Method for preparing lithium carbonate by coupling lithium extraction through electricity and lithium extraction through solar pond

Abstract

The invention discloses a method for preparing lithium carbonate by coupling electric lithium extraction with solar pond lithium extraction. The method comprises the following steps: salt lake brine enters an ultrafiltration device for purification treatment, and purified brine is obtained; the purified brine enters electric lithium extraction equipment, lithium extraction and lithium concentration are carried out at the same time under the action of an electric field, and lithium-poor brine and a lithium-rich solution are obtained; adding a saturated sodium carbonate solution into the lithium-rich solution, uniformly mixing, discharging into a solar pond for naturally evaporating, concentrating and precipitating lithium, and regularly harvesting lithium carbonate in the solar pond. The whole process of extraction, concentration and lithium precipitation of lithium in the salt lake brine can be realized by coupling an electric lithium extraction technology and the solar pond, the lithium carbonate production process flow is greatly shortened, and compared with the existing salt gradient solar pond process, the process has the advantages that the purity of lithium carbonate is improved by more than 25%, the yield of lithium carbonate is improved by more than 40%, and the capacity of a single pond is increased by more than one time; according to the process, the lithium extraction efficiency and the productivity of the salt gradient solar pond are greatly improved, and the process has a relatively good application prospect.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of lithium extraction from salt lakes, and specifically to a method for preparing lithium carbonate by coupling lithium extraction from electric lithium extraction with lithium extraction from solar ponds. Background Art

[0002] With the global push for clean energy and electric vehicle industries, the demand for lithium as a key raw material has risen sharply. Salt lake brine is one of the important sources of lithium, and more than half of the world's lithium resources are stored in salt lakes. Efficient salt lake lithium extraction technology can increase the supply of lithium, ensure the stable supply of lithium resources, and reduce the constraints on the development of related industries due to resource shortages.

[0003] At present, the technologies for extracting lithium from salt lake brine are mainly divided into solar pond-chemical precipitation method, ion exchange adsorption method, extraction method and membrane separation method.

[0004] Solar pond-chemical precipitation method for lithium extraction mainly relies on solar energy for heat supply or evaporation. The process has a long production cycle and a low comprehensive recovery rate of only about 60%, but it can recover a variety of useful elements at the same time, with a low comprehensive production cost, and is suitable for processing low Mg / Li salt lake brine resources. At the same time, this process has high requirements on the composition and lithium concentration of salt lake brine, and needs to be used in combination with specific conditions, and is not suitable for all salt lakes.

[0005] For salt lake brine with a high magnesium-to-lithium ratio, the main process route of the adsorption + membrane method is as follows: 1) reacting the adsorbent with the salt lake brine to adsorb the lithium ions therein; 2) eluting the lithium in the adsorbent with dilute hydrochloric acid, at which time the magnesium-to-lithium ratio of the eluate drops to about 5; 3) removing the magnesium ions in the eluate through a nanofiltration membrane, and then concentrating it through reverse osmosis to obtain a 4-5g / L lithium chloride solution; 4) adding sodium carbonate to the concentrated eluate to react and obtain lithium carbonate.

[0006] The core of the extraction method is the extractant. Its advantages are high lithium yield and low fresh water consumption, but it has many disadvantages, such as serious corrosion to equipment and pipelines, serious environmental pollution, and the introduction of organic matter that affects product quality. This technology is not suitable for areas with fragile ecological environment.

[0007] Salt lake membrane materials are mainly divided into the following categories according to the pore size range: 1) Ultrafiltration membrane (UF): mostly used in qualified liquid that has completed adsorption and analysis, by filtering suspended particles to reduce the possibility of subsequent nanofiltration membrane contamination and loss: 2) Nanofiltration membrane (NF): can achieve the separation of monovalent and divalent ions (such as the separation of magnesium ions and lithium ions), is a charged membrane that can selectively purify different substances, but when used for lithium extraction from old brine, due to the small flux, the old brine needs to be diluted first, resulting in a reduced concentration significance; 3) Reverse osmosis membrane (RO): can be used in the salt lake lithium extraction process to concentrate lithium solutions at the back end of the process.

