Method and device for improving evaporation efficiency of lithium hydroxide

Abstract

The invention relates to the field of lithium hydroxide preparation, and discloses a method and a device for improving the evaporation efficiency of lithium hydroxide. According to the method, the impurity ion concentration in the primary evaporator can be effectively reduced through multiple times of evaporation crystallization, the problem that energy consumption is increased due to the fact that the boiling point is increased due to the too high impurity ion concentration is solved, and the evaporation efficiency is improved; meanwhile, the mother liquor after crystallization is separated, concentrated and evaporated, so that the discharge amount of the high-lithium mother liquor is reduced, the yield of lithium hydroxide is increased, and the resource waste is reduced; and through repeated crystallization treatment and mother liquor separation, the content of impurity ions in the lithium hydroxide product is reduced, and high-purity lithium hydroxide can be obtained. The device adopted by the method is simple in structure and convenient to control, and has high industrial application value.

Description

Technical Field

[0001] The invention relates to the field of lithium hydroxide preparation, and in particular to a method and a device for improving the evaporation efficiency of lithium hydroxide. Background Art

[0002] Lithium hydroxide is an important basic lithium salt product. For example, lithium-based grease prepared with lithium hydroxide has the advantages of long service life, oxidation resistance, and high-temperature stability. In recent years, with the advent of high-nickel ternary electrode materials of nickel-cobalt-manganese oxide, as the only lithium source for high-nickel positive electrode materials, lithium hydroxide has greater advantages in sintering temperature and product performance than battery-grade lithium carbonate, and the future market prospects are very broad.

[0003] At present, the main method for preparing lithium hydroxide is to use abundant salt lake brine as the lithium source, remove impurities from the salt lake brine, and then prepare the alkaline solution containing lithium, sodium, and potassium through bipolar membrane electrodialysis, and then concentrate it multiple times through a triple-effect evaporator and an MVR evaporator. When the sodium hydroxide is nearly saturated, the mother liquor is discharged, and the lithium hydroxide solid is recrystallized after passing through a centrifuge. However, as the concentration of sodium hydroxide increases, the boiling point of the solution also increases, resulting in lower evaporation efficiency. In addition, the increase in sodium and potassium ions in one evaporation causes a large amount of sodium and potassium ions to continue to enter the recrystallization process, affecting the quality of the final product. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of low evaporation efficiency and more impurity ions in the product when preparing lithium hydroxide from salt lake brine in the prior art, and provide a method and device for improving the evaporation efficiency of lithium hydroxide. The method adopts a single-effect evaporation process, including a concentration crystallization process and a recrystallization process. Through two crystallization and purification processes, the content of impurity ions in the lithium hydroxide product is reduced, and the quality of lithium hydroxide is improved; the content of Na ions in the mother liquor generated after the initial crystallization is detected, and when the Na ion content is low, the mother liquor is recovered and the concentration crystallization process is repeated. When the Na ion content is high, the mother liquor is evaporated and concentrated to further extract lithium hydroxide, which not only effectively improves the recovery efficiency of lithium, but also avoids the defect of the solution being difficult to evaporate due to the excessively high impurity ion content in the single crystallization process, thereby improving the evaporation efficiency of the overall lithium hydroxide solution. The device used in the method mainly includes two evaporators for concentration crystallization and recrystallization and an evaporating kettle for evaporating and concentrating the mother liquor. The structure is simple and easy to control, which is conducive to industrial production application.

[0005] In order to achieve the above object, the present invention provides a method for improving the evaporation efficiency of lithium hydroxide, which comprises the following steps:

[0006] (1) allowing the lithium hydroxide solution obtained after the bipolar membrane electrodialysis treatment to enter a first evaporator for concentration and crystallization treatment, and then centrifuging the mixture after the concentration and crystallization treatment in a first centrifuge to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0007] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to an evaporation kettle for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in a second centrifuge to obtain a second lithium hydroxide crude crystal and a second mother liquor;

[0008] (3) transporting the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals to a second evaporator for recrystallization, and then centrifuging the recrystallized mixture in a third centrifuge to obtain lithium hydroxide and a third mother liquor, and returning the third mother liquor to the first evaporator for recycling.

