Method and device for extracting lithium from salt lake

Abstract

The invention discloses a method for extracting lithium from a salt lake and an extraction device. The method for extracting lithium from the salt lake provided by the invention comprises the following steps: salt lake brine is subjected to aluminum adsorbent adsorption, ultrafiltration impurity removal, multi-stage nanofiltration magnesium and boron removal, reverse osmosis concentration, ultrafiltration softening deep magnesium removal, resin magnesium and boron removal, MVR evaporation and other technological processes, and a battery-grade lithium carbonate product is obtained. According to the method, the membrane separation technology serves as a core, resin and an evaporation system serve as auxiliary materials, deep separation of magnesium and lithium in the salt lake brine is achieved, the boron removal rate and the lithium recovery rate are high, meanwhile, recycling of water resources is guaranteed, and the whole process has the advantages of being controllable, high in automation degree, low in production cost, small in pollution, high in water recovery rate and suitable for industrial production. The method can be applied to large-scale production of salt lake lithium extraction.

Description

Technical Field

[0001] The invention belongs to the technical field of separation, purification, and refining of lithium from salt lake brine, and specifically relates to a method and device for extracting lithium from a salt lake. Background Art

[0002] At present, the mining of lithium resources mainly comes from lithium ore and salt lake brine, among which lithium resources in brine account for more than 60% of the world's proven lithium resources, and are concentrated, mainly in Argentina, Chile, and Bolivia. From the perspective of reserves alone, the reserves of lithium resources in salt lake brine are greater than those in lithium ore. At present, most domestic lithium salts are extracted from ores, but with the continuous reduction of high-grade lithium ore and the continuous increase in the cost of lithium extraction from ore, the cost is about 100,000 to 150,000 yuan / ton. Since salt lakes are rich in lithium elements, and lithium extraction from salt lake brine has obvious cost advantages over lithium extraction from ore, the cost is about 40,000 to 60,000 yuan / ton. Therefore, extracting lithium from salt lake brine has become an inevitable trend in the development of lithium resources in the future. For example, Zhabuye Salt Lake, Jiezechaka Salt Lake, Longmu Co Salt Lake, Mami Co Salt Lake, Laguo Co Salt Lake, and Baqian Co Salt Lake are all developing lithium extraction projects.

[0003] The composition of salt lake brine is complex, containing a large number of metal and non-metal elements. Among them, magnesium is the element that interferes most with the lithium extraction process of salt lake brine. The salt lakes in Qinghai and Tibet in my country are mainly high-magnesium-lithium ratio salt lakes, among which the magnesium-lithium ratio of the salt lakes in the Qaidam Basin is as high as 50 or more. Because the physical and chemical properties of magnesium and lithium are very similar, the separation of magnesium and lithium is very difficult, which has become a technical bottleneck for the large-scale development of lithium resources in salt lake brine. The main methods for extracting lithium from salt lake brine and producing battery-grade lithium carbonate are: 1. Precipitation method The principle of the precipitation method is to use solar energy to naturally evaporate and concentrate the salt lake brine. After removing impurities by deboronization, calcium removal, and magnesium removal, a mixed precipitant or salting-out agent is added to the mother liquor to separate lithium in the form of precipitate. The precipitation method for extracting metallic lithium has been used in industry for a long time. The process is mature, simple to operate, and highly reliable. However, this method has poor adaptability to brine with high alkaline earth metal ion concentration and low lithium ion concentration. The precipitation method is divided into carbonate precipitation method, aluminate precipitation method, and boron-magnesium, boron-lithium co-precipitation method according to the specific process.

[0004] 2. Solvent extraction method Solvent extraction is a method of transferring solutes from the aqueous phase to the organic phase, which has a greater solubility for the solute, by utilizing the difference in solubility or distribution coefficient between the aqueous phase and the organic phase, thereby achieving the purpose of solute phase transfer separation. Solvent extraction is one of the main methods for selective separation and extraction of metal ions. The extractants that are currently being studied more include β-diketone extractants and neutral phosphorus-containing extractants.

[0005] (III) Adsorption method The adsorption method uses an adsorbent that is selective for lithium ions to bind lithium ions, and then elutes and extracts lithium ions under the action of an eluent, thereby separating lithium ions from other impurity ions. The key to this method lies in the selection of lithium ion adsorbents. Finding lithium ion adsorbents that are selective for lithium, recyclable, and have relatively low production costs is the key to the success of this method. According to the properties of the adsorbent, the adsorbent can be divided into two types: organic ion exchange adsorbents and inorganic ion exchange adsorbents. They mainly rely on the characteristics of the material itself to selectively adsorb lithium ions. Because of their high selectivity and memory effect, lithium can be better separated from other impurities. The types of adsorbents include aluminum-based adsorbents, layered adsorbents, and ion sieve adsorbents. However, the cost of extracting lithium by adsorption is high, and the adsorbent also has a certain adsorption to boron, which will result in a low purity of lithium after extraction. At the same time, the adsorbents used for carbonate salt lakes face the problem of wastewater generated by analysis affecting the environment.

[0006] (IV) Membrane separation method The membrane separation processes commonly used for lithium extraction from salt lakes mainly include nanofiltration and electrodialysis. Electrodialysis is a membrane separation process that uses ion exchange membranes as a medium and potential difference as a driving force. The electrodialysis process can make the single extraction rate of lithium reach more than 80%, and the removal rate of magnesium ions is more than 95%. The key to electrodialysis technology lies in the ion selective exchange membrane. The charged groups on the surface of the membrane can allow monovalent ions to pass through the membrane pores and prevent the penetration of divalent and multivalent ions. The principle of nanofiltration membrane separation is that the nanofiltration membrane can intercept divalent and higher metal cations, while monovalent lithium ions and sodium ions can pass through, thereby separating lithium ions from magnesium ions in potassium-extracting brine. A two-stage nanofiltration method is used to separate Mg from salt lake brine. 2+ Li + , reverse osmosis membrane enriches lithium-containing solution. After the nanofiltration membrane separation operation, the permeated water can be used as the influent of the reverse osmosis membrane to produce lithium salt, and the concentrated water can be used to extract magnesium salt, so that the inorganic salt resources in the salt lake brine can be comprehensively utilized. Although membrane separation technology can selectively separate monovalent salts and divalent salts at a low cost, the lithium recovery rate is low.

