Method and device for extracting lithium from salt lake brine

Abstract

The present application belongs to the technical field of salt lake brine resource extraction, and particularly relates to a method and device for extracting lithium from salt lake brine, which comprises the steps of high-low pressure double membrane magnesium removal, adsorption carbon removal, tower rectification, adsorption lithium extraction, kneading and cleaning, acidification resolution, and downstream leaching. The method and device can be used in combination to efficiently extract lithium from salt lake brine, with an extraction rate of greater than 90%, and ultimately obtain a lithium-rich liquid with TOC of less than or equal to 5 mg / L, magnesium of less than or equal to 5 mg / L, and lithium of greater than or equal to 1000 mg / L. The method and device can effectively improve the quality and extraction rate of the lithium-rich liquid, avoid incomplete organic matter treatment and system equipment and pipeline blockage, and effectively reduce energy consumption and operating costs during the extraction of lithium from salt lake brine.

Description

Technical Field

[0001] This invention belongs to the field of salt lake brine resource extraction technology, specifically relating to a method and apparatus for lithium extraction from salt lake brine. Background Technology

[0002] my country's salt lake resources are mainly distributed in Qinghai and Tibet. The main types of salt lakes are sulfate, chloride, and carbonate. The ions in these salt lake brines are diverse, primarily rich in K, Na, Mg, Li, B, and Cl. - SO4 2- Among them, lithium, potassium, and boron have resource recycling value, and these three resources are currently being vigorously developed both domestically and internationally, especially lithium and potassium resources.

[0003] In the process of lithium and potassium resource development, octadecylamine is usually added first to separate potassium (K) from salt lake brine in the form of KCl foam. After potassium extraction, a large amount of octadecylamine organic matter remains in the brine. This organic matter easily contaminates the adsorbent, reduces the adsorption efficiency of the adsorbent, and makes it difficult for the lithium carbonate products obtained at the end to meet the requirements of industrial-grade or battery-grade lithium carbonate products. The conventional method for removing organic matter is to carry out oxidation treatment after pretreatment. However, in the high-salt system of salt lake brine, the hydroxyl radicals generated by advanced oxidation are consumed by chloride ions and carbonate ions, resulting in a significant reduction in oxidation efficiency and poor organic matter treatment effect.

[0004] The most common method for lithium extraction is currently "adsorption + concentration + precipitation". However, most of my country's salt lakes are located in northwestern regions such as Qinghai and Tibet. Winter temperature changes can easily cause salts such as NaCl and MgCl2 to crystallize and precipitate during the lithium extraction process. After the crystallized salts adhere to the surface of the adsorbent, they not only greatly reduce the adsorption efficiency of the adsorbent, but also easily cause severe blockage of the adsorption tank and pipelines, making the system unable to operate normally. Current practices generally involve heating the influent water and insulating the tank. However, due to the large volume of water used for lithium extraction in salt lakes, the daily processing volume often reaches tens of thousands of cubic meters, resulting in high energy consumption for heating and insulation, and high operating costs. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method and apparatus for lithium extraction from salt lake brine, which solves the problems of low lithium extraction efficiency and poor organic matter treatment effect of the existing methods for lithium extraction from salt lake brine, and can effectively reduce energy consumption and operating costs in the process of lithium extraction from salt lake brine.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for lithium extraction from salt lake brine is provided, comprising the following steps: S1: High and low pressure dual-membrane magnesium removal: Magnesium removal treatment of lithium-containing brine is carried out by high pressure disc tube nanofiltration membrane and low pressure nanofiltration membrane. S2: Adsorption carbon removal: Organic matter in the brine after magnesium removal is adsorbed by adding macroporous resin to the adsorption carbon removal tank, and then a regenerator is added to obtain the regenerated solution. S3: Tower distillation: The regenerated liquid is distilled through a slanted tray to obtain a distillate that can be recycled as a regenerator; S4: Lithium adsorption: After removing organic matter, the brine enters the lithium adsorption tank, and titanium-based adsorbent is added to adsorb lithium ions in the brine onto the adsorbent. S5: Scrubbing and cleaning: The adsorbent after lithium adsorption is transferred to a scrubbing and cleaning tank, where crystalline salts and contaminants on the surface of the adsorbent are removed by adding warm water at 40-60°C and simultaneously introducing air. S6: Acidification and Desorption: The adsorbent after being rubbed and washed enters the acidification and desorption tank, and dilute hydrochloric acid is added for desorption to obtain lithium-rich solution; S7: Co-current rinsing: The adsorbent after lithium desorption enters the co-current rinsing tank and is rinsed with fresh water until the rinsing solution is neutral.

[0007] The beneficial effects of adopting the above technical solution are as follows: Step S1 uses a high-low pressure dual-membrane combination process to separate lithium and magnesium, improving the purity of lithium in the brine. The concentrated water is returned to the salt lake, while the new product water enters the adsorption and decarbonization tank in the downstream S2. A regenerator is added to the adsorption and decarbonization tank, and the organic matter in the brine is adsorbed by macroporous resin, reducing the TOC in the brine, improving the quality of the subsequent lithium-rich solution, and avoiding organic contamination or system blockage of the downstream lithium adsorbent. The generated regenerated liquid enters the inclined-hole tray, and the distillate produced by distillation can be recycled as a regenerator, reducing or eliminating the need for adsorption and decarbonization. The addition of regenerant during carbon regeneration reduces regenerant addition costs. The effluent after adsorption enters the lithium extraction tank in step S3, where lithium ions from the brine are adsorbed onto the adsorbent. The adsorbent after lithium adsorption is transferred to the rubbing and cleaning tank in step S4. Warm water at 40-60°C removes crystalline salts and contaminants from the adsorbent surface, preventing adsorption efficiency reduction due to adsorbent blockage caused by salts and contaminants. The introduced air enhances the cleaning effect. The adsorbent after rubbing and cleaning enters the acidification and desorption tank in step S5, where it is treated with 5%-15% dilute hydrochloric acid. Lithium from the adsorbent is released into the water to form a lithium-rich solution, which can be sold or further processed into lithium products. The adsorbent after lithium release enters a co-current rinsing tank in step S6, where it is rinsed with fresh water until the effluent is neutral. The adsorbent can then be recycled into the lithium extraction tank in step S3, while the effluent can be recycled into the high- and low-pressure dual-membrane magnesium removal system in step S1. By combining steps S1 to S7, efficient lithium extraction from salt lake brine can be achieved, with an extraction rate greater than 90%, while also improving the treatment efficiency of organic matter. The resulting lithium-rich solution is of high quality. The lithium-rich solution contains TOC ≤ 5 mg / L, magnesium ≤ 5 mg / L, and lithium ≥ 1000 mg / L. Furthermore, the wash liquid generated from the co-current rinsing is returned to the upstream high- and low-pressure dual-membrane magnesium removal system for further treatment. This dilutes the influent, reduces the salt content in the brine, and improves the permeate flux and recovery rate of the nanofiltration membrane. It avoids the problem of requiring a large amount of fresh water for dilution before magnesium removal in existing lithium extraction processes, saving a significant amount of fresh water and effectively reducing production costs and energy consumption. On the other hand, it solves the problem of where the wash liquid will go, creating a "closed loop" that requires no further treatment.

