponent approach of MIVM has better stability and reliability than coexistence theory. Therefore, the activities of component TiO2 were predicted in the ternary slags FeO-MnO-TiO2, MnO-SiO2-TiO2 and FeO-SiO2-TiO2 by MIVM, the corresponding isoactivity curves were plotted and the thermodynamic behavior tendency of constituent TiO2 in different slag systems was analyzed. This work has enriched the thermodynamic data of titanium-containing slag system and made up for the deficiency of high temperature experiment to some extent.

Reduction-Sulfurization Smelting Process of Waste Hydrogenation Catalysts, Automotive Exhaust Purifier Waste Catalysts, and Laterite Nickel Ore.

Reduction-sulfurization smelting is an effective method for treating solid hazardous waste and recovering valuable components from them. In this work, a waste hydrogenation catalyst (WHC), an automotive exhaust purifier waste catalyst (AEPWC), a vulcanizer, and laterite nickel ore were mixed, and the reduction smelting behavior of this solid waste was investigated. XRD (X-ray diffractometry), TG-DSC (thermogravimetric/differential scanning calorimetry), SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy), OM (optical microscopy), and ICP-OES (inductively coupled plasma-optical emission spectrometry) methods were used to examine the chemical composition, thermal stability, structure, and morphology, as well as the metal content of the samples. Under the Al2O3-FeO-SiO2 ternary slag system, at a smelting temperature of 1450 °C, smelting time of 2 h, mass ratio of coke, pyrite, and CaO to waste catalysts of 16, 25, and 0%, respectively, nickel (Ni) and molybdenum (Mo) recovery reached 91.1 and 92.9%, respectively, where average PGMs (platinum group metals, platinum (Pt), palladium (Pd), rhodium (Rh)) recovery reached 96%, although vanadium (V) recovery was only 25.1%. The characterization of the slag shows that Al, Si, and Fe are mainly bound in the form of chemical compounds, while V is intercalated with ferro- or aluminosilicate, which hinders the reduction and sulfurization of V. A series of tests using reduction smelting without sulfurization were also conducted, after which the Ni, Mo, and V recovery reached 96.8, 96.6, and 89.7%, respectively, while PGMs (Pt, Pd, Rh) recovery ranges from 90.2 to 98.0%. The collaborative disposal of primary ore and multisource solid waste has been achieved through two process paths: reducing smelting and reducing sulfurization smelting, which provide reference for the collaborative smelting of multisource secondary resources.

Sulfide Capacity and Activity of Iron Oxide in CaO–SiO<sub>2</sub>–FeO Ternary System at 1573 K

The knowledge of sulfide capacities of FeO-containing slags is necessary for better understanding the resulfurization reaction in hot metal pre-treatments. In this study, copper-iron-sulfur liquid alloy was equilibrated with CaO–SiO2–FeO ternary slag to measure sulfide capacities and FeO activities simultaneously at temperature below the melting point of pure iron. The experimental result that the sulfide capacity increased with increasing FeO content could be explained by the fact that FeO was a basic oxide, and the sulfide capacity of the CaO–SiO2–FeO ternary system was significantly larger than those of the CaO–SiO2–MgO, CaO–SiO2–AlO1.5 and CaO–SiO2–CaF2 ternary systems. Although the FeO activity and oxygen potential were raised by the FeO addition, the calculated value for sulfur distribution ratio between CaO–SiO2–FeO slag and hot metal increased with an increase in FeO content.

