CN109824065B - Method for separating magnesium and lithium and enriching lithium - Google Patents
Method for separating magnesium and lithium and enriching lithium Download PDFInfo
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Abstract
The invention discloses a method for separating magnesium and lithium and enriching lithium, which comprises the following steps: diluting and filtering the old brine in the salt pan to obtain nanofiltration raw water; allowing the nanofiltration raw water to enter a first nanofiltration separation device for magnesium-lithium separation to obtain first nanofiltration concentrated water and first nanofiltration fresh water; enabling the first nanofiltration fresh water to enter a reverse osmosis device for primary concentration to obtain reverse osmosis concentrated water and reverse osmosis fresh water; enabling the reverse osmosis concentrated water to enter a second nanofiltration separation device, and performing magnesium-lithium separation again to obtain second nanofiltration concentrated water and second nanofiltration fresh water; and enabling the second nanofiltration fresh water to enter an electrodialysis device for secondary concentration to obtain electrodialysis concentrated water and electrodialysis fresh water, wherein the electrodialysis concentrated water is a solution enriched with lithium ions. The invention couples four membrane separation technologies of ultrafiltration, nanofiltration, reverse osmosis and electrodialysis in a certain sequence, and fully utilizes the advantages of various membrane separation technologies to finish the high-efficiency separation and enrichment of lithium in the salt lake brine with high magnesium-lithium ratio.
Description
Technical Field
The invention relates to a method for separating magnesium and lithium and enriching lithium, belonging to the technical field of solution separation and purification.
Background
Lithium is an important element for promoting the world progress, is listed as national mineral products, and is a key object for the macroscopic regulation and supervision and management of mineral resources. The lithium resource has wide application in various fields of national economy such as aerospace, electrical and electronic and metal smelting, and the development and development of the lithium resource are important in the competition of energy high lands in China and are important requirements of China. The industrial reserve of lithium resources which is proved to be in China is located in the second place of the world, wherein the lithium brine accounts for 79 percent of the total reserve of the lithium resources, and the prospective reserve of the lithium brine of salt lakes in Qinghai-Tibet plateau areas is equivalent to the total reserve which is proved to be in China at present. However, the salt lake brine in the Qinghai region has the obvious characteristics of high magnesium and low lithium, the chemical properties of magnesium and lithium are similar, and the difficulty of separating and extracting lithium is increased due to the existence of a large amount of magnesium.
The single method for extracting lithium from salt lake brine and enriching lithium is difficult to realize the aim of efficiently enriching and concentrating lithium while realizing the separation of magnesium and lithium from the salt lake brine. In addition, in the process of enriching lithium in part of salt lake brine, in order to achieve the concentration of lithium required by preparing high-purity lithium salt, evaporation concentration equipment is required to be used for concentrating brine after magnesium and lithium are separated, so that the production efficiency of the high-purity lithium salt is reduced, and the energy consumption in the evaporation concentration process is high, so that the production cost of the high-purity lithium salt is increased.
The existing methods for extracting lithium from salt lake brine comprise a calcination method, an adsorption method, a nanofiltration membrane separation method, an electrodialysis method and the like. The methods are applied to the lithium extraction in the salt lake, but different methods have respective advantages and disadvantages and need certain perfection and improvement. For example, the calcining method has high energy consumption for extracting lithium and can generate environmental pollution in the calcining process; the adsorption and lithium extraction process is easy to generate the dissolution loss of the adsorbent; organic pollution is easy to generate in the process of extracting lithium, and an extracting agent can corrode equipment; the nanofiltration method needs to dilute the original brine, so that the fresh water consumption is high and the process energy consumption is high; the problems of large lithium loss and low current efficiency exist in the process of extracting lithium from salt lake brine by electrodialysis.
For example, cn03108088.x, discloses a nanofiltration process for separating magnesium and enriching lithium from salt lake brine. The method is used for carrying out magnesium-lithium separation and lithium enrichment on lithium-containing brine or a lithium-containing solution through a nanofiltration technology, and preparing lithium carbonate or lithium hydroxide from the obtained lithium-rich brine, so that the lithium extraction from the salt lake brine with high magnesium-lithium ratio is realized, and the method is simple in process flow, reliable in operation and low in energy consumption. However, the lithium-rich brine obtained by separating and enriching the lithium-containing brine has low lithium ion content; the concentrated solution at the high pressure side returns to the stock solution tank for circulation, so that the magnesium-lithium separation effect is reduced; and the intermittent cycle operation process has low efficiency and poor continuity, and is not favorable for popularization and application, industrial demonstration and large-scale production.
In addition, CN 201310035015.7 discloses a treatment method for separating lithium from salt lake brine with high magnesium-lithium ratio. Firstly, carrying out nanofiltration treatment on the evaporated and desulfurized old brine by using a nanofiltration device, then feeding the obtained lithium-rich produced water into a reverse osmosis device for concentration to obtain reverse osmosis concentrated water, and then carrying out salt field evaporation on the deeply magnesium-removed reverse osmosis concentrated water to obtain the lithium-rich brine. The water produced by nanofiltration after nanofiltration treatment in the patent process has higher magnesium-lithium ratio, so that the lithium-rich brine obtained after subsequent reverse osmosis concentration and salt pan evaporation still maintains higher magnesium-lithium ratio; and the lithium-rich water produced after reverse osmosis concentration has low lithium ion concentration, and the lithium ion concentration required for preparing high-purity lithium carbonate can be achieved only by evaporation in a salt pan. However, the evaporation process of the salt pan is greatly influenced by seasons, the yield and the quality of products are unstable, and meanwhile, the leakage loss of the salt pan is high, so that the yield and the utilization rate of lithium are low; in addition, the recycling proportion of reverse osmosis fresh water in the process is low, and the recycling of the fresh water is not facilitated.
For another example, CN 201310731430.6 discloses a method and an apparatus for extracting lithium chloride from bittern. In the patent, desorption liquid obtained after lithium-containing old brine in an old brine pool is absorbed and analyzed is filtered by a coarse filter and then is sent to a nanofiltration device for magnesium-lithium separation; concentrating the nanofiltration permeate by using a reverse osmosis device to obtain reverse osmosis concentrate; and finally, further concentrating the reverse osmosis concentrated solution through a salt drying or evaporation process to extract high-purity lithium chloride bittern. However, when the aluminum salt adsorbent is used for adsorbing lithium in bittern, the problems of low desorption rate, high solvent loss rate of the adsorbent, low adsorption capacity and short service life of the adsorbent exist; and the concentration multiple of lithium is low in the reverse osmosis concentration process, the lithium content in the reverse osmosis concentrated water is low, and salt drying or evaporation is still required to be carried out subsequently to further improve the lithium ion concentration.
