Sintering magnesium oxide obtained by the chemical beneficiation of magnesite

Conclusions A quantitative relationship was established for sintering chemically beneficiated magnesite and a method of obtaining the MgO; we also established the parameters of hydrolysis of the magnesium chloride, the quantity of residual volatiles, the temperature and rate of thermal activation of residual volatiles, the temperature and rate of thermal activation of the magnesium oxide, not washed, and washed to get rid of the calcium impurities, and also the completeness of the hydration of the magnesium oxide during leaching.A production flow line is proposed for obtaining from the enriched material sintered periclase clinkers differing in density and degree of purity.Translated from Ogneupory, No. 7, pp. 43–50, July, 1982.     

Structure and properties of fused periclase and periclase-chromite blocks produced from beneficiated starting materials

Conclusions Fused periclase and periclase-chromite blocks containing a high proportion of highmelting oxides of magnesium and chrome were produced from beneficiated starting materials.The structure and properties of the periclase and periclase-chromite were analyzed zonewise in the blocks. The thickness of the block zones with a high content of magnesium oxide and the yield of high-quality periclase and periclase-chromite depend on the degree of purity of the chemical composition of the starting materials.The content of magnesium oxide is highest and the proportion of contaminating oxides low in fused periclase produced from chemically beneficiated Satkin magnesite, and in the monocrystalline subzones of the blocks. An increase in the proportion of chromite in the mix results in a higher porosity and in a higher content of spinel and ferrochrome in the fused material. The properties are optimal in the case of a periclase-chromite material from a mix containing 15–20% chromite.Translated from Ogneupory, No. 3, pp. 37–44, March, 1978.     

Sintering of magnesium hydroxide obtained from magnesium chloride solutions

Conclusions We studied two batches of magnesium hydroxide obtained by precipitating out (using dolomite milk) from magnesium chloride solution formed when processing potassium ores.The effect of the compaction pressure, the firing temperature, and prior heat treatment on the sintering process of magnesium hydroxide was investigated.The experimental samples of magnesium hydroxide exhibit high sinterability and facilitate the production of periclase powders (powder bodies) having a porosity of 6.8–9.9% at a firing temperature of 1600°C. The degree of sintering of magnesium hydroxide increases with increasing compaction pressure and firing temperature. Prior heat treatment of the material at 800–1000°C intensifies the sintering process with simultaneous reduction of shrinkage.The studies conducted on the specimens prepared from a fired briquette established that the periclase (magnesite) powder obtained from magnesium hydroxide is suitable for the production of magnesia refractories.A. V. Kushchenko and G. G. Eliseeva (UkrNIIO) participated in this investigation.Translated from Ogneupory, No. 2, pp. 7–10, February, 1988.     

Effect of Some Lithium Compounds on Sintering of MgO

The addition of 0.25% or more of certain lithium compounds, particularly the halides, facilitates the pressing and sintering of reactive forms of high-purity magnesium oxide. Densities up to 3.46 gm. per cm.³ have been obtained at 1400°C. with reagent-grade magnesium oxide containing 0.5% lithium chloride as an additive. The effectiveness of lithium salts as sintering catalysts for magnesium oxide depends on the original surface area and particle size of the MgO. After autoclaving at 150 lb. per sq. in. gauge for 2 hours, samples of MgO sintered at 1400°C. with 0.5%of LiCl showed a water absorption comparable to that of fused magnesium oxide. Similar samples of lithium-treated periclase had about the same resistance to attack by a NaOH-FeO melt as pure MgO fired at 1800° to 1850°C.     

Raw material sources of magnesium oxide of the central and Western Ukraine

Conclusions For the purpose of elimination of importing of periclase powders it is desirable to organize the production of magnesium oxide from nontraditional resources. Three large bases of production may be mentioned: Crimea, Poltava Oblast, and the Western Ukraine. These bases are not alternatives and only introduction of all of them would make it possible to completely eliminate importation of periclase powders, which is becoming increasingly burdensome.Production of magnesium oxide may be organized in the shortest time in the Western Ukraine on the basis of processing the by-products production of Stebnik Potassium Plant and of the dolomites of Zavadovsk and/or Kuze deposits since there is shut-down production capacity with a large production infrastructure and sufficient free facilities within the limits of its own land. There are requirements for the by-products and wastes of production of magnesium oxide, which makes it possible to organize practically waste-free production.To open up the raw material source of the Central Ukraine, Poltava Oblast bischofite, it is first necessary to confirm the bischofite reserves in the established order. Opening up of the bischofite deposit requires a composite approach to processing of it and use of ground water accompanying extraction of petroleum and gas.The creation of a corporation is desirable for solution of problems of introduction of all three sources and coordination and concentration of the efforts of all sides interested in this.Translated from Ogneupory, No. 2, pp. 23–27, February     

