Method for recovering rare earth elements from rare earth raw materials containing rare earth elements.

Abstract

To provide a method for recovering rare earth elements from rare earth raw materials containing rare earth elements. [Solution] The present invention relates to a method for recovering rare earth elements from rare earth raw materials, comprising the steps of alkali treatment of a mixture of a reducing agent containing a reducing metal with a standard reduction potential lower than that of goethite and the rare earth tailings, and leaching the rare earth elements from the alkali-treated mixture using a eutectic solvent, wherein the rare earth raw material contains 10% by weight or more of goethite.

Description

Technical Field

[0001] The present invention relates to a method for recovering rare earth elements from rare earth raw materials containing rare earths.

Background Art

[0002] Conventionally, methods for separating and recovering rare earths from rare earth tailings vary depending on the type. In the case of monazite where rare earths exist as phosphate minerals, a pretreatment step for switching rare earth phosphates, which are insoluble in acids, into an extractable form precedes. This pretreatment step is roughly classified into an acid decomposition method and an alkali decomposition method.

[0003] In the acid decomposition method, mainly sulfuric acid is used. After mixing sulfuric acid and monazite and roasting at a high temperature of 200°C or higher, rare earths are recovered through water leaching. However, the recovery of rare earths through the acid decomposition method has the disadvantage that impurities other than rare earths are also leached out, making the subsequent separation and purification process complicated.

[0004] The alkali decomposition method is classified into a dry method and a wet method. The dry method removes phosphates by mixing and roasting NaOH or Na2CO3, and the wet method reacts with a NaOH solution to switch rare earth phosphates into rare earth hydroxides, and then leaches rare earths with an inorganic acid solution later. However, such an alkali decomposition technique is a method applicable to monazite concentrates with a low iron content. When applied to rare earth tailings containing a large amount of iron oxides, iron oxides are formed during the alkali treatment process, so there is a disadvantage that selective leaching of rare earths is not easy when using inorganic acids.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The object of the present invention is to provide a method for recovering rare earth elements from rare earth raw materials containing rare earth elements. [Means for solving the problem]

[0007] The object of the present invention described above is a method for recovering rare earth elements from rare earth raw materials, comprising the steps of alkali treatment of a mixture of a reducing agent containing a reducing metal with a standard reduction potential lower than that of goethite and the rare earth tailings, and leaching the rare earth elements from the alkali-treated mixture using a eutectic solvent, wherein the rare earth raw material contains 10% by weight or more of goethite.

[0008] The rare earth raw material includes rare earth tailings, in which the rare earth element is contained in a phosphate mineral, and at least a portion of the phosphate mineral may be dephosphorized by the alkali treatment.

[0009] The phosphate mineral comprises at least one of monazite and floresite, and at least a portion of the goethite may be reduced by the alkali treatment.

[0010] The alkaline treatment may be carried out in a wet manner, and the leaching may be performed on the immersion obtained from the alkaline treatment.

[0011] The reducing metal comprises at least one of magnesium, iron, and aluminum, and the reducing agent may be used in an amount of 1 to 20 equivalents relative to the goethite content in the rare earth tailings.

[0012] The reducing agent may contain permanent magnet powder.

[0013] The reducing agent comprises NdFeB permanent magnet powder, and the reducing agent may be used in an amount of 3 to 10 equivalents relative to the goethite content in the rare earth tailings.

[0014] The rare earth element may include any one of cerium, samarium, lanthanum, neodymium, praseodymium, and dysprosium.

[0015] The alkali treatment may be performed using NaOH.

[0016] The eutectic solvent may be a eutectic solvent of ethylene glycol and maleic acid.

[0017] In the rare earth tailings, the content of total rare earth oxides is 5-20% by weight, goethite is 30-80% by weight, the alkali treatment is performed at 100-160 °C for 1 hour to 10 hours at a solid-liquid ratio of 1:5 to 1:20 (w / v) using an aqueous NaOH solution with a concentration of 20-70% or 40-60%, the leaching is performed at 50-85 °C for 1 hour to 24 hours at a solid-liquid ratio of 1:100 to 50:100 (w / w), and the reducing agent may be used at 5-7 equivalents relative to the goethite content in the rare earth tailings.

Advantages of the Invention

[0018] According to the present invention, a method for recovering rare earth elements from a rare earth raw material containing rare earths is provided.

Brief Description of the Drawings

[0019] [Figure 1] It is a flowchart of a method for recovering rare earth elements according to an embodiment of the present invention. [Figure 2] It shows the XRD pattern after NaOH roasting in Experimental Example 1. [Figure 3] It shows the XRD pattern after NaOH immersion in Experimental Example 3. [Figure 4] It shows the XRD pattern after NaOH immersion according to the amount of NdFeB used in Experimental Example 4. [Figure 5] It shows the leaching efficiency according to the amount of NdFeB used in Experimental Example 4.

