METHOD FOR PRODUCING METALLIC ALUMINUM AND POLYSILICON WITH HIGH-SILICON ALUMINUM-CONTAINING RESOURCE

Abstract

The present application belongs to the technical field of aluminum metallurgy, and specifically relates to a method for producing metallic aluminum and polysilicon with a high-silicon aluminum-containing resource. The method includes: pretreating the high-silicon aluminum-containing resource to obtain an aluminum-silicon oxide material; the aluminum-silicon oxide material is used to produce a metallic aluminum product and a copper-aluminum-silicon alloy with silicon enriched by molten salt electrolysis in a double-chamber electrolytic cell; and the copper-aluminum-silicon alloy is used to produce an aluminum-silicon alloy and/or polysilicon by molten salt electrolysis in a single-chamber electrolytic cell, and further separating the aluminum-silicon alloy by physical methods to obtain polysilicon. The present application has characteristics such as low production cost, continuous electrolysis operations, high product quality, and environmental friendliness.

Claims

1. A method for producing metallic aluminum and polysilicon with a high-silicon aluminum-containing resource, comprising the following steps: step (1): pretreating the high-silicon aluminum-containing resource to obtain an aluminum-silicon oxide material; step (2): with the aluminum-silicon oxide material as an electrolysis raw material, conducting molten salt electrolysis in a double-chamber electrolytic cell to prepare metallic aluminum and a copper-aluminum-silicon alloy, wherein the double-chamber electrolytic cell is divided into an anode chamber and a cathode chamber to physically separate an anode electrolyte from a cathode electrolyte; the anode chamber is provided with an anode, and the cathode chamber is provided with a cathode; a copper-aluminum alloy is accommodated at a bottom of the double-chamber electrolytic cell, and the copper-aluminum alloy is in contact with each of the anode electrolyte and the cathode electrolyte; and under energized operation conditions, the aluminum-silicon oxide material is fed into the anode chamber, such that the metallic aluminum is produced in the cathode chamber and the copper-aluminum alloy at the bottom of the double-chamber electrolytic cell is transformed into the copper-aluminum-silicon alloy; and step (3): taking the copper-aluminum-silicon alloy out, placing the copper-aluminum-silicon alloy in a single-chamber electrolytic cell, and conducting molten salt electrolysis to prepare an aluminum-silicon alloy and/or polysilicon, wherein in the single-chamber electrolytic cell, a bottom melt is a copper-aluminum-silicon alloy anode, a middle melt is a refining electrolyte, and an upper melt is an aluminum melt cathode; and under energized operation conditions, Al and Si in the copper-aluminum-silicon alloy are oxidized, enter the refining electrolyte, and then are reduced at the aluminum melt cathode to obtain the aluminum-silicon alloy and/or the polysilicon.

2. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (1), a Al.sub.2O.sub.3/SiO.sub.2 mass ratio in the high-silicon aluminum-containing resource is 1:(0.5-7), and the high-silicon aluminum-containing resource comprises one or more selected from the group consisting of high-silicon bauxite, fly ash, coal gangue, kaolin, and alunite.

3. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the anode is a carbon anode or an inert anode.

4. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the anode electrolyte is a fluoride system or a chloride system, and the fluoride system comprises 60 wt % to 90 wt % of a cryolite, 5 wt % to 25 wt % of AlF.sub.3, 1 wt % to 5 wt % of Al.sub.2O.sub.3, and 0 wt % to 15 wt % of an additive, wherein the cryolite is one or more selected from the group consisting of Na.sub.3AlF.sub.6, Li.sub.3AlF.sub.6, and K.sub.3AlF.sub.6 and the additive is one or more selected from the group consisting of LiF, NaF, KF, CaF.sub.2, MgF.sub.2, and BaF.sub.2.

5. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the cathode electrolyte comprises 20 wt % to 70 wt % of a weighting agent, 15 wt % to 50 wt % of AlF.sub.3, 13 wt % to 40 wt % of NaF, and 20 wt % or less of an additive, wherein the weighting agent is BaCl.sub.2 and/or BaF.sub.2 and the additive is one or more selected from the group consisting of LiF, Li.sub.3AlF.sub.6, Na.sub.3AlF.sub.6, CaF.sub.2, MgF.sub.2, NaCl, LiCl, CaCl.sub.2, and MgCl.sub.2.

6. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), a Al content in the copper-aluminum alloy is 55 at % to 80 at %.

7. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (3), the refining electrolyte comprises 20 wt % to 40 wt % of BaF.sub.2, 40 wt % to 70 wt % of cryolite, 5 wt % to 25 wt % of AlF.sub.3, 0 wt % to 10 wt % of a fluorine-silicon compound, and 0 wt % to 15 wt % of an additive, wherein the cryolite is one or more selected from the group consisting of Na.sub.3AlF.sub.6, Li.sub.3AlF.sub.6, and K.sub.3AlF.sub.6, the fluorine-silicon compound is one or more selected from the group consisting of Na.sub.2SiF.sub.6, K.sub.2SiF.sub.6, Li.sub.2SiF.sub.6, and SiF.sub.4, and the additive is one or more selected from the group consisting of LiF, NaF, KF, CaF.sub.2, and MgF.sub.2.

8. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (3), the aluminum melt cathode is a pure metallic aluminum melt or a silicon-containing metallic aluminum melt.

9. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), when the double-chamber electrolytic cell works normally, an anode current density is 0.1 A/cm.sup.2 to 1.5 A/cm.sup.2 and a temperature is 800? C. to 1,000? C.

10. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (3), the aluminum-silicon alloy is used to produce polysilicon by a physical method and/or a chemical method, wherein the physical method comprises one or more selected from the group consisting of a liquation method, a segregation in solidification process, a vacuum distillation method, and a directional solidification method, and the chemical method comprises an acid pickling method and an electrorefining method.

11. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (1), in the aluminum-silicon oxide material, a total content of Al.sub.2O.sub.3 and SiO.sub.2 is higher than or equal to 90.0%, a content of Al.sub.2O.sub.3 is higher than or equal to 40.0%, and a content of SiO.sub.2 is higher than or equal to 0.1%.

12. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the cathode is one or a composite of two or more selected from the group consisting of graphite, aluminum, and TiB.sub.2/C.

13. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the anode electrolyte is a chloride system, and the chloride system is CaCl.sub.2 or comprises CaCl.sub.2 and one or more selected from the group consisting of NaCl, KCl, BaCl.sub.2, CaF.sub.2, LiCl, and CaO.

14. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), the cathode electrolyte comprises 20 wt % to 40 wt % of BaF.sub.2, 15 wt % to 50 wt % of AlF.sub.3, 20 wt % to 40 wt % of NaF, and 10 wt % to 20 wt % of CaF.sub.2 or the cathode electrolyte comprises 50 wt % to 65 wt % of BaCl.sub.2, 15 wt % to 30 wt % of AlF.sub.3, 13 wt % to 30 wt % of NaF, and 0 wt % to 5 wt % of NaCl.

15. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (2), and the copper-aluminum alloy remains a liquid during a normal electrolytic work, and a density of the copper-aluminum alloy is greater than a density of the anode electrolyte and a density of the cathode electrolyte.

16. The method for producing the metallic aluminum and polysilicon with the high-silicon aluminum-containing resource according to claim 1, wherein in step (3), when the single-chamber electrolytic cell works normally, an anode current density is 0.01 A/cm.sup.2 to 1.0 A/cm.sup.2 and a temperature is 800? C. to 1,100? C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] To describe the technical solutions in the embodiments of the present application or in the prior art clearly, the accompanying drawings required for describing the embodiments or the prior art are briefly described below. Apparently, the accompanying drawings in the following description merely show some embodiments of the present application, and a person of ordinary skill in the art may still derive other accompanying drawings from these accompanying drawings without creative efforts.

[0053] FIG. 1 is a flow chart of the method for producing metallic aluminum and polysilicon with a high-silicon aluminum-containing resource;

[0054] FIG. 2 is a schematic diagram of a cross section of the double-chamber electrolytic cell of the present application, [0055] where reference numerals in FIG. 2: 1: insulating separator, 2: cathode, 3: metallic aluminum, 4: cathode electrolyte, 5: copper-aluminum alloy, 6: electrolytic cell body, 7: anode electrolyte, and 8: anode; and

[0056] FIG. 3 is a schematic diagram of a cross section of the single-chamber electrolytic cell of the present application, [0057] where reference numerals in FIG. 3: 9: cathode, 10: aluminum melt, 11: refining electrolyte, 12: copper-aluminum-silicon alloy, 13: conductive carbon block, 14: conductive steel bar, 15: electrolytic cell body, and 16: insulating refractory brick liner.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] To make the objectives, technical solutions, and advantages of the present application clearly, the technical solutions of the present application will be described in detail below. Apparently, the embodiments described are merely some rather than all of the embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present application without creative efforts should fall within the protection scope of the present application.

