Production process of sodium silicate
Sodium silicate in aqueous solution can be produced through two main and distinct processes:
- Melting process and subsequent dissolution;
- Hydrothermal process;
MELTING OR VITRIFICATION PROCESS
This process involves the reaction at high temperature (1400°C) between quartz (SiO2) and sodium carbonate (Na2CO3) Na2CO3 + m SiO2 = Na2OmSiO2 + CO2
The reaction takes place in special furnaces; in the process carbon dioxide (CO2) is formed, which is released in the gaseous state and anhydrous sodium silicate (Na2OmSiO2) in the molten state (magma). The magma liquid is then rapidly cooled and reduced to pieces. Because of its appearance, this silicate is called glassy sodium silicate or water-soluble glass (waterglass). To be used, the glassy sodium silicate must be hydrated and then dissolved in water, depending on the reaction:
Na2Om SiO2 + nH2O = Na2Om SiO2nH2O
The operation is performed in high pressure and high temperature special autoclaves. As soon as the desired concentration is reached, the sodium silicate solution is discharged from the autoclave, purified by decantation and/or filtration and after the appropriate analytical controls, with possible corrective actions, sent to the storage tank.
The hydrothermal process consists of chemical attack of quartz with caustic soda in aqueous solution:
2 NaOH + m SiO2 + (n -1 ) H2O = Na2Om SiO2n H2O
The reaction takes place in high pressure and high temperature special reactors pressure at high temperature, obtaining in this case the sodium silicate directly in the hydrated state and in aqueous solution. The sodium silicate solution is then discharged from the autoclave, purified by decantation and/or filtration and after the appropriate analytical controls and possible corrective actions, sent to its storage tank.