Quartz sand is a hard, wear-resistant and chemically stable silicate mineral, and its main mineral composition is SiO2 The color of quartz sand is milky white or colorless translucent, hardness is 7, brittle, no cleavage, shell fracture, oil luster, density is 2.65, bulk density (1.6 for 1-20 mesh, 1.5 for 20-200 mesh), its chemical thermal and mechanical properties are obviously heterotropic, insoluble in acid, slightly soluble in KOH solution, melting point is 1750 ℃. Quartz has high fire resistance. In industry, quartz sand is often divided into ordinary quartz sand, refined quartz sand, high-purity quartz sand, fused quartz sand, etc.
Normal quartz sand, i.e. SiO 2 °≥ 90-99% Fe 2O 2 ₃≤ 0.06-0.02%, fire resistance 1750 ℃, appearance of large particles, yellow skin Capsule on the surface. The size range is 5-220 mesh, which can be produced according to the user’s requirement. Ordinary quartz sand is a kind of water treatment filter material which is made of natural quartz ore through crushing, washing, drying and secondary screening. The filter material has the characteristics of no impurities, no edges and corners, high density, high mechanical strength, long pollution carrying capacity line and long service cycle. It is an ideal material for chemical water treatment. Main uses: metallurgy, black silicon carbide, glass and glass products, enamel, cast steel, water filtration, foam alkali, chemical industry, spray noise and other industries.
chemical composition ： SiO₂ 99.9-99.95%、 Fe₂O₃ 5PPM-25PPM max 、Li₂O 1-2PPM max、 Al₂O₃ 20-30PPM max、K₂O 20-25PPM max、 Na₂O 10-20PPM max
Physical properties: colorless transparent block, particle or white powder; relative specific gravity: 2.21; Mohs hardness: 7.0; pH value: 6.0.
The high-purity quartz sand, i.e. SiO₂≥99.5—99.9％ Fe₂O₃≤0.005％ , is made of natural crystal of Grade 1-3 and high-quality natural stone through careful selection and fine processing. The range of particle size is 1-0.5mm, 0.5-0.1mm, 0.1-0.01mm, 0.01-0.005mm, which can be produced according to the requirements of users.
Refined quartz sand, also known as acid washed quartz sand, is made by complex processing of high-quality ores, SiO₂≥99—99.5％ Fe₂O₃≤0.02—0.015％. The particle size range is 5-480 mesh. It can be produced according to the user’s requirements. The appearance is white or crystalline. Main uses: advanced glass, glass products, refractories, melting stone, precision casting, grinding wheel, etc
Generally, the electric stone roller is used in combination with water washing separation. The specific process is as follows: first, the large ore is broken into small stones by the jaw crusher (the jaw crusher feed inlet and discharge outlet should be equipped with a drain pipe; in this way, the soil and other impurities on the ore surface can be removed). The broken small ore is added to the stone roller for crushing (the water level of the water roller is always suitable to submerge the ore), and the small ore is crushed under the rolling rolling compaction of the stone roller When the required particle size flows out with water (a screen is arranged around the stone mill), the sand is carried by the lifting device to the separation equipment (or screening machine) for grading, and the graded sand mixture flows into the sedimentation tank for completion.
Advantages: less contact iron in production process, mature process and less investment.
Disadvantages: high failure rate and frequent maintenance of electric wheel roller.
After raw ore crushing → wet rod mill grinding → high frequency screen classification (to remove coarse particles), after separation → hydraulic classification (to remove fine particles), products with qualified particle size enter magnetic separator for iron removal, and iron removal products are dehydrated (or dried). The difficulty of this process lies in the removal of iron from the material after grinding
- The vertical ring high gradient magnetic separator has good iron removal effect and large investment;
- High field strength permanent magnet bars (12000gs) are combined to form a reflux tank for iron removal, which has good iron removal effect, low investment and complicated process;
- The combined magnetic separation of domestic ordinary wet magnetic separator has medium investment and average iron removal effect. For example: permanent magnet roller magnetic separator, electromagnetic slurry magnetic separator, etc.
This process has serious wear and tear to the equipment and brings in more iron impurities, which increases the difficulty of magnetic separation, reduces the quality of products and improves the operation cost of products
This process has serious wear and tear to the equipment and brings in more iron impurities, which increases the difficulty of magnetic separation, reduces the quality of products and improves the operation cost of products
The artificially selected ore is fed into the specially designed ball mill (lining plate quartzite; discharging mode: middle and grinding tail discharging) by the bar type vibrating feeder. The mixed sand after grinding is input to the first screening machine for separation by the belt conveyor (the upper limit of the finished sand can be separated with the castor plate according to the requirements, which is generally 20 mesh and 16 mesh). The coarse sand with 20 mesh can continue to enter the ball mill for grinding The screened mixed sand is sent to the cage type dynamic separator for separation. According to the actual requirements, the fine powder of 120 mesh is separated, and the sand after air separation is screened by multi-layer vibrating screen, 20 ~ 40 mesh, 40 ~ 60 mesh, 60 ~ 80 mesh, 80 ~ 120 mesh, etc. the dust points in the whole process are effectively controlled, no dust spillover, and the environment is friendly.
The outstanding advantages of this process are as follows
- Special design of ball mill, smooth discharge, less over grinding and high sand production rate;
- It can meet the requirements of large production, with single line capacity of 2 ~ 20 t / h and low labor cost;
- Innovative process design, the process of first removing fine powder by air separation and then screening, improves the screening rate, reduces the fine powder attached to the finished sand, and improves the product quality and grade.
