Purification of high purity quartz sand

Time:2019-9-4 9:55:53

  High-purity quartz sand generally refers to quartz powder with SiO 2 content higher than 99.9%, which is mainly used in IC integrated circuits and quartz glass industries. Its high-grade products are more widely used in large-scale and ultra-large-scale integrated circuits, optical fibers, lasers, aerospace, military. High purity quartz sand is a neutral inorganic filler, which does not contain crystalline water and does not participate in the chemical reaction of the filler. It is a very stable mineral filler. It is widely used in plastics, rubber, ceramics and coatings. It can not only increase the new functions of products, but also save a lot of raw materials. 

  Purification of quartz sand:
  Purification of quartz sand is a highly difficult separation technology to obtain refined quartz sand or high purity quartz sand (such as electronic products) by removing small or trace impurities from quartz sand. In recent years, the main technological process for producing high purity quartz sand in China is as follows: raw silica is washed out by washing machine, crusher is roughly broken, qualified quartz material is put into roasting furnace, roasted at 850-980 (?) for 6 hours, after roasting, quartz material is dragged into clean water for water quenching, and impurities are removed by manual sorting. After magnetic separation, quartz sand is put into an acid cylinder equipped with HCl and HF mixed acid for one week. Then high purity quartz sand is prepared by flotation, dehydration, baking, cooling and packaging.
  Main process and technical requirements of quartz sand purification:
  1. Coarse dressing: remove the obvious impurities and foreign substances in all kinds of quartz raw ores; 2. Crush: use professional crusher to crush quartz raw ores to particles with a diameter of 1-20mm; 3. Water quenching: put burned quartz particles in cold water for rapid cooling in order to remove bubbles, water marks and some wrapped impurities in minerals. The purpose of quality is to crack minerals. Water quenching treatment of quartz calcination, also known as thermal fragmentation, refers to the crystalline transformation of quartz (alpha quartz beta quartz beta squamous quartz) occurring during calcination at high temperature, so that the volume of quartz increases, and the original defect degree in the crystal becomes more serious. When water quenching, the volume of the crystal suddenly decreases, and the internal stress at the defect increases rapidly, which promotes the crystal. A method of breaking a body at a defect. The crystal breaks at the defect, which exposes the inclusions and impurities in the cracks in the original quartz to the surface of the particles, and can be easily removed by acid treatment.
  4. Crushing: Ultrafine quartz sand with particle size of 5-50 um is prepared by wet or dry grinding; 5. Magnetic separation: high-gradient magnetic separation equipment with magnetic field strength of 50-15 000 Gauss is selected to remove magnetic minerals in the ore, such as limonite, hematite, mica, garnet, pyrite, ilmenite, etc.


         Generally, at least two stages of magnetic separation are arranged in the process. The main purpose of one stage magnetic separation is to remove the strong magnetic substances in the ore and avoid adverse effects on the follow-up work. The second stage of magnetic separation is mainly to remove weak and very weak magnetic minerals from the ore. A section of magnetic separation generally uses permanent magnet high magnetic cylinder magnetic separator, magnetic field generally 6000-8000 Gauss. The second stage of magnetic separation generally uses permanent magnet high gradient magnetic separator or electromagnetic induction magnetic separator. The former is more acceptable than the latter because of its low energy consumption, light weight, higher magnetic gradient and relatively low investment.
  Some people think that it is the function of reducing iron, but in fact it is not. Practice has proved that magnetic separation can reduce the content of impurities such as aluminium, potassium and sodium to a certain extent, and some impurities that can be removed by magnetic separation can not be removed by acid pickling and flotation. Magnetic separation is an indispensable and important process in the preparation of high purity quartz.
  6. Classification: Classification equipment is used to divide raw materials into many kinds of granularity range products according to the standard, and in the subsequent treatment, according to the granularity range, the classification equipment can be divided into screening machine and airflow classification equipment. It can be selected according to the requirement of output and grain size range.
  7. Roasting: Quartz raw ore particles are roasted for 2-5 hours in a professional roaster at 300-1500 C. Chlorination roasting is the main method for removing quartz lattice impurities. There are great differences in the action mode and effect between different chlorinating agents and lattice impurities. (Specific effects can be linked to the minor edition, which can provide more detailed information.) 8. Water crushing: The burned quartz particles are quickly cooled in hot water at room temperature to dissolve the soluble substances produced by roasting, and then heated for 0.5-2 hours to increase the solubility of the soluble substances in water.
  9. Flotation: The impurities with specific gravity less than 1 are removed by adding flotation agent to the water-crushed fine quartz sand powder. It mainly removes non-magnetic impurities, such as feldspar, pure muscovite and so on.
  10. Deionized water washing: wash the residual flotation agent and the impurities on the surface of quartz sand with deionized water; 11. Drying: first air-drying (drying) the quartz sand washed with deionized water to remove large quantities of water, and then drying it in special drying equipment, and heating it to 100-200 degrees C; 12. acid leaching: after drying. When quartz sand is added to the impregnating tank, acid (sulphuric acid, hydrochloric acid or hydrofluoric acid) used for acid leaching is added rapidly under the condition of drying and high temperature. The concentration of acid is 5%-20%. Under the condition of 30-100 C, it is stirred at constant temperature for 2-24 hours to remove trace metal and non-metallic impurities in fine powder of quartz sand; acid leaching is the purification process of high purity quartz sand. One of the most important processes is to prepare quartz glass for light source or quartz material for photovoltaic and semiconductor devices. The main purpose of acid leaching is to remove acid-soluble metal oxides and some silicate minerals as well as trace impurities such as soluble aluminium and iron in ores. After roasting, water quenching, sorting and high intensity magnetic separation, most of the oxide and impurity minerals have been removed, but there are still some oxide and impurity minerals in grain boundaries, micro-cracks and crystals, which are difficult to remove. Therefore, long-term acid leaching is used to remove such impurities. 

  Of course, in order to achieve the goal, the process may be adjusted according to the situation of the original ore, such as two-stage pickling and pre-acid leaching. In a word, in order to produce high-purity quartz, the means can be used as far as possible and the methods can be thought of as far as possible. In some processes, ultrasonic wave and other processes will be added to guarantee the pickling effect.
13. Deionized washing: The raw materials after acid leaching are washed with deionized water to remove the acid liquor contained in the raw materials until they are neutral; 14. Drying and packaging: drying the raw materials with special drying equipment, and vacuum packaging in the purification workshop to obtain the products.

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