Method for improving the filtration effect of a slurry of a reconditioning slag leaching

Abstract

The application provides a method for improving the filtering effect of overhaul slag acid leaching slurry, relates to the technical field of electrolytic aluminum solid waste disposal and resource utilization, and solves the technical problem that the existing acid-alkali combined leaching method for treating overhaul slag is limited by the difficulty in filtering acid leaching slurry. The application comprises the following steps: crushing and ball milling electrolytic aluminum overhaul slag to obtain overhaul slag powder; slurry preparation is performed on the overhaul slag powder to obtain overhaul slag slurry; the overhaul slag slurry is subjected to pressurized alkali leaching treatment by using a sodium hydroxide solution to obtain alkali leaching slurry; solid-liquid separation is performed on the obtained alkali leaching slurry to obtain alkali leaching residue and alkali leaching filtrate; the obtained alkali leaching residue is washed and then slurry preparation is performed at a liquid-solid ratio of 4-6:1, concentrated sulfuric acid is added, acid leaching is performed, and acid leaching slurry is obtained; a flocculating agent is added to the obtained acid leaching slurry, and solid-liquid separation is performed to obtain acid leaching residue and acid leaching filtrate. The application effectively improves the solid-liquid separation efficiency of overhaul slag acid leaching slurry and realizes smoothness of the entire process flow.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolytic aluminum solid waste disposal and resource utilization, in particular to a method for improving the filtering effect of overhaul slag acid leaching slurry. BACKGROUND

[0002] The overhaul slag is the waste slag generated by the repair and replacement of the cathode lining of the electrolytic cell in the electrolytic aluminum production process. According to the actual electrolytic aluminum production, the overhaul slag is further divided into waste cathode and waste refractory material. The waste cathode is a graphite cathode carbon block of the electrolytic cell, which will penetrate a large amount of electrolyte in the long-term electrolytic production process. The graphite cathode carbon block eroded by the electrolyte mainly contains 50-70% of C, about 30% of fluoride, and a small amount of NaCN. The waste refractory material is a dry-type anti-seepage material eroded by the electrolyte, including heat preservation bricks, refractory bricks, castable materials and silicate plates. Generally, the electrolyte will only erode the dry-type anti-seepage material and sinter into a whole. The main chemical component is NaAlSiO4 (commonly known as: nepheline), and the fluoride mainly exists in the form of NaF, containing a small amount of Na3AlF6 and β-Al2O3.

[0003] A large amount of research has been done on the disposal and comprehensive utilization of aluminum electrolysis overhaul slag. Generally, it is divided into two categories: wet treatment and pyrometallurgical treatment. The wet treatment process mainly includes water immersion method, alkali leaching method, acid leaching method, and acid-alkali combined leaching method. The aluminum electrolysis overhaul slag contains a large amount of NaAlSiO4. After the electrolytic aluminum overhaul slag is acid leached, a large amount of Si forms silica gel in the acid leaching slurry of the overhaul slag. In the solid-liquid separation process, a large amount of silica gel adheres to the surface of the filter cloth, causing difficulty in solid-liquid separation of the slurry, which hinders the entire process flow and greatly reduces the disposal efficiency of the aluminum electrolysis overhaul slag. The acid-alkali combined leaching method has high harmless and resource utilization degrees, but it is limited by the difficulty in filtering the acid leaching slurry. SUMMARY

[0004] The purpose of the present application is to provide a method for improving the filtering effect of acid leaching slurry of overhaul slag, to solve the technical problem of the difficulty in filtering the acid leaching slurry of the existing acid-alkali combined leaching method for treating the overhaul slag.

