High purity quartz sand is produced from high-grade quartz stone (SiO2 content greater than 99.80%) through processes such as beneficiation, jaw crushing, calcination, water quenching, hammer breaking, roller breaking, screening, magnetic separation and color separation, acid pickling, flotation, wet screening, water washing, solid-liquid separation, sand baking, strong magnetic separation, etc.

The general application path of high-purity quartz sand products from middle and low-end to high-end is light source industry (99.5%~99.99%), high-end optical devices, laser devices (more than 99.99%), and optical fiber communication, semiconductor, photovoltaic, 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 photovoltaic industry, the total industrial output value of quartz products industry has maintained a rapid growth.

semiconductor

Quartz is an indispensable raw material in the semiconductor field. Quartz products are more or less used in almost all processes, from the production of auxiliary parts to the tools used for actual silicon wafer processing. Quartz crucible is used for manufacturing monocrystalline silicon, quartz glass bell cover is used for lithography engineering, and quartz boat and quartz support made of quartz tube can be used for IC epitaxy, diffusion and lithography engineering. The rapid development of the semiconductor industry will drive the demand growth of high-purity quartz materials in the upstream.

Optical fiber communication

In the field of optical fiber communication, high-purity quartz glass is an important material in the process of optical fiber production. It is widely used in the manufacture of optical fiber preform and optical fiber drawing process, in which the purity of mandrel is the highest (greater than 5N). The optical fiber semiconductor market has high requirements for the purity, specification accuracy and quality stability of quartz materials. Most domestic quartz product manufacturers do not have the ability to produce high-purity quartz sand and electronic grade quartz products. Therefore, at present, domestic optical fiber semiconductor manufacturers still mainly import quartz products from foreign enterprises. International well-known quartz Enterprises - Hollysys, maitu, shinyue quartz, etc. occupy most of China's optical fiber semiconductor application market. The raw materials for manufacturing optical fiber core rod and sleeve are mainly monopolized by unimin. At present, optical fiber preform quartz sleeve products mainly rely on imports. The cost of imported optical fiber quartz sleeve is high, and there is a strong demand for domestic replacement.

At present, the state has formulated a number of current national, industrial and local standards for the quartz industry. For example, for photovoltaic high-purity quartz sand, it is required that white particles with a certain degree of transparency have no discoloration; The particle size of quartz sand shall be 70~350 μ M, and the cumulative mass fraction within the particle size range shall be greater than or equal to 90%. Particle size less than 100 μ M or greater than 300 μ The cumulative mass fraction of m shall be less than 1%. The silica content shall be greater than or equal to 99.99%, and the loss on ignition shall be less than or equal to 0.01%; The content of impurity elements shall be less than or equal to 25 μ G/g, in which the total content of potassium, lithium and sodium is less than 2.5 μ G/g and other specific indicators.

According to the purity of commercial quartz products, Harben classifies the processed quartz according to the total amount of impurities. In this classification scheme, the total amount of impurities is less than 50 μ G/g quartz is defined as high-grade quartz material, including high-purity quartz (total impurity elements: 8 ~ 50 μ G/g), extremely pure quartz (total impurity elements: 1 ~ 8 μ G/g) and ultra pure quartz (total impurity elements < 1 μ G/g). Among them, the latter two are scarce or absent in nature, and need to be processed and synthesized with natural quartz raw materials with high purity.

When studying kyanite quartzites in different regions of Norway, m ü ller and others tried to judge whether naturally produced quartz can be used as high-purity quartz according to the content of Al and Ti in quartz. Generally, the element content of Al and Ti in quartz is high, so it is difficult to remove them through simple purification process, and fine purification will increase the production cost. Therefore, the content of Al and Ti in quartz is the main factor restricting the purity of quartz. Accordingly, when the contents of Al and Ti in quartz are less than 25ug/g and 10 μ G/g natural quartz can be classified as high-purity quartz.

It is worth noting that Harben's classification of quartz is based on commercial quartz products, which is difficult to apply to naturally produced quartz. At the same time, there are many kinds of impurity elements in quartz. The content of each impurity element in quartz and its influence on Purification and processing are different. Therefore, it is necessary to consider the upper limit of the content of main impurity elements rather than simply set the upper limit of the total amount. Although the standard proposed by M ü ller et al. Can be applied to natural quartz and mainly considers the influence of Al and Ti content, it fails to fully consider other impurity elements.

Based on the above reasons and the progress of quartz research, m ü ller et al. Revised the evaluation criteria. The correction scheme mainly investigated the contents of nine major harmful elements in quartz, including Na, K, Li, Al, CA, Fe, Ti, B and P. the allowable upper limits of the contents of each impurity element are al < 30 μ G/g, Ti ＜ 10 μ G/g, Na ＜ 8 μ G/g, K ＜ 8 μ G/g, Li ＜ 5 μ G/g, CA ＜ 5 μ G/g, Fe ＜ 3 μ G/g, P ＜ 2 μ G/g and B < 1 μ G/g, and the total amount of these elements shall not exceed 50 μ G/g, such quartz can be used as high-purity quartz. M ü ller's evaluation scheme is applicable not only to natural quartz, but also to processed quartz products, with wider applicability. In addition, m ü ller et al. Pointed out that the trace elements of quartz can be obtained through in-situ analysis and testing, such as EPMA, laicp-ms or Sims, in order to avoid being affected by foreign minerals and inclusions. Theoretically, the result of in-situ analysis and test is the superposition of lattice impurity element content and submicroscopic inclusion element content. If in-situ analysis shows that the impurity element content of quartz is too high, the potential for natural quartz to be purified into high-purity quartz is relatively small.

At present, the maximum purity of large-scale production can reach more than 99.999% (5N). The price of the product is closely related to the purity. The silicon dioxide content of the low-end product is 99.5 ~ 99.99% (2 ~ 4N), and the price is about 600~800 yuan per ton. The purity of the middle end product is 99.995~9.999% (4~5n). The product price is about 30000 yuan per ton. The price of high-end high-purity quartz sand of 5N or more is 60000 yuan per ton, and the market is in short supply.