What is the role of cryolite in electrolytic aluminum?

What is the role of cryolite in electrolytic aluminum?

First, cryolite is the flux of the aluminum industry, and alumina will be dissolved in cryolite, like a solution.

Just as salt dissolves in water, cryolite is the solvent and alumina is the solute. The electrolysis of alumina is not in the true sense of "melt electrolysis", in fact, the melting is cryolite, alumina is just a dispersion, dispersed in liquid cryolite, the anion in the liquid is a complex atomic group, not a simple oxygen ion. The alumina is dissolved with cryolite as the solvent and then electrolyzed. Cryolite plays a key role here, which solves the difficulties of high melting point of alumina (up to 2 050 ° C), non-conductive, and unable to electrolysis alone. After the alumina is dissolved into cryolite, it can be electrolyzed at a temperature of 940 980 ° C. It's much easier to dissolve than to melt, so the natural melting point is lower. It can be said that if there were no cryolite, there might not be such a large-scale aluminum industry in the world, the price would not be so low, and the application would not be so extensive.

Two, electrolytic aluminum must use cryolite reasons are:

1, cryolite does not contain elements that correct the electrical properties of aluminum, good stability, under normal conditions do not decompose, do not volatilize, do not delix, melting point is higher than aluminum, good electrical conductivity, saving electricity, etc.

2, at the electrolytic temperature, the density of cryolite-alumina liquid is 10% less than the density of aluminum liquid, so the electrolytic aluminum liquid can be deposited on the cathode below the electrolyte, which can reduce the oxidation loss of aluminum, and greatly simplify the structure of aluminum electrolytic cell.

3. It can dissolve alumina well, and the melt composed of it can be electrolyzed below the melting point of pure cryolite; And good liquidity.

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