Method for extracting lithium from salt lake brine

Abstract

The present application relates to a kind of high yield method for extracting lithium from salt lake brine, specifically including using lithium extraction adsorbent to absorb lithium in salt lake brine, then eluting, desorbing, obtaining lithium-containing desorption solution, then concentrating lithium-containing desorption solution, obtaining lithium-containing concentrated solution;Lithium phosphate can be prepared by adding phosphate-containing reagent to lithium-containing desorption solution or concentrated solution and controlling reaction temperature and pH value.The lithium yield is high during the preparation process of the method, and the method is simple, and the lithium phosphate obtained can be used to prepare battery material lithium iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of lithium extraction from salt lakes, and more particularly to a method for extracting lithium from salt lake brine with high yield. Background Technology

[0002] Lithium and its compounds are widely used in batteries, medicine, aerospace, chemicals, and national defense due to their excellent properties, playing a vital role in economic development and being hailed as the "new energy of the 21st century." Lithium resources mainly come from lithium ore and salt lake brines, with salt lake brines having the highest lithium content, accounting for 66% of the world's lithium reserves. my country is a major lithium resource country, ranking among the world's largest in terms of reserves. Among them, the salt lake lithium resources in Qinghai and Tibet account for more than 85% of my country's total reserves.

[0003] Lithium extraction from salt lake brine is a simple, low-cost, and environmentally friendly process that meets market demand. Currently, research on lithium extraction primarily focuses on salt lake brine. However, most existing technologies involve obtaining a lithium-rich solution from the brine, then precipitating lithium using sodium carbonate solution or by introducing CO2 under alkaline conditions to obtain lithium carbonate. These precipitation techniques result in lithium concentrations in the mother liquor exceeding 1 g / L, and lithium losses during precipitation can reach over 15%. CN109019642A discloses a method for extracting lithium carbonate from salt lake brine, but this invention has a low lithium carbonate recovery rate, between 40% and 52%. CN104828846A discloses a method for purifying and separating mixed lithium carbonate salts using high-temperature brine, but this invention also has a low lithium carbonate yield, around 50%.

[0004] CN110357055A discloses a method for extracting lithium from salt lake brine and preparing lithium phosphate, as well as its applications. The method described in this invention achieves a lithium extraction rate of >94% from salt lake brine. However, the above invention is limited by the brine grade and is only applicable to brine with a lithium concentration of 2-5 g / L. This type of brine is prepared by placing underground brine in salt fields and sun-drying it for more than 3 years, which is a long process. Removing calcium and magnesium ions from the brine with oxalic acid not only requires a large amount of chemicals, which is detrimental to environmental protection, but also generates a large amount of precipitate that carries lithium ions, resulting in excessive lithium loss.

[0005] Therefore, developing a high-yield, environmentally friendly lithium extraction technology from salt lakes that is not limited by the type and grade of brine is of great significance to the new energy field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for high-yield lithium extraction from salt lake brine, comprising using a lithium-extraction adsorbent to adsorb lithium in the salt lake brine, followed by rinsing and desorption to obtain a lithium-containing desorbent, and then concentrating the lithium-containing desorbent to obtain a lithium-containing concentrate; lithium phosphate can be prepared by adding a phosphate-containing agent to the lithium-containing desorbent or concentrate and controlling the reaction temperature and pH value.

[0007] A method for lithium extraction from salt lake brine includes the following steps:

[0008] Step 1: The brine is passed through an adsorbent to adsorb lithium, and then eluted to obtain a lithium-containing eluent.

[0009] Step 2: Add phosphate to the lithium-containing eluent to carry out the lithium precipitation reaction. After separation, the resulting precipitate is lithium phosphate.

[0010] In step 1, the lithium concentration in the brine is 0.02–5.0 g / L, and the adsorbent is at least one of aluminum salt adsorbent, titanium adsorbent, or manganese adsorbent; the lithium concentration in the lithium-containing eluent is 0.4–12.0 g / L.

