Process for electrolytic production of aluminum

Abstract

A new method for the electrolytic production of aluminum, using a new electrolyte composition and low temperature operation, is provided. The electrolyte comprises a mixture of aluminum fluoride-potassium fluoride with from about 2 wt. % to 6 wt. % of alumina. The new electrolyte allows for the electrolytical reduction of alumina at temperatures as low as 700° C. The lower temperature allows for the use of inert anodes, and is conducive to the use of wetted cathodes. The new electrolyte mixture has a higher solubility for alumina and remains entirely liquid, even with 5 wt. % of alumina present in the electrolyte during electrolysis. Oxygen (O 2 ) is the only gas generated during alumina electrolysis with the new electrolyte and the inert anodes, thus eliminating the production of greenhouse gases. Anodes and cathodes can be mounted in either a vertical, horizontal, or some other configuration.

1 . An improved electrolyte for the electrolysis of alumina (Al 2 O 3 ), the electrolyte comprising a mixture of aluminum fluoride (AlF 3 ) and potassium fluoride (KF).  
     
     
         2 . The electrolyte recited in  claim 1  wherein the aluminum fluoride (AlF 3 ) is present in a molar ratio with potassium fluoride (KF) greater than 1:1.  
     
     
         3 . The electrolyte recited in  claim 1 , the electrolyte further comprising from about 2 to 6 wt. % of aluminum oxide (alumina/Al 2 O 3 ).  
     
     
         4 . The electrolyte as recited in  claim 1  wherein the concentrations of the electrolyte's components remain constant during electrolysis.  
     
     
         5 . The electrolyte as recited in  claim 1  where the electrolyte is used to electrolyze the alumina to aluminum at from about 660° C. to 1000° C.  
     
     
         6 . The electrolyte as recited in  claim 3  wherein the electrolyte remains liquid during electrolysis.  
     
     
         7 . The electrolyte as recited in  claim 6  wherein inert anodes and wettable cathodes can be used with the electrolyte.  
     
     
         8 . A method for using inert anodes and wettable cathodes in the electrolytic production of aluminum comprising using the anodes and cathodes in an electrolysis process at a temperature from between 660° C. and 1000° C.  
     
     
         9 . The method as recited in  claim 8  wherein the anode is comprised of a material selected from the group consisting of metals, metal alloys, metal oxides, and cermets.  
     
     
         10 . The method as recited in  claim 8  wherein the alloys are copper alloys (aluminum-bronze) and are from about 1 wt. % to 20 wt. % aluminum (Al).  
     
     
         11 . The method as recited in  claim 8  wherein the cathode is made of a material selected from the group consisting of metal borides, metal boride-carbon composites, metal boride-containing coatings on substrates, graphite, molybdenum, and tungsten.  
     
     
         12 . The method as recited in  claim 8  where the anode contains an oxygen-containing film.  
     
     
         13 . The method as recited in  claim 12  wherein the oxygen containing film is formed during the electrolysis process.  
     
     
         14 . The method as recited in  claim 11  wherein the material coats one side of the inert anode to create a bipolar electrode for use in multipolar electrolytic cells.  
     
     
         15 . The method as recited in  claim 8  wherein the distance between the anode and cathode remains constant.  
     
     
         16 . The method as recited in  claim 8  wherein the electrodes can be arranged in a vertical configuration.  
     
     
         17 . The method as recited in  claim 8  wherein the electrodes can be arranged in a slanted configuration.  
     
     
         18 . The method as recited in  claim 8  wherein O 2  is the only gas generated by electrolysis.  
     
     
         19 . The method as recited in  claim 16  wherein the vertical configuration of the cell creates electrolyte recirculation pathways.  
     
     
         20 . A method for electrolyzing alumina below 1000° C., the method comprising: 
 a) supplying an electrolyte containing more than 35 mol % potassium fluoride (KF) and more than 30 mol % aluminum fluoride (AlF 3 );    b) injecting alumina with the electrolyte; and    c) subjecting the electrolyte to a voltage.