Method and device for improving evaporation efficiency of lithium hydroxide

Abstract

The present application relates to the field of lithium hydroxide preparation, and discloses a method and device for improving the evaporation efficiency of lithium hydroxide. The method can effectively reduce the impurity ion concentration in the primary evaporator through multiple evaporation and crystallization, avoid the problem of high energy consumption caused by the increase of boiling point due to the high concentration of impurity ions, and improve the evaporation efficiency. At the same time, the separation and concentration evaporation of the mother liquor after crystallization reduce the discharge amount of high lithium mother liquor, improve the yield of lithium hydroxide, and reduce resource waste. Multiple crystallization treatment and mother liquor separation reduce the content of impurity ions in lithium hydroxide products, which is conducive to obtaining high-purity lithium hydroxide. The device used in the method has a simple structure and is easy to control, and has high industrial application value.

Description

TECHNICAL FIELD

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

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

[0003] Currently, the main method for preparing lithium hydroxide is to use abundant salt lake brine as lithium source. After impurities are removed from the salt lake brine, lithium, sodium and potassium containing alkali liquor is prepared by bipolar membrane electrodialysis. Then, the lithium, sodium and potassium containing alkali liquor is concentrated multiple times by a three-effect evaporator and an MVR evaporator. When the concentration of sodium hydroxide is close to saturation, the mother liquor is discharged. Lithium hydroxide solid is subjected to recrystallization after being separated by a centrifugal machine. However, as the concentration of sodium hydroxide increases, the boiling point of the solution also increases, resulting in low evaporation efficiency. In addition, a large amount of sodium and potassium ions continuously enter the recrystallization process, affecting the quality of the final product. SUMMARY

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

[0005] To achieve the above-mentioned purpose, the present application provides a method for improving the evaporation efficiency of lithium hydroxide, which comprises the following steps:

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

[0007] (2) the concentration of Na ions in the first mother liquor is detected, when the concentration of Na ions is less than 50 g / L, the first mother liquor is returned to the first evaporator for recycling; when the concentration of Na ions is greater than or equal to 50 g / L, the first mother liquor is fed into an evaporation kettle for evaporation and concentration treatment, and then the mixture after evaporation and concentration treatment is centrifuged in a second centrifuge to obtain second lithium hydroxide coarse crystals and a second mother liquor;

[0008] (3) the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are fed into a second evaporator for recrystallization treatment, and then the mixture after recrystallization treatment 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.

[0009] Preferably, in step (1), the concentration and crystallization treatment includes a temperature of 80-90℃ and a pressure of 350-450mbar.

[0010] Preferably, in step (2), the evaporation and concentration treatment includes a temperature of 90-130℃ and a pressure of 300-400mbar.

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

[0012] Preferably, in step (3), the recrystallization treatment includes a temperature of 80-90℃ and a pressure of 350-450mbar.

[0013] The second aspect of the present application provides a device for improving the evaporation efficiency of lithium hydroxide, which comprises:

[0014] a first evaporator and a first centrifuge, lithium hydroxide solution is subjected to concentration and crystallization treatment in the first evaporator, and then the mixture after concentration and crystallization treatment 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, when the concentration of Na ions 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 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 for evaporation concentration treatment, and then the mixture after the evaporation concentration treatment is centrifuged in the second centrifuge to obtain second lithium hydroxide coarse crystals and a second mother liquor;

[0016] a second evaporator and a third centrifuge, the first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are subjected to recrystallization treatment in the second evaporator, and then the mixture after the recrystallization treatment is centrifuged in the third centrifuge to obtain lithium hydroxide and a third mother liquor, which 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, the first evaporator is provided with a first discharge port connected with a first discharge pump for transporting the mixture after the concentration crystallization treatment to the first centrifuge.

[0019] Preferably, the first centrifuge is provided with a first mother liquor outlet connected with a first branch and a 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 is returned 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 evaporating kettle through the second valve.

[0020] Preferably, the second evaporator is provided with a second discharge port connected with a second discharge pump for transporting the mixture after the recrystallization treatment to the third centrifuge.