[0011] In step 1, the brine is made from chloride-type salt lake brine, magnesium sulfate subtype salt lake brine, carbonate-type salt lake brine, deep underground brine, etc.

[0012] In step 2, the lithium concentration in the lithium-containing eluent is 0.4–12.0 g / L; when the lithium concentration in the lithium-containing eluent is 0.4–1.5 g / L, it needs to be concentrated before being sent to the precipitation reaction.

[0013] The concentration process described herein is one or a combination of several of the following: reverse osmosis membrane, forward osmosis membrane, electrodialysis, and evaporation.

[0014] Phosphate solutions can be one or more combinations of phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0015] The amount of phosphate used is calculated based on a phosphate to lithium ion molar ratio of 1:3, and phosphate can be used in excess of 3 to 15 wt%.

[0016] The pH value during the precipitation reaction can be controlled above 9.0, preferably 10.0 to 14.0.

[0017] pH value is achieved by adding one or more of the following: sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0018] The precipitate is separated by centrifugation, sedimentation or filtration, and the separated precipitate is dried.

[0019] The filtration method refers to first filtering through a ceramic membrane, and then filtering the ceramic membrane concentrate through a plate and frame filter. The pore size of the ceramic membrane is 10-500 nm. After filtration through the ceramic membrane, the surface is cleaned by cross-flow of acid solution at a cross-flow velocity of 1-10 m / s.

[0020] The cross-flow cleaning time is calculated using the following steps:

[0021] Step S1: Obtain the particle size differential distribution data of iron phosphate under different reaction conditions, and then obtain the pore size differential distribution data of different ceramic membranes.

[0022] Step S2 involves concentrating precipitated ferric phosphate suspensions with different particle size distributions through ceramic membranes with different pore size distributions under different cross-flow velocities. After concentration, the ceramic membranes are rinsed and cleaned with different cross-flow rinsing times, and the flux recovery rate under different rinsing times is calculated.

[0023] Step S3: For each set of experimental results in step S2, iterate through the particle size values ​​on the particle size differential distribution data, and obtain the particle size value d smaller than the current particle size value at each iteration. pi The area S of the curve integral pi (i = 1...n), and simultaneously obtain pore sizes greater than d from the pore size differential distribution data. di The area S of the curve integral di , where d di =d pi +δ, where δ is a parameter; calculate the sum of areas S i =S pi +S di After all traversals are completed, the sum of the areas S is obtained. i Maximum value S in a vector max ;

[0024] S4. Based on the data obtained in step S3, fit the following formula. Where N refers to the membrane flux recovery rate, t is the cross-flow cleaning time, and a and b are parameters;

[0025] S5, perform ceramic membrane concentration treatment for new iron phosphate precipitation, and take N'=α×N as the target recovery rate of the membrane cleaning process, where α is a parameter, and substitute it into equation (1) to calculate the optimal cleaning time.

[0026] α is taken as 0.9-0.95, and δ is taken as 30-50nm.

[0027] A lithium extraction device from salt lake brine, comprising:

[0028] Adsorbent tank, used for adsorbing lithium from brine;

[0029] A salt concentration device, connected to the adsorbent tank, is used to concentrate the eluent from the adsorbent tank.

[0030] The reactor, connected to the concentration side of the salt concentration unit, is used to carry out a lithium precipitation reaction on the concentrated feed liquid;

[0031] The phosphate addition tank and the alkali addition tank are connected to the reactor respectively, and are used to add phosphate and alkali to the reactor;

[0032] A solid-liquid separation device, connected to a reactor, is used to separate the generated precipitate into solid and liquid components.

[0033] The solid-liquid separation device is one or a combination of centrifuges, sedimentation tanks, and filters.

[0034] The solid-liquid separation device includes a ceramic membrane and a plate and frame filter connected in sequence.

[0035] It also includes: a dryer, connected to the solid-liquid separation device, used to dry the separated solids.

[0036] It also includes: an eluent addition tank, connected to the adsorbent tank, used for eluting the adsorbent.

