What is The Role of Dolomite in Refractory Materials?
2023-08-30
Dolomite is a binary compound consisting of magnesite (MgCO3) and calcite (CaCO3) in a 1:1 ratio, making it the second-largest alkaline refractory raw material after magnesite. It is primarily used for the production of dolomite refractory materials. Dolomite refractories are predominantly employed in the synthesis of magnesia-calcium refractories. To expand the application of dolomite resources in refractories, research has been conducted on synthesizing calcium aluminate cement (CMA) containing magnesia-aluminum spinel using natural dolomite. CMA, as an innovative type of refractory material, exhibits exceptional stability, shock resistance, slag erosion resistance, and other functionalities that enable its extensive utilization and may potentially drive the advancement of the dolomite industry.
About Dolomite
Characteristic
The mineral dolomite belongs to the trigonal crystal system and has a chemical composition of CaMg(CO3)2. It is primarily composed of calcium carbonate and magnesium carbonate minerals, with a 1:1 ratio of CaCO3 to MgCO3. Dolomite exhibits complete cleavage and rhombohedral crystallization. Its color ranges from white, gray, flesh-colored, colorless, green, brown, black to dark pink. It is transparent to translucent and possesses a glassy luster. With a hardness rating of 3.5-4 and specific gravity ranging from 2.85-2.9.
Cause of Formation
Dolomite is commonly found in crystalline limestone and other magnesium-rich metamorphic rocks. It occurs partly within hydrothermal veins and carbonate formations, occasionally serving as a cementing agent for various sedimentary rocks. Dolomite is the predominant mineral responsible for rock formation in carbonate deposits. Dolomite is formed through the replacement of calcium with magnesia from limestone. Its occurrence primarily takes place within the crystalline limestone zone beneath the Nanao schist during the PreTertiary period. The ore sac exhibits a convex, layered or irregular structure.
Dolomite Development Prospects
Dolomite mineral resources are abundant, but the availability of high quality resources is limited. Of particular concern is the scarcity of high-quality dolomite ore resources suitable for magnesium smelting. Continued development and exploitation over the years has led to a decline in the availability of high-quality resources. Currently, dolomite ore is primarily used to produce basic products with low added value. These include crushing and processing into dolomite powder or lightly calcining it for applications in the metallurgical flux and environmental protection industries. However, these processes only involve simple primary mineral processing with minimal product value addition. Therefore, in order to enhance the value proposition of dolomite mineral resources, it becomes imperative to engage in deep processing activities that extend the industrial chain associated with dolomite mining. This will allow us to venture into the higher end of the industry by manufacturing and processing premium products such as magnesium alloys and high-calcium magnesia calcium refractory materials.
Dolomite Refractory
Dolomite refractory materials possess notable advantages, including high refractoriness and excellent thermal shock resistance. Moreover, they exhibit the ability to adsorb non-metallic inclusions such as S, P, Al2O3, SiO2 in molten steel and effectively purify it. Consequently, dolomite is extensively employed in stainless steel refining furnaces. Furthermore, dolomite can be calcined into dolomite sand and subsequently transformed into dolomite bricks. These bricks contain a substantial amount of free CaO that readily reacts with C2S present in cement kiln materials to generate stable C3S and form a consistent kiln skin. As a result of these properties, they are highly suitable for utilization within the firing belt of cement rotary kilns.
Currently, countries like Germany, Japan, and the United States widely utilize dolomite as a refractory material. Specifically within European and American markets, dolomite bricks have emerged as the most commonly utilized refractory material for cement kiln firing belts; more than 80% of cement kiln firing belts in the United States are composed of dolomite bricks.
Dolomite Firebrick
The natural dolomite is calcined to produce dolomite sand, which is then used for manufacturing dolomite bricks with a CaO content of ≥40% and an MgO content of ≥35%. These bricks also contain trace amounts of SiO2, Al2O3, Fe2O3, and other impurities. When the mass ratio of CaO to MgO is less than 1.39, they are referred to as magnesia dolomite bricks. Dolomite bricks find their primary applications in stainless steel refining furnaces and cement kilns; however, only a limited number of cement kilns in China utilize imported dolomite bricks.
