Method for recycling fluorine and aluminum resources in waste cathode carbon block

Abstract

The invention discloses a method for recycling fluorine and aluminum resources in waste cathode carbon blocks, and belongs to the field of comprehensive utilization of aluminum electrolysis solid waste resources. The method mainly comprises the following steps: grinding and crushing the waste cathode carbon block, sieving, leaching villiaumite, cryolite and the like in the waste cathode carbon block by adopting an aluminum salt solution, and carrying out solid-liquid separation to obtain primary filtrate and primary filter residue; fluoride, aluminum oxide and the like in the primary filter residues are leached out through a strong acid solution, and secondary filtrate and secondary filter residues are obtained through solid-liquid separation; mixing the primary filtrate and the secondary filtrate under the conditions of certain temperature and proper pH value to generate hydrated aluminum hydroxyfluoride precipitate, roasting the generated hydrated aluminum hydroxyfluoride to obtain aluminum trifluoride, returning the filtrate to a leaching process for repeated recycling, and recovering sodium salt in the filtrate through a fractional crystallization method. The method is simple in technological process, mild in condition and high in recovery efficiency, and a new technology is provided for green recovery of fluorides in the waste cathode carbon blocks in the electrolytic aluminum industry and high-value utilization of aluminum and fluorine resources.

Description

Technical Field

[0001] The invention relates to a method for recovering fluorine-aluminum resources in waste cathode carbon blocks (SCC), belonging to the technical field of comprehensive utilization of solid waste resources in aluminum electrolysis. Background Art

[0002] Spent cathode carbon blocks (SCC) refer to the carbon slag that falls off to ensure the normal regular maintenance and replacement of aluminum electrolysis production under the mechanical wear and thermal shock of high-temperature molten electrolyte and the damage of solution penetration to the cathode carbon blocks of aluminum electrolysis. In the aluminum electrolysis industry, about 30 to 50 kg of spent cathode carbon blocks are produced for every ton of primary aluminum produced. At present, the annual emission of SCC in my country exceeds 1.6 million tons. In view of the harm of SCC to human health and the ecological environment, it has been included in the "National List of Hazardous Wastes (2021 Edition)", and its hazardous characteristics are leaching toxicity; the "Environmental Protection Tax Law of the People's Republic of China" implemented in 2018 imposes environmental protection taxes on the discharge of hazardous wastes such as SCC. Therefore, the source enterprises of SCC face huge environmental pressure, and the harmless treatment and resource utilization of SCC are urgent.

