An ionic liquid and its preparation and application

Abstract

The present invention discloses an ionic liquid and its preparation and application. The chemical name of the ionic liquid is 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminium salt, and the structure is shown below. The present invention provides a metal leaching agent containing the ionic liquid, which is mixed with ionic liquid and water in a mass ratio of 8.5:2-8. The present invention provides a metal leaching method based on the metal leaching agent. The metal leaching agent system of the present invention has both good oxidizability and coordination ability, can leach gold, palladium, and platinum, has a fast leaching speed and a high extraction rate, and does not require an external oxidant when used.

Description

Technical Field

[0001] The invention relates to an ionic liquid and a preparation method thereof, and application of the ionic liquid in preparing a metal leaching agent, as well as a metal leaching method based on the metal leaching agent. Background Art

[0002] As a type of non-renewable resource, precious metals are widely used in aviation materials, automobiles, jewelry, catalysts and electroplating industries. However, there is a serious imbalance in the global distribution and supply and demand of precious metal resources, highlighting the importance of their recycling and reuse.

[0003] With the development of the electronics industry, precious metals play an increasingly important role in improving the performance of printed circuit boards.

[0004] Chemical recycling is a traditional technology for waste recycling, mainly including pyrometallurgy and hydrometallurgy. Pyrometallurgy is to use high temperature to melt precious metals in other metal smelting materials or molten salts to form alloys, and then further refine them. Hydrometallurgy mainly uses aqua regia, nitric acid and other substances to dissolve or precipitate precious metals from electronic waste, and then process them.

[0005] The basic principle of biological recovery is to use the oxidizing property of trivalent iron ions to oxidize and dissolve other metals in precious metal alloys. The divalent iron ions are then oxidized by bacteria into trivalent iron ions, which greatly reduces the use of iron ions. Biological recovery of precious metals has the advantages of high efficiency, low cost, low energy consumption, and low pollution, and has broad application prospects.

[0006] Ionic liquids have many unique and favorable properties, such as environmental friendliness, maintaining a liquid state at near room temperature, designable structure, almost zero vapor pressure, strong polarity, flame resistance, good thermal and chemical stability, and excellent electrical and thermal conductivity. Ionic liquids can be used as green solvents in the process of recovering precious metals and have important application value.

[0007] Although ionic liquids have been intensively studied and widely used in metal ion extraction, there is not much research on the extraction of elemental precious metals by ionic liquids. Summary of the invention

[0008] The primary purpose of the present invention is to provide a new type of ionic liquid - 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt, which has good oxidation and metal coordination capabilities.

[0009] The second object of the present invention is to provide a method for preparing 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazole trichloromonobromoaluminum salt.

[0010] The third object of the present invention is to provide a metal leaching agent based on the ionic liquid, which has the advantages of high efficiency, green environmental protection and sustainability.

[0011] The fourth object of the present invention is to provide a metal leaching method based on the metal leaching agent.

[0012] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0013] In the first aspect, the present invention provides an ionic liquid, whose chemical name is 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt, and its structure is shown below:

[0014]

[0015] In a second aspect, the present invention provides a method for preparing 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazole trichloromonobromoaluminum salt, the preparation method comprising:

[0016] (1) Dewatering and evacuating the reaction vessel;

[0017] (2) adding nitroxide piperidinol, solvent dichloromethane and 4-bromobutyryl chloride to a reaction vessel under nitrogen protection, placing the reaction vessel in an ice-water bath, slowly adding pyridine, and then stirring the resulting mixture at 20-30° C. for 24-48 hours. After sufficient reaction, filtering to remove the precipitate, washing the filtrate with water, sodium bicarbonate aqueous solution, dilute hydrochloric acid solution, and finally washing with deionized water, adding anhydrous magnesium sulfate to the resulting solution and drying it, rotary evaporating to remove the solvent and concentrating in vacuo to obtain 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl);

[0018] (3) dissolving the 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl) obtained in step (2) in acetonitrile, and adding 1-methylimidazole thereto, stirring the resulting mixture at 50-80° C. for reaction for 24-48 hours, removing the solvent after sufficient reaction, washing the sample with ether, and drying under vacuum to obtain 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide;

[0019] (4) adding the 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide obtained in step (3), protective agent n-heptane and anhydrous aluminum chloride into a reaction vessel and mixing them evenly, stirring the resulting mixture at 60-80° C. for 2-3 hours, and after sufficient reaction, pouring the upper n-heptane protective agent, and vacuum drying the lower product to obtain 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt.

