CN110643836A

CN110643836A - Extraction system, extraction method and application for separating magnesium from magnesium-containing brine by using secondary amide/alkyl ester composite solvent to extract lithium

Info

Publication number: CN110643836A
Application number: CN201911093157.2A
Authority: CN
Inventors: 杨立新; 刘长; 李聪; 周钦耀; 李海博; 李娜
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2019-11-08
Filing date: 2019-11-08
Publication date: 2020-01-03
Anticipated expiration: 2039-11-08
Also published as: CN110643836B

Abstract

The invention discloses an extraction system, an extraction method and application for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium. The extraction system contains secondary amide and alkyl ester which are respectively composed of single compounds or a mixture of more than two compounds, the total number of carbon atoms in a molecule is respectively 12-188-20, and the freezing point of an extraction system is less than 0 ℃. The volume ratio of the organic phase to the brine phase is 1-10: 1, and the brine density is 1.25-1.38 g/cm³And performing single-stage or multi-stage countercurrent extraction at the temperature of 0-50 ℃, performing back extraction to obtain a low magnesium-lithium ratio water phase, and performing concentration, impurity removal and preparation to respectively obtain lithium chloride, lithium carbonate and lithium hydroxide products. The excellent effects of the present invention: the secondary amide extractant has simple molecular structure and easy production, and the alkyl ester improves the physical properties of the composite solvent such as viscosity and the like; li⁺The multi-stage extraction rate is high, the lithium-magnesium separation coefficient is large, and the acid-base consumption is greatly reduced by using water for back extraction; the extraction separation process flow is short, the dissolution loss of an extraction system is small, and the method has good industrial application value.

Description

Extraction system, extraction method and application for separating magnesium from magnesium-containing brine by using secondary amide/alkyl ester composite solvent to extract lithium

Technical Field

The invention relates to a method for extracting lithium from magnesium-containing brine, in particular to an extraction system for separating magnesium from magnesium-containing brine by using a composite solvent to extract lithium, an extraction method and application thereof.

Background

Since this century, the application of lithium in the field of new energy has reached an unprecedented and alarming level both in depth and breadth, and people have made thousands of batteries as power sources for electric vehicles and tens of thousands of batteries as combined structures for energy storage devices, so that the use of lithium materials in 3C products has become increasingly widespread and widespread, and the demand for lithium has increased day by day. Lithium is taken as a key anode and cathode material and an electrolyte raw material in the battery and is obtained from natural resources, and Australia, Chilean, China and Argentina are major countries for producing and storing lithium ores in the world according to the annual book statistics of American mineral products in 2019. China has two types of brine type and hard rock type lithium reserves simultaneously, wherein the amount of salt lake lithium resources accounts for about 80% of the domestic reserves, and the proven lithium salt resource storage amount of the Qinghai firewood Da Mu basin is up to 1982 ten thousand tons (calculated by LiCl) [ beautiful Wu, Liu xi Fang, Zheng xi Ping, etc.. modern chemical engineering, 2017,37(5), 1-5 ].

However, the lithium resources of brine in China are obviously different from those of salt lake brine in 'lithium triangle' region in south America, and besides Tibet Zaubuye carbonate type brine, a large amount of magnesium sulfate subtype brine and magnesium chloride type brine are distributed and extracted from the brineIt is difficult to extract lithium, and a large amount of magnesium salt needs to be removed from the coexisting lithium and magnesium, so that a particularly effective lithium and magnesium separation method is lacked for a long time. The existing production technology for developing the lithium resource in the Qinghai salt lake mainly comprises 4 technologies of an ion adsorption method, a calcination leaching method, a membrane separation method and a solvent extraction method, and all the technologies have defects to different degrees. The extraction method is a method for separating lithium and magnesium by utilizing the special extraction performance of an organic solvent on lithium, and is considered to be the most promising lithium extraction method for brine with high magnesium-lithium ratio [ Song J.F., Nghem L.D., LiX.M., He T.Environ.Sci.: Water Res. technol.,2017,3(4), 593-]The quality of the extracting agent is a key factor of the technical process. Taking tributyl phosphate (TBP) as an extracting agent and FeCl₃The system of co-extractant is continuously and widely researched, and the Jilianmin et al in the patent of invention granted by CN105039743B use TBP and surfactant to form composite extractant to reduce equipment corrosion, extractant dissolution loss and degradation in acidic environment. In the Yuanyuan industry and the like, neutral phosphorus-oxygen compounds and different tertiary amides are selected to be combined or only the tertiary amides are used as an extracting agent in multiple Chinese patent applications such as application numbers 201610383061, X and 201610560041.5, the extraction rate of lithium in brine is improved under the co-extraction effect of iron salts, but the loaded organic phase still needs to be back-extracted by concentrated hydrochloric acid. While the bengqingfen and the like use pyrrole hexafluorophosphate ionic liquid (CN106498184B) and phosphate ionic liquid (CN108866352A), and the Gaojie and the like use TBP-BA-FeCl₃Solvent oil (CN102001692B) was also studied extensively as an extractant for lithium extraction from salt lake brines.

However, the extraction method has not completed the scale test verification and screening of the extracting agent all the time, and the most suitable extraction system has not been found so far. The contradiction of extraction and back extraction and the contradiction of acid and alkali consumption always exist in the lithium extraction technology of the solvent extraction method, the contradiction is not solved fundamentally, the solvent extraction method cannot be a competitive method, and the reason lies in the development of an extraction system and an extraction technology. The alkyl ester is used as a neutral solvent with rich sources and stable property under the catalysis of no acid and alkali, is beneficial to two-phase separation, and can form a new extraction system by combining with other effective components. After the salt lake high magnesium-lithium ratio brine is converted into low magnesium-lithium ratio brine by lithium-magnesium separation, basic chemical products such as lithium chloride, lithium carbonate and lithium hydroxide required in the market can be prepared.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides an extraction system, an extraction method and application for economically and effectively separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium.

The technical scheme and the technical process provided by the invention are as follows:

1. an extraction system for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium, wherein the extraction system contains A and B substances; wherein the A-type substance is a secondary amide and consists of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (I):

wherein R is₁Selected from C2-C12 alkyl or C3-C12 cycloalkyl containing single ring structure, R₂Selected from C1-C11 alkyl or C3-C11 cycloalkyl containing single ring structure, and R₁And R₂The sum of the number of carbon atoms contained in the two groups being 11 to 17, wherein the alkyl or cycloalkyl group includes various isomers (due to R)₁、R₂Is variable when R₁、R₂When uniquely identified, class A is a single compound, and mixtures thereof refer to compounds that follow R₁、R₂A mixture of two or more compounds produced by the change of (1);

wherein the B-type substance is alkyl ester and consists of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (II):

wherein R is₃Selected from C1-C12 alkyl, R₄Is selected fromC1-C15 alkyl, and R₃And R₄The sum of the number of carbon atoms contained in the two alkyl groups is 7 to 19, wherein the alkyl group contains various linear isomers or isomers with branched chains (due to R)₃、R₄Is variable when R₃、R₄When uniquely identified, class B is a single compound, and mixtures thereof refer to compounds that follow R₃、R₄A mixture of two or more compounds produced by the change of (1);

the freezing point of the extraction system containing the substances A and B is less than 0 deg.C (the freezing point of a single component constituting the extraction system may be less than, equal to or greater than 0 deg.C, the conditions for the extraction system of the present invention can be satisfied when the freezing point of the single component is less than 0 deg.C, and when the freezing point of the single component is greater than or equal to 0 deg.C, the single component may be mixed with other components having freezing points less than 0 deg.C, and dissolved to finally form a mixture having a freezing point less than 0 deg.C).