[0003] Many aspects of exploration have been carried out to address this problem. In the harmless treatment of SCC, a Chinese patent (application number: 202221777296.4) discloses a flotation recovery system for waste cathode carbon blocks, including a crushing system, a flotation and resource recovery system, and a first conveying device connected in sequence, wherein the crushing system and the flotation and resource recovery system are connected through the first conveying device. However, this system is relatively expensive. A Chinese patent (application number: 202311684862.6) discloses a method for resource treatment of waste cathodes of electrolytic aluminum and separation of electrolyte and solid carbon, wherein the waste cathode is roasted at 1400-800°C in an oxygen-free environment for 1-12 hours, and then the solid, liquid, and gas phases are separated and collected to obtain gas phase dust-collecting electrolyte, solid carbon blocks, and liquid electrolytes, respectively. The dust-collecting electrolyte is subjected to cyanide removal and roasting and carbon removal to obtain an electrolyte product. This method obtains carbon of higher purity and has obvious economic benefits. A Chinese patent (application number: 202010062001.4) discloses a method for recycling waste cathode carbon blocks from aluminum electrolysis, which comprises the following steps: (1) crushing and screening the waste cathode carbon blocks to obtain carbon particles; (2) mixing the carbon particles with a sulfuric acid solution to obtain slurry A, and then leaching under pressure to obtain slurry B; (3) evaporating and concentrating slurry B to a water content of less than 8% by mass to obtain slurry C; (4) adding concentrated sulfuric acid to slurry C to obtain slurry D, and then roasting at 150-300°C for 0.5-10 hours, and then roasting at 300-600°C for 0.5-8 hours to obtain roasted carbon; (5) heating the roasted carbon to 1200-3000°C and keeping the temperature for 0.5-20 hours to obtain purified carbon. This method does not generate high-temperature fluorine-containing flue gas and fluorine-containing wastewater during the treatment process, and can recover fluorine, aluminum and carbonaceous materials. A Chinese patent (application number: 202310142389.2) discloses a method for recovering graphite from waste cathode carbon blocks from aluminum electrolysis, which uses low-melting-point inorganic salts to carry out molten salt roasting of waste cathode carbon blocks from aluminum electrolysis to obtain roasted materials and flue gas, and places the roasted materials and acidic solution in a mechanical activation device for leaching. After the reaction is completed, solid-liquid separation is carried out to obtain acidic leachate and residual solid materials, and then the residual solid materials are washed and dried in turn to obtain graphite and washing liquid. At the same time, a recycling process for by-products such as flue gas and acidic leachate is also designed. This method avoids environmental pollution of waste gas and waste liquid, realizes the green recovery of high-quality graphite resources of waste cathode carbon blocks from aluminum electrolysis, the safe dissociation of cyanide / fluorine toxic components, and the regeneration and recycling of molten salt roasting agents.

[0004] Regarding the treatment and disposal of SCC, literature research has found that the physical separation method has a low cost but a low recovery rate; the pyrometallurgical treatment has a better effect but consumes a lot of energy; the hydrometallurgical process is simple and has low energy consumption. At present, there are few industrial treatments of SCC, and most of them are in the laboratory stage. The existing hydrometallurgical processes mostly use one-step aluminum salt leaching and one-step strong acid leaching such as hydrochloric acid, sulfuric acid or nitric acid, which have problems such as low leaching efficiency and harsh reaction conditions. In order to further promote the recycling of SCC and prepare AlF3 products, the present invention designs a two-step leaching method, namely aluminum salt-strong acid combined leaching, which has milder reaction conditions and improves the leaching rate of fluorine. Summary of the invention

[0005] In order to solve the above problems, realize the large-scale and efficient utilization of waste cathode carbon block (SCC) resources, reduce environmental pollution and achieve sustainable development, the main purpose of the present invention is to propose a recovery method for aluminum salt-strong acid combined enhanced SCC leaching. The two-step leaching of aluminum salt and strong acid can increase the leaching amount of fluorine and improve the fluorine removal rate to achieve harmless treatment and resource utilization of SCC.

[0006] The technical solution of the present invention is:

[0007] A method for recycling waste cathode carbon blocks comprises the following steps:

[0008] (1) grinding and crushing the waste cathode carbon block, leaching it with an acidified aluminum salt solution, and filtering to obtain a primary filtrate and a primary filter residue;

[0009] (2) using the primary filter residue as a raw material for strong acid leaching, and filtering to obtain a secondary filtrate and a secondary filter residue;

[0010] (3) After mixing the primary filtrate and the secondary filtrate, a precipitation reaction is carried out at a certain temperature and an appropriate pH condition, and the fluorine-containing aluminum precipitate residue is obtained by filtration, and the fluorine-containing aluminum precipitate residue is calcined at a high temperature to obtain AlF3;

[0011] (4) Recovering the sodium salt from the filtrate obtained by filtering after the precipitation reaction.

[0012] The SCC described in the present invention includes SCC generated in the electrolytic aluminum, aluminum recycling or aluminum processing industries.

[0013] In the step (1), the grinding is carried out by dry ball milling, the time is controlled to be 0.5 to 2 hours, and the speed of the ball mill is controlled to be 200 to 400 rpm.

