JPS5844729B2 - Aluminium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing carbon dioxide from a feedstock consisting of an oxide of aluminum and a carbon-containing compound under carbothermal conditions in a single seed operation.
The present invention relates to a new and improved method for producing metallic aluminum having an aluminum carbide weight of less than about 5% by weight.

Even a very cursory review of the prior art for the thermal production of aluminum immediately reveals that tremendous efforts have been made by many people to find an alternative to the traditional electrolytic process for producing aluminum. be understood.

It has long been recognized by those skilled in the art that the use of thermal reduction processes for the production of aluminum, as opposed to electrolytic processes, offers many theoretical advantages.

Unfortunately, the thermal methods previously proposed for producing aluminum suffer from one drawback.

This drawback was due to the simple fact that there was no way to produce large amounts of aluminum in substantially pure form by thermal methods.

It will be readily appreciated that the difficulty in producing aluminum by thermal methods lies not in producing the aluminum by reducing the aluminum-containing ore, but in recovering the aluminum in substantially pure form. .

Many prior patents and literature provide theories or explanations for the various back reactions that occur between aluminum and various carbon-containing compounds in the feedstock.

As a result of previous research efforts, it has been determined that to date there is no industrial method for producing aluminum other than by electrolytic methods.

In general, traditional aluminum thermal production methods can be divided into two categories: one that makes aluminum into a vapor state; In other words, it is formed as liquid aluminum.

The main problem with methods in which aluminum is produced in the vapor state is that the aluminum vapor is highly reactive with the carbon monoxide that is necessarily formed during the reaction, thereby forming aluminum-carbon compounds.

Although various patents and literature provide many teachings for minimizing the reaction between aluminum and carbon monoxide, the solutions proposed in the past have generally been impractical.

One solution to this common problem when aluminum is made in a vapor state is described in U.S. Pat. No. 3,607,221.
No.

Although the method of this patent allows aluminum to be made in a substantially pure state, it requires very high operating temperatures and is therefore problematic in terms of construction materials.

It was recognized that the problems described above regarding the reverse reaction between aluminum and carbon monoxide could be avoided by not converting the aluminum into a vapor state.

It is known that if the process is carried out under conditions such that aluminum is formed in a liquid state, this liquid aluminum is relatively inert towards carbon monoxide and is therefore free of back reaction products. ing.

Although many methods for producing aluminum in liquid state have been described and patented in the literature, none of these methods have been successful in producing aluminum with low aluminum carbide clouds.

The reason for this failure of the prior art method is easily understood in view of the fact that aluminum carbide is soluble in molten aluminum, and the solubility of aluminum carbide in aluminum increases as the temperature increases.

Aluminum carbide is present in carbothermal production processes due to the fact that it is either introduced as a reactant or is formed without reducing reaction centers.

This is because aluminum is highly reactive with carbon and certain aluminum-carbon compounds to give aluminum carbide.

Since conventional methods must be carried out at high temperatures to produce aluminum, the liquid aluminum produced is relatively unreactive with carbon oxide, but does not react with aluminum carbide, which is necessarily present in the system. Combing thus results in aluminum contaminated with carbides.

Aluminum containing more than about 5% carbide contaminants by weight, for example, becomes a hard, non-flowing mass when the temperature is somewhat lower than the reaction temperature, and if you transfer it from one place to another except at high temperatures. This is extremely undesirable for many reasons, including extreme difficulty.

Furthermore, electrical energy is consumed in the production of aluminum, and if it is contaminated with more than about 5 aluminum carbides, additional energy must be used for the next cycle operation, reducing the electricity consumption. It should be understood that this method becomes industrially unrivaled in this respect.

Various proposals have been made regarding methods for removing aluminum carbide from mixtures with aluminum, and there are many patents and publications on this subject.

The present invention is not concerned with the removal of aluminum carbide from aluminum, but rather with a process for the carbothermal production of aluminum that does not contain any substantial amount of aluminum carbide.

The present invention accomplishes what commercial engineers have long desired and what engineers have thought to be theoretically impossible.

In fact, as can be seen from the Examples herein, aluminum containing very little aluminum carbide is produced in large quantities by carbothermal reduction.

The present invention concerns the carbothermal reduction of alumina-containing ores and has certain defining features as its distinguishing features and as a point of difference from prior art methods.

First, the present invention was originally a dual temperature method, and aluminum was the first
It can be seen that it is produced in the high temperature reaction zone and then collected at a much lower temperature.

