The preparation of high-purity quartz minerals is firstly the selection of mineral sources, the identification of high-purity mineral sources, and the identification of their potential utilization value. Secondly, different targeted treatment processes are selected for the impurity types and occurrence forms of different mineral sources and the end use of the products; Finally, it is checked whether the impurity content after purification is satisfactory.
According to the physical or chemical differences between quartz ore and gangue minerals, a suitable method is selected for sorting. The purification and beneficiation methods mainly include: color selection, re-election, magnetic separation, electrostatic separation, flotation, acid leaching, hot chlorine. And so on.
Fig.1 Flow chart of high-purity quartz ore beneficiation and purification process
1 quartz ore selection
China's quartz ore is rich in mineral impurities, gas-liquid inclusions and elemental impurities, while the latter two are more difficult to remove by ordinary methods. Therefore, according to the appearance of the ore, the crystal quality, surface impurities, color, inclusions and light transmittance, etc., the ore containing less elemental impurities and inclusion impurities is the basis for the subsequent purification of high-purity quartz. High grade, economical and stable high-purity quartz products can be produced with high grade and large reserves.
2 calcination and water quenching
Calcination and water quenching are beneficial to the next step of grinding mineral dissociation in quartz ore, which can remove some large gas-liquid inclusions.
Quartz ore is calcined at high temperature. At high temperature, the quartz crystal form undergoes large volume expansion. 573°C, 870°C, and 1470°C are the crystal transition point temperatures. Due to the different expansion rates of impurities and quartz, the rapid temperature difference is utilized. The quartz ore causes large cracks. Cracks often occur at the interface between the inclusions and the quartz matrix, so that the impurities are fully exposed, and some of the gas-liquid inclusions can be removed. At the same time, the water quenching treatment is beneficial to further grinding.
When the crack reaches a certain level, it forms a fracture. After the fracture, the inclusion impurities are easily exposed on the surface of the quartz ore particles or form intergranular dissociation.
3 crushing and scrubbing
Smashing is the process of reducing the particle size of a mineral under mechanical force. The purpose of crushing in different industries is different. For example, ceramics, cement and other industries only require a certain particle size composition. However, in the mineral processing industry, the purpose of comminution is to require the useful components and unwanted components of the symbiosis in the mineral to dissociate, which is conducive to the subsequent sorting of concentrates and tailings.
The standard equipment for crushing and dissociating minerals is a rake and cone crusher , coarsely crushed quartz ore to centimeter level and scrubbed to remove clay and iron oxides adhering to the mineral surface.
The crushing and grinding process, due to the relatively hard quartz mine, frequent contact with the equipment, it is inevitable to introduce impurities. High-purity quartz pulverization process In order to solve the above problems, alternative technologies include self-grinding and high-pressure pulse pulverization.
The self-grinding machine uses the pulverized material itself as a grinding medium to greatly reduce the contamination of the material by the mill media.
High-pressure pulse pulverization has been commercialized in recent years, a new technology for the field of mineral selective dissociation and high-purity processing. It uses a high-voltage pulse discharge to form a tiny plasma channel in the mineral and generates a shock wave. The fracture along the grain boundary and the selective dissociation from the mineral grains are the only dissociation methods known to directly act between the grain boundaries. The advantages are: no mechanical contact with quartz ore, no introduction of impurities; selective cracking of mineral grain boundaries, most of the mineral impurities are present between quartz grain boundaries, which may expose impurities between grain boundaries, selectivity Dissociation of mineral impurities and gas-liquid inclusions in the crystal can improve the efficiency of subsequent purification, minimize over-pulverization and consume less energy.
After the pulverization, the rubbing mud is wiped off, and the scrubbing is performed by mechanical stirring to rub the ore particles with each other and washed with water. This is effective for removing the thin film iron and mud impurity minerals on the surface of the quartz particles, and then further purifying the quartz sand by the classification operation.
At present, there are mainly methods such as mechanical scrubbing and ultrasonic scrubbing. For mechanical scrubbing, it is generally believed that the main factors affecting the scrubbing effect are the structural characteristics of the scrubbing machine itself, followed by the process factors: including scrubbing time, concentration, and the like. Studies have shown that the scrub concentration of sand mine is the best between 50~60%. If it is too large or too small, it will reduce the erasing effect of impurity minerals. The scrubbing time should not be too long. If it is too long, it will increase equipment wear and energy consumption. The scrubbing process has a good effect on the iron oxide film on the quartz surface. For example, after a certain amount of quartz sand ore is washed by water and classified and de-sludged, mechanical scrubbing is performed, and the removal rate of Fe2O3 is 47.4%. In comparison, ultrasonic scrubbing is more efficient than mechanical methods.
4 classification and color selection
Grading is a process of sorting depending on the specific gravity, shape or size of the particles. According to the quartz glass melting process requirements, the particle size distribution of high-purity quartz raw materials should be controlled within a certain range (generally 75μm~100μm), while the high-purity quartz raw material pulverization process produces a wide range of product size distribution, which needs to be classified. Processed to meet the particle size requirements of quartz glass.
The grading process can also act as de-sludge to reduce iron content, because quartz is harder than iron-containing minerals, and under the same grinding conditions, the minerals with low hardness are easy to grind, and studies have shown that SiO2 in quartz sand The grade decreases as the grain size of the quartz sand becomes finer.
