A method for cooperatively extracting bromine and lithium from oil and gas field brine

Abstract

This invention addresses problems such as electrode scaling, extractant poisoning, and process mismatch in the recovery of bromine and lithium resources from oil and gas field brine, providing a three-stage coupled enhanced recovery method. The method first reduces calcium ion concentrations in the brine to below 5 mg / L and magnesium ion concentrations to below 2 mg / L through a deep purification step; then, bromine is extracted by electro-oxidation under acidic conditions, recovering the bromine product; finally, the debromination tailwater is adjusted to pH 10-13, and lithium is extracted using a synergistic extraction system containing multi-branched alkyl-substituted naphthenic acid derivatives and space configuration modifiers. This invention creates favorable conditions for subsequent electro-oxidation and extraction through deep purification, and achieves highly selective lithium separation under alkaline conditions through a structured extraction system, significantly extending the electrode cleaning cycle and extractant lifespan, and improving product purity. This method achieves efficient synergistic recovery of bromine and lithium, and has promising industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and wastewater treatment technology, specifically relating to a coupled and enhanced method for synergistic extraction of bromine and lithium from oil and gas field brines, which is particularly suitable for the comprehensive development and utilization of complex oil and gas field brines that are simultaneously rich in bromide and lithium ions. Background Technology

[0002] Oil and gas field brine is highly mineralized wastewater generated during oil and gas extraction. It is rich in valuable elements such as lithium, bromine, potassium, and boron, and has significant comprehensive recovery value. Lithium is a key raw material for the new energy industry, while bromine is an important chemical raw material. Recovering these two resources from oil and gas field brine can not only realize the resource utilization of waste but also alleviate the dependence on foreign sources for these resources.

[0003] In existing technologies, bromine extraction and lithium extraction are mostly studied as independent process units, lacking a systematic approach to the synergistic design of the two resource extraction processes. In practical applications, the following technical bottlenecks exist: (1) Impurity interference. The content of calcium and magnesium ions in oil and gas field brine is high (up to several grams per liter). In the electro-oxidation bromine extraction process, calcium and magnesium ions are prone to form hydroxide precipitates on the cathode surface, leading to electrode scaling, decreased current efficiency, increased electrolysis voltage, and frequent equipment shutdowns for cleaning; in the alkaline extraction lithium extraction process, calcium and magnesium ions will irreversibly combine with the extractant, leading to extractant poisoning and decreased selectivity. (2) Mismatch in process sequence. However, in the alkaline lithium extraction process (pH usually > 11), bromine ions are easily oxidized or volatilized and lost, resulting in a decrease in bromine recovery rate; at the same time, the lithium extractant may be contaminated by bromine oxides or brominated byproducts, accelerating extractant aging. Some processes adopt the sequence of bromine extraction followed by lithium extraction. However, if the brine before bromine extraction is not thoroughly cleaned, calcium and magnesium ions will still cause electrode scaling during the electro-oxidation process; and if the brine after bromine extraction is directly used for alkaline extraction, the residual calcium and magnesium will still cause extractant poisoning. (3) Lack of technical gaps in synergistic design. In existing technologies, the three units of impurity removal, bromine extraction, and lithium extraction are often treated separately, lacking systematic synergistic design. For example, conventional precipitation impurity removal can only reduce calcium and magnesium to tens of milligrams per liter, which is difficult to meet the requirements of electro-oxidation for scale-free conditions and alkaline extraction for high-purity feed (the scale critical value is usually 10-20 mg / L for calcium ions and 5-10 mg / L for magnesium ions); the electro-oxidation bromine extraction process does not consider creating favorable conditions for subsequent extraction; and the design of the alkaline extraction system does not make full use of the pretreatment effects of front-end impurity removal and bromine extraction.

