China has unique natural magnesite resources, especially in Liaoning Province. only is magnesite reserves mining volume one in the world, but also the production export of magnesia refractory materials rank first in the world. Relying on resource advantages, the main products of Chinese enterprises producing magnesia refractory raw materials include light burned magnesia, sintered magnesia, fused magnesia, etc. In this article, the author introduces analyzes the development history, production status existing problems of magnesium refractory raw materials products.
Magnesium raw materials refer to magnesium-containing minerals that can be used to produce magnesium refractory materials, magnesium chemical materials, metal magnesium other products, which are mainly divided into solid minerals such as magnesite, dolomite, brucite, etc. liquid minerals such as seawater, Salt lake brine, etc. Magnesite is one of the most important refractory raw materials in the world. It is mainly used for calcining light-burned magnesia (CCM), sintered magnesia (DBM), fused magnesia (FM) other refractory materials. Basic materials.
China is one of the countries with the most abundant magnesite resources in the world, mainly distributed in Liaoning Shandong provinces, concentrated in Liaoning province. Currently, the magnesite reserves identified in Liaoning Province are 3.413 billion tons, accounting for about 85% of the country 20% of the world. The reserves exploitation of magnesite in Liaoning, as well as the production export of magnesia refractories, rank first in the world. At present, there are 12 mining areas that have been geologically explored in Liaoning, the annual mining of special, first, second, third grade ores with MgO content ≥44% is about 16 million tons, mainly for production enterprises in the province. Liaoning magnesite is a crystalline ore, with large crystal particles difficult to sinter. The line standard YB / T 5208-2004 established a natural magnesite standard with an MgO content of 33% to 47%.
Lightly burned magnesium oxide. At present, China uses magnesite as a raw material, it is processed into light-burned magnesia powder (CCM) by light burning in a reverberatory furnace. It has a large number a wide range of uses. Lightly burned magnesia powder is a very important basic material of magnesia. It is applied to different grades of sintered magnesia (DBM) according to its different chemical composition, particle size performance, which is different Al2O3 CaO. The raw materials with the content are composed of magnesium aluminum spinel sand, magnesia calcium sand other composite materials, producing fused magnesia (FM, refractory grade electrical grade), converter slag splashing protection furnace magnesium ball, etc. The above products are mainly used as raw materials for refractory products. In addition, these products are also raw materials for magnesium chemical products such as light MgO, light MgCO3, magnesium fertilizer, magnesium building materials, feed additives, etc.
Traditional light-burned magnesium oxide is made by roasting raw ore in a reverberatory furnace. The 70 years to 80 years of survival development of light-burned magnesium oxide produced by using a reverberatory furnace have been eliminated because the kiln has its outstanding characteristics: simple practical process; low investment, quick launch easy operation; suitable for southern Liaoning Features of magnesite. In the past ten years, the kiln-type production process has also been greatly improved, mainly manifested in: the use of clean fuel, the original direct burning of bituminous coal is changed to the gas produced by the simple gas generator as the fuel for roasting, to avoid fuel ash content. Lightly burned magnesium oxide pollution basically solves the environmental pollution caused by black smoke emissions improves thermal efficiency; the kiln type is transformed to increase the volume of the kiln, increase the output, reduce the fuel consumption.
However, there are still the following problems in the production of light-burned magnesia powder by roasting magnesite in the reverberatory furnace: simple mining activities manual mining; the kiln is operated manually, the temperature stability of the kiln is poor, the energy consumption is high; The crushed ore is discarded the material consumption is high; the flue gas is untreated pollutes the environment; the cooling is open the working conditions are poor, which makes the current recruitment difficult; the grinding equipment is backward, the particle size control is poor, the final product quality is low the fluctuation is large.
Therefore, the production of light-burned magnesium oxide in China must be controlled the entire process of mining-finished products-packaging, production according to user requirements, research promotion of advanced light-burned magnesium oxide roasting technology furnaces, large suspension kilns, multi-layer furnaces (consumable Furnace MHK) is used for light burning efficient light burning magnesium oxide fine grinding equipment.
Sintered magnesia. The national standard GB / T2273-2007 specifies the physical chemical properties of various sintered magnesia used in the production of refractory materials with an MgO content of 83% to 98%. the perspective of historical development, sintered magnesia is also known as metallurgical sand, refired magnesia, mid-range magnesia, high-purity magnesia.
Metallurgical sand. During China's five-year plan (1952 ~ 1957), the sand-making workshop used the semi-dry process of fine grinding of ore, spheroidizing disk, grate machine, rotary kiln to produce metallurgical sand for open hearth sintering furnace bottom repair. As the steel-making open hearth furnace was changed to a converter, the product was eliminated in the 1990s.
Reburn magnesite. At present, China's total output of sintered magnesia is 4 million to 4.5 million tons per year. Following the industry habits, sintered magnesia can be roughly divided into reburned magnesia, mid-range magnesia, high-purity magnesia.
Before the 1980s, for more than 30 years, the production of sintered magnesia in the country was mainly undertaken by the original Angang Dashiqiao Magnesium Mine, which used 25 cubic meters, 32 cubic meters, 40 cubic meters, 47 cubic meters 55 cubic meters. The cubic meter shaft kiln, which uses coke as fuel massive magnesite as raw material, adopts one-step calcination artificial discharge to produce 92% MgO re-ignited magnesia, which provides raw materials for bricks for steel-making open hearth furnaces nationwide.
