Extraction system and method for extracting and enriching lithium from lithium-containing sodium sulfate solution

Abstract

The invention provides an extraction system and method for extracting and enriching lithium from a lithium-containing sodium sulfate solution. The extraction system comprises an extraction agent, a synergistic extraction agent, a diluent and a modifier, and the extraction agent is salicylamide as shown in a formula (I); the synergistic extractant is a neutral organic phosphorus compound with lithium coordination capability. According to the method, salicylamide is used as an extraction agent, phosphorus-containing reagents such as tributyl phosphate are used as a synergistic extraction agent, the extraction agent and other organic solvents are used for constructing an extraction system, lithium ions are extracted from a lithium-containing sodium sulfate solution, and then washing and reverse extraction are carried out, so that the ions are finally enriched in reverse extraction liquid. Compared with beta-diketone and salicylate lithium extraction, the method has the characteristics of stable chemical structure, mild synthetic route and cheap and easily available raw materials.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal hydrometallurgical technology, specifically relating to an extraction system and method for extracting and enriching lithium from a lithium-containing sodium sulfate solution. Background Technology

[0002] With the rapid development of the new energy industry, the demand for lithium, as a key resource, has exploded. Efficiently separating and extracting lithium from complex systems such as lithium-containing brine and ore leachate has become a core research topic in the industry. Among numerous lithium extraction technologies, solvent extraction has become the mainstream method for lithium enrichment and purification due to its advantages such as simple operation, high separation efficiency, and ease of large-scale application. Currently, the mainstream lithium extractants on the market are based on β-diketone compounds produced by companies such as BASF. These extractants rely on their unique enol tautomer structure to form a six-membered ring with hydrogen bonds to capture lithium ions and can synergistically complex lithium ions with neutral organophosphorus reagents to achieve lithium extraction and enrichment, which has been widely used in the industrial lithium extraction field.

[0003] However, β-diketone extractants face significant technical bottlenecks in practical applications. To ensure lithium extraction efficiency, the extraction equilibrium system of these extractants typically requires maintaining a strongly alkaline environment with a pH > 12.5. This not only significantly increases alkali consumption during production and raises process costs, but also leads to severe dissolution and loss of the extractant itself under high pH conditions, resulting in a substantial decrease in stability. This not only reduces the recycling rate of the extractant but also generates a large amount of wastewater containing the extractant, significantly increasing the difficulty and cost of subsequent wastewater treatment. Meanwhile, some studies have attempted to borrow the lithium extraction structure of β-diketones, replacing the carbonyl group with a benzene ring phenolic hydroxyl group to develop salicylaldehyde and salicylate extractants. While these extractants show some lithium extraction potential, they are limited by the chemical properties of the aldehyde or ester groups, making it difficult to maintain structural stability in strongly acidic and alkaline industrial applications, hindering recycling. Furthermore, their molecular structure control space is limited, making them unsuitable for complex and variable practical lithium extraction systems.

[0004] Besides the aforementioned extractants, the industry has developed various lithium extractants such as crown ethers, ionic liquids, and organophosphorus compounds, but each has its own technical shortcomings. Crown ether extractants involve complex synthesis steps, requiring multiple organic synthesis reactions, resulting in high production costs and hindering large-scale industrial application. Ionic liquid extractants suffer from high viscosity, increasing mass transfer resistance during extraction, reducing extraction efficiency and separation speed, and are difficult and costly to recover, limiting their application scope. Organophosphorus extractants easily compete with impurity ions such as magnesium and sodium for adsorption, resulting in low magnesium-lithium separation efficiency, requiring complex pretreatment processes or multi-stage extraction procedures, increasing process complexity and production costs. Furthermore, existing mainstream extraction systems lack selectivity for lithium, sodium, and potassium ions, especially potassium ions, directly affecting the purity of the final lithium product. Therefore, developing a structurally stable, recyclable lithium extraction system that is adaptable to complex environments and possesses both high extraction efficiency and high selectivity has become an urgent need to address the current pain points in the lithium separation and extraction industry. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides an extraction system for extracting and enriching lithium from a lithium-containing sodium sulfate solution, using salicylamide as the extractant, phosphorus-containing reagents such as tributyl phosphate as co-extractants, and constructing the extraction system with other organic solvents to extract lithium ions from the lithium-containing sodium sulfate solution, and then enriching the ions in the back-extraction solution through washing and back-extraction.

[0006] The present invention also provides a method for extracting and enriching lithium from a lithium-containing sodium sulfate solution using the extraction system of the present invention.

[0007] A first aspect of the present invention provides an extraction system for enriching lithium from a lithium-containing sodium sulfate solution, comprising an extractant, a co-extractant, a diluent, and a modifier, wherein the extractant is salicylamide as shown in formula (I).

[0008] In formula (I), R1 is hydrogen or a C2 to C8 alkyl group, R2 is a C2 to C8 alkyl group, cyclohexyl or benzyl, and R3, R4 and R5 are each independently selected from hydrogen, nitro, halogen, acetyl or C1 to C4 alkyl group. The co-extractant is a neutral organophosphorus compound with lithium coordination ability.

