Method for regenerating hydrophobic deep eutectic solvent and method for leaching nickel

Abstract

To provide a method for enabling recovery of metal element leaching capacity of a deep eutectic solvent used for leaching a metal element from an ore containing the metal element.SOLUTION: A method for recycling a hydrophobic deep eutectic solvent disclosed here includes: preparing a hydrophobic deep eutectic solvent used for leaching a metal element from an ore containing the metal element; and bringing the hydrophobic deep eutectic solvent and hydrochloric acid into contact with each other. In the hydrophobic deep eutectic solvent, a hydrogen bond donor is a carboxy group-containing compound, and a hydrogen bond acceptor is chloride salt. The amount of use of the hydrochloric acid is such that hydrogen chloride is 1 mole or more with respect to 1 mole of the hydrogen bond acceptor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for regenerating a hydrophobic deep eutectic solvent used in leaching a metal element from an ore containing the metal element, and also to a nickel leaching method utilizing said method. [Background technology]

[0002] In recent years, the demand for various metals has been increasing. For example, lithium composite oxides containing transition metals such as Ni, Co, and Mn are used as the positive electrode active material of lithium ion secondary batteries, and the demand for transition metal elements has been increasing with the spread of lithium ion secondary batteries. Therefore, methods for obtaining sources of various metal elements, including transition metal elements, have been developed.

[0003] As one of such methods, a method is known in which metal elements are leached from ores containing the metal elements using a deep eutectic solvent (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Non-Patent Document 1] Gawen RTJenkin et al., “The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals”, Minerals Engineering, Volume 87, 1 March 2016, Pages 18-24 Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of intensive research, the present inventors have found that when a deep eutectic solvent in which the hydrogen bond donor is a carboxyl group-containing compound and the hydrogen bond acceptor is a chloride salt is used to leach metal elements from an ore, the metal element leaching ability of the recovered used deep eutectic solvent is significantly reduced. Here, there is a problem that a deep eutectic solvent with a significantly reduced metal element leaching ability cannot be reused and becomes waste.

[0006] On the other hand, nickel, among the transition metal elements, is used not only as a positive electrode active material for lithium-ion secondary batteries, but also in stainless steel, special steel, etc., and the demand for these is also increasing, so that the demand for nickel is rapidly increasing and the importance of a method for obtaining a nickel source is increasing.

[0007] Therefore, the present invention aims to provide a method capable of recovering the metal element leaching ability of a deep eutectic solvent used for leaching a metal element from an ore containing the metal element. Another object of the present invention is to provide a novel nickel leaching method. [Means for solving the problem]

[0008] The method for regenerating a hydrophobic deep eutectic solvent disclosed herein includes the steps of preparing a hydrophobic deep eutectic solvent used in leaching a metal element from a metal-containing ore, and contacting the hydrophobic deep eutectic solvent with hydrochloric acid. The hydrogen bond donor of the hydrophobic deep eutectic solvent is a carboxyl group-containing compound, and the hydrogen bond acceptor is a chloride salt. The amount of hydrochloric acid used is such that 1 mole or more of hydrogen chloride is used per mole of the hydrogen bond acceptor.

[0009] According to this configuration, it is possible to recover the metal element leaching ability of the deep eutectic solvent used for leaching metal elements from ore containing metal elements.

[0010] The nickel leaching method disclosed herein comprises the steps of obtaining a regenerated hydrophobic deep eutectic solvent by the method for regenerating a hydrophobic deep eutectic solvent disclosed herein, and contacting the regenerated hydrophobic deep eutectic solvent with nickel ore.

[0011] According to this configuration, a novel nickel leaching method is provided. [Brief description of the drawings]

[0012] [Figure 1] 1 is a flowchart showing each step of a method for regenerating a hydrophobic deep eutectic solvent according to the present invention. [Diagram 2] 1 is a flowchart showing the steps of a nickel leaching method utilizing a method for regenerating a hydrophobic deep eutectic solvent according to the present invention and a method for producing nickel sulfate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. In addition, matters not mentioned in this specification but necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field. In addition, the numerical range expressed as "A to B" in this specification includes A and B.

