Patent EA-005281-B1 (EA)
Title: A method and electrowinning cell for production of metal
Inventor: SILJAN OLE-JACOB
IPC: C25C3/06
Filed: 2002-02-13
Abstract: 1. A method for electrolytic production of aluminium metal from an electrolyte (E) comprising aluminium oxide, by performing electrolysis in at least one electrolysis chamber (22) containing said electrolyte and further comprising at least one inert anode (1) and at least one wettable cathode (2), where the anode evolves oxygen gas and the cathode has aluminium discharged onto it in the electrolysis process, said oxygen gas enforcing an electrolyte flow pattern upward and said produced aluminium flowing downward due to gravity, characterised in that the oxygen gas is further directed to flow into a gas separation chamber (14) arranged in communication with said electrolysis chamber (22), thus establishing an electrolyte flow pattern between said electrolysis chamber (22) and said gas separation chamber (14). 2. A method in accordance with claim 1, characterised in that the electrolyte flow pattern is directed by at least one partitioning wall, interior wall or "skirt" (9) deflecting the upward flowing electrolyte in the electrolysis chamber (22) into the gas separation chamber (14). 3. A method in accordance with claim 1, characterised in that the separated gas is removed from the gas separation chamber (14) by gas extraction means. 4. A method in accordance with claim 1, characterised in that the produced metal is drained from the cathodes (2) to an aluminium pool (11) in the bottom of the cell, and is removed from the cell by appropriate means for metal tapping. 5. A method in accordance with claim 1, characterised in that the electrolyte temperature is in the range 680-970 degree C. 6. A cell for electrolytic production of aluminium comprising at least one electrolysis chamber (22) containing an electrolyte, at least one inert anode (1) and at least one wettable cathode (2), characterised in that it further comprises a gas separating chamber (14) arranged in communication with said electrolysis chamber (22), where gas evolved in the process can be separated from the electrolyte. 7. An electrolysis cell in accordance with claim 6, characterised in that a partitioning wall (9) is arranged between the electrolysis chamber (22) and the gas separating chamber (14), the said wall having at least one opening (12,13) therethrough. 8. An electrolysis cell in accordance with claim 7, characterised in that the partitioning wall (9) has at least one upper opening (12) allowing the gas-containing electrolyte to flow from the electrolysis chamber (22) to the gas separating chamber (14), and at least one lower opening (13) through which electrolyte separated from the gas returns to the electrolysis chamber (22). 9. An electrowinning cell in accordance with claim 7, characterised in that the partitioning wall (9) is manufactured from aluminum oxide, aluminium nitride, silicon carbide, silicon nitride or combinations or composites thereof. 10. An electrowinning cell in accordance with claim 7, characterised in that the partitioning wall (9) is manufactured from oxide materials. 11. An electrowinning cell in accordance with claim 7, characterised in that the partitioning wall (9) is manufactured from oxide or materials consisting of a compound of one or several of the oxide components of the anode material, and additionally one or more oxide components. 12. An electrowinning cell in accordance with claim 7, characterised in that the partitioning wall (9) extends between two opposing side walls (24,25) of the cell, where its height may extend from the bottom (26) or the auxiliary floor (10) of the cell and upward to at least the upper level of the electrolyte. 13. An electrolysis cell in accordance with claim 7, characterised in that the partitioning wall (9) has a vertical extension and is further arranged such that an opening is provided below the lower end of the partitioning wall (9) and an opening of similar dimensions is provided between the upper end of the partitioning wall (9) and the upper level of the electrolyte (E). 14. An electrowinning cell in accordance with claim 6, characterised in that the gas separating chamber (14) has a volume large enough to reduce electrolyte flow rates sufficiently to separate any gas contained in the electrolyte. 15. An electrowinning cell in accordance with claim 6, characterised in that one or more gas separating chambers (14) can be arranged alongside at least one side of the cell. 16. An electrowinning cell in accordance with claim 6, characterised in that the gas separating chamber (14) is connected to at least one gas exhaust system (16) for extracting and collecting gases from the chamber. 17. An electrowinning cell in accordance with claim 16, characterised in that the exhaust system (16) is connected to an alumina feeding system (20) in which the hot off-gasses are used for heating the alumina feed stock and/or used for scrubbing cleaning of the off-gasses from the cell to remove fluoride vapours, fluoride particulates and/or dust before entering the gas collection system (28). 