A method and device for preparing lithium hydroxide

Abstract

The present invention relates to a method for preparing lithium hydroxide, which comprises the following steps: i) adsorbing and desorbing lithium-containing brine and then optionally concentrating to obtain a lithium-containing salt solution; ii) subjecting the lithium-containing salt solution to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution; iii) subjecting the product salt solution to bipolar membrane electrodialysis to obtain a product acid solution and a product alkaline solution, and using the product acid solution for adsorption-desorption in step i), and using the product alkaline solution for displacement electrodialysis in step ii). The method of the present invention uses lithium-containing brine as a raw material, and prepares lithium hydroxide by an adsorption method coupled to an electrodialysis method. The process steps of the present invention are simple in actual operation mode, low in long-term energy consumption, low in the amount of reagent added in the entire process and low in wastewater discharge, strong in environmental friendliness, and high in industrial operability.

Description

Technical Field

[0001] The invention relates to a method and a device for preparing lithium hydroxide. Background Art

[0002] Lithium hydroxide is an important inorganic chemical product, and its preparation has always been a hot topic of concern and research.

[0003] At present, the preparation methods of lithium hydroxide can be divided into ore method and salt lake method. The ore method uses lithium-containing ore as raw material to prepare lithium hydroxide, and there is still a lot of room for improvement in terms of product purity, production efficiency and degree of automation. The salt lake method uses salt lake brine as raw material, including chemical precipitation method, solvent extraction method, adsorption method, etc. The chemical precipitation method is a technology that adds chemical agents to salt lake brine to precipitate and separate lithium ions. It has the advantages of simple process and low energy consumption, but its recovery rate is low and there are many wastes. The solvent extraction method uses organic phases to extract and separate lithium ions. Its advantages are fast rate and high purity. Its disadvantages are that the extractant is expensive, easy to dissolve, and the equipment is susceptible to corrosion. The adsorption method uses adsorbents and desorbents to directly adsorb lithium from salt lake brine and separate lithium-rich solutions. The adsorption method has good selectivity and high purity, but its disadvantages are slow rate and easy loss of adsorbents.

[0004] CN 115924939 A discloses a method for preparing lithium hydroxide, which comprises obtaining a potassium hydroxide solution by electrolysis and crystallizing it, and then reacting the potassium hydroxide crystals with lithium chloride to generate lithium hydroxide. In this method, the lithium hydroxide solution before crystallization into salt contains a large number of impurity ions, and the crystallization process needs to be additionally controlled. The steps are complicated, the operation is difficult, and the energy consumption is large, and the environmental pollution is large.

[0005] In summary, the lithium hydroxide preparation methods in the prior art each have their own advantages, but their disadvantages cannot be ignored, such as low recovery rate, large amount of waste, difficult operation, high energy consumption, high cost, and environmental unfriendliness.

[0006] Therefore, there is a need in the art for a method for preparing lithium hydroxide that can improve or overcome at least one of the above-mentioned disadvantages. Summary of the invention

[0007] In view of the above problems and needs, a first aspect of the present invention provides a method for preparing lithium hydroxide, which comprises the following steps:

[0008] i) subjecting the lithium salt-containing brine to adsorption-desorption and subsequent optional concentration to obtain a lithium salt-containing solution;

[0009] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0010] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0011] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0012] A second aspect of the present invention provides lithium hydroxide obtained according to the method of the present invention.

[0013] A third aspect of the present invention provides a device for preparing lithium hydroxide, the device comprising:

[0014] an adsorption-desorption unit for adsorbing and desorbing the lithium-containing brine and subsequently optionally concentrating it to obtain a lithium-containing salt solution;

[0015] A displacement electrodialysis unit, used for performing displacement electrodialysis on the lithium salt solution to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0016] The bipolar membrane electrodialysis unit is used to perform bipolar membrane electrodialysis on the product salt solution to obtain a product acid solution and a product alkaline solution, and then use the product acid solution for adsorption-desorption in step i) and use the product alkaline solution for displacement electrodialysis in step ii).

[0017] The method and device of the present invention use lithium salt brine as raw material, and prepare lithium hydroxide by adsorption method coupled with electrodialysis method. The process steps of the present invention are simple in actual operation mode, with low long-term energy consumption, and a closed process loop is achieved at the same time, most of the wastewater is recycled, the amount of reagent added in the whole process is small, the amount of wastewater discharged is small, the environment is highly friendly, and the industrial operability is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a method flow diagram of an exemplary embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram showing the method steps of an exemplary embodiment of the present invention is shown;

[0020] Figure 3 An exemplary schematic diagram of the bipolar membrane electrodialysis of the present invention is shown;

[0021] Figure 4 A schematic diagram of a method flow diagram of an exemplary embodiment of the present invention is shown;

[0022] Figure 5 A schematic diagram of a method flow diagram of an exemplary embodiment of the present invention is shown;

[0023] Figure 6A schematic diagram of a method flow diagram of an exemplary embodiment of the present invention is shown;

[0024] Figure 7 A schematic diagram of a method flow diagram of an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0025] In order to make the invention objectives, technical solutions and beneficial technical effects of this application clearer, this application will be described in detail below.

[0026] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0029] If there is no special explanation, all steps of the present application can be performed sequentially, randomly, or simultaneously. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) performed simultaneously. For example, the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), (b), etc.

[0030] Unless otherwise specified, the terms used in this application have the same meanings as those generally understood by those skilled in the art.

[0031] Unless otherwise specified, the operations mentioned in this application are carried out at room temperature and normal pressure.

[0032] If not specifically stated, the operations mentioned in this application can be implemented by methods known to those skilled in the art.

[0033] Unless otherwise specified, the equipment, devices, instruments, parts, materials, agents, etc. mentioned in this application can be obtained by methods known to those skilled in the art.

[0034] Unless otherwise specified, the indicators mentioned in this application, such as concentration, flow rate, current density, etc., can be measured by methods known to those skilled in the art.

[0035] like Figure 1 As an example, the present invention provides a method for preparing lithium hydroxide, such as Figure 2 By way of example, it includes the following steps:

[0036] i) subjecting the lithium salt-containing brine to adsorption-desorption and subsequent optional concentration to obtain a lithium salt-containing solution;

[0037] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0038] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0039] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0040] Each step of the present invention is described in detail below.

