The processing of quartz ore into high-purity quartz is the process of separating various impurities in the quartz raw material as much as possible. First, the quartz minerals and gangue minerals are dissociated by crushing and grading to obtain quartz particles of the corresponding size. The lattice impurities are effectively separated from the quartz.
1. Pulverization-classification pretreatment technology
The pulverization-classification pretreatment in the process of high-purity quartz processing is to first dissociate the effective monomers of quartz and gangue minerals and release fluid inclusions, and second, to provide raw materials with suitable particle size range for subsequent quartz purification and processing.
In the process of quartz pulverization, not only the effective monomer dissociation of gangue minerals in quartz should be considered, but also the reduction of secondary pollution to quartz should be considered. In order to avoid secondary pollution of quartz by iron impurities during the grinding process, zirconium balls, agate, etc. are generally used as grinding media.
As a commonly used process in quartz crushing, thermal crushing not only reduces the hardness of quartz blocks and crushing energy consumption, but also reduces the possibility of secondary pollution of quartz by reducing the contact time between quartz and grinding media; at the same time, micro-cracks are generated on the surface of quartz. , which is beneficial to the chemical purification of quartz.
High-voltage pulse crushing utilizes the shock wave generated in the quartz block by high-voltage discharge, so that the quartz is more easily broken along the crystal boundary containing impurities, which is beneficial to the exposure of impurities in the quartz.
Classification is the process of sorting particles based on their specific gravity, shape or size. High-purity quartz not only has strict technical requirements for purity, but also has strict requirements for particle size distribution.
Grading can also separate some fine-grained sludge impurities. Since quartz is harder than iron-bearing minerals, gangue minerals are easier to grind under the same crushing conditions. The grade of SiO2 in quartz sand varies with the particle size of quartz sand. thin and lower.
2. Quartz co-associated independent mineral separation technology
Quartz can be associated with a variety of minerals. Color separation, scrubbing, gravity separation, magnetic separation and flotation are currently the most effective methods to separate co-associated independent minerals from quartz.
The most common methods for sorting mineral impurities in quartz are magnetic separation and flotation. The multi-stage strong magnetic separation can not only separate the strong magnetic and weak magnetic mineral impurities that have been dissociated from the quartz, but also has a certain sorting effect on the magnetic mineral inclusions and conjoined bodies in the quartz. Silicate minerals such as mica and feldspar are one of the main sources of aluminum impurities in quartz. Because of their similar physical and chemical properties to quartz, flotation is often used for separation. In order to effectively reduce the aluminum impurity content in quartz, multiple selections are essential.
The type, content and occurrence state of mineral impurities in natural quartz are very complex. It is necessary to select a targeted combined beneficiation process according to the nature of the quartz raw material to improve the separation effect of quartz and independent mineral impurities.
After pretreatment and physical sorting, most of the independent mineral impurities in quartz have been separated, and the SiO2 content can generally reach about 99.9%, but it does not meet the technical requirements of high-purity quartz. This is mainly because pretreatment and physical sorting only have a significant effect on the separation of quartz and independent mineral impurities, and have little effect on reducing inclusion impurities and lattice impurities in quartz.
3. Inclusion impurities and quartz separation technology
Almost all natural quartz minerals contain mineral inclusions and fluid inclusions. The existence of a large number of inclusions not only increases the difficulty of processing high-purity quartz, but also limits the quality of high-purity quartz.
(1) Mixed acid dissolution of mineral inclusions
Mixed acid dissolution of mineral inclusions utilizes the feature that quartz can only be dissolved in hydrofluoric acid, while impurities of other mineral inclusions can be dissolved by acid to achieve the separation of quartz and impurities. Commonly used acids are sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid. Wait.
(2) High temperature burst of fluid inclusions
During the high-temperature calcination of quartz, when the internal pressure of the fluid inclusions is greater than the bound pressure of quartz on the inclusions as the temperature increases, the fluid inclusions burst suddenly and the internal impurities are released, and then the impurities inside the fluid inclusions can be dissolved by subsequent acid cleaning. .
(3) Chlorination degassing
Chlorination degassing is a high-temperature treatment method of heating quartz to 1000-1500 ℃ and introducing Cl2, HCl or mixed gas, which can not only make metal impurity elements volatilize gaseous chloride salts at high temperature, but also affect the fluid in quartz. The inclusions have a certain removal effect.
4. Lattice impurity removal technology
There are only Si-O bonds in completely pure quartz crystals, but due to the existence of isomorphic substitution, a large number of metal-oxygen (Me-O) bonds are introduced into natural quartz, which are the main impurities in natural quartz minerals. one of the sources.
In the process of purifying quartz by acid leaching, TerryB et al. believed that the energy and properties of the Me-O bonds in the quartz lattice determine the difficulty of separation of metal impurity elements:
Me (Li+, Na+, K+)-O bond has the smallest energy and is the easiest to destroy, but because alkali metal ions play a role in balancing the charge in quartz, it cannot be effectively removed;
Me (Fe3+, Cu2+, Ca2+, Mn2+, etc.)-O bond energy is second, and it is a lattice impurity element that is easier to remove in quartz;
Me (Al3+, Ti4+)-O bond energy is larger, Al and Ti replace Si in the quartz lattice to form new [AlO4] and [TiO4], which are the most difficult lattice impurity elements in quartz to remove.
Quartz exists in many different crystal forms in nature. In the process of crystal transformation of quartz, the crystal structure of quartz will also change, and impurities existing in the crystal lattice may migrate and diffuse to the surface of quartz particles to increase the possibility of being removed. At a high temperature of 1500 ℃, the phase transformation of quartz to cristobalite will occur, the fracture and reorganization of bonds will occur, and the quartz lattice will expand, which is conducive to the migration and diffusion of metal impurity elements to the quartz surface. Compared with calcination in vacuum atmosphere, the conversion rate of quartz to cristobalite is higher during calcination in nitrogen atmosphere, and the migration and diffusion efficiency of impurity elements in the quartz lattice may be higher.
Chlorination roasting is that at a temperature lower than the melting point of quartz, the impurity components in quartz and the chlorinating agent are converted into chlorides and volatilized. During the high temperature chlorination roasting process, there is a crystal transformation of quartz, which makes the crystal lattice in the quartz crystal change. Metal ions may migrate and diffuse to the surface of quartz, and chemically react with HCl, NH4Cl and Cl2 to become volatile components to achieve separation from quartz, and also prevent impurity elements from migrating and diffusing into the quartz lattice during the cooling process. .
Generally speaking, the technology of using natural quartz minerals to process high-purity quartz has gradually matured. The pretreatment is mainly to fully dissociate and expose the impurities in the natural quartz, and the physical beneficiation has a significant effect on separating the impurities from the quartz and the co-associated independent minerals. Inclusion impurities and lattice impurities determine the limit of purification and processing of quartz ore. Although the removal technology of these two impurities has been studied for a long time, the effect is not good, which is the focus of future research on high-purity quartz processing.