CN108314065B - Full-membrane separation method for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine - Google Patents
Full-membrane separation method for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine Download PDFInfo
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Abstract
The invention discloses a full-membrane separation method for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine, which comprises the following steps: (1) pretreating salt lake brine by using a microfiltration purification system to remove suspended matters, colloids and other impurities in the salt lake brine, and then diluting the salt lake brine by using fresh water to obtain microfiltration pretreated brine; (2) sending the obtained microfiltration pretreated brine into a nanofiltration salt separating system, and separating to obtain a filtrate mainly containing monovalent cations and a concentrated solution mainly containing multivalent cations; (3) sending the filtrate obtained in the step (2) into a membrane concentration system, and concentrating to obtain a lithium-rich concentrated solution; (4) and (4) feeding the lithium-rich concentrated solution obtained in the step (3) into a nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane. The process has the advantages of low energy consumption, high recovery rate, low production cost, continuous and controllable process, high reliability, low magnesium-lithium ratio of the prepared lithium extraction mother liquor, high lithium ion concentration and stable quality, and can be used for large-scale production.
Description
Technical Field
The invention belongs to the technical field of membrane separation, and particularly relates to a full-membrane separation process for producing a lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine.
Background
Lithium and its compounds play an extremely important role in the fields of energy, petrochemical industry, metallurgy, ceramics, medicine, aerospace, refrigeration and the like, and are called "energy metals of the 21 st century". The salt lake brine is an important source of lithium, and more than 80% of the total lithium salt production in the world currently comes from the salt lake brine.
At present, the main methods for extracting lithium from salt lake brine comprise an evaporation crystallization separation method, a precipitation method, a calcination leaching method, an organic solvent extraction method, an ion exchange adsorption method, an electrodialysis method, a scholar method, a nanofiltration method and the like, and the post-treatment steps generally comprise impurity removal, concentration, precipitation and the like. The pretreatment process for extracting lithium, the product quality and the economic benefit have great relationship with the concentration of lithium and the magnesium-lithium ratio in the brine. The low lithium concentration and the high magnesium-lithium ratio can seriously limit the process combination mode of extracting lithium from the brine, and influence the feasibility and the economic benefit of the brine. The nanofiltration method can effectively separate monovalent ions from multivalent ions, but the conventional nanofiltration system can treat salt lake brine with very high salt content after diluting the salt lake brine for many times.
Chinese patent application No. 201310571755.2 discloses that magnesium ions and lithium ions are separated by a nanofiltration system, lithium ions are enriched by a reverse osmosis system, and the concentration of lithium ions can reach the concentration required for refining lithium carbonate by evaporation and concentration in a salt pan; however, the nanofiltration system designed by the application has only one stage, the magnesium-lithium separation capacity is limited, the treatment effect on the brine with high magnesium-lithium ratio is poor, and the limitation is realized; in addition, the reverse osmosis concentration still needs to take longer time for salt field evaporation and further concentration to ensure that the lithium ion concentration meets the requirement of preparing lithium carbonate. The chinese patent application No. 201610751304.0 discloses that a forward osmosis system can concentrate lithium-containing solution and enrich lithium ions, however, because the magnesium ion removal effect of the primary nanofiltration system and the lithium ion concentration in the produced water are limited, alkali is still added to deeply remove magnesium after forward osmosis concentration, and the refined lithium-containing solution is further concentrated by high-energy-consumption multi-effect evaporation to increase the lithium ion concentration; and the forward osmosis system uses ammonium bicarbonate solution as an extraction solution, which can not be obtained from local materials, and fully utilizes salt obtained by tedding in a salt pan.
Most of the salt lake brine in China is a sulfate type and a chloride type, and has the two remarkable characteristics of high lithium content and high magnesium-lithium ratio, so that how to economically and effectively utilize the salt lake brine to prepare high-purity lithium salt becomes the key for developing and utilizing the salt lake lithium resources in China.
Disclosure of Invention
Aiming at the technical problems, the invention provides a full-membrane separation process for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine, which makes full use of the advantages of a microfiltration membrane, a nanofiltration membrane, a reverse osmosis membrane and a forward osmosis membrane, reasonably configures the stage number and the membrane component of a nanofiltration system according to the quality of brine, can effectively remove magnesium ions, solves the problem of separation of lithium and magnesium in brine, and concentrates nanofiltration filtrate through the forward osmosis system with extremely low energy consumption, improves the concentration of lithium ions in the solution and obtains the lithium extraction mother liquor. The process has the advantages of low energy consumption, high recovery rate, low production cost, continuous and controllable process, high reliability, low magnesium-lithium ratio of the prepared lithium extraction mother liquor, high lithium ion concentration and stable quality, and can be used for large-scale production.
The invention is realized by the following technical scheme.
A full-membrane separation method for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine comprises the following steps:
(1) pretreating salt lake brine by using a microfiltration purification system to remove suspended matters, colloids and other impurities in the salt lake brine, and then diluting the salt lake brine by 2-5 times by using fresh water to obtain microfiltration pretreated brine;
(2) feeding the microfiltration pretreated brine obtained in the step (1) into a multi-stage nanofiltration salt separation system, and separating multivalent cations and part of monovalent cations in the microfiltration pretreated brine to obtain filtrate mainly containing monovalent cations and concentrated solution mainly containing multivalent cations;
(3) sending the filtrate obtained in the step (2) into a membrane concentration system, and concentrating to obtain a lithium-rich concentrated solution;
(4) and (4) feeding the lithium-rich concentrated solution obtained in the step (3) into a nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane.
