Metal separation method and ore dressing method using same

Abstract

Provided is a metal separation method for separating a rare earth metal from an aqueous solution that contains iron and the rare earth metal, the metal separation method including a step for adding ammonium sulfate to the aqueous solution, a step for adding an alcohol to the aqueous solution, and a step for crystallizing a salt of the rare earth metal in a state where the iron contained in the aqueous solution is held in a liquid phase. Also provided is an ore dressing method including: a flotation step for causing flotation of a rare earth mineral from an ore that contains iron and the rare earth metal; and a post-flotation crystallization step for crystallizing a salt of the rare earth metal through the aforementioned metal separation method, using, as the aqueous solution, a tailings aqueous solution included in tailings generated in the flotation step.

Description

Metal separation method and mineral dressing method using the same

[0001] The present invention relates to a metal separation method for separating rare earth metals from an aqueous solution containing iron and rare earth metals.

[0002] A method for separating rare earth minerals from a mixture of various ores containing rare earth metals involves separating (selectively extracting) the rare earth minerals from other gangue minerals by flotation. For example, Patent Document 1 describes a method for flotation of bastnasite from barite, fluorite, and a rare earth composite ore containing bastnasite as a rare earth mineral. Specifically, the method describes conditioning an ore slurry with a sulfonate collector, simultaneously recovering barite and fluorite prior to bastnasite by froth flotation, and then conditioning the residue from the flotation of the barite and fluorite at a high temperature to separate bastnasite from the other gangue minerals by flotation.

[0003] In such flotation, rare earth metals may remain in the solution discarded after flotation, which can result in a loss of rare earth metal recovery. If the rare earth metals could be re-recovered from such a discarded solution, the yield of rare earth metals would be improved, but since the solution also contains iron, which was contained in the ore containing rare earth metals, dissolved as a mixture, it has been necessary to separate and recover the iron and rare earth metals in order to recover the rare earth metals.

[0004] However, iron and rare earth metals have similar chemical properties, and therefore are generally difficult to separate. For example, a method of precipitating and removing iron by alkali treatment is commonly used as a method for chemically separating iron from a solution containing iron and other metals. However, in such a method, metals that are prone to form hydroxide precipitates, such as rare earth metals, precipitate together with the iron, making it difficult to separate and recover the rare earth metals from an aqueous solution containing iron and rare earth metals. Separation is particularly difficult when the concentration of iron in the solution is low, resulting in a problem of a low recovery rate of the rare earth metals.

[0005] JP 55-119456

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a metal separation method capable of efficiently separating iron and rare earth metals from an aqueous solution containing iron and rare earth metals.

[0007] While conducting intensive research in light of this concept of technological development, the present inventors have completed a new metal separation method that can efficiently separate iron and rare earth metals contained in an aqueous solution by performing crystallization using methanol and ammonium sulfate.

[0008] That is, the metal separation method according to the present invention for achieving the above object is a metal separation method for separating rare earth metals from an aqueous solution containing iron and rare earth metals, and comprises the steps of adding ammonium sulfate to the aqueous solution, adding an alcohol to the aqueous solution, and crystallizing a salt of the rare earth metal while keeping the iron contained in the aqueous solution in a liquid phase.

[0009] A further characteristic feature of the metal separation method according to the present invention is that the rare earth metals are light rare earths and heavy rare earths, and the rare earth metals may be lanthanum, neodymium, and gadolinium.

[0010] According to this metal separation method, rare earth metals can be crystallized from an aqueous solution containing iron and rare earth metals while iron is dissolved in the liquid phase, thereby enabling efficient separation of iron and rare earth metals contained in the aqueous solution. Furthermore, this metal separation method can be carried out easily because it can be performed at room temperature and atmospheric pressure. For example, when recovering rare earth metals, only the rare earth metals crystallize, allowing only the rare earth metals to be separated as a solid phase from an aqueous solution containing iron and rare earth metals, thereby enabling highly efficient and simple recovery of valuable rare earth metals.

[0011] The ore dressing method according to the present invention for achieving the above-mentioned object is characterized by comprising: a flotation step of flotation of rare earth minerals from ore containing iron and rare earth metals; and a post-flotation crystallization step of crystallizing salts of the rare earth metals from an aqueous solution of tailings generated in the flotation step by the above-mentioned metal separation method.

[0012] According to this ore dressing method, rare earth metal salts are crystallized from the aqueous solution contained in the tailings generated in the flotation process by the above-mentioned metal separation method, so that the rare earth metals contained in the tailings can be recovered in the flotation process. This makes it possible to recover rare earth metals that would normally be discarded as tailings, thereby improving the recovery rate of rare earth metals in the process of dressing rare earth metal ores.

[0013] A further characteristic feature of the ore dressing method according to the present invention is that, in the ore dressing method for separating the rare earth mineral from the ore containing barite and fluorite, the method includes, before the flotation step, a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, and a second reverse flotation step for reverse flotation of fluorite.