The effect of C content in MgO–C on dissolution behavior in CaO–SiO2–Al2O3 slag

This study was conducted to observe the dissolution behavior of MgO–C in CaO–SiO2–Al2O3 ternary slag using the Single Hot Thermocouple Technique (SHTT). The composition of the slag was CaO (41.5 wt%), SiO2 (41.5 wt%), Al2O3 (17 wt%), and MgO–C (0, 5, 10, 18 wt%). When the slag was completely melted, MgO–C particles were added and the dissolution behavior was observed in real time. Before the main experiment, the weight of MgO–C and slag was set by designing a stability diagram for the short circuit problem of the thermocouple (TC) caused by the bubble reaction. Comparing the dissolution behavior of MgO and MgO–C revealed that the dissolution time of MgO was shorter than that of MgO–C in which bubbles occurred. When the C content of MgO–C was 10 wt% or more, particle fragmentation was observed, and the dissolution time decreased as the C content increased. Bubbles were formed in the sample to which C was added. The main bubble reaction was C(s) + SiO2(l) = CO(g) + SiO(g) based on thermodynamic analysis and weight loss measurements where the total partial pressure was PT = PCO + PSiO = 0.18 atm. In addition, the kinetic behavior of weight loss as a function of time strongly depended on the C content, and thus, it depended on the effective C surface area.

Effect of surface properties of MgO on its dissolution and spinel growth in CaO–SiO2–Al2O3 slag

The dissolution behavior of MgO in CaO–SiO2–Al2O3 ternary slag at the interface of single-crystal, dense poly-crystal, and porous poly-crystal MgO was investigated to evaluate the effect of the surface properties of the MgO. The experimental results revealed that a detached spinel layer formed at the MgO interface due to the change in thermodynamic condition of the slag, which was independent of the surface properties. On the other hand, it was also confirmed that the growth rate and morphology of the detached spinel layer strongly depended on the surface properties, such as porosity and curvature of MgO. During the formation of the spinel layer at the interface during MgO dissolution, a kinetic approach adopting parabolic relation theory was employed to determine the correlation between the surface properties and the spinel growth mechanism.

Interfacial reactions between impurities and slag onset of Si purification by slag addition

The interfacial reactions between impurities (Al and Ti) and slag onset of Si purification by 51 mol% SiO2–34 mol% CaO–15 mol% MgO slag addition were studied to enhance impurity removal efficiency from Si. The Al distribution behavior at the Si/Slag interface was investigated; a short reaction time (10 s) resulted in the formation of successive SiO2–CaO–MgO–Al2O3 layers in the slag with a thickness of 10 µm; increasing the reaction time (60 s) resulted in the entire ternary slag being changed into SiO2–CaO–MgO–Al2O3 quaternary slag due to the diffusion of Al2O3. It was shown that the highest impurity removal rate of Al could be achieved at the onset of the slag refining process. Based on the Ti distribution at the Si/slag interface, the slag refinement with 51 mol% SiO2–34 mol% CaO–15 mol% MgO had no effect on Ti removal.

Microstructural analysis by molecular dynamics simulation of aluminate ternary slag with alkaline oxide

The influence mechanism of Na2O, K2O, MgO, and BaO on the microstructural characteristics of aluminate-based ternary melts was investigated using molecular dynamics simulation to guide performance adjustments. When the MxO mass fraction was 4 wt%, compared with alkaline earth metal oxides, adding alkaline metal oxides can stabilize the Al-O bond and Al-O coordination better. The sequence of Mx+ close to the [AlO4]5− tetrahedron was Mg2+<Ca2+<Ba2+<Na+<K+, and M+ primarily compensates for the [AlO4]5- tetrahedron charge, while more AlV was formed in two-valence alkaline aluminate to balance the excess negative charge. As the MxO mass concentration increased, in the K2O-Al2O3-CaO, Na2O-Al2O3-CaO, and BaO-Al2O3-CaO systems, the Mx+ replaced Ca2+ in the [AlO4]5− tetrahedron and approached Ot to balance the excess negative charge, while in the MgO-Al2O3-CaO system, Mg2+ replaced Ca2+ in Onb and approached Ot to form non-bridging Al-O-Mg. Combined with the synergistic effect of Mx+, AlV, and Ot, the melt structure complexity followed the trend of MgO-Al2O3-CaO<Na2O-Al2O3-CaO<K2O-Al2O3-CaO<BaO-Al2O3-CaO with a certain mass fraction of MxO.

