Development of low iron fused magnesia

The development of low iron fused magnesia and strengthening the construction of magnesite supply base

The magnesia refractory raw material industry is a typical resource-based industry. Since China's reform and opening up in the 1980s, due to the rapid increase in demand for magnesite raw materials and the low entry threshold for processing primary raw materials, the reasonable development of magnesite has been seriously damaged. Due to economic reasons, the selling price of magnesite super-grade ore is about 5 times of that of tertiary ore. The extensive mining and the serious phenomenon of discarding the rich and discarding the poor lead to a great waste of resources, and the more serious is the imbalance of mining and stripping. The author participated in the "spot survey" of 12 key magnesite mines in Liaoning in 2005, and estimated that the debt of rock stripping at that time was more than 100 million tons, but the situation has not changed fundamentally since then, which has caused difficulties in mining some high-quality ores. In recent years, the original super-grade ore has been very rare, and the first-grade ore is in short supply. The ore quality landslide has caused the average MgO content of magnesia to drop by more than 0.5%.

Therefore, in order to make rational and effective use of limited resources, relevant laws and regulations must be carefully implemented, and magnesite mines and old mines with an annual mining capacity of more than 300000 tons should be further integrated to implement large-scale mining and intensive management; Carry out detailed survey of existing mining areas, mine according to mining design, make up for the debt of rock stripping in key mines, and extend the service life of the mine; Promote beneficiation technology and comprehensively utilize medium-low grade ores. At present, relevant enterprises have gradually realized that it is no longer possible to maintain the production of high-quality raw materials only by relying on raw ore to produce raw materials; Only by beneficiation and purification of raw ore can high-quality primary raw materials be produced to ensure the normal production of raw materials. After Haicheng Magnesium Mine General Plant successfully started the flotation system, many enterprises have completed flotation projects, and other enterprises have also started to prepare, and the comprehensive utilization of flotation tailings is also under study.

In the next three to five years, the promotion of magnesite flotation technology and the subsequent processing of high-purity Mg (OH) 2 produced by Tibet cryptocrystalline magnesium ore and Qinghai "salt lake magnesium extraction" will provide high-quality raw material supply guarantee for China's magnesite production.

Production of high-quality light-burned magnesium oxide

According to foreign exchange information, the annual consumption of light burned magnesium oxide (CCM) in the world is about 10 million tons. China is a major producer of light burned magnesium oxide in the world, with an annual output of 3.5 million to 4 million tons. In Japan, the United States and other countries, the proportion of light burned magnesia used for sintered magnesia and non-refractory materials was 80:20 in the 1990s, and then gradually changed to 70:30, now about 65:35. Large light burning plants built in foreign countries have a wide variety of products and a wide range of uses. Therefore, we should not only focus on the development of the use of light burned magnesium oxide (CCM) and its application in refractory materials, but also vigorously cultivate magnesium chemical industry, magnesium building materials and other magnesite new material industries to adjust the structure of light burned magnesium oxide products. Only by establishing a large-scale light-calcined magnesium oxide centralized production base and forming a scale effect can there be reasonable investment, so as to adopt advanced calcination technology and furnaces to solve the problems of energy conservation and emission reduction, development of low-carbon economy and CO2 recovery from the source.

In order to cooperate with the "two-step calcination" process to produce high-purity magnesia in southern Liaoning Province, China not only uses the traditional reverberatory furnace to light calcine the magnesite lump ore, but also introduces the concentrate powder from the light calcination of magnesite in the foreign suspension furnace, and then uses the rotary kiln, fluidized bed furnace and new suspension furnace to light calcine the magnesite crushed ore. For example, the production of a multi-storey furnace (MHK) in an enterprise, as well as the large-scale air-flow suspension furnace for roasting Al (OH) 3 in the non-ferrous metal industry and the decomposition furnace outside the cement industry provide favorable conditions for the selection of light-burning magnesium oxide kiln.