[0014] As shown in Fig. 1, the method for regenerating a hydrophobic deep eutectic solvent according to this embodiment includes a step S101 of preparing a hydrophobic deep eutectic solvent used in leaching a metal element from an ore containing the metal element (hereinafter also referred to as a "used deep eutectic solvent preparation step"), and a step S102 of contacting the hydrophobic deep eutectic solvent with hydrochloric acid (hereinafter also referred to as a "hydrochloric acid contact step"). The hydrogen bond donor of the hydrophobic deep eutectic solvent is a carboxyl group-containing compound, and the hydrogen bond acceptor is a chloride salt. The amount of hydrochloric acid used is an amount such that 1 mole or more of hydrogen chloride is used per mole of the hydrogen bond acceptor.

[0015] First, the used deep eutectic solvent preparation step S101 will be described. In this step S101, the hydrophobic deep eutectic solvent may be prepared by leaching metal elements from ore containing metal elements, or a hydrophobic deep eutectic solvent obtained by leaching metal elements from ore containing metal elements by another person may be obtained.

[0016] The metal element contained in the ore is not particularly limited as long as it is a metal element that can be leached by a hydrophobic deep eutectic solvent. Examples include alkali metals (e.g., Li, Na, K, etc.), alkaline earth metals (e.g., Mg, Ca, Sr, Ba, etc.), transition metals (e.g., first transition elements, second transition elements, third transition elements, etc.). Among them, from the viewpoint of usability as a positive electrode active material for lithium ion secondary batteries, Li, Ni, Co, or Mn is preferred as the metal element, and Ni is more preferred. From the viewpoint of usability as various catalysts such as automobile exhaust gas purification catalysts, precious metal elements (especially Pt, Pd, or Rh) are preferred as the metal element.

[0017] The ore containing a metal element is not particularly limited, and examples thereof include gold ore, silver ore, copper ore, lead ore, tin ore, antimony ore, zinc ore, iron ore, iron sulfide ore, chromite ore, manganese ore, tungsten ore, molybdenum ore, nickel ore, and cobalt ore. Among them, nickel ore, cobalt ore, and manganese ore are preferred, and nickel ore is more preferred. As the nickel ore, nickel oxide ore (e.g., limonite ore, saprolite ore, etc.) is preferred.

[0018] In this embodiment, the hydrophobic deep eutectic solvent used has a hydrogen bond donor that is a carboxy group-containing compound and a hydrogen bond acceptor that is a chloride salt.

[0019] In this specification, the term "deep eutectic solvent" refers to a mixture containing a hydrogen bond donor and a hydrogen bond acceptor, at least one of which is solid at 25°C, and which is liquid at 25°C. Specifically, a deep eutectic solvent contains a substance that is solid at 25°C, but when a hydrogen bond donor and a hydrogen bond acceptor are mixed in a predetermined mixing ratio, a eutectic melting point depression occurs and the solvent becomes liquid at 25°C. Strictly speaking, a deep eutectic solvent is different from an ionic liquid because it does not consist of ions only in that it contains a hydrogen bond donor. Deep eutectic solvents are advantageous in that they are easily composed of substances with low environmental load compared to ionic liquids.

[0020] In this specification, the term "hydrophobic deep eutectic solvent" refers to a deep eutectic solvent that undergoes phase separation into an aqueous phase and a hydrophobic deep eutectic solvent phase when contacted with water at 25° C. The solubility of the hydrophobic deep eutectic solvent in water at 25° C. is preferably 1 g / 100 mL or less, more preferably 0.1 g / 100 mL or less, and even more preferably 0.01 g / 100 mL or less.