[0041] Step i) adsorbs and desorbs the lithium salt-containing brine and then optionally concentrates it to obtain a lithium salt-containing solution.

[0042] The term "lithium-containing brine" of the present invention refers to a salt solution containing lithium ions and optionally alkali metals, alkaline earth metal cations such as calcium, sodium, potassium, magnesium, and anions such as sulfate and chloride, and which has not been treated by the method of the present invention. In one embodiment of the present invention, the lithium-containing brine of the present invention can be derived from a lithium-rich salt lake, an extract of lithium ore (such as lepidolite, spodumene, lithium feldspar, etc.), or a recycle of lithium-containing products (such as lithium batteries, etc.). In a preferred embodiment of the present invention, the lithium-containing brine of the present invention is derived from a lithium-rich salt lake, such as Zabuye Salt Lake, Dachaidan Salt Lake, Xitaijinaier Salt Lake, etc.

[0043] In one embodiment of the present invention, the lithium salt-containing brine of the present invention may contain one or more lithium salts selected from, for example, lithium sulfate, lithium chloride, lithium dihydrogen phosphate and combinations thereof, preferably lithium chloride. + The concentration may be 10 to 15,000 mg / L, preferably 100 to 15,000 mg / L, and more preferably 150 to 15,000 mg / L.

[0044] In one embodiment of the present invention, the lithium salt-containing brine of the present invention may further contain one or more impurity ions, and the impurity ions may be selected from, for example, calcium ions, magnesium ions, boron ions, potassium ions and combinations thereof.

[0045] The term "lithium salt solution" of the present invention refers to a solution containing lithium ions obtained by adsorption-desorption and optional post-treatment of lithium salt brine. In the present invention, illustratively and not restrictively, the term "lithium salt solution" can refer to a desorption solution obtained by adsorption-desorption, a solution obtained by sequentially adsorption-desorption and nanofiltration, and a solution obtained by sequentially adsorption-desorption, nanofiltration, and reverse osmosis.

[0046] The term "adsorption-desorption" of the present invention refers to the use of an adsorbent to adsorb and separate ions from a material, and then the use of a desorbent to elute and separate the ions from the adsorbent. The adsorbent / desorbent used in the present invention may be known to those skilled in the art, and may be obtained or prepared by methods known to those skilled in the art. The "adsorption-desorption", "adsorption" and "desorption" mentioned in the present invention may be implemented in a manner known to those skilled in the art, without particular limitation on temperature, duration, pressure, pH value, dosage and separation method.

[0047] In one embodiment of the present invention, the adsorbent of the present invention has a selective adsorption capacity for lithium ions, and the adsorbent can be selected from, for example, a manganese-based adsorbent, an aluminum-based adsorbent, and a combination thereof, preferably a manganese-based adsorbent.

[0048] In one embodiment of the present invention, an adsorbent is used to load lithium ions in lithium-containing brine to the adsorbent, and then the adsorbent loaded with lithium ions is separated. The adsorbed lithium-containing brine can be returned to the adsorption step for recycling, or discharged as waste liquid, or subjected to other treatments known to those skilled in the art. The separated adsorbent loaded with lithium ions is desorbed by a desorbent to obtain a desorbed liquid (i.e., a lithium-containing salt solution).

[0049] In one embodiment of the present invention, the lithium-containing brine is adsorbed in a constant temperature oscillator, and the adsorbed lithium-containing brine is separated from the adsorbent loaded with lithium ions by a vacuum pump. Then, the lithium ions loaded in the adsorbent are eluted by a desorbent to obtain a desorption solution (i.e., a lithium-containing solution).

[0050] In another embodiment of the present invention, adsorption-desorption is performed in a resin tower. Specifically, the lithium salt-containing brine is passed through a resin tower with an adsorbent, and the lithium ions in the lithium salt-containing brine are loaded onto the adsorbent. Then, the desorbent is passed through the resin tower to elute the lithium ions loaded in the adsorbent to obtain a desorbent solution (i.e., a lithium salt solution).

[0051] In one embodiment of the present invention, the desorbent of the present invention may be selected from inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid and combinations thereof, preferably selected from hydrochloric acid.

[0052] In one embodiment of the present invention, the pH value of the desorbent of the present invention is 0.1-5.

[0053] In a preferred embodiment of the present invention, the method of the present invention is carried out continuously, and in the start-up phase of the implementation of the method of the present invention, a raw acid solution is introduced from the outside as a desorbent to start the desorption in step i). During the continuous implementation of the bipolar membrane electrodialysis in step iii), the obtained product acid solution is used as a desorbent for the desorption in step i), instead of introducing the raw acid solution from the outside, so that no other raw materials or reagents other than the lithium salt-containing brine need to be introduced from the outside during the continuous implementation of the method of the present invention.

[0054] In one embodiment of the present invention, the raw acid of the present invention can be selected from inorganic acids, such as sulfuric acid, hydrochloric acid and phosphoric acid and combinations thereof, preferably selected from hydrochloric acid. In one embodiment of the present invention, the pH value of the raw acid of the present invention is 0.1-5.

[0055] In one embodiment of the present invention, two-stage / multi-stage adsorption-desorption can be performed. That is, the product obtained by desorption (solution containing lithium ions) is subjected to adsorption-desorption again / multiple times. The adsorbent / desorbent and implementation conditions used in the two-stage / multi-stage adsorption-desorption can be the same or different. After the lithium-containing brine is subjected to two-stage / multi-stage adsorption-desorption, a lithium-containing salt solution is obtained.

[0056] In one embodiment of the present invention, the lithium salt solution obtained by adsorption-desorption is + The concentration may be 100-30,000 mg / L, preferably 400-30,000 mg / L.

[0057] In one embodiment of the present invention, after the lithium salt-containing brine is subjected to adsorption-desorption, it is optionally concentrated to obtain a lithium salt solution.

[0058] The term "concentration" in the present invention refers to increasing the lithium ion concentration in the solution. The concentration mentioned in the present invention can be one or more concentration methods known to those skilled in the art, such as nanofiltration, reverse osmosis, electrodialysis and mechanical vapor recompression; preferably nanofiltration and / or reverse osmosis; more preferably reverse osmosis.