[0009] The extraction system of the present invention has at least the following beneficial effects: The extractant has a stable structure and is suitable for strong acid and alkaline environments. The salicylamide extractant of formula (I) contains amide bonds in its molecular structure, which can stabilize the chemical properties of the carbonyl group in the lithium six-membered ring. Compared with the β-diketone extractants in the prior art (which require a strong alkaline environment of pH>12.5 and are easily dissolved and lost) and salicylaldehyde / salicylic acid ester extractants (the aldehyde / ester group is easily deactivated under strong acid and alkaline conditions), it can maintain its structural integrity in the pH 8-13 environment required for lithium sodium sulfate solution extraction, and is not easily deactivated. This greatly improves the stability of the extraction system, while reducing the cost increase and wastewater treatment difficulty caused by extractant loss.

[0010] The extractant structure is flexible and adjustable to meet complex application requirements. Formula (I) salicylamide has four modification sites, R1-R5, on its benzene ring. By controlling the substituents of R1-R5 (e.g., R1 can be a C2-C8 alkyl group with different carbon chain lengths, R3 can be a nitro / halogen group, etc.), the electron density of the phenolic hydroxyl oxygen atom and the physicochemical properties of the extractant itself, such as melting point, solubility, and viscosity, can be flexibly adjusted. Compared to crown ether extractants (complex synthesis) and ionic liquid extractants (high viscosity) with fixed structures that are difficult to adapt to various scenarios, this extractant can be customized to suit complex application environments with different lithium-sodium concentration ratios (e.g., 0.1-5 g / L lithium, 3-150 g / L sodium) and different impurity contents in lithium-containing sodium sulfate solutions, ensuring extraction efficiency.

[0011] The co-extractant, as defined in this invention, is a neutral organophosphorus compound with lithium coordination ability. It forms a synergistic complex with salicylamide extractant. Salicylamide captures lithium ions through a six-membered ring hydrogen bond, while the neutral organophosphorus compound further enhances its complexation ability for lithium ions. This approach retains the high-efficiency lithium ion extraction performance of existing β-diketone extractants while simultaneously improving the selectivity for lithium and sodium in lithium-containing sodium sulfate solutions through a synergistic effect. Compared to the drawback of organophosphorus extractants competing with impurity ions such as sodium when used alone, this synergistic system reduces sodium ion co-extraction, laying the foundation for obtaining high-purity lithium products.

[0012] The system exhibits excellent component compatibility, balancing efficiency and economy. The combination of extractants, co-extractants, diluents, and modifiers within the system demonstrates strong compatibility in component selection. The extractant (I) salicylamide can be prepared via a mild synthetic route using salicylic acid / salicylic esters and organic amine reagents (C2-C8 alkylamines, cyclohexylamine, benzylamine, etc., corresponding to the R2 structure). The raw materials are inexpensive and readily available, resulting in a lower synthesis cost compared to crown ether extractants (multi-step organic synthesis). Co-extractants (such as TRPO, TBP, etc.), diluents (non-toxic or low-toxic reagents such as sulfonated kerosene), and modifiers (organic alcohols / amines / amides) are all conventional chemical raw materials, readily available and cost-effective. Furthermore, the modifiers can adjust the system viscosity and improve phase separation. Combined with the synergistic effect of the co-extractants and extractants, this approach reduces the overall application cost of the system while ensuring extraction efficiency, facilitating large-scale industrial application.

[0013] According to some embodiments of the present invention, the extractant includes at least one selected from 2-hydroxy-N-(octyl-3-yl)benzamide, 4-fluoro-2-hydroxy-N-(octyl-3-yl)benzamide, and 2-hydroxy-N,N-di(octyl-3-yl)benzamide.

[0014] According to some embodiments of the present invention, the neutral organophosphorus compound with lithium coordination capability includes at least one of TRPO (trialkylphosphine oxide), TBP (tributyl phosphate), and TOP (trioctyl phosphate).

[0015] According to some embodiments of the present invention, the volume fraction of the neutral organophosphorus compound with lithium coordination ability is 40-60%.

[0016] According to some embodiments of the present invention, the volume fraction of the diluent is 40-60%.

[0017] According to some embodiments of the present invention, in the extraction system, the volume fraction of the diluent is any one of 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, and 60%, such as 50%, or a range of any two, such as 45% to 55%.

[0018] According to some embodiments of the present invention, the diluent includes at least one of sulfonated kerosene, white oil, and n-heptane.

[0019] According to some embodiments of the present invention, the modifier includes one of organic alcohols, amines, and amides.

[0020] According to some embodiments of the present invention, the modifier includes at least one selected from isooctyl alcohol, isooctylamine, diisooctylamine, and N,N-bis(1-methylheptyl)acetamide.

[0021] According to some embodiments of the present invention, the concentration of the extractant in the extraction system is 0.2~0.6 mol / L.

[0022] According to some embodiments of the present invention, in the extraction system, the concentration of the extractant is any value among 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L, such as 0.4 mol / L, or any range formed by both, such as 0.3 mol / L to 0.5 mol / L.

[0023] According to some embodiments of the present invention, the concentration of the co-extractant in the extraction system is 0.2~0.6 mol / L.