For another example, CN 201610583440.3 discloses a preparation method of battery-grade lithium carbonate. The patent utilizes a monovalent ion selective membrane to carry out electrodialysis treatment on eluent after lithium is absorbed and extracted, and separation of lithium and impurity ions such as magnesium, sulfate radicals, borate radicals and the like and concentration of lithium are completed. And after a lithium-rich concentrated solution with the lithium content of 10-20 g/L and the magnesium-lithium ratio of 0.1-1 is obtained, deep calcium and magnesium removal, lithium precipitation conversion, filtration washing, drying and cooling are carried out on the lithium-rich concentrated solution, and finally a battery-grade lithium carbonate product is obtained. The patent uses a multi-stage electrodialysis method to concentrate lithium in lithium-rich eluent, but because the concentration of lithium chloride in the eluent is low, multiple electrodialysis circulation operations are required, so that the concentration period is increased; the electrodialysis process has high power consumption and low current efficiency, increases the energy consumption in the concentration process and reduces the concentration efficiency; the finally obtained lithium-rich concentrated solution has higher magnesium-lithium ratio, increases the pressure of the subsequent magnesium removal and precipitation conversion processes, and increases the cost for obtaining a lithium carbonate product.
Therefore, the method for efficiently and reasonably synchronously realizing the separation of magnesium and lithium in the lithium-containing brine in the salt lake and the efficient concentration of lithium in the brine is very important for improving the lithium ion yield of the lithium-rich brine and reducing the process cost and energy consumption.
Disclosure of Invention
The invention mainly aims to provide a method for separating magnesium and lithium and enriching lithium, thereby overcoming the defects in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the embodiment of the invention provides a method for separating magnesium and lithium and enriching lithium, which comprises the following steps:
(1) diluting and filtering the old brine in the salt pan to obtain nanofiltration raw water;
(2) allowing the nanofiltration raw water to enter a first nanofiltration separation device for magnesium-lithium separation to obtain first nanofiltration concentrated water and first nanofiltration fresh water;
(3) enabling the first nanofiltration fresh water to enter a reverse osmosis device for primary concentration to obtain reverse osmosis concentrated water and reverse osmosis fresh water;
(4) enabling the reverse osmosis concentrated water to enter a second nanofiltration separation device, and performing magnesium-lithium separation again to obtain second nanofiltration concentrated water and second nanofiltration fresh water;
(5) and enabling the second nanofiltration fresh water to enter an electrodialysis device for secondary concentration to obtain electrodialysis concentrated water and electrodialysis fresh water, wherein the electrodialysis concentrated water is a solution enriched with lithium ions.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention mainly aims at the defects in the process of extracting lithium by membrane separation, innovatively couples four membrane separation technologies of ultrafiltration, nanofiltration, reverse osmosis and electrodialysis in a certain sequence, and fully utilizes the advantages of various membrane separation technologies to finish the efficient separation and enrichment of lithium in salt lake brine with high magnesium-lithium ratio.
(2) The multi-stage nanofiltration separation technology is fully utilized, the magnesium-lithium separation process can be effectively strengthened, the magnesium-lithium ratio of brine entering an electrodialysis device is reduced, the concentration pressure of the electrodialysis device is reduced, the concentration efficiency is improved, the lithium ion concentration in electrodialysis concentrated water is improved, qualified lithium-rich brine required for preparing high-purity lithium salt is obtained, the high-efficiency concentration of lithium in salt lake brine is completed while the magnesium-lithium separation of the salt lake brine is realized, the lithium ion concentration required for preparing the high-purity lithium salt is achieved, the lithium loss rate is low, and the lithium content in the lithium-rich brine is fully ensured.
(3) The concentration pressure of the electrodialysis unit is effectively reduced and the energy consumption and the production cost of the electrodialysis unit are reduced by innovatively adopting a three-stage nanofiltration technology; the method is favorable for improving the automation degree of the subsequent lithium salt production process, reducing the equipment investment in the lithium salt production process, greatly reducing the use amount of alkali in the refining magnesium removal stage and reducing the production cost of high-purity lithium salt.
(4) The salt lake brine after ultrafiltration impurity removal is sent to a separation unit, and the high-efficiency separation of magnesium and lithium in the salt lake brine is completed by fully utilizing the selectivity of a nanofiltration membrane on primary ions and divalent ions; then, feeding the nanofiltration fresh water with low magnesium-lithium ratio into a primary concentration unit for primary concentration of lithium, and then performing magnesium-lithium separation on the reverse osmosis concentrated water through a three-stage nanofiltration separation unit to further reduce the magnesium-lithium ratio of the reverse osmosis concentrated water; and then carrying out secondary concentration on the three-stage nanofiltration fresh water with low magnesium-lithium ratio and high lithium content by using an electrodialysis technology to achieve the lithium ion concentration required by preparing high-purity lithium salt, and fully utilizing the advantages of four membrane separation technologies in the process to complete magnesium-lithium separation of the salt lake brine and achieve the purpose of efficient concentration of lithium in the salt lake brine. The method has the advantages of simple process, good magnesium-lithium separation effect, short lithium concentration period and remarkable lithium concentration effect. The invention adopts a full physical process in the processes of magnesium-lithium separation and efficient lithium concentration, and does not pollute the environment. The process fully realizes the cyclic utilization of fresh water, improves the reuse rate of the fresh water, effectively reduces the energy consumption and the cost of the production process of the lithium-rich brine, and has outstanding economic advantages.
Drawings
FIG. 1 is a flow chart of a method for separating and enriching Mg and Li according to an embodiment of the present invention.
Detailed Description
In view of the deficiencies in the prior art, the inventors of the present invention have long studied and practiced in great numbers to provide a technical solution of the present invention, which will be further explained as follows.
As one aspect of the technical scheme of the invention, the invention relates to a method for separating magnesium and lithium and enriching lithium, which comprises the following steps:
(1) diluting and filtering the old brine in the salt pan to obtain nanofiltration raw water;
(2) allowing the nanofiltration raw water to enter a first nanofiltration separation device for magnesium-lithium separation to obtain first nanofiltration concentrated water and first nanofiltration fresh water;
(3) enabling the first nanofiltration fresh water to enter a reverse osmosis device for primary concentration to obtain reverse osmosis concentrated water and reverse osmosis fresh water;
(4) enabling the reverse osmosis concentrated water to enter a second nanofiltration separation device, and performing magnesium-lithium separation again to obtain second nanofiltration concentrated water and second nanofiltration fresh water;
(5) and enabling the second nanofiltration fresh water to enter an electrodialysis device for secondary concentration to obtain electrodialysis concentrated water and electrodialysis fresh water, wherein the electrodialysis concentrated water is a solution enriched with lithium ions.
