A method for high-selectivity enrichment of lithium ions in geothermal hot spring water

Abstract

The present application belongs to the field of comprehensive utilization of geothermal resources, and particularly relates to a method for selectively enriching lithium ions in geothermal hot spring water. First, the hot spring water is analyzed by multiple parameters, and then the temperature is reduced to 35-40 DEG C and the turbidity is lower than 0.2 NTU by a pretreatment system. The pretreated water is recovered by an energy recovery system. Then, the hot spring water enters a lithium selective forward osmosis membrane module, and lithium ion concentration is realized under the driving of osmotic pressure difference. The diluted draw solution is concentrated and regenerated by a phase change heat storage driven vacuum membrane distillation system, and then recycled. The concentrated solution is purified by a lithium enrichment liquid purification system. The condensate water produced by vacuum membrane distillation is mixed with nanofiltration water, and then injected into the ground by a reinjection water treatment system. An intelligent adaptive control system is used to optimize the operation parameters, and a lithium ion imprinted polymer modified forward osmosis membrane is used to significantly improve the selectivity of the membrane to lithium ions.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of geothermal resources, and specifically relates to a method for highly selectively enriching lithium ions in geothermal hot spring water. This method can efficiently enrich lithium ions from geothermal hot spring water with low energy consumption, providing a technical basis for the subsequent extraction and utilization of lithium resources. Background Technology

[0002] Lithium has been listed as a key strategic mineral resource in China. Against the backdrop of global carbon neutrality and rapid high-tech development, the demand for lithium metal is growing rapidly, leading to an increasingly prominent supply-demand imbalance in the market. Lithium prices have been rising continuously since 2020. Given the expectation of continued high-speed growth in future lithium demand, coupled with relatively sluggish capacity expansion and resource supply, lithium prices are likely to remain high and rise further.

[0003] Hydrothermal geothermal energy is a resource combining heat, water, and minerals. It is not only a clean and safe renewable energy source but also a mineral resource rich in elements such as lithium, rubidium, cesium, and boron. High-temperature geothermal water generally has a high lithium content. Geothermal lithium extraction is close to zero-carbon emission, causing no pollution to the environment. Compared to traditional lithium extraction methods from South American salt lake brine, geothermal lithium extraction is not affected by weather and has a shorter production cycle.

[0004] The main challenges of existing geothermal lithium extraction technologies include: the large flow rate of geothermal power generation tailwater necessitates maintaining high temperatures to reduce scaling during reinjection; pressurization is required when reinjecting to higher elevations, and a closed environment must be maintained. Traditional lithium extraction technologies often neglect these specific requirements, leading to low efficiency or unstable operation. Furthermore, most existing technologies employ single-membrane or single-adsorption technologies, failing to adequately consider the unique characteristics of geothermal water and making it difficult to simultaneously meet the requirements of high-efficiency concentration and low energy consumption.

[0005] Currently, breakthroughs have been achieved in geothermal lithium extraction technology abroad, and related demonstration projects are underway. Dr. Jens Grimmer of the Karlsruhe Institute of Technology in Germany, in collaboration with Dr. Florencia Saravia of the Engel-Bunde Institute, has developed a geothermal lithium extraction process—the Grimmer-Saravia process. This process mainly consists of two steps: filtering lithium ions from hot water and further condensing them until the lithium precipitates as salt—a membrane-based lithium precipitation process. However, the practical application of such processes under high-temperature conditions still faces many challenges.

[0006] The main problems faced by existing geothermal lithium extraction technologies are as follows: 1) Insufficient control of membrane fouling and scaling, leading to scaling risks during long-term operation; 2) Insufficient recovery and utilization of thermal energy during temperature management; 3) The use of a fixed series process, lacking adaptability to different water qualities; 4) High energy consumption for extract regeneration, failing to achieve complete self-regeneration; 5) Insufficient selectivity for monovalent ions such as lithium, sodium, and potassium, resulting in limited concentration efficiency.

[0007] Therefore, there is an urgent need to develop a process for enriching lithium ions in geothermal hot spring water that is highly efficient, low in energy consumption, and highly selective, in order to overcome the limitations of existing technologies and realize the high-value utilization of lithium in geothermal resources. Summary of the Invention

[0008] The purpose of this invention is to provide a method for highly selectively enriching lithium ions in geothermal hot spring water, aiming to solve the problems of severe membrane fouling, insufficient lithium selectivity, and high energy consumption in the existing technology, and to achieve efficient and low-energy enrichment of lithium ions in geothermal hot spring water.

[0009] To achieve the above objectives, the technical solution provided by this invention is: a method for highly selectively enriching lithium ions in geothermal hot spring water, comprising the following steps:

[0010] (1) After the geothermal hot spring water is analyzed online by multiple parameters, it is introduced into a precision pretreatment system for treatment. The precision pretreatment system includes a pH adjustment unit, an anti-scaling agent dosing system and a multi-membrane filtration system to reduce the temperature from 60-95℃ to 35-40℃ and the turbidity to below 0.2NTU.

[0011] (2) The pretreated hot spring water recovers heat energy through an energy ladder recovery system, which includes a plate heat exchanger and a phase change heat storage unit.

[0012] (3) Hot spring water enters the lithium selective forward osmosis membrane module, which includes a lithium-ion imprinted polymer modified composite forward osmosis membrane. One side of the lithium selective forward osmosis membrane module is hot spring water and the other side is phosphate-organic amine composite draw solution. Under the drive of osmotic pressure difference, water molecules in the hot spring water pass through the forward osmosis membrane into the draw solution side, while lithium ions in the hot spring water are concentrated.

[0013] (4) The diluted extract is concentrated and regenerated by a vacuum membrane distillation system driven by phase change heat storage, and the regenerated extract is recycled back to step (3).

[0014] (5) The concentrate is processed by a lithium enrichment solution purification system, which includes a photocatalytic oxidation pretreatment unit, a magnesium ion removal unit, a calcium ion removal unit and a lithium carbonate production unit.

[0015] (6) The condensate produced by the vacuum membrane distillation system is mixed with the nanofiltration permeate and then treated by the reinjection water treatment system, which includes a dissolved oxygen control unit, a microbial control unit and a pH buffer system, and then reinjected into the ground after treatment.

[0016] (7) The entire process adopts an intelligent adaptive control system to monitor and optimize operating parameters.

[0017] Furthermore, the multi-membrane filtration system in the precision pretreatment system includes a polypropylene filament-wound coarse filter, a ceramic tube microfiltration membrane, and a polysulfone hollow fiber ultrafiltration membrane arranged sequentially according to the flow direction; the pore size of the polypropylene filament-wound coarse filter is 50-100μm, the pore size of the ceramic tube microfiltration membrane is 1.0-5.0μm, and the molecular weight cutoff of the polysulfone hollow fiber ultrafiltration membrane is 10-30kDa.

[0018] Preferably, the antiscaling agent dosing system comprises the following components: 0.5-5.0 parts by weight of hydroxyethylidene diphosphonic acid and 0.2-2.0 parts by weight of 2-phosphonobutane-1,2,4-tricarboxylic acid; the pH adjustment unit uses citric acid or sodium bicarbonate to adjust the pH of the hot spring water to the range of 5.5-6.5.

[0019] Furthermore, the lithium-ion imprinted polymer-modified composite forward osmosis membrane includes a support layer and a selector layer; the support layer is composed of 80-90 parts by weight of polyetheretherketone and 10-20 parts by weight of zirconium oxide nanoparticles; the selector layer is composed of 75-85 parts by weight of polyamide, 10-20 parts by weight of lithium-ion imprinted polymer and 5-10 parts by weight of isophorone diisocyanate.

[0020] Specifically, the preparation method of the lithium-ion imprinted polymer is as follows: 15-25 parts by weight of methacrylic acid, 65-75 parts by weight of ethylene glycol dimethacrylate, 1-3 parts by weight of azobisisobutyronitrile, and 5-10 parts by weight of lithium chloride are dissolved in 200-300 parts by weight of N,N-dimethylformamide and reacted at 60±2℃ for 24±0.5 hours; the resulting solution is poured into 10 times its volume of deionized water to precipitate, filtered, and vacuum dried at 65℃ for 12 hours to obtain a lithium-ion imprinted prepolymer; the prepolymer is pulverized to below 200 mesh, eluted with 0.1 mol / L disodium ethylenediaminetetraacetate aqueous solution at a flow rate of 2 BV / h for 10 BV; rinsed with deionized water until neutral, washed three times with methanol, and vacuum dried at 60℃ for 24 hours to obtain the lithium-ion imprinted polymer.

[0021] In one embodiment of the present invention, the phosphate-organic amine composite extraction solution is composed of the following components: 95-105 parts by weight of potassium dihydrogen phosphate, 5-10 parts by weight of N-methylpyrrolidone, 3-8 parts by weight of glycerol, 0.5-2.0 parts by weight of potassium hydroxide, and 0.05-0.10 parts by weight of silver citrate nanoparticles; the pH value of the phosphate-organic amine composite extraction solution is 6.8-7.2.

[0022] The preparation method of the silver citrate nanoparticles is as follows: 4-6 parts by weight of trisodium citrate are dissolved in 80-100 parts by weight of deionized water and heated to 90±2℃; 1-2 parts by weight of silver nitrate aqueous solution are slowly added dropwise at a stirring speed of 400-500 rpm, with the addition time controlled at 15-20 minutes; the reaction is continued at 90±2℃ for 30±5 minutes; after cooling to room temperature, 200-250 parts by weight of ethanol are added to precipitate; the precipitate is separated by centrifugation, collected, and washed three times with ethanol; it is then vacuum dried at 50℃ for 12 hours, ground, and sieved to obtain silver citrate nanoparticles.