[0014] In the step (1), the SCC is ground and crushed and then passed through a 100-mesh vibrating screen, the particle size is less than 0.15 mm, and the cumulative yield under the screen is greater than 90%.

[0015] In step (1), the aluminum salt mainly comprises at least one of aluminum trichloride, aluminum tribromide, aluminum triiodide, aluminum sulfate, sodium aluminum sulfate, aluminum nitrate, aluminum phosphate and aluminum dihydrogen phosphate, and the aluminum salt concentration is 10-20 g / L; before leaching, a certain amount of 0.1-0.5 mol / L strong acid is added to the aluminum salt solution to adjust the pH to 1.0-2.0, and the acid is at least one of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, peroxydisulfuric acid, nitric acid and phosphoric acid.

[0016] In step (1), the reaction time is 1 to 5 hours, the reaction temperature is 30 to 90° C., the liquid-to-solid ratio is 10 to 30 mL / g, and the rotation speed is 300 to 500 rpm.

[0017] The substances leached from the aluminum salt in step (1) include: Na3AlF6, Na5Al3F 14 , AlF3, NaF, CaF2, etc.

[0018] The strong acid in step (2) mainly includes at least one of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, peroxydisulfuric acid, nitric acid and phosphoric acid, and the concentration of the strong acid is 1 to 5 mol / L.

[0019] In step (2), the reaction time is 1 to 5 hours, the reaction temperature is 30 to 90° C., the liquid-to-solid ratio is 10 to 30 mL / g, and the rotation speed is 300 to 500 rpm.

[0020] The substances leached by strong acid in step (2) include: Na3AlF6, Na5Al3F 14 , CaF2, Al2O3, etc.

[0021] The secondary filter residue in step (2) contains a large amount of carbon, which can be comprehensively recycled and utilized as fuel, reducing agent, prebaked anode and heavy metal adsorbent.

[0022] In step (3), the temperature of mixing the two filtrates is 50-90° C., and then a certain amount of 0.1-0.5 mol / L NaOH solution is added to adjust the pH of the mixed solution to 4.0-5.0, and the chemical precipitation reaction time is 1-5 hours.

[0023] The precipitated slag containing aluminum fluoride obtained by filtering in step (3) is roasted at a temperature of 300 to 800° C. for a time of 1 to 5 hours to obtain an aluminum trifluoride product.

[0024] The filtrate in step (4) is returned to step (1) and recycled for multiple times, so that more sodium chloride, sodium bromide, sodium iodide, sodium sulfate, sodium nitrate or sodium phosphate can be accumulated for recovery.

[0025] In step (4), the filtrate is circulated to accumulate a higher concentration of salt and then the filtrate is subjected to a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations are repeated to recover at least one of NaCl, NaBr, NaI, Na2SO4, NaNO3 and Na3PO4.

[0026] The filter residue obtained by solid-liquid separation in step (1), step (2) and step (3) is washed with deionized water until the pH of the washing liquid is neutral and then placed in an oven at 80 to 110° C. for drying for 6 to 10 hours.

[0027] The beaker, measuring cylinder, stirring rod, funnel, etc. used in step (1), step (2) and step (3) are all made of PP material.

[0028] SCC is produced in the process of electrolytic aluminum, recycled aluminum and aluminum processing. It contains carbon and various fluorine-containing components, such as Na3AlF6, Na5Al3F 14 , AlF3, NaF, CaF2, etc. The contents of various components vary with the production process and the waste aluminum raw materials. The existing physical separation method (flotation) has a large processing capacity, low cost and simple operation, but the purity of the recovered graphite carbon and fluoride is poor; the carbon material obtained by pyrometallurgy (high temperature roasting) has a high purity, but there are problems of waste gas pollution and high cost; the hydrometallurgy (acid leaching, alkali leaching, soluble aluminum salt leaching) process is simple and has low energy consumption. The aluminum salt-strong acid combined leaching and defluorination of SCC can obtain a higher fluoride leaching rate, and the leached waste residue is lower than the standard (100 mg / L) of the "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB 5085.3-2007), achieving harmlessness. At the same time, AHF is calcined and decomposed at high temperature to obtain AlF3; the evaporation, concentration and reflux of the filtrate is conducive to the step-by-step crystallization and recovery of various sodium salts from the waste liquid (Na mainly comes from the cryolite (Na3AlF6) in the first step of aluminum salt leaching SCC).