[0004] Therefore, how to overcome the "dual dilemma of impurity interference" and the "mutual constraints of process sequence" and develop a method that can protect both the electrode and the extractant and synergistically process lithium bromine resources is a key problem that urgently needs to be solved in the current technical field. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for the synergistic extraction of bromine and lithium from oil and gas field brines. It aims to solve problems such as electrode scaling, extractant poisoning, poor process compatibility, and low recovery rate that exist in the recovery of bromine and lithium from oil and gas field brines in existing technologies.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for co-extracting bromine and lithium from brine in oil and gas fields, characterized by comprising the following steps: Step S1, Deep impurity removal: Deep impurity removal: The oil and gas field brine is treated to remove impurities to obtain purified brine with calcium ion concentration below 5 mg / L and magnesium ion concentration below 2 mg / L. Step S2, Electro-oxidation for bromine extraction: The pH of the purified brine obtained in step S1 is adjusted to acidic, and electrolytic oxidation is performed to selectively oxidize bromide ions into elemental bromine; during the electrolysis process, elemental bromine is blown out by air stripping and absorbed by the absorbent to obtain bromine product, and debromination tail water is obtained at the same time. Step S3, Alkaline Extraction for Lithium Extraction: The pH of the debromination tailwater obtained in Step S2 is adjusted to alkaline, and extraction is performed using a synergistic extraction system containing a main extractant and a space configuration modifier. After back-extraction, a lithium-rich solution is obtained. The main extractant is a multi-branched alkyl-substituted cycloalkanoic acid derivative with the general structural formula RC. 10 H 15 O2, where R is C8-C 16 The multi-branched alkyl group has a branching degree ≥2; the space configuration regulator is an aryl carboxylic acid derivative with a large sterically hindered group; the mass ratio of the main extractant to the space configuration regulator is (3-5):1; Step S4, Lithium product preparation: The lithium-rich liquid obtained in step S3 is concentrated, precipitated or crystallized to obtain the lithium product.

[0007] As a preferred embodiment of the present invention, in step S1, the deep impurity removal includes sequential multi-stage precipitation and chelating resin adsorption.

[0008] As a preferred embodiment of the present invention, the multi-stage precipitation is a three-stage precipitation, comprising: 1a) primary precipitation: adjusting the pH to 6.5-7.5 and adding sodium carbonate to precipitate calcium ions; 1b) secondary precipitation: adjusting the pH of the first filtrate to 8.5-9.5 and adding a mixture of sodium hydroxide and sodium phosphate to precipitate magnesium and manganese ions; 1c) tertiary precipitation: adjusting the pH of the second filtrate to 10.5-11.5 and adding sodium carbonate for deep calcium removal.

[0009] As a preferred embodiment of the present invention, the chelating resin is an iminodiacetic acid type or an aminophosphate type chelating resin.

[0010] As a preferred embodiment of the present invention, the electro-oxidation bromine extraction in step S2 adopts a synergistic self-cleaning control method, including electrolysis using a three-stage adaptive potential control strategy: during the start-up phase, a voltage of 1.4-1.6 V vs. SCE is applied for 5-15 minutes; during the main oxidation phase, the voltage is adaptively adjusted to 1.0-1.3 V vs. SCE based on the real-time detected bromide ion concentration; during the deep oxidation phase, when the bromide ion concentration is <50 mg / L, a pulse voltage of 1.5-1.7 V vs. SCE is applied, with a pulse frequency of 0.1-1 Hz.

[0011] As a preferred embodiment of the present invention, in step S2, the current efficiency and inter-electrode voltage during the electrolysis process are monitored in real time. When the current efficiency decreases by more than 5% or the inter-electrode voltage increases by more than 10%, the reverse flushing procedure is automatically triggered.

[0012] As a preferred embodiment of the present invention, the space configuration modifier is selected from one or more of 2-(diphenylmethyl)-phenoxyacetic acid and 2-(di(4-alkylphenyl)methyl)-phenoxyacetic acid.

