Refractory Raw Materials Research Articles

Preparation of high-purity magnesia spinel refractory raw materials with spinel-wrapped periclase structures using bischofite from salt lake

A large amount of bischofite is produced in the process of potassium extraction from salt lake, which seriously affects the ionic balance of brine system. In this study, a high-purity magnesia spinel refractory raw material with a spinel-wrapped periclase structure was directly prepared using bischofite by a precipitation-sintering approach. A coupling process of one-time crude magnesium chloride solution recrystallization and three-time precipitates washing was employed to remove crucial impurities (sodium, potassium, boron, etc.) and prepare the magnesium hydroxide precipitates with a high purity of 99.37 %. The lightly calcined magnesia gained from the high-purity magnesium hydroxide precipitates and white corundum were then employed for preparing the refractory raw materials. The effects of particle size and dosage of white corundum on the phase distribution, microstructure, and physical properties of the materials were thoroughly studied. The results illustrated that the prepared refractory raw materials were mainly composed of periclase and spinel phases, showing a distinct spinel-wrapped periclase structure that could enhance the physical properties. Therefore, the prepared refractory raw materials showed a high bulk density of 3.46 g·cm−3, a low apparent porosity of 2.46 %, and a linear shrinkage rate of 12.33 %, under the optimum conditions of white corundum particle size of 3.00 μm and alumina/magnesia mass ratio of 3:10.

Fabrication of Y2O3-doped MgO refractory raw materials based on magnesium hydroxide from salt-lake brine

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y2O3 as an additive at 1780 °C. It avoided the substantial CO2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y2O3 was dispersed on the MgO grains boundaries in the fabricated MgO aggregates, resulting in a decrease in apparent porosity and enhancing the grains' boundaries. With 3 wt% addition of Y2O3, the apparent porosity and bulk density of the sample reached to 15.9 % and 3.10 g/cm3 from 37.9 % to 2.30 g/cm3 of blank control group, respectively. Compared to the blank control without Y2O3-adding, the sample with 5 wt% Y2O3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y2O3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y2O3-adding was employed to disperse the MgO grains boundaries and existed as separate phases for grains boundaries enhancement. The slag attack of the fabricated MgO–Y2O3 refractory raw materials were controlled by an inter-crystalline corrosion process.

Comparison of methods for enhancing gold recovery from double refractory concentrates using the technology of autoclave oxidation

The study aims to investigate the most efficient method for significant minimization of the impact of organic carbon on gold recovery from double refractory raw materials. We tested three double refractory gold-sulfide concentrates from different deposits with the content of gold from 23.5 to 40.9 g/t and total carbon from 1.2 to 9.5 wt %. Thermal treatment was carried out in a tubular rotary furnace that provided permanent temperature setting and rotation speed in the reactor. The initial concentrate was grinded as pulp in a Fritsch planetary mono mill Pulverisette 6. Autoclave oxidation was performed in Premex and Büchi titanium autoclaves. The technology of autoclave oxidation with the addition of a secondary oxidizer was found to be the most efficient, since it can increase gold recovery up to 97%. Another technology – hightemperature autoclave oxidation – also proved high performance; however, a significant increase in the residence time of the material in the autoclave (up to 120 min) at elevated temperatures is required to achieve this performance. According to the results, thermal treatment in general can provide a small increase in gold recovery (up to 4%). Due to this, it can be used as an additional processing with other methods analyzed in this article rather than as a self-sufficient technological solution. The studies revealed that the preliminary thermal treatment of concentrates entering autoclave oxidation shows a positive effect; high-temperature autoclave oxidation of concentrates with different carbon content provides high gold recovery for high-carbon concentrates; the use of a secondary oxidizer (in the form of nitric acid) also benefits the gold recovery. The high efficiency of the technology for concentrates with different carbon content allows us to recommend it for further research.