[0008] Furthermore, the magnesium-to-lithium mass ratio of the lithium-containing brine in S1 is 30:1 to 3000:1; the operating pressure of the high-pressure disc tube nanofiltration membrane is 30 to 120 bar; and the operating pressure of the low-pressure nanofiltration membrane is 5 to 30 bar.

[0009] The beneficial effects of adopting the above technical solution are as follows: High-pressure disc tube nanofiltration membrane (DTNF) can separate divalent or polyvalent ions such as magnesium from lithium in brine. After the salinity of the product water is reduced, low-pressure nanofiltration membrane (NF) further separates divalent or polyvalent ions such as magnesium from lithium, ensuring a more thorough separation of magnesium and lithium. In addition, the concentrate treated by low-pressure nanofiltration membrane (NF) is returned to the high-pressure nanofiltration membrane, which also dilutes the feed water of high-pressure disc tube nanofiltration membrane (DTNF), thereby reducing the amount of fresh water used in the high- and low-pressure dual-membrane magnesium removal system and reducing production costs. Furthermore, by using high-pressure disc tube nanofiltration membrane (DTNF) and low-pressure nanofiltration membrane (NF) in combination, the magnesium-to-lithium mass ratio in brine can be reduced from 30:1 to 3000:1 to 0.01 to 0.1:1, which can effectively improve the separation efficiency of lithium and magnesium, and improve the purity and extraction efficiency of lithium.

[0010] Furthermore, the macroporous resin in S2 has a particle size of 0.3–1.5 mm; the regenerant is methanol, ethanol, or acetone.

[0011] The beneficial effects of adopting the above technical solution are as follows: macroporous resin can adsorb organic matter in brine, reduce TOC in brine, improve the quality of subsequent lithium-rich solution, and avoid the problem of downstream lithium adsorbent being contaminated by organic matter or system blockage.

[0012] Furthermore, in S3, the tray spacing of the inclined hole tray is 350–650 mm, the feed temperature is 60–90 °C, the top temperature of the inclined hole tray is 60–75 °C, the bottom temperature is 100–110 °C, and the bottom operating pressure is 130–140 kPa.

[0013] The beneficial effects of adopting the above technical solution are as follows: the distillate produced by tower distillation can be recycled as a regenerator, reducing or avoiding the addition of regenerator during the adsorption carbon removal regeneration process, thereby reducing production costs and reducing the discharge of regenerated liquid.

[0014] Furthermore, the main chemical constituent elements of the titanium-based adsorbent in S4 are Ti, Li, C, H, and O, with a mass ratio of (1-1.8):(0.2-0.3):(0.7-2):(0.02-0.2):(2-3); the particle size of the titanium-based adsorbent is 1-5 mm, and the filling amount is 40%-50%.

[0015] The beneficial effects of adopting the above technical solution are as follows: the titanium-based adsorbent has a special structure with a layered structure as the main component and a prismatic crystal structure as the auxiliary component. It has a high adsorption capacity and good lithium selectivity, which can efficiently separate lithium ions from brine. At the same time, its desorption process does not require the consumption of a large amount of fresh water, and the resulting desorption solution has a high lithium content, thereby improving the lithium extraction rate.

[0016] Furthermore, a compound inhibitor is added to S4, with a dosage of 0.1–1 ml / L. The compound inhibitor is a mixture of racemic ferric tartrate, 1-octadecylamine hydrochloride, and sodium acetate. The mass percentage of the added racemic ferric tartrate is 0.3%–1.5%, the mass percentage of the added 1-octadecylamine hydrochloride is 15%–35%, the mass percentage of the added sodium acetate is 5%–25%, and the remainder is water.

[0017] The beneficial effects of adopting the above technical solution are as follows: the composite inhibitor has a better inhibitory effect on salt crystallization, and can inhibit the crystallization of different salts in salt lake brine, improve the lithium extraction efficiency, and avoid salt crystallization on the adsorbent surface, which would cause adsorbent blockage and reduce the adsorption effect; at the same time, the composite inhibitor can avoid the introduction of cyanide toxic components in conventional ferrocyanide inorganic inhibitors, which is environmentally friendly, and reduces the amount of nitrogen atoms added compared with conventional organic inhibitors such as triacetamide (N(CH2CONH2)3), which reduces the generation of explosive gas nitrogen trichloride and improves system safety.

[0018] Furthermore, the concentration of dilute hydrochloric acid in S6 is 5%–15%, the desorption rate is 1–2 BV / h, and the desorption residence time is 2–6h.

[0019] The beneficial effects of adopting the above technical solution are as follows: by adding dilute hydrochloric acid, the operating pH during acidification and desorption can be maintained at 1-3, which can improve the desorption efficiency and effect of desorbing lithium from the adsorbent into the water, and avoid the problem of consuming a large amount of fresh water during pure water desorption.

[0020] Furthermore, the pH of the co-current rinsing solution in S7 is 6–9, the rinsing rate is 2–4 BV / h, and the rinsing residence time is 0.5–2h.

[0021] The advantages of adopting the above technical solution are as follows: the wash liquid after co-current rinsing is returned to the front-end high and low pressure dual membrane magnesium removal system for further treatment. On the one hand, it has a dilution effect on the influent, which can reduce the brine salt content, improve the nanofiltration membrane flux and recovery rate, and avoid the problem of adding a large amount of fresh water for dilution before magnesium removal by the nanofiltration membrane in the existing lithium extraction process, thus effectively saving a large amount of fresh water. On the other hand, it solves the problem of the outlet of the wash liquid, so that the wash liquid forms a "closed loop" and does not need to be treated separately.