In some embodiments, the first nanofiltration separation device comprises at least a first nanofiltration separation unit and a second nanofiltration separation unit, the raw nanofiltration water firstly enters the first nanofiltration separation unit to be subjected to magnesium-lithium separation, so as to obtain first nanofiltration concentrated water and first nanofiltration fresh water, and the first nanofiltration fresh water then enters the second nanofiltration separation unit to be subjected to magnesium-lithium separation, so as to obtain the first nanofiltration concentrated water and the first nanofiltration fresh water.
In some preferred embodiments, the primary nanofiltration separation unit comprises a plurality of stages of primary nanofiltration separation modules connected in series, wherein each stage of primary nanofiltration separation module comprises nanofiltration separation membranes with different numbers and proportions, respectively, and the secondary nanofiltration separation unit comprises a plurality of stages of secondary nanofiltration separation modules connected in series, wherein each stage of secondary nanofiltration separation modules comprises nanofiltration separation membranes with different numbers and proportions, respectively.
Furthermore, in the primary nanofiltration separation unit, the number ratio of nanofiltration separation membranes contained in each section of primary nanofiltration separation module ranges from 185 to 365:85 to 165, and preferably ranges from 225 to 325:105 to 145.
Furthermore, in the secondary nanofiltration separation unit, the number ratio of nanofiltration separation membranes contained in each section of secondary nanofiltration separation module ranges from 35 to 115:5 to 45, and preferably ranges from 55 to 95:20 to 30.
Further, the nanofiltration separation membrane is selective for monovalent ions and divalent ions.
In some embodiments, the first nanofiltration separation device is used for magnesium-lithium separation at an operating pressure of 3.5-10.0 MPa, preferably 4.0-6.0 MPa.
In some embodiments, the concentration of lithium ions in the first nanofiltration fresh water is 0.1-2.0 g/L, preferably 0.5-1.2 g/L.
In some embodiments, the mass ratio of magnesium ions to lithium ions in the first nanofiltration fresh water is from 0.02 to 3.2: 1, preferably 0.05 to 0.2: 1.
in some embodiments, step (1) specifically comprises: and (3) carrying out primary dilution on the salt field old brine, sequentially feeding the salt field old brine subjected to primary dilution into a multi-medium filtering device and an ultrafiltration device for filtering, and then carrying out secondary dilution to obtain the nanofiltration raw water.
In some embodiments, the concentration of lithium ions in the salt pan old brine is 0.2-5.0 g/L, preferably 2.5-4.0 g/L.
In some embodiments, the mass ratio of magnesium ions to lithium ions in the salt pan old brine is 6-180: 1, preferably 6-55: 1.
In some embodiments, the reverse osmosis apparatus comprises multiple stages of reverse osmosis units connected in series, wherein each stage of reverse osmosis unit contains a different quantitative ratio of reverse osmosis membranes.
In some preferred embodiments, the quantity ratio range of each reverse osmosis membrane section is as follows: 98-190: 71-121: 24-60, preferably 132-156: 84-108: 33-51.
In some embodiments, the reverse osmosis device performs primary concentration at an operating pressure of 3.5 to 15.0MPa, preferably 3.5 to 10.0 MPa.
In some embodiments, the concentration of lithium ions in the reverse osmosis concentrated water is 2.0-10 g/L, preferably 3.0-5.0 g/L.
In some embodiments, the reverse osmosis concentrated water has a mass ratio of magnesium ions to lithium ions of 0.05 to 3.0: 1, preferably 0.07-0.2: 1.
in some embodiments, the second nanofiltration separation device comprises a plurality of stages of three-stage nanofiltration separation units connected in series, wherein each stage of three-stage nanofiltration separation units respectively comprises nanofiltration separation membranes with different quantitative ratios;
in some preferred embodiments, the quantity ratio range of each nanofiltration separation membrane section is as follows: 35 to 115:5 to 45, preferably 55 to 95:20 to 30.
Further, the nanofiltration separation membrane is selective for monovalent ions and divalent ions.
In some embodiments, the second nanofiltration separation device is operated at a pressure of 0.5 to 4.0MPa, preferably 0.8 to 2.0MPa, for magnesium-lithium separation.
In some embodiments, the concentration of lithium ions in the second nanofiltration fresh water is 1.5 to 4.5g/L, preferably 2.5 to 4.0 g/L.
In some embodiments, the mass ratio of magnesium ions to lithium ions in the second nanofiltration fresh water is from 0.01 to 1.2: 1, preferably 0.05 to 0.15: 1.
in some embodiments, the concentration of lithium ions in the electrodialysis concentrated water is 6-25 g/L, preferably 14-22 g/L.
In some embodiments, the mass ratio of magnesium ions to lithium ions in the electrodialysis concentrated water is 0.05-1.3: 1, preferably 0.07-0.2: 1.
in some embodiments, the second concentration employs an ion selective membrane comprising one of a homogeneous membrane, a semi-homogeneous membrane, and a heterogeneous membrane.
In some specific embodiments, the high-efficiency separation and enrichment of lithium in salt lake brine is realized by utilizing the coupling of various membrane separation processes, and mainly comprises the following steps:
(1) the pretreatment unit is used for carrying out salt field old brine dilution and impurity removal to obtain nanofiltration raw water:
old brine from a salt pan enters an old brine tank, is diluted for the first time and then is sent to a multi-media filter to filter mechanical impurities such as suspended matters, silt and the like;
then the mixture enters organic membrane ultrafiltration equipment, and impurities such as macromolecular substances, water-soluble polymers and the like are filtered by the organic membrane ultrafiltration equipment;
then the mixture is sent into a first nanofiltration separation device after secondary dilution. Wherein the concentration of lithium ions in the salt pan old brine is 0.2-5.0 g/L, preferably 2.5-4.0 g/L, and the mass ratio of magnesium ions to lithium ions is 6-180: 1, preferably 6-55: 1.
wherein, the diluting and pre-treating process is determined according to the characteristics of the salt lake brine.
(2) The first nanofiltration separation device is used for magnesium-lithium separation
The raw nanofiltration water enters a first nanofiltration separation device for magnesium and lithium separation, the key equipment of the first nanofiltration separation device is a multistage and multistage nanofiltration separation device, for example, the first nanofiltration separation device comprises a first-stage nanofiltration separation unit and a second-stage nanofiltration separation unit, and a high-quality and high-efficiency nanofiltration separation membrane capable of working under the condition of ultrahigh pressure is adopted. And (3) conveying the nanofiltration raw water to the high-pressure side of the first nanofiltration separation device, and efficiently separating magnesium and lithium in the brine by utilizing the pressure difference between two sides of the nanofiltration separation membrane and the difference of monovalent and divalent ion selectivity of the nanofiltration separation membrane, so as to reduce the magnesium-lithium mass ratio of the brine and improve the concentration of lithium ions in the first nanofiltration fresh water. The first nanofiltration concentrated water generated in the multi-stage separation process is recycled, so that the utilization rate and the yield of lithium ions are improved. Under the ultrahigh pressure separation effect of 4.0-6.0MPa of the separation unit, after multi-stage and multi-stage nanofiltration separation operation, the concentration of lithium ions in the first nanofiltration fresh water is 0.1-2.0 g/L, preferably 0.5-1.2 g/L, the mass ratio of magnesium ions to lithium ions is reduced to 0.02-3.2: 1, preferably 0.05-0.2: 1.
the nanofiltration separation membrane is used for separating magnesium and lithium in the brine by utilizing different interception performances of monovalent ions and divalent ions, so that the magnesium-lithium ratio of the old brine is reduced.
