Method for preparing battery grade lithium carbonate by extracting lithium from sulfate type salt lake sodium-removed brine

Abstract

The invention discloses a method for preparing battery-grade lithium carbonate by extracting lithium from sulfate-type salt lake sodium-removed brine, which comprises the following steps: 1) conveying extracted sulfate-type salt lake original brine to a sodium-removed salt pond for concentration to form sodium-removed brine with improved lithium concentration; 2) carrying out adsorption separation treatment on the sodium-removed brine to form qualified lithium liquid; (3) carrying out membrane separation treatment on the qualified lithium liquid to form a refined lithium concentrated solution; and 4) carrying out lithium precipitation treatment on the lithium refined concentrated solution to obtain the battery-grade lithium carbonate. Separation and extraction of lithium in sodium-removed brine with different lithium concentrations in a sulfate type salt lake and preparation of battery-grade lithium carbonate can be realized, meanwhile, the composition change of the brine after lithium extraction is extremely low, and subsequent product production is not influenced.

Description

Technical Field

[0001] The present invention relates to the technical field of salt chemical separation and purification, and in particular to a method for preparing battery-grade lithium carbonate by extracting lithium from desodiumized brine in a sulfate-type salt lake. Background Art

[0002] Lithium is the lightest metal in nature with the smallest atomic radius. It has active chemical properties. Lithium metal and its compounds are widely used in aviation, medicine, chemical industry, national defense, new energy and other fields. It is called "an important element that drives the world forward."

[0003] Salt lake brine can be divided into carbonate, sulfate, and chloride types based on its composition. Different types of salt lake brine have different compositions. Generally, sulfate and chloride salt lakes share the main characteristic of a high magnesium-ion ratio. After years of development, lithium extraction from salt lakes has developed a variety of lithium extraction technology solutions, including calcination leaching, solvent extraction, adsorption, membrane separation, and electrochemical deintercalation. Among these solutions, adsorption offers advantages in terms of lithium extraction cost, brine lithium grade requirements, environmental friendliness, and fresh water consumption, and has become the primary method for lithium extraction from salt lakes.

[0004] Currently, industrialized lithium extraction from salt lake brines primarily produces lithium carbonate products through direct extraction of lithium from raw brine. However, this process is plagued by issues such as large brine processing volumes and variability in brine quality, making stable production difficult. Furthermore, salt lake brine systems typically harbor multiple valuable elements that coexist or coexist. From the perspective of comprehensive brine resource utilization, a development approach that prioritizes lithium extraction while significantly impacting other resource extraction processes is undesirable. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a method for extracting lithium from desodiumized brine in sulfate salt lakes to prepare battery-grade lithium carbonate.

[0006] According to one aspect of the present invention, a method for extracting lithium from sulfate salt lake desodium brine to prepare battery-grade lithium carbonate comprises the following steps:

[0007] 1) The extracted sulfate salt lake brine is transported to a desodium salt pool for concentration to form desodium brine with increased lithium concentration;

[0008] 2) performing adsorption separation treatment on the desodiumized brine to form a lithium-qualified solution;

[0009] 3) performing membrane separation treatment on the lithium qualified solution to form a lithium refined concentrated solution;

[0010] 4) performing lithium precipitation treatment on the lithium refined concentrate to obtain battery-grade lithium carbonate.

[0011] Furthermore, in step 1), the raw brine is transported to a desodium salt pool after extraction for solarization and concentration, thereby increasing the lithium concentration in the brine and solarizing the brine into desodium brine.

[0012] In step 2), the sodium-free brine obtained by sun-drying is transported to the adsorption separation section of the workshop, and lithium in the brine is extracted and separated by adsorption separation to form a lithium-qualified solution.

[0013] In step 3), the lithium-extracted tail liquid from the adsorption separation section is transported back to the salt pond for further evaporation and enrichment and used in other production processes; while the qualified lithium liquid from the adsorption separation section enters the membrane separation section, and is subjected to nanofiltration, reverse osmosis, ion adsorption and impurity removal, and MVR forced evaporation to obtain a lithium refined concentrate.

