An experimental study of aluminium electrowinning using a nickel-based hydrogen diffusion anode

Laboratory scale electrolysis experiments were conducted to investigate the electrowinning of aluminium using hydrogen diffusion anodes. A potassium-based electrolyte (KF–AlF3–Al2O3), porous nickel alloy anode and molybdenum disk cathode were used in experiments at 750 °C. Hydrogen gas was supplied to the anode/electrolyte interface through the porous anode. Experiments were conducted in potentiostatic, galvanostatic and galvanodynamic modes. There was a measurable depolarisation of the anode potential and also anode reaction of hydrogen and oxygen ions in the bath to form water vapour was confirmed by the water vapour condensate found at the electrolysis exit gas pipe. Metallic aluminium was found on the spent cathode. The experiments conducted in the galvanodynamic mode suggested that the rate limiter for hydrogen oxidation was the availability of surface hydrogen at the anode/electrolyte interface. The anode surface corroded during electrolysis and impurities were found both in the molten bath and on the cathode.

Research highlights► Measurable depolarisation of the anode potential and formation of water vapour. ► Metallic aluminium was found on the spent cathode. ► HF emissions can be minimised by conducting the electrolysis at 750 °C. ► The nickel based anode surface corroded during electrolysis. ► Its application is constrained by the material limitation of the porous anode.