During the “14th Five-Year Plan” period, according to the country’s “carbon peak and carbon neutral” strategic plan, the photovoltaic industry will lead to explosive development. The outbreak of the photovoltaic industry has “created wealth” for the entire industrial chain. In this dazzling chain, photovoltaic glass is an indispensable link. Today, advocating energy conservation and environmental protection, the demand for photovoltaic glass is increasing day by day, and there is an imbalance between supply and demand. At the same time, low-iron and ultra-white quartz sand, an important material for photovoltaic glass, has also risen, and the price has increased and the supply is in short supply. Industry experts predict that low-iron quartz sand will have a long-term increase of more than 15% for more than 10 years. Under the strong wind of photovoltaic, the production of low-iron quartz sand has attracted much attention.
1. Quartz sand for photovoltaic glass
Photovoltaic glass is generally used as the encapsulation panel of photovoltaic modules, and it is in direct contact with the external environment. Its weather resistance, strength, light transmittance and other indicators play a central role in the life of photovoltaic modules and long-term power generation efficiency. The iron ions in the 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 lower than that of ordinary glass, and low-iron quartz sand with high silicon purity and low impurity content must be used.
At present, there are few high-quality low-iron quartz sands that are easy to mine in our country, and they are mainly distributed in Heyuan, Guangxi, Fengyang, Anhui, Hainan and other places. In the future, with the growth of the production capacity of ultra-white embossed glass for solar cells, high-quality quartz sand with limited production area will become a relatively scarce resource. The supply of high-quality and stable quartz sand will restrict the competitiveness of photovoltaic glass companies 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 a hot research topic.
2. Production of low-iron quartz sand for photovoltaic glass
2.1 Purification of Quartz Sand for Photovoltaic Glass
At present, the traditional quartz purification processes that are maturely applied in the industry include sorting, scrubbing, calcination-water quenching, grinding, sieving, magnetic separation, gravity separation, flotation, acid leaching, microbial leaching, high temperature degassing, etc., deep purification Processes include chlorinated roasting, irradiated color sorting, superconducting magnetic sorting, high temperature vacuum and so on. The general beneficiation process of domestic quartz sand purification has also been developed from the early “grinding, magnetic separation, washing” to “separation → coarse crushing → calcination → water quenching → grinding → screening → magnetic separation → flotation → acid The combined beneficiation process of immersion→washing→drying, combined with microwave, ultrasonic and other means for pretreatment or auxiliary purification, greatly improves the purification effect. In view of the low-iron requirements of photovoltaic glass, the research and development of quartz sand removal methods are mainly introduced.
Generally iron exists in the following six common forms in quartz ore :
① Exist in the form of fine particles in clay or kaolinized feldspar
②Attached to the surface of quartz particles in the form of iron oxide film
③Iron minerals such as hematite, magnetite, specularite, qinite, etc. or iron-containing minerals such as mica, amphibole, garnet, etc.
④It is in the state of immersion or lens inside the quartz particles
⑤ Exist in the state of solid solution inside the quartz crystal
⑥ A certain amount of secondary iron will be mixed in the crushing and grinding process
To effectively separate iron-containing minerals from quartz, it is necessary to first ascertain the occurrence state of iron impurities in the quartz ore and select a reasonable beneficiation method and separation process to achieve the removal of iron impurities.
(1) Magnetic separation process
The magnetic separation process can remove the weak magnetic impurity minerals such as hematite, limonite and biotite including conjoined particles to the greatest extent. According to the magnetic strength, magnetic separation can be divided into strong magnetic separation and weak magnetic separation. The strong magnetic separation usually adopts wet strong magnetic separator or high gradient magnetic separator.
Generally speaking, the quartz sand containing mainly weak magnetic impurity minerals such as limonite, hematite, biotite, etc., can be selected using a wet-type strong magnetic machine at a value above 8.0×105A/m; For strong magnetic minerals dominated by iron ore, it is better to use a weak magnetic machine or a medium magnetic machine for separation. [2] Nowadays, with the application of high-gradient and strong magnetic field magnetic separators, magnetic separation and purification have been significantly improved compared to the past. For example, using an electromagnetic induction roller type strong magnetic separator to remove iron under 2.2T magnetic field strength can reduce the content of Fe2O3 from 0.002% to 0.0002%.