[0013] As a preferred embodiment of the present invention, the extraction in step S3 is carried out under alkaline conditions, with an extraction pH of 10-13; the number of stages of multi-stage countercurrent extraction is 2-4, the extraction ratio O / A is (1:1)-(3:1), and the extraction temperature is 10-40℃; the back-extraction uses hydrochloric acid or sulfuric acid solution, with a back-extraction agent concentration of 0.5-2.0 mol / L.

[0014] Explanation of extraction principle In step S3 of this invention, a naphthenic acid derivative is used as the main extractant. The mechanism for lithium extraction under alkaline conditions is a cation exchange reaction. Naphthenic acid (RCOOH) dissociates in an alkaline aqueous solution: RCOOH ⇌ RCOO⁻ + H⁺. The dissociated RCOO⁻ combines with lithium ions to form the extractant RCOOLi, which enters the organic phase. This reaction needs to be carried out under alkaline conditions to promote complete dissociation of the carboxyl group and avoid competitive extraction between H⁺ and Li⁺.

[0015] This invention introduces multi-branched alkyl groups (R groups) into the main extractant molecule to create a steric hindrance effect. The multi-branched alkyl groups construct a "steric barrier" around the extractant molecule, achieving selective recognition based on differences in ionic radii: lithium ions, with their smaller radius (0.076 nm), can easily cross the steric barrier and coordinate with carboxylate groups; sodium ions (0.102 nm), potassium ions (0.138 nm), and calcium ions (0.100 nm), due to their larger ionic radii, have difficulty entering the coordination sites. A steric configuration modifier (such as diphenylmethylphenoxyacetic acid) promotes an ordered spatial arrangement of the extractant molecules through π-π stacking or hydrophobic interactions, enhancing the stability of the steric hindrance effect.

[0016] The beneficial effects of this invention are: (I) Breakthrough in Selectivity of Extraction Systems This invention constructs an extraction environment with precise steric hindrance by compounding a specific spatial configuration modifier into the main extractant (a multi-branched naphthenic acid derivative). As shown in Examples 1-2, this synergistic extraction system exhibits extremely high selectivity for lithium ions, with a lithium-sodium separation coefficient exceeding 3500, an order of magnitude improvement over the conventional naphthenic acid extraction system (Comparative Example 4, separation coefficient approximately 350). This "size exclusion" effect based on ionic radius enables highly efficient identification of lithium even in the presence of sodium, potassium, and calcium ions.

[0017] (ii) Synergistic effect of process coupling Synergistic effect of impurity removal and electro-oxidation: The deep impurity removal step of this invention reduces calcium and magnesium ions to below 5 mg / L and 2 mg / L, respectively, creating excellent scale-free conditions for electro-oxidation bromine extraction. As shown in Example 1, the electrode cleaning cycle can be extended to more than 500 hours, which is far superior to Comparative Example 1 (72 hours) and Comparative Example 3 (72 hours), significantly reducing operation and maintenance costs.

[0018] Synergistic effect of electro-oxidation and extraction: Electro-oxidation operates under acidic conditions, which not only efficiently recovers bromine (total recovery rate >98%), but also reduces alkali consumption by 20-30% in the debromination tailwater after neutralization compared to direct neutralization of the original brine. Simultaneously, the electro-oxidation process can partially oxidize and decompose reducing organic matter in the brine, avoiding contamination of the subsequent extractant and ensuring the long-term stability of the extraction system (extraction rate decay <5% after 50 cycles).

[0019] (III) Improvement of product quality Thanks to the high selectivity of deep impurity removal and extraction at the front end, the calcium and magnesium impurity content in the final lithium product (such as lithium carbonate) can be controlled to below 10 ppm and 5 ppm respectively, with a purity of over 99.5%, meeting the needs of high-end applications.