Further, in the step (1), the magnesium-lithium ratio of the salt lake brine is (10-1000): 1 in terms of mass ratio, the mass concentration of lithium ions is 0.1-5 g/L, and the pH value is 5-7.5.
Further, in the step (1), the number of the microfiltration purification system is 1-2, and the microfiltration purification system is formed by sequentially combining one or two of the filtration precision of 1-5 μm, 0.45-1 μm or 0.1-0.45 μm according to the pore size.
Furthermore, the microfiltration membrane of the microfiltration purification system is made of one or more of ceramic, polypropylene, polycarbonate, polyvinyl chloride, polysulfone, polyvinylidene fluoride or polytetrafluoroethylene.
Further, in the step (2), the number of stages of the multi-stage nanofiltration salt separation system is 1-3; the first-stage nanofiltration salt separation system adopts a DT nanofiltration membrane, the rejection rate of the DT nanofiltration membrane on magnesium sulfate is 70-95%, the rejection rate on sodium chloride is 1-5%, the operating pressure is 3-6 MPa, and the recovery rate is 50-70%.
Further, the second-stage nanofiltration salt separation system and the third-stage nanofiltration salt separation system adopt one of a roll-type membrane, a tubular membrane or a plate-type membrane, the rejection rate of the roll-type membrane, the tubular membrane or the plate-type membrane to magnesium sulfate is 90-98%, the rejection rate to sodium chloride is 5-10%, the operating pressure is 0.8-4 MPa, the recovery rate is 60-80%, and the filtering mode is cross-flow filtration.
Further, the nanofiltration salt separation system adopts an internal circulation mode, namely, part of concentrated solution of each stage of nanofiltration salt separation system flows back to the stock solution tank of the stage of nanofiltration salt separation system for circulation, wherein the temperature of the primary concentrated solution is reduced before flowing back, so that part of inorganic salt is saturated and separated out, the salt content of the concentrated solution is reduced, and the concentrated solution is filtered and then sent to the stock solution tank of the primary nanofiltration salt separation system; and the other part of the first-stage concentrated solution is discharged for other use, and the rest second-stage concentrated solution and the rest third-stage concentrated solution respectively flow back to the stock solution pools of the first-stage nanofiltration salt separation system and the second-stage nanofiltration salt separation system.
Further, the membrane concentration system is composed of a forward osmosis system or a combined system of the forward osmosis system and a reverse osmosis system; obtaining reverse osmosis filtrate and primary lithium-rich concentrated solution from a reverse osmosis system, and obtaining lithium-rich concentrated solution from a forward osmosis system; and (4) refluxing the reverse osmosis filtrate to a fresh water dilution system of the microfiltration purification system to prepare microfiltration pretreatment brine.
Further, the number of stages of the nanofiltration deep magnesium removal system is 1-2, and a full circulation mode is adopted, namely all concentrated water at each stage flows back to a stock solution tank of the nanofiltration salt separation system at the stage for circulation; one of a roll-type membrane, a tubular membrane or a plate-type membrane is used, the rejection rate of the membrane to magnesium sulfate is 90-99%, the rejection rate to sodium chloride is 5-10%, the operating pressure is 0.8-3 MPa, the recovery rate is 60-80%, and the filtering mode is cross-flow filtration.
Further, the nanofiltration salt separation system in the step (2) and the nanofiltration deep magnesium removal system in the step (4) adopt spiral wound membranes, tubular membranes or plate membranes, wherein monovalent ions selectively penetrate through the nanofiltration membranes, and the nanofiltration membranes are made of one or more of aromatic polyamide, polypiperazine amide, polyimide or sulfonated polysulfone.
The invention has the advantages and beneficial effects that:
(1) the invention takes a low-consumption and high-efficiency membrane separation process as a core, and selects a microfiltration system, a nanofiltration system, a reverse osmosis system and a forward osmosis system, and a DT nanofiltration system which is high-pressure resistant and has high efficiency of separating salt and reducing magnesium at high salt concentration (the DT nanofiltration system is suitable for high-concentration salt-containing water and is used under the condition of not diluting brine by a large factor). The method can be used for carrying out different combinations and configurations according to water quality, is flexible in design, wide in water quality of the salt lake brine capable of being treated, strong in applicability and capable of carrying out magnesium-lithium separation and lithium concentration enrichment on the salt lake brine with different lithium concentrations and magnesium-lithium ratios.
(2) The full-membrane separation process effectively avoids the defects of high corrosion to equipment, serious environmental pollution, high operation cost and the like of the traditional processes such as evaporation concentration, precipitation and salt reduction and the like in production, and reduces the production cost while ensuring higher enrichment degree and recovery rate of lithium ions.
(3) The full-membrane separation process is convenient to operate and maintain, and the membrane system is easy to configure, clean, install and transport, thereby being beneficial to popularization and application and carrying out large-scale production.
(4) The full-membrane separation process of the invention fully and effectively utilizes resources, wherein: the draw solution of the forward osmosis system can be salt lake brine from which mechanical impurities are removed, primary concentrated solution discharged by the nanofiltration salt separation system, or solution prepared from inorganic salt prepared by tedding the salt lake brine as draw solution; if the draw solution is salt lake brine from which mechanical impurities are removed, the draw solution can be sent to a nanofiltration salt separation system for reuse after being used; the reverse osmosis filtrate can flow back to the foremost end of the process and be used as fresh water for dilution, so that the extremely scarce fresh water in a high-salinity area is effectively saved. The process technology uses local materials according to local conditions, thereby not only saving the production cost, but also greatly reducing the environmental load, and having high efficiency and energy saving.