[0005] The embodiments of the present application are implemented by the following technical solutions:

[0006] A method for improving the filtering effect of acid leaching slurry of overhaul slag, comprising the following steps:

[0007] Step 1: crushing and ball milling the electrolytic aluminum overhaul slag to obtain overhaul slag powder;

[0008] Step two: the slurry of the overhauled slag is prepared by slurry preparation, and the slurry of the overhauled slag is treated by pressurized alkali leaching with sodium hydroxide to obtain an alkali leaching slurry;

[0009] Step three: the alkali leaching slurry obtained in step three is subjected to solid-liquid separation to obtain alkali leaching residue and alkali leaching filtrate;

[0010] Step four: the alkali leaching residue obtained in step three is washed once, then slurry preparation is performed at a liquid-solid ratio of (4-6):1, concentrated sulfuric acid (98%) is added, acid leaching is performed, and an acid leaching slurry is obtained;

[0011] Step five: a flocculating agent is added to the acid leaching slurry obtained in step four, and the reaction is carried out for 20-30 min, then solid-liquid separation is performed to obtain acid leaching residue and acid leaching filtrate;

[0012] The flocculating agent comprises the following raw materials: polyacrylamide, ferric chloride, gelatin, chitosan and / or chitosan derivatives.

[0013] According to the technical scheme, the overhauled slag powder is crushed and ball milled to a suitable particle size, and the alkali leaching is performed with sodium hydroxide, so that other cations can be avoided, and the obtained sodium salt can be recycled to prepare slagging agent or refining agent, etc., thereby further expanding the resource utilization degree. Meanwhile, the alkali leaching is performed under pressure, which is beneficial to efficient leaching of fluorine ions in the overhauled slag, and can improve the production efficiency and reduce the production cost. The reaction mechanism of the pressurized alkali leaching treatment of the overhauled slag slurry with sodium hydroxide is that sodium hexafluoroaluminate (Na3AlF6) in the overhauled slag reacts with sodium hydroxide to obtain aluminum hydroxide precipitate, and fluorine ions are leached out, and the reaction formula is: Na3AlF6+3NaOH=Al(OH)3↓+6NaF;

[0014] After the pressurized alkali leaching, the NaF in the alkali leaching slurry has been basically leached out and dissolved in the filtrate, and part of the difficult-to-dissolve cryolite has not been leached out. The difficult-to-dissolve cryolite is dissolved by slurry preparation and the addition of concentrated sulfuric acid for secondary leaching, and F - 、Al 3+ are leached out in large quantities and dissolved in the leaching solution.

[0015] When the acid leaching slurry is prepared, the liquid-solid ratio is controlled at (4-6):1, and the following aspects are considered:

[0016] 1) If the liquid-solid ratio is too low, the concentration of the acid leaching slurry is correspondingly increased. According to the actual production conclusion, a large amount of silica gel is generated during the acid leaching of the overhauled slag, and the concentration of the silica gel is correspondingly increased, which is not conducive to the subsequent solid-liquid separation of the slurry;

[0017] 2) According to the actual production conclusion, increasing the liquid-solid ratio has certain dilution effect on the silica gel concentration in the slurry, which can greatly improve the solid-liquid separation effect of the slurry, but too high liquid-solid ratio will also cause the increase of the filtrate amount, and in the subsequent production of cryolite, the large amount of acid leaching liquid is surplus, and the acid liquid and alkali liquid in the whole leaching system will be seriously unbalanced, which is not conducive to the stable operation of the production;

[0018] By adding a flocculating agent to the acid leaching slurry, solid-liquid separation is carried out after 20-30 minutes of reaction. By taking the above measures, the silica gel content in the acid leaching slurry of the large repair residue can be reduced, and a relatively small amount of silica gel will still exist in the leaching slurry. By adding a flocculating agent, the colloidal particles in the water are bonded and aggregated to form flocculation, further improving the filtration effect of the slurry.

[0019] However, the conventional flocculating agent polyacrylamide has poor clarification effect on the suspension containing viscous substances (silica gel), and the clarification time is long. Chitosan and / or chitosan derivatives can form small flocculation clusters and then settle, but chitosan flocculation is prone to turbidity. The present application designs a flocculating agent for the acid leaching slurry of the present application. After the formation of flocculation clusters by chitosan and / or chitosan derivatives, gelatin and ferric chloride are added to further enhance the flocculation effect, speed up the flocculation process, prevent the turbidity of small chitosan flocculation clusters, and finally add cationic polyacrylamide to wait for the end of flocculation. By using the above flocculating agent, the above flocculating agent and the sequential addition are used to effectively remove silica gel deposits and prevent filter blockage.

