Utilization value of magnesia chrome bricks for steel

Many countries, especially developed countries, attach great importance to the reuse of waste refractory materials. The reuse rate is generally high, and some steel plants have reached more than 80%. In this respect, the company started early and the technology is relatively mature. The reuse rate of refractory materials used by Shido Steel in Japan has reached 50%~100%. In the iron and steel industry of Japan, waste refractory materials are mainly used as substitutes for slag making mixture and molding sand. Some steel plants mainly use waste bricks as raw materials, and have developed ramming materials around the ladle bottom, ladle castables and shaping products. For example, unburned magnesia bricks are used in the electric furnace molten pool produced with 85% recycled materials and 15% new materials, magnesia carbon bricks are used in the electric furnace slag line produced with 90% recycled materials and 10% new materials, and RH bottom fired magnesia chrome bricks are all produced with recycled materials. The submerged nozzle brick was developed by Heiqi Company using waste corundum graphite products as raw materials; Ludao Iron and Steel Company has developed the secondary utilization process of slide block.

The waste refractory of the taphole is reused, which is mainly used as the aggregate of Al2O3-SiC-C castable. In the United States, waste refractory materials are used in desulfurizer, slag modifier (slagging agent), slag splashing furnace protection additive, raw materials of calcium aluminate cement, refractory concrete aggregate, paving materials, ceramic raw materials, raw materials for glass industry, granular materials for roof construction, abrasives, soil modifier, etc. It has also achieved good results in the research of using tlzx stone bricks as soil regulator and slag making agent. Valoref, a French company specializing in the global waste refractory business, has invented many technologies for recycling most of the waste refractory materials from glass, steel, chemical industry, waste incineration and other industries and the furnace dismantling method for recycling, which has made the recycling rate of refractory materials used in French glass kilns reach 60% in 1997.

In China, the utilization rate of waste refractory materials is not high, but in recent years, there has been great development, Waste refractory materials are usually used for metallurgy Auxiliary raw materials of the industry. Waste refractory bricks and amorphous refractory materials, including MgO-C bricks, are usually used for hot repair of furnace lining, casting hole opening agent, or raw materials for manufacturing new MgO-C bricks; waste Al2O3-C bricks can also be used as raw materials for manufacturing sliding plate bricks, submerged nozzle bricks, and protective sleeves. Waste refractory materials used for secondary utilization and repair are: Al2O3-ZrO2-SiO2 bricks, large bricks for glass furnaces, oxygen converters, and electric arc steelmaking MgO-C bricks for furnaces and ladles, magnesia chrome bricks for electric furnaces, etc. Baosteel has conducted research on the reuse of silicon carbide containing and carbon based post use refractories for equipment from magnesia carbon bricks used in ladles and converters to lining bricks of high-speed furnace iron ditches and mixer cars, and has initially achieved good results. Typical products include recycled magnesia carbon brick, ASC castable, etc.

1. Magnesia alumina spinel refractory

In a broad sense, spinel refers to minerals belonging to the spinel family. Its general chemical formula is AO · B2O3 or AB2O4, where A is a positive divalent ion and B is a positive trivalent ion. According to the chemical composition of positive trivalent ions, it can be divided into aluminum spinel, chromium spinel and iron spinel. Usually people are used to calling magnesia alumina spinel (MgAl2O4) spinel for short.

The international standard definition of magnesia alumina spinel refractory is that the mass fraction of magnesia and magnesia in the spinel composition is not less than 20%. The chemical formula of magnesia alumina spinel is MgA12O4 (abbreviated as MA), with magnesia accounting for 28.3% and alumina accounting for 71.7%. Generally, according to the theoretical chemical composition of the spinel, aluminum rich spinel, i.e. alumina solid solution spinel, will be formed on the side with more Al2O3 content, and magnesium rich spinel, i.e. periclase spinel coexistence spinel, will be formed on the side with more MgO content. As shown in Figure 1, spinel is a compound in the MgO-Al2O3 binary system, and its melting point is 2135 ℃. In the MgO-Al2O3 system, two eutectic melts are formed, which exist in the spinel periclase binary system and the spinel corundum binary system respectively. The chemical compositions of the two eutectic melts are 77/23 and 11/89 respectively, and their low eutectic temperatures are 2050 ℃ and 1925 ℃ respectively. It can be seen from Figure 1 that at high temperatures, the solubility of periclase in magnesia alumina spinel can reach 10wt%, The solubility of corundum in magnesia alumina spinel is higher. As mentioned above, there is no doubt that the spinel refractories composed of MgO and Al2O3 are highly refractory. In addition, compared with dolomite bricks and magnesia chrome bricks, the main advantage of spinel is that it has strong corrosion resistance to reducing atmosphere, free SO2/SO3 and free K2O/Na2O. At the same time, magnesia alumina spinel also has excellent thermal shock stability and wear resistance. Moreover, magnesia alumina spinel has high melting point, low thermal expansion coefficient and high hardness, which makes magnesia alumina spinel an indispensable part of refractories.