[0059] As shown in FIG. 1, a method for producing metallic aluminum and polysilicon with a high-silicon aluminum-containing resource is provided, mainly including the following steps:

[0060] step (1): the high-silicon aluminum-containing resource is pretreated to obtain an aluminum-silicon oxide material;

[0061] step (2): with the aluminum-silicon oxide material as an electrolysis raw material, molten salt electrolysis is conducted in a double-chamber electrolytic cell to prepare metallic aluminum and a copper-aluminum-silicon alloy; and

[0062] step (3): the copper-aluminum-silicon alloy is taken out and placed in a single-chamber electrolytic cell, and molten salt electrolysis is conducted to prepare an aluminum-silicon alloy and/or polysilicon.

[0063] In step (1), a Al.sub.2O.sub.3/SiO.sub.2 mass ratio in the high-silicon aluminum-containing resource is 1:0.5 to 1:7, and the high-silicon aluminum-containing resource includes one or more selected from the group consisting of high-silicon bauxite, fly ash, coal gangue, kaolin, and alunite; and in the aluminum-silicon oxide material, a total content of Al.sub.2O.sub.3 and SiO.sub.2 is higher than or equal to 90.0 wt %, a content of Al.sub.2O.sub.3 is higher than or equal to 40.0 wt %, and a content of SiO.sub.2 is higher than or equal to 0.1 wt %. A pretreatment process includes an alkali process, an acid process, and a combined process, and is characterized in that no deep desiliconization procedure or no deep iron/calcium removal procedure is required.

[0064] In step (2), the double-chamber electrolytic cell is shown in FIG. 2, where an electrolytic cell body 6 is divided by an insulating separator 1 into an anode chamber and a cathode chamber to physically separate an anode electrolyte 7 from a cathode electrolyte 4; the anode chamber is provided with an anode 8 (carbon anode or inert anode), and the cathode chamber is provided with a cathode 2 (ordinary graphite cathode or wettable cathode); and a copper-aluminum alloy 5 is accommodated at a bottom of the double-chamber electrolytic cell, and the copper-aluminum alloy 5 is in contact with each of the anode electrolyte 7 and the cathode electrolyte 4.

[0065] When the double-chamber electrolytic cell is energized and operates at 800? C. to 1,000? C., an anode current density is controlled at 0.1 A/cm.sup.2 to 1.5 A/cm.sup.2, and an aluminum-silicon oxide material is fed into the anode chamber, the aluminum-silicon oxide material undergoes an oxidation reaction on the anode to precipitate a gas, aluminum ions (dissolved and/or non-dissolved) and silicon ions (dissolved and/or non-dissolved) in the anode chamber are reduced into aluminum atoms and silicon atoms at the interface between the anode electrolyte 7 and the copper-aluminum alloy 5, respectively, and then the aluminum atoms and silicon atoms enter the liquid copper-aluminum alloy 5; and in the cathode chamber, the aluminum atoms of the copper-aluminum alloy 5 discharge at the interface between the cathode electrolyte 4 and the copper-aluminum alloy 5 to produce aluminum ions, and the aluminum ions enter the cathode electrolyte 4 and then are reduced into aluminum atoms to produce a liquid metallic aluminum melt 3, which floats on the cathode electrolyte 4. With the continuous progression of electrolysis, silicon is continuously enriched in the copper-aluminum alloy 5, and thus the copper-aluminum alloy is gradually converted into a copper-aluminum-silicon alloy.

[0066] If a Si content in the copper-aluminum-silicon alloy 5 is not high (Si<5 at %), the copper-aluminum-silicon alloy can be directly retained in the double-chamber electrolytic cell and continues to work, or metallic aluminum is timely supplemented to adjust a composition and melting point of the copper-aluminum-silicon alloy and then a resulting copper-aluminum-silicon alloy continues to work in the double-chamber electrolytic cell, such that silicon is further enriched in the alloy; and when a Si content in the copper-aluminum-silicon alloy is high (such as Si>5 at %), a part or all of the copper-aluminum-silicon alloy 5 at the bottom of the double-chamber electrolytic cell is withdrawn and placed in the single-chamber electrolytic cell, and molten salt electrolysis is conducted to prepare an aluminum-silicon alloy and/or polysilicon.

