Reducing the Temperature of the Hall-Héroult Process

[christian everett]

I am interested in whether it may be possible to reduce the temperature of the Hall-Héroult process for the electrolytic smelting of aluminum by using Li3AlF6 instead of cryolite (Na3AlF6) as the solvent for the aluminum oxide, and if this might be advantageous over current methods.

Li3AlF6 has a melting point 783°C (1,441.4 °F).

Pure cryolite (Na3AlF6) has a melting point of 1,012 °C (1,854 °F). With a small percentage of alumina (Al2O3) dissolved in it, its melting point drops to about 1,000 °C (1,830 °F). Aluminium fluoride, (AlF3) is added to the mixture to further reduce the melting point.

 

[TeethWhitener]

I am interested in whether it may be possible to reduce the temperature of the Hall-Héroult process for the electrolytic smelting of aluminum by using Li3AlF6 instead of cryolite (Na3AlF6) as the solvent for the aluminum oxide

Maybe. It depends on how soluble alumina is in lithium aluminum fluoride.

and if this might be advantageous over current methods.

This is more doubtful. Sodium is far more ubiquitous than lithium, and as a result, the synthetic cryolite used in aluminum refining is cheaper than synthetic lithium aluminum fluoride.

The prevalence of economic considerations in large scale industrial processes shows up from time to time. For instance, the low cost and high abundance of sodium is one reason why researchers are pursuing sodium ion battery technologies to displace lithium technologies.

 

[Borek]

Is there enough cheap lithium available on the market, or is it mostly consumed by the battery industry at the moment?

 

[TeethWhitener]

Is there enough cheap lithium available on the market, or is it mostly consumed by the battery industry at the moment?

That’s what I’m doubtful on. A quick search of Alibaba gives NaOH at ~ 500 USD/metric ton, while LiOH is ~ 25 000 USD/metric ton. I’m sure there are industrial ChemE’s on this forum that know the market better than I do. But most of the world’s lithium comes from a few mines in Argentina and Bolivia, whereas sodium is literally everywhere on earth, so it makes sense that there’d be such a price difference even with the focus on Li batteries.