An extraction system and method for extracting lithium from chloride-type salt lake brine

Abstract

This invention provides an extraction system and method for lithium extraction from chloride-type brine. The extraction system includes an extractant, a diluent, and ferric chloride. The extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate, dihexylhexyl phosphate, dibutyl-2-ethylhexyl phosphate, and dihexyl-2-ethylhexyl phosphate. This invention eliminates the formation of a third phase during lithium extraction from chloride-type brine using this extraction system, and exhibits low organic phase solubility, making it more environmentally friendly. The countercurrent cascade process results in a high lithium extraction rate. The extractant, diluent, and ferric chloride can all be recycled. The lithium extraction process using this system is simple and highly reliable.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction technology from salt lakes, and particularly relates to an extraction system and extraction method for extracting lithium from chloride-type salt lake brines. Background Technology

[0002] Lithium, with an atomic number of 3, is the lightest metal in the world. Lithium and its compounds are widely used in modern industry, including lithium batteries, lithium-ion batteries, heat-resistant glass, ceramics, and lithium-ion grease lubricants. Due to the rapid development of the new energy industry, lithium battery production has surged, leading to a significant increase in lithium consumption. A recent report released by the U.S. Geological Survey in 2023 showed that 80% of global lithium production is used in lithium battery manufacturing. China accounts for over 70% of the world's lithium battery production capacity, ranking first globally, thus having a huge demand for lithium. In 2022, China consumed 505,000 tons of lithium carbonate alone, accounting for 81% of the global total. Currently, China mainly relies on imports of lithium raw materials to meet domestic production needs.

[0003] my country is the world's fifth largest lithium resource country, with metallic lithium reserves of 5.4 million tons. More than 60% of my country's lithium resources are stored in salt lakes in the Qinghai-Tibet Plateau region, with the Qaidam Basin alone containing approximately 15 million tons of lithium resources (calculated as LiCl). However, the salt lakes in the Qinghai-Tibet Plateau region are of low grade and have very high magnesium-to-lithium ratios (50-2000). For example, the largest salt lake in China, the Qarhan Salt Lake (1.63 million tons), has a magnesium-to-lithium ratio as high as 1500.

[0004] To address the technical challenge of extracting lithium from high magnesium-to-lithium ratio brine in salt lakes, the academic community has developed various techniques, such as membrane separation, adsorption, precipitation-calcination, electrochemical deintercalation / intercalation, and solvent extraction. Solvent extraction technology has attracted significant attention due to its advantages of low cost, high efficiency, simple operation, and ease of industrial scale-up. Current lithium extraction systems from salt lakes all contain tributyl phosphate (TBP) in the organic phase, with TBP playing a major role. However, TBP systems are prone to the formation of a third phase, and TBP has a high solubility, which has adverse effects on the salt lake environment. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an extraction system and method for extracting lithium from chloride-type salt lake brine. This extraction system avoids the formation of a third phase during the lithium extraction process from chloride-type salt lakes, and has low solubility of the organic phase, making it more environmentally friendly; the lithium extraction rate is also high.

[0006] This invention provides an extraction system for lithium extraction from chloride-type salt lake brine, comprising an extractant, a diluent, and ferric chloride;

[0007] The extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate, dihexylhexyl phosphate, dibutyl-2-ethylhexyl phosphate, and dihexyl-2-ethylhexyl phosphate.

[0008] Preferably, the extractant accounts for 40-80 vol%, and the diluent accounts for 20-60 vol%.

[0009] The molar concentration ratio of lithium in ferric chloride to that in chloride-type salt lake brine is 1–2.

[0010] Preferably, the diluent is selected from kerosene, sulfonated kerosene, white oil, n-heptane, cyclohexane, or other C6-C13 hydrocarbons.

[0011] This invention provides a method for extracting lithium from chloride-type salt lake brine using the extraction system described above, comprising the following steps:

[0012] The extraction system was mixed with chloride-type brine from a salt lake with a pH of 1–3, and extracted to obtain a loaded organic phase.

[0013] The supported organic phase and washing solution are mixed and washed to obtain the organic phase product;

[0014] The organic phase product and the back-extracting agent are mixed and back-extracted to obtain a lithium-containing back-extracting solution.

[0015] Preferably, the volume ratio of the extraction system to the chloride-type salt lake brine with a pH of 1 to 3 is (3:1) to (1:5);

[0016] The extraction stage is one stage or multiple stages of countercurrent extraction; the multiple stages of countercurrent extraction are 3 to 10 stages.