[0014] According to this ore dressing method, barite and fluorite can be separated from a composite weathered ore containing barite and fluorite before bastnasite is flotation-separated, so that bastnasite can be efficiently separated in the bastnasite flotation step, thereby enabling high-concentration bastnasite to be obtained in the bastnasite flotation step.

[0015] Furthermore, a further characteristic feature of the ore dressing method according to the present invention is that the ore dressing method for separating the rare earth mineral from the ore containing barite and fluorite includes a first reverse flotation step of reverse flotation of barite from the ore containing barite and fluorite, and a crystallization step after first reverse flotation of the tailings, which is an aqueous solution contained in the tailings generated in the first reverse flotation step, and which crystallizes salts of the rare earth metals by the metal separation method described above.

[0016] According to this ore dressing method, barite can be separated from a composite weathered ore containing barite and fluorite, and therefore, when the rare earth minerals are subsequently subjected to flotation, for example, the rare earth minerals can be efficiently separated. Furthermore, since the rare earth metal salts can be crystallized and recovered by the above-mentioned metal separation method from the tailings containing rare earth minerals after the barite has been separated by reverse flotation, the rare earth metals contained in the tailings generated in the barite reverse flotation step can be recovered.

[0017] Furthermore, a further characteristic feature of the ore dressing method according to the present invention is that the ore dressing method for separating the rare earth mineral from the ore containing barite and fluorite includes a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, a second reverse flotation step for reverse flotation of the fluorite, and a post-second reverse flotation crystallization step for crystallizing a salt of the rare earth metal using an aqueous solution of tailings contained in the tailings generated in the second reverse flotation step as the aqueous solution by the metal separation method described above.

[0018] According to this ore dressing method, barite and fluorite can be separated from a composite weathered ore containing barite and fluorite, and therefore, when the rare earth minerals are subsequently subjected to flotation, for example, the rare earth minerals can be efficiently separated. Furthermore, since the rare earth metal salts can be crystallized and recovered by the above-mentioned metal separation method from the tailings containing rare earth minerals after the barite and fluorite have been separated by reverse flotation, the rare earth metals contained in the tailings generated in the reverse flotation step of barite and fluorite can be recovered.

[0019] FIG. 1 is a flow diagram showing an example of an embodiment of a metal separation method. FIG. 2 is a diagram showing the results of gadolinium crystallization in Comparative Example 1. FIG. 3 is a diagram showing the results of gadolinium crystallization in Comparative Example 2. FIG. 4 is a diagram showing the results of iron crystallization in Comparative Example 3. FIG. 5 is a graph showing the experimental results of Example 1. FIG. 6 is a graph showing the experimental results of Example 2. FIG. 7 is a flow diagram showing an ore dressing method according to a first embodiment. FIG. 8 is a cross-sectional schematic diagram of a flotation device used in the ore dressing method according to the first embodiment. FIG. 9 is a flow diagram showing a metal separation method in the ore dressing method according to the first embodiment. FIG. 10 is a flow diagram showing an ore dressing method according to a second embodiment. FIG. 11 is a flow diagram showing an ore dressing method according to another embodiment. FIG. 12 is a flow diagram showing an ore dressing method according to another embodiment.

[0020] Hereinafter, an embodiment of the metal separation method according to the present invention will be described. (Method for Separating Iron and Rare Earth Metals) The metal separation method according to the present invention is a metal separation method for separating rare earth metals from an aqueous solution containing iron and rare earth metals, and includes the steps of adding ammonium sulfate to the aqueous solution, adding an alcohol to the aqueous solution, and then crystallizing a salt of the rare earth metal while keeping the iron contained in the aqueous solution in the liquid phase. Figure 1 shows a flow diagram illustrating one embodiment of the metal separation method according to the present invention.

[0021] Conventionally, iron and rare earth metals (rare earths) have been very difficult to separate simply because of their similar physical and chemical properties, but the metal separation method according to the present invention makes it possible to crystallize rare earth metals in an aqueous solution containing iron and rare earth metals while maintaining iron in the liquid phase, thereby enabling efficient and simple separation of iron and rare earth metals contained in the aqueous solution. Furthermore, this metal separation method can be carried out easily because it can be carried out at room temperature and atmospheric pressure.

[0022] As described above, the metal separation method according to the present invention crystallizes only rare earth metals, allowing rare earth metals to be separated as a solid phase from an aqueous solution containing iron and rare earth metals. This allows for simple and efficient recovery of valuable rare earth metals. For example, when it is necessary to recover rare earth metals from an aqueous solution containing iron and rare earth metals while removing iron, this method allows for the iron removal operation and rare earth metal recovery operation to be performed efficiently and simply, which is believed to contribute to the stable operation of the rare earth metal recovery process. Furthermore, this method allows for the separation of only rare earth metals as a solid phase even when the iron concentration in the aqueous solution is low, allowing for the efficient and simple recovery of rare earth metals with fewer impurities.

