A selective lithium extraction reagent and method

Abstract

This invention provides a composite extractant and method for selective lithium extraction. The composite extractant comprises a neutral organophosphorus extractant and a diluent; the neutral organophosphorus extractant includes phosphine oxides and / or phosphate esters. The composite extractant provided by this invention has low water solubility, is stable under acidic and alkaline conditions, and exhibits high selectivity for both lithium-calcium and lithium-sodium compounds. It can effectively extract lithium in high-calcium, high-sodium brines with calcium ion concentrations greater than 160 g / L and sodium ion concentrations greater than 4 g / L, while showing low extraction rates for sodium and calcium.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology and relates to the selective extraction of lithium, and more particularly to a composite extractant and method for selective lithium extraction. Background Technology

[0002] In recent years, the demand for lithium, a crucial raw material for lithium-ion batteries, has been steadily increasing. A 2022 report by the U.S. Geological Survey indicated that global proven lithium reserves are approximately 89 million tons, primarily found in salt lake brines and spodumene, with salt lakes accounting for over 59%. While lithium-ion concentrations in salt lakes are generally low, the concentrations of other competing ions, such as sodium, potassium, magnesium, and calcium, are very high. Fully exploiting and utilizing lithium resources requires efficient and selective lithium extraction from salt lake brines containing high concentrations of competing ions. Extensive research and reports have been published on high magnesium-to-lithium ratios, but the challenges of high sodium-to-lithium and high calcium-to-lithium ratios particularly need to be addressed.

[0003] CN113981243A discloses a method for extracting and separating lithium from salt lake brine with a high sodium-to-lithium ratio. The method uses diketone compounds and halogen-containing organophosphorus compounds as the extraction system. The active hydrogen on the diketone exchanges with lithium ions, and the organophosphorus compounds act as co-extractants to participate in the complexation and coordination of lithium for extraction. This method achieves lithium extraction from salt lake brine. However, the extraction process requires the stepwise extraction of sodium, lithium, calcium, and magnesium, which is relatively complex.

[0004] Calcium ions have a stronger coordination ability than magnesium ions, making lithium separation more difficult in high-calcium systems. Current processes mainly involve the pre-removal of calcium ions. For example, CN104817096B adds sodium sulfate to old brine from high-calcium salt fields to precipitate calcium ions; CN114014340A uses low-temperature freezing to crystallize calcium chloride; CN114906864A uses evaporation and concentration to gradually precipitate calcium chloride crystals and other chlorides. Additionally, CN110777266A discloses a secondary amide composite solvent for extracting lithium from high-calcium brine, but experimental results show that the single-stage extraction rate of lithium is generally below 50%, while the extraction rate of calcium is higher, resulting in a low lithium-calcium separation coefficient.

[0005] Therefore, to address the issue of lithium extraction from high-calcium and high-sodium brines, a composite extractant and method for selective lithium extraction are needed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite extractant and method for selective lithium extraction, which can selectively extract lithium from high-sodium and high-calcium brines and has good prospects for industrial application.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite extractant for selective lithium extraction, the composite extractant comprising a neutral organophosphorus extractant and a diluent;

[0009] The neutral organophosphorus extractant includes phosphine oxides and / or phosphate esters.

[0010] The composite extractant provided by this invention uses a neutral organophosphorus compound as the extractant to extract Li + and [FeCl4] - The extractant is extracted into the organic phase in the form of a neutral complex. The composite extractant provided by this invention has low water solubility and is stable under acid and alkaline conditions. It can treat brine with complex ion content, wherein the lithium ion concentration is greater than 0.1 g / L, the calcium ion concentration is greater than 160 g / L, the sodium ion concentration is greater than 4 g / L, the chloride ion concentration is greater than 280 g / L, the calcium-lithium mass ratio is 450-1800, the sodium-lithium mass ratio is 20-70, and it has high selectivity for both lithium-calcium and lithium-sodium ions.