The lower temperature at which the aluminum is collected is chosen such that it is physically impossible for the aluminum carbide to be dissolved by the aluminum.

This is because, as previously stated, the ability of aluminum to dissolve unreacted aluminum carbide is strictly a function of temperature.

In this way, the aluminum is produced at one temperature and then transferred over the cold unreacted feed material to a second zone where the aluminum is kept at a substantially lower temperature where it cannot physically dissolve the aluminum carbide in large quantities. flowing into the stream.

A very important feature of the novel method of the invention lies in the type of heating applied to this first zone.

The novel method of the present invention absolutely requires that only a small amount of the feed material be heated to the reaction temperature at a given time, and that the majority of the feed material must be kept at a temperature well below the reaction temperature.

This requirement is completely contradictory to any of the conventionally practiced methods.

When carrying out thermal operations, it seems almost inevitable that one of the main objectives is to heat the charge in the reaction zone to the reaction temperature as quickly and as uniformly as possible in order to ensure complete reaction. This must be understood immediately.

It is not surprising that previous researchers have undertaken just such an effort.

In fact, it has been found that when uniform heating as described above is carried out, aluminum cannot be produced in a pure state.

In the novel method of the present invention, uniform heating of the charge material is not employed; in fact, in the hottest part of the reaction zone, the majority of the charge material is not at reaction temperature at any given time, and such conditions are carefully maintained. It's dripping.

Uniform heating of a large portion of the feed material is believed to be the main reason why previous researchers have failed to produce substantially pure aluminum with carbon heat treatment that provides condensed aluminum instead of aluminum vapor.

This reason seems rather self-evident in hindsight.

If the entire charge is heated to the reaction temperature, the aluminum that is formed and flows over the charge will come into contact with the carbon as well as the aluminum carbide originally present in the furnace at high temperatures, thus producing less aluminum carbide in a single furnace operation. I'm sure you can't get anything.

If the charge is heated non-uniformly, i.e. substantially only the surface of the charge is heated such that aluminum is produced from the surface-heated material, and this aluminum is heated over the unreacted parts of the charge that have not reached high temperatures. It has been found that low aluminum carbide contamination of aluminum can be produced in a single furnace operation if the condensed aluminum is allowed to flow so that the aluminum carbide produced does not substantially melt.

Naturally, another portion of the charge is then exposed to this high heat and the cycle continues.

FIG. 1 of the accompanying drawings represents a furnace suitable for carrying out the method of the invention.

A lid 2 and a viewing tube 3 are provided on the furnace body 1.

Inspection tubes 4 and 5 are also provided.

Insulation is shown at 6 and 7. graphite rod 9
A crucible 8 is connected to the positive end of the direct current supply through.

The negative electrode 10 is vertically adjustable by a screw mechanism 12 and is insulated from the furnace lid 2 by an electrically non-conductive vacuum gland 11.

Figure 2 shows the configuration of a plasma arc that is used to apply a direct current to the charged material used in carrying out the method of the present invention, and Figure 3 shows the configuration of a plasma arc used in carrying out the method of the present invention for transmitting half-wave direct current. FIG. 4 shows a furnace suitable for carrying out the method of the invention using the plasma arc configuration of FIG. 2.

As previously mentioned, the novel process of the present invention involves two temperature operations, a hot zone where the aluminum production reactions take place and a cold zone where the aluminum is transported and collected while preventing the aluminum from substantially combing the unreacted carbides. I need.

The furnace is charged with a mixture of a carbon-containing compound, preferably aluminum carbide and/or carbon, and an aluminum oxide-containing material.

Since it is desirable to produce substantially pure aluminum, the aluminum oxide-containing material is preferably high-purity alumina, i.e., Beyer alumina, although the process of the present invention can also be operated with impure alumina and aluminum oxycarbide; The resulting product is free of carbide contamination but contains impurities normally present in alumina ore.

Preferably, the ratio of aluminum oxide-containing compound to carbon-containing compound is adjusted such that a 1:1±0.05 atomic ratio of carbon to oxygen is included in the charge.

The process of the present invention is carried out at any pressure greater than about 0.1 atmospheres.

It has been found that pressures below about 0.1 atmospheres do not form liquid aluminum under practical operating conditions.

On the other hand, thermodynamic considerations show that evaporation losses decrease as pressure increases above about 0.1 atm.

However, the use of high pressures requires equipment capable of handling these pressures, and it is therefore clear that the selection of pressures above about 1.0 atmospheres depends on the economical balance between energy loss due to evaporation and equipment cost.

