How is silica processing processed?
Processing method Silica is chemically processed. In addition to reduction and production of elemental silicon, the parent product of silicon compound, sodium silicate (commonly known as water glass), is first obtained, which includes alkali and sodium sulfate methods.
Alkali-based silicas are insoluble in water and acids, but sodium silicates are easily generated with alkalis, so the alkali method is the main method of silica chemical processing. Alkali method is divided into dry method (soda method) and wet method (soda method).
1 dry method (soda method) silica containing more than 99% of silica crushed to 50 to 80 mesh, with a certain proportion of soda ash, calcined at a high temperature of 1100 ~ 1350 °C 4 ~ 6h, the formation of a molten material, the reaction The formula is: xSiO2+nNa2CO3─→nNa2O·xSiO2+nCO2
The molar ratio of x and n in the formula is referred to as the modulus of sodium silicate, and the modulus of sodium silicate for industrial use is generally 1.0 to 3.8. Selecting different ingredients ratios can result in products with different moduli. Alkali is easy to lose in high temperature production, so the amount of alkali is often slightly higher than the theoretical amount required by the modulus.
The obtained molten material contains, in addition to sodium silicate, water-insoluble matter such as unreacted silica, and is dissolved in water to separate insoluble matters from the melt to obtain a colorless transparent viscous liquid, that is, a sodium silicate product.
The dry process is easy to manufacture high modulus sodium silicate products, and the production conditions are not too harsh and it is easy for industrial production. However, large energy consumption and poor operating conditions.
2 Wet method (caustic soda method) The content of silica powder (SiO2) above 120 mesh is higher than 99%). It is mixed with caustic soda in a certain proportion (depending on the product modulus) and placed in a pressurized reaction vessel with stirring. In the steam heating to 175 °C above, the pressure is controlled at 811kPa above, the reaction 4 ~ 6h, filtered after cooling, to remove unreacted silica, liquid sodium silicate products can be obtained, the reaction formula is: xSiO2+2nNaOH─→nNa2O ·xSiO2+nH2O
Wet energy consumption is low and the operating environment is good, but it is not easy to obtain high modulus products.
The sodium sulfate method crushes silica containing up to 98% of silicon dioxide to 80 mesh, mixes it with sodium sulfate (the ratio of which is determined by the modulus of the product) and pulverized coal in a certain proportion, and reacts in a reverberatory furnace. First, sodium sulfate is reduced to sodium sulfide, and the latter is reacted with silica to obtain sodium silicate, and sulfur dioxide is released at the same time. The reaction formula is: Na2SO4+4C─→Na2S+4CO
nNa2S+xSiO2+3/2nO2─→nNa2O·xSiO2+nSO2
In the reaction, sodium sulfate is often incompletely reduced, and it floats on the surface of the sodium silicate melt in a molten state at a high temperature, which is called nitrate water. The nitrate water is highly corrosive and easily erodes the lining of the lining and can easily explode when exposed to water. In addition, sulfur dioxide is produced in the reaction and it pollutes the environment, so it is rarely used in industry.
Product Uses Sodium silicate and silica are the main products derived from the chemical processing of silica. Sodium silicate is the most widely used and the most used product in the chemical processing of silica. It is used not only in the manufacture of various silicon compounds, but also as a binder for paperboard, plywood, some metal materials and foundry industries, soap, and washing. Agent additives, paper properties improver, in the textile industry for cotton scouring and bleaching auxiliaries, fabric fire protection agent, dye chromogenic agent. In addition, it is also used as a cement coagulant, wood preservative, and egg preservatives. After modified, sodium silicate can also be used as interior and exterior wall coatings. Aluminum silicate can be used as raw materials for glass and ceramics, and can also be used as paint pigments. Lithium silicate can be used as anti-corrosion paint, metal surface protection agent.
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