Chemistry of inorganic compounds – Halogen or compound thereof – Binary fluorine containing compound
Patent
1993-02-26
1995-11-28
Langel, Wayne
Chemistry of inorganic compounds
Halogen or compound thereof
Binary fluorine containing compound
423490, 423111, 423119, 423131, 588244, 588246, C01F 702, C01D 302
Patent
active
054705592
ABSTRACT:
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.
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Grolman Robert J.
Holywell George C.
Kimmerle Frank M.
Turcotte Gilles R.
Alcan International Limited
Langel Wayne
Vanoy Timothy C.
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