A method for removing magnesium from salt lake brine

Abstract

The present invention relates to a method for removing magnesium from salt lake brine, the method comprising the following steps: (1) extracting magnesium in the salt lake brine under the condition of pH value of 8-10 by using an extraction system containing an extractant, and then performing solid-liquid separation to obtain a magnesium-loaded organic phase; (2) performing gas-liquid-liquid three-phase extraction on the magnesium-loaded organic phase obtained in step (1) to obtain a magnesium stripping solution; (3) heat-treating the magnesium stripping solution obtained in step (2) to obtain a magnesium product. The method for removing magnesium provided by the present invention can separate magnesium and lithium in the salt lake brine, obtain a magnesium-loaded organic phase, and finally obtain a magnesium product with high purity, and the purity of the obtained magnesium product can reach more than 99%.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, and in particular to a method for removing magnesium from salt lake brine. Background Art

[0002] Lithium is the lightest metal and is widely used in electronics, chemistry, new energy, pharmaceuticals and other fields. Lithium resources in nature are mainly found in solid ores and liquid brines. Among them, salt lake brine has the advantages of large lithium resources and low cost, and is an important source of lithium resources. Since salt lake brine also contains magnesium ions, the similarity of magnesium and lithium properties makes it difficult to develop lithium resources in salt lakes. Therefore, in order to develop and utilize lithium resources in salt lake brine, magnesium must be removed from the salt lake brine first.

[0003] At present, the main methods for separating magnesium and lithium from brine are precipitation, calcination, adsorption and extraction. Among them, the precipitation method consumes a lot of alkali, has a low lithium recovery rate, and the alkali residue produced is easy to cause secondary pollution; the calcination method has a large amount of water evaporation, high energy consumption, and high requirements and losses on equipment; the adsorption method has problems such as high adsorbent cost, low adsorption capacity and adsorbent dissolution.

[0004] CN112174170A discloses a process for deep removal of magnesium from salt lake brine by a double alkali combined method. The process utilizes sodium carbonate and sodium hydroxide to precipitate magnesium and realizes the precipitation and separation of magnesium. However, about 0.10 g / L of magnesium still remains in the solution after magnesium removal, and the filtration process of magnesium slag is relatively difficult and difficult to operate continuously. At the same time, the large amount of alkaline magnesium slag produced is a hazardous waste that is extremely difficult to handle and may even cause serious harm to the environment.

[0005] CN109019641A discloses a method for separating magnesium and lithium from sodium sulfate subtype salt lake brine and enriching lithium. The method is for sodium sulfate subtype salt lake brine, and uses a variable temperature method to concentrate the brine, and finally achieves the separation of lithium and magnesium. The process has high energy consumption, a long production cycle, and a high lithium loss rate.

[0006] Therefore, developing a method for removing magnesium from salt lake brine that is low-cost, highly efficient, has a large processing volume and is easy to industrialize is an issue that is urgently needed. Summary of the invention

[0007] In view of the above problems, the purpose of the present invention is to provide a method for removing magnesium from salt lake brine. Compared with the prior art, the method provided by the present invention can separate magnesium and lithium from salt lake brine efficiently and at low cost, and can purify the separated magnesium to obtain a magnesium product, thereby ultimately realizing the resource utilization of magnesium.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for removing magnesium from salt lake brine, the method comprising the following steps:

[0010] (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH of 8-10, and then separating to obtain a magnesium-loaded organic phase;

[0011] (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase back extraction to obtain a magnesium stripping solution;

[0012] (3) heat-treating the magnesium stripping solution obtained in step (2) to obtain a magnesium product.