[0059] In one embodiment of the present invention, the lithium salt-containing brine is subjected to adsorption-desorption and then nanofiltration to obtain a lithium salt solution and nanofiltration concentrated water. Optionally, the nanofiltration concentrated water obtained by nanofiltration is used for adsorption-desorption to achieve waste liquid recycling.

[0060] Among them, the nanofiltration mentioned in the present invention can be implemented in a manner known to those skilled in the art, and there are no special restrictions on temperature, duration, pressure and flow rate. The nanofiltration membrane used in the present invention can be known to those skilled in the art, and its filtration pore size can be a size suitable for the method of the present invention known to those skilled in the art, and it can be obtained or prepared in a manner known to those skilled in the art. The nanofiltration concentrated water mentioned in the present invention refers to a solution with a low lithium ion concentration that does not pass through the nanofiltration membrane. Correspondingly, a solution with a high lithium ion concentration that passes through the nanofiltration membrane is called nanofiltration produced water (that is, a lithium salt solution that has been nanofiltered). After nanofiltration, the divalent impurity ions in the lithium salt solution are removed.

[0061] In one embodiment of the present invention, specifically, the nanofiltration membrane used in the present invention can be selected from, for example, DL4040F50 of Suez, NF90-4040 of Dow, MPS-34-2540-A2X of Coriolis, and combinations thereof, preferably MPS-34-2540-A2X of Coriolis.

[0062] In one embodiment of the present invention, the lithium salt-containing brine is subjected to adsorption-desorption and then reverse osmosis to obtain a lithium salt solution and reverse osmosis product water. Optionally, the reverse osmosis product water obtained by reverse osmosis is used in other process steps of the method of the present invention, preferably in the bipolar membrane electrodialysis in step iii) to achieve waste liquid recycling.

[0063] The reverse osmosis mentioned in the present invention can be implemented in a manner known to those skilled in the art, and there are no particular restrictions on temperature, duration, pressure, flow rate, etc. The reverse osmosis membrane used in the present invention can be known to those skilled in the art, and can be obtained or prepared in a manner known to those skilled in the art. The reverse osmosis water mentioned in the present invention refers to a solution with a low lithium ion concentration that passes through the reverse osmosis membrane, and accordingly, a solution with a high lithium ion concentration that does not pass through the reverse osmosis membrane is called reverse osmosis concentrated water (i.e., a lithium salt solution that has passed through the reverse osmosis step).

[0064] In one embodiment of the present invention, specifically, the reverse osmosis membrane used in the present invention can be selected from, for example, Bw30-400 / 34i of Dupont, PROC10 of Hyde Energy (HY), LGBW400HG of LG, and combinations thereof, preferably LGBW400HG of LG.

[0065] In one embodiment of the present invention, the Li salt solution containing lithium by reverse osmosis + The concentration may be 100-60000 mg / L, preferably 400-60000 mg / L, more preferably 400-50000 mg / L.

[0066] In the present invention, the inventors unexpectedly found that the use of reverse osmosis in the method of the present invention can comprehensively achieve the following purposes: (1) further concentrate the lithium-containing brine, thereby facilitating the improvement of the efficiency of preparing lithium hydroxide; (2) the reverse osmosis product water can be recycled without being discharged, thereby realizing the recycling of waste liquid; (3) as one of the characteristics of the reverse osmosis process, the content of various impurity ions in the reverse osmosis product water is quite low, which makes it possible to hardly introduce additional impurity ions in the process of recycling the reverse osmosis product water, thereby reducing the accumulation of impurities caused by recycling; (4) when the reverse osmosis product water is used for the bipolar membrane electrodialysis in step iii), the reverse osmosis product water can be conducive to the bipolar membrane electrodialysis reaction.

[0067] In a preferred embodiment of the present invention, the lithium salt-containing brine is subjected to adsorption-desorption, followed by nanofiltration and then reverse osmosis to obtain a lithium salt solution, nanofiltration concentrate and reverse osmosis product water; optionally, the nanofiltration concentrate obtained by nanofiltration is used for adsorption-desorption, and the reverse osmosis product water obtained by reverse osmosis is used for bipolar membrane electrodialysis in step iii).

[0068] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0069] The replacement electrodialysis mentioned in the present invention can be implemented in a manner known to those skilled in the art, without any particular limitation on temperature, duration, pressure, flow rate, etc.

[0070] In one embodiment of the present invention, the displacement electrodialysis mentioned in the present invention adopts a plurality of anion exchange membranes and cation exchange membranes to be alternately arranged between the cathode and the anode to form an ion exchange membrane array. The anion / cation exchange membrane used for the displacement electrodialysis of the present invention can be known to those skilled in the art, and it can be obtained or prepared in a manner known to those skilled in the art. The anion exchange membrane used for displacement electrodialysis can be selected from, for example, AMX of Astom, FAS of Fumatech, AMVN of Asahi Glass Co., Ltd. (AGC) of Japan, and combinations thereof, preferably selected from AMVN of Asahi Glass Co., Ltd. (AGC) of Japan; the cation exchange membrane used for displacement electrodialysis can be selected from, for example, CMX of Astom, FKS of Fumatech, CMVN of Asahi Glass Co., Ltd. (AGC) of Japan, and combinations thereof, preferably selected from CMVN of Asahi Glass Co., Ltd. (AGC) of Japan.

[0071] The compartment form of the displacement electrodialysis of the present invention may be a common channel (compartment) form known to those skilled in the art, such as four channels, etc. In one embodiment of the present invention, the displacement electrodialysis of the present invention is in a four-channel form.

[0072] In one embodiment of the present invention, the displacement electrodialysis mentioned in the present invention is implemented in the manner disclosed in CN 116808832A, and the contents of this patent application are fully incorporated herein by reference.

[0073] In the method of the present invention, the following reaction occurs during the displacement electrodialysis process to obtain lithium hydroxide and a product salt:

[0074] LiX+MOH→MX+LiOH

[0075] in,

[0076] LiX: refers to lithium salt, wherein Li refers to lithium ion, and X refers to anion, such as sulfate, chloride, dihydrogen phosphate, etc.;

[0077] MOH: refers to a base, wherein M refers to a cation, such as sodium ion, potassium ion, ammonium ion, etc., and OH refers to a hydroxide ion;

[0078] MX: refers to the product salt, wherein M and X are as described above;

[0079] LiOH: refers to lithium hydroxide.