In the extraction system, the volume percentage of the A-type substances in the whole organic phase for extraction is 50-100%, and the end value is not 100%; the volume percentage of the B-type substance in the whole organic phase is 0-50% by taking the synergistic effect, and the end value is not 0%.

The extraction system consisting of the substances A and B also comprises diluent No. 260 solvent oil, No. 300 solvent oil or sulfonated kerosene for dilution.

2. An extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium, which comprises the following steps:

s1, taking magnesium-containing brine as a brine phase before extraction; wherein, in the magnesium-containing brine, the concentration of lithium ions is 0.1-21 g/L, the concentration of magnesium ions is 80-125 g/L, the concentration of chloride ions is 200-400 g/L, the mass ratio of magnesium to lithium is 4.8-1100: 1, and the density of the brine at 20 ℃ is 1.25-1.38 g/cm³The pH value of the brine is 1-7;

s2, taking the extraction system in the step 1 as an organic phase before extraction;

s3, mixing the organic phase before extraction and the brine phase before extraction according to the volume ratio of 1-10: 1, performing single-stage extraction or multi-stage countercurrent extraction, and separating the two phases to obtain a loaded organic phase and an extracted brine phase.

The magnesium-containing brine also contains one or more of sodium ions, potassium ions, iron ions, ferrous ions, sulfate radicals, boric acid, or borate ions.

The magnesium-containing brine comprises lithium-containing salt lake brine, but is not limited to the brine.

Further, in the step S3, the extraction temperature is 0-50 ℃; the mixing of the two phases is carried out by stirring, and the separation of the two phases after extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

Further, after the step S3, the method further includes the steps of:

s4, taking water as a back extraction agent, carrying out single-stage back extraction or multi-stage counter-current back extraction on the loaded organic phase, wherein the volume ratio of the back extraction agent to the loaded organic phase is 1: 1-20, and carrying out two-phase separation to obtain a back-extracted organic phase and a back-extracted aqueous phase;

s5, returning the organic phase after back extraction to the step S2, and realizing the recycling of the extraction system.

Further, in the step S4, the back extraction temperature is 0-50 ℃; the two-phase mixing is carried out by a stirring mode, and the two-phase separation after back extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

3. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium in the preparation of lithium chloride products further comprises the following steps after the step S4:

s6, further removing oil, purifying and concentrating the back-extracted water phase, and then adding an impurity removing agent to remove sulfate radicals and residual magnesium ions to obtain a lithium chloride solution after water phase refining; the impurity removing agent is one or more compounds of calcium oxide, calcium hydroxide, calcium chloride, barium chloride, sodium carbonate, sodium oxalate or sodium hydroxide;

s7, concentrating, crystallizing, separating and drying the refined lithium chloride solution to obtain the lithium chloride product.

4. The application of the extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent in obtaining lithium carbonate serving as a lithium product comprises the following steps after the step S4:

and S8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product.

5. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium in the preparation of lithium hydroxide products further comprises the following steps after the step S4:

s9, electrolyzing the refined lithium chloride solution to obtain a lithium hydroxide product, and simultaneously by-producing hydrogen and chlorine, wherein the hydrogen and chlorine can be used for producing hydrochloric acid;

or after the step S6, the method further includes the steps of:

s8, adding sodium carbonate into the refined lithium chloride solution to obtain lithium carbonate precipitate, and separating and drying the lithium carbonate precipitate to obtain a lithium carbonate product;

and S10, adding calcium hydroxide emulsion into the prepared lithium carbonate, carrying out solid-liquid reaction, separating to obtain a lithium hydroxide solution, and concentrating, crystallizing and drying the lithium hydroxide solution to obtain a lithium hydroxide product.

The secondary amide type compound used in the examples of the present invention was synthesized by reacting an organic acid chloride or acid anhydride with a primary amine in a stoichiometric ratio, purified by washing with water and distillation under reduced pressure, and evaluated by detection using a gas chromatograph-mass spectrometer model 7890A/5975C of agilent usa. The source of the alkyl ester type compound used in the examples of the present invention was obtained from chemical products company.

Compared with the prior art, the invention has the advantages that a secondary amide/alkyl ester composite solvent consisting of the compounds shown in the formula (I) and the formula (II) is used as a new extraction system, so that a new extraction method for separating magnesium from magnesium-containing brine and extracting lithium and application thereof are obtained, unexpected effects are achieved, a literature report that a solvent consisting of a mixture of secondary amide and alkyl ester is used as a brine lithium extraction system is not seen, and a new technology is provided for the current development of a lithium resource of salt lake brine with high magnesium-lithium ratio. The invention has the following advantages:

1) the secondary amide as the A substance in the extraction system has simple molecular structure, easily obtained source, easy production and extraction effect, is a novel special-effect component for separating magnesium and extracting lithium from magnesium-containing brine, wherein the secondary amide functional group is a key part for separating lithium and magnesium and extracting lithium, and hydrogen atoms on N-H are arranged before and after extraction¹Shift of H NMR spectrum to low field, for Li⁺Plays a key role in the extraction. The alkyl ester is used as the B substance in the extraction system and is easy to synthesize, the physical properties such as the viscosity, the freezing point and the like of the composite solvent can be effectively improved, the mixing entropy of the system is increased, and the synergistic effect is generated.

2) In ensuring Li⁺On the premise of single-stage extraction capacity with a certain size, the loaded organic phase is compatible and easy to be directly back-extracted by water, and acid does not need to be used for strengthening Li⁺The back extraction does not need to use alkali to neutralize the acid in the front to restore the extraction capacity of the organic phase and the acid-base property of the water phase, greatly reduces the acid-base consumption in the separation process of the lithium and magnesium brine, realizes the bidirectional balance of the extraction and the back extraction processes, and extracts Li⁺While also facilitating Li⁺Back extraction of (4). After the magnesium-containing brine is subjected to multi-stage countercurrent extraction, the lithium-magnesium separation coefficient is large, and the mass ratio of magnesium to lithium in the water phase after back extraction is remarkably reduced.

3) The whole extraction and separation process is greatly simplified, the organic phase is directly recycled, the corrosion degree of equipment is low, and the production process is easy to control. The low density of the organic phase is suitable for the two-phase separation when the loaded organic phase is back-extracted with water. By adjusting the molecular structure and composition of the extraction system, the solubility of the preferred extraction system in water is significantly reduced compared to the solubility of TBP.

Description of the figures

FIG. 1 is a block diagram of the process flow of the present invention for the separation of magnesium from magnesium-containing brines to extract lithium using a secondary amide/alkyl ester composite solvent.

Table 31 shows the common names, corresponding canonical names and code numbers of the secondary amides of substance A referred to in the examples of the present invention.

Table 32 shows the common names, corresponding specification names and CAS numbers of the alkyl esters of the substances B mentioned in the examples of the present invention.

Detailed Description

The invention is further illustrated by the following examples:

example 1

Li in brine of salt lake in Qinghai Chaaida basin⁺And Mg²⁺The content of the magnesium is 2.01g/L and 113.43g/L respectively, the mass ratio of the magnesium to the lithium is 56.43:1, wherein, Na⁺、K⁺、Cl^-、

And B₂O₃The contents are respectively 3.83, 1.60, 325.98, 44.00 and 8.14g/L, and the brine density is 1.34g/cm³The pH value of the brine is 4.3. 10mL of the brine is taken in a 100mL ground conical flask, then 21mL of N-isooctyl butyramide extractant and 9mL of methyl laurate synergistic extractant are added into the conical flask, the volume of the synergistic extractant occupies 30 percent of the volume of an organic phase, and the volume ratio of the organic phase to the salt lake brine is 3: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. The mixed liquid was then transferred to a 250mL plastic test cartridge and separated bench-top in model LD5-10Centrifuging at 4000r/min for 8min in a core machine, separating two phases to obtain extracted brine sample and loaded Li⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:3 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The extraction rate E, the back-extraction rate S, the partition ratio D, and the lithium-magnesium separation coefficient β were calculated from the concentrations, and the results are shown in table 1.

