Method for separating metal salts

Abstract

To provide a simple and cost-effective separation method that is applicable even to a solution containing rare earth metals at low concentrations.MEANS: A metal salt separation method is a method for separating rare earth metals from an aqueous solution containing the rare earth metals. This method includes the steps of: adding ammonium sulfate to the aqueous solution containing the rare earth metals; further adding alcohol; and crystallizing salts of the rare earth metals. In the aqueous solution containing the rare earth metals, the concentration of each rare earth metal is equal to or lower than 100 ppm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for separating metal salts.

Background Art

[0002] For present-day Japan, which does not produce rare earth ores, it is urgent to establish a recycling technology for rare earth metals. In this regard, although it can be expected that existing technologies can be applied when recovering rare earth metals contained at a certain high concentration in a solution, when dealing with a low-concentration solution containing 100 ppm or less, existing technologies are complicated and costly, so the development of a simple and low-cost method for separating and concentrating low-concentration resources is desired.

[0003] The present inventors have hitherto developed a technique for changing the solubility of an aqueous solution containing metal ions by using methanol and ammonium sulfate and efficiently separating and recovering it as a solid phase (Patent Document 1), but there were the same problems as described above.

[0004] In particular, for Japan, an island country, the development of a simple and low-cost method for separating and concentrating low-concentration resources from submarine surface sediments (so-called submarine mud), which are regarded as promising resources, is desired.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, when dealing with a low-concentration solution containing rare earth metals at 100 ppm or less, conventional separation methods are complicated and costly, and there has been a demand for a separation method that is simple and low-cost and applicable to solutions containing rare earth metals at low concentrations. The inventors of this invention have diligently studied and completed the following invention in order to solve the above problems. [Means for solving the problem]

[0007] [1] A method for separating a rare earth metal from an aqueous solution containing the rare earth metal, The process comprises adding ammonium sulfate to an aqueous solution containing the rare earth metal, adding alcohol, and crystallizing a salt of the rare earth metal. A method for separating metal salts, wherein the concentration of each rare earth metal in the aqueous solution containing the rare earth metals is 100 ppm or less.

[0008] [2] The method for separating metal salts according to [1], wherein the aqueous solution containing the rare earth metal contains an acid.

[0009] [3] The method for separating a metal salt according to [1] or [2], wherein the alcohol is a mixture of one or more alcohols selected from methanol, ethanol, and propanol.

[0010] [4] The concentration of ammonium sulfate is 2 mol / L below Let's assume that [1]~[3] figure A method for separating metal salts as described in item 1.

[0011] [5] The separation method according to any one of [1] to [4], wherein the rare earth metal is one or more selected from the group consisting of neodymium, samarium, terbium, dysprosium, and erbium.

[0012] [6] The separation method according to any one of [1] to [5], wherein the aqueous solution containing the rare earth metal is an aqueous solution obtained by acid leaching of seafloor surface sediments. [Effects of the Invention]

[0013] The present invention provides a method for separating metal salts that allows for the simple, low-cost, and efficient recovery of rare earth metals from low-concentration solutions containing 100 ppm or less of rare earth metals. Furthermore, by concentrating the solution into a solid phase, this method significantly contributes to the compact storage and improved handling of rare earth resources. [Brief explanation of the drawing]

[0014] [Figure 1] This is a flowchart illustrating an example of an embodiment of the metal salt separation method of the present invention. [Figure 2] This graph shows the results of Example 1. [Modes for carrying out the invention]

[0015] <Method for separating metal salts> The present invention relates to a method for separating metal salts, which is a method for separating rare earth metals from an aqueous solution containing rare earth metals, comprising the steps of adding ammonium sulfate, adding alcohol, and crystallizing the metal salt to the aqueous solution containing the rare earth metals, wherein the concentration of each rare earth metal in the aqueous solution containing the rare earth metals is 100 ppm or less. Figure 1 shows a flowchart illustrating an example of an embodiment of the metal salt separation method of the present invention.

[0016] Normally, methods utilizing crystallization result in residual liquid near saturation concentration, which can leave some of the target material remaining. However, the rare earth metal separation method of the present invention achieves highly efficient separation even at low concentrations of the target material, and since almost all of it precipitates in the solid phase, the separation efficiency and the solid phase recovery rate of the component of interest are extremely high. Even in solutions containing the target substance at low concentrations, the relative concentration in the solid phase increases when the majority of the target substance is converted into a solid phase, making handling easier in subsequent separation operations. In the existing technology, separation effects have been shown in regions where the concentration of the separation target is relatively high. However, it has been newly shown that the separation effect is also effective for a solution with a separation target of 100 ppm or less as in the present application. This has provided a way for the effective utilization of rare earths, which have not been utilized despite having high utilization value as resources in the past, and is a great contribution of the present invention.