[0029] The present invention utilizes Al 3+ F is removed by coagulation, ion exchange, adsorption, etc. - In the aluminum salt leaching process of SCC, Al 3+ Soluble and insoluble F in SCC - It has a strong affinity and can combine to form a stable aluminum-fluoride complex [AlF i ] 3-i , promoting further dissolution of fluoride and increasing the leaching rate of fluorine. The reaction equations are shown in (1) to (5). + It reacts with the fluoride and oxide remaining in the filter residue after aluminum salt leaching to leach as much impurities as possible into the solution. The reaction equations are shown in (6) to (10).

[0030] Na3AlF6+2Al3+ →3Na + +3AlF2 + (1)

[0031] Na5Al3F 14 +4Al 3+ →7AlF2 + +5Na + (2)

[0032] 2AlF3+Al 3+ →3AlF2 + (3)

[0033] 2NaF+Al 3+ →2Na + +AlF2 + (4)

[0034] CaF2+2Al 3+ →Ca 2+ +2AlF 2+ (5)

[0035] Na3AlF6+6H + →3Na + +Al 3+ +6HF (6)

[0036] NaF+H + →Na + +HF (7)

[0037] CaF2+2H + →Ca 2+ +2HF (8)

[0038] Al2O3+6H + →2Al 3+ +3H2O (9)

[0039] SiO2+HF→SiF4+2H2O (10)

[0040] The present study shows that a single aluminum salt leaching process can leach more fluorides such as AlF3, NaF, and CaF2 in SCC, but Na3AlF6 and Na5Al3F 14 Substances such as these can only be completely dissolved in alkali and cannot be dissolved in Al 3+ The fluoride ions in the leaching solution need to be precipitated under acidic conditions to form hydrated aluminum hydroxyfluoride precursor (AHF), and the alkaline leaching process is not used. Therefore, the overall fluorine leaching rate is not ideal. The single strong acid leaching process can make the ΔG of most acid leaching reactions at higher concentrations and temperatures θ<0, so strong acid leaching can obtain a higher fluorine leaching rate, but the leaching conditions of this process are harsh, and the reaction temperature is as high as 140°C, which is not recommended from the perspective of energy conservation. The aluminum salt-strong acid combined leaching process makes up for the shortcomings of the single leaching process. It first leaches aluminum salts and then strong acid leaching, which can not only ensure a higher fluorine leaching rate, but also help to reduce the strict high temperature conditions of the strong acid leaching reaction. In addition, AHF is finally calcined and decomposed at high temperature to obtain AlF3; the evaporation, concentration and reflux of the leachate can not only reduce the generation of waste liquid, but also help to recover a variety of sodium salts to achieve environmental protection and comprehensive recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is an illustration of the process flow of the present invention.

[0042] Figure 2 This is the XRD phase spectrum of spent cathode carbon block (SCC) before and after treatment.

[0043] As can be seen from the figure, after single aluminum salt or strong acid leaching, the characteristic peaks of fluorides such as Na3AlF6 and CaF2 in the leached residue are weakened, but the residual fluorides are still relatively large, so the fluorine leaching rate is low and the carbon purity is low. After aluminum salt-strong acid combined leaching, the strong acid dissolves the remaining fluorides and oxides in the primary filter residue after aluminum salt leaching to a certain extent, and the characteristic peaks of fluorides in the secondary filter residue are significantly weakened, so the fluorine leaching rate is significantly improved, and the carbon purity is also increased. This shows that the present invention can significantly improve the fluorine leaching rate in SCC and the purity of carbon in the leached residue.

