CA1060216A - Treatment of aluminous material - Google Patents
Treatment of aluminous materialInfo
- Publication number
- CA1060216A CA1060216A CA239,961A CA239961A CA1060216A CA 1060216 A CA1060216 A CA 1060216A CA 239961 A CA239961 A CA 239961A CA 1060216 A CA1060216 A CA 1060216A
- Authority
- CA
- Canada
- Prior art keywords
- metal
- flux
- liquid
- skim
- container
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
- C22B21/0084—Obtaining aluminium melting and handling molten aluminium
- C22B21/0092—Remelting scrap, skimmings or any secondary source aluminium
-
- 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
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/04—Working-up slag
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
A B S T R A C T
Aluminous material such as furnace skim, drosses and residues is treated to recover aluminium metal. The material, preferably hot, is fed into a liquid salt flux layer floating on molten aluminium and agitated with the flux so that the metal passes into the molten aluminium.
The process may be carried out in a forewell or sidewell of a reverberatory furnace or in a box divided into two compartments. The aluminous material may be added to a vessel with a hole in the bottom held in a body of molten aluminium, a flux layer being provided in the vessel.
Aluminous material such as furnace skim, drosses and residues is treated to recover aluminium metal. The material, preferably hot, is fed into a liquid salt flux layer floating on molten aluminium and agitated with the flux so that the metal passes into the molten aluminium.
The process may be carried out in a forewell or sidewell of a reverberatory furnace or in a box divided into two compartments. The aluminous material may be added to a vessel with a hole in the bottom held in a body of molten aluminium, a flux layer being provided in the vessel.
Description
1060~16 The present invention relates to the treatment of aluminous material comprising furnace skimmings, drosses and metal residues with a view to recovery of metal values.
- In particular it relates to the recovery of aluminium from furnace_skimmings arising--in the melting and processing of aluminium and aluminium base alloys (hereinafter all referred to as aluminium).
In the melting of aluminium, especially when dirty or fine scrap is included in the metal charge, it is found that a soft pasty layer of metal and oxide forms on the metal surface. This is conveniently termed "skim". Skim - is also formed when a body of liquid metal is stirred, e.g.
in the case of alloying operations, or on transfer from one furnace hearth to another. In order to tap clean - metal from the furnace it is necessary to remove the skim, and normally much liquld metal lS entrained in it leading to considerable losses of metal unless the skim is Rubsequently treated. By sprinkling powdered salt flux of "fluid" type on the skim it is possible to remove it without dragging off so much metal, but it is more usual to add a "drying" flux which will cause the skim to ignite and in this way, although some aluminium is burnt, a significant amount of metal is released from the skim ïnto the metal bath and the remaining skim is more powdery in nature and can be remo~ed with less metal entrainment.
Other methods of treating the skim involve skimming it off the metal surface into a crucible, adding flux to cau~e - some ignition of skim and/or agglomeratio~ of the oxide, and mechanically stirring the skim to liberate some of the entrainsd metal. These methods only give recoveries of
- In particular it relates to the recovery of aluminium from furnace_skimmings arising--in the melting and processing of aluminium and aluminium base alloys (hereinafter all referred to as aluminium).
In the melting of aluminium, especially when dirty or fine scrap is included in the metal charge, it is found that a soft pasty layer of metal and oxide forms on the metal surface. This is conveniently termed "skim". Skim - is also formed when a body of liquid metal is stirred, e.g.
in the case of alloying operations, or on transfer from one furnace hearth to another. In order to tap clean - metal from the furnace it is necessary to remove the skim, and normally much liquld metal lS entrained in it leading to considerable losses of metal unless the skim is Rubsequently treated. By sprinkling powdered salt flux of "fluid" type on the skim it is possible to remove it without dragging off so much metal, but it is more usual to add a "drying" flux which will cause the skim to ignite and in this way, although some aluminium is burnt, a significant amount of metal is released from the skim ïnto the metal bath and the remaining skim is more powdery in nature and can be remo~ed with less metal entrainment.
Other methods of treating the skim involve skimming it off the metal surface into a crucible, adding flux to cau~e - some ignition of skim and/or agglomeratio~ of the oxide, and mechanically stirring the skim to liberate some of the entrainsd metal. These methods only give recoveries of
-2- ~
'' ' -'' , , :
.: , . . ~ . ..... , :, 1066~216 from one-third to two thirds of the metal content of the skim. Much oxide fume is reLeased when the crucibles are emptied. Another method of treating skim is to feed it into rotary salt furnaces, but although metal recovery may be impr-oved thi~ in~olves an en~ironmental problem owing to volatilisation of the ~alt from the furnace.
More recently it has been proposed to recover metal from sXim and drosse~ by mixing them cold with solid salt flux and melting in an induction furnace. This has the advantage that the salt is not overheated, the metal is not oxidised by the products of gas combustion, and the stirrin$ action of the induced current~ assists agglomeration of the metal. However the capital equipment involved is costly, the furnace lining requires frequent replacement and the method will only treat ~-metal-rich drosses. It is not therefore suitable for treatment of skim which has undergone extensive slow oxidation or has fired in the furnace before being removed. All these method~ in which skim is allowed to cool and is subsequently reheated for further proce sing will inevitably involve some loss of metal through oxidation as well as consumption of energy in replacing the lost heat. -We have now found that if fre~hly generated hot skim is fed into a layer of liquid salt flux floating upon a body of liquid aluminium, then substantially all the metal content of the skim is quickly transferred to the body of liquid aluminium when the skim i~ gently : .- . ' ' ' ' '': ': ' ' -.
