Method and integrated system for lithium enrichment and boron removal from salt lake brine

Abstract

The application discloses a method and integrated system for enriching lithium and removing boron from salt lake brine, and belongs to the technical field of lithium resource purification. The method comprises the following steps: S1. primary electrodialysis of the salt lake brine to obtain a primary low-boron lithium concentrate and a primary boron-rich dilute solution; S2. reverse osmosis of the primary boron-rich dilute solution to obtain a reverse osmosis concentrate; S3. nanofiltration of the reverse osmosis concentrate to remove boron and obtain a nanofiltration lithium concentrate; S4. mixing of the nanofiltration lithium concentrate and hydrochloric acid and then secondary electrodialysis to obtain a secondary low-boron lithium concentrate; the secondary low-boron lithium concentrate is returned to step S1 and mixed with the salt lake brine; and the water inlet of the primary electrodialysis and the secondary electrodialysis is controlled to have a pH of 7-12. The method provided by the application effectively improves the enrichment and purification efficiency of lithium and the removal efficiency of boron, and is simple and easy to implement. The application further provides an integrated system for implementing the above method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium resource purification, in particular to a method and integrated system for lithium enrichment and boron removal from salt lake brine. BACKGROUND

[0002] Lithium resources mainly exist in salt lake brine, lithium ore and seawater, among which lithium in salt lake brine accounts for more than half of all lithium resources. China is relatively rich in lithium resources, with a known reserve of about 5.1 million tons, of which nearly 80% exists in brine. The cost of producing lithium from brine is usually 30%-50% lower than that of producing lithium from lithium ore, so extracting lithium from salt lake brine is currently the most important way to obtain lithium resources. In addition to lithium resources, salt lake brine also contains a large amount of boron impurities; however, existing lithium extraction technologies cannot achieve efficient removal and selective separation of boron in salt lake brine, and the residual boron in the brine will affect the purity and quality of the recovered lithium product. Therefore, it is urgent to develop an efficient boron removal technology suitable for salt lake brine; the core of this technology is to simultaneously achieve lithium enrichment and boron removal.

[0003] Existing boron removal technologies usually include nanofiltration and adsorption, but these methods still have many shortcomings. For example, in the traditional nanofiltration process, boron elements still exist in the nanofiltration membrane permeate because boron acid molecules / ions can also pass through the nanofiltration membrane, and the residual boron concentration is high, so the boron removal effect is poor. In the adsorption boron removal process, the resin quickly adsorbs and saturates due to the high boron content in the brine, so resin regeneration needs to be performed frequently, which increases the acid consumption in the elution process, resulting in high processing cost and a large amount of acidic wastewater.

[0004] Single reverse osmosis is a common technology for lithium enrichment, but it cannot remove boron. Single nanofiltration can only remove boron but cannot enrich lithium. The combination of the two still has the problems of low lithium concentration in the lithium recovery liquid and poor boron removal effect, and the recovered lithium product cannot meet the requirements of battery grade.

[0005] In summary, in the current technology, it is difficult to simultaneously achieve lithium enrichment and boron removal, and the purity of the obtained lithium-containing product is insufficient and the cost is high. SUMMARY

[0006] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a method for lithium enrichment and boron removal from salt lake brine, which can effectively improve the lithium concentration and purity and reduce the boron concentration in the obtained first low-boron lithium concentrated liquid, and the process is simple, low-cost and easy to implement.

[0007] The present application also provides an integrated system for implementing the above-mentioned method.

[0008] According to the embodiment of the first aspect of the present application, a method for enriching lithium and removing boron from salt lake brine is provided, the method comprising the following steps:

[0009] S1. performing primary electrodialysis on the salt lake brine to obtain a primary low-boron lithium concentrate and a primary boron-rich diluate;

[0010] S2. performing reverse osmosis on the primary boron-rich diluate to obtain a reverse osmosis concentrate;

[0011] S3. performing nanofiltration to remove boron from the reverse osmosis concentrate to obtain a nanofiltration lithium concentrate;

[0012] S4. performing secondary electrodialysis on the nanofiltration lithium concentrate to obtain a secondary low-boron lithium concentrate;

[0013] The secondary low-boron lithium concentrate is returned to step S1 and mixed with the salt lake brine.

[0014] The water inlet of the primary electrodialysis and the secondary electrodialysis controls the pH to be 7-12.

[0015] The method according to the embodiment of the present application has at least the following beneficial effects:

[0016] (1) In the conventional technology, the boron removal process mostly needs to be performed under acidic conditions first, and then under alkaline conditions, so the conventional technology needs to consume a large amount of acid and alkali, and the cost is high.

[0017] The method provided by the present application is performed within the pH range of 7-12, basically does not need to be adjusted in pH, or the adjustment range is very small, the amount of acid and alkali reagents consumed is also significantly reduced, and the cost is more economical.

[0018] (2) In principle, under acidic conditions, boron mainly exists in the form of boric acid molecules (B(OH)3), and under alkaline conditions, boron mainly exists in the form of charged borate (B(OH)4 - ). Since the boric acid molecule has a neutral charge, it tends to diffuse into the ion exchange membrane, and as for the negatively charged borate, due to the good counterion selectivity of the ion exchange membrane, it tends not to diffuse into the cation exchange membrane (CEM), but can be transmitted through the anion exchange membrane (AEM).

