Method and system for purifying a solution for extracting lithium from aluminum production wastes by electrolysis

Abstract

FIELD: processing aluminium production waste by electrolysis.SUBSTANCE: method for purifying a solution for extracting lithium from aluminium production waste by electrolysis includes adding an alkaline mixture to the solution for extracting lithium until the pH of the solution for extracting lithium reaches a first predetermined pH value and carrying out a first reaction in the solution for extracting lithium, then filtering the solution for extracting lithium to obtain a first filtrate and a first filter residue, respectively. The alkaline mixture comprises a regulator and a stabilizer; the regulator is added to the lithium extraction solution after adding the stabilizer to the lithium extraction solution; the stabilizer comprises calcium sulphate; the regulator comprises calcium oxide and / or calcium hydroxide; and the first predetermined pH value is equal to 11-11.5; adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches the second predetermined pH value and performing a second reaction in the first filtrate, then filtering the first filtrate to obtain a purified solution and a second filter residue, respectively, wherein the second predetermined pH value is equal to 11.5-12. Washing the first filter cake and the second filter cake by adding a washing liquid to the first filter cake and the second filter cake to form a washing suspension, then filtering the washing suspension to obtain a washing filtrate, and returning the washing filtrate to the lithium extraction solution for processing. When adding the stabilizer, the ratio of the mass of the stabilizer to the volume of the lithium extraction solution is from 6 to 10 kg / m3; and / or the amount of the added regulator is the amount at which the pH of the lithium extraction solution reaches the first specified pH value. The decalcifying agent comprises sodium carbonate; the actual amount of sodium carbonate added is 1.5-3.0 times greater than the theoretical amount of sodium carbonate added; the theoretical amount of sodium carbonate added is determined by the concentration of calcium ions in the first filtrate; and / or the catalyst comprises sodium hydroxide, and when sodium hydroxide is added, the ratio of the mass of sodium hydroxide to the volume of the first filtrate is from 0.2 to 0.5 kg / m3. The first reaction time is from 30 to 60 minutes after the pH of the lithium extraction solution reaches the first predetermined pH value; and / or the second reaction includes a decalcification reaction and a catalytic reaction, wherein the decalcification reaction is carried out for 20-30 minutes and then the catalytic reaction is carried out for 20-30 minutes. The ratio of liquid to solid matter of the washing liquid and the first filter residue and / or the second filter residue during washing is from 3:1 to 4:1; and / or the number of washes is 1-2.EFFECT: completely removing impurities in the lithium extraction solution under the condition of a low lithium loss rate.2 cl, 4 dwg, 1 tbl, 3 ex

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese Patent Application No. 202310546111.1, filed on May 12, 2023, which is incorporated herein by reference in its entirety.

[0003] FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0004] The invention relates to the field of processing aluminum production waste by electrolysis and, in particular, to a method and system for purifying a solution for extracting lithium from aluminum production waste by electrolysis.

[0005] STATE OF THE ART

[0006] Aluminum electrolysis waste is waste generated during the electrolytic aluminum production process. Since most of the current alumina raw materials produced in Shanxi, Henan, and other areas in China contain lithium elements, during the operation of the electrolytic cell, lithium elements continuously enrich the electrolyte and penetrate the cathode and lining of the cell, causing the lithium content in the electrolyte and lining to continuously increase. When the electrolytic cell is damaged, the cathode and lining must be completely replaced, resulting in a large amount of waste, which is the slag produced during the overhaul of the electrolytic cell. The slag has a high lithium content, and the remaining electrolyte also has a high lithium content.At the same time, since lithium carbonate currently has a high price, there is a growing number of studies on extracting lithium from aluminum production waste by electrolysis and producing lithium carbonate products.

[0007] The current technology for extracting lithium from aluminum smelting waste by electrolysis and producing lithium carbonate products mainly focuses on the process of dissolving lithium salts. The key process of purifying the lithium extraction solution lacks sufficiently detailed records, and most of them are too simple. Furthermore, the types of impurities removed are relatively few and incomplete. Meanwhile, the lithium loss rate is too high, so the recovery rate of lithium carbonate products is too low. Therefore, the existing technology is difficult to apply in practice. Therefore, comprehensively removing impurities in the lithium extraction solution under conditions of low lithium loss rate is a technical challenge that urgently requires solutions.

[0008] DISCLOSURE OF THE INVENTION

[0009] A method and system for purifying a lithium extraction solution from aluminum production waste by electrolysis are disclosed, which can solve the technical problems in the field of technology that it is difficult to completely remove impurities in the lithium extraction solution under the condition of a low lithium loss rate.

[0010] In a first aspect, according to an embodiment of the present invention, there is provided a method for purifying a lithium extraction solution of aluminum production waste by electrolysis, the method comprising: adding an alkaline mixture to the lithium extraction solution until the pH of the lithium extraction solution reaches a first predetermined pH value and carrying out a first reaction in the lithium extraction solution, and then filtering the lithium extraction solution to obtain a first filtrate; wherein the alkaline mixture contains a regulator and a stabilizer, the regulator is added to the lithium extraction solution after adding the stabilizer to the lithium extraction solution; the stabilizer contains calcium sulfate; the regulator contains calcium oxide and / or calcium hydroxide; the first predetermined pH value is 11-11.5;and adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches a second predetermined pH value and carrying out a second reaction in the first filtrate, and then filtering the first filtrate to obtain a purified solution, wherein the second predetermined pH value is 11.5-12.

[0011] In a second aspect, according to one embodiment of the present invention, there is provided a method for purifying a lithium extraction solution of aluminum production waste by electrolysis, the method comprising: adding an alkaline mixture to a lithium extraction solution until the pH of the lithium extraction solution reaches a first predetermined pH value and carrying out a first reaction in the lithium extraction solution, and then filtering the lithium extraction solution to obtain a first filtrate and a first filter cake, respectively; wherein the alkaline mixture contains a regulator and a stabilizer, and the regulator is added to the lithium extraction solution after the stabilizer is added to the lithium extraction solution; the stabilizer contains calcium sulfate, and the regulator contains calcium oxide and / or calcium hydroxide; the first predetermined pH value is 11-11.5;and adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches a second predetermined pH value and performing a second reaction in the first filtrate, and then filtering the first filtrate to obtain a purified solution and a second filter cake, respectively; and washing the first filter cake and the second filter cake by adding a washing liquid to the first filter cake and the second filter cake to form a washing slurry, and then filtering the washing slurry to obtain a washing filtrate, and returning the washing filtrate to the lithium extraction solution for processing.

[0012] In a third aspect, according to the embodiments of the present invention, a system for purifying a solution for extracting lithium from aluminum production waste by electrolysis is further provided, the system is adapted to the above-described method, the system comprises at least two cleaning devices, the cleaning device comprises: a filter unit comprising a liquid receiving tray, a stirring motor, a scraper and a filter mesh; the filter mesh is located on the lower surface of the liquid receiving tray; the outlet end of the stirring motor is connected to the scraper, the scraper is located above the filter mesh; and a liquid receiving unit comprising a liquid receiving tank, a vacuum interface, an inlet port, an outlet port and a stirring blade; the liquid receiving tank is located directly below the filter mesh;the inlet and outlet are respectively distributed on two sides of the liquid receiving tank, and the vacuum interface and the outlet are located on one side of the liquid receiving tank; the stirring paddle is located in the liquid receiving tank, and the stirring paddle is fixedly connected to the extended end of the stirring motor.

[0013] BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings, which are incorporated in and constitute a part of these application materials, illustrate certain embodiments of the present invention and serve to explain the principles of the invention together with the description.

[0015] To more clearly illustrate embodiments of the invention or technical solutions in the prior art, the accompanying drawings necessary for use in describing the embodiments or prior art are briefly presented below. Obviously, for those skilled in the art, other accompanying drawings can also be derived from these accompanying drawings without creative effort.

[0016] Fig. 1 illustrates a flow chart of a method for purifying a solution for extracting lithium from aluminum production waste by electrolysis in accordance with some embodiments of the invention;

[0017] Fig. 2 illustrates a detailed flow chart of a method for purifying a lithium extraction solution from aluminum production waste by electrolysis in accordance with some embodiments of the invention;

[0018] Fig. 3 illustrates a flow chart of a method for purifying a solution for extracting lithium from aluminum production waste by electrolysis in accordance with other embodiments of the invention; and

[0019] Fig. 4 illustrates a schematic diagram of the structure of a device for purifying a solution for extracting lithium from aluminum production waste by electrolysis in accordance with some embodiments of the invention.

[0020] Legend: 1 - Filter unit; 11 - Liquid receiving tray; 12 - Mixing motor; 13 - Scraper; 14 - Filter mesh; 2 - Liquid receiving unit; 21 - Liquid receiving tank; 22 - Vacuum interface; 23 - Inlet; 24 - Outlet; 25 - Mixing blade; 3 - Residue unloading unit; 31 - Shovel trolley; 32 - Shovel trolley track; 33 - Filter residue groove; 34 - Shovel trolley partition.

[0021] IMPLEMENTATION OF THE INVENTION

[0022] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention more clearly understood, the technical solutions in the embodiments of the invention will be clearly and fully described below in conjunction with the accompanying drawing according to the embodiments of the invention. Obviously, the described embodiments are some embodiments of the invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without any creative efforts fall within the scope of legal protection claimed by the present invention.

[0023] Unless otherwise stated, various raw materials, reagents, tools and equipment used in the invention are commercially available or obtained by existing methods.

[0024] The existing technology of lithium extraction from aluminum production waste by electrolysis and obtaining lithium carbonate products mainly considers the process of dissolving lithium salts, including:

[0025] (1) A water-soluble inorganic salt is added to the electrolyte to leach the lithium salt after heat treatment of the electrolyte. After the lithium salt is leached, the electrolyte is filtered to obtain filtrate B, and then an alkali (sodium hydroxide or potassium hydroxide) or an aqueous alkali solution is added to filtrate B to remove aluminum ions in filtrate B. Filtrate B is then filtered to obtain filtrate C, and carbonate is added to filtrate C to obtain a lithium carbonate precipitate.

[0026] (2) The electrolyte is subjected to an acidification reaction with nitric acid, and the electrolyte after the acidification reaction is filtered to obtain a filtrate. The filtrate is processed several times to obtain sodium nitrate, calcium fluoride, and lithium salt products. A soluble calcium salt or calcium hydroxide is added to the third filtrate to remove fluoride ions in the filtrate. The third filtrate is then filtered to obtain a fourth filtrate and a calcium fluoride precipitate. Oxalic acid is added to the fourth filtrate to precipitate excess calcium ions.

[0027] (3) The lithium-containing waste is crushed, then an inorganic acid solution is added to the crushed lithium-containing waste to cause lithium fluoride and the like in the lithium-containing waste to react with the inorganic acid solution, and the product after the reaction is filtered to obtain filtrate D. Sodium bicarbonate is added to filtrate D to remove iron in filtrate D, and then filtrate D is filtered to obtain filtrate E. Sodium hydroxide is added to filtrate E to remove aluminum in filtrate E, and then filtrate E is filtered to obtain filtrate F. Sodium oxalate is added to filtrate F to remove cobalt in filtrate F, and then filtrate F is filtered to obtain filtrate G, and then sodium carbonate is added to filtrate G to precipitate and obtain lithium carbonate.

[0028] The components of aluminum electrolysis waste mainly include electrolyte, carbonaceous slag, and overhaul slag. The main components of the electrolyte are Na3AlF6, calcium fluoride, alumina, K2NaAlF6, LiNa2AlF6, and LiF. The components of overhaul slag are relatively complex, mainly including carbon, aluminum silicon, sodium fluoride, calcium fluoride, lithium fluoride, cryolite, iron, and so on. The main components of carbonaceous slag are carbon and electrolyte.

[0029] Currently, industrial lithium extraction technologies for aluminum production waste by electrolysis mainly include three types: direct acid leaching, acid or salt leaching after roasting, and salt leaching. Regardless of which of the above technologies is used for lithium extraction, the lithium extraction solution will inevitably contain impurities other than lithium. These impurity elements mainly include fluorine, calcium, magnesium, iron, aluminum, boron, silicon, manganese, nickel, copper, and so on. These impurities must be removed to ensure the purity of the final lithium carbonate product.

[0030] As shown in Fig. 1, according to the first aspect of the disclosure of the invention, according to one embodiment, a method for purifying a solution for extracting lithium from aluminum production waste by electrolysis is provided. The method includes:

[0031] Step S11, adding an alkaline mixture to the lithium extraction solution until the pH of the lithium extraction solution reaches a first predetermined pH value and carrying out a first reaction in the lithium extraction solution, and then filtering the lithium extraction solution to obtain a first filtrate; and

[0032] Step S12, adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches the second predetermined pH value and carrying out a second reaction in the first filtrate, and then filtering the first filtrate to obtain a purified solution.

[0033] In one or more embodiments of the invention, the first predetermined pH value is 11-11.5, and the second predetermined pH value is 11.5-12.

[0034] The first set pH is adjusted to 11-11.5 by adding an alkaline mixture (such as a stabilizer and regulator), on the one hand, to stabilize the lithium ions in the lithium extraction solution so that the lithium ions exist in a stable and highly soluble form. On the other hand, the pH of the lithium extraction solution is adjusted to 11-11.5 so that fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, and part of the magnesium ions, etc. in the lithium extraction solution can be effectively removed, so as to ensure the fluoride ion concentration in the lithium extraction solution is below 10 mg / L, and the concentration of other impurity ions is close to or equal to 0.

[0035] The second set pH value is adjusted to 11.5-12 by adding decalcifying agent and catalyst, so that calcium ions and magnesium ions in the first filtrate can be effectively removed.

[0036] In some embodiments of the invention, the alkaline mixture comprises a regulator and a stabilizer, wherein the regulator is added to the lithium extraction solution after the stabilizer is added to the lithium extraction solution.

[0037] In some embodiments of the invention, the stabilizer comprises calcium sulfate and the regulator comprises calcium oxide and / or calcium hydroxide.

[0038] In addition to lithium, lithium extraction solution also contains impurities such as fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, magnesium ions, etc. In the first reaction of lithium extraction solution, adding calcium sulfate to lithium extraction solution can stabilize the lithium ions in the lithium extraction solution, causing the lithium ions to exist in the form of stable and highly soluble lithium sulfate, thereby preventing lithium loss. On the other hand, the pH of the lithium extraction solution is adjusted to 11-11.5 by adding calcium oxide and / or calcium hydroxide to the lithium extraction solution, so that fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, part of magnesium ions, etc.in the lithium extraction solution can be effectively removed, so that the concentration of fluoride ions in the lithium extraction solution is below 10 mg / L, and the concentration of other impurity ions is close to or equal to 0.

[0039] In some embodiments of the invention, when the stabilizer is added, the weight to volume ratio of the stabilizer to the lithium extraction solution is from 6 kg / m 3 up to 10 kg / m 3 ; and / or the amount of the added regulator is an amount at which the pH of the lithium extraction solution reaches the first predetermined pH value.

[0040] The amount of the stabilizer and regulator added is adjusted to stabilize the lithium ions in the lithium extraction solution and ensure that the lithium ions exist in the form of stable and highly soluble lithium sulfate. On the other hand, fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, and some magnesium ions in the lithium extraction solution can be effectively removed, ensuring that the fluoride ion concentration in the lithium extraction solution is below 10 mg / L, and the concentration of other impurity ions is close to or equal to 0.

[0041] In some embodiments, the decalcifying agent comprises sodium carbonate. The actual amount of sodium carbonate added is 1.5 to 3.0 times the theoretical amount of sodium carbonate added. The theoretical amount of sodium carbonate added is determined by the calcium ion concentration in the first filtrate.

[0042] In some embodiments, the catalyst comprises sodium hydroxide. When sodium hydroxide is added, the weight to volume ratio of sodium hydroxide to the first filtrate is between 0.2 kg / m 3 up to 0.5 kg / m 3 .

[0043] Adjusting the amount of decalcifying agent and catalyst added ensures that lithium ions in the first filtrate do not combine with carbonate after the addition of sodium carbonate, thereby preventing lithium loss. Even if a small amount of lithium ions combine with carbonate, the lithium ions and carbonate will be separated after the addition of sodium hydroxide as a catalyst, and the carbonate will combine with calcium to further remove calcium ions. Lithium ions remain free in the first filtrate, thus preventing lithium loss.

[0044] The special principle of decalcification and catalysis is that, according to the solution dynamics, the tendency of sodium to combine with carbonate is higher than the tendency of lithium to combine with carbonate. After adding the decalcifying agent, calcium ions in the first filtrate preferentially combine with the carbonate in the first filtrate to carry out the decalcification reaction. When lithium ions combine with carbonate to form lithium carbonate in the first filtrate after adding the decalcifying agent, sodium hydroxide is added as a catalyst to raise the pH of the first filtrate to the second predetermined pH value, separating lithium ions from carbonate. The carbonate combines with calcium to further remove calcium ions to form sodium carbonate.

[0045] In some embodiments of the invention, the first reaction time is from 30 to 60 minutes after the pH of the lithium extraction solution reaches a first predetermined pH value.

[0046] In some embodiments, the second reaction comprises a decalcification reaction and a catalytic reaction, wherein the decalcification reaction is carried out for 20-30 minutes, and then the catalytic reaction is carried out for 20-30 minutes. The catalytic reaction is a catalytic decalcification reaction.

[0047] Fluoride ions, magnesium ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, etc. in the lithium extraction solution can be effectively removed by adjusting the first reaction time.

[0048] Calcium ions, magnesium ions, etc. in the first filtrate can be effectively removed by adjusting the second reaction time.

[0049] In some embodiments, the method further comprises:

[0050] determine, according to the concentration of calcium ions in the purified solution, the need for a second purification of the purified solution;

[0051] Determination that if the calcium ion concentration in the purified solution is less than 10mg / L, there is no need for secondary purification of the purified solution;

[0052] Adding sodium carbonate to purify the purified solution for the second time if the calcium ion concentration in the purified solution is more than 50 mg / L; and

[0053] Purifying the purified solution using resin for the second time if the calcium ion concentration in the purified solution is between 10mg / L and 50mg / L.

[0054] The calcium ion concentration is used to determine whether the calcium ions in the purified solution have been completely removed. This is because, except for a small amount of calcium ions contained in the lithium extraction solution itself, most of the calcium ions are introduced by calcium oxide and / or calcium hydroxide added during the first reaction. Furthermore, the calcium ion concentration can indirectly judge whether other impurities in the lithium extraction solution have been completely removed, thereby ensuring the purification effect and ensuring that the fluoride ion concentration and calcium ion concentration in the purified lithium extraction solution are below 10 mg / L, and the concentration of other impurity ions is close to or equal to 0.

[0055] A method for purifying a solution for extracting lithium from aluminum production waste by electrolysis is provided in accordance with the embodiment of the invention according to the second aspect of the invention, and the method comprises:

[0056] Step S21, adding an alkaline mixture to the lithium extraction solution until the pH of the lithium extraction solution reaches a first predetermined pH value, and carrying out a first reaction in the lithium extraction solution, and then filtering the lithium extraction solution to obtain a first filtrate and a first filter cake, respectively;

[0057] Step S22, adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches a second predetermined pH value and performing a second reaction in the first filtrate, and then filtering the first filtrate to obtain a purified solution and a second filter cake respectively; and

[0058] Step S23, washing the first filter cake and the second filter cake by adding washing liquid to the first filter cake and the second filter cake to form a washing slurry, and then filtering the washing slurry to obtain a washing filtrate, and returning the washing filtrate to the lithium extraction solution for processing.

[0059] The first filter cake and the second filter cake obtained as a result of the first reaction and the second reaction are washed with a washing liquid to form a washing slurry, then the washing slurry formed by the washing liquid as a result of washing the first filter cake and the second filter cake is filtered to obtain a washing filtrate, and the washing filtrate is returned to the lithium extraction solution for processing, thereby effectively restoring the lithium elements in the first filter cake and the second filter cake, so that almost no lithium is lost during the purification process.

[0060] In some embodiments of the invention, the ratio of liquid in the form of a washing liquid and solid in the form of a first filter cake and / or a second filter cake during washing is from 3:1 to 4:1; and / or the number of washes is 1-2 times.

[0061] The washing effect can be ensured by adjusting the liquid-solid ratio and the washing number; the lithium ions in the first filter cake and the second filter cake are washed to obtain a clean first filter cake and second filter cake, and the wash filtrate is returned for treatment, thereby ensuring that there is no loss of lithium during the purification process.

[0062] In some embodiments, the method further comprises:

[0063] S24, determine whether the purified solution needs to be purified a second time according to the calcium ion concentration in the purified solution.

[0064] The method according to the second aspect of the invention differs from the method according to the first aspect of the invention in that a first filter cake and a second filter cake are obtained, and the first filter cake and the second filter cake are processed. The processing of the first filtrate and the second filtrate in this method is the same as the processing in the method described in the first aspect, and therefore will not be described in detail. Since the method for purifying a solution for lithium extraction of aluminum production waste by electrolysis uses part of the technical solutions of the above-mentioned embodiments, it at least has all the advantages provided by the technical solutions of the above-mentioned embodiments, which will not be described in detail here.

[0065] As shown in Fig. 4, according to the embodiments according to the third aspect of the invention, a system for purifying a solution for extracting lithium from aluminum production waste by electrolysis is further provided, wherein the system is adapted to the above-described method based on the general inventive concept, wherein the system includes at least two purification devices, wherein the purification device includes:

[0066] a filter unit 1 that includes a liquid receiving tray 11, a stirring motor 12, a scraper 13 and a filter mesh 14; the filter mesh 14 is located on the lower surface of the liquid receiving tray 11; the outlet end of the stirring motor 12 is connected to the scraper 13, and the scraper 13 is located above the filter mesh 14;

[0067] a liquid receiving unit 2 that includes a liquid receiving tank 21, a vacuum interface 22, an inlet 23, an outlet 24 and a stirring blade 25; the liquid receiving tank 21 is located directly below the filter mesh 14; the inlet 23 and the outlet 24 are respectively located on two sides of the liquid receiving tank 21, and the vacuum interface 22 and the outlet 24 are located on one side of the liquid receiving tank 21; the stirring blade 25 is located in the liquid receiving tank 21, and the stirring blade 25 is fixedly connected to the extended end of the stirring motor 12.

[0068] The purification device comprises: a filtering unit 1 comprising a liquid receiving tray 11, a stirring motor 12, a scraper 13 and a filter mesh 14; and a liquid receiving unit 2 comprising a liquid receiving tank 21, a vacuum interface 22, an inlet 23, an outlet 24 and a stirring blade 25. In this way, two-stage filtration can be achieved by the filtering unit 1, and the filtrates after each filtration are stored in the liquid receiving unit 2 to facilitate subsequent processing, thereby obtaining a pure lithium extraction solution.

[0069] The system is implemented based on the above-mentioned method, and the method steps can be related to the above-mentioned embodiments of the present invention. Since the system for purifying the solution for lithium recovery from aluminum production waste by electrolysis uses part or all of the technical solutions of the above-mentioned embodiments, it at least has all the advantages provided by the technical solutions of the above-mentioned embodiments of the present invention, which will not be described in detail here.

[0070] In some embodiments of the invention, the cleaning system further comprises:

[0071] residue unloading unit 3, which comprises a shovel cart 31, a track for a shovel cart 32 and a groove for a filter residue 33. The track for a shovel cart 32 is located at the upper part of the liquid receiving tank 21, is located under the filter mesh 14 and is located around the open end of the liquid receiving tank 21. The shovel cart 31 slides along the track for a shovel cart 32 to remove the filter residue filtered by the filter mesh 14, and the groove for a filter residue 33 is located on the side of the liquid receiving tank 21.

[0072] In one embodiment of the present invention, the residue unloading unit 3, comprising a shovel cart 31, a track for a shovel cart 32, a groove for a filter residue 33 and a partition of a shovel cart 34, is installed in such a way that the residue unloading unit 3 can cooperate with a scraper 13 to scrape the first filter residue and the second filter residue remaining in the filtering stage to the edge of the filter mesh 14 by means of the scraper 13, and the shovel cart 31 with its own motor slides along the track for a shovel cart 32 in such a way that the shovel cart 31 acts as a scraper shovel, thereby ensuring that the filter residues fall into the groove for a filter residue 33 for unloading.

[0073] In some embodiments of the invention, in order to provide a scraping effect of the shovel cart 31, a shovel cart partition 34 is placed on the shovel cart 31, located in a position opposite to the direction of rotation of the shovel cart 31. In this way, the filter residues are collected on the surface of the shovel cart 31 as the shovel cart 31 moves, and after the shovel cart 31 is rotated to an appropriate position in the filter residue groove 33, the filter residues can easily fall into the filter residue groove 33.

[0074] The technical solutions according to the present invention are described below, along with some embodiments. It should be understood that these examples are used for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods without specified conditions in the following examples are generally carried out in accordance with national standards of China. If there are no corresponding national standards in China, general international standards, customary conditions, or conditions recommended by the manufacturer should be used.

[0075] Example 1

[0076] First, calcium sulfate is added to the lithium extraction solution as a stabilizer in an amount of 6 kg / m3 3, and then calcium oxide is added to the lithium extraction solution to adjust the pH of the lithium extraction solution to 11. This removes fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, and some magnesium ions from the lithium extraction solution. The reaction caused by the addition of calcium sulfate and calcium oxide can be carried out in a lithium extraction solution purification device, the steps of which are as follows:

[0077] The lithium extraction solution is added to the liquid receiving tank 21 of the purification device; the vacuum interface 22 and the outlet port 24 are closed; and the stirring motor 12 is turned on to drive the stirring paddle 25 to rotate. After the inlet port 23 is opened to add calcium sulfate to the lithium extraction solution, calcium oxide is added to adjust the pH of the lithium extraction solution to 11, and the first reaction is carried out in the lithium extraction solution. The first reaction time is 60 minutes. The suspension after the first reaction is introduced into the liquid receiving tray 11 of another purification device; the outlet port 24 of the liquid receiving tank 21 is closed; the vacuum device connected to the vacuum interface 22 is turned on, and the inlet port 23 is closed, so that the liquid receiving tank 21 is in a state of negative pressure.The stirring motor 12 is switched on to rotate the scraper 13, and thus the filter residues filtered by the filter mesh 14 continuously move to the edge of the liquid receiving tray 11; the residue unloading unit 3 is switched on, and the shovel-trolley 31 and the shovel-trolley partition 34 move along the track for the shovel-trolley 32 to rake the filter residues to the edge of the liquid receiving tray 11, and after the shovel-trolley 31 makes one circle, the filter residues are poured into the filter residue groove 33 for unloading. After the filtration is completed, the first filtrate and the first filter residue are obtained. The concentration of ions in the first filtrate is measured. Now the concentration of fluoride ions is less than 10 mg / l, and the concentration of iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, etc. is close to or equal to 0.

[0078] The vacuum device is turned off, the vacuum interface 22 is closed, and the inlet port 23 is opened; sodium carbonate whose amount is 1.5 times the theoretical value is added to the liquid receiving tank 21; the stirring motor 12 is turned on to drive the stirring paddle 25 to carry out the reaction for 30 minutes, and then sodium hydroxide is added in an amount of 0.2 kg / m3 3to adjust the pH of the first filtrate to 11.5 to carry out the reaction for 30 minutes. The outlet 24 is opened to introduce the liquid in the liquid receiving tank 21 into the next purification device to repeat the operations to obtain a second filtrate and a second filter cake; and the concentration of ions in the second filtrate is measured, the concentration of calcium ions in the second filtrate is below 10 mg / L, the concentration of fluoride ions in the second filtrate is below 10 mg / L, and the concentrations of iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, etc. are close to or equal to 0; there is virtually no loss of lithium ions, and a purified solution is obtained.

[0079] If the calcium ion concentration in the second filtrate is higher than 50 mg / L, sodium carbonate is added to the second filtrate to remove it at an amount equal to 1.5 times the theoretical value, so that the calcium ion concentration in the second filtrate is reduced to below 10 mg / L; if the calcium ion concentration in the second filtrate is between 10 mg / L and 50 mg / L, the second filtrate is fed to a resin purification device, and the calcium ions in the second filtrate are further removed by ion exchange, so that the calcium ion concentration in the second filtrate is reduced to below 10 mg / L, and a purified solution is obtained.

[0080] The washing liquid having a liquid-solid ratio of 3:1 to the first filter cake and the second filter cake is used to wash the first filter cake and the second filter cake 2 times, then filtered to obtain a wash filtrate, and the wash filtrate is returned to the lithium extraction solution for cyclic lithium extraction.

[0081] Example 2

[0082] When comparing Example 2 with Example 1, the differences between Example 2 and Example 1 are as follows:

[0083] First, calcium sulfate is added to the lithium extraction solution as a stabilizer in an amount of 10 kg / m3 3Calcium hydroxide is then added to adjust the pH of the lithium extraction solution to 11.5 for a reaction of 30 minutes, and then the lithium extraction solution is filtered to obtain the first filtrate. Sodium carbonate, the amount of which is 3.0 times the theoretical value, is added to the first filtrate for a reaction of 20 minutes, and then sodium hydroxide is added at a rate of 0.5 kg / m3. 3 to adjust the pH of the first filtrate to 12 to carry out the reaction for 20 minutes, and then the first filtrate is filtered to obtain a purified solution.

[0084] The washing liquid having a liquid-solid ratio of 4:1 to the first filter cake and the second filter cake is used to wash the first filter cake and the second filter cake 2 times, then filtered to obtain a washing filtrate, and the washing filtrate is returned to the lithium extraction solution for cyclic lithium extraction.

[0085] Example 3

[0086] When comparing Example 3 with Example 1, the differences between Example 3 and Example 1 are as follows:

[0087] First, calcium sulfate as a stabilizer in the amount of 8 kg / m 3is added to the lithium extraction solution. Calcium hydroxide is then added to adjust the pH of the lithium extraction solution to 11.3 for a reaction of 45 minutes, and then the lithium extraction solution is filtered to obtain the first filtrate. Sodium carbonate, the amount of which is 2.2 times the theoretical value, is added to the first filtrate for a reaction of 25 minutes, and then sodium hydroxide is added at a rate of 0.35 kg / m3. 3 to adjust the pH of the first filtrate to 11.8 to carry out the reaction for 25 minutes, and then the first filtrate is filtered to obtain a purified solution.

[0088] The washing liquid having a liquid-solid ratio of 4:1 to the first filter cake and the second filter cake is used to wash the first filter cake and the second filter cake once, then filtered to obtain a washing filtrate, and the washing filtrate is returned to the lithium extraction solution for cyclic lithium extraction.

[0089] Relevant data and results:

[0090] The purified solution obtained in Example 1 was tested, and the results are shown in Table 1.

[0091]

[0092] a solution obtained from lithium extraction solution 1 after processing according to Example 1, and purified solution 2 is a purified solution obtained from lithium extraction solution 2 after processing according to Example 1.

[0093] According to one or more technical solutions of embodiments of the invention, at least the following technical effects or advantages are achieved:

[0094] (1) According to some embodiments of the invention, a method is provided for purifying a lithium extraction solution of aluminum production waste by electrolysis. While ensuring that the lithium content in the lithium extraction solution is substantially not lost, impurity ions in the lithium extraction solution can be removed so that the concentration of fluoride ions and calcium ions after purification is less than 10 mg / L, and the concentration of iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions, etc. is close to or equal to 0.

[0095] (2) According to some embodiments of the invention, a system for purifying a lithium extraction solution of aluminum production waste by electrolysis is also provided, which can continuously carry out filtering and purification reaction of the lithium extraction solution, achieve a simplification of the equipment configuration by more than 50%, and improve the purification efficiency.

[0096] According to some embodiments of the present invention, a method is provided for purifying a lithium extraction solution of aluminum production waste by electrolysis, wherein, compared with a conventional solution purification process, a stabilizer is first added to ensure that the lithium in the lithium extraction solution exists in the form of stable, highly soluble lithium sulfate (since lithium sulfate has high solubility in water, 100 g of water can dissolve 25.7 g of lithium sulfate at 20°C); then an adjuster is added to adjust the pH of the lithium extraction solution, thereby removing fluoride ions, iron ions, aluminum ions, boron ions, silicon ions, manganese ions, nickel ions, copper ions and a part of the magnesium ions in the lithium extraction solution; then sodium carbonate and sodium hydroxide are added to remove calcium ions, magnesium ions, etc. in the lithium extraction solution, thereby completing the removal of impurity ions in the lithium extraction solution.The pH and addition of stabilizers and catalysts are simultaneously controlled at various stages, ensuring zero lithium loss in the lithium extraction solution. The fluoride and calcium ion concentrations in the purified solution are below 10 mg / L, and the concentration of other impurity ions is close to or equal to 0, ensuring complete removal of impurities in the lithium extraction solution while ensuring virtually no lithium loss.

[0097] Various embodiments of the present invention may exist in the form of a range. It should be understood that the description in the form of a range is given only for convenience and simplicity and should not be perceived as an strict limitation on the scope of protection of the present invention; therefore, it should be considered that the described range specifically discloses all possible sub-ranges, as well as individual values ​​​​within such a range. For example, the description of a range from 1 to 6 should be considered as disclosing sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6 and from 3 to 6, and a single number in the stated range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In some embodiments of the invention, when a numerical range is indicated herein, it is meant to include any recited number (fractional or integer) within the stated range.

[0098] In the present invention, unless otherwise indicated, the directional words used, such as "upper" and "lower", refer to the direction of the figure in the drawing. In some embodiments of the invention, in the description of the present application materials, the terms "including", "including", and the like mean "including but not limited to". In the invention, relative terms such as "first" and "second" are used only to distinguish one object or operation from another and do not necessarily require or imply any actual connection or sequence between these objects or operations. In the present invention, "and / or" describes the relationship between related objects, indicating that there may be three relationships. For example, A and / or B may refer to: A separately, A and B separately, B separately. Moreover, A and B may be singular or plural. In the present invention, "at least one" refers to one or more, and "a plurality" refers to two or more."At least one," "at least one of the following," or similar expressions refer to any combination of these elements, including single elements or any combination of multiple elements. For example, "at least one of a, b, or c" or "at least one of a, b, and c" may be: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c may be single or multiple.

[0099] The above descriptions represent only a few embodiments of the invention, enabling those skilled in the art to understand and implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principle defined in the invention may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for purifying a solution for extracting lithium from aluminum production waste by electrolysis, comprising: adding an alkaline mixture to the lithium extraction solution until the pH of the lithium extraction solution reaches a first predetermined pH value and carrying out a first reaction in the lithium extraction solution, then filtering the lithium extraction solution to obtain a first filtrate and a first filter cake, respectively; wherein the alkaline mixture contains a regulator and a stabilizer; the regulator is added to the lithium extraction solution after the stabilizer is added to the lithium extraction solution; the stabilizer contains calcium sulfate; the regulator contains calcium oxide and / or calcium hydroxide; and the first predetermined pH value is 11-11.5; and adding a decalcifying agent and a catalyst to the first filtrate until the pH of the first filtrate reaches a second predetermined pH value and carrying out a second reaction in the first filtrate, then filtering the first filtrate to obtain a purified solution and a second filter cake, respectively, wherein the second predetermined pH value is 11.5-12; washing the first filter cake and the second filter cake by adding a washing liquid to the first filter cake and the second filter cake to form a washing slurry, then filtering the washing slurry to obtain a washing filtrate, and returning the washing filtrate to the lithium extraction solution for processing; Moreover, when adding a stabilizer, the ratio of the mass of the stabilizer to the volume of the solution for lithium extraction is from 6 to 10 kg / m3 3 ; and / or the amount of the regulator added is the amount at which the pH of the lithium extraction solution reaches the first set pH value; wherein the decalcifying agent contains sodium carbonate; the actual amount of sodium carbonate added is 1.5-3.0 times greater than the theoretical amount of sodium carbonate added; the theoretical amount of sodium carbonate added is determined by the concentration of calcium ions in the first filtrate; and / or the catalyst contains sodium hydroxide, and when sodium hydroxide is added, the ratio of the mass of sodium hydroxide to the volume of the first filtrate is from 0.2 to 0.5 kg / m3 3 ; wherein the first reaction time is from 30 to 60 minutes after the pH of the lithium extraction solution reaches the first predetermined pH value; and / or the second reaction includes a decalcification reaction and a catalytic reaction, wherein the decalcification reaction is carried out for 20-30 minutes and then the catalytic reaction is carried out for 20-30 minutes; wherein the liquid to solid ratio of the washing liquid and the first filter residue and / or the second filter residue during washing is from 3:1 to 4:1; and / or the number of washes is 1-2; In this case, the concentration of fluoride ions and calcium ions in the purified solution for lithium extraction is below 10 mg / l.

2. The cleaning method according to paragraph 1, characterized in that it additionally includes: adding sodium carbonate to purify the purified solution for a second time if the concentration of calcium ions in the purified solution exceeds 50 mg / L; and purifying the purified solution a second time using resin if the concentration of calcium ions in the purified solution is between 10 and 50 mg / L.

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