1060;~16 agitated with the flux. In this way the recovery of metal from the skim is much greater than can be obtained by even prolonged rabbling of thle skim upon the metal ~urface and ~prinkling o~ powdered flux upon it during the operation. The layer of liquid flux used in the process of the present invention should be deep enough for the skim to be at least partially and preferably at least Yubstantially immersed in the flux. In one aspect the present invention provides a method of treating aluminous material comprising furnace skim, drosse~ or metal residue~ by means of salt fluxes in which the aluminous material, preferably hot, is fed into a liquid salt flux layer floating upon a body of liquid aluminium and the aluminouR material is agitated with the flux whereby substantially all the metal content of the aluminous material passe~ into the body of aluminium.
The aluminouc material may be added batch wise in such quantities a~ can be substantially immersed in the salt layer and then gently ~tlrred to liberate the metal~
leaving the salt layer ready to accept a further quantity of skim. Preferably skim is transferred directly from the bath of a reverbatory furnace to the salt layer. 1 ;
Thus the invention is capable of providing a simple method of treating hot furnace skim to give very high recovery of the metal co~tent without the need for elaborate equipment~ without grave environmental problems through evolution of oxide or salt fume, and without the metal and energy losses involved in cooling and reheating the skim.
., 1060Z~6 The flux layer is confined to a predetermined area and the quantity of flux used in relation to the predetermined area is such as to provide initially a liquid layer of at least 1 cm and preferably at least 2 cm deep, though 5-10 cm depth iæ desirable ~ince more skim can be added at one time.
The temperature of the met~l will not be less than 650 C and preferably not less than 700C. Con~iderably higher temperatures may be used but above about 850C
the volatility of the flux may be con~idered objectionable.
The salt flux u~ed may consist of mixture~ of the alkali ænd alkaline earth metal chlorides, incl~ding MScl2~ and may contain one or more fluorides of the alkali and alkaline earth metal~, including MgF2, and will--be thinly--fluid at tempera*ure~ above abou* 675C.-Suitable compositions are based on KCl and NaCl in eutectic proportions or in equal portion~ by weight-with additions of 0-5% CaF2~ 0-25% NaF, or 0-20% MgC12. With CaF2 additions, the flux i~ fumele~s in operation and haa adequate coagulating power for dispersed metal.
With the NaF additions the coagulating power of the flux is increased but slight fuming may occur, whereas with MgC12 additions the wetting power of the flux i8 increased but some evolution of HCl wi~l be encountered, particularly in damp atmosphere~.
In one embodiment of the invention aluminium is heated in a reverberatory furnace provided with a side well~ a layer of liquid salt flux is provided upon the metal in the side well~ and the skim formed in the main ~-hearth i~ transferred to the sid,e well, said ~kim being _5_ ' ' . . : .' .' '.'. , . ,:
: ~ .' ; ' . . '' :
~-- 10602~6 agitated with the flux whereby su~stantially all the metal content of the skim pa~seq into the body of liquid metal in the side well. The metal in the furnace and the metal in the side well are preferably in communication below the layer of flux.
When the invention is operated in conjunction with a side well or forewell~ the metal in the main hearth can be conveniently skimmed by pushing or drawing the skim directly into such sidewell or forewell. This has many advantages. The skimming can be done as soon as the metal charge is melted and before the floating skim has undergone significant oxidation. The skim is already above the melting point of the metal and will disintegrate rapidly on entering the flux layer, very little stirring being needed. The skimmed-metal in the main hearth will then be directly exposed to the heat of the furnace and .. . . . .:-will not be partially insulated therefrom by a layer of skim, 80 making for thermal economy in the furnace operation. Moreover the heat contained in the skim is preserved and is not lost through allowing the skim to cool down with subsequent need to remelt it for later processing. There is no oxide fumesuch as is frequently evolved when skim is taken from the furnace and allowed to cool; nor i8 there any ,108s of aluminium incurred through deliverate burning part of the skim in order that some metal will be liberated through the increase in temperature. In this preferred process, should any qkim be allowed inadvertently to catch fire in the main hearth, then burning is immediately extinguished when the ~kim is :. i fed into the flux covered side well. There i9 no objectionable salt fume generated. Finally all need for equipment for crushing, grinding~ screening and remelting of skim (e.g. in induction furnaces) i4 avoided.
The sidewell may conveniently be fitted with insulating lids, and provided with a gas burner or other heating device whereby the temperature of the metal can, if desired~ be raised above that in the main hearth. The side well may extend alongside a short length only of one wall of the furnace, for example alongside one or more drossing doors. Alternatively the flux layer may be confined to part only of a side well, e.g. by means of a baffle wall or floating barrier.
It is also possible to portion off part of the furnace hearth e.g. by means of a baffle wall, and to carry out the process of the present invention within such portion of the furnace.
The process of the present invention is not confined to skim but may be used to treat metal-containing residue~, dro~ses or finely divided scrap metaI. Such materials are preferably preheated prior to feeding into the side well, otherwise the rate of melting will be comparatively slow. Skim formed on earlier occasions may also be fed into the side well 9 and i~ again desirably preheated preferably to a temperature of at ~east 500C. Pre-warming to remove moisture should be of course carried out on grounds of safety. If desired, a metal pump may be used to increase the circulation of hot metal between the main hearth and the side well.
- :
.
- . : . : , .. . .
Another say of carrying out the process is to use a small reverberatory furnace with side well, in wh~ch the main hearth iq not employed as a melting furnace but merely aq a means of providing hot metal to the side well.
