Alkali leaching recovery method for shell blocks in electrolytic aluminum factory

Abstract

The invention discloses an alkaline leaching recovery method for shell blocks in an electrolytic aluminum factory. The alkaline leaching recovery method comprises the following steps: S1, pretreatment; s2, leaching reaction; s3, primary solid-liquid separation; s4, treating the leachate; and S5, treatment of leaching residues. The method has the advantages that (1) cryolite in the shell surface block of the electrolytic aluminum factory is dissolved under the alkaline condition and then reacts with alkaline calcium, so that the shell surface block is dissolved thoroughly; wherein the alkaline calcium can be selected from carbide slag or calcium hydroxide, particularly, the carbide slag is common solid waste, and the aim of comprehensively utilizing waste can be achieved by taking the carbide slag as a main auxiliary material; (2) aluminum hydroxide and anhydrous sodium carbonate are obtained after the alkaline leaching liquid is treated, and higher economic benefits can be generated; (3) after leaching acid is added into the leaching residues, the purposes of reducing the content of lithium fluoride and CaAl2 (OH) 8 in the solid waste and increasing the main content of calcium fluoride are achieved; and adding sodium carbonate into the residual lithium salt solution to purify and separate out a calcium carbonate product, and then carrying out subsequent treatment to further obtain a lithium carbonate product.

Description

Technical Field

[0001] The invention relates to the technical field of shell surface block recovery in an aluminum electrolytic plant, and in particular to an alkali leaching recovery method for shell surface blocks in an aluminum electrolytic plant. Background Art

[0002] The scrapped shell blocks produced by the electrolytic aluminum plant are electrolyte hard shells on the surface of the metallic aluminum liquid, which contain metallic aluminum, metallic lithium and cryolite. At present, lithium carbonate manufacturers mainly recycle the metallic lithium as one of the raw materials for lithium carbonate required by the new energy industry. The main recycling method is to grind the shell blocks into powder through a jaw crusher, a cone mill and a Raymond mill, and then add hydrochloric acid or sulfuric acid to the powder to react, converting fluorine into metacryosphere, aluminum trifluoride and other substances, and sodium into sodium chloride or sodium sulfate, so as to achieve the purpose of decomposing Na3AlF6. At the same time, the lithium in the shell blocks is also converted into lithium chloride or lithium sulfate; the decomposed acid slag is filtered and washed to obtain aluminum fluoride slag, and an acidic decomposition liquid containing a large amount of aluminum and fluorine is obtained; the acidic decomposition liquid is then added with sodium carbonate, calcium carbonate or calcium hydroxide for purification and impurity removal, and the impurity removal slurry is filtered and washed to obtain aluminum fluoride calcium purification slag and sodium chloride lithium solution or sodium sulfate lithium solution. The purified sodium chloride lithium or sodium sulfate lithium solution is then evaporated and concentrated to increase the lithium content, and then sodium carbonate solution is added to precipitate lithium carbonate.

[0003] The above method mainly recovers lithium, and sodium chloride or sodium sulfate is recovered as a by-product, while the aluminum-fluorine slag is treated as solid waste, and aluminum and fluorine are not recovered, resulting in a waste of resources; and, during the purification and impurity removal, a large amount of aluminum precipitates and adsorbs lithium, resulting in a low recovery rate of metallic lithium. Summary of the invention

[0004] The object of the present invention is to provide a method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching.