Generally, the practical pressure for the process of the invention is a system pressure of about 0.5 to 10 atmospheres, preferably 1 to 5 atmospheres.

It will be appreciated that one embodiment of the invention described below also uses a plasma torch.

In these cases, the torch itself applies pressure due to its power density.

That is, it is recognized that the pressure directly under the torch at the reaction site can be greater than the pressure further away from the torch.

It is well known that the particular pressure and temperature utilized are interdependent, as is clear from an elementary consideration of the laws of thermodynamics.

There is a large body of literature describing the required temperatures for various pressures.

However, the exact temperature required for a given pressure will depend on the interpretation of the thermodynamic data.

However, in general, to operate at 1 atm, approximately 250
A temperature of 0'K is required.

Therefore, from a practical standpoint it is difficult to define the exact temperature required for the reaction to proceed at any given constant pressure.

Also, perhaps more importantly, specifying these specific temperatures has no practical significance.

This is because the instruments used to measure temperature in actual furnace operation utilize optical principles, and because of the presence of electrodes, the charged material cannot be seen.

The temperatures utilized in the novel process of the present invention specify that sufficient heat must be used to drive the reaction at any given constant pressure, but that too high a temperature must be avoided as the aluminum formed will evaporate from the furnace. It will be.

However, from a practical standpoint, the reduction of alumina-containing ores to make aluminum is endothermic and the reaction itself controls the temperature.

It has been found that there is a very advantageous way to carry out the process of the invention irrespective of all the principles mentioned above regarding temperature and pressure.

It has been found that precise control of the reaction can be achieved by applying the open arc to the surface of the charge to be reduced and adjusting the electric density of the arc impinging on the charge, as described below.

Electrical density per square inch of material hit by the arc is 1
It has been found that the reaction proceeds as desired if maintained between 0 and 50 kilowatts.

The reaction itself controls the temperature at higher arc densities, since the reaction absorbs heat when the arc density exceeds its minimum limit.

The term "electrical density per square inch of charge material" refers to the total power supplied to the arc (i.e. amperes x volts)
is divided by the area of the charged material hit by the arc.

When using a plasma torch, the internal power supply is ignored and only the transfer current is taken into account when calculating the electrical density.

A convenient way to measure the total area covered by the arc is to use optical instruments.

The area hit by the arc becomes incandescent and its area can be measured.

If the surface of the charging material is not flat, the area of the arc applied to the hearth can be measured without adding additional charging material.

As already mentioned, one of the requirements of the new method of the present invention is that the charge material fed to the first hot zone is not uniformly heated as in the prior art method.

For the reasons discussed above, it will be apparent that the aluminum produced in this system will flow through the feed and, if the feed is hot, this aluminum will dissolve unreacted aluminum carbide and become a carbon-contaminated product.

It has been found that a convenient method of carrying out heating in accordance with the present invention is to utilize an open arc, with the adjustable electrode being negative relative to the charge material to be reacted.

The term "open arc" refers to an arc from an electrode that is not in physical contact with the charge material to be reacted.

In this embodiment, the charge material is placed in a furnace and an open arc is applied from a suitable electrode, such as a conventional graphite electrode.

If the power of the arc is such that it produces an electrical density of 10 to 50 kilowatts per square inch of charge material impinged by the arc, preferably 25 to 35 kilowatts per square inch of the charge material, the surface of the charge material is as desired. It will be heated to temperature.

However, this condition alone cannot ensure that the charge material is not heated uniformly.

For this, the arc must be an intermittent arc,
That is, it has been found that for a given area of the feed material, it must be on for a certain amount of time and off for a certain amount of time.

This type of operation, hereinafter referred to as intermittent operation, means that a particular portion of the feed material is supplied by an open arc for 10% of the total time.
This means that ~50% is subjected to direct current electrical heating.

In one example, the charge material is arced for one minute, then arced off for two minutes, and then arced for another minute.

In a preferred embodiment of the present invention, the arc is 1/120~
Preferably, the heating is applied for 90 seconds and then turned off for an appropriate period of time so that heating occurs only for 10-50% of the total time.

It will be readily appreciated that there are many other ways to accomplish this intermittent heating than simply turning the arc on and off.

For example, multiple groups of electrodes can be used over a relatively large surface area, with each electrode turned on and off at appropriate times within the aforementioned guidelines.

Alternatively, the electrode may be left on continuously but moved over the surface of the charge material by mechanical means such that the arc hits a particular surface area 10-50% of the total time.