[0014] In step 4), the lithium refined concentrate enters the lithium precipitation section, and is precipitated with soda ash, washed with pure water, and dried to remove magnetism to obtain a battery-grade lithium carbonate product.

[0015] The raw brine in step (1) is sulfate salt lake brine, which is generally obtained from salt lake deposits through well mining or channel mining. The chemical composition of the brine is: [Li + ] mass concentration is 0.05~0.3g / L, [Na + ] mass concentration is 70~100g / L, [K + ] mass concentration is 3~12g / L, [Mg 2+ ] mass concentration is 12~30g / L, [Cl - ] mass concentration is 150~250g / L, [SO4 2- ] mass concentration is 15-35 g / L, [B2O3] mass concentration is 0.3-3 g / L; and / or, the desodium brine is the brine after sodium chloride is precipitated in the desodium salt pool, and the chemical composition of the brine is: [Li + ] mass concentration is 0.35~0.8g / L, [Na + ] mass concentration is 15~75g / L, [K + ] mass concentration is 8~28g / L, [Mg 2+ ] mass concentration is 30~85g / L, [Cl - ] mass concentration is 150~250g / L, [SO4 2- ] mass concentration is 30~75g / L, and [B2O3] mass concentration is 1~6g / L.

[0016] The adsorption separation section in step (2) includes a brine pretreatment process, an adsorption process, a washing process, a desorption process and a replacement process.

[0017] The pretreatment process of the adsorption separation section is mainly performed by a coarse filtration device, an organic adsorption device and a heat exchange device, wherein the coarse filtration device is one or more of a plate and frame filtration device, a ceramic membrane device, and an ultrafiltration device; the organic adsorption device adopts a fixed bed adsorption device, and the filler is one or more of zeolite molecular sieve, mesoporous silica, porous organic polymer, and macroporous adsorption resin; the heat exchange device is one of a plate heat exchanger and a shell and tube heat exchanger.

[0018] The adsorption process, washing process, desorption process and replacement process of the adsorption separation section are all carried out in a continuous moving bed device. The continuous moving bed consists of a disc with multiple resin columns and a porous distribution valve. The number of resin columns can be 10 to 30. The adsorption, washing, desorption and replacement processes are completed by rotating the disc and switching the valve port.

[0019] The continuous moving bed of the adsorption separation section is filled with lithium adsorbent, and the adsorbent type used is aluminum-based adsorbent.

[0020] The pretreatment process of the adsorption separation stage uses a coarse filtration device to remove large-sized impurities such as silt and salt particles from the de-sodium brine. The organic adsorption device removes organic molecules from the de-sodium brine to obtain purified de-sodium brine. Preferably, a plate and frame ultrafiltration device is used in series, followed by an organic adsorption device to obtain purified de-sodium brine.

[0021] The heat exchange device in the pretreatment section mainly exchanges heat for the purified desodiumized brine and desorption water. The temperature of the brine is controlled at 18°C-35°C after heat exchange, and the temperature of the desorption water is controlled at 30°C-45°C after heat exchange.

[0022] The feed for the adsorption process of the adsorption separation section is the purified de-sodiumized brine after heat exchange, and the feed flow rate is 2.6-7.5BV / h. The purified de-sodiumized brine becomes lithium extraction tail liquid after the adsorption process.

[0023] The feed for the washing process of the adsorption separation section is pure water, and the feed flow rate is 1.5 to 4.5 BV / h. After the pure water undergoes the washing process, the discharged liquid is the washing liquid, which is returned and mixed with the purified de-sodium brine.

[0024] The feed for the desorption process of the adsorption separation section is pure water after heat exchange, and the feed flow rate is 1.5 to 9 BV / h. After the desorption process, the discharged liquid is a lithium qualified liquid.

[0025] The feed for the displacement process of the adsorption separation section is purified desodiumized brine, with a feed flow rate of 0.8 to 3 BV / h. After the displacement process, the discharged liquid is the displacement liquid, of which part is sent back to the pure water heat exchange device, and part is sent to the water collecting tank to produce pure water. The part sent back to the pure water heat exchange device requires an instantaneous conductivity range of 0 to 100 μs / cm.