[0013] The present invention extracts magnesium from salt lake brine by using an extraction system containing an extractant under the condition of pH value of 8-10, thereby separating magnesium and lithium in the salt lake brine, allowing magnesium to enter the magnesium-loaded organic phase, while lithium is retained in the raffinate, and the raffinate can be used to extract high value-added lithium elements. The magnesium-loaded organic phase obtained by the present invention is further subjected to gas-liquid-liquid three-phase extraction to obtain a magnesium stripping solution, and the magnesium stripping solution is further heat-treated to obtain a magnesium product, which is mainly high-purity magnesium carbonate, and the purity of the magnesium carbonate can reach more than 99%. The method provided by the present invention can remove magnesium from salt lake brine, and can further extract magnesium to obtain a magnesium product with higher utilization value and purity, and has the advantages of low processing cost, large processing volume and high processing efficiency. Compared with the currently commonly used alkali neutralization method, the magnesium removal method provided by the present invention can avoid the generation of alkaline magnesium slag, and is environmentally friendly, can be continuously operated, and is easy to industrialize.

[0014] An extraction system containing an extractant is used to extract magnesium from salt lake brine at a pH value of 8-10. The pH value may be, for example, 8, 8.5, 9, 9.5 or 10, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0015] The present invention preferably controls the pH value of the extraction within a specific range, so as to achieve a better extraction effect.

[0016] The present invention has no particular limitation on the separation method, which may be any separation method known in the art, such as filtration or centrifugation.

[0017] Preferably, the concentration of magnesium in the salt lake brine in step (1) is 0.1-3 g / L, for example, it can be 0.1 g / L, 0.2 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, 2.2 g / L, 2.5 g / L, 2.8 g / L or 3 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] Preferably, the concentration of lithium in the salt lake brine is 0.1-1.5 g / L, for example, it can be 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, 1.2 g / L or 1.5 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] The salt lake brine described in the present invention is the common low-magnesium salt lake brine in the art, the magnesium concentration is generally 0.1-3g / L, the lithium concentration is generally 0.1-1.5g / L, and the salt lake brine also contains other elements such as sodium, potassium, calcium or aluminum.

[0020] Preferably, the extraction system in step (1) comprises an extractant and a diluent.

[0021] Preferably, the volume ratio of the extractant to the diluent is (0.05-0.5):1, for example, it can be 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the volume ratio of the salt lake brine to the extraction system is (0.2-5):1, for example, it can be 0.2:1, 0.5:1, 1:1, 2:1, 3:1, 4:1 or 5:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the diluent comprises a hydrocarbon.

[0024] The present invention has no particular limitation on the hydrocarbon, which may be any hydrocarbon known in the art that can be used as a diluent, such as n-dodecane, sulfonated kerosene, S-150 solvent oil or aviation kerosene.

[0025] Preferably, the extractant in step (1) comprises any one of an oxime extractant, a β-diketone extractant or a long-chain fatty acid extractant, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of an oxime extractant and a β-diketone extractant, a combination of a β-diketone extractant and a long-chain fatty acid extractant, or a combination of an oxime extractant, a β-diketone extractant and a long-chain fatty acid extractant.

[0026] Preferably, the oxime extractant includes any one of 5,8-diethyl-7-hydroxy-6-dodecylhydroxyoxime, 5-dodecyl-2-hydroxybenzaldehyde oxime or 1-(2-hydroxy-5-nonylphenyl)ethanone oxime, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of 5,8-diethyl-7-hydroxy-6-dodecylhydroxyoxime and 5-dodecyl-2-hydroxybenzaldehyde oxime, a combination of 5-dodecyl-2-hydroxybenzaldehyde oxime and 1-(2-hydroxy-5-nonylphenyl)ethanone oxime, or a combination of 5,8-diethyl-7-hydroxy-6-dodecylhydroxyoxime, 5-dodecyl-2-hydroxybenzaldehyde oxime and 1-(2-hydroxy-5-nonylphenyl)ethanone oxime.

[0027] Preferably, the β-diketone extractant includes any one of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone or decylphenyl-ethyl-β-diketone, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of dodecylphenol-alkyl-β-diketone and dodecylphenyl-ethyl-β-diketone, a combination of dodecylphenyl-ethyl-β-diketone and decylphenyl-ethyl-β-diketone, or a combination of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone and decylphenyl-ethyl-β-diketone.