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

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

[0023] The device for improving evaporation efficiency of lithium hydroxide provided by the application mainly comprises two evaporators for concentration and crystallization treatment and recrystallization treatment and an evaporation kettle for evaporating concentrated mother liquor, has simple structure, is controlled individually for multiple evaporation devices and is favorable for maintaining stability of product quality; through multiple recycling of mother liquor after crystallization, evaporation efficiency of lithium hydroxide is improved, and industrial production application is facilitated. BRIEF DESCRIPTION OF DRAWINGS

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

[0025] REFERENCE SIGNS

[0026] 1-1, first evaporator; 1-2, first centrifuge; 1-3, first valve; 1-4, second valve; 2-1, evaporation kettle; 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 application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the application, and are not intended to limit the application.

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and values are approximations that are understood to encompass values approximating these endpoints. For numeric ranges, the endpoints between the various ranges, the endpoints between the various ranges and the individual point values, and the individual point values can be combined with one another to generate one or more new numeric ranges that are to be considered as being specifically disclosed herein.

[0029] In the description of the present application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating relative importance, or implying the number of the indicated technical features. Therefore, unless otherwise specified, the features defined with "first", "second" can explicitly or implicitly include one or more of the features; the meaning of "multiple" is two or more. The term "comprise" and any variation thereof means non-exclusive inclusion, and one or more other features, integers, steps, operations, units, components and / or combinations thereof can exist or be added.

[0030] In the description of the present application, the term "comprising" and any variation thereof, means the inclusion of one or more other features, integers, steps, operations, units, components and / or combinations thereof, without being exclusive of the other features, integers, steps, operations, units, components and / or combinations thereof. The terms "central", "transverse", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and other terms indicating relative or positional relationships are described based on the orientation or relative position relationship shown in the drawings, and are only for the convenience of the simplified description of the present application, and do not indicate that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0031] In addition, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0032] As shown in Figure 1 The method for improving the evaporation efficiency of lithium hydroxide according to the present application comprises the following steps:

[0033] (1) The lithium hydroxide solution obtained after bipolar membrane electrodialysis treatment is fed into a first evaporator 1-1 for concentration and crystallization treatment, and then the mixture after 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) The concentration of Na ions in the first mother liquor is detected, when the concentration of Na ions is less than 50 g / L, the first mother liquor is returned to the first evaporator 1-1 for recycling; when the concentration of Na ions is greater than or equal to 50 g / L, the first mother liquor is fed into an evaporation kettle 2-1 for evaporation and concentration treatment, and then the mixture after evaporation and concentration treatment is centrifuged 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 fed into a second evaporator 3-1 for recrystallization treatment, and then the mixture after recrystallization treatment is centrifuged in a 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 application, preferably, in step (1), the concentration and crystallization treatment is carried out at a temperature of 80-90°C and a pressure of 350-450 mbar. More preferably, the concentration and crystallization treatment is carried out at a temperature of 82-88°C and a pressure of 370-430 mbar. In the present application, the above-mentioned concentration and crystallization conditions can be used to make lithium hydroxide in the solution crystallize preferentially, because 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 the same conditions, thereby reducing the amount of impurity ions mixed in.

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

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

[0039] In the present application, the above-mentioned evaporation and concentration conditions can be used to quickly concentrate the first mother liquor with a Na ion content of more than 50 g / L to a concentration close to the crystallization concentration (240-320 g / L) of Na ions at a higher temperature, so as to make the Li in the solution crystallize as much as possible before the Na ions reach the crystallization concentration, thereby improving the yield of lithium hydroxide. The second mother liquor obtained after the separation of the concentrated mixture can be transported to an external system for subsequent lithium precipitation treatment, thereby improving the utilization rate.

[0040] In the method of the present application, preferably, in step (3), the recrystallization treatment is carried out at a temperature of 80-90°C and a pressure of 350-450 mbar. More preferably, the recrystallization treatment is carried out at a temperature of 82-88°C and a pressure of 370-430 mbar. In the present application, the above-mentioned conditions are used to dissolve and recrystallize the first lithium hydroxide coarse crystal obtained by the concentration and crystallization treatment and the second lithium hydroxide coarse crystal obtained by the evaporation and concentration treatment, so as to improve the purity and quality of the lithium hydroxide product and further reduce the content of Na, K and other impurity ions.