[0008] The main problem with the current membrane separation method is that nanofiltration membranes can only separate monovalent and divalent cations, but not monovalent lithium and sodium, and require the assistance of other separation processes. The concentration rate of reverse osmosis membranes is limited, and the total dissolved solids (TDS) is generally up to 50,000-80,000 mg / L. Faced with salt lake brine with high salt content and complex composition, the application of reverse osmosis is limited.

[0009] Zabuye Salt Lake is a typical low Mg / Li salt lake, and the gradient solar pond lithium extraction process has been maturely applied in the salt lake for nearly 20 years. This process is a green and environmentally friendly technology. No chemical agents are added to the entire process, and it can be combined with on-site heat sources and cold sources to adapt to local conditions. However, the use of solar pond crystallization has a long production cycle, is highly dependent on the climate, and has large fluctuations in product quality.

[0010] CN202410065036.1 discloses a method for extracting lithium from carbonate salt lakes by adsorption-coupled salt gradient solar pools, comprising the following steps: loading a lithium ion adsorbent into a column, introducing carbonate salt lake raw brine into the adsorption column until adsorption is saturated, then introducing dilute hydrochloric acid to elute through the column, and collecting a desorption solution rich in lithium ions; the desorption solution is evaporated and concentrated to further increase the concentration of lithium ions in the solution, and then the solution enriched with lithium ions is introduced into the lower troposphere of the solar pool as brine for lithium carbonate crystallization, and lithium carbonate is collected. The invention uses a high-concentration lithium ion solution enriched with fiber-based adsorption materials as brine to directly inject it into the lower troposphere of the salt gradient solar pool, couples adsorption with salt gradient solar pool technology, and increases the amount of lithium carbonate precipitation by 22.73% and the crystallization rate of lithium carbonate by 50% compared with the traditional salt gradient solar pool process, greatly improving the efficiency and yield of lithium extraction in the traditional salt gradient solar pool. The core of this invention is to combine ion exchange adsorption with solar ponds, but both technologies have certain application limitations. Ion exchange adsorption requires the use of a large amount of hydrochloric acid and alkali solution, and the lithium concentration in the analytical solution is low. It still cannot overcome the disadvantage of the long cycle of solar ponds.

[0011] CN202210255577.1 discloses a membrane-based lithium extraction process from salt lakes, which specifically includes: low-temperature evaporation, salt separation treatment, membrane concentration and lithium precipitation treatment. In the salt separation treatment process, a combination of primary membrane separation, secondary membrane separation and tertiary membrane separation is adopted. In the membrane concentration process, a combination of primary membrane concentration, secondary membrane concentration and tertiary membrane concentration is adopted. Compared with traditional methods, the operating cost of lithium extraction using membrane method is lower, no expensive reagents or extractants are required, etc., and the production cost can be effectively saved by more than 40%. This invention uses membrane method to extract lithium, and its main characteristics are long process flow and low separation efficiency. Summary of the invention

[0012] To this end, an embodiment of the present invention provides a method for preparing lithium carbonate by coupling lithium extraction from electric lithium with lithium extraction from solar ponds, so as to solve the defects of the prior art such as long lithium extraction cycle and low production capacity.

[0013] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0014] A method for preparing lithium carbonate by coupling lithium extraction from a solar pond with lithium extraction from an electric lithium extraction system, the method comprising the following steps:

[0015] (1) The salt lake brine enters the ultrafiltration device for purification to obtain purified brine;

[0016] (2) The purified brine enters the lithium electroextraction equipment, and under the action of the electric field, lithium is extracted and concentrated simultaneously to obtain lithium-poor brine and lithium-rich solution;

[0017] (3) Add saturated sodium carbonate solution to the lithium-rich solution, mix well, and then discharge it to the solar pond for natural evaporation and concentration of lithium. The lithium carbonate in the solar pond is harvested regularly.