Characterization of refractory bricks from selected Cameroonian kaolins

AbstractThree clay materials (codded MY3, KG and KK) from western Cameroon were selected and investigated for the production of refractory bricks. Samples MY3 and KG are kaolinite-rich materials, having clay mineral contents of 88% and 72%, respectively, whereas KK is a sand-rich material with a total clay content of 44%. Chamottes were prepared using each clay, and the ground chamottes were later used in the refractory formulation, with each raw clay used as a binding phase. After firing, the X-ray diffraction analyses of all of the refractory bricks indicated the same mineral assemblage made of quartz, cristobalite and mullite. The cristobalite is due to high-temperature conversion of quartz, whereas the mullite is due to clay mineral conversion. The evaluation of the linear shrinkage, physical properties (including bulk density and open porosity) and mechanical testing through refractoriness under load and compressive strength indicates that all of these clays could be used as raw materials for standard clay refractory materials. These results stand as a proof for the potential for these locally available materials to be used as raw materials for refractories that could be locally produced to reduce the cost of access to refractory raw materials faced by industries located in Cameroon.

Performance enhancement of free CaO containing magnesia by in situ intergranular CaAl2O4 and MgAl2O4

Magnesia refractory raw material with free CaO has inherent weaknesses of low resistance to hydration, thermal shock and slag penetration. In this work, micro-sized Al2O3 powder was added into such magnesia with the purpose of improving its comprehensive performances. The results showed that with increasing Al2O3 content, CaAl2O4 and MgAl2O4 phases were sequentially formed at the MgO grain boundaries, which enlarged the MgO grains and reduced the apparent porosity. Owing to the transformation of free CaO to CaAl2O4, reduction of apparent porosity and covering of intergranular MgAl2O4 on MgO grains, hydration of the specimens was inhibited effectively by introducing the Al2O3 addition. The formed CaAl2O4 and MgAl2O4 phases lowered the thermal expansion coefficient and induced crack deflection, and therefore residual flexural strength ratio after thermal shock tests increased remarkably from 15.1% to 33.2% with increasing Al2O3 addition from 0 wt% to 7 wt%. Moreover, slag penetration resistance of the specimens was improved effectively with raising the Al2O3 content to 3 wt%, attributing to the increase in MgO grain size, decrease in apparent porosity and formation of high stable intergranular CaAl2O4 phase. However, further increasing Al2O3 content would dramatically accelerate the slag penetration owing to the decrease in grain size and formation of more unstable intergranular MgAl2O4 phase.

Characterization of Ijero-Ekiti Quartz as Refractory Raw Material for Industrial Furnace

Characterization of Ijero-Ekiti Quartz as Refractory Raw Material for Industrial Furnace

Chromite ore addition to serpentinized magnesite mining wastes for the production of refractory products following thermal treatment

Taking a circular approach to mining facilities requires the further exploitation of produced solid wastes, which are now considered as potential raw materials. This research aims to the re-utilization of specific mining wastes, containing mainly geologically degraded serpentinized minerals, produced during the minerals’ enrichment process of extractive magnesite industry, combined with the addition of chromite ore, aiming to the upgrading of refractory properties of the product, by applying the appropriate thermal treatment. A representative sample examined, corresponding to the proper blending of different mineral waste samples from several waste piles of mining area, combined with various chromite ore’s content, followed by the investigation of optimum thermal treatment, considering the applied temperature and time. The scope was to maximize the (desired) forsterite mineral phase in the product and, hence, to improve its refractory properties. The optimum results (e.g., considering the firing shrinkage level and the mechanical strength) achieved by the application of thermal treatment at 1300 °C and after heating time for 120–240 min. The refractory properties generally improved after mixing of examined mining wastes and chromite ore, due to the achievement of the best molar ratio of constituents [MgO]/[SiO2] = 2.2, regarding the additive, enhancing the formation of forsterite, whereas the application of heating temperatures over 1300 °C led to the melting of enstatite mineral phase, resulting to the degradation of product. The obtained results reveal that the produced sintered products can exhibit better refractory properties, and can be used as refractory raw materials for relevant applications up to 1300 °C.

