Ionic liquid, preparation method and application of ionic liquid in extraction of precious metal

Abstract

The invention is suitable for the technical field of precious metal separation, and provides an ionic liquid which is an indole ionic liquid. The invention also provides a preparation method of the ionic liquid, which comprises the following steps: mixing indoline, halogenated alkane and acetonitrile, heating, carrying out quaternization reaction, and cooling to room temperature after the reaction is completed to obtain a reaction intermediate product solution; acetonitrile in the reaction intermediate product solution is removed, and a reaction intermediate is obtained; dissolving the reaction intermediate in dichloromethane, mixing with an aqueous solution of lithium bis (trifluoromethylsulfonyl) imide to perform anion exchange reaction, washing the solution until a silver chloride detection water layer does not contain Br <-> or Cl <->, removing dichloromethane, and drying to remove water to obtain the ionic liquid. The invention also provides an application of the ionic liquid in extraction of precious metals. The ionic liquid has extremely high extraction and separation efficiency on gold ions, the extraction efficiency of the gold ions can reach 99%, and the preparation method is simple, high in practicability and easy to popularize.

Description

Technical Field

[0001] The invention belongs to the technical field of precious metal separation, and in particular relates to an ionic liquid, a preparation method and application thereof in extracting precious metals. Background Art

[0002] Gold has stable chemical properties and is relatively difficult to extract in nature. Due to its scarcity, it is regarded as the "king of metals" and is widely used in many fields such as jewelry, modern electronics, aviation and medicine. With the accelerating pace of scientific and technological innovation, people's demand for gold is also increasing. However, its resources are limited, so recovering gold from waste liquid and enhancing the utilization capacity of renewable resources are the inevitable development trends.

[0003] Existing ionic liquids, such as imidazole, pyrrole, and guanidine ionic liquids, have an extraction performance for gold. Under certain conditions, they can only enrich the form of gold tetrachloride ions, but cannot directly extract gold. For practical applications, additional reduction is required. For example, patent applications CN117625980A, CN110042235A, and CN115433130A disclose methods for preparing ionic liquids and extracting gold. At the same time, there is also a separate problem that oxygen needs to be used as a catalyst, and conditions such as controlling temperature changes or dissolving in an organic solvent to form an organic phase are required to achieve efficient extraction of gold ions, and the subsequent reduction method is required to obtain gold. In addition, patent application CN102531991A discloses a method for preparing indole ionic liquids. The drugs used in this technical solution are highly corrosive, increasing the risk of exposure, and the synthesis steps are numerous and complex.

[0004] At present, gold ion enrichment is mainly achieved by methods such as adsorption, electrolysis, precipitation, oxidation-reduction and traditional extraction, but these methods need to obtain gold element through complex purification processes such as hydrogenation and calcination in the later stage. At present, in the research on one-step recovery and extraction of precious metals, the extraction of gold element is mainly achieved by the principle of chemical reduction. Compared with other methods for reducing and extracting gold ions, the adsorption method combines a reducing agent with an adsorbent, and reduces and obtains gold element while adsorbing gold ions. For example, patent applications CN117861638A, CN101036874A, CN113684371A, etc. disclose methods for reducing gold, but their technical solutions can only partially reduce gold ions, and there are also disadvantages such as low adsorption capacity, the need for pre-recovery methods such as electrochemical reduction, the need for electrochemical technology with high energy consumption, and the long time required for the reduction process (12-144h), which makes it difficult to achieve rapid and efficient recovery of gold ions. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide an ionic liquid, aiming to solve the problems raised in the above background technology.

[0006] The embodiment of the present invention is implemented as follows: an ionic liquid, wherein the ionic liquid is an indole ionic liquid, and its structural formula is shown in Formula 1:

[0007]

[0008] Wherein, n is a natural number between 5 and 7.

[0009] Another object of the present invention is to provide a method for preparing an ionic liquid, comprising the following steps:

[0010] Mixing indoline, alkyl halide and acetonitrile and heating them to carry out quaternization reaction, and cooling to room temperature after the reaction is completed to obtain a reaction intermediate product solution;

[0011] removing acetonitrile from the reaction intermediate product solution to obtain a reaction intermediate;

[0012] The reaction intermediate was dissolved in dichloromethane and mixed with an aqueous solution of lithium bis(trifluoromethylsulfonyl)imide to carry out anion exchange reaction. The solution was washed until the water layer was free of Br by silver chloride detection. - or Cl - , remove dichloromethane, dry and remove water to obtain the ionic liquid.

