METHOD FOR PRODUCING METAL ALUMINUM BY MOLTEN SALT ELECTROLYSIS OF ALUMINUM OXIDE

Abstract

A method for producing metal aluminum by molten salt electrolysis of aluminum oxide is provided. The method for producing metal aluminum by molten salt electrolysis of aluminum oxide uses an electrolytic cell. The electrolytic cell is divided into an anode chamber and a cathode chamber, and is filled with melts such as anolyte, catholyte and an alloy medium. The electrolytic cell is powered on to operate and an aluminum oxide raw material is added to the anode chamber to obtain high-purity metal aluminum in the cathode chamber. The disclosure provides an aluminum electrolysis method having the advantages of strong electrolysis operation adaptability, large selectivity of electrolysis materials and raw materials, being energy saving and environmentally friendly, and being capable of directly producing refined aluminum or high-purity aluminum.

Claims

1. A method for producing metal aluminum by a molten salt electrolysis of aluminum oxide, comprising: using an electrolytic cell divided into an anode chamber and a cathode chamber, after the electrolytic cell is powered on to operate, adding an aluminum oxide raw material to the anode chamber to obtain a metal aluminum product in the cathode chamber, wherein the anode chamber and the cathode chamber are configured to physically separate an anolyte from a catholyte, the anode chamber is provided with an anode, and the cathode chamber is provided with a cathode; and a bottom of the electrolytic cell is filled with an alloy medium, and the alloy medium respectively contacts the anolyte and the catholyte and is configured to form electrochemical reaction interfaces of aluminum ions/aluminum atoms and serve as a transfer medium of the aluminum atoms.

2. (canceled)

3. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the anolyte is a fluoride system containing 60 to 90 wt % of cryolite, 5 to 30 wt % of AlF.sub.3, 1 to 10 wt % of Al.sub.2O.sub.3, and 0 to 15 wt % of an additive; and the cryolite is one or more of Na.sub.3AlF.sub.6, Li.sub.3AlF.sub.6, and K.sub.3AlF.sub.6, and the additive is one or more of LiF, NaF, KF, CaF.sub.2, MgF.sub.2, BaF.sub.2, and NaCl.

4. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the anolyte is a chloride system; and the chloride system is CaCl.sub.2), or the chloride system comprises CaCl.sub.2) and one or more of NaCl, KCl, BaCl.sub.2, CaF.sub.2, LiCl, and CaO and a mole percentage of the CaCl.sub.2) in the chloride system is not lower than 50%.

5. (canceled)

6. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the catholyte is a pure fluoride system containing 20 to 40 wt % of BaF.sub.2, 30 to 50 wt % of AlF.sub.3, 15 to 40 wt % of NaF, and 0 to 20 wt % of an additive; and the additive is one or more of CaF.sub.2, LiF, Li.sub.3AlF.sub.6, and MgF.sub.2.

7. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the catholyte is a fluoride-chloride system containing 50 to 70 wt % of BaCl.sub.2, 15 to 30 wt % of AlF.sub.3, 10 to 30 wt % of NaF, and 0 to 15 wt % of an additive; and the additive is one or more of LiF, Li.sub.3AlF.sub.6, CaF.sub.2, MgF.sub.2, NaCl, LiCl, CaCl.sub.2, and MgCl.sub.2.

8. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the anode is a carbon anode or an inert anode.

9. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the cathode is one or a composite of graphite, aluminum, and an inert wettable cathode material.

10. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 1, wherein the alloy medium is an alloy formed by Al and one or more of Cu, Sn, Zn, Ga, In, Bi, and Sb; and the alloy medium remains a liquid state during a normal electrolysis and has a density greater than a density of the anolyte or a density of the catholyte.

11. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 10, wherein the alloy medium is an AlCu alloy, and an Al content in the alloy medium is 40 to 75 wt %.

12. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 3, wherein the alloy medium is an alloy formed by Al and one or more of Cu, Sn, Zn, Ga, In, Bi, and Sb; and the alloy medium remains a liquid state during a normal electrolysis and has a density greater than a density of the anolyte or a density of the catholyte.

13. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 4, wherein the alloy medium is an alloy formed by Al and one or more of Cu, Sn, Zn, Ga, In, Bi, and Sb; and the alloy medium remains a liquid state during a normal electrolysis and has a density greater than a density of the anolyte or a density of the catholyte.

14. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 6, and the alloy medium is an alloy formed by Al and one or more of Cu, Sn, Zn, Ga, In, Bi, and Sb; and the alloy medium remains a liquid state during a normal electrolysis and has a density greater than a density of the anolyte or a density of the catholyte.

