CN111777054A - A method for synergistic defluorination by microwave-ultrasonic-alkali leaching of waste cathode carbon blocks in aluminum electrolysis - Google Patents

Abstract

The invention discloses a method for removing fluorine by the microwave-ultrasonic-alkaline leaching cooperation of aluminum electrolysis waste cathode carbon blocks, and relates to an aluminum electrolysis waste cathode treatment technology. Crushing waste cathode carbon blocks, screening to obtain particles, putting the particles into a crucible, putting the crucible into a high-temperature microwave reactor, introducing oxygen to remove cyanide in the heating process, introducing protective gas, and performing microwave high-temperature roasting; finely grinding the roasted cathode carbon block, pouring finely ground carbon powder into alkali liquor, and carrying out alkali liquor leaching treatment by ultrasonic assistance; and after leaching, separating and filtering, and drying the solid materials to obtain the regenerated carbon powder with the purity of over 90 percent. The method can effectively remove fluoride in the cathode carbon block, so that the carbon block can be recycled, the method is simple and efficient to operate, and the harmless utilization of the aluminum electrolysis solid waste can be realized.

Description

A method for synergistic defluorination by microwave-ultrasonic-alkali leaching of waste cathode carbon blocks in aluminum electrolysis

technical field

The invention relates to a technology for treating waste and used cathodes of aluminum electrolysis, in particular to a method for synergistic fluorine removal by microwave-ultrasonic-alkali leaching of waste and used cathode carbon blocks of aluminum electrolysis.

Background technique

In the process of electrolytic aluminum production, the new electrolytic cell will be replaced in 5 to 8 years, and the replaced cathode is the waste cathode. The main reason for the replacement was that the aluminum electrolytic cell was broken by the infiltration of impurities such as sodium fluoride, and the liquid in the tank leaked from the crack, resulting in the inability to continue production. In recent years, with the sharp increase in the demand for aluminum, the aluminum electrolysis industry has also developed rapidly, and the scale of production lines has increased rapidly. The problem that electrolytic aluminum plants urgently need to solve.

The waste cathode carbon block is mainly composed of carbonaceous materials and electrolyte components, of which the content of carbonaceous materials is 30-70%, and the degree of graphitization is as high as 80-90%; the content of electrolyte components is 30-70%, and the main components are cryolite, Sodium fluoride, calcium fluoride, cyanide, etc., mineral materials rich in graphitized carbon and fluoride salts.

At present, the treatment of waste cathodes is not paid enough attention in China, and most of them are piled up in the open air, which causes great pollution to the environment, mainly in: 1) fluoride and cyanide in waste cathodes seep into the soil with rainwater, reducing crop yields; 2 ) has an irreversible effect on the growth of animals and plants, making plants black, deforming animal joints, and even paralyzing; 3) Long-term exposure to humid conditions will release harmful gases and pollute the atmosphere. Therefore, spent cathodes are characterized as hazardous waste. At the same time, the available resources in the waste cathodes have not been effectively recovered, resulting in a serious waste of resources. In addition, in recent years, the state has paid more and more attention to environmental protection. In 2016, aluminum electrolysis cell overhaul slag has been clearly listed in the "National List of Hazardous Wastes" (Order No. 39 of the Ministry of Environmental Protection in 2016), becoming one of the main sources of solid environmental pollution in the aluminum electrolysis industry. Therefore, it is imminent to recycle the active ingredients of waste cathodes.

There are two main treatment methods for waste cathodes: wet method and fire method, which are physical separation, high temperature heat treatment, and chemical leaching. The fire method is mainly used for harmless treatment to eliminate harmful components such as fluoride and cyanide in the carbon block. The principle is to separate harmful substances according to the combustion and boiling points of the substances. Furnace and tube furnace have the disadvantages of long processing time, slow heating rate and long holding time. The wet process is mainly used in the comprehensive utilization of waste cathode resources, so that the various components are separated. The wet method is divided into two methods: physical separation and chemical leaching. Physical separation is to separate carbon and fluoride according to factors such as solubility, density, and surface properties. Chemical leaching is also used for the separation of carbon and fluoride. The difference in chemical properties is used for separation, and finally high-purity carbon and electrolyte are obtained. The main problems of wet method are incomplete treatment, long reaction time, and difficulty in disposal of waste liquid. The invention solves the problems of incomplete reaction, long treatment time and waste liquid to a certain extent, and greatly shortens the production efficiency.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for the synergistic defluorination of aluminum electrolysis waste cathode carbon block microwave-ultrasonic-alkali leaching, which solves the problems of long treatment time, large amount of waste liquid, difficult treatment and incomplete reaction. The comprehensive treatment of waste cathode carbon blocks by immersion ultrasonic treatment greatly shortens the production efficiency and can be used in large-scale continuous production. It has an extremely important guiding role in saving resources and reducing energy consumption to obtain usable carbon blocks and their subsidiary products.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions: a method for synergistic defluorination by microwave-ultrasonic-alkali leaching of aluminum electrolysis waste cathode carbon blocks, which is characterized in that it comprises the following steps:

a) crushing the waste cathode carbon block of the aluminum electrolytic cell, screening to obtain particles with a particle size of 1-3 cm, the particle size is greater than 3 cm and returned to be crushed again, and the particle size is less than 1 cm and enters the grinding stage;

b) Put the waste cathode carbon block obtained after crushing into a crucible, and place it in a high-temperature microwave reactor. When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced, and when the temperature reaches 400°C, the oxygen is stopped. And continue to introduce protective gas, microwave high-temperature roasting of waste cathode carbon block under protective gas environment, so that cryolite, fluoride electrolyte and cathode carbon in carbon block are physically separated;

c) finely grinding the cathode carbon block after microwave roasting to obtain carbon powder with a particle size of less than 100 meshes;

d) Pour the finely ground toner into the lye, and carry out the lye leaching treatment by ultrasonic assistance to remove the residual fluoride and cyanide in the toner;

e) After the leaching is completed, separate and filter to obtain solid material and filtrate respectively. The solid material is dried to obtain regenerated carbon powder with a purity of more than 90%, and the filtrate is recycled and reused by evaporation and separation.

A further technical solution is that in the microwave high-temperature roasting process in the step b), microwaves are used to directly act on the waste cathode carbon blocks for high-temperature roasting, the microwave power is 1-10kW, the microwave frequency is 2450±50 or 915±50MHz, and the heating rate is It is 30～150℃/min, the roasting temperature is 1000～1200℃, and the holding time is 30～90min.

A further technical solution is that the middle of the crucible used in the step b) is provided with an isolation net, and through holes with a diameter of less than 0.5 cm are distributed on the isolation net.

A further technical scheme is that the crucible is one of corundum crucible, quartz crucible and mullite crucible.

A further technical solution is that the temperature measuring device adopted in the step b) is a thermocouple temperature measuring device or an infrared temperature measuring device.

A further technical solution is that the protective gas used in the step b) is at least one of argon and nitrogen.

A further technical solution is that the alkali solution selected in the step d) is at least one of NaOH and KOH, the solution concentration is that the alkali solution concentration is 0.4-1.2 mol/L, and the solid-liquid ratio is 1:2-15.

A further technical solution is that the ultrasonic power used in the ultrasonic-assisted alkali leaching process in step d) is 2-10 kW, the treatment time is 30-120 min, the temperature of the water bath is 50-90 °C, and the stirring speed is 600-3000 r/min.

Reaction mechanism:

According to the different absorbing properties of each substance, the carbon block has strong wave absorbing performance, which can make the carbon block material heat up rapidly. The cyanide is oxidized to form a non-toxic gas for removal. This process can remove most of the cyanide, and the loss of carbon blocks is very small and negligible.

After the cyanide is oxidized and removed, the temperature rises and the protective gas is introduced at the same time, so that the temperature rises rapidly to the melting point of the fluoride, so that it is precipitated, and a defluorination treatment is performed, and the precipitate left at the bottom of the crucible through the isolation net is recovered. The main components of the precipitate It is cryolite, which can be directly recycled and reused.

For each fluoride that is not precipitated, chemical reaction is used to expose the particle surface under the action of ultrasonic cavitation effect, and the high temperature and high pressure generated by the cavitation effect accelerates the chemical reaction, which shortens the processing time and can also be used for industrial production. , which has guiding significance for the large-scale treatment of aluminum electrolysis waste cathodes to recover cryolite and carbon.

Compared with the prior art, the beneficial effects of the present invention are:

1. In the microwave environment, the absorbing properties of various substances in the waste cathode carbon block are different. Among them, the carbon has a strong absorbing performance, which makes the carbon block heat up rapidly under microwave to reach the melting point of other substances except the carbon block. The fluoride (NaF, CaF ₂ , Na ₃ AlF ₆ ) reaches its melting point, so that the bond layer with the surrounding carbon is opened, and finally flows out as a white liquid, so as to achieve the purpose of removing most of the fluoride. In this process, the removal of fluoride The rate of cyanide is as high as 50-70%, which greatly shortens the follow-up treatment process, and in the process, cyanide is oxidized to form a non-toxic gas that can be directly discharged, and no toxic gas is generated in the process.

