CA1103613A - Aluminum purification - Google Patents
Aluminum purificationInfo
- Publication number
- CA1103613A CA1103613A CA283,490A CA283490A CA1103613A CA 1103613 A CA1103613 A CA 1103613A CA 283490 A CA283490 A CA 283490A CA 1103613 A CA1103613 A CA 1103613A
- Authority
- CA
- Canada
- Prior art keywords
- aluminum
- electrolyte
- porous
- molten
- process according
- 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.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/24—Refining
Abstract
Abstract of the Disclosure A process for purifying aluminum alloys comprises providing molten aluminum alloy in a container having a porous wall therein capable of containing molten aluminum in the container and being permeable by the molten electrolyte. Aluminum is electrolytically transported through the porous wall to a cathode thereby substantially separating the aluminum from alloying constituents.
Description
~10;~6~3 This invention relates to a method for purifying aluminum alloys, and more particularly to a method for electrolytically purifying aluminum alloys such as aluminum-silicon alloys.
Alùminum-silicon alloys have been conventionally prepared by adding to commercial grade aluminum a desired amount of silicon, normally prepared independently, consequently resulting in a relatively high priced alumin~m alloy product. In other processes, the aluminum-silicon alloys are prepared directly from alumin~silica ore. For example, Seth et al U.S.
Patent 3,661,562 disclose that aluminum-silicon alloy can be prepared in a blast furnace wherein coke or other suitable carbonaceous material is fed into one reaction zone and a mixture of coke and alumina-silica ore is fed into a second reaction zone. Hot carbon monoxide gases produced by combustion of the coke are introduced into the second reaction for reducing the alumina-silica ore. However, such or similar methods of producing aluminum-silicon alloys often result in the alloy having very high silicon and iron contents which normally have to be reduced or lowered for the alloy to have commercial utility. One method of keeping the iron content low in such alloys is to use alumina-silica containing ores with low iron content.
Another method involves the steps of lowering the iron content bv physieal beneficiation prior to the reduction process. However, because of the unfavorable economics and extra steps involved, it is preferred to start with an alumina-silica containing ore having a high iron content, which, of course, results in an alloy being high in silicon and iron as noted above and the need for purification thereof.
Purification of aluminum alloys using electrolytic cells is disclosed in the prior art. For example, Hoopes U.S~ Patent 673,364 discloses that if impure aluminum, in a melted state, is used as an anode in an electrolytic cell, especially one in which the electrolyte contains fused aluminum fluoride and a fluoride of a metal more electropositive than aluminum, pure aluminum will be deposited at the cathode and fluorine is set free at the anode when current is passed through the cell.
11~3~3 3 In another method of purifying aluminum-silicon alloys, Sullivan et al in U.S. Patent 3,798,140 disclose electrolytically producing aluminum and silicon from aluminum-silicon alloys using a NaCl, KCl and AlC13 or AlF3 electrolyte. The aluminum-silicon alloy is provided as an anode in a perforated graphite anode crucible. A perforated graphite screen is provided around a cathode and around an aluminacrucible to prevent any fine silicon liberated during the electrolysis from floating into the cathode department. However, production of purified aluminum in this process is limited by its effective current density which is only 150 to 200 amps/ft in the chloride-fluoride electrolyte.
The present invention overcomes the problems in the prior art by separating aluminum from alloying constituents such as silicon and iron and the like in a highly economical manner.
An object of the present invention is to purify aluminum alloys.
Another object of the present invention is to purify aluminum alloys containing high levels of alloying constituents such as silicon, iron and the like.
Yet another object of the present invention is to provide an electrolytic method of purifying aluminum.
Yet another object of the present invention is to produce high purity aluminum.
These objects are accomplished by the process of the invention which generally comprises the following steps: (a) providing the aluminum alloy in a molten state in a container having a porous wall there-in, said porous wall being capable of containing molten aluminum in the container, the porous wall being permeable by a molten electrolyte; and (b) Plectrolytically transferring aluminum through said porous wall to a cathode in the presence of the electrolyte, thereby substantially purifying said aluminum by separating it from its alloying constituents. This is characterized in the facts that tl) said porous wall is a porous membrane,
Alùminum-silicon alloys have been conventionally prepared by adding to commercial grade aluminum a desired amount of silicon, normally prepared independently, consequently resulting in a relatively high priced alumin~m alloy product. In other processes, the aluminum-silicon alloys are prepared directly from alumin~silica ore. For example, Seth et al U.S.