15. The method for producing the metal aluminum by the molten salt electrolysis of the aluminum oxide according to claim 7, and the alloy medium is an alloy formed by Al and one or more of Cu, Sn, Zn, Ga, In, Bi, and Sb; and the alloy medium remains a liquid state during a normal electrolysis and has a density greater than a density of the anolyte or a density of the catholyte.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the examples of the disclosure or the technical solutions in the prior art, the accompanying drawings used in the description of the examples or the prior art will be briefly described below. Apparently, the accompanying drawings in the following description are only some examples of the disclosure, and those skilled in the art can obtain other drawings according to these drawings without any creative work.

[0054] The FIGURE is a schematic sectional view of an electrolytic cell according to the disclosure.

[0055] In the FIGURE, 1anode, 2electrolytic cell body, 3anolyte, 4alloy medium, 5catholyte, 6metal aluminum product, 7cathode.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] In order to make the objectives, technical solutions and advantages of the disclosure clearer, the technical solutions of the disclosure will be described in detail below. Apparently, the described examples are merely some, rather than all the examples of the disclosure. All other embodiments obtained by those of ordinary skill in the art based on the examples of the disclosure without creative work are within the protection scope of the disclosure.

[0057] A method for producing metal aluminum by molten salt electrolysis of aluminum oxide in the disclosure is operated at a temperature of 700 to 950? C. in a powered environment, and the anode current density is 0.1-1.5 A/cm.sup.2. Aluminum oxide raw material is added to the anolyte of anode chamber, the anode loses electrons and evolves gas, and aluminum ions (dissolved and/or non-dissolved) are reduced and enter a liquid alloy medium. At the same time, in the cathode chamber, aluminum atoms in the liquid alloy medium lose electrons at the interface to form aluminum ions that enter a catholyte, and aluminum ions in the catholyte are reduced into metal aluminum atoms that enter the aluminum liquid floating on the catholyte.

[0058] The addition speed of the aluminum oxide raw material is calculated and determined based on the current intensity and the current efficiency according to Faraday's law.

[0059] In the disclosure, the anolyte and the catholyte are physically separated by the electrolytic cell, and both the anolyte and the catholyte contact the alloy medium, so that the interface reaction of aluminum ions/aluminum atoms and migration of aluminum atoms are completed by means of the alloy medium. Therefore, in order to effectively separate the catholyte from the anolyte, the structure of the electrolytic cell is shown in the FIGURE.

[0060] The electrolytic cell body 2 is divided into an anode chamber and a cathode chamber in space. The anode chamber is filled with the anolyte 3, and the anode 1 is inserted into the anolyte 3. The cathode chamber is filled with the catholyte 5, and the cathode 7 is inserted into the catholyte 5 or the liquid metal aluminum product 6. The bottom of the electrolytic cell is filled with the alloy medium 4 that respectively contacts the anolyte 3 and the catholyte 5 but does not contact the anode 1 or the cathode 7.

[0061] In addition to the electrolytic cell as shown in the FIGURE, the structure of the electrolytic cell may also be designed into various forms, for example, the electrolytic cell may be a U-shaped electrolytic cell. In addition, the electrolytic cell may be in a variety of shapes. For example, the electrolytic cell may be not limited to a round bottom, but can also be a trapezoidal bottom or a flat bottom.

[0062] Any aluminum electrolytic cell that can realize physical separation between the anolyte and the catholyte and the mediation function of the alloy medium can be applied to the method of the disclosure.

[0063] In large-scale application, the electrolytic cells may be operated and connected in series or in parallel.

Example 1

[0064] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 60 wt %. Both the anode and the cathode were graphite rods.

[0065] The anolyte included: 80.3 wt % Na.sub.3AlF.sub.6+12.2 wt % AlF.sub.3+2.5 wt % Al.sub.2O.sub.3+3.0 wt % CaF.sub.2+1.0 wt % MgF.sub.2+1.0 wt % LiF.

[0066] The catholyte included: 35.0 wt % BaF.sub.2+30.0 wt % AlF.sub.3+30.0 wt % NaF+5.0 wt % CaF.sub.2.

[0067] The electrolytic cell was heated to 940? C. and held for 2 h. The electrolytic cell was powered on while controlling an anode current density at 1.2 A/cm.sup.2. After the electrolysis was started, an aluminum oxide raw material containing 95.5 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 10 h.

[0068] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.980%.

Example 2

[0069] The bottom of the electrolytic cell was filled with a pre-alloyed CuAlZn alloy in which an Al content was 60 wt % and a Zn content was 5 wt %. The anode was a graphite rod, and the cathode was a TiB.sub.2-coated graphite.

