An extractant, an extraction system for extracting lithium, and a method for extracting lithium

Abstract

The present invention discloses an extractant for extracting lithium, which is characterized in that: the extractant is an ionic liquid in which the anion is the form of enol deprotonated and the cation is a quaternary ammonium salt cation, and its structure is shown in formula (1), where R1, R2, R3, R4, R5, and R6 are the same or different, and each independently is H or C1−C 15 alkyl group or C6−C 15 aryl group. This extractant has high selectivity, does not emulsify, and has low extractant loss. It can efficiently extract lithium from a lithium-containing solution, and the extractant has a long cycle life, significantly reducing the operating cost of lithium extraction. The present invention further relates to a method for extracting lithium using this extractant. (1)

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical separation. Specifically, it relates to an extractant for efficiently extracting lithium with low loss, and further relates to an extraction system containing the extractant and a method for extracting lithium using the extractant. Background Art

[0002] Lithium salts are the core raw materials of lithium-ion batteries. With the gradual popularization of electric vehicles, the demand for lithium salts in the domestic and international markets is increasing continuously. However, lithium is usually associated with various alkali metals and non-metal impurities, resulting in low extraction yield of lithium, low purity of lithium salt products, and relatively high production costs.

[0003] Solvent extraction is a commonly used method for efficiently extracting and separating metals, and is widely applicable in the smelting fields of non-ferrous metals such as copper, nickel, cobalt, and rare earth elements. A typical solvent extraction system for separating lithium from other alkali metals (such as sodium, potassium, rubidium, cesium) and some non-metal impurities (such as fluorine, silicon, etc.) is a synergistic solvent extraction system based on diketone and alkylphosphine oxide. This extraction system has a relatively high separation coefficient. However, due to the structural characteristics of alkylphosphine oxide itself, the extraction system using alkylphosphine oxide is prone to emulsification; moreover, since this extraction system can effectively extract lithium only under alkaline conditions with pH > 11, under such conditions, the diketone molecules hydrolyze to form sodium salts. Since the water solubility of diketone sodium salts is significantly higher than that of their molecular form, the loss of the extractant in water is large, greatly reducing the recycling life of the extractant. Therefore, the diketone-alkylphosphine oxide synergistic extraction system is difficult to be widely promoted and used on a large scale.

[0004] Aiming at the problems of the prior art, the present invention provides an ionic liquid-type extractant for extracting lithium, which has high extraction selectivity, no emulsification, low loss of the extractant, can efficiently extract lithium from a lithium-containing solution, and has a long recycling life, which can significantly reduce the operating cost of extracting lithium. Summary of the Invention

[0005] Aiming at the problems of the prior art, the present invention provides an ionic liquid-type extractant for extracting lithium, which has high extraction selectivity, no emulsification, low loss of the extractant, can efficiently extract lithium from a lithium-containing solution, and has a long recycling life, which can significantly reduce the operating cost of extracting lithium.

[0006] An extractant for extracting lithium, characterized in that: the extractant is an ionic liquid based on enol and quaternary ammonium salt, its anion is the form after enol loses a hydrogen ion, its cation is a quaternary ammonium salt cation, and the structure of the extractant is shown in formula (1): (1)

[0007] wherein R1, R2, R3, R4, R5, and R6 may be the same or different and are each independently H or a C1-C 15 alkyl group or a C6-C 15 aryl group; for example, the C1-C 15 alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, 2-methyl-butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, or pentadecyl; the aryl group may be phenyl, methylphenyl, ethylphenyl, propylphenyl, butylphenyl, hexylphenyl, octylphenyl, or nonylphenyl, etc.

[0008] The extractant is one of the following compounds.

[0009] [PhOOC7][N 8881 , and its structural formula is: ,

[0010] [PhOOPh][N 8881 , and its structural formula is: ,

[0011] [PhOOC 12 [N 8881 , and its structural formula is: ,

[0012] [C8OOC8][N 8881 , and its structural formula is: ,

[0013] [PhOOC8][N 6661 , and its structural formula is: , and

[0014] [PhOOC8][N 6666 , and its structural formula is: .