[0007] (V) Calcination method This method uses lithium-rich brine after potassium and boron extraction as raw material, removes water through solar evaporation, and obtains evaporation concentration to contain Li + The amount of 2% is about 2%, and finally soda ash is added for precipitation and drying to obtain lithium carbonate products, with a lithium yield of about 90%. The use of this method to extract lithium is conducive to the comprehensive utilization of resources such as lithium and magnesium, and the consumption of raw materials is relatively low; however, the removal of magnesium will make the process more complicated, and the equipment will be severely corroded during the production process, and the amount of water evaporated will be large. Summary of the invention

[0008] The purpose of the present invention is to provide a method and device for extracting lithium from salt lake brine using membrane integration technology. The method selectively adsorbs lithium by adsorption according to the water quality of salt lake brine, and simultaneously improves the quality of lithium by ultrafiltration removal of impurities, nanofiltration separation and magnesium removal, reverse osmosis concentration of lithium concentration, and resin removal of magnesium and boron removal, and finally obtains battery-grade lithium carbonate by lithium precipitation, washing, and drying. The method has the advantages of high lithium recovery rate, good controllability, high degree of automation, low production cost, low pollution, high water recovery rate, etc., and is suitable for large-scale production of lithium extraction from salt lakes.

[0009] To achieve the above object, the present invention provides the following technical solutions: In a first aspect, the present invention provides a method for extracting lithium from salt lake brine, comprising the following steps: (1) The salt lake brine is adsorbed and analyzed, and the desorbed liquid is subjected to primary ultrafiltration UF1 treatment; (2) subjecting the produced water obtained by the first-level ultrafiltration UF1 treatment to first-level reverse osmosis RO1 treatment, and subjecting the obtained concentrated water to first-level nanofiltration NF1 treatment and second-level nanofiltration NF2 treatment; (3) subjecting the produced water obtained by the secondary nanofiltration NF2 treatment to secondary reverse osmosis RO2 treatment, and subjecting the obtained concentrated water to tertiary nanofiltration NF3 treatment; (4) adding alkali to the produced water obtained by the three-stage nanofiltration NF3 treatment, and sequentially subjecting the obtained softened liquid to a two-stage ultrafiltration UF2 treatment, a four-stage nanofiltration NF4 treatment, a five-stage nanofiltration NF5 treatment, and a three-stage reverse osmosis RO3 treatment; (5) treating the concentrated water obtained by the three-stage reverse osmosis RO3 treatment with a calcium and magnesium removal resin and a boron removal resin in sequence; (6) The produced water obtained by the boron removal resin treatment is subjected to MVR evaporation concentration, and the obtained concentrated solution is subjected to lithium precipitation reaction to obtain lithium carbonate.

[0010] In the above method, in step (1), the water quality test data of the salt lake brine is: TDS is 500000~600000 mg / L, pH is between 6~8, the mass ratio of magnesium ion to lithium ion is (300~500):1, the potassium ion concentration is 1000~3000 mg / L, the sodium ion concentration is 2000~5000 mg / L, and the sulfate concentration is 30000~50000 mg / L; the salt lake brine is surface brine.

[0011] In the above method, in step (1), the adsorption conditions are: using a rotating disk resin device, the resin device is equipped with 10 to 20 resin columns, and the resin columns are equipped with lithium adsorbent; the adsorption rate is 1 to 3 BV / h; the magnesium-to-lithium ratio of the salt lake brine after adsorption is (10 to 20): 1. The magnesium-to-lithium ratio of the salt lake brine after adsorption is (10 to 20): 1.

[0012] In the above method, in step (1), the analysis conditions are: using water for analysis, the conductivity of the water is less than 10μs / cm, the analysis rate is 2~5 BV / h; the TDS of the analysis solution is 10000~20000mg / L.

[0013] In the above method, in step (1), the conditions of the first-stage ultrafiltration UF1 treatment are: the ultrafiltration membrane used is one of a hollow fiber membrane, a spiral membrane, a ceramic membrane and a tubular membrane; the pore size of the ultrafiltration membrane is 10-50 nm; water is added for washing during the first-stage ultrafiltration UF1 treatment, and the amount of water added is 1 / 2-1 times the amount of water inlet; the content of suspended matter in the obtained produced water is less than 1 mg / L. The recovery rate of the first-stage ultrafiltration UF1 treatment is controlled to be above 95%.

[0014] In the above method, in step (2), the conditions of the primary reverse osmosis RO1 treatment are: the membrane element used is a Dow reverse osmosis membrane, and its material is a polyamide or polyethersulfone material; the concentration multiple is 2 to 4 times, and the operating pressure is 15 to 30 bar; the magnesium ion content in the obtained concentrated water is 1000 to 10000 mg / L.

[0015] In the above method, in step (2), the conditions of the primary nanofiltration NF1 treatment and the secondary nanofiltration NF2 treatment are as follows: the nanofiltration membrane used is a rolled nanofiltration membrane with a pore size of 300-600 Da; the separation layer material of the nanofiltration membrane is one of polysulfone, polyethersulfone and polyamide materials; the surface charge of the nanofiltration membrane is positive or negative; the operating pressure is 10-40 bar; water is added for filtration during operation, and the amount of water added is 1 / 2-1 times the amount of water inlet; the mass ratio of magnesium to lithium in the resulting produced water is 1:(5-10). The primary nanofiltration NF1 treatment and the secondary nanofiltration NF2 treatment have a retention rate of 80%-95% for magnesium ions in salt lakes, a retention rate of 20%-40% for lithium ions, and a water recovery rate of 75%-85%.

[0016] In the above method, in step (3), the conditions of the secondary reverse osmosis RO2 treatment are: the membrane element used is a Dow reverse osmosis membrane, and its material is a polyamide or polyethersulfone material; the concentration multiple is 3 to 5 times, and the operating pressure is 20 to 50 bar.

