Quartz sand, also known as silica sand, is a common non-metallic mineral material, and its application area is very extensive. The mineral processing and purification of quartz sand in China and its deep processing and exploitation are relatively late, and are mainly used in the construction industry, glass manufacturing, ceramic industry and foundry industry. One of the common points in these fields is that the demand for quartz sand is large and the quality of raw materials is low. For high quality quartz sands from some areas in our country, basically no mineral dressing is purified or slightly purified so as to meet the needs of industrial sand.
At present, the extraction and purification technology of quartz sand in the United States is the most advanced, characterized by large industrial output, specialized equipment and high production automation, and its products have been developed to sixth generations. High purity and ultra high purity quartz sand made from mineral processing and purification has been widely used in aerospace, atomic energy technology, laser, optical cable communication, military industry and other high-tech fields.
Quartz sand purification is a highly difficult separation technology to remove a small amount of or trace impurities in quartz sand and obtain refined quartz sand or high pure quartz sand (such as electronic grade products). In recent years, the purification process of quartz sand at home and abroad is mainly carried out in the following aspects.
1. Water washing, grading desliming
The grade of SiO2 in quartz sand decreases with the fineness of the grain size of quartz, and the grade of impurity minerals such as iron and aluminum is just the opposite. This phenomenon is particularly evident in the mineral quartz sand containing a large amount of clay. Therefore, it is very necessary to choose quartz sand raw ore before the election, and desliming step by step, and the effect is obvious. For example, the chemical composition of the ore deposit in the Maling mountain in Suqian, Jiangsu is SiO279.38%, Fe2O31.68% and Al2O311.28%, and the particle size of -0.1mm is 27.65%. After washing and degrading the original ore, the grade of SiO2 rises to 86.36%, Fe2O3 is reduced to 0.49%, and Al2O3 is reduced to 6.79%, and the purification effect is more remarkable except for impurity. Water washing and grading degash as a pretreatment method of ore before selection is very common, but the removal effect is not remarkable for the thin film iron and adhesive impurities that exist on the surface of quartz sand.
Scrubbing is the use of mechanical force and grinding force between the sand particles to remove the thin film iron, bonding and muddy impurities, and further grind unprepared mineral aggregates on the surface of quartz sand, and then to further purify quartz sand by classification operation. At present, there are two main methods, rod rubbing and mechanical scrubbing, for machinery. Scrubbing, it is generally believed that the main factors affecting the scrubbing effect are the structural features and configuration forms of the scrubbing machine, followed by technological factors, including scrubbing time and scrubbing concentration. The research shows that the best effect is between the scrubbing concentration of the sand ore in 50%-60% and the difficulty of purifying the quartz sand to a certain extent; In principle, the washing time should not be too long to meet the quality requirements of the product initially. Because of the long time, it will increase the wear of the equipment, increase the energy consumption and increase the cost of refining and purification. As for some quartz placer, the mechanical scrubbing and erasing effect is not very ideal, so it is more common and mature in China's rod friction washing industry.
3. Magnetic separation
The adoption of magnetic separation technology can eliminate the weakly magnetic impurity minerals including hematite, limonite and biotite. High intensity magnetic separation usually adopts wet high intensity magnetic separator or high gradient magnetic separator. Generally speaking, the quartz sand, mainly containing limonite, hematite, biotite and other weakly magnetic impurities, can be selected by the wet strong magnetic machine above 10000 Ostra. Seto Shiyingsa carried out the experimental conditions. The results showed that the magnetic separation and magnetic field intensity had an important effect on the removal of iron. With the increase of the number of magnetic separators, the iron content decreased gradually, while the iron content could be removed under a certain magnetic field intensity. However, the iron removal rate had not changed much even after the magnetic field intensity was higher. In addition, the finer the size of quartz sand, the better the effect of iron removal is due to the high iron content in fine quartz sand. When there are more impurities in the sand of quartz sand, only scrubbing, degouging and magnetic separation can not be purified from quartz sand into high pure sand, so further purification is needed.
In view of the serious environmental impact of fluoride containing waste water on the environment, the "fluorine free acid floatation method" appeared in 70s, for example, in the separation of feldspar and quartz in Japan, the flotation of sulfuric acid or hydrochloric acid (PH=2) and the flotation of high aliphatic amines and sodium petroleum sulfonate were successfully obtained, and the fluorine free acid free flotation was a recent year. A new flotation separation process for quartz feldspar was developed. It has not been reported that the application of industrial production has not been reported. The isoelectric point of mica and quartz is similar, the separation is difficult, the flotation of anion collector under acidic conditions, or two methods of anion collector under alkaline conditions, can get good results. Generally speaking, after cleaning, desliming, magnetic separation and flotation, the purity of quartz sand can reach 99.3%-99.9%, basically meeting the needs of industrial sand.
5. Acid leaching
Acid leaching is the use of quartz insoluble in acid (except HF) and other impurities in minerals can be dissolved by acid solution, which can further purify quartz. Acids commonly used for acid leaching include sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid, etc. The experience shows that these acids have good removal effect on nonmetallic minerals in quartz, but have significant influence on different metal impurities, the types and concentrations of acid. It is generally believed that the removal of Fe and Al by various dilute acids has significant effect, while the removal effect of Ti and Cr is thicker sulfuric acid, water or HF. Acid leaching is carried out. Usually acid acids are used to remove impurities from minerals. Taking into account the effect of HF on the dissolution of quartz, the HF concentration is generally not more than 10%.
Besides acid concentration, acid dosage, acid leaching time, temperature and ore agitation can affect the acid leaching effect of quartz. The control of various factors of acid leaching should be based on the requirement of the final grade of quartz, reducing the concentration of acid, temperature and dosage, reducing the time of acid leaching, so as to realize the purification of quartz at a low cost of mineral processing. In some European and American countries, because of the strict requirements for iron in quartz, the acid leaching and purification of quartz are studied systematically, and a quartz mineral purification plant with acid leaching is established. High purity quartz sand with a purity of 99.99% can be obtained by acid leaching of quartz sand.
6. Microbial leaching
The film iron or impregnated iron on the surface of quartz sand particles by microorganism is a newly developed iron removal technology. According to the results of foreign studies, it has achieved good results with the use of Aspergillus niger, Penicillium, Pseudomonas, polymyxin, bacilli and other microorganisms to remove the quartz surface film iron. The removal of iron by Aspergillus was the best. The removal rate of Fe2O3 was over 75%, and the grade of concentrate Fe2O3 was as low as 0.007%. At present, the removal of iron from microorganism is in the laboratory research stage, and the large-scale industrial production still needs further experimental research.
With the progress of science and technology, the demand for silicon in high technology will also increase, and the exhaustion of natural crystal resources makes people have to turn their eyes to the substitute of natural crystal - high pure and ultra high pure quartz sand. Therefore, it is of great practical significance to actively explore and promote the progress of quartz sand dressing purification technology, to realize the cost of refined quartz sand, high purity and ultra high pure quartz sand, to make large quantities of industrial production, to make up the shortage of natural crystal resources and to meet the needs of high technology silicon.