[0023] (Aqueous Solution Containing Iron and Rare Earth Metals) The aqueous solution containing iron and rare earth metals in the present invention is not particularly limited as long as it is an aqueous solution containing dissolved iron and rare earth metals to be separated in the present invention. It may be a solution prepared by dissolving a metal salt of a rare earth metal in water, or a solution containing an acid leachate obtained by leaching a solid containing a rare earth metal or a metal salt of a rare earth metal with an acid such as sulfuric acid. The rare earth metal may be singular or plural. Furthermore, metals other than iron and rare earth metals or their metal salts may also be contained. Therefore, for example, the aqueous solution containing iron and rare earth metals in the present invention may be an aqueous solution contained in tailings from the ore flotation described below.

[0024] In the present invention, examples of rare earth metals to be separated include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0025] Furthermore, rare earth metals to be separated in the present invention include light rare earths and heavy rare earths, and when rare earth metals are classified into light rare earths and heavy rare earths, light rare earths include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium, and heavy rare earths include gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium. Of these, of the rare earth metals to be separated in the present invention, lanthanum and neodymium are preferred as light rare earths, and gadolinium is preferred as heavy rare earth.

[0026] The concentration of the rare earth metal salt in the aqueous solution containing iron and rare earth metal is not particularly limited, but an aqueous solution having a metal salt concentration in the range of 0.001 mol / L to 1 mol / L is usually used. If the salt concentration is too low, crystallization of the salt may be difficult, whereas if the salt concentration is too high, purification may be insufficient.

[0027] In addition, the iron to be separated in the present invention is Fe ２＋(ferric ion), Fe ３＋ They are dissolved in aqueous solutions in the form of cations, complexes, colloids, etc. Rare earth metals are also dissolved in aqueous solutions in the form of cations, complexes, etc.

[0028] The iron salt concentration in the aqueous solution containing iron and rare earth metals is not particularly limited, but an aqueous solution with a concentration in the range of 0.001 mol / L to 1 mol / L is usually used. If the salt concentration is too low, crystallization of the metal salt may be difficult, whereas if the salt concentration is too high, purification may be insufficient.

[0029] (Step of Adding Ammonium Sulfate) In the metal separation method of the present invention, first, ammonium sulfate is added to an aqueous solution containing iron and rare earth metals, as shown in Figure 1. It is desirable to add ammonium sulfate to the aqueous solution containing iron and rare earth metals so that the ammonium sulfate concentration in the aqueous solution containing iron and rare earth metals has a lower limit of preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, and even more preferably 0.1 mol / L or more, and an upper limit of preferably 5 mol / L or less, more preferably 3 mol / L or less, and even more preferably 2 mol / L or less.

[0030] (Step of adding alcohol) An alcohol is added to the solution obtained in the step of adding ammonium sulfate. Examples of alcohols that can be used include methanol, ethanol, and propanol, which are poor solvents for water and have a dielectric constant lower than that of water, and two or more of these may be mixed and used. Among these, methanol is preferred because it is inexpensive and easy to recover.

[0031] Regarding the amount of alcohol to be added, the lower limit of the alcohol concentration in the aqueous solution after the addition of alcohol is the concentration at which rare earth metal salts crystallize, and based on the experimental results in the Examples described later, it is preferably 10 wt % or more, more preferably 20 wt % or more. The upper limit of the alcohol concentration is lower than the concentration at which iron salts crystallize, and based on the experimental results in the Examples described later, it is preferably 50 wt % or less, more preferably 45 wt % or less.

[0032] The optimal amount of alcohol to be added varies depending on the amount of ammonium sulfate to be added. To lower the concentration of ammonium sulfate, simply increase the concentration of alcohol. To suppress the amount of alcohol to be added, simply increase the amount of ammonium sulfate to be added.

[0033] As described above, the alcohol may be added after the addition of ammonium sulfate, or the steps may be reversed, i.e., the alcohol is added first and then the ammonium sulfate is added, or ammonium sulfate and the alcohol may be added simultaneously. When ammonium sulfate is added later, it may be added so that the concentration becomes as described above, based on the solution excluding the alcohol.

[0034] (Step of Crystallizing Rare Earth Metal Salt) After adding ammonium sulfate and alcohol in the above step, the rare earth metal salt is crystallized in the step of crystallizing the rare earth metal salt. In the step of crystallizing the rare earth metal salt, it is preferable to mix the aqueous solution by shaking or stirring as necessary. The mixing time is not particularly limited as long as ammonium sulfate is dissolved, and can be, for example, about 10 seconds to 10 minutes.

[0035] In the step of crystallizing the rare earth metal salt, the solution is mixed as described above and then allowed to stand, whereby the rare earth metal salt crystallizes as a solid phase, and iron is separated as a liquid phase while being retained in the aqueous solution. The standing time may be a time sufficient for the rare earth metal salt to crystallize, and may be, for example, about 10 minutes to 3 hours.

[0036] After the rare earth metal salt crystallizes, solid-liquid separation is performed by filtration. The rare earth metal salt, which is the filtration residue, can be recovered as a solid phase, and the iron-containing aqueous solution, which is the filtrate, can be recovered. The above operations are usually performed at room temperature and atmospheric pressure, but the temperature and pressure may be changed as necessary.

