Analysis of high purity quartz sand resources and processing technology

High-purity quartz sand is the basic raw material for microelectronics, optical fibre communications, aerospace and other high-tech industries, and has an important strategic position. With the continuous progress of science and technology, the demand for high purity quartz sand is growing, and its preparation technology has become the focus of research. In this paper, we will discuss the resource characteristics of high-purity quartz sand, impurity analysis, processing procedures and current technology, and analyse the current problems and future research direction.

First，Resource characteristics of high-purity quartz sand

High-purity quartz sand refers to quartz sand with SiO₂ content greater than 99.95%, Fe₂O₃ content less than 0.0001%, Al₂O₃ content less than 0.01%. The SiO₂ content of common industrial quartz sand is between 96% and 99%, which is mainly used in glass products, ceramic products, mechanical casting and other fields. High-purity quartz sand, on the other hand, is widely used in high-tech industries, such as aerospace, bioengineering, electronics, optical fibre communications and military industries.

At present, there are three main methods to prepare high-purity quartz sand: chemical synthesis, natural crystal processing and deep purification of quartz minerals. Although chemical synthesis method can prepare high-purity quartz sand, but the high cost of raw materials, energy consumption, low yield, difficult to large-scale industrial applications. Natural crystal processing method is more common in China, but the natural crystal resources are limited, and after years of mining has been gradually depleted. Therefore, the preparation of high-purity quartz sand through the deep purification of quartz minerals has become the main research direction in the future.

Second, the quartz ore mineral type and impurity analysis

Quartz minerals can be divided into magmatic, metamorphic, hydrothermal and sedimentary types according to their mineralisation and physicochemical properties, and the corresponding quartz rocks are granite pegmatite, vein quartzite, quartzite and quartz sandstone. Among them, granite pegmatite and quartz vein quartz in the quartz grain crystallinity is coarse, easy to dissociate the monomer, is the preparation of high-purity quartz sand ideal raw materials. American Unimin company is to granite pegmatite as raw material for the production of high-purity quartz sand, almost monopolised the international market 4N8 (SiO₂>99.998%) and above the production of high-end quartz sand products.

Impurities in quartz minerals are mainly divided into three categories: vein mineral impurities, inclusions impurities and crystal structure impurities. The common accompanying mineral impurities are feldspar, mica, rutile, calcite, etc. The main impurity elements are Al, Fe, Ca, Mg, Li, Na, K, Ti, B, H and so on. Among them, Al and Fe are the most abundant impurities in quartz, which not only exist in the form of associated minerals, but also tend to replace Si⁺ in the quartz lattice to form new aluminium-oxygen tetrahedra and iron oxygen tetrahedra, and at the same time, introduce charges such as K⁺, Na⁺, Li⁺, etc. to compensate for impurities. The impurities in the crystal lattice are difficult to remove and become the main bottleneck in the processing of high purity quartz sand.

Third, the processing of high purity quartz sand

The processing of high-purity quartz sand mainly includes four stages: pre-selection preparation, pre-selection, mineral sorting and deep purification.

Pre-selection preparation: the quartz into the mill before the calcination of about 1000 ℃ and water quenching, high temperature calcination, quartz and chalcopyrite crystalline transformation, impurities and quartz expansion rate is different, in the water quenching effect, the particles produced a large number of cracks, to facilitate the subsequent grinding and sorting.

Pre-sorting: Remove thin film iron, bonded material and muddy impurity minerals on the surface of quartz sand through water washing, desliming and scrubbing processes. For example, after water washing and classification and desliming of quartz sand from Malingshan Mine in Suqian, Jiangsu Province, the grade of SiO₂ increased from 78.39% to 86.36%, and the content of Al₂O₃ decreased to 6.79%.

Mineral sorting: Magnetic separation and flotation are the most commonly used processes to separate quartz sand from associated veins. The magnetic impurity minerals such as hematite, limonite, etc. are removed by multi-stage weak and strong magnetic separation, while flotation can effectively remove feldspar, mica and other non-magnetic associated impurity minerals in the quartz sand.

Deep purification: Remove impurities in inclusions and lattice through acid leaching, alkali leaching, high temperature roasting and other processes. High-temperature roasting can make the inclusions expand and rupture by heat, so that the impurities are exposed to the surface, and finally the impurities are removed by chemical leaching.