[0037] The salt concentration device is one or more combinations of reverse osmosis membrane, forward osmosis membrane, electrodialysis, and evaporation device.

[0038] The average pore size of the ceramic membrane ranges from 20 to 500 nm.

[0039] Beneficial effects

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention has a wider range of applications and is almost not limited by the type and grade of brine. It can be applied to brine with lithium concentration of 0.02 to 5.0 g / L, such as chloride-type salt lake brine, magnesium sulfate subtype salt lake brine, carbonate-type salt lake brine, and deep underground brine. It can be brine directly extracted from underground or the surface, or brine that has been evaporated and concentrated to precipitate salt.

[0042] (2) During the lithium precipitation process, the lithium recovery rate is high, ranging from 93.0% to 99.5%.

[0043] (3) The preparation process described in this invention is simple to operate, low in cost, and does not require the consumption of a large amount of chemical reagents, and has no environmental hazards.

[0044] (4) In the process of recovering lithium phosphate, the present invention uses a ceramic membrane for filtration and recovery. The cleaning time parameter of the ceramic membrane can be calculated by a prediction method. The predicted cleaning time value can effectively save unnecessary parameter exploration process in the membrane cleaning process. Attached Figure Description

[0045] Figure 1 This is a flowchart of a method for high-yield lithium extraction from salt lake brine.

[0046] Figure 2 This is a diagram of a lithium extraction apparatus.

[0047] Figure 3 These are the particle size distribution of iron phosphate and the pore size distribution of the ceramic membrane.

[0048] Figure 4 This is a correlation analysis chart between predicted and calculated values.

[0049] Figure 5 This is a comparison of flux recovery rates under different cleaning conditions.

[0050] The components include: 1. Adsorbent tank; 2. Eluent addition tank; 3. Salt concentration device; 4. Reactor; 5. Phosphate addition tank; 6. Alkali addition tank; 7. Solid-liquid separation device; 8. Ceramic membrane; 9. Plate and frame filter; and 10. Dryer. Detailed Implementation

[0051] The purpose of this invention is to extract lithium from lithium-containing brine. The lithium-containing brine used as the processing raw material can be chloride-type salt lake brine, magnesium sulfate subtype salt lake brine, carbonate-type salt lake brine, deep underground brine, etc. It can be extracted directly from underground or the surface, or it can be brine that has been evaporated and concentrated to precipitate salt. The lithium concentration in the salt lake brine is 0.02 to 5.0 g / L.

[0052] To achieve the above objectives, the steps of the present invention are detailed below:

[0053] Step (1): The brine from the salt lake is fed into a device containing a lithium extraction adsorbent for adsorption. After adsorption, the lithium extraction adsorbent is rinsed and desorbed, and the lithium-containing desorbed liquid is collected.

[0054] Step (2): The lithium-containing desorbed solution is sent to a concentration device for concentration to obtain a lithium-containing concentrate;

[0055] Step (3): The lithium-containing desorption solution or lithium-containing concentrate is sent into the lithium precipitation device, a phosphate solution is added, and the reaction pH and reaction temperature are controlled. The reaction precipitate is collected as lithium phosphate.

[0056] In step (1), optionally, the lithium extraction adsorbent can be at least one of aluminum salt adsorbent, titanium adsorbent or manganese adsorbent.

[0057] Optionally, the lithium concentration in the lithium-containing desorption solution is 0.4–12.0 g / L; wherein, the lithium-containing desorption solution with a lithium concentration of 0.4–1.5 g / L is sent to a concentration device; the lithium-containing desorption solution with a lithium concentration of 1.5–12.0 g / L can be sent to a concentration device or directly sent to a lithium precipitation device.

[0058] In step (2), optionally, the concentration device can be one or more combinations of reverse osmosis membrane, forward osmosis membrane, electrodialysis, and evaporation device.

[0059] Optionally, the lithium concentration in the lithium-containing concentrate is 1.5 to 20.0 g / L.

[0060] Optionally, the phosphate-containing solution may be one or more combinations of phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0061] The concentration of the phosphate-containing solution is 15–50 wt%.