[0021] Examples of the carboxyl group-containing compound that is a hydrogen bond donor include fatty acids such as formic acid, acetic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, eicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, and triacontanoic acid; oxalic acid, malonic acid, succinic acid, adipic acid, itaconic acid, and the like. Examples of suitable carboxylic acid compounds include polycarboxylic acid compounds such as benzoic acid, aromatic carboxylic acid compounds such as phenylacetic acid, 3-phenylpropionic acid, trans-cinnamic acid, and other aromatic compounds having a carboxyl group-containing substituent; levulinic acid; and carboxyl group-containing compounds having a hydroxyl group, such as lactic acid, tartaric acid, ascorbic acid, citric acid, 4-hydroxybenzoic acid, p-coumaric acid, caffeic acid, gallic acid, and other acidic acids.

[0022] As the hydrogen bond donor, these can be used alone or in combination of two or more kinds.

[0023] As the hydrogen bond donor, a fatty acid is preferable, a fatty acid having 8 to 12 carbon atoms is more preferable, and decanoic acid is further preferable.

[0024] Examples of chloride salts that are hydrogen bond acceptors include quaternary ammonium chlorides, quaternary phosphonium chlorides, tertiary ammonium chlorides, and primary ammonium chlorides.

[0025] Examples of quaternary ammonium chlorides include choline chloride, tetrabutylammonium chloride, tetraethylammonium chloride, tetramethylammonium chloride, methyltrioctylammonium chloride, tetraoctylammonium chloride, acetylcholine chloride, chlorocholine chloride, fluorocholine chloride, and N-(2-hydroxyethyl)-N,N-dimethylbenzenemethanaminium chloride.

[0026] Examples of the quaternary phosphonium chloride include methyltriphenylphosphonium chloride, benzyltriphenylphosphonium chloride, and the like.

[0027] An example of a tertiary ammonium chloride is 2-(diethylamino)ethanol hydrochloride.

[0028] An example of a primary ammonium chloride is ethylamine hydrochloride (ethylammonium chloride).

[0029] As the hydrogen bond acceptor, these can be used alone or in combination of two or more kinds.

[0030] As the hydrogen bond acceptor, a quaternary ammonium chloride is preferable, and an ammonium chloride having four alkyl groups each having 1 to 8 carbon atoms is more preferable.

[0031] In the hydrophobic deep eutectic solvent, it is particularly preferred that the hydrogen bond donor is a fatty acid and the hydrogen bond acceptor is a quaternary ammonium chloride.

[0032] The hydrophobic deep eutectic solvent can be prepared according to a known method. For example, the hydrophobic deep eutectic solvent can be prepared by dry blending the hydrogen bond donor and the hydrogen bond acceptor and stirring or kneading at or above the eutectic point of the hydrophobic deep eutectic solvent. Alternatively, the hydrophobic deep eutectic solvent can be prepared by dissolving the hydrogen bond donor and the hydrogen bond acceptor in a solvent and then removing the solvent.

[0033] What is prepared in step S101 is a hydrophobic deep eutectic solvent (hereinafter also referred to as a "used hydrophobic deep eutectic solvent") that has been used to leach metal elements from ore containing metal elements. Leaching of metal elements from ore containing metal elements can be performed by contacting the ore with a hydrophobic deep eutectic solvent. Thus, the used hydrophobic deep eutectic solvent is one that has been contacted with the ore. Contact between the ore and the hydrophobic deep eutectic solvent can typically be performed by immersing the ore in the hydrophobic deep eutectic solvent. During contact, stirring, heating, ultrasonic irradiation, etc. may be performed to increase leaching efficiency.

[0034] A component other than the hydrophobic deep eutectic solvent (e.g., an acid, an oxidizing agent, etc.) may be used to leach the metal element from the ore.

[0035] The used hydrophobic deep eutectic solvent may contain ores containing metal elements, but preferably does not contain ores containing metal elements. Therefore, the used hydrophobic deep eutectic solvent is preferably one from which ores containing metal elements have been removed by solid-liquid separation treatment such as filtration.

[0036] The used hydrophobic deep eutectic solvent may or may not contain the leached metal element. Therefore, the used hydrophobic deep eutectic solvent may be one from which the leached metal element has been recovered. Therefore, the used hydrophobic deep eutectic solvent may be one that has been subjected to a process for separating a specific metal element (e.g., extraction with an acid aqueous solution) in addition to the above-mentioned leaching process for the metal element.

