Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Patent
1997-06-04
1999-08-17
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
423132, 423163, 588246, C01F 100, C01F 700, C22B 2100, C22B 100
Patent
active
059390352
DESCRIPTION:
BRIEF SUMMARY
The present invention generally relates to a process for treating a material containing inorganic matter. More specifically, the present invention relates to a process for reducing and/or removing inorganic matter from spent potlining which is obtained from electrolytic reduction cells used in aluminium smelting.
Aluminium is manufactured using a high temperature process in which alumina is electrolytically reduced in a molten bath of cryolite. This process is conducted in cells, often called pots, and a typical aluminium smelter contains hundreds of pots connected in series. The metallic outer structure of the pot contains an interior bottom lining of refractory brick and a further inner lining of carbon which also extends to cover the side walls. The carbon lining serves as the cathode and also protects the metallic structure of the pot from contact and corrosion by the molten bath of cryolite.
The severe operating conditions experienced within the pot lead to a progressive deterioration of the carbon lining to the extent where either leakage of the inner contents occurs or the aluminium product contains an unacceptably high level of impurities e.g. iron. At this stage, the pot is decommissioned and the lining completely replaced. The lining which includes carbon, a mixture of inorganic fluorides and inorganic oxides and refractory brick is known as spent potlining (hereinafter referred to as "SPL").
SPL usually contains 20 to 40% by weight of carbon and significant quantities of cryolite and other aluminium containing compounds in the form of carbides, nitrides, fluorides and oxides. Sodium fluoride, sodium carbonate and calcium fluoride are also present. Therefore, SPL is no longer considered to be a carbon based residue containing inorganic impurities, but rather a complex matrix of inorganic compounds containing large quantities of fluorides and having carbon as one component.
As SPL contains environmentally harmful and biologically toxic constituents, major restrictions are imposed on its transportation, treatment, storage, handling and disposal. SPL cannot be disposed of in a conventional manner without prior processing to remove the harmful and toxic constituents. The basis for such strict environmental controls is as follows: arsenic will be leached and enter the environment; and arsenic may result in the release of hydrogen cyanide; environment as demonstrated by the migration, mobility and persistence of free and complex cyanides, fluorides and arsenic; and per year throughout the world.
In view of these major environmental restrictions, numerous processes for treating SPL have been investigated and the majority of these have included either high temperature treatment, wet processes or combinations thereof.
High temperature treatment of SPL destroys cyanide by oxidation, but fluoride emission to the atmosphere is considerable. Furthermore this treatment, which usually produces refractory slags and ash, does not allow the more valuable components of SPL, such as, aluminium compounds to be recovered for use in the aluminium industry because these compounds are made chemically refractory as a result of the use of high temperatures in the presence of air.
Most of the wet processes have involved leaching by either water, sulphuric acid or caustic solutions in an attempt to extract the inorganic values from the carbonaceous matrix. However, these processes have proved to be inadequate in that they have either failed to completely remove the hazardous constituents or have generated products which are not readily disposable, recyclable or marketable. For example, caustic processes extract aluminium from SPL as a water-soluble aluminate and then convert this to cryolite. The demand for cryolite is minimal as this solid is formed in excess as an unwanted by-product of the aluminium smelting process.
A requirement accordingly exists for an improved process for reducing and/or removing inorganic matter from materials containing inorganic matter, such as SPL, so that these materials can be safely disposed o
REFERENCES:
patent: 2411806 (1946-11-01), Riesmeyer et al.
patent: 3486845 (1969-12-01), Vancil et al.
patent: 5352419 (1994-10-01), Jenkins
patent: 5470559 (1995-11-01), Grolman et al.
patent: 5558847 (1996-09-01), Kaaber et al.
Adrien Robert Jacques
Besida John
Covey Geoffrey Harold
O'Donnell Thomas Aloysius
Pong Teresa Kit-Hing
Bos Steven
The University of Melbourne
LandOfFree
Process for treating spent potlining containing inorganic matter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for treating spent potlining containing inorganic matter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for treating spent potlining containing inorganic matter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-312779