[0062] More preferably, the concentration of the phosphate-containing solution is 25–40 wt%.

[0063] The amount of phosphate-containing solution used is calculated based on a phosphate to lithium ion molar ratio of 1:3, and phosphate can be in excess by 3 to 15 wt%.

[0064] More preferably, the phosphate group may be in excess by 5-10 wt%.

[0065] Optionally, the pH value can be controlled above 9.0.

[0066] Further preferably, the pH value can be controlled between 10.0 and 14.0.

[0067] Optionally, the pH control is achieved by adding one or more of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0068] Optionally, the reaction temperature is controlled between 30 and 100°C.

[0069] Further preferably, the reaction temperature is controlled at 60–90°C.

[0070] Optionally, the lithium yield during the lithium precipitation process is between 93.0% and 99.5%.

[0071] Optionally, in step (3), the collection of the reaction precipitate can be achieved through centrifugation, sedimentation, membrane separation, etc., preferably using a ceramic membrane for separation. The concentrated solution from the ceramic membrane can be filtered through a plate and frame filter to obtain wet material. After drying, the purity of the lithium phosphate of the present invention is not less than 90%.

[0072] Further optimization involves using acid to cross-flow clean the surface of the ceramic membrane channels after concentration to restore membrane flux.

[0073] Further optimization revealed that the optimal cleaning time for the ceramic membrane cross-flow was calculated using the following steps:

[0074] Step S1 involves obtaining the differential particle size distribution data of ferric phosphate under different reaction conditions, and then obtaining the differential pore size distribution data of different ceramic membranes. The particle size distribution data can be obtained from the suspension after the precipitation reaction using a laser particle size analyzer. For the precipitation process of ferric phosphate, different reaction conditions will result in precipitates with varying particle size distributions. Typically, most particles are between 30-50 nm in size, but some particles are very small, such as those between 10-15 nm. The pore size distribution of the ceramic membrane can be detected using the bubble pressure method. While ceramic membranes have a narrow pore size distribution, they still contain some larger pores. For example, a ceramic membrane with an average pore size of 50 nm may have pores of 100 nm or even a few of 150 nm on its surface. If small-diameter precipitated particles penetrate into the larger pores, they can cause pore blockage. During the cross-flow cleaning process, these blockage particles are not easily removed by the scouring of the membrane surface. They can only be slowly removed from the pores by allowing some outward permeation through the membrane surface over a longer period of time. This results in ceramic membranes with excessive pore blockage requiring longer cleaning times.

[0075] Step S2 involves concentrating the precipitated ferric phosphate suspension with different particle size distributions through a ceramic membrane with different pore size distributions. The concentration process is carried out under different cross-flow velocities. After concentration, the ceramic membrane is rinsed and cleaned with different cross-flow rinsing times, and the flux recovery rate under different rinsing durations is calculated. The purpose of this step is to obtain initial accumulated data on the cleaning effect of the ceramic membrane under different precipitated particle parameters. Typically, the flux recovery rate is a percentage, but it rarely reaches 100%, but is close to this value, such as around 90%.

[0076] Step S3: For each set of experimental results in step S2, iterate through the particle size values ​​on the particle size differential distribution data, and obtain the particle size value d smaller than the current particle size value at each iteration. pi The area S of the curve integral pi (i = 1...n), and simultaneously obtain pore sizes greater than d from the pore size differential distribution data. di The area S of the curve integral di , where d di =d pi +δ, where δ is a parameter; calculate the sum of areas S i =S pi +S di After all traversals are completed, the sum of the areas S is obtained. i Maximum value S in a vector max ;like Figure 3As shown, the left side displays the particle size distribution. At the cutting line (i.e., the currently traversed numerical point), the integral area of ​​the curves smaller than the particle size represents the proportion of particles smaller than this current particle size. These smaller particles are more likely to clog the membrane pores, causing membrane blockage; while... Figure 3 The right side shows the pore size distribution of the ceramic membrane; the dicing line represents d. di The location of membrane pore size is usually determined by the overlap of particles on the membrane surface. Even if the pore size is slightly larger than the particle size, the accumulation of particles will prevent pore blockage. Therefore, when evaluating pore blockage, a certain margin can be appropriately relaxed (δ in the above formula). For example, if the particle size being traversed is 30 nm, taking δ = 20 nm allows us to examine the proportion of large pores with a diameter greater than 50 nm. During each traversal, two integral areas are obtained, representing the proportion of small particles and large pores, respectively. When the sum of these two integral areas is maximized, it means that small particles and large pores achieve the best match. This also represents the extent to which small particles can enter larger pores under the current particle size / distribution characteristics. Furthermore, it indicates the proportion of pores occupied by small particles during concentration under these conditions, which affects the membrane cleaning effect.

