Continuous segmented coupling composite lithium extraction process based on high-salt low-lithium complex gas field produced water system

Abstract

The invention relates to a continuous segmented coupling composite lithium extraction process based on a high-salt low-lithium complex gas field produced water system, which is characterized in that lithium ions in produced water are efficiently recovered under the condition of ultralow lithium ion concentration aiming at complex water quality characteristics of high-concentration hydrogen sulfide, calcium ions, organic pollutants, oil, suspended matters and the like in gas field produced water. According to the method disclosed by the invention, the adaptive capacity of the adsorbent to the water quality characteristics of the gas field produced water is remarkably improved, the engineering problems of poisoning and blockage of the adsorbent are overcome, and meanwhile, the problem of rapid failure of the desorption liquid in a membrane concentration section due to hardness ion enrichment is solved through multi-section impurity removal coupling concentration.

Description

Technical Field

[0001] This invention relates to a lithium extraction technology, specifically a process for the efficient recovery of ultra-low concentration lithium under complex gas field produced water quality conditions. It is a continuous segmented coupled composite lithium extraction process based on a high-salt, low-lithium complex gas field produced water system. Background Technology

[0002] In recent years, lithium, bromine, and potassium resources have received widespread attention. Lithium, as one of the important mineral resources, is not only used in traditional chemical, metallurgical, pharmaceutical, and refrigeration industries, but also widely used in emerging fields such as atomic energy, new electronic materials, and ceramic materials. It is a key raw material for electric vehicles and nuclear fusion power generation and is known as "white oil".

[0003] Existing research on liquid lithium extraction mainly focuses on brine from salt lakes, where the main cations are Li. + Na + K + Ca 2+ Mg 2+ and B 3+ And Li + The content is generally low; the main anion is SO4. 2- Cl - CO3 2- The success of brine lithium extraction technology depends on the absolute concentration of Li+ in the brine and the complexity of associated ions. This is because the presence of divalent magnesium ions, boron, and other elements causes numerous problems in separating Li+ from other cations. Currently, salt lakes, due to their clear water quality, typically have TOC levels (represented by organic pollutants) below 10 mg / L. The main interfering ions are magnesium ions, while calcium ion concentrations are low. Therefore, for lithium extraction from salt lakes, the raw water usually enters the lithium extraction unit directly. The main process is adsorption + nanofiltration + concentration + lithium precipitation.

[0004] Common treatment methods for produced water from gas fields include reinjection, evaporation, and discharge. Currently, reinjection is the most frequently used method because it is relatively easy to treat, only removing oil and suspended solids from the water to meet standards and the requirements of the reinjection layer. However, the discharge and comprehensive utilization of produced water from gas fields are newer methods that have emerged in recent years due to increasingly stringent environmental protection requirements. Taking existing projects as an example, the comprehensive utilization of produced water with high mineralization from gas fields can achieve water compliance while recovering salt. Currently, the resource utilization of salt mainly focuses on sodium chloride and sodium sulfate, with little recovery of other valuable elements such as bromine, iodine, potassium, and lithium. These valuable elements are either directly reinjected into the formation or treated as mixed salt as solid waste, resulting in a significant waste of resources.

[0005] The produced water from gas fields has the following main characteristics:

[0006] (1) The water quality is complex, the water volume increases significantly, the suspended solids are high, and it is difficult to settle.

[0007] (2) The mineralization is generally above tens of thousands to hundreds of thousands of mg / l. In addition to containing a large amount of chloride, it also contains heavy metal ions or harmful substances such as sulfides, Cd, Pb, Ba, and As.

[0008] (3) High hardness, calcium ions form complex complexes with substances in water, making it difficult to remove hardness.

[0009] (4) The extracted water from sulfur-containing gas fields contains hydrogen sulfide, which is highly corrosive and difficult to process.

[0010] (5) The organic matter concentration is high and the salt content is high. It is difficult to remove COD and TDS at the same time, and the treatment cost is high.

