Existing form of gas-liquid inclusion in quartz and method for beneficiation and purification

In the natural world, SiO2 mainly exists in the form of natural crystal , quartzite , vein quartz , quartz sandstone, etc. With the increasing demand for high-purity quartz sand raw materials, natural crystal resources are depleted, but the raw materials for quartz glass can be replaced by crystal. There are very few ore deposits. Generally, quartzite contains more gas-liquid inclusions. Only the hydrothermal growth type and metamorphic rock type quartz ore contain relatively little gas-liquid inclusions. Therefore, it is very important to prepare high-purity quartz sand to replace natural crystal by beneficiation and purification.

Photomicrograph of gas-liquid inclusions in quartz

1. Classification of impurities in quartz

Quartz ore usually contains a large amount of impurities. According to the composition and structure of impurities, it can be divided into two categories: structural constitutive impurities and non-structural impurities.

Non-structural impurities refer to substances adhering to the surface of quartz crystals or accompanied by quartz crystals, such as feldspar , mica and other impurities, by scrubbing, flotation, color selection, magnetic separation, acid leaching, water quenching, ultrasonic treatment, etc. The beneficiation and purification process can be effectively removed.

The structural constitutive impurities are impurities formed in the quartz crystal under certain geological conditions of the quartz crystal. Mainly based on impurity ions and fluid inclusions (gas-liquid inclusions).

2. What is mineral inclusion?

Mineral inclusions are diagenetic ore-forming fluids (gas-liquid fluids or silicate melts) that are encased in mineral crystal lattices or pockets during mineral crystal growth and are still sequestered in the main minerals and The part of the mineral that has a phase boundary.

Mineral inclusions can generally be divided into primary inclusions, pseudo-secondary inclusions, and secondary inclusions.

Photomicrographs of inclusions in pegmatite and beryl

Solid phase inclusions in a-beryl;

a melt fluid inclusion in b-beryl;

Melting fluid and fluid inclusions in c-beryl;

a CO2-rich fluid inclusion in d-beryl;

Pure CO2 inclusions in e-beryl;

F-heterogeneous inclusions of minerals in quartz.

3. Inclusion characteristics in quartz

Quartz inclusions generally contain gas or liquid, so they are also called fluid inclusions or gas-liquid inclusions. Quartz ore generally contains fluid inclusions, which are wrapped with H2, O2, N2, CO, CO2, etc. along with mineral growth. Formed in a quartz crystal.

The inclusions are usually present in the quartz crystal in the form of inclusion bodies or individual inclusions. Since these inclusions are usually located inside the quartz crystal and most of their volume is small (micron order), the existing beneficiation and purification process is difficult to complete. Removed.

4. Classification of inclusions in quartz

Single crystal quartz containing gas-liquid inclusions (magnification 200 times)

Due to the different environment and mechanism of crystal growth, quartz gas-liquid inclusions also have large differences in quantity, distribution and composition. There are three different types of inclusions in quartz: primary, pseudo-secondary and secondary. Due to the differences in the properties of these three inclusions, the current beneficiation and purification process also has great differences in the removal effects of these three types of inclusions.

The primary inclusions are formed along with the growth of quartz crystals and exist on the crystal faces of quartz crystals, so the primary inclusions are difficult to remove by existing purification processes.

The secondary inclusions are relatively easy to remove because the secondary inclusions are formed after the quartz crystals are crystallized and are mainly distributed in the crack healing sites of the quartz particles.

5. Formation mechanism of inclusions in quartz

(1) The growth rate of quartz crystals changes, and this difference causes the main mineral to capture the surrounding fluid medium to form inclusions.

(2) The growth mechanism of quartz crystals changes under special circumstances.

(3) During the growth of quartz crystal, the concentration of the surrounding fluid medium changes.

(4) The micro-solid, liquid, and gas phases interact with the growth force of the quartz crystal face.

6. Effect of gas-liquid inclusions on quartz glass

Gas-liquid inclusions are the main reason for the generation of bubbles in quartz glass. The presence of bubbles directly affects the purity and performance of quartz glass. This is because the gas-liquid inclusions in quartz contain a certain amount of H2O, which is in the process of melting quartz glass at high temperature. The H2O in the gas-liquid inclusion reacts with the SiO2 melt to increase the hydroxyl content to form bubbles. Therefore, gas-liquid inclusion removal is the key and difficult point to achieve the purification of quartz ore instead of crystal to prepare high-end quartz glass raw materials.

7. Method for removing gas-liquid inclusions in quartz

(1) High temperature chlorination degassing method

The quartz sand is heated to 1000-1200 ° C and the Cl 2 and HCl gas are introduced under high temperature. This method utilizes the reaction of Cl 2 and impurity ions under high temperature conditions, and the gaseous salt formed by the reaction can be microcracked from the quartz crystal. It is discharged to achieve the effect of purification. This method has a certain removal effect on the hydroxyl groups in the quartz.