[0009] Preferably, in step (1), the conditions for the concentration and crystallization treatment include: a temperature of 80-90° C. and a pressure of 350-450 mbar.

[0010] Preferably, in step (2), the conditions of the evaporation concentration treatment include: a temperature of 90-130° C. and a pressure of 300-400 mbar.

[0011] Preferably, the evaporation concentration treatment makes the concentration of Na ions in the treated mixture be 240-320 g / L.

[0012] Preferably, in step (3), the conditions for the recrystallization treatment include: a temperature of 80-90° C. and a pressure of 350-450 mbar.

[0013] A second aspect of the present invention provides a device for improving the evaporation efficiency of lithium hydroxide, the device comprising:

[0014] a first evaporator and a first centrifuge, wherein the lithium hydroxide solution is concentrated and crystallized in the first evaporator, and then the mixture after the concentration and crystallization is centrifuged in the first centrifuge to obtain first lithium hydroxide coarse crystals and a first mother liquor, and then the concentration of Na ions in the first mother liquor is detected, and when the Na ion concentration is less than 50 g / L, the first mother liquor is returned to the first evaporator for recycling;

[0015] an evaporating kettle and a second centrifuge, when the Na ion concentration in the first mother liquor is greater than or equal to 50 g / L, transporting the first mother liquor to the evaporating kettle for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in the second centrifuge to obtain second lithium hydroxide coarse crystals and a second mother liquor;

[0016] The second evaporator and the third centrifuge are used to recrystallize the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals in the second evaporator, and then the recrystallized mixture is centrifuged in the third centrifuge to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator for recycling.

[0017] Preferably, the device further comprises a bipolar membrane electrodialysis device for providing the lithium hydroxide solution.

[0018] Preferably, a first discharge port is provided at the bottom of the first evaporator, and the first discharge port is connected to a first discharge pump for conveying the mixture after the concentrated crystallization treatment to a first centrifuge.

[0019] Preferably, the first mother liquor outlet of the first centrifuge is connected to the first branch and the second branch, the first branch is provided with a first valve, and the second branch is provided with a second valve, when the concentration of Na ions in the first mother liquor is less than 50 g / L, the first mother liquor returns to the first evaporator through the first valve; when the concentration of Na ions in the first mother liquor is greater than or equal to 50 g / L, the first mother liquor is transported to the evaporator through the second valve.

[0020] Preferably, a second discharge port is provided at the bottom of the second evaporator, and the second discharge port is connected to a second discharge pump for conveying the mixture after the recrystallization treatment to a third centrifuge.

[0021] Preferably, the evaporator is heated by steam and is provided with a stirrer.

[0022] According to the method for improving the evaporation efficiency of lithium hydroxide of the present invention, the content of impurity ions in the lithium hydroxide product is reduced and the quality of lithium hydroxide is improved through two crystallization purification processes; the content of Na ions in the mother liquor generated after the first crystallization is detected, and when the Na ion content is low, the mother liquor is returned and recycled, and when the Na ion content is high, the mother liquor is evaporated and concentrated to a concentration close to the Na precipitation concentration, so as to extract lithium hydroxide as much as possible, which not only effectively improves the utilization efficiency of lithium, but also avoids the defect of the single crystallization process that the solution is difficult to evaporate due to the excessively high impurity ion content, thereby improving the evaporation efficiency of the overall lithium hydroxide solution.

[0023] According to the device for improving the evaporation efficiency of lithium hydroxide described in the present invention, it mainly includes two evaporators for concentrated crystallization treatment and recrystallization treatment and an evaporating kettle for evaporating and concentrating the mother liquor. It has a simple structure and can control multiple evaporating devices separately, which is beneficial to maintaining the stability of product quality. By recycling the mother liquor after crystallization for many times, the evaporation efficiency of lithium hydroxide is improved, which is convenient for industrial production application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a device for improving the evaporation efficiency of lithium hydroxide provided by the present invention.

[0025] Description of Reference Numerals

[0026] 1-1, first evaporator; 1-2, first centrifuge; 1-3, first valve; 1-4, second valve; 2-1, evaporator; 2-2, second centrifuge; 3-1, second evaporator; 3-2, third centrifuge; 4, bipolar membrane electrodialysis device; 5-1, first discharge pump; 5-2, second discharge pump. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0028] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0029] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating relative importance or implicitly indicating the number of technical features indicated. Therefore, unless otherwise specified, features defined as "first" and "second" may explicitly or implicitly include one or more of the features; "plurality" means two or more. The term "including" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof may exist or be added.

