Search Results (31)

Coal combustion generates significant volumes of ash, a technogenic by-product that poses a serious threat to regional environmental sustainability (environmental chemical contamination and air pollution). This study aims to assess the feasibility of utilizing this type of ash as a raw material component in the fabrication of refractory bricks and to investigate the fundamental properties of the resulting experimental products. Ash was incorporated into the batch composition at concentrations ranging from 10% to 40% by weight, blended with clay and water, then shaped through pressing and subjected to firing at 1000 °C and 1100 °C in an air atmosphere for 2 h. After complete cooling, the samples were subjected to compressive strength testing. Samples containing 40 wt% coal ash exhibited insufficient compressive strength and were therefore excluded from subsequent investigations. For the remaining samples, apparent density, open porosity and slag resistance were determined. The microstructural characterization was performed, and the phase composition of the samples was analyzed. The results revealed that the phase composition of the experimental samples differs significantly from that of the reference sample (ShA-grade chamotte brick in accordance with GOST 390-96, currently used as lining in metallurgical furnaces across the country), exhibiting a higher mullite content and the absence of muscovite. A small amount of kaolinite was detected in the experimental samples even after a 2-h firing process. This observation may be attributed to the effect of kaolinite crystallinity on the transformation process from kaolinite to metakaolinite. The mechanical strength of the experimental samples meets the relevant standards, while slag resistance demonstrated an improvement of approximately 15%. Open porosity was found to decrease in the experimental samples. In addition, a change in the pore size distribution was observed. Notably, the proportion of pores larger than 10,000 nm was significantly reduced. These findings confirm the feasibility of incorporating coal ash as a viable raw material component in the formulation of refractory materials. Full article

This study investigates graphite separation from Lithium-Ion Battery (LIB) black mass (which is a mixture of anode and cathode materials) via froth flotation coupled with an open-loop recycling approach for the graphite (froth) product. Black mass samples originating from different LIB types were used to produce a carbon-poor and a carbon-enriched fractions. The optimization of the flotation parameters was carried out depending on the black mass chemistry, i.e., the number of flotation stages and the dosing of flotation agents. The carbon-enriched product (with a carbon content of 92 wt.%, corresponding to a recovery of 89%) was subsequently used as a secondary carbon source for refractory material (magnesia carbon brick). Analyses of brick chemistry, as well as thermo-mechanic properties in terms of density, porosity, cold crushing strength (CCS), hot modulus of rupture (HMOR—the maximum bending stress that can be applied to a material before it breaks), and thermal conductivity showed no negative influence on brick quality. It could be demonstrated that flotation graphite can principally be used as a secondary source for non-battery applications. This is a highly valuable example that contributes to a more complete closure of a battery’s life cycle in terms of circular economy. Full article

This review examines the degradation of refractory materials in aluminum reduction cells, focusing specifically on contamination caused by the cryolite-based bath. Aluminosilicate refractories, particularly Ordinary Refractory Bricks, play a vital role in maintaining the structural integrity and thermal balance of these cells under demanding operational conditions. The interaction between the molten bath and refractory linings leads to chemical reactions and mineralogical changes that modify the mechanical and thermal properties of the material over time. The study integrates findings from industrial autopsies, laboratory experiments, and a comprehensive review of the existing literature to identify and analyze the mechanisms of degradation. By analyzing the findings obtained from these methodologies, this review explores how cryolitic infiltration triggers transformations that compromise performance and reduce the lifespan of refractory linings. Covering a broad temperature range (665–960 °C), the study addresses key challenges in understanding bath-induced contamination and provides insights into how to improve the durability and efficiency of refractory materials in aluminum production. Full article

The selection of refractory bricks significantly impacts the operational performance of brick structures in high-temperature environments. In this study, a coupled thermal stress model of a refractory brick structure was established and validated by means of thermal expansion experiments. This paper innovatively combined the brick number, brick thickness, and brick material to investigate their influence on brick structural performance. The results indicated that the influence of the brick number on the temperature was less significant than that of brick thickness. However, the brick number had a greater effect on vertical displacement and principal compressive stress than brick thickness, with the maximum differences being 342.3% and 28.9%. Compared to brick thickness, brick material had a more significant effect on vertical displacement and principal compressive stress, with the maximum differences being 77.1% and 67.4%. Additionally, the influence of brick material properties on vertical displacement and principal compressive stress was greater than that of the brick number, with the maximum differences being 77.6% and 65%. Therefore, when selecting refractory bricks, it is advisable to consider the brick material first, the brick number second, and the brick thickness last. This study offers theoretical guidance for refractory brick structure design and material selection in high-temperature applications. Full article