Similarly, the charge material can be moved in and out of the arc by mechanical means such that the electrode remains on and the arc covers a constant area 10-50% of the time.

It has been found advantageous to make the adjustable electrode negative with respect to the charge material and to use an open DC arc.

The reason for this is that the negative electrode receives less heat while emitting electrons than the anode material.

Under direct current electric arc operation with a movable negative electrode, the charge material receives most of the heat while the electrode remains cool enough to avoid excessive evaporation of the carbon.

This minimizes the opportunity for hot carbon vapor to contact the condensed aluminum product to form aluminum carbide and dissolve into the aluminum product.

It has been found that a negative graphite electrode relative to the aluminum anode can melt aluminum without adding more than 0.3% Al 4 C3 to the aluminum.

Open arcs are considered desirable.

This is because the surface temperature of the charge has the opportunity to drop rapidly during arc interruptions, and as a result of heat transfer to cooler parts of the furnace during arc interruptions, most of the charge remains at the required low temperature. It is.

During the high temperature operation mentioned above, the carbon monoxide that is formed is removed from the system while the aluminum is in a condensed state so that practically no aluminum compounds are formed in the reverse reaction.

The second step of the novel process of the invention consists in removing the condensed aluminum at a temperature such that no substantial amount of aluminum carbide is dissolved in the aluminum.

The temperature of this second stage should not exceed 1250<0>C, preferably between 670 and 1000<0>C.

One method for this is to keep a liquid pool of aluminum inside the furnace and float the feed material on top of it, heat the feed material as described above to create a condensed state of aluminum, and then bring the resulting aluminum to the temperature described above. The idea is to allow the water to flow into a liquid pool of aluminum that is maintained at

As those skilled in the art know, liquid metals are excellent conductors of heat, transferring heat from the arc and charge to areas where it is rapidly lost through the furnace walls, roof and floor, thus ensuring the necessary temperature control. Make it familiar.

Although maintaining a liquid pool of aluminum is an effective way to ensure the temperature control described above, there are other methods and therefore maintaining a liquid pool of aluminum is not an absolute requirement for the novel method of the present invention. should be understood.

For example, the action of an open arc tends to blow the formed aluminum away from the unreacted charge so that the condensed aluminum cools rapidly and cannot liquefy large amounts of aluminum carbide if it passes over the unreacted charge. It has been found that temperatures are sufficiently low.

The aluminum produced can also be removed from the unreacted feed material simply by mechanical means.

For example, a sloped bed may be used to cool the resulting condensed aluminum immediately from the reaction zone to a temperature low enough to prevent dissolution of large amounts of aluminum carbide as it passes over the unreacted feed material.

Another way to achieve the same result is to use a two-stage hearth, with the upper and lower stages of the hearth being large enough to allow the aluminum to flow from the upper to the lower stage, but so that the feed material cannot pass through. This includes connection by a group of passages.

Thus, when an arc is applied to the charge in the upper stage to form liquid aluminum, the condensed aluminum flows through the charge into the second stage of the hearth without the aluminum carbide coming into contact with it.

For the novel process of the present invention to be effective, the liquid aluminum produced must be at a temperature of about 1250° C. as it flows over the unreacted feed material.
The following temperature is required, preferably 670 to 1000°C.

On the other hand, after the condensed aluminum is drawn off from the unreacted feed material or other carbon source, it can be at any temperature since there is no unreacted feed material or carbon source and therefore no aluminum carbide to dissolve into the aluminum. .

Another important aspect of the novel method of the present invention is that since an open arc is used, a closed furnace can be used instead of one that is exposed to the atmosphere.

The use of closed furnaces is also useful from an environmental point of view since very little gas may have to be treated to remove contaminants to meet environmental standards.

Closed furnaces also allow carbon monoxide released during the process to be used as fuel.

Although it is not necessary to use a closed furnace in the novel method of the present invention for producing aluminum, the use of a closed furnace is more economical in terms of environmental protection and energy management, making the method of the present invention even more useful. Become.

As already mentioned, it is necessary to use an open arc to carry out the method of the present invention, and this open arc can be formed by using a normal graphite electrode as described above, but there is a specific example in which a plasma torch is used to obtain the open arc. is preferred.

The use of graphite electrodes provides heat at a reasonable power density and a pressurized gas effect that tends to move the aluminum formed on the charge surface away from the charge, but has the disadvantage of introducing a small amount of carbon into the product. be.