[0017] Preferably, the volume ratio of the supported organic phase to the washing liquid is (10:1) to (50:1);

[0018] The washing process consists of one or more counter-current washing stages, wherein the number of stages in the multi-stage counter-current washing is 2 to 4.

[0019] Preferably, the volume ratio of the organic phase product to the stripping agent is (10:1) to (50:1);

[0020] The back-extraction stage is one stage or more countercurrent back-extraction stages, and the number of stages in the multi-stage countercurrent back-extraction stage is 2 to 4 stages.

[0021] Preferably, the washing solution is a mixed solution of hydrochloric acid and a chloride-containing inorganic salt, wherein the concentration of hydrochloric acid is 0.5–3 mol / L and the concentration of chloride ions is ≥6 mol / L.

[0022] Preferably, the stripping agent is hydrochloric acid, and the concentration of the hydrochloric acid is 6-8 mol / L.

[0023] Preferably, the chloride ion content in the chloride-type salt lake brine with a pH of 1 to 3 is not less than 223 g / L.

[0024] This invention provides an extraction system for lithium extraction from chloride-type brine, comprising an extractant, a diluent, and ferric chloride; the extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate, dihexylhexyl phosphate, dibutyl-2-ethylhexyl phosphate, and dihexyl-2-ethylhexyl phosphate. This invention's extraction system for lithium extraction from chloride-type brine avoids the formation of a third phase, exhibits low organic phase solubility, and is more environmentally friendly; through a countercurrent cascade process, the lithium extraction rate is high. In this invention, the extractant, diluent, and ferric chloride can all be recycled. The process for lithium extraction from chloride-type brine using this extraction system is simple and has high operational reliability. Detailed Implementation

[0025] This invention provides an extraction system for lithium extraction from chloride-type salt lake brine, comprising an extractant, a diluent, and ferric chloride;

[0026] The extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate (DEHEHP), dihexylhexyl phosphate (DHHP), dibutyl-2-ethylhexyl phosphate (DBEHP), and dihexyl-2-ethylhexyl phosphate (DHEHP).

[0027] The meanings of the above letter abbreviations are shown in the table below:

[0028] B Butyl H Jiji EH 2-Ethylhexyl D two

[0029] The solubility of the extractants used in this invention is 0.22 mg / L for DBEHP, 0.12 mg / L for DHHP, 0.05 mg / L for DHEHP, and 0.02 mg / L for DEHEHP. Solubility refers to the solubility of the extractant in water at room temperature. In this invention, the solubility of all the above-mentioned extractants is lower than that of TBP (TBP's solubility is 0.38 mg / L).

[0030] In this invention, the extractant is prepared by the following method:

[0031] 300 mL of toluene and 9.2 g of sodium were added to a 500 mL four-necked flask. 0.4 mol of dialkyl phosphite was slowly added dropwise under vigorous stirring for approximately 1 hour. After most of the sodium had reacted, the mixture was refluxed at 110–118 °C with stirring to ensure complete sodium reaction. The mixture was cooled to room temperature, and 0.4 mol of alkyl bromide was slowly added dropwise. The mixture was refluxed at 116–118 °C with stirring until the dialkyl phosphite stain disappeared from the silica gel paper chromatogram. The mixture was then cooled to room temperature, and the sodium bromide was washed away with 4 × 200 mL of distilled water. The organic phase was dried over anhydrous sodium sulfate, and the mixture was distilled under reduced pressure. The fraction collected yielded the product extractant.

[0032] The reaction that occurs in the above preparation method is as follows:

[0033] (R1O)2POH+NaOH→(R1O)2PONa+H2O

[0034] (R1O)2PONa+R2Br→R2P(O)(OR1)2+NaBr

[0035] In the above formula, if R1 = n-butyl and R2 = 2-ethylhexyl, then the extractant is DBEHP;

[0036] If R1 = R2 = n-hexyl, then the extractant is DHHP;

[0037] If R1 = n-hexyl and R2 = 2-ethylhexyl, then the extractant is DHEHP;

[0038] If R1 = R2 = 2-ethylhexyl, then the extractant is DEHEHP.