[0044] Figure 3 This is a graph showing the mass fractions of various components in the leached residue of waste cathode carbon blocks (SCC) under the optimal process conditions (aluminum salt leaching: 16 g / L, 60°C, 3h, 14 mL / g, 450 rpm; strong acid leaching: 3 mol / L, 70°C, 3h, 16 mL / g, 450 rpm).

[0045] As can be seen from the figure, the carbon content in the leached residue is as high as 90.15%, and only contains a small amount of Na3AlF6, Na5Al3F 14 and Al2O3 and other impurities. Carbon has high calorific value, reducibility, conductivity and adsorption and other economic utilization values. Therefore, the leaching slag can be considered as a fuel and reducing agent in the metallurgical industry to prepare aluminum electrolysis prebaked anodes, heavy metal adsorbents, etc., so as to realize the resource recycling of leaching slag.

[0046] In summary, this process has the characteristics of simple operation and efficient processing. DETAILED DESCRIPTION

[0047] The following examples are intended to further illustrate the present invention, but are not intended to limit the present invention.

[0048] Take the waste cathode carbon block (SCC) produced by a renewable resource recycling enterprise in my country as an example. The main element contents were measured as (wt.%): F 40.12%, C 22.1%, Na 19.9%, Al 10.6%, O 2.8%, Ca1.78%, S0.84%, K 0.68%, etc.

[0049] Comparative Example 1

[0050] After the SCC was ground, it was sieved into 100 mesh samples and placed in a vacuum drying oven at 100℃ for 6 hours. 10g of the sample was mixed with deionized water in a PP beaker at a liquid-solid ratio of 20mL / g, and the temperature was controlled at 60℃. After reacting at a speed of 450rpm for 3 hours, the solid-liquid separation was performed to obtain the filtrate and the residue. The residue was rinsed with deionized water until the pH of the washing liquid was neutral and then dried for use.

[0051] Characterization and analysis showed that the fluorine leaching rate of SCC was 0.69% and the carbon content in the leached residue was 27.49%.

[0052] The fluoride concentration of the leaching residue was measured to be 119.93 mg / L through leaching toxicity analysis, which does not meet the requirements of the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0053] Comparative Example 2

[0054] After the SCC was ground, the sample was sieved to 100 mesh and placed in a vacuum drying oven at 100℃ for 6h. 10g of the sample was mixed with 16g / L Al2(SO4)3 solution with a pH of 1.5 after sulfuric acid acidification at a liquid-solid ratio of 14mL / g in a PP beaker, the temperature was controlled at 60℃, and the reaction was carried out at 450rpm for 3h, and the solid-liquid separation was performed to obtain the filtrate and the residue. The residue was rinsed with deionized water until the pH of the washing liquid was neutral and then dried for use. 0.1mol / L NaOH solution was added to adjust the pH of the filtrate to 4.6, and the hydrated hydroxyaluminum fluoride precursor (AHF) was obtained by precipitation at 90℃ for 4h. After solid-liquid separation, it was rinsed with deionized water until the pH of the washing liquid was neutral, and then dried and weighed. Finally, the solid was placed in a tubular furnace and calcined at 550℃ for 3h to decompose the product AlF3. The filtrate was recovered by evaporation, concentration, crystallization and filtration.

[0055] Characterization and analysis showed that the fluorine leaching rate of SCC was 56.25%, the carbon content in the leached residue was 56.61%, the purity of AlF3 was 88.43%, and the average purity of the recovered sodium salt was 97.18%.

