Waste cathode carbon block purification device and high-valued treatment method

Abstract

The invention belongs to the field of solid waste treatment and high-value utilization of aluminum electrolysis waste cathode carbon blocks, and particularly relates to a waste cathode carbon block purification device which comprises an electrolytic tank, a power supply, a positive plate, a negative plate, a guide rod, a porous insulating container and a circulating pump, and the waste cathode carbon blocks in the porous insulating container are purified through current. The device can adjust the discharge distance, control the electrolyte concentration and adjust the current and voltage, waste cathode carbon can be electrolyzed and pulverized to the maximum extent, a large number of impurities on the surface of the carbon material are removed, the purification effect is achieved, and the surface of the carbon material of a blocky structure is relatively smooth; the method has important significance on high-valued treatment of the aluminum electrolysis waste cathode carbon block, and meanwhile, the electrolyte is recycled, so that secondary pollution is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste treatment and high-value utilization of spent cathode carbon blocks from aluminum electrolysis, and particularly relates to a device and method for purifying spent cathode carbon blocks. Background Art

[0002] During the long-term service, the spent cathode carbon blocks of aluminum electrolysis are continuously penetrated and chemically eroded by high-temperature aluminum liquid and molten salt electrolyte. At the same time, due to the influence of process parameters such as electrolytic cell life, damage reasons, current capacity, electrolyte system, lining structure and material type, and operation system, they have complex inorganic salt components, mainly including fluorides (NaF, Na3AlF6, CaF2), cyanides (NaCN, Na3Fe(CN)6, Na4Fe(CN)6), aluminum compounds (Al2O3, Al4C3, AlN, NaAl 11 O 17 ) and aluminosilicates (Al2SiO5, NaAlSiO4, NaAlSi3O8).

[0003] At present, the comprehensive recovery and treatment of waste cathode carbon is difficult and costly, making it difficult to achieve large-scale industrial treatment. The treatment method for waste cathode carbon from aluminum electrolysis is often open-air storage and landfill. This type of treatment not only occupies a large amount of land, but also in special circumstances (such as rainy and snowy weather), the soluble fluoride in the waste cathode carbon decomposes and seeps into the soil or groundwater, and also produces toxic and harmful gases that pollute the air, posing a great threat to the environment, humans and animals.

[0004] Numerous studies have been conducted on the harmless treatment and recovery of valuable components of spent cathode carbon, including flotation separation, high-temperature pyrometallurgical treatment, and wet treatment. Both high-temperature pyrometallurgical and wet treatments work by adding calcium / silicon-containing reagents to promote the stable solidification of fluorides and providing a high-temperature oxidizing environment or adding enhanced oxidizing agents to achieve the oxidative decomposition of cyanides. These processes are simple, and the resulting solid residues generally meet the requirements of the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB / 5085.3-2007). However, during the treatment process, the carbonaceous materials burn, vaporize, or enter the solid residue, converting the vast majority of fluorides into CaF2 and Ca4Si2F2O7. Only a minimal amount is converted into HF, which is absorbed by the alumina and returned to the electrolytic cell for use. This wastes significant amounts of graphite carbon and fluoride salt resources. Furthermore, the solid waste residues are complex in composition, have little economic value, and have a low overall utilization rate, posing a risk of secondary pollution.

[0005] In addition, the purity of graphite carbon recovered by flotation is generally low, which limits the comprehensive utilization of the recovered products. Deep purification must be carried out through a coupled chemical leaching process, which increases the complexity of the process flow. At the same time, the flotation medium produced contains a variety of fluorides (NaF, Na3AlF6, CaF2) with different solubility characteristics and highly toxic cyanide, which poses a serious risk of secondary pollution. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a device and method for purifying waste cathode carbon blocks, which realizes the electrolytic purification of waste cathode carbon blocks through an electrolytic cell, and realizes the recycling of electrolyte through a circulating pump. By adjusting the distance between positive and negative plates, electrolyte concentration and current and voltage, the waste cathode carbon can be purified to the maximum extent, which is of great significance to the high-value treatment of waste cathode carbon blocks from aluminum electrolysis.

[0007] In order to solve the above technical problems, the present invention provides a device for purifying waste cathode carbon blocks.

[0008] It includes an electrolytic cell, a power supply, a positive plate, a negative plate, a guide rod, a water outlet, a porous insulating container, and a circulation pump, and purifies the waste cathode carbon blocks in the porous insulating container through electric current;

[0009] The electrolytic cell body is an electrolytic cell, including at least one inlet pipe or discharge pipe, and is connected to the porous insulating container; a negative electrode plate is provided on the lower side of the inner portion of the electrolytic cell body, and a support sleeve is fixedly connected to the lower side of the negative electrode plate mounting groove;

[0010] The porous insulating container is arranged inside the electrolytic cell body and is used to hold the waste cathode carbon blocks; a positive plate is arranged on the top of the porous insulating container; the positive plate and the negative plate are connected to each other through a guide rod to achieve current conduction; the bottom of the side of the porous insulating container is provided with a bottom plate with holes or fence gaps, and the waste cathode carbon blocks are placed on the upper part of the bottom plate, and the top of the carbon blocks are in contact with the positive plate.

[0011] The electrolytic cell includes but is not limited to a single electrolytic cell, a double electrolytic cell, and a multi-electrolytic cell;

[0012] Optionally, the porous insulating container comprises a body and a liner;

[0013] Optionally, the body material is selected from polytetrafluoroethylene (PTFE), polypropylene (PP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP), soluble polytetrafluoroethylene (PFA);

[0014] Optionally, the lining material is selected from one or more of polytetrafluoroethylene (PTFE), polypropylene (PP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP) and soluble polytetrafluoroethylene (PFA);

[0015] Optionally, the materials of the positive electrode plate, the negative electrode plate, and the guide rod are independently selected from one or more of metal, conductive ceramic, and graphite;

[0016] Optionally, the metal is selected from one of the following elements: iron (Fe), tungsten (W), copper (Cu), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), titanium (Ti), zirconium (Zr), lead (Pd), cadmium (Cd), niobium (Nb), yttrium (Y), rhodium (Rh), tantalum (Ta), platinum (Pt) and germanium (Ge), or an alloy product containing multiple elements;

[0017] Optionally, the conductive ceramic is selected from WC, TiC, NbC, Cr3C2, Mo2C, VC, ZrC, SiC, V2O5, Ag2S, TiO2, Nb2O5, CdO, CsO, MoO3, CdS, WO3, BaO, SnO2, Ta2O5, BaTiO3, PbCrO4, ZnO, ZnF2, Fe2O3, Cr2O3, MnO, CoO, NiO, Cu2O, SnO, Pr2O3, Sb2S3, MoO2, SiC, Co3O4, TiS2, Mn3O4, Cr3C2, Mo2C, VC, ZrC, SiC, CuAl2O4, NiAl2O4, CuCr2O4, NiCr2O4, ZnCr2O4, FeAl2O4, CrB2, TaB2, ZrB2, TiB2, ReB2, Mo2FeB2, Mo2NiB2, WCoB, CaB6, NiFe2O4 and CuFe2O4, or a composite conductive ceramic material of two or more.

[0018] Optionally, the electrolytic cell is used to contain an electrolyte, wherein the electrolyte in the electrolyte is selected from one or more of an inorganic acid, an inorganic base, a strong acid and strong base salt, a strong base and weak base salt, a strong acid and weak base salt, and a weak acid and weak base salt inorganic base, and the inorganic acid and the inorganic base cannot coexist in the same electrolyte solution;

[0019] Optionally, the inorganic acid is selected from one or more of sulfuric acid, nitric acid, perchloric acid, ferric acid and hydrochloric acid;

[0020] Optionally, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, aluminum hydroxide and magnesium hydroxide;

[0021] Optionally, the strong acid and strong base salt is selected from one or more of sodium chloride, sodium fluoride, sodium sulfate, sodium nitrate, potassium chloride, potassium fluoride, potassium sulfate, potassium nitrate, potassium bisulfate and sodium bisulfate;

[0022] Optionally, the strong base weak acid salt is selected from one or more of potassium ferrate, potassium carbonate, and potassium bicarbonate;

[0023] Optionally, the strong acid and weak base salt is selected from one or more of ammonium chloride, ammonium sulfate and ammonium nitrate;

[0024] Optionally, the salt of weak acid and weak base is selected from ammonium bicarbonate.

[0025] Optionally, the electrolyte is selected from inorganic acids;

[0026] Optionally, the inorganic acid is selected from one or more of sulfuric acid, nitric acid and hydrochloric acid;

[0027] Optionally, the inorganic acid is selected from sulfuric acid.

[0028] Optionally, the electrolyte is selected from inorganic bases;

[0029] Optionally, the inorganic base is selected from sodium hydroxide and potassium hydroxide;

[0030] Optionally, the inorganic base is selected from sodium hydroxide.

[0031] The present invention also provides a method for purifying waste cathode carbon blocks using the above-mentioned device, which comprises the following steps:

[0032] S1. Place the waste cathode carbon blocks in an insulating porous container;

[0033] S2. Install the positive and negative plates and guide rods for testing in the electrolytic cell;

[0034] S3. Pour electrolyte into the electrolytic cell;

[0035] S4. Turn on the power supply, adjust the electrolysis parameters, and start electrolysis;

[0036] S5, pulverizing the waste cathode carbon block by electrolysis to obtain a solid-liquid mixture;

[0037] S6, the solid-liquid mixture is sequentially subjected to solid-liquid separation, washing and drying to obtain a solid powder;

[0038] S7. The solid powder is dried to obtain a purified carbon powder product.

[0039] Optionally, in step S4, the electrolysis temperature of the electrolysis method is 20-1000°C.

[0040] Optionally, in step S4, the electrolysis current density is controlled at 0.1 to 100 A / cm 2 between;

[0041] Optionally, in step S4, the electrolysis current density is controlled at 0.1 to 100 A / cm 2 For carbon blocks with high impurity content, it is recommended to use a higher current density (1-2A / cm 2 ); For carbon blocks with low impurity content or relatively complete block structure, it is recommended to use a lower current density (0.1~1A / cm 2 );

[0042] Optionally, in step S4, the power source used in the electrolysis method is selected from any one of a direct current power source, an alternating current power source, and a pulse current;

[0043] Optionally, in step S4, the power source used in the electrolysis method is selected from a direct current power source;

[0044] Optionally, the DC power supply is selected from a constant current DC power supply or a constant voltage DC power supply;

[0045] Optionally, the current of the constant current DC power supply is 0.1 to 2000A;

[0046] Optionally, the voltage of the constant voltage DC power supply is 0.1 to 1000 V;

[0047] Optionally, the voltage of the AC power supply is 200V to 500kV;

[0048] Optionally, the frequency of the pulse current is 10 Hz to 10 6 Hz.

[0049] Optionally, in step S7, the drying temperature is between 20 and 1000°C.

[0050] Beneficial effects:

[0051] 1. The present invention provides a device that can perform high-value treatment and purification on waste cathode carbon blocks. The device can adjust the discharge interval, control the electrolyte concentration, and adjust the current and voltage. It can maximize the electrolytic pulverization of waste cathode carbon. A large amount of impurities covering the surface of the carbon material have been removed to achieve a purification effect. The surface of the block-structured carbon material is relatively smooth. It is of great significance to the high-value treatment of waste cathode carbon blocks from aluminum electrolysis. At the same time, the electrolyte is recycled to reduce secondary pollution.

[0052] 2. The electrolyte in the electrolyte of the present invention promotes the electrolytic reaction through ionic conduction. The electric current drives the anodic oxidation reaction, causing the carbon matrix in the waste cathode to oxidize (generating CO2), while releasing soluble impurities such as fluoride (Na3AlF6) and cyanide (NaCN). Acidic electrolytes can dissolve metal oxide impurities, while alkaline electrolytes are suitable for dissolving non-metallic impurities. The electric current drives the oxidation of surface carbon atoms to generate CO2 (acidic conditions) or carbonate (alkaline conditions), resulting in surface etching and porous structure. The higher the concentration of the electrolyte provided by the present invention, the better the conductivity of the electrolyte and the faster the reaction rate, but too high a concentration may cause local overheating of the electrolyte or increased corrosiveness, affecting the integrity of the carbon material; when the concentration is low, the reaction rate slows down and the purification efficiency decreases.

[0053] 3. The current density of the present invention is a key process parameter in the electrolysis process, directly affecting the reaction rate and purification effect. The higher the current density, the faster the electrolysis reaction rate and the higher the purification efficiency of the spent cathode. However, excessively high current density may cause local overheating, electrolyte decomposition, or damage to the carbon material structure. At lower current density, the reaction rate is slower, reducing purification efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is an SEM image of the original waste cathode carbon block in step S1 of Example 1 of the present application;

[0055] Figure 2 This is an SEM image of the toner product in step S4 of Example 1 of the present application. DETAILED DESCRIPTION

[0056] The waste cathode carbon blocks of the aluminum electrolytic cells used in the following examples were obtained from a manufacturer in Henan.

[0057] The waste cathode carbon block was cut into several waste cathode carbon block samples with a size of 9 cm × 6 cm × 3 cm. Three waste cathode carbon block samples were randomly selected, and the three waste cathode carbon block samples were mechanically crushed and further ground to a fineness of ≤100 mesh.

[0058] Table 1 shows the industrial analysis of spent cathodes. The heating temperature is 800°C. Above 800°C, the fluoride salts in the spent cathodes volatilize, affecting data accuracy. The spent cathode raw material has a low fixed carbon content of only 71.96%, while the ash content is high at 27.74%. Impurities account for 28.04% of the total weight of the spent cathodes.

[0059] Table 1 Industrial analysis of spent cathode carbon blocks

[0060]

[0061]

[0062] Example 1

[0063] In this embodiment, a device and experimental method for purifying waste cathode carbon blocks specifically include the following steps:

[0064] S1. Select polytetrafluoroethylene as the raw material for the electrolytic cell container, select graphite rods as the positive and negative electrode guide rods, use the waste cathode carbon block sample as the anode, place the anode in a polytetrafluoroethylene porous container with a radius of 5 cm and a height of 13 cm, and use a circular graphite plate with a radius of 8 cm as the cathode. Place the anode and cathode in an electrolytic cell, respectively, and fill the electrolytic cell with 5000 ml of electrolyte solution. Use a constant current DC power supply to pulverize the waste cathode carbon block to obtain a solid-liquid mixture; wherein the electrolyte aqueous solution is selected from concentrated sulfuric acid, the DC current is 10 A, and the electrolysis temperature is 20°C;

[0065] S2. The solid-liquid mixture obtained in step S1 is allowed to stand at 20° C. for 24 hours, and then the solid-liquid separation is carried out by suction filtration to obtain a filter cake. The filter cake is washed once with pure water and dried in an oxygen-free environment at a drying temperature of 100° C. for 24 hours to obtain a solid powder. The liquid obtained after the solid-liquid separation of the solid-liquid mixture can be recycled as the electrolyte solution in step S1.

[0066] The carbon powder slurry obtained in step S4 and step S2 is sequentially subjected to solid-liquid separation and drying to obtain a carbon powder product; the solid powder obtained in step S1 and step S4 of Example 1 is subjected to scanning electron microscopy, wherein the scanning electron microscopy results of the original sample are as follows: Figure 1 The SEM test results of the solid powder obtained by S4 are shown in Figure 2 The solid powder obtained in step S4 of Example 1 was subjected to industrial analysis, and the test results are shown in Table 2.

[0067] Table 2 Industrial analysis indicators of Example 1

[0068] Element Example 1 test results unit Ordinary ash 5.10 ％ Volatile matter 6.79 ％ C 90.11 ％ Fixed carbon 86.43 ％ F 0.32 ％

[0069] Depend on Figure 1 and Figure 2 It can be seen that the present application adopts electrolysis to pulverize the waste cathode carbon blocks, and about 80% of the impurities covering the surface of the carbon material have been removed; the surface of the block-structured carbon material is relatively smooth.

[0070] Example 2

[0071] Compared with Example 1, the only difference of Example 2 is that the current density used in step S1 is 2A / cm 2 The solid powder obtained in step S4 of Example 2 was subjected to industrial analysis, and the test results are shown in Table 3.

[0072] Table 3 Industrial analysis indicators of Example 2

[0073] Element Example 2 test results unit Ordinary ash 5.41 ％ Volatile matter 4.87 ％ C 91.52 ％ Fixed carbon 89.73 ％ F 0.18 ％

[0074] As can be seen from Table 3, the electrolytic method is used to pulverize the waste cathode carbon blocks, which can more thoroughly separate the fluorine element in the waste cathode carbon blocks and increase the fixed carbon content.

[0075] Comparative Example 1

[0076] Compared with Example 1, the only difference of Comparative Example 1 is that stainless steel is used as the negative electrode plate material. The solid powder obtained in step S4 of Comparative Example 1 was subjected to industrial analysis, and the test results are shown in Table 4.

[0077] Table 4 Industrial analysis indicators of Example 1 and Comparative Example 1

[0078] Ingredient test results Example 1 Comparative Example 1 unit Ordinary ash 5.10 5.07 ％ Volatile matter 6.79 7.48 ％ C 90.11 89.82 ％ Fixed carbon 86.43 85.97 ％ F 0.32 0.41 ％

[0079] As can be seen from Table 4, the carbon powder product obtained by using graphite plate as the negative electrode plate raw material has a higher fixed carbon content and a better purification effect than that obtained by using stainless steel as the negative electrode plate raw material.

[0080] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A device for purifying waste cathode carbon blocks, characterized by: The device comprises an electrolytic cell, a power supply, a positive plate, a negative plate, a guide rod, a water outlet, a porous insulating container, and a circulation pump, and purifies the waste cathode carbon blocks in the porous insulating container by electric current; The electrolytic cell body is an electrolytic cell, including at least one inlet pipe or discharge pipe, and is connected to the porous insulating container; a negative electrode plate is provided on the lower side of the inner portion of the electrolytic cell body, and a support sleeve is fixedly connected to the lower side of the negative electrode plate mounting groove; The porous insulating container is arranged inside the electrolytic cell body and is used to hold the waste cathode carbon blocks; a positive plate is arranged on the top of the porous insulating container; the positive plate and the negative plate are connected to each other through a guide rod to achieve current conduction; the bottom of the side of the porous insulating container is provided with a bottom plate with holes or fence gaps, and the waste cathode carbon blocks are placed on the upper part of the bottom plate, and the top of the carbon blocks are in contact with the positive plate.

2. The device according to claim 1, characterized in that: The porous insulating container includes a body and a liner; Optionally, the body material is selected from polytetrafluoroethylene (PTFE), polypropylene (PP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP), soluble polytetrafluoroethylene (PFA); Optionally, the lining material is selected from one or more of polytetrafluoroethylene (PTFE), polypropylene (PP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP) and soluble polytetrafluoroethylene (PFA).

3. The device according to claim 1, characterized in that: The materials of the positive plate, negative plate and guide rod are independently selected from one or more of metal, conductive ceramic and graphite; Optionally, the metal is selected from one of the following elements: iron (Fe), tungsten (W), copper (Cu), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), titanium (Ti), zirconium (Zr), lead (Pd), cadmium (Cd), niobium (Nb), yttrium (Y), rhodium (Rh), tantalum (Ta), platinum (Pt) and germanium (Ge), or an alloy product containing multiple elements; Optionally, the conductive ceramic is selected from WC, TiC, NbC, Cr3C2, Mo2C, VC, ZrC, SiC, V2O5, Ag2S, TiO2, Nb2O5, CdO, CsO, MoO3, CdS, WO3, BaO, SnO2, Ta2O5, BaTiO3, PbCrO4, ZnO, ZnF2, Fe2O3, Cr2O3, MnO, CoO, NiO, Cu2O, SnO, Pr2O3, Sb2S3, MoO2, SiC, Co3O4, TiS2, Mn3O4, Cr3C2, Mo2C, VC, ZrC, SiC, CuAl2O4, NiAl2O4, CuCr2O4, NiCr2O4, ZnCr2O4, FeAl2O4, CrB2, TaB2, ZrB2, TiB2, ReB2, Mo2FeB2, Mo2NiB2, WCoB, CaB6, NiFe2O4 and CuFe2O4, or a composite conductive ceramic material of two or more.

4. The device according to claim 1, characterized in that: The electrolytic cell is used to contain an electrolyte, wherein the electrolyte in the electrolyte is selected from one or more of an inorganic acid, an inorganic base, a strong acid and strong base salt, a strong base and weak base salt, a strong acid and weak base salt, and a weak acid and weak base salt and an inorganic base, and the inorganic acid and the inorganic base cannot coexist in the same electrolyte solution; Optionally, the inorganic acid is selected from one or more of sulfuric acid, nitric acid, perchloric acid, ferric acid and hydrochloric acid; Optionally, the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, aluminum hydroxide and magnesium hydroxide; Optionally, the strong acid and strong base salt is selected from one or more of sodium chloride, sodium fluoride, sodium sulfate, sodium nitrate, potassium chloride, potassium fluoride, potassium sulfate, potassium nitrate, potassium bisulfate and sodium bisulfate; Optionally, the strong base weak acid salt is selected from one or more of potassium ferrate, potassium carbonate, and potassium bicarbonate; Optionally, the strong acid and weak base salt is selected from one or more of ammonium chloride, ammonium sulfate and ammonium nitrate; Optionally, the salt of weak acid and weak base is selected from ammonium bicarbonate.

5. The device according to claim 4, characterized in that The electrolyte is selected from inorganic acids; Optionally, the inorganic acid is selected from one or more of sulfuric acid, nitric acid and hydrochloric acid; Optionally, the inorganic acid is selected from sulfuric acid.

6. The device according to claim 4, characterized in that The electrolyte is selected from inorganic bases; Optionally, the inorganic base is selected from sodium hydroxide and potassium hydroxide; Optionally, the inorganic base is selected from sodium hydroxide.

7. A method for purifying waste cathode carbon blocks and increasing their value by using the device according to any one of claims 1 to 6, comprising the following steps: S1. Place the waste cathode carbon blocks in an insulating porous container; S2. Install the positive and negative plates and guide rods for testing in the electrolytic cell; S3. Pour electrolyte into the electrolytic cell; S4. Turn on the power supply, adjust the electrolysis parameters, and start electrolysis; S5, pulverizing the waste cathode carbon block by electrolysis to obtain a solid-liquid mixture; S6, the solid-liquid mixture is sequentially subjected to solid-liquid separation, washing and drying to obtain a solid powder; S7. The solid powder is dried to obtain a purified carbon powder product.

8. The high-value processing method according to claim 7, characterized in that: In step S4, the electrolysis temperature of the electrolysis method is 20-1000°C.

9. The high-value processing method according to claim 7, characterized in that: In step S4, the electrolysis current density is controlled at 0.1 to 100 A / cm 2 between; Optionally, in step S4, the power source used in the electrolysis method is selected from any one of a direct current power source, an alternating current power source, and a pulse current; Optionally, in step S4, the power source used in the electrolysis method is selected from a direct current power source; Optionally, the DC power supply is selected from a constant current DC power supply or a constant voltage DC power supply; Optionally, the current of the constant current DC power supply is 0.1 to 2000A; Optionally, the voltage of the constant voltage DC power supply is 0.1 to 1000 V; Optionally, the voltage of the AC power supply is 200V to 500kV; Optionally, the frequency of the pulse current is 10 Hz to 10 6 Hz.

10. The high-value processing method according to claim 7, characterized in that: In step S7, the drying temperature is between 20 and 1000°C.

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