[0020] Preferably, in step (2), the molar ratio of the nitroxide piperidinol, 4-bromobutyryl chloride and pyridine is 1:0.8-1.5:0.5-1.5.

[0021] Preferably, in step (3), the mass ratio of the 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl) to 1-methylimidazole is 1:0.2-0.35.

[0022] Preferably, in step (4), the mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium bromide and anhydrous aluminum chloride is 3:0.9-1.1.

[0023] In a third aspect, the present invention provides a metal leaching agent containing the ionic liquid, which is prepared by mixing 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt and water in a mass ratio of 8.5:2-8.

[0024] Preferably, the mass ratio of the 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazole trichloromonobromoaluminum salt to water is 8.5:4-6, most preferably 8.5:6.

[0025] In a fourth aspect, the present invention provides a metal leaching method based on the metal leaching agent, the metal leaching method comprising:

[0026] 1) obtaining the metal leaching agent containing the ionic liquid;

[0027] 2) Add the sample containing precious metals into the metal leaching agent obtained in step 1) and stir thoroughly to leach the precious metals.

[0028] Preferably, the precious metal is at least one of gold, palladium and platinum.

[0029] Preferably, the sample containing precious metals is precious metal powder or gold ore particles.

[0030] Preferably, the feed mass ratio of the ionic liquid to the noble metal is controlled to be 2800-9000:1.

[0031] Preferably, in step 2), the leaching temperature is controlled to be 40-80°C, and more preferably, the leaching temperature is 60-80°C. Within this temperature range, the gold leaching system has excellent gold leaching efficiency. The most preferred leaching temperature is 60°C.

[0032] Compared with traditional metal leaching agents, the present invention has the following advantages:

[0033] 1. The ionic liquid system used in the metal leaching agent of the present invention is an environmentally friendly compound, which has almost no harm to the environment and people during the production process, meets the requirements of building an environmentally friendly society at present, and is a sustainable development system;

[0034] 2. The metal leaching agent system of the present invention has good oxidizability and coordination ability, can leach gold, palladium and platinum, has a fast leaching speed and a high extraction rate, and does not require an external oxidant when used;

[0035] 3. The metal leaching agent of the present invention can be used for metallurgical treatment at low temperature, with mild conditions and low overall energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide 1 H NMR spectra.

[0037] Figure 2 This is the mass spectrum of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazole trichloromonobromoaluminum salt. DETAILED DESCRIPTION

[0038] The present invention is described below with specific examples. It is necessary to point out that the embodiments are only used to further illustrate the present invention, but cannot be understood as limiting the scope of protection of the present invention, and the present invention is not limited thereto in any way. Personnel skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0039] The 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazole trichloromonobromoaluminum salt used in the present invention was prepared by the method of Example 1:

[0040] Example 1

[0041] 1. Add 4.3g of nitroxyl piperidinol to a 100mL three-necked flask with a magnet, then inject 30mL of dichloromethane into the flask, install a condenser, add 5.09g of 4-bromobutyryl chloride into the three-necked flask, place the flask in a 0℃ ice water bath, and then slowly add 2.18g of pyridine into the flask. Stir the mixture at 20-30℃ for 24 hours.

[0042] 2. Filter to remove the precipitate, and wash the filtrate with 30 ml of water and 30 ml of 10% NaHCO 3 The solution was washed with an aqueous solution, 30 ml of 2 mol / L dilute HCl, and 30 ml of water in sequence. The washed solution was dried over anhydrous magnesium sulfate, and then the solvent was removed by rotary evaporation and concentrated in vacuo to obtain a red viscous liquid, namely 4-(4-bromobutyl)-(2,2,6,6-tetramethyl-piperidin-1-oxyl), with a yield of 76%.

[0043] 3. Add 2.77g of 4-(4-bromobutyl)-(2,2,6,6-tetramethyl-piperidin-1-oxyl) to a 100mL three-necked flask with a magnetic rod, then inject 30mL of acetonitrile into the flask, install a condenser, and then slowly inject 1.23g of 1-methylimidazole into the solution. Continue stirring and raise the temperature to 80°C. Stir and react for 48h. Then remove the solvent by rotary evaporation, wash the sample with anhydrous ether several times, and vacuum dry to obtain a red viscous liquid, namely 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide, with a yield of 70%. The substance 1 H NMR spectra Figure 1 .