TABLE 1 Complex solvent of N-isooctylbutanamide and methyl laurate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of^*

^*Wherein the meaning of the symbols is respectively specified^a: the temperature of the extraction is controlled by the temperature,^b: the volume ratio of the organic phase to the aqueous phase,^c：Li⁺the extraction rate is higher than that of the raw materials,^d：Mg²⁺the extraction rate is higher than that of the raw materials,^e： Li⁺the proportion of the ingredients is distributed according to the formula,^f：Mg²⁺the proportion of the ingredients is distributed according to the formula,^g: the separation coefficient of lithium and magnesium is high,^h: the mass ratio of magnesium to lithium in the organic phase after extraction,ⁱ: the mass ratio of magnesium to lithium in the extracted brine;^j: the back-extraction temperature is higher than the normal temperature,^k: the volume ratio of water to the organic phase,^l：Li⁺the back-extraction rate of the copper is improved,^m：Mg²⁺the back-extraction rate of the copper is improved,ⁿ：Li⁺the distribution ratio of the back extraction is controlled,^o： Mg²⁺the distribution ratio of the back extraction is controlled,^p: the back-extraction separation coefficient of lithium and magnesium,^q: the mass ratio of magnesium to lithium in the organic phase after back extraction,^r: the mass ratio of magnesium to lithium in the water phase after back extraction; the same applies to the symbols in tables 2 to 30 below.

As can be seen from Table 1, Li⁺The single-stage extraction rate is 55.27 percent, and Mg²⁺The single-stage extraction rate is 0.21%, and the lithium-magnesium separation coefficient is 561.64. Li⁺Single stage back extraction of 68.38%, Mg²⁺The single-stage back extraction rate is 88.68%, the lithium-magnesium separation coefficient after back extraction is 0.28, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 0.28.

Example 2

27mL of N-butyl nonanamide extractant and 3mL of ethyl nonanoate synergist were taken in a 100mL ground conical flask, the synergist accounted for 10% of the volume of the organic phase, and then 6mL of the salt lake brine obtained in example 1 was added thereto, and the volume ratio of the organic phase to the salt lake brine was 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺Concentration, calculating the experimental results asShown in table 2.

TABLE 2 composite solvent of N-butyl nonanamide and ethyl nonanoate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 2, Li⁺The single-stage extraction rate is 76.94 percent, and Mg²⁺The single-stage extraction rate is 3.42%, and the lithium-magnesium separation coefficient is 94.26. Li⁺The single-stage stripping rate was 75.52%, Mg²⁺The single-stage back extraction rate is 89.96%, the lithium-magnesium separation coefficient after back extraction is 0.34, and the mass ratio of magnesium to lithium in the water phase is reduced to 2.98.

Example 3

24mL of N-isoamyl octanoamide extractant and 6mL of isopropyl myristate co-extractant are taken in a 100mL ground conical flask, the co-extractant occupies 20% of the volume of the organic phase, and then 6mL of salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 0 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 3.

TABLE 3 Complex solvent of N-isopentyl octanoyl amide and isopropyl myristate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 3, Li⁺The single-stage extraction rate is 70.76 percent, and Mg²⁺The single-stage extraction rate is 3.13%, and the lithium-magnesium separation coefficient is 74.86. Li⁺Single stage back extraction of 86.43%, Mg²⁺The single-stage back extraction rate is 88.78%, the lithium-magnesium separation coefficient after back extraction is 0.81, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 2.56.

Example 4

27mL of N-isoamyl octanoamide extractant and 3mL of decyl caprate synergist are taken in a 100mL ground conical flask, the synergist occupies 10% of the volume of an organic phase, and then 6mL of the salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to carry out the addition and subtraction of the brine phase in the extraction and back extraction processesThe water phase is subjected to constant volume, prepared into an analysis solution, sampled and analyzed for Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 4.

TABLE 4 Complex solvent of N-isopentyl caprylamide and decyl caprate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 4, Li⁺The single-stage extraction rate is 78.90 percent, and Mg²⁺The single-stage extraction rate is 1.91%, and the lithium-magnesium separation coefficient is 192.04. Li⁺The single-stage back extraction rate is 80.30 percent, and Mg²⁺The single-stage back extraction rate is 89.85%, the lithium-magnesium separation coefficient after back extraction is 0.46, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 1.53.

Example 5

24.0mL of N-isooctyl isovaleramide extractant and 6mL of isopropyl palmitate co-extractant are taken in a 100mL ground conical flask, the co-extractant occupies 20% of the volume of the organic phase, and then 6mL of the salt lake brine obtained in example 1 is added, wherein the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting the Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and EDTA capacityThe titration method is used for carrying out constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 5.

TABLE 5 Complex solvent of N-isooctyl isovaleramide and isopropyl palmitate for Li in brine of a salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 5, Li⁺The single-stage extraction rate is 51.03 percent, and Mg²⁺The single-stage extraction rate is 3.52%, and the lithium-magnesium separation coefficient is 28.56. Li⁺The single-stage back extraction rate was 93.13%, Mg²⁺The single-stage back extraction rate is 87.30 percent, the lithium-magnesium separation coefficient after back extraction is 1.97, and the mass ratio of magnesium to lithium in the water phase is reduced to 3.65.

Example 6

27mL of N-amyl isononanoamide extractant and 3mL of amyl valerate synergistic extractant are put in a 100mL ground conical flask, the synergistic extractant occupies 10% of the volume of an organic phase, 10mL of salt lake brine in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 3: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding water according to the volume ratio of 1:3 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting Japanese Shimadzu AA-7000 type protogenCarrying out constant volume on a brine phase and a water phase in the extraction and back extraction processes by a standard addition method of a sub-absorption spectrophotometer and an EDTA capacity titration method to prepare an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 6.

TABLE 6 composite solvent of N-pentylisononanamide and amyl valerate for Li in brine of a salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 6, Li⁺The single-stage extraction rate is 43.87 percent, and Mg²⁺The single-stage extraction rate is 3.28%, and the lithium-magnesium separation coefficient is 23.07. Li⁺The single-stage back extraction rate is 92.21 percent, and Mg²⁺The single-stage back extraction rate is 84.11%, the lithium-magnesium separation coefficient after back extraction is 2.23, and the mass ratio of magnesium to lithium in the water phase is reduced to 3.85.

Example 7

38mL of N-amyl isononanoamide extractant and 2mL of ethyl decanoate synergist are put in a 100mL ground conical flask, the synergist occupies 5% of the volume of an organic phase, 10mL of the salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. Then mix the mixtureThe resultant was transferred to a 250mL plastic test tube and centrifuged at 4300r/min for 8min in a model LD5-10 desktop centrifuge to yield a back-extracted organic phase and an aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 7.

TABLE 7 composite solvent of N-amyl isononanamide and ethyl caprate for Li in brine of a salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 7, Li⁺The single-stage extraction rate is 52.68 percent, and Mg²⁺The single-stage extraction rate is 1.10%, and the lithium-magnesium separation coefficient is 100.07. Li⁺The single-stage back extraction rate is 93.61%, Mg²⁺The single-stage back extraction rate is 85.83%, the lithium-magnesium separation coefficient after back extraction is 2.42, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.08.

Example 8

24mL of N-isooctyl-isocaproamide extractant and 6mL of methyl myristate synergist are taken to be placed in a 100mL ground conical flask, the synergist occupies 20% of the volume of an organic phase, and then 6mL of the salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer,back extraction and two-phase mixing were carried out at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 8.