[0037] Next, the hydrochloric acid contact step S102 will be described. As a result of intensive research by the present inventors, it was found that the cause of the decrease in the metal element leaching ability of the used hydrophobic deep eutectic solvent is the consumption of hydrogen chloride (HCl) during the leaching of metal elements from the ore. Therefore, by carrying out the step S102, the used deep eutectic solvent is brought into contact with hydrochloric acid, and hydrogen chloride (HCl) is replenished to the used deep eutectic solvent. This makes it possible to restore the metal element leaching ability of the used deep eutectic solvent.

[0038] Hydrochloric acid is an aqueous solution of hydrogen chloride. The amount of hydrochloric acid used is an amount in which hydrogen chloride is 1 mole or more per mole of hydrogen bond acceptor of the hydrophobic deep eutectic solvent. In such an amount, the metal element leaching ability of the used hydrophobic deep eutectic solvent can be significantly restored. From the viewpoint of further restoring the metal element leaching ability of the used hydrophobic deep eutectic solvent, the amount of hydrochloric acid used is preferably 1.5 moles or more, more preferably 1.8 moles or more, and even more preferably 2 moles or more of hydrogen chloride per mole of hydrogen bond acceptor of the hydrophobic deep eutectic solvent. The upper limit of the amount of hydrochloric acid used is not particularly limited. From the viewpoint of avoiding the use of a large excess of hydrochloric acid, the amount of hydrochloric acid used is preferably 50 moles or less, more preferably 30 moles or less, and even more preferably 10 moles or less of hydrogen chloride per mole of hydrogen bond acceptor of the hydrophobic deep eutectic solvent.

[0039] In step S102, the method of contacting the hydrophobic deep eutectic solvent with hydrochloric acid is not particularly limited. For example, the contact method is mixing the hydrophobic deep eutectic solvent with hydrochloric acid. At this time, the hydrophobic deep eutectic solvent and hydrochloric acid are usually immiscible, so phase separation occurs. The hydrogen chloride contained in the hydrochloric acid moves to the hydrophobic deep eutectic solvent phase, and the hydrogen chloride is replenished to the hydrophobic deep eutectic solvent.

[0040] In order to improve the efficiency of hydrogen chloride transfer, the mixture of the hydrophobic deep eutectic solvent and hydrochloric acid may be shaken or stirred using a known shaking or stirring device used in liquid-liquid extraction. Alternatively, a known emulsion flow device may be used to contact the hydrophobic deep eutectic solvent with hydrochloric acid.

[0041] The contact temperature and contact time may be appropriately determined depending on the contact method. The contact temperature may be room temperature (e.g., 25°C ± 10°C), or the contact may be performed at a temperature above 35°C and below the boiling point of hydrochloric acid. The contact time is, for example, 1 minute to 120 hours, and preferably 30 minutes to 24 hours.

[0042] After the contact, the hydrophobic deep eutectic solvent phase can be recovered to obtain a regenerated hydrophobic deep eutectic solvent (i.e., the metal element leaching ability is restored). Thus, according to the method for regenerating a hydrophobic deep eutectic solvent according to the present embodiment, the metal element leaching ability of the deep eutectic solvent used for leaching a metal element from an ore containing the metal element can be restored.

[0043] The regenerated hydrophobic deep eutectic solvent can be reused for leaching of metal elements. The hydrophobic deep eutectic solvent reused for leaching of metal elements can be regenerated again by carrying out the step S102. Therefore, by utilizing the method for regenerating a hydrophobic deep eutectic solvent according to this embodiment, the hydrophobic deep eutectic solvent can be repeatedly used for leaching of metal elements from ore containing metal elements. This prevents the hydrophobic deep eutectic solvent from becoming waste, which is advantageous in terms of the environment, costs, and the like.