[0019] Based on the above principle, the neutral charge boric acid can be transmitted through two types of membranes (CEM and AEM), while the negatively charged borate can only be transmitted through one type of membrane (i.e. AEM), so in the ideal case, the effective membrane surface area available for boric acid is twice that of borate; in another aspect, boric acid can pass through two types of membranes, Li + can also pass through the cation exchange membrane, so when boron exists in the form of boric acid, it cannot be separated from Li +Effective separation is achieved, and when boron exists in the form of borate, it can be separated from lithium ions.

[0020] In addition, due to the large amount of Cl in the salt lake brine - , and Cl - The migration rate is higher than that of B(OH)4 - Several orders of magnitude higher, therefore Cl - The presence of B(OH)4 inhibits - Transmitted via AEM. Based on this, B(OH)4 - Only a small amount passes through AEM, while a large amount is retained, meaning it is difficult to pass through any ion exchange membrane, while Li + They are separated, which further improves the separation efficiency of lithium and boron.

[0021] This invention cleverly utilizes this characteristic to achieve highly efficient boron removal (effective separation of lithium and boron) by adjusting the pH of the first-stage electrodialysis to alkaline, which is about 10% higher than that of traditional acidic electrodialysis.

[0022] (3) Since the current efficiency of low-concentration electrodialysis is low, the present invention improves the current efficiency of the electrodialysis process and the Li yield by adding a first-stage reverse osmosis process between the two-stage electrodialysis to preliminarily concentrate the feed solution.

[0023] (4) Due to the negatively charged property of nanofiltration membranes under alkaline conditions, they can effectively intercept negatively charged B(OH)4. - B4O5(OH)4 2- To remove boron-containing substances, this invention incorporates a nanofiltration boron removal process before the second-stage electrodialysis, which can effectively improve the overall boron removal efficiency.

[0024] (5) The preparation method provided by the present invention includes the reflux of the secondary low boron lithium concentrate, which can recover and use lithium in the salt lake brine as much as possible and avoid resource waste.

[0025] In summary, the method provided by this invention can significantly improve the enrichment efficiency of lithium and the removal efficiency of boron by setting parameters such as steps and pH, and also reduce costs.

[0026] According to some embodiments of the present invention, step S1 further includes ultrafiltration of the salt lake brine before the primary electrodialysis. This removes impurities such as silt from the salt lake brine.

[0027] According to some embodiments of the present invention, in step S1, the lithium concentration in the salt lake brine is 3-6 g / L. For example, it can be about 4 g / L or about 5 g / L.

[0028] According to some embodiments of the present invention, in step S1, the boron concentration in the salt lake brine is 0.5–3 g / L. Specifically, it can be about 1 g / L or about 2 g / L.

[0029] According to some embodiments of the present invention, in step S1, the brine of the salt lake further includes sodium; the concentration of sodium is 5-6 g / L. For example, it can be about 5.5 g / L.

[0030] According to some embodiments of the present invention, in step S1, the brine of the salt lake further includes potassium; the concentration of potassium is 0.5 to 2 g / L. For example, it can be about 1 g / L or about 1.5 g / L.

[0031] According to some embodiments of the present invention, in step S1, the brine of the salt lake further includes chlorine; the concentration of chlorine is 25-45 g / L. For example, it can be about 30 g / L or about 35 g / L.

[0032] According to some embodiments of the present invention, in step S1, the pH of the influent for the primary electrodialysis is 7 to 10. Specifically, it can be approximately 8 or 9. If the pH of the brine is not within the range required by the present invention, the pH can be adjusted using acid-base adjusters such as sodium hydroxide or hydrogen chloride.

[0033] According to some embodiments of the present invention, in step S1, the endpoint of the first-stage electrodialysis is that the conductivity of the first-stage boron-rich desalination solution is 19 mS / cm to 21 mS / cm. For example, it can be approximately 20 mS / cm.

[0034] According to some embodiments of the present invention, in step S1, the pH of the primary boron-rich desalination solution is 9.5 to 10.5.

[0035] According to some embodiments of the present invention, in step S1, the lithium concentration in the primary low-boron lithium concentrate is ≥10 g / L. Specifically, it can be about 12 g / L, 13 g / L, 14 g / L, or about 15 g / L.

[0036] According to some embodiments of the present invention, in step S1, the boron concentration in the primary low-boron lithium concentrate is ≤0.05 g / L. Specifically, it can be about 0.04 g / L, 0.03 g / L, or about 0.02 g / L.

[0037] According to some embodiments of the present invention, in step S1, the lithium concentration in the primary boron-rich desalination solution is ≤2 g / L. Specifically, it can be approximately 1.5 g / L, 1 g / L, or approximately 0.5 g / L.

[0038] According to some embodiments of the present invention, in step S1, the concentration of boron in the primary boron-rich desalination solution is ≥0.8 g / L. For example, it can be about 1.0 g / L, 1.2 g / L, 1.5 g / L, or about 2 g / L.

[0039] According to some embodiments of the present invention, in step S1, the temperature at which the first-stage electrodialysis is performed is 25–35°C. For example, it can be approximately 30°C.