[0005] The present invention is implemented by the following technical scheme: A method for recovering shell surface blocks from an electrolytic aluminum plant by alkali leaching, comprising the following steps: S1: Preprocessing The shell blocks of the electrolytic aluminum plant are crushed and the elemental aluminum therein is sorted out, specifically, it can be sorted manually; then finely ground into powder of no more than 120 meshes to obtain powder to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with alkaline calcium and water in a solid-liquid ratio of 1:2-6 to prepare a slurry, wherein the weight ratio of Na3AlF6 to alkaline calcium in the shell surface block is 0.8-1.0, and a leaching slurry is obtained after leaching reaction; the alkaline calcium added is calcium hydroxide, for example, and the reaction process is as follows: 2Na3AlF6+ 7Ca(OH)2= 6NaOH + 6CaF2↓+CaAl2(OH)8↓ 2Na2LiAlF6+ 7Ca(OH)2= 4NaOH + 2LiOH + 6CaF2↓+ CaAl2(OH)8↓ Na3AlF6+ 2Ca(OH)2=2NaF + NaAlO2+ 2CaF2↓+2H2O Na3AlF6+ Ca(OH)2=NaAlF4+ 2NaOH + CaF2↓ +2H2O 2KF+ Ca(OH)2=2KOH+ CaF2↓ Li + +F - = LiF↓ S3: Primary solid-liquid separation The leached slurry obtained from S2 is subjected to a solid-liquid separation to obtain CaAl2(OH) 8、 The leaching residue is mainly composed of CaF2 and LiF, and the leaching solution is mainly composed of NaOH, LiOH, NaAlO2 and KOH; S4: Leachate treatment The leachate obtained in S3 is treated to obtain aluminum hydroxide and anhydrous sodium carbonate; S5: Leaching residue treatment The leached residue obtained from S3 is treated to obtain calcium fluoride, calcium carbonate and lithium carbonate.

[0006] Furthermore, the reaction temperature of S2 is 40-105° C., and the reaction time is 30-300 min.

[0007] Furthermore, the specific processing process of S5 is as follows: S5-1: The leaching residue obtained in S3 is mixed with leaching acid and water to obtain a leaching residue slurry with a solid-liquid ratio of 1:1-4, and the pH is adjusted to 0.5-5, the temperature is 30-100°C, and the reaction time is 30-300min; the reaction equation is as follows: CaAl2(OH)8+2HCl=2Al(OH)3↓+CaCl2+2H2O Ca(OH)2 + 2HCl = CaCl2 + 2H2O 2LiF + CaCl2 = 2LiCl + CaF2↓ S5-2: performing secondary solid-liquid separation on the leached residue slurry obtained in S5-1 to obtain a calcium fluoride product containing a small amount of aluminum hydroxide; S5-3: adding sodium carbonate to the solution obtained by the secondary solid-liquid separation for purification, adjusting the pH to 6, the purification temperature to 30-100° C., and the time to 30-300 min, and then performing a third solid-liquid separation to obtain calcium carbonate; S5-4: The solution obtained from the three solid-liquid separations is reacted with a 10-30% soda ash solution to obtain a lithium carbonate slurry, the reaction temperature is 80-100°C, the reaction time is 30-300 min, and the soda ash is 10-30% more than the lithium in the solution; S5-5: performing four solid-liquid separations on the lithium carbonate slurry to obtain wet lithium carbonate and a crystallization mother liquor; S5-6: first add water to the wet lithium carbonate solution obtained in S5-5 to make a slurry, wash off the surface solution, and improve its purity; then perform solid-liquid separation to obtain hydrous lithium carbonate, and dry the hydrous lithium carbonate to obtain a lithium carbonate product; S5-7: adding hydrochloric acid, sulfuric acid or nitric acid to the crystallization mother solution obtained in S5-5 to obtain a sodium salt solution; S5-8: evaporating and concentrating the sodium salt solution obtained in S5-7 and then centrifuging to obtain a sodium salt crystal product; S5-9: Repeat the processing steps from S5-4 to S5-8 for the mother liquor obtained by centrifugation in S5-8.

[0008] Furthermore, the leaching acid in S5-1 is hydrochloric acid, sulfuric acid or nitric acid.

[0009] Furthermore, the specific processing process of S4 is as follows: S4-1: Cool the leaching solution obtained in S3 and add an alkaline extractant (HBL121 or 3938H) to separate the lithium salt solution to obtain a first solution; S4-2: introducing carbon dioxide gas into the first solution obtained in S4-1 to obtain a first sodium carbonate slurry containing aluminum hydroxide; the reaction equation is as follows: CO2 + 2NaOH = Na2CO3 + H2O 2NaAlO2+ CO2+ 3H2O = 2Al(OH)3↓ + Na2CO3 2KOH + CO2 = K2CO3 + H2O S4-3: subjecting the first sodium carbonate slurry to five solid-liquid separations to separate the aluminum hydroxide product, thereby obtaining a second sodium carbonate solution; S4-4: evaporating and crystallizing the second sodium carbonate solution to obtain a second sodium carbonate slurry, and then centrifuging to obtain a sodium carbonate solid and a saturated sodium carbonate solution; S4-5: Flash-drying the sodium carbonate solid to obtain anhydrous sodium carbonate.