[0044] As described above, the demand for nickel is rapidly increasing, and the importance of a method for obtaining a nickel source is increasing. From another aspect, the nickel leaching method according to this embodiment includes a step S201 of obtaining a regenerated hydrophobic deep eutectic solvent by the above-mentioned method for regenerating a hydrophobic deep eutectic solvent (hereinafter also referred to as a "deep eutectic solvent regeneration step"), and a step S202 of contacting the regenerated hydrophobic deep eutectic solvent with nickel ore (hereinafter also referred to as a "nickel leaching step"). Steps S201 and S202 in FIG. 2 are steps included in the nickel leaching method according to this embodiment.

[0045] The deep eutectic solvent regeneration step S201 can be carried out by carrying out the above-mentioned used deep eutectic solvent preparation step S101 and hydrochloric acid contact step S102.

[0046] The nickel ore used in the nickel leaching step S202 is preferably, but not limited to, nickel oxide ore. The nickel oxide ore is not particularly limited as long as it is an oxide ore containing nickel. Examples of nickel oxide ore include limonite ore and saprolite ore. Nickel oxide ore typically contains nickel oxide (NiO) and iron oxide (Fe2O3) as components.

[0047] The nickel ore may be one that has been subjected to a crushing process, a classification process, etc. By subjecting the nickel ore to a crushing process, a classification process, etc., the particle size of the nickel ore can be adjusted to a predetermined range (for example, a median size D50 determined by a laser diffraction scattering method is 0.01 to 1000 μm, preferably 1 to 100 μm), thereby improving the leaching efficiency. The crushing process, the classification process, etc. can be performed according to a known method.

[0048] The amount of the hydrophobic deep eutectic solvent used relative to the nickel ore is not particularly limited. The amount of the hydrophobic deep eutectic solvent used relative to 100 parts by mass of the nickel ore is, for example, 10 to 100,000 parts by mass, and preferably 100 to 10,000 parts by mass.

[0049] The contact of the nickel ore with the hydrophobic deep eutectic solvent can be carried out according to a known method, for example, by placing the nickel ore and the hydrophobic deep eutectic solvent in a container and immersing the nickel ore in the hydrophobic deep eutectic solvent.

[0050] When the nickel ore and the hydrophobic deep eutectic solvent are brought into contact with each other, the mixture of the nickel ore and the hydrophobic deep eutectic solvent may be stirred. The stirring may be performed by a known method (e.g., a method using a stirring device equipped with a stirring bar, a stirring blade, etc.). When the nickel ore and the hydrophobic deep eutectic solvent are brought into contact with each other, ultrasonic waves may be irradiated.

[0051] The contact between the nickel ore and the hydrophobic deep eutectic solvent can be carried out at room temperature (specifically, 25°C). From the viewpoint of increasing the leaching rate, heating may be carried out when the nickel ore and the hydrophobic deep eutectic solvent are brought into contact with each other. Heating can be carried out by using a known means, such as an oil bath, a mantle heater, a strip heater (ribbon heater, etc.), or a planar heater (e.g., a film heater, a silicon rubber heater, etc.), for the container. The heating temperature is not particularly limited, but is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. On the other hand, from the viewpoint of energy efficiency, the heating temperature is preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 70°C or lower.

[0052] When the nickel ore is brought into contact with the hydrophobic deep eutectic solvent, pressure may be applied. The pressure may be applied according to a known method.

[0053] The time for contacting the nickel ore with the hydrophobic deep eutectic solvent is not particularly limited and can be appropriately determined depending on the type and amount of the hydrophobic deep eutectic solvent used, the particle size of the nickel ore, the temperature, etc. The time for contacting the nickel ore with the hydrophobic deep eutectic solvent is, for example, 1 minute to 100 hours, and preferably 1 hour to 50 hours.

[0054] To enhance the rate of nickel leaching, the nickel ore may be contacted with the hydrophobic deep eutectic solvent in the presence of an organic acid, which can form a single phase (the organic phase) when mixed with the hydrophobic deep eutectic solvent.

[0055] The organic acid is preferably a strong acid. In this specification, the term "strong acid" refers to an acid having a pKa of less than 0. Suitable examples of strong organic acids include organic sulfonic acid compounds such as methanesulfonic acid (pKa = -1.9), benzenesulfonic acid (pKa = -2.8), and p-toluenesulfonic acid (pKa = -2.8).

