Method for recycling waste cathode of soluble calcium salt

Abstract

The disclosure provides a method for recycling waste cathode by soluble calcium salt. The method for recycling waste cathode by soluble calcium salt comprises the following steps: S1, screening waste cathode; S2, mixing soluble calcium salt with water to prepare first slurry; S3, mixing first powder and the first slurry, and performing flotation under the assistance of ultrasonic, separating upper flotation foam, and then filtering to obtain first filtrate and first filter residue; S4, performing acid leaching on the first filter residue, and filtering to obtain second filtrate and second filter residue, wherein the second filter residue is calcium fluoride; S5, evaporating the second filtrate to obtain aluminum salt; and S6, evaporating and drying the first filtrate to obtain an alkali mainly containing sodium hydroxide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum electrolyte extraction and recovery, and particularly relates to a method for recycling waste cathodes by using soluble calcium salt. BACKGROUND

[0002] With the development of the world industry, the demand for aluminum materials is increasing year by year. At present, the main method for producing aluminum still relies on electrolysis. Therefore, with the expansion of aluminum production, the waste cathodes produced during the production of aluminum will also increase greatly because the anode is an essential consumable for aluminum electrolysis. The waste cathodes contain a large amount of toxic substances such as cyanide. Piling up not only causes a large waste of land area, but also causes great harm to the environment. Therefore, it is urgent to find a green and environmentally friendly method for recycling waste cathodes.

[0003] Chinese patent CN116143114A discloses a method for recovering graphite from aluminum electrolysis waste cathode carbon blocks and preparing prebaked anodes therefrom. The method uses mechanical activation combined with strong oxidizing agents to activate and de-cyanate the waste cathode carbon blocks at low temperature, and then uses an acid-hydrofluoric acid mixed acid system composed of sodium fluoride and an acid solution to recover the graphite in the aluminum electrolysis waste cathode carbon blocks by high-pressure acid leaching, so as to decompose the cyanide in the waste cathode carbon blocks and recover the graphite. However, this method requires harsh conditions, uses strong oxidizing agents, hydrofluoric acid and additional fluoride, all of which are highly toxic and dangerous reagents. After leaching, a large amount of secondary fluorine-containing wastewater will be generated, and the high-pressure acid leaching environment has serious hidden dangers, which cannot be industrialized.

[0004] Chinese patent CN116440448A discloses a method for pyrolysis and detoxification treatment of electrolytic aluminum waste cathode carbon blocks. When the electrolytic aluminum waste cathode carbon blocks are pyrolyzed and treated at 750℃, binary molten salt NaCl-Na2CO3 is added to reduce the initial temperature of SCCB decomposition. However, this method only harmlessly treats the waste cathodes and does not involve the recovery of high-value elements contained therein.

[0005] Patent CN 116426981 A discloses a method for preparing carbon paste from graphite recovered from aluminum electrolysis waste cathode carbon blocks. The method uses organic solvents such as KH550 silane coupling agent solution to separate graphite powder from waste cathode carbon block powder, and combines with mixed binders to prepare carbon paste. The use of organic solvents in this method is costly, and the use of toxic organic solvents causes great inconvenience to production operations and equipment selection. Patent CN 114535260 A discloses a method for treating aluminum electrolysis waste cathode carbon blocks and its application. The method includes crushing and screening the waste cathode carbon blocks to obtain fine particle materials and coarse particle materials. The fine particle materials are subjected to acid treatment to obtain a carbon-containing slurry. The coarse particle materials and the carbon-containing slurry are mixed with a magnesium source to produce a cementitious material containing waste cathodes. This method can recover carbon from waste cathodes, but it produces a large amount of fluorine-containing wastewater during acid leaching, and it requires additional magnesium source, which is in short supply in China, limiting its large-scale promotion.

[0006] At present, there are many studies on the treatment of waste cathodes in industrial production environment. However, due to environmental restrictions and the maturity of the process, large-scale industrialized recovery of waste cathodes has not reached a leading level. For example, the traditional wet method has low carbon separation efficiency and causes serious waste. When the fire method is used, the graphite loss is large, which reduces the amount of collected carbon, and generates fluorine-containing gas, and the embedded particles are fine. Therefore, it is very important to develop a method for recovering waste cathodes using soluble calcium salt. SUMMARY

[0007] One technical problem to be solved by the present application is that in the current waste cathode treatment method, the traditional wet method has low carbon separation efficiency and requires a large amount of auxiliary raw materials, and in the fire method, the graphite loss is large, which generates fluorine-containing gas and pollutes the environment.

