High-purity quartz refers to quartz sand with a SiO2 content of 99.92% to 99.99%, and the general required purity is above 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 optical fiber communication, solar photovoltaic, aerospace, electronics and other industries. High-tech industries such as semiconductors have a very important strategic position.

 In addition to the main mineral quartz, quartz raw materials are usually accompanied by impurity minerals such as feldspar, mica, clay and iron. The purpose of beneficiation and purification is to use appropriate beneficiation methods and technological processes to improve product purity and reduce impurity content according to the different requirements of products on particle size and impurity content. The beneficiation and purification of quartz sand depends on the content of impurities such as Al2O3, Fe2O3, Ti, Cr, etc., the state of occurrence and the requirements for product particle size.

  It is generally believed that other than silicon oxide 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 that are mature in the industry include sorting, scrubbing, calcination-water quenching, grinding, screening, magnetic separation, gravity separation, flotation, acid leaching, high temperature degassing, etc. The deep purification process includes chlorine Chemical roasting, irradiation color sorting, superconducting magnetic separation, high temperature vacuum, etc.

  Iron-containing impurities and aluminum-containing impurities in quartz raw materials are considered to be the main harmful impurities, so the progress and development of purification methods and technological processes of quartz raw materials are also mainly reflected in the effective removal of iron-containing impurities and aluminum-containing impurities.

Removal of iron impurities

(1) Occurs in clay or kaolinized feldspar in the state of fine particles;

(2) Adheres to the surface of quartz particles in the form of iron oxide films; 

(3) Iron minerals or iron-bearing minerals;

(4) Diffusion state Occurs in quartz particles;

(5) exists in quartz crystals in the state of solid solution.

For different iron occurrence states, the following sorting and purification methods are generally used:

a. sieving and grading; b. scrubbing and reselection; c. magnetic separation; d. pickling; e. microbial leaching.

Removal of aluminum impurities

The aluminum-containing impurities in quartz raw materials mainly come from feldspar, mica and clay minerals. The alumina component in clay minerals can be removed by scrubbing and grading desliming processes, while for alumina existing in feldspar and other minerals, flotation and electrical separation are mainly used to achieve the purpose of removing alumina.

For aluminum impurities, the following sorting and purification methods can generally be used:

a. Flotation method with fluorine; b. Flotation method without fluorine; c. Chlorination roasting method.                                                      

High-purity quartz is the basic raw material of high-tech products such as aerospace, electronic industry, electric light source tube, optical instrument, optical fiber communication, etc., and requires a high content of SiO2. And with the advancement of science and technology, especially the development of microelectronics technology, the demand for high-purity quartz will increase exponentially, and its quality requirements will become higher and higher.

However, due to the gradual depletion of natural resources crystals, it is imperative to find substitutes for crystals. Therefore, actively researching and exploring quartz purification technology is of great significance to realize the low-cost and large-scale industrial production of high-purity quartz.

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