As previously mentioned, it has been found that graphite electrodes, which are negative with respect to the aluminum anode, can melt aluminum without containing more than about 0.3 weight of aluminum carbide relative to the aluminum.

However, with graphite electrodes, if the arc is extinguished, the only practical way to recreate an arc of this power density is to lower the electrode until it hits the charge material and makes electrical contact. There are also practical operational drawbacks in that .

This type of operation creates the problem of the charge material hitting the electrodes.

If too much charge material hits the electrodes, the discharge properties of the electrodes will change, interfering with the overall operation.

To avoid these problems, careful control of arc impact between the carbon or graphite electrode and the charge material must be used.

Using a plasma torch has the advantage that carbon is not included in the product and that an arc can be created even when the jet nozzle is completely removed from the vicinity of the charging material, thus avoiding the above-mentioned difficulties experienced when using ordinary graphite electrodes. be able to.

Further, even if the jet is stopped for some reason, the jet can be made again without bringing any part of the jet making device into contact with the charged material.

A further advantage of plasma jets is that, in addition to the normal tendency of the arc column to displace the product aluminum from the feed material, the jet also has a gas flow (an essential feature of plasma jet operation) that displaces the product aluminum of the arc jet. The aluminum has a greater tendency to be removed from the reaction site, so the aluminum cools rapidly and does not dissolve large amounts of unreacted feed material.

If you create another circuit and connect a second power supply between the plasma jet anode element and the hearth so that the arc column is drawn from the negative electrode to the hearth instead of from the negative electrode to the jet nozzle, use plasma jet. An even greater advantage can be seen.

Such operation results in very little current flowing through the nozzle.

Most of the current flows to the hearth. Even if the jet nozzle is far away from the feed material (e.g. 3 to 6 inches)
A very slow heating rate is obtained at the reaction site.

This provides ample opportunity for the feed material to pass under the jet without hitting the case of the jet device.

If for any reason the transfer current, ie the current from the negative electrode to the hearth, is interrupted, the internal jet power supply maintains the jet between the negative electrode and the positive jet nozzle in normal plasma jet operation.

It therefore serves as a pilot light for re-creating the jet through the second power supply to the hearth at any time without physically moving the jet relative to the hearth.

Starting and stopping of the transfer power between the negative electrode and the hearth is 60% per second
It is extremely fast as it is done in cycles.

In fact, in one preferred embodiment of using a plasma jet in the present invention, half-wave DC power (e.g. 60
(cycle half-wave direct current) is used.

Thus, in 1/2 cycle a switch occurs between the plasma torch negative internal electrode and the hearth positive.

When the voltage of the AC feed is reversed, the rectifier blocks the transfer current from the hearth back to the internal electrodes of the jet.

With this type of half-wave transition between the inner electrode of the jet and the hearth, the peak power applied to the target area, primarily the reaction site, is approximately 4 times the average power delivered to the target area.
It is understood that twice.

The heating rate of the charge material by the plasma jet is less important when the arc is not carried than when the arc is carried to the charge material.

Therefore, in the half-cycle when the arc is not carried to the feed material, the material is exposed to the relatively cold temperature of the furnace (e.g. 1200°C).
Heat can be dissipated into the wall.

It is therefore easy to understand that the very high temperature (2300°C) required for the reaction occurs only in a very thin layer where the jet hits the feed material, while the body of the feed material and its surroundings are at a much lower temperature. be done.

The high temperature area is only a small portion of one inch thick when using half wave DC jet switching.

No practical method has yet been found to perform half-wave DC switching using a simple carbon electrode.

When the arc is extinguished because the voltage returns to O, it must be re-created by some complicated method with carbon or graphite electrodes.

2 and 3 show the structure of a plasma torch used in the novel method of the invention.

In both figures, 14 designates the orifice of the plasma jet casing, 15 the casing, and 16 the cathode or radiation electrode of the plasma jet which is insulated from the casing 15 by an insulator 22.

In the conventional normal plasma jet application, the power supply 1
9 applies a negative voltage to the electrode 16 with respect to the nozzle 14 and the casing 15.

Electrons are emitted from the tip of the electrode 16, and the force of the gas between the nozzle and the electrode tip suppresses direct discharge between the electrode 16 and the nozzle.

Instead, the electrons flow out and then return to nozzle 1.
4, the jet becomes a pencil-shaped jet with a sharp tip and is unrelated to any other part of the anode surface.

In other words, this jet exists and is held without going around any other anode surface.