[0008] To solve the above technical problems, the present disclosure provides a method for recovering waste cathodes using soluble calcium salt, which comprises:

[0009] S1, crushing the waste cathode and screening out the part with a particle size of ≤200 to prepare a first powder;

[0010] S2, mixing the soluble calcium salt with water to prepare a first slurry;

[0011] S3, uniformly mixing the first powder and the first slurry for leaching, and controlling the reaction pH value. After the reaction is completed, ultrasonic assisted flotation is carried out in an ultrasonic tank, and separation is carried out to obtain upper foam and lower mixed slurry;

[0012] S4, drying the upper foam to obtain carbon powder, and filtering the lower mixed slurry to obtain a first filtrate and a first residue;

[0013] S5, evaporating and drying the first filtrate to obtain sodium hydroxide containing trace potassium hydroxide.

[0014] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein the soluble calcium salt in S2 comprises one or more of calcium oxide, calcium hydroxide, calcium formate, and calcium propionate.

[0015] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein the mass ratio of the soluble calcium salt to water in S2 is 1:(1-10).

[0016] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein the specific conditions of the reaction in S3 are that the liquid-solid ratio is 5-60, the temperature is 20-200°C, the time is 0.5-8h, the pH of the reaction is 9-14, and the pressure of the reaction is 0.1Mpa-15Mpa.

[0017] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein the specific conditions of the acid leaching reaction in S5 are that the liquid-solid ratio is 1-20, the temperature is 20-220°C, the time is 0.5-5h, and the pressure is 0.1Mpa-15Mpa, wherein the acid leaching solution is any one of hydrochloric acid, sulfuric acid, and nitric acid, and the concentration of the acid leaching solution is 0.1-10mol / L.

[0018] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein if the Ca ion content in the second filtrate in S5 exceeds 0.5g / L, soluble carbonate is added to the second filtrate and filtered to obtain calcium carbonate precipitate to remove Ca ions in the second filtrate.

[0019] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein the soluble carbonate comprises one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, and potassium carbonate.

[0020] In some embodiments, the method for recycling spent cathodes in aluminum electrolysis by soluble calcium salt, wherein before evaporating and drying the first filtrate in S6, if the Ca ion content in the first filtrate exceeds 0.5g / L, soluble carbonate is first added to the first filtrate and filtered to remove Ca ions in the first filtrate, and if the Li ion content in the first filtrate exceeds 0.5g / L, soluble carbonate is continuously added to the first filtrate and filtered to remove Li ions in the first filtrate.

[0021] In some embodiments, the method for recycling spent cathode of soluble calcium salt in aluminum electrolyte, wherein the first residue in S3 can also be used to prepare alumina by the Bayer process, and the first filtrate after removing Ca ions and Li ions can be used as a solvent in S3.

[0022] By the technical scheme, the method for recycling spent cathode of soluble calcium salt provided by the application has the advantages that, in the whole process, fluorine is not contained in the waste water after leaching due to the combination of calcium and fluorine, and the waste water can be recycled as by-products, and no dangerous gas containing fluorine is generated; the carbon in the spent cathode is effectively separated, high-purity graphite carbon powder is obtained, no auxiliary material needs to be added for extracting the carbon, the operation is simple and the risk coefficient is low, no pollution to the environment is caused, and the electrolyte in the spent cathode can be recycled at high value. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is an experimental flow chart of the method for recycling spent cathode of soluble calcium salt disclosed by the embodiments of the present disclosure; DETAILED DESCRIPTION

[0024] The drying in the embodiments of the present application is drying at 90℃ for 12h. The evaporation is at 100℃ until solid is precipitated.

[0025] The present application will be described in detail below with reference to the embodiments.

[0026] Embodiment 1

[0027] S1 takes spent cathode of an aluminum plant (Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other: 3.8wt%), crushes the spent cathode, and sieves out the part with particle size ≤200 purposes to make first powder;

[0028] S2 takes 40g of calcium oxide, stirs after adding 2L of water, and makes first slurry;

[0029] S3 takes 20g of first powder, uniformly mixes according to liquid-solid ratio of 50 with first slurry, and leaches at temperature of 90℃ for 3h, then uses ultrasonic assistance to perform flotation separation, wherein the ultrasonic time is 2h, the ultrasonic power is 400W, and the pH value is controlled to be 11 during leaching;

[0030] S4 dries the upper foam to obtain carbon powder, filters the remaining slurry after flotation to obtain first filtrate and first residue;

[0031] S5 adding 3 mol / L nitric acid with liquid-solid ratio of 4 into the first residue, and acid leaching at 50℃ for 0.5h to obtain second residue and second filtrate, and the second residue is dried to obtain calcium fluoride, and the second filtrate is evaporated and dried to obtain aluminum salt;

[0032] S6 evaporating and drying the remaining first filtrate in S4 to obtain a mixed solid of sodium hydroxide and potassium hydroxide.