[0056] The ratio of organic acid to deep eutectic solvent is not particularly limited.The mass ratio of organic acid to hydrophobic deep eutectic solvent is, for example, 6 mass% or more, preferably 7 mass% or more, more preferably 8 mass% or more, even more preferably 9 mass% or more, and most preferably 10 mass% or more.On the other hand, the mass ratio of organic acid to hydrophobic deep eutectic solvent is, for example, 30 mass% or less, preferably 25 mass% or less, and more preferably 20 mass% or less.

[0057] When contacting the nickel ore with the hydrophobic deep eutectic solvent, other components (e.g., water, reducing agents, oxidizing agents, organic solvents other than organic acids, various additives) may be used within a range that does not significantly impair the effects of the present invention (e.g., less than 10 mass%, less than 5 mass%, or less than 1 mass% relative to the hydrophobic deep eutectic solvent).

[0058] After contact, the hydrophobic deep eutectic solvent containing the leached nickel (i.e., nickel leachate) can be recovered by a known solid-liquid separation method (e.g., filtration, etc.). Nickel can be extracted from the recovered nickel leachate according to a known method. The hydrophobic deep eutectic solvent after nickel extraction can be reused in the nickel leaching method according to this embodiment.

[0059] The nickel leaching method according to the present embodiment is novel, and the nickel leaching method according to the present embodiment can be repeatedly carried out by carrying out a step of extracting nickel from the nickel leaching solution and recovering the hydrophobic deep eutectic solvent. Therefore, it is possible to prevent the hydrophobic deep eutectic solvent from becoming waste, which is advantageous in terms of the environment, cost, etc.

[0060] Regarding nickel extraction from the recovered nickel leachate, the obtained nickel leachate is subjected to back extraction using sulfuric acid to obtain an aqueous phase containing nickel sulfate (hereinafter also referred to as the "back extraction step"), whereby nickel can be obtained as nickel sulfate.

[0061] Therefore, the method including the deep eutectic solvent regeneration step S201, the nickel leaching step S202, and the stripping step S203 is a method for producing nickel sulfate as shown in Fig. 2. Here, nickel sulfate is mainly used as the nickel source of the positive electrode active material of lithium ion secondary batteries. Therefore, the method for producing nickel sulfate is of high industrial value as a new method for securing nickel sulfate as the nickel source of the positive electrode active material of lithium ion secondary batteries.

[0062] The stripping step S203 will now be described. In the stripping step S203, stripping is performed using sulfuric acid as an extraction solvent (i.e., aqueous phase). In other words, nickel that has migrated from the nickel ore to the hydrophobic deep eutectic solvent phase is transferred to the aqueous phase. Sulfuric acid is used to convert the anion (SO4 2- ) source.

[0063] The concentration of sulfuric acid is not particularly limited as long as nickel can be transferred to the aqueous phase, and is, for example, 1 mol / L (1M) or more. Here, the nickel ore may contain iron oxide (Fe2O3). In particular, nickel oxide ore typically contains iron oxide. In the stripping step S203, the use of high-concentration sulfuric acid can suppress the transfer of Fe to the aqueous phase. That is, nickel sulfate with little iron component contamination can be obtained. From this viewpoint, the concentration of sulfuric acid is preferably 1.5 mol / L or more, more preferably 2 mol / L or more, even more preferably 2.5 mol / L or more, and most preferably 3 mol / L or more. The upper limit of the concentration of sulfuric acid is not particularly limited and is determined by technical limitations. The concentration of sulfuric acid may be 15 mol / L or less, 10 mol / L or less, 7.5 mol / L or less, or 5 mol / L or less.

[0064] Here, the nickel leachate may be diluted with a hydrophobic organic solvent before stripping with sulfuric acid. By diluting the nickel leachate with an organic solvent, the migration of Fe to the aqueous phase can be suppressed, and nickel sulfate with less iron component contamination can be obtained. In addition, the viscosity of the nickel leachate can be adjusted by the dilution, making stripping easier and improving productivity. In particular, when the viscosity of the nickel leachate (or the hydrophobic deep eutectic solvent) is high (e.g., when the hydrogen bond acceptor is tetrabutylammonium chloride), the effect of improving productivity is greater.