Vaporization of Vanadium Pentoxide from CaO-SiO2-VOx Slags During Alumina Dissolution

The vaporization of vanadium pentoxide from CaO-SiO2-VOx ternary slags using different gas treatment regimens and parallel vacuum gas extirpation to treat V-bearing slags at 1873 K has been developed in the present study. The novelty of the present study is to monitor the effect of parallel alumina dissolution on the vaporization phenomenon. Vanadium pentoxide has high vapor pressure at the temperatures over 1500 K. When CaO-SiO2-VOx ternary slags, kept in dense alumina crucibles, are injected with oxygen, V2O5 gas bubbles are formed which are forced out by using vacuum extirpation. The vanadium pentoxide could be then collected in the exhaust gases. The mechanism of the process phenomenon is described as the formation of V2O5 gas phase resulting from the oxidation of the lower-valent oxides present in the slag. This gas phase would form microbubbles in the molten slag bulk phase due to low surface tension between the gas phase and the slag, thereby increasing the contact surface. At the same time, the crucible material would dissolve in the slag causing an increase in the slag viscosity. Due to the high slag viscosity of the bulk slag, these microbubbles formed would have difficulty in coalescing and reaching the slag surface. The escaping of the bubbles into the gas phase is enabled by the vacuum extirpation.

Effect of Fluorine on Melt Structure for CaO–SiO&lt;sub&gt;2&lt;/sub&gt;–CaF&lt;sub&gt;2&lt;/sub&gt; and CaO–Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;–CaF&lt;sub&gt;2&lt;/sub&gt; by Molecular Dynamics Simulations

The melt structure with fluorine addition has been investigated using molecular dynamics (MD) simulation for the CaO–SiO2–CaF2 and CaO–Al2O3–CaF2 ternary slag system. By analyzing the coordination number of the network framework, the results indicate that the structure of Si–O tetrahedron is more stable than the structure of Al–O tetrahedron. F− ions are dominantly coordinated with Ca2+, there is a dynamic equilibrium between Ca2+ and the coordination anions (O2− and F−) in both systems, and the total coordination number (CN) is maintained between 6 and 7. The analysis of the distribution of oxygen types demonstrates the degree of polymerization (DOP) of network structure in CaO–SiO2–CaF2 system is lower than that in CaO–Al2O3–CaF2 system. Although the addition of CaF2 can lower the viscosity of both slag systems, the microscopic reasons for that are completely different: in CaO–SiO2–CaF2 system, CaF2 actually acts as network diluent, and creates the space where particles can move longer. But in CaO–Al2O3–CaF2 system, CaF2 can depolymerize the network structure of the melt.

First principle study of electronic structural and physical properties of CaO[sbnd]SiO2[sbnd]Al2O3 ternary slag system by using Ab Initio molecular and lattice dynamics

In current first principle studies the electronic, structural and physical properties of CaOSiO2Al2O3 ternary slag system were calculated by ab initio molecular dynamics (AIMD) and ab initio lattice dynamics (AILD) simulations, based on density functional theory (DFT). The density of states (DOS) and electrons density difference (EDD) were evaluated to understand the bonding nature of slag network structure. Furthermore, the atomic and bond population analysis shows that the SiO bonds are stronger as compared to AlO and CaO bonds in molten slag. The radial distribution function (RDF) and mean square displacement (MSD) were obtained at 1773 K, which are used to calculate the diffusion coefficient and viscosity of ternary slag system. Moreover, the temperature dependence of diffusion coefficient and viscosity were investigated in the range of 1350–2100 K. The calculated results indicate that the diffusion coefficient decreases and viscosity increases at high temperature for CSA slag system.

Estimating the density and molar volume of ferrite-based ternary molten slags by geometrical model

Ferrite-based slags are the basic systems in the pyrometallurgical production of copper, and the density and molar volume of these systems are of vital importance for optimizing the metallurgical process. However, due to the high melting points of melts and the expensive trial costs, experimental methods are inefficient to obtain all the data needed. As a result, a geometrical model has been applied to the estimation of density and molar volume of ferrite-based ternary slags. The calculated results agree well with experimental data in three ferrite-based ternary systems of Fe2O3–CaO–FeO, Fe2O3–BaO–FeO and Fe2O3–CaO–Cu2O. The mean deviation of the predicted results by the present model is lower than those by various empirical models for corresponding systems. The application of the present will enrich the data of density and molar volume for more ternary melts.