[0056] The fluoride concentration of the leaching residue was measured to be 64.95 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0057] Comparative Example 3

[0058] After the SCC was ground, it was sieved into 100 mesh samples and placed in a vacuum drying oven at 100℃ for 6h. Take 10g of the sample and mix it with 3mol / L hydrochloric acid solution in a PP beaker at a liquid-solid ratio of 16mL / g. The temperature was controlled to 70℃. After reacting at 450rpm for 3h, the solid-liquid separation was performed to obtain the filtrate and the residue. The residue was rinsed with deionized water until the pH of the washing liquid was neutral and then dried for use. Add 0.1mol / L NaOH solution to adjust the pH of the filtrate to 4.6, react at 90℃ for 4h to precipitate the hydrated hydroxyaluminum fluoride precursor (AHF). After solid-liquid separation, rinse with deionized water until the pH of the washing liquid was neutral, dry and weigh. Finally, the solid was placed in a tubular furnace and calcined at 550℃ for 3h to decompose the product AlF3. The filtrate was recovered by evaporation, concentration, crystallization and filtration to obtain NaCl.

[0059] Characterization and analysis showed that the fluorine leaching rate of SCC was 43.25%, the carbon content in the leached residue was 44.94%, the purity of AlF3 was 87.71%, and the average purity of the recovered sodium salt was 97.03%.

[0060] The fluoride concentration of the leaching residue was measured to be 80.64 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0061] Comparative Example 4

[0062] After the SCC is ground, the sample is sieved to 100 mesh and placed in a vacuum drying oven at 100℃ for 6h. Take 10g of the sample and mix it with 3mol / L hydrochloric acid solution in a PP beaker at a liquid-solid ratio of 16mL / g, control the temperature to 70℃, react at 450rpm for 3h, and then separate the solid and liquid to obtain a primary filtrate and a primary filter residue. The primary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried, and then mixed with 16g / L Al2(SO4)3 solution with a pH of 1.5 after sulfuric acid acidification at a liquid-solid ratio of 14mL / g, control the temperature to 60℃, and react at 450rpm for 3h, and then separate the solid and liquid to obtain a secondary filtrate and a secondary filter residue. The secondary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried for use. The primary filtrate and the secondary filtrate were mixed in a 90°C constant temperature water bath, and 0.1 mol / L NaOH solution was added to adjust the pH of the secondary filtrate to 4.6, and then reacted for 4 hours to precipitate the hydrated hydroxyaluminum fluoride precursor (AHF). After solid-liquid separation, it was rinsed with deionized water until the pH of the washing liquid was neutral, then dried and weighed. Finally, the solid was placed in a tube furnace and calcined at 550°C for 3 hours to decompose the product AlF3. The filtrate was recovered by a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations were repeated to obtain Na2SO4 and NaCl.

[0063] Characterization and analysis showed that the fluorine leaching rate of SCC was 79.15%, the carbon content in the leached residue was 83.54%, the purity of AlF3 was 90.25%, and the average purity of the recovered sodium salt was 96.84%.

[0064] The fluoride concentration of the leaching residue was measured to be 33.92 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0065] Example 1

[0066] After the SCC is ground, the sample is sieved to 100 mesh and placed in a vacuum drying oven at 100℃ for 6h. Take 10g of the sample and mix it with 16g / L Al2(SO4)3 solution with pH=1.5 after sulfuric acid acidification at a liquid-solid ratio of 15mL / g in a PP beaker, control the temperature to 60℃, react at 450rpm for 3h, and then separate the solid and liquid to obtain a primary filtrate and a primary filter residue. The primary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried, and then mixed with 3mol / L hydrochloric acid solution at a liquid-solid ratio of 15mL / g, control the temperature to 70℃, and react at 450rpm for 3h, and then separate the solid and liquid to obtain a secondary filtrate and a secondary filter residue. The secondary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried for use. The primary filtrate and the secondary filtrate were mixed in a 90°C constant temperature water bath, and 0.1 mol / L NaOH solution was added to adjust the pH of the secondary filtrate to 4.6, and then reacted for 4 hours to precipitate the hydrated hydroxyaluminum fluoride precursor (AHF). After solid-liquid separation, it was rinsed with deionized water until the pH of the washing liquid was neutral, then dried and weighed. Finally, the solid was placed in a tube furnace and calcined at 550°C for 3 hours to decompose the product AlF3. The filtrate was recovered by a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations were repeated to obtain Na2SO4 and NaCl.