[0065] As the hydrophobic organic solvent, hydrocarbons are suitable, and examples thereof include aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, etc., and aromatic hydrocarbons such as benzene, toluene, etc. Of these, aromatic hydrocarbons are preferred, and toluene is more preferred.

[0066] The amount of the hydrophobic organic solvent used is not particularly limited and can be appropriately determined depending on the viscosity of the leachate. The amount of the hydrophobic organic solvent used is, for example, 1 to 100% by volume, preferably 5 to 50% by volume, based on the leachate.

[0067] The extraction solvent (i.e., the aqueous phase) may contain components other than sulfuric acid within a range that does not significantly impair the effects of the present invention (e.g., less than 10% by mass, less than 5% by mass, or less than 1% by mass).

[0068] The amount of sulfuric acid used relative to the nickel leaching solution is not particularly limited, and is, for example, 1:0.05-20, and preferably 1:0.2-5, in terms of leaching solution:sulfuric acid (volume ratio).

[0069] The stripping can be carried out according to a known method. After stripping, the aqueous phase can be recovered to obtain a solution containing nickel sulfate. Nickel sulfate can be crystallized from the solution containing nickel sulfate according to a known method, and then recovered to obtain nickel sulfate.

[0070] Depending on the application of nickel sulfate, nickel sulfate may be recovered in the form of an aqueous solution without precipitating nickel sulfate from the solution containing nickel sulfate. In this case, the solution containing nickel sulfate may be used as is for the desired application, or may be used after being subjected to a treatment such as neutralization.

[0071] According to the above-mentioned method for producing nickel sulfate, nickel sulfate can be easily obtained. In addition, since the hydrophobic deep eutectic solvent can be reused, the amount of waste generated can be reduced. EXAMPLES

[0072] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0073] [Examples 1 to 3 and Comparative Examples 1 to 5] <Preparation of used hydrophobic deep eutectic solvent> A liquid in which decanoic acid as a hydrogen bond donor and trioctylmethylammonium chloride as a hydrogen bond acceptor were mixed in a volume ratio of 2:1 was placed in a container equipped with a stirring blade. Nickel oxide ore was added in an amount of 10 g / L to this container, and the mixture was stirred at 60°C and a rotation speed of 400 rpm for 24 hours to leach nickel into the hydrophobic deep eutectic solvent. After the nickel oxide ore was collected by filtration, sulfuric acid with a concentration of 5 M (mol / L) was added to the filtrate (hydrophobic deep eutectic solvent) in a volume ratio of 1:1. The mixture was shaken for 1 hour to move the leached nickel into the aqueous phase. The hydrophobic deep eutectic solvent phase was then extracted to collect the hydrophobic deep eutectic solvent. Meanwhile, ICP analysis was performed on the collected nickel oxide ore and the leachate to determine the amount of Ni leached.

[0074] <Regeneration of used hydrophobic deep eutectic solvents> Next, the replenishment solution shown in Table 1 was added to the recovered hydrophobic deep eutectic solvent so that the volume ratio was 1:1. After shaking for 1 hour, the hydrophobic deep eutectic solvent phase was extracted. In this way, the hydrophobic deep eutectic solvent was recovered. However, in Comparative Example 1, the regeneration treatment with the replenishment solution was not performed, and the solvent was used for the next nickel re-leaching.

[0075] <Nickel releaching with regenerated hydrophobic deep eutectic solvent> The recovered hydrophobic deep eutectic solvent was placed in a vessel equipped with an agitator, and nickel oxide ore was added again at an amount of 10 g / L. This was stirred at 60°C and a rotation speed of 400 rpm for 24 hours to allow nickel to be leached into the hydrophobic deep eutectic solvent. The nickel oxide ore was recovered by filtration, and the leachate and the recovered nickel oxide ore were subjected to ICP analysis to determine the amount of Ni leached. The Ni re-leaching rate was calculated as the ratio (%) of the amount of Ni leached in the re-leaching to the amount of Ni leached in the first leaching. The results are shown in Table 1.