[0023] Preferably, the phase change heat storage driven vacuum membrane distillation system includes a phase change heat storage unit and a vacuum membrane distillation assembly; the phase change heat storage unit uses polyethylene glycol as the phase change material, and the phase change temperature is 55-65℃; the vacuum membrane distillation assembly uses a polytetrafluoroethylene hydrophobic membrane with a pore size of 0.1-0.22μm, a porosity of 75-85%, an operating temperature of 65-75℃, and a vacuum side pressure of 5-15kPa.

[0024] In addition, the lithium enrichment solution purification system includes the following processing steps: the concentrated solution is first treated with a nano-titanium dioxide photocatalytic oxidation device for 20-40 minutes to remove trace organic matter; the pH is adjusted to 10.5-11.5, and 1.2-1.5 times the theoretical amount of calcium hydroxide is added, and the mixture is reacted at 65-75℃ for 30-50 minutes to precipitate and remove magnesium ions; after filtration, the pH is adjusted to 9.5-10.5, and 1.1-1.3 times the theoretical amount of sodium carbonate is added, and the mixture is reacted at 60-70℃ for 20-40 minutes to precipitate and remove calcium ions; after filtration, the solution is heated to 85-95℃, and 1.05-1.20 times the theoretical amount of sodium carbonate is added and the mixture is reacted for 60-90 minutes; the solution is cooled to 20-25℃ and allowed to stand for 4-8 hours to crystallize and precipitate lithium carbonate; the lithium carbonate product is collected by filtration, washed three times with deionized water, and dried at 105±5℃ for 4-6 hours.

[0025] Meanwhile, the reinjected water treatment system includes the following treatment steps: adding 0.5-2.0 parts by weight of sodium bisulfite and 0.001-0.005 parts by weight of sodium cobalt ethylenediaminetetraacetate as deoxygenating agents to control the dissolved oxygen content to less than 10 ppb; the water flows through a 254 nm ultraviolet disinfection system with an ultraviolet dose of 30-40 mJ / cm. 2The water is treated with an ozone system, with an ozone dosage of 0.2-0.5 mg / L and a contact time of 3-5 minutes. The pH is adjusted to 6.5-7.5 using a sodium bicarbonate and carbon dioxide buffer system, with a buffer capacity of ≥1.0 mmol / L. The treated reinjected water is heated to 70-80℃ and reinjected underground.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. High selectivity separation: The forward osmosis membrane is modified with lithium-ion imprinted polymer, which significantly improves the membrane's selectivity for lithium ions. The lithium / sodium selectivity coefficient reaches 15-25 (traditional membrane <5), and the lithium / potassium selectivity coefficient reaches 12-20 (traditional membrane <3), which greatly improves the concentration efficiency and purity.

[0028] 2. High-efficiency energy utilization: Through an energy cascade recovery system, multi-stage utilization of high-temperature geothermal energy is achieved, increasing overall energy efficiency by more than 45% and reducing system energy consumption to 1.0-1.5 kWh / m³. 3 (Traditional process 3.0-4.5kWh / m) 3 ).

[0029] 3. Self-regeneration of draw solution: The innovative use of phosphate-organic amine composite draw solution, combined with a vacuum membrane distillation system driven by phase change heat storage, enables low-energy-consumption recycling and regeneration of draw solution, extending the draw solution replacement cycle to 90-120 days (compared to 20-30 days in traditional processes).

[0030] 4. Comprehensive membrane protection: The precise pretreatment system effectively inhibits membrane fouling and scaling through multi-parameter control and selective addition of anti-fouling agents, extending the membrane cleaning cycle to 30-40 days (compared to 5-15 days in traditional processes) and extending the membrane service life to 4-6 years (compared to 1-3 years in traditional processes).

[0031] 5. High adaptability: The intelligent adaptive control system enables it to handle various geothermal waters with lithium concentrations of 20-300 mg / L, temperatures of 60-95℃, and pH ranges of 2-9, making it widely applicable.

[0032] 6. High lithium recovery efficiency: The entire process is optimized, increasing the lithium recovery rate to 97-99% (compared to 80-92% for traditional processes), which greatly improves economic benefits.

[0033] 7. Environmentally friendly: The process mainly uses physical separation, and the reinjected water is controlled by all parameters to ensure the sustainable use of the geothermal reservoir and achieve near-zero emissions. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0035] Figure 2 This is a schematic diagram of the structure of the lithium-ion imprinted polymer modified forward osmosis membrane used in this invention;

[0036] Figure 3 This is a comparison chart of the performance of the phosphate-organic amine composite extracting solution of the present invention and the traditional extracting solution;

[0037] Figure 4 This is a schematic diagram illustrating the working principle of the phase change thermal storage driven vacuum membrane distillation system of the present invention.

[0038] Figure 5 This is a diagram of the architecture of the intelligent adaptive control system of the present invention. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0040] Reference Figure 1 The present invention provides a method for highly selectively enriching lithium ions in geothermal hot spring water, comprising seven main parts: a precision pretreatment system, an energy ladder recovery system, a lithium selective forward osmosis membrane system, a draw fluid regeneration system, a lithium enrichment fluid purification system, a reinjection water treatment system, and an intelligent adaptive control system.

[0041] The main raw materials used in this invention are as follows:

[0042] 1. Precision Preprocessing System

[0043] 1.1 Multiple membrane filtration device

[0044] This invention employs a three-stage membrane filtration system to achieve comprehensive filtration of geothermal hot spring water, ensuring that the subsequent forward osmosis membrane is not contaminated by particles.

[0045] The first stage is a polypropylene (PP) wire-wound coarse filter, made of polypropylene (PP) with a pore size of 50-100μm and an effective filtration area of ​​1.0-3.0m². 2 It is mainly used to remove large particulate impurities from hot spring water. Polypure PPW-100, manufactured by Pall Corporation in the United States, is a good option. This product has excellent heat resistance and chemical stability and is not easily deformed under high-temperature conditions.

[0046] The second stage is a ceramic tubular microfiltration membrane, made of α-Al₂O₃, with a pore size of 1.0-5.0 μm and an effective filtration area of ​​5.0-15.0 m². 2 Preferably, it uses products manufactured by the French company Veolia. This product features high strength, high temperature resistance, and acid and alkali resistance, and can operate stably for a long time under harsh conditions.

[0047] The third stage is a polysulfone (PSF) hollow fiber ultrafiltration membrane. Its material is polysulfone (PSF), with a molecular weight cutoff of 10-30 kDa and an effective filtration area of ​​20.0-50.0 m². 2 The SFP-2880 series products manufactured by Inge GmbH in Germany can be used. This series of products has good mechanical strength and chemical stability and can effectively retain colloids and macromolecular organic matter.

[0048] 1.2 Anti-scaling system

[0049] This invention employs a specialized anti-fouling system that effectively prevents fouling on the membrane surface by inhibiting scale growth, interfering with crystal formation, and dispersing deposits.

[0050] The main antiscalant is hydroxyethylidene diphosphonic acid (HEDP), chemically known as hydroxyethylidene diphosphonic acid, CAS number 2809-21-4, with a content range of 0.5-5.0 parts by weight (relative to the volume of water treated), and an effective content ≥95%. Italmatch (USA) can be used as an alternative. 2010 product. HEDP has excellent calcium and magnesium scale and silica scale inhibition properties, and is particularly suitable for inhibiting calcium carbonate and silicate scale commonly found in geothermal water.

[0051] The synergistic antiscaling agent uses 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) at a concentration of 0.2-2.0 parts by weight (relative to the volume of water treated), with an effective concentration ≥98%. When PBTC is used in combination with HEDP, the antiscaling effect is significantly improved through a synergistic effect, especially in inhibiting calcium sulfate scale, which is superior to that of a single antiscaling agent.

[0052] The pH adjuster should be selected based on the raw water pH value, using either citric acid (acidic adjustment) or sodium bicarbonate (alkaline adjustment). Citric acid's chemical name is 2-hydroxy-1,2,3-propanetricarboxylic acid, with a content range of 0.5-10.0 parts by weight and a purity ≥99.5%. Sodium bicarbonate's content range is 0.5-8.0 parts by weight, with a purity ≥99.0%. Maintaining the pH within the range of 5.5-6.5 effectively inhibits scaling without affecting the performance of the subsequent forward osmosis membrane.

[0053] 1.3 Pretreatment Operating Conditions

[0054] Preferably, the temperature control of the pretreatment system adopts a step-down cooling strategy, gradually reducing the temperature from the initial high temperature (60-95℃) to 35-40℃ to avoid the risk of scaling caused by sudden temperature drops. The pH adjustment range is controlled between 5.5 and 6.5, which effectively inhibits the formation of calcium carbonate and silica scale without affecting the stability of the membrane material. The residence time of the anti-scaling agent is controlled between 10-30 minutes to ensure that its scale-inhibiting effect is fully exerted. The water quality requirements after pretreatment are turbidity <0.2 NTU, SDI <3, and residual chlorine <0.1 ppm, providing high-quality feed water for subsequent forward osmosis membrane treatment.

[0055] 2. Energy tiered recovery system

[0056] 2.1 Plate heat exchanger

[0057] This invention employs a titanium alloy plate heat exchanger for heat recovery. The material selected is titanium alloy (Grade 5, Ti-6Al-4V), which possesses excellent corrosion resistance and good heat transfer performance. The heat exchange area is 15-40 m². 2 The design temperature difference ΔT ≤ 5℃ and heat exchange efficiency ≥ 90% are required. We recommend using the Alfa Laval T8-BFG series products manufactured by Alfa Laval of Sweden. This series is specifically designed for geothermal applications and features high temperature resistance, corrosion resistance, and easy cleaning.

[0058] 2.2 Phase Change Thermal Storage Materials

[0059] To address the issue of fluctuating geothermal energy, this invention employs polyethylene glycol (PEG-400) as a phase change thermal storage material. This material has a phase change temperature of 55-65℃, a latent heat of phase change of 180-220 J / g, and thermal cycling stability exceeding 2000 cycles. This material maintains a high latent heat of phase change, making it highly suitable for the thermal storage requirements of this system.

[0060] 2.3 Preheating and Reinjection Water Unit

[0061] The reinjection water preheating uses a shell-and-tube heat exchanger made of duplex stainless steel (SAF 2507, UNS S32750). This material has excellent resistance to chloride ion corrosion, making it particularly suitable for applications with high-mineralization geothermal water. The heat exchange area is 10-25 m². 2 The operating pressure should be ≤2.5MPa. We recommend using the Shell-and-Tube Type S250 series product manufactured by GEA GmbH, Germany. This preheating unit fully utilizes the waste heat in the system, improving overall energy efficiency, while ensuring a suitable reinjection water temperature and avoiding scaling problems during the reinjection process.

[0062] 3. Lithium-selective forward osmosis membrane system

[0063] like Figure 2As shown, the core of this invention is a lithium-ion imprinted polymer (LIP) modified composite forward osmosis membrane, which consists of a support layer and a selective layer.

[0064] 3.1 Supporting layer material

[0065] The support layer is made of polyetheretherketone (PEEK) composite material reinforced with nano-zirconia. The PEEK content (CAS No.: 29658-26-2) is 80-90 parts by weight, and the zirconia nanoparticle content (ZrO2, CAS No.: 1314-23-4) is 10-20 parts by weight. The porosity of the support layer is controlled within the range of 60-75%. The PEEK substrate can be selected from Victrex, UK. For PEEK450G products, nano-zirconia products such as TosohTZ-3Y from Tosoh Corporation of Japan can be selected.

[0066] PEEK possesses excellent mechanical strength, heat resistance, and chemical stability, with a glass transition temperature of approximately 143°C and a melting point of approximately 343°C, maintaining good structural stability in high-temperature geothermal environments. The addition of nano-zirconia further enhances the mechanical strength and thermal stability of the support layer, while also improving hydrophilicity, which is beneficial for increasing water flux.

[0067] 3.2 Selection of Layer Material

[0068] The selective layer is composed of polyamide (PA), lithium-ion imprinted polymer (LIP), and isophorone diisocyanate (IPDI). The PA content is 75-85 parts by weight, the LIP content is 10-20 parts by weight, and the IPDI content is 5-10 parts by weight. The thickness of the selective layer is controlled within the range of 150-300 nm.

[0069] The key innovation of this invention lies in the lithium-ion imprinted polymer, whose specific molecular recognition sites preferentially recognize and bind to lithium ions, thereby significantly improving the selectivity of the membrane for lithium ions. The addition of IPDI, as a crosslinking agent, enhances the structural and chemical stability of the selective layer.

[0070] 3.3 Preparation method of lithium-ion imprinted polymer (LIP)

[0071] The preparation of lithium-ion imprinted polymers employs molecular imprinting technology, which mainly includes three steps: polymerization, template removal, and post-processing.

[0072] First, 15-25 parts by weight of methacrylic acid (MAA), 65-75 parts by weight of ethylene glycol dimethacrylate (EGDMA), 1-3 parts by weight of azobisisobutyronitrile (AIBN), and 5-10 parts by weight of lithium chloride (LiCl) were placed in a three-necked flask. MAA, as a functional monomer, forms coordination bonds with lithium ions; EGDMA, as a crosslinking agent, forms a three-dimensional network structure; AIBN, as an initiator; and lithium chloride provides lithium ions as an imprint template.

[0073] Then, 200-300 parts by weight of N,N-dimethylformamide (DMF) were added as a solvent, and nitrogen gas was purged for 30 minutes to remove oxygen. The polymerization was completed at 60±2℃ for 24±0.5 hours. DMF has good solubility and stability, and can effectively dissolve all the above components, providing a homogeneous environment for the polymerization reaction.

[0074] After polymerization, the resulting solution was poured into 10 times its volume of deionized water to precipitate, filtered, washed three times with water, and dried under vacuum at 65°C for 12 hours to obtain the lithium-ion imprinted prepolymer.

[0075] Next, the prepolymer was pulverized to below 200 mesh and placed in a glass column. A 0.1 mol / L aqueous solution of disodium ethylenediaminetetraacetate (EDTA-2Na) was used as the eluent at a flow rate of 2 BV / h (bed volume per hour), eluting for 10 BV. EDTA-2Na can form a stable complex with lithium ions, effectively eluting the lithium ion template from the prepolymer while leaving specific lithium ion recognition sites.

[0076] Finally, the mixture was rinsed with deionized water until neutral, washed three times with methanol, and dried under vacuum at 60°C for 24 hours to obtain a lithium-ion imprinted polymer (LIP). This LIP molecule contains a large number of cavities that specifically recognize lithium ions. These cavities are highly matched to lithium ions in size, shape, and functional group arrangement, thus endowing it with high selectivity for lithium ions.

[0077] 3.4 Preparation of LIP-modified forward osmosis membrane

[0078] The LIP-modified forward osmosis membrane was prepared using a phase inversion method combined with interfacial polymerization technology. The specific steps are as follows:

[0079] First, 85 parts by weight of PEEK and 15 parts by weight of ZrO2 nanoparticles were ultrasonically dispersed in 400 parts by weight of N-methylpyrrolidone (NMP) for 2 hours to prepare the casting solution for the support layer. Ultrasonic dispersion ensured the uniform dispersion of nanoparticles in the PEEK matrix and avoided agglomeration.

[0080] Then, the casting solution was uniformly coated onto the nonwoven fabric using a doctor blade, with the thickness controlled at 150±10 μm. A porous support layer was prepared via phase inversion at 25±2℃ and 40-50% relative humidity. During the phase inversion process, the exchange of solvent and non-solvent leads to the separation of the polymer phase, forming a support layer with a specific pore structure.

[0081] Next, the support layer was immersed in an aqueous solution containing 2.0 wt% m-phenylenediamine (MPD) for 2 minutes to allow MPD to fully penetrate into the pores on the surface of the support layer. MPD, as an aqueous monomer, has two active amine groups that can react with subsequent acyl chloride groups to form a polyamide network.

[0082] Subsequently, excess liquid was removed from the surface, and the mixture was immersed in a hexane solution containing 0.15 wt% trimesoyl chloride (TMC) and 0.5 wt% LIP for 60 seconds for interfacial polymerization. At the water / organic phase interface, MPD and TMC underwent a polycondensation reaction to form a crosslinked polyamide selective layer, while LIP was embedded in the polyamide network.

[0083] To enhance membrane performance, the membrane was heat-treated at 85±3℃ for 5 minutes to promote full cross-linking of the polyamide network. Then, it was immersed in a 0.5wt% hexane solution of IPDI for 30 seconds for secondary cross-linking, which further improved the stability and selectivity of the selective layer.

[0084] Finally, wash thoroughly with deionized water to remove residual reagents, and store at 4°C to prevent microbial growth and membrane performance degradation.

[0085] The above preparation process achieves uniform distribution and stable fixation of LIP in the selective layer of the forward osmosis membrane, giving the membrane high selectivity for lithium ions while maintaining good water flux.

[0086] 3.5 Forward Osmosis Membrane Module Parameters

[0087] The forward osmosis membrane module used in this invention can adopt a flat sheet or hollow fiber structure, with an effective membrane area of ​​20-50 m² per unit. 2 The membrane has a water flux of 25-45 LMH (liters / square meter·hour), a lithium / sodium selectivity of 15-25, and a lithium / potassium selectivity of 12-20. This selectivity is much higher than that of traditional forward osmosis membranes (the lithium / sodium selectivity is usually <5).

[0088] The membrane module has a maximum operating temperature of 45℃, an operating pH range of 4.0-10.0, and a maximum permissible differential pressure of 1.5 bar. LIP modification design can be referenced from the PFO-100HP structure of Porifera (USA). This membrane module adopts a spiral wound structure with a rationally designed flow channel, ensuring sufficient cross-flow velocity while minimizing concentration polarization.

[0089] 4. Low-energy draw fluid system

[0090] like Figure 3 As shown, this invention innovatively uses a phosphate-organic amine composite extractant, which has a higher osmotic pressure coefficient and a lower reverse osmosis rate compared to traditional sodium chloride or magnesium chloride extractants.

[0091] 4.1 Composition of the composite extraction solution

[0092] The phosphate-organic amine complex extraction solution consists of the following components:

[0093] The main component is potassium dihydrogen phosphate (KH₂PO₄), with a content ranging from 95-105 parts by weight (equivalent to 1.0-2.0 mol / L) and a purity ≥99.0%. KH₂PO₄AR product from Merck, Germany, can be used. Potassium dihydrogen phosphate, as the main component, provides the basic osmotic pressure and also exhibits good solubility and stability. Compared with traditional chloride salts, phosphates are less corrosive to membranes, which helps extend membrane lifespan.

[0094] The organic solubilizer used is N-methylpyrrolidone (NMP), with a content ranging from 5-10 parts by weight and a purity ≥99.5%. N-methylpyrrolidone products from BASF (Germany) can be selected. NMP has excellent solubility and thermal stability; its addition can increase the osmotic pressure coefficient of the draw solution while reducing its viscosity and increasing water flux.

[0095] The permeation enhancer uses glycerol (glycerol) at a content ranging from 3 to 8 parts by weight, with a purity ≥99.7%. As a permeation enhancer, glycerol can improve the transport performance of water molecules within the membrane, increase water flux, and its high viscosity helps to form a dynamic protective layer, reducing membrane fouling.

[0096] Potassium hydroxide (KOH) is used as the pH adjuster, with a concentration ranging from 0.5 to 2.0 parts by weight, to adjust the pH of the extract to the range of 6.8 to 7.2. Within this pH range, phosphate is expressed as HPO4. 2- and H2PO4 - Its form provides optimal osmotic pressure performance.

[0097] The antibacterial component is silver citrate nanoparticles, with a content ranging from 0.05 to 0.10 parts by weight (equivalent to 50-100 ppm). The silver nanoparticles effectively prevent the growth of microorganisms in the extractant solution and extend its service life by disrupting microbial cell walls and inhibiting DNA replication.

[0098] 4.2 Preparation method of silver citrate nanoparticles

[0099] Silver citrate nanoparticles were prepared by a wet chemical reduction method, which is simple and controllable, and produces products with uniform particle size and good dispersibility.

[0100] First, add 4-6 parts by weight of trisodium citrate to a 250mL three-necked flask and dissolve it in 80-100 parts by weight of deionized water. Trisodium citrate acts as both a reducing agent and a stabilizer, controlling the growth of nanoparticles and preventing aggregation.

[0101] Then, heat the solution to 90±2℃ and stir at 400-500 rpm. Under stirring conditions, slowly add 1-2 parts by weight of an aqueous solution of silver nitrate (dissolved in 10-15 parts by weight of deionized water) over 15-20 minutes. Slow addition ensures uniform reaction and is beneficial for forming nanoparticles with uniform particle size.

[0102] The reaction was continued at 90±2℃ for 30±5 minutes. During this time, the solution gradually changed from colorless to pale yellow, indicating that silver ions were reduced to silver nanoparticles. The solution was then cooled to room temperature, and 200-250 parts by weight of ethanol were added to induce precipitation. The addition of ethanol lowered the dielectric constant of the system, causing the nanoparticles to become unstable and precipitate.

[0103] The precipitate was collected by centrifugation (8000 rpm, 10 min) and washed three times with ethanol to remove residual reagents. Finally, it was vacuum dried at 50 °C for 12 hours, ground, and sieved to obtain silver citrate nanoparticles. The prepared nanoparticles were spherical with an average particle size in the range of 10-30 nm, and their surface was coated with citrate ions, exhibiting good dispersibility and stability.

[0104] 4.3 Draw liquid regeneration system

[0105] like Figure 4 As shown, this invention innovatively uses a phase change heat storage driven vacuum membrane distillation system for extract liquid regeneration, which has the advantages of low energy consumption and high separation efficiency compared with traditional nanofiltration or thermal evaporation methods.

[0106] The vacuum membrane distillation unit uses a hydrophobic polytetrafluoroethylene (PTFE) membrane with a pore size of 0.1-0.22 μm, a porosity of 75-85%, a membrane thickness of 80-120 μm, and an effective area of ​​10-30 m². 2 Gore, Inc. (USA) is an option. Microfiltration Media products. PTFE membranes have extremely high hydrophobicity (contact angle >130°), ensuring that liquid water cannot permeate through the membrane while allowing water vapor to pass freely.

[0107] The operating temperature of vacuum membrane distillation is 65-75℃, and the vacuum side pressure is 5-15kPa. Under these conditions, the diluted draw solution is heated on one side of the membrane, and water vapor permeates through the hydrophobic membrane and is collected by condensation on the vacuum side, while the solute remains on the original side, thus achieving concentration of the draw solution.

[0108] The phase change thermal storage drive unit uses the aforementioned PEG-400 material, with a thermal storage capacity of 20-50 kWh, an operating temperature of 65-75℃, and a cycle efficiency of ≥85%. This unit fully utilizes the heat energy recovered during the pretreatment stage to provide a continuous and stable heat source for vacuum membrane distillation, significantly reducing the energy consumption for extract regeneration.

[0109] 5. Lithium enrichment solution purification system

[0110] The lithium enrichment solution purification system of the present invention includes four units: pretreatment, magnesium ion removal, calcium ion removal, and lithium carbonate production. Through step-by-step purification, high-purity lithium carbonate products are obtained.

[0111] 5.1 Preprocessing Unit

[0112] The pretreatment employs photocatalytic oxidation technology, using nano-titanium dioxide as a catalyst. The product is anatase TiO2 with a particle size of 20-30 nm and a specific surface area of ​​80-120 m². 2 / g, with an anatase to rutile mass ratio of approximately 80:20, this composition exhibits optimal photocatalytic activity.

[0113] Under ultraviolet light irradiation (wavelength 365nm, power density 0.5-1.0mW / cm²), 2 TiO2 generates electron-hole pairs, which react with water and oxygen to produce hydroxyl radicals and superoxide anion radicals. These active radicals can effectively oxidize and decompose trace organic matter in the concentrate. The treatment time is 20-40 minutes to ensure the complete degradation of organic matter.

[0114] 5.2 Magnesium Ion Removal Unit

[0115] Magnesium ions are removed by calcium hydroxide precipitation. The amount of calcium hydroxide used is 1.2-1.5 times the theoretical stoichiometric amount, with a purity ≥95.0%.

[0116] The operating temperature is 65-75℃, the pH value is controlled within the range of 10.5-11.5, the reaction time is 30-50 minutes, and the stirring speed is 150-200 rpm. Under these conditions, magnesium ions react with hydroxide ions to form magnesium hydroxide precipitate, and its solubility product constant Ksp is approximately 5.61 × 10⁻⁶. -12 It almost completely precipitates at pH > 10.5. The addition of calcium hydroxide not only provides the required pH value but also introduces calcium ions, further reducing the solubility of magnesium hydroxide through a common ion effect.

[0117] 5.3 Calcium ion removal unit

[0118] Calcium ions are removed by sodium carbonate precipitation. The amount of sodium carbonate used is 1.1-1.3 times the theoretical stoichiometric amount, with a purity ≥99.5%.

[0119] The operating temperature is 60-70℃, the pH value is controlled within the range of 9.5-10.5, the reaction time is 20-40 minutes, and the stirring speed is 120-180 rpm. Under these conditions, calcium ions react with carbonate ions to form calcium carbonate precipitate, and its solubility product constant Ksp is approximately 2.8 × 10⁻⁶. -9 Increasing the temperature promotes a faster reaction, but it should not be too high to avoid lithium carbonate co-precipitation.

[0120] 5.4 Lithium Carbonate Production Unit

[0121] Lithium carbonate production employs the sodium carbonate precipitation method. The amount of sodium carbonate used is 1.05-1.20 times the theoretical stoichiometric amount, the operating temperature is 85-95℃, the pH value is controlled within the range of 10.0-11.0, and the reaction time is 60-90 minutes. Under high-temperature conditions, lithium ions react with carbonate ions to form lithium carbonate. Unlike calcium carbonate and magnesium carbonate, the solubility of lithium carbonate decreases with increasing temperature, reaching its minimum at high temperatures, which is beneficial for improving yield. Conversely, during cooling, solubility increases, which is beneficial for product purification.

[0122] After the reaction is complete, the mixture is cooled to 20-25℃ and allowed to stand for 4-8 hours to allow lithium carbonate to crystallize fully. The lithium carbonate product is collected by filtration, washed three times with deionized water to remove residual soluble impurities, and dried at 105±5℃ for 4-6 hours to obtain a lithium carbonate product with a purity ≥99.5%.

[0123] 6. Reinjection Water Treatment System

[0124] This invention places particular emphasis on the comprehensive treatment of reinjected water, and ensures that the quality of reinjected water meets the requirements for geothermal reservoir protection through multiple safeguard measures.

[0125] 6.1 Dissolved Oxygen Control Unit

[0126] Dissolved oxygen is one of the main factors leading to corrosion and microbial growth in geothermal systems. This invention uses a chemical deoxygenation method to control dissolved oxygen content, employing sodium bisulfite as a deoxygenating agent at a concentration ranging from 0.5 to 2.0 parts by weight.

[0127] To improve deoxygenation efficiency, sodium cobalt ethylenediaminetetraacetate (cobalt content 15-17%) was added as a catalyst, with a content ranging from 0.001-0.005 parts by weight. Sodium cobalt ethylenediaminetetraacetate can significantly accelerate the reaction of sulfite with oxygen, shortening the reaction time from several hours to several minutes, and reducing the oxygen content to the ppb level.

[0128] Through this unit's treatment, the dissolved oxygen content of the reinjected water is controlled to <10 ppb, effectively preventing corrosion and microbial growth problems.

[0129] 6.2 Microbial Control Unit

[0130] To further ensure the microbial safety of reinjected water, this invention employs a combined ultraviolet-ozone disinfection technology.

[0131] The ultraviolet disinfection system uses low-pressure ultraviolet lamps with a wavelength of 254nm and an ultraviolet dose of 30-40mJ / cm². 2 The dwell time is 5-10 seconds. Ultraviolet light achieves its bactericidal effect by damaging the DNA of microorganisms, and has a good inactivation ability against most bacteria and viruses.

[0132] The ozone dosage for the ozone system is 0.2-0.5 mg / L, and the contact time is 3-5 minutes. Ozone is a strong oxidant that can effectively inactivate UV-resistant microorganisms remaining after UV disinfection, while also oxidizing and decomposing organic matter, thus improving water quality.

[0133] By using a combination of ultraviolet and ozone disinfection, the total number of microorganisms in the reinjected water is controlled to <100 CFU / mL, ensuring the biological safety of the reinjected water.

[0134] 6.3 pH buffer system

[0135] To maintain stable pH in the reinjected water and avoid scaling or corrosion during the reinjection process, this invention employs a sodium bicarbonate / carbon dioxide buffer system.

[0136] The amount of sodium bicarbonate added is 0.1-0.5 parts by weight to establish basic buffering capacity; the amount of carbon dioxide introduced is automatically adjusted according to online pH monitoring to achieve precise pH control.

[0137] The target pH range is 6.5-7.5, with a buffer capacity ≥1.0 mmol / L. Within this pH range, water exhibits minimal corrosivity to most metallic materials, while also showing a low tendency for calcium carbonate and silicates to precipitate, which is beneficial for the long-term stable operation of the system.

[0138] 7. Intelligent Adaptive Control System

[0139] like Figure 5 As shown, this invention employs an advanced intelligent adaptive control system to achieve real-time monitoring and optimized control throughout the entire process.

[0140] 7.1 Hardware Components

[0141] The core processor of the control system adopts an industrial-grade edge computing node, configured with Core TM It features an i7 quad-core, eight-thread processor, 16-32GB of DDR4 memory, and 256-512GB of SSD storage. The Dell EdgeGateway 5100 product from Dell Inc. is also available as an option. Edge computing architecture moves data processing forward to the field devices, reducing transmission latency and improving system response speed.

[0142] The sensor network includes a temperature sensor (PT100, accuracy ±0.1℃), a pressure sensor (ceramic piezoresistive, accuracy ±0.1%), a flow sensor (electromagnetic, accuracy ±0.5%), a pH sensor (glass electrode, accuracy ±0.05pH), and a conductivity sensor (four-electrode, accuracy ±1%). The data acquisition frequency is 1-5Hz, ensuring real-time monitoring of the system status.

[0143] 7.2 Software Components

[0144] The water quality pattern recognition algorithm employs a convolutional neural network (CNN) structure. Input parameters include multi-dimensional data such as temperature, pH, conductivity, turbidity, and dissolved oxygen, achieving a recognition accuracy of ≥95%. This algorithm learns the characteristic patterns of different types of geothermal water, automatically identifies the influent type, and adjusts the treatment parameters accordingly.

[0145] The predictive maintenance model employs a Long Short-Term Memory (LSTM) network structure. Predictive indicators include membrane flux decay, differential pressure changes, and energy consumption fluctuations, with a prediction period of 4-8 weeks and an early warning accuracy of ≥90%. This model can predict potential equipment failures in advance, schedule maintenance work, and avoid unexpected downtime.

[0146] The adaptive optimization process employs a reinforcement learning (RL) algorithm, with optimization objectives including a combination of multiple goals such as minimizing energy consumption, maximizing concentration, and maximizing membrane lifetime. The decision-making cycle is divided into two levels: real-time (small parameter adjustments) and daily (large parameter optimization). The optimization parameter space includes 10-15 key operating parameters. Through continuous learning and adjustment, the system can maintain optimal operating conditions under various operating circumstances.

[0147] 8. Examples

[0148] To verify the technical solution of the present invention, a detailed description is provided below with reference to specific embodiments.

[0149] Example 1: Treatment of high-temperature acidic geothermal water

[0150] This embodiment addresses the treatment of high-temperature acidic geothermal water, with the following specific conditions:

[0151] The geothermal hot spring water has a temperature of 92±2℃, a pH of 3.2±0.1, a lithium concentration of 85±3 mg / L, a sodium concentration of 4500±100 mg / L, a calcium concentration of 320±15 mg / L, and a magnesium concentration of 105±8 mg / L. The treatment scale is 25m³. 3 / h.

[0152] Precision pretreatment system: pH adjusted to 6.0±0.1, 4.0 parts by weight of HEDP and 1.5 parts by weight of PBTC added. The multi-membrane filtration system uses a PP wire-wound coarse filter with an 80μm pore size (effective area 2.5m²). 2 ), ceramic tubular microfiltration membrane with a pore size of 3.0 μm (effective area 10.0 m²). 2 ) and a PSF hollow fiber ultrafiltration membrane with a molecular weight cutoff of 20 kDa (effective area 35.0 m²) 2 After pretreatment, the turbidity decreased to 0.15 NTU and the SDI decreased to 2.3.

[0153] Energy recovery system: Titanium alloy plate heat exchanger with a heat exchange area of ​​30m² 2 The design temperature difference is 3℃, and the heat exchange efficiency is 93%. The phase change thermal energy storage unit uses PEG-400 material, with a phase change temperature of 60℃ and a thermal energy storage capacity of 35kWh. The total recovered heat energy accounts for 68%, and the final temperature drops to 38℃.

[0154] Lithium-selective forward osmosis membrane system: LIP-modified membranes were prepared using the following parameters: the support layer consisted of 85 parts by weight of PEEK and 15 parts by weight of ZrO2; the selective layer consisted of 80 parts by weight of PA, 15 parts by weight of LIP, and 5 parts by weight of IPDI. LIP preparation involved dissolving 20 parts by weight of MAA, 70 parts by weight of EGDMA, 1.5 parts by weight of AIBN, and 8 parts by weight of LiCl in 250 parts by weight of DMF. The draw solution consisted of 100 parts by weight of KH2PO4, 8 parts by weight of NMP, 5 parts by weight of glycerol, 1.5 parts by weight of KOH, and 0.08 parts by weight of silver citrate nanoparticles, with a pH of 7.0.

[0155] Draw-out liquid regeneration system: Vacuum membrane distillation temperature is 70℃, vacuum degree is 10kPa, using a PTFE hydrophobic membrane with a pore size of 0.15μm and a porosity of 80%, with an effective area of ​​20m². 2 .

[0156] Lithium purification system: uses anatase TiO2 (particle size 25nm, specific surface area 100m²). 2The magnesium ions were removed by photocatalytic oxidation of (g) for 30 minutes. The amount of Ca(OH)₂ was 1.3 times the theoretical stoichiometry, and the reaction was carried out at 70℃ and pH 11.0 for 45 minutes. The amount of Na₂CO₃ was 1.15 times the theoretical stoichiometry, and the reaction was carried out at 65℃ and pH 10.0 for 30 minutes to remove calcium ions. Finally, the reaction was carried out at 90℃ for 80 minutes, cooled to 23℃, and allowed to stand for 6 hours to crystallize and precipitate lithium carbonate.

[0157] Reinjection water treatment: Add 1.5 parts by weight of NaHSO3 and 0.003 parts by weight of CoNa2EDTA, and control dissolved oxygen at 8 ppb. UV dose is 35 mJ / cm². 2 The ozone dosage was 0.3 mg / L, and the contact time was 4 minutes. The pH was adjusted to 7.0, and the buffer capacity was 1.2 mmol / L.

[0158] Operational results show that lithium concentration reached 965±15 mg / L, a concentration factor of 11.4 times, with a system energy consumption of 1.15 kWh / m³. 3 The draw solution replacement cycle is up to 95 days, the membrane cleaning cycle is up to 35 days, the lithium recovery rate is 98.5%, and the final lithium carbonate product purity is 99.7%.

[0159] Example 2: Treatment of medium-temperature geothermal water with high lithium content

[0160] This embodiment focuses on the treatment of medium-temperature geothermal water with high lithium content, under the following specific conditions:

[0161] The geothermal hot spring water has a temperature of 75±1℃, a pH of 7.5±0.1, a lithium concentration of 180±5 mg / L, a sodium concentration of 2200±80 mg / L, and a magnesium concentration of 150±10 mg / L. The treatment scale is 30m³. 3 / h.

[0162] Precision pretreatment system: pH adjusted to 5.8±0.1, 2.5 parts by weight of HEDP and 1.0 part by weight of PBTC added. The multi-membrane filtration system uses a 60μm PP wire-wound coarse filter (effective area 2.0m²). 2 ), ceramic tubular microfiltration membrane with a pore size of 2.0 μm (effective area 12.0 m²). 2 ) and a PSF hollow fiber ultrafiltration membrane with a molecular weight cutoff of 15 kDa (effective area 40.0 m²) 2 After pretreatment, the turbidity decreased to 0.12 NTU and the SDI decreased to 2.0.

[0163] Energy recovery system: Titanium alloy plate heat exchanger with a heat exchange area of ​​35m² 2The design temperature difference is 2.5℃, and the heat exchange efficiency is 95%. The phase change thermal storage unit uses PEG-400 material, with a phase change temperature of 58℃ and a thermal storage capacity of 40kWh. The total recovered heat energy accounts for 72%, and the final temperature drops to 36℃.

[0164] Lithium-selective forward osmosis membrane system: LIP-modified membranes were prepared using the following parameters: the support layer consisted of 82 parts by weight of PEEK and 18 parts by weight of ZrO2; the selective layer consisted of 78 parts by weight of PA, 17 parts by weight of LIP, and 5 parts by weight of IPDI. LIP preparation involved dissolving 18 parts by weight of MAA, 72 parts by weight of EGDMA, 2.0 parts by weight of AIBN, and 8 parts by weight of LiCl in 230 parts by weight of DMF. The draw solution consisted of 105 parts by weight of KH2PO4, 7 parts by weight of NMP, 6 parts by weight of glycerol, 1.2 parts by weight of KOH, and 0.07 parts by weight of silver citrate nanoparticles, with a pH of 7.2.

[0165] Draw-out liquid regeneration system: Vacuum membrane distillation temperature is 68℃, vacuum degree is 12kPa, using a PTFE hydrophobic membrane with a pore size of 0.18μm and a porosity of 78%, with an effective area of ​​25m². 2 .

[0166] Lithium purification system: uses anatase TiO2 (particle size 22nm, specific surface area 110m²). 2 The magnesium ions were removed by photocatalytic oxidation of (g) for 25 minutes. The amount of Ca(OH)₂ was 1.4 times the theoretical stoichiometry, and the reaction was carried out at 72℃ and pH 11.2 for 40 minutes. The amount of Na₂CO₃ was 1.1 times the theoretical stoichiometry, and the reaction was carried out at 65℃ and pH 10.2 for 35 minutes to remove calcium ions. Finally, the reaction was carried out at 92℃ for 70 minutes, cooled to 22℃, and allowed to stand for 5 hours to crystallize and precipitate lithium carbonate.

[0167] Reinjection water treatment: Add 1.2 parts by weight of NaHSO3 and 0.002 parts by weight of CoNa2EDTA, and control dissolved oxygen at 6 ppb. UV dose is 38 mJ / cm². 2 The ozone dosage was 0.35 mg / L, and the contact time was 3.5 minutes. The pH was adjusted to 7.2, and the buffer capacity was 1.3 mmol / L.

[0168] Operational results show that lithium concentration reached 2160±25 mg / L, a concentration factor of 12.0 times, with a system energy consumption of 1.05 kWh / m³. 3 The draw solution replacement cycle is 110 days, the membrane cleaning cycle is 38 days, the lithium recovery rate is 99.0%, and the final lithium carbonate product has a purity of 99.8%.

[0169] Example 3: Treatment of low-lithium neutral geothermal water

[0170] This embodiment focuses on the treatment of neutral geothermal water with low lithium content, under the following specific conditions:

[0171] The geothermal hot spring water has a temperature of 82±2℃, a pH of 6.8±0.1, a lithium concentration of 45±2 mg / L, a sodium concentration of 3500±100 mg / L, a magnesium concentration of 85±5 mg / L, and a treatment capacity of 40m³. 3 / h.

[0172] Precision pretreatment system: pH adjusted to 6.2±0.1, 3.0 parts by weight of HEDP and 1.2 parts by weight of PBTC added. The multi-membrane filtration system uses a 70μm PP wire-wound coarse filter (effective area 2.8m²). 2 ), ceramic tubular microfiltration membrane with a pore size of 2.5 μm (effective area 15.0 m²). 2 ) and a PSF hollow fiber ultrafiltration membrane with a molecular weight cutoff of 25 kDa (effective area 45.0 m²) 2 After pretreatment, the turbidity decreased to 0.10 NTU and the SDI decreased to 1.8.

[0173] Energy recovery system: Titanium alloy plate heat exchanger with a heat exchange area of ​​38m² 2 The design temperature difference is 2.0℃, and the heat exchange efficiency is 96%. The phase change thermal storage unit uses PEG-400 material, with a phase change temperature of 62℃ and a thermal storage capacity of 45kWh. The total recovered heat energy accounts for 75%, and the final temperature drops to 35℃.

[0174] Lithium-selective forward osmosis membrane system: LIP-modified membranes were prepared using the following parameters: the support layer consisted of 80 parts by weight of PEEK and 20 parts by weight of ZrO2; the selective layer consisted of 75 parts by weight of PA, 20 parts by weight of LIP, and 5 parts by weight of IPDI. LIP preparation involved dissolving 15 parts by weight of MAA, 75 parts by weight of EGDMA, 2.5 parts by weight of AIBN, and 7.5 parts by weight of LiCl in 220 parts by weight of DMF. The draw solution consisted of 102 parts by weight of KH2PO4, 9 parts by weight of NMP, 7 parts by weight of glycerol, 1.0 part by weight of KOH, and 0.06 parts by weight of silver citrate nanoparticles, with a pH of 6.9.

[0175] Draw-out liquid regeneration system: Vacuum membrane distillation temperature is 72℃, vacuum degree is 8kPa, using a PTFE hydrophobic membrane with a pore size of 0.12μm and a porosity of 82%, with an effective area of ​​28m². 2 .

[0176] Lithium purification system: uses anatase TiO2 (particle size 28nm, specific surface area 95m²). 2The magnesium ions were removed by photocatalytic oxidation of (g) for 35 minutes. The amount of Ca(OH)₂ was 1.5 times the theoretical stoichiometry, and the reaction was carried out at 68℃ and pH 11.3 for 45 minutes. The amount of Na₂CO₃ was 1.2 times the theoretical stoichiometry, and the reaction was carried out at 62℃ and pH 10.3 for 30 minutes to remove calcium ions. Finally, the reaction was carried out at 88℃ for 85 minutes, cooled to 21℃, and allowed to stand for 7 hours to crystallize and precipitate lithium carbonate.

[0177] Reinjection water treatment: Add 1.0 parts by weight of NaHSO3 and 0.004 parts by weight of CoNa2EDTA, and control dissolved oxygen at 5 ppb. UV dose is 40 mJ / cm². 2 The ozone dosage was 0.4 mg / L, and the contact time was 3 minutes. The pH was adjusted to 6.8, and the buffer capacity was 1.5 mmol / L.

[0178] Operational results show that when lithium is concentrated to 495±10 mg / L, the concentration factor reaches 11.0 times, and the system energy consumption is 1.20 kWh / m³. 3 The draw solution replacement cycle is up to 100 days, the membrane cleaning cycle is up to 36 days, the lithium recovery rate is 97.5%, and the final lithium carbonate product purity is 99.6%.

[0179] Example 4: LIP modified membrane with endpoint value design

[0180] This embodiment explores the influence of endpoint values ​​of LIP-modified membrane preparation parameters, under the following specific conditions:

[0181] The geothermal hot spring water has a temperature of 85±2℃, a pH value of 7.2±0.1, a lithium concentration of 120±5mg / L, and a treatment capacity of 20m³. 3 / h.

[0182] LIP preparation: 15 parts by weight of MAA (low endpoint value), 75 parts by weight of EGDMA (high endpoint value), 1.0 parts by weight of AIBN (low endpoint value) and 5 parts by weight of LiCl (low endpoint value) were dissolved in 300 parts by weight of DMF (high endpoint value).

[0183] Forward osmosis membrane preparation: The support layer consists of 90 parts by weight of PEEK (high end value) and 10 parts by weight of ZrO2 (low end value); the selector layer consists of 85 parts by weight of PA (high end value), 10 parts by weight of LIP (low end value) and 5 parts by weight of IPDI (low end value).

[0184] Other process parameters were similar to those in Example 1. The results showed that when lithium was concentrated to 1080±20 mg / L, the concentration factor was 9.0 times, the lithium / sodium selectivity coefficient was 15.2, the lithium / potassium selectivity coefficient was 12.5, and the lithium recovery rate was 96.0%. Although the selectivity was slightly lower than in Example 1, it was still significantly better than that of a conventional forward osmosis membrane.

[0185] Example 5: Draw-out liquid composition using endpoint value design

[0186] This embodiment explores the influence of endpoint values ​​on the composition of the extractant, under the following specific conditions:

[0187] The geothermal hot spring water has a temperature of 80±2℃, a pH value of 7.0±0.1, a lithium concentration of 150±5mg / L, and a treatment capacity of 35m³. 3 / h.

[0188] The extract solution consisted of 95 parts by weight of KH2PO4 (low end value), 10 parts by weight of NMP (high end value), 8 parts by weight of glycerol (high end value), 2.0 parts by weight of KOH (high end value), and 0.10 parts by weight of silver citrate nanoparticles (high end value), with a pH of 6.8.

[0189] Preparation of silver citrate nanoparticles: 6 parts by weight of trisodium citrate (high end value), 80 parts by weight of deionized water (low end value), 2 parts by weight of silver nitrate (high end value), dropwise for 15 minutes (low end value), reaction temperature 90℃, reaction time 35 minutes.

[0190] Other process parameters are similar to those in Example 2. Operating results show that when lithium is concentrated to 1710±25 mg / L, the concentration factor is 11.4 times, and the system energy consumption is 1.10 kWh / m³. 3 The reverse osmosis rate of the extractant is 0.18 g / m³. 2 The h value is slightly higher than that of Example 2, but still within an acceptable range.

[0191] Example 6: Exploring system performance under different temperature conditions

[0192] This embodiment addresses the changes in system performance under different temperature conditions by testing at three temperature points: 25℃, 35℃, and 45℃ (the highest operating temperature of the forward osmosis membrane).

[0193] The raw water lithium concentration was 100 mg / L, and other conditions were similar to those in Example 1. Results showed that the water flux gradually increased with increasing temperature (25 LMH at 25°C, 38 LMH at 35°C, and 42 LMH at 45°C), but the membrane selectivity decreased slightly (lithium / sodium selectivity coefficients were 23.5, 20.8, and 17.2, respectively). Considering both flux and selectivity, 35-40°C was the optimal operating temperature range.

[0194] Example 7: Exploring system performance under different pH conditions

[0195] This embodiment tests the changes in system performance under different pH conditions at three points: pH 4.0, 7.0, and 10.0.

[0196] The raw water lithium concentration was 130 mg / L, and other conditions were similar to those in Example 3. The results showed that the system performed best under neutral conditions (pH 7.0), with a lithium concentration factor of 11.2 times and a lithium recovery rate of 98.2%. Under acidic conditions (pH 4.0), lithium selectivity slightly improved, but water flux decreased; under alkaline conditions (pH 10.0), water flux increased, but lithium selectivity decreased.

[0197] Example 8: Purification conditions using endpoint value design

[0198] This embodiment explores the influence of purification condition endpoint values, with specific parameters as follows:

[0199] Photocatalytic oxidation: treatment time 20 minutes (low end value), TiO2 particle size 30nm (high end value).

[0200] Magnesium ion removal: Ca(OH)2 dosage is 1.5 times the theoretical stoichiometric amount (high-end value), temperature is 75℃ (high-end value), and reaction time is 50 minutes (high-end value).

[0201] Calcium ion removal: Na2CO3 dosage is 1.3 times the theoretical stoichiometric amount (high end value), temperature is 60℃ (low end value), and reaction time is 40 minutes (high end value).

[0202] Lithium carbonate production: Na2CO3 dosage is 1.2 times the theoretical quantification (high end value), temperature is 95℃ (high end value), reaction time is 60 minutes (low end value), cooling temperature is 20℃ (low end value), and standing time is 8 hours (high end value).

[0203] The lithium concentration in the concentrate was 1000 mg / L, and other conditions were similar to those in Example 1. The results showed that the final lithium carbonate product had a purity of 99.8%, a lithium recovery rate of 98.8%, and a more uniform particle size distribution (D50 = 12 μm).

[0204] Example 9: Verifying Long-Term Operational Stability

[0205] This embodiment underwent a 6-month long-term stability test to simulate actual industrial application conditions.

[0206] The raw water conditions were similar to those in Example 2. The system operated continuously for 180 days, with membrane cleaning performed every 30 days, and system performance changes were recorded during this period. The results showed that the system maintained good stability during long-term operation: the lithium concentration factor remained stable between 11.5 and 12.0, and the energy consumption remained between 1.05 and 1.20 kWh / m³. 3 Within the specified range, membrane flux decline rate is <5% / month, and lithium recovery rate is consistently >98%.

[0207] Comparative Example 1: Using a conventional forward osmosis membrane (without LIP modification)

[0208] This comparative example uses the same conditions as Example 1, but replaces the LIP-modified forward osmosis membrane with a conventional TFC forward osmosis membrane (non-lithium ion imprinted polymer modified).

[0209] The results showed that when using a conventional membrane, lithium was concentrated to only 680 mg / L, with a concentration factor of 8.0, a lithium / sodium selectivity of only 4.5, a lithium recovery rate of 92.5%, and a product purity of 98.8%. This is significantly lower than the performance of Example 1 (concentration factor 11.4, lithium / sodium selectivity 19.5, lithium recovery rate 98.5%, and product purity 99.7%).

[0210] Comparative Example 2: Using conventional sodium chloride extraction solution

[0211] This comparative example uses the same conditions as Example 2, but replaces the phosphate-organic amine complex extract with the conventional 4.0 mol / L sodium chloride extract.

[0212] Operational results show that energy consumption increases to 1.65 kWh / m³ when using conventional extraction fluid. 3 (Compared to 1.05 kWh / m in Example 2) 3 The draw solution replacement cycle was shortened to 35 days (compared to 110 days in Example 2), and the reverse salt permeability increased to 0.45 g / m³. 2 ·h (compared to 0.15 g / m in Example 2) 2 (h). This fully demonstrates the superiority of the phosphate-organic amine composite extraction solution of the present invention.

[0213] Comparative Example 3: Non-anti-scaling system

[0214] This comparative example uses the same conditions as Example 3, but removes the anti-fouling system (without HEDP and PBTC added).

[0215] The operational results show that without the anti-fouling system, the membrane cleaning cycle is shortened to only 10 days (compared to 36 days in Example 3). During long-term operation, the membrane flux decreases significantly (by 25% after 30 days), the lithium concentration factor drops to 9.5 times, and the lithium recovery rate drops to 95.2%. This demonstrates the importance of the anti-fouling system in maintaining the long-term stable operation of the system.

[0216] Comparative Example 4: No Energy Recovery System

[0217] This comparative example uses the same conditions as Example 1, but removes the energy ladder recovery system and directly cools the hot spring water to the required temperature.

[0218] Operational results show that without an energy recovery system, total energy consumption increases to 2.30 kWh / m³. 3 (Compared to 1.15 kWh / m in Example 1) 3 The energy consumption of the extractant regeneration section, in particular, has increased by 100%, from the original 0.35 kWh / m³. 3 Increased to 1.20 kWh / m 3 The increase reached 240%. This demonstrates the significant role of the energy cascade recovery system in reducing total energy consumption.

[0219] Comparative Example 5: No intelligent adaptive control system

[0220] This comparative example uses the same conditions as Example 2, but replaces the intelligent adaptive control system with fixed parameter settings.

[0221] The operational results show that when operating with fixed parameters, the system's adaptability to fluctuations in raw water quality is significantly reduced: when the lithium concentration in the raw water fluctuates from 180 mg / L to 140 mg / L or 220 mg / L, the concentration factor changes by ±18% (compared to ±5% in Example 2), and energy consumption fluctuates by ±15% (compared to ±3% in Example 2). This demonstrates the importance of the intelligent adaptive control system in maintaining stable system operation.

[0222] 9. System Performance and Technical Effect Analysis

[0223] To comprehensively evaluate the technical effects of this invention, system performance tests were conducted on the above embodiments and comparative examples, focusing on key indicators such as lithium concentration efficiency, energy consumption, lithium selectivity, membrane lifespan, and product quality. The test results are shown in Table 1.

[0224] Table 1. Comparison of performance test results for each embodiment and comparative example

[0225]

[0226]

[0227] Note: System adaptability refers to the range of system performance changes when raw water parameters fluctuate by ±20%.

[0228] Based on the data analysis in Table 1, the present invention has the following significant technical effects:

[0229] 1. High Selectivity Separation: The lithium / sodium selectivity coefficients of Examples 1-5 were 15.2-21.2, which is much higher than the 4.5 of Comparative Example 1 (conventional membrane). This high selectivity is due to the specific recognition sites of the lithium-ion imprinted polymer, which enables preferential enrichment of lithium ions.

[0230] 2. High energy efficiency: The energy consumption of Examples 1-5 is 1.05-1.25 kWh / m². 3 Compared to Comparison Example 4 (without energy recovery), 2.30 kWh / m 3 The concentration was reduced by approximately 54%, compared to 1.65 kWh / m³ for Comparative Example 2 (conventional extract). 3 This reduces energy consumption by approximately 36%. This low-energy advantage stems from the multi-stage utilization of high-temperature geothermal energy by the energy cascade recovery system, as well as the phase change thermal storage-driven extractant regeneration system.

[0231] 3. High concentration ratio: The lithium concentration ratios of Examples 1-5 are 9.0-12.0 times, which is significantly higher than 8.0 times (conventional membrane) of Comparative Example 1 and 9.5 times (non-anti-fouling system) of Comparative Example 3. This high concentration efficiency is due to the high selectivity of the LIP modified membrane and the synergistic optimization of various parts of the system.

[0232] 4. Significantly extended membrane life: The membrane cleaning cycle of Examples 1-5 was 32-38 days, which is much longer than the 15 days of Comparative Example 1 (conventional membrane) and the 10 days of Comparative Example 3 (without anti-fouling). This long life characteristic stems from the effective protection of the anti-fouling system and the optimized design of the membrane material.

[0233] 5. Improved draw solution stability: The draw solution replacement cycle in Examples 1-5 was 85-110 days, significantly longer than the 35 days in Comparative Example 2 (conventional draw solution). This improved stability stems from the low reverse osmosis characteristics (0.15-0.25 g / m³) of the phosphate-organic amine composite draw solution. 2 ·h, compared to 0.45 g / m in Comparative Example 2 2 It has the effective antibacterial effect of silver citrate nanoparticles (with a low concentration of approximately 62%).

[0234] 6. High lithium recovery rate: The lithium recovery rates of Examples 1-5 are 96.0-99.0%, which is significantly higher than 92.5% of Comparative Example 1 (conventional membrane) and 95.2% of Comparative Example 3 (without anti-fouling). This high recovery rate directly improves economic efficiency and reduces the loss of lithium resources.

[0235] 7. Strong system adaptability: In Examples 1-5, when the raw water parameters fluctuated by ±20%, the system performance changed by only ±4-8%, which is far better than the ±18% of Comparative Example 5 (without intelligent control). This adaptability is due to the real-time monitoring and parameter optimization of the intelligent adaptive control system.

[0236] 10. Analysis of the Best Implementation Plan

[0237] Through comparative analysis, Example 2 (treatment of medium-temperature geothermal water with high lithium content) can be identified as the optimal implementation scheme of the present invention. This scheme achieves optimal results in lithium concentration factor (12.0), lithium / sodium selectivity (21.2), and energy consumption (1.05 kWh / m³). 3 The membrane cleaning cycle (38 days), draw solution replacement cycle (110 days), lithium recovery rate (99.0%), and product purity (99.8%) all reached the optimal or near-optimal levels.

[0238] The superior performance of this optimal solution stems primarily from the following optimizations:

[0239] 1. Optimization of membrane material ratio: The ratio of PEEK:ZrO2 = 82:18 for the support layer and PA:LIP:IPDI = 78:17:5 for the selectivity layer achieves the best balance between membrane permeability and selectivity, with a water flux of 40 LMH while maintaining high lithium selectivity.

[0240] 2. Optimization of the extract composition: The combination of 105 parts by weight of KH2PO4, 7 parts by weight of NMP, and 6 parts by weight of glycerol provides high osmotic pressure difference and low reverse salt permeation, while maintaining good rheological properties.

[0241] 3. Precise control of process parameters: Precise control of key parameters such as temperature, pH, and pressure ensures that the system operates under optimal conditions. In particular, precise control of pretreatment pH (5.8±0.1) and strict maintenance of forward osmosis membrane temperature (36±1℃) provide a guarantee for the system's performance.

[0242] 4. High energy efficiency: The heat exchange efficiency of the energy recovery system reaches 95%, and the total recovered heat energy accounts for 72%, which significantly reduces the system's energy consumption, especially providing 90% of the heat energy required for the regeneration of the extractant.

[0243] 5. Purification process optimization: Precise control of the dosage of Ca(OH)2 and Na2CO3, as well as optimization of reaction temperature and time, ensured the effective removal of impurities such as magnesium and calcium and the generation of high-purity lithium carbonate.

[0244] 6. Application of intelligent control system: Water quality identification accuracy reaches over 95%, automatic parameter optimization enables the system to adapt to ±4%, and it can still maintain stable performance when the raw water fluctuates.

[0245] This optimal solution not only excels in technical indicators but also has significant economic and environmental benefits in practical applications: compared with traditional technologies, the cost of treating each ton of geothermal water is reduced by about 40%, the energy consumption for producing each ton of lithium carbonate is reduced by about 60%, and the environmental protection goal of near-zero emissions is achieved.

[0246] This invention provides a process for enriching lithium ions in geothermal hot spring water using lithium-ion selective enhanced forward osmosis membrane concentration technology. Through innovative technologies such as lithium-ion imprinted polymer modified forward osmosis membrane, phosphate-organic amine composite extractant, energy ladder recovery system, phase change heat storage driven extractant regeneration system, and intelligent adaptive control, the efficient enrichment of lithium ions in geothermal hot spring water is achieved.

[0247] Compared with existing technologies, this invention has high selectivity (lithium / sodium selectivity coefficient 15-25) and low energy consumption (1.0-1.5 kWh / m³). 3 With significant advantages such as high concentration ratio (8-12 times), long membrane life (membrane cleaning cycle 30-40 days), and high lithium recovery rate (97-99%), it provides a new technical path for the high-value utilization of lithium in geothermal resources and has broad application prospects.

Claims

1. A method for highly selectively enriching lithium ions in geothermal hot spring water, characterized in that, Includes the following steps: (1) After the geothermal hot spring water is analyzed online through multiple parameters, it is introduced into a precision pretreatment system for treatment. The precision pretreatment system includes a pH adjustment unit, an anti-scaling agent dosing system, and a multi-membrane filtration system to reduce the temperature from 60-95℃ to 35-40℃ and the turbidity to below 0.2 NTU. The anti-scaling agent dosing system includes the following components: 0.5-5.0 parts by weight of hydroxyethylidene diphosphonic acid and 0.2-2.0 parts by weight of 2-phosphonobutane-1,2,4-tricarboxylic acid. The pH adjustment unit uses citric acid or sodium bicarbonate to adjust the pH of the hot spring water to the range of 5.5-6.

5. (2) The pretreated hot spring water recovers heat energy through an energy ladder recovery system, which includes a plate heat exchanger and a phase change heat storage unit. (3) Hot spring water enters a lithium selective forward osmosis membrane module, which includes a lithium-ion imprinted polymer-modified composite forward osmosis membrane. The lithium-ion imprinted polymer-modified composite forward osmosis membrane includes a support layer and a selective layer. The support layer consists of 80-90 parts by weight of polyetheretherketone (PEEK) and 10-20 parts by weight of zirconium oxide nanoparticles. The selective layer consists of 75-85 parts by weight of polyamide, 10-20 parts by weight of lithium-ion imprinted polymer, and 5-10 parts by weight of isophorone diisocyanate. One side of the lithium selective forward osmosis membrane module contains hot spring water, and the other side contains a phosphate-organic amine composite draw solution. The phosphate-organic amine composite draw solution consists of the following components: 95-105 parts by weight of potassium dihydrogen phosphate, 5-10 parts by weight of N-methylpyrrolidone, 3-8 parts by weight of glycerol, 0.5-2.0 parts by weight of potassium hydroxide, and 0.05-0.10 parts by weight of silver citrate nanoparticles. The pH value of the phosphate-organic amine composite draw solution is 6.8-7.2 in parts by weight; under the drive of osmotic pressure difference, water molecules in the hot spring water pass through the forward osmosis membrane into the draw solution side, while lithium ions in the hot spring water are concentrated. (4) The diluted draw solution is concentrated and regenerated by a phase change heat storage driven vacuum membrane distillation system. The phase change heat storage driven vacuum membrane distillation system includes a phase change heat storage unit and a vacuum membrane distillation component. The phase change heat storage unit uses polyethylene glycol as the phase change material and the phase change temperature is 55-65℃. The vacuum membrane distillation component uses a polytetrafluoroethylene hydrophobic membrane with a pore size of 0.1-0.22μm, a porosity of 75-85%, an operating temperature of 65-75℃, and a vacuum side pressure of 5-15kPa. The regenerated draw solution is recycled back to step (3). (5) The concentrate is processed by a lithium enrichment solution purification system, which includes a photocatalytic oxidation pretreatment unit, a magnesium ion removal unit, a calcium ion removal unit and a lithium carbonate production unit. (6) The condensate produced by the vacuum membrane distillation system is mixed with the nanofiltration permeate and then treated by the reinjection water treatment system, which includes a dissolved oxygen control unit, a microbial control unit and a pH buffer system, and then reinjected underground after treatment; (7) The entire process adopts an intelligent adaptive control system to monitor and optimize operating parameters.

2. The method for highly selectively enriching lithium ions in geothermal hot spring water according to claim 1, characterized in that, The multi-membrane filtration system in the precision pretreatment system includes a polypropylene filament-wound coarse filter, a ceramic tube microfiltration membrane, and a polysulfone hollow fiber ultrafiltration membrane arranged sequentially according to the flow direction; the pore size of the polypropylene filament-wound coarse filter is 50-100μm, the pore size of the ceramic tube microfiltration membrane is 1.0-5.0μm, and the molecular weight cutoff of the polysulfone hollow fiber ultrafiltration membrane is 10-30kDa.

3. The method for highly selective enrichment of lithium ions in geothermal hot spring water according to claim 1, characterized in that, The preparation method of the lithium-ion imprinted polymer is as follows: Dissolve 15-25 parts by weight of methacrylic acid, 65-75 parts by weight of ethylene glycol dimethacrylate, 1-3 parts by weight of azobisisobutyronitrile, and 5-10 parts by weight of lithium chloride in 200-300 parts by weight of N,N-dimethylformamide, and react at 60±2℃ for 24±0.5 hours. The resulting solution was poured into 10 times its volume of deionized water to precipitate, filtered, and vacuum dried at 65°C for 12 hours to obtain the lithium-ion imprinted prepolymer. The prepolymer was pulverized to below 200 mesh and eluted with a 0.1 mol / L aqueous solution of disodium ethylenediaminetetraacetate at a flow rate of 2 BV / h for 10 BV elution. The polymer was rinsed with deionized water until neutral, washed three times with methanol, and then vacuum dried at 60°C for 24 hours to obtain the lithium-ion imprinted polymer.

4. The method for highly selectively enriching lithium ions in geothermal hot spring water according to claim 1, characterized in that, The preparation method of the silver citrate nanoparticles is as follows: Dissolve 4-6 parts by weight of trisodium citrate in 80-100 parts by weight of deionized water and heat to 90±2℃; At a stirring speed of 400-500 rpm, slowly add 1-2 parts by weight of an aqueous solution of silver nitrate, and control the addition time to 15-20 minutes. Continue the reaction at 90±2℃ for 30±5 minutes, cool to room temperature, and then add 200-250 parts by weight of ethanol to precipitate. Centrifugation was performed, the precipitate was collected and washed three times with ethanol, vacuum dried at 50°C for 12 hours, ground and sieved to obtain silver citrate nanoparticles.

5. The method for highly selectively enriching lithium ions in geothermal hot spring water according to claim 1, characterized in that, The lithium enrichment solution purification system includes the following processing steps: The concentrate is first treated with a nano-titanium dioxide photocatalytic oxidation device for 20-40 minutes to remove trace amounts of organic matter. Adjust the pH to 10.5-11.5, add 1.2-1.5 times the theoretical amount of calcium hydroxide, and react at 65-75℃ for 30-50 minutes to precipitate and remove magnesium ions; After filtration, adjust the pH to 9.5-10.5, add 1.1-1.3 times the theoretical amount of sodium carbonate, and react at 60-70℃ for 20-40 minutes to precipitate and remove calcium ions; After filtration, heat the solution to 85-95℃, add 1.05-1.20 times the theoretical stoichiometric amount of sodium carbonate, and react for 60-90 minutes. Cool to 20-25℃ and let stand for 4-8 hours to crystallize and precipitate lithium carbonate; The lithium carbonate product was collected by filtration, washed three times with deionized water, and dried at 105±5℃ for 4-6 hours.

6. The method for highly selective enrichment of lithium ions in geothermal hot spring water according to claim 1, characterized in that, The reinjection water treatment system includes the following treatment steps: Add 0.5-2.0 parts by weight of sodium bisulfite and 0.001-0.005 parts by weight of sodium cobalt ethylenediaminetetraacetate as deoxidizers to control the dissolved oxygen content to less than 10 ppb; Water flows through a 254nm ultraviolet disinfection system with an ultraviolet dose of 30-40mJ / cm². The ozone system is used for treatment, with an ozone dosage of 0.2-0.5 mg / L and a contact time of 3-5 minutes. The pH was adjusted to 6.5-7.5 using a sodium bicarbonate and carbon dioxide buffer system, with a buffer capacity greater than or equal to 1.0 mmol / L. The treated reinjection water is heated to 70-80℃ and reinjected underground.

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