US 4,222,830 AGranted

Production of extreme purity aluminum

AssigneeAluminum Company of America

InventorsRobert K. Dawless, Stanley C. Jacobs

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Abstract

A process for purifying impure aluminum comprises introducing the impure aluminum to the anode layer of an electrolytic cell of the type having a bottom layer of molten aluminum-copper alloy constituting the anode layer and having a top layer of molten aluminum constituting a cathode layer, the cathode and anode layers separated by an electrolyte layer. Aluminum is electrolytically transported from the anode to the cathode in a first purification step and then fractionally crystallized to remove further impurities therefrom by crystallizing pure aluminum and thereafter separating the molten remaining part, which is high in impurities, from the purified aluminum. The impure molten aluminum portion is then recycled back to the electrolytic cell or to another fractional crystallization step.

Claims19

Dependent claims

An improved process for purifying aluminum containing impurities comprising:

(a) introducing said aluminum to the anode layer of an electrolytic cell of the type having a bottom layer of molten aluminum constituting said anode layer and having a top layer of molten aluminum constituting a cathode layer, said anode layer separated from said cathode layer by an electrolyte layer;
(b) electrolytically transporting aluminum from said anode layer through said electrolyte layer to said cathode layer while leaving said impurities in said anode layer thereby partially purifying said aluminum, said transporting being capable of recovering aluminum at the cathode consisting essentially of 99.993 wt.% aluminum;
(c) thereafter, removing a portion of said partially purified molten aluminum from said cathode layer;
(d) fractionally crystallizing said molten aluminum portion in a crystallization cell to remove eutectic impurities therefrom by solidifying a fraction of said molten aluminum, said solid fraction having a higher purity than that constituting the remaining molten aluminum fraction, thereby concentrating said eutectic impurities in said molten fraction, said crystallizing adapted to recover aluminum product consisting essentially of 99.999 wt.% aluminum when the feed to the process is about 99.993 wt.%;
and
(e) separating said molten fraction from said solid fraction to provide said purified aluminum, said improved process suited to recover 50 wt.% of the feed to the process.

3 more elements

An improved process for purifying aluminum containing impurities comprising:

(a) introducing said aluminum to the anode layer of an electrolytic cell of the type having a bottom layer of molten aluminum constituting said anode layer and having a top layer of molten aluminum constituting a cathode layer, said anode layer separated from said cathode layer by an electrolyte layer;
(b) electrolytically transporting aluminum from said anode layer through said electrolyte layer to said cathode layer thereby partially purifying said aluminum by leaving a substantial amount of said impurities in said anode layer;
(c) thereafter, removing a molten portion of said partially purified aluminum from said cathode layer;
(d) subjecting said molten portion to a first fractional crystallization step to remove eutectic impurities therefrom by crystallization a fraction of said molten aluminum portion, said crystallized fraction having a higher purity than the remaining molten fraction thereby concentrating said eutectic impurities in said remaining molten fraction;
(e) separating said molten fraction from said solid fraction to provide said purified aluminum;
(f) further subjecting said remaining molten fraction containing said concentrated eutectic impurities to a second fractional crystallization step to further concentrate said eutectic impurities by crystallizing a part of said remaining molten fraction;
and
(g) separating the molten aluminum from said second fractional crystallization step containing said further concentrated impurities and returning it in molten form to the anode of said electrolytic cell and returning the crystallized fraction from said second crystallization step back to said first fractional crystallization step along with partially purified aluminum from said cathode layer of said electrolytic cell for further purification, the improved process being capable of recovering 90 wt.% of the feed aluminum introduced to the anode of the electrolytic cell as product consisting essentially of 99.999 wt.% aluminum.

5 more elements

Dependencies are inferred from the claim text.