[0037] The above-mentioned "crystallization as a solid phase" means that, based on 100 wt% of the rare earth metal salt to be separated in the solution before separation, preferably 40 wt% or more, more preferably 70 wt% or more, and even more preferably 99 wt% or more can be crystallized as a solid phase. Furthermore, the above-mentioned "separation as a liquid phase" means that preferably 80 wt% or more, more preferably 95 wt% or more, and even more preferably 99 wt% or more of the iron salt contained in the aqueous solution before separation is retained and remains in the liquid phase.

[0038] Examples of the metal separation method according to the present invention will be described below. The following examples demonstrate the effectiveness of the metal separation method according to the present invention. It goes without saying that the following examples are provided to explain the present invention in detail, and the scope of the invention is defined by the claims.

[0039] Comparative Example 1 (Confirmation of Crystallization Behavior of Rare Earth Metals) Figure 2 shows the weight change of gadolinium in the liquid phase when various concentrations of ammonium sulfate are dissolved in an aqueous solution with a gadolinium concentration of 0.1 mol / L. The results shown in Figure 2 show that the weight of gadolinium in the liquid phase does not change even when the ammonium sulfate concentration is increased to 4 mol / L. In other words, it was found that gadolinium does not crystallize in this ammonium sulfate concentration range.

[0040] Comparative Example 2 (Confirmation of Crystallization Behavior of Rare Earth Metals) Figure 3 shows the relationship between the weight of gadolinium in the liquid phase and the methanol concentration when various concentrations of methanol were added to an aqueous solution with a gadolinium concentration of 0.1 mol / L and an ammonium sulfate concentration of 0.2 mol / L. The results shown in Figure 3 show that when the methanol concentration in the aqueous solution exceeds 30 wt%, a decrease in the weight of gadolinium in the liquid phase is confirmed and gadolinium crystallizes into a solid phase.

[0041] Comparative Example 3 (Confirmation of Iron Crystallization Behavior) Figure 4 shows the results of crystallization performed by adding various concentrations of methanol to an aqueous solution containing dissolved iron ions at a concentration of 0.1 mol / L and ammonium sulfate at a concentration of 0.5 mol / L. The results shown in Figure 4 indicate that under these conditions, the weight of iron in the liquid phase does not change until the methanol concentration reaches 40 wt%, indicating that the iron is retained in the aqueous solution. Furthermore, when the methanol concentration exceeds 40 wt%, the weight of iron in the liquid phase decreases, indicating that iron crystallizes. These results suggest that iron remains in the liquid phase in the relatively low methanol concentration range, and that crystallization of rare earth metals in such a methanol concentration range may enable separation of iron and rare earth metals in an aqueous solution.

[0042] Example 1 (Separation of Iron and Rare Earth Metals (Light Rare Earths)) In this example, light rare earths lanthanum and neodymium were used as rare earth metals to separate iron and rare earth metals contained in an aqueous solution. FIG. 5 shows an example of experimental results in which ammonium sulfate and methanol were added to an aqueous solution containing iron and rare earth metals lanthanum and neodymium, and the iron, lanthanum, and neodymium were separated from each other. This experiment simulated the processing of ores containing monazite and banestsite as rare earth minerals. Ammonium sulfate was added to an aqueous solution containing 36 mg of lanthanum, 46 mg of neodymium, and 2.8 mg of iron, so that the ammonium sulfate concentration was 0.2 mol / L. After the addition of ammonium sulfate, methanol was further added to the aqueous solution to investigate the crystallization behavior of lanthanum, neodymium, and iron. Under these experimental conditions, the iron ion concentration was 0.01 mol / L, the lanthanum concentration was 0.05 mol / L, and the neodymium concentration was 0.05 mol / L. In FIG. 5, no change in the weight of iron in the liquid phase is observed within the range of methanol concentrations used in this experiment, and therefore it can be seen that iron is retained in the liquid phase at least when the methanol concentration is 45 wt % or less.

[0043] On the other hand, a decrease in the weights of lanthanum and neodymium was detected at methanol concentrations of 10 wt% or higher, indicating that lanthanum and neodymium begin to crystallize in the liquid phase at methanol concentrations of 10 wt% or higher. Furthermore, when the methanol concentration is 20 wt% or higher, lanthanum and neodymium are no longer detected in the liquid phase, indicating that all of the lanthanum and neodymium in the liquid phase have crystallized, resulting in a state in which no lanthanum or neodymium is dissolved in the liquid phase, but only iron. From these results, it was found that in the metal separation method of this embodiment, the methanol concentration is preferably 10 wt% or higher and 45 wt% or lower, and more preferably 20 wt% or higher and 45 wt% or lower. Furthermore, from these results, it was found that the separation of iron and rare earth metals by this method proceeds well even in aqueous solutions with a relatively low iron ion concentration.