[0017] In the above method, in step (3), the conditions of the three-stage reverse osmosis RO3 treatment are as follows: the membrane element used is a high-pressure membrane, the material of which is a polyamide material, and the molecular weight cutoff is 100 to 300 Da; the operating pressure is 10 to 40 bar, and water is added for filtration during operation, and the amount of water used is 1 / 4 to 1 times the amount of water inlet; In the above method, in step (3), the conditions of the three-stage nanofiltration NF3 treatment are: the material of the membrane element used is a polyamide material, and the molecular weight cutoff is 100 to 300 Da.

[0018] In the above method, in step (4), alkali is added to the produced water after the three-stage nanofiltration NF3 treatment to adjust the pH to 8-10; the alkali is one or more of sodium hydroxide, calcium hydroxide and potassium hydroxide.

[0019] In the above method, in step (4), the conditions for the secondary ultrafiltration UF2 treatment are: the ultrafiltration membrane used is one of a central control fiber membrane, a spiral membrane, a ceramic membrane and a tubular membrane, and the membrane pore size is 10-50 nm; the volume of the concentrated solution does not exceed 5% of the water volume of the unit; and the recovery rate of lithium in the secondary ultrafiltration UF2 treatment reaches more than 90%.

[0020] In the above method, in step (4), the conditions of the four-stage nanofiltration NF4 treatment and the five-stage nanofiltration NF5 treatment are as follows: the membrane element used is a rolled nanofiltration membrane with a pore size of 100-300 Da, the separation layer material of the membrane is one of polysulfone, polyethersulfone and polyamide, and the surface of the membrane is positively charged or negatively charged; the operating pressure is 10-40 bar, and the water recovery rate is 75%-85%; water is added for filtration during operation, and the amount of water used is 1 / 2-1 times the amount of inlet water; the boron content in the obtained produced water is less than 10 mg / L, and the lithium-magnesium ratio is greater than 500:1; the membrane elements used in the four-stage nanofiltration NF4 treatment and the five-stage nanofiltration NF5 treatment have a boron retention rate of 50-80% and a lithium ion retention rate of 20%-40%.

[0021] In the above method, in step (4), the conditions of the three-stage reverse osmosis RO3 treatment are: the membrane element used is a high-pressure membrane, the material of which is a polyamide material, and the molecular weight cutoff is 100-300 Da; the concentration multiple is 3-6 times, the lithium content after concentration reaches 6-10 g / L, and the operating pressure is 20-50 bar.

[0022] In the above method, in step (5), the resin used in the calcium and magnesium removal resin treatment is a cationic resin; and the resin used in the boron removal resin treatment is a resin formed by cross-linking styrene and divinylbenzene and having a polyamine hydroxyl functional group.

[0023] In the above method, in step (6), the lithium concentration in the concentrated solution obtained by MVR evaporation and concentration reaches 20-30 g / L.

[0024] In the above method, in step (6), the conditions of the lithium precipitation reaction are: temperature of 60-90°C, stirring rate of 200-800 r / min, and time of 1-3h. The sodium carbonate is added in the form of an aqueous solution with a concentration of 150-300 g / L, and the addition is stopped when the pH of the reaction solution reaches 8-9.

[0025] In the above method, in step (6), the post-treatment includes the following steps: separating, washing and drying the lithium carbonate precipitate to obtain battery-grade lithium carbonate powder; wherein the separation device is a plate-frame filter press or a centrifuge, the water used for washing is pure water, and the washing water is returned to the MVR evaporation unit, and the drying device can be a spray dryer, a disc dryer, a flash dryer, a vacuum dryer, etc. The lithium carbonate powder obtained after drying has a purity of more than 99.5%, and the impurity index meets the battery-grade requirements.

[0026] In the present invention, the method further comprises the following water treatment steps: In step (1), the salt lake brine tail liquid after adsorption is returned to the salt lake; In step (2), the concentrated water after the first-stage ultrafiltration UF1 treatment and the concentrated water after the first-stage nanofiltration NF1 treatment are returned to the salt lake; the concentrated water after the second-stage nanofiltration NF2 treatment is returned to continue the first-stage nanofiltration NF1 treatment; In step (3), the concentrated water after the third-stage nanofiltration NF3 treatment is returned to continue the first-stage nanofiltration NF1 treatment; In step (4), the concentrated water after the secondary ultrafiltration UF2 treatment is returned to the salt lake; the concentrated water after the fourth-stage nanofiltration NF4 treatment is returned to continue the third-stage nanofiltration NF3 treatment; the concentrated water after the fifth-stage nanofiltration NF5 treatment is returned to continue the fourth-stage nanofiltration NF4 treatment; The produced water after the primary reverse osmosis RO1 treatment in step (2), the produced water after the secondary reverse osmosis RO2 treatment in step (3), the produced water after the tertiary reverse osmosis RO3 treatment in step (5), and the condensed water after the MVR evaporation concentration in step (6) are subjected to the fourth-stage reverse osmosis RO4 treatment, and the obtained produced water is recycled; the concentrated water after the fourth-stage reverse osmosis RO4 treatment is subjected to the fourth-stage nanofiltration NF4 treatment; The membrane element used in the four-stage reverse osmosis RO4 treatment is a reverse osmosis membrane, which is made of one or more of polyamide materials, polyethersulfone materials and polysulfone materials, and has a pressure resistance of 40-60 bar.

[0027] In a second aspect, the present invention provides a device for extracting lithium from salt lake brine by the above method, comprising the following units connected in sequence: a lithium adsorbent unit, a first-level ultrafiltration UF1 (Ultra Filtration) unit, a first-level reverse osmosis RO1 (Reverse Osmosis) unit, a first-level nanofiltration NF1 (Nanofiltration) unit, a second-level nanofiltration NF2 unit, a second-level reverse osmosis RO2 unit, a third-level nanofiltration NF3 unit, a second-level ultrafiltration UF2 unit, a fourth-level nanofiltration NF4 unit, a fifth-level nanofiltration NF5 unit, a third-level reverse osmosis RO3 unit, a calcium and magnesium removal resin unit, a boron removal resin unit, an MVR (mechanical vapor recompression, steam mechanical recompression technology) evaporation unit, and a lithium precipitation reaction unit.