[0028] Preferably, the long-chain fatty acid extractant includes any one of 4-methyl-2-propyldecanoic acid, 3-propylundecanoic acid, 2-propyltridecanoic acid, 2-propyltetradecanoic acid or isostearic acid, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of 4-methyl-2-propyldecanoic acid and 3-propylundecanoic acid, a combination of 2-propyltridecanoic acid and 2-propyltetradecanoic acid, or a combination of 2-propyltridecanoic acid, 2-propyltetradecanoic acid and isostearic acid.

[0029] Preferably, the magnesium concentration in the magnesium-loaded organic phase of step (1) is 0.49-5 g / L, for example, 0.49 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the gas-liquid-liquid three-phase back extraction system in step (2) comprises a first liquid phase, a second liquid phase and a gas phase.

[0031] Preferably, the first liquid phase comprises a magnesium loaded organic phase.

[0032] Preferably, the second liquid phase comprises water.

[0033] Preferably, the volume ratio of the first liquid phase to the second liquid phase is (0.1-20):1, for example, it can be 0.1:1, 1:1, 2:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1 or 20:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the gas phase comprises acid gases.

[0035] Preferably, the acid gas comprises CO2.

[0036] Preferably, the pH value of the gas-liquid-liquid three-phase back extraction in step (2) is 6-7, for example, it can be 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] The present invention preferably controls the pH value of the gas-liquid-liquid three-way back extraction within a specific range, so as to achieve a better back extraction effect.

[0038] Preferably, the gas-liquid-liquid three-phase stripping method includes single-stage stripping or multi-stage stripping.

[0039] Preferably, the multi-stage stripping comprises multi-stage countercurrent stripping.

[0040] The present invention has no special limitation on the number of stages of the multi-stage extraction, which can be adjusted according to actual working conditions, and is generally 1-10 stages.

[0041] The present invention has no special limitation on the extraction and stripping devices, which may be any device for extraction or stripping in the art, such as an extraction tower or an extractor.

[0042] Preferably, the magnesium concentration in the magnesium stripping solution of step (2) is greater than 9 g / L, for example, it may be 10 g / L, 11 g / L or 12 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the temperature of the heat treatment in step (3) is 60-90°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] As a preferred technical solution of the present invention, the method comprises the following steps:

[0045] (1) extracting magnesium from salt lake brine with an extraction system containing an extractant at a pH value of 8-10, and then separating to obtain a magnesium-loaded organic phase; the concentration of magnesium in the salt lake brine is 0.1-3 g / L, and the concentration of lithium is 0.1-1.5 g / L; the extraction system comprises an extractant and a diluent; the volume ratio of the extractant to the diluent is (0.05-0.5):1; the volume ratio of the salt lake brine to the extraction system is (0.2-5):1; the extractant comprises any one of an oxime extractant, a β-diketone extractant or a long-chain fatty acid extractant, or a combination of at least two of them; the oxime extractant comprises 5,8-diethylhexane; The extractant comprises any one or a combination of at least two of 7-hydroxy-6-dodecylhydroxyoxime, 5-dodecyl-2-hydroxybenzaldehyde oxime or 1-(2-hydroxy-5-nonylphenyl)ethanone oxime; the β-diketone extractant comprises any one or a combination of at least two of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone or decylphenyl-ethyl-β-diketone; the long-chain fatty acid extractant comprises any one or a combination of at least two of 4-methyl-2-propyldecanoic acid, 3-propylundecanoic acid, 2-propyltridecanoic acid, 2-propyltetradecanoic acid or isostearic acid; the magnesium concentration in the magnesium-loaded organic phase is 0.49-5 g / L;

[0046] (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase phase extraction at a pH value of 6-7 to obtain a magnesium stripping solution; the gas-liquid-liquid three-phase phase extraction system comprises a first liquid phase, a second liquid phase and a gas phase; the first liquid phase comprises a magnesium-loaded organic phase; the second liquid phase comprises water; the volume ratio of the first liquid phase to the second liquid phase is (0.1-20):1; the gas phase comprises CO2; the magnesium concentration in the magnesium stripping solution is >9 g / L;

[0047] (3) heat treating the magnesium stripping solution obtained in step (2) at 60-90° C. to obtain a magnesium product.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The method for removing magnesium from salt lake brine provided by the present invention can separate magnesium and lithium in salt lake brine through extraction with an extractant, gas-liquid-liquid three-phase extraction and heat treatment to obtain a magnesium-loaded organic phase, and finally obtain a high-purity magnesium product. Under optimal conditions, the recovery rate of magnesium can reach more than 96.4%, and the purity of magnesium carbonate can reach more than 99%.

