Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Reexamination Certificate
1999-11-01
2001-04-17
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
C205S386000, C205S387000, C205S372000, C205S380000
Reexamination Certificate
active
06217739
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the electrolytic production of aluminum. More particularly, the invention relates to the production of commercial purity aluminum with an electrolytic reduction cell including inert anodes.
BACKGROUND OF THE INVENTION
The energy and cost efficiency of aluminum smelting can be significantly reduced with the use of inert, non-consumable and dimensionally stable anodes. Replacement of traditional carbon anodes with inert anodes should allow a highly productive cell design to be utilized, thereby reducing capital costs. Significant environmental benefits are also possible because inert anodes produce no CO
2
or CF
4
emissions. Some examples of inert anode compositions are provided in U.S. Pat. Nos. 4,374,050, 4,374,761, 4,399,008, 4,455,211, 4,582,585, 4,584,172, 4,620,905, 5,794,112 and 5,865,980, assigned to the assignee of the present application. These patents are incorporated herein by reference.
A significant challenge to the commercialization of inert anode technology is the anode material. Researchers have been searching for suitable inert anode materials since the early years of the Hall-Heroult process. The anode material must satisfy a number of very difficult conditions. For example, the material must not react with or dissolve to any significant extent in the cryolite electrolyte. It must not react with oxygen or corrode in an oxygen-containing atmosphere. It should be thermally stable at temperatures of about 1,000° C. It must be relatively inexpensive and should have good mechanical strength. It must have high electrical conductivity at the smelting cell operating temperatures, e.g., about 900-1,000° C., so that the voltage drop at the anode is low.
In addition to the above-noted criteria, aluminum produced with the inert anodes should not be contaminated with constituents of the anode material to any appreciable extent. Although the use of inert anodes in aluminum electrolytic reduction cells has been proposed in the past, the use of such inert anodes has not been put into commercial practice. One reason for this lack of implementation has been the long-standing inability to produce aluminum of commercial grade purity with inert anodes. For example, impurity levels of Fe, Cu and/or Ni have been found to be unacceptably high in aluminum produced with known inert anode materials.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a process for producing high purity aluminum using inert anodes. The method includes the steps of passing current between an inert anode and a cathode through a bath comprising an electrolyte and aluminum oxide, and recovering aluminum comprising a maximum of 0.15 weight percent Fe, 0.1 weight percent Cu, and 0.03 weight percent Ni.
Additional aspects and advantages of the invention will occur to persons skilled in the art from the following detailed description thereof
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Liu Xinghua
Ray Siba P.
Weirauch, Jr. Douglas A.
Alcoa Inc.
Bell Bruce F.
Klepac Glenn E.
Levine Edward L.
Towner Alan G.
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