Alternatively a brick lined box may be used in which there is provided a baffle wall which divides the box into two compartments that are in communication below the base of the baffle wall or by means of channels passing through the baffle wall. Means is provided for heating liquid metal in one of the chambers, for example conventional gas or oil burners, electric radiant tubes, a channel inductor, or gas fired immersion heaters. The box is partly filled with liquid metal, and the temperature maintained at the desired level by application of heat to one of the chambers. The ~lux required for -carrying out the process is applied to the other chamber.
tap hole may be provided in order to lower the level of liquid metal when required, or alternatively an overflow pipe may be provided. Either the small reverberatory furnace or the divided brickbox may be made portable and lifted or wheeled from one large melting or holding furnace to another in order to collect and treat the skim generated in ~uch large furnace.
It will be seen that in these embodiments of the invention a method is provided of treating aluminou~
material by means of salt fluYes in which the aluminous material i~ transferred to a layer of liquid salt flux floating upon a body of liquid aluminium in such quantities at a time as can be at least substantially immersed in the flux layer, said body of liquid -8- , . , .
,~ ,.
, . ~ .
aluminium being in sub-surface communiCation with another body of liquid aluminium for which means of heating iS
provided~ and said skim being agitated with the fluX whereby substantially all the metal Content of the skim pasSes into the body of the metal.
Another form of portable treatment unit whiCh has proved very suitable for aluminous material~ particularly when the quantities to be treated at one time are not very large~ is comprised of an externally heated non-metallic crucible divided by a baffle wall into chambers ~hich are in communication below the baffle wall.
SuCh eqUipment is advantageous where the aluminous material to be treated i8 below the desired temperature and may give rise to partial freezing of the liquid salt flux layer. In such caseS the ability to apply external heating to the treatment unit enables the fluX to be remelted quic~ly.
Where metal at temperatureS of 800C or more is readily available~ e.g. at aluminium smelters~ it is possible to carry out the treatment of skim in accordance with the present invention using very simple equipment.
For example a trough lined with suitable refractory material and without either a baffle wall or separate heatins means may be employed.
The prewarmed trough may be placed below the drossing door Of a reverberatory furnace~ metal at 800-850 C
poured into the trough~ fluX added~ and the furnace skim drawn from the metal surface directly into the trough.
After a short period of agitation~ the liberated metal may be collected through ; tap hole near the base of the trough.
In yet another embodiment of the invention the skim or the like i8 sub~tantially immersed in a pool of liquid flux floating on a liquid metal bath, the flux pool ~ -being confined by means of a container partially immersed in the liquid bath and in communication therewith through one or more holes in the lower part of the container, and a stream of liquid metal is fed into the container so as to agitate the skim with the liquid flux.
Preferably the container is of round section.
Preferably the metal stream is fed into the container in a broadly tangential direction, so that the metal flows l round the ~ide of the container, thereby creating a , vortex in the container. It is undesirable however to create sufficient circular motion to cause the liquid flux to be carried down into the bath of metal. One -or more baffles may be applied to the central part of the metal surface within the container in order to prevent a central vortex from forming whil~t still retainiD~ the circular motion of the metal round the periphery of the container. Two baffles intersecting at right angles to form a cross may be used, the length of the baffles being preferably fro~ one tenth to one half of the diameter of the container and the baffles extending at least 1 in. .
below the level of the metal during operation of the - equipment.
The container may be a crucible of plumbago, silicon carbide bonded with alumina, a mixture of zircon and alumina~ or any other refractory material which is -1~-, Rufficiently re~i~tant to the acti~n of liquid aluminium and to therm~l shock.
S~im to be treated by the process i8 preferably fresh and hot but cold skim can also be treated by this embodiment. ~ith cold skim it is particularly desirable that the liquid metal stream should not be too cold and a temperature of 725-800C is preferred.
The container may be conveniently supported from above by meanR of a ring in known manner. Alternatively, when the "hole" in the container is 90 large that there is no bottom wall at all and the container is in effect a ring, the ring may be allowed to float upon the metal ~urface in which case the metal stream may be applied in a direction other than tangential~ for example vertically downwards~ A handle may be attached to the ring and the ',' ring moved about underneath the metal stream so that the metal stream is brought successively into contact with all the skim contained within the ring.
If desired the metal stream may be dispensed with and the skim agitated with the flux by moving the ring backward and forwards over the metal surface.
Embodiment~ of the present in~ention will now be described by way of example only with reference to the accompanying drawings which show diagrammatically alternative forms of apparatus for carrying out the process of the present invention.
In the drawings:
-Figure~ 1, 2 and 5 are vertical sections through different apparatus for carrying out the invention, -}1-.
1060;~16 Figure 3 i~ a plan view of the apparatus of Figure 2, and Figure ~ i8 a plan view of another apparatus for carrying out the invention, and Figures 6 and 7, Figures 8 and 9 and Figures 10 and 11 are respectively vertical sections and plan view~ of apparatus for carrying out other embodiment~
of the invention.
In Figure 1 a crucible 1, which may for example be made of cast iron, plumbago or ~ilicon carbide, is heated externally by means of a gas burner 2. The crucible is filled partly with liquid aluminium 3, upon which float~ a layer of liquid flux 4. Skim 5 is charged to the crucible to be substantially immersed in the layer and is gently agitated with the stirring tool 6.