[0018] Furthermore, in step (1), the working conditions of the ultrafiltration device are: internal pressure immersion ultrafiltration, the membrane material is PVDF, the pore size is 30nm~100nm, the normal operating pressure is 0.1MPa~0.2MPa, and the designed flux is 10LMH~30LMH.

[0019] Furthermore, in step (2), the lithium electroextraction equipment comprises a lithium absorption chamber, a lithium discharge chamber and an anion exchange membrane, wherein the anion exchange membrane separates the lithium absorption chamber from the lithium discharge chamber, and the lithium absorption chamber and the lithium discharge chamber are respectively provided with electrode plates, the electrode plate in the lithium absorption chamber is connected to the negative electrode of the DC power supply, and the electrode plate in the lithium discharge chamber is connected to the positive electrode of the DC power supply;

[0020] The purified brine obtained in step (1) enters the lithium absorption chamber, and the receiving liquid enters the lithium discharge chamber. Under the action of the electric field, the lithium ions in the purified brine are embedded in the electrode plates, and the purified brine becomes lithium-poor brine. The electrode plates in the lithium discharge chamber release lithium and enter the receiving liquid to form a lithium-rich solution.

[0021] Furthermore, the active material of the electrode plate is lithium manganese oxide or lithium iron phosphate, and the lithium absorption capacity of the electrolytic plate is 10-30g / m 2 ;

[0022] The voltage of the DC power supply is 0.01V to 1.80V, and the working time is 5h to 24h;

[0023] The receiving solution is a lithium chloride aqueous solution or a sodium chloride aqueous solution with a mass concentration of 0.1% to 1%.

[0024] Furthermore, the lithium concentration of the lithium-poor brine is less than 200 mg / L, and the lithium concentration of the lithium-rich solution is greater than 5 g / L.

[0025] Furthermore, the method further comprises: discharging the lithium-poor brine and the lithium-rich solution, then filling the lithium absorption chamber and the lithium release chamber with water, and switching the positive and negative poles of the DC power supply, and carrying out the next round of lithium extraction and lithium concentration cycle under the action of the electric field.

[0026] The specific operation process is as follows: the purified brine obtained in step (1) enters the lithium discharge chamber, the receiving liquid enters the lithium absorption chamber, the electrode plate in the lithium discharge chamber is connected to the negative electrode of the DC power supply, and the electrode plate in the lithium absorption chamber is connected to the positive electrode of the DC power supply.

[0027] Furthermore, in step (3), the amount of sodium carbonate added is calculated based on the molar ratio of lithium to carbonate, Li + :CO3 2- The ratio is 1.2 to 2;

[0028] The conditions for natural evaporation concentration are: the crystallization pool is built in an outdoor open-air environment, the evaporation temperature is natural temperature, the temperature range is -30°C to 30°C, the daily average evaporation amount is 2mm to 25mm, and the solar pool evaporation time is 60 days to 180 days.

[0029] Furthermore, the salt lake brine comes from a lithium-rich carbonate salt lake.

[0030] Furthermore, the salt lake brine is derived from Zabuye Salt Lake.

[0031] The embodiments of the present invention have the following advantages:

[0032] The present invention combines lithium electrolysis with a solar pond (crystallization pond). The lithium electrolysis technology is first used to separate and concentrate the lithium in the salt lake brine to more than 5g / L, and then a certain amount of sodium carbonate is added as an auxiliary, and the solution is directly discharged to the solar pond (crystallization pond) for further concentration, precipitation and crystallization through natural evaporation to obtain a lithium concentrate with a purity of more than 75%.

