Method for comprehensively recycling fluorine-fixing cathode carbon blocks

Abstract

The invention provides a method for comprehensively recycling a fluorine-fixing cathode carbon block, which realizes the effective recovery of carbon resources and fluorine resources in the waste cathode carbon block through the working procedures of low-temperature fused salt conversion, wet grinding leaching, wet grinding alkaline conversion, neutralization, acid leaching, flotation, evaporative crystallization and the like on the waste cathode carbon block. According to the method, conversion and separation of fluorides and cyanides in the waste cathode carbon blocks are achieved through low-temperature molten salt conversion and wet grinding leaching, fluorinated products enter the leaching residues, cyanidation products are converted into nitrate products to complete detoxification of the cyanides and enter the leaching liquid, the leaching residues are subjected to wet grinding alkali conversion separation to obtain alkali conversion residues and alkali conversion liquid, and the alkali conversion residues and the alkali conversion liquid are recycled. Neutralizing the alkali transfer liquid, and performing evaporative crystallization to obtain sodium fluoride; and the alkali transfer slag is subjected to sulfuric acid leaching, flotation and other operations to obtain graphite, gypsum and recyclable magnesium nitrate hexahydrate, and resource utilization of the waste cathode carbon blocks is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hazardous solid waste treatment, and particularly relates to a method for comprehensive recycling of a fluorine-fixed cathode carbon block. Background Art

[0002] China is the country with the largest production of primary aluminum in the world. According to the statistics of the National Bureau of Statistics, the global production of primary aluminum in 2018 was approximately 64.336 million tons, of which the production in China was 36.485 million tons, accounting for 56.7% of the global total. As is well known, metallic aluminum is mainly produced by the electrolysis method. During the electrolysis of aluminum, electrolytes such as aluminum fluoride, cryolite, and sodium fluoride are usually added to reduce the electrolysis temperature, thereby achieving the effect of energy conservation. However, as the electrolysis process continues, F - , Na + plasma will gradually penetrate into the cathode, anode, and thermal insulation board of the aluminum electrolysis cell, resulting in damage to their structures and inability to continue operating efficiently. Therefore, the lining of the electrolysis cell and the cathode and anode materials need to be replaced regularly, and the replacement cycle is generally 3 - 6 years, thus generating a large amount of waste cell lining materials including waste cathode carbon blocks. According to statistics, about 5 - 10 kg of waste cathode carbon blocks are produced for every 1 ton of metallic aluminum produced. The waste cathode carbon block contains 60 - 70% carbon component and 30% - 40% electrolyte component, and is a mineral resource rich in carbon and fluorides. Taking the electrolytic aluminum production in China in 2020 of about 37.08 million tons as an example, it is estimated that the waste cathode carbon blocks produced in China every year are about 200,000 - 400,000 tons. The waste cathode carbon block belongs to hazardous solid waste. If not treated or utilized in time, toxic substances such as fluorides and cyanides in it will be transferred to the atmosphere, soil, and groundwater through wind, sun, and rain, seriously threatening the health and survival of animals, plants, and humans.

[0003] Therefore, how to provide a method for comprehensive recycling of a fluorine-fixed cathode carbon block, realizing the conversion of fluorides through low-temperature molten salt conversion and the detoxification of cyanides through wet grinding leaching, so as to achieve the harmless treatment and resource utilization of waste cathode carbon blocks, is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for comprehensive recycling of a fluorine-fixed cathode carbon block to solve at least one of the above technical problems.

[0005] To achieve the above object, a first aspect of the present invention provides a method for comprehensive recycling of fluorine-fixed cathode carbon blocks. The method includes the following steps: S1. Perform low-temperature molten salt conversion on waste cathode carbon blocks and magnesium nitrate hexahydrate to obtain calcined slag; S2. Perform wet grinding and leaching on the calcined slag to obtain leached residue and leachate; S3. Add sodium hydroxide to the leached residue for wet grinding and alkali conversion to obtain alkali conversion liquid and alkali conversion residue; S4. Add hydrofluoric acid to the alkali conversion liquid for neutralization to obtain neutralized liquid; S5. Perform evaporation crystallization on the neutralized liquid to obtain sodium fluoride and sodium fluoride crystallization mother liquor, and recycle the sodium fluoride crystallization mother liquor to the wet grinding and alkali conversion; S6. Add sulfuric acid to the alkali conversion residue for acid leaching to obtain acid leached residue and acid leachate; S7. Perform flotation on the acid leached residue to obtain graphite and gypsum; S8. Add calcium nitrate and the leachate to the acid leachate for reaction to obtain regenerated residue and regenerated liquid; S9. Perform evaporation crystallization on the regenerated liquid to obtain magnesium nitrate hexahydrate and magnesium nitrate crystallization mother liquor, recycle the magnesium nitrate hexahydrate to the low-temperature molten salt conversion, and recycle the magnesium nitrate crystallization mother liquor to the acid leachate.