Figure 2 showc a section of a reverberatory furnace 21, fitted with a side well, 22. Metal 23, in the side well is in communication with that in the main hearth 24~ by channels 25, e~tending through or belou a baffle wall 26~ A salt flux layer 27, is provided on the metal in the side well and skim 28, forming on the metal surface in the main hearth i~ drawn into the ~ide well using the ~craping tool 29.
Figure 3 shows a plan view of the same furnace in which the main hearth 31, i4 separated from the side well, 32~ by means of the baffle wall 33. A stirring tool 34, is used to agitate the skim with the flux in the side well 32.
.' , '. ~ . ~
..
Figure 4 shows a plan view of a furnace for ¦ .
treatment of ~kim. The furnace consist~ of a refractory l .
lined box 41, divided by a baffle wall ~2, into two :
chambers in communication through channels in the baffle .
wall. One chamber 43, is provided with a ga~ burner 44, whilst the other cham~er 45, receives a layer of flux and is used to treat the skim. :
Figure 5 show~ a sectional view of a mobile furnace .
for skim treatment which can be taken to large reverberatory furnaces for charging with skim. The mobile furnace consi~t~ of a refractory lined box 51, ~ :
as shown in Figure 4, comprising a heating chamber 52, ;
and a qkim treatment chamber 53, having a layer of flux floating on the metal therein. The mobile furnace i~
placed adjacent to a large reverberatory furnace 54, and the skim 55, formed on the metal 56, in the large furnace, is Rcraped into the treatment chamber 53, of the mobile furnace u~ing the tool 57.
In the embodiment of Figures 6 and 7, a crucible 61 contains a central hole at the bottom 62~ and optionally one or more holes 63, in the side wall~ and is immersed in molten aluminium with the holes below .
the metal level 64. A jet of liquid aluminium 65, from :~ .
a conventional pouring device impinges on the wall of ~
the crucible, producing a circular motion therewith. ~: .
The crucible contains a layer of molten salt flux .
and skim 66 is added ~o that it is substantially immersed in the flux. The motion of the metal in the .
crucible causes agitation of the ~kim in contact with ~.
, . -13- .
'" '. :
,~ -, , , , '~ ' ' ` ' ' ' , ~06V21~i the liquid ~alt.
Figures 8 and 9 show another method of carrying out the invention. In thi~ case the crucible ha~ the whole of the bottom removed and a cruciform baffle 80 is placed in such a position aq to prevent formation of a vortex even with a faxt moving metal stream.
Figure~ 10 and 11 sho~ a further method of carrying out the invention. The refractory ring 111, floats on the liquid metal 64, and i8 moved about by means of the handle 112, so that all parts of skim 113, contained within the ring can be brought under the metal stream 114, and thereby a~itated with the salt flux 115.
The invention will be illustrated by the following Example.
Example In one experiment to illu~trate the efficacy of the process, 17.8 kg of aluminium was melted in a crucible (Crucible A) and converted into skim by prolonged blowing of compressed air into the metal. The skim produced was periodically removed and fed into a salt pool approx. 10 cm deep floating on 17.2 kg of liquid metal in a second crucible (Crucible B). The skim was agitated in the liquid flux pool for about 15 secg.
after each addition. When all the q~im had been added, the contents of Crucible B were stirred for about 30 ;
secs. and then carefully caqt~ 33.3 kg of clean metal being obtained. A small amount of metal remaining in Crucible A was also weighed (1.0 kg), so that the quantity of clean metal used to produce the skim .
, .
. -- .
1060Z16 1~
transferred to Crucible B could be ascertained by difference. Allowing for the weight of metal originally present in Crucible B, it will be seen that 16.8 kg of metal was converted into skim and 16.1 kg :
was recovered from this skim in the form of clean metal, making a recovery of 95.8%. The metal temperature in :
each crucible was 700-720 C.
In the course of many tests carried out in accordance with the present invention on ~luminous 10 materials with the metal content ranging from about 40 .
wt.% to over 95 wt.%~ we have found that the metal recovery obtained con~istently exceeds 90 wt.% and generally exceeds 95 wt.% of the metallic content of the -material. -'. .
,, ' ., :' - ; .
... , ' . - ~.
,, ''
'' ' -'' , , :
.: , . . ~ . ..... , :, 1066~216 from one-third to two thirds of the metal content of the skim. Much oxide fume is reLeased when the crucibles are emptied. Another method of treating skim is to feed it into rotary salt furnaces, but although metal recovery may be impr-oved thi~ in~olves an en~ironmental problem owing to volatilisation of the ~alt from the furnace.
More recently it has been proposed to recover metal from sXim and drosse~ by mixing them cold with solid salt flux and melting in an induction furnace. This has the advantage that the salt is not overheated, the metal is not oxidised by the products of gas combustion, and the stirrin$ action of the induced current~ assists agglomeration of the metal. However the capital equipment involved is costly, the furnace lining requires frequent replacement and the method will only treat ~-metal-rich drosses. It is not therefore suitable for treatment of skim which has undergone extensive slow oxidation or has fired in the furnace before being removed. All these method~ in which skim is allowed to cool and is subsequently reheated for further proce sing will inevitably involve some loss of metal through oxidation as well as consumption of energy in replacing the lost heat. -We have now found that if fre~hly generated hot skim is fed into a layer of liquid salt flux floating upon a body of liquid aluminium, then substantially all the metal content of the skim is quickly transferred to the body of liquid aluminium when the skim i~ gently : .- . ' ' ' ' '': ': ' ' -.