[0050] (2) The method for removing magnesium from salt lake brine provided by the present invention has low cost, high treatment efficiency, large treatment capacity, continuous operation, environmental friendliness, no secondary pollution, and is easy to industrialize. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for removing magnesium from salt lake brine, the method comprising the following steps:

[0054] (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH of 9, and then filtering to obtain a magnesium-loaded organic phase; the concentration of magnesium in the salt lake brine is 1.5 g / L, and the concentration of lithium is 0.2 g / L; the extraction system comprises an extractant and a diluent; the volume ratio of the extractant to the diluent is 0.27:1; the volume ratio of the salt lake brine to the extraction system is 2.6:1; the extractant is 5,8-diethyl-7-hydroxy-6-dodecanoic acid oxime, and the diluent is n-dodecane;

[0055] (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase three-stage countercurrent stripping at a pH value of 6.5 to obtain a magnesium stripping solution; the first liquid phase of the gas-liquid-liquid three-phase is the magnesium-loaded organic phase; the second liquid phase is water; the volume ratio of the first liquid phase to the second liquid phase is 2.5:1; and the gas phase is CO2;

[0056] (3) heat-treating the magnesium stripping solution obtained in step (2) at 75° C. to obtain a magnesium carbonate product.

[0057] Example 2

[0058] This embodiment provides a method for removing magnesium from salt lake brine, the method comprising the following steps:

[0059] (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH of 8, and then filtering to obtain a magnesium-loaded organic phase; the concentration of magnesium in the salt lake brine is 3 g / L, and the concentration of lithium is 0.6 g / L; the extraction system comprises an extractant and a diluent; the volume ratio of the extractant to the diluent is 0.5:1; the volume ratio of the salt lake brine to the extraction system is 0.2:1; the extractant is dodecylphenol-alkyl-β-diketone, and the diluent is sulfonated kerosene;

[0060] (2) subjecting the magnesium-loaded organic phase obtained in step (1) to three-stage gas-liquid-liquid countercurrent stripping at a pH of 6 to obtain a magnesium stripping solution; the first liquid phase of the gas-liquid-liquid three-phase is the magnesium-loaded organic phase; the second liquid phase is water; the volume ratio of the first liquid phase to the second liquid phase is 18:1; and the gas phase is CO2;

[0061] (3) heat-treating the magnesium stripping solution obtained in step (2) at 90° C. to obtain a magnesium carbonate product.

[0062] Example 3

[0063] This embodiment provides a method for removing magnesium from salt lake brine, the method comprising the following steps:

[0064] (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH of 10, and then filtering to obtain a magnesium-loaded organic phase; the concentration of magnesium in the salt lake brine is 0.1 g / L, and the concentration of lithium is 1.2 g / L; the extraction system comprises an extractant and a diluent; the volume ratio of the extractant to the diluent is 0.05:1; the volume ratio of the salt lake brine to the extraction system is 5:1; the extractant is 4-methyl-2-propyldecanoic acid, and the diluent is S-150 solvent oil;

[0065] (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase three-stage countercurrent stripping at a pH value of 7 to obtain a magnesium stripping solution; the first liquid phase of the gas-liquid-liquid three-phase is the magnesium-loaded organic phase; the second liquid phase is water; the volume ratio of the first liquid phase to the second liquid phase is 20:1; and the gas phase is CO2;

[0066] (3) heat-treating the magnesium stripping solution obtained in step (2) at 60° C. to obtain a magnesium carbonate product.

[0067] Example 4

[0068] This embodiment provides a method for removing magnesium from salt lake brine. The only difference compared with Embodiment 1 is that the pH of the gas-liquid-liquid three-phase extraction in step (2) is 8.

[0069] Example 5

[0070] This embodiment provides a method for removing magnesium from salt lake brine. The only difference compared with Example 1 is that the extractant in step (1) is replaced by tributyl phosphate.