[0011] Preferably, the phosphine oxide comprises any one or a combination of at least two of tri-n-octylphosphine oxide, tri-n-butylphosphine oxide, diisooctyl methylphosphonate, di-sec-octyl methylphosphonate, diisooctyl isopropylphosphine oxide, diisopentyl methylphosphine oxide, dibutyl butyl dibutylphosphine oxide, or triphenylphosphine oxide. Typical but non-limiting combinations include the combination of tri-n-octylphosphine oxide and tri-n-butylphosphine oxide, the combination of diisooctyl methylphosphine oxide and di-sec-octyl methylphosphine oxide, the combination of diisooctyl isopropylphosphine oxide and diisopentyl methylphosphine oxide, or the combination of dibutyl butyl dibutylphosphine oxide and triphenylphosphine oxide.

[0012] Preferably, the phosphate ester compound includes any one or a combination of at least two of the following: triisobutyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, triisopropylphenyl phosphate, butyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, di(2-ethylhexyl)phenyl phosphate, tris(p-tert-butylphenyl) phosphate, tris(o-ethylphenyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, octyl dibutyl phosphate, or butyl dioctyl phosphate, typically but not limitingly. The combinations of these compounds include triisobutyl phosphate and butyl dioctyl phosphate, trioctyl phosphate and triphenyl phosphate, tricresyl phosphate and triisopropylphenyl phosphate, butyl diphenyl phosphate and 2-ethylhexyl diphenyl phosphate, di(2-ethylhexyl)phenyl phosphate, tri(p-tert-butylphenyl) phosphate and tri(o-ethylphenyl) phosphate, or tri(2,2,2-trifluoroethyl) phosphate, octyl dibutyl phosphate and butyl dioctyl phosphate.

[0013] Preferably, the diluent comprises C4-C 14 Alkanes, C4-C 14 ester compounds, C4-C14 Any one or at least two combinations of alcohols or kerosene solvents, typically but not limitingly including C4-C4 combinations. 14 Alkanes and C4-C 14 Combinations of ester compounds, C4-C 14 Combinations of alcohols with kerosene solvents, or C4-C 14 Alkanes, C4-C 14 ester compounds, C4-C 14 A combination of alcohols and kerosene solvents.

[0014] For example, the C4-C 14 The alkanes include n-octane and / or n-butane.

[0015] For example, the C4-C 14 Ester compounds include ethyl acetate and / or propyl acetate.

[0016] For example, the C4-C 14 The alcohols include n-octanol and / or n-butanol.

[0017] For example, the kerosene solvent includes sulfonated kerosene and / or 260# solvent oil.

[0018] Preferably, the volume of the diluent is 10-60% of the volume of the composite extractant, for example, it can be 10%, 20%, 30%, 40%, 50% or 60%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the composite extractant further comprises a ketone co-extractant;

[0020] The ketone co-extractants include water-insoluble alkyl ketones and / or water-insoluble aromatic ketones.

[0021] Preferably, the alkyl ketone comprises any one or a combination of at least two of diisobutyl ketone, methyl isobutyl ketone, 2-heptanone, 2-octanone, 2-nonanone, methyl nonyl ketone, or dipentyl ketone. Typical but non-limiting combinations include combinations of diisobutyl ketone and methyl isobutyl ketone, combinations of 2-heptanone and 2-octanone, combinations of 2-nonanone and methyl nonyl ketone, combinations of diisobutyl ketone, methyl isobutyl ketone, and 2-heptanone, or combinations of 2-nonanone, methyl nonyl ketone, and dipentyl ketone.

[0022] Preferably, the aromatic ketone includes acetophenone.

[0023] Preferably, the volume ratio of the neutral organophosphorus extractant to the ketone co-extractant is (1-4):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In a second aspect, the present invention provides a method for selectively extracting lithium from brine, the method using a composite extractant as described in the first aspect.

[0025] Preferably, the method includes the following steps:

[0026] (1) After adjusting the pH value of the brine, ferric chloride is mixed with the brine to obtain the aqueous phase before extraction;

[0027] (2) The aqueous phase obtained in step (1) is mixed with the composite extractant for extraction, and the organic phase and aqueous phase are separated.

[0028] The extraction method provided by this invention uses a composite extractant, which can efficiently and selectively extract lithium from high-calcium and high-sodium brine. The separation coefficient between lithium-calcium and lithium-sodium is high, and the extraction effect is good.