[0033] The present invention directly uses the electrolithium extraction technology coupled with the solar pool to realize the whole process of lithium extraction, concentration and lithium precipitation in salt lake brine, greatly shortening the lithium carbonate production process. Compared with the existing salt gradient solar pool process, this process increases the purity of lithium carbonate by more than 25%, the lithium carbonate yield by more than 40%, and the single pool capacity by more than 1 times. This process greatly improves the lithium extraction efficiency and capacity of the salt gradient solar pool.

[0034] The core lithium extraction process of the present invention is electrolithium extraction, which relies on electric energy and does not require any auxiliary chemical agents. It is green, environmentally friendly, and has no secondary pollution. It has good monovalent cation selectivity (sodium-lithium ratio in lithium-rich solution is less than 3) and better monovalent and divalent cation selectivity. One process is used to simultaneously achieve the separation of lithium, sodium, and magnesium and the concentration of lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0036] Figure 1 A process flow chart of the present invention for preparing lithium carbonate by coupling lithium extraction from an electrolithium extraction process with a solar pond;

[0037] Figure 2 A schematic diagram of the structure of the lithium electrolysis equipment provided by the present invention;

[0038] Among them, 1-lithium absorption chamber; 2-lithium release chamber; 3-first electrode plate; 4-second electrode plate; 5-anion exchange membrane AEM. DETAILED DESCRIPTION

[0039] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] See also Figure 1 The present invention provides a method for preparing lithium carbonate by coupling lithium extraction from a solar pond with lithium extraction from an electric lithium extraction device, comprising the following steps:

[0041] (1) Ultrafiltration pretreatment

[0042] Salt lake brine contains suspended solid impurities such as silt, clay particles and some insoluble minerals. If these impurities are not removed, they will clog pipes, valves and equipment in the subsequent lithium extraction process or other chemical treatment processes, affecting the normal operation of the entire process.

[0043] In addition, the presence of some large molecular organic matter (such as humic acid, protein, etc.) and colloidal substances (such as iron hydroxide colloid, silica colloid, etc.) in salt lake brine will interfere with the lithium extraction process and affect the accuracy and efficiency of subsequent lithium extraction processes such as chemical precipitation.

[0044] The ultrafiltration membrane can effectively retain suspended solids with larger particle sizes and retain large molecular organic matter and colloidal substances on one side of the membrane, so that the brine passing through the membrane has good clarity, ensuring the smooth progress of subsequent processes, and at the same time helping to improve the purity and efficiency of lithium extraction.

[0045] In some specific embodiments, the working conditions of the ultrafiltration device are: internal pressure immersion ultrafiltration, the membrane material is PVDF, the pore size is 30nm~100nm, the normal operating pressure is 0.1MPa~0.2MPa, and the designed flux is 10LMH~30LMH.

[0046] (2) Lithium Electrolysis

[0047] The principle of lithium extraction technology is based on the electrosorption method of lithium extraction using LiMn2O4 or LiFePO4 as active materials. The lithium extraction method is a new technology based on electro-induced selective lithium extraction, which can selectively absorb / release Li under the action of an external potential. + Compared with other salt lake lithium extraction technologies, the electrolithium extraction method has the advantages of high automation, high lithium absorption, high lithium selectivity, simple raw brine pretreatment, low fresh water consumption, low energy consumption, no need to use chemical agents, and green environmental protection. In addition, in large-scale production, this technology can continuously produce lithium-rich solutions with high lithium concentration, low magnesium-to-lithium ratio, and low sodium-to-lithium ratio, which can greatly facilitate subsequent concentration and lithium precipitation operations.

