Slag Structure Research Articles

Influence of Cr2O3 on the Viscous Flow Behavior and Structure of Cr‐Containing Molten Titanium Slag

Herein, the influence of Cr2O3 on the viscous flow behavior and structure of Cr‐containing molten titanium slag is investigated in this work. The melting and viscosity properties are studied by hemisphere method and rotating cylinder method, respectively. In addition, the structure of Cr‐containing molten titanium slag is investigated by Raman spectroscopy. It is shown in the results that the melting temperature and viscosity both increase with the increase of Cr2O3 content. The activation energy for viscous flow increases with increasing Cr2O3 content, which is in the same trend as viscosity. When the Cr2O3 content increases from 0% to 3%, the simpler 6‐coordinated Ti4+ and TiO44− monomer unit transformed into more complex O–Ti–O deformation and Ti2O64− chain unit. Furthermore, the fraction of relatively complex silicate structural units shows an increasing trend. Cr2O3 behaves as a network former and enhances the degree of polymerization of network structure, and the variation of Cr‐containing molten titanium slag structure is consistent with the increasing trend of viscosity.

The Viscosity of Na2O-B2O3-CaO-SiO2-Al2O3 Slags

The molding powder is an important supplement material in the continuous casting process, which plays a decisive role in the condition of continuous casting and the surface quality of the slab. The viscosity of the Na2O-B2O3-CaO-SiO2-Al2O3 slag system was studied by using the internal cylinder rotation method, and the viscosity data within the range of experimental slag composition were analyzed. The result shows that the viscosity of slag decreases gradually with the increase of borax (Na2O·2B2O3) content, where the content of O2- in the slag increases and the polymerization degree of the network structure decreases in the slag. When the Al2O3 contents increase, the amount of free oxygen decreases in the slag, which increases the degree of polymerization of the slag structure and results in the viscosity increasing. The calculation result of the prediction equation for viscosity has a small deviation.

Study on the formation mechanism and mechanical properties of composite foam slurry material for mine plugging

The development of tough, energy and shock absorbing materials is the key to solving the problem of long-term plugging the air leakage to prevent and control coal spontaneous combustion. To study the mechanical behavior and energy absorption characteristics of composite foam slurry material (CFSM) for mine plugging, the effect of activator on the properties of CFSM was investigated, and the whole process of CFSM under uniaxial compression were analyzed systematically. The results indicated that activator could improve the compressive strength of CFSM by dissolving the vitreous structure of slag and generating more hydration products, further improving the structural compactness. Moreover, CFSM exhibited the unique deformation damage patterns and energy absorption effects during stress loading. Based on thecompressive stress-strain curve, the damage failure pattern of CFSM was mainly caused by shear stress and exhibited three main characteristic stages, including elastic-plastic stage, plateau stage and crush compact stage. The material showed elastic deformation of the bubble pores and local micro cracks in the elastic-plastic stage. The platform stage was characterized by the development of fissures until complete penetration. The bubble pores of the material were gradually compacted and became dense in the compacting stage, and ultimately retained a certain compressive strength. Unlike the direct splitting damage of traditional grouting materials, CFSM showed obvious energy and shock absorption effect in the process of compression. Part of the energy was transformed into the elastic energy of the bubble pore for releasing when disturbed by external impact, resulting in deformation of the bubble pore. The other part of the pressure was transformed into plastic fracture energy, causing cracks in the bubble hole or collapse. The findings of this study could help for better understanding of the mechanism of long-lasting prevention coal spontaneous combustion by foamed gelling plugging materials, and eventually provide more ideas for the development of green and safe mine plugging materials.