[0006] In the first aspect, in S1, the addition amount of magnesium nitrate hexahydrate is 1-2 times the theoretical reaction molar ratio of fluoride in the waste cathode carbon blocks, the temperature of the low-temperature molten salt conversion is 100-600 °C, and the time of the low-temperature molten salt conversion is 2-8 h.

[0007] In the first aspect, in S2, the process parameters of the wet grinding and leaching include: liquid-solid ratio is 4-10 mL / g, ball-to-material ratio is 6-10, ball milling time is 0.5-1.5 h, and ball milling speed is 100-200 r / min.

[0008] In the first aspect, in S3, the addition amount of sodium hydroxide is 1-2 times the theoretical reaction molar ratio of fluoride in the leached residue.

[0009] In the first aspect, the process parameters of the wet grinding and alkali conversion include: liquid-solid ratio is 1-4 mL / g, ball-to-material ratio is 8-12, ball milling time is 2-4 h, and ball milling speed is 400-600 r / min.

[0010] In the first aspect, in S5, the temperature of the evaporation crystallization is 100-110 °C.

[0011] In the first aspect, in S6, the addition amount of sulfuric acid is 1.5-2.0 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali conversion residue; the process parameters of the acid leaching include: acid leaching time is 0.2-2 h, liquid-solid ratio is 8-14 mL / g, acid leaching temperature is 25-50 °C, and stirring speed is 200-600 r / min.

[0012] In the first aspect, in the S7, the process parameters of the flotation include: the flotation time is 3 - 6 min, the flotation rotation speed is 1200 - 1600 r / min, and the dosage of the flotation reagent is 50 - 100 g / t. Among them, the flotation reagent is kerosene and No. 2 oil.

[0013] In the first aspect, in the S8, the addition amount of calcium nitrate is 1 - 2 times the theoretical reaction molar ratio of sulfate radicals in the acid leaching solution.

[0014] In the first aspect, in the S9, the temperature of the evaporation crystallization is 100 - 110 °C.

[0015] Beneficial effects:

[0016] A method for comprehensive recycling of a fluorine - fixed cathode carbon block provided by the present invention first performs low - temperature roasting on waste cathode carbon blocks and magnesium nitrate hexahydrate to convert the fluorides in the waste cathode carbon blocks. Immediately afterwards, wet - grinding leaching is performed on the roasted slag to achieve the conversion of cyanides in the waste cathode carbon blocks, so that the fluorinated products enter the leaching residue, and the cyanided products are converted into nitrate products to complete the detoxification of cyanides. Secondly, sodium hydroxide is added to the leaching residue, and through the wet - grinding process, the fluorinated products in the leaching residue can be completely dissolved into the alkali - conversion liquid, and the insoluble alkali - conversion slag is treated by sulfuric acid acid leaching. Then, hydrofluoric acid is added to the alkali - conversion liquid for a neutralization reaction, and the obtained neutralized liquid is subjected to evaporation crystallization to obtain sodium fluoride and a sodium fluoride crystallization mother liquor, where the sodium fluoride crystallization mother liquor can be recycled to the wet - grinding alkali - conversion process. Finally, a flotation operation is performed on the acid - leaching residue obtained by sulfuric acid acid leaching to obtain graphite and gypsum; calcium nitrate is added to the acid - leaching solution obtained by sulfuric acid acid leaching for a displacement reaction to obtain a regenerated slag mainly composed of calcium sulfate and a regenerated liquid mainly composed of magnesium nitrate. Evaporation crystallization is performed on the regenerated liquid to obtain magnesium nitrate hexahydrate and a magnesium nitrate crystallization mother liquor. The magnesium nitrate crystallization mother liquor can be recycled to the acid - leaching solution, and magnesium nitrate hexahydrate is used as a raw material to continue the low - temperature molten salt conversion with the waste cathode carbon blocks, thereby completing the comprehensive utilization of the waste cathode carbon blocks and realizing the harmless treatment of the waste cathode carbon blocks. The present invention realizes the conversion and separation of fluorides and cyanides in the waste cathode carbon blocks through low - temperature molten salt conversion and wet - grinding leaching, so that the fluorinated products enter the leaching residue, and the cyanided products are converted into nitrate products to complete the detoxification of cyanides and enter the leaching solution. The leaching residue is subjected to wet - grinding alkali - conversion separation to obtain alkali - conversion slag and alkali - conversion liquid. The alkali - conversion liquid is neutralized and subjected to evaporation crystallization to obtain sodium fluoride, which can be used as a phosphating accelerator, agricultural insecticide, sealing material, preservative, etc. in the coating industry; the alkali - conversion slag is subjected to sulfuric acid acid leaching, flotation and other operations to obtain graphite, gypsum and recyclable magnesium nitrate hexahydrate, realizing the resource utilization of the waste cathode carbon blocks.