[0039] In this invention, the structural formula of the DBEHP is:

[0040]

[0041] The structural formula of the DHHP is:

[0042]

[0043] The structural formula of DHEHP is:

[0044]

[0045] The structural formula of DEHEHP is:

[0046]

[0047] The extractant in this invention comprises 40-80 vol%, and the diluent comprises 20-60 vol%.

[0048] In the extraction system provided by this invention, the molar concentration ratio of ferric chloride to lithium in chloride-type salt lake brine is 1 to 2.

[0049] In this invention, the diluent is selected from kerosene, sulfonated kerosene, white oil, n-heptane, cyclohexane, or other C6-C13 hydrocarbons.

[0050] The content of ferric chloride in the extraction system described in this invention is expressed in terms of iron ions.

[0051] In a specific embodiment, the extraction system is 60 vol% DHHP + 40 vol% sulfonated kerosene, loaded with 18 g / L of iron ions;

[0052] Alternatively, the extraction system may be 70 vol% DEHEHP + 30 vol% sulfonated kerosene, loaded with 14 g / L of iron ions;

[0053] Alternatively, the extraction system may be 70 vol% DHEHP + 30 vol% sulfonated kerosene, loaded with 16 g / L of iron ions;

[0054] Alternatively, the extraction system may be 60 vol% DBEHP + 40 vol% sulfonated kerosene, loaded with 14 g / L of iron ions;

[0055] Alternatively, the extraction system may be 40 vol% DEHEHP + 30 vol% DHHP + 30 vol% sulfonated kerosene, loaded with 14 g / L of iron ions;

[0056] Alternatively, the extraction system may be 30 vol% DBEHP + 30 vol% DHEHP + 40 vol% sulfonated kerosene, loaded with 14 g / L of iron ions.

[0057] This invention provides a method for extracting lithium from chloride-type salt lake brine using the extraction system described above, comprising the following steps:

[0058] The extraction system was mixed with chloride-type brine from a salt lake with a pH of 1–3, and extracted to obtain a loaded organic phase.

[0059] The supported organic phase and washing solution are mixed and washed to obtain the organic phase product;

[0060] The organic phase product and the back-extracting agent are mixed and back-extracted to obtain a lithium-containing back-extracting solution.

[0061] This invention employs solvent extraction to extract lithium. Instead of directly extracting lithium from the salt lake water, the lake water is concentrated by sun-drying in a salt pond to obtain brine, which is then selectively extracted using solvent extraction. This invention targets chloride-type salt lakes, where the inorganic salts are primarily chloride-type inorganic salts with a high concentration of chloride ions.

[0062] This invention involves mixing an extraction system with chloride-type brine from a salt lake at a pH of 1–3, followed by extraction to obtain a loaded organic phase. The volume ratio of the extraction system to the chloride-type brine at a pH of 1–3 is (3:1) to (1:5); in specific embodiments, the volume ratio is 2:1, 1.5:1, or 1:1. The extraction process consists of one or more stages of countercurrent extraction; the number of stages in the multi-stage countercurrent extraction is 3–10. The pH value of the chloride-type brine is 1.15, 2.40, 1.86, 1.95, 2.65, or 2.40. The extraction process can be six, seven, four, or eight stages of countercurrent extraction.

[0063] In this invention, the chloride ion content in the chloride-type salt lake brine with a pH of 1-3 is not less than 223 g / L. In a specific embodiment, the chloride-type salt lake brine includes Li... + 1.97 g / L, 1.16 g / L, or 1.69 g / L. The chloride-type salt lake brine includes Cl... - 304g / L, 315g / L or 330g / L.

[0064] In this invention, the extraction time is 10-20 min; the extraction is carried out at room temperature; preferably, the extraction is 10 min, and the phases are separated after standing for 5 min.

[0065] After obtaining the supported organic phase, the present invention mixes the supported organic phase with a washing solution and washes it to obtain the organic phase product. In the present invention, the washing solution is a mixed solution of hydrochloric acid and a chloride-containing inorganic salt, wherein the concentration of hydrochloric acid is 0.5-3 mol / L and the chloride ion concentration is ≥6 mol / L. The mixed solution of hydrochloric acid and the chloride-containing inorganic salt, as a washing solution, can remove most of the impurities in the organic phase. In a specific embodiment, the chloride-containing inorganic salt is magnesium chloride; the washing solution is a mixed solution of 1 mol / L HCl and 3 mol / L MgCl2; or the washing solution is a mixed solution of 2 mol / L HCl and 3 mol / L MgCl2; or the washing solution is a mixed solution of 1.5 mol / L HCl and 3 mol / L MgCl2.