(5) The nanofiltration salt separation system and the membrane concentration system have high magnesium reduction efficiency and large concentration multiple, compared with the traditional process, the magnesium-lithium ratio (calculated by mass ratio) of brine can be greatly reduced, the lithium ion concentration is improved, the complicated processes of magnesium removal by an alkaline method, precipitation impurity removal and the like are avoided, and the loss of lithium resources is greatly reduced.
(6) The water-loop heat pump system absorbs heat in the refluxed first-stage concentrated solution through the heat exchanger and transfers the heat to the front end of the full-membrane separation process, so that the temperature of the microfiltration pretreatment brine is increased, the solubility of inorganic salt is increased, and the problem of supersaturation and precipitation of the inorganic salt in the concentrated solution at a lower temperature is avoided.
Drawings
FIG. 1 is a schematic flow chart of a method of a full-membrane separation process for producing a lithium extraction mother liquor from salt lake brine according to the invention.
Fig. 2 is a process flow diagram of the full membrane separation process for producing lithium extraction mother liquor from salt lake brine according to example 1 of the present invention.
Fig. 3 is a process flow diagram of the full membrane separation process for producing lithium extraction mother liquor from salt lake brine according to example 2 of the present invention.
Fig. 4 is a process flow diagram of the full membrane separation process for producing lithium extraction mother liquor from salt lake brine according to example 3 of the present invention.
FIG. 5 is a schematic process flow diagram of the full membrane separation process for producing lithium extraction mother liquor from salt lake brine according to example 4 of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention in any way.
FIG. 1 shows a block flow diagram of the method of the present invention. The invention relates to a full membrane separation process for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine, which has various implementation modes and comprises the following steps:
(1) and (3) pretreating the salt lake brine by using a microfiltration purification system, removing suspended matters, colloids and other impurities in the salt lake brine, and then diluting the salt lake brine by 2-5 times by using fresh water to obtain microfiltration pretreated brine.
Wherein the magnesium-lithium ratio of the salt lake brine is (10-1000): 1 in terms of mass ratio, the mass concentration of lithium ions is 0.1-5 g/L, and the pH value is 5-7.5.
The number of the stages of the microfiltration purification system is 1-2, and the microfiltration purification system is formed by sequentially combining one or two of the filtration precision of 1-5 mu m, 0.45-1 mu m or 0.1-0.45 mu m according to the pore size; the microfiltration membrane of the microfiltration purification system is made of one or more of ceramic, polypropylene, polycarbonate, polyvinyl chloride, polysulfone, polyvinylidene fluoride or polytetrafluoroethylene.
(2) And (2) feeding the microfiltration pretreated brine obtained in the step (1) into a multi-stage nanofiltration salt separation system, and separating multivalent cations and part of monovalent cations in the microfiltration pretreated brine to obtain filtrate mainly containing monovalent cations and concentrated solution mainly containing multivalent cations.
Wherein the number of stages of the nanofiltration salt separation system is 1-3; the first-stage nanofiltration salt separation system adopts a DT nanofiltration membrane, the rejection rate of the DT nanofiltration membrane on magnesium sulfate is 70-95%, the rejection rate on sodium chloride is 1-5%, the operating pressure is 3-6 MPa, and the recovery rate is 50-70%; the second-stage nanofiltration salt separation system and the third-stage nanofiltration salt separation system adopt one of a roll-type membrane, a tubular membrane or a plate-type membrane, the rejection rate of magnesium sulfate is 90-98%, the rejection rate of sodium chloride is 5-10%, the operating pressure is 0.8-4 MPa, the recovery rate is 60-80%, and the filtering mode is cross-flow filtration.
The nanofiltration salt separation system adopts an internal circulation mode, namely part of concentrated solution of each stage of nanofiltration salt separation system flows back to a stock solution tank of the stage of nanofiltration salt separation system for circulation, wherein the temperature of the first stage of concentrated solution is reduced before flowing back, the first stage of concentrated solution is realized by a water-loop heat pump system with the cooling water temperature of 5-10 ℃, part of inorganic salt is promoted to be saturated and separated out, the salt content of the concentrated solution is reduced, and the concentrated solution is filtered and then sent into the stock solution tank of the first stage of nanofiltration salt separation system; the water-ring heat pump system adopts a mechanical online descaling technology, a movable nylon brush is arranged on a heat exchanger of the water-ring heat pump system, and inorganic salt deposited on a coil pipe of the heat exchanger is removed; meanwhile, a heat source of the water-loop heat pump system is used for increasing the temperature of the microfiltration pretreatment brine. And the other part of the first-stage concentrated solution is discharged for other use, and the rest second-stage concentrated solution and the rest third-stage concentrated solution respectively flow back to the stock solution pools of the first-stage nanofiltration salt separation system and the second-stage nanofiltration salt separation system.
The nanofiltration salt separating system adopts monovalent ions to selectively permeate a nanofiltration membrane, and the nanofiltration membrane is made of one or more of aromatic polyamide, polypiperazine amide, polyimide or sulfonated polysulfone.
(3) And (3) sending the filtrate obtained in the step (2) into a membrane concentration system, and concentrating to obtain a lithium-rich concentrated solution.
Wherein, the membrane concentration system is composed of a forward osmosis system or a combined system of the forward osmosis system and a reverse osmosis system; obtaining reverse osmosis filtrate and primary lithium-rich concentrated solution from a reverse osmosis system, and obtaining lithium-rich concentrated solution from a forward osmosis system; and (4) refluxing the reverse osmosis filtrate to a fresh water dilution system of the microfiltration purification system to prepare microfiltration pretreatment brine.