[0017] The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are specifically exemplified below. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present specification or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 Flow chart of a method for comprehensive recycling and utilization of a fluorine-fixing cathode carbon block provided by the present invention Figure 1 ;

[0020] Figure 2 Flow chart of a method for comprehensive recycling and utilization of a fluorine-fixing cathode carbon block provided by the present invention Figure 2 。 Detailed Embodiments

[0021] The following will specifically describe the present invention in combination with the specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention, rather than to limit the present invention.

[0022] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention pertains. In case of contradiction, this specification shall prevail.

[0023] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be obtained by existing methods.

[0024] Please refer to Figure 1-2, a method for comprehensive recycling of a fluorine-fixed cathode carbon block provided by the present application, the method comprising the following steps: S1. performing low-temperature molten salt conversion on waste cathode carbon blocks and magnesium nitrate hexahydrate to obtain calcined slag; S2. performing wet grinding leaching on the calcined slag to obtain leached residue and leachate; S3. adding sodium hydroxide to the leached residue and performing wet grinding alkali conversion to obtain an alkali conversion solution and alkali conversion residue; S4. adding hydrofluoric acid to the alkali conversion solution for neutralization to obtain a neutralization solution; S5. performing evaporation crystallization on the neutralization solution to obtain sodium fluoride and a sodium fluoride crystallization mother liquor, and recycling the sodium fluoride crystallization mother liquor to the wet grinding alkali conversion; S6. adding sulfuric acid to the alkali conversion residue for acid leaching to obtain acid leached residue and acid leachate;

[0025] S7. performing flotation on the acid leached residue to obtain graphite and gypsum; S8. adding calcium nitrate and the leachate to the acid leachate for reaction to obtain a regenerated residue and a regenerated solution; S9. performing evaporation crystallization on the regenerated solution to obtain magnesium nitrate hexahydrate and a magnesium nitrate crystallization mother liquor, recycling the magnesium nitrate hexahydrate to the low-temperature molten salt conversion, and recycling the magnesium nitrate crystallization mother liquor to the acid leachate.

[0026] Specifically, a method for comprehensive recycling of a fluorine-fixed cathode carbon block provided by the present invention first performs low-temperature roasting on waste cathode carbon blocks and magnesium nitrate hexahydrate to convert the fluorides in the waste cathode carbon blocks. Immediately afterwards, the roasted slag is wet-ground and leached to achieve the conversion of cyanides in the waste cathode carbon blocks, so that the fluorination products enter the leaching slag, and the cyanidation products are converted into nitrate products to complete the detoxification of cyanides. Secondly, sodium hydroxide is added to the leaching slag, and through a wet-grinding process, the fluorination products in the leaching slag can be completely dissolved into the alkali conversion liquid, and the insoluble alkali conversion slag is treated by sulfuric acid leaching. Then, hydrofluoric acid is added to the alkali conversion liquid for a neutralization reaction, and the obtained neutralization liquid is evaporated and crystallized to obtain sodium fluoride and a sodium fluoride crystallization mother liquor, wherein the sodium fluoride crystallization mother liquor can be recycled to the wet-grinding alkali conversion. Finally, a flotation operation is performed on the acid leaching slag obtained by sulfuric acid leaching to obtain graphite and gypsum; calcium nitrate is added to the acid leaching liquid obtained by sulfuric acid leaching for a displacement reaction to obtain a regeneration slag mainly composed of calcium sulfate and a regeneration liquid mainly composed of magnesium nitrate. The regeneration liquid is evaporated and crystallized to obtain magnesium nitrate hexahydrate and a magnesium nitrate crystallization mother liquor. The magnesium nitrate crystallization mother liquor can be recycled to the acid leaching liquid, and magnesium nitrate hexahydrate is used as a raw material to continue the low-temperature molten salt conversion with the waste cathode carbon blocks, thereby completing the comprehensive utilization of the waste cathode carbon blocks and realizing the harmless treatment of the waste cathode carbon blocks. The present invention realizes the conversion and separation of fluorides and cyanides in waste cathode carbon blocks through low-temperature molten salt conversion and wet-grinding leaching, so that the fluorination products enter the leaching slag, and the cyanidation products are converted into nitrate products to complete the detoxification of cyanides and enter the leaching liquid. The leaching slag is wet-ground and alkali-converted to separate the alkali conversion slag and the alkali conversion liquid. The alkali conversion liquid is neutralized and evaporated and crystallized to obtain sodium fluoride, which can be used as a phosphating accelerator, an agricultural insecticide, a sealing material, a preservative, etc. in the coating industry; the alkali conversion slag is subjected to sulfuric acid leaching, flotation and other operations to obtain graphite, gypsum and recyclable magnesium nitrate hexahydrate, realizing the resource utilization of waste cathode carbon blocks.

