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

Definitions

• the present invention relates to the recovery of aluminum from mixtures comprising aluminum and aluminum carbide, and it concerns more particularly a process for treating such mixtures with a flux.
• aluminum may beextracted from said aluminum-aluminum carbide mixtures by means of various procedures, for example, by means of a flux consisting of molten metallic halides.
• the quantities of flux employed are quite large and, by a weight comparison, are at least equal to and usually greater than the quantity of the treated mixtures.
• the process enables a quick and substantially complete recovery of the free aluminum contained in the mixtures of alumi- This can be achieved ir-- respective of the aluminum oxide contentof the mixtures and independent of the manner in which the alumi-. num-aluminum carbide mixtures were obtained. Likewise, the process of this invention presents economic ad-l num and aluminum carbide.
• object of this invention is the recovery of aluminum from mixtures of aluminum and aluminum carbide obtained from the carbothermal reduction of aluminum oxide.
• a further object of this invention is the recovery of aluminum in a manner which will permit the recovery of substantially all the elemental aluminum values contained in the aluminum-aluminum carbide mixtures.
• An additional object of this invention is to provide a process for the recovery of aluminum in a highly efficient and economical manner.
• a further object of this invention is to provide a process for extracting the aluminum contained in mixtures comprising aluminum and aluminum carbide wherein said mixture is added to a flux, the amount by weight of the added mixtures being greater than the amount of the flux employed.
• the quantity of mixtures comprising aluminum and aluminum carbide treated by flux according to this invention may be heavier than the quantity of flux. It has been surprisingly dis covered that the aluminum may be more efficiently recovered when smaller amounts of flux are employed.
• process is such that the quantity of flux used in comparison with that of the mixture is preferably of the same order or magnitude as the quantity of aluminum carbide contained in the mixtures.
• quantity of flux used in comparison with that of the mixture is preferably of the same order or magnitude as the quantity of aluminum carbide contained in the mixtures.
• the instant invention consists of a process which re-I carbide by weight, an amount of flux, between 50-55% of the weight of the total mixture, may be employed.
• the flux compositions employed in accordance with this invention preferably include the chlorides, bromides, or fluorides of the alkaline and alkaline earth metals.
• chlorides, bromides, or fluorides of the alkaline and alkaline earth metals For example, sodium, potassium, and lithium fluoride, and chlorides of sodium and potassium may 'be employed alone or in combination.
• additions of aluminum fluoride may be employed whereby the surface tension of'the flux relative to that of the treated mixture is reduced.
• the introduction of calcium chloride is to be avoided because it tends to increase the surface tension, thus impeding the intermixing of the mixture and flux.
• mixtures containing aluminum and aluminum carbide at a temperature not exceeding about 1200" C. are introduced progressively into the molten flux.
• the flux is carefully stirred in order to enable rapid and intimate contact with said mixture. Formation of an emulsion of metallic aluminum is to be avoided since such an emulsion would tend to separate out together with the slurry which will be formed.
• the temperature of the flux is greater than the melting point of the flux by an amount of at least 100 C. It is preferred not to heat the flux to a temperature too close to that of the boiling point because the increase in vapor pressure tends to impede the progress of the separation. Use may be made of a fiux'maintained at a temperature between about 900-1000 C., preferably about 950 C.
• Portions of the mass may be subjected to cooling from the bottom to the top and then from the top to the bottom a variable number of times. That is, a heat exchanger will traverse the mass vertically, extracting heat in a progressive fashion. In any case, the last traverse will always be from the bottom to the top. A procedure of this type has been found to facilitate the separation of the sizes formed. In some instances, cooling may be effected only by a regularly ascending procedure from the bottom to the top of the mass.
• cooling may be effected in a non-uniform or discontinuous manner.
• the mass being treated may be submitted to successive coolings, followed-by partial reheatings.
• Another feature of this invention which may be utilized in combination with or independently of the cooling feature, consists in adding to the flux or slurry a small quantity of a substance in powdered form which does not melt at the process temperatures and is inert towards the flux components and treated mixtures.
• These addition agents include aluminum oxide, carbon, and/or aluminum carbide.
• a setting or congealing of the mass and the substantially complete separation of liquid aluminum is more readilyobtained by the use of these additives.
• the quantity of these additives or combinations thereof corresponds to a few percent, for example, between 2-15% of the weight of the flux, and preferably about 5% of the weight of the flux.
• the congealment is, of course, obtained without these additives when the final quantities of aluminum carbide containing mixtures have been added.