[0044] Example 2: Separation of Iron and Rare Earth Metals (Heavy Rare Earths) In this example, iron and rare earth metals contained in an aqueous solution were separated using gadolinium, a heavy rare earth metal. Figure 6 shows an example of experimental results for separating iron and gadolinium from an aqueous solution containing iron and gadolinium as a rare earth metal, using ammonium sulfate and methanol. In this experiment, ammonium sulfate was added to an aqueous solution containing 95 mg of gadolinium and 10.3 mg of iron, so that the ammonium sulfate concentration was 0.2 mol / L. After the addition of ammonium sulfate, methanol was further added to the aqueous solution to investigate the crystallization behavior of lanthanum, neodymium, and iron. Under these conditions, the iron ion concentration was 0.14 mol / L, and the gadolinium ion concentration was 0.1 mol / L. Figure 6 shows that no change in the weight of iron in the liquid phase was observed within the range of methanol concentrations used in this experiment, indicating that iron was retained in the liquid phase at least when the methanol concentration was 45 wt % or less.

[0045] On the other hand, a decrease in the weight of gadolinium in the liquid phase was detected when the methanol concentration was 10 wt% or higher, indicating that gadolinium begins to crystallize at methanol concentrations of 10 wt% or higher. Furthermore, it was found that when the methanol concentration was 20 wt% or higher, all of the gadolinium in the liquid phase crystallized, resulting in a state in which no gadolinium was dissolved in the liquid phase but only iron was dissolved. From these results, it was found that in the metal separation method of this embodiment, the methanol concentration is preferably 10 wt% or higher and 45 wt% or lower, and more preferably 20 wt% or higher and 45 wt% or lower.

[0046] From the above results, it was found that the crystallization method using ammonium sulfate and methanol according to the present invention can efficiently separate iron and rare earth metals from an aqueous solution of rare earth metals containing the rare earth metals and iron. Therefore, for example, when it is necessary to recover only the valuable rare earth metals from an aqueous solution of rare earth metals containing iron and rare earth metals, it was found that iron can be removed while the iron is retained in the liquid phase, and the rare earth metals precipitated as a solid phase can be easily recovered.

[0047] Next, the ore dressing method according to the present invention will be described in detail with reference to the drawings. Fig. 8 is a flow chart showing a first embodiment of the ore dressing method according to the present invention. The ore dressing method according to this embodiment is a method for separating bastnaesite or monazite as a rare earth mineral from an ore containing barite and fluorite. The method includes flotation steps T2 to T5 in which rare earth minerals are floated from an ore containing iron and rare earth metals, and a post-flotation crystallization step C1 in which a tailings aqueous solution contained in the tailings generated in the flotation steps is used as the aqueous solution to be treated and a rare earth metal salt is crystallized by the metal separation method according to the present invention. Prior to the flotation steps, the method includes first reverse flotation steps S2 to S5 in which barite is reverse floated from the ore containing barite and fluorite, and second reverse flotation steps R2 to R5 in which fluorite is reverse floated.

[0048] In other words, the ore dressing method according to this embodiment is a method for separating bastnaesite from ore containing barite and fluorite, and comprises the following steps, in the order listed: a first reverse flotation step S2 to S5 for reverse flotation of barite from the ore; a second reverse flotation step R2 to R5 for reverse flotation of fluorite; flotation steps T2 to T5 for subsequent flotation of bastnaesite; and a post-flotation crystallization step C1 for crystallizing rare earth metal salts from the aqueous tailings generated in the flotation step, using the aqueous tailings solution contained in the tailings as the aqueous solution to be treated by the metal separation method according to the present invention.

[0049] The ore dressing method of the present invention, configured as described above, enables separation of bastnasite or monazite at a high concentration rate from bastnasite ore or monazite ore containing barite, fluorite, silica, and iron oxide. Furthermore, by recovering rare earth minerals from the aqueous tailings solution contained in the tailings generated in the flotation process, it is possible to prevent rare earth minerals from being discarded in a dissolved state in the aqueous tailings solution and improve the recovery rate of rare earth minerals. Since deposits containing such ores are abundant in the Pacific region, such as Vietnam and China, this method enables separation of bastnasite or monazite at a high concentration rate from ore extracted in these regions. Hereinafter, bastnasite will be used as an example of a rare earth mineral.

[0050] In the mineral dressing method according to this embodiment, first, ore is crushed and classified (S0) to a particle size where individual minerals can be liberated, as shown in Fig. 7. In this embodiment, the ore is crushed and classified by conventional crushing and classification techniques until the proportion of particles of 45 µm or less becomes 80%.

[0051] The crushed and classified slurry is then conditioned (S1) with sodium silicate and barium chloride. Sodium silicate is used as a gangue inhibitor, and barium chloride is used as a barite activator. These are standard reagents used in the beneficiation of barite-containing ores.

[0052] The slurry is further conditioned (S1) with a collector for barite. For example, the collector is a mixture of 20 to 30 wt % petroleum sulfonate, 20 to 30 wt % sulfosuccinate, and 10 to 30 wt % sulfosuccinamate.

[0053] The above reagents are mixed and dissolved in an aqueous solution, preferably at room temperature or higher, to a concentration of 10 to 20%, and then the emulsion is added to the slurry. After these conditions are met, the barite is selectively floated away from bastnaesite and fluorite in the first reverse flotation step S2 to S5, which reverse flotation the barite. This allows high-quality barite to be recovered with a high recovery rate.