TABLE 8 Complex solvent of N-isooctyl-isohexanamide and methyl myristate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 8, Li⁺The single-stage extraction rate is 43.54 percent, and Mg²⁺The single-stage extraction rate is 1.37%, and the lithium-magnesium separation coefficient is 55.52. Li⁺Single stage back extraction of 91.36%, Mg²⁺The single-stage back extraction rate is 89.36%, the lithium-magnesium separation coefficient after back extraction is 1.26, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 1.74.

Example 9

25.6mL of N-isooctyl caprylamide extractant and 6.4mL of hexyl hexanoate synergic extractant are taken in a 100mL ground conical flask, the synergic extractant occupies 20% of the volume of the organic phase, then 8mL of salt lake brine in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting at 10 ℃ for 20 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). The loaded organic phase was transferred to another 100mL ground flask and deionized water was added at a volume ratio of 1:4 to the organic phaseAnd (3) putting the water into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 10 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 9.

TABLE 9 Complex solvent of N-isooctyl octanoyl amide and hexyl hexanoate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 9, Li⁺The single-stage extraction rate is 39.81 percent, and Mg²⁺The single-stage extraction rate is 4.68 percent, and the lithium-magnesium separation coefficient is 13.57. Li⁺The single-stage back extraction rate was 87.31%, Mg²⁺The single-stage back extraction rate is 75.73%, the lithium-magnesium separation coefficient after back extraction is 2.21, and the mass ratio of magnesium to lithium in the water phase is reduced to 5.75.

Example 10

12mL of N-isobutyl isononanoamide, 12mL of N-isoamyl octanoyl amide as an extractant and 6mL of butyl hexanoate as a synergist are put into a 100mL ground conical flask, the synergist occupies 20% of the volume of an organic phase, and then 6mL of the salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Loading organicTransferring the phases to another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the organic phase, placing the mixture in a DF-101S type heat collection type constant temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 10.

TABLE 10 composite solvent of N-isobutyl isononanamide, N-isopentyl octanoylamide and butyl hexanoate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 10, Li⁺The single-stage extraction rate is 71.70 percent, and Mg²⁺The single-stage extraction rate is 0.83%, and the lithium-magnesium separation coefficient is 302.72. Li⁺Single stage back extraction of 88.34%, Mg²⁺The single-stage back extraction rate is 88.03%, the lithium-magnesium separation coefficient after back extraction is 1.03, and the mass ratio of magnesium to lithium in the water phase is reduced to 0.65.

Example 11

9.6mL of N-isopentyl caprylamide, 9.6mL of N- (3-pentyl) caprylamide (heated liquid) extractant and 4.8mL of ethyl myristate synergist were placed in a 100mL ground conical flask, and the synergist accounted for 20% of the volume of the organic phase, and then 6mL of the salt lake brine obtained in example 1 was added thereto, and the volume ratio of the organic phase to the salt lake brine was 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. The combined liquid was then transferred to a 100mL plastic test cylinder and spun at 4000r/min in a model LD5-10 bench top centrifugeCentrifuging for 8min, separating two-phase interface to obtain extracted brine sample and loaded Li⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:4 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 11.

TABLE 11 Complex solvent of N-isopentyl octanoyl amide, N- (3-pentyl) octanoyl amide and ethyl myristate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 11, Li⁺The single-stage extraction rate is 58.53 percent, and Mg²⁺The single-stage extraction rate is 1.81%, and the lithium-magnesium separation coefficient is 76.57. Li⁺The single-stage back extraction rate is 94.89%, Mg²⁺The single-stage back extraction rate is 83.21%, the lithium-magnesium separation coefficient after back extraction is 3.75, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.53.

Example 12

Taking 10.5mL of N-isoamyl isooctyl amide, 10.5mL of N-isooctyl valeramide extractant and 9mL of isooctyl acetate synergistic extractant in a 100mL ground conical flask, wherein the synergistic extractant occupies 30 percent of the volume of an organic phase, and then adding 6mL of salt lake brine obtained in example 1, wherein the volume ratio of the organic phase to the salt lake brine is 5:1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 12min in an LD5-10 type desk centrifuge at the rotating speed of 4800r/min, the interface of two phases is clear, and the extracted brine sample and the loaded Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4800r/min for 12min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 12.

TABLE 12 composite solvent of N-isopentyl isooctyl amide, N-isooctyl valeramide and isooctyl acetate for Li in brine of salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 12, Li⁺The single-stage extraction rate is 43.69 percent, and Mg²⁺The single-stage extraction rate is 2.04%, and the lithium-magnesium separation coefficient is 37.26. Li⁺Single stage back extraction 68.21%, Mg²⁺The single-stage back extraction rate is 32.60%, the lithium-magnesium separation coefficient after back extraction is 4.44, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.26.

Example 13

Taking 10.5mL of N-isopentyl caprylamide, 10.5mL of N-cyclopropyl capramide extractant and 9mL of methyl laurate synergistic extractant in a 100mL ground conical flask, and adding the synergistic extractantThe volume of the organic phase is 30 percent, and 10mL of the salt lake brine obtained in example 1 is added, wherein the volume ratio of the organic phase to the salt lake brine is 3: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and is centrifuged for 10min at the rotating speed of 4000r/min in an LD5-10 type desk centrifuge, the interface of two phases is clear, and the extracted brine sample and the Li load are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:3 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4000r/min for 10min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 13.

TABLE 13 composite solvent of N-isopentyl caprylamide, N-cyclopropyl capramide and methyl laurate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 13, Li⁺The single-stage extraction rate is 36.42 percent, and Mg²⁺The single-stage extraction rate is 0.92%, and the lithium-magnesium separation coefficient is 61.69. Li⁺Single stage back extraction of 74.22%, Mg²⁺The single-stage back extraction rate is 91.45 percent, the lithium-magnesium separation coefficient after back extraction is 0.27, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.76.

Example 14

32mL of N-pentyliso-carbonylThe nonanamide extractant and 4mL of ethyl decanoate and 4mL of methyl laurate were placed in a 100mL ground conical flask, the synergist occupies 20% of the volume of the organic phase, 10mL of the salt lake brine obtained in example 1 was added, and the volume ratio of the organic phase to the salt lake brine was 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder, and is centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4000r/min, the two-phase interface is clear, and the extracted brine sample and the Li load are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:4 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 14.

TABLE 14 Complex solvent of N-pentylisononanamide, ethyl decanoate and methyl laurate for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 14, Li⁺The single-stage extraction rate is 39.31 percent, and Mg²⁺The single-stage extraction rate is 0.59%, and the lithium-magnesium separation coefficient is 109.76. Li⁺The single-stage back extraction rate is 98.07 percent, and Mg²⁺The single-stage back extraction rate is 97.82%, the lithium-magnesium separation coefficient after back extraction is 1.13, and the mass ratio of magnesium to lithium in the water phase is reduced to 0.84.

Example 15

32mL of N-amyl isononanamide extractant, 4mL of ethyl decanoate synergist and 4mL of No. 260 solvent oil diluent are put into a 100mL ground conical flask, wherein the synergist and the diluent account for 20% of the volume of the organic phase. Then 10mL of the salt lake brine obtained in example 1 was added thereto, and the volume ratio of the organic phase to the salt lake brine was 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder, and is centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4000r/min, the two-phase interface is clear, and the extracted brine sample and the Li load are obtained after phase separation⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:4 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 15.

TABLE 15 combination of N-pentylisononanamide, ethyl decanoate and No. 260 mineral spirits for Li in brine of Qinghai salt lake⁺With Mg²⁺Two-phase separation of

As can be seen from Table 15, Li⁺The single-stage extraction rate is 44.79 percent, and Mg²⁺The single-stage extraction rate is 1.01 percent, and the lithium-magnesium separation coefficient is 83.71. Li⁺Single stage back extraction of 88.15%, Mg²⁺The single-stage back extraction rate is 93.88 percent, the lithium-magnesium separation coefficient after back extraction is 0.48, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.36.