[0030] In the description of the present application, the term "include" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof may exist or be added. Terms indicating orientation or positional relationships such as "center", "lateral", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are described based on the orientation or relative positional relationships shown in the drawings, and are only simplified descriptions for the convenience of describing the present application, rather than indicating that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present application.

[0031] In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internally connected between two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] like Figure 1 As shown, the method for improving the evaporation efficiency of lithium hydroxide according to the present invention comprises the following steps:

[0033] (1) the lithium hydroxide solution obtained after the bipolar membrane electrodialysis treatment is introduced into a first evaporator 1-1 for concentration and crystallization treatment, and then the mixture after the concentration and crystallization treatment is centrifuged in a first centrifuge 1-2 to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0034] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator 1-1 for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to an evaporation kettle 2-1 for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in a second centrifuge 2-2 to obtain second lithium hydroxide coarse crystals and a second mother liquor;

[0035] (3) The first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are transported to the second evaporator 3-1 for recrystallization, and then the mixture after recrystallization is centrifuged in the third centrifuge 3-2 to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling.

[0036] In the method of the present invention, preferably, in step (1), the conditions for the concentration and crystallization treatment include: a temperature of 80-90°C and a pressure of 350-450 mbar. More preferably, the conditions for the concentration and crystallization treatment include: a temperature of 82-88°C and a pressure of 370-430 mbar. In the present invention, the above-mentioned concentration and crystallization conditions are adopted to enable lithium hydroxide in the solution to be crystallized preferentially. Since the solubility of lithium hydroxide is about 40 g / L in this temperature range, which is lower than the solubility of sodium hydroxide and potassium hydroxide under these conditions, the amount of impurity ions mixed in is reduced.

[0037] In the method of the present invention, preferably, in step (2), the conditions of the evaporation concentration treatment include: a temperature of 90-130° C. and a pressure of 300-400 mbar. More preferably, the conditions of the evaporation concentration treatment include: a temperature of 95-125° C. and a pressure of 310-390 mbar. Most preferably, more preferably, the conditions of the evaporation concentration treatment include: a temperature of 100-120° C. and a pressure of 320-380 mbar.

[0038] In the method of the present invention, preferably, the evaporation concentration treatment makes the concentration of Na ions in the treated mixture 240-320 g / L. More preferably, the evaporation concentration treatment makes the concentration of Na ions in the treated mixture 245-310 g / L.

[0039] In the present invention, by adopting the above-mentioned evaporation and concentration conditions, the first mother liquor with a Na ion content greater than 50 g / L can be quickly concentrated at a higher temperature to a concentration close to that at which Na ions can be precipitated (240-320 g / L), and the Li in the solution is crystallized and precipitated as much as possible before the Na ions reach the precipitation concentration, thereby improving the yield of lithium hydroxide. The second mother liquor obtained after separation of the concentrated mixture can be transported to an external system for subsequent treatment such as lithium precipitation to improve the utilization rate.

[0040] In the method of the present invention, preferably, in step (3), the conditions of the recrystallization treatment include: a temperature of 80-90° C. and a pressure of 350-450 mbar. More preferably, the conditions of the recrystallization treatment include: a temperature of 82-88° C. and a pressure of 370-430 mbar. In the present invention, the above conditions are used to dissolve and recrystallize the first lithium hydroxide crude crystals obtained by the concentration and crystallization treatment and the second lithium hydroxide crude crystals obtained by the evaporation and concentration treatment to improve the purity and quality of the lithium hydroxide product and further reduce the content of impurity ions such as Na and K.

[0041] According to the method for improving the evaporation efficiency of lithium hydroxide of the present invention, the content of impurity ions in the lithium hydroxide product is reduced and the quality of lithium hydroxide is improved through two crystallization purification processes; the content of Na ions in the mother liquor generated after the initial crystallization is detected, and when the Na ion content is low, the mother liquor is recovered and repeatedly concentrated and crystallized, and when the Na ion content is high, the mother liquor is evaporated and concentrated to further extract lithium hydroxide, which not only effectively improves the lithium ion yield of the system, but also avoids the defect of the single crystallization process that the solution is difficult to evaporate due to the excessively high impurity ion content, thereby improving the evaporation efficiency of the overall lithium hydroxide solution.