[0066] The volume ratio of the supported organic phase to the washing liquid is (10:1) to (50:1); in a specific embodiment, the volume ratio of the supported organic phase to the washing liquid is 30:1 or 20:1. The washing process consists of one or more countercurrent washing stages, with the number of stages being 2 to 4; in a specific embodiment, the washing process consists of two or three countercurrent washing stages.

[0067] Wash for 15 to 25 minutes, preferably 20 minutes, at room temperature.

[0068] After obtaining the organic phase product, the present invention mixes the organic phase product with a back-extraction agent and back-extracts to obtain the organic phase product. The back-extraction agent is hydrochloric acid, and the concentration of the hydrochloric acid is 6-8 mol / L; in a specific embodiment, the concentration of the hydrochloric acid is 6 mol / L or 8 mol / L. The back-extraction temperature is room temperature; the time is 15-25 min, preferably 20 min.

[0069] The volume ratio of the organic phase product to the stripping agent is (10:1) to (50:1); in specific embodiments, the volume ratio of the organic phase product to the stripping agent is 25:1, 30:1, or 20:1. The stripping process consists of one or more stages of countercurrent stripping, with two to four stages for multi-stage countercurrent stripping. In specific embodiments, the stripping process consists of three stages of countercurrent stripping or two stages of countercurrent stripping.

[0070] In this invention, countercurrent extraction and countercurrent washing are two parts of a complete fractionation process. That is, to ensure lithium recovery, the lithium-containing washing residue is incorporated into the countercurrent extraction for further lithium extraction. The lithium extraction rate mentioned in the examples refers to the lithium extraction rate of the continuous and complete fractionation process, not just the extraction section.

[0071] In this invention, the extractant, ferric chloride, and diluent can all be recycled.

[0072] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of an extraction system and method for lithium extraction from chloride-type salt lake brine provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0073] Example 1

[0074] 1) Preparation of the extraction system: 60 vol% DHHP + 40 vol% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 18g / L;

[0075] 2) Extraction: The pH of the salt lake brine was adjusted to 1.15. The ratio of organic phase to brine (O / A) was 2:1. The mixture was shaken at room temperature for 10 minutes, allowed to stand for 5 minutes to separate the phases, and the organic and aqueous phases were analyzed. The extraction rate of lithium in the single-stage extraction was 75.3%.

[0076] 3) Washing: The washing solution was 1 mol / L HCl + 3 mol / L MgCl2, with an O / A ratio of 20. The mixture was shaken at room temperature for 20 minutes. After three stages of countercurrent washing, most impurities were removed from the organic phase. Following six stages of countercurrent extraction and three stages of countercurrent washing, 96.45% of the lithium was extracted into the organic phase.

[0077] 4) Back-extraction: The back-extraction solution was 6 mol / L HCl, the back-extraction ratio was O / A = 25, and the mixture was shaken at room temperature for 20 minutes. After two-stage countercurrent back-extraction, the back-extraction rate of each element was close to 100%.

[0078] Table 1. Elemental composition of salt lake brine, organic phase products, and back-extraction solution in Example 1.

[0079]

[0080] Example 2

[0081] 1) Preparation of the extraction system: 70 vol% DEHEHP + 30 vol% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 14g / L;

[0082] 2) Extraction: The pH of the salt lake brine was adjusted to 2.40. The ratio of organic phase to brine (O / A) was 1.5:1. The mixture was shaken at room temperature for 10 minutes, allowed to stand for 5 minutes to separate the organic and aqueous phases for analysis. The extraction rate of lithium in a single-stage extraction was 71%.

[0083] 3) Washing: The washing solution was 2 mol / L HCl + 3 mol / L MgCl2, with an O / A ratio of 20. The mixture was shaken at room temperature for 20 minutes. After two stages of countercurrent washing, most impurities were removed from the organic phase. Following seven stages of countercurrent extraction and two stages of countercurrent washing, 98.28% of the lithium was extracted into the organic phase.

[0084] 4) Back-extraction: The back-extraction solution was 8 mol / L HCl, and the back-extraction ratio was O / A = 30. The mixture was shaken at room temperature for 20 minutes. After two-stage countercurrent back-extraction, the back-extraction rate of each element was close to 100%.