[0011] (6) The levels of valuable elements such as bromine, iodine, potassium and lithium in the produced water of the gas field vary greatly, with the content in different blocks differing by 2 to 10 times.

[0012] (7) The lithium concentration in gas field produced water is usually between 20 mg / L and 100 mg / L, while the lithium ion concentration in old salt lake brine is usually ≥300 mg / L. Therefore, gas field produced water is a low-lithium brine.

[0013] High concentrations of hydrogen sulfide, barium ions, calcium ions, and chemical additives in gas field produced water are extremely rare in salt lakes and cannot appear simultaneously. To extract lithium ions from unsaturated gas field produced water, it is necessary to solve the problems of adsorbent poisoning and clogging caused by the above substances, as well as the rapid scaling and failure of subsequent membrane concentration devices. Summary of the Invention

[0014] The purpose of this invention is to address the limitation of existing lithium extraction technologies in producing gas field water due to its inability to extract lithium under certain water quality conditions. This is achieved by implementing a multi-stage, tightly coupled process to enable lithium extraction from produced gas field water. Specifically, it addresses the complex water quality characteristics of produced gas field water, including high concentrations of hydrogen sulfide, calcium ions, organic pollutants, oil, and suspended solids, achieving efficient lithium ion recovery under ultra-low lithium ion concentration conditions. This invention significantly improves the adaptability of adsorbents to the characteristics of produced gas field water, overcomes engineering problems such as adsorbent poisoning and clogging, and solves the problem of rapid desorption of the desorbent in the membrane concentration stage due to hardness ion enrichment through multi-stage impurity removal coupled with concentration.

[0015] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0016] A continuous segmented coupled composite lithium extraction process based on a complex produced water system in a high-salt, low-lithium gas field includes the following steps:

[0017] The produced water from the gas field is collected and sent to a high-efficiency vortex microbubble device to remove most of the oil and suspended solids while reducing the organic matter content in the water;

[0018] After being treated by the high-efficiency cyclone microbubble device, the effluent is adjusted to pH 2-5 and then pumped to the stripping tower. Air is blown out using the outlet of the blower. The gas that has been stripped of sulfides enters the absorption tower and is absorbed to obtain sulfur. The desulfurized effluent enters the catalytic oxidation device to remove reducing inorganic substances and some organic substances in the water through catalytic oxidation.

[0019] The oxidized water from the catalytic oxidation unit enters the hardness ion circulating fluidized bed mineralization separation unit. A capture agent (a macromolecular substance with a high sensitivity group to hardness ions, referred to as hardness ion capture agent) is used to remove the main hardness ions in the water. Then, the hardness ions are separated from the raw water by the density difference between the circulating mineralization capture agent and the water, so that the total hardness of the raw water is reduced to less than 150 mg / L.

[0020] After mineralization and separation of hardness ions, the raw water enters a filtration device for two-stage filtration and purification. The extracted water from the filtration device then enters a lithium extraction adsorption tower. Lithium ions in the raw liquid come into contact with the adsorbent (lithium ion adsorbent, an adsorbent material that adsorbs lithium ions, such as manganese-based or aluminum-based adsorbents, etc.) and selectively adsorb lithium ions. After adsorption saturation, a desorption solution (lithium ions remain in the adsorbent after being adsorbed and need to be separated from the adsorbent using a solution, called the desorption solution) is introduced to desorb the lithium from the adsorbent, resulting in a relatively pure lithium-containing solution, which is then sent to the concentration and purification section for lithium extraction.

[0021] The tail liquid after lithium adsorption is discharged into the reinjection pool; the lithium-containing desorption liquid obtained from the adsorption section is concentrated by multiple membranes and deeply impurities are removed to remove hardness ions brought into the desorption liquid during the adsorption process, so that the total hardness is controlled below 50 mg / L, and a pure lithium-rich solution is obtained.