Molecular simulation investigation of pore structure impact on the wettability and flotation efficiency of coal gasification fine slag

Coal gasification slag is a kind of solid waste that exhibits suboptimal resource utilization and contributes to environmental pollution. Flotation is a common method of sorting coal gasification fine slag. However, the adverse influence of the well-developed pores structure of residual carbon on wettability and flotation efficiency is not adequately addressed in the literature. In this research, the adsorption characteristics of water molecules in the residual carbon model with different pore structures were investigated by Grand Canonical Monte Carlo simulation. We employed molecular dynamics simulations and mathematical models to investigate the mechanism of pore water movement. Additionally, the influence of pore structure on the flotation effect of coal gasification fine slag was explored for molecular dynamics simulations and flotation experiments. The results indicated that water molecules were adsorbed and aggregated in the residual carbon pores in the form of clusters. The cluster size decreased as the porosity decreased. Moreover, the same pore model showed an equivalent adsorption of water molecules. The binding effect of residual carbon on water molecules was stronger for smaller pore sizes. However, the simulation and experimental findings demonstrated that the more developed the pore structure of coal gasification fine slag, the lower its flotation efficiency. Finally, various methods of strengthening the flotation of coal gasification fine slag are theoretically verified. The findings of this research elucidate the underlying microscopic mechanism responsible for the adsorption of water molecules by residual carbon pores. Moreover, we explicate the principle of weakening the pore wetting effect and lay a theoretical foundation for developing advanced flotation techniques for coal gasification fine slag. It provides some theoretical guidance and technical support for realizing high-value utilization of coal gasification slag with specific environmental and resource benefits.

An Experimental Study to Improve the Nutrients and the Mechanical Properties of Copper Tailings Sand in China’s Arid Zone by Biomineralization of Locally Isolated Urease-Producing Bacteria

Microbially induced carbonate precipitation (MICP) technology is an environmentally friendly technique that can contribute to tailings consolidation and ecosystem restoration. Our study found that local MICP bacteria, Lysinibacillus fusiformis, could remediate copper tailings pollution at different slope positions (K1, K2, and K3) in arid areas. We analyzed the effect of MICP treatment on the slag from macro- to microscopic levels with a dissolution test, soil physical and chemical tests, wind tunnel testing experiments, and scanning electron microscopy (SEM). The results demonstrated that the MICP bacteria, L. fusiformis, effectively remodeled the slag structure, thereby preventing the diffusion of tailing slag caused by wind erosion. This structural remodeling resulted in a significant increase in slag strength (maximum strength: 2707 KPa) and an increased content of CaCO3. Furthermore, it led to a significant reduction in total salinity content (36.4–43.6%), pH (4.1–4.4%), and improvement in nutritional status (total potassium content (16–31.4%) and the available phosphorus content (2.1–2.3 times) of the tailings slag (p < 0.05). There was also a 15% increase in urease and catalase activity in K1, a 7% increase in invertase activity in K3 (p < 0.05), and a significant increase in carbon and nitrogen microbial biomass in K1, K2, and K3 (p < 0.05).

The Effect of SiC on the Phase Composition and Structure of Mixed Slag

In order to investigate the influence of SiC on the composition and structure of mixed slag (blast-furnace slag: steel slag = 1:9), the chemical composition, equilibrium-phase composition, and microscopic morphological characteristics and elemental distribution in the microscopic region of the SiC-reagent-tempered slag samples were analyzed by X-ray diffractometer (XRD), FactSage7.1 thermodynamic analysis software, scanning electron microscope, and energy spectrum analyzer. It was found that the main physical phases of the tempered slag samples were magnesia–silica–calcite (Ca3Mg(SiO4)2, C3MS2), calcium–aluminum yellow feldspar (Ca2Al2SiO7, C2AS), C2S, and iron alloy. Theoretical calculations suggest that the experimental temperature should be higher than 1500 °C to facilitate the combination of P5+ with Fe and Mn in the liquid phase to form an alloy, reduce the P5+ content in the tempered slag, and create conditions for the self-powdering of the conditioned slag. The doping of the SiC reagent can increase the liquid phase line temperature and reduce the binary basicity in the liquid phase; the liquid phase line temperatures were 1150 °C, 1200 °C, and 1300 °C and the basicities in the liquid phase were 4.68, 4.13, and 3.10 for the doping amounts of 3%, 4%, and 5% of the SiC reagent, respectively. The mixed slag doped with 4% SiC reagent achieves self-powdering and reduction of ferroalloys during the air-cooling and cooling processes, realizing the purpose of “resource utilization” of blast-furnace slag and steel slag.