[0026] The single-step processing time of the continuous moving bed device in the adsorption separation section is 8 to 20 minutes.

[0027] In lithium qualified solution, [Li + ] mass concentration 0.35~0.8g / L, [Na + ] mass concentration is 0.05~0.5g / L, [K + ] mass concentration is 0.03~0.1g / L, [Mg 2+ ] mass concentration is 0.08~1g / L, [Cl - ] mass concentration is 1.8~7g / L, [SO4 2- ] mass concentration is 0.03~0.1g / L, and [B2O3] mass concentration is 0.1~1g / L.

[0028] The lithium extraction tail liquid in step 3) is transported back to the enrichment tank through a pipeline for further evaporation and concentration, and the adsorption process is brought into the fresh water after evaporation, and then used in other production processes.

[0029] The membrane separation section in step 3) includes a membrane separation device, an ion adsorption tower, and an MVR device.

[0030] Among them, the operating pressure of the nanofiltration device of the membrane separation device is 1.0~4.0MPa, the operating pressure of the reverse osmosis device of the membrane separation device is 2.5~6.0MPa, and the concentration ratio of the MVR device is 2~6.

[0031] The membrane separation device is composed of one stage reverse osmosis (1 stage) + one stage nanofiltration (2 to 4 stages) + two stages reverse osmosis (1 stage) + two stages nanofiltration (1 to 2 stages) + three stages nanofiltration (2 to 3 stages).

[0032] The ion adsorption tower adopts fixed bed adsorption, and the adsorption device filler is one or more of chelating resin, boron removal resin, potassium removal resin, and zeolite material; further, the ion adsorption tower is placed after the second stage nanofiltration and after the third stage nanofiltration respectively.

[0033] The qualified lithium solution is concentrated by reverse osmosis, and the lithium mass concentration in the obtained reverse osmosis concentrated water is 1.2-2 g / L. The reverse osmosis concentrated water is separated by nanofiltration, and the obtained nanofiltration produced water is separated by the subsequent reverse osmosis concentrated water and nanofiltration, and a membrane refined liquid is obtained after a stage of adsorption.

[0034] The membrane refined liquid is adjusted to pH 8-11 using caustic soda or liquid alkali, and then undergoes three-stage nanofiltration and two-stage adsorption to obtain lithium refined liquid, which is then concentrated by an MVR device to obtain lithium refined concentrated liquid.

[0035] The produced water obtained in the reverse osmosis concentration process of the above membrane lithium separation section is returned to the adsorption separation section as desorption water to reduce water consumption.

[0036] In lithium refined concentrate, [Li + ] mass concentration is 18~30g / L, [Na+ ] mass concentration is 0.1~5g / L, [K + ] mass concentration is 0.2~3g / L, [Mg 2+ ] mass concentration is 0~0.010g / L, [Cl - ] mass concentration is 92~160g / L, [SO4 2- ] mass concentration is 0~0.010g / L, and [B2O3] mass concentration is 0~0.010g / L.

[0037] The lithium precipitation section in step 4) consists of a soda ash preparation process, a lithium precipitation reaction process, a washing process, and a drying and demagnetization process.

[0038] The soda ash preparation process includes a soda ash preparation device and a refining and separation device. The soda ash preparation device is mainly composed of a soda ash feeder and a stirred reactor, and the refining and separation device is a plate and frame filter press.

[0039] Soda ash is prepared by dissolving in pure water at a dissolution temperature of 35°C to 80°C. After stirring and dissolving, add a 40% by mass caustic soda solution or liquid caustic soda in an amount of 0.5% to 5% of the soda ash. Continue stirring for 10 to 20 minutes, and then filter through a plate and frame to obtain a refined soda ash solution. The prepared concentration of the refined soda ash solution is 20% to 32%.