[0071] Comparative Example 1

[0072] This comparative example provides a method for removing magnesium from salt lake brine, the only difference compared with Example 1 is that the pH of the extraction in step (1) is 7.

[0073] Comparative Example 2

[0074] This comparative example provides a method for removing magnesium from salt lake brine, which is different from Example 1 only in that the pH of the extraction in step (1) is 11.

[0075] The magnesium concentrations in the magnesium-loaded organic phase and the magnesium stripping solution of Examples 1-5 and Comparative Examples 1-2 were measured using an inductively coupled plasma optical emission spectrometer ICP-OES. The results are shown in Table 1.

[0076] The purity of the magnesium carbonate described in Examples 1-5 and Comparative Examples 1-2 was determined by the method described in GB / T 27814-2011 Anhydrous Magnesium Carbonate. The results are shown in Table 1.

[0077] The recovery rate of magnesium in the magnesium carbonate described in Examples 1-5 and Comparative Examples 1-2 was calculated as follows:

[0078] Extraction rate:

[0079] Stripping rate:

[0080] Among them, V A 、V O and V' A Respectively represent the volume of salt lake brine in the extraction stage, the volume of magnesium-loaded organic phase and the volume of magnesium stripping solution in the stripping stage, in L; C A , C O and C' A They represent the magnesium concentration in the salt lake brine in the extraction stage, the magnesium concentration in the magnesium-loaded organic phase, and the magnesium concentration in the magnesium stripping solution, respectively, in g / L.

[0081] The recovery rate of magnesium is: P(Mg)=Ex(Mg)×St(Mg), in %.

[0082] The results are shown in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] In Table 1, “-” means that there is little or no product and the data cannot be measured.

[0087] From Table 1, we can see the following points:

[0088] (1) It can be seen from the data of Examples 1-5 that the method for removing magnesium from salt lake brine provided by the present invention can remove magnesium from salt lake brine and obtain a magnesium product. Under optimal conditions, the recovery rate of magnesium can reach more than 96.4%, and the purity of magnesium carbonate can reach more than 99%.

[0089] (2) A comprehensive comparison of the data of Example 1 and Example 4 shows that the pH of the gas-liquid-liquid three-phase extraction in Example 1 is 6.5, compared with the pH of 8 in the gas-liquid-liquid three-phase extraction in Example 4. The recovery rate of magnesium in Example 1 is 96.4%, and the purity of magnesium carbonate is 99.5%, while the recovery rate of magnesium in Example 4 is only 37.1%, and the purity of magnesium carbonate is 99.1%. This shows that the present invention preferably controls the pH of the gas-liquid-liquid three-phase extraction within a specific range, which can improve the recovery rate of magnesium and the purity of magnesium carbonate.

[0090] (3) A comprehensive comparison of the data of Example 1 and Example 5 shows that the only difference between Example 5 and Example 1 is that the extractant is replaced by tributyl phosphate. The recovery rate of magnesium in Example 5 is much lower than that in Example 1, and the purity of the product cannot be determined due to the small amount of the product. This shows that the preferred extractant of the present invention includes any one of an oxime extractant, a β-diketone extractant or a long-chain fatty acid extractant, or a combination of at least two of them, which can improve the recovery rate of magnesium and the purity of magnesium carbonate.

[0091] (4) Comprehensively comparing the data of Example 1 and Comparative Examples 1-2, the only difference between Comparative Example 1 and Example 1 is that the extraction pH is 7, and the only difference between Comparative Example 2 and Example 1 is that the extraction pH is 11. The recovery rate of magnesium and the purity of magnesium carbonate in Comparative Example 1 are lower than those in Example 1. In Comparative Example 2, a precipitate of Mg is formed, and Mg cannot be extracted. This shows that the present invention controls the extraction pH within a specific range, which can improve the recovery rate of magnesium and the purity of magnesium carbonate.

[0092] In summary, the method for removing magnesium from salt lake brine provided by the present invention can separate magnesium and lithium in salt lake brine through extraction with an extractant, gas-liquid-liquid three-phase extraction and heat treatment, obtain a magnesium-loaded organic phase, and ultimately obtain a magnesium product with a higher purity.