[0041] The method for improving the evaporation efficiency of lithium hydroxide according to the present application reduces the content of impurity ions in the lithium hydroxide product through two crystallization purification processes, and improves the quality of lithium hydroxide; the content of Na ions in the mother liquor produced after the first crystallization is detected, when the content of Na ions is low, the mother liquor is recovered and repeatedly concentrated and crystallized, when the content of Na ions 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 that the solution is difficult to evaporate due to the too high content of impurity ions in the single crystallization process, thereby improving the evaporation efficiency of the whole lithium hydroxide solution.

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

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

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

[0045] The evaporation kettle 2-1 and the second centrifuge 2-2, when the concentration of Na ions in the first mother liquor is greater than or equal to 50g / L, the first mother liquor is sent to the evaporation kettle 2-1 for evaporation and concentration treatment, and then the mixture after the evaporation and concentration treatment is centrifuged in the second centrifuge 2-2 to obtain the second lithium hydroxide coarse crystal and the second mother liquor;

[0046] The second evaporator 3-1 and the third centrifuge 3-2, the first lithium hydroxide coarse crystal and the second lithium hydroxide coarse crystal are recrystallized in the second evaporator 3-1, and then the mixture after the recrystallization treatment is centrifuged in the third centrifuge 3-2 to obtain lithium hydroxide and the 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 application, preferably, the device further comprises a bipolar membrane electrodialysis device 4 for providing the lithium hydroxide solution. In the specific embodiment of the present application, the raw material for providing the lithium hydroxide solution is mainly salt lake brine, and the lithium hydroxide solution obtained after treatment 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 preparation of lithium hydroxide, Na ions are selected as the marker ions of impurity ions, and the concentration of Na ions is used as the basis for controlling the lithium hydroxide crystallization process, so as to avoid the impurity ions being precipitated together with lithium hydroxide and causing the quality of lithium hydroxide product to decrease.

[0048] In the device of the present application, preferably, the first evaporator 1-1 is provided with a first discharge port at the bottom, and the first discharge port is connected with a first discharge pump 5-1 for conveying the mixture after the concentration and crystallization treatment to a first centrifuge 1-2.

[0049] In the device of the present application, preferably, the first centrifuge 1-2 is connected with a first branch and a second branch at the first mother liquor outlet, 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 conveyed to the evaporation kettle 2-1 through the second valve 1-4.

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

[0051] In the device of the present application, preferably, the evaporation kettle 2-1 is heated by steam, and the upper side of the kettle body is provided with a steam inlet, and the lower side of the kettle body is provided with a steam outlet. The use of steam heating can more efficiently heat the kettle body and control the temperature; the evaporation kettle 2-1 is further provided with a stirrer for improving the evaporation concentration efficiency.

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

[0053] In the specific embodiment of the present application, the method for improving the evaporation efficiency of lithium hydroxide is carried out in the aforementioned device, and comprises the following steps:

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

[0055] (2) The concentration of Na ions in the first mother liquor is detected, when the concentration of Na ions is less than 50g / L, the first mother liquor is returned to the first evaporator 1-1 through the first branch of the first valve 1-3 for recycling; when the concentration of Na ions is greater than or equal to 50g / L, the first mother liquor is transported to the evaporation kettle 2-1 through the second branch of the second valve 1-4 for evaporation and concentration treatment under the conditions of a temperature of 90-130℃ and a pressure of 300-400mbar, so that the concentration of Na ions in the mixture after the evaporation and concentration treatment is 240-320g / L, and then the mixture is transported to the second centrifuge 2-2 for centrifugal separation, to obtain the second lithium hydroxide coarse crystal and the second mother liquor, and the second mother liquor is transported to an external system for lithium precipitation;

[0056] (3) The first lithium hydroxide coarse crystal and the second lithium hydroxide coarse crystal are transported to the second evaporator 3-1 for recrystallization treatment under the conditions of a temperature of 80-90℃ and a pressure of 350-450mbar, and then the mixture after the recrystallization treatment is transported to the third centrifuge 3-2 by the second discharge pump 5-2 for centrifugal separation, to obtain lithium hydroxide and the third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling.