[0020] (iv) Wide adaptability to raw materials This invention is applicable to various oil and gas field brines with lithium ion concentrations of 50-2000 mg / L, bromide ion concentrations of 100-10000 mg / L, calcium ion concentrations of ≤10 g / L, and magnesium ion concentrations of ≤5 g / L. The process parameters of each unit can be flexibly adjusted according to the quality of the raw water. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process flow of the coupled enhancement method for synergistic bromine and lithium extraction from oil and gas field brine according to the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Characteristics of the raw brine used in the examples: Raw material brine A: Li⁺ 210 mg / L, Br⁻ 450 mg / L, Cl⁻ 95 g / L, Ca²⁺ 8.5 g / L, Mg²⁺ 3.6 g / L, Mn²⁺ 0.5 g / L, Na 50 g / L, dissolved organic matter 42 mg / L, pH 7.0.

[0023] Raw material brine B: Li⁺ 580 mg / L, Br⁻ 3200 mg / L, Ca²⁺ 4.2 g / L, Mg²⁺ 1.8 g / L, Na 60 g / L, pH 6.8.

[0024] Example 1 (Basic Example, using raw material brine A) (1) Deep impurity removal 1a) Primary precipitation: Take 10 L of brine A, adjust the pH to 7.0, add sodium carbonate (the amount added is 1.3 times the molar amount of calcium ions), stir for 1.5 h, filter, and obtain the first filtrate (Ca²⁺ 1.0 g / L).

[0025] 1b) Secondary precipitation: Adjust the pH of the first filtrate to 9.0, add a mixture of sodium hydroxide and sodium phosphate (mass ratio 2.5:1, the amount added is 1.2 times the total molar amount of residual calcium, magnesium and manganese), stir for 1.5 h, filter, and obtain the second filtrate (Mg²⁺ 0.12 g / L, Mn²⁺ 0.03 g / L).

[0026] 1c) Tertiary precipitation: Adjust the pH of the second filtrate to 11.0, add sodium carbonate (the amount added is 1.2 times the molar amount of residual calcium ions), stir for 1 h, filter, and obtain the third filtrate (Ca²⁺ 0.03 g / L).

[0027] 1d) Chelating resin purification: The third filtrate was passed through an iminodiacetic acid-type chelating resin column (flow rate 5 BV / h) to obtain purified brine. Testing showed that the purified brine contained 3 mg / L Ca²⁺, 1 mg / L Mg²⁺, 98.5% Li⁺ retention, and 97.5% Br⁻ retention.

[0028] (2) Electro-oxidation for bromine extraction The purified brine was adjusted to pH 2.5 with sulfuric acid and then injected into an electro-oxidation device (titanium-based ruthenium-iridium-tin oxide coated electrode, electrode area 100 cm², electrode spacing 1.5 cm, effective volume 2 L). The initial cleaning cycle was set to 200 hours.

[0029] A three-stage adaptive potential control was adopted: in the start-up stage, 1.5 V vs. SCE was applied for 8 min; in the main oxidation stage, the voltage was adaptively adjusted to 1.0-1.3 V vs. SCE according to the online bromide ion concentration, and electrolysis was carried out for 120 min, during which the bromide ion concentration decreased from 450 mg / L to 42 mg / L; in the deep oxidation stage, when the bromide ion concentration was <50 mg / L, a pulse voltage of 1.6 V vs. SCE with a frequency of 0.5 Hz was applied for 15 min, during which the bromide ion concentration decreased to 6 mg / L.

[0030] During electrolysis, microporous aeration coupled with Venturi jet stripping (air flow rate 5 L / min, gas-liquid volume ratio 100:1) was used. The bromine-containing gas was absorbed with 15 wt% NaOH to obtain a sodium bromide solution (containing approximately 36 g / L of bromine). After acidification, the sodium bromide solution was oxidized with chlorine and then distilled to obtain the bromine product. The total bromine recovery rate was 98.5%.