[0015] The present invention further relates to an extraction system, which comprises the extractant and diluent of the present invention, wherein the content of the extractant is 3 vol% - 60 vol%, and the content of the diluent is 97 vol% - 40 vol%, based on the total volume of the extraction system.

[0016] The diluent may be selected from any one of alkanes (such as kerosene, D70 solvent oil), aromatics (such as toluene, S150 solvent oil), or any mixture thereof.

[0017] The present invention further relates to a method for extracting lithium from a lithium-containing solution, characterized in that: this method uses the extractant of the present invention, and this method comprises the following steps:

[0018] (1) Dissolve the extractant according to the present invention in a diluent to prepare an organic phase, where the volume concentration of the extractant in the organic phase is 3 vol% - 60 vol% based on the total volume of the organic phase;

[0019] (2) Measure the concentration of lithium in the lithium-containing solution to be tested, add an appropriate amount of base thereto to obtain the aqueous phase to be extracted;

[0020] (3) Introduce the organic phase prepared in step (1) and the aqueous phase obtained in step (2) into an extraction device for countercurrent extraction reaction to obtain a lithium-loaded organic phase;

[0021] (4) Countercurrent wash the lithium-loaded organic phase in step (3) with a washing solution to obtain a washed organic phase;

[0022] (5) Perform countercurrent stripping on the washed organic phase in step (4) to obtain a stripped organic phase and a high-purity lithium salt solution;

[0023] (6) Return the stripped organic phase to the organic phase storage tank for reuse in countercurrent extraction of lithium.

[0024] In step (1), the diluent is any one of alkanes (such as kerosene, D70 solvent oil, etc.), aromatics (such as toluene, S150 solvent oil, etc.), or any mixture thereof.

[0025] In step (2), the base can be selected from sodium hydroxide, potassium hydroxide, ammonia water, or any mixture thereof. The addition amount of the base in the solution is such that the concentration of the base is 0.5 - 3.0 times the molar concentration of lithium, based on the molar concentration of lithium in the lithium-containing solution to be tested.

[0026] In step (3), the extraction device can use an extraction clarifier, an extraction tower, or a centrifugal extractor, and the number of extraction stages is 1 - 20, and the volume ratio of the organic phase to the aqueous phase is 1:50 - 50:1.

[0027] In step (4), the washing solution is any one of water, dilute hydrochloric acid, or dilute sulfuric acid, and the concentration of the hydrochloric acid or sulfuric acid solution is 0.01 - 3.0 mol / L; the volume ratio of the organic phase to the washing solution is 1:50 - 50:1, and the number of washing stages is 1 - 20.

[0028] In step (5), an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, a carbonic acid solution (carbon dioxide is introduced into water), or an aqueous phosphoric acid solution is used as the stripping solution for stripping, and its concentration is 0.03 - 6.0 mol / L; the volume ratio of the organic phase to the stripping solution is 1:50 - 50:1, and the number of stripping stages is 1 - 20.

[0029] The lithium recovery rate achieved by using the extractant of the present invention through the method of the present invention can reach more than 99%, the lithium purity can reach more than 99.5%, and the loss of the extractant in the raffinate is < 10 ppm.

[0030] The present invention further relates to the use of the extractant according to the present invention for extracting lithium. The extractant of the present invention can be advantageously used for efficiently extracting lithium from various lithium-containing solutions such as salt lake brine, oilfield brine, battery leachate, ore leachate, lithium precipitation mother liquor, lithium-containing wastewater, etc.