[0013] Preferably, the halogenated alkane is one or more of hexyl bromide, heptyl bromide and octane bromide.

[0014] Preferably, the molar ratio of indoline to halogenated alkane is 1:2 to 2.5.

[0015] Preferably, the temperature of the quaternization reaction is 70-80° C. and the time is 48-72 hours.

[0016] Preferably, the molar ratio of the reaction intermediate to lithium bis(trifluoromethylsulfonyl)imide is 1:1 to 1.5.

[0017] Preferably, the anion exchange reaction is carried out at room temperature and for 6 to 12 hours.

[0018] Another object of the embodiment of the present invention is to provide an application of ionic liquid in extracting precious metals, comprising the following steps:

[0019] The ionic liquid and the aqueous phase containing gold ions are mixed and shaken for extraction, and the layers are separated. The layer adhering to the tube wall is the ionic liquid containing gold ions, and the upper layer is the raffinate aqueous phase.

[0020] Preferably, the solvent of the gold ion-containing aqueous phase is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.1 to 4 mol / L.

[0021] Preferably, the dosage ratio of the ionic liquid to the aqueous phase containing gold ions is 0.01-0.1 mmol:5 mL, and the concentration of gold ions in the aqueous phase containing gold ions is 0.5-30 mmol / L.

[0022] In the embodiment of the present invention, the conventional ionic liquid is used as an extractant to improve the reducing agent for reducing gold in one step, and the gold ions can be extracted and reduced to gold element in one step. - As the anion of the ionic liquid, the ionic liquid has the excellent properties of low viscosity, high hydrophobicity and strong stability, which solves the problem that the mass transfer in the extraction process is blocked due to the high viscosity of the ionic liquid and relies on organic solvents, and can eliminate the pollution of the environment by the volatilization of organic solvents, thereby increasing production safety; after the ionic liquid and the aqueous phase containing gold ions are mixed, no additional heating is required, and the ionic liquid will form a homogeneous phase with the metal solution (the aqueous phase containing gold ions), and the gold element can be reduced in one step, thereby achieving the purpose of extracting gold, with high reduction efficiency and short equilibrium time. The ionic liquid provided in the embodiment of the present invention has extremely high extraction and separation efficiency for gold ions, and the extraction efficiency of gold ions can reach 99%;

[0023] The preparation method provided by the embodiment of the present invention is simple, practical and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of the preparation of an ionic liquid provided in an embodiment of the present invention and a flow chart of the application of the ionic liquid in the one-step extraction and reduction of gold ions to gold element;

[0025] Figure 2 The XPS spectrum provided for Example 4 of the present invention;

[0026] Figure 3 The results of gold ion extraction rate and elemental gold yield of Examples 1-4 of the present invention and Comparative Examples 1-4 are compared. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] An ionic liquid, the preparation method of which is as follows Figure 1 As shown, the specific steps include:

[0029] (1) mixing indoline, alkyl halide and acetonitrile and heating them, and carrying out a quaternary amination reaction under reflux, and cooling the mixture to room temperature after the reaction is completed to obtain a reaction intermediate product solution; wherein the molar ratio of indoline to alkyl halide is 1:2-2.5 (preferably 1:2.1), the amount ratio of indoline to acetonitrile is 60 mmol:100 mL, the temperature of the quaternary amination reaction is 70-80° C., and the time is 48-72 h (preferably 75° C., 72 h);

[0030] (2) removing acetonitrile from the reaction intermediate product solution by rotary evaporation to obtain a reaction intermediate, which is then washed with petroleum ether for multiple times. The structural formula of the intermediate (indoline bromide) is shown in Formula 2:

[0031]

[0032] (3) dissolving the reaction intermediate in dichloromethane and mixing it with an aqueous solution of lithium bis(trifluoromethylsulfonyl)imide to carry out anion exchange reaction, wherein the molar ratio of the reaction intermediate to lithium bis(trifluoromethylsulfonyl)imide is 1:1-1.5 (preferably 1:1.5), the temperature of the anion exchange reaction is room temperature, and the time is 6-12 hours (preferably 12 hours), after the anion exchange reaction, the aqueous phase is removed, the organic phase is washed, and the organic phase is removed again and dried to obtain an ionic liquid, wherein the aqueous phase is the upper layer of the system obtained by the anion exchange, the reagent for washing the organic phase is deionized water, and the washing is carried out until no halogen ions are detected in the washing liquid, and the drying temperature is 60-80° C. and the time is 36-48 hours (preferably 75° C., 48 hours).