Example 16

15mL of N-isooctyl valeramide extractant, 1.5mL of methyl laurate synergistic extractant and 13.5mL of No. 300 solvent oil diluent are placed in a 100mL ground conical flask together, wherein the synergistic extractant occupies 5% of the volume of an organic phase, and the diluent occupies 45% of the volume of the organic phase, and then 6mL of the salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 30min at 0 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:1 of the loaded organic phase to the organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 30 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 16.

TABLE 16 Complex System of N-isooctylpentanamide, methyl laurate and No. 300 mineral spirit for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 16, Li⁺The single-stage extraction rate is 32.33 percent, and Mg²⁺The single-stage extraction rate is 0.68%, and the lithium-magnesium separation coefficient is 66.26. Li⁺Single stage back extraction of 79.48%, Mg²⁺The single-stage back extraction rate is 58.56%, the lithium-magnesium separation coefficient after back extraction is 2.75, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 0.87.

Example 17

14mL of N-isooctyl valeramide, 2mL of N-ethyl lauramide (liquid after heating) extractant and 4mL of ethyl laurate synergistic extractant are put into a 100mL ground conical flask, the volume of the synergistic extractant occupies 20 percent of the volume of an organic phase, 10mL of salt lake brine obtained in example 1 is added, and the volume ratio of the organic phase to the salt lake brine is 2: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:1 of the loaded organic phase to the organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated and the results are shown in Table 17.

TABLE 17 composite solvent of N-isooctyl pentanamide, N-ethyl lauramide and ethyl laurate for Li in brine of salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 17, Li⁺The single-stage extraction rate is 38.96 percent, and Mg²⁺The single-stage extraction rate is 1.04%, and the lithium-magnesium separation coefficient is 60.72. Li⁺Single stage back extraction of 79.77%, Mg²⁺The single-stage back extraction rate is 72.93%, the lithium-magnesium separation coefficient after back extraction is 1.46, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.38.

Example 18

Putting 8mL of N-isooctyl amide, 2mL of N-dodecyl acetamide extractant and 10mL of ethyl laurate synergistic extractant into a 100mL ground conical flask, wherein the synergistic extractant occupies 50% of the volume of an organic phase, and then adding 2mL of magnesium-containing brine into the ground conical flask, wherein the volume ratio of the organic phase to the brine is 10: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents of the brine are 19.77, 94.91 and 377.85g/L respectively, the mass ratio of magnesium to lithium is equal to 4.80:1, and the density of the brine is 1.32g/cm³The pH value of the brine is 7.0. Inserting polytetrafluoroethylene stirring rod into conical flask, mixing and stirring at 50 deg.C with DW-1-60 type DC constant speed stirrer, and extracting for 20 min. Then naturally clarifying and settling the mixed liquid for 60min, and separating two phases to obtain an extracted brine sample and a loaded Li⁺、Mg²⁺The organic phase of (a). The loaded organic phase was transferred to another 100mL ground flask, deionized water was added at a volume ratio of 1:20 to the organic phase, a Teflon stir bar was inserted, back extraction was performed with a DW-1-60 model DC constant speed stirrer at 50 ℃ and the two phases were mixed for 20 min. And naturally clarifying and settling the mixed liquid for 60min, and separating two phases to obtain an organic phase and a water phase after back extraction.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 18.

TABLE 18 composite solvent of N-isooctyl amide, N-dodecyl acetamide and ethyl laurate for Li in certain magnesium-containing brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 18, Li⁺The single-stage extraction rate is 46.00 percent, and Mg²⁺The single-stage extraction rate is 2.56%, and the lithium-magnesium separation coefficient is 32.41. Li⁺The single-stage back extraction rate is 45.08 percent, and Mg²⁺The single-stage back extraction rate is 57.40%, the lithium-magnesium separation coefficient after back extraction is 0.61, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 0.34.

Example 19

28.2mL of N-isooctyl valeramide, 0.5mL of N-isooctyl neodecanoamide, 0.5mL of N-isooctyl-1-cyclopropyl formamide and 0.5mL of N-hexyl-3-cyclopentyl propionamide are taken as extracting agents, 0.15mL of methyl laurate synergistic extraction agent and 0.15mL of No. 260 solvent oil diluent are put in a 100mL grinding conical flask, wherein the extracting agent accounts for 99% of the volume of an organic phase, the synergistic extraction agent accounts for 0.5% of the volume of the organic phase, and the diluent accounts for 0.5% of the volume of the organic phase. Then 3mL of magnesium-containing brine is added into the brine, and the volume ratio of the organic phase to the brine is 10: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents of the brine are respectively 3.63, 81.40 and 255.97g/L, the mass ratio of magnesium to lithium is equal to 22.45:1, and the density of the brine is 1.25g/cm³The pH value of the brine is 5.8. Putting a magneton into a ground conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing, putting the conical flask into a DF-101S heat collection type constant temperature heating magnetic stirrer, mixing and stirring at 0 ℃ and extracting for 30 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4200r/min, obtaining a brine sample after extraction and a Li load after phase separation, wherein the interface of two phases is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:10 of the loaded organic phase, placing the mixture into a DF-101S heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 30 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4200r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 19.

TABLE 19 Complex System of N-isooctyl pentanamide, N-isooctyl neodecanoamide, N-isooctyl-1-cyclopropylcarboxamide, N-hexyl-3-cyclopentylpropionamide, methyl laurate and No. 260 mineral oil for Li in certain magnesium-containing brines⁺With Mg²⁺Two-phase separation of

As can be seen from Table 19, Li⁺The single-stage extraction rate is 32.88 percent, and Mg²⁺The single-stage extraction rate is 1.35%, and the lithium-magnesium separation coefficient is 35.80. Li⁺Single stage back extraction of 55.12%, Mg²⁺The single-stage back extraction rate is 69.21%, the lithium-magnesium separation coefficient after back extraction is 0.55, and the mass ratio of magnesium to lithium in the water phase is reduced to 1.16.

Example 20

10mL of N-isooctyl valeramide extractant, 0.1mL of dodecyl isobutyrate co-extractant and 9.9mL of No. 260 solvent oil diluent are put into a 100mL ground conical flask, wherein the extractant occupies 50% of the volume of the organic phase, the co-extractant occupies 0.5% of the volume of the organic phase, and the diluent occupies 49.5% of the volume of the organic phase. Then 2mL of magnesium-containing brine is added into the brine, and the volume ratio of the organic phase to the brine is 10: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents of the components are respectively 0.11, 120.62 and 352.42g/L, the mass ratio of magnesium to lithium is equal to 1096.55:1, and the density of brine is 1.33g/cm³The pH value of the brine is 5.6. Placing a magnet in a ground conical flask, inserting a matched air condenser tube into the mouth of the conical flask to prevent liquid from splashing, placing the conical flask in a DF-101S heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting at 0 deg.CAnd (3) 30 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4200r/min, obtaining a brine sample after extraction and a Li load after phase separation, wherein the interface of two phases is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:10 of the loaded organic phase, placing the mixture into a DF-101S heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 30 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4200r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 20.

TABLE 20 Complex System of N-isooctyl valeramide, dodecyl isobutyrate and No. 260 solvent oil for Li in certain magnesium-containing brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 20, Li⁺The single-stage extraction rate is 77.83 percent, and Mg²⁺The single-stage extraction rate is 3.58%, and the lithium-magnesium separation coefficient is 94.86. Li⁺Single stage back extraction of 85.37%, Mg²⁺The single-stage back extraction rate is 50.64%, the lithium-magnesium separation coefficient after back extraction is 5.68, and the mass ratio of magnesium to lithium in the water phase is reduced to 29.92.