Now referring to FIG. 2, if electrode 16 and other conductive surface 1
When a second power supply is connected between 8 and another DC voltage (for example 100 volts) is connected from this supply 20 through switch 21, the arc is switched and the voltage between electrode 16 and nozzle 1 is
4 instead of flowing between electrode 16 and target area 18.

If the charge material 17 is within the target area of this transition arc, it heats up quickly and effectively and receives most of the energy imparted to the arc.

Under this mode of operation using the second power supply 20, the charge material is heated very effectively and quickly if a simple conventional plasma torch is brought into the vicinity of the charge material.

FIG. 3 shows how half-wave switching is provided.

Also in this case, when the second power supply devices 23 and 24 do not supply power between the electrode 16 and the material 1T, the power supply 19
maintains the arc.

The alternating current voltage through the transformer 23 passes current through the rectifier 24 to the hearth 18 and the charging material 1γ to the electrode 1.
If the direction is such that 6 is negative, then during that half cycle, current is sent from the negative electrode 16 towards the charge material, imparting heat to the charge material.

If the alternating current voltage across transformer 23 is reversed such that electrode 16 is positive with respect to hearth 18, rectifier 24 blocks the passage of current and arc transfer ceases.

In this case, the arc returns to the shape of a normal plasma jet drawn between the electrode 16 and the nozzle 14 and maintained by the power supply 19.

As already mentioned, the advantage of this type of arc switching is that the surface of the charged material is heated to a sufficiently high temperature (e.g. 2300°C) and the reaction between alumina and carbon proceeds to form condensed aluminum and carbon monoxide. The fact is that in the opposite half of the AC cycle, which blocks the passage of current, the feed material is not heated but radiates heat to a temperature of around 1200°C.

Therefore, the interior of the charged material is relatively low temperature, an essential condition for preventing carbide from being incorporated into the manufactured aluminum.

Similarly, in the mode of arc transfer, the surrounding feed material particles that are not impacted by the arc are transferred to the four regions where the produced aluminum is held until removal, where aluminum carbide is imparted to the aluminum as the aluminum passes across them. It does not heat up to a sufficiently high temperature.

The present invention will be explained below with reference to Examples.

Example 1 A furnace was constructed to allow electric arc heating in a vacuum or controlled atmosphere.

A steel furnace body 1 with a lid 2, a viewing tube 3 and an inspection tube 4
and 5 (not used in this example).

Bubble alumina castable refractories 6 and carbon beds 7 provide thermal insulation.

A graphite crucible 8 was connected through a graphite rod 9 to the positive terminal of a direct current source.

The negative electrode 10 is made of graphite and has a non-conductive vacuum ground 1.
1 was electrically isolated from the furnace lid.

The electrode 10 was vertically adjustable by a screw mechanism 12.

- A vacuum line (not shown) from the furnace lid 2 was connected to a vacuum pump via a bag filter to remove carbon oxides.

First, the furnace was heated by applying an arc of 4 KW power at a reduced pressure of 15"Hg below atmospheric pressure, or about 1/2 atmosphere.

This arc struck an area approximately V4" diameter above the crucible at bar 9.

443 grams of molten aluminum was added when the crucible was heated to a non-glossy glow after the arc was turned off.

This aluminum was heated to about 1000° C. by applying an arc for several minutes.

A14C358,55/pair 41.1 metallurgical grade Al2
One approximately 8 g pellet made by cold pressing the O3 ratio mixture with a 5 starch binder was skimmed of the aluminum and then floated on top of the molten aluminum pool.

This pellet was placed directly under the negative electrode.

The pressure of the system was reduced to 8-10//Hg below atmospheric pressure.

An arc of 30V and 500 amps was applied for 30 seconds during which time the pellets were observed to react and form aluminum and coalesce with the starting pool.

After stopping the arc and returning the furnace to atmospheric pressure by flowing arcon through the sight tube, removing the sight glass 13 and skimming the pool to expose the NO1 oxide melt, two more pellets were placed directly under the negative electrode. Floated on top of the pool.

The temperature of the pool was approximately 1100°C.

Return the viewing glass and lower the system pressure by 8 to 10"H below atmospheric pressure.
The temperature was lowered to below g, and a 15 KW arc was applied again to cover the intersection between the pellet and the metal pool.

The arc target area was approximately 3/4" in diameter.

The arc was applied for 60 seconds, during which time aluminum was created on the exposed surface of the pellet at the intersection of the pellet and the starting pool until most of the pellet was consumed and the formed aluminum coalesced with the molten pool.

This circulation process was repeated until 83 g of the charge material had been reacted.