• the mixtures comprising aluminum carbide and aluminum are preferably obtained in the form of grains of sizes nearly equal to or smaller than 20 mm. in their largest dimension.
• These particles may be obtained by crushing or grinding the raw, solidified products coming from the carbothermal reduction of aluminum oxide.
• the crushing or grinding may be carried out on cold or heated material.
• the material is heated in many cases since the masses coming from the carbothermal reduction are of considerable size and very hard when cold.
• the masses are heated to temperatures above or below the melting point of aluminum. If above the melting point, the particles obtained comprise particles of aluminum and aluminum carbide, and also particles of free aluminum which has exuded due to the pressures of the crushing operation.
• the comminuting is preferably carried out in an anhydrous or inert atmosphere, and jaw or cylindrical crushers are cited as an example of the apparatus that may be employed.
• the working surfaces of the apparatus may be sprinkled with powdered, fusible salts which will protect the metallic surfaces from corro sion by the liquid aluminum.
• the mixtures coming from the carbothermal reduction may be desirable to submit to a coarse crushing, followed by a second substantially identical fine crushing operation.
• This second crushing is preferably carried out on the cold material.
• the action of a ball or rolling mill upon this material induces a shearing action in the grains.
• the mixtures thus obtained are in the form of flakes having a thickness of the order of 1-3 mm., with the largest dimensions about 10-20 mm. It is preferable not to convert the mixtures into too fine a powder.
• the size of the grains should not be less than about 3 mm. in their smallest dimension. If in too small a 'form, the aluminum carbide 'will tend to be hydrolyzed in contact with a not strictly anhydrous atmosphere.
• powder obtained in too fine a form, or in fact all the powders which are to be used may be agglomerated into pellets.
• This powder generally exhibits the property of being self-compacting.
• non-aqueous binding agents such as heavy hydrocarbons and pitch, may be employed.
• the flux may be agglomerated in the desired proportions with the powdered mixture and the process carried out from this point.
• a special feature of this invention consists in a process wherein the aluminum-aluminum carbide mixtures are pretreated with a molten fiux.
• This flux is substantially of the type previously described, but it is employed in an amount by weight greater than the amount of the mixture. Amounts of 1.l2.5 times the amount of the mixture, and particularly 1.3 times the amount of the mixture, will be employed.
• the mixtures are added rapidly to the molten flux which has been heated to between about 850-l000 C.
• the mixtures may be heated up to about 1200 C. or may be added cold, the latter alternative being resorted to in order to'avoid overheating and vaporization of the flux.
• the pretreatment is carried out in a rotary furnace with an approximately horizontal axis, and in which the feeding axis is sloping against the rotation axis.
• the pretreatment will consist of kneading for a few minutes to several hours, the duration of-the kneading varying inversely with the temperature of the treated mixture, and varying directly with the quantity of preheated flux and flux temperature.
• decantation for a few minutes results in a bottom layer consisting substantially of molten aluminum, a top layer of flux, and an intermediate layer comprising fiux, aluminum carbide and metallic aluminum.
• This latter layer is in the form of an emulsion or slurry and can be used as the flux in the aluminum extraction process of this invention.
• the flux and slurry may be used again in another'pretreating operation before a process in accordance with this invention is resorted to. It can be seen As an that the pretreatment accomplishes, among other things,
• Example 1 An electric furnace was employed comprising a ver tical crucible of 40 cm. internal diameter and 100 cm. heighth. The furnace was equipped with a stirrer made out of a graphite vertical bar of about cm. diameter and it was induction heated.
• the stirring was continued for about minutes While progressively lowering the temperature down to about 850 C.
• the slurry had then become practically solid and had congealed against the walls and bottom of the crucible while the liquid aluminum had gathered in the core.
• the aluminum was then poured out by tilting the furnace.
• Example 2 A rotating furnace with a horizontal axis was provided containing 250 kg. of flux substantially consisting of a eutectic mixture of sodium chloride and potassium chloride, melted and heated to a temperature of the order of 900 C. Into this furnace there was progressively introduced within about 2 hours, 450 kg. of a mixture identical to that of Example 1. The mixture was similarly composed of flakes of about 3 mm. thickness, the other dimensions being of the order of 8-20 mm. The rotating speed of the furnace was about 6 revolutions per minute.
