Electrical Conductivity of Low-Temperature Potassium Cryolite Electrolytes Suitable for Innovation of Aluminum Preparation

Abstract

Innovations of aluminum electrolysis process are focused on the inert electrodes and the new types of electrolytes with lower temperature of primary crystallization. The main component in new types of molten systems can be a potassium cryolite. Advantages of these electrolytes are low possible working temperature (above 660 • C) and sufficient solubility of an electrochemical active compound (alumina) at these temperatures. The electrical conductivity is one of the most important properties of the electrolytes. Electrochemical impedance spectroscopy was used as a suitable measurement method for determination of the electrical conductivity. Potassium cryolite-based mixtures with the different molar ratios (molar ratio of KF and AlF 3 ) and with various additives were studied as a function of the temperature. The molar ratio of binary melt KF-AlF 3 varied from 1.2 to 1.5 with the step of 0.1. The temperature dependence (from 655 • C to 850 • C) and the influence of the addition of Al 2 O 3 , CaF 2 , MgF 2 and LiF on the electrical conductivity were obtained. The electrical conductivity was measured by tube-type cell with stationary electrodes; AC-techniques with a sine wave signal in the high frequency range were applied. Temperature and concentration dependencies of conductivity in the studied systems were described by non-linear regression equation.

Electrical conductivity of low-temperature sodium-potassium cryolite melts

“…The values of electrical conductivity decreased with lower MR and decreasing temperature in all measured systems. This trend is the same as in previous investigated binary systems NaF-AlF 3 (Kubiňáková et al, 2018_2) or KF-AlF 3 (Kubiňáková et al, 2018_3). The higher addition of NaF leads to higher electrical conductivity (Fig.…”

“…Electrical conductivity of pure sodium cryolite and potassium cryolite systems (NaF-AlF 3 and KF-AlF 3 , respectively) was measured in the low temperature area (Kubiňáková et al, 2018_2;Kubiňáková et al, 2018_3). Electrical conductivity higher than that of KF-AlF 3 melts is an advantage of the NaF-AlF 3 system.…”

Review—Primary Production of Aluminium with Oxygen Evolving Anodes

“…83 The electrical conductivity of the K-cryolite decreases with temperature. 84 Kubinakova et al 85 investigated the electrical conductivity of KF-AlF 3 melt (also with additives like Al 2 O 3 , CaF 2 , MgF 2 and LiF). The addition of Al 2 O 3 , CaF 2 , and MgF 2 to KF-AlF 3 melt would reduce the electrical conductivity of the mixture, a similar effect was reported for the sodium-based mixture.…”

Electrochemical Characterization of Low-Temperature Molten Mixture Systems Suitable as an Innovation in Aluminum Technology

“…Physico-chemical properties of the first two low-temperature options (NaF-AlF 3 and KF-AlF 3 , as described above) were summarized in z E-mail: emilia.kubinakova@stuba.sk a review 2 and the information about the electrical conductivity was supplemented and summarized in a recent research. [9][10][11][12] The electrical conductivity of NaF-KF-AlF 3 system has been studied only in recent years.…”

“…This work completes the systematic research of the electrical conductivity in the low-temperature cryolite mixtures made by our group. [9][10][11][12] The electrical conductivities of the sodium-potassium cryolite system in wide concentration and temperature ranges have been studied. The operating temperature varied from 660 • C to at least 870 • C and MR changed from 1.5 to 1.2 (with the step 0.1).…”