[0054] The first reverse flotation process S2 to S5 is composed of a roughing process S2 and refinement processes S3 to S5. In the refinement processes S3 to S5, three refinement stages are performed. The roughing process S2 is performed using, for example, a Fagergren flotation machine, and the refinement processes S3 to S5 are performed using, for example, a Denver-type flotation machine.

[0055] 8 shows a cross-sectional schematic diagram of the flotation device used in the first reverse flotation steps S2 to S5. The flotation device 1 comprises a rotating shaft 2, an impeller 3 fixed below the rotating shaft 2 and rotating together with the rotating shaft 2, a stationary hood 4 which serves as a circulation passage for circulating the fluid F to be treated and bringing it into contact with air by rotating the impeller 3, a housing 6 capable of containing the slurry F, which is the fluid to be treated, and a power unit 9 which rotates the rotating shaft 2. In addition, an air inlet pipe 41 is disposed above the stationary hood 4, and negative pressure is generated in the bladeless space of the impeller 3 between the impeller 3 and the rotating shaft 2 by the rotation of the impeller 3, and this negative pressure causes outside air to be sucked into the slurry F through the air inlet pipe 41.

[0056] Furthermore, the outer surface of the housing 6 is provided with a plurality of ultrasonic vibration devices 7 that apply ultrasonic vibration to the slurry F, which is the liquid to be flotation-treated. This makes it possible to apply ultrasonic vibration to the slurry F inside the housing 6 and the air sucked into the slurry F. In addition, an air inlet 5 for introducing air is provided on the outer surface of the housing 6. The air supplied from the air inlet 5 is pressurized air, and this air can be introduced into the slurry F in addition to the outside air supplied from the air inlet pipe 41, thereby promoting the separation effect by flotation.

[0057] Returning to Figure 7, in this embodiment, the first reverse flotation steps S2 to S5 include an ultrasonic vibration application step in which ultrasonic vibrations are applied to the slurry F, which is the liquid to be flotation-treated. The ultrasonic vibration application step may be the entire period from the start to the end of each of the first reverse flotation steps S2 to S5, or only the latter half of the entire period from the start to the end of each step. Furthermore, the ultrasonic vibration application step may be provided in either the rough selection step S2 or the refining steps S3 to S5.

[0058] The tailings from the first reverse flotation step S2-S5 are subjected to a conventional desliming process R0, which separates the fine particles containing bastnaesite from the coarse particles. In the fine particle fraction, more than 95% of the particles are less than 6 μm in size.

[0059] The slurry that has been subjected to the desliming treatment R0 is then subjected to a stepwise conditioning R1 using inhibitors and conditioners that are typically used in the flotation of fluorite-containing ores.

[0060] After the condition setting R1, the second reverse flotation steps R2 to R5 are carried out, in which fluorite is floated using a collector suitable for processing complex ores. The fluorite collector is composed of 70% amine oleic acid and 30% alkyl ethyl phosphate. This collector is advantageous in that it improves the selectivity between bastnaesite and fluorite. The removal of fluorite in these second reverse flotation steps R2 to R5 is important for obtaining a high concentration of bastnaesite in the subsequent flotation of bastnaesite.

[0061] The second reverse flotation process R2 to R5 is composed of a roughing process R2 and refinement processes R3 to R5. The refinement processes R3 to R5 comprise three stages of refinement. The roughing process R2 is carried out using, for example, a Fagergren flotation machine, and the refinement processes R3 to R5 are carried out using, for example, a Denver-type flotation machine.

[0062] As with the first reverse flotation processes S2 to S5, the second reverse flotation processes R2 to R5 also include an ultrasonic vibration imparting step in which ultrasonic vibrations are imparted to the slurry F, which is the liquid to be flotation-treated, using the flotation apparatus 1 shown in Figure 2. The ultrasonic vibration imparting step may be the entire period from the start to the end of each of the second reverse flotation processes R2 to R5, or only the latter half of the entire period from the start to the end of each process. Furthermore, the ultrasonic vibration imparting step may be provided only in either the rough selection process R2 or the refining processes R3 to R5.

[0063] The flotation process in the ore dressing method according to this embodiment includes flotation steps T2 to T5, in which bastnaesite is recovered by flotation. By reverse-floating barite and fluorite in the first reverse flotation steps S2 to S5 and the second reverse flotation steps R2 to R5, the bastnaesite concentration supplied to the roughing step T2 of the flotation process increases by approximately four times. As an example, a component test of the ore showed that the REO was approximately 6% before treatment, but after flotation of barite and fluorite, the REO was 25% at the stage of supplying the ore to the roughing step T2 of the flotation process.

[0064] In the flotation of bastnasite, the tailings from the second reverse flotation steps R2 to R5 are thickened (T0) by a conventional method, and then conditioned (T1) using a standard conditioner. Then, flotation steps T2 to T5 are carried out, in which the bastnasite is floated using a collector suitable for processing complex ores. This collector is composed of 60 to 70 wt% aminated tall oil fatty acid, 20 to 30 wt% sarcosine-based collector, and 10 wt% secondary amine. This collector can improve the selectivity of bastnasite relative to iron oxide and silica stone, thereby increasing the yield of bastnasite.