[0067] In step (3), the single-chamber electrolytic cell is shown in FIG. 3, where a bottom structure of an electrolytic cell body 15 is a conductive carbon block 13 provided with a conductive steel bar 14, and surrounding inner walls of the electrolytic cell body each are provided with an insulating refractory brick liner 16; and in the single-chamber electrolytic cell, a bottom melt is a copper-aluminum-silicon alloy 12 as an anode, a middle melt is a refining electrolyte 11, and an upper melt is an aluminum melt 10 (a pure aluminum melt or an aluminum-silicon alloy melt) communicating with a cathode 9.

[0068] When the single-chamber electrolytic cell is energized and operates at a 800? C. to 1,100? C. and an anode current density is controlled at 0.01 A/cm.sup.2 to 1.0 A/cm.sup.2, Al and Si in the copper-aluminum-silicon alloy 12 are oxidized successively, enter the refining electrolyte 11, and are reduced at the cathode aluminum melt 10 to produce an aluminum-silicon alloy and/or polysilicon.

[0069] The aluminum-silicon alloy is used to produce polysilicon by physical methods and/or chemical methods, where the physical methods include one or more selected from the group consisting of the liquation method, the segregation in solidification process, the vacuum distillation method, and the directional solidification method, and the chemical methods include the acid pickling method and the electrorefining method; and the physical method is preferred.

[0070] After full electrolysis in the single-chamber electrolytic cell, aluminum and most of silicon in the copper-aluminum-silicon alloy can be removed to produce crude copper including a small amount of silicon; silicon-containing or silicon-free crude aluminum (a by-product) is obtained after physical separation of the aluminum-silicon alloy; and the crude aluminum and the crude copper are fused to obtain a copper-aluminum alloy, and the copper-aluminum alloy is returned to step (2), thereby completing the closed circulation of copper.

Example 1

[0071] High-aluminum coal gangue (Al.sub.2O.sub.3 content: 42.7 wt %, and aluminum/silicon ratio: 1.5) was calcined at 950? C. for 1.5 h, then ball-milled, washed with dilute hydrochloric acid, and then pre-desiliconized with a 20% NaOH solution at 100? C. for 1 h to obtain a desiliconization ash, and the desiliconization ash was thoroughly mixed with non-metallurgical grade alumina (Al.sub.2O.sub.3 content: 95.9 wt %, and SiO.sub.2 content: 0.20 wt %) to obtain an aluminum-silicon oxide material with a Al.sub.2O.sub.3 content of 86.5 wt % and a SiO.sub.2 content of 7.8 wt %.

[0072] A pre-alloyed CuAl alloy with an Al content of 55 at % was accommodated at a bottom of a double-chamber electrolytic cell, graphite was adopted as an anode, and graphite was adopted as a cathode. A composition of an anode electrolyte was as follows: 81 wt % Na.sub.3AlF.sub.6+8 wt % AlF.sub.3+3 wt % Al.sub.2O.sub.3+6 wt % KF+2 wt % CaF.sub.2+2 wt % LiF; and a composition of a cathode electrolyte was as follows: 23 wt % BaF.sub.2+27 wt % AlF.sub.3+37 wt % NaF+13 wt % CaF.sub.2. The double-chamber electrolytic cell was heated to 1,000? C. and kept at this temperature for 2 h, a direct current was introduced to control an anode current density at 1.5 A/cm.sup.2, and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 60 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.974 wt %.

[0073] After the electrolysis, the copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of 7.6 at %. The copper-aluminum-silicon alloy was taken out and placed as an anode at a bottom of a single-chamber electrolytic cell, a graphite rod was adopted as a cathode, and a refining electrolyte was 30 wt % BaF.sub.2+32 wt % Na.sub.3AlF.sub.6+30 wt % Li.sub.3AlF.sub.6+5 wt % AlF.sub.3+3 wt % Na.sub.2SiF.sub.6. The single-chamber electrolytic cell was heated to 1,000? C. and kept at this temperature for 2 h; first-stage electrolysis was conducted for 3.5 h at 1,000? C. and an anode current density of 0.8 A/cm.sup.2, and after the first-stage electrolysis was completed, metallic aluminum (a product at the cathode) was taken out; and then the single-chamber electrolytic cell was heated to 1,100? C., second-stage electrolysis was conducted for 3 h at 1,100? C. and an anode current density of 0.2 A/cm.sup.2 to obtain a liquid aluminum-silicon alloy and a solid polysilicon particle at the cathode.