[0029] Preferably, the pH value in step (1) is 0-2.0, for example, it can be 0, 0.5, 1.0, 1.5 or 2.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, in the aqueous phase before extraction described in step (1), the molar ratio of iron ions to lithium ions is (1-6):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the volume ratio of the composite extractant to the aqueous phase before extraction in step (2) is (1-10):1, for example, it can be 1:1, 2:1, 4:1, 5:1, 6:1, 8:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the extraction method in step (2) includes single-stage extraction and / or multi-stage countercurrent extraction.

[0033] Preferably, the method further includes: back-extracting the organic phase obtained in step (2).

[0034] Preferably, the volume ratio of the back-extraction agent to the organic phase used in the back-extraction is 1:(1-20), for example, it can be 1:1, 5:1, 10:1, 15:1 or 20:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the stripping agent comprises an acid.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] The composite extractant provided by this invention has low water solubility, is stable under acid and alkaline conditions, and has high selectivity for both lithium-calcium and lithium-sodium. It can effectively extract lithium in high-calcium and high-sodium brines with calcium ion concentrations greater than 160 g / L and sodium ion concentrations greater than 4 g / L, while exhibiting low extraction rates for sodium and calcium. Detailed Implementation

[0038] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0039] Example 1

[0040] This embodiment provides a composite extractant, the composition of which includes 60 vol% dibutyl phosphate, 20 vol% methyl isobutyl ketone, and 20 vol% sulfonated kerosene.

[0041] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.69 g / L, calcium ion concentration of 160 g / L, sodium ion concentration of 5.75 g / L, and chloride ion concentration of 296 g / L.

[0042] The selective lithium extraction method includes the following steps:

[0043] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH = 1.3, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 1.3:1, resulting in the aqueous phase before extraction;

[0044] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 1 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0045] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 1 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 55% for Li, 6% for Na, and 0.1% for Ca. Furthermore, the Fe content in the back-extraction phase was... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0046] Example 2

[0047] This embodiment provides a composite extractant, the composition of which includes 50 vol% diisoamyl methyl phosphate, 30 vol% acetophenone, and 20 vol% n-octane.

[0048] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.35 g / L, calcium ion concentration of 160 g / L, sodium ion concentration of 6.9 g / L, and chloride ion concentration of 310 g / L.

[0049] The selective lithium extraction method includes the following steps:

[0050] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH=1.5, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 2:1, resulting in the aqueous phase before extraction;

[0051] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 1 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0052] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 1 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 47% for Li, 3.6% for Na, and 0.2% for Ca. The separation coefficients for Li / Na and Li / Ca were 23 and 364, respectively. Furthermore, Fe in the back-extraction phase... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0053] Example 3

[0054] This embodiment provides a composite extractant, the composition of which includes 70 vol% octyl dibutyl phosphate, 20 vol% methyl nonyl ketone, and 10 vol% diethylbenzene.

[0055] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.35 g / L, calcium ion concentration of 160 g / L, sodium ion concentration of 6.9 g / L, and chloride ion concentration of 310 g / L.

[0056] The selective lithium extraction method includes the following steps:

[0057] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH = 1.0, add FeCl3 co-extractant to make Fe...3+ With Li + The molar ratio was 2.5:1, resulting in the aqueous phase before extraction;

[0058] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 2 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0059] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 1 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 62% for Li, 4.0% for Na, and 0.5% for Ca. The separation coefficients for Li / Na and Li / Ca were 38 and 298, respectively. Furthermore, Fe in the back-extraction phase... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0060] Example 4

[0061] This embodiment provides a composite extractant, the composition of which includes 60 vol% triisobutyl phosphate, 30 vol% dipentyl ketone, and 10 vol% n-octanol.

[0062] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.244 g / L, calcium ion concentration of 161 g / L, sodium ion concentration of 12.9 g / L, and chloride ion concentration of 320 g / L.

[0063] The selective lithium extraction method includes the following steps:

[0064] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH = 1.3, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 3:1, resulting in the aqueous phase before extraction;

[0065] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 1 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0066] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 1 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+The concentrations were tested, and the extraction rates were calculated to be 61% for Li, 5.3% for Na, and 0.6% for Ca. The separation coefficients for Li / Na and Li / Ca were 28 and 238, respectively. Furthermore, Fe in the back-extraction phase... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0067] Example 5

[0068] This embodiment provides a composite extractant, the composition of which includes 60 vol% tri-n-butylphosphine oxide, 30 vol% diisobutyl ketone, and 10 vol% ethyl acetate.