[0080] The lithium hydroxide solution obtained according to the method of the present invention has a Li + The concentration may be 23000-37000 mg / L, preferably 26000-37000 mg / L.

[0081] In a preferred embodiment of the present invention, the method of the present invention is carried out continuously, and in the start-up phase of the implementation of the method of the present invention, a raw alkali solution is introduced from the outside to start the displacement electrodialysis in step ii). During the continuous implementation of the bipolar membrane electrodialysis in step iii), the product alkali solution obtained by the bipolar membrane electrodialysis is used for the displacement electrodialysis in step ii), instead of introducing the raw alkali solution from the outside, so that no other raw materials other than the lithium salt-containing brine need to be introduced from the outside during the implementation of the method of the present invention. The types of the raw alkali and the product alkali can be the same or different, preferably the same.

[0082] The raw alkali mentioned in the present invention may include an alkali suitable for displacement electrodialysis known to those skilled in the art, and its solution concentration may be a concentration suitable for displacement electrodialysis. In one embodiment of the present invention, the raw alkali of the present invention may include one or more alkalis selected from the following substances: sodium hydroxide, potassium hydroxide, ammonia water, preferably sodium hydroxide. The concentration of the raw alkali solution of the present invention is 0.75~2.3 mol / L, preferably 1.2~2 mol / L.

[0083] In one embodiment of the present invention, the current density J1 of the displacement electrodialysis is 300-380 A / m 2 , preferably 350-380A / m 2 ; Voltage U1 is 10-20V, preferably 12-17V.

[0084] The product salt mentioned in the method of the present invention is related to the type of base used in the displacement electrodialysis.

[0085] In one embodiment of the present invention, the product salt of the present invention may include one or more salts selected from the following substances: sodium chloride, sodium sulfate, potassium chloride, potassium sulfate and combinations thereof; preferably sodium chloride, sodium sulfate and combinations thereof; more preferably sodium chloride. The concentration of the product salt solution of the present invention is 30,000 to 160,000 mg / L, more preferably 60,000 to 120,000 mg / L.

[0086] In a preferred embodiment of the present invention, the product salt solution of the present invention is used for bipolar membrane electrodialysis in step iii) to achieve waste liquid recycling. Optionally, the product salt solution of the present invention can be adjusted to a concentration value by a method known to those skilled in the art to meet the requirements of the bipolar membrane electrodialysis process in step iii).

[0087] The lithium salt dilute solution mentioned in the present invention is a solution obtained by converting the lithium salt solution after the replacement electrodialysis treatment, wherein Li + The concentration is lower than that of the lithium salt solution. In one embodiment of the present invention, the method of the present invention may further include recovering and concentrating the lithium salt dilute solution to obtain a lithium salt recovery solution, and using the lithium salt recovery solution for the displacement electrodialysis in step ii).

[0088] The recovery and concentration treatment of the lithium salt dilute solution may include concentration methods known to those skilled in the art, such as nanofiltration, reverse osmosis, recovery electrodialysis and mechanical vapor recompression, preferably recovery electrodialysis.

[0089] In a preferred embodiment of the present invention, the method of the present invention further comprises subjecting the lithium salt dilute solution to recovery electrodialysis treatment to obtain a lithium salt recovery solution, and using the lithium salt recovery solution for the replacement electrodialysis in step ii). + The concentration is higher than that of lithium salt dilute solution, and the Li + The concentration may be 3000-10000 mg / L, preferably 4000-10000 mg / L.

[0090] The recovery electrodialysis mentioned in the present invention can be implemented in a manner known to those skilled in the art, without any particular limitation on temperature, duration, pressure, flow rate, etc.

[0091] In one embodiment of the present invention, the ion exchange membrane used for recovering electrodialysis can be one or more ion exchange membranes known to those skilled in the art, and it can be obtained or prepared in a manner known to those skilled in the art. The anion exchange membrane used for recovering electrodialysis can be selected from, for example, AMX of Astom, FAS of Fumatech, AMVN of Asahi Glass Co., Ltd. (AGC) and combinations thereof, preferably AMVN of Asahi Glass Co., Ltd. (AGC); the cation exchange membrane used for recovering electrodialysis can be selected from, for example, CMX of Astom, FKS of Fumatech, AMVN of Asahi Glass Co., Ltd. (AGC) and combinations thereof, preferably CMVN of Asahi Glass Co., Ltd. (AGC) and combinations thereof, preferably CMVN of Asahi Glass Co., Ltd. (AGC) of Asahi Glass Co., Ltd. (AGC).

[0092] In a preferred embodiment of the present invention, the anion exchange membrane used in the recovery electrodialysis is the same as that used in the displacement electrodialysis, and / or the cation exchange membrane used in the recovery electrodialysis is the same as that used in the displacement electrodialysis.

[0093] In one embodiment of the present invention, the lithium salt recovery solution is directly used for displacement electrodialysis; or, the lithium salt recovery solution is mixed with a lithium salt-containing solution and then used for displacement electrodialysis.

[0094] In one embodiment of the present invention, the current density J3 of the recovery electrodialysis is 260-350A / m 2 , preferably 280-320A / m 2 ; Voltage U3 is 10-20V, preferably 12-17V.

[0095] In one embodiment of the present invention, the solution in the device for performing recovery electrodialysis (as system waste liquid) is partially or completely discharged periodically or when certain conditions are met to reduce or eliminate impurities accumulated in the system.

[0096] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product alkaline solution, and then using the product acid solution for adsorption-desorption in step i), and using the product alkaline solution for displacement electrodialysis in step ii).

[0097] The bipolar membrane electrodialysis mentioned in the present invention can be implemented in a manner known to those skilled in the art, without any particular limitation on temperature, duration, pressure, flow rate, etc.

[0098] The bipolar membrane used in the present invention may be known to those skilled in the art, and may be obtained or prepared by methods known to those skilled in the art. In one embodiment of the present invention, the bipolar membrane used in the present invention may be selected from, for example, FMB of Fumatech, NeoseptaBP-1E of Astom, AR130BP of Suez, and combinations thereof, preferably NeoseptaBP-1E of Astom.