[0022] Sodium carbonate is added to a lithium-rich solution, followed by crystallization and drying to obtain industrial-grade lithium carbonate.

[0023] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on a complex gas field produced water system with high salt and low lithium, the total hardness of the gas field produced water is between 10,000 mg / L and 30,000 mg / L. In addition to containing a large amount of chloride ions, it also contains sulfides, Cd, Pb, Ba, As heavy metal ions, or harmful substances. The concentration of lithium in the gas field produced water is typically between 20 mg / L and 100 mg / L.

[0024] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on the produced water system of a complex high-salt, low-lithium gas field, the oil concentration in the effluent treated by the high-efficiency cyclone microbubble device is controlled to be ≤20mg / L and the suspended solids concentration to be ≤30mg / L.

[0025] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system, the hydrogen sulfide concentration in the desulfurized produced water is less than 30 mg / L.

[0026] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on the produced water system of a complex high-salt, low-lithium gas field, after two-stage filtration and purification, the oil concentration in the effluent is ≤5mg / L, the suspended solids concentration is ≤5mg / L, and the TOC concentration is ≤20mg / L.

[0027] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on the produced water system of a complex high-salt, low-lithium gas field, the segmented process of nanofiltration and deep impurity removal is coupled to control the concentration of organic matter (TOC) in the desorption solution that causes subsequent process failure to be <10 mg / L and the total hardness to be <150 mg / L. Then, the lithium ion concentration in the desorption solution is increased to 8000 mg / L to 15000 mg / L through the RO + electrodialysis dual membrane method.

[0028] Furthermore, in the aforementioned continuous segmented coupled composite lithium extraction process based on the produced water system of a complex high-salt, low-lithium gas field, the lithium ion concentration in the pure lithium-rich solution is ≥12000 mg / L.

[0029] Gas field produced water is complex in quality, with significant volume increases, high suspended solids, and difficulty in sedimentation. Mineralization is generally tens to hundreds of thousands of mg / L or higher, and total hardness is typically 10,000 to 30,000 mg / L. Besides high levels of chloride ions, it also contains sulfides, Cd, Pb, Ba, As, and other heavy metal ions or harmful substances. Lithium concentration in gas field produced water is typically 20 to 100 mg / L, while in saline lake brine, lithium ion concentration is usually ≥300 mg / L. Gas field produced water is classified as low-lithium brine. Lithium extraction is performed under these gas field produced water conditions using a multi-stage pretreatment system: flotation, desulfurization, oxidation, mineralization separation, and continuous segmented coupling of two-stage filtration. This controls the pretreated effluent oil concentration to ≤5 mg / L, suspended solids concentration to ≤5 mg / L, and TOC concentration to ≤20 mg / L. This addresses the issues of adsorbent fouling by organic matter and heavy metal poisoning.

[0030] In the context of complex produced water quality from gas fields, after pretreatment, low-concentration lithium ions in the raw water are adsorbed and enriched using adsorbents. After desorption, while the desorbate contains abundant lithium ions, it also contains a large number of hardness ions and impurities. A segmented process of nanofiltration and deep impurity removal is coupled to control the TOC concentration (which causes subsequent process failures) in the desorbate to <10 mg / L and the total hardness to <150 mg / L. Then, a dual-membrane method of RO + electrodialysis is used to increase the lithium ion concentration in the desorbate to 8000 mg / L–15000 mg / L before it enters the evaporation and lithium precipitation section. Ultimately, continuous and stable operation of the entire process is achieved, with an overall lithium ion recovery rate >80%. The purity of the product lithium carbonate is ≥99.2%.

[0031] Compared with existing technologies, the beneficial effects of this invention are:

[0032] a) It solved the problem of lithium ion enrichment caused by adsorbent poisoning and blockage due to the complex water quality of gas field produced water.