[0017] (Aqueous solution containing rare earth metals) The aqueous solution containing rare earth metals is not particularly limited as long as it is an aqueous solution in which the rare earth metals to be separated are dissolved. It may be a solution prepared by dissolving a metal salt of a rare earth metal in water, or an acid leachate obtained by leaching a solid containing a rare earth metal and / or a metal salt of a rare earth metal with an acid such as sulfuric acid or hydrochloric acid. Also, the rare earth metals contained may be single or plural. Further, metals other than rare earth metals and / or their metal salts may be contained.

[0018] In the present invention, examples of the rare earth metals to be separated include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium. Among them, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium are preferable, and further, neodymium, samarium, terbium, dysprosium, erbium are more preferable.

[0019] Examples of the metals other than rare earth metals include general base metals such as iron, magnesium, copper, lead, and rare metals such as lithium, beryllium, rubidium, strontium, indium, cesium, barium, thallium, bismuth, thorium, uranium, etc.

[0020] The concentration of each rare earth metal in the aqueous solution is 100 ppm or less, preferably 80 ppm or less, more preferably 50 ppm or less, still more preferably 35 ppm or less, still more preferably 15 ppm or less, still more preferably 5.0 ppm or less, particularly preferably 1.0 ppm or less, and most preferably 0.10 ppm or less. The concentration of metals other than rare earth metals that are not the separation target is not particularly limited, and it may be in a wide concentration range from several ppm to 1 mol / L.

[0021] Conventionally, in the case of a separation method using crystallization, the metal to be targeted in the solution needed to be at a certain high concentration. However, in the present invention, crystallization and separation can be carried out even at the low concentrations as described above. Therefore, separation is possible without performing a concentration operation. Also, even if the desired rare earth metal is present at a low concentration in the aqueous solution, it is possible to preferentially separate the rare earth metal from other metals (even if the other metals are present at a high concentration).

[0022] (Step of adding ammonium sulfate) In the method for separating the metal salt of the present application, first, ammonium sulfate is added to an aqueous solution containing a rare earth metal. In the method of the present application, the lower limit of the ammonium sulfate concentration of the resulting solution is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, still more preferably 0.1 mol / L or more, and the upper limit is preferably 5 mol / L or less, more preferably 3 mol / L or less, still more preferably 2 mol / L or less.

[0023] (Step of adding alcohol) Alcohol is added to the solution obtained in the above step. Examples of alcohols that can be used include methanol, ethanol, propanol, etc., which show poor solvent solubility in water and have a dielectric constant lower than that of water. These may be used alone or in a mixture of two or more. Among them, methanol, which is inexpensive and easy to recover, is preferred. The amount of alcohol added should be such that the alcohol concentration of the solution after addition is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more. The optimal amount of alcohol to add will vary depending on the amount of ammonium sulfate added. To lower the concentration of ammonium sulfate, increase the alcohol concentration; to reduce the amount of alcohol added, increase the amount of ammonium sulfate added.

[0024] As described above, the alcohol may be added after the ammonium sulfate, or the process may be reversed, with the alcohol being added first and then the ammonium sulfate, or the ammonium sulfate and alcohol may be added simultaneously. If the ammonium sulfate is added later, it should be added to the solution from which the alcohol has been removed, so that the concentration reaches the level described above.

[0025] (Process for crystallizing metal salts) Through the above process, ammonium sulfate and BiA After adding ammonium sulfate, it is preferable to mix the solution by shaking or stirring as needed. The mixing time is not particularly limited and should be sufficient for the ammonium sulfate to dissolve; for example, it can be about 10 seconds to 10 minutes.

[0026] Subsequently, the metal salt crystallizes by allowing the solution to stand. The standing time should be sufficient for the metal salt to crystallize, for example, 10 minutes to 3 hours.

[0027] After the metal salt crystallizes, solid-liquid separation can be performed by filtration to obtain the crystallized metal salt as a solid phase, and a solution containing the uncrystallized metal salt as a liquid phase. The crystallized metal salt may be washed with an aqueous solution having the same alcohol and ammonium sulfate concentrations as the original solution. The above operations are usually performed at room temperature and pressure, but the temperature and pressure may be changed as needed.