[0022] To implement the above technical solution, the present invention provides an apparatus for lithium extraction from salt lake brine, comprising: High and low pressure dual-membrane magnesium removal system is used to separate divalent or polyvalent ions such as magnesium from lithium; The adsorption carbon removal tank is connected to the high and low pressure dual-membrane magnesium removal system and is used to adsorb organic matter in the brine. Inclined perforated trays, connected to one side of the adsorption and carbon removal tank, are used for distillation regeneration liquid; The lithium adsorption tank, connected to the carbon adsorption tank, is used to adsorb lithium ions from the brine onto the adsorbent. The rubbing and cleaning tank, connected to the adsorption lithium extraction tank, is used to remove crystalline salts and contaminants from the surface of the adsorbent. An acidification and desorption tank, connected to a rubbing and washing tank, is used to desorb lithium from the adsorbent into water to form a lithium-rich solution. The co-current rinsing tank is connected to the kneading and washing tank on one side and the adsorption and lithium extraction tank on the other side, and is used to rinse the adsorbent. The adsorption carbon removal tank, adsorption lithium extraction tank, kneading and washing tank, acidification and desorption tank, and co-current rinsing tank are all floating bed structures, which can make the adsorbent in a suspended and flowing state.

[0023] The beneficial effects of using the above-mentioned device to implement the lithium extraction method from salt lake brine are as follows: the adsorption decarbonization tank, adsorption lithium extraction tank, kneading and washing tank, acidification and desorption tank, and co-current rinsing tank are all floating bed structures. By controlling the upward flow velocity of the water in the floating bed, the adsorbent packing material can be kept in a fluidized state, i.e., a suspended flow state, which can improve the adsorption efficiency of the adsorbent and facilitate subsequent lithium extraction. At the same time, at least two sets of adsorption decarbonization tanks and adsorption lithium extraction tanks are set up, which can make the adsorption lithium extraction process cyclical. When one set enters the kneading and washing stage, the other set can start adsorption, thereby realizing the continuous alternating operation of the device, which can effectively improve the lithium extraction efficiency.

[0024] Furthermore, the high-low pressure dual-membrane magnesium removal system includes a first high-pressure pump, a high-pressure disc tube nanofiltration membrane, a first product water tank, and a low-pressure nanofiltration membrane connected in sequence. The low-pressure nanofiltration membrane is connected to the first high-pressure pump, and its product water side is also connected to a second product water tank. The second product water tank is connected to a carbon removal booster pump, which is connected to the adsorption carbon removal tank.

[0025] The beneficial effects of adopting the above technical solution are as follows: High-pressure disc tube nanofiltration membrane (DTNF) can separate divalent or polyvalent ions such as magnesium from lithium. After the salinity of the product water is reduced, it is further separated from lithium by low-pressure nanofiltration membrane (NF). The concentrated water after low-pressure nanofiltration membrane (NF) treatment is returned to the high-pressure nanofiltration membrane, which dilutes the feed water of high-pressure disc tube nanofiltration membrane (DTNF), thereby reducing the amount of fresh water used in the high- and low-pressure dual-membrane magnesium removal system and reducing production costs. Furthermore, by using high-pressure disc tube nanofiltration membrane (DTNF) and low-pressure nanofiltration membrane (NF) in combination, the magnesium-to-lithium mass ratio in the brine can be reduced from 30:1 to 3000:1 to 0.01:1 to 0.1:1, which can effectively improve the separation efficiency of lithium and magnesium, and improve the purity and extraction efficiency of lithium.

[0026] In summary, the beneficial effects of the lithium extraction method and apparatus from salt lake brine provided by this invention are as follows: (1) By using the method and apparatus for lithium extraction from salt lake brine of the present invention, high-efficiency extraction of salt lake brine can be achieved, with a lithium extraction rate of more than 90%, and the removal efficiency of organic matter can be improved. The resulting lithium-rich liquid has good quality, with TOC ≤ 5 mg / L, magnesium ≤ 5 mg / L, and lithium ≥ 1000 mg / L. This avoids the problem of incomplete treatment of organic matter and can also effectively reduce energy consumption and operating costs in the process of lithium extraction from salt lake brine.

[0027] (2) The high and low pressure dual membrane magnesium removal system in this invention adopts a high and low pressure dual membrane combination process, which can separate lithium and magnesium, improve the purity of lithium in the brine, and the concentrated water after low pressure nanofiltration (NF) treatment can be returned to the high pressure nanofiltration membrane to dilute the feed water of the high pressure disc tube nanofiltration membrane (DTNF), thereby reducing the amount of fresh water used in the high and low pressure dual membrane magnesium removal system and reducing production costs.

[0028] (3) The macroporous resin in the adsorption decarbonization tank of the present invention can adsorb organic matter in the brine, reduce the TOC in the brine, improve the quality of the subsequent lithium-rich liquid, and avoid the problem of the lithium adsorbent being contaminated by organic matter or the system being blocked.

[0029] (4) The distillate produced by the inclined plate in this invention can be recycled as a regenerator, which can reduce or avoid the addition of regenerator during the adsorption carbon removal regeneration process, thereby reducing production costs and energy consumption.

[0030] (5) The adsorption lithium extraction process in this invention uses a combination of titanium-based adsorbents and composite inhibitors. The titanium-based adsorbents can adsorb lithium ions in the brine onto the adsorbent, thereby increasing the lithium extraction rate. Compared with conventional single inhibitors such as ferrocyanide or triacetamide, the composite inhibitors have a better salt crystallization inhibition effect, which can inhibit salt crystallization in salt lake brine, avoid crystallization of crystalline salt on the surface of the adsorbent, and prevent the adsorbent from becoming clogged and reducing the adsorption effect, thereby reducing the lithium extraction efficiency. At the same time, the composite inhibitors are more environmentally friendly and can reduce the generation of explosive gas nitrogen trichloride, thereby improving the system safety.

[0031] (6) The rubbing and cleaning tank in this invention can efficiently remove crystalline salts and contaminants from the surface of the adsorbent by adding hot water and air, thus avoiding the problem of reduced adsorption effect caused by adsorbent blockage due to salts and contaminants.