Magnesia-calcium Brick
The two types of magnesia-calcium bricks are distinguished by their raw materials: one is produced using synthetic magnesia-calcium sand as the primary ingredient, while the other is made from dolomite sand (or magnesia dolomite sand) and magnesia sand, commonly known as magnesia dolomite brick. Currently, the most widely used refractory product is fired magnesia-calcium/magnesia-dolomite brick with a CaO content of 20%, which serves as a lining material for stainless steel refining furnaces and replaces environmentally and health hazardous magnesia-chromium bricks.
New Type Refractory
Studies have been conducted on the synthesis of calcium aluminate cement containing magnesia-alumina spinel using natural dolomite ore to enhance the utilization of dolomite resources in refractories. This novel type of refractory binder possesses a reduced CaO content and incorporates magnesia-alumina spinel, thereby offering superior high-temperature volume stability, thermal shock resistance, and slag erosion resistance when compared to conventional aluminate cement. Furthermore, significant advancements have been achieved in synthesizing lightweight refractory materials with calcium aluminate-magnesia-alumina spinel derived from natural dolomite ore and various aluminum sources, as well as in developing composite materials consisting of calcium aluminate-magnesia-alumina spinel that exhibit resistance against erosion caused by cement clinker.
The entire equipment of the Raymond mill consists of the main machine, reducer, analyzer, pipe device, blower, dust collector, jaw crusher, bucket elevator, electromagnetic vibration feeder, electric control system and more. It features an integral drive with bevel gears and utilizes a thin oil lubrication system for high efficiency and large output while requiring a small investment. Additionally, it is energy-saving and environmentally friendly making it an excellent choice in the field of large non-metallic ore powder.
The production line of the ultrafine mill typically includes a hammer crusher, bucket elevator, storage bin, vibration feeder, micro-grinding host, frequency conversion classifier, double cyclone collector, pulse dust removal system, high-pressure fan, air compressor, electrical control system and so on. The bulk material is initially crushed by the hammer crusher into feed particles with an appropriate size (approximately 1cm) for the operation of the ultrafine mill. Subsequently, by adjusting the speed of the mill analysis machine to achieve the desired fineness according to production requirements. Manual packaging into bags or utilization of an automatic micro-powder baler can be chosen as per preference. Different types of grinding machines can also be selected based on specific needs. Advanced technology has been introduced to ensure excellent processing of ultrafine powder with adjustable and controllable fineness. The finished product can reach a fineness level of d97≤5μm in one pass. Additionally equipped with a pulse dust collector and silencer room for environmentally friendly protection.
Grinding Precess
The First Stage: Crushing In the initial stage of dolomite processing, the bulk material is crushed into smaller pieces by a crusher. This process ensures that the feed material reaches the desired fineness required for further milling.
The Second Stage: Grinding Once the dolomite material is broken down into small pieces, it is then transported to a silo using an elevator. From there, it is evenly and quantitatively fed into the grinding room of the mill through a vibration feeder. Depending on the specific requirements of fine powder processing, vertical grinding or Raymond grinding may be chosen. For ultrafine powder processing, options like CLUM ultrafine vertical mill or HGM ring roller micro-mill are commonly used.
The Third Stage: Grading After undergoing grinding, the material goes through a grading process using a separator. The purpose of this step is to separate any unqualified powder from those that meet quality standards. Any unqualified powder identified during grading is sent back to be re-ground in order to ensure optimal particle size distribution and product quality.
The Fourth Stage: Powder collection To collect and separate fine powders from air flow generated during grinding, they are directed towards a dust collector via pipes. The collected finished powder then enters a finished product bin through discharge ports with assistance from conveying devices such as conveyors or bucket elevators. Finally, depending on packaging requirements, these powders can be transfered for efficient packaging processes.
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