[0085] Table 2. Elemental composition of salt lake brine, organic phase products, and back-extraction solution in Example 2.

[0086]

[0087] Example 3

[0088] 1) Preparation of the extraction system: 70 vol% DHEHP + 30 vol% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 16g / L;

[0089] 2) Extraction: The pH of the salt lake brine was adjusted to 1.86. The ratio of organic phase to brine (O / A) was 1.5:1. The mixture was shaken at room temperature for 10 minutes, allowed to stand for 5 minutes to separate the organic and aqueous phases for analysis. The extraction rate of lithium in a single-stage extraction was 68.7%.

[0090] 3) Washing: The washing solution was 1.5 mol / L HCl + 3 mol / L MgCl2, with a washing ratio of O / A = 20. The mixture was shaken at room temperature for 20 minutes. After three stages of countercurrent washing, most impurities were removed from the organic phase. After six stages of countercurrent extraction and three stages of countercurrent washing, the lithium extraction rate reached 97.6%.

[0091] 4) Back-extraction: The back-extraction solution was 8 mol / L HCl, with a back-extraction ratio of O / A = 20. The mixture was shaken at room temperature for 20 minutes. After two-stage countercurrent washing, the back-extraction rate of each element was close to 100%.

[0092] Table 3. Elemental composition of salt lake brine, organic phase products, and back-extraction solution in Example 3.

[0093]

[0094] Example 4

[0095] 1) Preparation of the extraction system: 60 vol% DBEHP + 40 vol% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 14g / L;

[0096] 2) Extraction: The pH of the salt lake brine was adjusted to 1.95, the ratio of organic phase to brine O / A was 1:1, the mixture was shaken at room temperature for 10 minutes, and allowed to stand for 5 minutes to separate the phases. The organic phase and aqueous phase were separated for analysis. The extraction rate of lithium in single-stage extraction was 82%.

[0097] 3) Washing: The washing solution was 2 mol / L HCl + 3 mol / L MgCl2, with an O / A ratio of 20. The mixture was shaken at room temperature for 20 minutes. After two stages of countercurrent washing, most impurities were removed from the organic phase. Following four stages of countercurrent extraction and two stages of countercurrent washing, 97.56% of the lithium was extracted into the organic phase.

[0098] 4) Back-extraction: The back-extraction solution was 8 mol / L HCl, and the back-extraction ratio was O / A = 20. The mixture was shaken at room temperature for 20 minutes. After two-stage countercurrent back-extraction, the back-extraction rate of each element was close to 100%.

[0099] Table 4. Elemental composition of salt lake brine, organic phase products, and back-extraction solution in Example 4.

[0100]

[0101] Example 5

[0102] 1) Preparation of the extraction system: 40 vol% DEHEHP + 30 vol% DHHP + 30% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 14g / L;

[0103] 2) Extraction: The pH of the salt lake brine was adjusted to 2.65, the ratio of organic phase to brine O / A was 1:1, the mixture was shaken at room temperature for 10 minutes, and allowed to stand for 10 minutes for phase separation. The organic phase and aqueous phase were separated for analysis. The extraction rate of lithium in single-stage extraction was 78.6%.

[0104] 3) Washing: The washing solution was 1.5 mol / L HCl + 3 mol / L MgCl2, with an O / A ratio of 20. The mixture was shaken at room temperature for 20 minutes. After two stages of countercurrent washing, most impurities were removed from the organic phase. Following four stages of countercurrent extraction and two stages of countercurrent washing, 99.63% of the lithium was extracted into the organic phase.

[0105] 4) Back-extraction: The back-extraction solution was 6 mol / L HCl, the back-extraction ratio was O / A = 20, and the mixture was shaken at room temperature for 20 minutes. After two-stage countercurrent back-extraction, the back-extraction rate of each element was close to 100%.

[0106] Table 5. Elemental composition of salt lake brine, organic phase products, and back-extraction solution in Example 5.

[0107]

[0108] Example 6

[0109] 1) Preparation of the extraction system: 30 vol% DBEHP + 30 vol% DHEHP + 40 vol% sulfonated kerosene, mixed evenly, and loaded with Fe. 3+ 14g / L;

[0110] 2) Extraction: The pH of the salt lake brine was adjusted to 2.40, the ratio of organic phase to brine O / A was 1.5:1, the mixture was shaken at room temperature for 10 minutes, and allowed to stand for 10 minutes for phase separation. The organic phase and aqueous phase were separated for analysis. The extraction rate of lithium in single-stage extraction was 73.4%.