[0028] The tail liquid outlet of the lithium adsorbent unit is connected to the salt lake brine.

[0029] The concentrated water outlet of the first-stage ultrafiltration UF1 unit and the concentrated water outlet of the first-stage nanofiltration NF1 unit are connected to the salt lake brine.

[0030] The concentrated water outlet of the secondary nanofiltration NF2 unit and the concentrated water outlet pipeline of the tertiary nanofiltration NF3 unit are connected to the water inlet pipeline of the primary nanofiltration NF1 unit.

[0031] The concentrated water outlet of the secondary ultrafiltration UF2 unit is connected to the salt lake brine.

[0032] The concentrated water outlet of the fourth-stage nanofiltration NF4 unit is connected to the water inlet pipeline of the third-stage nanofiltration NF3 unit.

[0033] The concentrated water outlet of the five-stage nanofiltration NF5 unit is connected to the water inlet pipeline of the four-stage nanofiltration NF4 unit.

[0034] The first-stage ultrafiltration UF1 unit, the first-stage nanofiltration NF1 unit, the third-stage nanofiltration NF3 unit, and the fourth-stage nanofiltration NF4 unit are provided with an inlet for water for filtration washing.

[0035] The device also includes a four-stage reverse osmosis RO4 unit; the water outlet of the first-stage reverse osmosis RO1 unit, the water outlet of the second-stage reverse osmosis RO2 unit, the water outlet of the third-stage reverse osmosis RO3 unit and the evaporation condensate outlet of the MVR evaporation unit are connected to the inlet pipeline of the four-stage reverse osmosis RO4 unit. The concentrated water outlet of the four-stage reverse osmosis RO4 unit is connected to the inlet pipeline of the four-stage nanofiltration NF4 unit.

[0036] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, the salt lake brine is subjected to the process of aluminum adsorbent adsorption, ultrafiltration impurity removal, multi-stage nanofiltration magnesium removal and boron removal, reverse osmosis concentration, ultrafiltration softening deep magnesium removal, resin magnesium removal and boron removal, and MVR evaporation to obtain a battery-grade lithium carbonate product. The entire system has strong stability, high controllability, and high degree of automation. Compared with the prior art, the extraction method provided by the present invention has low energy consumption, low investment, high recovery rate, and environmental protection. It realizes the extraction of battery-grade lithium carbonate products from salt lakes with a high magnesium-lithium ratio, provides a new process for salt lake lithium extraction technology, solves existing technical problems, and creates higher value for lithium resource development at home and abroad. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A process diagram for extracting lithium from salt lake brine using membrane integration technology provided by the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0040] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0041] Example 1: Device for extracting lithium from salt lake brine using membrane integration technology The device comprises the following units connected in sequence: a lithium adsorbent unit, a primary ultrafiltration UF1 unit, a primary reverse osmosis RO1 unit, a primary nanofiltration NF1 unit, a secondary nanofiltration NF2 unit, a secondary reverse osmosis RO2 unit, a tertiary nanofiltration NF3 unit, a secondary ultrafiltration UF2 unit, a quaternary nanofiltration NF4 unit, a quintuple nanofiltration NF5 unit, a tertiary reverse osmosis RO3 unit, a calcium and magnesium removal resin unit, a boron removal resin unit, an MVR evaporation unit, a lithium precipitation reaction unit, and a quaternary reverse osmosis RO4 unit; The tail liquid outlet of the lithium adsorbent unit is connected to the salt lake brine; the concentrate outlet of the first-level ultrafiltration UF1 unit and the concentrate outlet of the first-level nanofiltration NF1 unit are connected to the salt lake; the concentrate outlet of the second-level nanofiltration NF2 unit and the concentrate outlet pipeline of the third-level nanofiltration NF3 unit are connected to the water inlet pipeline of the first-level nanofiltration NF1 unit; the concentrate outlet of the second-level ultrafiltration UF2 unit is connected to the salt lake brine; the concentrate outlet of the fourth-level nanofiltration NF4 unit is connected to the water inlet pipeline of the third-level nanofiltration NF3 unit; the concentrate outlet of the fifth-level nanofiltration NF5 unit is connected to the water inlet pipeline of the fourth-level nanofiltration NF4 unit; the first-level ultrafiltration UF1 unit, the first-level nanofiltration NF1 unit, the third-level nanofiltration NF3 unit, and the fourth-level nanofiltration NF4 unit are provided with a water inlet for filtration washing.

[0042] The resin device used in the lithium adsorbent unit is a turntable type, and the resin device contains 10 to 20 resin columns, and the resin columns contain lithium adsorbents; the adsorption rate of the lithium adsorbent unit is 1 to 3 BV / h, the conductivity of the analyzed pure water is less than 10μs / cm, and the analysis rate is 2 to 5 BV / h; The ultrafiltration membrane used in the first-stage ultrafiltration UF1 unit and the second-stage ultrafiltration UF2 unit is one of a hollow fiber membrane, a spiral membrane, a ceramic membrane and a tubular membrane; the pore size of the ultrafiltration membrane is 10-50 nm; The membrane elements used in the primary reverse osmosis RO1 unit and the secondary reverse osmosis RO2 unit are Dow reverse osmosis membranes, which are made of polyamide or polyethersulfone materials; The membrane element used in the three-stage reverse osmosis RO3 unit is a high-pressure membrane made of polyamide material with a molecular weight cutoff of 100 to 300 Da; The nanofiltration membrane used in the first-stage nanofiltration NF1 unit and the second-stage nanofiltration NF2 unit is a rolled nanofiltration membrane with a pore size of 300-600 Da. The separation layer material of the membrane is one of polysulfone, polyethersulfone and polyamide materials. The surface charge of the membrane is positive or negative. The membrane element used in the three-stage nanofiltration NF3 unit is made of polyamide material with a molecular weight cutoff of 100 to 300 Da; The ultrafiltration membrane used in the secondary ultrafiltration UF2 unit is one of a central control fiber membrane, a spiral membrane, a ceramic membrane and a tubular membrane, and the membrane pore size is 10-50nm; The membrane elements used in the four-stage nanofiltration NF4 unit and the five-stage nanofiltration NF5 unit are rolled nanofiltration membranes with a pore size of 100-300 Da, the separation layer material of the membrane is one of polysulfone, polyethersulfone and polyamide, and the surface of the membrane is positively charged or negatively charged; The resin used in the calcium and magnesium removal resin unit is a cationic resin; The resin used in the boron removal resin unit is a resin with a polyamine hydroxyl functional group formed by cross-linking styrene and divinylbenzene.

