Technology and performance characteristics of dolomite sand

The synthesis of dolomite sand is based on the full analysis of the chemical composition of dolomite, the phase relationship and melting relationship of the CaO-MgO-Fe2O3-Al2O3-SiO2 quinary system at high temperature, and the price of dolomite sand is based on the characteristics of each mineral phase and its manufacture and use. It is a magnesia-calcium sand developed by artificially controlling its composition and structure with magnesite and dolomite as raw materials. Practice has shown that synthetic magnesia dolomite sand has many advantages compared with ordinary dolomite sand.

According to the analysis of phase composition characteristics, the w(MgO)/w(CaO) ratio of synthetic magnesia dolomite sand and the total amount of impurities were first established. According to the situation of raw material resources in my country, generally according to w(MgO)/W(CaO)=(75±2)/(20±2), the total amount of impurities Fe2O3, Al2O3 and SiO2 is lower than 2.5% (or 15%) level, Select raw materials, and use a two-step calcination process to manufacture synthetic sand.

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In the above process flow, whether the magnesite raw material is selected or selected (flotation, thermal separation, etc.) should be determined according to the purity of the raw material and the chemical composition requirements of the synthetic sand. The light burning temperature of magnesite and dolomite should vary depending on the origin of the raw materials. According to local practices, there are the following empirical expressions:

Dolomite sand for sale Dolomite sand

Magnesite light burning temperature = raw material decomposition temperature + (250 ± 20) ℃

Generally, magnesite is lightly fired at 900~1000°C, while dolomite is lightly fired at 1000~1100°C, which can maintain good activity and play a thermochemical breaking effect on the digestion and aging of light-fired powder. The final MgO and CaO grains are 1~3 μm, which will be further refined when digested with water. After fine grinding, it will greatly improve its dispersion. This is one of the keys to two-step calcination activation sintering. An enterprise in southern Liaoning uses this process to produce synthetic sand with a content of MgO+CaO higher than 97% and a CaO content of 20% to 25%. High-pressure briquetting (blank) and high-temperature calcination are also critical. The density of briquetting (blank) is generally between 1.85-2.10g/cm3, up to 2.35g/cm3. Calcination can be carried out in rotary kiln, shaft kiln and tunnel kiln. At present, shaft kiln is mainly used for calcination in China. . If a rotary kiln is used for calcination, the calcination temperature of the synthetic sand can be further increased. If the calcination temperature can be increased to above 1800℃, high-quality synthetic magnesia dolomite sand with anti-hydration type can be obtained. The synthetic magnesia dolomite sand can also adopt a one-step calcination process, that is, superfine grinding of high-purity magnesia concentrate and dolomite, the content of -320 mesh is more than 90%, the molding pressure is more than 137MPa, and the calcination temperature of the shaft kiln is 1700~1800℃.

The optimized raw material of synthetic magnesia dolomite sand has more reasonable composition, more uniform composition, and more scientific and reasonable manufacturing process. Therefore, many of its properties are superior to traditional sintered dolomite sand. First of all, the chemical purity of synthetic sand is high, the ratio of MgO/CaO is reasonable (usually controlled at 75/25), and the mineral composition is more ideal. The main crystalline phase periclase and calcite have a combined content of more than 90%, and the highest purity is 95% or even more than 97%. The matrix phase is dominated by tricalcium silicate with high melting point (C3S, decomposed at 2070°C), and the contents of C4AF and C2F with low melting point are generally less. Second, the microstructure is good. Because the synthetic sand raw materials are lightly fired, fully mixed, finely ground and calcined at high temperature, the periclase and calcite crystals are well developed, and the periclase grains have a high degree of direct bonding and are connected into a network; the periclase is evenly filled in the In the intercrystalline space of periclase, it is surrounded by it. The matrix phase C3S granular or irregular crystals are mostly agglomerated. A small amount of C4AF and C2F in the dolomite sand are distributed among the above crystals, which are irregular and isolated. Table 2-1 shows the effect of calcination temperature on the grain size of periclase and calcite.

The chemical mineral composition and microstructure characteristics of synthetic magnesium dolomite sand determine its high temperature resistance, high high temperature strength, strong slag erosion resistance, and good hydration resistance; the upper crystal phase MgO (melting point 2800 ℃) , CaO (melting point 2570 ℃) and the main matrix phase C2S (2070 ℃ decomposed into CaO and liquid phase) are high melting point minerals, which determine the material has high high temperature resistance. The higher calcination temperature makes the periclase grains develop into polygons, the degree of direct bonding is enhanced, and the high temperature flexural strength is correspondingly improved. The easily hydratable CaO in the magnesia dolomite sand is uniformly filled in the voids between the MgO crystals or wrapped in the MgO grains, which shields the hydration channel of CaO to a certain extent and improves the hydration resistance of the synthetic sand. .