Abstract：Dolomite ore is first calcined (or fused) to obtain magnesia-calcium raw materials (such as dolomite sand/magnesia-dolomite sand, magnesia-calcium sand, magnesia-calcium-iron sand), and then prepared into various dolomite-based refractory materials.
Dolomite is a double salt composed of magnesite (MgCO3) and calcite (CaCO3) at a ratio of 1:1. It is the second largest alkaline refractory raw material after magnesite, and is mainly used to prepare dolomite refractory materials.
Dolomite ore is first calcined (or fused) to obtain magnesia-calcium raw materials (such as dolomite sand/magnesia-dolomite sand, magnesia-calcium sand, magnesia-calcium-iron sand), and then prepared into various dolomite-based refractory materials. In addition to the advantages of high refractoriness, slag erosion resistance and good thermal shock resistance, dolomite refractory materials can absorb S, P and non-metallic inclusions such as Al2O3 and SiO2 in molten steel, and also have the effect of purifying molten steel , so it is widely used in stainless steel refining furnaces; in addition, because dolomite bricks contain a large amount of free CaO, it is very easy to react with C2S in cement kiln materials to form C3S, forming a stable kiln skin, so it is suitable for use in cement rotary kiln firing bring.
Dolomite bricks are made of dolomite sand calcined from natural dolomite. Dolomite bricks contain w (CaO) ≥ 40%, w (MgO) ≥ 35%, and also contain a small amount of SiO2, Al2O3, Fe2O3 and other impurities. If the mass ratio of CaO and MgO in the brick is less than 1.39, it is called magnesia dolomite brick.
In order to improve thermal shock resistance, ZrO2+ dolomite bricks and ZrO2+ magnesium dolomite bricks have been developed. Dolomite bricks are mainly used in stainless steel refining furnaces (such as AOD, VOD furnaces, etc.) and cement kiln firing zones.
For example, for the lining of AOD furnaces, fired dolomite bricks are currently used in Germany, pure dolomite bricks are used in other European countries, and magnesia dolomite bricks are used in Japan. In addition, dolomite brick is the most commonly used refractory material in the firing zone of cement kilns in Europe and America, and 86% of the firing zone of cement kilns in the United States use this product. However, due to the fact that dolomite bricks are easy to absorb moisture and hydrate during transportation, storage and kiln shutdown, and have poor thermal shock resistance, they are generally used in kilns with an annual operating rate of more than 80%. Only a few manufacturers in China use cement rotary kilns. Imported dolomite bricks are used.
There are two types of magnesia-calcium bricks: one is magnesia-calcium bricks produced with synthetic magnesia-calcium sand as the main raw material; the other is magnesia-calcium bricks produced with dolomite sand (or magnesia-dolomite sand) and magnesia as the main raw materials. , Also known as magnesium dolomite brick. At present, fired magnesia-calcium bricks/magnesia-dolomite bricks with w (CaO) of 20% are the synthetic magnesia-calcium refractory products with the largest output and consumption in China. They are mainly used as linings for stainless steel refining furnaces (AOD furnaces, VOD furnaces, etc.) material, replacing magnesia-chrome bricks that are extremely harmful to the environment and human body, and the use effect is good. China's fired magnesia-calcium brick has become the main refractory material in the stainless steel industry. In addition, China also produces a certain amount of fired magnesia calcium bricks/magnesia dolomite bricks with w (CaO) ≥ 30%.
Sintered dolomite sand, magnesia and/or graphite with different particle sizes as the main raw material, refractory material that can be used directly without firing, has the advantages of energy saving, good thermal shock stability, simple production process, and good slag resistance sex.
At present, the unburned magnesia-calcium (carbon) bricks produced in China have a w (CaO) of 10% to 30%, which belongs to magnesia-calcium products with medium and low calcium, and is mainly used in refining furnaces such as LF-VD or LF and VOD furnaces Bottom and molten pool parts, GOR furnace bottom part, the effect is good. But now China's unburned magnesia-calcium (carbon) bricks have not been popularized and applied in large quantities. The reason is that the price is relatively high; the second is that the performance needs to be improved.
Dolomite can also be used to prepare various magnesium-calcium amorphous refractory materials, such as electric furnace bottom ramming material, tundish coating material, ladle gunning material, converter gunning material, RH furnace gunning material, self-flowing hot-filling material, etc. refractory material. Among them, the largest amount is the magnesia-calcium-iron dry ramming material for the bottom of the electric furnace, which is made of iron-containing magnesia-dolomite synthetic sand (magnesia-calcium-iron sand) as raw material, and the use effect is good.
At present, China encourages the development of electric furnace steelmaking, and the number of UHP electric furnaces continues to increase, and the demand for various dry furnace bottom ramming materials will also continue to increase. In addition, the gunning material developed by using dolomite is used for the repair of converters, electric furnaces, ladle slag lines, RH insertion pipes and other parts. Spreadable material, dry material, excellent performance.
At present, dolomite is mainly used in the synthesis of magnesium-calcium refractory materials in refractory materials. In order to expand the application of dolomite resources in refractory materials, some studies have used natural dolomite ore to synthesize calcium aluminate cement containing magnesium-aluminum spinel. Calcium aluminate cement (CMA) containing microcrystalline magnesium aluminum spinel is a new type of binder for refractory materials, its CaO content is reduced and magnesium aluminum spinel is contained, compared with ordinary aluminate cement, it has more It has excellent high temperature volume stability, thermal shock resistance and slag erosion resistance.
Today's iron and steel industry is developing towards the super steel technology goal of "high cleanliness, high uniformity, and ultra-fine grain". Chemical stability, especially free CaO has the effect of purifying molten steel, correspondingly, the demand for dolomite refractory materials will also increase, and dolomite refractory materials have great development prospects.
In the field of cement industry, for some reason, some enterprises in China are still using magnesia-chrome bricks in the firing zone and transition zone of cement rotary kilns, while dolomite bricks have excellent high temperature resistance, kiln skin hanging and resistance to alkaline substances It can be used in the firing zone and transition zone of cement kiln to replace magnesia-chromium refractory bricks. At present, only a few manufacturers in China use imported dolomite bricks in cement rotary kilns, and dolomite bricks are used in the firing zone of cement rotary kilns in China. There is a lot of room for development. However, dolomite-based refractory materials are difficult to sinter. At the same time, refractory materials made of dolomite sand are easy to absorb water and hydrate to form hydroxides during storage and repeated use, resulting in volume expansion and resulting in cracking and pulverization of the product. Achilles' heel limits the application and development of dolomite refractories.
Therefore, in the future, we will increase the research on this aspect, so as to increase the application of dolomite resources in refractory materials, and save the relatively small reserves of magnesite. Use dolomite to develop new refractory materials, such as new aluminate cement, calcium hexaaluminate-spinel lightweight refractory materials, etc.
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