The absorption liquid of the forward osmosis system is salt lake brine from which mechanical impurities are removed, primary concentrated liquid discharged by the nanofiltration salt separation system or solution prepared from one or more of sodium chloride, bischofite and magnesium sulfate prepared by tedding the salt lake brine; when the draw solution is salt lake brine from which mechanical impurities are removed, the draw solution and microfiltration pretreatment brine are combined after the forward osmosis system finishes working, and the draw solution and the microfiltration pretreatment brine are uniformly mixed and then sent to the nanofiltration salt separation system.
The forward osmosis system uses a forward osmosis membrane in the form of one of a flat plate, a roll or a hollow fiber; the forward osmosis membrane is made of one of cellulose triacetate, polybenzimidazole, polyacrylonitrile, polysulfone or polyether sulfone.
When the operating pressure of the reverse osmosis system is 4-6MPa, single-stage concentration is adopted, the filtering mode is cross-flow filtration, the salt rejection rate reaches 97-98%, and the recovery rate is 60-80%; the reverse osmosis membrane component adopts a roll type and is made of one or more of aromatic polyamide, polypiperazine amide, polyimide or sulfonated polysulfone.
(4) And (4) feeding the lithium-rich concentrated solution obtained in the step (3) into a nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane.
The number of stages of the nanofiltration deep magnesium removal system is 1-2, and a full circulation mode is adopted, namely all concentrated water at each stage flows back to a stock solution tank of the nanofiltration salt separation system at the stage for circulation; the method comprises the following steps of (1) using one of a roll-type membrane, a tubular membrane or a plate-type membrane, wherein the rejection rate of the membrane to magnesium sulfate is 90-99%, the rejection rate of the membrane to sodium chloride is 5-10%, the operation pressure is 0.8-3 MPa, the recovery rate is 60-80%, and the filtration mode is cross-flow filtration; monovalent ions are adopted to selectively penetrate a nanofiltration membrane, and the material of the nanofiltration membrane is one or more of aromatic polyamide, polypiperazine amide, polyimide or sulfonated polysulfone.
The mass concentration of lithium ions in the obtained lithium extraction mother liquor is 20-40 g/L, and the magnesium-lithium ratio (in terms of mass ratio) is less than 0.2.
The invention is further illustrated by the following specific examples.
Example 1:
as shown in fig. 2, the three-stage nanofiltration salt separation system, the forward osmosis system, the reverse osmosis system, and the nanofiltration deep magnesium removal system are selected in this embodiment. The method comprises the following steps:
(1) the pH value of the solution is 5, the mass concentration of magnesium ions is 115.10g/L, the mass concentration of lithium ions is 0.384g/L, and the ratio of magnesium to lithium (calculated by mass ratio) is 300 by using a microfiltration purification system: 1, pretreating the salt lake brine to remove suspended matters, colloids and other impurities in the salt lake brine, and then diluting the salt lake brine by 2.5 times with fresh water to obtain microfiltration pretreated brine.
Wherein, the microfiltration purification system is formed by sequentially combining two microfiltration systems with the filtration precision of 3 μm and 0.22 μm, and the microfiltration membranes are sequentially made of polycarbonate and polysulfone.
(2) And (2) sending the microfiltration pretreated brine obtained in the step (1) into a three-stage nanofiltration salt separation system for treatment, and separating divalent magnesium ions from monovalent lithium ions to obtain filtrate with high lithium ion content and concentrated solution with high magnesium ion content.
The three-stage nanofiltration salt separation system adopts a nanofiltration membrane which is selectively penetrated by univalent ions and preferentially intercepted by multivalent ions, and an aromatic polyamide nanofiltration membrane is selected. In this embodiment, the first-stage nanofiltration salt separation system uses a DT nanofiltration membrane, which has a rejection rate of 70% for magnesium sulfate, a rejection rate of 3% for sodium chloride, an operating pressure of 5MPa, and a recovery rate of 70%; the second-stage nanofiltration salt separation system and the third-stage nanofiltration salt separation system use rolled nanofiltration membranes, the rejection rate of the rolled nanofiltration membrane on magnesium sulfate is 90%, the rejection rate on sodium chloride is 7%, the operating pressure is 2MPa and 1.5MPa respectively, the recovery rate is 80%, and a cross-flow filtration mode is adopted.
And each stage of nanofiltration salt separation system can generate corresponding filtrate and concentrated solution, the primary filtrate and the secondary filtrate are both sent into a stock solution pool of the next stage of nanofiltration salt separation system, and part of the concentrated solution at each stage reflows to the stock solution pool of the nanofiltration salt separation system for circulation. Meanwhile, the other part of the first-stage concentrated solution is discharged outside, and the rest second-stage concentrated solution and third-stage concentrated solution respectively flow back to the stock solution tanks of the first-stage nanofiltration salt separation system and the second-stage nanofiltration salt separation system. The magnesium-lithium ratio (by mass ratio) of the third-stage filtrate reaches 1.1:1, and the lithium ion concentration reaches 0.321 g/L.
And (3) cooling the primary concentrated solution by a water-loop heat pump system with the temperature of 5 ℃ of cooling water before refluxing to ensure that inorganic salts such as potassium sulfate, sodium sulfate and the like are saturated and separated out, reduce the salt content of the concentrated solution, and sending the filtered concentrated solution into a stock solution tank of a primary nanofiltration salt separation system.