[0027] In some possible embodiments, in the step S1, the addition amount of the magnesium nitrate hexahydrate is 1-2 times the theoretical reaction molar ratio of the fluorides in the waste cathode carbon blocks, the temperature of the low-temperature molten salt conversion is 100-600 °C, and the time of the low-temperature molten salt conversion is 2-8 h.

[0028] Those skilled in the art can understand that by adding an excessive amount of magnesium nitrate hexahydrate to the waste cathode carbon blocks, the easily soluble fluorides in the waste cathode carbon blocks can be completely converted into insoluble fluoride precipitates, and at the same time, the temperature and time are controlled to avoid the generation of various carbonaceous derivatives.

[0029] In some possible embodiments, in the step S2, the process parameters of the wet-grinding leaching include: the liquid-solid ratio is 4-10 mL / g, the ball-to-material ratio is 6-10, the ball-milling time is 0.5-1.5 h, and the ball-milling speed is 100-200 r / min.

[0030] In order to separate fluoride precipitates from roasted slag and complete the conversion of cyanide in waste cathode carbon blocks, water is used as the leaching solvent to wet-mill the roasted slag, obtaining leaching residues containing fluoride ions and leaching solutions containing nitrate ions. Among them, the leaching solution can be used in the subsequent magnesium nitrate regeneration process to reduce the dosage of calcium nitrate.

[0031] In some possible embodiments, in the step S3, the addition amount of sodium hydroxide is 1 - 2 times the theoretical reaction molar ratio of fluoride in the leaching residues.

[0032] In some possible embodiments, the process parameters of the wet grinding and alkali conversion include: liquid-solid ratio of 1 - 4 mL / g, ball-to-material ratio of 8 - 12, ball milling time of 2 - 4 h, and ball milling speed of 400 - 600 r / min.

[0033] Those skilled in the art can understand that by adding a small amount of sodium hydroxide, an alkaline environment is provided for the dissolution of the leaching residues, so that fluoride ions are transferred to the alkali conversion solution and calcium and magnesium ions are transferred to the alkali conversion residues, thereby realizing the separation of fluoride ions from calcium and magnesium ions and improving the purity of sodium fluoride in the evaporation and crystallization process.

[0034] In some possible embodiments, in the step S5, the temperature of the evaporation and crystallization is 100 - 110 °C.

[0035] In some possible embodiments, in the step S6, the addition amount of sulfuric acid is 1.5 - 2.0 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali conversion residues; the process parameters of the acid leaching include: acid leaching time of 0.2 - 2 h, liquid-solid ratio of 8 - 14 mL / g, acid leaching temperature of 25 - 50 °C, and stirring speed of 200 - 600 r / min.

[0036] This is because acid leaching with sulfuric acid can separate calcium and magnesium ions in the alkali conversion residues, enabling calcium ions to enter the acid leaching residues and magnesium ions to enter the acid leaching solution, providing a material basis for subsequent flotation and magnesium nitrate regeneration.

[0037] In some possible embodiments, in the step S7, the process parameters of the flotation include: flotation time of 3 - 6 min, flotation speed of 1200 - 1600 r / min, and dosage of flotation reagents of 50 - 100 g / t, where the flotation reagents are kerosene and No. 2 oil.

[0038] In some possible embodiments, in the step S8, the addition amount of calcium nitrate is 1 - 2 times the theoretical reaction molar ratio of sulfate radicals in the acid leaching solution.

[0039] Those skilled in the art can understand that by adding calcium nitrate to the sulfuric acid leaching solution, the replacement of sulfate with nitrate can be completed. Meanwhile, the generated calcium sulfate regeneration slag precipitate can be used for building materials, and the magnesium nitrate regeneration solution can be used as a raw material to continue the low-temperature molten salt conversion with waste cathode carbon blocks after evaporation crystallization and purification, thereby realizing the recycling of materials.

[0040] In some possible embodiments, in the step S9, the temperature of the evaporation crystallization is 100 - 110 °C.

[0041] The following further elaborates the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0042] Example 1

[0043] A method for comprehensive recycling and utilization of a fluorine-fixed cathode carbon block specifically includes the following steps:

[0044] (1) Low-temperature molten salt conversion: Roast the waste cathode carbon block with magnesium nitrate hexahydrate to obtain a roasted slag. Among them, the addition amount of magnesium nitrate hexahydrate is 1.2 times the theoretical reaction molar ratio of fluoride in the waste cathode carbon block, the roasting temperature is 150 °C, and the roasting time is 2 h;

[0045] (2) Wet grinding and leaching: Perform wet grinding and leaching on the roasted slag to obtain a leaching residue and a leaching solution. Among them, water is used as the leaching agent, the liquid-solid ratio is 4 mL / g, the ball-to-material ratio is 6, the ball milling time is 0.5 h, and the ball milling speed is 100 r / min;