Modes for Carrying Out the Invention

[0020] Since eutectic solvents have unique leaching characteristics for metal oxides depending on their types, if a eutectic solvent that does not dissolve iron oxide is used as the leaching solvent, rare earths can be separated from iron by selectively leaching the rare earths. However, in order to selectively separate the iron component in the rare earth leaching using a eutectic solvent, the iron component must be in the form of divalent or trivalent iron oxide. However, goethite (FeOOH) contained in rare earth tailings is converted to trivalent iron hydroxide (Fe(OH)3) during the alkali pretreatment process, resulting in a decrease in the selective leaching rate. This is because, unlike metallic iron (Fe) and divalent iron (Fe , , ,

[0024] ,

[0023] , , ,

[0026] , , , ,

[0022] , ,

[0025] ) which is converted to magnetite (Fe3O4) after NaOH immersion, in the case of trivalent iron (Fe 3+ ), it is converted to NaFeO2 and then to Fe(OH)3 during the subsequent washing process. Therefore, for the selective leaching of rare earths, a process of converting goethite in rare earth tailings to divalent or trivalent iron oxide is required in the pretreatment process.

[0021] In the present invention, after adding a reducing agent capable of reducing goethite contained in rare earth tailings during the pretreatment process of immersing rare earth tailings with sodium hydroxide and performing pretreatment, a method is provided to maximize the selective leaching rate of rare earths through rare earth leaching using a eutectic solvent.

[0022] Hereinafter, the present invention will be described in more detail with reference to the drawings.

[0023] Hereinafter, unless otherwise mentioned in the description, % means weight %.

[0024] The attached drawings are only an example illustrated to more specifically explain the technical idea of the present invention, and the idea of the present invention is not limited to the attached drawings.

[0025] A method for recovering rare earth elements according to an embodiment of the present invention will be described with reference to FIG. 1.

[0026] First, a rare earth raw material is prepared (S100).

[0027] Rare earth raw materials may, but are not limited to, rare earth tailings and waste magnets. Hereinafter, rare earth tailings will be used as an example of a rare earth raw material.

[0028] In rare earth tailings, the total rare earth oxide (TREO) content may be 5-20% by weight or 6-15% by weight.

[0029] The rare earth elements contained in the rare earth tailings may include one of the following: cerium, samarium, lanthanum, neodymium, praseodymium, and dysprosium.

[0030] Rare earth tailings may contain goethite (FeOOH) in amounts of 10% to 90% by weight, 10% to 80% by weight, 10% to 70% by weight, 30% to 90% by weight, 30% to 80% by weight, 50% to 80% by weight, or 60% to 80% by weight.

[0031] In rare earth tailings, rare earth elements may be contained within phosphate minerals. The phosphate minerals may contain either monazite or floresite.

[0032] In rare earth tailings, monazite and floresite may be present in amounts of 3-20% by weight or 6-12% by weight, respectively.

[0033] Rare earth tailings may include quartz, hematite, ilmenite, and chlorite, in addition to goethite and phosphate minerals.

[0034] Next, the rare earth tailings are subjected to alkali treatment using a reducing agent. The alkali treatment targets a mixture of the reducing agent and the rare earth tailings.

[0035] The reducing agent contains a reducing metal with a standard reduction potential lower than that of goethite. The reducing metal may include at least one of magnesium, iron, and aluminum. Specifically, the reducing agent may be iron powder or permanent magnet powder, and the permanent magnet powder may include NdFeB permanent magnet powder.

[0036] The reducing agent may be used in amounts of 1 to 20 equivalents, 3 to 10 equivalents, or 5 to 7 equivalents relative to the goethite content in the rare earth tailings.

[0037] The alkaline treatment may consist of a dry treatment or a wet treatment, but is not limited to either. NaOH, Na2CO3, Ca(OH)2, or NH4OH may be used.

[0038] In the dry process, NaOH bead and rare earth tailings may be mixed in a mass ratio of 2:1 to 1:2, and then roasted at 400 to 600°C for 1 to 5 hours.

[0039] Wet treatment (alkaline immersion or NaOH immersion) may be carried out at 100-160°C for 1-10 hours using an aqueous NaOH solution of 20-70% or 40-60% concentration with a solid-liquid ratio of 1:5-1:20 (w / v) or 1:8-1:15 (w / v).

[0040] During the alkali treatment process, phosphate minerals are dephosphorylated, and at least some of the goethite is reduced.

[0041] Subsequently, rare earth elements are leached from the alkali-treated mixture using a eutectic solvent (S300).

[0042] In the case of wet alkaline treatment, leaching is performed on the immersed material obtained from the alkaline treatment. Alternatively, leaching may be performed after washing the immersed material (until the pH of the washing water becomes neutral).

[0043] In the case of dry alkaline treatment, the roasted mixture is washed with water or the like, and then leaching is performed.