[0074] The aluminum-silicon alloy was first separated by the segregation in solidification process to obtain a polysilicon ingot, and the polysilicon ingot and the solid polysilicon particle were remelted, slowly cooled, and directionally solidified to obtain polysilicon with a purity of 99.9%.

Example 2

[0075] High-silicon bauxite (Al.sub.2O.sub.3 content: 62.8 wt %, and aluminum/silicon ratio: 5.5) was fine-ground and then subjected to autoclaving-leaching with a NaOH solution of Na.sub.2O.sub.k=220 g/L at 240? C., a leaching solution was diluted, settled, and filtered to obtain a sodium aluminate solution, and without a deep desiliconization treatment using a lime, the sodium aluminate solution was cooled to 75? C., then subjected to crystal seed decomposition, and then calcined at 1,000? C. to obtain an aluminum-silicon oxide material with a Al.sub.2O.sub.3 content of 97.6 wt % and a SiO.sub.2 content of 0.46 wt %.

[0076] A pre-alloyed CuAl alloy with an Al content of 75 at % was accommodated at a bottom of a double-chamber electrolytic cell, graphite was adopted as an anode, and graphite was adopted as a cathode. A composition of an anode electrolyte was as follows: 80 wt % K.sub.3AlF.sub.6+12 wt % AlF.sub.3+3 wt % Al.sub.2O.sub.3+3 wt % LiF+2 wt % CaF.sub.2; and a composition of a cathode electrolyte was as follows: 60 wt % BaCl.sub.2+22 wt % AlF.sub.3+17 wt % NaF+1 wt % NaF. The double-chamber electrolytic cell was heated to 900? C. and kept at this temperature for 2 h, a direct current was introduced to control an anode current density at 1.2 A/cm.sup.2, and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 12 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.988 wt %.

[0077] The copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of less than 0.1 at %. Thus, the above electrolysis experiment could still be continuously conducted for a long time to continuously produce metallic aluminum in a cathode chamber and enrich silicon in the alloy. When a silicon content in a copper-aluminum-silicon alloy was not less than 5 at %, electrolysis was conducted with the copper-aluminum-silicon alloy as an anode in a single-chamber electrolytic cell to obtain an aluminum-silicon alloy and/or polysilicon.

Example 3

[0078] Fly ash (Al.sub.2O.sub.3 content: 35.3 wt %, and aluminum/silicon ratio: 0.6) was subjected to leaching at 95? C. for 3 h with hydrochloric acid of a concentration of about 30%, where a liquid-to-solid ratio was 5 mL/g; a resulting leaching system was filtered to obtain a crude aluminum chloride solution, and without iron/calcium removal by an ion exchange method or a precipitation method, the crude aluminum chloride solution was directly subjected to evaporative concentration under a negative pressure to obtain an aluminum chloride crystal; and the aluminum chloride crystal was subjected to two-stage calcination at 500? C. and 1,000? C. to obtain an alumina material, and then the alumina material was mixed with a specified amount of a silicon-containing leaching residue to obtain an aluminum-silicon oxide material with a Al.sub.2O.sub.3 content of 82.7 wt %, a SiO.sub.2 content of 10.3 wt %, and a Fe.sub.2O.sub.3 content of 1.1 wt %.

[0079] A pre-alloyed CuAl alloy with an Al content of 70 at % was accommodated at a bottom of a double-chamber electrolytic cell, a CaRuO.sub.3 ceramic material was adopted as an inert anode, and TiB.sub.2 coated graphite was adopted as a cathode. An anode electrolyte was CaCl.sub.2LiCl in a molar ratio of 70:30, and a composition of a cathode electrolyte was as follows: 25 wt % BaF.sub.2+40 wt % AlF.sub.3+25 wt % NaF+10 wt % CaF.sub.2. The double-chamber electrolytic cell was heated to 820? C. and kept at this temperature for 2 h, a direct current was introduced to control an anode current density at 0.2 A/cm.sup.2, and before and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 24 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.976 wt %.