Specifically, a nanofiltration separation process with more than two stages is arranged according to the characteristics of salt lake brine, and primary nanofiltration fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nanofiltration process to further reduce the magnesium-lithium ratio in permeate liquid and improve the lithium ion concentration; the first nanofiltration fresh water obtained after the second-stage nanofiltration can continuously enter the next-stage nanofiltration process to further improve the concentration of lithium ions, and the like. Besides multi-stage nanofiltration, a multi-stage series connection mode is also creatively adopted in the primary and secondary nanofiltration processes, and each stage respectively contains nanofiltration separation membranes with different quantity ratios, so that the utilization rate of lithium ions is improved, and the lithium yield is improved. Exchanging heat between concentrated water generated after primary nanofiltration separation and industrial fresh water used for primary dilution from the outside, and then discharging the concentrated water and the industrial fresh water to a salt pan for recycling so as to fully utilize energy in the concentrated water and reduce discharge of waste water; and returning the first nanofiltration concentrated water generated after the secondary nanofiltration separation to the primary nanofiltration separation unit for secondary dilution of the original halogen so as to reduce the usage amount of the industrial fresh water, reduce the production cost, improve the utilization rate of lithium ions in the process and improve the lithium yield of the separation unit.
(3) The reverse osmosis device carries out primary concentration
And (4) feeding the first nanofiltration fresh water subjected to magnesium-lithium separation in the last step into a reverse osmosis device for primary concentration. And (3) performing primary concentration on the first nanofiltration fresh water obtained by the first nanofiltration separation device by adopting a multi-section reverse osmosis unit, further increasing the concentration of lithium ions, generating reverse osmosis fresh water, performing secondary dilution on brine by using the generated reverse osmosis fresh water, and enabling the reverse osmosis concentrated water to enter a third-stage nanofiltration separation unit in the second nanofiltration separation device for magnesium-lithium separation again. After the reverse osmosis primary concentration, the concentration of lithium ions in the reverse osmosis concentrated water is 2.0-10 g/L, preferably 3.0-5.0 g/L; the mass ratio of the magnesium ions to the lithium ions is 0.05-3.0: 1. preferably 0.07-0.2: 1.
wherein, the reverse osmosis membrane commonly used for seawater desalination is adopted, and the lithium ion content in the reverse osmosis concentrated water can be greatly improved after one-time concentration. According to the separation characteristics of the reverse osmosis membrane and the unique ion content characteristics of the salt lake brine, the primary concentration adopts a multi-section series connection mode, and each section contains reverse osmosis membranes with different quantity ratios, so that the energy consumption of the process is reduced, the rationality of the whole system is improved, and the lithium permeability in the reverse osmosis fresh water is fully reduced.
(4) The second nanofiltration separation device is used for magnesium-lithium separation
And (3) the lithium-rich brine subjected to primary concentration in the previous step enters a third-stage nanofiltration separation unit in a second nanofiltration separation device to reinforce the magnesium-lithium separation process. The key equipment of the three-stage nanofiltration separation unit is a multi-stage nanofiltration separation device, and a high-quality and high-efficiency primary and divalent ion selective nanofiltration separation membrane is adopted in the separation process. And feeding the lithium-rich brine subjected to primary concentration into the high-pressure side of a three-stage nanofiltration separation unit, strengthening the magnesium-lithium separation process of the lithium-rich brine by utilizing the pressure difference between two sides of the nanofiltration membrane and the selectivity difference of the nanofiltration membrane on monovalent and divalent ions, reducing the magnesium-lithium mass ratio of the brine again, and greatly increasing the lithium ion concentration in the second nanofiltration fresh water. The second nanofiltration concentrated water generated in the three-stage nanofiltration separation process is recycled, so that the utilization rate and the yield of lithium ions in the technological process are improved. After the separation operation, the concentration of lithium ions in the second nanofiltration fresh water is 1.5-4.5 g/L, preferably 2.5-4.0 g/L, and the mass ratio of magnesium ions to lithium ions is 0.01-1.2: 1, preferably 0.05-0.15: 1.
the second nanofiltration separation device utilizes the interception performance of the nanofiltration separation membrane on univalent and bivalent ions to strengthen the magnesium-lithium separation process of reverse osmosis concentrated water. According to the separation characteristics of the nanofiltration separation membrane and the unique ion content characteristics of the salt lake brine, the three-stage nanofiltration separation unit in the second nanofiltration separation device adopts a multi-stage series connection mode, and each stage respectively contains nanofiltration separation membranes with different quantity ratios, so that the energy consumption of the separation process is reduced, the rationality of the whole system is improved, the magnesium-lithium ratio of the nanofiltration fresh water is effectively reduced, and the lithium ion content of the nanofiltration fresh water is improved.
(5) The electrodialysis device carries out secondary concentration
And (4) feeding the second nanofiltration fresh water subjected to the magnesium and lithium nanofiltration separation in the last step into an electrodialysis device for secondary concentration. And (3) carrying out secondary concentration on the second nanofiltration fresh water by adopting an electrodialysis device, further improving the concentration of lithium ions, and controlling the magnesium-lithium ratio of the finally obtained electrodialysis concentrated water to be 0.05-1.3: 1, preferably 0.07-0.2: 1, the concentration of lithium ions can reach 6-25 g/L, preferably 14-22 g/L.
The ion selective membrane adopted by the secondary concentration comprises a homogeneous membrane, a semi-homogeneous membrane, a heterogeneous membrane and the like, preferably adopts a homogeneous ion exchange membrane, has high selective permeability, low resistance, excellent stability, strong acid and strong base resistance and high concentration efficiency, has similar components to common ion exchange resin, and has long service life. After electrodialysis concentration, electrodialysis fresh water is returned to the reverse osmosis device for recycling, so that the utilization rate of lithium ions in the whole process is improved, and the yield of the lithium ions is improved.
The technical solutions of the present invention will be described in further detail below with reference to several preferred embodiments and accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The test methods in the following examples, which are not specified under specific conditions, are generally carried out under conventional conditions.