Hot press compaction of magnesium oxide obtained by decomposing certain compounds

Conclusions A study was made of the densification during hot pressing at 1300–1600°C of magnesium oxide activated by decomposing the hydroxide and the basic magnesium hydrocarbonate. During decomposition of these compounds at 500–700°C with a soak of 15 min, magnesium oxide forms that is actively compacted almost to the theoretical density (98.5–99.5%) at relatively low temperatures (1500–1600°C) and pressures of 150 kg/cm².We investigated the influence of the time and temperature of heat processing of the hydroxide and the basic hydrocarbonate of magnesium on the fineness of the grains and the defects of the crystalline lattices of periclase thus formed, and also on the capacity for subsequent compaction during hot pressing.The reduction in the degree of compaction during hot pressing of the materials, heat processed at temperatures below 500°C, is due to the increase in the content in them of undecomposed residue, which hinders the diffusion sintering in subsequent stages of pressing.A reduction in the degree of compaction with rise in temperature of heat processing above 500°C or with an increase in the heat-processing time with the optimum temperature, is connected not with a reduction in the defects of the crystalline lattice of the periclase formed, but with the sizes and physical state of its particles.We also studied the effect of additions of magnesium oxide obtained by heat processing the hydroxide or the basic hydrocarbonate of magnesium on the compaction during hot pressing of industrial magnesia. The introduction of 10–20% of this additive ensures a reduction in the optimum pressing temperature of 100–300°C and an increase in the density of the specimens almost to theoretical.Translated from Ogneupory, No.2, pp.46–53, February, 1967.     

The sintering kinetics of well-brine magnesia

Conclusions The sintering of well-brine magnesium hydroxide proceeds in accordance with the laws governing solid-phase sintering, regardless of its degree of purity (within an MgO content of 96–98%) and of the type of precipitant used.The contraction kinetics of the magnesium hydroxide under isothermal conditions is characterized by the fact that l/lis approximately proportional to t^1/2. The contraction and compaction rates are at a maximum at 1000–1300°C and decrease significantly at higher temperatures.The contraction rate of specimens from calcined magnesium hydroxide was found to be 2–3 times lower than that of dried magnesium hydroxide.The specimens are compacted while contracting; in the elimination of the open pores P/P is approximately proportional to t^1/2 and in that of the closed pores to t^1/3.With an increase in the temperature from 1000 to 1700°C the compaction of the material is accompanied by periclase recrystallization. The periclase grains begin to grow rapidly after 1500C at an open porosity of 10–12%.At a temperature above 1500°C the recrystallization rate is so high that some open pores are entrapped in the growing crystals, resulting in closed porosity, the elimination of which is difficult. The sintering rate increases sharply at the same time.Given these general regularities, which support earlier findings, it is possible that the contraction will vary slightly with the chemical composition and heat treatment conditions of the specimens of well-brine magnesium hydroxide.Translated from Ogneupory, No. 6, pp. 39–44, June, 1974.     

Production technology and quality of fused periclase

Conclusions A relationship was established between certain technological parameters, properties, and structural features of fused periclase.It was shown that the main factors in obtaining high quality periclase are the purity of the raw materials, determining the high MgO concentration in periclase; rational fusing cycle, ensuring migration of the impurities into the skin of the block and governing the features of the structure of the crystals; magnetic separation, permitting the ferromagnetic particles and part of the silicates to be removed; and crushing and milling, ensuring the optimum grain-size composition in the powder.A properly selected combination of these factors will improve the quality of the fused periclase and increase the resistance of periclase thermoelectric heating elements and refractories in service.Translated from Ogneupory, No. 2, pp. 5–10, February, 1979.     