[0077] S4. Based on the data obtained in step S3, fit the following formula. Where N refers to the membrane flux recovery rate, t is the cross-flow cleaning time, and a and b are parameters; the magnitude of the proportional parameter in S3 is inversely proportional to the membrane cleaning recovery rate, and the cleaning recovery rate has a marginal effect with the cleaning time. Therefore, the relationship between the recovery rate and the integral area and the cleaning time can be constructed.

[0078] S5, perform a new ferric phosphate precipitate ceramic membrane concentration treatment, and take N' = α × N as the target recovery rate for the membrane cleaning process, where α is a parameter that can be taken as 0.9-0.95. Substitute these values ​​into the above formula to calculate the optimal cleaning time. In this step, a 100% recovery rate is usually not achieved during membrane cleaning. Therefore, when α = 0.9-0.9, the set cleaning objective can be considered achieved, and cleaning can be stopped. The cleaning time at this point is the final estimated value.

[0079] Based on the above methods, the device used in this patent is as follows: Figure 2 As shown, it includes:

[0080] Adsorbent tank 1 is used for adsorbing lithium from brine;

[0081] Salt concentration device 3 is connected to adsorbent tank 1 and is used to concentrate the eluent from adsorbent tank 1.

[0082] Reactor 4 is connected to the concentration side of salt concentration device 3 and is used to carry out lithium precipitation reaction on the concentrated liquid.

[0083] Phosphate addition tank 5 and alkali addition tank 6 are respectively connected to reactor 4 and are used to add phosphate and alkali to reactor 4;

[0084] Solid-liquid separation device 7 is connected to reactor 4 and is used to separate the generated precipitate into solid and liquid components.

[0085] The solid-liquid separation device 7 is one or a combination of centrifuge, sedimentation tank, and filter.

[0086] The solid-liquid separation device 7 includes a ceramic membrane 8 and a plate and frame filter 9 connected in sequence.

[0087] It also includes a dryer 10, connected to the solid-liquid separation device 7, for drying the separated solids.

[0088] It also includes: an eluent addition tank 2, which is connected to the adsorbent tank 1 and is used to elute the adsorbent.

[0089] The salt concentration device 3 is one or more combinations of reverse osmosis membrane, forward osmosis membrane, electrodialysis, and evaporation device.

[0090] The average pore size of the ceramic membrane 8 is in the range of 20-500 nm.

[0091] Example 1

[0092] The brine used in this embodiment is a chloride-type brine, containing sodium, calcium, lithium, boron, and chloride ions at concentrations of 89.0 g / L, 20.5 g / L, 0.02 g / L, 0.21 g / L, and 199.5 g / L, respectively. Figure 1 The diagram shows the flow of this embodiment. The method of this embodiment includes the following steps:

[0093] The brine was fed into a device containing an aluminum-based adsorbent for adsorption. After adsorption, the brine was washed and desorbed in sequence, and the lithium-containing desorbed liquid was collected with a lithium concentration of 0.4 g / L.

[0094] The lithium-containing desorption solution was fed into a reverse osmosis membrane unit for concentration to obtain a lithium-containing concentrate with a lithium concentration of 1.5 g / L.

