The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Nov. 28, 1995
Filed:
Feb. 26, 1993
Robert J Grolman, Chicoutimi, CA;
George C Holywell, Kingston, CA;
Frank M Kimmerle, Jonquiere, CA;
Gilles R Turcotte, Chicoutimi, CA;
Alcan International Limited, Montreal, CA;
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.