[0043] The produced water outlet of the first-stage reverse osmosis RO1 unit, the produced water outlet of the second-stage reverse osmosis RO2 unit, the produced water outlet of the third-stage reverse osmosis RO3 unit and the evaporation condensate outlet of the MVR evaporation unit are connected to the inlet pipe of the fourth-stage reverse osmosis RO4 unit; the concentrated water outlet of the fourth-stage reverse osmosis RO4 unit is connected to the inlet pipe of the fourth-stage nanofiltration NF4 unit; the membrane element used in the fourth-stage reverse osmosis RO4 unit is a Dow reverse osmosis membrane, which is made of polyamide, polyethersulfone or polysulfone material, and has a pressure resistance of 40-60 bar.

[0044] Example 2: Method for extracting lithium from salt lake brine using membrane integration technology This embodiment provides a method for extracting lithium from salt lake brine using the above device, such as Figure 1 As shown, the following steps are included: (1) Select salt lake brine from Tibet, with a TDS of 500,000-600,000 mg / L and a density of 1.0-1.3 g / cm 3 , pH between 6 and 8, Mg 2+ The content is about 100000mg / L, Li + The content is about 200mg / L, B 3+ The content is about 600 mg / L, and the magnesium-lithium ratio is about 500:1, which is a high magnesium-lithium ratio salt lake; (2) Lithium adsorbent unit - UF1 unit: The salt lake brine is pumped into the lithium adsorbent unit. The resin device used in the unit is a turntable type, equipped with 10 to 20 resin columns. The resin columns are filled with aluminum adsorbents, the main materials of which are Li2SO4.2Al(OH)3.nH2O or LiCl.2Al(OH)3.nH2O. The adsorbent has specific adsorption for lithium ions in the brine. The main principle is speculated to be that the lithium ions in the salt lake enter the octahedral cavity in the aluminum hydroxide layer in the form of naked ions and are adsorbed. For ion balance, chloride ions or sulfate ions in the anions also enter the interlayer. The screening effect and the difference in hydration between lithium ions and other ions are the reasons why aluminum adsorbents have good selectivity for lithium. The turntable adsorption column can realize adsorption and analysis simultaneously. When the brine is sent into the resin column, the adsorption efficiency is controlled by adjusting the flow rate of the adsorption column, and the lithium ion content of the tail liquid after adsorption is detected to determine whether the adsorption is saturated. The adsorption rate of the resin column is 1 to 3 BV / h. After the adsorbent is saturated, it is analyzed using pure water. The conductivity of the pure water is required to be within 10 μs / cm, and the analysis rate is 2 to 5 BV / h.

[0045] After adsorption and analysis by adsorbent, the lithium ion content in the brine increased from 200 mg / L to 500 mg / L, while the magnesium ion content decreased to 2500 mg / L, and the magnesium-lithium ratio dropped to 5:1.

[0046] Since the analytical solution contains impurities in the salt lake brine and particulate matter after resin dissolution, the suspended matter content of the analytical solution is 5-10 mg / L, so the analytical solution is sent to the UF1 unit to remove insoluble suspended matter using an ultrafiltration membrane. The ultrafiltration membrane is a ceramic membrane with a pore size of 30-50 nm and a membrane element temperature tolerance of 60-70°C. The operating inlet pressure of the unit is 1-5 bar, and the operating flux is 200-300 L / m -2 h -1 During the operation, pure water is added to filter the residual lithium ions in the concentrated water to reduce the lithium content in the concentrated water as much as possible. The conductivity of the pure water is required to be less than 10μs / cm, the amount of pure water added is 1 / 2 of the water inlet of the UF1 unit, the unit's produced water SS (suspended solids) ≤ 1mg / L, the produced water recovery rate is controlled at more than 95%, and the remaining concentrated water is returned to the salt lake.

[0047] (3) RO1 unit-NF1 unit-NF2 unit: Since the TDS content of the water produced by the UF1 unit is low, the subsequent separation of monovalent / divalent salts requires a large amount of treatment and the separation effect is poor, the UF1 produced water is sent to the RO1 unit for concentration before this, and the concentration multiple is controlled at 3 times, and the lithium ion content is increased to 1381 mg / L. The membrane element used in this unit is a Dow reverse osmosis membrane with an operating pressure of 20 bar. The magnesium ion content in the concentrated water after RO1 treatment is high, and the NF1 unit is used for primary separation and magnesium removal. The membrane element brands selected for this unit are Suez, Hyde Energy, Koch, Minard or Times Vorton. The separation layer material of the membrane is polyamide, with a molecular weight cutoff of 300-600 Da and an operating pressure of 15 bar. After the primary nanofiltration NF1 treatment, the magnesium ion removal rate reaches more than 80%, and the magnesium content in the produced water is 1100 mg / L. At the same time, by adding filtration water to reduce the retention of monovalent lithium ions, the lithium ion content in the nanofiltration concentrate is reduced to 45 mg / L and returned to the salt lake, thereby maximizing the recovery of lithium. The filtration water consumption is 1 / 2 of the unit water intake.

[0048] The water produced by the first-stage nanofiltration NF1 is continuously sent to the second-stage nanofiltration NF2 unit to remove magnesium. The operating conditions and membrane elements of this unit are consistent with those of NF1. After treatment by the NF2 unit, the magnesium ion drops to 140 mg / L, and the removal rate reaches 87%. Since this unit does not add water for filtration, the lithium sulfate or lithium chloride retained in the concentrated water is returned to the NF1 unit for continued use, increasing the recovery rate of lithium, which reaches 97%. After two-stage nanofiltration to remove magnesium, the ratio of magnesium to lithium in the produced water of NF2 is 1:7.