Effect of sintering atmosphere on microstructures and properties of synthesized microporous MgO refractory raw material

AbstractEffects of sintering atmosphere on the microstructure and strength of magnesite were investigated using magnesite powder as raw material through X‐ray diffraction, scanning electron microscopy, mercury porosimetry measurement, and so on. The results showed that the sintering atmosphere strongly affected the sintering behavior of magnesite. The specimens sintered in the reducing atmosphere had more and finer micro‐sized pores inside the MgO particles compared with that in the oxidizing atmosphere at the same sintering temperature. Besides, MgO refractory raw material containing porous MgO microparticles with core–shell structure was obtained through the carbothermal reduction of MgO microparticles and subsequent oxidation of Mg vapor at the surface of MgO particles at 1500°C in the reducing atmosphere. At the reducing atmosphere and 1500°C, the microporous MgO refractory raw material with the core–shell structure of external dense and internal porous had an apparent porosity of 22.1% and a compressive strength of 51.6 MPa.

ПЕРСПЕКТИВНАЯ ОЦЕНКА РЕСУРСОВ АЛЬТЕРНАТИВНЫХ ВИДОВ АЛЮМОСИЛИКАТНОГО ОГНЕУПОРНОГО СЫРЬЯ ДАЛЬНЕВОСТОЧНОГО РЕГИОНА РОССИИ

The presence of a refractory industry characterizes the degree of industrialization. countries. Of the more than two hundred countries in the world, there is a developed refractory industry in about 35 countries. In Russia, the extraction and production of natural refractory raw materials is carried out in small quantities, amounting to units of percent of the total required quantity. The main raw material for its production is scarce and expensive alumina imported from China and other countries, 2/3 of which fall on aluminosili-cate refractories. According to the results of regional and thematic works on the territory of the Far Eastern Region of Russia, the scales of development of high-alumina formations of various genetic types have been determined: sedimentary-metamorphic (sillimanite, distene, andalusian), hydrothermal-metasomatic (alunite, alunite-dickite, alunite-diasporic), sedimentary (kaolinite), magmatic (anorthosite, labrador-anorthosite, nepheline and leucite), according to physico-chemical and technological properties (alumina content of 20-40% or more, fire resistance over 1580°C), the results of industrial research satisfying the requirements for refractory raw materials of alternative types. The presented rather extensive factual material on natural types of fire-resistant raw materials in the Far East testifies to the great potential for the formation of a raw material base for the production of refractories, the prospects of which are quite definite for the economy.

Study of refractory raw materials of the Republic of Kazakhstan

Important aspects of increasing the competitiveness of domestic metallurgy and mechanical engineering are increasing the durability of thermal units and involving non-traditional, cheaper energy resources in production. One of these resources is carbon waste from the aluminum industry - electrode scrap and waste from the carbon lining of electrolyzers. The problem of their use as substitutes for solid fuels (coke coal) in the metallurgical, engineering and energy industries is fluorine- and alkali-containing salts that impregnate them, destroying the traditional lining of thermal units. The development of effective refractories resistant to fluorine- and alkali-containing corrodants (melts and gases) makes it possible to increase the competitiveness and efficiency of thermal units both through the use of cheaper energy carriers and by increasing the duration of their campaign. An important aspect is the simultaneous disposal of hazardous industrial waste and the reduction of the environmental burden on the ecosphere of the Republic of Kazakhstan. The basis for the development of new refractory materials resistant to fluorine- and alkali-containing corrodants is the analysis of the existing raw material base of the Republic of Kazakhstan and the choice of materials that make it possible to obtain aluminosilicate refractories with increased chemical resistance. In the work, the phase and chemical composition of refractory clays and kaolins of the Republic of Kazakhstan were studied, their rheological and thermophysical properties were investigated. Selected raw materials for the development of technology for the production of dense aluminosilicate refractory products.

Utilization of recycled corundum as a refractory raw material: Characteristics and performance evaluation

Recycled corundum is a sustainable CaO–containing fused corundum obtained from aluminum–chromium slag. To effectively promote the application of recycled corundum, we characterized its physicochemical properties, sintering properties, and ladle slag corrosion resistance and compared them with those of white fused corundum. We also performed thermodynamic calculations to analyze the effect of CaO on recycled corundum under sintering and slag corrosion conditions. The experimental results indicated that recycled corundum has a lower thermal conductivity than white fused corundum and comparable sintering performance and better ladle slag resistance properties. The thermodynamic calculation results demonstrated that CaO promoted liquid sintering at temperatures above 1600 °C and a higher amount of CaAl4O7 formed after the ladle slag corrosion. The results of this study provided basic theoretical guidance for using recycled corundum as a substitute for white fused corundum in ladle–lining refractories.