[0033] (b) It solved the problem of high concentrations of calcium ions entering the membrane concentration section, which was not present in lithium extraction from salt lakes, causing the membrane section to fail rapidly.

[0034] c) It solves the problem of achieving high recovery rates in the device under ultra-low lithium concentration conditions, achieving an overall recovery rate of ≥70% in the device, while the overall lithium ion recovery rate in the salt lake lithium extraction device is about 50% to 60%. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a continuous segmented coupled composite lithium extraction process based on a complex gas field produced water system with high salt and low lithium, according to Embodiment 1 of the present invention. Detailed Implementation

[0036] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0037] Any feature disclosed in this specification (including the claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments. The chemical reagents used in the following method for lithium extraction from produced water in gas fields include PAM, PAC, hardness ion trapping agent, lithium ion adsorbent, hydrochloric acid, hydrogen sulfide absorbent, sodium hydroxide, sodium carbonate, etc., all of which are commercially available products.

[0039] Example 1:

[0040] The target is produced water from a lithium-bearing gas field in an oil and gas field in Sichuan Province, with a treatment capacity of 500m³. 3 / d, the extracted water is characterized by high hardness, high sulfur content, high COD, and high salinity. Details of its water quality are shown in Table 1.

[0041] Table 1. Water quality of produced water from lithium gas fields

[0042] Indicator Item pH hydrogen sulfide CODcr SS Oil Total Hard lithium TDS unit Dimensionless mg / L mg / L mg / L mg / L mg / L mg / L mg / L control value 5～7 500 1000 100 100 13500 80 110000

[0043] Given the high concentration of pollutants in the produced water, comprehensive pretreatment is required to remove oil, suspended solids, hydrogen sulfide, total hardness, COD, etc., in order to reduce interference in the lithium extraction adsorption stage and increase the lithium recovery rate.

[0044] I. High-efficiency cyclone microbubble air flotation process

[0045] The efficient swirl microbubble flotation process is used to perform preliminary oil and suspension removal on the produced water. After preliminary treatment, the oil content of the flotation effluent is less than 30 mg / L and the suspended solids content is less than 20 mg / L.

[0046] II. Desulfurization process

[0047] After the treated produced water is adjusted to pH 3-4, it is pumped to a stripping tower for desulfurization (desulfurization can be achieved using existing technology). Then, air is blown out from the blower outlet, and the gas that has been desulfurized enters the absorption tower. After absorption and reaction, sulfur is obtained. The desulfurized produced water enters the catalytic oxidation unit, and the hydrogen sulfide content in the effluent is less than 30 mg / L.

[0048] III. Catalytic Oxidation Process

[0049] COD has a significant impact on the lithium adsorption section. After desulfurization, the treated water enters the catalytic oxidation unit to remove reducing inorganic substances and some organic substances in the water through catalytic oxidation. After catalytic oxidation treatment, the hydrogen sulfide content is less than 1 mg / L and the COD is less than 200 mg / L.

[0050] IV. Hardness Ion Separation Process

[0051] The produced water contains hardness ions such as calcium, magnesium, barium, and strontium, which greatly affect the adsorption process. Therefore, the effluent from the catalytic oxidation unit enters a hardness ion circulating fluidized bed mineralization separation unit. Using a capture agent (existing technology), the main hardness ions in the water are removed. After treatment by the hardness ion circulating fluidized bed mineralization separation process, the total hardness of the effluent is below 150 mg / L.

[0052] The biggest differences between the above steps and other lithium extraction processes from salt lakes are as follows:

[0053] 1. Unlike salt lake brine, produced water from oil and gas fields usually has extremely high hardness. Hardness ions pose a great threat to lithium extraction adsorbents during the lithium extraction process. In this invention, after the hardness ions are significantly reduced, the risk of subsequent adsorbent poisoning and clogging is greatly reduced, and the service life of the adsorbent is significantly extended.