[0070] The anolyte included: 50.0 wt % Na.sub.3AlF.sub.6+30.0 wt % Li.sub.3AlF.sub.6+13.5 wt % AlF.sub.3+2.0 wt % Al.sub.2O.sub.3+3.0 wt % CaF.sub.2+1.5 wt % MgF.sub.2.

[0071] The catholyte included: 65.0 wt % BaCl.sub.2+20.0 wt % AlF.sub.3+13.0 wt % NaF+2.0 wt % NaCl. The electrolytic cell was heated to 860? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.6 A/cm.sup.2. After the electrolysis was started, an aluminum oxide raw material containing 91.2 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 10 h.

[0072] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.970%.

Example 3

[0073] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 50 wt %. The anode was a graphite rod, and the cathode was a TiB.sub.2-coated graphite.

[0074] The anolyte was CaCl.sub.2.

[0075] The catholyte included: 20.0 wt % BaF.sub.2+35.0 wt % AlF.sub.3+30.0 wt % NaF+15.0 wt % CaF.sub.2.

[0076] The electrolytic cell was heated to 850? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.7 A/cm.sup.2. Before and after the electrolysis was started, an aluminum oxide raw material containing 98.8 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 10 h.

[0077] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.989%.

Example 4

[0078] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 62 wt %. The anode was inert anode made of a 15 wt % Fe-70 wt % Cu-35 wt % Ni alloy material, and the cathode was graphite.

[0079] The anolyte included: 70.0 wt % K.sub.3AlF.sub.6+21.5 wt % AlF.sub.3+3.5 wt % Al.sub.2O.sub.3+4.0 wt % LiF+1.0 wt % CaF.sub.2.

[0080] The catholyte included: 55.0 wt % BaCl.sub.2+27.0 wt % AlF.sub.3+16.0 wt % NaF+2.0 wt % CaF.sub.2.

[0081] The electrolytic cell was heated to 870? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.8 A/cm.sup.2. After the electrolysis was started, an aluminum oxide raw material containing 98.7 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 10 h.

[0082] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.995%.

Example 5

[0083] The bottom of the electrolytic cell was filled with a pre-alloyed SnAl alloy in which an Al content was 20 wt %. The anode was a graphite anode, and the cathode was a TiB.sub.2-coated graphite.

[0084] The anolyte included CaCl.sub.2) and LiCl in a mole ratio of 1:1.

[0085] The catholyte included: 60.0 wt % BaCl.sub.2+20.0 wt % AlF.sub.3+15.0 wt % NaF+5.0 wt % LiCl.

[0086] The electrolytic cell was heated to 800? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.4 A/cm.sup.2. Before and after the electrolysis was started, an aluminum oxide raw material containing 97.2 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 15 h.

[0087] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.986%.

Example 6

[0088] The bottom of the electrolytic cell was filled with a pre-alloyed InAl alloy in which an Al content was 10 wt %. Both the anode and the cathode were graphite rods.

[0089] The anolyte included: 65.0 wt % Na.sub.3AlF.sub.6+20.5 wt % AlF.sub.3+3.5 wt % Al.sub.2O.sub.3+8.0 wt % KF+3.0 wt % CaF.sub.2.

[0090] The catholyte included: 25.0 wt % BaF.sub.2+36.0 wt % AlF.sub.3+27.0 wt % NaF+10.0 wt % CaF.sub.2+2.0 wt % Li.sub.3AlF.sub.6.

[0091] The electrolytic cell was heated to 900? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.5 A/cm.sup.2. After the electrolysis was started, an aluminum oxide raw material containing 98.9 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 12 h.

[0092] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.994%.

Example 7

[0093] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 45 wt %. The anode was inert anode made of a CaRuO.sub.3 ceramic material, and the cathode was a TiB.sub.2/C composite.

[0094] The anolyte included CaCl.sub.2), NaCl and CaO in a mole ratio of 50:48:2.

[0095] The catholyte included: 60.0 wt % BaCl.sub.2+23.0 wt % AlF.sub.3+17.0 wt % NaF.

[0096] The electrolytic cell was heated to 840? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 0.2 A/cm.sup.2. Before and after the electrolysis was started, an aluminum oxide raw material containing 94.6 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 20 h.

[0097] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.975%.

Example 8

[0098] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 70 wt %. The anode was inert anode made of a NiFe.sub.2O.sub.4-18 wt % NiO-17 wt % Cu cermet composites, and the cathode was a graphite rod.

[0099] The anolyte included: 42.3 wt % Na.sub.3AlF.sub.6+28.2 wt % K.sub.3AlF.sub.6+23.0 wt % AlF.sub.3+2.5 wt % Al.sub.2O.sub.3+4.0 wt % LiF.