[0046] (3) Wet grinding and alkali conversion: Add sodium hydroxide to the leaching residue for wet grinding and alkali conversion to obtain an alkali conversion solution and an alkali conversion residue. Among them, the addition amount of sodium hydroxide is 1 times the theoretical reaction molar ratio of fluoride in the leaching residue, the liquid-solid ratio is 1 mL / g, the ball-to-material ratio is 8, the ball milling time is 2 h, and the ball milling speed is 400 r / min;

[0047] (4) Neutralization: Add hydrofluoric acid to the alkali conversion solution for neutralization to obtain a neutralization solution;

[0048] (5) Sodium fluoride evaporation crystallization: Perform evaporation crystallization on the neutralization solution to obtain sodium fluoride and a sodium fluoride crystallization mother liquor, and the sodium fluoride crystallization mother liquor is recycled to the wet grinding and alkali conversion process;

[0049] (6) Acid leaching: Sulfuric acid is added to the alkali-converted slag for acid leaching to obtain acid-leached slag and acid-leached solution; among them, the addition amount of sulfuric acid is 1.5 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali-converted slag, the acid-leaching time is 0.2 h, the liquid-solid ratio is 8 mL / g, the acid-leaching temperature is 25 °C, and the stirring speed is 200 r / min;

[0050] (7) Flotation: The acid-leached slag is flotation-treated with 100 g / t of flotation reagents to obtain graphite and gypsum; among them, the flotation reagents are kerosene and No. 2 oil, the flotation time is 6 min, and the flotation rotation speed is 1600 r / min;

[0051] (8) Magnesium nitrate regeneration: Calcium nitrate and leaching solution are added to the acid-leached solution for reaction to obtain regenerated slag and regenerated solution; among them, the addition amount of calcium nitrate is 1.2 times the theoretical reaction molar ratio of sulfate radicals in the acid-leached solution, and the regenerated slag can be used as building materials;

[0052] (9) Evaporation crystallization of magnesium nitrate: The regenerated solution is subjected to evaporation crystallization to obtain magnesium nitrate hexahydrate and magnesium nitrate crystallization mother liquor. The magnesium nitrate hexahydrate is recycled to the low-temperature molten salt conversion, and the magnesium nitrate crystallization mother liquor is recycled to the magnesium nitrate regeneration.

[0053] The test results show that the recovery rate of fluorine is 98.89%, and the purity of sodium fluoride is 97.50%.

[0054] Example 2

[0055] A method for comprehensive recycling of a fluorine-fixed cathode carbon block specifically includes the following steps:

[0056] (1) Low-temperature molten salt conversion: The waste cathode carbon block and magnesium nitrate hexahydrate are roasted to obtain roasted slag; among them, the addition amount of magnesium nitrate hexahydrate is 2.0 times the theoretical reaction molar ratio of fluorides in the waste cathode carbon block, the roasting temperature is 200 °C, and the roasting time is 8 h;

[0057] (2) Wet grinding and leaching: The roasted slag is wet-ground and leached to obtain leached slag and leached solution; among them, water is used as the leaching agent, the liquid-solid ratio is 10 mL / g, the ball-to-material ratio is 10, the ball-milling time is 1.0 h, and the ball-milling rotation speed is 200 r / min;

[0058] (3) Wet grinding and alkali conversion: Sodium hydroxide is added to the leached slag for wet grinding and alkali conversion to obtain alkali-converted liquid and alkali-converted slag; among them, the addition amount of sodium hydroxide is 1.5 times the theoretical reaction molar ratio of fluorides in the leached slag, the liquid-solid ratio is 4 mL / g, the ball-to-material ratio is 12, the ball-milling time is 4 h, and the ball-milling rotation speed is 500 r / min;

[0059] (4) Neutralization: Hydrofluoric acid is added to the alkali-converted liquid for neutralization to obtain a neutralized solution;

[0060] (5) Evaporation and crystallization of sodium fluoride: Evaporate and crystallize the neutralized solution to obtain sodium fluoride and the mother liquor of sodium fluoride crystallization. The mother liquor of sodium fluoride crystallization is recycled to the wet grinding and alkali conversion process;

[0061] (6) Acid leaching: Add sulfuric acid to the alkali conversion residue for acid leaching to obtain acid leached residue and acid leaching solution. Among them, the addition amount of sulfuric acid is 2 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali conversion residue, the acid leaching time is 2 h, the liquid-solid ratio is 14 mL / g, the acid leaching temperature is 50 °C, and the stirring speed is 300 r / min;

[0062] (7) Flotation: Use 50 g / t of flotation reagent to float the acid leached residue to obtain graphite and gypsum. Among them, the flotation reagent is kerosene and No. 2 oil, the flotation time is 3 min, and the flotation rotation speed is 1200 r / min;

[0063] (8) Magnesium nitrate regeneration: Add calcium nitrate and leaching solution to the acid leaching solution for reaction to obtain regeneration residue and regeneration solution. Among them, the addition amount of calcium nitrate is 1.8 times the theoretical reaction molar ratio of sulfate radical in the acid leaching solution, and the regeneration residue can be used as building materials;

[0064] (9) Evaporation and crystallization of magnesium nitrate: Evaporate and crystallize the regeneration solution to obtain magnesium nitrate hexahydrate and the mother liquor of magnesium nitrate crystallization. Magnesium nitrate hexahydrate is recycled to the low-temperature molten salt conversion, and the mother liquor of magnesium nitrate crystallization is recycled to the magnesium nitrate regeneration.