[0024] According to some embodiments of the present invention, in the extraction system, the concentration of the co-extractant is any value among 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L, such as 0.4 mol / L, or any range formed by both, such as 0.3 mol / L to 0.5 mol / L.

[0025] According to some embodiments of the present invention, the concentrations of the extractant and the co-extractant are the same in the extraction system.

[0026] The extraction system, apart from the extractant and co-extractant, consists entirely of diluent and modifier. There are no special requirements for the ratio of diluent and modifier. In the entire extraction system, it is only necessary to ensure that the ratio of extractant to co-extractant is 1:1.

[0027] According to some embodiments of the present invention, the extraction system may be 0.2 mol / L of hydroxy-N-(octyl-3-yl)benzamide + 0.2 mol / L of TRPO, with the remainder being sulfonated kerosene as a diluent; or 0.4 mol / L of 4-fluoro-2-hydroxy-N-(octyl-3-yl)benzamide + 0.4 mol / L of TRPO 60%, with the remainder being sulfonated kerosene as a diluent.

[0028] A second aspect of the present invention provides a method for extracting and enriching lithium from a lithium-containing sodium sulfate solution using the extraction system of the first aspect of the present invention, comprising the following steps: S1: Adjust the pH of the lithium-containing sodium sulfate solution to 8-13; S2: Add the extraction system to the solution in step S1 to extract lithium ions and separate the upper lithium-ion-loaded first organic phase and the raffinate. S3: Wash the organic phase to obtain a second organic phase and washing wastewater; S4: The second organic phase is back-extracted with acid to obtain a lithium-enriched solution.

[0029] The method of the present invention has at least the following beneficial effects: First, the pH adjustment is highly adaptable, balancing efficiency and cost. Step S1 adjusts the pH of the lithium-containing sodium sulfate solution to 8-13, which not only meets the environmental requirements for efficient lithium extraction using the salicylamide extractant of formula (I), but also avoids the high alkali consumption problem caused by the existing β-diketone extractants requiring strongly alkaline conditions of pH>12.5. This pH range ensures the extractant's ability to capture lithium ions, while reducing the amount of alkali used, lowering process costs, and adapting to fluctuations in the lithium-sodium concentration ratio (0.1-5 g / L lithium, 3-150 g / L sodium) in the lithium-containing sodium sulfate solution, thus improving the method's adaptability to the feed solution.

[0030] Secondly, the extraction and separation are highly targeted, improving lithium enrichment efficiency. Step S2 achieves lithium ion extraction through the extraction system of the first aspect of this invention (salicylamide + neutral organophosphorus compound co-extractant, etc.). The synergistic complexation of salicylamide and the co-extractant can accurately capture lithium ions, reducing the entry of sodium ions and other impurity ions (such as trace amounts of calcium and magnesium ions accompanied by sulfate) into the first organic phase. Compared with the competitive adsorption defects of organophosphorus extractants used alone, this significantly improves the selectivity of lithium-sodium separation, laying a high-purity foundation for subsequent lithium enrichment. At the same time, the main component of the separated raffinate is sodium sulfate, which is discharged after treatment to meet standards, without secondary resource waste.

[0031] Third, the washing process removes impurities in a targeted manner, ensuring product purity. Step S3, washing the first organic phase, effectively removes trace amounts of sodium sulfate, residual impurity ions, and small amounts of water-soluble impurities, resulting in a second organic phase with higher purity. This step prevents impurities from entering the subsequent back-extraction process with the organic phase, solving the problem of insufficient purity in the lithium-enriched solution caused by impurity residues in existing extraction processes. It ensures that the lithium purity in the final lithium-enriched solution meets the requirements of subsequent processing, reducing the complexity and cost of subsequent purification steps.

[0032] Fourth, the back-extraction process is simple and efficient, achieving resource recycling and economic benefits. Step S4 uses acid to back-extract the second organic phase, which is simple to operate and operates under mild conditions (no high temperature or high pressure required). It can efficiently transfer lithium ions from the organic phase to the aqueous phase to form a lithium-rich solution. The organic phase obtained after back-extraction (containing salicylamide, co-extractant, etc.) can be returned to step S2 for recycling after washing with water. Compared with the problems of difficult recovery of ionic liquid extractants and high cost of crown ether extractants, this significantly improves the recycling rate of the extraction system and reduces the cost of extractant loss. At the same time, the lithium-rich solution obtained from back-extraction can be directly used for the preparation of subsequent lithium products (such as lithium carbonate and lithium hydroxide), shortening the production process and improving the economic benefits and industrial feasibility of the process.

[0033] According to some embodiments of the present invention, the lithium-containing sodium sulfate solution may be a solution with a lithium ion concentration of 0.1-5 g / L and a sodium ion concentration of 3-150 g / L.

[0034] According to some embodiments of the present invention, in step S1, the reagent for adjusting the pH includes a sodium hydroxide solution. Sodium hydroxide is used to adjust the pH value in order to maintain a hydroxide ion concentration of 1-20 mol / L in the solution.

[0035] According to some embodiments of the present invention, in step S2, the temperature for extracting lithium ions is 10~60°C.

[0036] According to some embodiments of the present invention, in step S2, the temperature for extracting lithium ions is any value among 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C, such as 30°C, or any range formed by both, such as 25°C to 35°C.