[0031] After 200 hours of operation, the current efficiency decreased by 4.2%, and the inter-electrode voltage increased by 6%, but cleaning was not triggered. After 500 hours of operation, the current efficiency decreased by 5.8%, triggering backflushing (pure water backflushing for 5 minutes). After flushing, the current efficiency recovered to 98% of the initial value.

[0032] (3) Lithium extraction by alkaline extraction Preparation of the extraction system: Main extractant: multi-branched cycloalkanoic acid derivative (R is C 12 Multi-branched alkyl group (branching degree 2.5) 15 vol%, 2-(diphenylmethyl)-phenoxyacetic acid 3 vol%, phase modifier 2-octanol 5 vol%, sulfonated kerosene 77 vol% (main extractant: space configuration modifier mass ratio approximately 4:1).

[0033] The pH of the debromination tailwater was adjusted to 12.5 (alkaline conditions) with NaOH, filtered, and the original extract was obtained (Li⁺ 205 mg / L, Na⁺ 14 g / L, Ca²⁺ < 1 mg / L, Mg²⁺ < 1 mg / L).

[0034] Two-stage countercurrent extraction was performed at an O / A ratio of 2:1, at 25°C, with each stage lasting 10 min. The raffinate aqueous phase contained 6 mg / L Li⁺ and 14 g / L Na⁺, with an extraction efficiency of 97.1%. The supported organic phase was back-extracted with 1.2 mol / L HCl (O / A ratio of 2:1, at 25°C, for 10 min) to obtain a lithium-rich back-extract (Li⁺ 2.1 g / L, Na⁺ 0.08 g / L, lithium-sodium separation coefficient approximately 3800). After 50 cycles of extractant recycling, the raffinate contained 9 mg / L Li⁺, with an extraction efficiency of 95.6%, representing a decrease of 1.5%.

[0035] (4) Lithium product preparation The lithium-rich back-extraction solution was concentrated 6 times (2.2 MPa) by nanofiltration. Sodium carbonate (1.1 times the molar amount of Li⁺) was added to the concentrate, and the reaction was carried out at 90°C for 1 hour. After filtration, washing, and drying, lithium carbonate was obtained. Analysis showed that the lithium carbonate purity was 99.5%, the calcium content was 8 ppm, and the magnesium content was 3 ppm. The total lithium recovery rate was 92.5%.

[0036] Example 2 (different regulators, using raw material brine A) The experiment was essentially the same as in Example 1, except that the steric morphology modifier used was 2-(di(4-methylphenyl)methyl)-phenoxyacetic acid. The lithium extraction rate was 96.8%, the raffinate contained 7 mg / L Li⁺, the lithium-sodium separation coefficient was approximately 3900, the extraction rate was 95.1% after 50 extraction cycles, the lithium carbonate purity was 99.4%, calcium was 9 ppm, and magnesium was 4 ppm.

[0037] Example 3 (Verifying the effect of potential control, using raw material brine A) It is basically the same as Example 1, except that step S2 uses constant potential 1.2 V vs. SCE electrolysis (omitting the three-stage adaptive control).

[0038] The total bromine recovery rate was 88.5%, and cleaning was triggered after 300 hours of operation. The total lithium recovery rate was 90.2%.

[0039] Example 4 (Verifying the effect of extractant ratio, using raw material brine A) This is essentially the same as Example 1, except that the mass ratio of the main extractant to the steric morphology modifier was changed. The results are as follows: With a mass ratio of 6:1:1 and raffinate containing 15 mg / L Li⁺, the extraction rate was 92.7%, and the lithium-sodium separation coefficient was approximately 1200. Mass ratio 4:1 (Example 1): Raffinate Li⁺ 6 mg / L, extraction rate 97.1%, lithium-sodium separation coefficient approximately 3800. With a mass ratio of 2:1 and raffinate containing 21 mg / L Li⁺, the extraction rate was 89.8%, and the lithium-sodium separation coefficient was approximately 800. The results showed that the optimal extraction performance could be obtained when the ratio of the main extractant to the regulator was in the range of (3-5):1.