[0010] Furthermore, the cooling temperature in S4-1 is 40°C.

[0011] Furthermore, the lithium salt solution separated in S4-1 is sent to S5-3 and purified together with the solution obtained from the secondary solid-liquid separation by adding sodium carbonate.

[0012] Furthermore, the alkaline calcium in S2 is carbide slag or calcium hydroxide.

[0013] The advantages of the present invention are as follows: (1) cryolite in the shell blocks of the electrolytic aluminum plant is dissolved under alkaline conditions and then reacts with alkaline calcium, so that the shell blocks are completely dissolved; the alkaline calcium can be selected from carbide slag or calcium hydroxide, which has a lower cost than hydrochloric acid or sulfuric acid; in particular, carbide slag is a general solid waste, and the present invention uses it as the main auxiliary material, which can achieve the purpose of comprehensive utilization of wastes and reduce solid waste emissions; (2) after the alkaline leaching liquid is added with an alkaline extractant to extract lithium, carbon dioxide is introduced, and then five solid-liquid separations are performed to obtain an aluminum hydroxide product, and the second sodium carbonate solution after the five solid-liquid separations is evaporated, crystallized, and flash dried to obtain anhydrous sodium carbonate, which is nearly 10 times more valuable than sodium chloride and sodium sulfate, and can produce more High economic benefits; (3) After the leaching residue is added with leaching acid, the CaAl2(OH)8 in the alkaline leaching residue can be decomposed into aluminum hydroxide and calcium salt, and the calcium salt can be combined with lithium fluoride to further produce calcium fluoride. After solid-liquid separation, a calcium fluoride product containing aluminum hydroxide can be obtained, thereby achieving the purpose of reducing the content of lithium fluoride and CaAl2(OH)8 in solid waste and increasing the main content of calcium fluoride, thereby improving economic benefits; the remaining lithium salt solution is purified by adding sodium carbonate to separate the calcium carbonate product, and then after subsequent treatment, a lithium carbonate product can be further obtained. The produced lithium carbonate product has a low sodium characteristic and has the conditions for producing industrial-grade and battery-grade lithium carbonate, and has a high economic value. DETAILED DESCRIPTION

[0014] Example 1: A method for recovering shell surface blocks from an electrolytic aluminum plant by alkali leaching, comprising the following steps: S1: Preprocessing The shell blocks of the aluminum smelter are crushed to separate the elemental aluminum therein, and then finely ground into 120 mesh powder to obtain the powder to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with calcium hydroxide and water in a solid-liquid ratio of 1:2 to prepare a slurry, wherein the weight ratio of Na3AlF6 to alkaline calcium in the shell surface block is 0.8, the reaction temperature is 40°C, the reaction time is 300 minutes, and a leaching slurry is obtained after a leaching reaction; S3: Primary solid-liquid separation The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid; S4: Leachate treatment The leachate obtained in S3 is treated to obtain aluminum hydroxide and anhydrous sodium carbonate; the specific treatment process of S4 is as follows: S4-1: Cool the leaching solution obtained in S3 to 40° C. and add an alkaline extractant to separate the lithium salt solution to obtain a first solution; S4-2: introducing carbon dioxide gas into the first solution obtained in S4-1 to obtain a first sodium carbonate slurry containing aluminum hydroxide; S4-3: subjecting the first sodium carbonate slurry to five solid-liquid separations to separate the aluminum hydroxide product, thereby obtaining a second sodium carbonate solution; S4-4: evaporating and crystallizing the second sodium carbonate solution to obtain a second sodium carbonate slurry, and then centrifuging to obtain a sodium carbonate solid and a saturated sodium carbonate solution; S4-5: Flash-drying the sodium carbonate solid to obtain anhydrous sodium carbonate.

