DEPOLARIZED GAS ANODES FOR ELECTROWINNING OF ALUMINIUM FROM CRYOLITEALUMINA MELTS IN A LABORATORY CELL

摘要

Consumable carbon anodes are used in the electrowinning of aluminium by the Hall-Heroult process and in other proposed processes for electrowinning in molten salts. Emissions of CO_2 may be eliminated by introducing an inert oxygen evolving anode, which however will require a higher anode potential. By introducing natural gas or hydrogen to the anode the CO_2 emissions can be reduced and the anode potential can be lowered. Laboratory experiments were carried out in a modified Hall- Heroult electrolyte with excess AlF_3 at 850 -. Anodes of platinum, tin oxide and graphite were tested during electrolysis at constant current, with the supply of argon, methane and hydrogen through or at the anodes. Laboratory studies showed that by introducing both hydrogen and methane separately through a porous SnO_2 anode in molten Na_3AlF_6-AlF_3-Al_2O_3 (4.5 wt.%) at 850- the anode potential was found to be lowered by several hundred millivolts for a limited time during electrolysis.