LAUSR

In the present study, theoretical analysis and electrolysis testing in the laboratory scale demonstrated the potential of Al metal production by electrolysis in a NaF-AlF3-Al2O3 melt with a cryolite ratio (CR; molar ratio of NaF/AlF3) of 1.3. Subsequently, the electrochemical processes of Al deposition on a tungsten cathode in this melt at 860 °C were comprehensively evaluated by cyclic voltammetry, potentiodynamic cathodic polarization, square wave voltammetry, chronopotentiometry, and potentiostatic electrolysis. The results revealed Al deposition on the tungsten cathode, first as an Al4W alloy at approximately − 0.14 V (vs W), and then as liquid metallic Al-containing a co-deposition of metallic Na at − 0.94 V (vs W). The reduction of Al4W alloy and the deposition of metallic Al were both diffusion-controlled and quasi-reversible. The diffusion coefficient of the Al(Ш) ions was calculated to be 1.77 × 10−8 cm2 s−1. The square wave voltammetry curves indicated that the process of AlF4− ion reduction involved both a three-electron transfer reaction resulting in Al deposition (AlF4− → Al), and a two-electron transfer reaction resulting in the formation of monovalent aluminum ions AlF2− (AlF4− → AlF2−). The chronopotentiometry results revealed that the critical cathodic current for Al deposition was approximately 150 mA. X-ray diffraction (XRD) measurements and scanning electron microscope (SEM) observations confirmed that Al4W alloy and metallic Al existed on the electrode surface after potentiostatic electrolysis.