[0040] The lithium refined concentrate and the soda ash refined liquid are fed into a lithium precipitation reactor for reaction at a reaction temperature of 75°C to 95°C and a stirring rate of 45 to 240 r / min. After the feeding is completed, stirring is continued for 5 to 15 minutes, and the slurry is simultaneously ultrasonicated. After the stirring is completed, ultrasonication is continued for 5 to 15 minutes, and the ultrasonic frequency range is 10 to 200 kHz. After the ultrasonication is completed, the slurry is kept warm and aged for 10 to 45 minutes to obtain a lithium carbonate slurry.

[0041] The lithium carbonate slurry is subjected to solid-liquid separation in a centrifuge to obtain a crude lithium carbonate product, which is sent to a washing process for two-stage countercurrent washing and separation to obtain a battery-grade lithium carbonate wet product. The washing temperature is 75° C. to 95° C., the washing time is 10 to 30 minutes, and the solid-liquid ratio is 1:1.2 to 1:5.

[0042] The battery-grade lithium carbonate wet product enters a drying and demagnetization process. The product drying device is one of airflow drying and flash drying. After the material is dried, it is demagnetized by a demagnetizer to obtain a battery-grade lithium carbonate product.

[0043] Beneficial effects: The present invention is aimed at extracting lithium from desodium brine in sulfate salt lakes. Its advantage is that compared with the existing old brine lithium extraction process, it avoids most of the lithium loss in the brine during the salt field enrichment process, and shortens the lithium extraction cycle; at the same time, compared with the original brine lithium extraction process, the use of desodium brine lithium extraction can well control the lithium grade of the brine during the lithium extraction process, the process is more stable during the production process, and the lithium concentration is higher than that of the original brine, which can reduce the scale of the lithium extraction equipment and the water consumption of lithium extraction. After stable operation, it has almost no impact on the extraction and production of valuable elements such as potassium salt, which meets the premise of comprehensive utilization of brine resources.

[0044] In addition, the process of the present invention carries out a pretreatment process on the brine, reducing the risk of fouling and clogging the adsorption system and membrane system during the brine lithium separation process, selecting aluminum-based adsorption materials for lithium separation and extraction, and no other ions are introduced into the brine. Except for the reduction of lithium chloride and the increase of water proportion in the tail liquid after adsorption, the chemical composition and proportion of other elements are consistent with those of the brine before lithium extraction. It is friendly to the mine environment and there is no problem of introducing pollution sources.

[0045] In addition, the present invention utilizes an adsorption device coupled with a membrane separation device to extract lithium, which can not only increase the reuse rate of water but also reduce water consumption. The lithium precipitation stage adopts ultrasonic crystallization technology, which reduces the inclusion and entrainment of impurities in the product during the crystallization process and reduces the possibility of crystal agglomeration. The quality of the produced products is stable and the degree of uniformity is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and other aspects, features and advantages of the embodiments of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0047] Figure 1 Flowchart of a method for preparing battery-grade lithium carbonate by extracting lithium from sulfate-type salt lake desodium brine according to Example 1 of the present invention;

[0048] Figure 2 This is a flow chart of the sodium removal brine adsorption separation section according to Example 1 of the present invention;

[0049] Figure 3 is a flow chart of a membrane separation section according to Example 1 of the present invention;

[0050] Figure 4 This is a flow chart of the lithium deposition section according to Example 1 of the present invention;

[0051] Figure 5 Schematic diagram of the connection of adsorption columns in the adsorption separation section according to Example 1 of the present invention. DETAILED DESCRIPTION

[0052] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention may be implemented in many different forms, and the present invention should not be construed as limited to the specific embodiments set forth herein. Instead, these embodiments are provided to explain the principles of the present invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the present invention and various modifications suitable for specific intended applications.

[0053] As used herein, the term "including" and its variations are open terms meaning "including but not limited to". The terms "based on", "according to", etc. mean "based at least in part on", "based at least in part on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc. may refer to different or the same objects. Other definitions may be included below, whether explicit or implicit. Unless the context clearly indicates otherwise, the definition of a term is consistent throughout the specification.

