The history of magnesia

Two calcium fused magnesia which good sintered magnesia. National standard GB/T2273-2007 specifies the physical and chemical properties of various sintered magnesia with MgO content of 83% to 98% suitable for the production of refractory materials. From the historical development point of view, sintered magnesia is also known as metallurgical sand, heavy burned magnesia, medium grade magnesia, high purity magnesia. Amorphous refractory Shaped refractory

During China's five-year plan (1952 ~1957), the first phase of Anshan Iron and Steel Company's Dashiqiao Magnesia Brick Plant, a production factory of alkaline refractory materials assisted by the former Soviet Union, was put into operation. The sand making workshop adopted the semi-dry process of ore fine grinding, ball forming plate, grate and rotary kiln to produce metallurgical sand for open-hearth sintering furnace bottom and repair. The product was phased out in the 1990s as the open-hearth steelmaking furnace was converted to a converter.

At present, the total output of sintered magnesia in China is 4 million to 4.5 million tons per year. Following the industry habits, sintered magnesia can be roughly divided into heavy burned magnesia, medium grade magnesia, high purity magnesia. Before the 1980s, in a period of more than 30 years, the national production of sintered magnesia was mainly undertaken by the former Anshan Iron and Steel Dashiqiao magnesia mine, which successively used 25 cubic meters, 32 cubic meters, 40 cubic meters, 47 cubic meters and 55 cubic meters of shaft kilns, using coke as fuel and massive magnesite as raw materials. Take a step of calcination and artificial discharge to produce heavy burned magnesia with 92% MgO content of electric-grade magnesia powder,97 fused magnesia,98 fused magnesia, to provide raw materials for the country's steelmaking open hearth bricks.

The defects of this process are: the ore utilization rate is low, and the fine particle ore can not be used; With high impurity content, ash in coke will cause pollution to magnesia, so that the content of SiO2 and Al2O3 in magnesia will increase, and the higher MgO content can only be guaranteed at 92%; The continuous operation is poor, the large magnesite ore is decomposed by heat and produces small particles attached to the kiln wall, and the materials in the kiln are prone to "clumped", which results in frequent changes in the material flow and thermal system in the kiln, resulting in outage accidents that cannot realize mechanized operation; The density of magnesia is low, and the magnesite is pre-decomposed in the kiln, releasing CO2 into lightly burned MgO, but its MgCO3 "master salt illusion" still exists, which is not conducive to the further densification of magnesia, and the bulk density of sintered magnesia is only between 3.0 and 3.1 grams per cubic centimeter. Serious environmental pollution, magnesite decomposition of a large number of CO2 and combustion flue gas mixed with fine coke particles and light burning dust fly out of the kiln, polluting the environment, high temperature flue gas treatment is difficult.

Before China's heavy burned magnesia is still calcined with second and third grade ores in solid fuel shaft kilns, the MgO content of magnesia is 90%~92%, and the bulk density per cubic centimeter is more than 3.10 grams. Refired magnesia is the main raw material for the production of ordinary magnesia fired bricks and amorphous refractories. The current annual output in Liaoning Province is estimated at 2.5 million tons. Due to the use of tertiary mines, the product price is low and there is a market, it is difficult to eliminate at present.

Medium grade magnesia. In order to improve the density and purity of magnesia, a two-step process research and industrial test of calcined magnesia have been carried out in China's refractory industry. The adoption of new technology and process suitable for national conditions has promoted the technological progress of sintered magnesia production. In the early 1980s, Haicheng magnesia mine used high-quality magnesite to light burn in the reflecting furnace, fine grinding with Raymond, semi-dry two-stage press ball, and calcination by coke shaft kiln to produce medium grade magnesia with MgO content ≥95% and bulk 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 widely used to produce synthetic sand products such as synthetic magnesia-calcium sand.

High purity magnesia. In 1980, the former mining Department of the Ministry of Metallurgy organized the implementation of the project of "new process technology and high temperature shaft kiln for producing high-quality and high purity magnesia from natural magnesite", and built a pilot production line with an annual output of 7,000 tons of high purity magnesia in Haicheng magnesia mine. In view of the difficult sintering characteristics of large crystalline magnesite, a new two-step calcining process of light burning, grinding, high pressure ball pressing and dead burning of magnesite was developed. The target of MgO content of high purity magnesia ≥98% and volume density of 3.30 grams per cubic centimeter has been achieved. Based on the use of powder ore, they adopted the flotation process, and introduced key equipment with an annual output of 50,000 tons of high purity magnesia production line from Europe: suspension roaster, roller mill, high pressure ball press, high temperature oil shaft kiln, etc., independent research combined with the introduction of the end of China's history of no high purity magnesia.

Based on China's national conditions, the production process of high-purity magnesia is mostly: the selection of high-quality magnesite, light burning in the reflection kiln of gas as fuel, the light burning powder is fine ground with Raymond machine, dry pressure press ball, and finally calcined in the high temperature oil shaft kiln, the production of MgO content of 97%, the bulk density of 3.25 grams per cubic centimeter to 3.30 grams of high-purity magnesia. The process equipment is completely domestic, and the products meet the requirements of most magnesia refractory materials in China, and a certain amount of exports.

Fused magnesia. The development of fused magnesia is accompanied by the development of MgO-C brick production technology and rapid development. High-quality MgO-C bricks require not only high purity and density, but also large grain size of magnesia, which is usually obtained by the electromelting process. Fused magnesia is made from magnesite (preparation of ordinary fused magnesia) or lightly fired MgO (preparation of large crystalline fused magnesia) as raw materials by melting and slowly cooling in an electric furnace. Among them, low iron (Fe2O3) large crystalline fused magnesia is a good filling insulation material in electrical components. However, because the production of fused magnesia consumes a lot of electricity, it belongs to the industry which is restricted by the energy policy, and its development will be impacted by the implementation of the classified electricity price policy.

Nowadays, the focus of technology development of fused magnesite production enterprises is energy saving, improving comprehensive utilization of magnesite resources and dust control. The main technical measures include: research on comprehensive energy-saving technology for preparing fused magnesia, dust control, waste heat recovery and so on. Liaoning Province is taking corresponding treatment measures, summing up experience to solve the problem of smoke pollution in the production of electric furnaces and the recovery of waste heat from the cooling of magnesia melting lead.

At the same time, in the face of the decline in the grade of magnesite (MgO content of MgO98 grade fused magnesite is only 97.2%), some enterprises adopt the flotation process, and use fine ore powder and light fired MgO pressure ball ore into the furnace for electric melting, which not only greatly reduces the unit power consumption of fused magnesite, but also improves the harvest rate of high-grade fused magnesite.