[0033] A method for extracting and reducing gold ions to gold element from an aqueous phase in one step, such as Figure 1 As shown, the following steps are included:

[0034] The above-mentioned ionic liquid and the aqueous phase containing gold ions are mixed and shaken for extraction, and the layers are separated. The layer adhering to the tube wall is the ionic liquid containing gold ions, and the upper layer is the raffinate aqueous phase; wherein the solvent of the aqueous phase containing gold ions is a hydrochloric acid solution, the concentration of the hydrochloric acid solution is 0.1-4 mol / L (preferably 0.1-2 mol / L), the dosage ratio of the ionic liquid and the aqueous phase containing gold ions is 0.01-0.1 mmol:5 mL (preferably 0.05 mmol:5 mL), the concentration of gold ions in the aqueous phase containing gold ions is 0.5-30 mmol / L, the temperature for mixed and shaken extraction is 25°C, and the time is 5 min-3 h (preferably 10 min-3 h).

[0035] In the following examples, unless otherwise specified, the materials and equipment used are commercially available in the art;

[0036] In the following examples, unless otherwise specified, all are conventional methods;

[0037] After the extraction and separation process is completed, the concentration of gold ions in the raffinate is measured by atomic absorption spectrometer (AA-6880) or inductively coupled plasma spectrometer (ICAP-7850), and the extracted product is detected by XPS.

[0038] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0039] Example 1: Synthesis of indole ionic liquid [diEIDN][Tf2N], specifically comprising the following steps:

[0040] Step 1: Add 60 mmol indoline, 126 mmol bromopentane and 100 mL acetonitrile to a 250 mL eggplant-shaped bottle, heat to 75°C, condense and reflux for 72 hours, and cool to room temperature. After the solution turns black, remove acetonitrile by vacuum distillation, and wash the solid with petroleum ether several times to obtain a black intermediate product ([diEIDN][Br]);

[0041] The second step is to dissolve [diEIDN][Br] in 50 mL of dichloromethane, then add an aqueous solution containing 126 mmol of lithium bis(trifluoromethylmethanesulfonyl)amide, and react at room temperature for 12 hours. After the reaction is complete, remove the upper aqueous phase, wash the organic phase with deionized water for multiple times, and perform rotary evaporation on the washed organic phase to remove the organic phase. Finally, the obtained ionic liquid is vacuum dried at 75°C for 48 hours to obtain the final product [diEIDN][Tf2N].

[0042] The ionic liquid prepared in Example 1 is applied to the reduction process of gold ions, which specifically includes the following steps:

[0043] The first step is to take 0.02 mmol of ionic liquid to form an ionic liquid phase;

[0044] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0045] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0046] Atomic absorption measurement showed that when the ratio of gold to ionic liquid was 1:1, no gold concentration was detected in the aqueous solution of the raffinate phase. The gold ion extraction rate was tested by ICP, and XPS proved that the yield of gold was 75.3%.

[0047] Example 2: Synthesis of indole ionic liquid [diFIDN][Tf2N], specifically comprising the following steps:

[0048] Step 1: Add 60 mmol indoline, 126 mmol bromohexane and 100 mL acetonitrile to a 250 mL eggplant-shaped bottle, heat to 75° C., condense and reflux for 72 h, and cool to room temperature. After the solution turns black, remove acetonitrile by vacuum distillation, and wash the solid with petroleum ether several times to obtain a black intermediate product ([diFIDN][Br]);

[0049] The second step is to dissolve [diFIDN][Br] in 50 mL of dichloromethane, then add an aqueous solution containing 126 mmol of lithium bis(trifluoromethylmethanesulfonyl)amide, and react at room temperature for 12 hours. After the reaction is complete, remove the upper aqueous phase, wash the organic phase with deionized water for multiple times, and perform rotary evaporation on the washed organic phase to remove the organic phase. Finally, the obtained ionic liquid is vacuum dried at 75°C for 48 hours to obtain the final product [diFIDN][Tf2N].

[0050] The ionic liquid prepared in Example 2 is applied to the reduction process of gold ions, which specifically includes the following steps:

[0051] The first step is to take 0.02 mmol of ionic liquid to form an ionic liquid phase;

[0052] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0053] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0054] Atomic absorption measurement showed that when the ratio of gold to ionic liquid was 1:1, no gold concentration was detected in the aqueous solution of the raffinate phase. The gold ion extraction rate was tested by ICP, and XPS proved that the yield of gold was 82.1%.