1060;~16 agitated with the flux. In this way the recovery of metal from the skim is much greater than can be obtained by even prolonged rabbling of thle skim upon the metal ~urface and ~prinkling o~ powdered flux upon it during the operation. The layer of liquid flux used in the process of the present invention should be deep enough for the skim to be at least partially and preferably at least Yubstantially immersed in the flux. In one aspect the present invention provides a method of treating aluminous material comprising furnace skim, drosse~ or metal residue~ by means of salt fluxes in which the aluminous material, preferably hot, is fed into a liquid salt flux layer floating upon a body of liquid aluminium and the aluminouR material is agitated with the flux whereby substantially all the metal content of the aluminous material passe~ into the body of aluminium.
The aluminouc material may be added batch wise in such quantities a~ can be substantially immersed in the salt layer and then gently ~tlrred to liberate the metal~
leaving the salt layer ready to accept a further quantity of skim. Preferably skim is transferred directly from the bath of a reverbatory furnace to the salt layer. 1 ;
Thus the invention is capable of providing a simple method of treating hot furnace skim to give very high recovery of the metal co~tent without the need for elaborate equipment~ without grave environmental problems through evolution of oxide or salt fume, and without the metal and energy losses involved in cooling and reheating the skim.
., 1060Z~6 The flux layer is confined to a predetermined area and the quantity of flux used in relation to the predetermined area is such as to provide initially a liquid layer of at least 1 cm and preferably at least 2 cm deep, though 5-10 cm depth iæ desirable ~ince more skim can be added at one time.
The temperature of the met~l will not be less than 650 C and preferably not less than 700C. Con~iderably higher temperatures may be used but above about 850C
the volatility of the flux may be con~idered objectionable.
The salt flux u~ed may consist of mixture~ of the alkali ænd alkaline earth metal chlorides, incl~ding MScl2~ and may contain one or more fluorides of the alkali and alkaline earth metal~, including MgF2, and will--be thinly--fluid at tempera*ure~ above abou* 675C.-Suitable compositions are based on KCl and NaCl in eutectic proportions or in equal portion~ by weight-with additions of 0-5% CaF2~ 0-25% NaF, or 0-20% MgC12. With CaF2 additions, the flux i~ fumele~s in operation and haa adequate coagulating power for dispersed metal.
With the NaF additions the coagulating power of the flux is increased but slight fuming may occur, whereas with MgC12 additions the wetting power of the flux i8 increased but some evolution of HCl wi~l be encountered, particularly in damp atmosphere~.
In one embodiment of the invention aluminium is heated in a reverberatory furnace provided with a side well~ a layer of liquid salt flux is provided upon the metal in the side well~ and the skim formed in the main ~-hearth i~ transferred to the sid,e well, said ~kim being _5_ ' ' . . : .' .' '.'. , . ,:
: ~ .' ; ' . . '' :
~-- 10602~6 agitated with the flux whereby su~stantially all the metal content of the skim pa~seq into the body of liquid metal in the side well. The metal in the furnace and the metal in the side well are preferably in communication below the layer of flux.
When the invention is operated in conjunction with a side well or forewell~ the metal in the main hearth can be conveniently skimmed by pushing or drawing the skim directly into such sidewell or forewell. This has many advantages. The skimming can be done as soon as the metal charge is melted and before the floating skim has undergone significant oxidation. The skim is already above the melting point of the metal and will disintegrate rapidly on entering the flux layer, very little stirring being needed. The skimmed-metal in the main hearth will then be directly exposed to the heat of the furnace and .. . . . .:-will not be partially insulated therefrom by a layer of skim, 80 making for thermal economy in the furnace operation. Moreover the heat contained in the skim is preserved and is not lost through allowing the skim to cool down with subsequent need to remelt it for later processing. There is no oxide fumesuch as is frequently evolved when skim is taken from the furnace and allowed to cool; nor i8 there any ,108s of aluminium incurred through deliverate burning part of the skim in order that some metal will be liberated through the increase in temperature. In this preferred process, should any qkim be allowed inadvertently to catch fire in the main hearth, then burning is immediately extinguished when the ~kim is :. i fed into the flux covered side well. There i9 no objectionable salt fume generated. Finally all need for equipment for crushing, grinding~ screening and remelting of skim (e.g. in induction furnaces) i4 avoided.
The sidewell may conveniently be fitted with insulating lids, and provided with a gas burner or other heating device whereby the temperature of the metal can, if desired~ be raised above that in the main hearth. The side well may extend alongside a short length only of one wall of the furnace, for example alongside one or more drossing doors. Alternatively the flux layer may be confined to part only of a side well, e.g. by means of a baffle wall or floating barrier.
It is also possible to portion off part of the furnace hearth e.g. by means of a baffle wall, and to carry out the process of the present invention within such portion of the furnace.
The process of the present invention is not confined to skim but may be used to treat metal-containing residue~, dro~ses or finely divided scrap metaI. Such materials are preferably preheated prior to feeding into the side well, otherwise the rate of melting will be comparatively slow. Skim formed on earlier occasions may also be fed into the side well 9 and i~ again desirably preheated preferably to a temperature of at ~east 500C. Pre-warming to remove moisture should be of course carried out on grounds of safety. If desired, a metal pump may be used to increase the circulation of hot metal between the main hearth and the side well.
- :
.
- . : . : , .. . .
Another say of carrying out the process is to use a small reverberatory furnace with side well, in wh~ch the main hearth iq not employed as a melting furnace but merely aq a means of providing hot metal to the side well.