[0020] Preferably, in the step five, the content of the flocculating agent component is: 1-3 parts of cationic polyacrylamide; 300-400 parts of ferric chloride; 30-40 parts of chitosan and / or chitosan derivative; 20-50 parts of gelatin;

[0021] The chitosan derivative can be: hydroxymethyl chitosan, hydroxyethyl chitosan, carboxymethyl chitosan, chitosan quaternary ammonium salt, chitosan hydrochloride, etc.

[0022] By using the technical solution, a flocculating agent with appropriate component ratio is selected to further improve the flocculation effect.

[0023] Preferably, in the step five, the flocculating agent is gradually added in the acid leaching container under stirring according to the component content and order; the addition order is: first add chitosan and / or chitosan derivative, stir thoroughly, then add gelatin, ferric chloride, and finally add polyacrylamide.

[0024] By using the technical solution, the silica gel is first flocculated into small flocculation clusters by chitosan and / or chitosan derivative, and then other flocculating agent components are added for further flocculation, which enhances the flocculation effect and reduces the flocculation time.

[0025] Preferably, in the step five, the total amount of the flocculant accounts for 0.1% of the acid leaching material.

[0026] By using the technical scheme, 0.1% is added under stirring and mixing, and the flocculant is fully mixed with the acid leaching material to meet the flocculation requirement.

[0027] Preferably, in the step one, the crushing includes primary crushing and secondary crushing, the particle size of the residue obtained by the primary crushing is less than 600 mm, and the particle size of the residue obtained by the secondary crushing is less than 10 mm.

[0028] By using the technical scheme, the particle size and the particle size distribution range of the residue can be smaller through twice crushing, so that the ball milling is more favorable, the ball milling efficiency and effect are improved, and the ball milling time is shortened.

[0029] Preferably, in the step two, the alkali leaching NaOH solution used in the pressurized alkali leaching treatment has a concentration of 15-30 g / L, a pressurized pressure of 0.2-0.5 MPa, and a temperature of 70-120 ℃, and the pressurized alkali leaching treatment is performed for 2-4 h.

[0030] If the pressurized pressure or the reaction temperature is too low, the efficient leaching of the fluoride ions in the overhauling residue is difficult to achieve, and if the pressurized pressure or the reaction temperature is too high, the equipment investment, production cost and energy consumption are greatly increased, and when the leaching rate of the fluoride ions reaches a certain range, further increasing the pressure or the temperature does not significantly improve the leaching rate of the fluoride ions. By controlling the above pressurized alkali leaching treatment conditions, the efficient leaching of the fluoride ions in the overhauling residue is realized, the production cost is controlled, and the production process difficulty is reduced.

[0031] If the concentration of NaOH is too low, the leaching effect of the fluoride ions is poor, and if the concentration of NaOH is too high, on the one hand, although the leaching rate of the fluoride ions is improved, when the leaching rate of the fluoride ions reaches a certain range, it is difficult to further significantly improve the leaching effect of the fluoride ions, and on the other hand, Al(OH)3 is prone to be dissolved, which affects the separation effect of fluorine. In addition, it should be noted that the liquid-solid ratio in the alkali leaching treatment refers to the mass ratio of the NaOH solution to the overhauling residue, if the liquid-solid ratio is too small, the leaching efficiency of the fluoride ions is reduced, if the liquid-solid ratio is too large, the solution consumption is large, the production investment and the post-processing difficulty are increased, and Al(OH)3 is also prone to be dissolved. By controlling the above alkali leaching treatment conditions, the production cost is controlled, and the leaching rate of the fluoride ions is improved on the basis of reducing the operation difficulty.

[0032] If the pressure alkali leaching treatment time is too short, the leaching yield of fluorine ions is low; if the pressure alkali leaching treatment time is too long, the production efficiency is reduced. By controlling the pressure alkali leaching treatment time in the above range, the production efficiency and the leaching yield of fluorine ions can be better balanced.

[0033] Preferably, in the step two, the water used for the size mixing is system back liquid, and the size mixing is carried out at a liquid-solid ratio of 4:1, and the system back liquid is the washing liquid generated by washing the alkali leaching residue in the step four.

[0034] By using the technical scheme, the washing liquid can be directly reused without treatment, which can achieve fluorine enrichment and balance the system water, and zero external discharge, and the water can be reasonably reused, and waste and pollution can be reduced.