[0055] Example 3: Synthesis of indole ionic liquid [diGIDN][Tf2N], specifically comprising the following steps:

[0056] Step 1: Add 60 mmol indoline, 126 mmol bromoheptane and 100 mL acetonitrile to a 250 mL eggplant-shaped bottle, heat to 75° C., condense and reflux for 72 h, and cool to room temperature. After the solution turns black, remove acetonitrile by vacuum distillation, and wash the solid with petroleum ether several times to obtain a black intermediate product ([diGIDN][Br]);

[0057] In the second step, [diGIDN][Br] was dissolved in 50 mL of dichloromethane, and then an aqueous solution containing 126 mmol of lithium bis(trifluoromethylmethanesulfonyl)amide was added, and the reaction was carried out at room temperature for 12 hours. After the reaction was complete, the upper aqueous phase was removed, and the organic phase was washed with deionized water for multiple times. The washed organic phase was rotary evaporated to remove the organic phase. Finally, the obtained ionic liquid was vacuum dried at 75°C for 48 hours to obtain the final product [diGIDN][Tf2N].

[0058] The ionic liquid prepared in Example 3 is applied to the reduction process of gold ions, which specifically includes the following steps:

[0059] The first step is to take 0.02 mmol of ionic liquid to form an ionic liquid phase;

[0060] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0061] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0062] Atomic absorption measurement showed that when the ratio of gold to ionic liquid was 1:1, no gold concentration was detected in the aqueous solution of the raffinate phase. The gold ion extraction rate was tested by ICP, and XPS proved that the yield of gold was 87.6%.

[0063] Example 4: Synthesis of indole ionic liquid [diHIDN][Tf2N], specifically comprising the following steps:

[0064] Step 1: Add 60 mmol indoline, 126 mmol bromooctane and 100 mL acetonitrile to a 250 mL eggplant-shaped bottle, heat to 75° C., condense and reflux for 72 h, and cool to room temperature. After the solution turns black, remove acetonitrile by vacuum distillation, and wash the solid with petroleum ether several times to obtain a black intermediate product ([diHIDN][Br]);

[0065] The second step is to dissolve [diHIDN][Br] in 50 mL of dichloromethane, then add an aqueous solution containing 126 mmol of lithium bis(trifluoromethylmethanesulfonyl)amide, and react at room temperature for 12 hours. After the reaction is complete, the upper aqueous phase is removed, and the organic phase is washed with deionized water for multiple times. The washed organic phase is rotary evaporated to remove the organic phase. Finally, the obtained ionic liquid is vacuum dried at 75°C for 48 hours to obtain the final product [diHIDN][Tf2N].

[0066] The ionic liquid prepared in Example 4 is applied to the reduction process of gold ions, which specifically includes the following steps:

[0067] The first step is to take 0.02 mmol of ionic liquid to form an ionic liquid phase;

[0068] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0069] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0070] Atomic absorption measurements showed that, in the case of a 1:1 ratio of gold to ionic liquid, no gold concentration was detected in the raffinate aqueous solution. The gold ion extraction rate was tested by ICP, and XPS proved that the yield of gold was 99.9%. Figure 2 shown.

[0071] Comparative Example 1: Extraction process of gold ions by piperidine ionic liquid PP13FSI:

[0072] The first step is to take 0.02 mmol of ionic liquid of N-propyl-N-methylpiperidinium (fluorosulfonyl) imide salt to form an ionic liquid phase;

[0073] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0074] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0075] Atomic absorption measurements showed that when the ratio of gold to ionic liquid was 1:1, the concentration of gold tetrachloride ions was still detected in the aqueous solution of the raffinate phase. The extraction rate of gold was 30.2%, and no gold element was generated after long-term storage. Further XPS testing revealed no gold element peak.

[0076] Comparative Example 2: Extraction process of gold ions by guanidine ionic liquid [DIOTMG] [NTf2]:

[0077] The first step is to take 0.02 mmol of the ionic liquid of tetramethylguanidine derivative bis(trifluoromethane)sulfonyl imide salt to form an ionic liquid phase;

[0078] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0079] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0080] Atomic absorption measurements showed that when the ratio of gold to ionic liquid was 1:1, the concentration of gold tetrachloride ions was still detected in the aqueous solution of the raffinate phase. The extraction rate of gold was 35.4%, and no gold element was generated after long-term storage. Further XPS testing revealed no gold element peak.

[0081] Comparative Example 3: Extraction process of gold ions by imidazole ionic liquid [EA-IM][NTf2]:

[0082] The first step is to take 0.02 mmol of ester-functionalized imidazole bis(trifluoromethane)sulfonyl imide salt ionic liquid to form an ionic liquid phase;

[0083] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0084] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0085] Atomic absorption measurement showed that when the ratio of gold to ionic liquid was 1:1, the concentration of gold tetrachloride ions was still detected in the aqueous solution of the raffinate phase. The extraction rate of gold was 33.3%, and no gold element was generated after long-term storage. Further XPS analysis revealed no gold element peak.