[0065] The flotation steps T2 to T5 are composed of a roughing step T2 and refinement steps T3 to T5. In the refinement steps T3 to T5, three refinement stages are performed. The roughing step T2 is performed using, for example, a Fagergren flotation machine, and the refinement steps T3 to T5 are performed using, for example, a Denver-type flotation machine.

[0066] Similarly to the first reverse flotation steps S2 to S5, the flotation steps T2 to T5 also include an ultrasonic vibration imparting step in which ultrasonic vibrations are imparted to the slurry F, which is the liquid to be flotation-treated, using the flotation apparatus 1 shown in Figure 2. The ultrasonic vibration imparting step may be the entire period from the start to the end of each of the flotation steps T2 to T5, or only the latter half of the entire period from the start to the end of each step. Furthermore, the ultrasonic vibration imparting step may be provided only in either the rough selection step T2 or the refining steps T3 to T5.

[0067] The process further includes a post-flotation crystallization step C1 in which the tailings aqueous solution contained in the tailings generated in the flotation steps T2 to T5 is treated as a target solution and rare earth metal salts are crystallized using the metal separation method of the present invention. As shown in Figure 9, the post-flotation crystallization step C1 involves pre-treating the tailings discharged from the flotation steps T2 to T5 to remove solid components such as gangue, and then using the pre-treated tailings aqueous solution as a target solution, crystallizing rare earth metal salts using the metal separation method as shown in Figure 1, and separating and recovering the crystallized solid components. The tailings aqueous solution from which the rare earth metals have been recovered by this separation and recovery is recovered or discharged as the final tailings shown in Figure 7.

[0068] A beneficiation test was conducted using an ore containing 55% barite, 5% fluorite, and 10% rare earth ore, using the beneficiation method shown in Figure 7. After pulverization in the crushing and classification step S0, a slurry with a pulp concentration of 45% was prepared. Each conditioning step was carried out at a temperature of 80°C for 20 minutes. The conditioned pulp was subjected to flotation for 8 minutes each in the rough selection step and the refinement step. In this example, only the refinement step S5, the refinement step R5, and the refinement step T5 were designated as ultrasonic vibration application steps, and ultrasonic vibration was applied to the slurry F. As described above, ore dressing was carried out by improving the efficiency of dressing by using only the dressing steps S5, R5, and T5 as ultrasonic vibration application steps, and the REO concentration in the dressed ore obtained in the third dressing step T5 of the final flotation steps T2 to T5 was analyzed. As a result, an REO of 50 to 60% was achieved without the separation and recovery of rare earth metals in the post-flotation crystallization step C1. Therefore, an REO of 60% or more can be achieved by separating and recovering rare earth metals in the post-flotation crystallization step C1.

[0069] Next, a second embodiment of the ore dressing method according to the present invention will be described. Figure 10 is a flow chart showing the second embodiment of the ore dressing method according to the present invention. This embodiment differs from the above-described embodiment in that the first reverse flotation step, the second reverse flotation step, and the cleaning steps of the flotation step each have five steps, whereas the above-described embodiment has three steps. Furthermore, in the post-flotation crystallization step C1, the tailings aqueous solution contained in the tailings generated in the flotation steps T2 to T5 is used as the aqueous solution to be treated, and rare earth metal salts are crystallized by the metal separation method according to the present invention. In this alternative embodiment, the tailings aqueous solution contained in the tailings generated in the flotation steps T2 to T7 is used as the aqueous solution to be treated, and rare earth metal salts are crystallized by the metal separation method according to the present invention.

[0070] In this example, the refining steps S6-S7, R6-R7, and T6-T7 were ultrasonic vibration application steps, and ultrasonic vibrations were applied to the slurry F. In this example, by performing ore dressing under the same other conditions as in Example 1, the refining efficiency was improved by the ultrasonic vibration application steps in the refining steps S6-S7, R6-R7, and T6-T7. It is believed that the REO concentration in the refined ore obtained in the fifth refining step T7 in the final flotation steps T2-T7 can be 85-95% REO without the separation and recovery of rare earth metals in the post-flotation crystallization step C1. Therefore, it is believed that an REO of 95% or more can be achieved by separating and recovering rare earth metals in the post-flotation crystallization step C1.

[0071] Other embodiments are listed below. (1) The first and second embodiments are ore dressing methods for separating bastnaesite as a rare earth mineral from ore containing barite and fluorite, and include a flotation step for flotation of rare earth minerals from ore containing iron and rare earth metals, and a post-flotation crystallization step C1 for crystallizing a salt of a rare earth metal from an aqueous solution of tailings generated in the flotation step by the metal separation method according to the present invention, and further including: In the above, the ore dressing method has a first reverse flotation step of reverse flotation of barite from the ore containing barite and a second reverse flotation step of reverse flotation of fluorite, but is not limited to this. The method may omit the first reverse flotation step of reverse flotation of barite from the ore containing barite and fluorite, and the second reverse flotation step of reverse flotation of fluorite, and instead include a flotation step of flotation of rare earth minerals from the ore before the flotation steps, and a post-flotation crystallization step C1 in which the tailings generated in the flotation step are converted into an aqueous solution for treatment.