[0015] S5: Leaching residue treatment The leaching residue obtained in S3 is treated to obtain calcium fluoride, calcium carbonate and lithium carbonate. The specific treatment process of S5 is as follows: S5-1: The leached residue obtained in S3 is mixed with hydrochloric acid and water to obtain a leached residue slurry with a solid-liquid ratio of 1:1, and the pH is adjusted to 0.5, the temperature is 30°C, and the reaction time is 300 min; S5-2: performing secondary solid-liquid separation on the leached residue slurry obtained in S5-1 to obtain a calcium fluoride product; S5-3: The solution obtained by the secondary solid-liquid separation is purified by adding sodium carbonate, the pH is adjusted to 6, the purification temperature is 30° C., and the time is 300 min, and then the solid-liquid separation is performed three times to obtain calcium carbonate; S5-4: The solution obtained from the three solid-liquid separations is reacted with a 10% soda ash solution to obtain a lithium carbonate slurry. The reaction temperature is 80°C, the reaction time is 300 min, and the soda ash is 30% more than the lithium in the solution. S5-5: performing four solid-liquid separations on the lithium carbonate slurry to obtain wet lithium carbonate and a crystallization mother liquor; S5-6: first adding water to the wet lithium carbonate solution obtained in S5-5 to prepare a slurry, then performing solid-liquid separation to obtain hydrous lithium carbonate, and then drying the hydrous lithium carbonate to obtain a lithium carbonate product; S5-7: adding hydrochloric acid to the crystallization mother solution obtained in S5-5 to obtain a sodium salt solution; S5-8: evaporating and concentrating the sodium salt solution obtained in S5-7 and then centrifuging to obtain a sodium salt crystal product (sodium chloride); S5-9: Repeat the processing steps from S5-4 to S5-8 for the mother liquor obtained by centrifugation in S5-8.

[0016] The lithium salt solution separated in S4-1 is sent to S5-3 and purified together with the solution obtained from the secondary solid-liquid separation by adding sodium carbonate.

[0017] Embodiment 2: A method for recovering shell surface blocks from an electrolytic aluminum plant by alkali leaching, comprising the following steps: S1: Preprocessing The shell blocks of the aluminum smelter are crushed to separate the elemental aluminum therein, and then finely ground into 100-mesh powder to obtain the powder to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with calcium hydroxide and water at a solid-liquid ratio of 1:6 to prepare a slurry, wherein the weight ratio of Na3AlF6 to alkaline calcium in the shell surface block is 1.0, the reaction temperature is 105°C, the reaction time is 30 minutes, and a leaching slurry is obtained after leaching reaction; S3: Primary solid-liquid separation The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid; S4: Leachate treatment The leachate obtained in S3 is treated to obtain aluminum hydroxide and anhydrous sodium carbonate; the specific treatment process of S4 is as follows: S4-1: Cool the leaching solution obtained in S3 to 40° C. and add an alkaline extractant to separate the lithium salt solution to obtain a first solution; S4-2: introducing carbon dioxide gas into the first solution obtained in S4-1 to obtain a first sodium carbonate slurry containing aluminum hydroxide; S4-3: subjecting the first sodium carbonate slurry to five solid-liquid separations to separate the aluminum hydroxide product, thereby obtaining a second sodium carbonate solution; S4-4: evaporating and crystallizing the second sodium carbonate solution to obtain a second sodium carbonate slurry, and then centrifuging to obtain a sodium carbonate solid and a saturated sodium carbonate solution; S4-5: Flash-drying the sodium carbonate solid to obtain anhydrous sodium carbonate.

[0018] S5: Leaching residue treatment The leaching residue obtained in S3 is treated to obtain calcium fluoride, calcium carbonate and lithium carbonate. The specific treatment process of S5 is as follows: S5-1: The leached residue obtained in S3 is mixed with sulfuric acid and water to obtain a leached residue slurry with a solid-liquid ratio of 1:4, and the pH is adjusted to 5, the temperature is 100°C, and the reaction time is 30 minutes; S5-2: performing secondary solid-liquid separation on the leached residue slurry obtained in S5-1 to obtain a calcium fluoride product; S5-3: adding sodium carbonate to the solution obtained by the secondary solid-liquid separation for purification, adjusting the pH to 6, the purification temperature to 100° C., the time to 30 min, and then performing a third solid-liquid separation to obtain calcium carbonate; S5-4: The solution obtained from the three solid-liquid separations is reacted with a 30% soda ash solution to obtain a lithium carbonate slurry. The reaction temperature is 100°C, the reaction time is 30 minutes, and the soda ash is 10% more than the lithium in the solution. S5-5: performing four solid-liquid separations on the lithium carbonate slurry to obtain wet lithium carbonate and a crystallization mother liquor; S5-6: first adding water to the wet lithium carbonate solution obtained in S5-5 to prepare a slurry, then performing solid-liquid separation to obtain hydrous lithium carbonate, and then drying the hydrous lithium carbonate to obtain a lithium carbonate product; S5-7: adding sulfuric acid to the crystallization mother solution obtained in S5-5 to react and obtain a sodium salt solution; S5-8: evaporating and concentrating the sodium salt solution obtained in S5-7 and then centrifuging to obtain a sodium salt crystal product (sodium sulfate); S5-9: The mother liquor obtained by centrifugation in S5-8 is returned to S5-4.

