Reducing the Temperature of the Hall-Héroult Process

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Discussion Overview

The discussion centers on the potential for reducing the temperature of the Hall-Héroult process used in the electrolytic smelting of aluminum by substituting lithium aluminum fluoride (Li3AlF6) for cryolite (Na3AlF6) as the solvent for aluminum oxide. Participants explore the implications of this substitution, including its feasibility and economic considerations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that using Li3AlF6 could lower the melting point of the process compared to Na3AlF6, which has a higher melting point.
  • Others argue that the solubility of alumina in lithium aluminum fluoride is uncertain and may affect the feasibility of this substitution.
  • Concerns are raised about the economic viability of lithium compared to sodium, noting that sodium is more abundant and cheaper, which could impact the practicality of using Li3AlF6.
  • One participant questions the availability of cheap lithium, suggesting that it is primarily consumed by the battery industry, which could limit its use in aluminum smelting.
  • Another participant provides a price comparison between sodium hydroxide and lithium hydroxide, highlighting the significant cost difference and its implications for industrial processes.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and economic implications of using Li3AlF6 in the Hall-Héroult process. There is no consensus on whether this substitution would be advantageous or practical.

Contextual Notes

The discussion highlights limitations related to the availability and cost of lithium, as well as the uncertainty surrounding the solubility of alumina in lithium aluminum fluoride. These factors may influence the overall feasibility of the proposed substitution.

christian everett
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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.
 
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christian everett said:
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.
christian everett said:
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.
 
Is there enough cheap lithium available on the market, or is it mostly consumed by the battery industry at the moment?
 
Borek said:
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.