The water-ring heat pump system adopts a mechanical online descaling technology, a movable nylon brush is arranged on a heat exchanger of the water-ring heat pump system, and inorganic salt deposited on a coil pipe of the heat exchanger is removed; meanwhile, a heat source of the water-loop heat pump system can be used for increasing the temperature of the microfiltration pretreatment brine.
(3) Feeding the third-stage filtrate obtained in the step (2) into a reverse osmosis system for concentration to obtain reverse osmosis filtrate and primary lithium-rich concentrated solution; and then sending the obtained primary lithium-rich concentrated solution into a forward osmosis system for concentration treatment to obtain the lithium-rich concentrated solution.
The operating pressure of the reverse osmosis system is 4MPa, the salt rejection rate reaches 97%, and in the embodiment, a rolled reverse osmosis membrane is selected and the aromatic polyamide is used. And refluxing the obtained reverse osmosis filtrate to a fresh water dilution system of the microfiltration purification system to prepare microfiltration pretreatment brine. The forward osmosis membrane component used by the forward osmosis system is in a TFC flat membrane form, and the forward osmosis membrane is made of polysulfone and polyethersulfone; the drawing liquid is salt lake brine from which mechanical impurities are removed. After the forward osmosis system finishes working, combining the draw solution with the microfiltration pretreatment brine, uniformly mixing, and then sending into a nanofiltration salt separation system.
(4) And (4) sending the lithium-rich concentrated solution obtained in the step (3) into a first-stage nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane.
The primary nanofiltration deep magnesium removal system adopts a full circulation mode, namely primary concentrated water completely reflows to a stock solution pool of the nanofiltration deep magnesium removal system for circulation; a nanofiltration membrane which is selectively penetrated by univalent ions and preferentially intercepted by multivalent ions is selected. In this embodiment, the first-stage nanofiltration deep magnesium removal system uses a roll-type nanofiltration membrane, the nanofiltration membrane is made of aromatic polyamide, the rejection rate of the aromatic polyamide is 90% for magnesium sulfate, the rejection rate of the aromatic polyamide is 8% for sodium chloride, the operation pressure is 2.5MPa, the recovery rate is 75%, and a cross-flow filtration mode is adopted.
In the embodiment, the mass concentration of magnesium ions in the lithium extraction mother liquor is 30.448g/L, the mass concentration of lithium ions is 29.890g/L, and the ratio of magnesium to lithium (by mass ratio) is 0.12: 1. the concentration of lithium ions is 77.8 times of that of salt lake brine.
In this example, the components of brine in each stage of the process of extracting lithium from salt lake brine are shown in table 1:
TABLE 1 ingredient Table (g/L) of brine in each stage of example 1
| Species of | Mg2+ | Li+ | Mg2+/Li+ |
| Salt lake brine | 115.10 | 0.384 | 300:1 |
| Microfiltration pretreatment brine | 46.04 | 0.154 | 300:1 |
| First-stage filtrate | 19.73 | 0.193 | 102:1 |
| First-order concentrated solution | 107.43 | 0.063 | 1249:1 |
| Second stage filtrate | 2.865 | 0.248 | 11.6:1 |
| Third stage filtrate | 0.361 | 0.321 | 1.1:1 |
| Primary lithium-rich concentrate | 2.694 | 2.395 | 1.1:1 |
| Lithium-rich concentrated solution | 25.863 | 22.992 | 1.1:1 |
| Lithium extraction mother liquor | 30.448 | 29.890 | 0.12:1 |
| First-stage concentrated water | 93.107 | 2.293 | 40.6:1 |
Example 2:
as shown in fig. 3, the two-stage nanofiltration salt separation system is adopted in this embodiment, which is one less than the nanofiltration salt separation system of embodiment 1, and the other parts are the same as embodiment 1 except for the following differences. In this embodiment:
(1) the pH value of the salt lake brine is 6.4, the mass concentration of magnesium ions is 51.75g/L, the mass concentration of lithium ions is 0.535g/L, and the magnesium-lithium ratio (in mass ratio) is 100: 1, diluting the salt lake brine by 5 times, sequentially combining two microfiltration systems with the filtering precisions of 1 mu m and 0.1 mu m to form the microfiltration purification system, and sequentially using polypropylene and polyvinylidene fluoride as the microfiltration membrane.
(2) In the embodiment, a two-stage nanofiltration salt separation system is adopted, the first-stage nanofiltration salt separation system uses a DT nanofiltration membrane, the rejection rate of the DT nanofiltration membrane on magnesium sulfate is 95%, the rejection rate on sodium chloride is 5%, the operating pressure is 3MPa, and the recovery rate is 65%; the second-stage nanofiltration salt separation system uses a tubular nanofiltration membrane, the rejection rate of the tubular nanofiltration membrane on magnesium sulfate is 98%, the rejection rate on sodium chloride is 10%, the operating pressure is 4MPa, and the recovery rate is 75%. The nanofiltration membrane is made of polypiperazine amide, the magnesium-lithium ratio (by mass ratio) of the secondary filtrate reaches 0.53:1, and the lithium ion concentration reaches 0.188 g/L.
(3) In this embodiment, the reverse osmosis system has an operating pressure of 4.5MPa, and a rolled reverse osmosis membrane is selected and made of polypiperazine amide. The forward osmosis membrane is a roll-type membrane, the forward osmosis membrane is made of cellulose triacetate, and a solution with the concentration of 4mol/L is prepared by utilizing bischofite prepared by tedding salt lake brine and is used as an extraction solution.
