Sintered magnesite sand.
Usually sintered magnesite sand is the product of direct calcination with magnesite in vertical kiln and rotary kiln. According to the MgO mass fraction calibrated magnesium sand grade, generally the highest grade up to w(MgO)=98%. China magnesite sand base mainly in the south of Liaoning, pure quality. The main impurities in the raw material are SiO2 and CaO, Fe2O3 mass fraction is not high. Sintered magnesia sand by according to the preparation process and magnesium oxide quality fraction is divided into heavy-burning magnesia sand, mid-grade magnesia sand and high-purity magnesia sand.
The following table shows the physical and chemical index of common sintered magnesium sand
| type | w(MgO)/% | w(SiO2)/% | w(CaO)/% | CaO/SiO2 molar ratio | Volume density/g·cm3 |
| MS98A | ≥97.7 | ≤0.3 | ≥3 | ≥3.40 | |
| MS98B | ≥97.7 | ≤0.4 | ≥2 | ≥3.35 | |
| MS98C | ≥97.5 | ≤0.4 | ≥2 | ≥3.30 | |
| MS97A | ≥97.0 | ≤0.5 | ≥2 | ≥3.40 | |
| MS97B | ≥97.0 | ≤0.6 | ≥2 | ≥3.35 | |
| MS97C | ≥97.0 | ≤0.8 | ≥3.30 | ||
| MS96A | ≥96.0 | ≤1.0 | ≥3.30 | ||
| MS96B | ≥96.0 | ≤1.5 | ≥3.25 | ||
| MS95A | ≥95.0 | ≤2.0 | ≤1.6 | ≥3.25 | |
| MS95B | ≥95.0 | ≤2.2 | ≤1.6 | ≥3.20 | |
| MS93A | ≥93.0 | ≤3.0 | ≤1.6 | ≥3.20 | |
| MS93B | ≥93.0 | ≤3.5 | ≤1.6 | ≥3.18 | |
| NS90A | ≥90.0 | ≤4.0 | ≤1.6 | ≥3.20 | |
| NS90B | ≥90.0 | ≤4.8 | ≤2.0 | ≥3.18 |
1.Heavy burned magnesia sand.
Heavy burned magnesite sand is magnesite, magnesite, seawater and brine magnesium hydroxide and other raw materials in 1600 ~ 1900 ℃ fully sintered and obtained the product. Sintered magnesite sand is sintered from magnesite in China. Using MgO mass fraction greater than 46.0% of magnesite lump ore and solid fuel blocks mixed, into the vertical kiln calcined magnesite sand production. The mass fraction of MgO is 89%~98%. Because of the high degree of sintering of magnesite sand, so sometimes also called dead burn magnesite sand.
The following table shows the technical index of typical heavy burned magnesium sand
Chemical composition (mass fraction)/%
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.27 | 3.87 | 1.86 | 92.48 | 0.62 | 0.90 | 3.16 |
The microstructure of heavy-burned magnesite sand is characterized by the main crystalline phase of magnesite, and the crystals are mostly rounded and irregularly granular. Its crystal size and shape depends on the purity of raw material and sintering temperature. Generally, the size of magnesite crystals in refired magnesite sand is small, between 20~60μm. The intercrystalline phase is often accompanied by silicate phase, the composition fluctuates between C3S-C2S-C3MS2-M2S. Magnesite a magnesite between the silicate phase of the colloidal bond is mainly. The intergranular open pores are more long.
2. Mid-grade magnesium sand.
Using MgO mass fraction greater than 46.5% of magnesite, lightly burned by the reflection furnace, and then finely ground, mixed with water, ball pressed, mixed with solid fuel blocks into the vertical kiln calcined production of magnesium sand.MgO mass fraction of about 95%, also known as mid-range magnesium sand.
The following table shows the technical specifications of typical mid-grade magnesium sand
Chemical composition (mass fraction)/%
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Bulk density/g-cm-3 |
| 0.50 | 1.95 | 1.58 | 94.63 | 0.34 | 1.00 | 3.17 |
The microstructure of middle-grade magnesite sand is characterized by the main crystalline phase of magnesite, the crystals are mostly rounded and irregular granular body, the crystal size is mostly between 50~100μm, the intercrystal is often accompanied by silicate phase, the composition fluctuates between C3S-C2S-C3MS2-M2S. Square magnesite a magnesite between the main silicate phase of the cementation bond between the crystals more open pores.
3. High-purity magnesium sand.
The use of MgO mass fraction greater than 47% of magnesite, lightly burned to obtain a good high purity of lightly burned magnesium powder as raw material, by fine grinding, dry ball pressing, into the ultra-high temperature oil vertical kiln calcination production of magnesium sand MgO mass fraction of 96.5% to 98%, known as high purity magnesium sand.
The following table shows the typical high purity magnesium sand technical index
Chemical composition (mass fraction)/%
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.30 | 0.70 | 1.35 | 96.90 | 0.25 | 0.80 | 3.20 |
The microstructure of high purity magnesite sand is characterized by the main crystalline phase of magnesite crystal. The crystal size is between 30~100um. Intracrystalline, intercrystalline more round closed pores, pore size is mostly less than 10μm. intercrystalline silicate is less.
4. Seawater magnesium sand.
Seawater and brine contains soluble magnesium salt, with chemical and thermal decomposition method to produce MgO, by high temperature calcination into seawater magnesium sand and brine magnesium sand. Seawater and brine is a renewable resource compared with magnesite, while magnesite is a non-renewable resource.
China due to the magnesite ore reserves are abundant, for a long time metallurgical enterprises are mainly based on the production of magnesium sand from magnesite ore, and mainly low-grade magnesium sand. Using two-step calcination method, can produce high-purity magnesium sand with purity close to 97%, so far it is still difficult to produce ultra-high purity magnesium sand not less than 99% with heavy firing method.
Therefore, from the actual situation in our country, the use of a single physical method to produce a large number of high-purity magnesium sand from the ore more than 98%, especially not less than 99% of the ultra-high-purity magnesium sand is still more difficult. And from seawater, especially from the brine production of high purity and ultra-high purity magnesium sand is obviously much easier, it has more advantages than from magnesite production of high purity magnesium sand. Seawater magnesium sand MgO mass fraction up to 99.5%, the general seawater magnesium sand is also in 98% to 99%.
The following table shows the typical technical specifications of seawater magnesium sand
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.25 | 0.23 | 0.53 | 98.85 | 0.03 | 0.11 | 3.20 |
Typical microstructure characteristics of seawater magnesite sand is the main crystalline phase magnesite crystal size uniform, pure texture, material multiple grain boundaries and microporous structure. Magnesite crystals usually in 30-50μm, intercrystalline silicate phase less, more direct bonding between crystals, intracrystalline, intercrystalline more closed pores, pore size uniform, pore size mostly in 5μm or less.
The magnesia bricks produced by Kerry refractory material manufacturers with magnesia as raw material are: ordinary magnesia bricks, magnesia-aluminum bricks, magnesia-chromium bricks, magnesia-carbon bricks, direct bonding magnesia-chromium bricks, etc.; magnesia refractory castables are: aluminum-magnesia (aluminum spinel) refractory castables, magnesia light insulation castables, etc.