Alternatively a brick lined box may be used in which there is provided a baffle wall which divides the box into two compartments that are in communication below the base of the baffle wall or by means of channels passing through the baffle wall. Means is provided for heating liquid metal in one of the chambers, for example conventional gas or oil burners, electric radiant tubes, a channel inductor, or gas fired immersion heaters. The box is partly filled with liquid metal, and the temperature maintained at the desired level by application of heat to one of the chambers. The ~lux required for -carrying out the process is applied to the other chamber.
tap hole may be provided in order to lower the level of liquid metal when required, or alternatively an overflow pipe may be provided. Either the small reverberatory furnace or the divided brickbox may be made portable and lifted or wheeled from one large melting or holding furnace to another in order to collect and treat the skim generated in ~uch large furnace.
It will be seen that in these embodiments of the invention a method is provided of treating aluminou~
material by means of salt fluYes in which the aluminous material i~ transferred to a layer of liquid salt flux floating upon a body of liquid aluminium in such quantities at a time as can be at least substantially immersed in the flux layer, said body of liquid -8- , . , .
,~ ,.
, . ~ .
aluminium being in sub-surface communiCation with another body of liquid aluminium for which means of heating iS
provided~ and said skim being agitated with the fluX whereby substantially all the metal Content of the skim pasSes into the body of the metal.
Another form of portable treatment unit whiCh has proved very suitable for aluminous material~ particularly when the quantities to be treated at one time are not very large~ is comprised of an externally heated non-metallic crucible divided by a baffle wall into chambers ~hich are in communication below the baffle wall.
SuCh eqUipment is advantageous where the aluminous material to be treated i8 below the desired temperature and may give rise to partial freezing of the liquid salt flux layer. In such caseS the ability to apply external heating to the treatment unit enables the fluX to be remelted quic~ly.
Where metal at temperatureS of 800C or more is readily available~ e.g. at aluminium smelters~ it is possible to carry out the treatment of skim in accordance with the present invention using very simple equipment.
For example a trough lined with suitable refractory material and without either a baffle wall or separate heatins means may be employed.
The prewarmed trough may be placed below the drossing door Of a reverberatory furnace~ metal at 800-850 C
poured into the trough~ fluX added~ and the furnace skim drawn from the metal surface directly into the trough.
After a short period of agitation~ the liberated metal may be collected through ; tap hole near the base of the trough.
In yet another embodiment of the invention the skim or the like i8 sub~tantially immersed in a pool of liquid flux floating on a liquid metal bath, the flux pool ~ -being confined by means of a container partially immersed in the liquid bath and in communication therewith through one or more holes in the lower part of the container, and a stream of liquid metal is fed into the container so as to agitate the skim with the liquid flux.
Preferably the container is of round section.
Preferably the metal stream is fed into the container in a broadly tangential direction, so that the metal flows l round the ~ide of the container, thereby creating a , vortex in the container. It is undesirable however to create sufficient circular motion to cause the liquid flux to be carried down into the bath of metal. One -or more baffles may be applied to the central part of the metal surface within the container in order to prevent a central vortex from forming whil~t still retainiD~ the circular motion of the metal round the periphery of the container. Two baffles intersecting at right angles to form a cross may be used, the length of the baffles being preferably fro~ one tenth to one half of the diameter of the container and the baffles extending at least 1 in. .
below the level of the metal during operation of the - equipment.
The container may be a crucible of plumbago, silicon carbide bonded with alumina, a mixture of zircon and alumina~ or any other refractory material which is -1~-, Rufficiently re~i~tant to the acti~n of liquid aluminium and to therm~l shock.
S~im to be treated by the process i8 preferably fresh and hot but cold skim can also be treated by this embodiment. ~ith cold skim it is particularly desirable that the liquid metal stream should not be too cold and a temperature of 725-800C is preferred.
The container may be conveniently supported from above by meanR of a ring in known manner. Alternatively, when the "hole" in the container is 90 large that there is no bottom wall at all and the container is in effect a ring, the ring may be allowed to float upon the metal ~urface in which case the metal stream may be applied in a direction other than tangential~ for example vertically downwards~ A handle may be attached to the ring and the ',' ring moved about underneath the metal stream so that the metal stream is brought successively into contact with all the skim contained within the ring.
If desired the metal stream may be dispensed with and the skim agitated with the flux by moving the ring backward and forwards over the metal surface.
Embodiment~ of the present in~ention will now be described by way of example only with reference to the accompanying drawings which show diagrammatically alternative forms of apparatus for carrying out the process of the present invention.
In the drawings:
-Figure~ 1, 2 and 5 are vertical sections through different apparatus for carrying out the invention, -}1-.
1060;~16 Figure 3 i~ a plan view of the apparatus of Figure 2, and Figure ~ i8 a plan view of another apparatus for carrying out the invention, and Figures 6 and 7, Figures 8 and 9 and Figures 10 and 11 are respectively vertical sections and plan view~ of apparatus for carrying out other embodiment~
of the invention.
In Figure 1 a crucible 1, which may for example be made of cast iron, plumbago or ~ilicon carbide, is heated externally by means of a gas burner 2. The crucible is filled partly with liquid aluminium 3, upon which float~ a layer of liquid flux 4. Skim 5 is charged to the crucible to be substantially immersed in the layer and is gently agitated with the stirring tool 6.
Figure 2 showc a section of a reverberatory furnace 21, fitted with a side well, 22. Metal 23, in the side well is in communication with that in the main hearth 24~ by channels 25, e~tending through or belou a baffle wall 26~ A salt flux layer 27, is provided on the metal in the side well and skim 28, forming on the metal surface in the main hearth i~ drawn into the ~ide well using the ~craping tool 29.