[0054] Example 1

[0055] Figure 1 The present invention is a flowchart of a method for extracting lithium from sulfate salt lake desodium brine to prepare battery-grade lithium carbonate according to an embodiment of the present invention.

[0056] Reference Figure 1 First, a sulfate salt lake brine (i.e., raw brine) is obtained and transported to a desodium salt pool to obtain desodium brine 1# with increased lithium concentration through natural evaporation.

[0057] Secondly, the desodiumized brine 1# is subjected to adsorption separation treatment to form a lithium qualified solution.

[0058] Specifically, the sodium-depleted brine 1# is transported to the pretreatment section by a pump, and after plate and frame coarse filtration and ultrafiltration membrane fine filtration, the resulting filtrate enters the organic adsorption separation device, and after adsorption, purified sodium-depleted brine is obtained.

[0059] The purified de-sodiumized brine enters the adsorption separation section. The continuous moving bed of the adsorption separation section is composed of, for example, 30 adsorption columns. Specifically, the 30 adsorption columns are formed as follows: Figure 5 See Figure 2 and Figure 5 Four consecutive adsorption columns are used in parallel as part of the brine adsorption section. Each parallel adsorption column is connected in series with three adsorption columns to form the adsorption process. The washing process is composed of three consecutive adsorption columns in series. The desorption process is composed of three consecutive adsorption columns in parallel. Each adsorption column is connected in series with two adsorption columns to form a total of 9 adsorption columns. The replacement process is composed of a single adsorption column.

[0060] The single-step operation time of the continuous moving bed is set to 15 minutes, the switching time of the moving bed is 1 minute, the feed flow rate of the adsorption section single column is 3.8BV / h, the feed flow rate of the washing section single column is 3.3BV / h, the feed flow rate of the desorption section single column is 4.7BV / h, and the feed flow rate of the replacement section single column is 1.1BV / h.

[0061] Next, the lithium qualified solution is subjected to membrane separation treatment to form a lithium refined concentrated solution.

[0062] Figure 3 1 is a flow chart of a membrane separation section according to Example 1 of the present invention.

[0063] Reference Figure 3 The qualified lithium liquid enters a reverse osmosis device, the fresh water side of the reverse osmosis device supplies fresh water for the return adsorption separation section, and the concentrated water side is connected to a nanofiltration device.

[0064] The first stage nanofiltration device uses a two-stage nanofiltration device. The concentrated water of the first stage nanofiltration device goes to the second stage nanofiltration device. The first stage nanofiltration device is connected to the second stage reverse osmosis device. The concentrated water of the second stage nanofiltration device is discharged, and its produced water is connected to the second stage reverse osmosis device.

[0065] The water produced by the second-stage reverse osmosis device is regulated by a proportional valve to send part of the water to the first-stage nanofiltration device to be mixed with the concentrated water produced by the first-stage nanofiltration device, and the remaining water is returned to the adsorption separation section; the concentrated water of the second-stage reverse osmosis device is connected to the second-stage nanofiltration device.

[0066] The two-stage nanofiltration device is set to 1 level, its concentrated water is connected to the first-stage nanofiltration device of the first-stage nanofiltration device, and its produced water is connected to a first-stage ion adsorption tower.

[0067] The water produced by the first stage ion adsorption tower is connected to the three-stage nanofiltration device, and the water produced can be dosed with medicine by the set dosing device before entering the three-stage nanofiltration device.

[0068] The three-stage nanofiltration is set up in two stages. The concentrated water of the first-stage nanofiltration device is connected to the second-stage nanofiltration device. The water produced by the first-stage nanofiltration device is connected to the second-stage ion adsorption tower. The water produced by the second-stage ion adsorption tower goes to MVR for concentration. The water produced by the second-stage nanofiltration device is returned to the first-stage nanofiltration device, and its concentrated water is sent out; the MVR concentrated liquid goes to the next section, and the condensed water returns to the adsorption separation section.