Periclase-spinel products based on sintered materials for vacuum treatment of steel outside the furnace

Conclusions A technology was developed for periclass-spinel, low-silica chrome-concentrate (SiO₂ <1.5%) and sintered periclase (MgO 91–92%, SiO₂ < 3%). As regards the resistance in the walls of the metal zone of circulation vacuum equipment, these refractories are not inferior to PKhP periclase-chromite goods made from fused materials.In the production of PShKh articles it is recommended that titanium additives be used to ensure sintering of the chrome-concentrate to a low porosity, and to stabilize the properties of goods made with it.It is desirable to make wider tests of these refractories in vacuum units of different types. The introduction of PShKh articles based on sintered materials in the walls instead of PKhP articles should reduce the consumption of scarce fused materials for vacuum treatment and cut the costs of the linings.Translated from Ogneupory, No. 7, pp. 32–36, July, 1991.Deceased.     

A Technology for Production of Composite Refractory Materials for the Lining of Steel Ladles

Results of the testing of new refractory materials for the lining of steel ladles are reported. Refractories based on coarsely crystalline periclase (98% MgO) for the slag zone with an endurance of 55 – 60 heats and wear rate of 2.3 mm/heat were tested. For the bottom lining of the steel ladle, alumina-periclase-carbon refractories using fused or sintered alumomagnesian spinels are developed. Performance characteristics of the newly developed refractory materials are discussed.__________Translated from Novye Ogneupory, No. 1, pp. 6 – 9, January, 2005.     

Influence of mechanical activation of basic refractories and mixtures on sintering

Conclusions Mechanical activation leads to partial breakdown of the crystalline structures of refractory materials, conferring a higher reaction state on them. This is manifest as a reduction in the temperature range in which the magnesite and dolomite undergo conversions during heating, and also in the greater degree of exposure of the periclase and chrome concentrate.The porosity of the clinker obtained from activated sintered periclase with (CaO + SiO₂) >3.5%, fused periclase obtained from magnesite calcined in a shaft furnace, raw magnesite and periclase-skin, is reduced by more than an order compared with the original. It is considerably less for periclase-chromite skin, is reduced by more than an order compared with the original. It is considerably less for periclase-chromite skin, sintered periclase with (CaO + SiO₂) <3.5%, fused periclase-chromite, and periclase obtained from Kul'dursk brucite.To determine the possibility of applying these results in production conditions, research is now being conducted to select effective production activators, e.g., equipment with an elastic deformable working component.The authors would like to thank N. B. Kusin'sh, G. I. Vikulina, G. N. Bondarenko, and A. P. Kima for assistance in completing this work.Translated from Ogneupory, No. 3, pp. 14–17, March, 1993.     

水氯镁石制备金属镁的过程集成与能量分析

以无水氯化镁和氧化镁作为中间产物,电解和热还原为两个关键方法,集成各种相关过程,构建了从水氯镁石到金属镁的综合过程网络,其中涉及24个物种、20个化学过程和25个工艺路线;建立了最低能耗分析模型用于简单和复合过程的能量分析;利用物质的标准生成焓和多温等压摩尔热容,计算得出全部反应过程及工艺过程的能量消耗和热量移除。结果表明基于还原法的最优路径是水氯镁石用石灰法转为氢氧化镁,进而煅烧成氧化镁,再铝热还原成金属镁,该过程能耗360.15 kJ/mol,放出热量–315.46 kJ/mol;基于电解法的最优路径是石灰乳法生成氢氧化镁,再煅烧成氧化镁,通过在熔融电解质中电解生成金属镁,该过程能耗738.54 kJ/mol,放出热量–135.42 kJ/mol。无水氯化镁制备耗能高,不在最优路径中。     

Manufacturing of magnesium hydroxide from natural magnesium chloride sources

Various processes for manufacturing magnesium hydroxide have been considered and tested in order to decide whether they can be employed to the full-scale production of this product from natural sources (bischofite and magnesium chloride brines). The process for the synthesis of magnesium hydroxide from magnesium chloride using sodium hydroxide has been improved.     

Sintering magnesium oxide made from magnesium hydroxycarbonate

Conclusions The studies have shown that the fine structure of activated MgO depends on whether the temperature regime under which the magnesium hydroxycarbonate is calcined is fast or slow. In the rapid activation regime, subdispersed particles of MgO with maximum defects of the crystal lattice are formed and this help the diffusion sintering of the MgO.The use of nonaqueous organic binding agents which burn out rapidly in the 300–460°C interval and (in the case of the slow activation regimes) the addition of chrome-spinel and ZrO₂ also improve the sintering of MgO.The high initial disperseness of MgO and the presence of a surface-active binder make it possible by firing at 1500–1600°C to produce a high-density material which is suitable for the manufacture of dense and thermal shock resistant periclase articles.Deceased.Translated from Ogneupory, No. 5, pp. 47–51, May, 1979.     