(4) In the embodiment, the first-stage nanofiltration deep magnesium removal system uses the tubular nanofiltration membrane, the nanofiltration membrane is made of polypiperazine amide, the rejection rate of the polypiperazine amide on magnesium sulfate is 99%, the rejection rate of the polypiperazine amide on sodium chloride is 10%, the operation pressure is 3MPa, and the recovery rate is 60%.
In the embodiment, the components of the brine in each stage in the process of extracting lithium by using the salt lake brine are shown in table 2; the mass concentration of lithium ions in the lithium extraction mother liquor is 16.233g/L, and the magnesium-lithium ratio (in terms of mass ratio) reaches 0.53:1, the mass concentration of the lithium ions is 30.34 times of that of the salt lake brine.
TABLE 2 ingredient Table (g/L) of brine in each stage of example 2
| Species of | Mg2+ | Li+ | Mg2+/Li+ |
| Salt lake brine | 51.75 | 0.535 | 100:1 |
| Microfiltration pretreatment brine | 10.35 | 0.107 | 100:1 |
| First-stage filtrate | 1.479 | 0.139 | 10.6:1 |
| First-order concentrated solution | 28.093 | 0.048 | 585.3:1 |
| Second stage filtrate | 0.099 | 0.188 | 0.53:1 |
| Primary lithium-rich concentrate | 0.961 | 1.824 | 0.53:1 |
| Lithium-rich concentrated solution | 8.553 | 16.233 | 0.53:1 |
| Lithium extraction mother liquor | 1.426 | 20.129 | 0.071:1 |
Example 3:
as shown in fig. 4, the two-stage nanofiltration depth magnesium removal system is adopted in this embodiment, which is one more than the nanofiltration depth magnesium removal system of embodiment 1, and the other parts are the same as embodiment 1 except for the following differences.
(1) In this embodiment, the pH of the salt lake brine is 5.7, the mass concentration of magnesium ions is 101.18g/L, the mass concentration of lithium ions is 0.102g/L, and the dilution is 2 times, the microfiltration purification system is formed by sequentially combining two microfiltration systems with the filtration precision of 1 μm and 0.22 μm, and the microfiltration membranes are sequentially made of polypropylene and polytetrafluoroethylene.
(2) In this embodiment, the first-stage nanofiltration salt separation system uses DT nanofiltration membranes, the rejection rate of the DT nanofiltration membrane is 95% for magnesium sulfate, the rejection rate of the DT nanofiltration membrane is 1% for sodium chloride, the operating pressure is 6MPa, and the recovery rate is 55%, the second-stage and third-stage nanofiltration salt separation systems use plate nanofiltration membranes, and the nanofiltration membranes are made of aromatic polyamide; the rejection rate of the magnesium sulfate is 95 percent, the rejection rate of the sodium chloride is 5 percent, the operation pressure is 2MPa and 1.5MPa respectively, and the recovery rate is 60 percent. The ratio of magnesium to lithium of the third-stage filtrate reaches 5.5:1 by mass, and the concentration of lithium ions reaches 0.118 g/L.
(3) In this embodiment, the operating pressure of the reverse osmosis system is 5MPa, the rejection rate of the salt reaches 98%, and the draw solution used by the forward osmosis system is the first-stage concentrated solution discharged by the nanofiltration salt separation system. The forward osmosis system uses a hollow fiber forward osmosis membrane; the forward osmosis membrane is made of polybenzimidazole.
(4) In the embodiment, the two-stage nanofiltration deep magnesium removal system adopts a full circulation mode, the first-stage nanofiltration deep magnesium removal system and the second-stage nanofiltration deep magnesium removal system both use rolled nanofiltration membranes, the rejection rate of the rolled nanofiltration membranes is 95% for magnesium sulfate, the rejection rate of the rolled nanofiltration membranes is 5% for sodium chloride, the operation pressure is 2.5MPa and 1.5MPa respectively, and the recovery rate is 80%.
In the embodiment, the components of the brine in each stage in the process of extracting lithium by using the salt lake brine are shown in table 3; the lithium ion concentration in the lithium extraction mother liquor is 17.701g/L, the lithium ion mass concentration is 173.5 times of that of salt lake brine, and the magnesium-lithium ratio (in mass ratio) is 1000:1 to 0.06: 1.
TABLE 3 ingredient Table (g/L) of brine in each stage of example 3
| Species of | Mg2+ | Li+ | Mg2+/Li+ |
| Salt lake brine | 101.18 | 0.102 | 1000:1 |
| Microfiltration pretreatment brine | 50.59 | 0.051 | 1000:1 |
| First-stage filtrate | 27.591 | 0.066 | 418:1 |
| First-order concentrated solution | 78.698 | 0.033 | 2385:1 |
| Second stage filtrate | 4.245 | 0.088 | 48:1 |
| Third stage filtrate | 0.654 | 0.118 | 5.5:1 |
| Primary lithium-rich concentrate | 6.961 | 1.256 | 5.5:1 |
| Lithium-rich concentrated solution | 68.217 | 12.302 | 5.5:1 |
| First grade water production | 8.527 | 14.753 | 0.578:1 |
| Lithium extraction mother liquor | 1.065 | 17.701 | 0.06:1 |
Example 4:
as shown in fig. 5, the first-stage nanofiltration salt separation system is adopted in the present embodiment, and only the forward osmosis system and the first-stage nanofiltration deep magnesium removal system are adopted. In this embodiment:
(1) and (3) a microfiltration purification system is utilized to realize the purification of the lithium ion with pH of 7.5, the mass concentration of lithium ions of 2.390g/L and the magnesium-lithium ratio (by mass ratio) of 10:1, pretreating the salt lake brine, and then diluting the salt lake brine by 2 times with fresh water to obtain microfiltration pretreated brine.