2. An isolation net is set in the crucible, so that the fluorine-containing material in the molten state is mainly cryolite through the isolation net and remains at the bottom of the crucible, which is convenient for the recovery and reuse of cryolite.

3. The pulverized carbon powder is put into a plastic beaker and immersed in the alkaline solution. During the heating process of the water bath, the materials after microwave high temperature roasting are subjected to secondary deep removal through ultrasonic cavitation vibration, stirring and alkaline immersion synergistic treatment. Fluorine can effectively remove fluoride in waste cathode carbon block by using ultrasonic effect and Bayer method. The removal rate of fluoride in aluminum electrolysis waste cathode carbon block is as high as 90-96%.

4. After crushing the waste cathode carbon block, the particle size is limited to 1-3cm, which is conducive to microwave penetration heating, and can fully precipitate each fluoride in a short time. If the particle size is too large, it is not conducive to rapid precipitation. If the particle size is too small, it will be affected by the protective gas, and it is easy to be blown out with the gas.

Description of drawings

FIG. 1 is a schematic flow chart of the present invention.

FIG. 2 is a scanning electron microscope image of the untreated waste cathode carbon block in Example 6. FIG.

FIG. 3 is the EDS spectrum of the untreated waste cathode carbon block in Example 6. FIG.

FIG. 4 is a scanning electron microscope image of the waste cathode carbon block after defluorination in Example 6. FIG.

FIG. 5 is the EDS energy spectrum of the waste cathode carbon block after defluorination in Example 6. FIG.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clear, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

In this embodiment, the waste cathode carbon block contains 58.4% carbon, 14.7% oxygen, 12.7% fluorine, 9.37% sodium, and 0.8% calcium by weight percentages and the balance is alumina and its trace elements.

Crush the waste cathode carbon block into a particle size of 1 to 3 cm, crush it again if it is larger than 3 cm, and enter the grinding stage if it is less than 1 cm, then put the cathode carbon block into a crucible, the crucible is a quartz crucible, and the sample is placed above the isolation net. The sample volume accounts for 2/3 of the crucible volume, and the crucible is placed in a high temperature microwave equipment.

When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced to oxidize and remove most of the cyanide. When the temperature reaches 400°C, the oxygen supply is stopped and argon gas is continuously introduced as a protective gas, and the cathode carbon block is subjected to high-temperature microwave. For the roasting treatment, the roasting temperature is 1000°C and the holding time is 30min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. The microwave equipment used in the whole process has a microwave frequency of 2450±50MHz, a microwave power of 1000W, and a heating rate of 30℃/min. Thermocouples are used to measure the temperature of waste cathode carbon blocks.

The white crystalline material left under the isolation net after being processed by the high temperature microwave equipment is recovered. After removing a small amount of white attachments on the surface of the carbon block on the isolation net, it is put into a grinding machine for grinding to obtain carbon powder with a particle size of less than 100 mesh.

Put the pulverized carbon powder into a sodium hydroxide solution with a concentration of 0.4mol/L, the solid-liquid ratio is 1:2, and leaching is carried out under the condition of an ultrasonic water bath. The ultrasonic leaching power is 2000W, and the time is 30min. The temperature is 50 °C, and the stirring speed is 600 r/min; the remaining fluoride and cyanide in the carbon powder are leached, and the filtrate and filter residue are obtained by filtration and separation after the leaching is completed;

The leached filter residue was placed in a vessel and placed in a constant temperature drying oven at a temperature of 60° C. for 12 hours, and the fluorine removal rate was as high as 90% after testing. The filtrate is neutralized and evaporated to obtain cryolite for reuse.

Example 2

In this embodiment, the waste cathode carbon block contains 58.4% carbon, 14.7% oxygen, 12.7% fluorine, 9.37% sodium, and 0.8% calcium by weight percentages and the balance is alumina and its trace elements.

Crush the waste cathode carbon block into a particle size of 1 to 3 cm, crush it again if it is larger than 3 cm, and enter the grinding stage if it is smaller than 1 cm, then put the cathode carbon block into a crucible, the crucible is corundum crucible, and the sample is placed above the isolation net. The sample volume accounts for 2/3 of the crucible volume, and the crucible is placed in a high temperature microwave equipment.