Refractory flue walls in anode baking furnaces are exposed to harsh conditions during operation, affecting the structural properties of the material. The flue walls in industrial furnaces degrade over time to the point where they no longer perform as intended and must be replaced. Earlier studies of spent refractory lining from anode baking furnaces have shown considerable densification of the flue wall bricks, where the densification varies significantly from the anode side to the flue side of the brick. The observed densification is proposed to be caused by high-temperature creep, and the aim of this work was to determine whether the uneven densification across the brick could be modeled using a finite element method (FEM) implementing high-temperature steady-state creep. Finite element modeling was used to model steady-state creep for a material similar to that used in the baking furnace. Thermal and physical parameters and boundary conditions were chosen to simulate the conditions in an anode baking furnace. Refractory samples of pristine and spent lining from the baking furnace were also analyzed with X-ray computed tomography (CT), with a reduction in the porosity confirming the densification during operation. The FEM modeling demonstrated that high-temperature creep could explain the observed densification in the spent flue walls. The present findings may be useful in relation to increasing the lifetime of industrial flue walls. Full article

This study investigates the synthesis of magnesia–hercynite-based refractories using blends of magnesia powder, aluminum dross (AD), mill scale (MS), and graphite, focusing on the effects of carbon concentration and heating temperature. The results demonstrate successful synthesis at 1550 °C and 1650 °C, with high magnesia content (C80 and D80) leading to the formation of distinct phases, including MgO, FeAl₂O₄, MgFeAlO₄, CaMg(SiO₄), and Ca₃Mg(SiO₄)₂, which influence the ceramic’s microstructure and mechanical properties. Increased magnesia content reduces porosity and enhances crushing strength, while heating to 1650 °C significantly improves densification and nearly doubles cold crushing strength, from 43.77–58.97 MPa at 1550 °C to 76.79–95.67 MPa at 1650 °C. These findings suggest that the synthesized refractories exhibit properties comparable to commercial magnesia–hercynite bricks, with potential for the further development for industrial rotary kiln applications. Full article

This study aimed to uncover the chronology and production technologies of ancient bricks unearthed from various locations in Upper Assam, Northeast India. To achieve this goal, complementary spectroscopic techniques such as Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) coupled with Energy Dispersive Spectrometer (EDS), as well as Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL/IRSL) dating, were applied. FTIR and XRD analyses revealed the presence of quartz, feldspar (microcline, orthoclase, albite), kaolinite, chlorite, cerussite, palygorskite, magnetite, hematite, and organic carbon. The mineralogical composition indicates two distinct groups with firing temperatures below 650 °C and above ~800 °C. These two groups could be the first indication of the presence of two civilizations or at least two different production technologies involving different firing temperatures and kiln atmospheric conditions. Further, the SEM-EDS study suggests that both calcareous and non-calcareous clays were used in brick making, which have low and high refractory properties, respectively. The internal morphology of the samples shows the existence of micropores and microfractures, indicating the influence of higher-temperature firing. Absolute dating techniques associate the two brick groups with different age ranges: a firing temperature above ~800 °C indicates a superior technology corresponding to a production period between the 7th and 10th centuries CE. In contrast, a temperature below 650 °C indicates a technologically less advanced group of people, with the age group dated between the 11th and 14th centuries CE. Full article

A heat recovery coke oven (HRCO) is one of important approaches to achieving a carbon peak and carbon neutrality in China. However, the steady operation of an HRCO is significantly influenced by the internal working conditions and the quality of lining refractories. In this work, a comprehensive study of the internal working conditions of an HRCO was carried out. The results suggest that the partition wall (PW) between the carbonization and combustion chambers is the most vulnerable area, with the corresponding traditional silica bricks inadequate for the service requirements. A reference based on a comparison of the average thermal stress and high-temperature compressive strength is offered for evaluating and selecting silica bricks for the PW. New optimized silica bricks within the reference are verified to be more applicable to the actual working conditions of an HRCO than the traditional silica bricks. As such, this work provides valuable guidance for the optimization and selection of silica bricks for the PW in an HRCO. Full article