[0035] Preferably, in the step four, the pH value is 2.0-3.0, the acid leaching temperature is 50-60 DEG C, and the acid leaching time is 4-6 h.

[0036] The acid leaching pH value is controlled to be 2.0-3.0. The following aspects are considered:

[0037] 1) When the pH is less than 7, only silicic acid molecules exist in the water, and no silicate ions exist, when the pH value is low, the colloidal silicic acid in the water is obviously increased, which is not conducive to the subsequent solid-liquid separation of the slurry;

[0038] 2) The increase of the pH of the leaching slurry can inhibit the generation of colloidal silicic acid in the solution, but the leaching rate of F and Al in the large repair residue is also affected, according to the data query, the silicic acid is stable in the range of pH=2-3, based on the above two points, the acid leaching pH value is controlled to be 2.0-3.0;

[0039] The acid leaching temperature is 50-60 DEG C. With the increase of the temperature, the leaching rate of F and Al is generally increased, and the viscosity of silica gel and the temperature are inversely proportional, the higher the temperature, the lower the viscosity of the silica gel, and the better the flow performance, on the contrary, the lower the temperature, the higher the viscosity of the silica gel, and the worse the flow performance. According to the embodiment of the present application, when the leaching temperature is controlled to be 50-60 DEG C, the soluble F and Al in the large repair residue have been basically leached out, and the main components in the remaining residue are the insoluble tetrakaidecabasic fluorphosphate and alpha-alumina, and the increase of the temperature has little effect on the leaching, and the leaching effect, the filtering effect and the cost are comprehensively considered, and the acid leaching temperature is controlled to be 50-60 DEG C.

[0040] The acid leaching time is 4-6 h. The following aspects are considered:

[0041] 1) According to the embodiment of the present application, with the consumption of sulfuric acid and the content of F and Al in the leaching residue as the judgment basis, the content of F and Al in the leaching residue gradually decreases with the extension of time, and when 4-6h, the content of F and Al in the leaching residue tends to be stable and no longer changes; the pH value of the acid leaching slurry fluctuates greatly within 1-4h, and the leaching process needs to continuously supplement sulfuric acid to maintain the system pH value, and after 4-6h, the pH value can tend to be stable, which side by side verifies that the leaching time is controlled within 4-6h, and the soluble metal ions in the leaching residue have been basically leached completely, and the remaining is the hardly soluble cryolite and alpha-alumina.

[0042] 2) If the leaching time is too long, the H4SiO4 solution in the slurry will be placed for a long time, and amorphous silicon dioxide will precipitate and appear in the form of colloidal ions, precipitates or gels, which is not conducive to the subsequent solid-liquid separation of the leaching slurry. Based on the above factors, the acid leaching time is 4-6h.

[0043] Preferably, the alkali leaching residue is washed once and then subjected to acid leaching and slurry preparation.

[0044] The following aspects are considered:

[0045] 1) The alkali leaching residue is washed, and the acid leaching and leaching are directly carried out without washing, which greatly increases the consumption of sulfuric acid, resulting in an increase in processing cost;

[0046] 2) If a large amount of sulfuric acid is added, the concentration of sulfate ions in the system will be greatly increased, resulting in an increase in the content of sodium sulfate salt in the acid leaching slurry, which is not conducive to the subsequent solid-liquid separation of the slurry;

[0047] 3) Under the condition that the slurry flow is constant, if the pH value of the slurry is too high, the flow of sulfuric acid to be added will also be increased accordingly, which will affect the safety. Based on the above factors, the alkali leaching residue needs to be washed before acid leaching and slurry preparation, and the number of washing times can be adjusted according to the actual production, which can be one washing or two washings.

[0048] Preferably, it further comprises a step six: adding the alkali leaching filtrate obtained in step three and the acid leaching filtrate obtained in step five into a neutralization process, and neutralizing and treating, so that the neutralization and precipitation of the alkali leaching filtrate and the acid leaching filtrate can prepare cryolite and aluminum fluoride.

[0049] By using the technical scheme, the acid and alkali waste liquids generated by the acid and alkali combined leaching of the overhaul residue are reasonably neutralized and treated, pollution is reduced, the precipitates generated by neutralization are reasonably reused to prepare cryolite and aluminum fluoride, and the rational utilization of resources is realized.