Example 1
(1) The used old brine comes from a sulfate type salt lake in Qinghai, the lithium ion content in the old brine is 2.5g/L, and the Mg/Li mass ratio is 50. The old brine enters a multi-media filter for removing impurities such as suspended matters, silt and the like in the brine after being diluted for one time, and then enters organic ultrafiltration equipment for completely removing the impurities. And (4) the nanofiltration raw water obtained by secondary dilution of the old brine after complete impurity removal enters a separation unit to carry out magnesium-lithium separation. The old brine is diluted 15 times in the whole process.
(2) The pretreated brine enters a separation unit for magnesium-lithium separation, and the content of magnesium ions in the obtained nanofiltration fresh water is reduced to 0.12 g/L; the lithium ion content was 0.95g/l and the Mg/Li mass ratio was 0.125.
The magnesium-lithium separation unit mainly comprises a monovalent ion selective nanofiltration membrane, and the operating pressure is 5.0 MPa. According to the characteristic of high magnesium-lithium ratio of salt lake brine, a multi-stage nanofiltration process is arranged, primary nano fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nano filtration process to further reduce the magnesium-lithium ratio in a permeate liquid, improve the lithium ion concentration of the permeate liquid, and recycle the primary nano concentrated water; and the secondary nano-fresh water obtained after the secondary nano-filtration separation is continuously fed into the next-stage nano-filtration process to further improve the concentration of lithium ions, and the secondary nano-concentrated water is recycled, so that the process is similar to the process. The finally obtained nanofiltration fresh water enters a reverse osmosis unit for primary concentration, and the nanofiltration concentrated water is directly reused for diluting the old brine for recycling, so that the discharge of waste water is reduced, and the energy utilization rate is improved.
(3) And the separated nanofiltration fresh water enters a reverse osmosis system for primary concentration to obtain reverse osmosis concentrated water, wherein the content of lithium ions in the reverse osmosis concentrated water is 3.5g/L, and the mass ratio of Mg to Li is 0.146.
The operating pressure of the primary concentration unit is 8.0MPa, and the reverse osmosis fresh water obtained in the primary concentration process is directly reused for diluting old brine, so that the utilization rate of the fresh water is improved; and the reverse osmosis concentrated water enters a three-stage nanofiltration separation unit for magnesium and lithium separation.
(4) The reverse osmosis concentrated water after primary concentration enters a three-stage nanofiltration separation unit to be subjected to magnesium-lithium separation process enhancement, the content of lithium ions in the obtained three-sodium fresh water is 4.0g/L, and the mass ratio of Mg/Li is 0.07.
The operating pressure of the three-stage nanofiltration separation unit is 2.0MPa, and the three-stage nanofiltration concentrated water generated by the three-stage nanofiltration separation unit returns to the secondary nanofiltration separation process, so that the utilization rate of lithium is improved; and allowing the trina fresh water to enter an electrodialysis system for secondary concentration.
(5) And allowing the trinexano fresh water to enter an electrodialysis system for secondary concentration, wherein the lithium ion content in the concentrated solution after the secondary concentration is 20g/L, and the Mg/Li mass ratio is 0.07.
And the electrodialysis fresh water obtained in the secondary concentration process enters a reverse osmosis system, the recovery of residual lithium and the recycling of fresh water are realized through a primary concentration unit, and the lithium ion content in the electrodialysis concentrated water obtained in the secondary concentration process reaches the lithium ion concentration required for preparing high-purity lithium salt.
The overall process flow can be seen in fig. 1.
The compositions of the salt lake brine and the solutions of the respective stages used in the above examples are shown in Table 1.
TABLE 1 compositions of the old brine and solutions of the stages in the examples
By the embodiment, magnesium and lithium separation and efficient lithium enrichment of sulfate type salt lake brine are realized, and finally obtained electrodialysis concentrated water can be directly used for preparing high-purity lithium salt. The yield of lithium ions in the magnesium-lithium separation process is more than 88%, the yield of lithium ions in the whole concentration system is more than 95%, and the utilization rate of lithium ions in the whole process is effectively improved.
Example 2
(1) The used old brine comes from a sulfate type salt lake in Qinghai, the lithium ion content in the old brine is 2.5g/L, and the Mg/Li mass ratio is 50. The old brine enters a multi-media filter for removing impurities such as suspended matters, silt and the like in the brine after being diluted for one time, and then enters organic ultrafiltration equipment for completely removing the impurities. And (4) the old brine after complete impurity removal enters a separation unit for magnesium and lithium separation through secondary dilution. The old brine is diluted 15 times in the whole process.
(2) The pretreated brine enters a separation unit for magnesium-lithium separation, and the content of magnesium ions in the obtained nanofiltration fresh water is reduced to 0.23 g/L; the lithium ion content was 0.65g/L, and the Mg/Li mass ratio was 0.30.
The magnesium-lithium separation unit mainly comprises a monovalent ion selective nanofiltration membrane, and the operating pressure is 3.5 MPa. According to the characteristic of high magnesium-lithium ratio of salt lake brine, a multi-stage nanofiltration process is arranged, primary nano fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nano filtration process to further reduce the magnesium-lithium ratio in a permeate liquid, improve the lithium ion concentration of the permeate liquid, and recycle the primary nano concentrated water; and the secondary nano-fresh water obtained after the secondary nano-filtration separation is continuously fed into the next-stage nano-filtration process to further improve the concentration of lithium ions, and the secondary nano-concentrated water is recycled, so that the process is similar to the process. The finally obtained nanofiltration fresh water enters a reverse osmosis unit for primary concentration, and nanofiltration concentrated water is recycled, so that the discharge of waste water is reduced, and the energy utilization rate is improved.
(3) And the separated permeate enters a reverse osmosis system for primary concentration, and the obtained reverse osmosis concentrated water has the lithium ion content of 2.9g/L and the Mg/Li mass ratio of 0.345.
The operating pressure of the primary concentration unit is 3.5MPa, and the reverse osmosis fresh water obtained in the primary concentration process is directly reused for diluting old brine, so that the utilization rate of the fresh water is improved; and the reverse osmosis concentrated water enters a three-stage nanofiltration separation unit for magnesium and lithium separation.
(4) The reverse osmosis concentrated water after primary concentration enters a three-stage nanofiltration separation unit to reinforce the magnesium-lithium separation process, and the obtained three-stage nanofiltration fresh water has the lithium ion content of 3.3g/L and the Mg/Li mass ratio of 0.18.
The operating pressure of the three-stage nanofiltration separation unit is 2.0MPa, and the three-stage nanofiltration concentrated water generated by the three-stage nanofiltration separation unit returns to the secondary nanofiltration separation process, so that the utilization rate of lithium is improved; and allowing the trina fresh water to enter an electrodialysis system for secondary concentration.
