The unique physical and chemical properties of high-purity quartz sand make it a pivotal position in aviation, aerospace, electronics, machinery, and today's rapidly growing IT industry. Its intrinsic molecular chain structure, crystal shape and lattice change law make it have high temperature resistance, small thermal expansion coefficient, high insulation, resonance effect and its unique optical characteristics, and are widely used in high-purity quartz glass products and semiconductor technology. And the defense technology and cutting-edge technology and other fields.

The production process of high-purity quartz sand is similar, and it is generally subjected to processes such as beneficiation , crushing, magnetic separation, acid treatment (acid leaching and pickling), flotation, pressure filtration, drying, grading and packaging, etc. The order of different enterprises may be different. Some enterprises also add calcination, water quenching, wet grinding, chlorination, high-purity water washing, vacuum dehydroxylation and other processes. The process of acid leaching and purification is an important part.

First, the key impurities in quartz sand

01

Impurity elements in quartz sand

The most direct measure of the purity level of high-purity quartz sand is the raw material of alkali metals, transition key element content, aluminum and boron. Quartz glass products for different applications have different requirements, so before studying quartz purification technology, it is necessary to understand the main impurity elements that need to be controlled.

1 alkali metal elements, including: potassium (K), sodium (Na), lithium (Li)

Alkali metal oxides have a very strong "broken net" effect in quartz glass structures. Quartz glass in the high temperature state, usually the phenomenon of twinning, deformation, etc., are related to a small amount of alkali metal dissolution.

2 transition metal elements, including: copper (Cu), iron (Fe), manganese (Mn), chromium (Cr), nickel (Ni,) zinc (Zn)

Transition metal elements have a variety of oxidation states, often in a certain color, which has a particularly serious effect on the quality of high-purity quartz glass. If a trace amount of transition element dissolves or dissolves into the silicon solution, it can induce poor conductivity, which can negatively affect the reliability and foresight of the instrument, and can cause the quartz glass to produce color spots or cause high temperature discoloration, which affects the light penetration. Over rate.

02

Iron impurities in quartz ore

1 is present in fine-grained clay minerals

Clay is weathered from feldspar , limestone , shale, etc. The composition of the clay contains silicates of a mixture of mica , quartz, limonite, chlorite, calcite and amphibole, and the particle size is very fine, mainly composed of particles of 10 um or less.

2 is present in magnetic minerals in heavy minerals

Heavy minerals refer to minerals with a specific gravity greater than 2.9. Most of these minerals are magnetic or weakly magnetic, and iron is a basic constituent of these minerals.

Second, the commonly used acid species for acid treatment

01

Hydrochloric acid (hydrogen chloride)

Hydrogen chloride is a colorless and pungent odor gas. The aqueous solution of hydrogen chloride is acidic, called chlorinated acid. It is customarily called hydrochloric acid. Dry hydrogen chloride does not react with more active metals such as zinc, magnesium , iron, and most metal oxides. However, the wet hydrogen chloride gas is chemically active and can react with the above metals and oxides.

02

oxalic acid

Also known as oxalic acid, acid repair, is the simplest dibasic acid. Colorless monoclinic or prismatic crystal or white powder. It can be used as a complexing agent, masking agent, precipitant or reducing agent. It can be used to precipitate calcium, magnesium, thorium and rare earth elements. Common oxalate have sodium oxalate, potassium, calcium oxalate, ferrous oxalate, antimony oxalate and ammonium hydrogen oxalate.

Third, the mechanism and process of acid treatment and purification

The preliminary process for removing impurities in quartz sand can be washed, reselected, magnetically selected, and floated. However, for the production of high-purity quartz sand, the removal of thin film iron is an important issue. The method for removing the thin film iron mainly includes washing, ultrasonic cleaning and pickling, and the most common and effective method is pickling.

The purpose of acid treatment is to eliminate some impurity minerals that are poorly soluble in water and soluble in acid, such as metal oxides or fine silicate minerals. Usually, a mixed acid composed of hydrochloric acid, nitric acid, sulfuric acid and hydrofluoric acid is used. The volume ratio should be determined according to the surface contamination of the raw material, and the acid treatment also has a certain effect on eliminating the inclusions on the surface of the powder. The effect is better at high temperatures.

Fourth, acid leaching purification process and parameters

01

Hydrochloric acid method

The washed quartz sand was added to a hydrochloric acid solution having a concentration of 18%, and the amount of hydrochloric acid was 5% by weight of the quartz sand. Then heat to 80 ~ 90 ° C for 2 ~ 3 hours, and finally filtered and dried.

02

Gaseous hydrogen chloride method

The washed quartz sand was placed in a reaction vessel, heated to 80 ° C, and then fed with hydrogen chloride gas for 15 minutes, and then washed with water. The product of hydrogen chloride and iron oxide, FeCl3, was dissolved in water and removed.

V. Main factors affecting the leaching speed of impurities

01

Acid concentration

The rate of impurity leaching increases as the concentration of the acid increases, but if the concentration is too large, not only the components which are not desired to be dissolved but also the cost are increased.

02

Amount of quartz sand

The impurity leaching speed generally increases as the amount of quartz sand decreases, because this ensures that the concentration of impurities in the solution is always low, which is advantageous for accelerating the leaching speed. Therefore, using a large amount of acid to treat a small amount of quartz sand can increase the rate of impurity leaching, of course, also taking into account cost and benefit factors.

summary

Different industries in China have different requirements for the purity and impurity element content of SiO2 in quartz sand. The raw ore for producing high-purity quartz sand is different. The acid treatment process is different, and the impact on the quality of the final product is not the same. On the basis of selecting high-grade raw materials ore, selecting the appropriate acid treatment process can effectively reduce the pressure of other processes such as flotation, magnetic separation, etc., and can effectively improve the quality of the final product.

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