Electrolytes with low melting temperature

crusts of solidified electrolyte may be formed on the cathode surface, increasing the electrical resistance. At the NaF-AlF3 eutectic the alumina solubility is as low as about 2-3% [6]. 

If a KF-AIF3 electrolyte is used, it has a eutectic with a melting point of 560 °C [6, 21, 22]. In that electrolyte, no crust is formed on the cathode, and the alumina solubility is higher than in the NaF-AlF3 eutectic, at 5 wt% [23, 24]. There are two reasons for the absence of crust from the cathode surface. 

The metallic aluminium solubility in cryolite-alumina melts decreases with the temperature decrease. Likewise this also decreases with the cryolite rate decrease. If it is supposed that these dependences are also available in the case of K3 AlFg melts, an increase of current efficiency will result in those melts. 

Some other salts can be added to the KF-AIF3 melt to improve its physico-chemical properties. Thus, the electrolyte density should be lower than that of molten aluminium at the electrolysis temperature. The electrical resistance of the electrolyte must be adequate to produce enough heat to maintain the electrolyte in 

However, alumina coming from Bayer plants contains up to 0.5% Na20. Therefore the KF-AIF3 electrolyte will quickly be contaminated by NaF. One solution could be to use KOH instead of NaOH in Bayer plants for alumina production. 

---

However, when decreasing the interpolar distance, less heat is produced in the cell. There are two solutions to prevent solidification of the electrolyte one is to change the thermal insulation, the other is to use an electrolyte with low melting temperature. 

---