[0033] The overall process has a recovery rate of 98.82% for C, and the purity of carbon is 99.02%.

[0034] Example 2

[0035] S1 taking waste cathode (Na: 13.8wt%, Al: 6.6wt%, F: 16.3wt%, O: 9.6wt%, Si: 1.5wt%, Ca: 2.2wt%, C: 46.2wt%, and other: 3.8wt%) from an aluminum factory, crushing and sieving to obtain a first powder with particle size ≤200;

[0036] S2 taking 40g of calcium oxide and adding 1.8L of water to prepare a first slurry;

[0037] S3 taking 20g of the first powder and uniformly mixing with the first slurry according to a liquid-solid ratio of 30, and leaching at a temperature of 90℃ for 3h, then using ultrasonic assistance for flotation, ultrasonic time 2h, ultrasonic power 400W, and controlling the pH value to be 11 during leaching;

[0038] S4 drying the upper foam to obtain carbon powder, and filtering the remaining slurry after flotation to obtain first filtrate and first residue;

[0039] S5 adding 5 mol / L sodium hydroxide with liquid-solid ratio of 5 into the first residue, and leaching at 100℃ for 4h to obtain second residue and second filtrate, and the second residue is dried to obtain calcium fluoride, and the second filtrate is added with seed to obtain aluminum oxide precipitate, and the remaining second filtrate is repeatedly used in the next alkaline leaching process (Bayer process);

[0040] S6 applying the remaining second filtrate in S4 to the alkaline leaching process (Bayer process) in S5

[0041] The overall process has a recovery rate of 98.79% for C, and the purity of carbon is 99.18%.

[0042] Example 3

[0043] The implementation method is the same as that of Example 1, except that:

[0044] The soluble calcium salt used in S2 is calcium chloride, and the mass ratio of the first powder to the soluble calcium salt is 1:10;

[0045] The liquid-solid ratio in the leaching process in S3 is 60, the leaching temperature is 200°C, the leaching time is 5h, and the pH value is controlled at 9;

[0046] The liquid-solid ratio in the acid leaching process in S5 is 1, the leaching temperature is 90°C, and the leaching time is 5h;

[0047] The overall process has a recovery rate of 98.15% for C, and the purity of the carbon is 98.97%.

[0048] Example 4

[0049] The implementation method is the same as that in Example 1, except that:

[0050] The mass ratio of the first powder to the soluble calcium salt in S2 is 1:3;

[0051] The liquid-solid ratio in the leaching process in S3 is 40, the leaching temperature is 90°C, the leaching time is 1h, and the pH value is controlled at 10;

[0052] The overall process has a recovery rate of 98.61% for C, and the purity of the carbon is 98.90%.

[0053] Example 5

[0054] The implementation method is the same as that in Example 1, except that:

[0055] The soluble calcium salt used in S2 is calcium hydroxide, and the mass ratio of the first powder to the soluble calcium salt is 1:7;

[0056] The liquid-solid ratio in the leaching process in S3 is 5, the leaching temperature is 110°C, the leaching time is 2h, and the pH value is controlled at 10.5;

[0057] The liquid-solid ratio in the acid leaching process in S5 is 10, the leaching temperature is 55°C, and the leaching time is 2.5h;

[0058] The overall process has a recovery rate of 98.55% for C, and the purity of the carbon is 99.05%.

[0059] Example 6

[0060] The implementation method is the same as that in Example 1, except that:

[0061] The mass ratio of the first powder to the soluble calcium salt in S2 is 1:6;

[0062] The liquid-solid ratio in the leaching process in S3 is 60, the leaching temperature is 60°C, the leaching time is 2h, and the pH value is controlled at 9;

[0063] The liquid-solid ratio in the acid leaching process in S5 is 4, the leaching temperature is 55°C, and the leaching time is 2.5h;

[0064] The recovery rate of C in the whole process was 98.98%, and the purity of carbon was 99.10%.

