Electrochemical Deposition of Metals, Alloys and Oxygen from Natural Minerals—II. Cathode Processes in the Electrodeposition of Si and Al From K-Feldspar Dissolved in Cryolite

The electrodeposition of silicon and aluminium from molten Na3AlF6–SiO2–Al2O3 and Na3AlF6–KAlSi3Os systems on graphite and molybdenum electrodes at 1000°C was studied. For the determination of the mechanism of the cathode process polarization curves and cyclic voltammetry measurements were used. The reduction mechanism involves a two step reduction of silicon-containing species:Si(IV) + 2e− → Si(II) (1)Si(II)+2e− → Si(0)(2)followed by a single step reduction of aluminium-containing species:Al(III) + 3e− → Al(0). (3)The composition of the cathodic deposits, obtained upon the potentiostatic conditions, was determined to confirm the proposed mechanism for the electrodeposition of Si and Al in cryolite–K–feldspar melts.