[0040] According to some embodiments of the present invention, in step S2, the pH of the feed water for reverse osmosis is 3 to 10. In actual production, this pH does not require additional adjustment; usually, simply limiting the pH of the feed water for the first-stage electrodialysis is sufficient to obtain a first-stage boron-rich desalination solution within that pH range.

[0041] According to some embodiments of the present invention, in step S2, the operating pressure of the reverse osmosis is 0.5 to 2.5 MPa. For example, it can be about 1.0 MPa or about 2.0 MPa.

[0042] According to some embodiments of the present invention, in step S2, the concentration factor of the reverse osmosis is 1.5 to 2.5 times. For example, it can be about 2.0 times.

[0043] According to some embodiments of the present invention, in step S2, the lithium concentration in the reverse osmosis concentrate is 1.0 to 3.0 g / L. Specifically, it can be about 1.5 g / L, 2.0 g / L, or about 2.5 g / L.

[0044] According to some embodiments of the present invention, in step S2, the boron concentration in the reverse osmosis concentrate is 1.6 to 2.4 g / L. Specifically, it can be about 1.8 g / L, 2.0 g / L, or about 2.2 g / L.

[0045] According to some embodiments of the present invention, in step S3, the pH of the feed water for nanofiltration boron removal is 3 to 10. In actual production, this pH does not require additional adjustment; usually, simply limiting the pH of the feed water for the first-stage electrodialysis is sufficient to obtain a reverse osmosis concentrate within that pH range.

[0046] According to some embodiments of the present invention, in step S3, the operating pressure for nanofiltration to remove boron is 0.5 to 2.5 MPa. Specifically, it can be about 1.0 MPa or about 2.0 MPa.

[0047] According to some embodiments of the present invention, in step S3, the lithium concentration in the nanofiltration lithium concentrate is 3 to 7 g / L. For example, it can be about 4 g / L, 5 g / L, or about 6 g / L.

[0048] According to some embodiments of the present invention, in step S3, the boron concentration in the nanofiltration lithium concentrate is 0.3 to 2 g / L. For example, it can be about 0.5 g / L, 1 g / L, or about 1.5 g / L.

[0049] According to some embodiments of the present invention, in step S4, the pH of the feed water (i.e., the mixture) for the secondary electrodialysis is 7 to 10. Specifically, it can be about 8 or 9.

[0050] According to some embodiments of the present invention, in step S4, before performing the secondary electrodialysis, the nanofiltration lithium concentrate and hydrochloric acid are mixed. That is, the secondary electrodialysis is performed using a mixture of the nanofiltration lithium concentrate and the hydrochloric acid. Due to the large amount of Cl... - It has been separated from the system along with the primary low-boron lithium concentrate. The main anion present in the nanofiltration lithium concentrate is B(OH)4. - Therefore, in order to maintain the electroneutrality of the solution, during the migration of Li... + At the same time, B(OH)4 - It will also migrate into the concentrate, reducing boron removal efficiency. Based on this principle, this invention adds HCl to the secondary electrodialysis process to introduce Cl. - This inhibits B(OH)4 - The membrane permeate, thereby improving the boron removal efficiency of secondary electrodialysis. Furthermore, the introduced H... + It can also mix with hydroxide ions in water to form water. Compared with other exogenous chloride ions, adding HCl can avoid cation contamination and improve the purity of the concentrated lithium.

[0051] According to some embodiments of the present invention, the chloride ion concentration in the mixture of the nanofiltration lithium concentrate and the hydrochloric acid is 15–35 g / L. Specifically, it can be about 20 g / L, 25 g / L, or about 30 g / L. This improves the separation efficiency of lithium and boron.

[0052] According to some embodiments of the present invention, in the method, the overall lithium yield is ≥99%. Specifically, it can be approximately 99.5%.

[0053] According to some embodiments of the present invention, the overall boron removal efficiency in the method is ≥90%. Specifically, it can be about 91%, 92%, 93%, 94%, or about 95%.

[0054] According to some embodiments of the present invention, in step S4, the current efficiency of the secondary electrodialysis is ≥75%. Specifically, it can be about 75.2%, 75.4%, or about 75.5%.

[0055] According to an embodiment of a second aspect of the present invention, an integrated system for the method is provided, the integrated system comprising: sequentially connected components.

[0056] A primary electrodialysis unit, comprising a primary electrodialysis unit inlet, a primary concentration chamber, a primary dilute chamber, and a primary electrode solution tank;

[0057] A reverse osmosis unit, comprising a reverse osmosis unit inlet, a reverse osmosis unit concentrate outlet, and a reverse osmosis unit desalination outlet; the reverse osmosis unit inlet is connected to the primary desalination chamber.

[0058] The nanofiltration unit includes a nanofiltration unit inlet, a nanofiltration unit concentrate outlet, and a nanofiltration unit desalination outlet; the nanofiltration unit inlet and the reverse osmosis unit concentrate outlet are connected.

[0059] A secondary electrodialysis unit, comprising a secondary electrodialysis unit inlet, a secondary concentrate tank, a secondary dilute tank, and a secondary electrode liquid tank; the secondary electrodialysis unit inlet and the nanofiltration unit concentrate outlet are connected;

[0060] The secondary concentration chamber is connected to the inlet of the primary electrodialysis unit.

[0061] Since the integrated system adopts all the technical solutions of the methods in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0062] According to some embodiments of the present invention, the primary concentration chamber tank is provided with a primary concentration chamber outlet.

[0063] According to some embodiments of the present invention, the primary desalination chamber tank is provided with a primary desalination chamber outlet.

[0064] According to some embodiments of the present invention, the primary electrodialysis unit includes a tank, a positive electrode and a negative electrode disposed on the tank wall, and a cation exchange membrane and an anion exchange membrane disposed between the positive electrode and the negative electrode and disposed alternately.

[0065] The space formed by the positive electrode and the cation exchange membrane closest to the positive electrode, and the space formed by the negative electrode and the anion exchange membrane closest to the negative electrode, constitute the primary electrode liquid tank;

[0066] The space formed by the cation exchange membrane and the anion exchange membrane constitutes the primary concentration chamber and / or the primary dilute chamber. Specifically,

[0067] The distance between the cation exchange membrane constituting the primary concentration chamber and the positive electrode is less than the distance between the anion exchange membrane and the positive electrode.

[0068] The distance between the cation exchange membrane constituting the primary dilute chamber and the positive electrode is greater than the distance between the anion exchange membrane and the positive electrode.

[0069] The primary dilute chamber and the primary concentrate chamber are alternately arranged.

[0070] According to some embodiments of the present invention, the ratio of the total volume of the primary desalination chamber to the total volume of the primary concentration chamber is 7 to 9:1. Specifically, it can be approximately 8:1. This provides sufficient space to accommodate the primary boron-rich desalination solution and enables preliminary lithium concentration.

[0071] According to some embodiments of the present invention, in the primary electrodialysis unit, there is circulating flow between the components, and the flow rates of the circulating flow are relatively uniform. This avoids pressure differences between the components affecting the electrodialysis process.

[0072] At the beginning of operation of the primary electrodialysis unit:

[0073] In the primary electrodialysis unit, the electrode tank is filled with an electrolyte solution to enhance conductivity.

[0074] The brine from the salt lake is injected into the primary freshwater chamber tank;

[0075] The primary concentration chamber is filled with deionized water;

[0076] As the positive and negative electrodes become conductive, lithium ions in the primary dilute chamber pass through the cation exchange membrane into the primary concentrate chamber and are enriched; chloride ions and other ions pass through the anion exchange membrane into the primary concentrate chamber and are enriched; because the migration rate of chloride ions is much greater than that of boron-containing B(OH)4... - Ions, therefore boron remains enriched in the primary desalination chamber.

[0077] According to some embodiments of the present invention, the electrolyte solution added to the electrode tank comprises an aqueous sodium sulfate solution. The concentration of the aqueous sodium sulfate solution is 2-5 wt%. For example, it can be about 3 wt% or about 4 wt%.

[0078] According to some embodiments of the present invention, the structure of the secondary electrodialysis unit is the same as that of the primary electrodialysis unit. In actual production, its overall or partial dimensions can be adjusted as needed to adapt to production requirements.

[0079] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0080] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0081] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0082] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0083] Figure 1 This is a schematic diagram of the integrated system provided in Embodiment 1 of the present invention.

[0084] Figure 2 This is a detailed structural diagram of the primary electrodialysis unit in the integrated system provided in Embodiment 1 of the present invention.

[0085] Figure 3 This is a schematic diagram of the working principle of the primary electrodialysis unit in the integrated system provided in Embodiment 1 of the present invention.

[0086] Figure label:

[0087] The system includes a primary electrodialysis unit 100, a primary electrodialysis unit inlet 110, a primary desalination chamber outlet 120, a primary concentration chamber outlet 130, an anion exchange membrane 140, a cation exchange membrane 150, a negative electrode 160, and a positive electrode 170.

[0088] Reverse osmosis unit 200, reverse osmosis unit inlet 210, reverse osmosis unit concentrate outlet 220, reverse osmosis unit desalination outlet 230;

[0089] Nanofiltration unit 300, nanofiltration unit inlet 310, nanofiltration unit concentrate outlet 320, nanofiltration unit desalination outlet 330;

[0090] The secondary electrodialysis unit 400, the secondary electrodialysis unit inlet 410, the secondary desalination chamber outlet 420, and the secondary concentration chamber outlet 430 are all included. Detailed Implementation

[0091] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0092] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0093] Example 1

[0094] refer to Figures 1-2 This example provides an integrated system for a method of removing boron from lithium-rich brine in salt lakes, specifically comprising the following sequentially connected components:

[0095] The primary electrodialysis unit 100 includes a primary electrodialysis unit inlet 110, a primary concentration chamber tank, a primary dilute chamber tank, and a primary electrode liquid tank; the primary concentration chamber tank is provided with a primary concentration chamber outlet 130; the primary dilute chamber tank is provided with a primary dilute chamber outlet 120.

[0096] The primary electrodialysis unit 100 includes a tank, a positive electrode 170 and a negative electrode 160 disposed on the tank wall, and a cation exchange membrane 150 and an anion exchange membrane 140 disposed between the positive electrode 170 and the negative electrode 160 and alternately arranged.

[0097] The space formed by the positive electrode 170 and the nearest cation exchange membrane 150, and the space formed by the negative electrode 160 and the nearest anion exchange membrane 140, constitute the primary electrode liquid tank.

[0098] The space formed by the cation exchange membrane 150 and the anion exchange membrane 140 is a primary concentration chamber and / or a primary dilute chamber, as referenced. Figure 2 The outlets 130 and 120 of the first-stage concentrate chamber and the first-stage desalination chamber are set in alternating positions.

[0099] The reverse osmosis unit 200 includes a reverse osmosis unit inlet 210, a reverse osmosis unit concentrate outlet 220, and a reverse osmosis unit desalination outlet 230; the reverse osmosis unit inlet 210 is connected to the primary desalination chamber tank via the primary desalination chamber outlet 120.

[0100] Nanofiltration unit 300 includes nanofiltration unit inlet 310, nanofiltration unit concentrate outlet 320 and nanofiltration unit desalination outlet 330; nanofiltration unit inlet 310 and reverse osmosis unit concentrate outlet 220 are connected.

[0101] The secondary electrodialysis unit 400 includes a secondary electrodialysis unit inlet 410 (connected to the nanofiltration unit concentrate outlet 320), a secondary concentration chamber tank, a secondary dilute chamber tank, and a secondary electrode liquid tank; the secondary concentration chamber tank is provided with a secondary concentration chamber outlet 430; the secondary dilute chamber tank is provided with a secondary dilute chamber outlet 420; overall, the structure of the secondary electrodialysis unit 400 is similar to that of the primary electrodialysis unit 100.

[0102] The secondary concentration chamber is connected to the secondary concentration chamber outlet 430 and the primary electrodialysis unit inlet 110.

[0103] Example 2

[0104] This example uses the integrated system provided in Example 1 to provide a method for removing boron from lithium-rich brine in salt lakes. The specific steps are as follows:

[0105] S1. After ultrafiltration (removing solids and other impurities), the salt lake brine is subjected to primary electrodialysis through a primary electrodialysis unit 100 to obtain a primary low-boron lithium concentrate and a primary boron-rich desalination solution.

[0106] The salt lake brine used in this example is a simulated solution, specifically prepared from sodium chloride, lithium chloride, potassium chloride and sodium borate, and its pH is adjusted to 10 with NaOH; the salt lake brine contains 5 g / L of Li, 1 g / L of B, 5.5 g / L of Na, 1 g / L of K, and approximately 30 g / L of Cl.

[0107] During the first-stage electrodialysis process, the first-stage electrode tank is filled with a 4 wt% sodium sulfate solution; the first-stage dilute chamber tank is filled with the brine from the salt lake prepared in this step; and the first-stage concentrate chamber tank contains deionized water. The volume ratio of the first-stage dilute chamber tank to the first-stage concentrate chamber tank is 8:1. During operation, the feed liquids in the first-stage dilute chamber tank, the first-stage concentrate chamber tank, and the first-stage electrode tank of the first-stage electrodialysis unit 100 circulate through independent pipes, and the liquid flow rate in each compartment remains consistent to avoid pressure differences between them that could cause osmosis.

[0108] Mechanism reference during primary electrodialysis Figure 3 As shown, in the specific operation process, cations and anions selectively pass through the cation exchange membrane and anion exchange membrane, ultimately leading to the enrichment of lithium and boron in the concentration chamber and dilute chamber, respectively. X in the figure... - This refers to anions with a negative charge. In actual production, considering the migration rates of different types of anions, halide ions are preferred to be used here.

[0109] During the first-stage electrodialysis process, the temperature is controlled at 30–35℃ (the temperature may fluctuate slightly during operation, but as long as it is controlled within the above range, it will not significantly affect the first-stage electrodialysis process). The pH value of the solution in the first-stage dilute chamber is monitored in real time using a pH meter and stabilized within the range of 9.5–10.5 (fluctuations may occur during operation, but controlling it within the above range will not affect the test results). The conductivity of the first-stage dilute chamber is tested using a conductivity meter, and electrodialysis is stopped when the conductivity reaches 20 mS / cm.

[0110] In this example, a first-stage boron-rich desalination solution is produced from the first-stage desalination tank; a first-stage low-boron lithium concentrate is produced from the first-stage concentration tank and discharged from the integrated system through the first-stage concentration tank outlet 130; wherein, the first-stage low-boron lithium concentrate has a Li content of 10-15 g / L and a B content of 0.03-0.05 g / L (specific values ​​are shown in Table 1); the first-stage boron-rich desalination solution has a Li content of 1.5 g / L and a B content of 1.1 g / L.

[0111] S2. The primary boron-rich desalination solution obtained in step S1 enters the reverse osmosis unit 200 through the primary desalination chamber outlet 120 and the reverse osmosis unit inlet 210 for reverse osmosis concentration by 2 times. During the reverse osmosis process, the operating pressure is 2.5 MPa, and the pH of the primary boron-rich desalination solution is around 10. The reverse osmosis concentrate obtained in this step has a Li content of 2.9 g / L and a B content of 2.3 g / L.

[0112] The wastewater generated in this step is discharged from the integrated system through the freshwater outlet 230 of the reverse osmosis unit.

[0113] S3. The reverse osmosis concentrate obtained in step S2 is transferred to the nanofiltration unit 300 via the reverse osmosis unit concentrate outlet 220 and the nanofiltration unit inlet 310 for nanofiltration boron removal, yielding a nanofiltration lithium concentrate. The obtained nanofiltration lithium concentrate contains 3.3 g / L of Li and 1.4 g / L of B. The nanofiltration effluent obtained in this step is discharged from the integrated system via the nanofiltration unit freshwater outlet 330.

[0114] The operating pressure for nanofiltration boron removal is 2.5 MPa, and the pH of the reverse osmosis concentrate is around 10.

[0115] S4. The pH of the nanofiltration lithium concentrate obtained in step S3 is adjusted to 7 with HCl. The chloride ion concentration of the resulting mixture is 20 g / L. The concentrate is then transferred to the secondary electrodialysis unit 400 via the nanofiltration unit concentrate outlet 320 and the secondary electrodialysis unit inlet 410 for secondary electrodialysis to obtain a secondary low-boron lithium concentrate and a secondary boron-rich desalination solution. The secondary low-boron lithium concentrate is returned to step S1 and mixed with the brine of the salt lake. The secondary boron-rich desalination solution is discharged from the system via the secondary desalination chamber outlet 420.

[0116] During the process, the pH of the secondary concentration chamber is maintained at around 7, and the other parameter control and operation steps are the same as those in the primary electrodialysis in step S1.

[0117] The composition of the intermediate liquid obtained in each step of this example is the composition after the integrated system has been running stably. The other embodiments and comparative examples are the same.

[0118] Example 3

[0119] This example uses the integrated system provided in Example 1 to provide a method for removing boron from lithium-rich brine in salt lakes. The specific steps are as follows:

[0120] S1. After ultrafiltration (removing solids and other impurities), the salt lake brine is subjected to primary electrodialysis through a primary electrodialysis unit 100 to obtain a primary low-boron lithium concentrate and a primary boron-rich desalination solution.

[0121] The salt lake brine used in this example is a simulated solution, specifically prepared from sodium chloride, lithium chloride, potassium chloride and sodium borate, and its pH is adjusted to 10 with NaOH; the salt lake brine contains 5 g / L of Li, 1 g / L of B, 5.5 g / L of Na, 1 g / L of K, and approximately 30 g / L of Cl.

[0122] During the first-stage electrodialysis process, the first-stage electrode tank is filled with a 4 wt% sodium sulfate solution; the first-stage dilute chamber tank is filled with the brine from the salt lake prepared in this step; and the first-stage concentrate chamber tank contains deionized water. The volume ratio of the first-stage dilute chamber tank to the first-stage concentrate chamber tank is 8:1. During operation, the feed liquids in the first-stage dilute chamber tank, the first-stage concentrate chamber tank, and the first-stage electrode tank of the first-stage electrodialysis unit 100 circulate through independent pipes, and the liquid flow rate in each compartment remains consistent to avoid pressure differences between them that could cause osmosis.

[0123] Mechanism reference during primary electrodialysis Figure 3 As shown, in the specific operation process, cations and anions selectively pass through the cation exchange membrane and anion exchange membrane, ultimately leading to the enrichment of lithium and boron in the concentration chamber and dilute chamber, respectively. X in the figure... - This refers to anions with a negative charge. In actual production, considering the migration rates of different types of anions, halide ions are preferred to be used here.

[0124] During the first-stage electrodialysis process, the temperature is controlled at 30–35℃ (the temperature may fluctuate slightly during operation, but as long as it is controlled within the above range, it will not significantly affect the first-stage electrodialysis process). The pH value of the solution in the first-stage dilute chamber is monitored in real time using a pH meter and stabilized within the range of 9.5–10.5 (fluctuations may occur during operation, but controlling it within the above range will not affect the test results). The conductivity of the first-stage dilute chamber is tested using a conductivity meter, and electrodialysis is stopped when the conductivity reaches 20 mS / cm.

[0125] In this example, a first-stage boron-rich desalination solution is produced from the first-stage desalination tank; a first-stage low-boron lithium concentrate is produced from the first-stage concentration tank and discharged from the integrated system through the first-stage concentration tank outlet 130; wherein, the first-stage low-boron lithium concentrate has a Li content of 10-15 g / L and a B content of 0.03-0.05 g / L (specific values ​​are shown in Table 1); the first-stage boron-rich desalination solution has a Li content of 1.5 g / L and a B content of 1.1 g / L.

[0126] S2. The primary boron-rich desalination solution obtained in step S1 enters the reverse osmosis unit 200 through the primary desalination chamber outlet 120 and the reverse osmosis unit inlet 210 for reverse osmosis concentration by 2 times. During the reverse osmosis process, the operating pressure is 2.5 MPa, and the pH of the primary boron-rich desalination solution is around 10. The reverse osmosis concentrate obtained in this step has a Li content of 2.9 g / L and a B content of 2.3 g / L.

[0127] The wastewater generated in this step is discharged from the integrated system through the freshwater outlet 230 of the reverse osmosis unit.

[0128] S3. The reverse osmosis concentrate obtained in step S2 is transferred to the nanofiltration unit 300 via the reverse osmosis unit concentrate outlet 220 and the nanofiltration unit inlet 310 for nanofiltration boron removal, yielding a nanofiltration lithium concentrate. The obtained nanofiltration lithium concentrate contains 3.4 g / L of Li and 1.2 g / L of B. The nanofiltration interceptor obtained in this step is discharged from the integrated system via the nanofiltration unit freshwater outlet 330.