[0065] Example 7

[0066] The implementation method was the same as that of Example 1, except that:

[0067] The soluble calcium salt used in S2 was calcium formate, and the mass ratio of the first powder to the soluble calcium salt was 1:2;

[0068] The liquid-solid ratio of the leaching process in S3 was 50, the leaching temperature was 20℃, the leaching time was 3h, and the pH value was controlled at 12;

[0069] The liquid-solid ratio of the acid leaching process in S5 was 5, the leaching temperature was 20℃, and the leaching time was 4h;

[0070] The recovery rate of C in the whole process was 99.05%, and the purity of carbon was 98.79%.

[0071] Example 8

[0072] The soluble calcium salt used in S2 was calcium propionate, and the mass ratio of the first powder to the soluble calcium salt was 1:1;

[0073] The liquid-solid ratio of the leaching process in S3 was 50, the leaching temperature was 90℃, the leaching time was 8h, and the pH value was controlled at 12;

[0074] The liquid-solid ratio of the acid leaching process in S5 was 10, the leaching temperature was 30℃, and the leaching time was 5h;

[0075] The recovery rate of C in the whole process was 99.00%, and the purity of carbon was 98.57%.

[0076] The content illustrated in the above examples should be understood as that these examples are only used to more clearly illustrate the present application, and are not used to limit the scope of the present application, and the modifications of various equivalent forms of the present application by those skilled in the art all fall within the scope defined by the appended claims of the present application.

Claims

1. A method for recycling a spent cathode of a soluble calcium salt, characterized by: The method comprises the following steps: S1, crushing the waste cathode, and screening out a part with a particle size of less than or equal to 200 mesh to form a first powder; S2, mixing a soluble calcium salt, calcium oxide or calcium hydroxide with water to form a first slurry; The soluble calcium salt comprises one or both of calcium formate and calcium propionate. S3, uniformly mixing the first powder and the first slurry for leaching, and controlling the pH value of the reaction, and then performing ultrasonic-assisted flotation in an ultrasonic tank after the reaction is completed, and separating to obtain upper foam and lower mixed slurry; The reaction conditions are as follows: the liquid-solid ratio is 5-60, the temperature is 20-200 DEG C, the time is 0.5-8 h, the pH of the reaction is 9-14, and the pressure of the reaction is 0.1 Mpa-15 Mpa. S4, drying the upper foam to obtain carbon powder, and filtering the lower mixed slurry to obtain a first filtrate and a first filter residue; S5, acid leaching and filtering the first filter residue to obtain a second filter residue and a second filtrate, drying the second filtrate to obtain an aluminum salt, and drying the second filter residue to obtain calcium fluoride; S6, evaporating and drying the first filtrate to obtain sodium hydroxide containing a small amount of potassium hydroxide.

2. The method of recovering a soluble calcium salt from a spent cathode according to claim 1, wherein The mass ratio of the soluble calcium salt to water in S2 is 1:(1-10).

3. The method of recovering soluble calcium salt from spent cathode according to claim 1, characterized in that, The specific conditions of the acid leaching reaction in S5 are as follows: the liquid-solid ratio is 1-20, the temperature is 20-220 DEG C, the time is 0.5-5 h, and the pressure is 0.1 Mpa-15 Mpa; the acid leaching solution is any one of hydrochloric acid, sulfuric acid and nitric acid, and the concentration of the acid leaching solution is 0.1-10 mol / L.

4. The method of recovering soluble calcium salt from spent cathode according to claim 1, characterized in that, If the content of Ca ions in the second filtrate exceeds 0.5 g / L, soluble carbonate is added to the second filtrate for filtering to remove Ca ions in the second filtrate; The soluble carbonate comprises one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate and potassium carbonate.

5. The method of recovering soluble calcium salt from spent cathode according to claim 1, characterized in that, Before evaporating and drying the first filtrate in S6, if the content of Ca ions in the first filtrate exceeds 0.5 g / L, soluble carbonate is added to the first filtrate for filtering to remove Ca ions in the first filtrate; if the content of Li ions in the first filtrate exceeds 0.5 g / L, soluble carbonate is continuously added to the first filtrate for filtering to remove Li ions in the first filtrate.

6. The method of recovering soluble calcium salt from spent cathode according to claim 1, characterized in that, The first filter residue in S4 can also be used to prepare aluminum oxide by the Bayer method, and the first filtrate can be used as a solvent in the Bayer method after removing Ca ions and Li ions.

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