[0054] 2. If the existing dual-alkali method for hardening in the water treatment field is used, the cost of chemical dosing will increase the cost of lithium extraction by more than 30%. However, by using a special capture agent and a circulating fluidized bed mineralization separation device, the cost of the capture agent can be recovered, and the cost per ton of lithium extracted is about 5% to 10%. Therefore, the capture mineralization separation process has obvious advantages.

[0055] 3. This invention removes most of the hardness ions before the raw water enters the adsorbent, which greatly reduces the residual hardness ions in the desorption solution, significantly reduces the operating cost of the subsequent desorption solution impurity removal process, and effectively improves stability.

[0056] V. Two-stage filtration process

[0057] The raw water, after mineralization and separation of hardness ions, enters a filtration device for two-stage filtration and purification; the pretreated produced water undergoes deep impurity removal treatment, and the treated effluent has suspended solids of less than 1 mg / L and oil of less than 1 mg / L.

[0058] VI. Lithium Extraction Adsorption and Desorption Process

[0059] The extracted water from the filtration unit enters the lithium extraction adsorption tower; lithium ions in the feed liquid come into contact with the adsorbent and are selectively adsorbed; after adsorption saturation, desorption liquid is introduced to desorb the lithium in the adsorbent, resulting in a relatively pure lithium-containing solution, which is then sent to the concentration and purification section for lithium extraction.

[0060] The tail liquid after lithium adsorption is discharged into the reinjection pool; the lithium-containing desorption liquid obtained from the adsorption section is concentrated by multiple membranes and deeply impurities are removed to remove hardness ions brought into the desorption liquid during the adsorption process, so that the total hardness is controlled below 50 mg / L, and a pure lithium-rich solution is obtained.

[0061] The adsorption section uses manganese-based adsorbents. Through static adsorption, four adsorption tanks are filled with manganese-based adsorbents in a two-parallel-two-series configuration. Pretreated water is then introduced into the adsorption tower. After adsorption is complete, the adsorbents are washed with desorption liquid to obtain lithium-rich liquid and tailings. The lithium-rich liquid contains approximately 180 mg / L of lithium ions, and the tailings contain approximately 10 mg / L of lithium ions.

[0062] VII. Concentration and Purification Process

[0063] The lithium-rich solution is purified by nanofiltration, and the nanofiltration desalinated water is concentrated by reverse osmosis and electrodialysis, resulting in a lithium ion content of approximately 8000 mg / L.

[0064] VIII. Evaporation and Concentration Process

[0065] The electrodialysis concentrate is further concentrated by single-effect evaporation crystallization, and the lithium ion content of the concentrate is approximately 25,000 mg / L.

[0066] IX. Lithium deposition process

[0067] Sodium carbonate is added to the concentrated evaporation solution to produce lithium carbonate. Through filtration, washing, and drying, a high-purity lithium carbonate product can be obtained. Testing shows that the purity of the lithium carbonate is ≥99%.

[0068] The relevant parameters in the lithium carbonate preparation process of this embodiment are shown in Table 2.

[0069] Table 2. Statistical Table of Key Process Parameters for Lithium Carbonate Preparation from Lithium-Bearing Gas Field Produced Water

[0070]

[0071] Example 2:

[0072] The example is lithium-containing brine from an oilfield in Qinghai Province, with a treatment capacity of 2000 m³. 3 / d, the produced water is characterized by high hardness, high COD, high salinity, and high oil content. Details of its water quality are shown in Table 3.

[0073] Table 3. Water quality of produced water from lithium-containing gas fields

[0074] Indicator Item pH CODcr SS Oil Total Hard lithium TDS unit Dimensionless mg / L mg / L mg / L mg / L mg / L mg / L control value 6～7 3500 110 3100 25500 190 250000

[0075] Given the characteristics of the produced water being high in oil and free of hydrogen sulfide, an oil separation facility was added before air flotation, eliminating the need for desulfurization.