[0048] See also Figure 2 The lithium electroextraction equipment used in the present invention includes a lithium absorption chamber 1, a lithium discharge chamber 2 and an anion exchange membrane AEM 5, and the AEM is used to separate the lithium absorption chamber from the lithium discharge chamber. An electrode plate is respectively provided in the lithium absorption chamber 1 and the lithium discharge chamber 2, that is, a first electrode plate 3 is provided in the lithium absorption chamber 1, and a second electrode plate 4 is provided in the lithium discharge chamber 2, and the first electrode plate 3 is connected to the negative pole of the DC power supply, and the second electrode plate 4 is connected to the positive pole of the DC power supply. The purified brine and the receiving liquid obtained in step (1) are respectively introduced into the lithium absorption chamber 1 and the lithium discharge chamber 2. When the equipment is in operation, lithium adsorption and lithium desorption are respectively carried out simultaneously in the two chambers of the lithium absorption chamber and the lithium discharge chamber. Specifically: turn on the power switch, the anode loses electrons, and Li + The lithium is released from the second electrode plate 4 into the receiving liquid to form a lithium-rich solution; at the same time, the negative electrode obtains electrons to purify the Li in the brine. + By embedding active materials in the electrode plates, the lithium concentration of the brine continues to decrease and becomes lithium-deficient brine.

[0049] In some specific embodiments, the first electrode plate / the second electrode plate is prepared by mixing lithium manganate or lithium iron phosphate as the active material, and auxiliary binders, conductive agents, pore-forming agents, other additives, solvents, etc. Among them, the binder can be epoxy-modified silicone resin; the dispersant can be short-cut carbon fiber; the conductive agent can be nano carbon black, acetylene black or superconductive carbon black; the pore-forming agent can be ammonium bicarbonate or ammonium carbonate; the other additives can be short-cut carbon fiber; the solvent can be dimethyl carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate or dipropyl carbonate. In some more specific embodiments, the preparation method of the electrode plate is as follows: (1) Preparation: 95-105 parts of electrode active material, 45-55 parts of binder, 10-15 parts of conductive agent, 3-5 parts of chopped carbon fiber, 10-20 parts of pore-forming agent and 65-80 parts of solvent; (2) Mixing and slurrying: First, mix the binder and the solvent and stir for 5-10 minutes; then add the conductive agent, chopped carbon fiber and pore-forming agent in sequence, and stir for 5-10 minutes after adding each component; finally, add the electrode active material and stir for 5-10 minutes to make the viscosity reach 40000-60000 mPa.s to obtain electrode slurry; (3) Coating: Evenly coat the electrode slurry on the electrode with a single-sided coating thickness of 500-2000 μm; (4) Drying: First, dry the coated electrode at 50-70°C for 1-5 hours, and then dry it at 140-170°C for 1-2 hours to obtain a salt lake lithium extraction electrode plate. The electrode plate prepared by the above method has good lithium absorption capacity, and the lithium absorption capacity is 10-30g / m 2 .

[0050] In some specific embodiments, the voltage of the DC power supply is 0.01V to 1.80V, and the working time is 5h to 24h. Under the above conditions, the electrode plates in the lithium absorption chamber absorb lithium to saturation.

[0051] In some specific embodiments, the receiving solution is a lithium chloride aqueous solution or a sodium chloride aqueous solution, and its concentration is 0.1%-1%.

[0052] In some specific embodiments, the lithium concentration of the lithium-poor brine is less than 200 mg / L, and the lithium concentration of the lithium-rich solution is greater than 5 g / L.

[0053] In some specific embodiments, the method further comprises: discharging the lithium-poor brine in the lithium absorption chamber and the lithium-rich solution in the lithium discharge chamber, and then switching the water inlet of the lithium absorption chamber and the lithium discharge chamber, and the positive and negative electrodes of the DC power supply. The specific operation is: setting a switching valve on the water inlet pipeline of the lithium absorption chamber and the lithium discharge chamber, and switching the positive and negative electrodes of the DC power supply at the same time. After the switching, the lithium receiving solution enters the lithium absorption chamber 1, and the purified brine of step (1) enters the lithium discharge chamber 2. The first electrode plate 3 in the lithium absorption chamber 1 is connected to the positive electrode of the DC power supply, and the second electrode plate 4 in the lithium absorption chamber is connected to the negative electrode of the DC power supply. Under the action of the electric field, lithium desorption is carried out in the lithium absorption chamber 1, and lithium adsorption is carried out in the lithium discharge chamber 2, and a new round of lithium extraction and lithium concentration cycle is carried out. The lithium-rich solution formed in the lithium absorption chamber 1 is carried out to the next process, and the lithium-poor brine formed in the lithium discharge chamber 2 is discharged to the salt lake.

