Why use cryolite as raw material when smelting aluminum?

Why use cryolite as raw material when smelting aluminum?

In the aluminum smelting process, cryolite is used as the main raw material for aluminum smelting because:

  1. Pure cryolite does not contain any metal impurities with a more positive precipitation potential than aluminum. As long as no impurities are added from the outside during the operation, relatively pure aluminum can be obtained.

  2. Cryolite can dissolve alumina well. When the electrolysis temperature is 950℃-970℃, the solubility of alumina in cryolite solution is about 10%.

  3. At the electrolysis temperature, the density of cryolite-alumina solution is lower than that of molten aluminum at the same temperature. It can float on molten aluminum to prevent aluminum from oxidizing, and at the same time make the electrolyte and aluminum better separate.

  4. Cryolite has certain conductivity, so that the voltage drop of the electrolyte layer will not be too high.

  5. The cryolite melt has a certain fluidity at the electrolysis temperature, and the anode gas can be discharged from the electrolyte, which is beneficial to the cyclization of the electrolyte.

   6. In the molten state, cryolite basically does not absorb water and is not easy to volatilize, reducing material consumption and ensuring electrolyte stability.

   Cryolite is also called sodium hexafluoroaluminate or sodium aluminum fluoride. Its molecular formula is Na3AlF6. It is a kind of fine white crystals, tasteless, and has greater solubility than natural cryolite. Specific gravity 3, hardness 2~3, melting point is easy to absorb water and moisture, cryolite is mainly used as aluminum electrolysis flux, rubber and grinding wheel wear-resistant filler, enamel opalizer, glass sunscreen and metal flux, crop pesticides, under normal circumstances, It does not decompose, volatilize, and does not deliquescence. Its melting point is higher than that of aluminum. It has good electrical conductivity and saves energy. It can be said that without cryolite, there may not be such a large-scale aluminum industry in the world, and the price will not be so low. Nor will it be so extensive. The west coast of Greenland is the main producing area of cryolite. It was mined in 1987. Nowadays, sodium hexafluoroaluminate is artificially synthesized from fluorite for industrial use, and it is also produced in Spain, Russia and the United States.