[0065] The test results show that: the recovery rate of fluorine is 98.12%, and the purity of sodium fluoride is 98.43%.

[0066] Example 3

[0067] A method for comprehensive recovery and utilization of a fluorine-fixed cathode carbon block specifically includes the following steps:

[0068] (1) Low-temperature molten salt conversion: Roast the waste cathode carbon block with magnesium nitrate hexahydrate to obtain roasted residue. Among them, the addition amount of magnesium nitrate hexahydrate is 1.8 times the theoretical reaction molar ratio of fluoride in the waste cathode carbon block, the roasting temperature is 400 °C, and the roasting time is 4 h;

[0069] (2) Wet grinding and leaching: Wet grind and leach the roasted residue to obtain leached residue and leaching solution. Among them, water is used as the leaching agent, the liquid-solid ratio is 10 mL / g, the ball-to-material ratio is 8, the ball milling time is 1.2 h, and the ball milling rotation speed is 120 r / min;

[0070] (3) Wet grinding and alkali conversion: Add sodium hydroxide to the leached residue for wet grinding and alkali conversion to obtain alkali conversion liquid and alkali conversion residue. Among them, the addition amount of sodium hydroxide is 1.6 times the theoretical reaction molar ratio of fluoride in the leached residue, the liquid-solid ratio is 3 mL / g, the ball-to-material ratio is 10, the ball milling time is 3 h, and the ball milling rotation speed is 500 r / min;

[0071] (4) Neutralization: Hydrofluoric acid is added to the alkaline conversion solution for neutralization to obtain a neutralized solution;

[0072] (5) Evaporation crystallization of sodium fluoride: The neutralized solution is subjected to evaporation crystallization to obtain sodium fluoride and a mother liquor of sodium fluoride crystallization. The mother liquor of sodium fluoride crystallization is recycled to the wet grinding and alkaline conversion process;

[0073] (6) Acid leaching: Sulfuric acid is added to the alkaline conversion residue for acid leaching to obtain an acid leaching residue and an acid leaching solution. Among them, the addition amount of sulfuric acid is 1.8 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkaline conversion residue. The acid leaching time is 1 h, the liquid-solid ratio is 10 mL / g, the acid leaching temperature is 30 °C, and the stirring speed is 400 r / min;

[0074] (7) Flotation: The acid leaching residue is flotated with 70 g / t of flotation reagents to obtain graphite and gypsum. Among them, the flotation reagents are kerosene and No. 2 oil, the flotation time is 6 min, and the flotation rotation speed is 1300 r / min;

[0075] (8) Magnesium nitrate regeneration: Calcium nitrate and leaching solution are added to the acid leaching solution for reaction to obtain a regeneration residue and a regeneration solution. Among them, the addition amount of calcium nitrate is 1.4 times the theoretical reaction molar ratio of sulfate radicals in the acid leaching solution. The regeneration residue can be used for building materials;

[0076] (9) Evaporation crystallization of magnesium nitrate: The regeneration solution is subjected to evaporation crystallization to obtain magnesium nitrate hexahydrate and a mother liquor of magnesium nitrate crystallization. Magnesium nitrate hexahydrate is recycled to the low-temperature molten salt conversion, and the mother liquor of magnesium nitrate crystallization is recycled to the magnesium nitrate regeneration.

[0077] The test results show that the recovery rate of fluorine is 98.72%, and the purity of sodium fluoride is 97.71%.

[0078] Example 4

[0079] A method for comprehensive recycling of a fluorine-fixed cathode carbon block specifically includes the following steps:

[0080] (1) Low-temperature molten salt conversion: The waste cathode carbon block and magnesium nitrate hexahydrate are calcined to obtain a calcined residue. Among them, the addition amount of magnesium nitrate hexahydrate is 1.8 times the theoretical reaction molar ratio of fluorides in the waste cathode carbon block. The calcination temperature is 400 °C, and the calcination time is 8 h.