(2) Flotation process
Flotation is a process of separating mineral particles through different physical and chemical properties on the surface of mineral particles. The main function is to remove the related mineral mica and feldspar from the quartz sand. For the flotation separation of iron-containing minerals and quartz, finding out the occurrence form of iron impurities and the distribution form of each particle size is the key to choosing a proper separation process for iron removal. Most iron-containing minerals have a zero electric point above 5, which is positively charged in an acidic environment, and theoretically suitable for the use of anionic collectors.
Fatty acid (soap), hydrocarbyl sulfonate or sulfate can be used as anionic collector for flotation of iron oxide ore. Pyrite can be flotation of pyrite from quartz in a pickling environment with the classic flotation agent for isobutyl xanthate plus butylamine black powder (4:1). The dosage is about 200ppmw.
The flotation of ilmenite generally uses sodium oleate (0.21mol/L) as a flotation agent to adjust the pH to 4~10. A chemical reaction occurs between oleate ions and iron particles on the surface of the ilmenite to produce iron oleate, which is chemically adsorbed Oleate ions keep ilmenite with better floatability. The hydrocarbon-based phosphonic acid collectors developed in recent years have good selectivity and collection performance for ilmenite.
(3) Acid leaching process
The main purpose of the acid leaching process is to remove soluble iron minerals in the acid solution. The factors that affect the purification effect of the acid leaching include quartz sand particle size, temperature, time, acid type, acid concentration, solid-liquid ratio, etc., and increase the temperature and acid solution. Concentration and reducing the radius of the quartz particles can increase the leaching rate and leaching rate of Al. The purification effect of a single acid is limited, and the mixed acid has a synergistic effect, which can greatly increase the removal rate of impurity elements such as Fe and K. Common inorganic acids are HF, H2SO4, HCl, HNO3, H3PO4, HClO4, H2C2O4, generally two or more of them are mixed and used in a certain proportion.
Oxalic acid is a commonly used organic acid for acid leaching. It can form a relatively stable complex with the dissolved metal ions, and the impurities are easily washed out. It has the advantages of low dosage and high iron removal rate. Some people use ultrasound to assist the purification of oxalic acid, and found that compared with conventional stirring and tank ultrasound, probe ultrasound has the highest Fe removal rate, the amount of oxalic acid is less than 4g/L, and the iron removal rate reaches 75.4%.
The presence of dilute acid and hydrofluoric acid can effectively remove metal impurities such as Fe, Al, Mg, but the amount of hydrofluoric acid must be controlled because hydrofluoric acid can corrode the quartz particles. The use of different types of acids also affects the quality of the purification process. Among them, the mixed acid of HCl and HF has the best processing effect. Some people use HCl and HF mixed leaching agent to purify the quartz sand after magnetic separation. Through chemical leaching, the total amount of impurity elements is 40.71μg/g, and the purity of SiO2 is as high as 99.993wt%.
(4) Microbial leaching
Microorganisms are used to leaching thin film iron or impregnating iron on the surface of quartz sand particles, which is a recently developed technique for removing iron. Foreign studies have shown that the use of Aspergillus niger, Penicillium, Pseudomonas, Polymyxin Bacillus and other microorganisms to leaching iron on the surface of the quartz film has achieved good results, of which the effect of Aspergillus niger leaching iron optimal. The removal rate of Fe2O3 is mostly above 75%, and the grade of Fe2O3 concentrate is as low as 0.007%. And it was found that the effect of leaching iron with the pre-cultivation of most bacteria and molds would be better.
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 environmentally friendly, Peng Shou [5] et al. disclosed a method for preparing 10ppm low-iron quartz sand by a non-pickling process: natural vein quartz is used as a raw material, and three-stage crushing, The first stage grinding and the second stage classification can get 0.1~0.7mm grit; the grit is separated by the first stage of magnetic separation and the second stage of strong magnetic removal of mechanical iron and iron-bearing minerals to obtain magnetic separation sand; the magnetic separation of the sand is obtained by the second stage flotation Fe2O3 content is lower than 10ppm low-iron quartz sand, flotation uses H2SO4 as regulator, adjusts pH=2~3, uses sodium oleate and coconut oil-based propylene diamine as collectors. The prepared quartz sand SiO2≥99.9%, Fe2O3≤10ppm, meets the requirements of siliceous raw materials required for optical glass, photoelectric display glass, and quartz glass.