Degradation of alkali-activated slag subjected to water immersion

In this study, the impacts of tap water immersion on the pore solution, phase assemblages, gel chemistry and structure, and pore structure of alkali-activated slag (AAS) pastes were studied. AAS degrades under such condition and the potential mechanisms can be concluded as lower reaction rates, gel decomposition and carbonation. The leaching of Na+ and OH− at early stages hinders the reaction of slag, which leads to a slower formation of reaction products. Long-term leaching can result in gel decomposition after 90 d. Coarsened gel pores and capillary pores are both identified in water-immersed samples. Additionally, the leached Ca2+ can react with the dissolved CO2 in tap water to form calcium carbonate. A calcium carbonate layer is observed surrounding the paste while the inner matrix is free of carbonation. The insights provided by this paper contribute to understanding the behaviors and durability of AAS in underwater conditions.

Effect of Cr2O3 on the viscosity and structure of slag (or glass) of CaO-MgO-Al2O3-SiO2 system

Effect of Cr2O3 on the viscosity and structure of slag (or glass) of CaO-MgO-Al2O3-SiO2 system

Exploration of the amphoteric transition of Al2O3 on melt structure and viscosity of silicate slag

The amphoteric oxide Al2O3 has different behaviors in different chemical environments. In an acidic environment, Al3+ breaks the network structure while in an alkaline environment, Al3+ forms a three-dimensional network like Si4+. In this paper, the amphoteric effect of Al2O3 on the structure and viscosity of a five-oxide silicate system (SiO2–Al2O3–FeO–CaO–MgO) is studied. The viscosities with different Al2O3 contents were experimented on an inclined plane and compared by the flow length of liquid slags. The study shows that the melt viscosity increases and then decreases with increasing Al2O3 content. As Al2O3 increases, the coordination number of the basic cations increases, changing from a network destruction ion to a charge balance ion. And the coordination number of Al3+ has a higher shift from four to five. The detailed reaction pathways of the structural units are revealed through the variation of oxygen types. The addition of Al2O3 leads to the replacement of [SiO4]4- by [AlO4]5-, with a decrease in the contents of Si–O–Si and Si–O-M while an increase of Si–O–Al, Al–O–Al and TO. Therefore, the network strength increases first and then decreases which is consistent with the tendency of viscosity.

The effect of mechanical activation duration on the structure and physical properties of titanium slag

TiO2 is popular in modern industries, including dyestuffs, printing, and cosmetics. To convert titanium slag to TiO2 with maximum efficiency, mechanical activation is an important pretreatment step to control the particle size of the titanium slag and the subsequent leaching process. Our study used a planetary high-energy ball mill to wet the titanium slag by mechanical activation for 3, 9, and 15 h to obtain the optimized condition for particle size control of the pretreated titanium slag. The phase composition was characterized by XRD, FT-IR, and Raman spectroscopy. The main constituents of the titanium slag were determined to be rutile TiO2 and Fe3Ti3O10. Calculating the relative intensity showed that some encapsulated phases were opened because of mechanical activation. The weight and density of titanium slag in the same volume increased, resulting in significantly enhanced peaks. The results can greatly improve the efficiency of subsequent titanium dioxide production. A laser particle size analyzer and SEM characterized the mechanical activation product. The results showed that when the mechanical activation duration is 15 h, the titanium slag obtained has a small particle size and a uniform, smaller specific surface area, and narrow particle size distribution. The current report has not introduced wet grinding to pretreat titanium slag. This simple method can be effectively applied to pre-treat titanium slag raw materials.