[0042] In the present invention, the lithium ion yield of the system is the ratio of the lithium ion content in the obtained lithium hydroxide product to the lithium ion content in the added lithium hydroxide solution.

[0043] The device for improving the evaporation efficiency of lithium hydroxide according to the present invention comprises:

[0044] a first evaporator 1-1 and a first centrifuge 1-2, wherein the lithium hydroxide solution is concentrated and crystallized in the first evaporator 1-1, and then the mixture after the concentration and crystallization is centrifuged in the first centrifuge 1-2 to obtain first lithium hydroxide coarse crystals and a first mother liquor, and then the concentration of Na ions in the first mother liquor is detected, and when the Na ion concentration is less than 50 g / L, the first mother liquor is returned to the first evaporator 1-1 for recycling;

[0045] an evaporating kettle 2-1 and a second centrifuge 2-2, when the Na ion concentration in the first mother liquor is greater than or equal to 50 g / L, transporting the first mother liquor to the evaporating kettle 2-1 for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in the second centrifuge 2-2 to obtain a second lithium hydroxide coarse crystal and a second mother liquor;

[0046] The second evaporator 3-1 and the third centrifuge 3-2 are used to recrystallize the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals in the second evaporator 3-1, and then the recrystallized mixture is centrifuged in the third centrifuge 3-2 to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling.

[0047] In the device of the present invention, preferably, the device further comprises a bipolar membrane electrodialysis device 4 for providing the lithium hydroxide solution. In a specific embodiment of the present invention, the raw material for providing the lithium hydroxide solution is mainly salt lake brine, and the lithium hydroxide solution obtained after being treated by the bipolar membrane electrodialysis device 4 mainly contains Li, Na and K ions, and the content of Na ions is generally higher than that of K ions. Therefore, in the process of preparing lithium hydroxide, Na ions are selected as the marker ions of impurity ions, and the crystallization process of lithium hydroxide is controlled based on the concentration of Na ions, so as to avoid the precipitation of impurity ions together with lithium hydroxide, which leads to the quality decline of lithium hydroxide products.

[0048] In the device of the present invention, preferably, a first discharge port is provided at the bottom of the first evaporator 1-1, and the first discharge port is connected to a first discharge pump 5-1 for conveying the concentrated and crystallized mixture to the first centrifuge 1-2.

[0049] In the device of the present invention, preferably, the first mother liquor outlet of the first centrifuge 1-2 is connected to the first branch and the second branch, the first branch is provided with a first valve 1-3, and the second branch is provided with a second valve 1-4. When the concentration of Na ions in the first mother liquor is less than 50 g / L, the first mother liquor returns to the first evaporator 1-1 through the first valve 1-3; when the concentration of Na ions in the first mother liquor is greater than or equal to 50 g / L, the first mother liquor is transported to the evaporator 2-1 through the second valve 1-4.

[0050] In the device of the present invention, preferably, a second discharge port is provided at the bottom of the second evaporator 3-1, and the second discharge port is connected to a second discharge pump 5-2 for conveying the recrystallized mixture to the third centrifuge 3-2.

[0051] In the device of the present invention, preferably, the evaporating kettle 2-1 is heated by steam, a steam inlet is provided at the upper part of the side of the kettle body, and a steam outlet is provided at the lower part of the side of the kettle body. The use of steam heating can more efficiently heat the kettle body and control the temperature; the evaporating kettle 2-1 is also provided with a stirrer to improve the evaporation concentration efficiency.

[0052] In the device of the present invention, preferably, the second mother liquor outlet of the second centrifuge 2-2 is connected to an external system for conveying the second mother liquor to the external system for subsequent treatment.