[0067] Characterization and analysis showed that the fluorine leaching rate of SCC was 82.33%, the carbon content in the leached residue was 85.97%, the purity of AlF3 was 90.48%, and the average purity of the recovered sodium salt was 97.69%.

[0068] The fluoride concentration of the leaching residue was measured to be 28.26 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0069] Example 2

[0070] After the SCC is ground, the sample is sieved to 100 mesh and placed in a vacuum drying oven at 100℃ for 6h. Take 10g of the sample and mix it with 15g / L Al2(SO4)3 solution with pH=1.5 after sulfuric acid acidification at a liquid-solid ratio of 16mL / g in a PP beaker, control the temperature to 60℃, react at 450rpm for 3h, and then separate the solid and liquid to obtain a primary filtrate and a primary filter residue. The primary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried, and then mixed with 2mol / L hydrochloric acid solution at a liquid-solid ratio of 16mL / g, control the temperature to 70℃, and react at 450rpm for 3h, and then separate the solid and liquid to obtain a secondary filtrate and a secondary filter residue. The secondary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried for use. The primary filtrate and the secondary filtrate were mixed in a 90°C constant temperature water bath, and 0.1 mol / L NaOH solution was added to adjust the pH of the secondary filtrate to 4.6, and then reacted for 4 hours to precipitate the hydrated hydroxyaluminum fluoride precursor (AHF). After solid-liquid separation, it was rinsed with deionized water until the pH of the washing liquid was neutral, then dried and weighed. Finally, the solid was placed in a tube furnace and calcined at 550°C for 3 hours to decompose the product AlF3. The filtrate was recovered by a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations were repeated to obtain Na2SO4 and NaCl.

[0071] Characterization and analysis showed that the fluorine leaching rate of SCC was 85.61%, the carbon content in the leached residue was 89.75%, the purity of AlF3 was 89.90%, and the average purity of the recovered sodium salt was 97.62%.

[0072] The fluoride concentration of the leaching residue was measured to be 26.04 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0073] Example 3

[0074] After the SCC is ground, the sample is sieved to 100 mesh and placed in a vacuum drying oven at 100℃ for 6h. Take 10g of the sample and mix it with 16g / L Al2(SO4)3 solution with pH=1.5 after sulfuric acid acidification at a liquid-solid ratio of 14mL / g in a PP beaker, control the temperature to 60℃, react at 450rpm for 3h, and then separate the solid and liquid to obtain a primary filtrate and a primary filter residue. The primary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried, and then mixed with 3mol / L hydrochloric acid solution at a liquid-solid ratio of 16mL / g, control the temperature to 70℃, and react at 450rpm for 3h, and then separate the solid and liquid to obtain a secondary filtrate and a secondary filter residue. The secondary filter residue is rinsed with deionized water until the pH of the washing liquid is neutral and then dried for use. The primary filtrate and the secondary filtrate were mixed in a 90°C constant temperature water bath, and 0.1 mol / L NaOH solution was added to adjust the pH of the secondary filtrate to 4.6, and then reacted for 4 hours to precipitate the hydrated hydroxyaluminum fluoride precursor (AHF). After solid-liquid separation, it was rinsed with deionized water until the pH of the washing liquid was neutral, then dried and weighed. Finally, the solid was placed in a tube furnace and calcined at 550°C for 3 hours to decompose the product AlF3. The filtrate was recovered by a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations were repeated to obtain Na2SO4 and NaCl.

[0075] Characterization and analysis showed that the fluorine leaching rate of SCC was 87.14%, the carbon content in the leached residue was 90.15%, the purity of AlF3 was 91.39%, and the average purity of the recovered sodium salt was 98.07%.