[0100] The catholyte included: 22.0 wt % BaF.sub.2+46.0 wt % AlF.sub.3+26.0 wt % NaF+4.0 wt % CaF.sub.2+2.0 wt % LiF.

[0101] The electrolytic cell was heated to 880? C. and held for 2 h. A direct current was applied such that an anode current density was controlled at 1.0 A/cm.sup.2. After the electrolysis was started, a sand-like aluminum oxide raw material containing 99.1 wt % of Al.sub.2O.sub.3 was added regularly, and a total electrolysis time was 10 h.

[0102] After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.999%.

Example 9

[0103] This comparative example was different from Example 4 in that: on the basis of the anolyte including 70.0 wt % K.sub.3AlF.sub.6+21.5 wt % AlF.sub.3+3.5 wt % Al.sub.2O.sub.3+4.0 wt % LiF+1.0 wt % CaF.sub.2, 10 wt % of Al.sub.2O.sub.3 was also added, and the alloy medium was a CuAl alloy in which an Al content was 50 wt %. The other conditions were the same. After the electrolysis was completed, an Al content in the cathode product metal aluminum was measured as 99.991%, and moreover, there was still some undissolved aluminum oxide raw material on the alloy medium.

[0104] It could be inferred that even the aluminum oxide raw material that was added too fast or too much could stay on the alloy medium and continue to participate in the dissolution/electrochemical reaction, so as to maintain the continuous operation of the electrolysis process, and the purity of the obtained metal aluminum product was still relatively high.

Comparative Example 1

[0105] This comparative example was different from Example 1 in that: the bottom of the electrolytic cell was not filled with the alloy medium. The electrolyte was the same as the anolyte in Example 1, and the other conditions were the same. After the electrolysis was completed, the product metal aluminum was taken out of the electrolytic cell, and an Al content in the product metal aluminum was measured as 97.1%.

[0106] This indicated that in the absence of the alloy medium, there was no separation and impurity removal effect based on the electrochemical reaction at the alloy medium/electrolyte interface, and impurity elements Si and Fe directly entered the metal aluminum product, causing a reduction in product purity/grade.

Comparative Example 2

[0107] This comparative example was different from Example 4 in that: the bottom of the electrolytic cell was not filled with the alloy medium, and on the basis of the electrolyte including 70.0 wt % K.sub.3AlF.sub.6+21.5 wt % AlF.sub.3+3.5 wt % Al.sub.2O.sub.3+4.0 wt % LiF+1.0 wt % CaF.sub.2, 10 wt % of Al.sub.2O.sub.3 was also added (since there is no separation of the alloy medium, there was only one electrolyte in the electrolytic cell). The other conditions were the same. After the end of electrolysis, the product metal aluminum in the electrolytic cell was taken out, of which the Al content was measured as 97.8%, containing Fe, Si, Cu, Ni and other impurity elements. Some undissolved aluminum oxide raw material was also detected on the cell bottom.

[0108] This indicated that the aluminum oxide raw material that was added too fast or too much could hardly participate in the dissolution/electrochemical reaction effectively, thus forming the precipitate on the cell bottom. In addition, without the separation and impurity removal effect based on the electrochemical reaction at the alloy medium/electrolyte interface, the impurity element Si in the aluminum oxide raw material, and elements such as Cu, Ni and Fe generated after the surface of the inert anode was corroded directly entered the metal aluminum product, causing a reduction in the purity of the metal aluminum product.

Comparative Example 3

[0109] The bottom of the electrolytic cell was filled with metal aluminum with an Al content of 99.8%. Both the anode and the cathode were graphite rods. Both the anolyte and the catholyte included: 60.0 wt % Na.sub.3AlF.sub.6+12.0 wt % AlF.sub.3+5.0 wt % NaF+2.0 wt % CaF.sub.2+1.0 wt % MgF.sub.2+10.0 wt % NaCl+10.0 wt % KCl. The electrolytic cell was placed in an atmosphere filled with dry argon. The electrolytic cell was heated to 940? C. in a temperature programmed way, and held for 2 h. The electrolytic cell was powered on while controlling an anode current density at 0.8 A/cm.sup.2. After the electrolysis was started, a smelter grade aluminum oxide raw material containing 98.8 wt % of Al.sub.2O.sub.3 was added regularly. The addition speed was calculated and determined based on the current intensity and the current efficiency according to Faraday's law, and a total electrolysis time was 10 h. During the electrolysis process, irritating chlorine gas was found, and the electrolysis voltage fluctuated relatively widely. After the electrolysis was completed, no metal aluminum product was detected on the surface of the catholyte in the cathode chamber, and there was still unreacted aluminum oxide raw material under the metal aluminum on the bottom of the electrolytic cell, forming a precipitate/crust on the cell bottom.