[0057] The device for improving the evaporation efficiency of lithium hydroxide according to the present application mainly comprises two evaporators for concentrated and crystallized processing and recrystallization treatment, and an evaporation kettle for evaporation and concentration of the mother liquor, which has a simple structure and is beneficial to maintaining the stability of product quality by separately controlling multiple evaporation devices; the evaporation efficiency of lithium hydroxide is improved by recycling the mother liquor after crystallization multiple times, which is convenient for industrial production and application.

[0058] The method and device for improving the evaporation efficiency of lithium hydroxide according to the present application are further illustrated by the following examples. The examples are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

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

[0060] Example 1

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

[0062] (2) The concentration of Na ions in the first mother liquor is detected, when the concentration of Na ions is less than 50 g / L, the first mother liquor is returned to the first evaporator 1-1 for recycling through the first branch of the first valve 1-3; when the concentration of Na ions is greater than or equal to 50 g / L, the first mother liquor is transported to the evaporation kettle 2-1 through the second branch of the second valve 1-4, and is evaporated and concentrated under the condition of a temperature of 100°C and a pressure of 350 mbar, so that the concentration of Na ions in the mixture after the evaporated and concentrated processing is 300 g / L, and then the mixture is transported to the second centrifuge 2-2 for centrifugal separation, to obtain the second lithium hydroxide coarse crystal and the second mother liquor, and the second mother liquor is transported to an external system for lithium precipitation;

[0063] (3) The first lithium hydroxide coarse crystal and the second lithium hydroxide coarse crystal are transported to the second evaporator 3-1, and are recrystallized under the condition of a temperature of 85°C and a pressure of 400 mbar, and then the mixture after the recrystallized processing is transported to the third centrifuge 3-2 by the second discharge pump 5-2 for centrifugal separation, to obtain lithium hydroxide and the third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling;

[0064] Test results show that the purity (calculated as lithium hydroxide) of the obtained lithium hydroxide A1 is 99.6%, and the lithium ion yield of the system is 94.6%.

[0065] Example 2

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

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

[0068] (3) the first lithium hydroxide coarse crystal and the second lithium hydroxide coarse crystal are transported to the second evaporator 3-1, and are subjected to recrystallization treatment at a temperature of 80°C and a pressure of 350 mbar, and then the mixture after the recrystallization treatment is transported to the third centrifuge 3-2 through the second discharge pump 5-2 for centrifugal separation, to obtain lithium hydroxide and the third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling;

[0069] It is tested that the purity (calculated as lithium hydroxide) of the obtained lithium hydroxide A3 is 99.3%, and the lithium ion yield of the system is 93.4%.

[0070] Example 3

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

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

[0073] (3) The first lithium hydroxide coarse crystal and the second lithium hydroxide coarse crystal are transported to the second evaporator 3-1, and recrystallization treatment is performed at a temperature of 90°C and a pressure of 450 mbar, and then the mixture after the recrystallization treatment is transported to the third centrifuge 3-2 through the second discharge pump 5-2 for centrifugal separation, to obtain lithium hydroxide and a third mother liquor, and the third mother liquor is returned to the first evaporator 1-1 for recycling;

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

[0075] Comparative Example 1

[0076] The method of Example 1 is used, except that the lithium hydroxide solution is subjected to single concentration and crystallization treatment, the mother liquor produced after crystallization is not subjected to evaporation and concentration and recovery, and the Na ion concentration in the solution after crystallization is 330 g / L. It is tested that 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 quality of the obtained lithium hydroxide is reduced by 20% compared with Example 1.