When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced to oxidize and remove most of the cyanide. When the temperature reaches 400°C, the oxygen supply is stopped and argon gas is continuously introduced as a protective gas, and the cathode carbon block is subjected to high-temperature microwave. For roasting treatment, the roasting temperature is 1075°C and the holding time is 50min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. The microwave equipment used in the whole process has a microwave frequency of 2450±50MHz, a microwave power of 3kW, and a heating rate of 40℃/min. The temperature of the waste cathode carbon block is measured by infrared.

The white crystalline material left under the isolation net after being processed by the high temperature microwave equipment is recovered. After removing a small amount of white attachments on the surface of the carbon block on the isolation net, it is put into a grinding machine for grinding to obtain carbon powder with a particle size of less than 100 mesh.

Put the pulverized carbon powder into a sodium hydroxide solution with a concentration of 0.6mol/L, the solid-liquid ratio is 1:6, and leaching is carried out under the condition of an ultrasonic water bath. The ultrasonic leaching power is 4000W, and the time is 50min. The temperature is 60 °C, and the stirring speed is 1000 r/min; the remaining fluoride and cyanide in the carbon powder are leached, and the filtrate and filter residue are obtained by filtration and separation after the leaching is completed;

The leached filter residue was placed in a utensil and placed in a constant temperature drying oven at a temperature of 60°C for 12 hours, and the fluorine removal rate was as high as 92% after testing. The filtrate is neutralized and evaporated to obtain cryolite for reuse.

Example 3

In this embodiment, the waste cathode carbon block contains 58.4% carbon, 14.7% oxygen, 12.7% fluorine, 9.37% sodium, and 0.8% calcium by weight percentages and the balance is alumina and its trace elements.

Crush the waste cathode carbon block into a particle size of 1 to 3 cm, crush it again if it is larger than 3 cm, and enter the grinding stage if it is less than 1 cm, then put the cathode carbon block into a crucible, the crucible is a quartz crucible, and the sample is placed above the isolation net. The sample volume accounts for 2/3 of the crucible volume, and the crucible is placed in a high temperature microwave device.

When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced to oxidize and remove most of the cyanide. When the temperature reaches 400°C, the oxygen supply is stopped and argon gas is continuously introduced as a protective gas, and the cathode carbon block is subjected to high-temperature microwave. For the roasting treatment, the roasting temperature is 1120°C and the holding time is 60min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. The microwave equipment used in the whole process has a microwave frequency of 915±50MHz, a microwave power of 5000W, and a heating rate of 60℃/min. Thermocouples are used to measure the temperature of waste cathode carbon blocks.

The white crystalline material left under the isolation net after being processed by the high temperature microwave equipment is recovered. After removing a small amount of white attachments on the surface of the carbon block on the isolation net, it is put into a grinding machine for grinding to obtain carbon powder with a particle size of less than 100 mesh.

Put the pulverized carbon powder into a potassium hydroxide solution with a concentration of 0.8mol/L, the solid-liquid ratio is 1:8, and leaching is carried out under the condition of an ultrasonic water bath. The ultrasonic leaching power is 5000W, and the time is 60min. The temperature is 70 °C, and the stirring speed is 1000 r/min; the remaining fluoride and cyanide in the carbon powder are leached, and the filtrate and filter residue are obtained by filtration and separation after the leaching is completed;

The leached filter residue was placed in a vessel and placed in a constant temperature drying oven at a temperature of 60°C for 12 hours. The fluorine removal rate was as high as 93% after testing. The filtrate is neutralized and evaporated to obtain cryolite for reuse.

Example 4

In this embodiment, the waste cathode carbon block contains 58.4% carbon, 14.7% oxygen, 12.7% fluorine, 9.37% sodium, and 0.8% calcium by weight percentages and the balance is alumina and its trace elements.

Crush the waste cathode carbon block into a particle size of 1 to 3 cm, crush it again if it is larger than 3 cm, and enter the grinding stage if it is less than 1 cm, then put the cathode carbon block into a crucible, the crucible is a mullite crucible, and the sample is placed above the isolation net. Put the sample volume into 2/3 of the crucible volume, and put the crucible into the high temperature microwave equipment.

