the "14th Five-Year Plan" period, according to the national strategic plan of "carbon peak, carbon neutralization", the photovoltaic industry will lead to explosive development. The outbreak of the photovoltaic industry "creates wealth" throughout the industrial chain. In this dazzling chain, photovoltaic glass is an indispensable link. In today's advocacy of energy conservation and environmental protection, the demand for photovoltaic glass is increasing day by day, and the imbalance between supply and demand is beginning to appear. At the same time, the important material for manufacturing photovoltaic glass, low-iron ultra-white quartz sand, is also rising, and the price is rising and in short supply. Industry experts predict that low-iron quartz sand will have a long-term growth of more than 15% for more than 10 years.
1. Iron ions in quartz sand are easy to dye, and in order to ensure the high solar transmittance of the original glass, the iron content of photovoltaic glass is required to be lower than that of ordinary glass, so low-iron quartz sand with high silicon purity and low impurity content must be used. Technical requirements of high-purity quartz sand for
photovoltaic (GB/T 32649 -2016)
SRC = "https://img7.ccement.com/richtext/img/zst1opxtl281673493337586. In the future, with the growth of the production capacity of ultra-white patterned glass for solar cells, the high-quality quartz sand with limited origin distribution will become a relatively scarce resource." The supply of high-quality and stable quartz sand will restrict the competitiveness of photovoltaic glass enterprises in the future. Therefore, how to effectively reduce the content of iron, aluminum, titanium and other impurity elements in quartz sand and prepare high purity quartz sand is the current research focus.
2. Production
of low-iron quartz sand for photovoltaic glass 2. The general beneficiation process of quartz sand purification in China has developed from the early "grinding, magnetic separation, washing" to the combined beneficiation process of "separation → coarse crushing → calcination → water quenching → grinding → screening → magnetic separation → flotation → acid leaching → washing → drying". Pretreatment or auxiliary purification is carried out by means of microwave, ultrasonic wave and the like, and the purification effect is greatly improved. [2-3] In view of the requirement of photovoltaic glass for low iron, the research and progress of iron removal method with quartz sand are mainly introduced. Iron
generally exists in quartz ore in the following six common forms:
① in the form of fine particles in clay or kaolinized feldspar
; ② in the form of iron oxide film attached to the surface
of quartz particles; ③ iron minerals hematite, magnetite, specularite, Iron ore, etc. Or iron-bearing minerals such as mica, hornblende, Garnet and the like
(4) are in a disseminated or lens state
inside quartz particles (5) exist inside
quartz crystals in a solid solution state (6) a certain amount of secondary iron
is mixed in the crushing and grinding process, and the iron impurity is required to be detected first to effectively separate the iron-bearing minerals from the quartz Reasonable beneficiation methods and processes are selected according to the occurrence state of quartz ore to realize the removal of iron impurities.
(1) Magnetic separation process
The magnetic separation process can remove the weakly magnetic impurity minerals such as hematite, limonite and biotite including intergrowth particles to the maximum extent. Magnetic separation can be divided into high-intensity magnetic separation and low-intensity magnetic separation according to the strength of magnetism, in which high-intensity magnetic separation usually uses wet high-intensity magnetic separator or high-gradient magnetic separator.
Generally speaking, for quartz sand mainly containing weak magnetic impurity minerals such as limonite, hematite and biotite, the wet high-intensity magnetic separator is used in 8. [2] Nowadays, with the application of high-gradient high-intensity magnetic field magnetic separator, the magnetic separation purification is significantly improved compared with the past. For example, the content of Fe2O3 can be reduced from 0.002% to 0.
(2) Flotation process
Flotation is a process of separating mineral particles by different physical and chemical properties on the surface of mineral particles. The main function is to remove the associated minerals mica and feldspar from the quartz sand. For the flotation separation of iron-bearing minerals from quartz, finding out the occurrence form of iron impurities and the distribution form of iron impurities in each particle size fraction is the key to determine the appropriate separation process for iron removal. Most of the iron-bearing minerals have a point of zero charge above 5 and are positively charged in acidic environment, so anionic collectors are suitable in theory.
Fatty acid (soap), alkyl sulfonate or sulfate can be used as anionic collector for flotation of iron oxide ore. The pyrite can be floated from quartz in the acid washing environment by using isobutyl xanthate and butylamine aerofloat (4:1) with a dosage of about 200ppmw. Sodium oleate (0) is commonly used for ilmenite
flotation. Hydrocarbon phosphonic acid collectors developed in recent years have good selectivity and collecting performance for ilmenite.
(3) Acid leaching process
The main purpose of acid leaching process is to remove soluble iron minerals in acid solution. The factors affecting the purification effect of acid leaching include quartz sand particle size, temperature, time, acid type, acid concentration, solid-liquid ratio, etc. The leaching rate and leaching rate of Al can be increased by increasing the temperature and acid concentration and decreasing the radius of quartz particles. The purification effect of single acid is limited, while the mixed acid has synergistic effect, which can greatly improve the removal rate of Fe, K and other impurities. Common inorganic acids include HF, H2SO4, HCl, HNO3, H3PO4, HClO4, and H2C2O4. Generally, two or more inorganic acids are mixed in a certain proportion.
