High-purity quartz sand refers to quartz mineral products with SiO2 content greater than 99.9%. It is a raw material for producing high-grade quartz products. It has excellent physical chemistry such as high temperature resistance, corrosion resistance, low thermal expansion, high insulation and light transmission. Its nature is widely used in high-tech industries such as optical fiber communication, solar photovoltaic, aerospace, electronics and semiconductors. Its strategic position is very important.

Table 1 US Unimin IOTA series products and Norwegian Crystallites AS company HPQ quartz sand chemical composition

Table 2 Chemical composition of high-purity quartz sand products from a quartz company in Jiangsu (ug/g)

"1" What is high purity quartz raw material?

High-purity quartz raw materials refer to natural quartz mineral resources that can be purified by the existing mature mineral processing technology to purify the purity of SiO2 to 99.9% and above. The purified high-purity quartz sand meets the stringent requirements of the modern high-tech industry.

The research shows that there are three basic geological conditions for high-purity quartz deposits with large scale, high grade and good quality:

(1) sufficient silicon source;

(2) no earlier associated metal deposit in order to ensure the purity of the silicon source and minerals;

(3) The appropriate tectonic setting is to provide a large-scale siliceous migration channel, a stable pressure-temperature, and a sufficient high-purity quartz crystallization time (PTt) and sufficient ore-forming space.

Crystal was once the main high-purity quartz raw material, but the domestic resource reserves are only 47 million tons. After more than 30 years of mining, it has gradually dried up and cannot meet the growing demand of high-purity quartz sand, vein quartz , quartzite and quartz sandstone . Gradually replace crystal as the main high-purity quartz raw material.

Table 3 Characteristics of quartz raw materials of different genetic types and priority application areas

"2" How to determine whether quartz ore can be used as high-purity quartz raw material?

The mineralogical characteristics of quartz ore formed under different geological origins are significantly different. The mineral composition, grain size characteristics, crystal structure and lattice impurities, chemical composition and impurity elements directly affect the quality of ore raw materials.

Learn mineralogy quartz process wherein the raw material, the nature of the ore detailed identification, quality quartz ore, mineral based solutions and product purification process direction is determined.

(1) Chemical composition

The chemical composition is a concentrated expression of the composition of each element in the quartz raw material. The content of the impurity elements in the ore has a key influence on the quality of the high-purity quartz sand processed and processed, which determines the economic value and application field of the product.

For example, quartz glass is one of the main products of high-purity quartz sand. Its performance index depends to some extent on the melting process. The chemical purity is only related to the purity of the raw materials, such as Al, B, P, alkali metal elements and key The content of transition metal elements exceeds the requirements, which will affect the melt viscosity and cause defects such as product devitrification, high temperature deformation, low softening point and light loss.

For trace elements harmful to the performance of high-purity quartz products, the 12 elements that have a greater influence are A1, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, and Ni, and the identification of these harmful elements is identified. The type of storage state and the specific existence form have important guiding significance for understanding the nature of raw materials and the process design of beneficiation and purification.

Table 4 Common occurrence states of trace elements in quartz raw materials

(2) Mineral composition

The mineral composition analysis of quartz raw materials can infer the formation process and mode of quartz ore, and select the appropriate beneficiation and purification method according to the type of gangue minerals.

The main chemical composition of the mineral-containing impurity elements of independent constitutes gangue minerals quartz raw material, especially those with higher levels of aluminosilicate minerals, and the alkali metal element A1 element (e.g., white mica), an impurity element is Carrier minerals, the type, content and particle size of these minerals have a serious impact on the quality of the quartz raw materials.

Feldspar and mica are the most common gangue minerals in quartz materials. Are other gangue minerals related to ore types?

Quartzite there zircon, tourmaline, calcite, pyrite, limonite, garnet gangue minerals;

Common opal quartz sandstone, chalcedony cements often also contain tourmaline, magnetite, titanium, hematite, iron, dolomite, rutile, and the like;

The vein quartz contains typical hydrothermal minerals, such as fluorite and iron minerals.

Qta-quartz, Ms- muscovite, Tur-tourmaline

Figure 1 Photograph of a quartz sandstone in Jiangyou

(3) Inlay granularity characteristics

There are significant differences in the grain size characteristics of the different types of quartz materials, which is closely related to the genesis of the deposit.

The grain size of the vein quartz is mainly affected by the ore-forming environment and magmatic activity. Aluminosilicate minerals such as muscovite are often co-existed. The size of the inlay of these minerals directly affects the monomer dissociation degree of quartz. When the particle size is smaller than the late quartz vein width, the gangue minerals can be dissociated from the continuous body.

The greater the strength of quartz diagenesis and metamorphism, the more obvious the difference in the grain size of other minerals. The type of porphyrin minerals such as muscovite is gradually changed from adjacent type to slit type or even wrapped. Easy to dissociate.

(4) Inclusion characteristics

During the growth of quartz crystals, residual hydrothermal components or secondary minerals are easily mixed into the inclusions, and high-pressure metamorphism may also lead to the formation of sub-mineral inclusions (such as rutile).

The inclusion itself provides rich mineralization information such as symbiotic combination, temperature and chemical composition of the fluid. The distribution, phase, uniform temperature and chemical composition of the inclusions can distinguish quartz from different genesis. For high-purity quartz raw materials, the type and content of inclusions have a significant effect on the quality of high-purity quartz sand. On the one hand, it constitutes the main source of impurity elements; on the other hand, it will also change the melting behavior of quartz industrial raw materials.

a, b is the microscopic morphology under polarized light microscope (orthogonal light); c, d is the microscopic morphology of quartz under scanning electron microscope

Fig. 2 Morphological characteristics of inclusions in a quartzite in Qinghai

(5) Lattice impurities

In addition to the gangue minerals and inclusions, a small amount of impurity elements are present in the quartz crystal in the form of isomorphism, forming lattice impurities in the quartz raw material.

Fig. 3 Schematic diagram of the similarity of trace elements in quartz crystal lattice

In the current processing of high-purity quartz minerals, the lattice impurities can hardly be removed, and the content of the crystals determines the limit of the purification potential of the raw materials.

(6) Crystal structure

Alpha-quartz (low-temperature quartz) is one of the most widely distributed minerals in the earth's crust and is widely found in magmatic, sedimentary and metamorphic rocks. The α-quartz crystal structure is a trigonal system. This crystal structure can exist stably under normal pressure and at a temperature lower than 573 ° C, and is almost the only source of high-purity quartz mineral.

(7) Thermal effect characteristics

The thermal properties of quartz are the specific manifestations of crystal structure, chemical composition and inclusion characteristics in the process of temperature and pressure changes. Thermal analysis of quartz raw materials is not only conducive to the identification of mineralogical features, but also important for post-processing.