[0050] The technical scheme of the embodiment of the present application has at least the following advantages and beneficial effects:

[0051] 1) The present application effectively improves the solid-liquid separation efficiency of the acid leaching slurry of the overhaul residue, and realizes the smoothness of the entire process flow;

[0052] 2、The method can avoid introducing other impurities and ensure the purity of the product in the subsequent process;

[0053] 3、The method does not affect the leaching effect of other valuable metal ions in the overhaul slag.

[0054] 4、The method is easy to control and is convenient for industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0056] Figure 1 The process flow diagram of the method for improving the filtration effect of the overhaul slag acid leaching slurry provided in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0057] Embodiment 1

[0058] A method for improving the filtration effect of the overhaul slag acid leaching slurry, comprising the following steps:

[0059] (1) The overhaul slag is subjected to primary crushing (particle size ≤600 mm) by using the existing jaw crusher, and then subjected to secondary crushing (particle size ≤10 mm) by using the impact crusher, to obtain the overhaul slag crushed material, which is then subjected to ball milling to obtain the powder material with a particle size of not greater than 75 μm;

[0060] (2) The overhaul slag powder material is subjected to slurry preparation according to a liquid-solid ratio of 4:1 to obtain the overhaul slag slurry, and the concentration of the NaOH solution is 20 g / L, and the pressure leaching is performed; the alkali leaching temperature is controlled to be 100℃, the pressure is controlled to be 0.3 MPa, and the leaching is performed for 4 h to obtain the overhaul slag alkali leaching slurry;

[0061] (3) The overhaul slag alkali leaching slurry is subjected to plate and frame filtration to obtain the alkali leaching residue;

[0062] (4) After the alkali leaching residue is washed once, slurry preparation is performed according to a liquid-solid ratio of 5:1, concentrated sulfuric acid (98%) is added to adjust the pH value to 1.0, the temperature is controlled to be 60℃, leaching is performed for 6 h, and plate and frame pressure filtration is performed after reaction for 30 minutes, and the filtrate amount is 10 m 3 / h.

[0063] Embodiment 2

[0064] The difference between the present embodiment and Embodiment 1 is that step (5) is further included in the present embodiment.

[0065] The hydroxymethyl chitosan 30 parts is added in sequence, fully stirred and mixed, then the gelatin 50 parts, the ferric chloride 350 parts, and finally the cationic polyacrylamide 3 parts are added. The content of the above flocculant components is about 0.1% of the acid leaching material. After 30 minutes of reaction, the plate and frame filter pressing is performed, and the filtrate amount is 25m 3 / h.

[0066] Example 3

[0067] The difference between the present example and Example 1 is that, in the present example, in the step (4), the concentrated sulfuric acid (98%) is added to adjust the pH value to 3.0, the temperature is controlled at 60℃, the leaching is performed for 6h, the plate and frame filter pressing is performed, and the filtrate amount is 15m 3 / h.

[0068] Example 4

[0069] The difference between the present example and Example 1 is that, in the present example, in the step (4), the concentrated sulfuric acid (98%) is added to adjust the pH value to 3.0, the temperature is controlled at 60℃, the leaching is performed for 6h, the plate and frame filter pressing is performed, and the filtrate amount is 15m 3 / h.

[0070] Example 5

[0071] The difference between the present example and Example 2 is that, in the present example, in the step (5), the content of the flocculant components is the same, but before being added, they are prepared in advance, and then all of them are added at one time in an amount of 0.1% of the acid leaching material. After 30 minutes of reaction, the plate and frame filter pressing is performed, and the filtrate amount is 18m 3 / h. As can be seen from Examples 1-5, Example 2 is the acid leaching slurry filtering method for the large repair slag according to the present application. Compared with Example 1, the filter pressing speed is improved by 2.5 times. Compared with Example 3, the filter pressing speed is improved by 1.67 times. Compared with Example 4, the filter pressing speed is improved by 1.47 times. Compared with Example 5, the filter pressing speed is improved by 1.39 times. Therefore, the method for improving the filtering effect of the acid leaching slurry of the large repair slag according to the present application can effectively improve the filtering effect of the acid leaching slurry of the large repair slag.