[0069] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.256 g / L, calcium ion concentration of 210 g / L, sodium ion concentration of 5 g / L, and chloride ion concentration of 391 g / L.

[0070] The selective lithium extraction method includes the following steps:

[0071] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH = 1.1, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 5:1, resulting in the aqueous phase before extraction;

[0072] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 1 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0073] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 1 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 72% for Li, 4.1% for Na, and 1.0% for Ca. The separation coefficients for Li / Na and Li / Ca were 60 and 258, respectively. Furthermore, Fe in the back-extraction phase... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0074] Example 6

[0075] This embodiment provides a composite extractant, the composition of which includes 30 vol% dibutyl phosphate, 10 vol% methyl isobutyl ketone, and 60 vol% sulfonated kerosene.

[0076] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.69 g / L, calcium ion concentration of 160 g / L, sodium ion concentration of 5.75 g / L, and chloride ion concentration of 296 g / L.

[0077] The selective lithium extraction method includes the following steps:

[0078] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH=0, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 6:1, resulting in the aqueous phase before extraction;

[0079] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 10 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0080] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 20 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 45% for Li, 1.0% for Na, and 0.3% for Ca. Furthermore, the Fe content in the back-extraction phase was... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0081] Example 7

[0082] This embodiment provides a composite extractant, the composition of which includes 40 vol% dibutyl phosphate, 20 vol% methyl isobutyl ketone, and 40 vol% sulfonated kerosene.

[0083] The composite extractant was used to selectively extract lithium from lithium-containing brine. The composition of the lithium-containing brine included: lithium ion concentration of 0.69 g / L, calcium ion concentration of 160 g / L, sodium ion concentration of 5.75 g / L, and chloride ion concentration of 296 g / L.

[0084] The selective lithium extraction method includes the following steps:

[0085] (1) Take lithium-containing brine, add hydrochloric acid to adjust the pH of the solution to pH=2, add FeCl3 co-extractant to make Fe... 3+ With Li + The molar ratio was 1:1, resulting in the aqueous phase before extraction;

[0086] (2) The aqueous phase before extraction was mixed with the composite extractant at O / A = 5 / 1 and extracted at 25°C. After extraction, the phases were allowed to separate and the loaded organic phase and raffinate phase were obtained.

[0087] (3) The supported organic phase was back-extracted with 6 mol / L hydrochloric acid solution, O / A = 10 / 1, to remove Li from the back-extracted phase and the aqueous phase after back-extraction. + Na + Ca 2+ The concentrations were tested, and the extraction rates were calculated to be 64% for Li, 3.2% for Na, and 0.4% for Ca. Furthermore, the Fe content in the back-extraction phase was... 3+ The concentration is 0, and the composite extractant after back-extraction can be recycled.

[0088] Example 8

[0089] This embodiment provides a composite extractant, which is the same as that in Example 1, and the brine composition treated is the same as that in Example 1.

[0090] Compared with Example 1, in control step (1), the pH value of the solution is adjusted to pH = 2.3, and the rest is the same as in Example 1.

[0091] Example 9

[0092] This embodiment provides a composite extractant, which is the same as that in Example 1, and the brine composition treated is the same as that in Example 1.

[0093] Compared with Example 1, in control step (1), the pH value of the solution is adjusted to make pH = 0.18, and the rest is the same as in Example 1.

[0094] Example 10

[0095] This embodiment provides a composite extractant, which is the same as that in Example 1, and the brine composition treated is the same as that in Example 1.

[0096] Compared with Example 1, in control step (1), Fe 3+ With Li + The molar ratio was 0.5:1, and all other aspects were the same as in Example 1.

[0097] Example 11

[0098] This embodiment provides a composite extractant, which is the same as that in Example 1, and the brine composition treated is the same as that in Example 1.

[0099] Compared with Example 1, in control step (1), Fe 3+ With Li +The molar ratio was 6.5:1, and all other aspects were the same as in Example 1.