Effect of varying Al2O3 contents of CaO–Al2O3–SiO2 slags on lumped MgO dissolution

This study utilized the single hot thermocouple technique to examine the dissolution behavior of lumped magnesium oxide (MgO) in CaO–Al2O3–SiO2 ternary slags. The aluminum oxide (Al2O3) content in the slag (C/S = 1) varied from 10% to 30%; the MgO sphere with a diameter of 1 mm was placed in molten slags at 1,550 °C. Results showed that the dissolution rate decreased as the Al2O3 content increased up to 20%. Over 20% Al2O3, MgAl2O4 was formed at the interface of MgO and it did not fully melt at 30% Al2O3. The dissolution behavior and the formation of MgAl2O4 were analyzed by a phase diagram provided by Factsage 7.0 software. In the case of less than 20% Al2O3 content, apparent sphere radii were measured; the shrinking core model was then applied to understand the dissolution mechanism. The dissolution rate of both slags was controlled by boundary layer diffusion. The dissolution rate at 20% Al2O3 slag appeared to fit the behavior to the boundary layer diffusion, although it deviated during the middle stage of the dissolution because of MgAl2O4 formation. The 10% Al2O3 slag fitted well to the boundary layer diffusion curve; the obtained diffusion coefficient was 0.94 × 10−9 m2/s.

Experimental Investigation of Thermo-Physical Properties of SAW Slag

In the present study, the thermo-physical properties of twenty-one submerged arc welding slags were analyzed using a rutile-basic system. The submerged arc welding slags were analysed using hot-disc and thermogravimetric techniques. Thermo-gravimetric analysis was performed from 25 °C to 900 °C to find the thermal stability and change in enthalpy of the slags. Multi-response optimization technique was used to derive the optimized slag formulations. Different regression models for thermo-physical properties were developed. Individual slag constituents have an antisynergistic effect on all the thermophysical properties except density. Binary and ternary slag mixture constituents significantly affect the thermophysical properties of submerged arc welding slag.

Oxygen Potential of High-Titania Slag from the Smelting Process of Ilmenite

Oxygen potential of TiO2-FeO-Ti2O3 ternary slags was determined by the electromotive force (EMF) method based on the solid electrolyte oxygen sensor at 2003 K (1730 °C). The effect of FeO content and Ti3+/Ti4+ mass ratio on the oxygen potential of the high-titania slag was also studied. At a fixed Ti3+/Ti4+ mass ratio of 3.11, the oxygen potential increased with increasing FeO content. Increase of Ti3+/Ti4+ mass ratio from 2.29 to 3.60 caused a significant decrease in the oxygen potential of the slag. Comparing measured oxygen potential with the calculated values indicated that the oxygen potential of the slag might be determined by FeO/Fe equilibrium reaction rather than TiO2/Ti2O3 reaction. In addition, the experimentally measured oxygen potential values were modeled by multiple linear regression analysis, and a semi-empirical mathematical correlation was established between the oxygen potential and slag compositions. The iso-oxygen potential distribution diagram based on the mathematical model was obtained for the high-titania slag.

Study of the Viscosity of a La2O3-SiO2-FeO Slag System

Abstract The viscosity and break temperature of La2O3–SiO2-FeO slag was investigated to develop low-Al2O3 or Al2O3-free slag for the effective recovery of rare-earth metals. When La2O3 content is fixed (45, 50 and 55 mass%), the viscosity and break temperature of La2O3–SiO2-FeO slag decrease with an increase in FeO content and a decrease in SiO2 content. A higher La2O3 content in the La2O3-SiO2-FeO ternary slag yields a lower slag viscosity but a higher break temperature. Individual minor components of Al2O3, MnO and B2O3 does not affect, or decreases slightly the viscosity of La2O3–SiO2-FeO slag, whereas the slag break temperature is reduced so that the reduction ability order is ranked as B2O3 &gt; Al2O3 &gt; MnO. A small amount of two components Al2O3 + MnO and Al2O3 + B2O3 has little effect on the viscosity of the slag but it has an additive effect on the slag break-temperature reduction.