• Example 3 A pretreatment was carried out in a rotating furnace with a horizontal axis containing 2800 kg. of a flux consisting substantially of molten sodium chloride. The flux was heated to about 950 C. and there was added thereto 2100 kg. of a mixture comprising 65% aluminum by weight. This mixture was introduced at a temperature of about 700-l000 C. by 7 additions of 300 kg. lasting 5-10 minutes each. The mixtures had been obtained by hot crushing and grinding with a jaw crusher and a cylinder crusher provided with a 3 mm. opening. This equipment was placed above the furnace in order that the latter was able to receive the hot particles issuing from the apparatus practically without any delay.
• Kneading was maintained for about 20 minutes while the rotating speed of the furnace was about 3 revolu tions per minute. This was followed by decantation for about 15 minutes, and the following values were obtained:
• the pretreatment thus permitted the extraction of about 55% by weight of the aluminum contained in the initial mixture.
• This second treatment thus enabled the extraction of about 50% by weight of the aluminum contained in the latertreated mixture.
• a process for recovering aluminum from a mixture comprising aluminum and aluminum carbide comprising the steps of preparing a molten flux capable of forming a slurry of said flux and aluminum carbide in said mixture and wherein the flux is at least one of the compounds selected from the group consisting of alkali metal halides and alkaline earth metal halides, progressively adding to said flux an amount by weight of a mixture of aluminum and aluminum carbide such that the aluminum carbide content of said mixture is approximately equal to the amount by weight of said flux but where in the amount of aluminum plus aluminum carbide is greater than the amount by weight of the flux, and agitating the combination of said mixture and said flux whereby substantially all the aluminum is separated out.
• a process for recovering aluminum from a mixture comprising aluminum and aluminum carbide comprising the steps of preparing a molten flux capable of forming a slurry of said flux and aluminum carbide in said mixture and wherein the flux is at least one of the compounds selected from the group consisting of alkali metal halides and alkaline earth metal halides, maintaining said flux at a temperature at least 100' C. above its melting point, progressively adding to said flux an amount by weight of a mixture of aluminum and aluminum carbide such that the aluminum carbide content of said mixture is approximately equal to the amount by weight of said flux but wherein the amount of aluminum plus aluminum carbide is greater than the amount by weight of the flux, and agitating the combination of said mixture and said flux whereby substantially all the aluminum is separated out.
• the flux comprises at least one member selected from the group consisting of the chlorides, bromides and fluorides of sodium, potassium and lithium.
• a process for recovering aluminum from a mixture comprising aluminum and aluminum carbide comprising the steps of preparing a molten flux capable of forming a slurry of said flux and aluminum carbide in said mixture and wherein the flux is at least one of the compounds selected from the group consisting of alkali metal halides and alkaline earth metal halides, maintaining said fiux at a temperature at least 100 C.
• the process of recovering aluminum from a mixture comprising aluminum and aluminum carbide comprising the steps of treating an amount of said mixture with a molten flux maintained at a temperature between 850-1000 C., and wherein the flux is at least one of the compounds selected from the group consisting of alkali metal halides and alkaline earth metal halides, the amount of said flux being 1.1-2.5 times greater by weight than the amount of said mixture, whereby there is obtained liquid aluminum, flux, and a slurry composed of aluminum, aluminum carbide and flux, separating out said slurry, progressively adding to said slurry an amount by Weight of a mixture of aluminum and aluminum carbide such that the aluminum carbide content of said mixture is approximately equal to the amount by weight of said slurry but wherein the amount of aluminum and aluminum carbide is greater than the amount of flux, and agitating the combination of said mixture and said slurry whereby substantially all the aluminum is separated out.
• the fiux comprises at least one member selected from the group consisting of the chlorides, bromides and fluorides of sodium, potassium and lithium.
• a process for the separation of aluminum from a mixture of aluminum and aluminum carbide comprising the steps of admixing the aluminum-aluminum carbide mixture with a flux which is capable of forming a slurry with aluminum carbide and wherein the flux is at least one of the compounds selected from the group consisting of alkali metal halides and alkaline earth metal halides and in which the flux is employed in an amount by weight at least as great as the amount of aluminum carbide but less than the total of aluminum and aluminum carbide, agitating the combination of flux and aluminum-aluminum carbide whereby aluminum is freed from the aluminum carbide while the aluminum carbide forms into a slurry with the flux.

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  • NL NL258035D patent/NL258035A/xx unknown
• 1959
  • 1959-11-18 FR FR810505A patent/FR1461309A/fr not_active Expired
• 1960
  • 1960-11-14 US US68617A patent/US3068092A/en not_active Expired - Lifetime
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