The microfiltration purification system is formed by sequentially combining two microfiltration systems with the filtration precision of 0.45 mu m and 0.1 mu m, and the microfiltration membranes are sequentially made of polyvinyl chloride and ceramic.
(2) And (2) sending the microfiltration pretreated brine obtained in the step (1) into a primary nanofiltration salt separation system for treatment to obtain primary filtrate with high lithium ion content and primary concentrated solution with high magnesium ion content.
The first-stage nanofiltration salt separation system uses a nanofiltration membrane which is selectively penetrated by univalent ions and preferentially intercepted by multivalent ions.
In the embodiment, the primary nanofiltration salt separation system uses a DT nanofiltration membrane, and the nanofiltration membrane is made of polyimide and sulfonated polysulfone; the rejection rate of the magnesium sulfate is 85 percent, the rejection rate of the sodium chloride is 3 percent, the operation pressure is 5MPa, and the recovery rate is 70 percent. The ratio (by mass ratio) of DT nanofiltration magnesium and lithium reaches 0.75:1, and the concentration of lithium ions reaches 2.436 g/L.
And returning one part of the first-stage concentrated solution to a stock solution pool of the nanofiltration salt separation system for circulation, and discharging the other part of the first-stage concentrated solution.
The first-stage concentrated solution is cooled by a water-loop heat pump system before backflow, and the specific conditions and operation and the water-loop heat pump system are the same as those in embodiment 1.
(3) And (3) sending the first-stage filtrate obtained in the step (2) into a forward osmosis system, and concentrating to obtain a lithium-rich concentrated solution.
The forward osmosis membrane used by the forward osmosis system is a CTA flat membrane, and the draw solution is a solution with the concentration of 4mol/L prepared by sodium chloride and magnesium sulfate which is prepared by tedding salt lake brine from which mechanical impurities are removed. After the forward osmosis system finishes working, combining the draw solution with the microfiltration pretreatment brine, uniformly mixing, and then sending into a nanofiltration salt separation system.
(4) And (4) sending the lithium-rich concentrated solution obtained in the step (3) into a first-stage nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane.
The primary nanofiltration deep magnesium removal system adopts a full circulation mode; a nanofiltration membrane which is selectively penetrated by univalent ions and preferentially intercepted by multivalent ions is selected. In this embodiment, the first-stage nanofiltration deep magnesium removal system uses a roll-type nanofiltration membrane, the rejection rate of the roll-type nanofiltration membrane on magnesium sulfate is 98%, the rejection rate on sodium chloride is 9%, the operating pressure is 0.8MPa, the recovery rate is 70%, and a cross-flow filtration mode is adopted.
In the embodiment, the components of the brine in each stage in the process of extracting lithium by using the salt lake brine are shown in table 3; the mass concentration of lithium ions in the lithium extraction mother liquor is 22.922g/L, the mass concentration of the lithium ions is 9.59 times of that of salt lake brine, and the magnesium-lithium ratio (in terms of mass ratio) is 10:1 to 0.032: 1.
TABLE 4 ingredient Table (g/L) of brine in each stage of example 4
| Species of | Mg2+ | Li+ | Mg2+/Li+ |
| Salt lake brine | 24.62 | 2.390 | 10:1 |
| Microfiltration pretreatment brine | 12.31 | 1.195 | 10:1 |
| First-stage filtrate | 0.879 | 1.554 | 0.57:1 |
| First-order concentrated solution | 38.982 | 0.357 | 109:1 |
| Lithium-rich concentrated solution | 10.988 | 19.425 | 0.57:1 |
| Lithium extraction mother liquor | 0.733 | 22.922 | 0.032:1 |
From the above examples, it can be seen that the lithium extraction mother liquor prepared by the full membrane separation method for producing the lithium extraction mother liquor from salt lake brine by using multi-stage nanofiltration salt separation of the present invention: for low-lithium and high-magnesium brine, the lithium concentration is increased from 0.102g/L to 17.701g/L and is increased by 173.5 times, and the magnesium-lithium ratio is reduced from 1000:1 to 0.06:1 in terms of mass ratio; for brine with lower magnesium-lithium ratio, the lithium concentration is increased from 2.390g/L to 22.922g/L and is increased by 9.59 times, and the magnesium-lithium ratio is reduced from 10:1 to 0.032:1 in terms of mass ratio; is suitable for further processing and producing lithium products. Therefore, the lithium extraction mother liquor prepared by the method not only has a lower magnesium-lithium ratio, but also has a higher lithium ion concentration, and is a full-membrane separation method with low energy consumption, high recovery rate, low production cost, continuous and controllable process and high reliability.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (8)
1. A full-membrane separation method for producing lithium extraction mother liquor by multi-stage nanofiltration separation of salt lake brine is characterized by comprising the following steps:
(1) pretreating salt lake brine by using a microfiltration purification system to remove suspended matters, colloids and other impurities in the salt lake brine, and then diluting the salt lake brine by 2-5 times by using fresh water to obtain microfiltration pretreated brine;
(2) feeding the microfiltration pretreated brine obtained in the step (1) into a multi-stage nanofiltration salt separation system, and separating multivalent cations and part of monovalent cations in the microfiltration pretreated brine to obtain filtrate mainly containing monovalent cations and concentrated solution mainly containing multivalent cations;
in the step (2), the number of stages of the multi-stage nanofiltration salt separation system is 1-3; the first-stage nanofiltration salt separation system adopts a DT nanofiltration membrane, the rejection rate of the DT nanofiltration membrane on magnesium sulfate in high-salinity brine is 70-95%, the rejection rate on sodium chloride is 1-5%, the operating pressure is 3-6 MPa, and the recovery rate is 50-70%;
the second-stage nanofiltration salt separation system and the third-stage nanofiltration salt separation system adopt one of a roll-type membrane, a tubular membrane or a plate-type membrane, the rejection rate of magnesium sulfate is 90-98%, the rejection rate of sodium chloride is 5-10%, the operating pressure is 0.8-4 MPa, the recovery rate is 60-80%, and the filtering mode is cross-flow filtration;
(3) sending the filtrate obtained in the step (2) into a membrane concentration system, and concentrating to obtain a lithium-rich concentrated solution;
(4) and (4) feeding the lithium-rich concentrated solution obtained in the step (3) into a nanofiltration deep magnesium removal system, and obtaining a lithium extraction mother solution after deep magnesium removal through a nanofiltration membrane.