[0040] Example 5 (Verifying adaptability to different water qualities, using raw material brine B) Using raw material brine B, the operation was carried out according to the steps of Example 1.

[0041] The brine was purified after deep impurity removal: Ca²⁺ 4 mg / L, Mg²⁺ 1.5 mg / L, and Li⁺ retention rate 98.7%.

[0042] Electro-oxidation for bromine extraction: initial bromine concentration 3200 mg / L, bromine recovery rate after electrolysis 98.9%, electrode cleaning cycle >500 hours.

[0043] Lithium extraction by alkaline extraction: The pH of the extraction solution was adjusted to 12.5, with Li⁺ 572 mg / L and the raffinate Li⁺ 12 mg / L. The extraction rate was 97.9%, and the lithium-sodium separation coefficient was approximately 3600.

[0044] Lithium carbonate product: purity 99.6%, calcium 7 ppm, magnesium 3 ppm, total lithium recovery rate 93.1%.

[0045] Example 6 (Verifying the performance of the extraction system separately, using a simulated feed solution) Prepare the simulated solution: Li⁺ 500 mg / L, Na⁺ 15 g / L, K⁺ 2 g / L, Ca²⁺ 50 mg / L, Mg²⁺ 30 mg / L, and adjust the pH to 12.5 with NaOH.

[0046] Single-stage extraction was performed using the extraction system described in Example 1, with a ratio of O / A = 2:1, at 25°C, and a mixing time of 10 min. The lithium extraction rate was measured to be 96.8%, the raffinate Li⁺ concentration was 16 mg / L, and the lithium-to-sodium ratio in the supported organic phase was >150:1, confirming that the extraction system exhibits excellent selectivity for lithium under alkaline conditions and is unaffected by interference from other ions.

[0047] Comparative Example 1 (without deep impurity removal) Raw brine A was subjected to conventional precipitation and impurity removal (pH 11.0, sodium carbonate added) to obtain preliminarily purified brine (Ca²⁺ 120 mg / L, Mg²⁺ 85 mg / L). Subsequent steps were the same as in Example 1.

[0048] Electro-oxidation for bromine extraction: After 72 hours of operation, the current efficiency decreased by 15%, the inter-electrode voltage increased by 22%, triggering cleaning, and the bromine recovery rate was 85.2%.

[0049] Alkaline extraction: Using the extraction system of Example 1, the raffinate contained 22 mg / L Li⁺, and the extraction rate was 89.5%. After 10 cycles of extraction, the extraction rate decreased to 71.5%.

[0050] The purity of lithium carbonate was 98.2%, calcium was 85 ppm, magnesium was 42 ppm, and the total lithium recovery rate was 70.3%.

[0051] Comparative Example 2 (Lithium extraction first, then bromine extraction) Raw brine A was purified by precipitation (same as steps 1a-1c in Example 1) to obtain preliminarily purified brine (Ca²⁺ 30 mg / L, Mg²⁺ 12 mg / L). Lithium was first extracted using the extraction system of Example 1 under alkaline conditions, during which a distinct bromine odor was observed. The raffinate contained 15 mg / L Li⁺, with an extraction rate of 92.9%. After lithium extraction, the tail water was electro-oxidized to extract bromine, with a bromine recovery rate of 86.5%. The overall lithium recovery rate was 81.2%, and the extraction rate decreased by 15% after 5 cycles of extractant circulation.

[0052] Comparative Example 3 (Refined with non-chelating resin) Step 1 of Example 1 is omitted (1 day). After three-stage precipitation, the purified brine has Ca²⁺ 30 mg / L and Mg²⁺ 12 mg / L. Subsequent steps are the same as in Example 1.

[0053] Electro-oxidation: After 72 hours of operation, the current efficiency decreased by 8.5%, the inter-electrode voltage increased by 15%, and cleaning was triggered.