This study provides a characterization of materials from wastes and outcrops of two inactive bauxite mines located close to Sant Joan de Mediona and Peramola, Spain. Mineralogy was determined via powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Thermal properties were measured via differential thermal analysis–thermogravimetry (DTA-TG) and gresification tests. The crystalline phases are medium-high crystalline kaolinite and variable amounts of illite, quartz, calcite, boehmite, hematite and rutile/anatase. DTA show two endothermic peaks produced by the dehydroxylation of minerals: the first peak, at 530–538 °C, belongs to boehmite; the second peak, at 535–568 °C, corresponds to kaolinite. An exothermic peak at 950–978 °C is associated with mullite crystallization. The optimal sintering temperatures obtained from the gresification curves (firing shrinkage and water absorption) were 970 °C for carbonate-poor, illite-rich clays; 1100 °C for illite- and carbonate-poor samples; and near 1190 °C for carbonate-rich materials. The carbonate-poor samples fired at 1300 °C contain sillimanite and mullite, and the carbonate-rich materials are rich in gehlenite, anorthite, and hedenbergite. The mineralogy of these materials is sufficient to obtain ceramic materials with suitable properties, but not their low plasticity. They could be used in the formulation of bricks or as part of mixtures to produce refractory ceramics. Full article

Millimeter-scale magnesian refractory granules were found to be a unique magnesian-expansive component in steel slag. To systematically study the effects of these granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, an investigation of their existing forms and influence on the volume stability was conducted in this paper. The various-sizing waste–magnesium–chromate-based refractory brick (Mg-Cr brick) granules and different (FeO + MnO)/MgO ratios’ synthetic MgO·xFeO·yMnO ternary solid solutions granules were adopted to simulate magnesian-expansive granules by partially replacing manufactured sand in mortar. The 100 °C–3 h boiling and 213 °C–2 MPa–3 h autoclaving treatments were adopted as volume stability testing methods. The results indicated that whether Mg-Cr brick or MgO·xFeO·yMnO solid solution, the concentration of expansive stress and the anisotropy expansion came with the granular size rising weakening the volume stability of cement-based materials which contained magnesian-expansive granules, significantly. Meanwhile, this phenomenon resulted in the ineffectiveness of the single linear expansion rate when assessing the qualification of volume stability. Furthermore, it also changed the mortars’ failure mode from “muddy damage” to “break into blocks”. Especially, there is no volume stability issue when the MgO·xFeO·yMnO satisfied (FeO + MnO)/MgO ≥ 1.00. Considering the significant effect of the granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, it is imperative to enhance the detection of both MgO content and mineral existing forms in steel slag in practical applications. For recommendation, the threshold value of conducting autoclaved volume stability testing on steel slag should be set at MgO ≥ 3%. Furthermore, the qualification cannot be judged by the single linear expansion rate; the specimens’ appearance integrity and strength loss should also be noted. Full article

Agro-industrial wastes such as wheat husk (WH) are renewable sources of organic and inorganic substances, including cellulose, lignin, and aluminosilicates, which can be transformed into advanced materials with high added value. The use of geopolymers is a strategy to take advantage of the inorganic substances by obtaining inorganic polymers, which have been used as additives, e.g., for cement and refractory brick products or ceramic precursors. In this research, the WH native to northern Mexico was used as a source to produce wheat husk ash (WHA) following its calcination at 1050 °C. In addition, geopolymers were synthesized from the WHA by varying the concentrations of the alkaline activator (NaOH) from 16 M to 30 M, namely Geo 16M, Geo 20M, Geo 25M, and Geo 30M. At the same time, a commercial microwave radiation process was employed as the curing source. Furthermore, the geopolymers synthesized with 16 M and 30 M of NaOH were studied for their thermal conductivity as a function of temperature, in particular at 25, 35, 60, and 90 °C. The chemical composition of the WHA, determined by ICP, revealed a SiO₂ content close to 81%, which is similar to rice husk. The geopolymers were characterized using various techniques to determine their structure, mechanical properties, and thermal conductivity. The findings showed that the synthesized geopolymers with 16M and 30M of NaOH had significant mechanical properties and thermal conductivity, respectively, compared to the other synthesized materials. Finally, the thermal conductivity regarding the temperature revealed that Geo 30M presented significant performance, especially at 60 °C. Full article