In no case was the arc applied for more than 90 seconds.

What is arc and arc for the operation of charging raw materials into the furnace?
It was set at minute intervals.

The melt pool was kept at 100°C to 1250°C throughout this experiment.

The system pressure was 4"-10"Hg below atmospheric pressure.

After solidifying, I took out the metal and weighed it, it was 478.
g, which indicated that aluminum 35.9 was produced by charging the Al2O3/Al4C3 mixture of 83I.

The surface of the molten pool directly under the arc was undisturbed at the end of the experiment.

These three undisturbed chunks of metal are Al4
Analyzed for C3 content, 0.48 weight cake and 0.48 weight cake, respectively.
It was found that the amount of Al 4 C3 was 48% by weight and 0.28% by weight.

The aluminum metal produced was much purer than that produced by conventional single-furnace operations.

Example 2 The same furnace as in Example 1 was used, except that the pressure was reduced from the inspection tube 4 instead of from the lid.

Therefore, the viewing glass was left in place during the experiment.

61.2wt Al4C3 and 38.8wt Al2
244 g of the feed material having the composition O3 (compressed into pellets without added starch) were reacted in 33 cycles.

The arc application time did not exceed 60 seconds even in the case of a fall.

The minimum delay time between arc applications was 2 minutes.

The arc strength during the first 27 cycles was approximately 12°5 KW.

The cumulative arc application time was 0.459 hours.

The experimental time was 1.8 hours.

The arc was applied for a maximum of 60 seconds, but a rule was adopted to stop the arc within a shorter time if the charged materials had completely reacted.

The surface temperature of the melt pool was 823<0>C to 1180<0>C even in the case of collapse except for the last 6 arc applications.

In some of the last 6 operations the power is 21-22KW
The feed material, which had apparently remained unreacted in the previous cycle, was completely reacted.

The highest temperature of the product pool observed after these high power applications was 1320°C.

The system pressure during the experiment was 6-11"Hg below atmospheric pressure.

The weight of the initial aluminum pool was 515g.

Total aluminum recovered was 617 grams and net recovery of metal produced was 1029 grams.

Analysis of the aluminum produced showed that it contained only 2 parts by weight of aluminum carbide.

Example 3 This example shows how to practice the invention without combining the charge with a liquid aluminum pool.

This embodiment will be explained using the plasma arc shown in FIG. 2 with reference to FIG.

The furnace has an airtight shell 25 and a rotating conductive hearth 18 made of graphite.
, has a connecting post 26 that conducts current to a brush 27 that engages the hearth 18 and leads to the positive terminal of the DC power supply 20.

The negative terminal of the power supply 20 is connected to the internal electrode 16 of the plasma arc torch.

Further, the negative terminal of the power supply 19 is connected to the electrode 16, and the positive terminal of the power supply is connected to the casing 15 of the plasma torch.

An auxiliary hearth 28 also rotates with the hearth 18, and is made of an alumina refractory shaped to receive the metal produced by the reaction of the charge material under the plasma jet.

The hearth rotates at a rate of 0.2 revolutions per minute.

The casing 15 is offset from the center of the hearth so that as the hearth rotates, the charge passes under the arc and the arc is intermittently applied to the charge.

The feed material nodules contain alumina, aluminum carbide, carbon, furnace condensate and other carbon from this process.
It is made from a composition consisting of an aluminum compound, and a comprehensive analysis of this charge material shows an atomic ratio of carbon to oxygen of 1:1.

In this example, the charge consisted of furnace condensate with the following analysis: 108 pounds of aluminum, 32 pounds of oxygen, 12 pounds of carbon, plus 204 pounds of alumina, and 84 pounds of carbon.

The composite final charge also has a 1:1 atomic ratio of carbon to oxygen as analyzed below.

Aluminum 216 pounds Oxygen 128 pounds Carbon 96 pounds This final charge is made into nodules or pellets.

These feed material pellets 17 are fed to a raw material supply chute 29
is introduced into the hearth 18 by.

Power supplies 19 and 20 are activated to bring the torch casing within approximately 6 inches of the hearth and allow the arc to be carried from the torch to the charge pellets.

In other words, the arc strikes the feed material pellets in a wide arc pattern that is clearly distinguishable from the narrow arc pattern seen when the jet is operated purely plasma-wise without arc transfer.

As the hearth rotates and the pellets pass under the electrical charge, the reaction creates a shiny liquid surface on each pellet struck by the arc.