[0069] In this embodiment, the pressure of the first-stage reverse osmosis device is 2.2MPa; the pressure of the first-stage nanofiltration device of the first-stage nanofiltration device is 2.2MPa, and the pressure of the second-stage nanofiltration device of the first-stage nanofiltration device is 3.8MPa; the pressure of the second-stage reverse osmosis device is 4.5MPa, and the reverse osmosis water production ratio of the second-stage reverse osmosis device is adjusted to 35% to go to the first-stage nanofiltration device; the pressure of the second-stage nanofiltration device is 2.2MPa, the pressure of the first-stage nanofiltration device of the three-stage nanofiltration device is 2.0MPa, and the pressure of the second-stage nanofiltration device of the three-stage nanofiltration device is 3.5MPa. The dosing device adds sodium hydroxide, and the pH of the feed liquid is adjusted to 9.5. After MVR concentration, a refined lithium concentrate (i.e., lithium refined concentrate) 1# is obtained.

[0070] Finally, the lithium refined concentrate is subjected to lithium precipitation treatment to obtain battery-grade lithium carbonate.

[0071] Figure 4 Flowchart of the lithium deposition section according to Example 1 of the present invention. Figure 4 The refined lithium concentrate 1# obtained in the above process is preheated and reacted with the prepared soda ash solution. After the reaction is completed, the slurry is separated by a centrifuge, and the crude lithium carbonate material obtained is washed with two-stage countercurrent, then dried with air flow, and demagnetized to obtain a battery-grade lithium carbonate product.

[0072] In the embodiment, the concentration of the prepared soda ash is 25%, the preparation temperature of the soda ash is 50°C, the preheating temperature of the refined lithium concentrate 1# is 75°C, stirring is continued for 10 minutes after the feeding is completed, the stirring speed is 120r / min, the ultrasonic time is 15 minutes, the ultrasonic frequency is 85kHz, the insulation aging time is 25 minutes, and the insulation temperature of the reactor is 90°C; the solid-liquid ratio of the washing section is 1:3.2, and the insulation temperature of the washing section is 90°C.

[0073] Example 2

[0074] The difference between Example 2 of the present invention and Example 1 is that the number of adsorption columns used in the continuous moving bed adopted in the adsorption separation section is 10, wherein the adsorption section is connected in a four-column series, the washing section is connected in a two-column series, the desorption section is connected in a three-column series, and the replacement section is a single column; the flow rate of the single column in the adsorption section is 7.5BV / h, the flow rate of the washing section is 4.2BV / h, the flow rate of the desorption section is 5.8BV / h, and the flow rate of the replacement section is 0.9BV / h; other operating process methods and parameters are consistent with Example 1 and will not be repeated here.

[0075] Example 3

[0076] The difference between Example 3 of the present invention and Example 2 is that a third nanofiltration separation process is added to the three-stage nanofiltration separation section of the adsorption separation section, the first-stage nanofiltration product water is separated again, the third-stage nanofiltration product water is connected to the second-stage ion adsorption tower, the third-stage nanofiltration concentrated water is returned to the second-stage nanofiltration, and the pH of the first-stage nanofiltration inlet water is adjusted to 10.0; other operating process methods and parameters are consistent with Example 2 and will not be repeated here.

[0077] Example 4

[0078] The difference between Example 4 of the present invention and Example 1 is that the single-step processing time of the continuous moving bed adsorption device is 8 minutes, the adsorption feed flow rate is 7.5BV / h per column, the washing section flow rate is 6BV / h, the desorption section flow rate is 9BV / h, and the replacement section flow rate is 1.1BV / h; other operating process methods and parameters are consistent with those of Example 1 and will not be repeated here.

[0079] Example 5

[0080] The difference between Example 5 of the present invention and Example 1 is that the lithium concentration of the desodium brine used is 0.370 g / L, the feed flow rate of the adsorption section single column is 6.8 BV / h, the feed flow rate of the washing section single column is 3.3 BV / h, the feed flow rate of the desorption section single column is 4.7 BV / h, and the feed flow rate of the replacement section single column is 1.1 BV / h; other operating process methods and parameters are consistent with Example 1 and are not repeated here.