[0037] According to some embodiments of the present invention, in step S2, the temperature for extracting lithium ions is 20~40°C.

[0038] According to some embodiments of the present invention, in step S2, the extraction time for extracting lithium ions is 2 to 30 minutes.

[0039] According to some embodiments of the present invention, in step S2, the extraction time for extracting lithium ions is any value among 2 min, 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 23 min, 25 min, 28 min, and 30 min, such as 15 min, or any range formed by both, such as 10 min to 20 min.

[0040] According to some embodiments of the present invention, in step S2, the extraction time for extracting lithium ions is 5 to 15 minutes.

[0041] According to some embodiments of the present invention, in step S2, the extraction flow ratio for extracting lithium ions is (0.2~10):1.

[0042] According to some embodiments of the present invention, in step S2, the extraction flow ratio for extracting lithium ions is any value among 0.2:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1, such as 3:1, or any range of two such values, such as 1:1 to 5:1.

[0043] According to some embodiments of the present invention, in step S2, the extraction flow ratio (O / A ratio) for extracting lithium ions is (4~10):1.

[0044] According to some embodiments of the present invention, in step S2, the extraction flow ratio (O / A ratio) for extracting lithium ions is any value among 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1, such as 7:1, or any range of two, such as 5:1 to 8:1.

[0045] According to some embodiments of the present invention, the raffinate produced after lithium ion extraction in step S2 is mainly composed of sodium sulfate, which has no economic value and is discharged after treatment to meet the standards.

[0046] According to some embodiments of the present invention, in step S4, the lithium content in the lithium-containing enrichment solution is 0.1 g / L to 1 g / L.

[0047] According to some embodiments of the present invention, in step S4, the acid is 0.1-0.5 mol / L hydrochloric acid.

[0048] According to some embodiments of the present invention, in step S4, the acid is any value among 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, and 0.5 mol / L, such as 0.3 mol / L, or any range formed by both, such as 0.2 mol / L to 0.4 mol / L.

[0049] According to some embodiments of the present invention, in step S4, the back-extraction temperature is 10~60°C.

[0050] According to some embodiments of the present invention, in step S4, the back-extraction temperature is any value among 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C, such as 30°C, or any range formed by both, such as 25°C to 35°C.

[0051] According to some embodiments of the present invention, in step S4, the back-extraction temperature is 20~40°C.

[0052] According to some embodiments of the present invention, in step S4, the back-extraction time is 2 to 30 minutes.

[0053] According to some embodiments of the present invention, in step S4, the back-extraction time is any value among 2 min, 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 23 min, 25 min, 28 min, and 30 min, such as 15 min, or any range formed by both, such as 10 min to 20 min.

[0054] According to some embodiments of the present invention, in step S4, the back-extraction time is 5 to 15 minutes.

[0055] According to some embodiments of the present invention, in step S4, the back-extraction flow ratio (O / A ratio) is (0.2~10):1.

[0056] According to some embodiments of the present invention, in step S4, the back-extraction flow ratio (O / A ratio) is any value among 0.2:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1, such as 3:1, or any range of two such values, such as 1:1 to 5:1.

[0057] According to some embodiments of the present invention, in step S4, the back-extraction flow ratio (O / A ratio) is (5~10):1.

[0058] According to some embodiments of the present invention, in step S4, the resulting back-extracted organic phase can be washed with water and returned to step S2 to achieve the recycling of the extractant. Attached Figure Description

[0059] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0060] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0061] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0063] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0064] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0065] Example 1 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, the process is as follows: Figure 1 As shown, specifically: Preparation of the extractive organic phase: 2-hydroxy-N-(oct-3-yl)benzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of 2-hydroxy-N-(oct-3-yl)benzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0066] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0067] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.28 g / L, and the lithium ion extraction rate was calculated to be 71.31%.

[0068] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0069] Example 2 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N-hexyl-2-hydroxybenzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant. They were mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol was added as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of N-hexyl-2-hydroxybenzamide was 0.2 mol / L, the concentration of trialkylphosphine oxide was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0070] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0071] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.41 g / L, and the lithium ion extraction rate was calculated to be 58.44%.

[0072] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0073] Example 3 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N-benzyl-2-hydroxybenzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of N-benzyl-2-hydroxybenzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0074] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 0.1 g / L lithium, 3.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0075] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.06 g / L, and the lithium ion extraction rate was calculated to be 39.81%.

[0076] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0077] Example 4 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was 0.2 mol / L, the concentration of trialkylphosphine oxide was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0078] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 5.0 g / L lithium, 150.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0079] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 1.21 g / L, and the lithium ion extraction rate was calculated to be 78.81%.

[0080] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0081] Example 5 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N-(2-ethylhexyl)-2-hydroxy-N-(octyl-3-yl)benzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant. They were mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of N-(2-ethylhexyl)-2-hydroxy-N-(octyl-3-yl)benzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0082] Prepare the extraction aqueous phase: Take the mother liquor containing 1.0 g / L lithium and 30.0 g / L sodium from lithium carbonate crystallization as the extraction aqueous phase.

[0083] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.48 g / L, and the lithium ion extraction rate was calculated to be 51.86%.

[0084] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0085] Example 6 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N,N-dibutyl-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N,N-dibutyl-2-hydroxy-4-(trifluoromethyl)benzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0086] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 2.0 g / L lithium, 60.0 g / L sodium, and sulfate ions as the anion as the extraction aqueous phase.

[0087] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.88 g / L, and the lithium ion extraction rate was calculated to be 61.32%.

[0088] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0089] Example 7 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N-cyclohexyl-N-ethyl-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N-cyclohexyl-N-ethyl-2-hydroxy-4-(trifluoromethyl)benzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0090] Prepare the extraction aqueous phase: Take the mother liquor containing 1.0 g / L lithium and 30.0 g / L sodium from lithium carbonate crystallization as the extraction aqueous phase.

[0091] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.56 g / L, and the lithium ion extraction rate was calculated to be 43.33%.

[0092] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0093] Example 8 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 2-hydroxy-N,N-diisopropyl-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of 2-hydroxy-N,N-diisopropyl-4-(trifluoromethyl)benzamide was 0.2 mol / L, the concentration of trialkylphosphine oxide was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0094] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 3.0 g / L lithium, 90.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0095] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 1.49 g / L, and the lithium ion extraction rate was calculated to be 50.57%.

[0096] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0097] Example 9 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N,N-dihexyl-2-hydroxybenzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N,N-dihexyl-2-hydroxybenzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0098] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and carbonate ions as the anion as the extraction aqueous phase.

[0099] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.84 g / L, and the lithium ion extraction rate was calculated to be 15.42%.

[0100] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0101] Example 10 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N,N-diethyl-2-hydroxy-5-nitrobenzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N,N-diethyl-2-hydroxy-5-nitrobenzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0102] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and carbonate ions as the anion as the extraction aqueous phase.

[0103] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.88 g / L, and the lithium ion extraction rate was calculated to be 11.81%.

[0104] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0105] Example 11 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: N,N-dibutyl-2-hydroxy-5-methylbenzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of N,N-dibutyl-2-hydroxy-5-methylbenzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0106] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 0.1 g / L lithium, 3.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0107] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.06 g / L, and the lithium ion extraction rate was calculated to be 32.16%.

[0108] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0109] Example 12 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 3,5-Di-tert-butyl-N,N-diethyl-2-hydroxybenzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctylamine as a modifier to obtain the extractive organic phase. In the extractive organic phase, the concentration of 3,5-di-tert-butyl-N,N-diethyl-2-hydroxybenzamide was 0.2 mol / L, the concentration of trialkylphosphine oxide was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0110] Prepare the extraction aqueous phase: Take the mother liquor containing 1.0 g / L lithium and 30.0 g / L sodium from lithium carbonate crystallization as the extraction aqueous phase.

[0111] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.96 g / L, and the lithium ion extraction rate was calculated to be 3.54%.

[0112] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0113] Example 13 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 3,5-Di-tert-butyl-2-hydroxy-N-(oct-3-yl)benzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of 3,5-di-tert-butyl-2-hydroxy-N-(oct-3-yl)benzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0114] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0115] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 1.0 g / L, and the lithium ion extraction rate was calculated to be 0%.

[0116] Example 14 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 5-acetyl-2-hydroxy-N-(octyl-3-yl)benzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of 5-acetyl-2-hydroxy-N-(octyl-3-yl)benzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0117] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0118] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.78 g / L, and the lithium ion extraction rate was calculated to be 21.42%.

[0119] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0120] Example 15 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 5-fluoro-2-hydroxy-N-(octyl-3-yl)benzamide was used as the extractant, and tributyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of 5-fluoro-2-hydroxy-N-(octyl-3-yl)benzamide was 0.2 mol / L, the concentration of tributyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0121] Prepare the extraction aqueous phase: Take a lithium-containing solution containing 1.0 g / L lithium, 30.0 g / L sodium, and sulfate ions as the extraction aqueous phase.

[0122] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.66 g / L, and the lithium ion extraction rate was calculated to be 33.65%.

[0123] Back-extraction: The loaded organic phase obtained by extraction was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) = 1:1 and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation.

[0124] Example 16 A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution, specifically comprising: Preparation of the extractive organic phase: 5-chloro-2-hydroxy-N-(octyl-3-yl)benzamide was used as the extractant, and trioctyl phosphate was used as the co-extractant, mixed at a molar ratio of 1:1. Sulfonated kerosene was added as a diluent, and isooctanol as a modifier to the mixture to obtain the extractive organic phase. In the extractive organic phase, the concentration of 5-chloro-2-hydroxy-N-(octyl-3-yl)benzamide was 0.2 mol / L, the concentration of trioctyl phosphate was 0.2 mol / L, and the remainder was sulfonated kerosene.

[0125] Prepare the extraction aqueous phase: Take the mother liquor containing 1.0 g / L lithium and 30.0 g / L sodium from lithium carbonate crystallization as the extraction aqueous phase.

[0126] Extraction: The above-mentioned organic and aqueous phases were subjected to single-stage shaking extraction at an extraction ratio (O / A) of 1:1. The extraction pH was 13, the extraction temperature was room temperature, and the extraction time was 5 min. After the extraction reached equilibrium, the mixture was allowed to stand, and the lithium ion concentration was measured after phase separation. The residual lithium ion concentration in the aqueous phase was measured to be 0.58 g / L, and the lithium ion extraction rate was calculated to be 41.81%.

[0127] Back-extraction: The extracted supported organic phase was subjected to single-stage shaking back-extraction with a 0.5 mol / L hydrochloric acid solution. The back-extraction ratio (O / A) was 1:1, and the back-extraction time was 5 min. After the back-extraction reached equilibrium, the mixture was allowed to stand, and the sodium ion concentration was measured after phase separation. The sodium ion concentration in the aqueous phase after back-extraction was measured to be 0.95 g / L, and the sodium ion extraction rate was calculated to be 5.90%. The selectivity βLi / Na = 141.96.

[0128] Comparative Example 1 The effects of the concentration of the extraction system on lithium extraction were compared: N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed in a molar ratio of 1:1. Sulfonated kerosene and isooctanol were added as diluents and modifiers to this extraction system to obtain the extractable organic phase. The concentrations of the extractant and co-extractant in the extractable organic phase were 0.2 mol / L, 0.4 mol / L, and 0.6 mol / L, respectively, with the remainder being sulfonated kerosene and isooctanol. The extractable aqueous phase contained 1.0 g / L lithium ions, 30.0 g / L sodium ions, and sulfate ions as the anion; the pH was adjusted to 13. Extraction conditions: O / A ratio of 1:1, extraction temperature at room temperature, and extraction time of 5 min. Results: The extraction system composed of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide and trialkylphosphine oxide showed better extraction effect with higher concentration. The extraction effect was optimal when the system concentration was 0.6 mol / L, with an extraction rate of 89.13%.

[0129] Comparative Example 2 The effects of different types of co-extractants in the extraction system on lithium extraction were compared: N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide, tributyl phosphate, or trioctyl phosphate were used as co-extractants, mixed in a molar ratio of 1:1. Sulfonated kerosene was added as a diluent and isooctanol as a modifier to obtain the extractable organic phase. In the extractable organic phase, the concentration of the extractant and co-extractant was 0.6 mol / L, with the remainder being sulfonated kerosene and isooctanol. The extractable aqueous phase contained 1.0 g / L lithium ions, 30.0 g / L sodium ions, and sulfate ions as the anion; the pH was adjusted to 13. Extraction conditions: O / A ratio of 1:1, extraction temperature at room temperature, and extraction time of 5 min. Results: The extraction system consisting of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide and trialkylphosphine oxide had the best extraction effect. The lithium ion extraction rates from highest to lowest were: trialkylphosphine oxide > tributyl phosphate > trioctyl phosphate.

[0130] Comparative Example 3 The effects of different types of diluents in the extraction system on lithium extraction were compared: N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed in a molar ratio of 1:1. Sulfonated kerosene, white oil, or n-heptane was added as a diluent, and isooctanol as a modifier to obtain the extractable organic phase. In the extractable organic phase, the concentration of the extractant and co-extractant was 0.6 mol / L, with the remainder being diluent and isooctanol as the modifier. The extractable aqueous phase contained 1.0 g / L lithium ions, 30.0 g / L sodium ions, and sulfate ions as the anion; the pH was adjusted to 13. Extraction conditions: O / A ratio of 1:1, extraction temperature at room temperature, and extraction time of 5 min. Results: The extraction system consisting of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide and trialkylphosphine oxide showed the best extraction effect when sulfonated kerosene was used as the diluent. The lithium ion extraction rates from highest to lowest were: sulfonated kerosene > white oil > n-heptane.

[0131] Comparative Example 4 The effects of pH in the extraction system on lithium extraction were compared and studied: N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide was used as the extractant, and trialkylphosphine oxide was used as the co-extractant, mixed in a molar ratio of 1:1. Sulfonated kerosene was added as a diluent and isooctanol as a modifier to this extraction system to obtain the extractable organic phase. In the extractable organic phase, the concentration of the extractant and co-extractant was 0.6 mol / L, with the remainder being sulfonated kerosene and isooctanol. The extractable aqueous phase contained 1.0 g / L lithium ions, 30.0 g / L sodium ions, and sulfate ions as the anion. The pH of the solution was adjusted to 8, 9, 10, 11, 12, and 13. Extraction conditions: O / A ratio = 1:1, extraction temperature at room temperature, and extraction time of 5 min. Results: In the extraction system composed of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide and trialkylphosphine oxide, the higher the alkalinity, the better the extraction effect. The lithium ion extraction rates from largest to smallest were: 13 > 12 > 11 > 10 > 9 > 8.

[0132] The analyses of Examples 1-16 and Comparative Examples 1-4 are as follows: Firstly, the structure of salicylamide (differences in substituents) determines the lithium extraction efficiency.

[0133] Examples 1-16, by changing the substituents (R1-R5) and structural type (secondary amide / tertiary amide) of formula (I) salicylamide, exhibited significant differences in lithium extraction efficiency. Specifically: For high lithium extraction efficiency combinations: salicylamides with electronegative substituents such as fluorine and trifluoromethyl (e.g., N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide in Example 4 and 2-hydroxy-N-(oct-3-yl)benzamide in Example 1), the lithium ion extraction rate can reach 58.44%-78.81%, of which the extraction rate of Example 4 (lithium concentration 5 g / L, sodium concentration 150 g / L) is 78.81%, which proves that electronegative substituents can enhance the complexing ability of lithium ions by adjusting the electron density of the oxygen atom of the phenolic hydroxyl group, and are suitable for complex systems with high lithium-sodium concentration ratios; For combinations with low lithium extraction efficiency: Substituents with large steric hindrance, such as tert-butyl (e.g., 3,5-di-tert-butyl-N,N-diethyl-2-hydroxybenzamide in Example 12 with an extraction rate of 3.54%, and 3,5-di-tert-butyl-2-hydroxy-N-(oct-3-yl)benzamide in Example 13 with an extraction rate of 0%), result in a loss of lithium extraction ability because the large substituents hinder the formation of hydrogen-bonded six-membered rings; Salicylamides containing weak electronegative / electron-donating substituents such as nitro and methyl (e.g., N,N-diethyl-2-hydroxy-5-nitrobenzamide in Example 10 with an extraction rate of 11.81%, and N,N-dihexyl-2-hydroxybenzamide in Example 9 with an extraction rate of 15.42%) have significantly lower lithium extraction efficiency than those with electronegative substituents.

[0134] This difference indicates that the substituents of salicylamides need to take into account both electronic and steric effects. By selecting appropriate substituents (such as fluorine and trifluoromethyl) and structures (secondary amides are preferred over tertiary amides), it is possible to adapt to lithium-containing sodium sulfate solutions with different lithium sodium concentrations and different anions (sulfate / carbonate). This confirms the technical advantage of the flexible and adjustable structure of the present invention and solves the problems of fixed structures and poor adaptability of existing β-diketones and salicylates.

[0135] Secondly, the effects of co-extractants, diluents, system concentration, and pH on lithium extraction performance are considered.

[0136] Comparative Examples 1-4, through single-variable validation, clarified the optimization direction of key parameters of the extraction system: Regarding system concentration: Comparative Example 1 shows that when the concentrations of N-(2-ethylhexyl)-2-hydroxy-4-(trifluoromethyl)benzamide and trialkylphosphine oxide (TRPO) are increased from 0.2 mol / L to 0.6 mol / L, the extraction rate increases from 78.81% (Example 4) to 89.13%, demonstrating that the higher the concentrations of the extractant and co-extractant, the stronger the synergistic ability to complex lithium ions. However, a balance must be struck between cost and solubility (excessive concentration can easily lead to difficulties in system stratification). Regarding the types of co-extractants: Comparative Example 2 shows that the effect of co-extractants on improving lithium extraction efficiency is TRPO > tributyl phosphate (TBP) > trioctyl phosphate (TOP). Among them, TRPO has the best synergistic effect with salicylamide due to its longer alkyl chain and more coordination sites. This explains why TRPO / TBP was preferentially selected as co-extractants in Examples 1-4, and also proves that the synergistic system of salicylamide + neutral organophosphorus compound requires the selection of a suitable type of co-extractant. Regarding the type of diluent: Comparative Example 3 verified that the effect of diluent on lithium extraction efficiency is sulfonated kerosene > white oil > n-heptane. Sulfonated kerosene has good compatibility with salicylamide and co-extractants, and low viscosity, which can reduce mass transfer resistance and improve extraction efficiency. This is consistent with the practice of using sulfonated kerosene as diluent in Examples 1-16, which solves the problem of high viscosity and poor mass transfer of existing ionic liquid extractants. Regarding pH value: Comparative Example 4 shows that when the pH value is increased from 8 to 13, the extraction rate increases significantly (13 > 12 > ... > 8). However, the system of the present invention has lithium extraction capability in the pH range of 8-13 (for example, the extraction rate of Example 4 is 78.81% at pH 13, and it can still maintain an extraction rate of more than 50% if the pH is reduced to 10). Compared with the existing β-diketones that require strong alkaline conditions of pH > 12.5, this invention significantly reduces alkali consumption and wastewater treatment costs, demonstrating the advantage of the wide pH adaptability range of the present invention.

[0137] Thirdly, the extraction system of the present invention has high lithium-sodium selectivity, which can ensure the purity of lithium products.

[0138] Example 16 clarified the lithium-sodium selectivity advantage of this system by measuring the sodium ion concentration in the back-extraction solution: In this example, the lithium ion extraction rate was 41.81%, while the sodium ion extraction rate was only 5.90%, and the lithium-sodium selectivity coefficient β(Li / Na) reached 141.96, proving that the synergistic system of salicylamide and co-extractant can efficiently identify lithium and sodium ions, reducing sodium ion co-extraction. In comparison with existing technologies: organophosphorus extractants often compete with sodium and magnesium ions for adsorption, resulting in lithium-sodium selectivity coefficients typically below 50; β-diketone extractants have insufficient selectivity for potassium and sodium, leading to low purity lithium products. The high selectivity of this system directly solves the industry pain points of difficult lithium-sodium separation and low product purity, laying the foundation for the subsequent preparation of high-purity lithium products (such as battery-grade lithium carbonate).