The life of the hearth is the main limiting link of the campaign of a blast furnace. As the equipment for holding molten iron in the furnace, the high-temperature molten iron is in direct contact with the refractory, which makes the refractory have a larger temperature increase. If the temperature gradient inside the refractory is large, it generates large thermal stress and causes the refractory to crack. Blast furnace gas and molten iron intrude into the gap, which directly causes melting erosion and other chemical erosion with carbon bricks. It aggravates the erosion degree of the furnace and seriously affects the production life of the furnace. Therefore, the furnace often occurs with different types of severe depression erosion in the late service of the blast furnace. In this study, the calculation model of the thermal fluid-solid coupling considering the molten iron flow and the solidification of molten iron was established. This calculation model was applied to study thermal stresses in the furnace with severe erosion. Based on the calculation model, the effect of blast furnace production parameters and deadman condition on thermal stresses in the furnace with severe depression erosion were analyzed, including tapping productivity, tapping temperature, cooling intensity, and deadman geometry. The research results are of great significance for prolonging the safe production life of blast furnaces. Full article

Metallic copper production via the pyrometallurgical route is hindered due to the increased presence of gangue in the clay minerals in copper sulfide concentrates and its unpredictable effect on this operation. In this study, the relationship between smelting copper slag composition, including the clay components and the refractory brick wear, was investigated in experimental laboratory tests. Synthetic fayalite slags doped with 2, 5, or 8 wt% high-purity kaolinite or montmorillonite were introduced into magnesia chromite refractory crucibles and melted in an electrical furnace under the controlled partial pressure of oxygen (10⁻⁸ atm) for 12 h at temperatures of 1250 and 1300 °C. After the experimental time, the crucibles were quenched in water, and the obtained samples were analyzed using the XRD, SEM, and ICP techniques. According to the results, at 1300 °C the presence of montmorillonite in the fayalite-based slag promoted infiltration through the refractory brick and increased the dissolution of the magnesia component from the hot face. In the case of the kaolinite, the infiltration was even higher, but the magnesia dissolution was delayed. Full article

Industrial symbiosis is one of the key approaches to meet sustainable and low carbon production targets. Thus, through circular approaches, it is possible to reduce the use of natural crude materials and make production processes waste-free in the metallurgical industry. The purpose of this study was to study the possibility of using various metallurgical waste and low-grade semi-finished products, which do not have a direct application area, in the production of heat-resistant carbon-containing refractory bricks through the combustion synthesis (CS) method. In the experiments, used metallurgical wastes were wet filter cake (FC), sludge (S), and refractory magnesite scrap (MS) while semi-products were rich and poor dust of chrome spinel (Cr-S). Simultaneously with the experiments, thermochemical simulation studies were carried out using the HSC Chemistry 6.12 to predict the thermodynamic properties of the reactions and possible reaction products. Thermal conductivity coefficients were determined in products in terms of thermal properties of composite samples, they were between 0.511 and 1.020 Wm/K. The phase compositions of the produced samples were determined via XRD technique. The TG-DTA technique was used to characterize thermal behavior of products. In addition, mechanical properties were determined by compression strength test. As a result of experiments, it was observed that Cr-S-rich-based samples showed a promising result in comparison to others: increasing amount of useful carbide phases were formed and demonstrated a high value of mechanical properties. Compression strength was increased from 2.7 MPa (sample №4) to 15.8 MPa (sample №1) with increasing chromite-containing phases in the green samples. Full article

During the roasting process of fluxed pellets in a coal-fired rotary kiln, the incomplete combustion of pulverized coal injection accelerates deposit formation, which further limits the production efficiency of fluxed pellets. In order to eliminate the above problem, this study investigated the influence of MgO on deposit formation mechanism. The thermodynamic analysis revealed that MgO could increase the melting temperature of silicates in fluxed pellets with 0.8–1.2 basicity (CaO/SiO₂) when roasted at 1200–1250 °C, thereby decreasing the amount of liquid phase that formed initial deposits. XRD and SEM analyses of deposit simulants demonstrated that the addition of MgO was conducive to form magnesium magnetite and ferri-diopside, thereby avoiding the formation of hedenbergite with lower melting temperature. Moreover, the softening-melting performance and adhesivity tests confirmed that MgO had a positive effect on reducing liquid-phase deposition and inhibiting the adhesion of deposits on refractory bricks below 1250 °C. The above studies indicated that the addition of MgO helped to slow down the deposit formation of fluxed pellets prepared by coal-fired rotary kiln. Full article