[0019] The lithium salt solution separated in S4-1 is sent to S5-3 and purified together with the solution obtained from the secondary solid-liquid separation by adding sodium carbonate.

[0020] Embodiment 3: A method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching, comprising the following steps: S1: Preprocessing The shell blocks of the aluminum smelter are crushed to separate the elemental aluminum therein, and then finely ground into 80 mesh powder to obtain the powder to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with calcium carbide slag and water at a solid-liquid ratio of 1:4 to prepare a slurry, wherein the weight ratio of Na3AlF6 to alkaline calcium in the shell surface block is 0.9, the reaction temperature is 80°C, the reaction time is 160 minutes, and a leaching slurry is obtained after the leaching reaction; S3: Primary solid-liquid separation The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid; S4: Leachate treatment The leachate obtained in S3 is treated to obtain aluminum hydroxide and anhydrous sodium carbonate; the specific treatment process of S4 is as follows: S4-1: Cool the leaching solution obtained in S3 to 40° C. and add an alkaline extractant to separate the lithium salt solution to obtain a first solution; S4-2: introducing carbon dioxide gas into the first solution obtained in S4-1 to obtain a first sodium carbonate slurry containing aluminum hydroxide; S4-3: subjecting the first sodium carbonate slurry to five solid-liquid separations to separate the aluminum hydroxide product, thereby obtaining a second sodium carbonate solution; S4-4: evaporating and crystallizing the second sodium carbonate solution to obtain a second sodium carbonate slurry, and then centrifuging to obtain a sodium carbonate solid and a saturated sodium carbonate solution; S4-5: Flash-drying the sodium carbonate solid to obtain anhydrous sodium carbonate.

[0021] S5: Leaching residue treatment The leaching residue obtained in S3 is treated to obtain calcium fluoride, calcium carbonate and lithium carbonate. The specific treatment process of S5 is as follows: S5-1: adding nitric acid and water to the leached residue obtained in S3 to obtain a leached residue slurry with a solid-liquid ratio of 1:2, adjusting the pH to 3, the temperature to 60°C, and the reaction time to 150 min; S5-2: performing secondary solid-liquid separation on the leached residue slurry obtained in S5-1 to obtain a calcium fluoride product; S5-3: The solution obtained by the secondary solid-liquid separation is purified by adding sodium carbonate, the pH is adjusted to 6, the purification temperature is 60° C., and the time is 150 min, and then the solid-liquid separation is performed three times to obtain calcium carbonate; S5-4: The solution obtained from the three solid-liquid separations is reacted with a 10-30% soda ash solution to obtain a lithium carbonate slurry, the reaction temperature is 90°C, the reaction time is 150 minutes, and the soda ash is 20% more than the lithium in the solution; S5-5: performing four solid-liquid separations on the lithium carbonate slurry to obtain wet lithium carbonate and a crystallization mother liquor; S5-6: first adding water to the wet lithium carbonate solution obtained in S5-5 to prepare a slurry, then performing solid-liquid separation to obtain hydrous lithium carbonate, and then drying the hydrous lithium carbonate to obtain a lithium carbonate product; S5-7: adding nitric acid to the crystallization mother solution obtained in S5-5 to obtain a sodium salt solution; S5-8: evaporating and concentrating the sodium salt solution obtained in S5-7 and then centrifuging to obtain a sodium salt crystal product (sodium nitrate); S5-9: The mother liquor obtained by centrifugation in S5-8 is returned to S5-4.

