BigPatents India

Methods and apparatus are disclosed for reducing sulfur impurities in aluminum electrolytic production cells (10, 20, 30, 40, 50) in order to significantly increase current efficiency of the cells. An impurity reduction zone may be created in the bath (13) of an inert anode (16a, 16b) cell by submerging a purifying electrode (17, 37, 47) in the bath (13). In another embodiment, an oxygen barrier tube (52), may be disposed in a portion of the bath (13). In a further embodiment, reductants such as aluminum, CO and/or CO>2< are added to the bath (13). In another embodiment, electrode current is interrupted or electrodes are removed from selected regions of the cell (10, 20, 30,40, 50) in order to allow gaseous impurities to escape from the bath (13). Sulfur impurity levels may also be reduced in inert anode cells (62) by scrubbing bath emissions (66) from the cell (62) before they are reintroduced into the cell (62), and by controlling sulfur impurity contents of materials (82) added to the cell (62).