[0129] The operating pressure for nanofiltration boron removal is 2.5 MPa, and the pH of the reverse osmosis concentrate is around 10.

[0130] S4. Maintain the pH of the nanofiltration lithium concentrate obtained in step S3 at 10, and then transfer it to the secondary electrodialysis unit 400 for secondary electrodialysis via the nanofiltration unit concentrate outlet 320 and the secondary electrodialysis unit inlet 410 to obtain secondary low-boron lithium concentrate and secondary boron-rich desalination solution; wherein, the secondary low-boron lithium concentrate is returned to step S1 and mixed with the salt lake brine; the secondary boron-rich desalination solution is discharged from the system via the secondary desalination chamber outlet 420.

[0131] During the process, the pH of the secondary concentration chamber is maintained at around 10, and the other parameter control and operation steps are the same as those in the primary electrodialysis in step S1.

[0132] Comparative Example 1

[0133] This example provides a method for removing boron from lithium-rich brine in salt lakes. The specific steps differ from those in Example 2 in that:

[0134] Steps S2 and S3 are excluded; the primary boron-rich desalination solution obtained in step S1 is directly subjected to secondary electrodialysis.

[0135] Comparative Example 2

[0136] This example provides a method for removing boron from lithium-rich brine in salt lakes. The specific steps differ from those in Example 2 in that:

[0137] (1) In step S1, the pH of the salt lake brine is adjusted to 3 by HCl; other parameters are the same as in Example 2.

[0138] The resulting low-boron lithium concentrate contains 10–15 g / L of Li and 0.1–0.5 g / L of B, while the primary boron-rich desalination solution contains 0.5–2 g / L of Li and 0.6–1.0 g / L of B.

[0139] (2) Steps S2 and S3 are not included; the primary boron-rich desalination solution obtained in step S1 is directly subjected to secondary electrodialysis, and the pH of the influent for secondary electrodialysis is controlled to be around 3.

[0140] Comparative Example 3

[0141] This example provides a method for removing boron from lithium-rich brine in salt lakes. The specific steps differ from those in Example 3 in that:

[0142] The default steps S2 and S3 are the default nanofiltration boron removal and reverse osmosis concentration steps; the primary boron-rich desalination solution obtained in step S1 is directly transferred to the secondary electrodialysis unit for secondary electrodialysis treatment.

[0143] Comparative Example 4

[0144] This example provides a method for removing boron from lithium-rich brine in salt lakes. The specific steps differ from those in Example 2 in that:

[0145] Step S3 is not included, i.e., the nanofiltration boron removal step is omitted, and the reverse osmosis concentrate obtained in step S2 is directly subjected to secondary electrodialysis treatment.

[0146] Comparative Example 5

[0147] This example provides a method for removing boron from lithium-rich brine in salt lakes. The specific steps differ from those in Example 2 in that:

[0148] Reverse the order of steps S2 and S3;

[0149] That is, the primary boron-rich desalination solution obtained in step S1 is directly subjected to nanofiltration to remove boron; and the resulting nanofiltration lithium concentrate is subjected to reverse osmosis concentration treatment, and then the resulting reverse osmosis concentrate is transferred to the secondary electrodialysis unit for secondary electrodialysis treatment.

[0150] In this example, the obtained reverse osmosis concentrate contains 2.8 g / L of Li and 1.7 g / L of B.

[0151] Test case

[0152] This example tested the lithium and boron content in the primary low-boron lithium concentrate obtained from the examples and comparative examples, as well as the corresponding lithium yield and boron removal rate. The current efficiency of the secondary electrodialysis was also calculated using the Faraday formula. The data were obtained from ICP-AES testing, and the specific calculation formula is as follows:

[0153] Lithium yield:

[0154] Li yield = (C t *V t ) / (C0*V0)×100%;

[0155] Among them, C t C0 (g / L) and V are the lithium concentrations in the final and initial solutions of the first-stage concentration chamber, respectively; t V0(L) and V0(L) are the final and initial solution volumes in the first-stage concentration chamber, respectively.

[0156] Boron removal rate:

[0157] B removal rate = (C t *V t ) / (C0*V0)×100%;

[0158] Among them, C t C0 (g / L) and V are the boron concentrations in the final and initial solutions of the first-stage concentration chamber, respectively; t V0(L) and V0(L) are the final and initial solution volumes in the first-stage concentration chamber, respectively.

[0159] Current efficiency:

[0160]

[0161] Where, n t,Li n 0,Li (mol) represent the Li in the concentration chamber (which can be used to calculate the current efficiency of primary and secondary electrodialysis). +The final and initial molar numbers; F is the Faraday constant; N is the number of membrane pairs; t(s) is the electrodialysis concentration time; I(A) is the operating current.

[0162] The specific test results are shown in Tables 1-3. The data in Tables 1-2 are the overall results after the entire cycle in the examples or comparative examples. For example, the concentration in Table 1 refers to the concentration of the first-stage low-boron lithium concentrate obtained after multiple cycles, or it can be the value after the integrated system has been running stably.

[0163] Table 1. Lithium and boron content in primary low-boron lithium concentrate

[0164] Element (g / L) Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Li 12.28 12.07 12.10 11.26 11.51 12.12 11.98 B 0.03 0.05 0.07 0.19 0.1 0.05 0.06

[0165] Table 2 Overall Lithium Yield and Boron Removal Rate

[0166] Element (%) Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Li 99.32 98.63 98.70 91.62 91.89 99.14 98.07 B 93.06 88.29 88.51 84.14 87.18 89.43 89.25

[0167] Table 3. Current efficiency of secondary electrodialysis

[0168] (％) Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 η (Li) 75.46 73.14 70.62 57.38 66.71 75.14 74.73

[0169] The results in the table above show that the lithium content and boron removal rate of the primary low-boron lithium concentrate prepared in Example 2 are significantly higher than those of the comparative examples. Comparing Examples 2 and 3, it is evident that the addition of HCl at the inlet of the second-stage electrodialysis in Example 2 is equivalent to introducing exogenous chloride ions, which has a significant positive impact on the subsequent separation of lithium and boron. Comparing Examples 2 and Comparative Examples 2-5, it is clear that adjusting the order of steps in the lithium-rich boron removal method, or omitting a step, will significantly reduce the lithium yield, boron removal efficiency, and the current efficiency of the second-stage electrodialysis. Comparing Comparative Examples 1 and 3, it is evident that if exogenous chloride ions are added to the second-stage electrodialysis, the boron removal efficiency and lithium yield are higher.

[0170] Comparing the current efficiency results of the secondary electrodialysis in Table 3, it can be seen that the method steps and parameter design provided by the present invention are reasonable, especially the introduction of the reverse osmosis section, which increases the ion concentration of the feed water for the secondary electrodialysis and thus improves the current efficiency of electrodialysis.

[0171] In summary, the method provided by this invention, combined with the integrated system provided by this invention, can significantly improve the enrichment degree of lithium and the removal efficiency of boron. It has many advantages such as cost saving and simple operation, and is expected to be widely used in lithium extraction from salt lake brine.

[0172] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for removing boron from lithium-rich brine in salt lakes, characterized in that, The method includes the following steps: S1. The brine from the salt lake is subjected to primary electrodialysis to obtain a primary low-boron lithium concentrate and a primary boron-rich desalination solution; the brine from the salt lake has a lithium concentration of 3~6 g / L and a boron concentration of 0.5~3 g / L; the primary low-boron lithium concentrate has a lithium concentration ≥10 g / L and a boron concentration ≤0.05 g / L. S2. The first-stage boron-rich desalination solution is subjected to reverse osmosis to obtain a reverse osmosis concentrate; the lithium concentration in the reverse osmosis concentrate is 1.0~3.0 g / L, and the boron concentration is 1.6~2.4 g / L. S3. The reverse osmosis concentrate is subjected to nanofiltration to remove boron, yielding a nanofiltration lithium concentrate; the lithium concentration in the nanofiltration lithium concentrate is 3~7 g / L, and the boron concentration is 0.3~2 g / L; S4. The nanofiltration lithium concentrate and hydrochloric acid are mixed and subjected to secondary electrodialysis to obtain a secondary low-boron lithium concentrate; the chloride ion concentration in the mixture of the nanofiltration lithium concentrate and the hydrochloric acid is 15~35 g / L. The secondary low-boron lithium concentrate is returned to step S1 and mixed with the salt lake brine. The pH of the influent for both primary and secondary electrodialysis is controlled at 7-12.

2. The method according to claim 1, characterized in that, In step S1, the endpoint of the first-stage electrodialysis is when the conductivity of the first-stage boron-rich desalination solution is 19 mS / cm to 21 mS / cm.

3. The method according to claim 1, characterized in that, In step S2, the operating pressure of the reverse osmosis is 0.5~2.5MPa; and / or, in step S3, the operating pressure of the nanofiltration boron removal is 0.5~2.5MPa.

4. An integrated system for implementing the method as described in any one of claims 1 to 3, characterized in that, The integrated system comprises the following components connected in sequence: A primary electrodialysis unit, comprising a primary electrodialysis unit inlet, a tank, a positive electrode and a negative electrode disposed on the wall of the tank, and a cation exchange membrane and an anion exchange membrane disposed between the positive electrode and the negative electrode and disposed alternately. The space formed by the positive electrode and the cation exchange membrane closest to the positive electrode, and the space formed by the negative electrode and the anion exchange membrane closest to the negative electrode, constitute a primary electrode liquid tank; The space formed by the cation exchange membrane and the anion exchange membrane is a primary concentration chamber and / or a primary dilute chamber. A reverse osmosis unit, comprising a reverse osmosis unit inlet, a reverse osmosis unit concentrate outlet, and a reverse osmosis unit desalination outlet; the reverse osmosis unit inlet is connected to the primary desalination chamber. The nanofiltration unit includes a nanofiltration unit inlet, a nanofiltration unit concentrate outlet, and a nanofiltration unit desalination outlet; the nanofiltration unit inlet and the reverse osmosis unit concentrate outlet are connected. A secondary electrodialysis unit, comprising a secondary electrodialysis unit inlet, a secondary concentrate tank, a secondary dilute tank, and a secondary electrode liquid tank; the secondary electrodialysis unit inlet and the nanofiltration unit concentrate outlet are connected; The secondary concentration chamber is connected to the inlet of the primary electrodialysis unit.

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