Vacuum impregnation treatment of microporous Al2O3-MgAl2O4 refractory raw materials with sub-micron pores and high strength

In the present work, we propose a novel method to decrease the pore size as well as to enhance the strength of microporous Al2O3-MgAl2O4 refractory raw materials, which were prepared by the vacuum impregnation treatment of porous Al2O3 powders with at MgCl2 solution. The effect of the MgCl2 content (0–32.5 wt%) on the phase distribution, microstructures, and physical properties of the refractory raw materials was thoroughly investigated. The results demonstrated that the sub-micron pore structure inside the pseudomorph particles was effectively preserved due to the volume expansion effect of spinel and the spinel sintering neck formation between Al2O3 microcrystallites. With the MgCl2 content increasing from 0 to 11.9 wt%, the pseudomorph particles contained many sub-micron pores resulting from the introduction of the MgCl2 solution, resulting in the decrease of the intra-particle pore size as well as the development of spinel sintering necks between pseudomorph particles. The strength of the aggregates was therefore enhanced. With a further increase of MgCl2 content to 24.2 and 32.5 wt%, the inter-particle pore sizes increased due to the volume expansion and Kirkendall effect associated with the spinel formation between pseudomorph particles, which were responsible for the progressive decrease of the strength. Overall, the optimized samples were microporous Al2O3-MgAl2O4 refractory aggregates with the addition of 11.9 wt% MgCl2, which exhibited an apparent porosity of 45.0%, a high compressive strength of 45.6 MPa, a median pore size of only 1.49 µm, and a high sub-micron pore volume content of 42.5 vol%. Meanwhile, it is possible to obtain the porous Al2O3-MgAl2O4 powders with a large number of sub-micron pores by crushing and sieving the optimized aggregates.

Mechanical Evaluation and Minerals Phases Identification of Fine and Coarse Okelele Block Clay Composites for Furnace Lining Application

The suitability of fine and coarse Okelele clays as refractory raw materials for furnace lining application was investigated. The clay samples were crushed and pounded with a mortar and pestle to a particle size of 20 microns. 230 g each of fine clay was mixed with 50 mls of water inside a bowl and stirred thoroughly to form homogenous plastic paste. 10 g, 15 g, 25 g, 35 g and 45 g of coarse clay were added respectively to the 230 g of homogenous fine clay paste in different container. The fine and coarse clays composites weighing 240 g, 245 g, 255 g, 265 g and 275 g were respectively put in a mold of dimension 3 x 5 x 6 cm and air dried for 7 days. The samples were fired at temperature of 1200 oC for five hours using Carbolite Furnace. After cooling, the fine and coarse clay composites of 240 g and 245g were broken by the heat and composites blocks 255 g, 265g and 275g were hardened and remove for compressive test analysis. The fine and coarse clays were characterized using X-ray Diffractometer PW1830forminerals phases’ identification. The result of XRD shows that the clay was majorly composed of Quartz and Kaolinite with the traces of other minerals such as Smectile, Illite/Mica, Albite, Jarosite, Gypsum and Pyrite. The Kaolinite contains aluminum silicate (Al2O3·2SiO2) and Quartz has the silicon and oxygen atoms. The compressive strength test result judged the 275 g fire block of clays composite the best with the maximum force breaks of 7652 N with deflection of 3.734 mm and Young Modulus of 212 N/mm2 for the time to failure of 22 seconds. The results proved that Okelele clays are suitable as refractory material for furnace lining application.

Preparation of tabular corundum aggregate from different sources alumina raw powder: Sintering kinetics and establishment of kinetics model

In this paper, we report the use of four types of commercial alumina raw powders as raw materials for the preparation of tabular corundum aggregates under the same conditions. The influence of the transition phases of alumina raw powder on the sintering kinetics of tabular corundum is discussed, the sintering model of materials with pseudomorphic structure is established, and the mechanisms underlying the different performances of various commercial tabular corundum samples are evaluated. The following conclusions were drawn based on the results of the study. (1) A double tetrakaidecahedron model was established and was shown to satisfactorily describes the sintering mechanism of alumina raw powder with pseudomorphic structure, which accords with the porosity change trend of sintered body and provides a basis for perfecting the sintering theory. (2) Compared with the other transition phases, γ-Al2O3 shows the largest phase transformation volume contraction, which provides the driving force for the sintering process via an increase in surface energy and mainly acts in the densification and grain growth stages. Thus, high-quality refractory raw materials are prepared with optimized physical properties and Intracrystalline pores or pore clusters in the crystal structure. The preparation of these high-quality refractory products is of importance for prolonging the life of these materials and also meeting rising energy demands.