Patent 3,661,562 disclose that aluminum-silicon alloy can be prepared in a blast furnace wherein coke or other suitable carbonaceous material is fed into one reaction zone and a mixture of coke and alumina-silica ore is fed into a second reaction zone. Hot carbon monoxide gases produced by combustion of the coke are introduced into the second reaction for reducing the alumina-silica ore. However, such or similar methods of producing aluminum-silicon alloys often result in the alloy having very high silicon and iron contents which normally have to be reduced or lowered for the alloy to have commercial utility. One method of keeping the iron content low in such alloys is to use alumina-silica containing ores with low iron content.
Another method involves the steps of lowering the iron content bv physieal beneficiation prior to the reduction process. However, because of the unfavorable economics and extra steps involved, it is preferred to start with an alumina-silica containing ore having a high iron content, which, of course, results in an alloy being high in silicon and iron as noted above and the need for purification thereof.
Purification of aluminum alloys using electrolytic cells is disclosed in the prior art. For example, Hoopes U.S~ Patent 673,364 discloses that if impure aluminum, in a melted state, is used as an anode in an electrolytic cell, especially one in which the electrolyte contains fused aluminum fluoride and a fluoride of a metal more electropositive than aluminum, pure aluminum will be deposited at the cathode and fluorine is set free at the anode when current is passed through the cell.
11~3~3 3 In another method of purifying aluminum-silicon alloys, Sullivan et al in U.S. Patent 3,798,140 disclose electrolytically producing aluminum and silicon from aluminum-silicon alloys using a NaCl, KCl and AlC13 or AlF3 electrolyte. The aluminum-silicon alloy is provided as an anode in a perforated graphite anode crucible. A perforated graphite screen is provided around a cathode and around an aluminacrucible to prevent any fine silicon liberated during the electrolysis from floating into the cathode department. However, production of purified aluminum in this process is limited by its effective current density which is only 150 to 200 amps/ft in the chloride-fluoride electrolyte.
The present invention overcomes the problems in the prior art by separating aluminum from alloying constituents such as silicon and iron and the like in a highly economical manner.
An object of the present invention is to purify aluminum alloys.
Another object of the present invention is to purify aluminum alloys containing high levels of alloying constituents such as silicon, iron and the like.
Yet another object of the present invention is to provide an electrolytic method of purifying aluminum.
Yet another object of the present invention is to produce high purity aluminum.
These objects are accomplished by the process of the invention which generally comprises the following steps: (a) providing the aluminum alloy in a molten state in a container having a porous wall there-in, said porous wall being capable of containing molten aluminum in the container, the porous wall being permeable by a molten electrolyte; and (b) Plectrolytically transferring aluminum through said porous wall to a cathode in the presence of the electrolyte, thereby substantially purifying said aluminum by separating it from its alloying constituents. This is characterized in the facts that tl) said porous wall is a porous membrane,
(2) ~he electrolyte comprises at least one salt selected from the group consisting of aluminum fluoride and aluminum ch~oride and at least one salt 1~36i3 selected from the group consisting of sodium, potassium, lithium, manganese and magnesium halide, and (3) the transferring is effected at a current density of greater than 500 amps/ft2 and a voltage range of 1 to 5 volts and with the electrolyte being maintained within a temperature range of 675 to 925C
In the drawings illustrating the invention:-Figure 1 shows in cross section a form of apparatus suitable forpractising the process of the invention; and Figure 2 is a schematic of an apparatus which can be operated on a continuous basis to provide purified aluminum in accord with the process of the invention.
Aluminum alloy as referred to herein is an alloy containing typically not more than 99.9 wt.% aluminum. However, alloys which can be purified in accordance with the present invention can contain large amounts of impurities. For example, the aluminum alloys can contain as much as 50 wt.% Si. Also, the alloys can contain large amounts of Fe, for example, 20 wt.%. In addition, other alloying constituents normally associated with aluminum, e.g. Ti, can usually be re ved in accordance with the present invention. Also, the alloying constituents can be reduced to a very low level. That is, the present invention can be useful in providing high purity aluminum, even when the starting material is relatively pure.
By reference to Figure 1, there is shown an electrolytic cell configuration 10 in which an aluminum alloy can be purified substantially in accordance with the present invention. The cell comprises an outer container 20 which, at least a portion thereof, is constructed of graphite or a like material which can act as a cathode in the cell. For example, the cell ~36:~3 may be constructed such that only bottom 21 or a portion thereof may serve as a cathode. Electrolytic cell 10 further comprises a second container 30 in communication with the cathode referred to by means of electrolyte 24. Container 30 serves as a vessel, as shown in Figure 1, in which aluminum alloy 32 is provided in molten form. Container 30 should be constructed of a material resistant to attack by molten aluminum alloy 32 and electrolyte 24 and must have a wall or a portion of a wall thereof permeable or penetrable by an ion containing one or more aluminum atoms which can be electrolytically transferred or transported through the wall to the cathode.