[0044] 4. Add 3.00g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide to a 100mL three-necked flask with a magnetic rod, then inject 30mL of n-heptane into the flask, install a condenser, and then slowly pour 0.99g of anhydrous aluminum chloride into the three-necked flask, stir at room temperature for 30 minutes. Raise the temperature to 80℃ and stir for 3h. After the reaction is completed, the upper layer is the protective agent n-heptane, and the lower layer is 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloro-monobromoaluminum salt. After removing n-heptane, the product is vacuum dried to obtain a red viscous liquid, namely 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloro-monobromoaluminum salt. The high-resolution mass spectrum of this substance is shown in Figure 2 .

[0045] 5. Dry under vacuum overnight before use.

[0046] Example 2

[0047] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:3. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 3.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0022g of gold powder and heat and stir at 60℃ for 3 hours.

[0048] The Au concentration of the solution was measured by atomic absorption spectrometer and was 2.09 ug / ml. The calculated dissolution rate was 81.70%.

[0049] Example 3

[0050] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:4. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 4.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0023g of gold powder and heat and stir at 60℃ for 3 hours.

[0051] The Au concentration of the solution was measured by atomic absorption spectrometer and was 2.26 ug / ml. The calculated dissolution rate was 94.33%.

[0052] Example 4

[0053] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:5. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 5ml of water and mix them evenly at room temperature to obtain a solution. 0.0023g of gold powder is added and heated at 60°C with stirring for 3 hours.

[0054] The Au concentration of the solution was measured by atomic absorption spectrometer and was 2.12 ug / ml. The calculated dissolution rate was 97.70%.

[0055] Example 5

[0056] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0020g of gold powder and heat and stir at 60℃ for 3 hours.

[0057] The Au concentration of the solution was measured by atomic absorption spectrometer and was 1.731.ug / ml. The calculated dissolution rate was 100.00%.

[0058] Example 6

[0059] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:7. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 7.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0023g of gold powder and heat and stir at 60℃ for 3 hours.

[0060] The Au concentration of the solution was measured by atomic absorption spectrometer to be 1.64 ug / ml, and the calculated dissolution rate was 89.84%.

[0061] Example 7

[0062] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:8. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 8.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0024g of gold powder and heat and stir at 60℃ for 3 hours.

[0063] The Au concentration of the solution was measured by atomic absorption spectrometer and was 1.42 ug / ml. The calculated dissolution rate was 80.46%.

[0064] Example 8

[0065] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0020g of gold powder and heat and stir at 50℃ for 3 hours.

[0066] The Au concentration of the solution was measured by atomic absorption spectrometer and was 1.55 ug / ml. The calculated dissolution rate was 89.90%.

[0067] Example 9

[0068] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0020g of gold powder and heat and stir at 70℃ for 3 hours.

[0069] The Au concentration of the solution was measured by atomic absorption spectrometer to be 1.724 ug / ml, and the calculated dissolution rate was 99.99%.

[0070] Example 10

[0071] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0022g of gold powder and heat and stir at 80℃ for 3 hours.

[0072] The Au concentration of the solution was measured by atomic absorption spectrometer to be 1.89 ug / ml, and the solubility was calculated to be 99.65%.

[0073] Embodiment 11

[0074] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. 0.0025g of palladium powder is added and heated at 60°C with stirring for 3 hours.

[0075] The Pd concentration of the solution was measured by atomic absorption spectrometer and was 2.15 ug / ml. The calculated dissolution rate was 99.76%.

[0076] Example 12

[0077] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. 0.0010g of platinum powder is added and heated at 60°C with stirring for 3 hours.

[0078] The Pt concentration of the solution was measured by atomic absorption spectrometer and was 0.711 ug / ml. The calculated dissolution rate was 82.47%.

[0079] Comparative Example 1

[0080] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0020g of gold powder and heat and stir at 40℃ for 3 hours.

[0081] The Au concentration of the solution was measured by atomic absorption spectrometer and was 1.36 ug / ml. The calculated dissolution rate was 78.88%.

[0082] Comparative Example 2

[0083] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and water is 8.5:2. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonoaluminum salt and 2.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0021g of gold powder and heat and stir at 60℃ for 3 hours.

[0084] The Au concentration of the solution was measured by atomic absorption spectrometer and was 1.36 ug / ml. The calculated dissolution rate was 75.12%.

[0085] Comparative Example 3

[0086] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium chloride and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium chloride and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0023g of gold powder and heat at 60℃ with stirring for 3 hours.

[0087] The Au concentration of the solution was measured by atomic absorption spectrometer to be 0.022 ug / ml, and the dissolution rate was calculated to be 1.10%.

[0088] Comparative Example 4

[0089] The mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium bromide and water is 8.5:6. Take 8.5g of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium bromide and 6.0ml of water and mix them evenly at room temperature to obtain a solution. 0.0022g of gold powder is added and heated at 60°C with stirring for 3 hours.