[0080] The copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of 0.3 at %. Thus, the above electrolysis experiment could still be continuously conducted for a long time to continuously produce metallic aluminum in a cathode chamber and enrich silicon in the alloy. When a silicon content in a copper-aluminum-silicon alloy was not less than 5 at %, electrolysis was conducted with the copper-aluminum-silicon alloy as an anode in a single-chamber electrolytic cell to obtain an aluminum-silicon alloy and/or polysilicon.

Example 4

[0081] High-aluminum fly ash (Al.sub.2O.sub.3 content: 49.0 wt %, and aluminum/silicon ratio: 1.1) was subjected to impurity removal through acid pickling to obtain an aluminum-silicon oxide material with an Al.sub.2O.sub.3 content of 48.4 wt % and a SiO.sub.2 content of 47.3 wt %.

[0082] A pre-alloyed CuAl alloy with an Al content of 65 at % was accommodated at a bottom of a double-chamber electrolytic cell, graphite was adopted as an anode, and a TiB.sub.2/C composite material was adopted as a cathode. An anode electrolyte was CaCl.sub.2), and a composition of a cathode electrolyte was as follows: 60 wt % BaCl.sub.2+20 wt % AlF.sub.3+20 wt % NaF. The double-chamber electrolytic cell was heated to 860? C. and kept at this temperature for 2 h, a direct current was introduced to control an anode current density at 1.0 A/cm.sup.2, and before and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 24 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.963 wt %.

[0083] After the electrolysis, the copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of 9.2 at %. The copper-aluminum-silicon alloy was taken out and placed as an anode at a bottom of a single-chamber electrolytic cell, a graphite rod was adopted as a cathode, and a refining electrolyte was 25 wt % BaF.sub.2+50 wt % Na.sub.3AlF.sub.6+15 wt % AlF.sub.3+5 wt % K.sub.2SiF.sub.6+3 wt % CaF.sub.2+2 wt % LiF. The single-chamber electrolytic cell was heated to 900? C. and kept at this temperature for 2 h; first-stage electrolysis was conducted for 6 h at 880? C. and an anode current density of 1.0 A/cm.sup.2, and after the first-stage electrolysis was completed, metallic aluminum (a product at the cathode) was taken out; and then the single-chamber electrolytic cell was heated to 1,050? C., second-stage electrolysis was conducted for 4 h at 1,050? C. and an anode current density of 0.5 A/cm.sup.2 to obtain an aluminum-silicon alloy at the cathode.

[0084] The aluminum-silicon alloy was subjected to vacuum distillation (1,100? C., and gas pressure: lower than 1 Pa) to obtain polysilicon with a purity of 99.9%.

Example 5

[0085] Fly ash (Al.sub.2O.sub.3 content: 49.8 wt %, and aluminum/silicon ratio: 1.2) was fine-ground and then pre-desiliconized with a 20% NaOH solution at 120? C., and a resulting system was filtered to obtain a desiliconization liquid and desiliconization ash; CO.sub.2 was blown into the desiliconization liquid, a resulting system was filtered, and a resulting filter residue was dried to obtain white carbon black; the desiliconization ash was subjected to autoclaving-leaching with a NaOH solution of Na.sub.2O.sub.k=230 g/L at 250? C., and a resulting leaching system was diluted and then filtered to obtain a sodium aluminate solution and a leaching residue; the leaching residue was sintered with soda lime to further recover Al.sub.2O.sub.3 in the leaching residue; and the sodium aluminate solution was cooled to 75? C. without a deep desiliconization treatment using a lime, a solid aluminum hydroxide crystal seed was added to allow crystal seed decomposition, resulting solid aluminum hydroxide was mixed with the white carbon black, and a resulting mixture was calcined at 900? C. to obtain an aluminum-silicon oxide material with a Al.sub.2O.sub.3 content of 90.4% and a SiO.sub.2 content of 5.6%.