Container 30 can be constructed from a conductive or non-conductive porous material. If container 30 is constructed from non-conductive porous material, an anode has to be projected into aluminum alloy 32 in order that the aluminum can be electro-lytically transported to the cathode. If container 30 is made from a conductive, porous material, then the container can act as the anode as shown in Figure 1.
With respect to the permeable wall, it is preferred that such material be a carbonaceous material when separation of constituents such as silicon, iron and the like from aluminum is desired. However, it is within the purview of the present invention to select other materials permeable by an ion contain-ing one or more aluminum atoms but which restricts the passage of constituents such as those just mentioned. The preferred carbo-naceous material suitable for use in the present invention is porous carbon or porous graphite having a maximum average pore diameter of 635 microns. An average pore diameter in the range of 5 to 425 microns can be used, with a preferred diameter being in the range of 20 to 220 microns. Porous carbon, obtainable from Union Carbide Corporation, Carbon Products Division, Niagara Falls, ~ew York, and referred to as PC-25 having an effective porosity of about 48% and an average pore diameter of about 120 microns has been found to be quite suitable. Porous carbon or other porous material used in this application is further char-acterized by being impenetrable or impermeable to molten aluminum and alloying constituents thereof in the absence of electric current being passed through the cell but permeable by molten salt used as the electrolyte.
With respect to the pore size, it should be noted that its size can vary depending on the amount of head, the tempera-ture of the molten aluminum, and the wettability of the porous member. Also, the electrolyte employed as well as the alloying constituents can affect the size of the pore which will be impenetrable or impervious to molten aluminum and alloying constituents thereof in the absence of electric current being passed through the cell. Thus it will be seen that in certain instances porous members having pores therein having a larger maximum pore diameter or having an average pore diameter larger than that indicated in the range above can be used in the instant invention and will be impermeable to the molten aluminum.
Electrolyte 24 is an important aspect of the present invention. The electrolyte should comprise an aluminum fluoride or chloride and at least one salt selected from the group con-sisting of lithium, potassium, sodium, manganese and magnesium halide with a preferred electrolyte comprising aluminum fluoride, lithium chloride and potassium chloride. The use of lithium chloride permits the use of high current densities without adversely affecting the operation of the cell as by heat genera-tion due to high resistance encountered in the electrolyte. The potassium chloride aids in the coalescence of purified aluminum 26 deposited at the cathode. That is, when lithium chloride is used without potassium chloride, aluminum deposited at the cathode can remain in divided particle form making its recovery 1~3~i3 from the cell difficult.
The electrolyte can comprise, by weight percent, 5 to 95~ LiCl, 4 to 70~ KCl and 1 to 25% AlF3. Preferably, the composition is 38 to 90% LiCl, 8 to 50% KCl and 2 to 12% AlF3.
AlC13 or MgC12 can be used instead of AlF3; NaCl can be used instead of KCl; and LiF can be used instead of LiCl but on a less preferred basis. It will be appreciated that combinations of the above salts can also be used but again on a less preferred basis.
The temperature of the electrolyte can affect the overall economics of the process. If the electrolyte temperature is too low, the purified aluminum can be difficult to collect.
Also, low temperatures can result in low electrolyte conductivity and consequently low cell productivity. Too high operating temperatures can diminish the useful life of the anode and cathode as well as cause vaporization of the salt. Thus, while the ternperature can range from 675 to 925C, a preferred tempera-ture is in the range of 700 to 850C.
In the process of the present invention, the cell can be operated at high current densities resulting in high yields of purified aluminum. Also, the cell can be operated at high current densities without encountering high resistances in the electrolyte and the resulting generation of undesirable heat and its attendant problems. The cell can be operated at a voltage of 1 to 5 volts and a current density in the range of 200 to 3000 amps/ft2, or in certain cases higher, with a preferred voltage being in the range of 1.5 to 4.5 volts and a minimum current density which should not be less than 200 amps/lt2 and preferably at least 300 amps/ft2.
In operation of the electrolytic cell, molten electro-lyte 24 is provided in container 20 and preferably kept at atemperature in the range of 700 to 850C. Aluminum alloy in molten form is placed in container 30. An electrical current is ~36~3 passed from the anode to the cathode and aluminum is transported by virtue of the electrolyte through the porous carbon to the cathode where it is deposited and collected. The porous wall restricts the passage of alloying constituents such as silicon and iron and other residues and hence prevents the contamination of the purified aluminum under these operating conditions. If container 30 is constructed from a conductive, porous material, purified aluminum 26 should not be permitted to accumulate in container 20 until it touches container 30 since this would short-circuit the cell.