(5) And allowing the trinexano fresh water to enter an electrodialysis system for secondary concentration, wherein the lithium ion content in the concentrated solution after the secondary concentration is 14g/L, and the Mg/Li mass ratio is 0.18.
And the electrodialysis fresh water obtained in the secondary concentration process enters a reverse osmosis system, the recovery of residual lithium and the recycling of fresh water are realized through a primary concentration unit, and the lithium ion content in the electrodialysis concentrated water obtained in the secondary concentration process reaches the lithium ion concentration required for preparing high-purity lithium salt.
The compositions of the salt lake brine and the solutions of the respective stages used in the above examples are shown in Table 2.
Table 2 example compositions of the old brine and the solutions at each stage.
By the embodiment, magnesium and lithium separation and efficient lithium enrichment of sulfate type salt lake brine are realized, and finally the obtained electrodialysis concentrated solution can be directly used for preparing high-purity lithium salt. The yield of lithium ions in the magnesium-lithium separation process is more than 70%, the yield of lithium ions in the whole concentration system is more than 75%, and the utilization rate of lithium ions in the whole process is effectively improved.
Example 3
(1) The used old brine comes from a sulfate type salt lake in Qinghai, the lithium ion content in the old brine is 0.2g/L, and the Mg/Li mass ratio is 180. The old brine enters a multi-media filter for removing impurities such as suspended matters, silt and the like in the brine after being diluted for one time, and then enters organic ultrafiltration equipment for completely removing the impurities. And (4) the old brine after complete impurity removal enters a separation unit for magnesium and lithium separation through secondary dilution. The old brine is diluted 15 times in the whole process.
(2) The pretreated brine enters a separation unit for magnesium-lithium separation, and the content of magnesium ions in the obtained nanofiltration fresh water is reduced to 0.32 g/L; the lithium ion content was 0.1g/L, and the Mg/Li mass ratio was 3.2.
The magnesium-lithium separation unit mainly comprises a monovalent ion selective nanofiltration membrane, and the operating pressure is 3.5 MPa. According to the characteristic of high magnesium-lithium ratio of salt lake brine, a multi-stage nanofiltration process is arranged, primary nano fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nano filtration process to further reduce the magnesium-lithium ratio in a permeate liquid, improve the lithium ion concentration of the permeate liquid, and recycle the primary nano concentrated water; and the secondary nano-fresh water obtained after the secondary nano-filtration separation is continuously fed into the next-stage nano-filtration process to further improve the concentration of lithium ions, and the secondary nano-concentrated water is recycled, so that the process is similar to the process. The finally obtained nanofiltration fresh water enters a reverse osmosis unit for primary concentration, and nanofiltration concentrated water is recycled, so that the discharge of waste water is reduced, and the energy utilization rate is improved.
(3) And the separated permeate enters a reverse osmosis system for primary concentration, and the obtained reverse osmosis concentrated water has the lithium ion content of 2.0g/L and the Mg/Li mass ratio of 3.0.
The operating pressure of the primary concentration unit is 3.5MPa, and the reverse osmosis fresh water obtained in the primary concentration process is directly reused for diluting old brine, so that the utilization rate of the fresh water is improved; and the reverse osmosis concentrated water enters a three-stage nanofiltration separation unit for magnesium and lithium separation.
(4) And the reverse osmosis concentrated water after primary concentration enters a three-stage nanofiltration separation unit to reinforce the magnesium-lithium separation process, and the obtained three-stage nanofiltration fresh water has the lithium ion content of 2.2g/L and the Mg/Li mass ratio of 1.2.
The operating pressure of the three-stage nanofiltration separation unit is 0.5MPa, and the three-stage nanofiltration concentrated water generated by the three-stage nanofiltration separation unit returns to the secondary nanofiltration separation process, so that the utilization rate of lithium is improved; and allowing the trina fresh water to enter an electrodialysis system for secondary concentration.
(5) And allowing the trinexano fresh water to enter an electrodialysis system for secondary concentration, wherein the lithium ion content in the concentrated solution after the secondary concentration is 6g/L, and the Mg/Li mass ratio is 1.3.
And the electrodialysis fresh water obtained in the secondary concentration process enters a reverse osmosis system, the recovery of residual lithium and the recycling of fresh water are realized through a primary concentration unit, and the lithium ion content in the electrodialysis concentrated water obtained in the secondary concentration process reaches the lithium ion concentration required for preparing high-purity lithium salt.
The compositions of the salt lake brine and the solutions of the respective stages used in the above examples are shown in Table 3.
Table 3 example compositions of the old brine and the solutions at each stage.
By the embodiment, magnesium and lithium separation and lithium enrichment of sulfate type salt lake brine are realized. The yield of lithium ions in the magnesium-lithium separation process is more than 60%, and the yield of lithium ions in the whole concentration system is more than 65%.
Example 4
(1) The used old brine comes from a sulfate type salt lake in Qinghai, the lithium ion content in the old brine is 5.0g/L, and the Mg/Li mass ratio is 6. The old brine enters a multi-media filter for removing impurities such as suspended matters, silt and the like in the brine after being diluted for one time, and then enters organic ultrafiltration equipment for completely removing the impurities. And (4) the old brine after complete impurity removal enters a separation unit for magnesium and lithium separation through secondary dilution. The old brine is diluted 15 times in the whole process.
(2) The pretreated brine enters a separation unit for magnesium-lithium separation, and the content of magnesium ions in the obtained nanofiltration fresh water is reduced to 0.1 g/L; the lithium ion content was 2.0g/L and the Mg/Li mass ratio was 0.05.
The magnesium-lithium separation unit mainly comprises a monovalent ion selective nanofiltration membrane, and the operating pressure is 9.0 MPa. According to the characteristic of high magnesium-lithium ratio of salt lake brine, a multi-stage nanofiltration process is arranged, primary nano fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nano filtration process to further reduce the magnesium-lithium ratio in a permeate liquid, improve the lithium ion concentration of the permeate liquid, and recycle the primary nano concentrated water; and the secondary nano-fresh water obtained after the secondary nano-filtration separation is continuously fed into the next-stage nano-filtration process to further improve the concentration of lithium ions, and the secondary nano-concentrated water is recycled, so that the process is similar to the process. The finally obtained nanofiltration fresh water enters a reverse osmosis unit for primary concentration, and nanofiltration concentrated water is recycled, so that the discharge of waste water is reduced, and the energy utilization rate is improved.
(3) And the separated permeate enters a reverse osmosis system for primary concentration, and the obtained reverse osmosis concentrated water has the lithium ion content of 4.1g/L and the Mg/Li mass ratio of 0.05.
The operating pressure of the primary concentration unit is 12MPa, and the reverse osmosis fresh water obtained in the primary concentration process is directly reused for diluting old brine, so that the utilization rate of the fresh water is improved; and the reverse osmosis concentrated water enters a three-stage nanofiltration separation unit for magnesium and lithium separation.