[0032] (7) The acidification desorption tank in this invention can desorb lithium on the adsorbent into water to form a lithium-rich solution by adding 5% to 15% dilute hydrochloric acid, thereby improving the desorption efficiency and lithium extraction efficiency of desorbing lithium on the adsorbent into water.

[0033] (8) In this invention, the washing liquid after being rinsed by the co-current rinsing tank is returned to the high and low pressure dual membrane magnesium removal system at the front end for further treatment. On the one hand, it has a dilution effect on the influent, which can reduce the salt content of the brine, increase the flux and recovery rate of the nanofiltration membrane, and effectively save a large amount of fresh water. On the other hand, it solves the problem of the outlet of the washing liquid, so that the washing liquid forms a "closed loop" and does not need to be treated separately.

[0034] (9) The adsorption lithium extraction tank, rubbing and washing tank, acidification and desorption tank and co-current rinsing tank in this invention can make the adsorption lithium extraction process cycled, realize the continuous alternating operation of the device, and effectively improve the adsorption efficiency and extraction efficiency of lithium.

[0035] (10) The adsorption carbon removal tank, adsorption lithium extraction tank, kneading and cleaning tank, acidification and desorption tank and co-current rinsing tank in this invention are all designed as floating bed structures. By controlling the upward flow velocity of the water in the floating bed, the adsorbent packing can be ensured to be in a fluidized state in the adsorption tank, reducing valves, pipelines and system structure, reducing or avoiding problems such as scaling or salt crystal blockage and leakage in pipelines, and reducing installation and maintenance costs.

[0036] (11) The adsorbent in this invention can be periodically transferred, making the rubbing and rinsing more thorough and facilitating the flow and dispersion between adsorbent particles. This avoids the problems of adsorbent scaling or clogging after salt crystallization, effectively improving lithium extraction efficiency. Attached Figure Description

[0037] Figure 1 This is a schematic flowchart of the lithium extraction method from salt lake brine of the present invention; Figure 2 This is a schematic diagram of the lithium extraction device from salt lake brine of the present invention; Figure 3 This is a schematic diagram of the internal structure of the adsorption tank in this invention.

[0038] Among them, 1-high pressure disc tube nanofiltration membrane; 2-low pressure nanofiltration membrane; 3-adsorption carbon removal tank; 4-slanted hole tray; 5-adsorption lithium extraction tank; 6-rubbing and washing tank; 7-acidification and desorption tank; 8-co-current rinsing tank; 9-upper water distributor; 10-adsorbent; 11-lower water distributor; 31-first adsorption carbon removal tank; 32-second adsorption carbon removal tank; 51-first adsorption lithium extraction tank; 52-second adsorption lithium extraction tank; 101-first high pressure pump; 102-second high pressure pump; 103-carbon removal booster pump; 104-first transfer pump; 105-second transfer pump; 106-third transfer pump; 107-fourth transfer pump; 201-first product water tank; 202-second product water tank. Detailed Implementation

[0039] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0040] Example 1 like Figure 1 As shown, the method for lithium extraction from salt lake brine provided by the present invention includes the following steps: S1: High and low pressure dual-membrane magnesium removal: Magnesium removal treatment of lithium-containing brine is carried out by high pressure disc tube nanofiltration membrane and low pressure nanofiltration membrane. S2: Adsorption carbon removal: Organic matter in the brine after magnesium removal is adsorbed by adding macroporous resin to the adsorption carbon removal tank, and then a regenerator is added to obtain the regenerated solution. S3: Tower distillation: The regenerated liquid is distilled through a slanted tray to obtain a distillate that can be recycled as a regenerator; S4: Lithium adsorption: After removing organic matter, the brine enters the lithium adsorption tank, and titanium-based adsorbent is added to adsorb lithium ions in the brine onto the adsorbent. S5: Scrubbing and cleaning: The adsorbent after lithium adsorption is transferred to a scrubbing and cleaning tank, where crystalline salts and contaminants on the surface of the adsorbent are removed by adding warm water at 40-60°C and simultaneously introducing air. S6: Acidification and Desorption: The adsorbent after being rubbed and washed enters the acidification and desorption tank, and dilute hydrochloric acid is added for desorption to obtain lithium-rich solution; S7: Co-current rinsing: The adsorbent after lithium desorption enters the co-current rinsing tank and is rinsed with fresh water until the rinsing solution is neutral.

[0041] In practice, lithium-containing brine is first added to a high-low pressure dual-membrane magnesium removal system. The lithium and magnesium are separated using a combined high-low pressure dual-membrane process. The concentrated water after separation is returned to the salt lake, while the fresh water enters the adsorption carbon removal tank 3. A regenerant is added to the adsorption carbon removal tank 3. Through the combined use of the regenerant and macroporous resin, organic matter in the brine is adsorbed, reducing the TOC (total organic matter content) of the brine. The resulting regenerated liquid enters the inclined-hole tray 4 for distillation. The distillate produced can be reused as regenerant in the adsorption carbon removal tank 3, while the residual liquid after distillation is outsourced for further processing. The fresh effluent from the adsorption carbon removal process enters the adsorption lithium extraction tank 5. Adsorbent 10 adsorbs lithium ions from the brine onto the adsorbent. The treated brine is returned to the salt lake, while the adsorbent 10 is then... The rubbing and washing tank 6 removes crystalline salts and contaminants from the surface of the adsorbent 10 by spraying in warm water at 40-60°C and simultaneously introducing air. The resulting wastewater undergoes secondary treatment within the plant, while the adsorbent 10 enters the acidification and desorption tank 7. The lithium on the adsorbent 10 is desorbed into the water using 5%-15% dilute hydrochloric acid to form a lithium-rich solution. The lithium-rich solution can be sold directly or further processed into lithium products. After lithium desorption, the adsorbent 10 enters the co-current rinsing tank 8, where it is rinsed with fresh water until the rinsing solution is neutral. Finally, the adsorbent 10 is recycled back into the adsorption and lithium extraction tank 5. The rinsing solution can be returned to the front-end high- and low-pressure dual-membrane magnesium removal system for recycling. This process achieves efficient lithium extraction from the salt lake brine while reducing production costs and energy consumption.