It will be appreciated by those skilled in the art that a number of anode containers, such as shown in Figure 1, may be positioned within the cathode or outer container 20 to increase the production of the cell. Also, it will be appreciated that other configurations employing the permeable membrane may be used. For example, container 20 may be constructed from a non-conductive material and the porous membrane may be used to divide the container, providin~ an area to contain the impure molten aluminum 32 and another area or space in which to provide the electrolyte. The aluminum may be purified by providing an anode in the impure aluminum and a cathode in the electrolyte and passing electric current therebetween.
By reference to Figure 2, there is shown an alternate embodiment of the electrolytic cell which can be operated on a continuous basis. The cell 10' comprises outer container 20' constructed of a material resistant to attack by purified alumi-num 26 or molten electrolyte 24 and a second container 30' which serves as a vessel in which aluminum alloy 32 is provided in molten form. The cell has a cathode 22 which projects into 3Q electrolyte 24. Underneath cathode 22, a receptacle 23 is positioned to receive purified aluminum 26 precipitated or deposited at the cathode. Receptaclè 23 has an outlet 27 through ~1~36~3 whi~h purified aluminum 26 can be removed continuously at a rate substantially commensurate with the rate of deposition thereof at cathode 22. Container 30', in the embodiment illustrated in Figure 2, has a porous wall 29 permeable or penetrable by an ion containing one or more aluminum atoms which can be electrolyti-cally transported through wall 29 to the cathode. An outlet 34 is provided so that residues or alloying constituents 36 remaining after aluminum has been separated therefrom can be removed. In the particular embodiment illustrated in Figure 2, side 29 of container 30' serves as the anode of the cell.
In the cell of the present invention, the distance "x"
(shown in Figure 2) between the anode and cathode should be closely controlled in order to aid in minimizing the voltage drop across the cell. Thus, the distance "x" between the cathode and anode should not be more than 1.0 inch and preferably not more than 0.5 inch.
The present invention is advantageous in removing silicon and iron and the like in aluminum alloys to a very low level. In addition, the present invention is capable of separating magnesium and the like from aluminum. That is, if the aluminum alloy to be purified contains magnesium or the like, i.e. less noble than aluminum, such included metal can pass through the porous membrane but is not normally deposited at the cathode. Magnesium and the like are normally dissolved in the bath and thus, are not prone to contaminate the purified aluminum deposited at the cathode.
The present invention, as well as providing purified aluminum, is advantageous in that it can provide high purity silicon. In addition, ferro-silicon compounds can be recovered since these materials do not pass through the porous membrane.
Furthermore, while it has been noted hereinabove that the inven-tion was particularly useful with respect to purifying aluminum ~3~3 alloys obtained from the high silicon ores, it is also useful in purifying aluminum scrap containing iron and silicon materials.
Also, the invention can be used to purify aluminum used in clad products, e.g. brazing alloy.
The following examples are still further illustrative of the invention.
Example I
An aluminum alloy containing 11.4 wt.% silicon and 0.21 wt.% iron was provided in molten form in an anode section of a cell~ A molten electrolyte consisting of 5 wt.% aluminum fluoride and 95% lithium chloride was used. The electrolyte temperature was 750C. The anode section was fabricated from porous carbon having an average pore diameter of 120 microns and a porosity of 48~. The distance between the anode and cathode was 0.4 inch.
An electric current, amperage 125 and voltage 4.2 at a current density of 650 amps/ft2 was passed across the cell. Purified aluminum collected at the cathode contained only 0.011 wt.%
silicon and 0.05 wt.~ iron.
Example II
The aluminum alloy of Example I was purified as in Example I except the electrolyte contained 5 wt.% AlF3, 10 wt.~
KCl and 85 wt.% LiCl. The cell was operated at 4.2 volts and a current density of about 700 amps/ft2. The purified aluminum collected at the cathode contained 0.009 wt.% Si and 0.015 wt~
Fe.
Example III
A clad product having a core of aluminum alloy 3105 (0.5% Mn, 0.5% Mg, remainder essentially Al) and a cladding on both sides thereof (composition being 9.75% Si, 1.5% Mg, remain-der essentially Al) was melted to provide an alu~inum alloy composition having 3.10% Si, 0.45% Fe, 0.11% Cu, 0.16% Mn and 0.56% Mg. For purposes of purification, the melt was provided in 1~3~3 an anode section and treated as in Example I except the electro-lyte composition was 10% AlF and 90% LiCl and the current density was 500 amps/ft2. Analysis of the purified aluminum showed only 0.002% Si, 0.004% Fe, 0.001% Cu, 0.004% Mn and 0.0003~ Mg, thus providing substantially 99.99% aluminum.