[0049] (4) RO2 unit-NF3 unit: The lithium concentration in the secondary nanofiltration NF2 water is lower than that in the primary nanofiltration NF1 water mainly because the addition of washing water in the NF1 unit dilutes the ion concentration. In order to increase the lithium concentration and reduce the amount of subsequent water treatment, the water produced by the NF2 unit is sent to the secondary reverse osmosis RO2 unit for concentration. The concentration multiple is about 3 times, and the lithium content is also increased to 3900 mg / L. The membrane element used in this unit is the same as that used in the RO1 unit, but the operation is higher than RO1, and the pressure reaches 25 bar. This is due to the increase in TDS content and the increase in osmotic pressure.

[0050] After being concentrated by the RO2 unit, the concentrated water is sent to the three-stage nanofiltration NF3 unit for three times of magnesium removal. The membrane element material used in the NF3 unit is consistent with that used in the NF1 and NF2 units, but the molecular weight cutoff is 100-300Da, the system operating pressure is 20bar, and the water consumption for washing and filtration during operation is 1 / 5 of the influent water. After being treated by the NF3 unit, the magnesium ion content is reduced to 64mg / L, and the removal rate reaches 89%. At the same time, boron is also reduced from 65mg / L to 20mg / L. The concentrated water of the NF3 unit contains a high level of lithium, which is returned to the NF1 unit for further recovery.

[0051] (5) UF2 unit: In order to further reduce the boron content in the produced water of the NF3 unit, it is necessary to add multi-stage nanofiltration. However, due to the neutral pH, the boron retention rate of the nanofiltration membrane is not high, so it is necessary to adjust the pH to about 9-10 so that the boron in the solution exists in the form of borates, mainly sodium borate, to increase the boron retention rate of the nanofiltration membrane. At the same time, considering that at the above pH, magnesium hydroxide colloid will precipitate and the conditions for entering the nanofiltration membrane cannot be met, a secondary ultrafiltration UF2 unit is added before nanofiltration. The pH of the produced water of the NF3 unit is adjusted to about 9.5 with sodium hydroxide and sent to the UF2 unit to remove the precipitated precipitate. The UF2 unit uses a ceramic membrane, and the pore size of the membrane element, the operating pressure of the membrane system, and the diafiltration method are all consistent with the UF1 unit, and the diafiltration water consumption is 1 / 5 of the imported water.

[0052] (6) NF4 unit - NF5 unit: After the secondary ultrafiltration UF2 treatment, the produced water is sent to the two-stage nanofiltration for deboronization treatment, and the two-stage nanofiltration is respectively NF4 unit and NF5 unit. The produced water of the UF2 unit first enters the NF4 system for primary deboronization, which reduces the boron content from 13mg / L to 5mg / L, and the removal rate is more than 60%. Due to the high pH and the small pore size of the nanofiltration membrane, the system's retention rate of lithium will increase. In order to recover and increase the recovery of lithium, a washing and filtration step is added to the NF4 unit. The amount of water used for washing and filtration is 1 / 2 of the water intake. According to the data, the lithium content in the concentrated water of the NF4 unit after washing and filtration is only about 200mg / L, and the lithium retention rate is less than 15%. This part of the NF4 concentrated water returns to the NF3 water inlet. The NF4 produced water continues to use the NF5 unit for further deboronization. The lithium content in the deborated concentrated water is high and is returned to the NF4 unit for recycling. The membrane element material surface used in the NF4 unit and the NF5 unit is negatively charged, the operating pressure is 25 bar, the water recovery rate of the two-stage nanofiltration is controlled at 75%~85%, the lithium recovery rate is greater than 97%, and the boron content in the NF5 produced water after two-stage boron removal nanofiltration treatment is only 2mg / L, and the magnesium ion and lithium ion contents are 1mg / L and 2320mg / L respectively, forming a refined lithium solution.

[0053] (7) RO3 unit - calcium and magnesium removal resin unit: In order to increase the lithium content in the refined lithium solution and reduce the energy consumption required for MVR evaporation, the water produced by the NF5 unit is concentrated by a three-stage reverse osmosis RO3 unit, and the water recovery rate is controlled at about 75%, that is, the content of each ion is increased by about 4 times, and the lithium ion rises to about 9000 mg / L. The membrane material used in the RO3 unit is a high-pressure membrane made of polyamide, and the operating pressure reaches about 45 bar. The concentrated water of the RO3 unit is sent to the calcium-magnesium removal resin unit to completely remove the hardness. The resin system uses a cationic resin, and the removal rate of divalent cations reaches more than 98%. From the data, it can be seen that the magnesium ion content in the RO3 concentrated water treated with the calcium-magnesium removal resin is zero. At the same time, after the solution passes through the resin system, the loss rate of lithium ions is less than 1%. The magnesium-removing water produced by the calcium-magnesium removal resin unit is continuously sent to the boron removal resin unit for deep boron removal. Similarly, the boron removal rate is greater than 99%, and the lithium loss rate is less than 1%. The functional group of the boron removal resin is polyamine hydroxyl, and the skeleton is a resin cross-linked with styrene and divinylbenzene. After two-stage resin treatment, the cation contents in the deboronated water were 9200 mg / L lithium, 1000 mg / L potassium, and 730 mg / L sodium.