[0081] Table 1 below shows the index parameters of each control section in the above embodiments.

[0082] Table 1

[0083]

[0084]

[0085] In summary, according to the method for extracting lithium from desodium brine of sulfate-type salt lakes to prepare battery-grade lithium carbonate according to an embodiment of the present invention, an adsorption + membrane separation + MVR + lithium precipitation device is used. By adjusting the connection process and operating parameters of the continuous moving bed and the membrane separation section, the separation and extraction of lithium from desodium brine with different lithium concentrations in sulfate-type salt lakes and the preparation of battery-grade lithium carbonate can be achieved. At the same time, the change in the brine composition after lithium extraction is extremely low, and does not affect the subsequent product production. Furthermore, the preparation of battery-grade lithium carbonate can also be achieved under different process and parameter adjustments.

[0086] Throughout this specification, the terms "exemplary," "example," and the like are used to mean "serving as an example, instance, or illustration" and do not imply "preferred" or "advantageous" over other embodiments. The detailed description includes specific details for the purpose of providing an understanding of the described techniques. However, these techniques can be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form to avoid obscuring the concepts of the described embodiments.

[0087] The above describes in detail the optional implementation methods of the embodiments of the present invention in conjunction with the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above implementation methods. Within the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the scope of protection of the embodiments of the present invention.

[0088] The foregoing description of this specification is provided to enable any person skilled in the art to implement or use the present disclosure. Various modifications to this disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but is intended to be consistent with the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing battery-grade lithium carbonate by extracting lithium from sulfate salt lake desodium brine, characterized in that: The steps include: 1) The extracted sulfate salt lake brine is transported to a desodium salt pool for concentration to form desodium brine with increased lithium concentration; 2) performing adsorption separation treatment on the desodiumized brine to form a lithium-qualified solution; 3) performing membrane separation treatment on the lithium qualified solution to form a lithium refined concentrated solution; 4) performing lithium precipitation treatment on the lithium refined concentrate to obtain battery-grade lithium carbonate.

2. The method according to claim 1, characterized in that In the raw brine of the sulfate salt lake, the mass concentration of lithium ions is 0.05-0.3 g / L, the mass concentration of sodium ions is 70-100 g / L, the mass concentration of potassium ions is 3-12 g / L, the mass concentration of magnesium ions is 12-30 g / L, the mass concentration of chloride ions is 150-250 g / L, the mass concentration of sulfate ions is 15-35 g / L, and the mass concentration of boron oxide is 0.3-3 g / L; and / or, in the desodiumized brine, the mass concentration of lithium ions is 0.35-0.8 g / L, the mass concentration of sodium ions is 15-75 g / L, the mass concentration of potassium ions is 8-28 g / L, the mass concentration of magnesium ions is 30-85 g / L, the mass concentration of chloride ions is 150-250 g / L, the mass concentration of sulfate ions is 30-75 g / L, and the mass concentration of boron oxide is 1-6 g / L.

3. The method according to claim 1, characterized in that The step 2) specifically includes: performing brine pretreatment, adsorption treatment, washing treatment, desorption treatment and replacement treatment on the desodium brine to form a lithium qualified solution.

4. The method according to claim 3, characterized in that The brine pretreatment is performed by a coarse filtration device, an organic adsorption device and a heat exchange device. The coarse filtration device includes at least one of a plate and frame filtration device, a ceramic membrane device and an ultrafiltration device. The organic adsorption device is a fixed bed adsorption device. The filler in the fixed bed adsorption device includes at least one of zeolite molecular sieve, mesoporous silica, porous organic polymer and macroporous adsorption resin. The heat exchange device includes a plate heat exchanger or a shell and tube heat exchanger. The adsorption treatment, washing treatment, desorption treatment and replacement treatment are all carried out in a continuous moving bed device, which includes a disc with multiple resin columns and a porous distribution valve. The adsorption treatment, washing treatment, desorption treatment and replacement treatment are completed by rotating the disc and switching the valve port of the porous distribution valve.