From the above examples, it can be seen that silicon and iron content of the aluminum were reduced rather signifi-cantly. Further, it can be seen that the invention is capable of producing high purity aluminum metal.
Various modifications may be made in the invention without departing from the spirit thereof, or the scope of the claims, and therefore, the exact form shown is to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are imposed by the prior art, or are specifically set forth in the appended claims.
In the drawings illustrating the invention:-Figure 1 shows in cross section a form of apparatus suitable forpractising the process of the invention; and Figure 2 is a schematic of an apparatus which can be operated on a continuous basis to provide purified aluminum in accord with the process of the invention.
Aluminum alloy as referred to herein is an alloy containing typically not more than 99.9 wt.% aluminum. However, alloys which can be purified in accordance with the present invention can contain large amounts of impurities. For example, the aluminum alloys can contain as much as 50 wt.% Si. Also, the alloys can contain large amounts of Fe, for example, 20 wt.%. In addition, other alloying constituents normally associated with aluminum, e.g. Ti, can usually be re ved in accordance with the present invention. Also, the alloying constituents can be reduced to a very low level. That is, the present invention can be useful in providing high purity aluminum, even when the starting material is relatively pure.
By reference to Figure 1, there is shown an electrolytic cell configuration 10 in which an aluminum alloy can be purified substantially in accordance with the present invention. The cell comprises an outer container 20 which, at least a portion thereof, is constructed of graphite or a like material which can act as a cathode in the cell. For example, the cell ~36:~3 may be constructed such that only bottom 21 or a portion thereof may serve as a cathode. Electrolytic cell 10 further comprises a second container 30 in communication with the cathode referred to by means of electrolyte 24. Container 30 serves as a vessel, as shown in Figure 1, in which aluminum alloy 32 is provided in molten form. Container 30 should be constructed of a material resistant to attack by molten aluminum alloy 32 and electrolyte 24 and must have a wall or a portion of a wall thereof permeable or penetrable by an ion containing one or more aluminum atoms which can be electrolytically transferred or transported through the wall to the cathode.
Container 30 can be constructed from a conductive or non-conductive porous material. If container 30 is constructed from non-conductive porous material, an anode has to be projected into aluminum alloy 32 in order that the aluminum can be electro-lytically transported to the cathode. If container 30 is made from a conductive, porous material, then the container can act as the anode as shown in Figure 1.
With respect to the permeable wall, it is preferred that such material be a carbonaceous material when separation of constituents such as silicon, iron and the like from aluminum is desired. However, it is within the purview of the present invention to select other materials permeable by an ion contain-ing one or more aluminum atoms but which restricts the passage of constituents such as those just mentioned. The preferred carbo-naceous material suitable for use in the present invention is porous carbon or porous graphite having a maximum average pore diameter of 635 microns. An average pore diameter in the range of 5 to 425 microns can be used, with a preferred diameter being in the range of 20 to 220 microns. Porous carbon, obtainable from Union Carbide Corporation, Carbon Products Division, Niagara Falls, ~ew York, and referred to as PC-25 having an effective porosity of about 48% and an average pore diameter of about 120 microns has been found to be quite suitable. Porous carbon or other porous material used in this application is further char-acterized by being impenetrable or impermeable to molten aluminum and alloying constituents thereof in the absence of electric current being passed through the cell but permeable by molten salt used as the electrolyte.
With respect to the pore size, it should be noted that its size can vary depending on the amount of head, the tempera-ture of the molten aluminum, and the wettability of the porous member. Also, the electrolyte employed as well as the alloying constituents can affect the size of the pore which will be impenetrable or impervious to molten aluminum and alloying constituents thereof in the absence of electric current being passed through the cell. Thus it will be seen that in certain instances porous members having pores therein having a larger maximum pore diameter or having an average pore diameter larger than that indicated in the range above can be used in the instant invention and will be impermeable to the molten aluminum.
Electrolyte 24 is an important aspect of the present invention. The electrolyte should comprise an aluminum fluoride or chloride and at least one salt selected from the group con-sisting of lithium, potassium, sodium, manganese and magnesium halide with a preferred electrolyte comprising aluminum fluoride, lithium chloride and potassium chloride. The use of lithium chloride permits the use of high current densities without adversely affecting the operation of the cell as by heat genera-tion due to high resistance encountered in the electrolyte. The potassium chloride aids in the coalescence of purified aluminum 26 deposited at the cathode. That is, when lithium chloride is used without potassium chloride, aluminum deposited at the cathode can remain in divided particle form making its recovery 1~3~i3 from the cell difficult.