[0072] (2) In the first and second embodiments, the ore dressing method for separating the rare earth mineral from the ore containing barite and fluorite includes a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, a subsequent second reverse flotation step for reverse flotation of the fluorite, a subsequent flotation step for flotation of the rare earth mineral, and a post-flotation crystallization step C1 in which a tailings aqueous solution contained in the tailings generated in the flotation step is used as the aqueous solution to be treated and a rare earth metal salt is crystallized by the metal separation method of the present invention. However, the present invention is not limited to this, and may also include a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, and a post-first reverse flotation crystallization step C2 in which a tailings aqueous solution contained in the tailings generated in the first reverse flotation step is used as the aqueous solution to be treated and a rare earth metal salt is crystallized by the metal separation method of the present invention, as shown in FIG. 11 . The first reverse flotation post-crystallization step C2 may be provided after the desliming step R0, as shown in Fig. 11. The first reverse flotation post-crystallization step C3 may be the same as the post-flotation crystallization step C1 shown in Fig. 9.

[0073] (3) In the first and second embodiments, the ore dressing method for separating the rare earth mineral from the ore containing barite and fluorite includes a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, a subsequent second reverse flotation step for reverse flotation of the fluorite, a subsequent flotation step for flotation of the rare earth mineral, and a post-flotation crystallization step C1 in which a tailings aqueous solution contained in the tailings generated in the flotation step is used as the aqueous solution to be treated and a rare earth metal salt is crystallized by the metal separation method of the present invention. However, the present invention is not limited to this, and may include a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite, a second reverse flotation step for reverse flotation of the fluorite, and a second post-reverse flotation crystallization step C3 in which a tailings aqueous solution contained in the tailings generated in the second reverse flotation step is used as the aqueous solution to be treated and a rare earth metal salt is crystallized by the metal separation method of the present invention, as shown in FIG. 12 . The second reverse flotation post-crystallization step C3 may be provided after the concentration step T0, as shown in Fig. 12. The second reverse flotation post-crystallization step C3 may be the same step as the post-flotation crystallization step C1 shown in Fig. 9.

[0074] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention.

[0075] As described above, it is possible to provide a metal separation method that can efficiently separate iron and rare earth metals from an aqueous solution containing iron and rare earth metals. As described above, the metal separation method of the present invention can be used to recover rare earth minerals from ores containing iron and rare earth metals, but it can also be used in other industrial fields, such as recycling rare earth metals from automobile motors, separating and concentrating rare earths from rare earth mud (e.g., seabed surface sediments), and concentrating aqueous solutions containing low concentrations of rare earths.

[0076] C1 Crystallization step after flotation C2 Crystallization step after second reverse flotation C3 Crystallization step after first reverse flotation S6 to S7 First reverse flotation step R6 to R7 Second reverse flotation step T2 to T7 Flotation step

Claims

1. A metal separation method for separating rare earth metals from an aqueous solution containing iron and rare earth metals, comprising the steps of adding ammonium sulfate to the aqueous solution, adding an alcohol to the aqueous solution, and crystallizing a salt of the rare earth metal while maintaining the iron contained in the aqueous solution in a liquid phase.

2. The method for separating metals according to claim 1, wherein the rare earth metals are light rare earths and heavy rare earths.

3. The metal separation method according to claim 2, wherein the rare earth metals are lanthanum, neodymium, and gadolinium.

4. A mineral dressing method comprising: a flotation step in which rare earth minerals are floated from ore containing iron and rare earth metals; and a post-flotation crystallization step in which an aqueous solution of tailings contained in the tailings generated in the flotation step is used as the aqueous solution to crystallize salts of the rare earth metals by the metal separation method described in claim 1.

5. A method for separating the rare earth minerals from the ore containing barite and fluorite, comprising, before the flotation step, a first reverse flotation step of reverse flotation of barite from the ore containing barite and fluorite, and a second reverse flotation step of reverse flotation of fluorite.

6. A method for separating rare earth minerals from ore containing barite and fluorite, comprising: a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite; and a post-first reverse flotation crystallization step for crystallizing salts of the rare earth metals using an aqueous solution of tailings contained in the tailings generated in the first reverse flotation step as the aqueous solution by the metal separation method described in claim 1.

7. A method for separating rare earth minerals from ore containing barite and fluorite, comprising: a first reverse flotation step for reverse flotation of barite from the ore containing barite and fluorite; a second reverse flotation step for reverse flotation of fluorite; and a post-second reverse flotation crystallization step for crystallizing salts of the rare earth metals using an aqueous solution of tailings contained in the tailings generated in the second reverse flotation step as the aqueous solution by the metal separation method described in claim 1.

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