[0081] (2) Wet grinding and leaching: The calcined residue is subjected to wet grinding and leaching to obtain a leaching residue and a leaching solution. Among them, water is used as the leaching agent, the liquid-solid ratio is 6 mL / g, the ball-to-material ratio is 10, the ball milling time is 1.3 h, and the ball milling rotation speed is 180 r / min;

[0082] (3) Wet grinding and alkali conversion: Sodium hydroxide is added to the leaching residue for wet grinding and alkali conversion to obtain an alkali conversion solution and an alkali conversion residue; among them, the addition amount of sodium hydroxide is 1.6 times the theoretical reaction molar ratio of fluoride in the leaching residue, the liquid-solid ratio is 4 mL / g, the ball-to-material ratio is 10, the ball milling time is 4 h, and the ball milling speed is 600 r / min;

[0083] (4) Neutralization: Hydrofluoric acid is added to the alkali conversion solution for neutralization to obtain a neutralized solution;

[0084] (5) Evaporation and crystallization of sodium fluoride: The neutralized solution is subjected to evaporation and crystallization to obtain sodium fluoride and a mother liquor of sodium fluoride crystallization, and the mother liquor of sodium fluoride crystallization is recycled to the wet grinding and alkali conversion process;

[0085] (6) Acid leaching: Sulfuric acid is added to the alkali conversion residue for acid leaching to obtain an acid leaching residue and an acid leaching solution; among them, the addition amount of sulfuric acid is 1.7 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali conversion residue, the acid leaching time is 1.2 h, the liquid-solid ratio is 10 mL / g, the acid leaching temperature is 40 °C, and the stirring speed is 500 r / min;

[0086] (7) Flotation: The acid leaching residue is flotation with 70 g / t of flotation reagent to obtain graphite and gypsum; among them, the flotation reagent is kerosene and No. 2 oil, the flotation time is 4 min, and the flotation speed is 1300 r / min;

[0087] (8) Magnesium nitrate regeneration: Calcium nitrate and leaching solution are added to the acid leaching solution for reaction to obtain a regeneration residue and a regeneration solution; among them, the addition amount of calcium nitrate is 1 times the theoretical reaction molar ratio of sulfate radical in the acid leaching solution, and the regeneration residue can be used as building materials;

[0088] (9) Evaporation and crystallization of magnesium nitrate: The regeneration solution is subjected to evaporation and crystallization to obtain magnesium nitrate hexahydrate and a mother liquor of magnesium nitrate crystallization, magnesium nitrate hexahydrate is recycled to the low-temperature molten salt conversion, and the mother liquor of magnesium nitrate crystallization is recycled to the magnesium nitrate regeneration.

[0089] The test results show that the recovery rate of fluorine is 97.52%, and the purity of sodium fluoride is 97.01%.

[0090] Example 5

[0091] A method for comprehensive recovery and utilization of a fluorine-fixed cathode carbon block specifically includes the following steps:

[0092] (1) Low-temperature molten salt conversion: The waste cathode carbon block and magnesium nitrate hexahydrate are roasted to obtain a roasted residue; among them, the addition amount of magnesium nitrate hexahydrate is 1.2 times the theoretical reaction molar ratio of fluoride in the waste cathode carbon block, the roasting temperature is 400 °C, and the roasting time is 6 h.

[0093] (2) Wet grinding and leaching: The roasted slag is subjected to wet grinding and leaching to obtain leached slag and leaching solution; among them, water is used as the leaching agent, the liquid-solid ratio is 8 mL / g, the ball-to-material ratio is 8, the ball milling time is 0.8 h, and the ball milling speed is 160 r / min;

[0094] (3) Wet grinding and alkali conversion: Sodium hydroxide is added to the leached slag for wet grinding and alkali conversion to obtain alkali conversion liquid and alkali conversion slag; among them, the addition amount of sodium hydroxide is 2 times the theoretical reaction molar ratio of fluoride in the leached slag, the liquid-solid ratio is 4 mL / g, the ball-to-material ratio is 12, the ball milling time is 4 h, and the ball milling speed is 600 r / min;

[0095] (4) Neutralization: Hydrofluoric acid is added to the alkali conversion liquid for neutralization to obtain neutralized liquid;

[0096] (5) Evaporation crystallization of sodium fluoride: The neutralized liquid is subjected to evaporation crystallization to obtain sodium fluoride and sodium fluoride crystallization mother liquor, and the sodium fluoride crystallization mother liquor is recycled to the wet grinding and alkali conversion process;

[0097] (6) Acid leaching: Sulfuric acid is added to the alkali conversion slag for acid leaching to obtain acid leached slag and acid leaching solution; among them, the addition amount of sulfuric acid is 2 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali conversion slag, the acid leaching time is 2 h, the liquid-solid ratio is 14 mL / g, the acid leaching temperature is 45 °C, and the stirring speed is 600 r / min;

[0098] (7) Flotation: The acid leached slag is flotation with 80 g / t of flotation reagent to obtain graphite and gypsum; among them, the flotation reagent is kerosene and No. 2 oil, the flotation time is 5 min, and the flotation speed is 1400 r / min;

[0099] (8) Magnesium nitrate regeneration: Calcium nitrate and leaching solution are added to the acid leaching solution for reaction to obtain regenerated slag and regenerated liquid; among them, the addition amount of calcium nitrate is 2 times the theoretical reaction molar ratio of sulfate radical in the acid leaching solution, and the regenerated slag can be used for building materials;

[0100] (9) Evaporation crystallization of magnesium nitrate: The regenerated liquid is subjected to evaporation crystallization to obtain magnesium nitrate hexahydrate and magnesium nitrate crystallization mother liquor, magnesium nitrate hexahydrate is recycled to the low-temperature molten salt conversion, and the magnesium nitrate crystallization mother liquor is recycled to the magnesium nitrate regeneration.