Example 21

14.6mL of N-isopentyl octanoamide, 0.22g N-cyclododecyl acetamide extractant, and 0.15mL of hexyl acetate co-extractant were placed in a 100mL ground flask, where the extractant accounted for 99% of the volume of the organic phase and the co-extractant accounted for 1% of the volume of the organic phase. Then 15mL of magnesium-containing brine is added into the brine, and the volume ratio of the organic phase to the brine is 1: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents of the components are respectively 0.12, 123.11 and 363.30g/L, the mass ratio of magnesium to lithium is equal to 1005.01:1, and the density of brine is 1.33g/cm³The pH value of the brine is adjusted to 1.0 by concentrated hydrochloric acid. Putting a magneton into a ground conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing, putting the conical flask into a DF-101S heat collection type constant temperature heating magnetic stirrer, mixing and stirring at 0 ℃ and extracting for 30 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4200r/min, obtaining a brine sample after extraction and a Li load after phase separation, wherein the interface of two phases is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:1 of the loaded organic phase into the ground conical flask, placing the ground conical flask and the organic phase into a DF-101S heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 30 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4200r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 21.

TABLE 21 composite solvent of N-isopentyl octanoyl amide, N-cyclododecyl acetamide and hexyl acetate for Li in certain magnesium-containing brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 21, Li⁺The single-stage extraction rate is 32.03 percent, and Mg²⁺The single-stage extraction rate is 0.59%, and the lithium-magnesium separation coefficient is 82.40. Li⁺Single stage back extraction of 88.09%, Mg²⁺The single-stage back extraction rate is 93.84%, the lithium-magnesium separation coefficient after back extraction is 0.48, and the mass ratio of magnesium to lithium in the water phase is reduced to 19.72.

Example 22

9.9mL of N-isooctylbutanamide, 0.087g N-cyclododecylacetamide extractant, 9.9mL of hexyl acetate co-extractant, and 0.1mL of No. 260 solvent oil diluent were placed in a 100mL ground flask, where the extractant accounted for 50% of the volume of the organic phase, the co-extractant accounted for 49.5% of the volume of the organic phase, and the diluent accounted for 0.5% of the volume of the organic phase. Then 2mL of magnesium-containing brine is added into the brine, and the volume ratio of the organic phase to the brine is 10: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents are respectively 20.42, 99.83 and 395.50g/L, the mass ratio of magnesium to lithium is equal to 4.89:1, and the brine density is 1.32g/cm³The pH value of the brine is 4.5. Putting a magneton into a ground conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing, putting the conical flask into a DF-101S heat collection type constant temperature heating magnetic stirrer, mixing and stirring at 0 ℃ and extracting for 30 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4200r/min, obtaining a brine sample after extraction and a Li load after phase separation, wherein the interface of two phases is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:10 of the loaded organic phase, placing the mixture into a DF-101S heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 0 ℃ for 30 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4200r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 22.

TABLE 22 Complex System of N-isooctylbutanamide, N-cyclododecylacetamide, hexyl acetate and No. 260 solvent oil for Li in certain magnesium-containing brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 22, Li⁺The single-stage extraction rate is 31.47 percent, and Mg²⁺The single-stage extraction rate is 1.87%, and the lithium-magnesium separation coefficient is 25.42. Li⁺Single stage back extraction of 89.70%, Mg²⁺The single-stage back extraction rate is 86.55%, the lithium-magnesium separation coefficient after back extraction is 1.35, and the mass ratio of magnesium to lithium in the water phase is reduced to 0.28.

Example 23

19mL of N-isooctyl valeramide, 0.1mL of N-ethyl-1- (4-pentylcyclohexyl) formamide, 0.1mL of N- (4-tert-butylcyclohexyl) caprylamide as an extractant and 4.8mL of ethyl myristate as a synergist are put into a 100mL ground conical flask, the synergist occupies 20% of the volume of an organic phase, 4mL of magnesium-containing brine is added, and the volume ratio of the organic phase to the brine is 6: 1. Li in the magnesium-containing brine⁺、 Mg²⁺、Cl^-And

the contents are respectively 1.21, 80.86, 202.53 and 53.56g/L, the mass ratio of magnesium to lithium is equal to 66.83:1, and the density of brine is 1.25g/cm³The pH value of the brine is 7.0. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4200r/min, obtaining a brine sample after extraction and a Li load after phase separation, wherein the interface of two phases is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:6 of the loaded organic phase to the organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4200r/min for 8min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 23.

TABLE 23 composite solvent of N-isooctyl pentanamide, N-ethyl-1- (4-pentylcyclohexyl) carboxamide, N- (4-tert-butylcyclohexyl) octanamide, and ethyl myristate for Li in certain magnesium-containing brines⁺With Mg²⁺Two-phase separation of

As can be seen from Table 23, Li⁺The single-stage extraction rate is 36.45 percent, and Mg²⁺The single-stage extraction rate is 4.39%, and the lithium-magnesium separation coefficient is 12.48. Li⁺Single stage back extraction of 68.03%, Mg²⁺The single-stage back extraction rate is 83.89%, the lithium-magnesium separation coefficient after back extraction is 0.41, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 9.93.

Example 24

19.2mL of N-isooctyl valeramide extractant and 4.8mL of ethyl laurate synergistic extractant are put into a 100mL ground conical flask, the synergistic extractant occupies 20% of the volume of an organic phase, then 8mL of magnesium-containing brine is added, and the volume ratio of the organic phase to the brine is 3: 1. Li in the magnesium-containing brine⁺、Mg²⁺And Cl^-The contents of the components are respectively 0.19, 109.26 and 319.69g/L, the mass ratio of magnesium to lithium is equal to 575.05:1, and the density of brine is 1.30g/cm³The pH value of the brine is 5.8. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 30min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 8min in an LD5-10 desktop centrifuge at the rotating speed of 4300r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transfer the loaded organic phase to another 100mL ground Erlenmeyer flaskDeionized water is added according to the volume ratio of 1:3 of the organic phase, the mixture is placed in a DF-101S type heat collection type constant temperature heating magnetic stirrer, and back extraction and two-phase mixing are carried out for 30min at the temperature of 20 ℃. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 24.

TABLE 24 composite solvent of N-isooctyl pentanamide and ethyl laurate for Li in magnesium-containing brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 24, Li⁺The single-stage extraction rate is 57.21 percent, and Mg²⁺The single-stage extraction rate is 2.26%, and the lithium-magnesium separation coefficient is 57.83. Li⁺Single stage back extraction of 88.61%, Mg²⁺The single-stage back extraction rate is 73.21%, the lithium-magnesium separation coefficient after back extraction is 2.85, and the mass ratio of magnesium to lithium in the water phase is reduced to 18.77.

Example 25

10mL of the salt lake brine obtained in example 1 is taken in a 100mL ground conical flask, 0.81g of ferric chloride hexahydrate with the purity of 99% is added into the conical flask to dissolve the ferric chloride hexahydrate, then 21mL of N-isopentyl octanoyl amide extractant and 9mL of methyl laurate synergistic extractant are added, the volume of the synergistic extractant accounts for 30% of that of an organic phase, and the volume ratio of the organic phase to the salt lake brine is 3: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 10min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, separating phases to obtain the extracted bitternWater samples and Li Supported⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:3 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 10min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 25.

TABLE 25 Fe content of N-isopentyl caprylamide and methyl laurate complex solvent in Qinghai salt lake³⁺Li in brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 25, Li⁺The single-stage extraction rate is 69.23 percent, and Mg²⁺The single-stage extraction rate is 0.97%, and the lithium-magnesium separation coefficient is 229.48. Li⁺Single stage back extraction of 90.96%, Mg²⁺The single-stage back extraction rate is 96.69%, the lithium-magnesium separation coefficient after back extraction is 0.34, and the mass ratio of magnesium to lithium in the aqueous phase is reduced to 0.84.