The electrolyte can comprise, by weight percent, 5 to 95~ LiCl, 4 to 70~ KCl and 1 to 25% AlF3. Preferably, the composition is 38 to 90% LiCl, 8 to 50% KCl and 2 to 12% AlF3.
AlC13 or MgC12 can be used instead of AlF3; NaCl can be used instead of KCl; and LiF can be used instead of LiCl but on a less preferred basis. It will be appreciated that combinations of the above salts can also be used but again on a less preferred basis.
The temperature of the electrolyte can affect the overall economics of the process. If the electrolyte temperature is too low, the purified aluminum can be difficult to collect.
Also, low temperatures can result in low electrolyte conductivity and consequently low cell productivity. Too high operating temperatures can diminish the useful life of the anode and cathode as well as cause vaporization of the salt. Thus, while the ternperature can range from 675 to 925C, a preferred tempera-ture is in the range of 700 to 850C.
In the process of the present invention, the cell can be operated at high current densities resulting in high yields of purified aluminum. Also, the cell can be operated at high current densities without encountering high resistances in the electrolyte and the resulting generation of undesirable heat and its attendant problems. The cell can be operated at a voltage of 1 to 5 volts and a current density in the range of 200 to 3000 amps/ft2, or in certain cases higher, with a preferred voltage being in the range of 1.5 to 4.5 volts and a minimum current density which should not be less than 200 amps/lt2 and preferably at least 300 amps/ft2.
In operation of the electrolytic cell, molten electro-lyte 24 is provided in container 20 and preferably kept at atemperature in the range of 700 to 850C. Aluminum alloy in molten form is placed in container 30. An electrical current is ~36~3 passed from the anode to the cathode and aluminum is transported by virtue of the electrolyte through the porous carbon to the cathode where it is deposited and collected. The porous wall restricts the passage of alloying constituents such as silicon and iron and other residues and hence prevents the contamination of the purified aluminum under these operating conditions. If container 30 is constructed from a conductive, porous material, purified aluminum 26 should not be permitted to accumulate in container 20 until it touches container 30 since this would short-circuit the cell.
It will be appreciated by those skilled in the art that a number of anode containers, such as shown in Figure 1, may be positioned within the cathode or outer container 20 to increase the production of the cell. Also, it will be appreciated that other configurations employing the permeable membrane may be used. For example, container 20 may be constructed from a non-conductive material and the porous membrane may be used to divide the container, providin~ an area to contain the impure molten aluminum 32 and another area or space in which to provide the electrolyte. The aluminum may be purified by providing an anode in the impure aluminum and a cathode in the electrolyte and passing electric current therebetween.
By reference to Figure 2, there is shown an alternate embodiment of the electrolytic cell which can be operated on a continuous basis. The cell 10' comprises outer container 20' constructed of a material resistant to attack by purified alumi-num 26 or molten electrolyte 24 and a second container 30' which serves as a vessel in which aluminum alloy 32 is provided in molten form. The cell has a cathode 22 which projects into 3Q electrolyte 24. Underneath cathode 22, a receptacle 23 is positioned to receive purified aluminum 26 precipitated or deposited at the cathode. Receptaclè 23 has an outlet 27 through ~1~36~3 whi~h purified aluminum 26 can be removed continuously at a rate substantially commensurate with the rate of deposition thereof at cathode 22. Container 30', in the embodiment illustrated in Figure 2, has a porous wall 29 permeable or penetrable by an ion containing one or more aluminum atoms which can be electrolyti-cally transported through wall 29 to the cathode. An outlet 34 is provided so that residues or alloying constituents 36 remaining after aluminum has been separated therefrom can be removed. In the particular embodiment illustrated in Figure 2, side 29 of container 30' serves as the anode of the cell.
In the cell of the present invention, the distance "x"
(shown in Figure 2) between the anode and cathode should be closely controlled in order to aid in minimizing the voltage drop across the cell. Thus, the distance "x" between the cathode and anode should not be more than 1.0 inch and preferably not more than 0.5 inch.
The present invention is advantageous in removing silicon and iron and the like in aluminum alloys to a very low level. In addition, the present invention is capable of separating magnesium and the like from aluminum. That is, if the aluminum alloy to be purified contains magnesium or the like, i.e. less noble than aluminum, such included metal can pass through the porous membrane but is not normally deposited at the cathode. Magnesium and the like are normally dissolved in the bath and thus, are not prone to contaminate the purified aluminum deposited at the cathode.