The high-purity quartz sand prepared by U.S. U.S. in 2006 using high-temperature chlorination degassing has obvious effects on the removal of gas-liquid inclusions. The company's IOTA series of high-purity quartz sand is in an absolute leading position in the world.

(2) Differential corrosion method

Under the corrosion of acid or alkali, the quartz crystal and the gas-liquid inclusion have different corrosion rates, so as to achieve the purpose of removing the gas-liquid inclusion. This treatment process can effectively remove gas-liquid inclusions in quartz ore, and some can approach the gas-liquid inclusion standard of the fourth-grade crystal. However, when the gas-liquid inclusions in the quartz are removed to a certain extent, the difference strength is further increased. The effect is no longer obvious.

(3) hot or cold burst method

When the quartz is in a high temperature condition, the interface between the quartz matrix and the gas-liquid inclusions therein causes a great pressure difference to cause the gas-liquid inclusion to burst, and the cleaning process can achieve the effect of removing the gas-liquid inclusion. At high temperatures, the phase change of quartz can cause the gas-liquid inclusions in the quartz to burst, and the gas-liquid inclusions can be effectively removed by the pickling process after the bursting.

Under extremely cold conditions, the removal effect of gas-liquid inclusions in quartz is related to the shape and size of the gas-liquid inclusion itself. Some large gas-liquid inclusions are easy to burst and remove, but it is difficult to remove tiny gas-liquid inclusions. .

Different types of quartz ore have different exhaust capacities at high temperatures, and the most exhaustive ones are hydrothermal quartz. And the heated quartz into cristobalite when the fluid inclusions in the alkali metal ion content thereof has some influence, so that cristobalite is more readily converted to a more favorable exhaust gas high alkali metal ion content inclusions aluminum ion content is low Liquid inclusions.

(4) Mechanical crushing method

The size of the gas-liquid inclusions in quartz is between about 1 and 50 μm. Theoretically, as long as the quartz ore is broken enough to remove most of the gas-liquid inclusions between the cracks in the quartz matrix. High-tech crushing methods (such as high-voltage electric crushing) make it easier to remove gas-liquid inclusions in quartz cracks.

(5) Microwave method

The gas-liquid inclusions in quartz ore are removed by microwave selective heating characteristics. Microwave is an alternating electromagnetic wave with unique selective heating, volume heating, high heating efficiency and the ability to heat high dielectric constant materials for several thousand degrees in a few minutes. These features have unique advantages for removing impurities with different dielectric constants.

The dielectric constant of SiO2 is 3-5F/m, the main component of gas-liquid inclusion is water, and the dielectric constant of water is up to 88F/m, which is easy to generate great pressure at the interface of gas-liquid inclusion, which promotes gas-liquid encapsulation. The body is "cracked", which makes it possible to remove the gas-liquid inclusions in the quartz sand.

The research shows that when quartzite is heated to 500 °C under the action of microwave field, the number of gas-liquid inclusions in minerals is reduced from 9159 to 992, and the removal effect is very obvious.

8. Microwave-acid leaching to remove gas-liquid inclusions

By measuring the light transmittance of quartz particles in a specific oil immersion oil, the degree of removal of gas-liquid inclusions in quartz minerals, that is, the change in the light transmittance of quartz, that is, the change in the content of gas-liquid inclusions in quartz, can be examined.

(1) Microwave

When the quartz sand is heated to 600 °C and 900 °C by microwave field, the content of gas-liquid inclusions drops sharply, the light transmittance increases from 71% to 86%, and the surface of quartz particles produces more and wider micro-cracks. Most of the gas-liquid inclusions burst under the action of the microwave field and escape along the microcracks.

This is due to the phase transition of quartz sand at 600 ° C and 900 ° C. At this time, the volume of quartz sand expands rapidly, causing microcracks on the surface, and a part of the gas-liquid inclusions can burst and escape along the microcracks.

(2) Acid leaching

After microwave heating of quartz sand, it is treated by mixed acid leaching. The acid leaching time is 6h, the pickling temperature is 80 °C, and the content of gas-liquid inclusions in the obtained quartz sand is reduced from 154.05ppm to 98.90ppm. The rate can reach 93%, the main impurity element content is 37.71ppm, which is close to the first-class crystal level.

9, the conclusion

Quartzite, vein quartz, quartz sandstone and other raw materials, comprehensive flotation, magnetic separation, color selection, microwave and acid leaching and other mineral processing and purification processes, and optimized according to the actual situation, it is entirely possible to prepare quartz glass and other industries to use High purity quartz.