[0028] In the present invention, it is preferable that the aqueous solution containing the rare earth metal to be separated contains an acid. The type of acid is not particularly limited, but examples include water-soluble organic acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and oxalic acid. Regarding the form in which the acid is included, the acid may be added to the solution in which the rare earth metal is dissolved, or the acid may be included in the form of an acid leaching solution obtained by leaching a solid containing the rare earth metal with an acid. The inventors believe that the presence of acid in the aqueous solution is a major factor in enabling the crystallization of low concentrations of rare earth metals by a predetermined method, and they are currently analyzing the mechanism behind this. The concentration of the acid in the aqueous solution is not particularly limited as long as it is sufficient to leach the target metal. For example, the lower limit is preferably 0.01 mol / L or higher, more preferably 0.05 mol / L or higher, and even more preferably 0.1 mol / L or higher. The upper limit is preferably 10 mol / L or lower, more preferably 5 mol / L or lower, even more preferably 1 mol / L or lower, and particularly preferably 0.5 mol / L or lower. [Examples]

[0029] < reference Example 1 (Confirmation of Nd crystallization behavior) Neodymium (Nd) 7.2 mg (NdCl3: 5.0 x 10) -3 Ammonium sulfate was added to an aqueous solution containing (mol / L) (ammonium sulfate concentration: 1.0 mol / L), and methanol was then added. The mixture was stirred for 1 minute and allowed to stand at room temperature for 30 minutes to observe the crystallization behavior of neodymium. The results are shown in Figures 2(a) and (b). From these results, it was found that at a methanol concentration of approximately 44.5 wt%, the Nd in the liquid phase decreased to approximately 1 mg, and Nd precipitated in the solid phase.

[0030] <Example 2 (Crystallization of rare earth metals from sulfuric acid-containing solution)> To an aqueous solution containing 0.2 mol / L of sulfuric acid and the various metals shown in Table 1 at the leaching concentrations in Table 1, 1 mol / L of ammonium sulfate was added to bring the methanol concentration to 44.5 wt%, the mixture was stirred for 1 minute, and then allowed to stand at room temperature for 10 minutes to observe the crystallization behavior of each metal. The results are shown in Table 1.

[0031] [Table 1]

[0032] The results in Table 1 show that, for example, when examining metal species such as Nd, Sm, Tb, Dy, and Er, even when they are present in the stock solution at concentrations of 15 ppm or less, treatment with ammonium sulfate and methanol causes almost all of them to move from the liquid phase to the solid phase, leaving only a small amount in the liquid. Furthermore, it was found that the concentration in the solid phase was approximately 32 to 34 times that of the stock solution, and a solid with concentrated rare earth metals was obtained after the solvent was removed.

[0033] <Example 3 (Crystallization of rare earth metals from hydrochloric acid-containing solution)> To an aqueous solution containing 0.2 mol / L hydrochloric acid and each of the metals shown in Table 1 at the leaching concentrations in Table 1, 1 mol / L ammonium sulfate was added to bring the methanol concentration to 44.5 wt%, the mixture was stirred for 1 minute, and then allowed to stand at room temperature for 10 minutes to observe the crystallization behavior of each metal. The results are shown in Table 2.

[0034] [Table 2]

[0035] The results in Table 2 show that, for example, when examining metal species such as Nd, Sm, Tb, Dy, and Er, even when they are present in the stock solution at a concentration of 1.0 ppm or less, treatment with ammonium sulfate and methanol causes almost all of them to move from the liquid phase to the solid phase, leaving only a small amount in the liquid. Furthermore, it was found that the concentration in the solid phase was approximately 11 to 13 times that of the stock solution, and a solid with concentrated rare earth metals was obtained after the solvent was removed. [Industrial applicability]

[0036] The present invention's method for separating metal salts is fundamentally applicable in fields where it is desirable to recover metals dissolved in a liquid phase as a water-soluble solid phase, and is applicable even to low-concentration regions where conventional crystallization was not possible. For example, it may be used in the recycling of rare earth metals from automobile motors, the separation and concentration of rare earths from rare earth mud (e.g., seabed surface sediments), and the concentration of low-concentration rare earth-containing aqueous solutions.

Claims

1. A method for separating a rare earth metal from an aqueous solution containing the rare earth metal, The process comprises adding ammonium sulfate to an aqueous solution containing the rare earth metal, adding alcohol, and crystallizing a salt of the rare earth metal. The concentration of each rare earth metal in the aqueous solution containing the rare earth metals is 100 ppm or less. Methods for separating metal salts.

2. The method for separating metal salts according to claim 1, wherein the aqueous solution containing the rare earth metal contains an acid.

3. The method for separating a metal salt according to claim 1 or 2, wherein the alcohol is one or a mixture of two or more alcohols selected from methanol, ethanol, and propanol.

4. The method for separating metal salts according to claim 1 or 2, wherein the concentration of ammonium sulfate is 2 mol / L or less.

5. The separation method according to claim 1 or 2, wherein the rare earth metal is one or more selected from the group consisting of neodymium, samarium, terbium, dysprosium, and erbium.

6. The separation method according to claim 1 or 2, wherein the aqueous solution containing the rare earth metal is an aqueous solution obtained by acid leaching of seabed surface sediments.

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