[0099] In one embodiment of the present invention, the bipolar membrane electrodialysis in step iii) is implemented by combining positive / negative electrodes, bipolar membranes, anion exchange membranes and cation exchange membranes. Wherein, the positive / negative electrodes and anion / cation exchange membranes used for bipolar membrane electrodialysis can be known to those skilled in the art, and can be obtained or prepared by methods known to those skilled in the art. In a preferred embodiment of the present invention, the anion exchange membrane used for bipolar membrane electrodialysis can be selected from, for example, AMX of Astom, FAS of Fumatech, AMVN of Asahi Glass Co., Ltd. (AGC) of Japan, and combinations thereof, preferably selected from AMVN of Asahi Glass Co., Ltd. (AGC) of Japan; the cation exchange membrane used for bipolar membrane electrodialysis can be selected from, for example, CMX of Astom, FKS of Fumatech, CMVN of Asahi Glass Co., Ltd. (AGC) of Japan, and combinations thereof, preferably selected from CMVN of Asahi Glass Co., Ltd. (AGC) of Japan.

[0100] In a preferred embodiment of the present invention, the anion exchange membrane used in the bipolar membrane electrodialysis and the displacement electrodialysis is the same, and / or the cation exchange membrane used in the bipolar membrane electrodialysis and the displacement electrodialysis is the same.

[0101] In a preferred embodiment of the present invention, the anion exchange membrane used in the bipolar membrane electrodialysis is the same as that used in the recovery electrodialysis, and / or the cation exchange membrane used in the bipolar membrane electrodialysis is the same as that used in the recovery electrodialysis.

[0102] In a preferred embodiment of the present invention, the anion exchange membrane used in bipolar membrane electrodialysis, displacement electrodialysis and recovery electrodialysis is the same, and / or the cation exchange membrane used in bipolar membrane electrodialysis, displacement electrodialysis and recovery electrodialysis is the same.

[0103] The compartment form of the bipolar membrane electrodialysis of the present invention can be a common compartment form known to those skilled in the art, such as two compartments, three compartments, four compartments, five compartments, etc. In a preferred embodiment of the present invention, the bipolar membrane electrodialysis of the present invention is a three-compartment form.

[0104] In the method of the present invention, Figure 3 As an example, the following reaction occurs during the bipolar membrane electrodialysis process to obtain the product acid and the product base:

[0105] MX+H2O→HX+MOH

[0106] in,

[0107] MX: refers to salt, wherein M and X are as described above;

[0108] H2O: refers to water;

[0109] HX: refers to the product acid, wherein H refers to hydrogen ion, and the description of X is as above;

[0110] MOH: refers to the product base, wherein the description of M and OH is as mentioned above.

[0111] In a preferred embodiment of the present invention, the method of the present invention is carried out continuously, and in the start-up phase of the implementation of the method of the present invention, a raw salt solution is introduced from the outside to start the bipolar membrane electrodialysis in step iii). During the continuous implementation of the displacement electrodialysis in step ii), the product salt solution obtained by the displacement electrodialysis is used for the bipolar membrane electrodialysis in step iii), instead of introducing the raw salt solution from the outside, so that no other raw materials other than the lithium salt-containing brine need to be introduced from the outside during the implementation of the method of the present invention. The types of the raw salt and the product salt can be the same or different, preferably the same.

[0112] In a preferred embodiment of the present invention, the method of the present invention is carried out continuously, and in the startup phase of the implementation of the method of the present invention, step iii) is first started, a raw salt solution is introduced from the outside to start the bipolar membrane electrodialysis in step iii), and the product acid solution obtained by the bipolar membrane electrodialysis is used as a desorbent to start the desorption in step i), and the product alkaline solution obtained by the bipolar membrane electrodialysis is used to start the displacement electrodialysis in step ii); as the displacement electrodialysis in step ii) is continuously implemented, the product salt solution obtained by the displacement electrodialysis is used for the bipolar membrane electrodialysis in step iii), to replace the introduction of the raw salt solution from the outside. Thus, it can be achieved that in the startup phase of the method of the present invention, other raw materials or reagents (such as raw acid solution and raw alkaline solution) other than the raw salt solution and the lithium-containing brine do not need to be introduced from the outside; at the same time, it is achieved that during the continuous implementation of the method of the present invention, other raw materials or reagents other than the lithium-containing brine do not need to be introduced from the outside.

[0113] The raw salt mentioned in the present invention may include salts suitable for bipolar membrane electrodialysis known to those skilled in the art, and the solution concentration may be a concentration suitable for bipolar membrane electrodialysis. In one embodiment of the present invention, the raw salt of the present invention may include one or more salts selected from the following substances: sodium sulfate, sodium chloride, sodium phosphate and sodium dihydrogen phosphate, preferably sodium chloride. The concentration of the raw salt solution of the present invention is 20000~200000 mg / L, preferably 50000~150000 mg / L, more preferably 50000~120000 mg / L.

[0114] In one embodiment of the present invention, the current density J2 of the bipolar membrane electrodialysis is 400-600A / m 2 , preferably 500-600A / m 2; Voltage U2 is 20-30V, preferably 22-37V.

[0115] In one embodiment of the present invention, the ratio of current density of displacement electrodialysis to bipolar membrane electrodialysis is J1: J2=0.5:1~0.95:1; preferably 0.58:1~0.64:1.

[0116] In one embodiment of the present invention, the ratio of current density of replacement electrodialysis to recovery electrodialysis is J1:J3=0.85:1~1.46:1; preferably 1.09:1~1.36:1.

[0117] In one embodiment of the present invention, the ratio of the current density of the bipolar membrane electrodialysis to the recovery electrodialysis is J2: J3 = 1.14:1 to 2.31:1; preferably 1.93:1 to 2.14:1.

[0118] The product acid and product base mentioned in the method of the present invention are related to the types of salts used in bipolar membrane electrodialysis.

[0119] In one embodiment of the present invention, the product acid of the present invention may include one or more acids selected from the following substances: hydrochloric acid, sulfuric acid and phosphoric acid; preferably hydrochloric acid. The concentration of the product acid solution of the present invention is 0.35~2 mol / L, preferably 0.75~2 mol / L, more preferably 0.9~1.85 mol / L. The pH value of the product acid solution of the present invention is 0.26~4. The product acid solution of the present invention may optionally contain impurity ions, and in the case of containing impurity ions, the amount of the impurity ions does not exceed 20 mg / L each.