Effect of modifying additions on the binding properties of lignosulfonates

The effect of various modifying additions to technical lignosulfonates used in the production of periclase (from fused and sintered periclase), chromite-periclase, and thermostable chromite-periclase articles is investigated. An acceptable strength for the green material for periclase articles is provided by lignosulfonates produced by the Kamsk Wood-Pulp and Paper Plant. The recommended modifying addition is carbamide. An addition of tall oil reduces the strength of greenware but improves the properties of articles after firing. Lignosulfonates with additions of carbamide, aluminum chloride, and titanium sulfate are considered the most efficient for chromium-containing articles.Translated from Ogneupory, No. 12, pp. 15 – 21, December, 1994.     

Service of rammed crucibles for melting noble metals in induction furnaces

Conclusions We prepared and tested in service crucibles of fused magnesium oxide with special additions, having a considerably higher resistance in induction-furnace conditions at temperatures of about 2000°C. The additives guaranteed the necessary sintering of the working zone in the crucible, and helped to form a direct bond between the crystals of periclase.The structure of the used crucibles is described. The formation of the zone structure is connected with the temperature gradient, and in the hot zones is accompanied by intensive recrystallization and growth of periclase crystals.Translated from Ogneupory, No. 5, pp. 19–23, May, 1969.     

有机溶剂-微波-水热法制备氢氧化镁晶须

以青海东台水氯镁石混合物为原料,以含一定量有机溶剂的氢氧化钠为沉淀剂,采用微波-水热法制备了氢氧化镁晶须。实验发现在水热温度为180℃,反应时间为1.5 h的条件下,氢氧化镁晶须产率与有机溶剂在反应体系中的质量分数有关,当质量分数为30%时可获得产率为80%的氢氧化镁晶须,但继续增加有机溶剂的质量分数晶须产率不再增加。扫描电镜照片显示粒子呈晶须形状、粒度分布均匀、分散性好、晶形好、纯度高。本实验不仅生产工艺简单,且生产成本低,具有较高的经济效益,可望充分利用盐湖镁资源进一步中试。     

A study of masses based on chemically synthesized materials in the system MgO-Cr2O3

Conclusions Additions in the form of TiO₂ or ZrO₂ are recommended in order to obtain effective sintering of the chemically synthesized composite MgO + MgCr₂O₄, obtained from the thermal decomposition of magnesium chromate. The articles prepared in accordance with the new process based on dense-sintered clinker have excellent physicochemical properties. The experimental tap hole blocks made using the clinker process showed 1.5 times greater resistance than that of fused periclase blocks when tested at the Nizhnetagilsk Metallurgical Combine.Translated from Ogneupory, No. 2, pp. 35–38, February, 1984.     

由菱镁矿制备高纯纳米氧化镁的新工艺

以菱镁矿、工业级硫酸铵和碳酸铵为原料,采用复配的表面改性剂,用液相沉淀法制备高纯纳米氧化铗粉体。在优化工艺条件下,制得平均粒径为65nm、纯度超过99．5％的纳米氧化镁粉体,产品粒径分布较窄,分散性良好。该工艺过程简单,产品质量稳定,适宜于工业化生产。     

Fabrication of periclase and magnesium aluminate spinel refractory from washed residue of secondary aluminum dross

A novel method for fabricating the periclase and magnesium aluminate spinel refractory from the secondary aluminum dross was proposed in the present work by adding magnesium oxide. The fabrication mechanism of the refractory was analyzed by thermogravimetric and differential thermal analysis, scanning electron microscopy, and X-ray Diffraction. The effects of MgO addition and sintering temperature on the mechanical properties and density of refractories were studied. The results showed that with the increase of sintering temperature, the purity, crystallinity, and densification of the refractory were significantly improved, and the porosity of the refractory was decreased. As an obvious second phase in the refractory, periclase can strengthen the grain–grain bonding and inhibit the grain boundary movement. With the increase of MgO addition, due to the significant reduction of porosity, the improvement of grain size uniformity and the absence of microcracks, the flexural strength and the impact toughness were significantly improved. When the MgO addition was 50 wt% at the sintering temperature of 1600 °C, the density and porosity of the refractory were 2.92 g/cm³ and 18.2%, while the flexural strength and impact toughness can reach 270 MPa and 3.7 MPa m^1/2, respectively.