Quartz sand classification equipment mainly includes: vibrating screen, centrifugal classifier, cyclone classifier, hydrocyclone and so on.
The optical detection system in the color sorting machine issues a command to the sorting device according to the difference in color and transparency between the mineral defective product and the qualified product, and uses the gas nozzle to inject high-pressure gas to the defective product to remove it from the qualified product. It is uneconomical to use artificial color for minerals below 40mm. The color sorter has the highest efficiency in the range of 3 to 5 mm.
5 flotation
Flotation is based on the difference of the natural or modified wettability of the mineral surface. The hydrophobic surface is easy to combine with the bubble. The bubble brings the hydrophobic mineral particles into the bubble layer by buoyancy, while the hydrophilic mineral is still suspended in the slurry, and the bubble layer is peeled off. The hydrophobic particles eventually reach the purpose of mineral separation.
Flotation is mainly used for removing the quartz ore symbiotic mica, feldspar minerals can also be phosphate containing flotation, iron minerals, additional flotation can be mixed during the removal of iron secondary crushing and grinding. The design of the flotation process depends on the type of minerals and the degree of dissociation.
6 magnetic separation
Magnetic separation using the difference in coefficient of quartz and sorting magnetic iron minerals can be removed paramagnetic and ferromagnetic minerals including hematite, titanium, iron and biotite, rutile, etc. even weakly magnetic minerals.
The number of magnetic separations and the increase of the strength of the magnetic field have a significant effect on the amount of iron removal. With the application of the high gradient magnetic field magnetic separator, the magnetic separation purification is significantly improved compared with the past.
7 re-election
The use of re-selection separation of mineral impurities and quartz density difference, but generally for the heavy minerals containing iron, and the secondary iron in the crushing grinding.
The re-election includes de-sludge and hydraulic classification. The commonly used equipments are mainly spiral concentrators, shakers, etc. The particle size range of the spiral concentrator and shaker is 2mm~50μm and 2mm~38μm respectively, and the sorting effect of the shaker is better.
8 high voltage electrostatic separation
High-voltage electrostatic separation utilizes the difference in conductivity of different mineral surfaces. After the feed is dried, it enters a high-voltage electrostatic field of up to 60~120kV/m. Under the action of electrostatic force and mechanical force, the separation of materials is realized. The conductivity of feldspar and quartz is 710 nS/m and 58 nS/m, respectively; the dielectric constants are 5.36 and 4.4, respectively.
The friction electrostatic separator is suitable for the separation of non-conductive minerals. When quartz particles are rubbed with feldspar particles, the dielectric constant of quartz is smaller than that of feldspar. The feldspar particles are easy to lose electrons positively charged, while the quartz particles are negatively charged and pass static electricity. The field function can separate feldspar from quartz, and the sorted particles range from 1mm to 75μm, which is a dry alternative to flotation feldspar.
9 heat treatment
The heat treatment utilizes the crystal transformation of quartz and the thermal explosion effect of the gas-liquid inclusion heating to release the gas and liquid in the quartz inclusion, and reduce the bubbles and impurities introduced by the gas-liquid inclusion during the quartz glass refining process.
The general treatment method is: under high temperature vacuum state, generally about 1500 °C, the inclusion of inclusions, in addition to the temperature factor is also related to the type of gas molecules, the smaller the gas molecules, the greater the diffusion coefficient, He, H2 is easy to diffuse and discharge; water Oxygen and the like are easily reacted with the melt; gases such as N2, CO, CO2, and CxHx (alkanes) are extremely difficult to be discharged from the melt, eventually forming bubbles.
10 acid dip
Because quartz is insoluble in acid (except HF), other impurity minerals can be dissolved by acid. Acid washing is used to remove acid-soluble iron ore and a part of silicate minerals, especially thin film iron on the surface of quartz particles. Dissolve part of the fluid inclusions.
Commonly used acids are sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, etc. The type and concentration of the acid, the time of acid leaching, the temperature, the degree of slurry agitation and the particle size of the quartz all affect the acid leaching effect.
Studies have shown that the use of an acid alone is not as good as the mixed acid. Professor Zhou Yongheng of South China Normal University proposed the optimum process conditions for acid-impregnated quartz impurities. The addition of HF reduced the Al content from 23.7 ppm to 15.1 ppm, but the loss rate of quartz reached 21%. Various studies have shown that high purity quartz cannot be achieved by using HCl or H2SO4 alone, and only high-purity quartz stone can be obtained by adding a mixed acid of HF.
11 thermal chlorination
During the thermal chlorination process, the quartz ore is heated to 1000-1200 ° C in a chlorine or hydrogen chloride atmosphere. Chlorine or hydrogen chloride reacts with alkali metals, alkaline earth metals, and transition metals in the quartz crystal lattice to form corresponding gas phase chlorides.
These lattice impurity contents are particularly demanding in high temperature lamps and semiconductor applications, and thermal chlorination is an indispensable treatment process for producing high purity quartz sand.
12 test
Ordinary quartz glass raw materials are generally equipped with X-ray fluorescence analysis (XRF) to meet the inspection requirements. High-purity quartz glass raw materials need to be able to test sub-ppm equipment, such as inductively coupled plasma mass spectrometry (ICP-MS).
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