[0076] The fluoride concentration of the leaching residue was measured to be 24.80 mg / L through leaching toxicity analysis, which meets the requirements of "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007) (100 mg / L).

[0077] The above description is only a preferred embodiment of the present invention. It should be pointed out that several improvements and modifications may be made without departing from the principle of the present invention. These improvements and modifications should also be considered as the protection scope of the present invention.

Claims

1. A method for recovering fluorine-aluminum resources from waste cathode carbon blocks. It is characterized in that The following steps are involved: (1) grinding and crushing the waste cathode carbon block, leaching it with an acidified aluminum salt solution, and filtering to obtain a primary filtrate and a primary filter residue; (2) using the primary filter residue as a raw material for strong acid leaching, and filtering to obtain a secondary filtrate and a secondary filter residue; (3) After the primary filtrate and the secondary filtrate are mixed, a precipitation reaction is carried out under a certain temperature and suitable pH conditions, and the fluorine-containing aluminum precipitate residue is obtained by filtration, and the fluorine-containing aluminum precipitate residue is roasted at a high temperature to obtain AlF 3 ; (4) Recovering the sodium salt from the filtrate obtained by filtering after the precipitation reaction.

2. The method according to claim 1, It is characterized in that In step (1), the waste cathode carbon blocks are ground and crushed to a particle size of less than 0.15 mm.

3. The method according to claim 1, It is characterized in that In step (1), the aluminum salt mainly comprises at least one of aluminum trichloride, aluminum tribromide, aluminum triiodide, aluminum sulfate, sodium aluminum sulfate, aluminum nitrate, aluminum phosphate and aluminum dihydrogen phosphate, and the aluminum salt concentration is 10-20 g / L; before leaching, a certain amount of 0.1-0.5 mol / L strong acid is added to the aluminum salt solution to adjust the pH to 1.0-2.0, and the acid is at least one of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, peroxydisulfuric acid, nitric acid and phosphoric acid.

4. The method according to claim 1 or 3, It is characterized in that In step (1), the reaction time is 1 to 5 hours, the reaction temperature is 30 to 90° C., the liquid-solid ratio is 10 to 30 mL / g, and the rotation speed is 300 to 500 rpm.

5. The method according to claim 1, It is characterized in that The strong acid in step (2) mainly includes at least one of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, peroxydisulfuric acid, nitric acid and phosphoric acid, and the concentration of the strong acid is 1 to 5 mol / L.

6. The method according to claim 1 or 5, It is characterized in that In step (2), the reaction time is 1 to 5 hours, the reaction temperature is 30 to 90° C., the liquid-to-solid ratio is 10 to 30 mL / g, and the rotation speed is 300 to 500 rpm.

7. The method according to claim 1, It is characterized in that The secondary filter residue in step (2) is comprehensively recycled and utilized as fuel, reducing agent, prebaked anode or heavy metal adsorbent.

8. The method according to claim 1, It is characterized in that In step (3), the temperature of mixing the two filtrates is 50-90° C., and then a certain amount of 0.1-0.5 mol / L NaOH solution is added to adjust the pH of the mixed solution to 4.0-5.0, and the chemical precipitation reaction time is 1-5 hours.

9. The method according to claim 1 or 8, It is characterized in that The precipitated slag containing aluminum fluoride obtained by filtering in step (3) is roasted at a temperature of 300 to 800° C. for a time of 1 to 5 hours to obtain an aluminum trifluoride product.

10. The method according to claim 1, It is characterized in that The filtrate in step (4) is returned to step (1) for recycling. After accumulating a higher concentration of salt, the filtrate is subjected to a step-by-step crystallization method, and the evaporation, concentration, crystallization and filtration operations are repeated to recover NaCl, NaBr, NaI, and Na 2 SO 4 、NaNO 3 and Na 3 PO 4 At least one of .

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