[0072] Specifically, the difference between Example 1 and Example 2 is the different acid leaching ph, and the difference between Example 3 and Example 2 is only whether the flocculating agent is added; the difference between Example 4 and Example 2 is the difference in the type of flocculating agent added; and the difference between Example 5 and Example 2 is the difference in the order of adding the flocculating agent. It can be seen that selecting a suitable ph value in acid leaching can inhibit the generation of colloidal silica while ensuring the leaching of F and Al in the overhaul slag; the addition of ordinary flocculating agent can also effectively improve the acid leaching filtration effect; and the component ratio of the flocculating agent proposed in the application can further improve the acid leaching filtration effect on the basis of the ordinary flocculating agent, and the flocculating agent component ratio combined with the flocculating agent addition order method proposed in the application can significantly improve the silica gel flocculation and sedimentation effect and speed up the acid leaching filtration speed.

[0073] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for improving the filtration effect of a spent acid leaching slurry, characterized in that: The method comprises the following steps: Step one: crushing and ball milling the overhaul slag of electrolytic aluminum to obtain overhaul slag powder; Step two: slurry preparation of the overhaul slag powder obtained in step one to obtain overhaul slag slurry, and pressurized alkali leaching treatment of the overhaul slag slurry by using sodium hydroxide solution to obtain alkali leaching slurry; Step three: solid-liquid separation of the alkali leaching slurry obtained in step three to obtain alkali leaching residue and alkali leaching filtrate; Step four: slurry preparation of the alkali leaching residue obtained in step three after washing, adding concentrated sulfuric acid, acid leaching and leaching to obtain acid leaching slurry; Step five: adding a flocculating agent to the acid leaching slurry obtained in step four for solid-liquid separation to obtain acid leaching residue and acid leaching filtrate; in the step five, the flocculating agent comprises the following components and contents: 1-3 parts of cationic polyacrylamide, 300-400 parts of ferric chloride, 30-40 parts of chitosan and / or chitosan derivatives, and 20-50 parts of gelatin; in the step five, the flocculating agent is gradually added in the order of component content under stirring in the acid leaching container, and solid-liquid separation is performed after reaction for 20-30 min; the adding order is: first adding chitosan and / or chitosan derivatives, then adding gelatin, ferric chloride, and finally adding cationic polyacrylamide; Step six: adding the alkali leaching filtrate obtained in step three and the acid leaching filtrate obtained in step five to a neutralization process for neutralization treatment, and using the neutralization precipitate of the alkali leaching filtrate and the acid leaching filtrate to prepare cryolite and aluminum fluoride.

2. The method for improving the filtration effect of the slurry of the acid leaching of the overhauled residue according to claim 1, characterized in that: In the step five, the total amount of the flocculating agent accounts for 0.1% of the acid leaching material.

3. The method for improving the filtration effect of the slurry for the acid leaching of the overhauled residue according to any one of claims 1-2, characterized in that: In the step one, the crushing comprises primary crushing and secondary crushing, the particle size of the slag obtained by the primary crushing is less than 600 mm, and the particle size of the slag obtained by the secondary crushing is less than 10 mm.

4. The method for improving the filtration effect of the slurry for the acid leaching of the overhauled residue according to any one of claims 1-2, characterized in that: In the step two, the sodium hydroxide solution has a concentration of 15-30 g / L, a pressurization pressure of 0.2-0.5 MPa, and an alkali leaching temperature of 70-120°C, and the pressurized alkali leaching treatment is performed for 2-4 h.

5. The method for improving the filtration effect of the slurry for the acid leaching of the overhauled residue according to any one of claims 1-2, characterized in that: In the step two, the water used for slurry preparation is system back liquid, and the slurry preparation is performed at a liquid-solid ratio of 4:1, wherein the system back liquid is the washing liquid generated by washing the alkali leaching residue in the step four.

6. The method for improving the filtration effect of the slurry for the acid leaching of the overhauled residue according to any one of claims 1-2, characterized in that: In the step four, the pH value of the acid leaching slurry is 2.0-3.0, the acid leaching leaching temperature is 50-60°C, and the acid leaching leaching time is 4-6 h.

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