[0120] In one embodiment of the present invention, the product alkali of the present invention may include one or more alkalis selected from the following substances: sodium hydroxide, potassium hydroxide, ammonia water, preferably sodium hydroxide. The concentration of the product alkali solution of the present invention is 0.75-2.3 mol / L, preferably 1.2~2 mol / L. The pH value of the product alkali solution of the present invention is 9~14. The product alkali solution of the present invention may optionally contain impurity ions, and in the case of containing impurity ions, the amount of the impurity ions does not exceed 20 mg / L respectively.

[0121] In one embodiment of the present invention, the product acid solution and product alkaline solution obtained by bipolar membrane electrodialysis of the present invention can be used in other processes in the method of the present invention. Optionally, the product acid solution and product alkaline solution of the present invention can be adjusted to their concentration values ​​to meet the requirements of other processes in a manner known to those skilled in the art.

[0122] In one embodiment of the present invention, the method of the present invention further comprises removing impurities from the lithium salt-containing brine before carrying out the adsorption-desorption in step i).

[0123] The term "impurity removal" of the present invention refers to the removal of other impurity ions other than lithium ions from lithium-containing brine, and the other impurity ions may be selected from, for example, insoluble solids and suspended matter. The impurity removal mentioned in the present invention may include one or more methods of removing impurity ions known to those skilled in the art, and may be implemented in a manner known to those skilled in the art.

[0124] In a preferred embodiment of the present invention, the impurity removal method of the present invention comprises passing the lithium salt-containing brine through one or more of a security filter, a microporous filter and a resin tower, preferably a microporous filter. The filtration pore size of the microporous filter used in the present invention can be, for example, 1 to 10 μm, preferably 5 μm.

[0125] In one embodiment of the present invention, the method of the present invention further comprises subjecting the lithium hydroxide solution obtained by displacement electrodialysis to one or more post-treatments of evaporation concentration, crystallization, separation, washing and drying.

[0126] In a preferred embodiment of the present invention, Figure 4 By way of example, the method of the present invention comprises the following steps:

[0127] i) subjecting the lithium salt-containing brine to adsorption-desorption and subsequent optional concentration to obtain a lithium salt-containing solution;

[0128] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution,

[0129] The lithium salt dilute solution is subjected to recovery electrodialysis to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used for the replacement electrodialysis in step ii);

[0130] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0131] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0132] In a preferred embodiment of the present invention, Figure 5 By way of example, the method of the present invention comprises the following steps:

[0133] i) subjecting the lithium salt-containing brine to adsorption-desorption and subsequent reverse osmosis to obtain a lithium salt solution and reverse osmosis product water, and using the reverse osmosis product water for the bipolar membrane electrodialysis in step iii);

[0134] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0135] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0136] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0137] In a preferred embodiment of the present invention, Figure 6 By way of example, the method of the present invention comprises the following steps:

[0138] i) subjecting the lithium salt-containing brine to adsorption-desorption and subsequent reverse osmosis to obtain a lithium salt solution and reverse osmosis product water,

[0139] Using the reverse osmosis product water for the bipolar membrane electrodialysis in step iii);

[0140] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution,

[0141] The lithium salt dilute solution is subjected to recovery electrodialysis to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used for the replacement electrodialysis in step ii);

[0142] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0143] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0144] In a preferred embodiment of the present invention, Figure 7 By way of example, the method of the present invention comprises the following steps:

[0145] i) adsorbing and desorbing the lithium salt brine and then performing nanofiltration, and then performing reverse osmosis to obtain a lithium salt solution, nanofiltration concentrated water and reverse osmosis product water,

[0146] Optionally, the nanofiltration concentrate is used for adsorption-desorption,

[0147] Using the reverse osmosis product water for the bipolar membrane electrodialysis in step iii);

[0148] ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution,

[0149] The lithium salt dilute solution is subjected to recovery electrodialysis to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used for the replacement electrodialysis in step ii);

[0150] iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution,

[0151] The product acid solution is used for adsorption-desorption in step i), and the product base solution is used for displacement electrodialysis in step ii).

[0152] The present invention also provides a lithium hydroxide solution obtained by the method of the present invention, wherein the purity of the lithium hydroxide solution is above 99.9%.

[0153] The present invention also provides a device for preparing lithium hydroxide, comprising:

[0154] an adsorption-desorption unit for adsorbing and desorbing the lithium-containing brine and subsequently optionally concentrating it to obtain a lithium-containing salt solution;

[0155] A displacement electrodialysis unit is used to perform displacement electrodialysis on a lithium salt solution to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution;

[0156] The bipolar membrane electrodialysis unit is used to perform bipolar membrane electrodialysis on the product salt solution to obtain a product acid solution and a product alkaline solution, and then the product acid solution is used for adsorption-desorption in step i), and the product alkaline solution is used for displacement electrodialysis in step ii).

[0157] In one embodiment of the present invention, the device of the present invention also includes a recovery electrodialysis unit for recovering the lithium salt dilute solution obtained by replacing the electrodialysis unit by electrodialysis to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used to replace the electrodialysis unit.

[0158] In one embodiment of the present invention, the device of the present invention further comprises an impurity removal unit for removing impurities from the lithium salt-containing brine.

[0159] In one embodiment of the present invention, the apparatus of the present invention may further optionally include a concentration unit for concentrating the lithium salt-containing brine after adsorption-desorption, thereby obtaining a lithium salt-containing solution.

[0160] In a preferred embodiment of the present invention, the device of the present invention optionally further comprises a nanofiltration unit for nanofiltration after adsorption-desorption of the lithium salt-containing brine, thereby obtaining a lithium salt solution and nanofiltration concentrated water. Optionally, the nanofiltration concentrated water obtained by nanofiltration is used in the adsorption-desorption unit to achieve waste liquid recycling.

[0161] In a preferred embodiment of the present invention, the device of the present invention further optionally includes a reverse osmosis unit for performing reverse osmosis after adsorption-desorption of the lithium salt-containing brine to obtain a lithium salt solution and reverse osmosis product water. Optionally, the reverse osmosis product water obtained by reverse osmosis is used in a unit in the device of the present invention, preferably in a bipolar membrane electrodialysis unit, to achieve waste liquid recycling.