[0086] A pre-alloyed CuAl alloy with an Al content of 60 at % was accommodated at a bottom of a double-chamber electrolytic cell, a 5 wt % Ni-10 wt % NiONiFe.sub.2O.sub.4 metal/ceramic composite material was adopted as an inert anode, and TiB.sub.2 coated graphite was adopted as a cathode. A composition of an anode electrolyte was as follows: 82 wt % Na.sub.3AlF.sub.6+12 wt % AlF.sub.3+2 wt % Al.sub.2O.sub.3+2 wt % CaF.sub.2+1 wt % MgF.sub.2+1 wt % LiF; and a composition of a cathode electrolyte was as follows: 35 wt % BaF.sub.2+30 wt % AlF.sub.3+30 wt % NaF+5 wt % CaF.sub.2. The double-chamber electrolytic cell was heated to 950? C. and kept at this temperature for 2 h, and then energized to control an anode current density at 0.8 A/cm.sup.2, and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 16 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.983 wt %.

[0087] The copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of 0.5 at %. Thus, the above electrolysis experiment could still be continuously conducted for a long time to continuously produce metallic aluminum in a cathode chamber and enrich silicon in the alloy. When a silicon content in a copper-aluminum-silicon alloy was not less than 5 at %, electrolysis was conducted with the copper-aluminum-silicon alloy as an anode in a single-chamber electrolytic cell to obtain an aluminum-silicon alloy and/or polysilicon.

Example 6

[0088] Preparation of an alumina material from high-aluminum fly ash (Al.sub.2O.sub.3 content: 45.2 wt %, and aluminum/silicon ratio: 1.2) by an alkali-leaching pre-siliconization-soda lime sintering method: The high-aluminum fly ash raw material was pre-desiliconized with a NaOH solution at 120? C. for 30 min, and a resulting system was filtered to obtain a desiliconization ash; the desiliconization ash was mixed with limestone, raw coal, Na.sub.2CO.sub.3, or the like to obtain a raw material in which a CaO/(SiO.sub.2+TiO.sub.2) molar ratio was 2.0 and a Na.sub.2O/(Al.sub.2O.sub.3+Fe.sub.2O.sub.3) molar ratio was 1.0, and the raw material was sintered at 1,200? C. for 4 h to obtain a sintered material; the sintered material was crushed and then dissolved in an 80? C. sodium carbonate solution to obtain a material solution with a Al.sub.2O.sub.3 content of 90 g/L to 110 g/L, and the material solution was filtered; and without a deep desiliconization treatment using a lime, CO.sub.2 was directly blown into a resulting filtrate to allow carbonation decomposition, and a resulting product was filtered out and calcined to obtain an aluminum-silicon oxide material with an Al.sub.2O.sub.3 content of 96.4 wt % and a SiO.sub.2 content of 0.42 wt %.

[0089] A pre-alloyed CuAl alloy with an Al content of 65 at % was accommodated at a bottom of a double-chamber electrolytic cell, a Cu-13 wt % Fe-37 wt % Ni alloy material was adopted as an inert anode, and graphite was adopted as a cathode. A composition of an anode electrolyte was as follows: 42.3 wt % Na.sub.3AlF.sub.6+28.2 wt % K.sub.3AlF.sub.6+22 wt % AlF.sub.3+2.5 wt % Al.sub.2O.sub.3+3 wt % CaF.sub.2+2 wt % LiF; and a composition of a cathode electrolyte was as follows: 22 wt % BaF.sub.2+46 wt % AlF.sub.3+26 wt % NaF+4 wt % CaF.sub.2+2 wt % LiF. The double-chamber electrolytic cell was heated to 880? C. and kept at this temperature for 2 h, a direct current was introduced to control an anode current density at 0.6 A/cm.sup.2, and after electrolysis started, the aluminum-silicon oxide material was regularly fed, where a total electrolysis time was 10 h. After the electrolysis was completed, an Al content in metallic aluminum (a product at the cathode) was determined to be 99.991 wt %.

[0090] The copper-aluminum alloy at the bottom of the double-chamber electrolytic cell was converted into a copper-aluminum-silicon alloy with a Si content of less than 0.1 at %. Thus, the above electrolysis experiment could still be continuously conducted for a long time to continuously produce metallic aluminum in a cathode chamber and enrich silicon in the alloy. When a silicon content in a copper-aluminum-silicon alloy was not less than 5 at %, electrolysis was conducted with the copper-aluminum-silicon alloy as an anode in a single-chamber electrolytic cell to obtain an aluminum-silicon alloy and/or polysilicon.

[0091] The above are merely specific implementations of the present application, but are not intended to limit the protection scope of the present application. Any variation or replacement readily conceived by a person skilled in the art within the technical scope disclosed in the present application shall fall within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.