China is a large country of silica minerals. A variety of siliceous material deposits have been developed in China, but high-grade deposits (SiO2 content > 99.95%) are quite rare. Purity quartz is purified siliceous raw mineral depth, widely used in a variety of glass, plastic materials microelectronic filler, casting machinery, metallurgy and chemical fields. With the rapid development of the national economy and science and technology, silicon raw materials have begun to be used in high-tech industries, such as semiconductor packaging materials, SiO2 film materials, optical fiber communication cable materials and aerospace. These fields have strict requirements on the quality of quartz sand, and the content of SiO2 is generally required to be above 99.9% (see Table 1). Since these industries are related to the long-term development of the country, the strategic position of high-purity quartz is very important.
1. Preparation of High Purity Quartz Quartz art impurities mainly of iron oxide and aluminum oxide, a metal oxide, wherein the portion adhered to the surfaces of quartz grains Fe2O3 in the form of an oxide film, A12O3 places clay minerals (such as kaolin, illite, The form of mica, etc.) is mixed. Therefore, the technical progress and development of the quartz sand purification method and process flow are also mainly reflected in the effective removal of iron and aluminum.
1.1 Initial purification of mineral processing 1.1.1 Scrubbing and scrubbing is the removal of thin film iron, bonding and muddy impurity minerals on the surface of quartz sand by mechanical force and abrasive stripping force between the sand and further shredding the unassembled mineral aggregate, scrubbing The un-monomer mineral aggregate can be smashed, and the preliminary purification effect on the raw material can be achieved through grading operation. Currently, there are mainly mechanical scrubbing and ultrasonic scrubbing. The main factors affecting the effect of the mechanical scrubbing method are the structural features and configuration forms from the scrubber, followed by the process factors (mainly including scrubbing time and scrubbing solids concentration). Studies have shown that the scrubbing solid concentration of quartz sand mine is the best between 50% and 60%. In principle, the scrubbing time is based on the initial product quality requirements. If the time is too long, it will increase equipment wear and increase costs.
Ultrasonic scrubbing is the use of ultrasonic waves to violently impact the quartz particles in the liquid, so that trace impurities or hydrated membranes on the surface of the particles are rapidly peeled off from the surface of the quartz particles, and become fine suspended matter under the action of the dispersing agent. After washing and separating, the purity of the quartz sand is greatly improved.
1.1.2 Magnetic Separation The magnetic separation process can remove weak magnetic impurities such as hematite, limonite and biotite including continuum particles. Strong magnetic separation usually uses a wet magnetic separator or a high gradient magnetic separator. In general, quartz sand containing mainly weak magnetic impurities such as limonite, hematite, and biotite can be selected by using a wet magnetic machine at 8.0×105 A/m or more; For ferromagnetic minerals dominated by iron ore, it is better to use a weak magnetic or medium magnetic machine for sorting.
1.1.3 Flotation The most typical process for flotation removal of associated mineral feldspar and mica in quartz is hydrofluoric acid as the activator. Under strong acid conditions (pH = 2 to 3), the amine cation collector is used . Flotation. However, with the increasing awareness of environmental protection, the fluorine-free flotation method is now widely used. For example, under the condition of strong acid (generally H2SO4) pH = 2 ~ 3, the anion-cation mixed collector is preferred to float the feldspar. This process has been widely used in Tongliao in Inner Mongolia and Changji in Xinjiang.
The common quartz sand flotation process can be summarized into five types, as shown in the figure below.
1.1.4 Magnetic Carrier Sorting As a new fine-grain beneficiation method, the magnetic carrier process has attracted wide attention in recent years. The principle of the process is that the magnetite particles are selectively attached to a mineral surface in the mixed suspension, and then the magnetic particles covered by the magnetite are removed by a magnetic separation process. Factors affecting the attachment of magnetite particles are the surface charge of minerals and magnetite, and the attachment of surfactants to the surface of these minerals. Many species can be sorted by controlling these parameters. In this process, a ferromagnetic phase is typically added to a non-magnetic or weakly magnetic suspension.
1.2 Fine purification process In general, after initial purification, the SiO2 content in quartz sand can reach 99.3%~99.9%. For higher purity, fine purification is required.
1.2.1 Acid Leaching Acid leaching is the use of quartz insoluble in acid (except HF), other impurity minerals can be dissolved by acid, thus achieving further purification of quartz. Acids commonly used for acid leaching are sulfuric acid, hydrochloric acid, nitric acid, acetic acid and hydrofluoric acid. The reducing agent is sulfurous acid and its salts. The above acids have a good removal effect on non-metallic impurity minerals in quartz. The removal of Fe and Al by various dilute acids is obvious, while the removal of Ti and Cr is mainly treated by concentrated sulfuric acid, aqua regia and hydrofluoric acid. The main factors affecting the acid treatment effect are acid concentration, temperature, time, and washing process. The acid leaching of impurity minerals is usually carried out using a mixed acid of the above-mentioned acid composition, and the HF acid concentration is generally not more than 10% in consideration of the dissolution of HF acid to quartz. The control of various factors of acid leaching should be based on the final grade requirements of quartz, to minimize the acid concentration, temperature and dosage, and to reduce the acid leaching time to achieve quartz purification at a lower beneficiation cost.
1.2.2 Microbial leaching Thin-film iron or dip-dyed iron on the surface of quartz sand particles by microorganisms is a recently developed iron removal technology. Foreign studies have shown that when the microorganisms such as Aspergillus niger, Penicillium, Pseudomonas, and Polymyxobacter are used to impregnate the quartz surface film, the effect of immersion of iron by Aspergillus niger is obtained. optimal. The removal rate of Fe2O3 is more than 75%, and the grade of concentrate Fe2O3 is 0.007% lower. It has also been found that the effect of leaching iron with a culture medium pre-incubated with most bacteria and molds is better. At present, microbial iron removal is in the laboratory research stage, and further trials are needed for large-scale production.
1.2.3 Other purification methods Due to the different requirements of different quartz products for impurity mineral content, some other purification methods are sometimes used for further purification. For example, electro-selection is to use a small difference in the electrical properties of quartz and impurity minerals to select trace mineral impurities; thermal chlorination method can remove gas-liquid impurities, impurity minerals and metal inclusions in quartz.
Conclusion (1) The method and process of purifying quartz sand are determined by the occurrence state of impurity minerals in raw sand, the cost of ore dressing and the industrial use of fine sand products.
(2) High-purity quartz sand produced by a series of processes such as scrubbing, magnetic separation, flotation, and acid leaching has basically met the quality requirements of the final product. However, secondary pollution should be strictly prevented in the production process. For example, deionized water should be used for purification water, and various professional equipment and tools should not pollute the final product as much as possible.
(3) Preparation of high-purity quartz sand, focusing on flotation and acid leaching treatment, especially the selection of acid in flotation reagents and acid leaching; with the enhancement of environmental awareness, the research on fluorine-free flotation process and pharmaceuticals is the tongue The focus of the research.
(4) High-purity quartz sand, as a basic material in large-scale and ultra-large-scale integrated circuits, optical fiber, laser, aerospace, and military, is increasingly demanding and has become a strategic product of the national economy. Combining chemistry, physics, microbiology, electromagnetic (wave) and other professional knowledge, research on the purification technology of high-purity quartz sand is an important development direction in the future.
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