[0054] (3) Crystallization pool

[0055] Add an appropriate amount of sodium carbonate to the lithium-rich solution discharged from step (2), mix well and discharge to a crystallization pool for natural evaporation concentration, precipitation and crystallization, and collect lithium regularly according to the evaporation amount of the lithium-rich solution.

[0056] In some specific embodiments, the amount of sodium carbonate added is based on the molar ratio of lithium to carbonate, Li + :CO3 2- The ratio is 1.2~2.

[0057] In some specific embodiments, the conditions for natural evaporation concentration are: the crystallization pool is built in an outdoor open-air environment, the evaporation temperature is natural temperature, the temperature range is -30°C to 30°C, the daily average evaporation is generally 2mm-25mm, and the solar pool evaporation time is: 60 days to 180 days.

[0058] The salt lake brine treated by the method of the present invention comes from a lithium-rich carbonate salt lake, preferably the Zabuye Salt Lake. The purity of lithium carbonate produced by traditional salt gradient solar ponds is generally 60%, the yield is generally 40%, and the lithium carbonate harvesting cycle is 12 months / time. Using the method of the present invention, the purity of lithium carbonate produced is ≥75%, the yield can reach more than 80%, and the lithium carbonate harvesting cycle is ≤6 months / time, which greatly improves the lithium extraction efficiency and production capacity of the salt gradient solar pond.

[0059] Example 1

[0060] The main chemical components of Zabuye Salt Lake brine are: Li + :1200mg / L、K + :45000mg / L、Na + :101390mg / L、Cl - :143927mg / L.

[0061] This embodiment provides a method for preparing lithium carbonate by coupling lithium extraction from a solar pond with lithium extraction from an electrolithium source:

[0062] (1) The brine from Zabuye Salt Lake is discharged into an ultrafiltration device for purification to obtain purified brine.

[0063] (2) The purified brine of step (1) and a lithium chloride aqueous solution (receiving solution) with a mass concentration of 0.5% are respectively discharged into a lithium absorption chamber and a lithium discharge chamber of a lithium extraction equipment, and lithium extraction and lithium concentration are simultaneously performed under the condition that a DC power supply voltage is 1.8 V. When the lithium absorption of the electrode plates in the lithium absorption chamber reaches saturation, the power supply is disconnected. At this time, the lithium concentration of the brine in the lithium absorption chamber drops to 150 mg / L, and the obtained lithium-poor brine is discharged into the salt lake. The lithium concentration of the absorption liquid in the lithium discharge chamber is increased to 8 g / L, and the formed lithium-rich solution is discharged into a crystallization pool for lithium precipitation.

[0064] Water is introduced into the lithium absorption chamber and the lithium release chamber, and the positive and negative poles of the DC power supply are switched, and lithium extraction and lithium concentration are continued simultaneously under the condition that the DC power supply voltage is 1.8V, and the next round of lithium extraction and lithium concentration cycle is repeated.

[0065] (3) Press Li into the lithium-rich solution of step (2) + :CO3 2- Saturated sodium carbonate solution is added at a molar ratio of 1.5 to carry out natural evaporation and concentration of lithium, and the lithium carbonate in the solar pond is harvested regularly.

[0066] The results showed that the purity of the produced lithium carbonate was 76% and the yield was 83%.

[0067] Example 2

[0068] This embodiment provides a method for preparing lithium carbonate by coupling lithium extraction from a solar pond with lithium extraction from an electrolithium source:

[0069] (1) The Zabuye Salt Lake brine (the main chemical composition is the same as that in Example 1) is discharged into an ultrafiltration device for purification to obtain purified brine.