This liquid flows over the rim of bed 18 into a sump formed between hearths 18 and 28 and forms a viscous product mass 30.

The carbon monoxide produced in the reaction is removed from the furnace through tube 31.

The furnace is operated at a pressure of substantially 1 atmosphere.

Hearth 18 is controlled at approximately 1000°C.

Approximately 85 g of the aluminum content added to the furnace with feed pellets 17 is recovered in the viscous mass 30 and the remainder is evaporated and carried away by the carbon monoxide escaping in the exhaust pipe 31.

This carried aluminum is captured as furnace condensate by simple cooling and filtration and returned to the feed preparation operation for circulation with the new feed.

Analysis of the viscous mass 30 showed that the aluminum contained 3% aluminum carbide.

After the auxiliary furnace 28 is filled with the products of the plasma reaction on the feed material 17, the plasma jet is moved to impinge on the melt 30 and the furnace casing is opened at 32 to allow air to enter.

Continuing the rotation of the furnace, the action of the arc carried by the plasma torch reverts the mass 30 to a liquid state, some air is carried along with this arc jet, and after 2-3 revolutions of the hearth the carbide content is reduced to 30%. Effective decarburization is performed to reduce the melt to a level where it flows at approximately 900'C.

Residues consisting of alumina, aluminum carbide, and aluminum are skimmed from pool 30 and removed from the furnace for recycling as part of the feed pellet composition along with the furnace condensate.

Approximately 60% of the product 30% by weight is aluminum carbide 0
．． Recovered as less than 2% pourable aluminum.

The melt is removed from the furnace by tilting the furnace in the conventional manner.

The torch is then returned to position to act on the feed material pellets 17 introduced for continuous operation.

Example 4 It should be understood that the decarburization reaction does not necessarily have to be carried out inside a furnace as described in Example 3.

Alternatively, the following method can be used.

Example 3 of making melt 30 from feed material pellets 17
A secondary torch (not shown) is provided to maintain the melt 30 in a liquid state without introducing air into the furnace.

When the product 30 has filled the chamber provided for it, it is removed at high temperature, i.e. approximately 1800° C., into a container outside the furnace.

This product, taken directly from the furnace, contains up to about 5 folds of aluminum carbide.

It will be understood from the above examples that the method of the invention is also applicable to aluminum and oxygen compounds other than Al2O3.

Thus, the term "aluminum oxide" is intended to include any compound of oxygen and aluminum (eg, aluminum tetraoxycarbide).

"Aluminum-carbon-containing compound" also includes aluminum carbide.

The only requirement for the feedstock is a carbon to oxygen atomic ratio of 1=1±
The point is 0.05.

In this connection, it is also noted that the furnace charge may consist of alumina and carbon, but this is not preferred.

It is known that when alumina and carbon react, at least one of the intermediate products is an aluminum carbon compound such as aluminum carbide.

Optimal conditions for making aluminum carbon compounds are not necessarily the same as aluminum production conditions.

It is therefore preferable to carry out the process of the invention in two separate steps when using only carbon as the reducing agent.

The first step is the reaction of alumina and carbon to produce an aluminum-carbon containing compound, as is well known to those skilled in the art, and the second step is the reaction of alumina and carbon to produce an aluminum-carbon containing compound, and the second step is the reaction of the feedstock with an atomic ratio of carbon to oxygen of 1:1. The product of the first step is charged with additional aluminum oxide and carbon.

[Brief explanation of drawings]

Figure 1 of the attached drawings is a sectional view of one of the furnaces used to carry out the method of the present invention, and Figure 2 shows an example of a plasma arc device used to carry out the method of the present invention. , FIG. 3 is a block diagram of yet another type of plasma arc device, and FIG. 4 shows the configuration of a furnace suitable for carrying out the method of the present invention using the plasma arc device shown in FIG. It is a model diagram.

Claims (1)

[Claims] 1(a) At least one selected from the group consisting of carbon, carbon-containing aluminum compounds, and mixtures thereof.
applying an open arc to a part of the surface of a charge material consisting of a seed material and aluminum oxide; (b) limiting the heating effect of the arc by controlling the time and applying the arc to a certain part of the surface of said charge material; , thus keeping the aluminum formed by the reaction of the charge materials in liquid form, but only heating a small portion of the charge material in the reaction zone to the reaction temperature, - 10,000,000,000 % of the charge material in the reaction zone. (C) the liquid aluminum formed under the arc is allowed to flow from the arc over the unreacted portions of the charge and is collected; Carbon thermodynamic method for producing aluminum from.