Technospheric mining of critical and strategic metals from nickel slag – Leaching with citric acid and hydrogen peroxide

Critical and strategic metals (CSMs), such as cobalt (Co) and nickel (Ni), are fundamental components of the high technology industry. Securing the supply of CSMs is fast becoming a priority for nations. Thus, secondary sources such as mine wastes, slags, tailings, and residues are being exploited to extract CSMs since they contain notable amounts of those metals. Recovering valuable metals from secondary sources can be categorised as technospheric mining. In this study, the extraction of cobalt and nickel from nickel slag was examined using a combination of an organic acid, citric acid, and hydrogen peroxide as the oxidant. Optimum conditions consisted of 1 M citric acid, 0.5% (v/v) hydrogen peroxide, at a temperature of 60 °C, a pulp density of 2.5%, a particle size of −100 + 75 μm, and an agitation speed of 400 rpm, for a period of 6 h. At the optimum conditions, 84.0% Ni and 91.7% Co were extracted from flash furnace (FF) slag, and 65.0% Ni and 99.1% Co from converter (CV) slag. It is expected that a combination of citric acid and hydrogen peroxide created peroxycitric acid in the solution, which is a strong oxidant and a key factor in the dissolution of the metals. The leach residue from FF slag showed a porous surface resulting from preferential dissolution within the slag structure. The residue from the converter (CV) slag mainly consisted of magnetite as a result of the dissolution of fayalite (Fe2SiO4). The kinetic studies demonstrated that the dissolution of Ni and Co from FF slag is controlled by diffusion. On the other hand, a rate controlling factor for Ni from CV slag is mixed control and for Co is a chemical reaction. Based on the temperature varied experiments, the calculated activation energy for Ni and Co from FF slag were 34.4 kJ/mol and 27.6 kJ/mol, respectively. The activation energies for the leaching of Ni and Co from the CV slag were 16.1 kJ/mol and 23.7 kJ/mol, respectively.

Insights into Interfacial Structure of Slag–Metal Interface During Desulfurization Through XPS and DFT Simulations

Insights into Interfacial Structure of Slag–Metal Interface During Desulfurization Through XPS and DFT Simulations

Effect of residual carbon on coal ash melting characteristics in reducing atmosphere

The melting behavior of coal ash at high temperatures directly affects slag discharge in gasifiers. Residual carbon is a key factor that influences the melting and transformation process of coal ash, affecting its melting characteristics, mineral composition, phase transformation, and melt structure. This study examines how residual carbon affects the melting process through mineral transformation, melt structure, phase transformation, atmosphere reaction, dissolution, and collapse of the physical structure of slag. The type and amount of residual carbon have different effects on the melting process. Changes in minerals result in complex changes in the phase transformation process. Residual carbon deprives some Fe and Si elements of the liquid phase, forming new aggregated minerals that compete with others. Residual carbon disrupts the equilibrium and eutectic structure of the system, dissociates the Si-O structure, and reduces the Fe-O structure, forming Fe0 or Fe2+. Free iron atoms form melt structures, such as Fe3C and FeSi.

Fluoride Evaporation of Low-Fluoride CaF2-CaO-Al2O3-MgO-TiO2-(Na2O-K2O) Slag for Electroslag Remelting

To elucidate the behavior of fluoride evaporation in an electroslag remelting process, the non-isothermal evaporation of the low-fluoride CaF2-CaO-Al2O3-MgO-TiO2-(Na2O-K2O) slag is studied using thermogravimetric analysis. The evaporation law of the melted slag is further verified using thermodynamic calculations. Fourier transformation infrared (FTIR) spectroscopy is used to evaluate the change in slag structure. It is discovered that the principal evaporating substances are CaF2, KF, and NaF, while the evaporation of MgF2, AlF3, and AlOF is less. KF evaporates absolutely in the early stage of the reaction, and CaF2 evaporates in a large proportion during the late reaction period. At 1500 °C, the order of vapor pressure is KF > CaF2. When K2O and Na2O are added to the residue sample at the same time, the evaporation ability of KF is stronger than that of CaF2 and NaF. As the K2O content increases from 0 to 8.3 wt%, evaporation increases from 0.76% to 1.21%. The evaporation rates of samples containing more K2O and those containing more Na2O are 1.48% and 1.32%, respectively. Under the same conditions, K2O has a greater effect on evaporation than Na2O. FTIR results show that the addition of K2O depolymerizes the network structure and that K2O can depolymerize the network structure better than Na2O.