Example 26

10mL of the salt lake brine obtained in example 1 was taken out of a 100mL ground conical flask, 0.58g of ferrous dichloride tetrahydrate with the purity of 99% was added to the flask to dissolve the ferrous dichloride, and then 38mL of N-amyl isononanoamide extractant and 2mL of ethyl decanoate synergist were added, wherein the synergist occupies 5% of the volume of the organic phase, and the volume ratio of the organic phase to the salt lake brine is 4: 1. Placing a magnet in the conical flask, which isInserting matched air condenser tube into bottle mouth to prevent liquid from splashing, placing in DF-101S type heat collection type constant temperature heating magnetic stirrer, mixing and stirring at 20 deg.C, and extracting for 20 min. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 10min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:4 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic cartridge and centrifuged at 4000r/min for 10min in a model LD5-10 bench top centrifuge to yield a back-extracted organic and aqueous phase.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 26.

TABLE 26 Fe content of N-pentylisononanamide and ethyl caprate complex solvent in Qinghai salt lake²⁺Li in brine⁺With Mg²⁺Two-phase separation of

As can be seen from Table 26, Li⁺The single-stage extraction rate is 56.70 percent, and Mg²⁺The single-stage extraction rate is 2.94%, and the lithium-magnesium separation coefficient is 43.31. Li⁺The single-stage back extraction rate is 90.23 percent, and Mg²⁺The single-stage back extraction rate is 97.24%, the lithium-magnesium separation coefficient after back extraction is 0.26, and the mass ratio of magnesium to lithium in the water phase is reduced to 3.15.

Example 27

21mL of N-isopentyl octanoyl amide extractant and 9mL of methyl laurate synergistic extractant which occupies 30% of the volume of an organic phase are taken in a 100mL ground conical flask, and 10mL of salt lake brine in example 1 is added into the synergistic extractantThe volume ratio of the organic phase to the salt lake brine is 3: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). And then, carrying out three-stage countercurrent extraction according to the extraction cascade cross operation steps to obtain a loaded organic phase and a residual brine phase after the three-stage countercurrent extraction.

Transferring the loaded organic phase after the three-stage countercurrent extraction to another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:3 of the loaded organic phase to the organic phase, placing the mixture in a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out single-stage back extraction and two-phase mixing for 20min at the temperature of 20 ℃. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 27.

TABLE 27 composite solvent of N-isopentyl caprylamide and methyl laurate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺Three stage counter current extraction and single stage back extraction conditions of

As can be seen from Table 27, Li was obtained after three-stage countercurrent extraction of brine⁺The extraction rate is 84.88%, Mg²⁺The extraction rate is 0.65%, and the lithium-magnesium separation coefficient reaches 920.40. Li⁺Single stage back extraction of 73.08%, Mg²⁺The single-stage back extraction rate is 89.21%, the lithium-magnesium separation coefficient after back extraction is 0.33,the mass ratio of magnesium to lithium is reduced to 0.53, and Li in brine⁺With Mg²⁺Effective separation is achieved. Multi-stage countercurrent extraction of Li in brine⁺The higher the extraction rate and the higher the lithium-magnesium separation coefficient are, the more the multistage countercurrent back-extraction stages are under the condition of reducing the water phase consumption, the more the Li in the water phase after back-extraction is favored⁺The concentration is increased.

And returning the back-extracted organic phase to be mixed with the brine phase before extraction again, thereby realizing the recycling of the extractant.

Then the aqueous phase solution obtained after back extraction is deoiled and concentrated to Li through double-effect evaporation⁺After the concentration is 30g/L, calcium chloride and barium chloride solutions are respectively added to completely precipitate to remove sulfate radicals in the calcium chloride and barium chloride solutions, sodium carbonate and sodium hydroxide solutions are respectively added to completely precipitate to remove Mg in the sodium chloride and barium chloride solutions²⁺And then evaporating and concentrating, cooling and crystallizing, filtering and drying the residual solution to obtain the anhydrous lithium chloride product.

And (3) placing the lithium chloride concentrated solution obtained after impurity removal and refining in an ion membrane electrolytic cell for electrolysis to obtain a lithium hydroxide solution with the mass concentration of 12% at the cathode, concentrating and crystallizing to obtain lithium hydroxide monohydrate, washing with water, and drying to obtain an anhydrous lithium hydroxide product. Meanwhile, hydrogen and chlorine are produced as by-products, and the hydrogen and the chlorine are further reacted to prepare hydrochloric acid.

Example 28

Li in brine of salt lake in Qinghai Chaaida basin⁺And Mg²⁺The content of the magnesium is 5.72g/L and 116.36g/L respectively, the mass ratio of the magnesium to the lithium is 20.34:1, wherein, Na⁺、K⁺、Cl^-、

And B₂O₃The content of the brine is respectively 2.70, 1.04, 346.21, 37.32 and 16.89g/L, and the brine density is 1.36g/cm³The pH value of the brine is 4.1. 6mL of the brine is put into a 100mL ground conical flask, and then 27mL of N-isooctyl isovaleramide extractant and 3mL of ethyl laurate synergistic extractant are added into the conical flask, wherein the synergistic extractant occupies 10% of the volume of an organic phase, and the volume ratio of the organic phase to the salt lake brine is 5: 1. Placing magnets in the conical flaskAnd a matched air condenser pipe is inserted into the bottle mouth of the extraction kettle to prevent liquid from splashing, and the extraction kettle is placed in a DF-101S type heat collection type constant temperature heating magnetic stirrer, mixed and stirred at the temperature of 20 ℃ and extracted for 20 min. Then the mixed liquid is transferred to a 250mL plastic test cylinder and centrifuged for 8min in an LD5-10 type desk centrifuge at the rotating speed of 4300r/min, the two-phase interface is clear, and an extracted brine sample and a load Li are obtained after phase separation⁺、Mg²⁺The organic phase of (a). And then, carrying out three-stage countercurrent extraction according to the extraction cascade cross operation steps to obtain a loaded organic phase and a residual brine phase after the three-stage countercurrent extraction.

Transferring the loaded organic phase after the three-stage countercurrent extraction to another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase to the organic phase, placing the mixture in a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out single-stage back extraction and two-phase mixing for 20min at the temperature of 20 ℃. The combined liquid was then transferred to a 250mL plastic cartridge and centrifuged at 4300r/min for 8min in a model LD5-10 bench top centrifuge to yield the back-extracted organic and aqueous phases. And then carrying out secondary countercurrent back extraction according to a cascade cross operation step to obtain an organic phase and a water phase after the secondary countercurrent back extraction.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 28.

TABLE 28 composite solvent of N-isooctyl isovaleramide and ethyl laurate for Li in brine of certain salt lake of Qinghai⁺With Mg²⁺In the case of three-stage countercurrent extraction and two-stage countercurrent back-extraction

As can be seen from Table 28, Li was obtained after three-stage countercurrent extraction of brine⁺The extraction rate is 82.67%, Mg²⁺The extraction rate is 1.25%, and the lithium-magnesium separation coefficient reaches 388.66. Li after the loaded organic phase is subjected to secondary counter-current back extraction⁺Back extraction rate86.06% of Mg²⁺The back extraction rate is 81.18 percent, the lithium-magnesium separation coefficient after back extraction is 1.43, the magnesium-lithium mass ratio is reduced to 0.29, and Li in brine⁺With Mg²⁺Effective separation is achieved.

