Method for recycling aluminum electrolysis spent cathode

Abstract

This invention belongs to the field of green treatment technology for waste aluminum electrolysis cathodes, specifically a method for recycling waste aluminum electrolysis cathodes, comprising the following steps: S1, obtaining waste aluminum electrolysis cathodes and an electrolyte molten pool; S2, adding the waste aluminum electrolysis cathode, crushed to a particle size of less than or equal to 1 mm, to the electrolyte molten pool and stirring to fully disperse it; S3, immersing a separator in the electrolyte molten pool at a first rotation speed for separation; S4, adjusting the separator to a second rotation speed and then disengaging it from the electrolyte molten pool, recovering the carbon particles in the separator; This invention can achieve high-purity carbon particle recovery and high-efficiency removal of electrolyte molten liquid from waste cathodes, and can be carried out online, significantly reducing energy consumption, realizing high-value resource recovery, and achieving efficient utilization of secondary resources.

Description

Technical Field

[0001] This invention belongs to the field of green treatment technology for waste cathodes from aluminum electrolysis, specifically a method for recycling waste cathodes from aluminum electrolysis. Background Technology

[0002] The world's leading process for producing metallic aluminum is the Hall effect molten salt electrolysis, using an aluminum electrolysis cell as the production equipment. This cell primarily consists of a carbon anode, a carbon cathode (including a carbon cathode block, a steel cathode rod, an insulation layer, and a seepage-proof layer), sidewalls, a cell shell, a cell cover, and conductive busbars. The carbon cathode's function is to hold molten aluminum and cryolite electrolyte, and to conduct current. During aluminum electrolysis, the strong corrosiveness of fluoride ions continuously erodes the carbon material on the cathode surface. Sodium ions in the electrolyte also penetrate into the cathode, reacting chemically with the cathode material to form metallic sodium or sodium compounds. These reaction products expand and damage the cathode's structure, gradually causing it to lose its original properties. Some electrolytes and impurities in the molten aluminum form a precipitate layer on the cathode surface, increasing its resistance, reducing its conductivity, and accelerating the erosion rate. When the erosion reaches a certain level, the cathode's performance and shape can no longer meet the requirements of the electrolysis process, rendering it completely unusable and generating waste cathodes, which are ultimately removed during major overhauls of the aluminum electrolysis cell.

[0003] Waste cathodes from aluminum electrolysis contain high-quality graphite resources and high-value fluoride salts. Industrially, flotation, alkaline leaching, and roasting-leaching methods are commonly used to treat them. Flotation utilizes the difference in hydrophobicity between carbon and electrolytes to separate them. While flotation is a short and low-cost process, it requires high-level pretreatment of the waste cathodes, and its efficiency is easily affected by particle size, flotation reagents, and operational procedures. Alkaline leaching utilizes the reaction of NaOH with Al₂O₃ and Na₃AlF₆ in the waste cathodes to generate Al(OH)₄. - The method of calcining and leaching involves calcining the waste cathode to decompose or volatilize harmful substances, followed by leaching the calcined product to recover useful components. This method has a high recovery rate, but the calcination process is energy-intensive and produces harmful gases.

[0004] In conclusion, avoiding the generation of waste gas, wastewater, and waste residue, and efficiently achieving comprehensive recycling and utilization of multiple components are crucial for promoting the green development of the aluminum electrolysis industry when processing waste cathodes from aluminum electrolysis. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for recycling waste cathodes from aluminum electrolysis, characterized by comprising the following steps: S1. Obtain a waste aluminum electrolysis cathode and an electrolyte molten pool, wherein the waste aluminum electrolysis cathode includes carbon particles and electrolyte to be recycled, and the electrolyte to be recycled is matched with the electrolyte melt in the electrolyte molten pool; S2. Add the aluminum electrolysis waste cathode, which is crushed to a particle size of less than or equal to 1 mm, to the electrolyte molten pool and stir to disperse it fully. The mass ratio of the electrolyte melt in the electrolyte molten pool to the aluminum electrolysis waste cathode is (6~9):1. The temperature of the electrolyte molten pool is 900~1000℃. S3. Immerse the separator in the electrolyte molten pool at a first rotation speed for separation, and maintain the separator rotating for a preset time. The first rotation speed is 500~1000 rpm. S4. After the separator is immersed in the electrolyte molten pool, it is adjusted to a second rotation speed and then detached from the electrolyte molten pool to recover the carbon particles in the separator. The second rotation speed is 600~700 rpm.

[0006] Furthermore, in step S2, the mass ratio of the electrolyte melt in the electrolyte pool to the aluminum electrolysis waste cathode is any one of 6:1, 7:1, 8:1, 9:1, or a range between both.

[0007] Furthermore, in step S2, the temperature of the electrolyte melting pool is any one of 900°C, 950°C, and 1000°C, or a range between two of them.

[0008] Furthermore, in step S3, the first rotational speed is any one of 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, or a range between two of them.

[0009] Furthermore, in step S4, the second rotational speed is any one of 600 rpm, 650 rpm, and 700 rpm, or a range between two of them.

[0010] In step S2, the electrolyte melt comprises 65wt%~80wt% Na3AlF6, 20wt%~30wt% AlF3, and 4wt%~6wt% CaF2.

[0011] In step S3, the preset time is 2-3 minutes.

[0012] Furthermore, in step S3, the preset time is any one of 2 minutes, 2.5 minutes, and 3 minutes, or a range between two of them.

[0013] Preferably, in step S2, the mass ratio of the electrolyte melt in the electrolyte pool to the aluminum electrolysis waste cathode is (7~8):1.

[0014] Preferably, in step S3, the preset time is 2 minutes and the first rotation speed is 900 rpm; In step S4, the second rotational speed is 700 rpm.

[0015] In step S3, the separator includes a rotor and a rotor housing, which are coaxially arranged and detachably connected. The rotor housing has filter holes equidistantly spaced around its perimeter to intercept the carbon particles and discharge the electrolyte melt. A liquid inlet is provided on one bottom surface of the rotor housing.

[0016] The separator further includes rotor blades, which are disposed at one end of the rotor and inside the rotor housing.

[0017] In step S4, the carbon content of the carbon particles is greater than or equal to 90%.

[0018] In step S4, the removal rate of the electrolyte to be recovered from the aluminum electrolysis waste cathode is greater than or equal to 80%.

[0019] This invention enables the recovery of high-purity carbon particles and the efficient removal of electrolyte melt from waste cathodes, all of which can be performed online, significantly reducing energy consumption and achieving high-value resource recovery and efficient utilization of secondary resources. This promotes the sustainable development of the aluminum electrolysis industry and also contributes to energy conservation and emission reduction. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the separator of the present invention.

[0022] Figure 2 The image shows the XRD pattern of the crushed aluminum electrolysis waste cathode from Example 1.

[0023] Figure 3 The image shows the XRD pattern of the carbon particles recovered in Example 1.

[0024] Wherein: 1-rotor, 2-liquid inlet, 3-rotor housing, 4-rotor blades.

[0025] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a method for recycling waste cathodes from aluminum electrolysis, comprising the following steps: S1. Obtain a waste aluminum electrolysis cathode and an electrolyte molten pool, wherein the waste aluminum electrolysis cathode includes carbon particles and electrolyte to be recycled, and the electrolyte to be recycled is matched with the electrolyte melt in the electrolyte molten pool; Waste cathodes from aluminum electrolysis, as secondary resources to be processed, contain high-quality graphite resources and high-value fluoride salt components. The electrolyte molten pool provides the necessary high-temperature environment and fluid medium for subsequent online separation, thereby achieving component separation by utilizing the differences in physical phase transitions.

[0028] S2. Add the aluminum electrolysis waste cathode, which is crushed to a particle size of less than or equal to 1 mm, to the electrolyte molten pool and stir to disperse it fully. The mass ratio of the electrolyte melt in the electrolyte molten pool to the aluminum electrolysis waste cathode is (6~9):1. The temperature of the electrolyte molten pool is 900~1000℃. Crushing the waste cathode to a particle size of less than 1 mm is to ensure that the carbon particles and electrolyte components achieve effective phase dissociation at the microscale. In the electrolyte molten pool at 900~1000℃, the electrolyte components mixed in the waste cathode change from solid to liquid phase after being heated, while the carbon particles, as high melting point substances, remain in solid phase, thus forming a uniformly dispersed solid-liquid mixture in the molten pool.

[0029] S3. Immerse the separator in the electrolyte molten pool at a first rotation speed for separation, and maintain the separator rotating for a preset time. The first rotation speed is 500~1000 rpm. The high-speed rotation of the separator within the molten pool generates a significant centrifugal field due to gravity. Utilizing the centrifugal force generated by the rotor blades inside the separator, the solid-liquid mixture is continuously drawn into the separator. Under the influence of centrifugal force, the electrolyte melt returns to the molten pool through filter holes (not shown in the figure), while the solid carbon particles are trapped on the inner wall of the separator. During this process, the circulating electrolyte melt continuously washes over the carbon particles adhering to the wall. Through this online scouring action, residual impurities trapped between the carbon particles are further removed, significantly improving the purity of the final product.

[0030] S4. After the separator is immersed in the electrolyte molten pool, it is adjusted to a second rotation speed and then detached from the electrolyte molten pool to recover the carbon particles in the separator. The second rotation speed is 600~700 rpm.

[0031] Adjusting the rotor speed to 600-700 rpm is to maintain this high speed during the process of the separator being lifted upwards from the electrolyte melt surface. This high speed can generate sufficient centrifugal force to overcome the surface tension and adhesion of the liquid electrolyte, thereby removing the residual liquid on the surface of the carbon particles to the greatest extent. This results in the final collection of high-purity carbon particles and achieves high-value resource recovery. The selection of the second speed is aimed at balancing the centrifugal force and the surface tension of the melt. Its value can be finely adjusted within a range according to the melt viscosity, or it can be kept consistent with the first speed.

[0032] The separator used to implement the above method includes: a rotor 1 and a rotor housing 3, the rotor 1 and the rotor housing 3 being coaxially arranged and detachably connected, the rotor housing 3 having filter holes (not shown in the figure) equidistantly spaced around its perimeter for intercepting the carbon particles and discharging the electrolyte melt, a liquid inlet 2 being provided on one bottom surface of the rotor housing 3, and a rotor blade 4 being provided at one end of the rotor 1, the rotor blade 4 being disposed inside the rotor housing 3.

[0033] The rotor blade 4, located at one end of the rotor 1, is inside the rotor housing. When the rotor 1 rotates at high speed, the rotor blade 4 not only drives the internal fluid to generate a centrifugal force field, but also generates a local negative pressure at the liquid inlet 2. This negative pressure can overcome the viscous resistance of the high-temperature melt and continuously and actively draw the mixture of suspended carbon particles and electrolyte melt in the molten pool into the separator.

[0034] The electrolyte solution in the electrolyte melting pool used in this embodiment of the invention has the following composition: Na3AlF6 80wt%, AlF3 15wt%, CaF2 5wt%.

[0035] Example 1 A method for recycling waste cathodes from aluminum electrolysis includes the following steps: S1. Obtain a waste aluminum electrolysis cathode and an electrolyte molten pool. The waste aluminum electrolysis cathode comprises carbon particles and electrolyte to be recycled. The electrolyte to be recycled is matched with the electrolyte melt in the electrolyte molten pool. The composition of the waste aluminum electrolysis cathode is: C 52.10wt%, Na 14.10wt%, Al 4.62wt%, K 0.92wt%, F 24.23wt%, O 1.51wt%, Ca 2.52wt%. S2. Add the aluminum electrolysis waste cathode, which has been crushed to a particle size of less than or equal to 1 mm, to the electrolyte molten pool and stir to disperse it fully. The mass ratio of the electrolyte melt in the electrolyte molten pool to the aluminum electrolysis waste cathode is 7:1, and the temperature of the electrolyte molten pool is 950°C. S3. The separator is immersed in the electrolyte molten pool at a first rotation speed for separation, and the separator is kept rotating for a preset time. The first rotation speed is 700 rpm. S4. After the separator is immersed in the electrolyte molten pool, it is adjusted to a second rotation speed and then detached from the electrolyte molten pool to recover the carbon particles in the separator. The second rotation speed is 700 rpm.

[0036] Please see Figure 2 , Figure 2 The image shown is the XRD pattern of the crushed aluminum electrolysis waste cathode from Example 1. Please refer to the following for further details. Figure 3 , Figure 3 The image shows the XRD pattern of the carbon particles recovered in Example 1. The XRD results indicate that the carbon particles are primarily composed of carbon. Figure 3 The diffraction peaks of the electrolyte components compared to Figure 2 It has significantly weakened.

[0037] The carbon content in the carbon particles was found to be 93.55%, and the removal rate of the electrolyte to be recovered was calculated to be 86.94%.

[0038] Example 2 Unlike Example 1, in step S3, the first rotational speed is 500 rpm.

[0039] The carbon content in the carbon particles was found to be 92.93%, and the removal rate of the electrolyte to be recovered was calculated to be 83.73%.

[0040] Example 3 Unlike Example 1, in step S3, the first rotational speed is 900 rpm.