(4) And the reverse osmosis concentrated water after primary concentration enters a three-stage nanofiltration separation unit to reinforce the magnesium-lithium separation process, and the obtained three-stage nanofiltration fresh water has the lithium ion content of 4.5g/L and the Mg/Li mass ratio of 0.04.
The operating pressure of the three-stage nanofiltration separation unit is 4.0MPa, and the three-stage nanofiltration concentrated water generated by the three-stage nanofiltration separation unit returns to the secondary nanofiltration separation process, so that the utilization rate of lithium is improved; and allowing the trina fresh water to enter an electrodialysis system for secondary concentration.
(5) And allowing the trinexano fresh water to enter an electrodialysis system for secondary concentration, wherein the lithium ion content in the concentrated solution after the secondary concentration is 23g/L, and the Mg/Li mass ratio is 0.04.
And the electrodialysis fresh water obtained in the secondary concentration process enters a reverse osmosis system, the recovery of residual lithium and the recycling of fresh water are realized through a primary concentration unit, and the lithium ion content in the electrodialysis concentrated water obtained in the secondary concentration process reaches the lithium ion concentration required for preparing high-purity lithium salt.
The compositions of the salt lake brine and the solutions of the respective stages used in the above examples are shown in Table 4.
Table 4 composition of the old brine and the solutions of the various stages in the examples.
By the embodiment, magnesium and lithium separation and efficient lithium enrichment of sulfate type salt lake brine are realized, and finally the obtained electrodialysis concentrated solution can be directly used for preparing high-purity lithium salt. The yield of lithium ions in the magnesium-lithium separation process is more than 90%, the yield of lithium ions in the whole concentration system is more than 95%, and the utilization rate of lithium ions in the whole process is effectively improved.
Comparative example 1
(1) The used old brine comes from a sulfate type salt lake in Qinghai, the lithium ion content in the old brine is 2.5g/L, and the Mg/Li mass ratio is 50. The old brine enters a multi-media filter for removing impurities such as suspended matters, silt and the like in the brine after being diluted for one time, and then enters organic ultrafiltration equipment for completely removing the impurities. And (4) the old brine after complete impurity removal enters a separation unit for magnesium and lithium separation through secondary dilution. The old brine is diluted 15 times in the whole process.
(2) The pretreated brine enters a separation unit for magnesium-lithium separation, and the content of magnesium ions in the obtained nanofiltration fresh water is reduced to 0.132 g/L; the lithium ion content was 0.9g/L, and the Mg/Li mass ratio was 0.147.
The magnesium-lithium separation unit mainly comprises a monovalent ion selective nanofiltration membrane, and the operating pressure is 5.0 MPa. According to the characteristic of high magnesium-lithium ratio of salt lake brine, a multi-stage nanofiltration process is arranged, primary nano fresh water obtained after the brine is subjected to primary nanofiltration separation enters a secondary nano filtration process to further reduce the magnesium-lithium ratio in a permeate liquid, improve the lithium ion concentration of the permeate liquid, and recycle the primary nano concentrated water; and the secondary nano-fresh water obtained after the secondary nano-filtration separation is continuously fed into the next-stage nano-filtration process to further improve the concentration of lithium ions, and the secondary nano-concentrated water is recycled, so that the process is similar to the process. The finally obtained nanofiltration fresh water enters a reverse osmosis unit for primary concentration, and nanofiltration concentrated water is recycled, so that the discharge of waste water is reduced, and the energy utilization rate is improved.
(3) And the separated nanofiltration fresh water enters a reverse osmosis system for primary concentration to obtain reverse osmosis concentrated water, wherein the content of lithium ions in the reverse osmosis concentrated water is 3.5g/L, and the mass ratio of Mg to Li is 0.152.
The operating pressure of the primary concentration unit is 8.0MPa, and the reverse osmosis fresh water obtained in the primary concentration process is directly reused for diluting old brine, so that the utilization rate of the fresh water is improved; and (4) enabling the reverse osmosis concentrated water to enter an electrodialysis system for secondary concentration.
(4) And (3) feeding the primary concentrated solution into an electrodialysis system for secondary concentration, wherein the lithium ion content in the concentrated solution after the secondary concentration is 16g/L, and the Mg/Li mass ratio is 0.154.
And the electrodialysis fresh water obtained in the secondary concentration process is blended with the lithium-rich solution obtained by the nanofiltration separation system, the recovery of residual lithium and the reuse of fresh water are realized through the reverse osmosis system, and the lithium ion content in the secondary concentrated solution reaches the lithium ion concentration required for preparing high-purity lithium salt.
The compositions of the brine and the solutions of the respective stages used in this comparative example are shown in Table 5.
TABLE 5 composition of the old brine and solutions of the various stages in the comparative examples
By the comparison example, the magnesium-lithium separation and the lithium enrichment of the sulfate type salt lake brine are realized. The yield of lithium ions in the magnesium-lithium separation process is higher than 86%, and the yield of lithium ions in the whole concentration system is higher than 80%, but because a three-stage nanofiltration technology is not adopted, the utilization rate of lithium ions in the whole process is still low, and the lithium concentration effect is poor.
Further, the present inventors also conducted tests with other raw materials and conditions listed in the present specification and the like in the manner of examples 1 to 4, and for example, also conducted tests with the first nanofiltration separation device for magnesium-lithium separation at operating pressures of 10.0MPa, 4.0MPa and 6.0MPa, the reverse osmosis device for primary concentration at operating pressures of 15.0MPa and 10.0MPa, the second nanofiltration separation device for magnesium-lithium separation at operating pressures of 0.8MPa and 2.0MPa, respectively; for another example, the concentration of lithium ions in the salt pan old brine is 0.2-5.0 g/L, and the mass ratio of magnesium ions to lithium ions in the salt pan old brine is 6-180: 1. the concentration of lithium ions in the first nanofiltration fresh water is 0.1-2.0 g/L, and the mass ratio of magnesium ions to lithium ions in the first nanofiltration fresh water is 0.02-3.2: 1. the lithium ion concentration in the reverse osmosis concentrated water is 2.0-10 g/L, and the mass ratio of magnesium ions to lithium ions in the reverse osmosis concentrated water is 0.05-3.0: 1. the concentration of lithium ions in the second nanofiltration fresh water is 1.5-4.5 g/L, and the mass ratio of magnesium ions to lithium ions in the second nanofiltration fresh water is 0.01-1.2: 1. the lithium ion concentration in the electrodialysis concentrated water is 6-25 g/L, and the mass ratio of magnesium ions to lithium ions in the electrodialysis concentrated water is 0.05-1.3: 1, and the like are respectively tested, and the high-efficiency separation and enrichment of lithium in the salt lake brine with high magnesium-lithium ratio can be realized, so the verification contents of each example are not described one by one, and only the examples 1-4 are taken as representatives to illustrate the excellence of the invention.