When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced to oxidize and remove most of the cyanide. When the temperature reaches 400°C, the oxygen supply is stopped and argon gas is continuously introduced as a protective gas, and the cathode carbon block is subjected to high-temperature microwave. For roasting treatment, the roasting temperature is 1150°C and the holding time is 50min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. The microwave equipment used in the whole process has a microwave frequency of 915±50MHz, a microwave power of 8000W, and a heating rate of 100℃/min. Thermocouples are used to measure the temperature of waste cathode carbon blocks.

The white crystalline material left under the isolation net after being processed by the high temperature microwave equipment is recovered, the carbon block on the isolation net is removed a small amount of white attachments on the surface, and then put into a grinding machine for grinding to obtain toner with a particle size of less than 150 mesh.

Put the pulverized carbon powder into a mixed solution of potassium hydroxide and sodium hydroxide with a concentration of 1.0mol/L, the solid-liquid ratio is 1:10, and leaching is carried out under the condition of ultrasonic water bath, and the ultrasonic leaching power is 5000W, The time is 75 min, the temperature of the water bath is 80 °C, and the stirring speed is 2500 r/min; the remaining fluoride and cyanide in the carbon powder are leached, and the filtrate and filter residue are obtained by filtration and separation after the leaching is completed;

The leached filter residue was placed in a vessel and placed in a constant temperature drying oven at a temperature of 60°C for 12 hours. The fluorine removal rate was as high as 95% after testing. The filtrate is neutralized and evaporated to obtain cryolite for reuse.

Example 5

In this embodiment, the waste cathode carbon block contains 58.4% carbon, 14.7% oxygen, 12.7% fluorine, 9.37% sodium, and 0.8% calcium by weight percentages and the balance is alumina and its trace elements.

Crush the waste cathode carbon block into a particle size of 1 to 3 cm, crush it again if it is larger than 3 cm, and enter the grinding stage if it is less than 1 cm, then put the cathode carbon block into a crucible, the crucible is a mullite crucible, and the sample is placed above the isolation net. Put the sample volume into 2/3 of the crucible volume, and put the crucible into the high temperature microwave equipment.

When the temperature of the waste cathode carbon block reaches 300°C, a small amount of oxygen is introduced to oxidize and remove most of the cyanide. When the temperature reaches 400°C, the oxygen supply is stopped and nitrogen is continuously introduced as a protective gas, and the cathode carbon block is subjected to high-temperature microwave roasting. Treatment, the calcination temperature was 1200 ° C, and the holding time was 90 min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. The microwave equipment used in the whole process has a microwave frequency of 2450±50MHz, a microwave power of 10000W, and a heating rate of 150℃/min. Thermocouples are used to measure the temperature of waste cathode carbon blocks.

The white crystalline material left under the isolation net after being processed by the high-temperature microwave equipment is recovered, and the carbon block on the isolation net is removed from the surface of a small amount of white attachments, and then placed in a grinding machine for grinding to obtain toner with a particle size of less than 120 mesh.

Put the pulverized carbon powder into potassium hydroxide solution with a concentration of 1.2mol/L, the solid-liquid ratio is 1:15, and leaching is carried out under the condition of ultrasonic water bath. The ultrasonic leaching power is 10000W, the time is 120min, and the water bath temperature The temperature is 90 °C, and the stirring speed is 3000 r/min; the remaining fluoride and cyanide in the carbon powder are leached, and the filtrate and filter residue are obtained by filtration and separation after the leaching is completed;

The leached filter residue was placed in a vessel and placed in a constant temperature drying oven at a temperature of 60°C for 12 hours. The fluorine removal rate was as high as 98% after testing. The filtrate is neutralized and evaporated to obtain cryolite for reuse.

Example 6

The waste cathode carbon block contains 58.4% of carbon, 14.7% of oxygen, 12.7% of fluorine, 9.37% of sodium and 0.8% of calcium by weight percentage, and the balance is alumina and its trace elements. The steps are shown in Figure 1. The cathode carbon block is subjected to microwave high temperature treatment by microwave, and the treatment temperature is 1200°C. The power was 2500W, the heating rate was 30°C/min, and the holding time was 90min. This process brings cryolite and other fluorides to a melting point, allowing them to separate from the carbon. In the early stage of microwave treatment, a small amount of oxygen was introduced when the waste cathode carbon block was heated to 300°C to oxidize and remove most of the cyanide. After the temperature reached 400°C, nitrogen was continuously introduced as a protective gas, and then the cathode carbon block was subjected to high-temperature microwave treatment. roasting process.