Oxalic acid is an organic acid commonly used in acid leaching, which can form stable complexes with dissolved metal ions, and impurities are easily washed out, with the advantages of less dosage and high iron removal rate. Ultrasonic-assisted purification of oxalic acid was used, and it was found that compared with conventional stirring and tank ultrasound, probe ultrasound had the highest removal rate of Fe, and the amount of oxalic acid was less than 4G/L, and the removal rate of Fe reached 75.
The coexistence of dilute acid and hydrofluoric acid could effectively remove Fe, Al, Mg and other metal impurities, but the amount of hydrofluoric acid should be controlled. This is because hydrofluoric acid can attack quartz particles. The use of different kinds of acid also affects the processing quality of purification, and the processing effect of HCl and HF mixed acid is the best. Some people use the mixed leaching agent of HCl and HF to purify the quartz sand after magnetic separation. Through chemical leaching, the total amount of impurity elements is 40.71 μg/G, and the purity of SiO2 is as high as 99.
(4) Microbial leaching
The film iron or disseminated iron on the surface of quartz sand particles is leached by microorganisms. It is a recently developed iron removal technology. Foreign studies have shown that Aspergillus niger, Penicillium, Pseudomonas, Bacillus polymyxidans and other microorganisms have achieved good results in iron removal from quartz surface film, among which Aspergillus niger has the best effect in iron removal. The removal rate of Fe2O3 is more than 75%, and the grade of Fe2O3 in concentrate is as low as 0. It is also found that the effect of leaching iron removal is better when the culture solution of most bacteria and fungi is cultured in advance. [2]
2.2 Other research progress
of quartz sand for photovoltaic glass In order to reduce the amount of acid, reduce the difficulty of sewage treatment and be friendly to the environment, Peng Shou et al. [5] disclosed a method for preparing 10 ppm low-iron quartz sand by a non-pickling process: natural vein quartz is used as a raw material, After three stages of crushing, one stage of grinding and two stages of classification, 0. 1 ~ 0. The prepared quartz sand SiO2 is more than 99.
On the other hand, with the depletion of high-quality quartz resources, the comprehensive utilization of low-end resources has been widely concerned. Xie Enjun of China Building Materials Bengbu Glass Industry Design and Research Institute Co., Ltd. used kaolin tailings to prepare low-iron quartz sand for photovoltaic glass. The main mineral composition of Fujian kaolin tailings is quartz, with a small amount of kaolinite, mica, feldspar and other impurities. The kaolin tailings are treated by the beneficiation process flow of grinding, hydraulic classification, magnetic separation and flotation to obtain the kaolin tailings with the grain size of 0.6-0.125mm, the content of which is more than 95%, the SiO2 of which is 99.62%, Al2O3 is 0.
Kaolin tailings contain a large amount of quartz resources, which can meet the requirements of photovoltaic ultra-clear glass raw materials through beneficiation, purification and deep processing, which also provides a new idea for the high-value comprehensive utilization of kaolin tailings resources.
3. Under the joint appeal of several photovoltaic module enterprises, in December 2020, the Ministry of Industry and Information Technology issued a document to clarify that the photovoltaic rolled glass project can not formulate a capacity replacement plan. Affected by the new policy, the expansion of photovoltaic glass production has increased since 2021. According to the public information, the production capacity of photovoltaic rolled glass with a clear production plan in 21/22 years will reach 22250/26590 t/d, with an annual growth rate of 68.4/48. Under the guarantee of policy and demand side, photovoltaic sand is expected to usher in explosive growth.
Photovoltaic Glass Industry Capacity
2015-2022
Domestic demand and output
of quartz sand 
Price Index of Low Iron Ore in https://img7.ccement.com/richtext/img/zzloencdrp1673493523398.2018-2021
Year: China's Overall Demand for Quartz Sand in 2020" Volume of 90.93 million tons, output of 87.65 million tons, net import of 327. According to public information, the consumption of quartz stone in 100 kg molten glass is about 72.2k G. According to the current expansion plan, the capacity increment of photovoltaic glass in 2021/2022 may reach 3.23/2.45 million t/d, calculated according to the annual production period of 360 days. Total production corresponds to the new demand for low-iron silica sand of 836/6.35 million tons per year, that is, the new demand for low-iron silica sand brought by photovoltaic glass in 2021/2022 alone accounts for 9.2%/7
of the total demand for quartz sand in 2020. Low-iron quartz is likely to usher in explosive growth with the help of the photovoltaic new energy industry. However, due to the shortage of quartz ore quantity and quality, quartz sand may become the bottleneck of the development of photovoltaic glass enterprises. Under the strong tuyere, Flat, Xinyi, Nanbo, Deli, Qibin and other companies have also announced the layout of low-iron quartz sand field, but overall, the current quartz sand resources of major glass factories are still unable to meet their own needs after a substantial expansion of production. It is particularly important and urgent for the exploration and excavation of high-quality quartz sand, the purification of quartz sand and the comprehensive development and utilization of low-end resources.
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