[0054] (8) MVR unit: The deboronated liquid is evaporated and concentrated by an MVR unit to increase the concentration of lithium. The evaporation system uses MVR technology, and the optimal operating conditions are a temperature of 85°C, an evaporation concentration multiple of about 3 times, and the lithium content after concentration reaches about 27g / L. The concentrated liquid obtained by the evaporation unit is sent to a lithium precipitation device after heat exchange. The device is equipped with stirring and heat preservation functions. The temperature of the concentrated lithium liquid after heat exchange is 95°C, and the stirring rate of the device is preferably 600-800 r / min. The lithium precipitation device is added with a sodium carbonate solution with a concentration of 150-300 g / L. When the pH reaches 8.5, the addition is stopped, and the timing and heat preservation are started. The heat preservation time is preferably 2 hours, and the lithium carbonate reaction is finally completed. The lithium carbonate and mother liquor are separated by a solid-liquid separation device. The solid-liquid separation device can be a plate-frame filter press or a centrifuge, preferably a plate-frame filter press. Pure water is used to wash the lithium carbonate solid while filtering, and the washing water returns to the inlet of the MVR unit. After washing, the lithium carbonate is dried using a disc dryer. The purity of the obtained lithium carbonate powder reaches more than 99.5%, and the content of other anionic and cationic impurities meets the standard requirements of battery grade.

[0055] (9) Four-stage reverse osmosis RO4 unit: The whole system requires a large amount of pure water as water for analysis, membrane washing and filtration, and resin regeneration. In order to improve water recovery and utilization, the water produced by RO1 unit, RO2 unit, RO3 unit and MVR unit evaporated condensed water are sent to the four-stage reverse osmosis RO4 unit for deep desalination. The concentrated water returns to the NF4 unit for further recovery of lithium ions. The desalinated water meets the system reuse water standard and is returned to each unit for utilization, realizing the maximum utilization of salt lake brine and reducing the amount of groundwater.

[0056] The water quality test data of the salt lake brine process section selected by the present invention are shown in Table 1.

[0057] Table 1. Water quality test data of salt lake brine process section

[0058] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for extracting lithium from a salt lake, comprising the following steps: (1) The salt lake brine is adsorbed and decomposed, and the obtained desorbed liquid is subjected to primary ultrafiltration UF1 treatment; (2) subjecting the produced water obtained by the first-level ultrafiltration UF1 treatment to first-level reverse osmosis RO1 treatment, and subjecting the obtained concentrated water to first-level nanofiltration NF1 treatment and second-level nanofiltration NF2 treatment; (3) subjecting the produced water obtained by the secondary nanofiltration NF2 treatment to secondary reverse osmosis RO2 treatment, and subjecting the obtained concentrated water to tertiary nanofiltration NF3 treatment; (4) adding alkali to the produced water obtained by the three-stage nanofiltration NF3 treatment, and the obtained softened liquid is sequentially subjected to a two-stage ultrafiltration UF2 treatment, a four-stage nanofiltration NF4 treatment, a five-stage nanofiltration NF5 treatment and a three-stage reverse osmosis RO3 treatment; (5) treating the concentrated water obtained by the three-stage reverse osmosis RO3 treatment with a calcium and magnesium removal resin and a boron removal resin in sequence; (6) The produced water obtained by the boron removal resin treatment is subjected to MVR evaporation concentration, and the obtained concentrated solution is subjected to lithium precipitation reaction to obtain lithium carbonate.

2. The method according to claim 1, characterized in that In step (1), the water quality test data of the salt lake brine are: TDS is 500000~600000 mg / L, pH is between 6~8, the mass ratio of magnesium ion to lithium ion is (300~500):1, the potassium ion concentration is 1000~3000 mg / L, the sodium ion concentration is 2000~5000 mg / L, and the sulfate concentration is 30000~50000 mg / L; the salt lake brine is surface brine; The adsorption conditions are as follows: using a rotating disk resin device, wherein 10 to 20 resin columns are installed in the resin device, and the resin columns are filled with lithium adsorbent; the adsorption rate is 1 to 3 BV / h; the magnesium-lithium ratio of the salt lake brine after adsorption is (10 to 20): 1; The analysis conditions are: using water for analysis, the analysis rate is 2-5 BV / h; the TDS of the analysis solution is 10000-20000 mg / L; The conditions of the first-stage ultrafiltration UF1 treatment are as follows: the ultrafiltration membrane used is one of a hollow fiber membrane, a rolled membrane, a ceramic membrane and a tubular membrane; the pore size of the ultrafiltration membrane is 10-50 nm; water is added for washing during the first-stage ultrafiltration UF1 treatment, and the amount of water added is 1 / 2-1 times the amount of water inlet; the content of suspended matter in the resulting produced water is less than 1 mg / L.

3. The method according to any one of claims 1 or 2, characterized in that: In step (2): The conditions of the primary reverse osmosis RO1 treatment are as follows: the membrane element used is a Dow reverse osmosis membrane, which is made of polyamide or polyethersulfone materials; the concentration multiple is 2 to 4 times, the operating pressure is 15 to 30 bar; the magnesium ion content in the concentrated water is 1000 to 10000 mg / L; The conditions of the primary nanofiltration NF1 treatment and the secondary nanofiltration NF2 treatment are as follows: the nanofiltration membrane used is a rolled nanofiltration membrane with a pore size of 300-600 Da; the separation layer material of the nanofiltration membrane is one of polysulfone, polyethersulfone and polyamide materials; the surface charge of the nanofiltration membrane is positive or negative; the operating pressure is 10-40 bar; water is added for filtration during operation, and the amount of water added is 1 / 2-1 times the amount of water inlet; the mass ratio of magnesium to lithium in the resulting produced water is 1:(5-10).

4. The method according to any one of claims 1 to 3, characterized in that: In step (3), the conditions of the secondary reverse osmosis RO2 treatment are as follows: the membrane element used is a Dow reverse osmosis membrane, and its material is a polyamide or polyethersulfone material; the concentration multiple is 3 to 5 times, and the operating pressure is 20 to 50 bar; The conditions of the three-stage reverse osmosis RO3 treatment are as follows: the membrane element used is a high-pressure membrane, the material of which is a polyamide material, and the molecular weight cutoff is 100-300 Da; the operating pressure is 10-40 bar, and water is added for filtration during operation, and the amount of water used is 1 / 4-1 times the amount of water inlet; The conditions of the three-stage nanofiltration NF3 treatment are as follows: the material of the membrane element used is polyamide material, and the molecular weight cut-off is 100-300 Da.