[0076] I. Degreasing process

[0077] After the produced water from the gas field is collected and treated with oil separation, the oil content in the produced water is less than 100 mg / L.

[0078] II. High-efficiency vortex microbubble air flotation process

[0079] The produced water after oil removal is treated with a high-efficiency vortex microbubble device, that is, the high-efficiency vortex microbubble flotation process is used to remove oil and suspended solids from the produced water. After preliminary treatment, the flotation effluent contains less than 30 mg / L and suspended solids less than 20 mg / L.

[0080] III. Catalytic Oxidation Process

[0081] COD has a significant impact on the lithium adsorption section. After desulfurization, the treated water enters the catalytic oxidation unit to remove reducing inorganic substances and some organic substances in the water through catalytic oxidation. After catalytic oxidation treatment, the oil content is less than 5 mg / L and the COD is less than 500 mg / L.

[0082] IV. Hardness Ion Separation Process

[0083] The produced water contains hardness ions such as calcium, magnesium, barium, and strontium, which greatly affect the adsorption process. Therefore, the effluent from the catalytic oxidation unit enters a hardness ion circulating fluidized bed mineralization separation unit. Using a capture agent (existing technology), the main hardness ions in the water are removed. After treatment by the hardness ion circulating fluidized bed mineralization separation process, the total hardness of the effluent is below 150 mg / L.

[0084] V. Two-stage filtration process

[0085] The raw water, after mineralization and separation of hardness ions, enters a filtration device for two-stage filtration and purification; the pretreated produced water undergoes deep impurity removal treatment, and the treated effluent has suspended solids of less than 1 mg / L and oil of less than 1 mg / L.

[0086] VI. Lithium Extraction Adsorption and Desorption Process

[0087] The extracted water from the filtration unit enters the lithium extraction adsorption tower; lithium ions in the feed liquid come into contact with the adsorbent and are selectively adsorbed; after adsorption saturation, desorption liquid is introduced to desorb the lithium in the adsorbent, resulting in a relatively pure lithium-containing solution, which is then sent to the concentration and purification section for lithium extraction.

[0088] The tail liquid after lithium adsorption is discharged into the reinjection pool; the lithium-containing desorption liquid obtained from the adsorption section is concentrated by multiple membranes and deeply impurities are removed to remove hardness ions brought into the desorption liquid during the adsorption process, so that the total hardness is controlled below 50 mg / L, and a pure lithium-rich solution is obtained.

[0089] The adsorption section uses aluminum-based adsorbents and employs a continuous cross-linking adsorption method. Thirty adsorption columns are connected in parallel and filled with aluminum-based adsorbents. Pretreated water is then introduced into the adsorption tower. After adsorption is complete, the adsorbent is washed with desorption liquid to obtain lithium-rich liquid and tailings. The lithium-rich liquid contains approximately 350 mg / L of lithium ions, and the tailings contain approximately 20 mg / L of lithium ions.

[0090] VII. Concentration and Purification Process

[0091] The lithium-rich solution is purified by nanofiltration, and the nanofiltration desalinated water is concentrated by reverse osmosis and electrodialysis, resulting in a lithium ion content of approximately 15,000 mg / L.

[0092] VIII. Evaporation and Concentration Process

[0093] The electrodialysis concentrate is further concentrated by single-effect evaporation crystallization, and the lithium ion content of the concentrate is approximately 25,000 mg / L.

[0094] IX. Lithium deposition process

[0095] Sodium carbonate is added to the concentrated evaporation solution to produce lithium carbonate. Through filtration, washing, and drying, a high-purity lithium carbonate product can be obtained. Testing shows that the purity of the lithium carbonate is ≥99%.

[0096] The relevant parameters in the lithium carbonate preparation process of this embodiment are shown in Table 4.