2. The full-membrane separation method for producing the lithium extraction mother liquor by the multi-stage nanofiltration separation of salts from the salt lake brine according to claim 1, wherein in the step (1), the mass ratio of magnesium to lithium of the salt lake brine is (10-1000): 1, the mass concentration of lithium ions is 0.1-5 g/L, and the pH value is 5-7.5.
3. The full-membrane separation method for producing the lithium extraction mother liquor by the multi-stage nanofiltration separation of salt from salt lake brine according to claim 1, wherein in the step (1), the number of the microfiltration purification system stages is 1-2, and the microfiltration purification system is formed by sequentially combining one or two of the filtration precision of 1-5 μm, 0.45-1 μm or 0.1-0.45 μm according to the pore size.
4. The full-membrane separation method for producing lithium-extracting mother liquor by multi-stage nanofiltration separation of salt from salt lake brine according to claim 3, wherein the microfiltration membrane of the microfiltration purification system is made of one or more of ceramic, polypropylene, polycarbonate, polyvinyl chloride, polysulfone, polyvinylidene fluoride or polytetrafluoroethylene.
5. The full-membrane separation method for producing the lithium extraction mother liquor by the multi-stage nanofiltration salt separation of the salt lake brine according to claim 1, wherein the nanofiltration salt separation system adopts an internal circulation mode, namely, a part of the concentrated solution of each stage of the nanofiltration salt separation system flows back to the raw liquor pool of the stage of the nanofiltration salt separation system for circulation, wherein the temperature of the primary concentrated solution is reduced before flowing back, so that part of inorganic salts are saturated and separated out, the salt content of the concentrated solution is reduced, and the concentrated solution is filtered and then sent to the raw liquor pool of the primary nanofiltration salt separation system; and the other part of the first-stage concentrated solution is discharged for other use, and the rest second-stage concentrated solution and the rest third-stage concentrated solution respectively flow back to the stock solution pools of the first-stage nanofiltration salt separation system and the second-stage nanofiltration salt separation system.
6. The full-membrane separation method for producing the lithium extraction mother liquor by the multi-stage nano-filtration of the salt lake brine according to claim 1, wherein the membrane concentration system is composed of a forward osmosis system or a combination system of the forward osmosis system and a reverse osmosis system; obtaining reverse osmosis filtrate and primary lithium-rich concentrated solution from a reverse osmosis system, and obtaining lithium-rich concentrated solution from a forward osmosis system; and (4) refluxing the reverse osmosis filtrate to a fresh water dilution system of the microfiltration purification system to prepare microfiltration pretreatment brine.
7. The full-membrane separation method for producing the lithium extraction mother liquor by the multi-stage nanofiltration separation of the salt lake brine according to claim 1, wherein the number of stages of the nanofiltration deep magnesium removal system is 1-2, and a full-circulation mode is adopted, namely, all concentrated water at each stage flows back to the raw liquor tank of the nanofiltration separation system at the present stage for circulation; one of a roll-type membrane, a tubular membrane or a plate-type membrane is used, the rejection rate of the membrane to magnesium sulfate is 90-99%, the rejection rate to sodium chloride is 5-10%, the operating pressure is 0.8-3 MPa, the recovery rate is 60-80%, and the filtering mode is cross-flow filtration.
8. The full-membrane separation method for producing lithium-extracting mother liquor by multi-stage nanofiltration salt separation of salt lake brine according to claim 1, wherein the nanofiltration salt separation system of step (2) and the nanofiltration deep magnesium removal system of step (4) both adopt a spiral membrane, a tubular membrane or a plate membrane, and the nanofiltration membrane is one or more of aromatic polyamide, polypiperazine amide, polyimide or sulfonated polysulfone.
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| CN111606334A (en) * | 2020-07-01 | 2020-09-01 | 启迪清源（北京）科技有限公司 | Method for converting carbonate type salt lake brine into chloride type brine |
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| CN114163049B (en) * | 2021-11-11 | 2023-10-24 | 山东海化集团有限公司 | Method for preparing magnesium sulfate heptahydrate by brine film method |
| CN115028149A (en) * | 2022-03-15 | 2022-09-09 | 瑜华科技(上海)有限公司 | Membrane method lithium extraction process for salt lake |
| CN115594204B (en) * | 2022-11-02 | 2023-12-26 | 河南倍杰特环保技术有限公司 | Lithium carbonate recovery system and method |
| CN115676856B (en) * | 2022-11-02 | 2024-01-30 | 河南倍杰特环保技术有限公司 | Method and system for extracting lithium from salt lake |
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