The present invention, as well as providing purified aluminum, is advantageous in that it can provide high purity silicon. In addition, ferro-silicon compounds can be recovered since these materials do not pass through the porous membrane.
Furthermore, while it has been noted hereinabove that the inven-tion was particularly useful with respect to purifying aluminum ~3~3 alloys obtained from the high silicon ores, it is also useful in purifying aluminum scrap containing iron and silicon materials.
Also, the invention can be used to purify aluminum used in clad products, e.g. brazing alloy.
The following examples are still further illustrative of the invention.
Example I
An aluminum alloy containing 11.4 wt.% silicon and 0.21 wt.% iron was provided in molten form in an anode section of a cell~ A molten electrolyte consisting of 5 wt.% aluminum fluoride and 95% lithium chloride was used. The electrolyte temperature was 750C. The anode section was fabricated from porous carbon having an average pore diameter of 120 microns and a porosity of 48~. The distance between the anode and cathode was 0.4 inch.
An electric current, amperage 125 and voltage 4.2 at a current density of 650 amps/ft2 was passed across the cell. Purified aluminum collected at the cathode contained only 0.011 wt.%
silicon and 0.05 wt.~ iron.
Example II
The aluminum alloy of Example I was purified as in Example I except the electrolyte contained 5 wt.% AlF3, 10 wt.~
KCl and 85 wt.% LiCl. The cell was operated at 4.2 volts and a current density of about 700 amps/ft2. The purified aluminum collected at the cathode contained 0.009 wt.% Si and 0.015 wt~
Fe.
Example III
A clad product having a core of aluminum alloy 3105 (0.5% Mn, 0.5% Mg, remainder essentially Al) and a cladding on both sides thereof (composition being 9.75% Si, 1.5% Mg, remain-der essentially Al) was melted to provide an alu~inum alloy composition having 3.10% Si, 0.45% Fe, 0.11% Cu, 0.16% Mn and 0.56% Mg. For purposes of purification, the melt was provided in 1~3~3 an anode section and treated as in Example I except the electro-lyte composition was 10% AlF and 90% LiCl and the current density was 500 amps/ft2. Analysis of the purified aluminum showed only 0.002% Si, 0.004% Fe, 0.001% Cu, 0.004% Mn and 0.0003~ Mg, thus providing substantially 99.99% aluminum.
From the above examples, it can be seen that silicon and iron content of the aluminum were reduced rather signifi-cantly. Further, it can be seen that the invention is capable of producing high purity aluminum metal.
Various modifications may be made in the invention without departing from the spirit thereof, or the scope of the claims, and therefore, the exact form shown is to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are imposed by the prior art, or are specifically set forth in the appended claims.
Claims (7)
1. A process for purifying aluminum alloy comprising:
(a) providing the aluminum alloy in a molten state in a container having a porous wall therein, said porous wall being capable of containing molten aluminum in the container, the porous wall being permeable by a molten electrolyte; and (b) electrolytically transferring aluminum through said porous wall to a cathode in the presence of the electrolyte, thereby substantially purifying said aluminum by separating it from its alloying constituents, characterized in that said porous wall is a porous membrane, the electrolyte comprises at least one salt selected from the group consisting of aluminum fluoride and aluminum chloride and at least one salt selected from the group consisting of sodium, potassium, lithium, manganese and magnesium halide, and the transferring is effected at a current density of greater than 500 amps/ft2 and a voltage range of 1 to 5 volts and with the electro-lyte being maintained within a temperature range of 675° to 925°C.
(a) providing the aluminum alloy in a molten state in a container having a porous wall therein, said porous wall being capable of containing molten aluminum in the container, the porous wall being permeable by a molten electrolyte; and (b) electrolytically transferring aluminum through said porous wall to a cathode in the presence of the electrolyte, thereby substantially purifying said aluminum by separating it from its alloying constituents, characterized in that said porous wall is a porous membrane, the electrolyte comprises at least one salt selected from the group consisting of aluminum fluoride and aluminum chloride and at least one salt selected from the group consisting of sodium, potassium, lithium, manganese and magnesium halide, and the transferring is effected at a current density of greater than 500 amps/ft2 and a voltage range of 1 to 5 volts and with the electro-lyte being maintained within a temperature range of 675° to 925°C.
2. The process according to claim 1 wherein the porous membrane has a maximum average pore diameter of 635 microns.
3. The process according to claim 1 wherein porous carbon is employed as the porous wall.
4. The process according to claim 3 wherein the porous carbon has an average pore diameter in the range of 5 to 425 microns.