[0041] The carbon content in the carbon particles was found to be 94.68%, and the removal rate of the electrolyte to be recovered was calculated to be 89.58%.

[0042] Please refer to Table 1, which shows the content of each element in the carbon particles recovered in the embodiments of the present invention.

[0043] Table 1 Comparative Example 1 Unlike Example 1, in step S2, the temperature of the electrolyte melt pool is 800°C.

[0044] The carbon content in the carbon particles was found to be 78.62%, and the removal rate of the electrolyte to be recovered was calculated to be 57.41%.

[0045] Comparative Example 2 Unlike Example 1, in step S2, the mass ratio of the electrolyte melt in the electrolyte pool to the aluminum electrolysis waste cathode is 5:1.

[0046] The carbon content in the carbon particles was found to be 81.62%, and the removal rate of the electrolyte to be recovered was calculated to be 70.41%.

[0047] Comparative Example 3 Unlike Example 1, in step S3, the first rotational speed is 400 rpm.

[0048] The carbon content in the carbon particles was found to be 85.37%, and the removal rate of the electrolyte to be recovered was calculated to be 69.25%.

[0049] Comparative Example 4 Unlike Example 1, in step S4, the second rotational speed is 500 rpm.

[0050] The carbon content in the carbon particles was found to be 88.41%, and the removal rate of the electrolyte to be recovered was calculated to be 74.63%.

[0051] Comparative Example 5 Unlike Example 1, in step S4, the separator is first removed from the surface of the electrolyte melt, and then the rotation speed is adjusted to the second rotation speed.

[0052] The carbon content in the carbon particles was found to be 83.29%, and the removal rate of the electrolyte to be recovered was calculated to be 66.78%.

[0053] This invention enables the recovery of high-purity carbon particles and the efficient removal of electrolyte melt from waste cathodes, all of which can be performed online, significantly reducing energy consumption and achieving high-value resource recovery and efficient utilization of secondary resources. This promotes the sustainable development of the aluminum electrolysis industry and also contributes to energy conservation and emission reduction.

[0054] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for recycling waste cathodes from aluminum electrolysis, characterized in that, Includes the following steps: S1. Obtain a waste aluminum electrolysis cathode and an electrolyte molten pool, wherein the waste aluminum electrolysis cathode includes carbon particles and electrolyte to be recycled, and the electrolyte to be recycled is matched with the electrolyte melt in the electrolyte molten pool; S2. Add the aluminum electrolysis waste cathode, which is crushed to a particle size of less than or equal to 1 mm, to the electrolyte molten pool and stir to disperse it fully. The mass ratio of the electrolyte melt in the electrolyte molten pool to the aluminum electrolysis waste cathode is (6~9):

1. The temperature of the electrolyte molten pool is 900~1000℃. S3. The separator is immersed in the electrolyte molten pool at a first rotation speed for separation, and the separator is kept rotating for a preset time. The first rotation speed is 500~1000 rpm. S4. After the separator is immersed in the electrolyte molten pool, it is adjusted to a second rotation speed and then detached from the electrolyte molten pool to recover the carbon particles in the separator. The second rotation speed is 600~700 rpm.

2. The method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step S2, the electrolyte melt comprises: 65wt%~80wt% Na3AlF6, 20wt%~30wt% AlF3 and 4wt%~6wt% CaF2.

3. The method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step S3, the preset time is 2-3 minutes.

4. The method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step S2, the mass ratio of the electrolyte melt in the electrolyte pool to the aluminum electrolysis waste cathode is (7~8):

1.

5. A method for recycling waste cathodes from aluminum electrolysis according to claim 3, characterized in that, In step S3, the preset time is 2 minutes and the first rotation speed is 900 rpm; In step S4, the second rotational speed is 700 rpm.

6. The method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step S3, the separator includes a rotor and a rotor housing, the rotor and the rotor housing are coaxially arranged and detachably connected, the rotor housing has filter holes equidistantly opened around its perimeter for intercepting the carbon particles and discharging the electrolyte melt, and a liquid inlet is provided on one bottom surface of the rotor housing.

7. A method for recycling waste cathodes from aluminum electrolysis according to claim 6, characterized in that, The separator also includes rotor blades, which are disposed at one end of the rotor and inside the rotor housing.

8. The method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, The carbon content of the carbon particles in step S4 is greater than or equal to 90%.

9. A method for recycling waste cathodes from aluminum electrolysis according to claim 1, characterized in that, In step S4, the removal rate of the electrolyte to be recovered from the aluminum electrolysis waste cathode is greater than or equal to 80%.

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