[0031] Hereinafter, taking the extraction of lithium from sulfate solution by [PhOOC7][N 8881 as an example, the mechanism of extracting lithium from lithium-containing solution by the extraction system according to the present invention will be described, and its reaction is shown in the following equation (1):

[0032] (1)

[0033] Among them, two [PhOOC7] - anions coordinate with one Li + cation to form a complex anion [(PhOOC7)2Li] - , and then form an ion pair [(PhOOC7)2Li][N 8881 + with a quaternary ammonium salt cation [N 8881 . The schematic diagram of the coordination structure of [(PhOOC7)2Li] - is shown in formula (2), and 4 oxygen atoms form a near-tetrahedral structure with Li + . The excess extractant that does not participate in lithium extraction exists in the form of ionic liquid [PhOOC7][N 8881 . Due to the extremely strong hydrophobicity of this ionic liquid and its very low water solubility, the loss of the extractant in the alkaline environment can be avoided. If the enol does not exist in the form of ionic liquid, then it will exist in the form of sodium salt in the alkaline environment, such as Na[PhOOC7], and the water solubility of sodium salt is significantly higher than that of ionic liquid, resulting in serious loss of the extractant.

[0034] (2)

[0035] The lithium [(PhOOC7)2Li][N 8881 in the loaded organic phase can be stripped by acid. Taking sulfuric acid stripping as an example, its mechanism is shown in equation (2):

[0036] (2)

[0037] The enol H(PhOOC7) and ammonium sulfate [N 8881 ​When extracting lithium under alkaline conditions with H2SO4, ionic liquid and [(PhOOC7)2Li][N are regenerated again and enter the next extraction - stripping cycle. 8881

[0038] Similarly, when stripping with hydrochloric acid, carbonic acid, and phosphoric acid, lithium chloride solution, lithium carbonate (or lithium bicarbonate) solution, and lithium dihydrogen phosphate solution are obtained respectively.

[0039] Beneficial effects

[0040] The extractant of the present invention is an ionic liquid extraction system composed of carbonyl enol and quaternary ammonium salt, which eliminates the emulsification phenomenon. It can highly selectively extract and extract lithium from solutions containing elements such as lithium, sodium, potassium, rubidium, cesium, silicon, fluorine, and chlorine under alkaline conditions. The separation factor between lithium and the above - mentioned impurity elements is > 1000. Since the extractant exists in the form of ionic liquid under alkaline conditions, the dissolution loss of the extractant under alkaline conditions is significantly reduced, and it can be recycled for a long time. Therefore, the operating cost of extracting and extracting lithium is greatly reduced; moreover, the total organic matter content (i.e., COD) in the raffinate is low, and the treatment of the raffinate is simple. Using the solvent extraction system of the present invention to extract and extract lithium from a lithium - containing solution (for example: a mixed solution of lithium, sodium, potassium (rubidium, cesium)) through the method of the present invention realizes the high - efficiency purification and concentration of lithium. Its process flow is shortened, the lithium recovery rate is high, and the treatment process of the raffinate is simple. The solvent extraction system and the method for extracting and extracting lithium of the present invention are of great significance for making full use of low - grade lithium resources. Specific embodiments

[0041] The following examples are used to illustrate the present invention more specifically, but the present invention is not restricted by any of these examples. Those skilled in the art can make various deformations within the technical concept of the present invention.

[0042] Example 1

[0043] The lithium - containing solution to be treated is the intermediate mother liquor in the production process of lithium hydroxide. The solution contains 21 g / L of lithium, 83 g / L of sodium, 12 g / L of potassium, and 55 g / L of hydroxide.

[0044] With 35 vol% [PhOOC7][N 8881and 65 vol% kerosene are formulated into an organic phase. The organic phase and the aqueous phase are subjected to 4-stage continuous countercurrent extraction in an extraction clarifier at a volume ratio of 6:1 to obtain a lithium-loaded organic phase, and the extraction rate of lithium is measured to be >99%. The lithium-loaded organic phase is continuously washed with 0.5 mol / L sulfuric acid to co-extract sodium and potassium at a volume ratio of 20:1 in the extraction clarifier for 3 stages, and the washing solution is returned to the inlet of the aqueous phase; the washed organic phase is continuously stripped with a saturated carbonic acid solution (carbon dioxide gas is introduced into water) at a volume ratio of 2:1 in the extraction clarifier for 2 stages to obtain a high-purity lithium bicarbonate solution with a lithium concentration of about 7 g / L, and its lithium purity is measured to be >99.8%. The lithium bicarbonate solution is heated to 90 °C for pyrolysis to obtain a battery-grade lithium carbonate product and a pyrolysis mother liquor. The pyrolysis mother liquor is again passed through carbon dioxide and recycled for stripping the loaded organic phase.