[0053] In a specific embodiment of the present invention, the method for improving the evaporation efficiency of lithium hydroxide according to the present invention is carried out in the aforementioned device, comprising the following steps:

[0054] (1) The lithium hydroxide solution obtained by the bipolar membrane electrodialysis device 4 is fed into the first evaporator 1-1, and is concentrated and crystallized at a temperature of 80-90° C. and a pressure of 350-450 mbar. The mixture after the concentration and crystallization is then transported to the first centrifuge 1-2 through the first discharge pump 5-1 for centrifugal separation to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0055] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator 1-1 through the first branch where the first valve 1-3 is located for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to the evaporator 2-1 through the second branch where the second valve 1-4 is located, and performing evaporation concentration treatment at a temperature of 90-130° C. and a pressure of 300-400 mbar, so that the concentration of Na ions in the mixture after evaporation concentration treatment is 240-320 g / L, and then conveying the mixture to the second centrifuge 2-2 for centrifugal separation to obtain second lithium hydroxide coarse crystals and a second mother liquor, and conveying the second mother liquor to an external system for lithium precipitation;

[0056] (3) The first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are transported to the second evaporator 3-1, and recrystallized at a temperature of 80-90°C and a pressure of 350-450 mbar. The recrystallized mixture is then transported to the third centrifuge 3-2 via a second discharge pump 5-2 for centrifugal separation to obtain lithium hydroxide and a third mother liquor. The third mother liquor is returned to the first evaporator 1-1 for recycling.

[0057] According to the device for improving the evaporation efficiency of lithium hydroxide described in the present invention, it mainly includes two evaporators for concentrated crystallization treatment and recrystallization treatment and an evaporating kettle for evaporating and concentrating the mother liquor. It has a simple structure and can control multiple evaporating devices separately, which is beneficial to maintaining the stability of product quality. By recycling the mother liquor after crystallization for many times, the evaporation efficiency of lithium hydroxide is improved, which is convenient for industrial production application.

[0058] The following examples further illustrate the method and device for improving the evaporation efficiency of lithium hydroxide of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0059] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0060] Example 1

[0061] (1) The lithium hydroxide solution obtained by the bipolar membrane electrodialysis device 4 is fed into the first evaporator 1-1, and concentrated and crystallized at a temperature of 85° C. and a pressure of 400 mbar. The mixture after the concentrated and crystallized treatment is then transported to the first centrifuge 1-2 through the first discharge pump 5-1 for centrifugal separation to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0062] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator 1-1 through the first branch where the first valve 1-3 is located for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to the evaporator 2-1 through the second branch where the second valve 1-4 is located, and performing evaporation concentration treatment at a temperature of 100° C. and a pressure of 350 mbar, so that the Na ion concentration in the mixture after evaporation concentration treatment is 300 g / L, and then conveying the mixture to the second centrifuge 2-2 for centrifugal separation to obtain second lithium hydroxide coarse crystals and a second mother liquor, and conveying the second mother liquor to an external system for lithium precipitation;

[0063] (3) conveying the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals to the second evaporator 3-1, performing recrystallization treatment at a temperature of 85° C. and a pressure of 400 mbar, and then conveying the recrystallized mixture to the third centrifuge 3-2 via the second discharge pump 5-2 for centrifugal separation to obtain lithium hydroxide and a third mother liquor, and returning the third mother liquor to the first evaporator 1-1 for recycling;

[0064] After testing, the purity of the obtained lithium hydroxide A1 (calculated as lithium hydroxide) was 99.6%, and the system lithium ion yield was 94.6%.

[0065] Example 2

[0066] (1) The lithium hydroxide solution obtained by the bipolar membrane electrodialysis device 4 is fed into the first evaporator 1-1, and concentrated and crystallized at a temperature of 80° C. and a pressure of 350 mbar. The mixture after the concentrated and crystallized treatment is then transported to the first centrifuge 1-2 through the first discharge pump 5-1 for centrifugal separation to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0067] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator 1-1 through the first branch where the first valve 1-3 is located for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to the evaporator 2-1 through the second branch where the second valve 1-4 is located, and performing evaporation concentration treatment at a temperature of 90° C. and a pressure of 380 mbar, so that the Na ion concentration in the mixture after evaporation concentration treatment is 250 g / L, and then conveying the mixture to the second centrifuge 2-2 for centrifugal separation to obtain second lithium hydroxide coarse crystals and a second mother liquor, and conveying the second mother liquor to an external system for lithium precipitation;

[0068] (3) conveying the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals to the second evaporator 3-1, performing recrystallization treatment at a temperature of 80° C. and a pressure of 350 mbar, and then conveying the recrystallized mixture to the third centrifuge 3-2 via the second discharge pump 5-2 for centrifugal separation to obtain lithium hydroxide and a third mother liquor, and returning the third mother liquor to the first evaporator 1-1 for recycling;

[0069] After testing, the purity of the obtained lithium hydroxide A3 (calculated as lithium hydroxide) was 99.3%, and the system lithium ion yield was 93.4%.

[0070] Example 3

[0071] (1) The lithium hydroxide solution obtained by the bipolar membrane electrodialysis device 4 is fed into the first evaporator 1-1, and concentrated and crystallized at a temperature of 90° C. and a pressure of 450 mbar. The mixture after the concentrated and crystallized treatment is then transported to the first centrifuge 1-2 through the first discharge pump 5-1 for centrifugal separation to obtain first lithium hydroxide coarse crystals and a first mother liquor;

[0072] (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator 1-1 through the first branch where the first valve 1-3 is located for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to the evaporator 2-1 through the second branch where the second valve 1-4 is located, and performing evaporation concentration treatment at a temperature of 110° C. and a pressure of 310 mbar, so that the Na ion concentration in the mixture after evaporation concentration treatment is 310 g / L, and then conveying the mixture to the second centrifuge 2-2 for centrifugal separation to obtain second lithium hydroxide coarse crystals and a second mother liquor, and conveying the second mother liquor to an external system for lithium precipitation;

[0073] (3) conveying the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals to the second evaporator 3-1, performing recrystallization treatment at a temperature of 90° C. and a pressure of 450 mbar, and then conveying the recrystallized mixture to the third centrifuge 3-2 via the second discharge pump 5-2 for centrifugal separation to obtain lithium hydroxide and a third mother liquor, and returning the third mother liquor to the first evaporator 1-1 for recycling;

[0074] After testing, the purity of the obtained lithium hydroxide A3 (calculated as lithium hydroxide) was 99.1%, and the system lithium ion yield was 92.1%.

[0075] Comparative Example 1

[0076] The method of Example 1 is adopted, except that the lithium hydroxide solution is subjected to a single concentration and crystallization treatment, the mother liquor produced after crystallization is not evaporated, concentrated and recovered, and the Na ion concentration in the solution after crystallization is 330 g / L. After testing, the purity of the obtained lithium hydroxide D1 (calculated as lithium hydroxide) is 98.03%, the system lithium ion yield is 90.6%, and the mass of the obtained lithium hydroxide is reduced by 20% compared with that in Example 1.

[0077] Comparative Example 2

[0078] The method of Example 1 is adopted, except that a process flow of using a triple-effect evaporator in the prior art is used to replace the single-effect evaporation in Example 1 and the mother liquor after the first evaporation is evaporated again. After testing, the purity of the obtained lithium hydroxide D1 (calculated as lithium hydroxide) is 99.0%, and the system lithium ion yield is 88.1%.

[0079] It can be seen from this that the method of the present invention adopts multiple single-effect evaporation concentration crystallization, and the mother liquor after the first evaporation is evaporated again, effectively reducing the concentration of impurity ions (mainly Na and K) in the primary evaporator, avoiding the defect of increasing the boiling point due to the excessively high concentration of impurity ions, which increases the energy consumption; the separation and concentrated evaporation of the mother liquor after crystallization reduces the discharge of high-lithium mother liquor, improves the yield of lithium hydroxide, and reduces resource waste; the Na ion content after the first mother liquor evaporation and concentration is controlled to be close to the Na ion precipitation concentration, and lithium ions are recovered as much as possible while avoiding the precipitation of impurity ions, thereby improving the system lithium ion yield. The lithium hydroxide prepared by the method of the present invention has a higher purity and system lithium ion yield than the lithium hydroxide obtained by the process of only performing a single concentration crystallization without re-evaporating the mother liquor, and can obtain more lithium hydroxide; compared with the process flow of using a triple-effect evaporator in the prior art, it has a higher system lithium ion yield. The device of the present invention has a simple structure and can be directly incorporated into other systems for utilizing salt lake brine resources, so that the mother liquor after lithium hydroxide precipitation can be effectively utilized, thereby improving the overall utilization efficiency of salt lake brine resources and having high industrial application value.

[0080] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for improving the evaporation efficiency of lithium hydroxide, characterized in that: The method comprises the following steps: (1) the lithium hydroxide solution obtained after bipolar membrane electrodialysis treatment is introduced into a first evaporator (1-1) for concentration and crystallization treatment, and then the mixture after the concentration and crystallization treatment is centrifuged in a first centrifuge (1-2) to obtain first lithium hydroxide coarse crystals and a first mother liquor; (2) detecting the concentration of Na ions in the first mother liquor, and when the Na ion concentration is less than 50 g / L, returning the first mother liquor to the first evaporator (1-1) for recycling; when the Na ion concentration is greater than or equal to 50 g / L, conveying the first mother liquor to an evaporating kettle (2-1) for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in a second centrifuge (2-2) to obtain a second lithium hydroxide crude crystal and a second mother liquor; (3) The first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are transported to the second evaporator (3-1) for recrystallization, and then the recrystallized mixture is centrifuged in the third centrifuge (3-2) to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator (1-1) for recycling.

2. The method according to claim 1, characterized in that In step (1), the conditions for the concentration and crystallization treatment include: a temperature of 80-90° C. and a pressure of 350-450 mbar.

3. The method according to claim 1, characterized in that In step (2), the conditions of the evaporation concentration treatment include: a temperature of 90-130° C. and a pressure of 300-400 mbar; Preferably, the evaporation concentration treatment makes the concentration of Na ions in the treated mixture be 240-320 g / L.

4. The method according to claim 1, characterized in that: In step (3), the conditions for the recrystallization treatment include: a temperature of 80-90° C. and a pressure of 350-450 mbar.

5. A device for improving the evaporation efficiency of lithium hydroxide, characterized in that: The device includes: a first evaporator (1-1) and a first centrifuge (1-2), wherein the lithium hydroxide solution is concentrated and crystallized in the first evaporator (1-1), and then the mixture after the concentrated and crystallized treatment is centrifuged in the first centrifuge (1-2) to obtain first lithium hydroxide coarse crystals and a first mother liquor, and then the concentration of Na ions in the first mother liquor is detected, and when the Na ion concentration is less than 50 g / L, the first mother liquor is returned to the first evaporator (1-1) for recycling; an evaporating kettle (2-1) and a second centrifuge (2-2), when the Na ion concentration in the first mother liquor is greater than or equal to 50 g / L, transporting the first mother liquor to the evaporating kettle (2-1) for evaporation concentration treatment, and then centrifuging the mixture after evaporation concentration treatment in the second centrifuge (2-2) to obtain second lithium hydroxide coarse crystals and a second mother liquor; A second evaporator (3-1) and a third centrifuge (3-2), the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are recrystallized in the second evaporator (3-1), and the mixture after recrystallization is then centrifuged in the third centrifuge (3-2) to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator (1-1) for recycling.

6. The device according to claim 5, characterized in that The device also includes a bipolar membrane electrodialysis device (4) for providing the lithium hydroxide solution.

7. The device according to claim 5, characterized in that A first discharge port is provided at the bottom of the first evaporator (1-1), and the first discharge port is connected to a first discharge pump (5-1) for conveying the mixture after the concentrated crystallization treatment to the first centrifuge (1-2).

8. The device according to claim 5, characterized in that The first mother liquor outlet of the first centrifuge (1-2) is connected to a first branch and a second branch, the first branch is provided with a first valve (1-3), and the second branch is provided with a second valve (1-4), when the concentration of Na ions in the first mother liquor is less than 50 g / L, the first mother liquor is returned to the first evaporator (1-1) through the first valve (1-3); when the concentration of Na ions in the first mother liquor is greater than or equal to 50 g / L, the first mother liquor is transported to the evaporating kettle (2-1) through the second valve (1-4).

9. The device according to claim 5, characterized in that A second discharge port is provided at the bottom of the second evaporator (3-1), and the second discharge port is connected to a second discharge pump (5-2) for conveying the mixture after the recrystallization treatment to the third centrifuge (3-2).

10. The device according to claim 5, characterized in that The evaporating kettle (2-1) is heated by steam and is provided with a stirrer.

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