[0042] In step S1, the salt content of the lithium-containing brine is 20% to 40%, and the magnesium-to-lithium mass ratio is 30:1 to 3000:1; the high-pressure disc tube nanofiltration membrane 1 (DTNF) operates at a pressure of 30 to 120 bar, and its recovery rate is 50% to 80%; the low-pressure nanofiltration membrane 2 (NF) operates at a pressure of 5 to 30 bar, and its recovery rate is 60% to 90%.

[0043] In practice, the high-pressure disc tube nanofiltration membrane 1 (DTNF) can separate divalent or polyvalent ions such as magnesium from lithium, while the low-pressure nanofiltration membrane 2 (NF) further separates divalent or polyvalent ions such as magnesium from lithium. The concentrate treated by the low-pressure nanofiltration membrane 2 (NF) is returned to the high-pressure nanofiltration membrane to dilute the feed water of the high-pressure disc tube nanofiltration membrane 1 (DTNF), thereby reducing the amount of fresh water used in the high- and low-pressure dual-membrane magnesium removal system and lowering production costs. By using the combination of the high-pressure disc tube nanofiltration membrane 1 (DTNF) and the low-pressure nanofiltration membrane 2 (NF), the magnesium-to-lithium mass ratio in the brine can be reduced from 30:1 to 3000:1 to 0.01:1 to 0.1:1, which can effectively improve the separation efficiency of lithium and magnesium, and improve the purity and extraction efficiency of lithium.

[0044] In step S2, the pH of the brine after magnesium removal is 5-10, its operating flow rate is 1-8 BV / h, and the fluidization regeneration flow rate is 0.5-5 BV / h; the TOC of the brine effluent after adsorption and carbon removal is ≤5 mg / L.

[0045] In step S2, the macroporous resin is in the form of spherical particles with a particle size of 0.3 to 1.5 mm; and the regenerant is methanol, ethanol or acetone.

[0046] During implementation, macroporous resin can adsorb organic matter in brine, reduce TOC in brine, improve the quality of subsequent lithium salt products, and avoid problems such as organic matter contamination or system blockage of the downstream lithium adsorbent 10, thereby improving lithium extraction efficiency.

[0047] In step S3, the column distillation adopts the inclined hole tray 4 for distillation. The tray spacing of the inclined hole tray 4 is 350-650mm, the feed temperature is 60-90℃, the top temperature of the inclined hole tray 4 is 60-75℃, the bottom temperature is 100-110℃, and the bottom operating pressure is 130-140kPa.

[0048] In practice, the distillate produced by the distillation of the inclined tray 4 can be recycled as a regenerator, which can reduce or avoid the addition of regenerator during the adsorption and decarbonization regeneration process, thereby reducing production costs.

[0049] In step S4, the adsorbent 10 is a titanium-based adsorbent 10, which is a mixture of lithium titanate and titanium dioxide. Its main chemical constituent elements are Ti, Li, C, H and O, and its mass ratio is (1~1.8):(0.2~0.3):(0.7~2):(0.02~0.2):(2~3). The titanium-based adsorbent 10 has a particle size of 1~5 mm and a filling amount of 40%~50%.

[0050] In step S4, the reaction pH in the lithium adsorption tank 5 is 7-11, the temperature is 0-50℃, and the flow rate is 20-60m / h. During implementation, the titanium-based adsorbent 10 can adsorb lithium ions in the brine onto the adsorbent 10, thereby improving the lithium extraction rate.

[0051] In step S5, the air intensity is 1 to 7 L / m·s, and the residence time is 0.5 to 2 h; air is introduced to enhance the cleaning effect and effectively remove crystalline salts or pollutants from the surface of the adsorbent 10.

[0052] In step S6, the concentration of dilute hydrochloric acid is 5%-15%, the pH of the acidification and desorption process is 1-3, the desorption rate is 1-2 BV / h, and the desorption residence time is 2-6h. Using an acidification and desorption solution with a pH of 1-3 can improve the desorption efficiency and lithium extraction efficiency of lithium on adsorbent 10 into water.

[0053] In step S7, the pH of the wash solution is 6-9, the rinsing rate is 2-4 BV / h, and the rinsing residence time is 0.5-2h. In practice, the wash solution after co-current rinsing is returned to the high-low pressure dual-membrane magnesium removal system at the front end for further treatment. On the one hand, it has a dilution effect on the influent, which can reduce the brine salt content, improve the nanofiltration membrane flux and recovery rate, and avoid the problem of adding a large amount of fresh water for dilution before magnesium removal by the nanofiltration membrane in the existing lithium extraction process, thus effectively saving a large amount of fresh water. On the other hand, it solves the problem of the outlet of the wash solution, so that the wash solution forms a "closed loop" and does not require further treatment.

[0054] Example 2 Based on Example 1, in step S4 of this example, a compound inhibitor is also added. The dosage of the compound inhibitor is 0.1-1 ml / L, and it is mesoferric tartrate and 1-octadecylamine hydrochloride (C 18 H 37 A mixture of NH2HCl, sodium acetate, and water.

[0055] In practice, the composite inhibitor has a better inhibitory effect on salt crystallization, and can inhibit the crystallization of different salts in salt lake brine. It avoids the crystallization of crystalline salt on the surface of adsorbent 10, which would cause the adsorbent 10 to become clogged and reduce the adsorption effect, thereby improving the lithium extraction efficiency. At the same time, the composite inhibitor can avoid the addition of cyanide toxic components in conventional ferrocyanide inorganic inhibitors, which is environmentally friendly. Moreover, it reduces the amount of nitrogen atoms added compared with conventional organic inhibitors such as triacetamide (N(CH2CONH2)3), which reduces the generation of explosive gas nitrogen trichloride and improves system safety.

[0056] In step S4, the mass percentage of racemic ferric tartrate is 0.3%–1.5%. After dissolution and dissociation, racemic ferric tartrate generates racemic tartrate ions, which, compared to chloride ions, have a stronger attraction to sodium ions, hindering the migration of sodium ions to chloride ions and thus inhibiting the formation of sodium chloride crystal nuclei, making it difficult for NaCl to crystallize. Additionally, the dissociated Fe... 3+ Both the positive and negative ions are charged groups. These positive and negative charged groups selectively adsorb onto inorganic salt crystal nuclei or microcrystals, occupying certain positions and altering the charge distribution on the crystal surface. This hinders the normal growth of inorganic salt crystals, causing them to become distorted, inhibiting the formation of crystal nuclei, or making the crystal particles loose and easily detached from the surface of the adsorbent 10. This achieves the inhibition of crystallization of different salts in salt lake brine and improves the extraction efficiency of lithium.