[0101] The test results show that: the recovery rate of fluorine is 97.97%, and the purity of sodium fluoride is 97.19%.

[0102] In summary, compared with the prior art, the technical solution provided by the present invention has the following advantages:

[0103] (1) The present invention realizes the conversion and separation of fluorides and cyanides in waste cathode carbon blocks through low-temperature molten salt conversion and wet grinding leaching, laying a foundation for the preparation of sodium fluoride;

[0104] (2) The present invention realizes the separation of calcium and magnesium ions through sulfuric acid leaching, combines the flotation process to realize the recovery of carbon resources in waste cathode carbon blocks, and combines the magnesium nitrate regeneration process to realize the recycling of materials.

[0105] (3) The method provided by the present invention has the advantages of low energy consumption and high conversion efficiency. It not only solves the safety hazard problems caused by the stacking of waste cathode carbon blocks, realizes the efficient recovery of carbon resources and fluorine resources in waste cathode carbon blocks, but also realizes the recycling of materials, forming the sustainable utilization of resources.

[0106] Finally, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0107] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0108] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for comprehensive recycling of fluorine-fixing cathode carbon blocks, characterized in that: The method comprises the following steps: S1, converting the waste cathode carbon block and magnesium nitrate hexahydrate into low-temperature molten salt to obtain roasted slag; S2, wet-grinding and leaching the roasted slag to obtain leached slag and leaching liquid; S3, adding sodium hydroxide to the leached residue, performing wet grinding and alkali conversion, and obtaining alkali conversion liquid and alkali conversion residue; S4, adding hydrofluoric acid to the alkali-converted liquid for neutralization to obtain a neutralized solution; S5, evaporating and crystallizing the neutralized solution to obtain sodium fluoride and sodium fluoride crystallization mother liquor, and the sodium fluoride crystallization mother liquor is recycled to the wet grinding alkali conversion; S6, adding sulfuric acid to the alkali-converted slag for acid leaching to obtain acid leaching slag and acid leaching liquid; S7, flotation the acid leaching residue to obtain graphite and gypsum; S8, adding calcium nitrate and the leaching solution to the acid leaching solution to react and obtain regenerated slag and regenerated solution; S9, evaporating and crystallizing the regenerated liquid to obtain magnesium nitrate hexahydrate and magnesium nitrate crystallization mother liquor, wherein the magnesium nitrate hexahydrate is reused in the low-temperature molten salt conversion, and the magnesium nitrate crystallization mother liquor is reused in the acid leaching liquid.

2. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S1, the amount of magnesium nitrate hexahydrate added is 1-2 times the theoretical reaction molar ratio of fluoride in the spent cathode carbon block, the temperature of the low-temperature molten salt conversion is 100-600°C, and the time of the low-temperature molten salt conversion is 2-8h.

3. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S2, the process parameters of the wet milling leaching include: liquid-solid ratio of 4-10 mL / g, ball-to-material ratio of 6-10, ball milling time of 0.5-1.5 h, and ball milling speed of 100-200 r / min.

4. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S3, the amount of sodium hydroxide added is 1-2 times the theoretical reaction molar ratio of fluoride in the leached residue.

5. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: The process parameters of the wet milling alkali conversion include: liquid-solid ratio of 1-4 mL / g, ball-to-material ratio of 8-12, ball milling time of 2-4 h, and ball milling speed of 400-600 r / min.

6. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S5, the temperature of the evaporation crystallization is 100-110°C.

7. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S6, the amount of sulfuric acid added is 1.5-2.0 times the theoretical reaction molar ratio of calcium and magnesium elements in the alkali-converted slag; the process parameters of the acid leaching include: acid leaching time of 0.2-2h, liquid-solid ratio of 8-14mL / g, acid leaching temperature of 25-50°C, and stirring speed of 200-600r / min.

8. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S7, the flotation process parameters include: flotation time of 3-6 min, flotation speed of 1200-1600 r / min, and dosage of flotation reagent of 50-100 g / t, wherein the flotation reagent is kerosene and No. 2 oil.

9. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S8, the amount of calcium nitrate added is 1-2 times the theoretical reaction molar ratio of sulfate in the acid leaching solution.

10. The method for comprehensive recycling of fluorine-fixing cathode carbon blocks according to claim 1, characterized in that: In S9, the temperature of the evaporation crystallization is 100-110°C.

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