[0095] The lithium-containing concentrate was fed into a lithium precipitation device and heated to 60°C. A 25 wt% phosphoric acid solution was added to ensure a 5 wt% excess of phosphate. The pH was adjusted to 10.0 with sodium hydroxide solution. After concentration using a 50 μm ceramic membrane, the solution was filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 90.1%.

[0096] The lithium recovery rate during the lithium precipitation process was 93.3%.

[0097] Example 2

[0098] This embodiment uses a magnesium sulfate subtype salt lake brine, in which the concentrations of the main ions sodium, magnesium, lithium, boron, chloride, and sulfate are 91.0 g / L, 30.9 g / L, 0.3 g / L, 0.35 g / L, 190.4 g / L, and 25.1 g / L, respectively. The specific operating steps are as follows:

[0099] The brine was fed into a device containing a manganese-based adsorbent for adsorption. After adsorption, the brine was washed and desorbed in sequence, and the lithium-containing desorbed liquid was collected with a lithium concentration of 0.8 g / L.

[0100] The lithium-containing desorption solution was sequentially fed into a reverse osmosis membrane, a forward osmosis membrane, an electrodialysis unit, and an evaporation unit for concentration to obtain a lithium-containing concentrate with a lithium concentration of 20.1 g / L.

[0101] The lithium-containing concentrate was fed into a lithium precipitation device and heated to 90°C. A 40 wt% disodium hydrogen phosphate solution was added to ensure a 10 wt% excess of phosphate. The pH was adjusted to 14.0 with sodium carbonate solution. After concentration using a 50 μm ceramic membrane, the solution was filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 98.3%.

[0102] The lithium recovery rate during the lithium precipitation process was 99.5%.

[0103] Example 3

[0104] This embodiment uses a carbonate-type salt lake brine, in which the concentrations of the main ions sodium, magnesium, lithium, boron, chloride, carbonate, and bicarbonate are 39.0 g / L, 1.3 g / L, 0.15 g / L, 0.75 g / L, 58 g / L, 2.1 g / L, and 1.4 g / L, respectively. The specific operating steps are as follows:

[0105] The brine was fed into a device containing a titanium-based adsorbent for adsorption. After adsorption, the brine was washed and desorbed in sequence, and the lithium-containing desorbed solution was collected with a lithium concentration of 12.2 g / L.

[0106] The lithium-containing desorption solution was directly fed into a lithium precipitation device and heated to 80°C. A 30 wt% sodium dihydrogen phosphate solution was added to ensure an 8 wt% excess of phosphate. The pH was adjusted to 12.0 with potassium hydroxide solution. After concentration using a 50 μm ceramic membrane, the solution was filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 98.5%.

[0107] The lithium recovery rate during the lithium precipitation process was 99.2%.

[0108] Example 4

[0109] This embodiment uses a brine that has been evaporated and concentrated to precipitate salt. The concentrations of the main ions magnesium, sodium, lithium, boron, and chloride ions in the brine are 118 g / L, 2.0 g / L, 5.0 g / L, 3.0 g / L, and 300 g / L, respectively. The specific operating steps are as follows:

[0110] The brine was fed into a device containing an aluminum-based adsorbent for adsorption. After adsorption, the brine was washed and desorbed in sequence, and the lithium-containing desorbed liquid was collected with a lithium concentration of 1.2 g / L.

[0111] The lithium-containing desorption solution was sequentially fed into a reverse osmosis membrane and an electrodialysis unit for concentration to obtain a lithium-containing concentrate with a lithium concentration of 10.3 g / L.

[0112] The lithium-containing desorption solution was directly fed into a lithium precipitation device and heated to 70°C. A sodium phosphate solution with a mass fraction of 35 wt% was added to ensure an excess of 7 wt% phosphate. The pH was adjusted to 13.0 with potassium carbonate solution. After concentration using a 50 μm ceramic membrane, the solution was filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 93.1%.

[0113] The lithium recovery rate during the lithium precipitation process was 99.0%.