Figure 3 shows a plan view of the same furnace in which the main hearth 31, i4 separated from the side well, 32~ by means of the baffle wall 33. A stirring tool 34, is used to agitate the skim with the flux in the side well 32.
.' , '. ~ . ~
..
Figure 4 shows a plan view of a furnace for ¦ .
treatment of ~kim. The furnace consist~ of a refractory l .
lined box 41, divided by a baffle wall ~2, into two :
chambers in communication through channels in the baffle .
wall. One chamber 43, is provided with a ga~ burner 44, whilst the other cham~er 45, receives a layer of flux and is used to treat the skim. :
Figure 5 show~ a sectional view of a mobile furnace .
for skim treatment which can be taken to large reverberatory furnaces for charging with skim. The mobile furnace consi~t~ of a refractory lined box 51, ~ :
as shown in Figure 4, comprising a heating chamber 52, ;
and a qkim treatment chamber 53, having a layer of flux floating on the metal therein. The mobile furnace i~
placed adjacent to a large reverberatory furnace 54, and the skim 55, formed on the metal 56, in the large furnace, is Rcraped into the treatment chamber 53, of the mobile furnace u~ing the tool 57.
In the embodiment of Figures 6 and 7, a crucible 61 contains a central hole at the bottom 62~ and optionally one or more holes 63, in the side wall~ and is immersed in molten aluminium with the holes below .
the metal level 64. A jet of liquid aluminium 65, from :~ .
a conventional pouring device impinges on the wall of ~
the crucible, producing a circular motion therewith. ~: .
The crucible contains a layer of molten salt flux .
and skim 66 is added ~o that it is substantially immersed in the flux. The motion of the metal in the .
crucible causes agitation of the ~kim in contact with ~.
, . -13- .
'" '. :
,~ -, , , , '~ ' ' ` ' ' ' , ~06V21~i the liquid ~alt.
Figures 8 and 9 show another method of carrying out the invention. In thi~ case the crucible ha~ the whole of the bottom removed and a cruciform baffle 80 is placed in such a position aq to prevent formation of a vortex even with a faxt moving metal stream.
Figure~ 10 and 11 sho~ a further method of carrying out the invention. The refractory ring 111, floats on the liquid metal 64, and i8 moved about by means of the handle 112, so that all parts of skim 113, contained within the ring can be brought under the metal stream 114, and thereby a~itated with the salt flux 115.
The invention will be illustrated by the following Example.
Example In one experiment to illu~trate the efficacy of the process, 17.8 kg of aluminium was melted in a crucible (Crucible A) and converted into skim by prolonged blowing of compressed air into the metal. The skim produced was periodically removed and fed into a salt pool approx. 10 cm deep floating on 17.2 kg of liquid metal in a second crucible (Crucible B). The skim was agitated in the liquid flux pool for about 15 secg.
after each addition. When all the q~im had been added, the contents of Crucible B were stirred for about 30 ;
secs. and then carefully caqt~ 33.3 kg of clean metal being obtained. A small amount of metal remaining in Crucible A was also weighed (1.0 kg), so that the quantity of clean metal used to produce the skim .
, .
. -- .
1060Z16 1~
transferred to Crucible B could be ascertained by difference. Allowing for the weight of metal originally present in Crucible B, it will be seen that 16.8 kg of metal was converted into skim and 16.1 kg :
was recovered from this skim in the form of clean metal, making a recovery of 95.8%. The metal temperature in :
each crucible was 700-720 C.
In the course of many tests carried out in accordance with the present invention on ~luminous 10 materials with the metal content ranging from about 40 .
wt.% to over 95 wt.%~ we have found that the metal recovery obtained con~istently exceeds 90 wt.% and generally exceeds 95 wt.% of the metallic content of the -material. -'. .
,, ' ., :' - ; .
... , ' . - ~.
,, ''
Claims (30)
1. A method of treating aluminous material comprising furnace skim, drosses or metal residues by means of salt fluxes in which the aluminous material is fed into a liquid salt flux layer floating on a body of liquid aluminum and the aluminous material is agitated with the flux whereby substantially all the metallic content of the aluminous material passes into the body of liquid aluminum, said flux comprising at least two halides selected from the group consisting of the chlorides and fluorides of the alkali and alkaline earth metals including magnesium and being thinly fluid at temperatures in excess of 675°C.
2. A method according to Claim 1 in which the aluminous material is substantially immersed in the liquid flux layer.
3. A method according to Claim 1 in which the aluminous material is at a temperature of at least 500°C
when fed into the liquid salt flux layer.
when fed into the liquid salt flux layer.
4. A method according to Claim 1 in which the aluminous material is furnace skim.
5. A method according to Claim 4 in which freshly drawn furnace skim without substantial cooling is fed into the liquid salt flux layer.
6. A method according to Claim 1 in which the body of liquid aluminum is in sub-surface communication with another body of liquid aluminum for which means of heating is provided.
7. A method according to Claim 1 in which the flux floats on a body of liquid aluminum in a side well of a reverberatory furnace containing molten aluminum.
8. A method according to Claim 7, in which the side well is in communication with the furnace below the level of liquid metal.
9. A method according to Claim 6 in which the body of molten metal is contained in a refractory-lined box divided into two compartments by a baffle, the compartments being in communication below the level of liquid metal, the flux floats on the metal in one compartment and the metal in the other compartment is heated.
