CA2495162A1

CA2495162A1 - Methods and apparatus for reducing sulfur impurities and improving current efficiencies of inert anode aluminum production cells

Info

Publication number: CA2495162A1
Application number: CA002495162A
Authority: CA
Inventors: Alfred F. Lacamera; Siba P. Ray; Xinghua Liu; Robert L. Kozarek; Jerry L. Roddy
Original assignee: Individual
Current assignee: Elysis LP
Priority date: 2002-08-05
Filing date: 2002-08-05
Publication date: 2004-02-12
Anticipated expiration: 2022-08-05
Also published as: WO2004013380A1; EP1534879A1; CN100430523C; EP1534879B1; NO344248B1; AU2002332463A1; CA2495162C; AU2002332463B2; BR0215834B1; CN1659313A; NO20051171L; BR0215834A

Abstract

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 CO2 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).

Claims

1. A method of operating an inert anode electrolytic aluminum production cell (10, 20, 30, 40, 50), the method comprising:
providing a cell (10, 20, 30, 40, 50) comprising an electrolytic bath (13), a cathode (12) and at least one inert anode (16a, 16b) located at or above a level of the cathode (12);
passing current between the at least one inert anode (16a, 16b) and the cathode (12) through the electrolytic bath (13); and maintaining a sulfur impurity concentration in the electrolytic bath (13) of less than about 500 ppm.

2. The method of Claim 1, wherein the sulfur impurity concentration is maintained below about 100 ppm.

3. The method of Claim 2, wherein the cell operates at a current efficiency of at least about 80 percent.

4. The method of Claim 2, wherein the cell operates at a current efficiency of at least about 90 percent.

5. The method of Claim 1, wherein the sulfur impurity concentration is maintained by providing an impurity reduction zone in the electrolytic bath (13).

6. The method of Claim 5, wherein the impurity reduction zone is provided by a purifying electrode (17, 37, 47) at least partially submerged in the electrolytic bath (13).

7. The method of Claim 5, wherein the impurity reduction zone is provided by an oxygen barrier member (18, 52) at least partially submerged in the electrolytic bath (13).

8. The method of Claim 5, wherein the impurity reduction zone is provided by adding a purifying reductant to the electrolytic bath (13).

9. The method of Claim 5, wherein the impurity reduction zone is provided by removing at least one inert anode from a region of the cell.

10. The method of Claim 5, wherein the impurity reduction zone is provided by interrupting electrical current through at least one electrode of the cell.

11. The method of Claim 1, wherein the sulfur impurity concentration is maintained by controlling sulfur impurities of materials added to the electrolytic bath (13).

12. The method of Claim 11, wherein the sulfur impurities are controlled by scrubbing sulfur impurities from gaseous emissions (66) generated from the electrolytic bath (13) prior to contacting the gaseous emissions (66) with alumina (82) that is added to the electrolytic bath (13).

13. The method of Claim 1, wherein the sulfur impurity concentration is maintained by controlling sulfur content of alumina (82) added to the bath (13).

14. The method of Claim 13, wherein the sulfur content of the alumina (82) is less than about 250 ppm.

15. The method of Claim 14, wherein the sulfur impurity concentration in the bath (13) is maintained below about 100 ppm.

16. The method of Claim 13, wherein the sulfur content of the alumina (82) is greater than about 250 ppm.

17. The method of Claim 16, wherein the sulfur impurity concentration in the bath (13) is maintained below about 250 ppm.

18. The method of Claim 16, wherein the sulfur impurity concentration in the bath (13) is maintained below about 100 ppm.

19. The method of Claim 1, wherein aluminum produced by the cell has maximum impurity levels of about 0.5 weight percent iron, about 0.2 weight percent copper and about 0.2 weight percent nickel.

20. The method of Claim 1, wherein the cell operates at a current efficiency of at least about 80 percent.

21. The method of Claim 1, wherein the cell operates at a current efficiency of at least about 90 percent.

22. An inert anode electrolytic aluminum production cell (10, 20, 30, 40, 50) comprising:
a cathode (12);
at least one inert anode (16a, 16b) located at or above a level of the cathode (12);
an electrolytic bath (13) communicating with the cathode (12) and the at least one anode (16a, 16b); and a sulfur impurity reduction zone within the electrolytic bath (13).

23. An inert anode electrolytic aluminum production cell ( 10, 20, 30, 40, 50) comprising:
a cathode (12);
at least one inert anode (16a, 16b);
an electrolytic bath (13) communicating with the cathode (12) and the at least one anode (16a, 16b); and a purifying electrode (17, 37, 47) at least partially submerged in the electrolytic bath (13) for providing a sulfur impurity reduction zone within the electrolytic bath (13).