Influence of TiO2, Al2O3, and Basicity on Viscosity and Structure of High Titanium-Bearing Blast Furnace Slag

The viscosity of high-titanium blast furnace slag with different TiO2 content, Al2O3 content, and basicity was measured at 1653-1773 K using the rotational cylinder method. The phase composition of the slag is measured by XRD. Phase diagram of the slags is calculated by FactSage software. Ionic network structure of the slags is analyzed by FT-IR. Results show that TiO2 depolymerizes the silicate network structure, reducing viscosity at high temperature, while increasing Al2O3 content generates a more complicated silicate, increasing viscosity. Basicity affects viscosity, with higher basicity resulting in lower viscosity above 1733 K. Perovskite significantly affects the viscosity of slag. This study provides an in-depth understanding of the relationship between the composition and viscosity of high-titanium blast furnace slag, which is very important for improving production efficiency.

Effect of Al and MgO on the simultaneous alloying of diamond wire saw silicon waste and Ti-bearing blast furnace slag

Diamond wire saw silicon waste (DWSSW) and Ti-bearing blast furnace slag (TBFS) are industrial solid wastes that contain large amounts of Si and Ti, whose accumulation unnecessarily wastes resources. In this paper, DWSSW and TBFS were mixed and melted in an induction furnace by simultaneous alloying, and Ti and Si were recovered by a Si-Ti alloy. In addition, the optimal material ratio of DWSSW and TBFS was determined. 10–30% reducing agent Al and 5–15% fluxing agent MgO were added to explore the effect of additives on the co-processing of DWSSW and TBFS. The results showed that Al promoted the reduction of Ti and the recovery of Si. When 20% Al was added, the recovery ratio of Ti in TBFS reached 95.62%, and the recovery ratio of Si reached 80.53%. Adding MgO changed the slag composition, simplified the slag structure, and reduced the viscosity. The recovery ratio of Ti from TBFS reached 96.18% when 15% MgO was added. The two additives promoted the alloying co-processing of DWSSW and TBFS, which provided a more efficient clean utilization process for these two solid wastes.

Insight into Interaction Behavior of CeAlO3 Substrate and CaO‐Al2O3‐Based Slag

Dissolution of inclusion in the melt is a common phenomenon in the metallurgy industry. In this article, the dissolution mechanism of CeAlO3 in CaO‐Al2O3‐Ce2O3‐MgO‐SiO2 slag is investigated at 1550 °C. After CeAlO3 dissolves into slag, the interfacial microstructure and the concentration profiles of the element between CeAlO3 and slag are observed by scanning electron microscopy‐energy dispersive spectroscopy. Results show that an intermediate product CaCeAl3O7 formed during CeAlO3 dissolves into the slag with w(CaO)/w(Al2O3) = 1. There is no intermediate product formed during CeAlO3 dissolves into the slag with w(CaO)/w(Al2O3) above 1.1. With the increase of w(CaO)/w(Al2O3) in the slag, the dissolution of CeAlO3 shifts from an indirect mechanism to a direct mechanism. The dissolution behavior of CeAlO3 in different slags has been discussed based on slag structure. In the first and second stages of dissolution, Ce3+ formed by dissociation of CeAlO3 at the interface diffuses into the slag, and Ca2+ in the slag diffuses to the interface. In the third stage, the solid‐phase precipitation when the concentration of Ca2+, Ce3+, and [AlO4]5− satisfies the nucleation concentration of CaCeAl3O7 in the concentration boundary layer (the region with large concentration gradient near the interface). Conversely, the solid‐phase precipitation could not occur in the concentration boundary layer.