Corrosion Resistance of MgO and Cr2O3-Based Refractory Raw Materials to PbO-Rich Cu Slag Determined by Hot-Stage Microscopy and Pellet Corrosion Test.

Chemical resistance of commercial refractory raw materials against Cu slag is critical to consider them as candidates for the production of refractories used in Cu metallurgy. In this study, we show the comparative results for the corrosion resistance of four commercial refractory raw materials—magnesia chromite co-clinkers FMC 45 and FMC 57, PAK, and fused spinel SP AM 70—against aggressive, low-melting PbO-rich Cu slag (Z1) determined by hot-stage microscopy (up to 1450 °C) and pellet test (1100 and 1400 °C). Samples were characterized after the pellet test by XRD, SEM/EDS, and examination of their physicochemical properties to explore the corrosion reactions and then assess comparatively their chemical resistance. Since many works have focused on corrosion resistance of refractory products, the individual refractory raw materials have not been investigated so far. In this work, we show that magnesia chromite co-clinker FMC 45 exhibits the most beneficial properties considering its application in the production of refractories for the Cu industry. Forsterite (Mg2SiO4) and güggenite (Cu2MgO3) solid solutions constitute corrosion products in FMC 45, and its mixture with slag shows moderate dimensional stability at high temperatures. On the other hand, the fused spinel SP AM 70 is the least resistant to PbO-rich Cu slag (Z1); it starts to sinter at 970 °C, followed by a fast 8%-shrinkage caused by the formation of güggenite solid solution in significant amounts.

Evaluation of remelting low-fluxing ferrotitanium slag as a potential refractory raw material: Thermal characteristics and stability

To effectively promote the utilization of metallurgical waste slag, studies on the characteristics and stability of waste slag are essential for waste reuse. Ferrotitanium slag is a byproduct of smelting ferrotitanium with thermite reduction. Low-fluxing ferrotitanium slag (LFS) is the main type of dumping slags produced by ferrotitanium smelting. In this study, an electric arc furnace was used to prepare remelting LFS (RLFS) for homogenization and impurity removal. The characteristics and thermal stability of RLFS as a refractory raw material were characterized. The thermal stability of RLFS was tested under different working conditions. A phase-structure transition mechanism of RLFS particles was established according to the thermal stability test and thermodynamic calculations. The Al2O3 content in RLFS exceeded 80%, and RLFS had lower thermal conductivity than brown corundum, but a similar thermal expansion coefficient. The results show that RLFS is a suitable substitute for corundum raw material; the thermal stability test results show that RLFS was susceptible to crack propagation in an oxidizing environment above 1280 °C. The findings of this research provide suggestions for the utilization of RLFS to improve the application stability of refractory products using recycled raw materials.

Interlaboratory comparison of the work quality of chemical-analytical units of a number of refractory industry enterprises in Ukraine in 2020

One of the ways to check the correctness of international standards use is interlaboratory comparison of the work results of testing laboratories. Such work has been carried out by JSC “The URIR named after A. S. Berezhnoy” for more than 20 years and allows one to assess the reproducibility and repeatability of chemical analyzes results of refractories and refractory raw materials at the manufacture of refractories and their certification in the both the chemical-analytical unit of the institute and laboratories of partner enterprises.
 The interlaboratory comparison of work quality of chemical-analytical units of a number of refractory industry enterprises in Ukraine (JSC “KDZ”, JSC “CRP”, JSC “VRP”) and JSC “The URIR named after A. S. Berezhnoy” was carried out. The discrepancy between the average results of chemical analysis in the chemical-analytical unit of refractory enterprises and in the laboratory of institute did not exceed the permissible value of γ in terms of ND. The work quality of chemical-analytical units of central refractory laboratories of all the above mentioned refractory enterprises was satisfactory. Recommendations for improving the accuracy of the chemical analysis results in the refractory enterprises laboratories that participated in the tests were not required.