Development of low cost and high grade magnesia

It is generally believed that the global high-end refractory market requires 98% MgO content for high-grade magnesia, 3.40g/cm3 bulk density of sintered magnesia and 3.50g/cm3 bulk density of fused magnesia. The annual consumption of high-grade magnesia by high-temperature industrial departments such as steel and cement is about 1 million tons.

The total annual output of sintered magnesia in China is about 4 million tons. Before and after 1980, the export volume of cheap natural magnesia from China increased sharply, and it has always occupied the international low-end magnesia market. In general, at present, the supply of middle and low end magnesia in the market exceeds the demand, so the production of this part of sintered magnesia should be controlled, especially the production of heavy sintered magnesia should be gradually reduced. Due to the decline of ore grade and the rise of fuel and labor prices, the quality of medium-grade magnesia and high-purity magnesia decreased significantly. In the future, the market demand for medium-grade and high-purity magnesia will increase, because the trend of medium-grade sand replacing heavy burnt sand downward and high-purity sand replacing part of fused sand upward is obvious.

After more than 30 years of disorderly mining, the reduction of high-quality magnesite ore and the decline of magnesite quality have become indisputable facts. At present, relevant enterprises have gradually realized the importance of ore flotation purification, and the promotion of mineral processing technology has become an inevitable trend. Starting from ore dressing, improve the ore grade, produce high-activity light-burned magnesia with energy-saving and high-efficiency light-burning equipment, and improve the quality of high-purity sand through production means such as dry-process high-pressure dry-bulb and clean fuel high-temperature calcination. It is also necessary to explore new processes and processes for magnesia production, so as to produce high-grade sintered magnesia with 98% MgO content and 3.40g/cm3 bulk density at low cost. The construction of a large production plant integrating beneficiation and production of high-purity magnesia conforms to the future development direction.

Improve the technical equipment of fused magnesia

Due to the competitive price of fused magnesia in China, a large number of western seawater magnesia manufacturers have closed down. At present, China accounts for 90% of the world market of fused magnesia with MgO content>98.5%, and its application is more extensive. However, this product requires high energy consumption and superior raw materials. Therefore, comprehensive promotion of improved technical equipment measures in the fused magnesia industry will help to reduce energy consumption and control quality, which is an inevitable trend of future development.

Focus on developing synthetic raw materials

At present, the synthetic raw materials based on magnesium oxide in Liaoning mainly include fused magnesia-chrome sand, sintered magnesia-calcium sand, sintered magnesia-alumina spinel sand, sintered magnesia-alumina iron sand, etc., with an annual output of more than 200000 tons. Magnesia-calcium refractories have excellent service performance, but their application is limited due to the hydration of CaO. Therefore, it is necessary to focus on the waterproof of magnesia-calcium refractories. It should be pointed out that MgO-Ca-based refractories can only remove sulfur and phosphorus impurities in steelmaking due to the presence of CaO; While CaO exists, it is impossible to prevent hydration, only to prevent its hydration.

With the increase of environmental protection, chromium-containing refractories will be withdrawn from the market, and the research and production of alternative products is imperative. Therefore, high-quality synthetic magnesia raw materials such as MgO-Al2O3, MgO-CaO, MgO-ZrO2, MgO-SiO2, MgO-Fe2O3, MgO-CaO-Fe2O3, MgO-Al2O3-ZrO2, MgO-CaO-ZrO2, MgO-Al2O3-Fe2O3 (FeO) should be further developed and produced for different purposes.

In general, magnesite is a non-renewable and indispensable strategic resource. Limiting and reducing its exploitation and improving its resource utilization rate will be the focus of all related work in the future. Therefore, the state should significantly reduce the export quota of magnesia and restrict the export of raw materials and ordinary magnesia products with low added value.

At the same time, enterprises with mining resources and conditions are encouraged to carry out large-scale technological transformation and equipment upgrading, or separate mining of raw materials, and focus on building a number of large raw material bases. Mining rock stripping, purification of low-grade ore, construction of large light burning and calcining equipment, and industrialization of new sand-making process need a lot of capital and new technology support, and there are certain risks. We hope that the relevant national departments will give support in policy, capital, science and technology.