Simulation and experimental study on the effect of iron on the structure and flow properties of coal ash slag

Slag fluidity is an important parameter affecting the stable operation of the gasifier. Above liquid temperature, slag fluidity is closely related to its structure. In the present study, the effect of iron on the three-dimensional connection state between [SiO4]4- and [AlO4]5- tetrahedrons in the SiO2-Al2O3-FeO-CaO slag system at 1773 K was deeply discussed by applying molecular dynamics (MD) simulation and ring statistics methods, and the slag network structure was divided into three rings with different functions according to the three-dimensional connection state. It was found that Fe2+ operated as a network modifier ion and substituted Si4+ and Al3+ in the slag and combined with O2–, thereby continuously depolymerizing higher-order rings into lower-order rings. This phenomenon simplified slag structure, reduced internal friction force, and improved fluidity. Finally, the ring distribution coefficient (Rdc) was defined and it was found that there was a linear relationship between Rdc and viscosity.

Viscosity Estimation of TiO2-Bearing Blast Furnace Slag with High Al2O3 at 1500 °C

Slag compositions are significant for the viscosity of blast furnace slag. An improved Urbain model (IUM) was proposed by introducing R5 ((X(CaO) + X(MgO) + 2X(TiO2))/(2X(SiO2) + 3X(Al2O3))) and N (X(MgO)/3X(Al2O3)) as the model parameters. By comparing IUM with other models, the model parameters of R5 and N are more reasonable and suitable for TiO2-bearing blast furnace slag, and IUM for predicting viscosity has a higher precision, and its relative error is only 10%. The viscosity isolines of the CaO–SiO2–15%Al2O3–MgO–2.5% TiO2 system were plotted, and the results show that the viscosity center of the slag is between Rw2 (w(CaO)/w(SiO2)) = 0.77–1.39 and Nw (w(MgO)/w(Al2O3)) = 0–1.37, the value of the viscosity center is 0.3 Pa·s, the viscosity increases gradually from the center to the outside, and the viscosity of the slag gradually decreases with the increase in Nw and Rw2. Furthermore, FTIR (Fourier Transform Infrared Spectroscopy) analysis was carried out in order to understand the mechanism between the slag structure and viscosity. With the increase in Nw and Rw2, the peak values of the symmetrical stretching vibration of non-bridging oxygen in the Si–O tetrahedral structure of slag decrease, and the slag structures depolymerize, which leads to the decrease in the viscosity of the slag.

Investigation on high-magnesium nickel slag treated by phase-separated activation as cementitious material

High-magnesium nickel slag is a hazardous waste from nickel smelting process with low pozzolanic activity. In order to improve the pozzolanic activity of high-magnesium nickel slag, this study produced a phase separation structure of high-magnesium nickel slag by activation treatment, and studied the effect of phase separation structure on the pozzolanic activity, engineering performance and hydration mechanism of high-magnesium nickel slag as cementitious material. The results showed that the phase separation structure was crucial for the pozzolanic activity of the high-magnesium nickel slag. It was confirmed by dissolution test that the phase separation structure significantly improved the pozzolanic activity of high-magnesium nickel slag. The main reason for the increase in slag activity is that the phase-separated glass consists of a silica-rich phase and an alkali-rich phase, which is rich in Mg, Fe, etc. (network modifiers), and the modifiers break Si–O–Si by producing "non-bridging" oxygen atoms (NBO), forming more Si-O-NBO and Si–O–2NBO, which disrupt the continuity of the glass network. Compared with the untreated high-magnesium nickel slag, the compressive strength of the geopolymer prepared from the high-magnesium nickel slag with a phase separation structure (W-HMNS) was increased by 69%. Its volume stability was also much better than that of geopolymers prepared from untreated high-magnesium nickel slag. The main hydration products of phosphoric acid activated W-HMNS based geopolymers were newberyite (MgHPO4·3H2O), and a small amount of aluminosilicates and hydrated calcium silicates. Together they make up the gel phase and the crystalline phase. A large number of gel phases such as newberyite wrapped unreacted quartz and crystallized newberyite form a dense gel-crystal structure, with crystal as the skeleton and colloidal as the bonding medium, increasing the density of geopolymer, forming a denser hardening body with higher strength. These results may provide some guidance for the practical application of high-magnesium nickel slag as a raw material to prepare geopolymer, and provide a new idea for improving the reactivity of slag.