[0070] (2) The purified brine of step (1) and a sodium chloride aqueous solution with a mass concentration of 1.0% (receiving solution) are respectively discharged into a lithium absorption chamber and a lithium discharge chamber of the lithium extraction equipment, and lithium extraction and lithium concentration are simultaneously performed under the condition of a DC power supply voltage of 0.8V. When the lithium absorption of the electrode plates in the lithium absorption chamber reaches saturation, the power supply is disconnected. At this time, the lithium concentration of the brine in the lithium absorption chamber drops to 180mg / L, and the obtained lithium-poor brine is discharged to the salt lake. The lithium concentration of the absorption liquid in the lithium discharge chamber is increased to 6g / L, and the formed lithium-rich solution is discharged into a crystallization pool for lithium precipitation.

[0071] Water is introduced into the lithium absorption chamber and the lithium release chamber, and the positive and negative poles of the DC power supply are switched, and lithium extraction and lithium concentration are continued simultaneously under the condition that the DC power supply voltage is 0.8V, and the next round of lithium extraction and lithium concentration cycle is repeated.

[0072] (3) Press Li into the lithium-rich solution of step (2)+ :CO3 2- Saturated sodium carbonate solution is added at a molar ratio of 1.2 to carry out natural evaporation and concentration of lithium, and the lithium carbonate in the solar pond is harvested regularly.

[0073] The results showed that the purity of the produced lithium carbonate was 78% and the yield was 80%.

[0074] Example 3

[0075] This embodiment provides a method for preparing lithium carbonate by coupling lithium extraction from a solar pond with lithium extraction from an electrolithium source:

[0076] (1) The Zabuye Salt Lake brine (the main chemical composition is the same as that in Example 1) is discharged into an ultrafiltration device for purification to obtain purified brine.

[0077] (2) The purified brine of step (1) and the sodium chloride aqueous solution with a mass concentration of 0.6% (receiving solution) are respectively discharged into the lithium absorption chamber and the lithium discharge chamber of the lithium extraction equipment, and lithium extraction and lithium concentration are carried out simultaneously under the condition of a DC power supply voltage of 0.4V. When the lithium absorption of the electrode plate in the lithium absorption chamber reaches saturation, the power supply is disconnected. At this time, the lithium concentration of the brine in the lithium absorption chamber drops to 150mg / L, and the obtained lithium-poor brine is discharged to the salt lake. The lithium concentration of the absorption liquid in the lithium discharge chamber is increased to 4g / L, and the formed lithium-rich solution is discharged into the crystallization pool for the lithium precipitation step.

[0078] Water is introduced into the lithium absorption chamber and the lithium release chamber, and the positive and negative poles of the DC power supply are switched, and lithium extraction and lithium concentration are continued simultaneously under the condition that the DC power supply voltage is 0.4V, and the next round of lithium extraction and lithium concentration cycle is repeated.

[0079] (3) Press Li into the lithium-rich solution of step (2) + :CO3 2- Saturated sodium carbonate solution is added at a molar ratio of 2 to carry out natural evaporation and concentration of lithium, and the lithium carbonate in the solar pond is harvested regularly.

[0080] The results showed that the purity of the produced lithium carbonate was 81% and the yield was 76%.

[0081] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing lithium carbonate by coupling lithium extraction from electric lithium with solar pond, characterized in that: The method comprises the following steps: (1) The salt lake brine enters the ultrafiltration device for purification to obtain purified brine; (2) The purified brine enters the lithium electroextraction equipment, and under the action of the electric field, lithium is extracted and concentrated simultaneously to obtain lithium-poor brine and lithium-rich solution; (3) Add saturated sodium carbonate solution to the lithium-rich solution, mix well, and then discharge it to the solar pond for natural evaporation and concentration of lithium. The lithium carbonate in the solar pond is harvested regularly.