[0054] Extraction: Slight emulsification occurred. After 15 cycles of extractant circulation, the Li⁺ concentration in the raffinate increased from 8 mg / L to 18 mg / L, and the extraction rate decreased by 12%.

[0055] Lithium recovery rate: 82.5%; Lithium carbonate: calcium: 42 ppm; Magnesium: 18 ppm.

[0056] Comparative Example 4 (Conventional Naphthenic Acid Extraction) Conventional naphthenic acid (without multi-branched structure) was used instead of the main extractant in Example 1, and no steric morphology modifier was added; otherwise, it was the same as in Example 1.

[0057] The raffinate contained 22 mg / L Li⁺, with an extraction rate of 89.5% and a lithium-sodium separation coefficient of approximately 350. After 20 cycles of extractant circulation, the raffinate contained 35 mg / L Li⁺, with an extraction rate of 82.5%. The lithium recovery rate was 80.2%, and the lithium carbonate calcium content was 25 ppm, while the magnesium content was 12 ppm.

[0058] Comparative Example 5 (only multi-branched cycloalkanoic acid, no steric configuration modifier) The same main extractant as in Example 1 was used, but no space configuration modifier was added. Other components and conditions remained the same as in Example 1.

[0059] The raffinate concentration of Li⁺ in the aqueous phase was 21 mg / L, with a lithium extraction rate of 89.3%; the lithium-sodium separation coefficient was approximately 920. After the extractant was recycled 20 times, the concentration of Li⁺ in the raffinate increased to 31 mg / L, and the extraction rate decreased to 84.8%.

[0060] Indicator Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Example 1 Example 5 Bromine recovery 85.20% 86.50% 87.30% 88.20% 88.20% 98.50% 98.9% Lithium recovery 70.30% 81.20% 82.50% 80.20% 89.3% 92.50% 93.1% Extractant lifetime 10 cycles 8 cycles 15 cycles 20 cycles 20 cycles >50 cycles >50 cycles Electrode cleaning cycles 72h 96h 72h 500h 500h >500h >500h Calcium content of lithium product 85 ppm 65 ppm 42 ppm 25 ppm 20 ppm 8 ppm 7 ppm Magnesium content of lithium product 42 ppm 28 ppm 18 ppm 12 ppm 8 ppm 3 ppm 3 ppm Lithium-sodium separation factor - - - ~350 ~920 ~3800 ~3600 The above results demonstrate that this invention, through the synergistic combination of deep impurity removal and a structured extraction system, achieves highly efficient recovery of bromine and lithium under alkaline conditions. All performance indicators are significantly superior to existing technologies. The synergistic extraction system of this invention exhibits extremely high selectivity for lithium ions, with a lithium-sodium separation coefficient exceeding 3500. Compared to the conventional naphthenic acid extraction system (Comparative Example 4, separation coefficient approximately 350), the selectivity is improved by approximately 10 times. Compared to the system containing only multi-branched naphthenic acids without a regulator (New Comparative Example, separation coefficient approximately 920), the introduction of the regulator further improves the selectivity by approximately 4 times. This indicates that the specific compound system of this invention produces a significant synergistic effect, achieving highly efficient selective recognition based on differences in ionic radii.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for co-extracting bromine and lithium from brine in oil and gas fields, characterized in that: Includes the following steps: S1. Deep impurity removal: The brine from the oil and gas field is treated to remove impurities, resulting in purified brine with calcium ion concentration below 5 mg / L and magnesium ion concentration below 2 mg / L. S2, Electro-oxidation for bromine extraction: The purified brine obtained in step S1 is adjusted to acidity and subjected to electrolytic oxidation to oxidize bromide ions into elemental bromine and recover it to obtain debrominated tailwater. S3, Alkaline extraction for lithium extraction: The debromination tail water obtained in step S2 is adjusted to alkaline, and extraction is carried out using a synergistic extraction system containing a main extractant and a space configuration modifier. After back-extraction, a lithium-rich solution is obtained. The main extractant is a multi-branched alkyl-substituted cycloalkanoic acid derivative with the general structural formula RC. 10 H 15 O2, where R is C8-C 16 Multi-branched alkyl groups with a degree of branching ≥2; The space configuration regulator is an aryl carboxylic acid derivative with a large steric hindrance group; The mass ratio of the main extractant to the space configuration modifier is (3-5):1; S4. Lithium product preparation: Prepare lithium products from the lithium-rich liquid obtained in step S3.

2. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 1, characterized in that: The deep impurity removal described in step S1 includes sequential multi-stage precipitation and chelating resin adsorption.

3. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 2, characterized in that: The multi-stage precipitation is a three-stage precipitation, including: 1a) Primary precipitation: Adjust the pH to 6.5-7.5, add sodium carbonate to precipitate calcium ions, and separate the solid and liquid to obtain the first filtrate; 1b) Secondary precipitation: Adjust the pH of the first filtrate to 8.5-9.5, add a mixture of sodium hydroxide and sodium phosphate to precipitate magnesium and manganese ions, and separate the solid and liquid to obtain the second filtrate; 1c) Tertiary precipitation: Adjust the pH of the second filtrate to 10.5-11.5, add sodium carbonate for deep calcium removal, and separate the solid and liquid to obtain the third filtrate.

4. The method for synergistic bromine and lithium extraction from oil and gas field brine according to claim 2, characterized in that: The chelating resin is an iminodiacetic acid type or an aminophosphate type chelating resin.

5. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 1, characterized in that: The electro-oxidation bromine extraction described in step S2 employs a synergistic self-cleaning control method, including a three-stage adaptive potential control strategy for electrolysis: during the start-up phase, a voltage of 1.4-1.6 V vs. SCE is applied for 5-15 minutes; during the main oxidation phase, the voltage is adaptively adjusted to 1.0-1.3 V vs. SCE based on the real-time detected bromide ion concentration; and during the deep oxidation phase, when the bromide ion concentration is <50 mg / L, a pulse voltage of 1.5-1.7 V vs. SCE is applied, with a pulse frequency of 0.1-1 Hz.

6. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 5, characterized in that: In step S2, the current efficiency and inter-electrode voltage during the electrolysis process are monitored in real time. When the current efficiency drops by more than 5% or the inter-electrode voltage rises by more than 10%, the reverse flushing procedure is automatically triggered.

7. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 1, characterized in that: The space configuration modifier is selected from one or more of 2-(diphenylmethyl)-phenoxyacetic acid and 2-(di(4-alkylphenyl)methyl)-phenoxyacetic acid.

8. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 1, characterized in that: The extraction described in step S3 is carried out under alkaline conditions with an extraction pH of 10-13; the number of stages in the multi-stage countercurrent extraction is 2-4, the extraction ratio O / A is (1:1)-(3:1), and the extraction temperature is 10-40℃; the back-extraction uses hydrochloric acid or sulfuric acid solution with a back-extraction agent concentration of 0.5-2.0 mol / L.

9. The method for co-extracting bromine and lithium from oil and gas field brine according to claim 1, characterized in that: The deep impurity removal in step S1 extends the electrode cleaning cycle of the electro-oxidation bromine extraction in step S2 to more than 500 hours; the deep impurity removal in step S1 and the electro-oxidation bromine extraction in step S2 together ensure that the extraction rate decreases by less than 5% after the extractant in step S3 is recycled 50 times.

10. A method for co-extracting bromine and lithium from oil and gas field brine according to any one of claims 1-9, characterized in that: The oil and gas field brine contains lithium ion concentrations of 50-2000 mg / L, bromide ion concentrations of 100-10000 mg / L, calcium ion concentrations of ≤10 g / L, and magnesium ion concentrations of ≤5 g / L.

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