[0057] In step S4, 1-octadecylamine hydrochloride (C 18 H 37 The mass percentage of NH2HCl is 15%–35%; 1-octadecylamine hydrochloride (C 18 H 37NH2HCl is composed of hydrophilic amino (-NH2) and hydrophobic alkane groups. This structure allows it to adsorb at the solid-liquid interface and even on different crystal planes, increasing the repulsive force between particles and hindering their aggregation. This allows the precipitated salt to form loose, small dendritic or snowflake-like crystals, preventing the salt from continuing to grow larger on its surface, thereby inhibiting salt crystallization.

[0058] In step S4, the mass percentage of sodium acetate is 5% to 25%, with the remainder being water. After sodium acetate dissolves and dissociates, not only can the positively and negatively charged groups selectively adsorb onto the inorganic salt crystal nuclei or microcrystals, occupying certain positions and changing the charge distribution on the crystal surface, thus hindering the normal growth of inorganic salt crystals, but the solution after sodium acetate hydrolysis is alkaline, which can maintain the alkaline environment required by the adsorbent 10 during the adsorption process, improve the adsorption efficiency, reduce or avoid the process of adjusting the pH by adding NaOH to the influent, and reduce production costs.

[0059] Comparative Example 1 Based on Example 2, to verify the inhibitory effect of different inhibitors on NaCl crystallization, this comparative example provides a blank group without inhibitor, a sodium ferrocyanide group with conventional inhibitors and a triacetamide group, and a combined inhibitor group. The experimental data obtained under the same conditions are shown in Table 1: Table 1

[0060] As shown in Table 1, compared with conventional inhibitors such as sodium ferrocyanide and triacetamide, the composite inhibitor has the best inhibitory effect on NaCl crystallization, with a salt inhibition rate of 99.3%, which is close to the point that NaCl does not crystallize. It can inhibit salt crystallization in salt lake brine, avoid crystallization of salt on the surface of adsorbent 10, which would cause adsorbent 10 to become clogged and reduce the adsorption effect, thereby improving the lithium extraction efficiency. It is also environmentally friendly, reducing the generation of explosive gas nitrogen trichloride and improving system safety.

[0061] Comparative Example 2 Based on the experiment of the composite inhibitor in Comparative Example 1, in order to verify the inhibitory effect of the composite inhibitor on NaCl crystallization under different dosages, this comparative example provided experimental groups with composite inhibitor dosages of 0.2 ml / L, 0.4 ml / L, 0.6 ml / L, and 0.8 ml / L. Under the same conditions, the experimental data obtained are shown in Table 2: Table 2

[0062] As shown in Table 2, when the dosage of the composite inhibitor is 0.6 mL / L, the inhibitory effect on NaCl crystallization is already very good, second only to the effect of preventing NaCl crystallization when the dosage is 0.8 mL / L. It can effectively inhibit the crystallization of different salts, avoid the crystallization of crystalline salts on the surface of adsorbent 10, which would cause the adsorbent 10 to become clogged and reduce the adsorption effect, and improve the lithium extraction efficiency.

[0063] Comparative Example 3 Based on the experiments of Comparative Example 2 on the composite inhibitor, in order to verify the inhibitory effect of the composite inhibitor groups under different pH conditions on NaCl crystallization under the same dosage of composite inhibitor, this comparative example provides experimental groups of composite inhibitors at pH=8, 9, 10, and 11, respectively. The experimental data obtained are shown in Table 3: Table 3

[0064] As shown in Table 3, when the pH of the adsorption influent is 10, the composite inhibitor has the best inhibitory effect on NaCl crystallization, which can prevent NaCl from crystallizing, avoid system equipment and pipeline blockage problems, and effectively improve lithium extraction efficiency.

[0065] To implement the above-described lithium extraction method and related embodiments from salt lake brine, the present invention provides a lithium extraction device from salt lake brine, comprising: High and low pressure dual-membrane magnesium removal system is used to separate divalent or polyvalent ions such as magnesium from lithium; The adsorption and decarbonation tank 3 is connected to the high and low pressure magnesium removal system and is used to adsorb organic matter in the brine. The inclined perforated tray 4 is connected to one side of the adsorption and carbon removal tank 3 and is used for distillation regeneration liquid; The lithium adsorption tank 5 is connected to the carbon adsorption tank 3 and is used to adsorb lithium ions in the brine onto the adsorbent 10. The rubbing and cleaning tank 6 is connected to the adsorption and lithium extraction tank 5 and is used to remove crystalline salts and contaminants from the surface of the adsorbent 10. The acidification and desorption tank 7 is connected to the kneading and washing tank 6 and is used to desorb lithium from the adsorbent 10 into water to form a lithium-rich solution. The co-current rinsing tank 8 is connected to the rubbing and washing tank 6 on one side and the adsorption and lithium extraction tank 5 on the other side, and is used to rinse the adsorbent 10. In use, the high- and low-pressure dual-membrane magnesium removal system can separate lithium and magnesium in brine and improve the purity of lithium. The adsorption decarbonization tank 3 can reduce the TOC in the brine. The inclined hole tray 4 can reduce or avoid the addition of regenerant during the adsorption decarbonization regeneration process. The adsorption lithium extraction tank 5 can adsorb lithium ions. The rubbing and washing tank 6 can remove crystalline salts and contaminants from the surface of the adsorbent 10. The acidification and desorption tank 7 can desorb lithium from the adsorbent 10 into the water to form a lithium-rich solution. The co-current rinsing tank 8 is used to rinse the adsorbent 10 until the rinsing solution is neutral. Through the coordinated use of the various structures in this device, lithium can be efficiently extracted from salt lake brine, resulting in a high-quality lithium-rich solution, while reducing energy consumption and operating costs.

[0066] In this invention, such as Figure 2 As shown, the high-low pressure dual-membrane magnesium removal system includes a first high-pressure pump 101, a high-pressure disc tube nanofiltration membrane 1 (DTNF), a first product water tank 201, and a low-pressure nanofiltration membrane 2 (NF) arranged in sequence. The low-pressure nanofiltration membrane 2 is connected to the first high-pressure pump 101, and its product water side is also connected to a second product water tank 202. The second product water tank 202 is connected to a carbon removal booster pump 103, which is connected to an adsorption carbon removal tank 3.

[0067] In operation, the first high-pressure pump 101 delivers lithium-containing brine from the salt lake to the high-pressure disc tube nanofiltration membrane 1 (DTNF). The DTNF separates divalent or polyvalent ions such as magnesium from lithium and then delivers the brine to the first product water tank 201. The product water in the first product water tank 201 is then delivered by the second high-pressure pump 102 to the low-pressure nanofiltration membrane 2 (NF). The low-pressure nanofiltration membrane 2 (NF) performs secondary magnesium removal on the product water before delivering it to the second product water tank 202. The second product water tank 202... The permeate in tank 2 is transported to adsorption and decarbonization tank 3 via decarbonization booster pump 103. Through the combined process of high-pressure disc tube nanofiltration membrane 1 (DTNF) and low-pressure nanofiltration membrane 2 (NF), lithium and magnesium can be completely separated, improving the purity of lithium in the brine. The concentrate treated by low-pressure nanofiltration membrane 2 (NF) can be returned to the high-pressure nanofiltration membrane to dilute the feed water of high-pressure disc tube nanofiltration membrane 1 (DTNF), thereby reducing the amount of fresh water used in the high-low pressure dual-membrane magnesium removal system and reducing production costs.

[0068] In this invention, such as Figure 2 As shown, the adsorption carbon removal tank 3 is equipped with at least a first adsorption carbon removal tank 31 and a second adsorption carbon removal tank 32. When in use, the regenerator and macroporous resin in the adsorption carbon removal tank 3 can effectively reduce the TOC in the brine, improve the quality of the subsequent lithium-rich liquid, and avoid the downstream lithium adsorbent 10 from being contaminated by organic matter or the system equipment and pipeline blockage.

[0069] In this invention, such as Figure 2As shown, an inclined perforated tray 4 is also provided on one side of the adsorption carbon removal tank 3, which can perform distillation treatment on the regenerated liquid produced by the adsorption carbon removal tank 3. The resulting distillate can be recycled as a regenerator, which can reduce or avoid the addition of regenerator during the adsorption carbon removal regeneration process, thereby reducing production costs and production energy consumption.

[0070] In this invention, such as Figure 2 As shown, the adsorption lithium extraction tank 5 is provided with at least a first adsorption lithium extraction tank 51 and a second adsorption lithium extraction tank 52. Both the first adsorption lithium extraction tank 51 and the second adsorption lithium extraction tank 52 are connected to the first transfer pump 104. The first transfer pump 104 is connected to the kneading and washing tank 6.

[0071] During use, when the permeate treated by the adsorption decarbonization tank 3 is transported to the adsorption lithium extraction process, a composite inhibitor group can be added. Under the combined action of the composite inhibitor group and the titanium adsorbent 10, lithium ions in the brine can be adsorbed onto the adsorbent 10. After adsorbing lithium ions, the adsorbent 10 can be periodically transferred to the rubbing and washing tank 6 by the first transfer pump 104, and each transfer time is 3 to 5 minutes. This is beneficial to the thoroughness of subsequent rubbing and rinsing, and also to the flow and dispersion between adsorbent 10 particles, avoiding the problem of scale formation or blockage after salt crystallization of the adsorbent 10.

[0072] In this invention, such as Figure 2 As shown, the kneading and washing tank 6 is connected to the second transfer pump 105, and the second transfer pump 105 is connected to the acidification and desorption tank 7.

[0073] In use, the rubbing and cleaning tank 6 can remove the crystalline salt and contaminants on the surface of the adsorbent 10 by spraying in warm water at 40-60°C and simultaneously introducing air. The resulting wastewater undergoes secondary treatment within the plant, while the adsorbent 10 is transported to the subsequent acidification and desorption tank 7 via the second transfer pump 105. The rubbing and cleaning tank 6 can prevent salt crystallization or contaminants from clogging the adsorbent 10, thereby improving the adsorption effect.

[0074] In this invention, such as Figure 2 As shown, the acidification and desorption tank 7 is connected to the third transfer pump 106, and the third transfer pump 106 is connected to the co-current rinsing tank 8.

[0075] In use, the acidification and desorption tank 7 can desorb the lithium on the adsorbent 10 into the water by adding 5% to 15% dilute hydrochloric acid to form a lithium-rich solution. The lithium-rich solution can be sold or further processed into lithium products. After the lithium is desorbed, the adsorbent 10 is transported to the co-current rinsing tank 8 by the third transfer pump 106.

[0076] In this invention, such as Figure 2 As shown, the co-current washing tank 8 is connected to the fourth transfer pump 107, and the fourth transfer pump 107 is connected to the adsorption lithium extraction tank 5.

[0077] In use, the co-current rinsing tank 8 uses fresh water to rinse the adsorbent 10 until the rinsing solution is neutral. After rinsing, the adsorbent 10 is transported to the adsorption lithium extraction tank 5 for recycling via the fourth transfer pump 107. The rinsing solution is then recycled back into the high and low pressure dual-membrane magnesium removal system, which can effectively reduce the production cost and energy consumption of lithium extraction.

[0078] In this invention, such as Figure 3 As shown, the upper end of the adsorption tank is equipped with an upper water distributor 9, the lower end with a lower water distributor 11, and the middle part is equipped with adsorbent 10. By setting the adsorbent 10 in the middle of the adsorption tank and combining it with the floating bed structure of the tank, and by controlling the upward flow velocity of the water, the adsorbent 10 packing can be ensured to be in a fluidized state in the adsorption tank. This reduces the number of valves, pipelines and system structures, and can reduce or avoid problems such as scaling or salt crystallization blockage and leakage in the pipeline, thereby reducing installation and maintenance costs.

[0079] In this invention, such as Figure 2 As shown, at least two sets of adsorption carbon removal tanks 3 are provided. When the first adsorption carbon removal tank 31 is saturated, the second adsorption carbon removal tank 32 is started. The first adsorption carbon removal tank 31 enters the regeneration system and is put into standby after regeneration. When the second adsorption tank 32 is saturated, it is switched back to the first adsorption carbon removal tank 31 that has completed regeneration for adsorption. This cycle is continuously operated, which can realize the continuous alternating operation of the device and improve the removal efficiency of organic matter.

[0080] In this invention, such as Figure 2 As shown, at least two sets of adsorption lithium extraction tanks 5 are provided. When the first adsorption lithium extraction tank 51 adsorbs lithium ions and the adsorbent 10 reaches saturation, the second adsorption lithium extraction tank 52 is started. The adsorbent 10 in the first adsorption lithium extraction tank 51 enters the kneading and washing tank 6, the acidification and desorption tank 7, and the co-current rinsing tank 8 in sequence, and finally enters the first adsorption lithium extraction tank 51 for use. This cycle is repeated to realize the continuous operation of the adsorption lithium extraction device, which improves the adsorption efficiency and extraction rate of lithium.

[0081] In summary, the method and apparatus for lithium extraction from salt lake brine provided by this invention, through the combined use of the lithium extraction method and apparatus, can achieve efficient extraction of lithium from brine, improve the quality and extraction rate of lithium-rich liquid, avoid problems such as incomplete treatment of organic matter and blockage of system equipment and pipelines, and effectively reduce the energy consumption and operating costs of the lithium extraction device from salt lake brine.

Claims

1. A method for extracting lithium from salt lake brine, characterized in that, Includes the following steps: S1: High and low pressure dual membrane magnesium removal: magnesium removal is performed on lithium-containing brine by using a high-pressure disc tube nanofiltration membrane (1) and a low-pressure nanofiltration membrane (2); S2: Adsorption carbon removal: The organic matter in the brine after magnesium removal is adsorbed by adding macroporous resin to the adsorption carbon removal tank (3), and then a regenerator is added to obtain the regenerated liquid. S3: Tower distillation: The regenerated liquid is distilled through a slanted tray (4) to obtain a distillate that is recycled as a regenerator; S4: Lithium adsorption: After removing organic matter, the brine enters the lithium adsorption tank (5), and titanium adsorbent is added to adsorb lithium ions in the brine onto the adsorbent (10). S5: Scrubbing and cleaning: The adsorbent (10) after lithium adsorption is transferred to the scrubbing and cleaning tank (6), and the crystalline salt and contaminants on the surface of the adsorbent (10) are removed by adding warm water at 40-60°C and simultaneously introducing air. S6: Acidification and Desorption: The adsorbent (10) after being rubbed and washed enters the acidification and desorption tank (7), and dilute hydrochloric acid is added for desorption to obtain lithium-rich solution; S7: Co-current rinsing: The adsorbent (10) after lithium desorption enters the co-current rinsing tank (8) and is rinsed with fresh water until the rinsing solution is neutral.

2. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The magnesium-to-lithium mass ratio of the lithium-containing brine in S1 is 30:1 to 3000:1; the operating pressure of the high-pressure disc-tube nanofiltration membrane (1) is 30 to 120 bar; and the operating pressure of the low-pressure nanofiltration membrane (2) is 5 to 30 bar.

3. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The macroporous resin in S2 has a particle size of 0.3–1.5 mm; the regenerant is methanol, ethanol, or acetone.

4. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The spacing between the trays of the inclined tray (4) in S3 is 350-650 mm, the feed temperature is 60-90℃, the top temperature of the inclined tray (4) is 60-75℃, the bottom temperature is 100-110℃, and the bottom operating pressure is 130-140 kPa.

5. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The main chemical components of the titanium adsorbent (10) in S4 are Ti, Li, C, H and O, and their mass ratio is (1~1.8):(0.2~0.3):(0.7~2):(0.02~0.2):(2~3); the titanium adsorbent (10) has a particle size of 1~5 mm and a filling amount of 40%~50%.

6. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: A compound inhibitor is also added to step S4, with an addition amount of 0.1–1 ml / L. The compound inhibitor is a mixture of racemic ferric tartrate, 1-octadecylamine hydrochloride, and sodium acetate. The mass percentage of the added racemic ferric tartrate is 0.3%–1.5%, the mass percentage of the added 1-octadecylamine hydrochloride is 15%–35%, the mass percentage of the added sodium acetate is 5%–25%, and the remainder is water.

7. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The concentration of dilute hydrochloric acid in S6 is 5% to 15%, the desorption rate is 1 to 2 BV / h, and the desorption residence time is 2 to 6h.

8. The method for lithium extraction from salt lake brine according to claim 1, characterized in that: The pH of the co-current rinsing solution in S7 is 6-9, the rinsing rate is 2-4 BV / h, and the rinsing residence time is 0.5-2h.

9. A lithium extraction device from salt lake brine, characterized in that, include: High and low pressure dual-membrane magnesium removal system is used to separate divalent or polyvalent ions such as magnesium from lithium; The adsorption carbon removal tank (3) is connected to the high and low pressure dual membrane magnesium removal system and is used to adsorb organic matter in the brine. The inclined perforated tray (4) is connected to one side of the adsorption decarbonization tank (3) and is used for distillation regeneration liquid; The lithium adsorption tank (5) is connected to the carbon adsorption tank (3) and is used to adsorb lithium ions in the brine onto the adsorbent (10). The rubbing and cleaning tank (6) is connected to the adsorption and lithium extraction tank (5) to remove crystalline salts and contaminants from the surface of the adsorbent (10); An acidification and desorption tank (7) is connected to a rubbing and washing tank (6) for desorbing lithium from the adsorbent (10) into water to form a lithium-rich solution. The co-current rinsing tank (8) is connected to the rubbing and washing tank (6) on one side and to the adsorption lithium extraction tank (5) on the other side, and is used to rinse the adsorbent (10); The adsorption carbon removal tank (3), adsorption lithium extraction tank (5), rubbing and washing tank (6), acidification and desorption tank (7), and co-current rinsing tank (8) are all floating bed structures, which can make the adsorbent (10) be in a suspended flow state.

10. The lithium extraction device from salt lake brine according to claim 9, characterized in that: The high-low pressure dual-membrane magnesium removal system includes a first high-pressure pump (101), a high-pressure disc tube nanofiltration membrane (1), a first product water tank (201), and a low-pressure nanofiltration membrane (2) connected in sequence. The low-pressure nanofiltration membrane (2) is connected to the first high-pressure pump (101), and a second product water tank (202) is also connected to its product water side. The second product water tank (202) is connected to a carbon removal booster pump (103), and the carbon removal booster pump (103) is connected to the adsorption carbon removal tank (3).

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