High-purity quartz sand is produced by high-grade quartzite (SiO2 content greater than 99.80%) through mineral processing, jaw crushing, calcination, water quenching, hammer breaking to roller breaking, screening, magnetic separation, pickling, flotation, wet screening, water washing, solid-liquid separation, roasted sand, strong magnetic separation and other processes.
The general application path of high-purity quartz sand products from low-end to high-end is the light source industry (99.5% to 99.99%), high-end optics, laser devices (more than 99.99%), to optical fiber communications, semiconductors, photovoltaics, microelectronics and other fields (99.995~ 99.9999%).
In recent years, with the rapid development of China's electronic information industry, electric light source industry, and the explosive growth of the photovoltaic industry, the total industrial output value of the quartz products industry has maintained rapid growth.
In the field of semiconductors, quartz is an indispensable raw material. Quartz products are used to a greater or lesser extent in almost every process, from the production of auxiliary components to the tools used for the actual wafer processing. Quartz crucibles are used to manufacture monocrystalline silicon, quartz glass bell covers are used for lithography engineering, and quartz boats and quartz brackets made of quartz tubes can be used for IC epitaxy, diffusion and lithography engineering. The rapid development of the semiconductor industry will drive the demand for upstream high-purity quartz materials.
In the field of optical fiber communication, high-purity quartz glass products are an important material in the production process of optical fiber. It is widely used in fiber preform making and fiber drawing process, where the purity requirements of the mandrel are the highest (greater than 5N). Optical fiber semiconductor market on the purity of quartz materials, specification accuracy, quality stability requirements are high, most of the domestic quartz products manufacturers do not have the ability to produce high-purity quartz sand and electronic grade quartz products, therefore, the current domestic optical fiber semiconductor manufacturers are still to foreign enterprises to import quartz products mainly. Internationally renowned quartz companies - Heraeus, Maitu, Xinyue quartz, etc. occupy most of the optical fiber semiconductor application market in China. The raw materials for the manufacture of fiber core rods and casings are mainly monopolized by Unimine. At present, optical fiber preform quartz casing products mainly rely on imports, and the cost of imported optical fiber quartz casing is high, and the demand for domestic substitution is strong.
At present, the state has formulated a number of current national standards, industry standards and local standards in the quartz industry. For example, for photovoltaic high-purity quartz sand requirements, white particles with certain transparency, no heterochromatic; the particle size of quartz sand should be in the range of 70 ~ 350μm, and the cumulative mass fraction in this particle size range should be greater than or equal to 90%. The cumulative mass fraction of particle size less than 100 μm or greater than 300 μm should be less than 1%. The silica content should be greater than or equal to 99.99%, the burn loss should be less than or equal to 0.01%, and the impurity element content should be less than or equal to 25 μg/g, of which the sum of potassium, lithium and sodium content should be less than 2.5 μg/g and other specific indicators.
Harben according to the purity of commercial quartz products, the processed quartz according to the total amount of impurities to classify, in this classification scheme, the total amount of impurity elements less than 50 μg / g of quartz defined as high-grade quartz materials, including high-purity quartz (total amount of impurity elements: 8 ~ 50 μg / g), very high purity quartz (total amount of impurity elements: 1 ~ 8 μg / g) and ultra-pure quartz (the total amount of impurity elements < 1 μg / g). Among them, the latter two are scarce or absent in nature and need to be processed and synthesized with highly pure natural quartz raw materials.
When studying the squartzite in different regions of Norway, Müller et al. tried to judge whether naturally produced quartz can be used as high-purity quartz based on the content of Al and Ti in quartz. Usually Al and Ti have a high element content in quartz, which is difficult to remove through a simple purification process, and fine purification will increase production costs, so the content of Al and Ti in quartz is the main factor restricting the purity of quartz. According to this, when the content of Al and Ti in quartz is less than 25ug/g and 10μg/g, respectively, natural quartz can be reduced to the category of high-purity quartz.
It is worth noting that Harben's division of quartz is based on commercial quartz products and is difficult to apply to naturally produced quartz. At the same time, there are many impurity elements in quartz, and the content of each impurity element in quartz and the impact on purification processing are not the same, so it is necessary to consider the upper limit of the content of the main impurity elements, rather than simply setting the upper limit of the total amount. Although the criteria proposed by Müller et al. can be applied to natural quartz and mainly consider the effects of Al and Ti content, they do not fully consider other impurity elements.
For these reasons and advances in quartz research, Müller et al. revised the judging criteria. The revision scheme mainly investigated the content of 9 major harmful elements in quartz, including Na, K, Li, Al, Ca, Fe, Ti, B and P, and the upper limits of each impurity element content were Al<30 μg/g, Ti < 10 μg/g, Na<8 μg/g, K<8 μg/g, Li<5 μg/g, Ca<5 μg/g, Fe<3 μg/g, P<2 μg/g and B<1 μg/g, and the total amount of these elements should not exceed 50 μg/g Only such quartz can be used as high-purity quartz. The evaluation scheme of Müller et al. is not only applicable to natural quartz, but also to processed quartz products, with wider applicability. In addition, Müller et al. pointed out that trace elements of quartz can be obtained by in situ analysis tests, such as EPMA, LAICP-MS or SIMS, in order to avoid the influence of foreign minerals and inclusions. Theoretically, the results obtained by in situ analysis tests are the superposition of lattice impurity element content and sub-micro inclusion element content, if in situ analysis shows that the impurity element content of quartz is too high, then the potential for natural quartz to be purified into high-purity quartz is relatively small.
At present, the highest purity achievable for large-scale production can reach more than 99.999% (5N). The price of its products is closely related to purity, and the silica content of low-end products is 99.5 to 99.99% (2 to 4N), and the price is about 600 to 800 yuan per ton. The purity of the mid-range product is between 99.995 and 9.999% (4 to 5N). The product price is about 30,000 yuan per ton. The high-end 5N or more high-purity quartz sand price at 60,000 yuan per ton, and the market is in short supply.
Source: Yang Xiaoyong, Sun Chao, Cao Jingya, Shi Jianbin. Research progress and development trend of high-purity quartz[J].Geological Frontier: 2021", edited by [Powder Technology Network], please indicate the source when reprinting!