[0093] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for removing magnesium from salt lake brine, characterized in that: The method comprises the following steps: (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH of 8-9.5, and then separating to obtain a magnesium-loaded organic phase; The extractant is a β-diketone extractant; The β-diketone extractant includes any one of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone or decylphenyl-ethyl-β-diketone or a combination of at least two thereof; The concentration of magnesium in the salt lake brine is 0.1-3 g / L; The concentration of lithium in the salt lake brine is 0.1-1.5 g / L; (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase back extraction to obtain a magnesium stripping solution; (3) heat-treating the magnesium stripping solution obtained in step (2) to obtain a magnesium product.

2. The method according to claim 1, characterized in that The extraction system in step (1) comprises an extractant and a diluent.

3. The method according to claim 2, characterized in that The volume ratio of the extractant to the diluent is (0.05-0.5):

1.

4. The method according to claim 1, characterized in that: The volume ratio of the salt lake brine to the extraction system is (0.2-5):

1.

5. The method according to claim 2, characterized in that: The diluent includes a hydrocarbon.

6. The method according to claim 1, characterized in that The magnesium concentration in the magnesium-loaded organic phase of step (1) is 0.49-5 g / L.

7. The method according to claim 1, characterized in that The gas-liquid-liquid three-phase reverse extraction system in step (2) comprises a first liquid phase, a second liquid phase and a gas phase.

8. The method according to claim 7, characterized in that The first liquid phase includes a magnesium-loaded organic phase.

9. The method according to claim 7, characterized in that: The second liquid phase includes water.

10. The method according to claim 7, characterized in that The volume ratio of the first liquid phase to the second liquid phase is (0.1-20):

1.

11. The method according to claim 7, characterized in that The gas phase includes acid gases.

12. The method according to claim 11, characterized in that The acid gas includes CO2.

13. The method according to claim 1, characterized in that The pH value of the gas-liquid-liquid three-phase back extraction in step (2) is 6-7.

14. The method according to claim 1, characterized in that The gas-liquid-liquid three-phase stripping method includes single-stage stripping or multi-stage stripping.

15. The method according to claim 14, characterized in that The multi-stage stripping includes multi-stage countercurrent stripping.

16. The method according to claim 1, characterized in that The magnesium concentration in the magnesium stripping solution of step (2) is greater than 9 g / L.

17. The method according to claim 1, characterized in that The temperature of the heat treatment in step (3) is 60-90°C.

18. The method according to claim 1, characterized in that The method comprises the following steps: (1) extracting magnesium from salt lake brine using an extraction system containing an extractant at a pH value of 8-9.5, and then separating to obtain a magnesium-loaded organic phase; the concentration of magnesium in the salt lake brine is 0.1-3 g / L, and the concentration of lithium is 0.1-1.5 g / L; the extraction system comprises an extractant and a diluent; the volume ratio of the extractant to the diluent is (0.05-0.5):1; the volume ratio of the salt lake brine to the extraction system is (0.2-5):1; the extractant is a β-diketone extractant; the β-diketone extractant comprises any one of dodecylphenol-alkyl-β-diketone, dodecylphenyl-ethyl-β-diketone or decylphenyl-ethyl-β-diketone, or a combination of at least two thereof; the concentration of magnesium in the magnesium-loaded organic phase is 0.49-5 g / L; (2) subjecting the magnesium-loaded organic phase obtained in step (1) to gas-liquid-liquid three-phase phase extraction at a pH value of 6-7 to obtain a magnesium stripping solution; the gas-liquid-liquid three-phase phase extraction system comprises a first liquid phase, a second liquid phase and a gas phase; the first liquid phase comprises a magnesium-loaded organic phase; the second liquid phase comprises water; the volume ratio of the first liquid phase to the second liquid phase is (0.1-20):1; the gas phase comprises CO2; the magnesium concentration in the magnesium stripping solution is >9 g / L; (3) heat treating the magnesium stripping solution obtained in step (2) at 60-90° C. to obtain a magnesium product.

Images