Comparative Example 4

[0110] The bottom of the electrolytic cell was filled with metal aluminum with an Al content of 99.8%. Both the anode and the cathode were graphite rods. Both the anolyte and the catholyte included: 60.0 wt % Na.sub.3AlF.sub.6+12.0 wt % AlF.sub.3+5.0 wt % NaF+2.0 wt % CaF.sub.2+1.0 wt % MgF.sub.2+10.0 wt % NaCl+10.0 wt % KCl. Moreover, high-purity aluminum with an Al content of 99.999% was placed on the surface of the catholyte. The electrolytic cell was placed in an atmosphere filled with dry argon. The electrolytic cell was heated to 940? C. in a temperature programmed way, and held for 2 h. During the process, it was found that the melted high-purity aluminum liquid could not stably float on the surface of the catholyte, but automatically settled to the cell bottom, that is, the electrochemical system shown in the FIGURE could not be formed.

Comparative Example 5

[0111] The bottom of the electrolytic cell was filled with metal aluminum with an Al content of 99.8%. Both the anode and the cathode were graphite rods. The anolyte included: 60.0 wt % Na.sub.3AlF.sub.6+12.0 wt % AlF.sub.3+5.0 wt % NaF+2.0 wt % CaF.sub.2+1.0 wt % MgF.sub.2+10.0 wt % NaCl+10.0 wt % KCl. The catholyte included: 35.0 wt % BaF.sub.2+30.0 wt % AlF.sub.3+30.0 wt % NaF+5.0 wt % CaF.sub.2. The electrolytic cell was placed in an atmosphere filled with dry argon. The electrolytic cell was heated to 940? C. in a temperature programmed way, and held for 2 h. During the process, it was found that the metal aluminum liquid on the bottom of the electrolytic cell automatically floated up to the surface of the catholyte, that is, the electrochemical system shown in the FIGURE could not be formed.

Comparative Example 6

[0112] The corundum crucible was filled with molten salts including 35.0 wt % BaF.sub.2+30.0 wt % AlF.sub.3+30.0 wt % NaF+5.0 wt % CaF.sub.2, and an excessive smelter grade aluminum oxide raw material containing 98.8 wt % of Al.sub.2O.sub.3 was added and held at 940? C. for 2 h such that the aluminum oxide raw material was sufficiently dissolved. Then, the molten salts in which saturated Al.sub.2O.sub.3 was dissolved were taken out by decantation, and the undissolved aluminum oxide raw material and the residual molten salts are left in the corundum crucible.

[0113] The bottom of the electrolytic cell was filled with a pre-alloyed CuAl alloy in which an Al content was 60 wt %. Both the anode and the cathode were graphite rods. The above molten salts in which saturated Al.sub.2O.sub.3 was dissolved were used as the anolyte, and the catholyte was 35.0 wt % BaF.sub.2+30.0 wt % AlF.sub.3+3 0.0 wt % NaF+5.0 wt % CaF.sub.2. The electrolytic cell was placed in an atmosphere filled with dry argon. The electrolytic cell was heated to 940? C. in a temperature programmed way, and held for 2 h. The electrolytic cell was powered on such that an anode current density was controlled at 0.8 A/cm.sup.2. During the electrolysis process, the voltage fluctuated up and down and then increased sharply in the later period, and the electrolysis stopped in an instant.

[0114] The reason for the above phenomenon may be that relatively more Al.sub.2O.sub.3 dissolved in the anolyte at the beginning of electrolysis could maintain the normal operation of the electrolysis, but both the electrolyte resistance and the cell voltage were relatively high. As the electrolysis proceeded, Al.sub.2O.sub.3 in the anolyte was consumed continuously, and the electrolyte resistance decreased. However, the concentration polarization led to the occurrence of the anode effect, and the voltage fluctuated and increased sharply in the later period.

[0115] In addition, the anolyte contained a large amount of barium salt. The addition of the barium salt greatly decreased the solubility of the aluminum oxide, such that the anolyte needed to be taken out frequently and the aluminum oxide raw material needed to be transferred and dissolved frequently, causing low production efficiency.

[0116] The foregoing descriptions are merely specific implementations of the disclosure, but are not intended to limit the protection scope of the disclosure. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the disclosure shall fall within the protection scope of the disclosure. Therefore, the protection scope of the disclosure shall be subject to the protection scope of the claims.