Fused periclase is finding increasing use for the production of refractories and powders, and also as an electrical insulating material in electrical engineering and certain other industries.The main criteria of the quality of this material are the magnesia concentration and the impurity oxide content. High demands are placed on the chemical composition of electricalengineering periclase in which the main-component concentration (MgO) for various grades (GOST 13236-73) is 95-98% and above. Metallurgists use powdered fused periclase containing 93-97% MgO. The behavior of refractories in electric-insulating materials in service is also determined by their fine structure and degree of crystal defectiveness, the mineral and spatial form of impurity distribution, and other factors.Fused periclase is produced from magnesite from the Satkinsk, Talsk and Kirgiteisk deposits, Kul'dursk brucites, and calcined magnesia from the production of Soviet and foreign chemical factories. Electrlcal-engineering periclase of high quality is obtained from chemically beneficiated magnesites [i, 2].The chemical composition and electrical properties of fused periclase (Table i) show that the quality of the product largely depends on the chemical composition of the materials ( Table 2). The chemical composition of brucite and magnesite may be improved by crushing before fusing to obtain lumps less than 60 mm in size, followed by screening off the grains below i0 mm in which the largest amounts of impurities are concentrated. The magnesia content is thereby raised by 1-1.5%.Experimental studies and practical work at Bogdanovich have established that the high purity of the periclase (with regard to chemical composition) is not always the factor determining the best electrical properties. For example, periclase fused from chemically pure magnesia corresponds to class-3 in terms of electrical resistance (GOST 13236-73). At the same time, periclase obtained from Satkinsk magnesite with a high content of Fe203 in some cases meets class-2 demands for electrical resistance.The original materials undergo complex physicochemical changes during melting. The growth of periclase crystals is accomplished in different sections of the block as a result of five basic processes (Fig. i, l-V). The block thus acquires a zonal structure [3]. Due to the irregular temperature field, disparate growth of crystals with thedifferent mechanisms and the action of gravitation as the periclase melts, there is marked differentiation in the melt's components, and the various zones of the block are enriched with magnesia, while the impurities accumulate in a skin, the central zone, and the melter dust. Most redistribution in the block is experienced by the calcium oxide and the silica, and the least by the iron and aluminum oxides [3].Trial industrial meltings with various materials showed that the block structure, the nature of the zones, and the amount of impurities in the periclase can be regulated through batch feed, melting rates, and cooling rates. For example, per...

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Nowadays about 200 million tons of phosphogypsum (PG) have been stored in the dumps of the chemical industry and non–ferrous metallurgy of Russia which pollutes the environment. This waste contains up to 98 % of two–water gypsum and impurities including rare earth metals (REM) in an amount of up to 0.5 % preventing its use in the production of building materials. A complex technology of FG recycling including extraction of REM, neutralization and dehydration of the pulp for using in the production of gypsum binders and Portland cement. Results of determination of density, grain, chemical and mineral compositions and structure of the product of recycling of FG of the “Sredneuralsky copper smelting plant” are presented. After the REM extraction, the PG is a loose lumpy mass with moisture content of 28–32 % which contains about 10 % of particles larger than 40 mm and not more than 60 % of particles less than 10 mm, it has a true density of 2.26 g/cm3, pH of aqueous extract is 5.95. It has the following chemical composition, mass. %: 0.87 SiО2; 0.93 A12O3; 0.20 Fe2O3; 31.00 CaO; 0.034 MgO; 44.27 SО3; 0.10 K2О; 0.42 Nа2О; 0.45 Р2О5(general); 20.73 of mass loss of ignition. The mineral composition of the PG processing product is represented by two-water gypsum and a slight amount of quartz. The possibility of using gypsum–containing waste in the production of gypsum binders and cement is considered. The effect of temperature and duration of firing, the dispersion, the type and quantity of chemical and mineral admixtures on physical and mechanical properties of gypsum binder, the influence of the type and amount of mineral additive on pelletizing and physic–mechanical properties of the granulated and pressed PG and its effects on setting time and strength of Portland cement are represented. It is recommended to use PG to obtain low–temperature and composite gypsum binders, regulation of Portland cement setting after extraction of REM. Keywords: phosphogypsum, recycling, composition, properties, technology, gypsum binder, Portland cement

Optimum formulations for castables intended for different service conditions are proposed. Silicon carbide castables containing ultradisperse particles of cement, silica fume, and electrofused corundum are developed. The castables do not weaken on heating and display superior operational properties: the compressive strength is 40 -80 MPa at sintering temperature 400°C and 50 -85 MPa at 1300°C, the strain onset temperature under a load of 0.2 MPa is 1700 -1510°C; thermal stability (1300°C -water) is better than 45 heating/cooling cycles (1300°C -water); no change in linear and volume dimensions was observed on heating. The newly-developed castables can find application in various sectors of industry, in particular, as the refractory material for the lining of Whiting furnaces and porcelain kilns.Under the new economy, survival of the refractory industry depends on the ability of the manufacturer to promptly respond to requests and concerns of the market, and to improve the production technology to meet consumers' needs. Under these conditions, there is a consistent tendency among foreign manufacturers to increase the share of unshaped castables in the overall balance of refractory materials. The relatively low labor input and ease of fabricability in the manufacture of refractories are the factors that have determined the ever-increasing use of unshaped refractories for the lining of intermediate and pouring ladle, for preparation of gunning mixes, etc. In recent years, the performance characteristics of unshaped refractory materials and linings based on them are becoming increasingly competitive with those of shaped components. The demand for unshaped and nonfired refractories, unlike that for shaped and fired materials, is constantly on the rise. Development and fabrication of vibrocast monolithic linings and components is another important field for creative efforts in the refractory industry.A survey of the literature has shown that refractory castables of corundum, aluminosilicate, and spinel composition have become widespread in the refractory industry. To the best of our knowledge, no data on the production of a new generation of refractory castables based on silicon carbide could be found in the domestic literature whereas these materials are commercially available from foreign manufacturers.Silicon carbide refractories, owing to their specific properties, have found wide application in different sectors of industry. Silicon carbide refractories, owing to their high heat conductivity, have found widespread use in the manufacture of muffles, furnace bottoms, and recuperators. The high mechanical strength and abrasive resistance over wide a temperature range make silicon carbide refractories a perfect material for fabrication of parts and components intended for service under heavy-duty conditions including low temperatures: guide rails and rods, cyclone lining, dust collectors, pipelines, troughs and other facilities subjected to intense abrasion, furnace cars, etc. Silicon carbide, owing to its specific ch...