[0045] Example 2

[0046] The lithium-containing solution to be treated is taken from the solution obtained after the recycled lithium battery is disassembled, crushed, leached and the divalent and trivalent metals are removed. It contains 2.7 g / L of lithium, 50 g / L of sodium, and trace amounts of cobalt, nickel, magnesium, etc.

[0047] 30 vol% [C8OOC8][N 8881 is dissolved in 70 vol% kerosene to formulate an organic phase. NaOH is added to the lithium-containing solution to make the NaOH concentration 0.45 mol / L to formulate an aqueous phase. The organic phase and the aqueous phase are subjected to 3-stage continuous countercurrent extraction in an extraction clarifier at a volume ratio of 2:1, and the extraction rate of lithium is >99%. The loaded organic phase is continuously washed with 0.2 mol / L sulfuric acid to co-extract sodium and potassium at a volume ratio of 20:1 in the extraction clarifier for 2 stages, and the washing solution is returned to the inlet of the aqueous phase; the washed organic phase is continuously stripped with 2 mol / L sulfuric acid at a volume ratio of 20:1 in the extraction clarifier for 2 stages to obtain a high-purity Li2SO4 solution with a lithium concentration of 25−27 g / L, and its lithium purity is >99.8%. The stripped organic phase is returned to the extraction section for recycling. The lithium sulfate solution is precipitated with sodium carbonate at 0.8 times the stoichiometric ratio of lithium at 80 °C to obtain battery-grade lithium carbonate with a purity of 99.8%.

[0048] Example 3

[0049] The solution to be treated is lithium-containing wastewater generated during the battery recycling process, with a lithium concentration of 0.6 g / L and a sodium concentration of 48 g / L.

[0050] 30 vol% [PhOOPh][N 8881It is dissolved in 70 vol% kerosene to prepare an organic phase. NaOH is added to the lithium-containing solution to make the concentration of NaOH 0.10 mol / L to prepare an aqueous phase. The organic phase and the aqueous phase are subjected to 4-stage continuous countercurrent extraction in an extraction clarifier according to a volume ratio of 1:3, and the extraction rate of lithium is measured to be >99%. The loaded organic phase continues to be washed with 1.0 mol / L hydrochloric acid for the co-extracted sodium in the extraction clarifier according to a volume ratio of 15:1 for 3 stages, and the washing solution is returned to the inlet of the aqueous phase; the washed organic phase continues to be stripped with 5.0 mol / L hydrochloric acid in the extraction clarifier according to a volume ratio of 20:1 for 2 stages to obtain a LiCl solution with a lithium concentration of 33−37 g / L and a sodium content of < 10 ppm. The LiCl solution is obtained as a LiCl product through evaporation crystallization.

[0051] Example 4

[0052] The solution to be treated is the mother liquor after lithium precipitation by adding sodium carbonate to the lithium sulfate solution, containing 2.6 g / L of lithium and 55 g / L of sodium.

[0053] With 35 vol% [PhOOC8][N 6661 It is dissolved in 65 vol% S150 solvent to prepare an organic phase. NaOH is added to the mother liquor after lithium precipitation to make the concentration of NaOH 0.40 mol / L, and this solution is used as the aqueous phase. The organic phase and the aqueous phase are subjected to 3-stage continuous countercurrent extraction in an extraction clarifier according to a volume ratio of 1:1, and the extraction rate of lithium is measured to be >99%. The lithium-loaded organic phase continues to be washed with 0.2 mol / L sulfuric acid for the co-extracted sodium in the extraction clarifier according to a volume ratio of 10:1 for 3 stages, and the washing solution is returned to the inlet of the aqueous phase; the washed organic phase continues to be stripped with 3 mol / L phosphoric acid in the extraction clarifier according to a volume ratio of 8:1 for 3 stages to obtain a lithium dihydrogen phosphate solution with a lithium concentration of 20−22 g / L. The lithium dihydrogen phosphate solution is obtained as a lithium dihydrogen phosphate product with a purity of >99.6% through evaporation crystallization.