The calcined cathode carbon block is ground to obtain carbon powder with a particle size of 200 meshes. Use sodium hydroxide solution with a concentration of 0.8mol/L and a solid-liquid ratio of 1:10 to carry out leaching under the condition of ultrasonic water bath, the leaching power is 6000W, the time is 90min, the water bath temperature is 80℃; the stirring speed is 2000r/min; The remaining fluoride and cyanide in the carbon powder are leached, and after the leaching is completed, the filtrate and the filter residue are obtained by filtration and separation; the carbon block with a fluorine removal rate as high as 98% is obtained.

The scanning electron microscope image and EDS energy spectrum of the untreated waste cathode carbon block are shown in Figures 2 and 3, respectively. It can be clearly seen that the distribution of each element is disorderly but the same elements are enriched together, and the proportion of carbon is relatively high. It can also be clearly seen that there is F ^- element, which is also proved by the EDS spectrum in Figure 3. The surface scanning electron microscope image and EDS energy spectrum of the waste cathode carbon block after deep defluorination are shown in Figures 4 and 5, respectively. It can be clearly seen from the figure that there is basically only carbon element, and the remaining elements are very few, almost completely removed, EDS The energy spectrum can also clearly see that the peak of carbon is the highest and the rest of the peaks are very small.

Although the present invention has been described herein with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of this disclosure. within the range. More particularly, various modifications and improvements in the component parts or arrangements are possible within the scope of the present disclosure, drawings and claims. In addition to variations and modifications to the component parts or arrangements, other uses will also be apparent to those skilled in the art.

Claims (8)

1. A method for removing fluorine by the cooperation of microwave-ultrasonic wave-alkaline leaching of aluminum electrolysis waste cathode carbon blocks is characterized by comprising the following steps:

a) crushing waste cathode carbon blocks of an aluminum electrolytic cell, screening to obtain particles with the particle size of 1-3 cm, returning to the crushing step when the particle size is larger than 3cm, and entering a grinding stage when the particle size is smaller than 1 cm;

b) putting the crushed waste cathode carbon blocks into a crucible, placing the crucible in a high-temperature microwave reactor, introducing a small amount of oxygen when the temperature of the waste cathode carbon blocks is raised to 300 ℃, stopping introducing the oxygen and continuously introducing protective gas when the temperature reaches 400 ℃, and roasting the waste cathode carbon blocks at high temperature by microwave under the environment of the protective gas to physically separate cryolite and fluoride electrolyte in the carbon blocks from the cathode carbon;

c) carrying out fine grinding treatment on the cathode carbon block after microwave roasting to obtain carbon powder with the granularity of less than 100 meshes;

d) pouring the finely ground carbon powder into alkali liquor, and carrying out alkali liquor leaching treatment by ultrasonic assistance to remove residual fluoride and cyanide in the carbon powder;

e) and after leaching, separating and filtering to obtain solid materials and filtrate respectively, drying the solid materials to obtain regenerated carbon powder with the purity of over 90%, and performing evaporation separation on the filtrate for recycling.

2. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: in the microwave high-temperature roasting process in the step b), microwaves are directly acted on the waste cathode carbon blocks for high-temperature roasting, the microwave power is 1-10 kW, the microwave frequency is 2450 +/-50 or 915 +/-50 MHz, the heating rate is 30-150 ℃/min, the roasting temperature is 1000-1200 ℃, and the heat preservation time is 30-90 min.

3. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: an isolation net is arranged in the middle of the crucible used in the step b), and through holes with the diameter smaller than 0.5cm are distributed on the isolation net.

4. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 3, wherein the method comprises the following steps: the crucible is one of a corundum crucible, a quartz crucible and a mullite crucible.

5. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: the temperature measuring device adopted in the step b) is a thermocouple temperature measuring device or an infrared temperature measuring device.

6. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: the protective gas used in the step b) is at least one of argon and nitrogen.

7. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: the alkali liquor selected in the step d) is at least one of NaOH and KOH, the solution concentration is that the alkali liquor concentration is 0.4-1.2 mol/L, and the solid-liquid ratio is 1: 2 to 15.

8. The method for removing fluorine in cooperation with microwave-ultrasonic-alkaline leaching of aluminum electrolysis waste cathode carbon blocks as claimed in claim 1, wherein the method comprises the following steps: the ultrasonic power adopted in the ultrasonic-assisted alkaline leaching process in the step d) is 2-10 kW, the treatment time is 30-120 min, the water bath temperature is 50-90 ℃, and the stirring speed is 600-3000 r/min.

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