Опыт развития, внедрения и стандартизации BIM (ТИМ)-проектирования в горнодобывающей отрасли

The modern metals industry is characterised by a downward trend in the quality of ores involved in processing, and conventional methods of extracting useful components are inefficient for raw materials with complex composition. To maintain the growing level of metal production it is required to introduce new efficient technologies for processing of low-grade and refractory ores as well as man-made deposits. The article describes processing methods of refractory raw materials with high cyanide content using copper-gold ores as an example, where gold is the primary commodity, and copper is the accompanying useful component. The most common method of processing copper-gold ores is preconcentration followed by selective leaching of copper and gold. In some cases, technologies involving copper by-products and cyanide recovery from the cyanide leaching solutions offer equally effective options for processing of the copper-gold ores and concentrates. Copper-gold ores are processed at gold mines using the cyanide procedures, supplemented if required by gravity and flotation concentration. In all variations of the cyanide treatment, most of copper minerals actively react with cyanides of alkali metals, binding the CN– ions into the copper complex of [Cu(CN3)]2–. This reaction results in an increased solvent consumption, as well as in number of challenges related to cleaning tailings and slurries from highly toxic cyanide compounds and dissolved copper. In addition to technological complications associated with the need to meet strict requirements for the maximum permissible concentrations, copper accumulated in the cycling solutions also causes a decrease in gold extraction from the processed ores.

ИЗУЧЕНИЕ ВЛИЯНИЯ ЗАПОЛНИТЕЛЯ НА ОСНОВЕ ОТХОДОВ КЕРАМОГРАНИТА НА ФИЗИКО-МЕХАНИЧЕСКИЕ СВОЙСТВА ГОРЯЧИХ МЕЛКОЗЕРНИСТЫХ АСФАЛЬТОБЕТОНОВ

The results of research are presented when replacing finely crushed mineral part of asphalt concrete with waste from the production of porcelain stoneware, which is a product of high-temperature firing of a mixture of refractory clay raw materials and feldspar rocks, which provides high physical and mechanical properties of waste and further road surface.

OLİVİNİN REFRAKTER HAMMADDESİ OLARAK KULLANIMI İÇİN DEMİR İÇERİĞİNİN MANYETİK AYIRMA İLE AZALTILMASI

Bu çalışmada, kromit zenginleştirilmesinde nihai artık olarak elde edilen bir olivin numunesindeki demir içeriğinin manyetik ayırma yöntemleri ile azaltılabilme potansiyeli incelenmiştir. Bu kapsamda, öncelikle numune +212, -212+150 ve -150 µm olarak üç fraksiyona ayrılmıştır. Sonrasında iri boyutlara kuru, ince boyuta ise yaş manyetik ayırma uygulanmıştır. Sonuçlar manyetik olmayan fraksiyonun ağırlık yüzdesi, Fe2O3 içeriği ve demir giderimi (%) gibi parametreler kullanılarak değerlendirilmiştir. Ayrıca manyetik olmayan fraksiyonlardaki mineralojik fazların miktarlarındaki değişimler XRD analizleri ile belirlenmiştir. +212 ve -212+150 µm için optimum değerlere sırasıyla 0,50-0,75 ve 1,0-2,0 A akım şiddeti aralıklarında ulaşılabileceği tespit edilmiştir. Her ne kadar karşılaştırılabilir olmasa da, -150 µm için efektif ayırmanın 2,0-3,0 A aralığında sağlandığı görülmüştür. Küçülen tane boyutu ile azalan demir içerikleri elde edilen bu sonuçları doğrular niteliktedir. XRD desenlerindeki demir içeriği yüksek fazların pik şiddetlerindeki azalışların da yine manyetik ayırma sonuçları ile uyumlu olduğu tespit edilmiştir. Genel sonuçlar, olivince zengin numunedeki demir içeriğinin manyetik ayırma ile refrakter hammaddesi için gerekli sınır değerlere çekilebileceğini göstermiştir.