18. An electrowinning cell in accordance with claim 6, characterised in that the electrolysis chamber (22) comprises an auxiliary floor (10) provided with at least one hole (17) preferably arranged below the cathode (s), whereby aluminium is allowed to pass through said hole and to be collected in a metal compartment (23) defined below said floor. 19. An electrowinning cell in accordance with claim 18, characterised in that the auxiliary floor (10) material is selected from aluminium nitride, silicon carbide, silicon nitride, oxide materials, refractory hard materials based on borides, carbides, nitrides, silicides or combinations or composites thereof. 20. An electrowinning cell in accordance with claim 18, characterised in that said aluminium in the metal compartment (23) can be extracted from the cell via one or more surge pipes or siphons (19) attached to the cell. 21. An electrowinning cell in accordance with claim 6, characterised in that the anodes (1) and the cathodes (2) are of a monopolar type arranged in an alternate manner, and further aligned vertically or inclined. 22. An electrowinning cell in accordance with claim 6, characterised in that the anodes and cathodes are of the bipolar type aligned vertically or inclined. 23. An electrowinning cell in accordance with claim 6, characterised in that the anodes and/or the cathodes consists of a plurality of smaller units integrated in one larger unit. 24. An electrowinning cell in accordance with claim 6, characterised in that the anodes are manufactured from dimensionally stable materials, preferably oxide based cermets, metals, metal alloys, oxide ceramics, and combinations or composites thereof. 25. An electrowinning cell in accordance with claim 6, characterised in that the cathodes are manufactured from electrically conductive refractory hard materials (RHM) based on borides, carbides, nitrides, silicides or mixtures thereof. 26. An electrowinning cell in accordance with claim 6, characterised in that the main surfaces of the anodes and cathodes are arranged in a manner adjacent to the short side wall of the cell. 27. An electrowinning cell in accordance with claim 6, characterised in that the cell has a lining that preferably consists of an electrically non-conductive material. 28. An electrowinning cell in accordance with claim 27, characterised in that the material of the cell lining is selected from aluminium oxide, aluminium nitride, silicon carbide, silicon nitride, and combinations thereof or composites thereof. 29. An electrowinning cell in accordance with claim 27, characterised in that the cell lining is manufactured from oxide materials. 30. An electrowinning cell in accordance with claim 27, characterised in that at least parts of the cell lining is manufactured from oxide or materials consisting of a compound of one or several of the oxide components of the anode material, and additionally one or more oxide components. 31. An electrowinning cell in accordance with claim 6, characterised in that the anodes and/or cathodes are connected to a periphery busbar system for electrical supply, where the connections can be introduced through the top, the sides or the bottom of the cell. 32. An electrowinning cell in accordance with claim 6, characterised in that the anodes and/or cathodes connections are cooled to provide heat exchange and/or heat recovery from said anode/cathode, and/or temperature control. 33. An electrowinning cell in accordance with claim 6, characterised in that the anodes and/or cathodes connections are cooled by means of water cooling or other liquid coolants, by gas cooling or by the use of heat pipes. 34. An electrowinning cell in accordance with claim 6, characterised in that it comprises at least one feeding tube for alumina where its inlet is located either at a position being close to a high-turbulence part in the electrolyte, and preferably in the interpolar space between one anode and one cathode, or in the gas separation chamber. 35. An electrowinning cell in accordance with claim 6, characterised in that the electrolyte flow pattern can be enhanced by introducing at least one diaphragm, interior wall or "skirt" (21) positioned between at least one anode and at least one cathode deflecting the upward flowing electrolyte into the gas separation chamber (14). 36. An electrowinning cell in accordance with claims 6 and 35, characterised in that the diaphragm (21) is manufactured from aluminum oxide, aluminium nitride, silicon carbide, silicon nitride or combinations or composites thereof. 37. An electrowinning cell in accordance with claims 6 and 35, characterised in that the diaphragm (21) is manufactured from oxide materials. 38. An electrowinning cell in accordance with claims 6 and 35, characterised in that the diaphragm (21) is manufactured from oxide or materials consisting of a compound of one or several of the oxide components of the anode material, and additionally one or more oxide components. 3