Development of low-iron fused magnesia

Development of low-iron magnesite and strengthening construction of magnesite supply base

Magnesium 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 the demand for magnesium raw materials and the low entry threshold for primary raw materials processing, the rational development of magnesite has been seriously undermined. Due to economic reasons, the price of magnesite super-grade ore is about five times that of third-grade ore. Mining is extensive, mining rich and abandoning poor phenomenon is serious, resulting in a great waste of resources, and more serious is the mining and stripping imbalance. In 2005, the author participated in the "spot adjustment" of 12 key magnesite mines in Liaoning Province. It was estimated that the debts of rock stripping at that time were over 100 million tons. The situation has not changed fundamentally since then, resulting in difficulties in mining some high-quality ores. In recent years, the original meaning of the super-grade ore has been very rare, the first-grade ore shortage, ore quality decline led to the average MgO content of magnesia decreased by more than 0.5%.

Therefore, in order to make rational and effective use of limited resources, we must conscientiously implement relevant laws and regulations, further integrate magnesite mines and old mines with an annual mining volume of more than 300,000 tons, implement large-scale mining and intensive management, do a good job in the detailed investigation of existing mining areas, mining according to mining design, make up for the debts of rock stripping in key mines, extend the service life of mines, and promote mineral processing technology and comprehensive utilization. Low and medium grade ores. At present, the relevant enterprises have gradually realized that the production of high-quality raw materials can not be maintained by relying on raw materials only; only by beneficiation and purification of raw ore, can high-quality primary raw materials be produced and the normal production of raw materials be guaranteed. Following the successful start-up of flotation system in Haicheng Magnesium Mine General Plant, many enterprises have built flotation projects, and other enterprises have begun to prepare, at the same time, the comprehensive utilization of flotation tailings is also under study.

In the next three to five years, the promotion of magnesite flotation technology, the follow-up processing of high-purity Mg (OH) 2 produced by Tibetan cryptocrystalline magnesite and Qinghai Salt Lake Magnesium Extraction will provide high-quality raw materials for the production of magnesite in China.

Production of High Quality Light Burned Magnesium Oxide

According to foreign exchange data, the annual consumption of lightly burned magnesia (CCM) in the world is about 10 million tons. China is the world's largest producer of lightly burned magnesia, with an annual output of 3.5 million to 4 million tons. Japan, the United States and other countries used light-burnt magnesia for sintering magnesia and non-refractory materials in the 1990s, the proportion of 80:20, and then gradually changed to 70:30, now roughly 65:35. Large-scale light-burning plants built abroad have many kinds of products and wide uses. Therefore, we should not only pay attention to the development of light burnt magnesia (CCM) for refractories, but also vigorously cultivate new magnesite materials industry, such as magnesium chemical industry and magnesium building materials, in order to adjust the product structure of light burnt magnesia. Only by establishing large-scale concentrated production base of light-burning magnesia and forming scale effect can reasonable investment be made, so that advanced roasting technology and kilns can be adopted to solve the problems of energy saving and emission reduction, low-carbon economy and CO2 recovery from the source.

In order to produce high-purity magnesia by "two-step calcination" process in southern Liaoning Province of China, not only magnesite lump ores are lightly burned in traditional reverberatory furnace, but also concentrate powders from foreign suspension furnace are introduced to lightly burn magnesite crushed ores successively in rotary kiln, fluidized bed furnace and new suspension furnace. For example, the commissioning of a multi-layer furnace (MHK) in an enterprise, as well as the large-scale airflow suspension furnace for roasting Al (OH) 3 in non-ferrous metals industry and the decomposition furnace outside the cement industry kiln provide favorable conditions for the selection of light-burning magnesia kiln.

Developing low-cost and high-grade magnesia

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

The total annual output of sintered magnesia in China is about 4 million tons. Around 1980, the export volume of cheap natural magnesia in China increased sharply, and it has occupied the international middle and low-end magnesia market. Generally speaking, the supply of middle and low-end magnesia in the market exceeds the demand. The output of this part of sintered magnesia should be controlled, especially the production of re-burned magnesia should be gradually reduced. Due to the decline of ore grade and the rise of fuel and labor prices, the quality of mid-grade magnesia and high-purity magnesia has decreased significantly. In the future, the market demand for mid-grade and high-purity magnesia will increase, because the trend of mid-grade sand replacing reburned sand downwards and high-purity sand replacing part of fused sand upwards is obvious.

After more than 30 years of disorderly mining, it is an indisputable fact that the quality of magnesite ore and magnesite is reduced. At present, the related enterprises have gradually realized the importance of ore flotation and purification, and it is an inevitable trend to popularize mineral processing technology. Starting from beneficiation, the grade of ore is improved, high activity light-burning magnesia is produced by energy-saving and efficient light-burning equipment, and the quality of high purity sand is improved by means of dry high pressure dry ball and high temperature calcination of clean fuel. It is also necessary to explore new technology and process of magnesia production in order to produce high-grade sintered magnesia with 98% MgO content and 3.40 g/cubic centimeter bulk density at low cost. It is in line with the future development direction to build a large-scale production plant integrating mineral processing and production of high-purity magnesia.

Improvement of Fused Magnesia Technology and Equipment

Because the price of fused magnesia in China is very competitive, 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, the product has high energy consumption and needs high-grade raw materials. Therefore, the comprehensive promotion and improvement of technical equipment measures in fused magnesia industry will help to reduce energy consumption and control quality, which is the inevitable trend of future development.

Focus on the development of synthetic raw materials

At present, the main synthetic materials based on magnesium oxide in Liaoning Province are fused magnesia-chrome sand, sintered magnesia-calcium sand, sintered magnesia-alumina spinel sand and sintered magnesia-alumina-iron sand, with an annual output of more than 200,000 tons. Magnesium-calcium refractories have excellent performance, but their application is limited due to the hydration of CaO. Therefore, the waterproofing problem of magnesia-calcium refractories should be studied emphatically. It should be pointed out that MgO-CaO refractories have the effect of removing sulphur and phosphorus impurities in steelmaking due to the presence of CaO, while CaO is not possible without hydration, only to prevent its hydration.

With the increase of environmental protection, chromium-containing refractories will withdraw from the market. It is imperative to research and produce alternative products. Therefore, high-quality synthetic magnesium materials such as MgO-Al2O3, MgO-CaO, MgO-ZrO 2, MgO-SiO 2, MgO-Fe2O3, MgO-CaO-Fe2O3, MgO-Al2O3-ZrO 2, MgO-CaO-ZrO 2, MgO-Al2O3-FeO should be further developed and produced for different purposes.

Generally speaking, magnesite as a non-renewable and indispensable strategic resource, restricting and reducing its mining and improving its resource utilization rate, is the focus of all related work in the future. Therefore, the state should greatly reduce the export quota of magnesia and limit the export of low value-added raw materials and ordinary magnesia products.

At the same time, enterprises with mining resources and conditions are encouraged to carry out large-scale technological renovation and equipment renewal, or to diversify the exploitation of raw materials and concentrate on building a number of large-scale raw material bases. Mine rock stripping, purification of low-grade ore, construction of large-scale light-burning and calcining equipment, industrialization of new sand-making process require a large amount of funds and new technical support, and there are certain risks. I hope relevant departments of the state will give support to policies, funds, science and technology.