It should be noted that, in the present context, an element defined by the phrase "comprising … …" does not exclude the presence of other identical elements in steps, processes, methods or experimental facilities including the element.
It should be understood that the above preferred embodiments are only for illustrating the present invention, and other embodiments of the present invention are also possible, but those skilled in the art will be able to adopt the technical teaching of the present invention and equivalent alternatives or modifications thereof without departing from the scope of the present invention.
Claims (15)
1. A method for separating magnesium and lithium and enriching lithium is characterized by comprising the following steps:
(1) diluting the old brine of the salt pan for the first time, sequentially feeding the diluted old brine of the salt pan into a multi-medium filtering device and an ultrafiltration device for filtering, and then diluting for the second time to obtain nanofiltration raw water, wherein the concentration of lithium ions in the old brine of the salt pan is 0.2-5.0 g/L, and the mass ratio of magnesium ions to lithium ions is 6-180: 1;
(2) the raw nanofiltration water enters a first nanofiltration separation device, the first nanofiltration separation device at least comprises a first-stage nanofiltration separation unit and a second-stage nanofiltration separation unit, the raw nanofiltration water firstly enters the first-stage nanofiltration separation unit to be subjected to magnesium-lithium separation to obtain first-stage nanofiltration concentrated water and first-stage nanofiltration fresh water, the first-stage nanofiltration fresh water then enters the second-stage nanofiltration separation unit to be subjected to magnesium-lithium separation to obtain first-stage nanofiltration concentrated water and first-stage nanofiltration fresh water, the first-stage nanofiltration separation unit comprises a first-stage nanofiltration separation module which is connected in series in multiple sections, the number ratio of nanofiltration separation membranes contained in each first-stage nanofiltration separation module is 185-365: 85-165, the second-stage nanofiltration separation unit comprises a second-stage nanofiltration separation module which is connected in series in multiple sections, the number ratio of nanofiltration separation membranes contained in each second-stage nanofiltration separation module is 35-115: 5-45, and the operating pressure of magnesium-lithium separation carried out by the first-stage nanofiltration, the concentration of lithium ions in the first nanofiltration fresh water is 0.1-2.0 g/L, and the mass ratio of magnesium ions to lithium ions is 0.02-3.2: 1;
(3) enabling the first nanofiltration fresh water to enter a reverse osmosis device for primary concentration to obtain reverse osmosis concentrated water and reverse osmosis fresh water;
(4) enabling the reverse osmosis concentrated water to enter a second nanofiltration separation device, and performing magnesium-lithium separation again to obtain second nanofiltration concentrated water and second nanofiltration fresh water, wherein the second nanofiltration separation device comprises three stages of nanofiltration separation units which are connected in series in multiple stages, the number ratio of nanofiltration separation membranes contained in each stage of three stages of nanofiltration separation units is 35-115: 5-45, the operating pressure of the second nanofiltration separation device for magnesium-lithium separation is 0.5-4.0 MPa, the lithium ion concentration in the second nanofiltration fresh water is 1.5-4.5 g/L, and the mass ratio of magnesium ions to lithium ions is 0.01-1.2: 1;
(5) enabling the second nanofiltration fresh water to enter an electrodialysis device for secondary concentration to obtain electrodialysis concentrated water and electrodialysis fresh water, wherein the electrodialysis concentrated water is a solution enriched with lithium ions;
the nanofiltration separation membrane has selectivity to monovalent ions and divalent ions, and an ion selection membrane is adopted in the secondary concentration.
2. The method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: in the primary nanofiltration separation unit, the number ratio of nanofiltration separation membranes contained in each primary nanofiltration separation module is 225-325: 105-145; in the secondary nanofiltration separation unit, the number ratio of nanofiltration separation membranes contained in each section of secondary nanofiltration separation module is 55-95: 20-30.
3. The method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the operation pressure of the first nanofiltration separation device for magnesium and lithium separation is 4.0-6.0 MPa.
4. The method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the concentration of lithium ions in the first nanofiltration fresh water is 0.5-1.2 g/L, and the mass ratio of magnesium ions to lithium ions is 0.05-0.2: 1.
5. the method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the concentration of lithium ions in the salt pan old brine is 2.5-4.0 g/L, and the mass ratio of magnesium ions to lithium ions is 6-55: 1.
6. the method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the reverse osmosis device comprises multiple sections of reverse osmosis units connected in series, wherein the number ratio of reverse osmosis membranes contained in each section of reverse osmosis unit is 98-190: 71-121: 24-60, the operating pressure of the reverse osmosis device for primary concentration is 3.5-15.0 MPa, the lithium ion concentration in the reverse osmosis concentrated water is 2.0-10 g/L, and the mass ratio of magnesium ions to lithium ions is 0.05-3.0: 1.
7. the method for separating and enriching lithium from magnesium and lithium according to claim 6, wherein: the reverse osmosis device comprises multiple sections of reverse osmosis units connected in series, wherein the reverse osmosis membranes in the reverse osmosis units are 132-156: 84-108: 33-51 in number ratio.
8. The method for separating and enriching lithium from magnesium and lithium according to claim 6, wherein: the operating pressure of the reverse osmosis device for primary concentration is 3.5-10.0 Mpa.
9. The method for separating and enriching lithium from magnesium and lithium according to claim 6, wherein: the concentration of lithium ions in the reverse osmosis concentrated water is 3.0-5.0 g/L, and the mass ratio of magnesium ions to lithium ions is 0.07-0.2: 1.
10. the method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the number ratio of nanofiltration separation membranes contained in each section of three-stage nanofiltration separation unit is 55-95: 20-30.
11. The method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the operating pressure of the second nanofiltration separation device for magnesium and lithium separation is 0.8-2.0 MPa.
12. The method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the concentration of lithium ions in the second nanofiltration fresh water is 2.5-4.0 g/L, and the mass ratio of magnesium ions to lithium ions is 0.05-0.15: 1.
13. the method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the concentration of lithium ions in the electrodialysis concentrated water is 6-25 g/L, and the mass ratio of magnesium ions to lithium ions is 0.05-1.3: 1.
14. the method for separating and enriching lithium from magnesium and lithium according to claim 13, wherein: the lithium ion concentration in the electrodialysis concentrated water is 14-22 g/L, and the mass ratio of magnesium ions to lithium ions is 0.07-0.2: 1.
15. the method for separating and enriching lithium from magnesium and lithium according to claim 1, wherein: the ion selective membrane includes one of a homogeneous membrane, a semi-homogeneous membrane, and a heterogeneous membrane.
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