5. The method according to any one of claims 1 to 4, characterized in that: In step (4), alkali is added to the produced water after the three-stage nanofiltration NF3 treatment to adjust the pH to 8-10; the alkali is one or more of sodium hydroxide, calcium hydroxide and potassium hydroxide; The conditions of the secondary ultrafiltration UF2 treatment are as follows: the ultrafiltration membrane used is one of a central control fiber membrane, a spiral membrane, a ceramic membrane and a tubular membrane, and the membrane pore size is 10-50 nm; the concentrated liquid volume does not exceed 5% of the unit inlet water volume; The conditions of the four-stage nanofiltration NF4 treatment and the five-stage nanofiltration NF5 treatment are as follows: the membrane element used is a rolled nanofiltration membrane with a pore size of 100-300 Da, the separation layer material of the membrane is one of polysulfone, polyethersulfone and polyamide, and the surface of the membrane is positively charged or negatively charged; the operating pressure is 10-40 bar, and the water recovery rate is 75%-85%; water is added for washing during operation, and the amount of water used is 1 / 2-1 times the amount of water inlet; the boron content in the obtained produced water is less than 10 mg / L, and the lithium-magnesium ratio is greater than 500:1; The conditions of the three-stage reverse osmosis RO3 treatment are as follows: the membrane element used is a high-pressure membrane, the material of which is a polyamide material, and the molecular weight cutoff is 100-300 Da; the concentration multiple is 3-6 times, the lithium content after concentration reaches 6-10 g / L, and the operating pressure is 20-50 bar.

6. The method according to any one of claims 1 to 5, characterized in that: In step (5), the resin used in the calcium and magnesium removal resin treatment is a cationic resin; The resin used in the boron removal resin treatment is a resin formed by cross-linking styrene and divinylbenzene and having a polyamine hydroxyl functional group.

7. The method according to any one of claims 1 to 6, characterized in that: In step (6), the lithium concentration in the concentrated solution obtained by MVR evaporation and concentration reaches 20-30 g / L; The conditions of the lithium precipitation reaction are: temperature of 60-90° C., stirring rate of 200-800 r / min, and time of 1-3 h.

8. The method according to any one of claims 1 to 7, characterized in that: In the method: In step (1), the salt lake brine tail liquid after adsorption is returned to the salt lake; In step (2), the concentrated water after the first-stage ultrafiltration UF1 treatment and the concentrated water after the first-stage nanofiltration NF1 treatment are returned to the salt lake; the concentrated water after the second-stage nanofiltration NF2 treatment is returned to continue the first-stage nanofiltration NF1 treatment; In step (3), the concentrated water after the third-stage nanofiltration NF3 treatment is returned to continue the first-stage nanofiltration NF1 treatment; In step (4), the concentrated water after the secondary ultrafiltration UF2 treatment is returned to the salt lake; the concentrated water after the fourth-stage nanofiltration NF4 treatment is returned to continue the third-stage nanofiltration NF3 treatment; the concentrated water after the fifth-stage nanofiltration NF5 treatment is returned to continue the fourth-stage nanofiltration NF4 treatment; The produced water after the primary reverse osmosis RO1 treatment in step (2), the produced water after the secondary reverse osmosis RO2 treatment in step (3), the produced water after the tertiary reverse osmosis RO3 treatment in step (5), and the condensed water after the MVR evaporation concentration in step (6) are subjected to the fourth-stage reverse osmosis RO4 treatment, and the obtained produced water is recycled; the concentrated water after the fourth-stage reverse osmosis RO4 treatment is subjected to the fourth-stage nanofiltration NF4 treatment; The membrane element used in the four-stage reverse osmosis RO4 treatment is a reverse osmosis membrane, which is made of one or more of polyamide materials, polyethersulfone materials and polysulfone materials, and has a pressure resistance of 40-60 bar.

9. An extraction device for implementing the method according to any one of claims 1 to 8, comprising the following units connected in sequence: a lithium adsorbent unit, a primary ultrafiltration UF1 unit, a primary reverse osmosis RO1 unit, a primary nanofiltration NF1 unit, a secondary nanofiltration NF2 unit, a secondary reverse osmosis RO2 unit, a tertiary nanofiltration NF3 unit, a secondary ultrafiltration UF2 unit, a quaternary nanofiltration NF4 unit, a quintuple nanofiltration NF5 unit, a tertiary reverse osmosis RO3 unit, a calcium and magnesium removal resin unit, a boron removal resin unit, an MVR evaporation unit, and a lithium precipitation reaction unit; The tail liquid outlet of the lithium adsorbent unit is connected to the salt lake brine; The concentrated water outlet of the first-stage ultrafiltration UF1 unit and the concentrated water outlet of the first-stage nanofiltration NF1 unit are connected to the salt lake brine; The concentrated water outlet of the secondary nanofiltration NF2 unit and the concentrated water outlet pipeline of the tertiary nanofiltration NF3 unit are connected to the water inlet pipeline of the primary nanofiltration NF1 unit; The concentrated water outlet of the secondary ultrafiltration UF2 unit is connected to the salt lake brine; The concentrated water outlet of the fourth-stage nanofiltration NF4 unit is connected to the water inlet pipeline of the third-stage nanofiltration NF3 unit; The concentrated water outlet of the five-stage nanofiltration NF5 unit is connected to the water inlet pipeline of the four-stage nanofiltration NF4 unit; The first-stage ultrafiltration UF1 unit, the first-stage nanofiltration NF1 unit, the third-stage nanofiltration NF3 unit, and the fourth-stage nanofiltration NF4 unit are provided with an inlet for water for filtration washing.

10. The extraction device according to claim 9, characterized in that: The device also includes a four-stage reverse osmosis RO4 unit; The water outlet of the first-stage reverse osmosis RO1 unit, the water outlet of the second-stage reverse osmosis RO2 unit, the water outlet of the third-stage reverse osmosis RO3 unit and the evaporation condensation water outlet of the MVR evaporation unit are connected to the inlet pipeline of the fourth-stage reverse osmosis RO4 unit; The concentrated water outlet of the four-stage reverse osmosis RO4 unit is connected to the inlet pipeline of the four-stage nanofiltration NF4 unit.

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