5. The method according to claim 4, characterized in that The heat exchange device is used to perform heat exchange on the purified desodium brine and desorbed water, wherein the temperature of the desodium brine after heat exchange is controlled to be 18°C-35°C, and the temperature of the desorbed water after heat exchange is controlled to be 30°C-45°C; The feed in the adsorption treatment process is the sodium-free brine after heat exchange, wherein the feed flow rate is 2.6 to 7.5 BV / h; the feed in the washing treatment process is pure water, wherein the feed flow rate is 1.5 to 4.5 BV / h; the feed in the desorption treatment process is pure water after heat exchange, wherein the feed flow rate is 1.5 to 9 BV / h; the feed in the replacement treatment process is the purified sodium-free brine, wherein the feed flow rate is 0.8 to 3 BV / h. The effluent with a conductivity range of 0 to 100 μs / cm after replacement is sent to a water collecting tank to produce pure water.

6. The method according to claim 1, characterized in that The step 3) is performed by a membrane separation device, an ion adsorption tower and an MVR device, wherein the membrane separation device includes a nanofiltration device and a reverse osmosis device; wherein the operating pressure of the nanofiltration device is 1.0 to 4.0 MPa, the operating pressure of the reverse osmosis device is 2.5 to 6.0 MPa, and the concentration ratio of the MVR device is 2 to 6.

7. The method according to claim 6, characterized in that The ion adsorption tower adopts fixed bed adsorption, and the filler in the ion adsorption tower is at least one of chelating resin, boron removal resin, potassium removal resin and zeolite material.

8. The method according to claim 1, characterized in that The step 4) specifically includes: performing soda ash preparation treatment, lithium precipitation reaction treatment, washing treatment, and drying and demagnetization treatment on the lithium refined concentrate to obtain battery-grade lithium carbonate; Among them, the soda ash preparation process is carried out by a soda ash preparation device and a refining and separation device, the soda ash preparation device includes a soda ash feeder and a stirred reactor, and the refining and separation device is a plate and frame filter press; the lithium precipitation reaction process is carried out by an insulated stirred reactor; the washing process is carried out by an insulated stirred reactor and a centrifuge; the drying and demagnetization process is carried out by a drying device and a demagnetization device.

9. The method according to claim 8, characterized in that In the soda ash preparation process, pure water is used to dissolve soda ash at a dissolution temperature of 35° C. to 80° C. After stirring and dissolving, a 40% by mass caustic soda solution or liquid caustic soda is added in an amount of 0.5% to 5% of the soda ash amount, and stirring is continued for 10 to 20 minutes. The soda ash is filtered through the plate and frame filter press to obtain a refined soda ash solution, wherein the concentration of the refined soda ash solution is 20% to 32%; During the lithium precipitation reaction treatment process, the lithium refined concentrate and the soda ash refined liquid are fed into the heat-insulated stirring reactor for reaction at a reaction temperature of 75°C to 95°C and a stirring rate of 45 to 240 r / min. After the feeding is completed, stirring is continued for 5 to 15 minutes, and the reaction slurry is ultrasonicated. After the stirring is completed, ultrasonication is continued for 5 to 15 minutes, and the ultrasonic frequency range is 10 to 200 kHz. After the ultrasonication is completed, the reaction slurry is kept warm and aged for 10 to 45 minutes to obtain lithium carbonate slurry; In the washing process, the crude lithium carbonate product obtained from the lithium carbonate slurry after solid-liquid separation is subjected to two-stage countercurrent washing and separation to obtain a battery-grade lithium carbonate wet product, wherein the washing temperature is 75° C. to 95° C., the washing time is 10 to 30 minutes, and the solid-liquid ratio is 1:1.2 to 1:5; During the drying and demagnetization treatment process, the battery-grade lithium carbonate wet product is subjected to air flow drying or flash drying, and then demagnetized by a demagnetizer to obtain a battery-grade lithium carbonate product.

10. The method according to claim 1, characterized in that The method further comprises: transporting the lithium extraction tail liquid obtained in step 2) to an enrichment tank for concentration treatment so as to be used for other production.

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