The defects of this process are: low ore utilization rate, fine ore can be used; high impurity content, ash in coke will pollute magnesia, so that the SiO2, Al2O3 content of magnesia increases, MgO content can only be guaranteed at 92% ; The continuous operability is poor, the large block of magnesite ore is decomposed by heat to produce small particles of ore adhered to the kiln wall, the material in the kiln is prone to "knotting", which causes frequent changes in the material flow thermal system in the kiln, resulting in shutdown. The accident could achieve mechanized operation; the density of magnesia is low, magnesite is decomposed in the kiln in the pre-tropical zone, releasing CO2 to become lightly burned MgO, but its "ghost salt illusion" of MgCO3 still exists, which is conducive to the further development of magnesia Densification, the bulk density of sintered magnesia is only between 3.0 grams 3.1 grams per cubic centimeter; the pollution environment is serious, magnesite decomposes a large amount of CO2 the burning flue gas is mixed with fine coke particles lightly burnt dust. Outside the kiln, it pollutes the environment the treatment of high-temperature flue gas is difficult.
At present, China's re-burned magnesia is still calcined in solid fuel shaft kiln with second- third-grade ores. The MgO content of magnesia is 90% ~ 92%, the bulk density is more than 3.10 grams per cubic centimeter. Heavy burned magnesia is the main raw material for the production of ordinary magnesia fired bricks unshaped refractory materials. The current annual output of Liaoning Province is estimated at 2.5 million tons; due to the availability of tertiary ores, the product price is low there is a market, which is difficult to eliminate at present.
Mid-range magnesia. In order to improve the density purity of magnesia, China's refractory industry has carried out two-step calcination process of magnesia industrial tests. The adoption of new technologies new processes suitable for national conditions has promoted the technological progress of sintered magnesia production. In the early 1980s, Haicheng Magnesium Mine was burned in high-quality magnesite ore in a reverberatory furnace, finely ground with a Raymond mill, semi-dry two-stage pressed balls, calcined by a coke shaft kiln to produce MgO content ≥95%, volume Mid-grade magnesia with a density ≥ 3.20 grams per cubic centimeter. This achievement has been rapidly promoted, resulting in an annual output of hundreds of thousands of tons of scale benefits. Since then the process has been promoted to produce synthetic magnesia-calcium sand other synthetic sand products.
High purity magnesia. In 1980, the Ministry of Mines of the former Ministry of Metallurgy organized the implementation of the "New Process Technology High-Temperature Shaft Kiln Natural Magnesite to Produce High Quality High Purity Magnesia", built a pilot production line with an annual output of 7 thousand tons of high purity magnesia in Haicheng Magnesium Mine The characteristic of crystalline magnesite is difficult to sinter, developed a new two-step calcination process of light burning, grinding, high pressure ball pressing dead burning of magnesite. After several years of research, it has achieved high purity magnesia MgO content ≥98%, volume density per A goal of 3.30 grams in cubic centimeters. Based on the use of fine ore, they adopted a flotation process, imported key equipment Europe with an annual output of 50,000 tons of high-purity magnesia production line: suspension roaster, roller mill, high-pressure ball machine, high-temperature oil shaft kiln, etc. The introduction ended the history of no high-purity magnesia in China.
Based on China's national conditions, most of the production processes of high-purity magnesia are: selection of high-quality magnesite, light burning in a reflection kiln using gas as fuel, fine grinding of light burning powder with a Raymond machine, dry pressing of balls with a high-pressure press Finally, it is calcined in a high-temperature oil shaft kiln to produce high-purity magnesia with an MgO content of 97% a bulk density between 3.25 grams 3.30 grams per cubic centimeter. The process equipment is completely localized, the product meets the requirements of most magnesia sands required by most high-grade magnesium refractory materials in China, has a certain amount of export.
Fused magnesia. The development of fused magnesia is accompanied by the rapid development of MgO-C brick production technology. High-quality MgO-C bricks require magnesia only to have higher purity density, but also to have a larger grain size, this magnesia is usually obtained by the electric melting process. The fused magnesia is made by using magnesite (preparation of ordinary fused magnesia) lightly burned MgO (preparation of large crystalline fused magnesia) as raw materials in an electric melting furnace slow cooling. Among them, the low iron (Fe2O3) large crystalline fused magnesia is also a good filling insulation material in electrical components. However, since the production of fused magnesia consumes a large amount of electrical energy, it is an industry restricted by the national energy policy, its development will be impacted by the implementation of the classified electricity price policy.
Nowadays, the technical development of fused magnesia production enterprises focuses on energy saving, improving the comprehensive utilization of magnesite resources dust control. The main technical measures are: to carry out comprehensive energy-saving technology research for preparing fused magnesia, smoke dust control, waste heat recovery, etc. Liaoning province is taking corresponding control measures summing up experience to solve the smoke pollution produced by electric furnace the waste heat recovery of magnesia smelter cooling.
At the same time, in the face of the problem of the decline of magnesite grade (MgO98 grade fused magnesia MgO content is only 97.2%), some companies use a flotation process to mix ore with concentrate powder lightly burned MgO ball into the furnace for electric melting. only has the unit power consumption of fused magnesia been significantly reduced, but the harvest rate of high-grade fused magnesia has also increased accordingly.
Daling Village, Guantun Town, Dashiqiao City, Liaoning Province
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