[0100] Example 12

[0101] This embodiment provides a composite extractant, the composition of which includes 30 vol% dibutyl phosphate, 50 vol% methyl isobutyl ketone, and 20 vol% sulfonated kerosene.

[0102] The brine and method used are the same as in Example 1.

[0103] Example 13

[0104] This embodiment provides a composite extractant, the composition of which includes 65 vol% dibutyl phosphate, 15 vol% methyl isobutyl ketone, and 20 vol% sulfonated kerosene.

[0105] The brine and method used are the same as in Example 1.

[0106] Example 14

[0107] This embodiment provides a composite extractant, the composition of which includes 80 vol% dibutyl phosphate and 20 vol% sulfonated kerosene.

[0108] The brine and method used are the same as in Example 1.

[0109] Table 1

[0110]

[0111]

[0112] As can be seen from Table 1:

[0113] The composite extractant provided by this invention exhibits high selectivity for low-concentration lithium in high-calcium, high-sodium systems, particularly for lithium-calcium, with selectivity far exceeding existing reports, demonstrating excellent application prospects. Under the preferred extraction conditions of this invention, the extraction rates for sodium and calcium are low, while the separation coefficients for lithium-sodium and lithium-calcium are high. However, increasing the extractant concentration increases the extraction rates of all three metals, but decreases the partition coefficients. Therefore, selecting the appropriate type and concentration of extractant and co-extractant is crucial for specific brine systems.

[0114] In summary, the composite extractant provided by this invention has low water solubility, is stable under acid and alkaline conditions, and has high selectivity for both lithium-calcium and lithium-sodium. It can effectively extract lithium in high-calcium and high-sodium brines with calcium ion concentrations greater than 160 g / L and sodium ion concentrations greater than 4 g / L, while exhibiting low extraction rates for sodium and calcium.

[0115] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a composite extractant for the selective extraction of lithium from high-calcium, high-sodium brine, characterized in that, The composite extractant consists of a neutral organophosphorus extractant, a ketone co-extractant, and a diluent. The neutral organophosphorus extractant is any one or a combination of at least two of the following: tri-n-butylphosphine oxide, diisoamyl methylphosphonate, butyl dibutyl phosphonate, triisobutyl phosphate, or dioctyl dibutyl phosphate. The ketone co-extractants include water-insoluble alkyl ketones and / or water-insoluble aromatic ketones; The alkyl ketones include any one or a combination of at least two of the following: diisobutyl ketone, methyl isobutyl ketone, 2-heptanone, 2-octanone, 2-nonanone, methyl nonyl ketone, or dipentyl ketone. The aromatic ketones include acetophenone; The calcium ion concentration in the high-calcium and high-sodium brine is greater than 160 g / L, and the sodium ion concentration is greater than 4 g / L. The volume ratio of the neutral organophosphorus extractant to the ketone co-extractant is (1-4):1; The volume of the diluent is 10-60% of the volume of the composite extractant; The selective extraction of lithium from high-calcium, high-sodium brine employs the following method, including the following steps: (1) After adjusting the pH value of the brine, ferric chloride is mixed with the brine to obtain the aqueous phase before extraction; (2) The aqueous phase obtained in step (1) before extraction is mixed with the composite extractant for extraction, and the organic phase and aqueous phase are separated. In step (1), the molar ratio of iron ions to lithium ions in the aqueous phase before extraction is (1-6):

1.

2. The application according to claim 1, characterized in that, The diluent includes C4-C. 14 Alkanes, C4-C 14 ester compounds, C4-C 14 Any one or a combination of at least two of alcohol compounds or kerosene solvents.

3. The application according to claim 1, characterized in that, The pH value in step (1) is 0-2.

0.

4. The application according to claim 1, characterized in that, The volume ratio of the composite extractant to the aqueous phase before extraction in step (2) is (1-10):

1.

5. The application according to claim 1, characterized in that, The extraction method described in step (2) includes single-stage extraction and / or multi-stage countercurrent extraction.

6. The application according to claim 1, characterized in that, The extraction method also includes: back-extracting the organic phase obtained in step (2).

7. The application according to claim 6, characterized in that, The volume ratio of the stripping agent to the organic phase used in the stripping process is 1:(1-20).

8. The application according to claim 7, characterized in that, The stripping agent includes an acid.

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