5. The process according to claim 1 wherein said electrolyte employed comprises at least one salt selected from the group consisting of aluminum fluoride and aluminum chloride and at least one salt selected from the group consisting of sodium, potassium, lithium, manganese and magnesium chloride.
6. The process according to claim 1 wherein the electrolyte consists essentially of 5 to 95 wt.% LiCl, 4 to 70 wt.% KC1 and 1 to 25 wt.% AlF3.
7. The process according to claim 1 wherein molten aluminum is electrolytically transferred at a current density in the range of 500 to 3000 amps/ft2.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US72548276A | 1976-09-22 | 1976-09-22 | |
| US725,482 | 1976-09-22 | ||
| US05/771,100 US4115215A (en) | 1976-09-22 | 1977-02-23 | Aluminum purification |
| US771,100 | 1977-02-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103613A true CA1103613A (en) | 1981-06-23 |
Family
ID=27111154
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA283,490A Expired CA1103613A (en) | 1976-09-22 | 1977-07-26 | Aluminum purification |
Country Status (14)
| Country | Link |
|---|---|
| JP (1) | JPS5339916A (en) |
| AU (1) | AU512224B2 (en) |
| BR (1) | BR7706198A (en) |
| CA (1) | CA1103613A (en) |
| DE (1) | DE2740732A1 (en) |
| ES (1) | ES462403A1 (en) |
| FR (1) | FR2365644A1 (en) |
| GB (1) | GB1568118A (en) |
| GR (1) | GR69793B (en) |
| HU (1) | HU177164B (en) |
| IT (1) | IT1090303B (en) |
| NO (1) | NO772964L (en) |
| PL (1) | PL200993A1 (en) |
| SE (1) | SE7709505L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4214955A (en) * | 1979-01-02 | 1980-07-29 | Aluminum Company Of America | Electrolytic purification of metals |
| NZ193092A (en) * | 1979-06-27 | 1983-09-30 | Pora Inc | Electrode for the deposition of aluminium from a molten electrolyte |
| JPS6091036U (en) * | 1983-11-30 | 1985-06-21 | サンスター株式会社 | toothbrush |
| DE4236337C1 (en) * | 1992-10-28 | 1994-01-27 | Goldschmidt Ag Th | Use of polyacrylic acid esters as dispersants |
| WO2023210748A1 (en) * | 2022-04-27 | 2023-11-02 | 国立大学法人東北大学 | Method for producing high-purity aluminum, production device, production system, and high-purity aluminum |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3798140A (en) * | 1973-02-01 | 1974-03-19 | Us Interior | Process for producing aluminum and silicon from aluminum silicon alloys |
-
1977
- 1977-03-22 PL PL20099377A patent/PL200993A1/en unknown
- 1977-07-14 AU AU27011/77A patent/AU512224B2/en not_active Expired
- 1977-07-26 CA CA283,490A patent/CA1103613A/en not_active Expired
- 1977-08-24 SE SE7709505A patent/SE7709505L/en unknown
- 1977-08-25 GB GB35747/77A patent/GB1568118A/en not_active Expired
- 1977-08-26 NO NO772964A patent/NO772964L/en unknown
- 1977-08-27 GR GR54247A patent/GR69793B/el unknown
- 1977-09-08 DE DE19772740732 patent/DE2740732A1/en not_active Ceased
- 1977-09-13 FR FR7727604A patent/FR2365644A1/en active Granted
- 1977-09-14 JP JP11006977A patent/JPS5339916A/en active Granted
- 1977-09-15 HU HU77AU383A patent/HU177164B/en unknown
- 1977-09-15 ES ES462403A patent/ES462403A1/en not_active Expired
- 1977-09-16 BR BR7706198A patent/BR7706198A/en unknown
- 1977-09-16 IT IT51046/77A patent/IT1090303B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| ES462403A1 (en) | 1978-06-01 |
| FR2365644A1 (en) | 1978-04-21 |
| IT1090303B (en) | 1985-06-26 |
| AU2701177A (en) | 1979-01-18 |
| NO772964L (en) | 1978-03-28 |
| PL200993A1 (en) | 1978-04-24 |
| FR2365644B1 (en) | 1980-08-01 |
| JPS5727943B2 (en) | 1982-06-14 |
| BR7706198A (en) | 1978-07-18 |
| AU512224B2 (en) | 1980-10-02 |
| JPS5339916A (en) | 1978-04-12 |
| GR69793B (en) | 1982-07-07 |
| GB1568118A (en) | 1980-05-29 |
| SE7709505L (en) | 1978-03-23 |
| DE2740732A1 (en) | 1978-03-23 |
| HU177164B (en) | 1981-08-28 |
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