High purity quartz is a kind of quartz sand with SiO 2 content of 99.92% – 99.99%, and its purity is generally more than 99.99%. It is the raw material for the production of high-grade quartz products. Because of its excellent physical and chemical properties such as high temperature resistance, corrosion resistance, low thermal expansion, high insulation and light transmittance, it is widely used in high-tech industries such as optical fiber communication, solar photovoltaic, aerospace, electronics and semiconductors.
In addition to the main mineral quartz, quartz is usually associated with feldspar, mica, clay, iron and other impurity minerals. The purpose of beneficiation and purification is to adopt appropriate beneficiation methods and process flow to improve the purity of products and reduce the impurity content according to the different requirements of particle size and impurity content of products. The mineral processing and purification of quartz sand depends on the content and occurrence of impurities such as Al₂O₃、Fe₂O₃、 Ti and Cr, as well as the requirements of product particle size.
It is generally believed that all impurities except silica are impurities, so the purification process of quartz is to increase the content of silica in the product as much as possible and reduce the content of other impurity components.
At present, the traditional quartz purification processes mature in industry include separation, scrubbing, calcination water quenching, grinding, screening, magnetic separation, gravity separation, flotation, acid leaching, high temperature degassing, etc. the deep purification processes include chlorination roasting, irradiation color separation, superconducting magnetic separation, high temperature vacuum, etc.
Iron and aluminum impurities in quartz raw materials are considered as the main harmful impurities, so the progress and development of purification methods and process flow of quartz raw materials are mainly reflected in the effective removal of iron and aluminum impurities.
Removal of impurities containing iron
There are five main forms of iron in quartz：
(1) It occurs in clay or kaolinized feldspar as fine particles;
(2) It is attached to the surface of quartz particles in the form of iron oxide film;
(3) Iron minerals or iron bearing minerals;
(4) It occurs in the interior of quartz grains in the form of diffusion;
(5) It exists in quartz crystal as solid solution.
According to different iron occurrence, the following separation and purification methods are generally adopted: A. screening and classification; B. scrubbing and gravity separation; C. magnetic separation; D. acid washing; e. microbial leaching.
Removal of impurities containing aluminum
The aluminum impurities in quartz mainly come from feldspar, mica and clay minerals. The alumina in clay minerals can be removed by scrubbing and desliming, while the alumina in feldspar and other minerals can be removed by flotation and electric separation.
For aluminum impurities, the following separation and purification methods can be generally used: A. flotation with fluorine; B. flotation without fluorine; C. chlorination roasting.
The specific production process of quartz purification is as follows: using vein quartz sand as raw material, quartz powder is purified by physical and chemical methods such as calcination, flotation and acid leaching, and the best purification process is obtained: 2% NaCl powder is added into the raw material, calcined at 820 ℃ for 2h, poured into the flotation solution for quenching, and then flotation. The pH value of flotation solution is 2, the concentration of anionic and anionic collectors sodium dodecyl sulfonate and Octadecylamine in solution is 0.82mg/l and 1.1mg/l respectively, the flotation time is 5min, and then the quartz powder is acid leached. The volume ratio of water, concentrated hydrochloric acid and 40% hydrofluoric acid in acid solution is 50 ∶ 50 ∶ 5, the acid leaching time is 8h, and the weight ratio of acid solution and quartz powder is 3 ∶ 1. After the best process, the impurity content of quartz powder reaches the standard of high-purity silica, the content of SiO 2 is 99.99% ~ 99.999%, the content of iron is 0.8 × 10-6, the content of aluminum is 16.1 × 10-6, and the content of titanium is 4.2 × 10-6.
Quartz purification is a process with high technical requirements. It has high requirements for the control of various parameters of the process, the cleanliness of the production workshop, and the operation specifications of workers. It is necessary to sum up experience in the production process.
Large grain quartz sand is used as refractory aggregate in various industrial kilns. The grain size is less than 20 ~ 30mm, so better grain shape and fire resistance are needed. The quartz ore is crushed to 80 ~ 120mm and then crushed to 20 ~ 30mm by cone crusher. The crushed material is lifted to the vibrating screen for screening by the closed bucket elevator, and about 20 mm is returned to the cone crusher for re crushing. The material less than 20 mm is stored in the silo, and the precise screening is carried out by several screening machines at the lower part of the silo. （0~1mm;1~5mm;5~10mm;10~20mm)
Solar photovoltaic glass is required to have higher transparency and whiteness, so the quartz sand is required to have low iron content and less impurities, and the fineness of the sand is between 28 and 140 mesh. For high-quality gangue quartz ore, the iron content is less than 20 ~ 80ppm, which can meet the requirements of photovoltaic glass without beneficiation and purification. Therefore, only dry sand with qualified particle size and distribution is needed.
The fillers used in the production process of artificial quartz slate are high wear-resistant quartz sand and quartz powder, and the content of fillers is about 90%. The raw materials for pressing quartz plate are opaque quartz, translucent quartz and transparent quartz with high whiteness. The fineness is 4 ~ 6 mesh, 6 ~ 8 mesh, 8 ~ 10 mesh, 10 ~ 20 mesh, 20 ~ 40 mesh, 40 ~ 70 mesh and 70 ~ 120 mesh.
With the rapid development of science and technology, high-tech industries such as optical power supply, electronic industry, optical communication, SiO 2 thin film materials, large-scale and ultra large scale integrated circuits, laser, aerospace, military industry, etc. are in great demand for high-grade quartz raw materials. However, due to the high quality requirements of these special quartz raw materials, the required content is usually more than 99.9%, even 99.99%, and the allowable impurity content is very low.