[0022] The lithium salt solution separated in S4-1 is sent to S5-3 and purified together with the solution obtained from the secondary solid-liquid separation by adding sodium carbonate.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching, characterized in that: The steps include: S1: Preprocessing The shell blocks of the aluminum smelter are crushed to separate the elemental aluminum therein, and then finely ground into powders not larger than 120 meshes to obtain powders to be processed; S2: Leaching reaction The powder to be treated obtained in S1 is mixed with alkaline calcium and water in a solid-liquid ratio of 1:2-6 to prepare a slurry, wherein the weight ratio of Na3AlF6 to alkaline calcium in the shell surface block is 0.8-1.0, and a leaching slurry is obtained after a leaching reaction; S3: Primary solid-liquid separation The leached slurry obtained in S2 is subjected to a solid-liquid separation to obtain leached residue and leached liquid; S4: Leachate treatment The leachate obtained in S3 is treated to obtain aluminum hydroxide and anhydrous sodium carbonate; S5: Leaching residue treatment The leached residue obtained from S3 is treated to obtain calcium fluoride, calcium carbonate and lithium carbonate.

2. The method for recovering shell surface blocks of an electrolytic aluminum plant by alkali leaching according to claim 1, characterized in that: The reaction temperature of S2 is 40-105°C, and the reaction time is 30-300 minutes.

3. The method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching according to claim 1, characterized in that: The specific processing process of S5 is as follows: S5-1: adding leaching acid and water to the leaching residue obtained in S3 to obtain a leaching residue slurry with a solid-liquid ratio of 1:1-4, adjusting the pH to 0.5-5, the temperature to 30-100°C, and the reaction time to 30-300min; S5-2: performing secondary solid-liquid separation on the leached residue slurry obtained in S5-1 to obtain a calcium fluoride product; S5-3: adding sodium carbonate to the solution obtained by the secondary solid-liquid separation for purification, adjusting the pH to 6, the purification temperature to 30-100° C., and the time to 30-300 min, and then performing a third solid-liquid separation to obtain calcium carbonate; S5-4: The solution obtained from the three solid-liquid separations is reacted with a 10-30% soda ash solution to obtain a lithium carbonate slurry, the reaction temperature is 80-100°C, the reaction time is 30-300 min, and the soda ash is 10-30% more than the lithium in the solution; S5-5: performing four solid-liquid separations on the lithium carbonate slurry to obtain wet lithium carbonate and a crystallization mother liquor; S5-6: first adding water to the wet lithium carbonate solution obtained in S5-5 to prepare a slurry, then performing solid-liquid separation to obtain hydrous lithium carbonate, and then drying the hydrous lithium carbonate to obtain a lithium carbonate product; S5-7: adding hydrochloric acid, sulfuric acid or nitric acid to the crystallization mother solution obtained in S5-5 to obtain a sodium salt solution; S5-8: evaporating and concentrating the sodium salt solution obtained in S5-7 and then centrifuging to obtain a sodium salt crystal product; S5-9: Repeat the processing steps from S5-4 to S5-8 for the mother liquor obtained by centrifugation in S5-8.

4. The method for recovering shell surface blocks of an electrolytic aluminum plant by alkali leaching according to claim 3, characterized in that: The leaching acid in S5-1 is hydrochloric acid, sulfuric acid or nitric acid.

5. The method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching according to claim 3, characterized in that: The specific processing process of S4 is as follows: S4-1: cooling the leaching solution obtained in S3 and adding an alkaline extractant to separate the lithium salt solution to obtain a first solution; S4-2: introducing carbon dioxide gas into the first solution obtained in S4-1 to obtain a first sodium carbonate slurry containing aluminum hydroxide; S4-3: subjecting the first sodium carbonate slurry to five solid-liquid separations to separate the aluminum hydroxide product, thereby obtaining a second sodium carbonate solution; S4-4: evaporating and crystallizing the second sodium carbonate solution to obtain a second sodium carbonate slurry, and then centrifuging to obtain a sodium carbonate solid and a saturated sodium carbonate solution; S4-5: Flash-drying the sodium carbonate solid to obtain anhydrous sodium carbonate.

6. The method for recovering shell surface blocks of an electrolytic aluminum plant by alkali leaching according to claim 5, characterized in that: The cooling temperature in S4-1 is 40°C.

7. The method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching according to claim 5, characterized in that: The lithium salt solution separated in S4-1 is sent to S5-3 and purified together with the solution obtained from the secondary solid-liquid separation by adding sodium carbonate.

8. The method for recovering shell surface blocks from an aluminum electrolytic plant by alkali leaching according to claim 1, characterized in that: The alkaline calcium in S2 is carbide slag or calcium hydroxide.