Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B21/00—Obtaining aluminium
  • C22B21/06—Obtaining aluminium refining
  • C22B21/062—Obtaining aluminium refining using salt or fluxing agents
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B21/00—Obtaining aluminium
  • C22B21/06—Obtaining aluminium refining
  • C22B21/064—Obtaining aluminium refining using inert or reactive gases

Definitions

• the invention relates to a method for removing alkali and alkaline earth metals from aluminum melts by introducing powdered aluminum fluoride into the melt.
• Electrolysis metal often has a considerable content of alkali and alkaline earth metals. Before the further processing of such contaminated melts, in particular before the casting into rolling bars, a reduction in the concentration of the undesired accompanying elements is inevitable in most cases.
• EP-A-0 065 854 discloses a process for removing alkali and alkaline earth metals from aluminum melts, in which powdered aluminum fluoride is introduced into a vortex produced in the melt. The treatment takes place in a cylindrical container with a capacity of 3 - 5 tons of molten aluminum. With this process, smaller batches of molten aluminum can be effectively cleaned in a relatively short time. However, the amount of aluminum fluoride required per ton of melt to be treated is quite high. In addition, special devices for stirring the melt must be provided.
• the inventor has set himself the goal of creating a method of the type mentioned at the outset with which the consumption of aluminum fluoride can be kept as low as possible while maintaining a high cleaning efficiency.
• the process should be able to be carried out without major retrofitting with existing melt treatment facilities.
• the aluminum fluoride is a carrier gas in an amount of 1-10 grams metered continuously per minute and the gas / powder mixture is continuously introduced into the melt, which is kept at a temperature between 690 and 780 ° C., by means of lances.
• the entry of aluminum fluoride in the melt in the form of a gas / powder mixture has the result that the aluminum fluoride is enclosed in gas bubbles in the melt and settles within the individual gas bubbles in their lower part.
• the actual chemical reaction between alkali and alkaline earth metals and the aluminum fluoride thus takes place at the gas / melt interface during the ascent phase of the gas bubbles to the melt surface. It is easy to see that a relatively small amount of aluminum fluoride is sufficient to cover the lower part of the gas bubble surface.
• the aluminum fluoride introduced with a carrier gas is better wetted by the melt than is the case with processes with direct powder introduction. This also explains the high efficiency of melt cleaning that can be achieved with a small amount of aluminum fluoride in the process according to the invention.
• the flow rate of the carrier gas is preferably between 40 and 200 liters per minute.
• the metallostatic pressure is decisive for determining the lower limit. With the upper limit the movement on the melt surface and thereby the formation of dross is limited.
• aluminum fluoride of a lower degree of purity ie with a content of up to about 20% aluminum oxide, can also be used.
• Cryolite with an excess content of aluminum fluoride is also suitable.
• Argon optionally with the addition of a halogen-substituted hydrocarbon, such as CCl2F2, is used as the preferred carrier gas.
• a halogen-substituted hydrocarbon such as CCl2F2
• other gases or gas mixtures such as are customary in the melt treatment of aluminum, can also be used.
• the addition of aluminum fluoride to the carrier gas can be carried out in a simple and effective manner via a jet mixer, as is described, for example, in US Pat. No. 4,295,883 for introducing gases into a melt stream.
• the flowing gas creates a negative pressure in the jet mixer, whereby the aluminum fluoride is sucked into the jet mixer and swirled in the gas stream.
• the method according to the invention is particularly suitable for the removal of sodium and lithium from aluminum-magnesium alloy melts and can be implemented with the usual smelting furnaces with purging gas treatment without major conversion.
• the aluminum fluoride is fed into the gas supply line, possibly via a jet mixer.
• the sodium content of the molten metal was 29 ppm before the treatment and 2 ppm after the treatment. During the treatment period of 2.5 hours, a total of only 525 grams of aluminum fluoride were used, corresponding to 18 grams per ton of molten metal treated.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture And Refinement Of Metals (AREA)
• ing And Chemical Polishing (AREA)
• Crucibles And Fluidized-Bed Furnaces (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Treating Waste Gases (AREA)
• Processing Of Solid Wastes (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=4205058

Family Applications (1)

Country Status (6)

Cited By (2)

Families Citing this family (7)

Citations (11)

Family Cites Families (2)

• 1988
  • 1988-03-14 US US07/167,982 patent/US4832740A/en not_active Expired - Fee Related
  • 1988-03-24 DE DE8888810195T patent/DE3868660D1/de not_active Expired - Lifetime
  • 1988-03-24 EP EP88810195A patent/EP0285566B1/fr not_active Expired - Lifetime
  • 1988-03-24 AT AT88810195T patent/ATE73171T1/de not_active IP Right Cessation
  • 1988-03-28 NO NO881370A patent/NO171799C/no unknown
  • 1988-03-29 IS IS3325A patent/IS3325A7/is unknown

Patent Citations (11)

Also Published As

Similar Documents

Legal Events