Alcan International Limited

George C Holywell

David K Creber

Jorgen Christensen

Meine Vandermeulen

Gilles R Turcotte

Frank M Kimmerle

Pasquale Ficara

Robert J Grolman

An electrolysis cell ( ) for producing a molten metal having a density less than a density of a molten electrolyte used for producing the metal in the cell. The cell includes a section ( ) for the electrolysis of a salt of the the metal contained in a molten electrolyte to form droplets of the metal in molten form contained in the electroylte; electrodes ( ) within the electrolysis section for effecting the electrolysis; a metal recovery section ( ) for separation of the metal from the electrolyte to form a molten metal layer, having an upper suface, floating on an upper surface of the molten electrolyte; a tapping device for periodically removing molten metal from the cell; and a reservoir ( ) for withdrawal and temporary holding of molten metal separated from the electrolyte in the metal recovery section. The reservoir has a means to remove liquid from the reservoir without permanently removing the liquid from the cell. The reservoir has a top, sides and bottom and has one or more openings in the top or sides of the container communicating with the metal recovery section. At least part of the opening(s) is maintained below the upper surface ( ) of the metal layer during at least part of normal cell operations, and all of the opening(s) is kept above the upper surface of the electrolyte in the metal recovery section for at least part of the normal cell operation. The sides and bottom are otherwise closed to prevent metal or electrolyte from freely flowing between the metal recovery section and the reservoir. The cell containing such a reservoir may accommodate high rates of metal production without unduly increasing cell size or requiring high heating requirements.

Molten salt electrolytic cell having metal reservoir

An electrolysis cell for recovery of metals that are lighter than the electrolyte used in the cell. The cell makes use of multiple electrode assemblies, and each assembly is provided with an individual hood at the top forming a gas collection chamber. The hood of each assembly collects gas generated by the assembly and isolates the gas thus generated from gas generated by other assemblies and from metal collecting in the cell outside the hoods. The invention also relates to an integrated unit made up of an electrode assembly and an associated hood for use in a cell of the above kind, and a method of recovering metal by operating a cell of the above kind.

Electrolysis cells

A process for recycling spent potlining material from aluminum reduction cells contaminated with fluoride and aluminum values. The process comprises first reducing the average particle size of the spent potlining material to smaller than 28 Tyler mesh to form a powder. The powder is then treated with an aqueous sodium hydroxide solution containing about 10 to 60 g/L of sodium hydroxide at a temperature in the range of between 60.degree. and 90.degree. C. to form a solution containing fluoride and sodium aluminate and a residual solid. The solution is removed from the residual solid and the content of NaOH is adjusted in the solution to the range of about 10 to 60 g/L of NaOH, if the content differs from this range, to produce a solution suitable for cyanide destruction. This solution is then heated to a temperature in the range of about 160.degree. to 220.degree. C. at a pressure in the range of about 150 to 350 p.s.i. for a time of between about 1/2 and 3 hours to destroy cyanide values in the solution. Water is evaporated from the resulting solution to cause fluoride compounds in the solution to crystallize. The fluoride crystals are then separated from the sodium aluminate-containing solution and may be recrystallized or reacted with calcium hydroxide to precipitate calcium fluoride from a solution of sodium hydroxide. The sodium hydroxide may the be used for the treatment of further potlining material.

Recycling of spent pot linings

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Kingston, Canada

George C Holywell