Then the aqueous phase solution obtained after back extraction is deoiled and concentrated to Li through double-effect evaporation⁺After the concentration is 20g/L, calcium chloride and barium chloride solutions are respectively added to completely precipitate to remove sulfate radicals in the calcium chloride and barium chloride solutions, sodium carbonate and sodium hydroxide solutions are respectively added to completely precipitate to remove Mg in the sodium chloride and barium chloride solutions²⁺To obtain a lithium chloride refined solution. Then adding sodium carbonate solution with the concentration of 250g/L into the lithium carbonate solution according to 1.1 times of the theoretical dosage of the lithium carbonate solution to generate lithium carbonate precipitate, and filtering and drying the lithium carbonate precipitate to obtain a lithium carbonate product.

Adding calcium hydroxide emulsion into the obtained lithium carbonate, heating and strongly stirring to carry out solid-liquid reaction to generate lithium hydroxide solution and calcium carbonate precipitate, separating two phases to obtain lithium hydroxide solution, carrying out reduced pressure concentration, crystallization and drying at the temperature of 140 ℃ to obtain lithium hydroxide monohydrate, and then carrying out reduced pressure heating at the temperature of 180 ℃ to obtain the anhydrous lithium hydroxide product.

Comparative example 1

30mL of methyl laurate is taken as an extractant and is put into a 100mL conical flask, and then 6mL of salt lake brine obtained in example 1 is added into the conical flask, wherein the volume ratio of the extractant to the salt lake brine is 5: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 10min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:5 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquids were then transferred to a 100mL plastic test cartridge in a model LD5-10 bench top centrifuge at 4000r/miAnd (3) centrifuging at the rotating speed of n for 10min to obtain an organic phase and a water phase after back extraction.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 29.

TABLE 29 methyl laurate solvent vs. Li in brine from a salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 29, Li at this time⁺The single-stage extraction rate of the product is not higher than 6.74%, which shows that the alkyl ester solvent is used for Li in salt lake brine⁺The extraction capacity is not large, and the separation effect of the lithium magnesium in the salt lake brine is obviously compared with that of the secondary amide used as an extracting agent. This comparative example serves as a counter example to the previous example, giving further details on the secondary amide extraction capacity.

Comparative example 2

36mL of ethyl myristate was used as an extractant in a 100mL ground conical flask, and 9mL of the salt lake brine obtained in example 1 was added thereto at a volume ratio of the extractant to the salt lake brine of 4: 1. Putting a magneton into a conical flask, inserting a matched air condenser pipe into the mouth of the conical flask to prevent liquid from splashing out, placing the conical flask into a DF-101S type heat collection type constant temperature heating magnetic stirrer, and mixing, stirring and extracting for 20min at 20 ℃. Then transferring the mixed liquid into a 100mL plastic test cylinder, centrifuging for 10min in an LD5-10 desktop centrifuge at the rotating speed of 4000r/min, obtaining an extracted brine sample and a loaded Li after phase separation, wherein the two-phase interface is clear⁺、Mg²⁺The organic phase of (a). Transferring the loaded organic phase into another 100mL ground conical flask, adding deionized water according to the volume ratio of 1:4 of the loaded organic phase, placing the mixture into a DF-101S type heat collection type constant-temperature heating magnetic stirrer, and carrying out back extraction and two-phase mixing at 20 ℃ for 20 min. The combined liquid was then transferred to a 100mL plastic test cartridge in a model LD5-10 bench centrifugeCentrifuging at 4000r/min for 10min to obtain organic phase and water phase after back extraction.

Respectively adopting a Japanese Shimadzu AA-7000 type atomic absorption spectrophotometer standard addition method and an EDTA volumetric titration method to perform constant volume on the brine phase and the water phase in the extraction and back extraction processes, preparing an analysis solution, and sampling and analyzing Li⁺And Mg²⁺The concentrations were calculated, and the results are shown in Table 30.

TABLE 30 Ethyl myristate solvent vs. Li in brine of a salt lake of Qinghai⁺With Mg²⁺Two-phase separation of

As can be seen from Table 30, Li at this time⁺The single-stage extraction rate is not higher than 1.06%, which shows that the alkyl ester solvent is used for Li in salt lake brine⁺The extraction capacity is very small, and the separation effect of the lithium magnesium in the salt lake brine is obviously compared with that of the secondary amide used as an extracting agent. This comparative example serves as a counter example to the previous example, giving further details on the secondary amide extraction capacity.

The above embodiments are only some examples provided for the selection of the present invention, and the embodiments of the present invention are not limited by the above embodiments. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, combination, and improvement made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Common names, corresponding canonical names and designations for the secondary amides of substance A referred to in the examples of Table 31

Common names, pairs of alkyl esters of substances B referred to in the examples of Table 32Shall specify name and CAS number^*

^*CAS number is american chemical abstracts registry number.

Claims

1. An extraction system for separating magnesium and extracting lithium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent is characterized in that the extraction system contains A and B substances; wherein the A-type substance is a secondary amide and consists of a single compound or a mixture of more than two compounds; wherein the single compound has a structure as shown in formula (I):

wherein R is₁Selected from C2-C12 alkyl or C3-C12 cycloalkyl containing single ring structure, R₂Selected from C1-C11 alkyl or C3-C11 cycloalkyl containing single ring structure, and R₁And R₂The sum of the numbers of carbon atoms contained in the two groups is 11 to 17, wherein the alkyl or cycloalkyl group includes various isomers;

wherein R is₃Selected from C1-C12 alkyl, R₄Selected from C1-C15 alkyl, and R₃And R₄The sum of the number of carbon atoms contained in the two alkyl groups is 7-19, wherein the alkyl groups contain various straight-chain or branched isomers;

the freezing point of the extraction system containing the substances A and B is less than 0 ℃.

2. The extraction system for extracting lithium from magnesium-containing brine by separating magnesium from the secondary amide/alkyl ester composite solvent according to claim 1, wherein the volume percentage of the substance A for extraction in the whole organic phase is 50-100%, and the terminal value is not 100%; the B-type substance has a synergistic effect, and accounts for 0-50% of the whole organic phase by volume, excluding 0% of the end point.

3. The extraction system for extracting lithium from magnesium-containing brine by using secondary amide/alkyl ester composite solvent as claimed in claim 1, further comprising diluent 260# solvent oil, 300# solvent oil or sulfonated kerosene for dilution.

4. An extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium is characterized by comprising the following steps:

s2, using the extraction system of any one of claims 1 to 3 as a pre-extraction organic phase;

5. The extraction method of claim 4, wherein the magnesium-containing brine further contains one or more of sodium ions, potassium ions, iron ions, ferrous ions, sulfate ions, boric acid, and borate ions.

6. The extraction process of claim 4, wherein the magnesium-containing brine comprises, but is not limited to, lithium-containing salt lake brine.

7. The extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using the secondary amide/alkyl ester composite solvent as claimed in claim 4, wherein in the step S3, the extraction temperature is 0-50 ℃; the mixing of the two phases is carried out by stirring, and the separation of the two phases after extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

8. The extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using secondary amide/alkyl ester composite solvent as claimed in claim 4, further comprising the step of, after said step S3:

9. The extraction method for separating magnesium and extracting lithium from magnesium-containing brine by using the secondary amide/alkyl ester composite solvent as claimed in claim 8, wherein in the step S4, the back extraction temperature is 0-50 ℃; the two-phase mixing is carried out by a stirring mode, and the two-phase separation after back extraction is carried out by a centrifugal separation mode or a clarification and sedimentation mode.

10. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium in the preparation of a lithium product, namely lithium chloride, is characterized by further comprising the following steps after the step S4:

11. Use of an extraction process for extracting lithium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to separate magnesium from the magnesium-containing brine, in obtaining lithium carbonate as a lithium product, wherein after step S4, the method further comprises the steps of:

12. The application of the extraction method for separating magnesium from magnesium-containing brine by using a secondary amide/alkyl ester composite solvent to extract lithium in the preparation of lithium hydroxide products is characterized by further comprising the following steps after the step S4:

or after the step S6, the method further includes the steps of: