Electrowinning of Aluminum and Scandium from KF-AlF₃-Sc₂O₃ Melts for the Synthesis of Al-Sc Master Alloys

Abstract

The main kinetic features of the aluminum and scandium electrowinning during the electrolysis of the KF-AlF 3 -Al 2 O 3 -Sc 2 O 3 melts were studied by means of voltammetry, stationary polarization, as well as electrolysis. Aluminum electrowinning from the KF-AlF 3 -Al 2 O 3 melt on tungsten cathode occurs in the potential range from −0.1 to −1.3 V relative to the potential of the aluminum electrode. Replacing Al 2 O 3 by Sc 2 O 3 in KF-AlF 3 melts leads to a co-electrowinning of aluminum and scandium with the same kinetic parameters. Based on the electrochemical measurements, the parameters of stable galvanostatic electrolysis of the melts under study were selected and electrolysis tests were carried out to obtain Al-Sc master alloys. The cathode current efficiencies during co-electrowinning of aluminum and scandium on tungsten were evaluated, and the microstructure of the obtained Al-Sc master alloys was studied. A novel approach for the synthesis of the Al-Sc master alloys proposed that includes the electrolysis of the KF-AlF 3 -based melts with the addition of Al 2 O 3 and Sc 2 O 3 , electrowinning of aluminum and scandium on a solid cathode, and dissolution of formed cathode deposit in liquid aluminum.

Electrochemical characterization of the liquid aluminium bipolar electrode for extraction of noble metals from spent catalysts

“…In the 1.3KF-AlF 3 melt reduction of aluminium starts at more negative potentials than in chloride-based melts (-0.1 V and more negative). The values are in good agreement with the previous results [22]. The peaks of the aluminium reduction process are not visible due to the background process but can be estimated with respect to the slope change before the wave of potassium evolution.…”

“…4b). It is briefly described earlier [22] that cathodic process is complicated by several parallel phenomena: a discharge of aluminium from different ionic forms, salt passivation, an appearance of dissolved aluminium near the cathode layer and rapid consumption of aluminium by the secondary process. This idea is supported by several experimental observations made in the current work:…”

“…Performance of the Al(III)/Al electrode studied in chloride [20,21] and fluoride [22][23]24] melts and reported in recent works with more attention to the cathodic process of Al(III) or Al(I) reduction. Deposition of Al on tungsten first leads to a formation of intermetallic compound Al 4 W [24].…”

Review—Synthesis of Aluminum Master Alloys in Oxide-Fluoride Melts: A Review

“…Considerable interest in the study of the kinetics and mechanism of the cathode process in low-melting KF-AlF 3 -Al 2 O 3 and NaF-AlF 3 -Al 2 O 3 systems in the temperature range of 700 °C-800 °C appeared relatively recently, [92][93][94][95][96] as more attention was focused on finding new electrode and structural materials for new aluminum production technologies. 97,98 It was shown [92][93][94][95] that during electrolysis of KF-AlF 3 -Al 2 O 3 melt in the temperature range of 700 °C-800 °C and CR from 1 to 2, the deposition of aluminum on graphite is accompanied by potassium discharge and rapid destruction of graphite, while a number of intermetallic compounds are formed on the platinum cathode. In works 93,94 the kinetics and mechanism of the cathodic process in the same melts was studied on glass carbon and tungsten, which have relatively good chemical resistance to aluminum.…”

Production of Al-Sc Alloy by Electrolysis from Cryolite Melt Using Secondary Feedstock Material

“…Previous work has been published suggesting molten salt electrolysis as a suitable method in the manufacture of Al-Sc alloys from fluoride-or chloride-based molten salts [3][4][5][6], using reasonably priced Sc 2 O 3 as raw material.…”