[0086] Comparative Example 4: Extraction process of gold ions by indole ionic liquid [diHIDN][Tf2N]:

[0087] The first step is to take 0.02 mmol of the ionic liquid of indoline bis(trifluoromethane)sulfonyl imide salt to form an ionic liquid phase;

[0088] Step 2: Take chloroauric acid separately, dissolve and dilute with 0.1 mol / L hydrochloric acid solution to prepare an aqueous phase with a gold ion concentration of 0.5 to 15 mmol / L;

[0089] The third step is to mix 0.05mmol ionic liquid phase and 5mL aqueous phase, place it in a constant temperature shaker at 25℃ and shake for 30s to 3h to achieve extraction. After the extraction is completed, the ionic liquid loaded with gold ions (extractant) is at the bottom of the centrifuge tube, and the raffinate phase is at the top of the aqueous phase. The concentration of gold ions in the raffinate phase is measured.

[0090] Atomic absorption measurement showed that when the ratio of gold to ionic liquid was 1:1, no gold concentration was detected in the aqueous solution of the raffinate phase. XPS analysis showed that the gold was reduced to the form of elemental gold.

[0091] The gold ion extraction rate and elemental gold yield of Example 1-Example 4 and Comparative Example 1-Comparative Example 4 are compared. Figure 3 As shown, according to Figure 3 It can be seen that the gold ion extraction rate and the elemental gold yield of the embodiment far exceed those of the comparative example.

[0092] In summary, the embodiment of the present invention uses ionic liquid to achieve efficient and direct one-step extraction of gold, AuCl4 -- It will preferentially react with N in the ionic liquid + Through redox reactions, the valence state changes to achieve one-step reduction extraction of gold; ionic liquids show excellent selectivity and reusability for gold ions, providing a new option for the efficient and green separation of gold ions and other metals in electronic waste, showing excellent industrial application potential.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An ionic liquid, It is characterized in that The ionic liquid is an indole ionic liquid, and its structural formula is shown in Formula 1: Wherein, the n is a natural number between 5-7.

2. A method for preparing the ionic liquid according to claim 1, It is characterized in that The following steps are involved: Mixing indoline, alkyl halide and acetonitrile and heating them to carry out quaternization reaction, and cooling to room temperature after the reaction is completed to obtain a reaction intermediate product solution; removing acetonitrile from the reaction intermediate product solution to obtain a reaction intermediate; The reaction intermediate was dissolved in dichloromethane and mixed with an aqueous solution of lithium bis(trifluoromethylsulfonyl)imide to carry out anion exchange reaction. The solution was washed until the water layer was free of Br by silver chloride detection. - or Cl - , remove dichloromethane, dry and remove water to obtain the ionic liquid.

3. The method for preparing the ionic liquid according to claim 2, It is characterized in that The halogenated alkane is one or more of hexyl bromide, heptyl bromide and octane bromide.

4. The method for preparing the ionic liquid according to claim 2, It is characterized in that The molar ratio of the indoline to the halogenated alkane is 1:2 to 2.

5.

5. The method for preparing the ionic liquid according to claim 2, It is characterized in that The temperature of the quaternization reaction is 70-80° C. and the time is 48-72 hours.

6. The method for preparing the ionic liquid according to claim 2, It is characterized in that The molar ratio of the reaction intermediate to lithium bis(trifluoromethylsulfonyl)imide is 1:1 to 1.

5.

7. The method for preparing the ionic liquid according to claim 2, It is characterized in that The temperature of the anion exchange reaction is room temperature, and the time is 3 to 6 hours.

8. Use of the ionic liquid according to claim 1 in extracting precious metals, It is characterized in that It is characterized by comprising the following steps: The ionic liquid and the water phase containing gold ions are mixed and shaken for extraction, and the layers are separated, and the layer adhering to the tube wall is the ionic liquid containing gold ions.

9. The use according to claim 8, It is characterized in that The solvent of the gold ion-containing aqueous phase is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.1-4 mol / L.

10. The use according to claim 8, It is characterized in that The dosage ratio of the ionic liquid to the aqueous phase containing gold ions is 0.01-0.1 mmol:5 mL, and the concentration of gold ions in the aqueous phase containing gold ions is 0.5-30 mmol / L.

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