[0077] Comparative Example 2

[0078] The method of Example 1 is used, except that the process flow using a three-effect evaporator in the prior art is used instead of the process flow of single-effect evaporation in Example 1 and re-evaporation treatment of the mother liquor after the first evaporation. It is tested that 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] Therefore, the method of the present application adopts multiple single-effect evaporation concentration crystallization, and the mother liquor after the first evaporation is subjected to evaporation treatment again, so that the concentration of impurity ions (mainly Na and K) in the first evaporator is effectively reduced, and the defect that the energy consumption is high due to the increase of the boiling point caused by the high concentration of impurity ions is avoided; the separation and concentration evaporation of the mother liquor after crystallization reduce the discharge amount of high-lithium mother liquor, improve the yield of lithium hydroxide, and reduce resource waste; the content of Na ions after the first mother liquor evaporation concentration is close to the precipitation concentration of Na ions, so that the impurity ions are avoided to be precipitated while the lithium ions are recovered as much as possible, and the system lithium ion yield is improved. The lithium hydroxide prepared by the method of the present application has higher purity and system lithium ion yield compared with the lithium hydroxide prepared by the process of only single concentration crystallization without re-evaporation treatment of the mother liquor, and more lithium hydroxide can be obtained; compared with the process flow of the prior art using a three-effect evaporator, the present application has higher system lithium ion yield. The device of the present application has a simple structure and can be directly incorporated into other systems for utilization of salt lake brine resources, so that the mother liquor after the precipitation of lithium hydroxide is effectively utilized, the overall utilization efficiency of salt lake brine resources is improved, and the present application has high industrial application value.

[0080] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for improving evaporation efficiency of lithium hydroxide, characterized by, The method comprises the following steps: (1) The lithium hydroxide solution obtained after bipolar membrane electrodialysis treatment is fed into a first evaporator (1-1) for concentration crystallization treatment, and then the mixture after the concentration crystallization treatment is centrifuged in a first centrifuge (1-2) to obtain first lithium hydroxide coarse crystals and a first mother liquor; (2) The concentration of Na ions in the first mother liquor is detected, when the concentration of Na ions is less than 50 g / L, the first mother liquor is returned to the first evaporator (1-1) for recycling; when the concentration of Na ions is greater than or equal to 50 g / L, the first mother liquor is fed into an evaporation kettle (2-1) for evaporation concentration treatment, and then the mixture after the evaporation concentration treatment is centrifuged in a second centrifuge (2-2) to obtain second lithium hydroxide coarse crystals and a second mother liquor; (3) The first lithium hydroxide coarse crystals and the second lithium hydroxide coarse crystals are fed into a second evaporator (3-1) for recrystallization treatment, and then the mixture after the recrystallization treatment is centrifuged in a 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 of claim 1, wherein, In step (1), the concentration crystallization treatment conditions include a temperature of 80-90°C and a pressure of 350-450 mbar.

3. The method of claim 1, wherein, In step (2), the evaporation concentration treatment conditions include a temperature of 90-130°C and a pressure of 300-400 mbar.

4. The method of claim 1, wherein, In step (2), the evaporation concentration treatment makes the concentration of Na ions in the treated mixture 240-320 g / L.

5. The method of claim 1, wherein, In step (3), the recrystallization treatment conditions include a temperature of 80-90°C and a pressure of 350-450 mbar.

6. A device for improving evaporation efficiency of lithium hydroxide, characterized by, The device comprises: A first evaporator (1-1) and a first centrifuge (1-2), the lithium hydroxide solution is subjected to concentration crystallization treatment in the first evaporator (1-1), and then the mixture after the concentration crystallization 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, when the concentration of Na ions is less than 50 g / L, the first mother liquor is returned to the first evaporator (1-1) for recycling; An evaporation kettle (2-1) and a second centrifuge (2-2), 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 fed into the evaporation kettle (2-1) for evaporation concentration treatment, and then the mixture after the evaporation concentration treatment is centrifuged 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 subjected to recrystallization treatment in the second evaporator (3-1), and then the mixture after the recrystallization treatment 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.

7. The apparatus of claim 6, wherein The device also comprises a bipolar membrane electrodialysis device (4) for providing the lithium hydroxide solution.

8. The apparatus of claim 6, wherein, The bottom of the first evaporator (1-1) is provided with a first discharge port connected with a first discharge pump (5-1) for conveying the mixture after the concentration and crystallization treatment to a first centrifuge (1-2).

9. The apparatus of claim 6, wherein, The first mother liquor outlet of the first centrifuge (1-2) is connected with 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 conveyed to the evaporation kettle (2-1) through the second valve (1-4).

10. The apparatus of claim 6, wherein, The bottom of the second evaporator (3-1) is provided with a second discharge port connected with a second discharge pump (5-2) for conveying the mixture after the recrystallization treatment to a third centrifuge (3-2).

11. The apparatus of claim 6, wherein, The evaporation kettle (2-1) is heated by steam and is provided with a stirrer.

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