On the other hand, with the depletion of high-quality quartz resources, the comprehensive utilization of low-end resources has attracted widespread attention. 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, which contains a small amount of impurity minerals such as kaolinite, mica, and feldspar. After the kaolin tailings are processed by the beneficiation process of “grinding-hydraulic classification-magnetic separation-flotation”, the content of 0.6~0.125mm particle size is greater than 95%, SiO2 is 99.62%, Al2O3 is 0.065%, Fe2O3 is 92×10-6 fine quartz sand meets the quality requirements of low-iron quartz sand for photovoltaic glass.
Shao Weihua and others from the Zhengzhou Institute of Comprehensive Utilization of Mineral Resources, Chinese Academy of Geological Sciences, published an invention patent: a method for preparing high-purity quartz sand from kaolin tailings. The method steps: a. Kaolin tailings are used as raw ore, which is sieved after being stirred and scrubbed to obtain +0.6mm material; b. +0.6mm material is ground and classified, and 0.4mm0.1mm mineral material is subjected to magnetic separation operation , To obtain magnetic and non-magnetic materials, the non-magnetic materials enter the gravity separation operation to obtain the gravity separation light minerals and the gravity separation heavy minerals, and the gravity separation light minerals enter the regrind operation to screen to obtain +0.1mm minerals; c.+0.1mm The mineral enters the flotation operation to obtain the flotation concentrate. The upper water of the flotation concentrate is removed and then ultrasonically pickled, and then sieved to obtain the +0.1mm coarse material as high-purity quartz sand. The method of the invention can not only obtain high-quality quartz concentrate products, but also has short processing time, simple process flow, low energy consumption, and high quality of the obtained quartz concentrate, which can meet the quality requirements of high-purity quartz.
Kaolin tailings contain a large amount of quartz resources. Through beneficiation, purification and deep processing, it can meet the requirements for the use of photovoltaic ultra-white glass raw materials. This also provides a new idea for the comprehensive utilization of kaolin tailings resources.
3. Market overview of low-iron quartz sand for photovoltaic glass
On the one hand, in the second half of 2020, the expansion-constrained production capacity cannot cope with the explosive demand under high prosperity. The supply and demand of photovoltaic glass is imbalanced, and the price is soaring. Under the joint call of many photovoltaic module companies, in December 2020, the Ministry of Industry and Information Technology issued a document clarifying that the photovoltaic rolled glass project may not formulate a capacity replacement plan. Affected by the new policy, the growth rate of photovoltaic glass production will be expanded from 2021. According to public information, the capacity of rolled photovoltaic glass with a clear plan for production in 21/22 will reach 22250/26590t/d, with an annual growth rate of 68.4/48.6%. In the case of policy and demand-side guarantees, photovoltaic sand is expected to usher in explosive growth.
2015-2022 photovoltaic glass industry production capacity
On the other hand, the substantial increase in the production capacity of photovoltaic glass may cause the supply of low-iron silica sand to exceed supply, which in turn restricts the actual production of photovoltaic glass production capacity. According to statistics, since 2014, my country’s domestic quartz sand production has generally been slightly lower than domestic demand, and supply and demand have maintained a tight balance.
At the same time, my country’s domestic low-iron quartz placer resources are scarce, concentrated in Heyuan of Guangdong, Beihai of Guangxi, Fengyang of Anhui and Donghai of Jiangsu, and a large amount of them need to be imported.
Low-iron ultra-white quartz sand is one of the important raw materials (accounting for about 25% of the raw material cost) in recent years. The price has also been rising. In the past, it has been around 200 yuan/ton for a long time. After the outbreak of the Q1 epidemic in 20 years, it has fallen from a high level, and it is currently maintaining stable operation for the time being.
In 2020, my country’s overall demand for quartz sand will be 90.93 million tons, the output will be 87.65 million tons, and the net import will be 3.278 million tons. According to public information, the amount of quartz stone in 100kg of molten glass is about 72.2kg. According to the current expansion plan, the capacity increase of photovoltaic glass in 2021/2022 may reach 3.23/24500t/d, according to the annual production Calculated over a 360-day period, the total production will correspond to the newly increased demand for low-iron silica sand of 836/635 million tons/year, that is, the new demand for low-iron silica sand brought by photovoltaic glass in 2021/2022 will account for the overall quartz sand in 2020 9.2%/7.0% of the demand. Considering that low-iron silica sand only accounts for a part of the total silica sand demand, the supply and demand pressure on low-iron silica sand caused by the large-scale investment of photovoltaic glass production capacity may be much higher than the pressure on the overall quartz sand industry.
—Article from Powder Network
Post time: Dec-11-2021