5 common treatment methods for quartz sand
Date:2021-10-17 15:05:33
Author:admin
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High-purity quartz sand is the material basis for the development of high-tech industries, and its application fields involve optical fiber, military, aerospace industries, etc. These fields have extremely strict requirements on the purity of quartz sand raw materials, requiring very low impurity content in quartz sand, especially extremely high impurity content such as Fe and Al. Therefore, the purification technology of quartz sand is related to the long-term development of China's high-tech fields. At present, the purification technology of high-purity quartz sand is monopolized by the United States, Germany and other countries, and the export of purification technology and products is restricted. Therefore, it is of great significance to master the purification technology of high-purity quartz.
Mineral impurities in quartz sand usually exist in the form of non-quartz minerals, such as feldspar, mica, garnet, zircon, ilmenite and many other minerals. These impurities mainly exist in the following ways:
(1) As a loose companion mineral, it has not chemically combined with quartz crystal;
(2) As mineral fragments, it is chemically and physically combined with quartz crystals on its surface. Such impurities are mainly iron-containing minerals and aluminum-containing minerals;
(3) Minerals wrapped by quartz particles or surrounded by quartz crystals combined with each other;
(4) As interstitial ions instead of silicon, these impurities mainly include: Al3+, Fe2+, Fe3+, B3+, Ti4+, Ge4+, P5+, etc. These ions replace Si4+ to form covalent bonds. When this happens, it is usually accompanied by doping of elements such as Li1+, K1+, Na1+ and H1+ to maintain the electrical neutrality of the SiO2 lattice. Al element is one of the main impurity elements in quartz ore, and Al3+ and Si4+ have similar radii, which can easily replace Si4+, and its content is usually as high as thousands of ppm. Therefore, the Al content is an important indicator of the quality of quartz ore.
At present, the purification process of quartz sand mainly includes mechanical crushing, magnetic separation, flotation, acid leaching, calcination, water quenching, high temperature chlorination roasting, etc., which can effectively remove metal ion impurities in the quartz crystal lattice.
1. Mechanical crushing
Mechanical pulverization is a method of using mechanical force to reduce the size of minerals. This process mainly separates the non-structural impurities in the quartz mineral from the quartz, exposes the impurities on the outer surface of the quartz particles, and improves the purification efficiency of the subsequent processes.
2. Magnetic separation
The principle of magnetic separation is a method of separating magnetic mineral impurities from quartz minerals according to the different magnetic properties of quartz minerals. The purpose of magnetic separation is to remove some magnetic minerals in the magnetic inclusions of quartz raw ore.
3. Flotation
Flotation is the selective separation of hydrophobic substances from hydrophilic substances according to the difference in wettability of natural or modified ore body surface. Flotation is mainly used to remove mica and feldspar minerals that are symbiotic with quartz, and it can also flotate phosphorus and iron-containing minerals.
4. Acid leaching
Acid leaching is a method of purifying quartz according to the different dissolving ability of quartz, mica and feldspar in acid solution. Acid leaching can effectively remove the oxide film on the surface of iron ore and quartz particles in the quartz. For mineral impurities such as mica and feldspar, hydrofluoric acid is generally used for dissolution. Commonly used acid media for acid leaching are hydrochloric acid, sulfuric acid, nitric acid, acetic acid and hydrofluoric acid.
5. Heat treatment
In the purification process of high-purity quartz, heat treatment refers to high-temperature calcination of quartz (800～900℃). Heat treatment has two functions in the quartz purification process. First, the quartz mineral is hard, with a Mohs hardness of 7, which is a difficult-to-grind mineral. However, quartz minerals have anisotropy in the internal crystal structure, and the expansion coefficient of impurities such as muscovite and silicate minerals in the minerals is different from that of quartz. Therefore, after high-temperature calcination and water quenching, quartz minerals will expand rapidly when heated, and will cause stress concentration during rapid cold and emergency shrinkage, leading to cracks in the minerals, thereby realizing the fragmentation of quartz.
The addition of a chlorinating agent during high-temperature calcination, that is, the purification of quartz by the chlorination roasting method, has been proven to be the most effective method for removing impurities in the quartz crystal lattice. The metal oxide is used to undergo a chlorination reaction with the chlorinating agent in a high temperature environment to generate gaseous metal chloride and volatilize, thereby achieving the purpose of removing metal oxide impurities.