[0076] [Table 1]

[0077] Comparative Example 1 is an example in which the used hydrophobic deep eutectic solvent was not regenerated. When regeneration was not performed, the Ni leaching ability of the hydrophobic deep eutectic solvent was significantly reduced, and the Ni re-leaching rate was only 10%. In contrast, in Comparative Example 2, an aqueous NaCl solution was used to regenerate the used hydrophobic deep eutectic solvent, and the Ni re-leaching rate was only 10%. - In Comparative Example 3, the used hydrophobic deep eutectic solvent was replenished with H + However, the Ni releaching rate was further reduced when only 10% was replenished.

[0078] In contrast, in Comparative Examples 4 and 5 and Examples 1 to 3, hydrochloric acid was used to hydrate the used hydrophobic deep eutectic solvent with H + and Cl - The results in Table 1 show that in Example 1, where the molar ratio of hydrogen chloride to the hydrogen bond acceptor in the hydrophobic deep eutectic solvent is 1, the Ni releaching rate was significantly improved. In Example 2, where the molar ratio is 2, the Ni releaching rate was 100%, and the Ni leaching ability was completely restored.

[0079] From the above results, it can be seen that the method for regenerating a hydrophobic deep eutectic solvent disclosed herein makes it possible to recover the metal element leaching ability of a deep eutectic solvent used to leach metal elements from ores containing metal elements.

[0080] Although the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0081] That is, the method for regenerating a hydrophobic deep eutectic solvent and the method for nickel leaching disclosed herein include the following items [1] to [4]. [1] A process for preparing a hydrophobic deep eutectic solvent used in leaching metal elements from an ore containing metal elements; and contacting the hydrophobic deep eutectic solvent with hydrochloric acid; The hydrogen bond donor of the hydrophobic deep eutectic solvent is a carboxyl group-containing compound and the hydrogen bond acceptor is a chloride salt; The amount of the hydrochloric acid used is such that hydrogen chloride is 1 mole or more per mole of the hydrogen bond acceptor. A method for regenerating hydrophobic deep eutectic solvents. [2] The method according to claim [1], wherein the amount of hydrochloric acid used is an amount such that 2 moles or more of hydrogen chloride are used per mole of the hydrogen bond acceptor. [3] The method of claim [1] or [2], wherein the hydrogen bond donor is a fatty acid and the hydrogen bond acceptor is a quaternary ammonium chloride. [4] A step of obtaining a regenerated hydrophobic deep eutectic solvent by the method for regenerating a hydrophobic deep eutectic solvent according to any one of claims [1] to [3]; contacting the regenerated hydrophobic deep eutectic solvent with nickel ore; 1. A method for leaching nickel comprising the steps of:

Claims

1. Providing a hydrophobic deep eutectic solvent used in leaching metal elements from an ore containing the metal elements; contacting the hydrophobic deep eutectic solvent with the hydrochloric acid by mixing the hydrophobic deep eutectic solvent with hydrochloric acid and shaking or stirring the resulting mixture; The hydrogen bond donor of the hydrophobic deep eutectic solvent is a fatty acid and the hydrogen bond acceptor is a quaternary ammonium chloride; The amount of hydrochloric acid used is such that hydrogen chloride is 1 mole or more per mole of the hydrogen bond acceptor. A method for regenerating hydrophobic deep eutectic solvents.

2. The method according to claim 1 , wherein the amount of hydrochloric acid used is such that 2 moles or more of hydrogen chloride are used per mole of the hydrogen bond acceptor.

3. Obtaining a regenerated hydrophobic deep eutectic solvent by the method for regenerating a hydrophobic deep eutectic solvent according to claim 1; contacting the regenerated hydrophobic deep eutectic solvent with nickel ore; 1. A method for leaching nickel comprising the steps of:

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