[0162] In a preferred embodiment of the present invention, the device of the present invention further comprises a post-treatment unit for subjecting the lithium hydroxide solution obtained in the displacement electrodialysis unit to one or more post-treatments of evaporation concentration, crystallization, separation, washing and drying. Example

[0163] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0164] The equipment used in the embodiment is as follows:

[0165] Precision filter: 10-inch precision filter, purchased from Wuhan Huamo Water Treatment Technology Co., Ltd.;

[0166] Adsorbent: Manganese adsorbent type III, purchased from Sichuan Fanyu Lithium Energy New Material Technology Co., Ltd.;

[0167] Nanofiltration equipment: PolyCera testing machine - PolyCera - PolyCera PS-1801, purchased from PolyCera (Shanghai) Technology Co., Ltd.;

[0168] Reverse osmosis equipment: RO-0, manufactured by Hangzhou Jiangrongdao Environmental Technology Co., Ltd.

[0169] Displacement electrodialysis equipment: EDM-0, manufactured by Hangzhou Jiangrongdao Environmental Technology Co., Ltd., of which the anion exchange membrane is AMVN from Asahi Glass Co., Ltd. (AGC) of Japan, and the cation exchange membrane is CMVN from Asahi Glass Co., Ltd. (AGC) of Japan;

[0170] Recycling electrodialysis equipment: CH-0, manufactured by Hangzhou Jiangrongdao Environmental Technology Co., Ltd., of which the anion exchange membrane is AMVN from Asahi Glass Co., Ltd. (AGC) of Japan, and the cation exchange membrane is CMVN from Asahi Glass Co., Ltd. (AGC) of Japan;

[0171] Bipolar membrane electrodialysis equipment: BPEM-0, manufactured by Hangzhou Jiangrongdao Environmental Technology Co., Ltd., of which the bipolar membrane is AR130BP from Suez, the anion exchange membrane is AMVN from Asahi Glass Co., Ltd. (AGC), and the cation exchange membrane is CMVN from Asahi Glass Co., Ltd. (AGC);

[0172] Other equipment: SHZ-D (III) circulating water multi-purpose vacuum pump, purchased from Shanghai Lichen Instrument Technology Co., Ltd.

[0173] The ion content in each solution was determined according to HJ 84-2016 standard "Inorganic Anions (F - , CI - 、NO2 - Br - 、NO3 - PO4 3- 、SO3 2- 、SO4 2- ) by Ion Chromatography.

[0174] Example 1

[0175] (1) Impurity removal: The lithium-containing brine is transported to a precision filter through a magnetic pump for filtration to remove insoluble solids and suspended matter.

[0176] (2) Adsorption: Add manganese adsorbent to the impurity-free lithium-containing brine (tested, its ion content is: lithium 300 mg / L, calcium 290 mg / L, magnesium 5000 mg / L, potassium 300 mg / L, boron 180 mg / L) for adsorption. Then use a vacuum pump to extract the liquid for solid-liquid separation to obtain an adsorbent loaded with lithium ions.

[0177] (3) Bipolar membrane electrodialysis: During the startup phase, sodium chloride solution is introduced from the outside into the bipolar membrane electrodialysis equipment BPEM-0, and its current density J2 is 600A / m 2 , the voltage U2 is 24.8V. After bipolar membrane electrodialysis, hydrochloric acid solution (the concentration is 1.75 mol / L after testing) and sodium hydroxide solution (the concentration is 1.75 mol / L after testing) are obtained. The hydrochloric acid solution and sodium hydroxide solution obtained in this step are used in the subsequent desorption step and displacement electrodialysis step respectively. During the continuous operation of this step, when the sodium chloride solution generated by the subsequent displacement electrodialysis meets the dosage requirements of this step, the sodium chloride solution generated by the displacement electrodialysis is used instead of the sodium chloride solution introduced from the outside.

[0178] (4) Desorption: The adsorbent loaded with lithium ions is desorbed using the hydrochloric acid solution obtained in the bipolar membrane electrodialysis step to obtain a desorption solution (the ion content of which is: lithium 488 mg / L, calcium 110 mg / L, magnesium 80 mg / L, potassium 80 mg / L, boron 60 mg / L).

[0179] (5) Nanofiltration: The desorption liquid is passed into the nanofiltration equipment PolyCera testing machine - PolyCera PS-1801. Nanofiltration is performed to obtain nanofiltration product water (after testing, its ion content is: lithium 600 mg / L, calcium 21 mg / L, magnesium 19 mg / L, potassium 42 mg / L, boron 36 mg / L) and nanofiltration concentrated water.

[0180] (6) Reverse Osmosis: The nanofiltration product water is passed through the reverse osmosis equipment RO-0 to obtain reverse osmosis concentrated water (i.e., lithium salt solution; after testing, its ion content is: lithium 12000 mg / L, calcium 32 mg / L, magnesium 40 mg / L, potassium 87 mg / L, boron 69 mg / L) and reverse osmosis product water, and the reverse osmosis product water is returned to the bipolar membrane electrodialysis step for reuse.

[0181] (7) Replacement electrodialysis: The lithium salt solution and the sodium hydroxide solution obtained in the bipolar membrane electrodialysis step are passed into the replacement electrodialysis device EDM-0, and the current density J1 is 380A / m 2 , the voltage U1 is 15.4V. After displacement electrodialysis, lithium hydroxide solution (tested, its ion content is 27000 mg / L lithium), sodium chloride solution (tested, its ion content is 120000 mg / L sodium chloride) and lithium salt solution (tested, its ion content is 4000 mg / L lithium) are obtained. The sodium chloride solution obtained by displacement electrodialysis is returned to the bipolar membrane electrodialysis step for reuse.

[0182] (8) Recovery electrodialysis: The lithium salt dilute solution is passed into the recovery electrodialysis equipment CH-0 for concentration, and its current density J3 is 300A / m 2 , the voltage U3 is 11.4 V. After the recovery electrodialysis, a lithium salt recovery solution (whose ion content is 120,000 mg / L lithium) is obtained, and the lithium salt recovery solution is returned to the replacement electrodialysis step for reuse.

[0183] Example 2

[0184] Embodiment 2 is substantially the same as Embodiment 1, except that:

[0185] The current density of the displacement electrodialysis is J1, which is 320A / m 2 ;

[0186] The current density J2 of bipolar membrane electrodialysis is 561A / m 2 ;

[0187] The current density J3 of the recovery electrodialysis is 320A / m 2 .

[0188] Example 3

[0189] Embodiment 3 is substantially the same as Embodiment 1, except that:

[0190] The current density J1 of displacement electrodialysis is 320A / m 2 ;

[0191] The current density J2 of bipolar membrane electrodialysis is 561A / m 2 ;

[0192] The current density J3 of the recovery electrodialysis is 330A / m 2 .

[0193] Example 4

[0194] Embodiment 4 is substantially the same as Embodiment 1, except that:

[0195] The current density of displacement electrodialysis is J1, which is 340A / m 2 ;

[0196] The current density J2 of bipolar membrane electrodialysis is 472A / m 2 ;

[0197] The current density J3 of the recovery electrodialysis is 246A / m 2 .

[0198] Example 5

[0199] Embodiment 5 is substantially the same as Embodiment 1, except that:

[0200] The current density of displacement electrodialysis is J1, which is 360A / m 2 ;

[0201] The current density J2 of bipolar membrane electrodialysis is 428A / m 2 ;

[0202] The current density J3 of the recovery electrodialysis is 253A / m 2 .

[0203] The above embodiments may spend different time in the startup phase, but they all run continuously for the same time after the startup phase (i.e., the duration of the continuous operation period is the same). SI )same.

[0204] During the continuous operation of the embodiment, the purity of the obtained lithium hydroxide solution is periodically tested in accordance with GB / T 11064 and GB / T 8766-2013.

[0205] The arithmetic mean of the historical lithium hydroxide product purities detected by the end of the continuous operation period of the embodiment is calculated as the average purity of the lithium hydroxide of this embodiment.

[0206] During the continuous operation of the embodiment, whenever the purity of the detected lithium hydroxide solution is lower than 99%, the solution in the recovered electrodialysis device is completely discharged (as system waste liquid) and the discharge amount is recorded. After the continuous operation period ends, the discharge amount of the system waste liquid during the continuous operation period of the embodiment is summed up to calculate the total system waste liquid amount W of the embodiment. SO .

[0207] The total amount of waste liquid discharged from the system according to the method of the present invention is W SO and the total liquid inflow of the system W SI , calculate the system waste liquid rate as follows:

[0208]

[0209] W SO : Total waste liquid volume of the system;

[0210] W SI : Total liquid intake into the system.

[0211] The system waste liquid rate corresponding to each embodiment is evaluated as follows:

[0212] Excellent: η≤1.5%.

[0213] Good: 1.5%<η≤3.00%;

[0214] Generally: η>3.00%.

[0215] The purity of the lithium hydroxide product obtained in each example is summarized in the following Table 1.

[0216] Table 1:

[0217]

Claims

1. A method for preparing lithium hydroxide, comprising the steps of: i) adsorbing and desorbing the lithium salt-containing brine to obtain a lithium salt solution; ii) subjecting the lithium salt solution obtained in step i) to displacement electrodialysis to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution, The lithium salt dilute solution is subjected to recovery electrodialysis to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used for the replacement electrodialysis in step ii); iii) subjecting the product salt solution obtained in step ii) to bipolar membrane electrodialysis to obtain a product acid solution and a product base solution, The product acid solution is used for adsorption-desorption in step i), and the product alkaline solution is used for displacement electrodialysis in step ii); in, The current density J1 of displacement electrodialysis is 300-380A / m 2 ; The current density J2 of bipolar membrane electrodialysis is 500-600A / m 2 ; The current density J3 of the recovery electrodialysis is 260-350A / m 2 .

2. The method according to claim 1, wherein: The method further comprises concentrating the lithium salt-containing brine after adsorption-desorption, thereby obtaining a lithium salt-containing solution.

3. The method according to claim 1, wherein: The ratio of the current density of displacement electrodialysis to that of bipolar membrane electrodialysis is J1: J2=0.5:1~0.95:

1.

4. The method according to claim 3, wherein: The ratio of the current density of displacement electrodialysis to that of bipolar membrane electrodialysis is J1: J2=0.58:1~0.64:

1.

5. The method according to claim 1, wherein: The ratio of the current density of replacement electrodialysis to recovery electrodialysis is J1: J3=0.85:1~1.46:

1.

6. The method according to claim 5, wherein: The ratio of the current density of replacement electrodialysis to recovery electrodialysis is J1: J3=1.09:1~1.36:

1.

7. The method according to claim 1, wherein: The ratio of the current density of bipolar membrane electrodialysis to that of recovery electrodialysis is J2: J3=1.14:1~2.31:

1.

8. The method according to claim 7, wherein: The ratio of the current density of bipolar membrane electrodialysis to that of recovery electrodialysis is J2: J3=1.93:1~2.14:

1.

9. The method according to claim 1, wherein: The current density J1 of displacement electrodialysis is 350-380A / m 2 .

10. The method according to claim 1, wherein: The current density J3 of the recovery electrodialysis is 280-320A / m 2 .

11. The method according to claim 2, wherein: The concentration includes one or more of nanofiltration, reverse osmosis, electrodialysis and mechanical vapor recompression.

12. The method according to claim 11, wherein: The concentration comprises reverse osmosis.

13. The method according to claim 12, wherein: The method further comprises: Reverse osmosis product water is obtained by performing reverse osmosis, and the reverse osmosis product water is used for the bipolar membrane electrodialysis in step iii).

14. A device for preparing lithium hydroxide, the device comprising: An adsorption-desorption unit, used for adsorbing and desorbing lithium-containing brine to obtain a lithium-containing salt solution; A displacement electrodialysis unit, used for performing displacement electrodialysis on the lithium salt solution to obtain a lithium hydroxide solution, a product salt solution and a lithium salt dilute solution; A recovery electrodialysis unit is used to perform recovery electrodialysis on the lithium salt dilute solution obtained by replacing the electrodialysis unit to obtain a lithium salt recovery solution, and the lithium salt recovery solution is used to replace the electrodialysis unit; The bipolar membrane electrodialysis unit is used to perform bipolar membrane electrodialysis on the product salt solution to obtain a product acid solution and a product alkaline solution, and then use the product acid solution for adsorption-desorption and the product alkaline solution for displacement electrodialysis.

15. The device according to claim 14, characterized in that The device also includes a concentration unit for concentrating the lithium-containing brine after adsorption-desorption, thereby obtaining a lithium-containing salt solution.

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