[0114] Example 5

[0115] The difference between this embodiment and Embodiment 3 is that the brine is fed into a device containing a manganese-based adsorbent for adsorption. After adsorption, rinsing and desorption are performed sequentially, and the lithium-containing desorbate is collected with a lithium concentration of 6.2 g / L. The lithium recovery rate during the lithium precipitation process is 98.3%.

[0116] All other conditions are exactly the same as in Example 3.

[0117] Example 6

[0118] The difference between this embodiment and Embodiment 5 is that the lithium-containing desorption solution is directly fed into the lithium precipitation apparatus and heated to 80°C. A mixed solution of dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and potassium phosphate (30 wt%) is added to ensure an 8 wt% excess of phosphate. The pH is adjusted to 11.0 with ammonia solution. After concentration using a 50 μm ceramic membrane, the solution is filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 98.1%. The lithium yield during the precipitation process is 98.0%.

[0119] All other conditions are exactly the same as in Example 5.

[0120] Example 7

[0121] The difference between this embodiment and Example 4 is that the lithium concentration of the brine used, after evaporation and concentration to precipitate salts, is 2.1 g / L. The lithium-containing desorption solution is directly fed into a lithium precipitation apparatus and heated to 80°C. A mixed solution of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate (30 wt%) is added to ensure a 6 wt% excess of phosphate. The pH is adjusted to 11.0 using a mixed solution of ammonium carbonate and ammonium bicarbonate. After concentration using a 50 μm ceramic membrane, the solution is filtered through a plate and frame filter, washed with hot water, and dried to obtain a white powder, which is lithium phosphate with a purity of 93.1%. The lithium yield during the precipitation process is 98.5%.

[0122] All other conditions are exactly the same as in Example 4.

[0123] Comparative Example 1

[0124] The difference between this embodiment and Example 1 is that a sodium carbonate solution with a mass fraction of 25 wt% is added to the lithium-containing concentrate to obtain lithium carbonate with a purity of 90.1%, wherein the lithium yield during the lithium precipitation process is 35.0%.

[0125] All other conditions are exactly the same as in Example 1.

[0126] Comparative Example 2

[0127] The difference between this embodiment and Example 2 is that a sodium carbonate solution with a mass fraction of 25 wt% was added to the lithium-containing concentrate to obtain lithium carbonate with a purity of 95.6%, wherein the lithium yield during the lithium precipitation process was 80.2%.

[0128] All other conditions are exactly the same as in Example 2.

[0129] The main technical indicators of each embodiment of the present invention are shown in Table 1.

[0130] Table 1

[0131]

[0132]

[0133] Example 8

[0134] To optimize the cleaning of ceramic membranes used for precipitation filtration in the process routes shown in Examples 1 above, based on the parameters of Example 1, lithium phosphate precipitation was carried out at different phosphate addition amounts (3-15 wt% excess) and different precipitation reaction temperatures (60-90℃), and the particle size distribution in the suspension of the precipitates under different conditions was measured. Simultaneously, ceramic membranes with an average pore size of 220-200 nm were used for filtration during the solid-liquid separation process, and the pore size distribution data of different specifications of ceramic membranes were measured. After filtration, cross-flow cleaning with 0.5 wt% HCl hydrochloric acid solution was performed. The membrane surface flow rate was set at 3 m / s, and the cleaning time was set to 10-100 min. Under different conditions (particle size distribution, pore size distribution, cleaning time), the obtained experimental data were fitted according to Equation (1) to obtain the expression for flux recovery rate, which in this example is:

[0135]

[0136] A comparison between the flux recovery rate calculated using the above formula and the actual recovery rate is shown below. Figure 4 As shown, the correlation coefficient R = 0.9581, indicating that the predicted value and the calculated value are in good agreement.

[0137] The lithium phosphate precipitation reaction and filtration separation were repeated under the conditions of Example 1, followed by cleaning at 10-minute intervals. The membrane flux recovery rate was calculated after each cleaning. The optimal cleaning time, calculated according to Equation 1, was 43.7 minutes. The measured flux recovery rates at different times are shown below. Figure 5 As shown, after 40-50 minutes, the flux recovery rate is relatively stable and no longer shows significant improvement, proving that this method can quickly predict the optimal membrane cleaning conditions.

Claims

1. A method for lithium extraction from salt lake brine, characterized in that, Includes the following steps: Step 1: The brine is passed through an adsorbent to adsorb lithium, and then eluted to obtain a lithium-containing eluent. Step 2: Add phosphate to the lithium-containing eluent to carry out the lithium precipitation reaction. After separation, the precipitate is obtained as lithium phosphate. In step 1, the lithium concentration in the brine is 0.02–5.0 g / L, and the adsorbent is at least one of aluminum salt adsorbent, titanium adsorbent, or manganese adsorbent; the lithium concentration in the lithium-containing eluent is 0.4–12.0 g / L; the brine refers to chloride-type salt lake brine, magnesium sulfate subtype salt lake brine, or carbonate-type salt lake brine. The separation is achieved by filtration, and the resulting precipitate is then dried. The filtration method refers to first filtering through a ceramic membrane, and then filtering the ceramic membrane concentrate through a plate and frame filter. The pore size of the ceramic membrane is 10-500 nm. After filtration through the ceramic membrane, the surface is cleaned by cross-flow of acid solution at a cross-flow velocity of 1-10 m / s. The cross-flow cleaning time is calculated using the following steps: Step S1: Obtain the particle size differential distribution data of lithium phosphate under different reaction conditions, and then obtain the pore size differential distribution data of different ceramic membranes. Step S2 involves concentrating the precipitated lithium phosphate suspension with different particle size differential distribution data through a ceramic membrane with different pore size differential distribution data. The concentration process is carried out under different cross-flow velocity conditions. After concentration, the ceramic membrane is rinsed and cleaned with different cross-flow cleaning times, and the flux recovery rate under different cleaning times is calculated. Step S3: For each set of experimental results in step S2, iterate through the particle size values ​​on the particle size differential distribution data and obtain the area S of the curve integral that is smaller than the current particle size value dpi at each iteration. pi , i = 1...n, and simultaneously obtain apertures greater than d from the aperture differential distribution data. di The area S of the curve integral di , where d di =d pi +δ, where δ is a parameter; calculate the sum of areas S i =S pi +S di After all traversals are completed, the sum of the areas S is obtained. i Maximum value S in a vector max ; S4. Based on the data obtained in step S3, fit the following formula. ； Where N refers to the membrane flux recovery rate, t is the cross-flow cleaning time, and a and b are parameters; S5, perform new lithium phosphate precipitation ceramic membrane concentration treatment, and take N'=α×N as the target recovery rate of the membrane cleaning process, where α is a parameter, and substitute it into equation (1) to calculate the optimal cleaning time; α is taken as 0.9-0.95, and δ is taken as 30-50nm.

2. The method for lithium extraction from salt lake brine according to claim 1, characterized in that, In step 2, the lithium concentration in the lithium-containing eluent is 0.4–12.0 g / L; when the lithium concentration in the lithium-containing eluent is 0.4–1.5 g / L, it needs to be concentrated before being sent to the precipitation reaction.

3. The method for lithium extraction from salt lake brine according to claim 2, characterized in that, The concentration process described herein is one or a combination of several of the following: reverse osmosis membrane, forward osmosis membrane, electrodialysis, and evaporation.

4. The method for lithium extraction from salt lake brine according to claim 1, characterized in that, Phosphate is a solution of one or more combinations of phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate. The amount of phosphate used is calculated based on a phosphate to lithium ion molar ratio of 1:3, with an excess of 3-15 wt% phosphate.

5. The method for lithium extraction from salt lake brine according to claim 1, characterized in that, The pH value should be controlled above 9.0 during the precipitation reaction; pH value is achieved by adding one or more of the following: sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, ammonia, ammonium carbonate, and ammonium bicarbonate.

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