[0111] 3) Washing: The washing solution was 2 mol / L HCl + 3 mol / L MgCl2, with an O / A ratio of 30. The mixture was shaken at room temperature for 20 minutes. After two stages of countercurrent washing, most impurities were removed from the organic phase. Following eight stages of countercurrent extraction and two stages of countercurrent washing, 99.56% of the lithium was extracted into the organic phase.

[0112] 4) Back-extraction: The back-extraction solution was 8 mol / L HCl, the back-extraction ratio was O / A = 30, and the mixture was shaken at room temperature for 20 minutes. After three stages of countercurrent back-extraction, the back-extraction rate of each element was close to 100%.

[0113] Table 6. Elemental composition of salt lake brine, supported organic phase, and back-extraction solution in Example 6.

[0114]

[0115] As shown in the above embodiments, this invention provides an extraction system for lithium extraction from chloride-type salt lake brine, comprising an extractant, a diluent, and ferric chloride; the extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate, dihexylhexyl phosphate, dibutyl-2-ethylhexyl phosphate, and dihexyl-2-ethylhexyl phosphate. In this invention, the extraction system for lithium extraction from chloride-type salt lake brine does not produce a third phase, and the organic phase exhibits low solubility, making it more environmentally friendly; the lithium extraction rate is high after a countercurrent cascade process. The extractant, diluent, and ferric chloride in this invention can all be recycled. The lithium extraction process using the above extraction system is simple and has high operational reliability. Experimental results show that after a countercurrent cascade process, the lithium extraction rate reaches 96.45%–99.63%, successfully preparing a lithium chloride enrichment solution from chloride-type salt lake brine.

[0116] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An extraction system for lithium extraction from chloride-type salt lake brines, comprising an extractant, a diluent, and ferric chloride; The extractant is selected from one or more of di(2-ethylhexyl)-2-ethylhexyl phosphate, dihexylhexyl phosphate, dibutyl-2-ethylhexyl phosphate, and dihexyl-2-ethylhexyl phosphate; The extractant comprises 40-80 vol, and the diluent comprises 20-60 vol%. The molar concentration ratio of lithium in ferric chloride to that in chloride-type salt lake brine is 1~2; The pH of the chloride-type salt lake brine is 1-3.

2. The extraction system according to claim 1, characterized in that, The diluent is selected from kerosene, sulfonated kerosene, white oil, n-heptane, cyclohexane, or other C6-C13 hydrocarbons.

3. A method for extracting lithium from chloride-type salt lake brine using the extraction system described in any one of claims 1 to 2, comprising the following steps: The extraction system was mixed with chloride-type brine from a salt lake with a pH of 1-3, and extracted to obtain a loaded organic phase. The supported organic phase and washing solution are mixed and washed to obtain the organic phase product; The organic phase product and the back-extracting agent are mixed and back-extracted to obtain a lithium-containing back-extracting solution.

4. The method according to claim 3, characterized in that, The volume ratio of the extraction system to the chloride-type salt lake brine with a pH of 1 to 3 is (3:1) to (1:5); The extraction stage is one stage or multiple stages of countercurrent extraction; the multiple stages of countercurrent extraction are 3 to 10 stages.

5. The method according to claim 3, characterized in that, The volume ratio of the supported organic phase to the washing liquid is (10:1) to (50:1); The washing process consists of one or more counter-current washing stages, wherein the number of stages in the multi-stage counter-current washing is 2 to 4.

6. The method according to claim 3, characterized in that, The volume ratio of the organic phase product to the stripping agent is (10:1) to (50:1); The number of stages of the back-extraction is one stage or more countercurrent back-extraction; the number of stages of the multi-stage countercurrent back-extraction is 2 to 4 stages.

7. The method according to claim 3, characterized in that, The washing solution is a mixed solution of hydrochloric acid and chlorine-containing inorganic salts, with the concentration of hydrochloric acid being 0.5~3 mol / L and the concentration of chloride ions being ≥6 mol / L.

8. The method according to claim 3, characterized in that, The stripping agent is hydrochloric acid, and the concentration of the hydrochloric acid is 6~8 mol / L.

9. The method according to claim 3, characterized in that, The chloride ion content in the chloride-type salt lake brine with a pH of 1-3 is not less than 223 g / L.

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