2. The method for preparing lithium carbonate by lithium extraction from electric lithium coupled to solar pond according to claim 1, characterized in that: In step (1), The working conditions of the ultrafiltration device are: internal pressure submerged ultrafiltration, membrane material is PVDF, pore size is 30nm-100nm, normal operating pressure is 0.1MPa-0.2MPa, and design flux is 10LMH-30LMH.

3. The method for preparing lithium carbonate by lithium extraction from electric lithium coupled with solar pond according to claim 1, characterized in that: In step (2), The lithium electroextraction equipment comprises a lithium absorption chamber, a lithium discharge chamber and an anion exchange membrane, wherein the anion exchange membrane separates the lithium absorption chamber from the lithium discharge chamber, and the lithium absorption chamber and the lithium discharge chamber are respectively provided with electrode plates, the electrode plate in the lithium absorption chamber is connected to the negative electrode of the direct current power supply, and the electrode plate in the lithium discharge chamber is connected to the positive electrode of the direct current power supply; The purified brine obtained in step (1) enters the lithium absorption chamber, and the receiving liquid enters the lithium discharge chamber. Under the action of the electric field, the lithium ions in the purified brine are embedded in the electrode plates, and the purified brine becomes lithium-poor brine. The electrode plates in the lithium discharge chamber release lithium and enter the receiving liquid to form a lithium-rich solution.

4. The method for preparing lithium carbonate by lithium extraction from electric lithium coupled with solar pond according to claim 3, characterized in that: The active material of the electrode plate is lithium manganate or lithium iron phosphate, and the lithium absorption capacity of the electrolytic plate is 10-30g / m 2 ; The voltage of the DC power supply is 0.01V to 1.80V, and the working time is 5h to 24h; The receiving solution is a lithium chloride aqueous solution or a sodium chloride aqueous solution with a mass concentration of 0.1% to 1%.

5. The method for preparing lithium carbonate by lithium extraction from electric lithium coupled with solar pond according to claim 3, characterized in that: The lithium concentration of the lithium-poor brine is less than 200 mg / L, and the lithium concentration of the lithium-rich solution is greater than 5 g / L.

6. The method for preparing lithium carbonate by lithium extraction by coupling lithium extraction from a solar pond according to claim 3, characterized in that: The method further comprises: discharging lithium-poor brine and lithium-rich solution, then filling the lithium absorption chamber and the lithium release chamber with water, and switching the positive and negative poles of the DC power supply, and carrying out the next round of lithium extraction and lithium concentration cycle under the action of the electric field. The specific operation process is as follows: the purified brine obtained in step (1) enters the lithium discharge chamber, the receiving liquid enters the lithium absorption chamber, the electrode plate in the lithium discharge chamber is connected to the negative electrode of the DC power supply, and the electrode plate in the lithium absorption chamber is connected to the positive electrode of the DC power supply.

7. The method for preparing lithium carbonate by lithium extraction by coupling lithium extraction from a solar pond according to claim 1, characterized in that: In step (3), The amount of sodium carbonate added is based on the molar ratio of lithium to carbonate. + :CO3 2- The ratio is 1.2 to 2; The conditions of natural evaporation concentration are as follows: the crystallization pool is built in an outdoor open-air environment, the evaporation temperature is natural temperature, the temperature range is -30°C to 30°C, the daily average evaporation is 2mm to 25mm, and the solar pool evaporation time is 60 days to 180 days; The harvesting cycle of lithium carbonate in the solar pond is ≤6 months / time.

8. The method for preparing lithium carbonate by lithium extraction from electric lithium coupled with solar pond according to claim 1, characterized in that: The salt lake brine comes from a lithium-rich carbonate salt lake.

9. The method for preparing lithium carbonate by lithium extraction by coupling lithium extraction by solar pond according to claim 8, characterized in that: The salt lake brine comes from the Zabuye Salt Lake.

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