[0139] Fourthly, salicylamide extractant has excellent stability and can be adapted to strongly alkaline environments and recycled.

[0140] Examples 1-16 were all extracted under strongly alkaline conditions at pH 13, and the organic phase after back-extraction could be recycled after washing with water (as mentioned in step 4 of the technical solution), without any significant decrease in extraction rate. In contrast, in existing technologies, the dissolution loss rate of β-diketones exceeds 20% at pH > 12.5, and the ester group cracking rate of salicylic esters exceeds 30% under strongly alkaline conditions. This comparison proves that the amide bond of salicylamide can stabilize the six-membered ring structure of lithium extraction, and it is not easily deactivated in strongly alkaline sodium sulfate solution containing lithium, thus solving the problems of poor stability and difficulty in recycling of existing extractants, and reducing the cost of extractant consumption and environmental pressure.

[0141] It is readily understood that this invention provides a method for extracting lithium from a sodium sulfate solution containing lithium ions. This method uses salicylamide as the extractant, phosphorus-containing reagents such as tributyl phosphate as co-extractants, and other organic solvents to construct an extraction system to extract lithium ions from the lithium-containing sodium sulfate solution. The extracted ions are then concentrated in the back-extraction solution through washing and back-extraction. Compared to lithium extraction using β-diketones and salicylates, this method offers advantages such as stable chemical structure, a mild synthetic route, and readily available and inexpensive raw materials.

[0142] It's also understandable that the extraction system composed of salicylamide and organophosphorus compounds, compared to the β-diketone extraction system, not only retains the high efficiency of lithium-ion extraction but also the high selectivity of lithium and sodium extraction. In terms of stability, salicylamide is superior to β-diketones. It is more resistant to lithium-containing solutions with strong acids or bases, less prone to deactivation during use, and easier to recycle.

[0143] Meanwhile, salicylamides offer greater structural flexibility. Secondary salicylamides can be synthesized without adding any catalyst by simply changing the salicylate ester and organic secondary amine; tertiary salicylamides are synthesized by generating acyl chloride from salicylic acid, followed by reaction with an organic amine reagent at room temperature. These two fixed synthetic methods, through the combination of inexpensive salicylic acid, salicylates, and organic amine reagents, can yield a variety of salicylamides with different structures to adapt to the complex environments of lithium-ion extraction.

[0144] It should be noted that salicylaldehyde or salicylic acid esters can achieve similar extraction effects, but the aldehyde and ester groups are easily converted or decomposed under strong acid or alkaline conditions, thus losing their extraction effect.

[0145] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An extraction system for extracting and enriching lithium from a lithium-containing sodium sulfate solution, characterized in that, It includes an extractant, a co-extractant, a diluent, and a modifier, wherein the extractant is salicylamide as shown in formula (I). In formula (I), R1 is hydrogen or a C2 to C8 alkyl group, R2 is a C2 to C8 alkyl group, cyclohexyl or benzyl, and R3, R4 and R5 are each independently selected from hydrogen, nitro, halogen, acetyl or C1 to C4 alkyl group. The co-extractant is a neutral organophosphorus compound with lithium coordination ability.

2. The extraction system according to claim 1, characterized in that, The extractant includes at least one of 2-hydroxy-N-(octyl-3-yl)benzamide, 4-fluoro-2-hydroxy-N-(octyl-3-yl)benzamide, and 2-hydroxy-N,N-di(octyl-3-yl)benzamide.

3. The extraction system according to claim 1, characterized in that, The neutral organophosphorus compound with lithium coordination capability includes at least one of trialkylphosphine oxide, tributyl phosphate, and trioctyl phosphate.

4. The extraction system according to claim 1, characterized in that, The diluent includes at least one of sulfonated kerosene, white oil, and n-heptane.

5. The extraction system according to claim 1, characterized in that, The modifier includes one of organic alcohols, amines, and amides.

6. The extraction system according to any one of claims 1 to 5, characterized in that, In the extraction system, the concentrations of the extractant and the co-extractant are the same; and / or, in the extraction system, the concentration of the extractant is 0.2~0.6 mol / L; and / or, in the extraction system, the concentration of the co-extractant is 0.2~0.6 mol / L.

7. A method for extracting and enriching lithium from a lithium-containing sodium sulfate solution using an extraction system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Adjust the pH of the lithium-containing sodium sulfate solution to 8-13; S2: Add the extraction system to the solution in step S1 to extract lithium ions and separate the upper lithium-ion-loaded first organic phase and the raffinate. S3: Wash the organic phase to obtain a second organic phase and washing wastewater; S4: The second organic phase is back-extracted with acid to obtain a lithium-enriched solution.

8. The method according to claim 7, characterized in that, In step S1, the reagent used to adjust the pH includes sodium hydroxide solution.

9. The method according to claim 7, characterized in that, In step S2, the temperature for extracting lithium ions is 10~60℃; and / or, the extraction time for extracting lithium ions in step S2 is 2~30min; and / or, the extraction flow ratio for extracting lithium ions in step S2 is 1 / 5~10 / 1.

10. The method according to claim 7, characterized in that, In step S4, the lithium content in the lithium-containing enrichment solution is 0.1 g / L to 1 g / L.

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