[0090] The Au concentration of the solution was measured by atomic absorption spectrometer to be 0.044 ug / ml, and the calculated dissolution rate was 2.32%.

[0091] Comparative Example 5

[0092] The mass ratio of 1-propyl-3-methylimidazolium tetrachloride and water is 8.5:6. Take 8.5g of 1-propyl-3-methylimidazolium tetrachloride and 6.0ml of water and mix them evenly at room temperature to obtain a solution. Add 0.0022g of gold powder and heat and stir at 60°C for 3 hours.

[0093] The Au concentration of the solution was measured by atomic absorption spectrometer to be 0.00 ug / ml, and the calculated dissolution rate was 0.00%.

Claims

1. An ionic liquid, whose chemical name is 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt, and whose structure is shown below:

2. A method for preparing an ionic liquid as claimed in claim 1, characterized in that: The preparation method is: (1) Dewatering and evacuating the reaction vessel; (2) adding nitroxide piperidinol, solvent dichloromethane and 4-bromobutyryl chloride to a reaction vessel under nitrogen protection, placing the reaction vessel in an ice-water bath, slowly adding pyridine, and then stirring the resulting mixture at 20-30° C. for 24-48 hours. After sufficient reaction, filtering to remove the precipitate, washing the filtrate with water, sodium bicarbonate aqueous solution, dilute hydrochloric acid solution, and finally washing with deionized water, adding anhydrous magnesium sulfate to the resulting solution and drying it, rotary evaporating to remove the solvent and concentrating in vacuo to obtain 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl); (3) dissolving the 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl) obtained in step (2) in acetonitrile, and adding 1-methylimidazole thereto, stirring the resulting mixture at 50-80° C. for reaction for 24-48 hours, removing the solvent after sufficient reaction, washing the sample with ether, and drying under vacuum to obtain 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide; (4) adding the 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium bromide obtained in step (3), protective agent n-heptane and anhydrous aluminum chloride into a reaction vessel and mixing them evenly, stirring the resulting mixture at 60-80° C. for 2-3 hours, and after sufficient reaction, pouring the upper n-heptane protective agent, and vacuum drying the lower product to obtain 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxy-4-piperidinyloxy)butyl)imidazolium trichloromonobromoaluminum salt.

3. The preparation method according to claim 2, characterized in that: In step (2), the molar ratio of the nitroxide free radical piperidinol, 4-bromobutyryl chloride and pyridine is 1:0.8-1.5:0.5-1.

5.

4. The preparation method according to claim 2, characterized in that: In step (3), the feed mass ratio of 4-(4-bromobutyl ester)-(2,2,6,6-tetramethylpiperidin-1-oxyl) to 1-methylimidazole is 1:0.2-0.

35.

5. The preparation method according to claim 2, characterized in that: In step (4), the feed mass ratio of 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyloxy)butyl)imidazolium bromide and anhydrous aluminum chloride is 3:0.9-1.

1.

6. A metal leaching agent containing the ionic liquid of claim 1, which is prepared by mixing the ionic liquid and water in a mass ratio of 8.5:2-8.

7. The metal leaching agent containing the ionic liquid according to claim 1 according to claim 6, characterized in that: The metal leaching agent is prepared by mixing the ionic liquid and water in a mass ratio of 8.5:4-6.

8. The metal leaching agent containing the ionic liquid according to claim 1 according to claim 7, characterized in that: The metal leaching agent is prepared by mixing the ionic liquid and water in a mass ratio of 8.5:

6.

9. A metal leaching method based on the metal leaching agent according to any one of claims 6 to 8, characterized in that: The metal leaching method comprises: 1) obtaining the metal leaching agent according to any one of claims 6 to 8; 2) Add the sample containing precious metals into the metal leaching agent obtained in step 1) and stir thoroughly to leach the precious metals.

10. The metal leaching method according to claim 9, characterized in that: The noble metal is at least one of gold, palladium and platinum.

11. The metal leaching method according to claim 9, characterized in that: The feed mass ratio of the ionic liquid to the noble metal is controlled to be 2800-9000:

1.

12. The metal leaching method according to claim 9, characterized in that: In step 2), the leaching temperature is controlled to be 40-80°C.

13. The metal leaching method according to claim 12, characterized in that: In step 2), the leaching temperature is controlled at 60-80°C.

14. The metal leaching method according to claim 13, characterized in that: In step 2), the leaching temperature is controlled to be 60°C.

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