[0097] Table 4. Statistical Table of Key Process Parameters for Lithium Carbonate Preparation from Lithium-Bearing Gas Field Produced Water

[0098]

[0099] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0100] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A continuous segmented coupled composite lithium extraction process based on a complex produced water system in a high-salt, low-lithium gas field, characterized in that... Includes the following steps: The produced water from the gas field is collected and sent to a high-efficiency vortex microbubble device to remove most of the oil and suspended solids while reducing the organic matter content in the water; After being treated by the high-efficiency cyclone microbubble device, the effluent is adjusted to pH 2-5 and then pumped to the stripping tower. Air is blown out using the outlet of the blower. The gas that has been stripped of sulfides enters the absorption tower and is absorbed to obtain sulfur. The desulfurized effluent enters the catalytic oxidation device to remove reducing inorganic substances and some organic substances in the water through catalytic oxidation. The oxidized water from the catalytic oxidation unit enters the hardness ion circulating fluidized bed mineralization separation unit. The main hardness ions in the water are removed by a capture agent. Then, the hardness ions are separated from the raw water by the density difference between the circulating capture agent and the water, so that the total hardness of the raw water is reduced to less than 150 mg / L. The raw water, after mineralization and separation of hardness ions, enters a filtration device for two-stage filtration and purification. The treated water after exiting the filtration device enters the lithium extraction adsorption tower; lithium ions in the feed liquid come into contact with the adsorbent and are selectively adsorbed. After adsorption saturation, a desorption solution is introduced to desorb the lithium in the adsorbent, resulting in a relatively pure lithium-containing solution, which is then sent to the concentration and purification section for adsorption and lithium extraction. The tail liquid after lithium adsorption is discharged into the reinjection pool; the lithium-containing desorption liquid obtained from the adsorption section is concentrated by multiple membranes and deeply impurities are removed to remove hardness ions brought into the desorption liquid during the adsorption process, so that the total hardness is controlled below 50 mg / L, and a pure lithium-rich solution is obtained. Sodium carbonate is added to a lithium-rich solution, followed by crystallization and drying to obtain industrial-grade lithium carbonate.

2. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: The total hardness of the produced water from the gas field is between 10,000 mg / L and 30,000 mg / L. In addition to containing a large amount of chloride ions, it also contains sulfides, Cd, Pb, Ba, As heavy metal ions or harmful substances. The concentration of lithium in the produced water from the gas field is usually between 20 mg / L and 100 mg / L.

3. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: In the effluent treated by the high-efficiency vortex microbubble device, the oil concentration is controlled to be ≤20mg / L and the suspended solids concentration is controlled to be ≤30mg / L.

4. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: The hydrogen sulfide concentration in the desulfurized water is less than 30 mg / L.

5. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: After two-stage filtration and purification, the effluent oil concentration is ≤5mg / L, suspended solids concentration is ≤5mg / L, and TOC concentration is ≤20mg / L.

6. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: By coupling nanofiltration and deep impurity removal in a segmented process, the concentration of organic matter (TOC) in the desorption solution that causes failure of subsequent processes is controlled to be <10 mg / L and the total hardness to be <150 mg / L. Then, the lithium ion concentration in the desorption solution is increased to 8000 mg / L to 15000 mg / L by a dual membrane method of RO + electrodialysis.

7. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: The lithium ion concentration in a pure lithium-rich solution is ≥12000 mg / L.

8. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: The capturing agent is a macromolecular substance with a hardness ion highly sensitive group.

9. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to claim 1, characterized in that: The adsorbent is a manganese-based adsorbent or an aluminum-based adsorbent.

10. The continuous segmented coupled composite lithium extraction process based on a complex high-salt, low-lithium gas field produced water system according to any one of claims 1-9, characterized in that: If the produced water has high oil content and does not contain hydrogen sulfide, an oil separator is added before the high-efficiency cyclone microbubble device for air flotation. After the water is treated by the high-efficiency cyclone microbubble device, the pH is adjusted to 2-5 and then pumped to the stripping tower, where the air stripping step is carried out using the air outlet of the blower.

Images