Claims

1. An extractant for extracting lithium, characterized in that: The extractant is an ionic liquid compound, its anion is in the form of the enol after losing a hydrogen ion, its cation is a quaternary ammonium salt cation, and its structure is shown in formula (1). （1） wherein R1, R2, R3, R4, R5, and R6 are the same or different and each independently is H or a C1-C 15 alkyl group or a C6-C 15 aryl group.

2. The extractant according to claim 1, characterized in that: The C1-C 15 alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, 2-methyl-butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl or pentadecyl; the C6-C 15 aryl group is phenyl, methylphenyl, ethylphenyl, propylphenyl, butylphenyl, hexylphenyl, octylphenyl or nonylphenyl.

3. The extractant according to claim 1 or 2, characterized in that: The extractant is one of the following compounds: [PhOOC7][N 8881 , and its structural formula is: , [PhOOPh][N 8881 , and its structural formula is: , [PhOOC 12 [N 8881 , and its structural formula is: , [C8OOC8][N 8881 , and its structural formula is: , [PhOOC8][N 6661 , and its structural formula is: , and [PhOOC8][N 6666 , and its structural formula is: .

4. A method for extracting lithium, characterized in that: This method uses the extractant according to any one of claims 1-3, and this method comprises the following steps: (1) Dissolve the extractant in a diluent to prepare an organic phase, and the volume concentration of the extractant in the organic phase is 3 vol% - 60 vol% based on the total volume of this organic phase; (2) Measure the lithium concentration in the lithium-containing solution to be tested, and add an appropriate amount of alkali thereto to obtain the aqueous phase to be extracted; (3) Feed the organic phase prepared in step (1) and the aqueous phase obtained in step (2) into an extraction device to carry out a countercurrent extraction reaction to obtain a lithium-loaded organic phase; (4) Countercurrently wash the lithium-loaded organic phase in step (3) with a washing solution to obtain a washed organic phase; (5) Carry out countercurrent stripping on the washed organic phase in step (4) to obtain a stripped organic phase and a high-purity lithium salt solution; (6) The stripped organic phase is returned to the organic phase storage tank and reused again for countercurrent extraction of lithium.

5. The method according to claim 4, wherein in step (1), the diluent is any one of kerosene, D70 solvent oil, toluene, S150 solvent oil or any mixture thereof; in step (2), the alkali is sodium hydroxide, potassium hydroxide, ammonia water or a mixture thereof; the addition amount of the alkali is such that the concentration of the alkali is 0.5 - 3.0 times the molar concentration of lithium, based on the molar concentration of lithium in the lithium-containing solution to be tested.

6. The method according to claim 4, wherein in step (3), the volume ratio of the organic phase to the aqueous phase is 1:30 - 30:

1.

7. The method according to claim 4, wherein in step (4), the washing solution is any one of water, dilute hydrochloric acid or dilute sulfuric acid, and the concentration of hydrochloric acid or sulfuric acid is 0.01 - 2.0 mol / L; the volume ratio of the organic phase to the washing solution is 1:30 - 30:

1.

8. The method according to claim 4, wherein in step (5), an aqueous hydrochloric acid solution, an aqueous sulfuric acid solution, an aqueous carbonic acid solution or a phosphoric acid solution is used as the stripping solution for stripping, and its concentration is 0.03 - 6.0 mol / L; the volume ratio of the organic phase to the stripping solution is 1:50 - 50:

1.

9. An extraction system, characterized in that: This extraction system comprises a diluent and the extractant according to any one of claims 1-3, wherein the content of the extractant is 3 vol% - 60 vol%, and the content of the diluent is 97 vol% - 40 vol% based on the total volume of this extraction system; the diluent is selected from any one of kerosene, D70 solvent oil, toluene, S150 solvent oil or any mixture thereof.

10. The use of the extractant according to any one of claims 1-3 or the extraction system according to claim 9 for extracting lithium from salt lake brine, oilfield brine, battery leachate, ore leachate, lithium precipitation mother liquor and lithium-containing wastewater.

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