10. A method according to Claim 7 in which the metal in the side well is heated.
11. A method according to Claim 8 in which metal is circulated between the furnace and side well by means of a pump.
12. A method according to Claim 9 in which metal is circulated between said compartments by means of a pump.
13. A method according to Claim 1 in which the skim is substantially immersed in a pool of liquid flux floating on the liquid metal, the pool being con-fined in a container partially immersed in the metal and in communication therewith through one or more holes in the immersed part of the container.
14. A method according to Claim 13 in which the container is of round section.
15. A method according to claim 13 in which agitation of the aluminous material with the liquid flux is produced by a stream of liquid metal directed into the container.
16. A method according to claim 15 in which the stream is fed to the container tangentially to create a vortex in the container.
17. A method according to claim 16 in which the container is provided with a central baffle extending below the metal surface.
18. A method according to Claim 17 in which the baffle is cruciform.
19. A method according to Claim 15 in which the baffle extends at least 1 inch below the level of metal in the container and extends across from 1/10 to 1/2 of the diameter of the container.
20. A method according to Claim 15 in which the container is bottomless and is moved in the horizontal direction below the stream of liquid metal.
21. A method according to claim 13 in which the container is bottomless and is moved over the metal surface.
22. A method according to Claim 1 in which the temperature of the body of liquid metal is 700°C to 850°C.
23. A method according to claim 1 in which the salt flux comprises a mixture of an alkali metal and/or alkaline earth chlorides.
24. A method according to claim 23, in which the flux contains one or more fluorides of the alkali and/or alkaline earth metals.
25. A method according to Claim 23 in which the salt flux contains substantially equal weights of NaCl and KCl.
26. A method according to Claim 23 in which the salt flux contains NaCl and KCl in substantially eutectic proportions.
27. A method according to Claim 24 in which the flux contains up to 5% calcium fluoride, up to 25% sodium fluoride or up to 20% magnesium fluoride by weight.
28. A method according to Claim 1 in which the flux layer is at least 1 cm deep.
29. A method according to Claim 28 in which the flux layer is from 5 to 10 cm. deep.
30. A method of treating aluminum skim by means of salt fluxes in which the hot skim is transferred to a layer of liquid salt flux floating upon a body of liquid aluminum in such quantities at a time as can be at least substantially immersed in the flux layer, said body of liquid aluminum being in subsurface communication with another body of liquid aluminum for which means of heating is provided, and said skim being agitated with the flux whereby substantially all the metal content of the skim passes into the body of the metal, said flux comprising at least two halides selected from the group consisting of the chlorides and fluorides of the alkali and alkaline earth metals including magnesium and being thinly fluid at temperatures in excess of 675°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4977874A GB1533704A (en) | 1974-11-18 | 1974-11-18 | Treatment of aluminous material |
| GB4079175 | 1975-10-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1060216A true CA1060216A (en) | 1979-08-14 |
Family
ID=26264504
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA239,961A Expired CA1060216A (en) | 1974-11-18 | 1975-11-17 | Treatment of aluminous material |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5176111A (en) |
| AU (1) | AU497757B2 (en) |
| CA (1) | CA1060216A (en) |
| CH (1) | CH609094A5 (en) |
| DE (1) | DE2551524A1 (en) |
| ES (1) | ES442735A1 (en) |
| FR (1) | FR2291281A1 (en) |
| IT (1) | IT1048740B (en) |
| NL (1) | NL7513459A (en) |
| NO (1) | NO753840L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1549979A (en) * | 1977-06-02 | 1979-08-08 | Thiem Corp | Flux compositions for use in recovering aluminium |
| FR2542015B1 (en) * | 1983-03-01 | 1988-07-22 | Inst Elektrokhimii Ural | SECONDARY ALUMINUM CHARGE TRANSFORMATION PROCESS |
| US4568430A (en) * | 1984-02-29 | 1986-02-04 | Swiss Aluminium Ltd. | Process for refining scrap aluminum |
| US4983216A (en) * | 1990-02-12 | 1991-01-08 | Aluminum Company Of America | Aluminum scrap melting |
| KR101711362B1 (en) * | 2015-03-03 | 2017-03-02 | 윤수현 | Aluminum melting furnace |
-
1975
- 1975-11-17 NO NO753840A patent/NO753840L/no unknown
- 1975-11-17 CA CA239,961A patent/CA1060216A/en not_active Expired
- 1975-11-17 DE DE19752551524 patent/DE2551524A1/en not_active Withdrawn
- 1975-11-18 CH CH1490575A patent/CH609094A5/en not_active IP Right Cessation
- 1975-11-18 AU AU86701/75A patent/AU497757B2/en not_active Expired
- 1975-11-18 ES ES442735A patent/ES442735A1/en not_active Expired
- 1975-11-18 NL NL7513459A patent/NL7513459A/en not_active Application Discontinuation
- 1975-11-18 FR FR7535148A patent/FR2291281A1/en active Granted
- 1975-11-18 JP JP13860775A patent/JPS5176111A/ja active Pending
- 1975-11-18 IT IT2940275A patent/IT1048740B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| FR2291281A1 (en) | 1976-06-11 |
| DE2551524A1 (en) | 1976-05-26 |
| AU8670175A (en) | 1977-05-26 |
| NL7513459A (en) | 1976-05-20 |
| ES442735A1 (en) | 1977-10-01 |
| AU497757B2 (en) | 1979-01-04 |
| IT1048740B (en) | 1980-12-20 |
| CH609094A5 (en) | 1979-02-15 |
| NO753840L (en) | 1976-05-19 |
| JPS5176111A (en) | 1976-07-01 |
| FR2291281B1 (en) | 1980-03-14 |
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