[0044] The eutectic solvent is a mixture of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD), and the hydrogen bond acceptors are choline chloride, ethylene glycol, N-ethyl-2-hydroxy-N,N-dimethylethanaminium chloride, 2-(chlorocarbonyloxy)-N,N,N-trimethylethanaminium chloride, N-benzyl-2-hydroxy-N,N-dimethylethanaminium, 1-aminoguanidine hydrochloride, and 1,3-diaminoguanidine hydrochloride. The hydrogen bond donor is selected from the group consisting of [hydrochloride], methanol, betaine hydrochloride, benzylcholine chloride, tetrabutylammonium chloride, glycerol, 1,2-propandiol, and 1,4-butanediol, and the hydrogen bond donor is selected from the group consisting of lactic acid, maleic acid, urea, acetamide, 1-methyl urea, 1,3-dimethyl urea, 1,1-dimethyl ureaThe following may be selected from the group consisting of 1-dimethyl urea, thiourea, benzamide, glycerol, ethylene glycol, malonic acid, benzoic acid, adipic acid, oxalic acid, succinic acid, citric acid, malic acid, glycolic acid, proline, glucose, p-toluenesulfonic acid, tartaric acid, fructose, phenol, menthol, decanoic acid, ibuprofen, lidocaine, and sucrose.

[0045] The eutectic solvent is not limited to this, but may be a eutectic solvent of ethylene glycol and maleic acid. Leaching may be carried out at 50 to 85°C for 1 to 24 hours with a solid-liquid ratio of 1:100 to 50:100 (w / w) or 5:100 to 15:100 (w / w).

[0046] Rare earth elements are selectively leached using a eutectic solvent.

[0047] The present invention will be described in detail below through experimental examples.

[0048] Rare earth tailings analysis

[0049] The rare earth tailings being studied are tailings from the flotation separation process of rare earth ore from a carbonate bedrock.

[0050] Content analysis of the rare earth tailings revealed a rare earth content of 8 wt.% and a TREO content of 9.6 wt.%. Table 1 shows the chemical composition analysis results (ICP-MS, ICP OES) of the rare earth tailings.

[0051] [Table 1]

[0052] As shown in Table 2, which is the result of quantitative mineral analysis (QXRD) of rare earth tailings, the rare earth ore minerals in the tailings consist of monazite and floresite, with the rest being mostly goethite (FeOOH).

[0053] [Table 2]

[0054] Monazite and florensite are both phosphate minerals, and their rare earth elements exist as REPO4 and REAl3(PO4)2(OH)6, respectively.

[0055] Experimental Example 1 - NaOH Alkali Treatment (Dry Method)

[0056] In order to selectively leach rare earth oxides from tailings using eutectic solvents (DESs), which are effective for rare earth oxide leaching, a pretreatment step for dephosphorylation must be performed first.

[0057] Dry alkaline treatment using NaOH was performed to dephosphorylate the tailings.

[0058] NaOH beads and tailings samples were mixed in a 1:1 mass ratio and then roasted at 500°C for 2 hours. After that, the samples were washed until the washing water became neutral, dried, and then leached in Ethylene glycol (EG)-Maleic acid (MA)DES, which is effective for light rare earth leaching, at a solid-liquid ratio of 5:100 (w / w) at 70°C for 7 hours.

[0059] The XRD pattern after NaOH roasting is shown in Figure 2, and the leaching rate after this pretreatment is shown in Table 3.

[0060] [Table 3]

[0061] The leaching results showed a low leaching rate of rare earth elements and an iron leaching rate of 13%, which differed from the usual experimental results where iron oxides were insoluble in EG-MA DES.

[0062] Experimental Example 2 - NaOH Alkali Treatment (Wet Method)

[0063] For the dephosphorylation of tailings, a wet treatment method called NaOH immersion was applied.

[0064] The sample was added to a 50% NaOH aqueous solution in a solid-liquid ratio of 1:10 (w / v), and then immersed in NaOH by reacting at 145°C for 5 hours. After washing until the pH of the sample washing water became neutral, the sample was roasted in a muffle furnace at 450°C for 3 hours to convert the iron hydroxide to iron oxide.

[0065] NaOH immersion XRD pattern analysis revealed no crystalline structure of iron oxide.

[0066] After adding the NaOH-immersed and roasted sample to EG-MA DES in a solid-liquid ratio of 5:100 (w / w) and reacting it at 70°C for 5 hours, the results were improved compared to the NaOH roasting method, but as shown in Table 4, the rare earth leaching rate and selectivity remained low.

[0067] [Table 4]

[0068] Rare earth tailings contain a large amount of goethite along with rare earth ore minerals. After NaOH treatment, this is converted to NaFeO2, and then the NaOH is removed in the washing step, converting it to amorphous gel-form iron hydroxide. This increases the number of washes required until the pH of the washing water becomes neutral, and the time required for solid-liquid separation increases significantly due to the gel-form iron hydroxide (more than 10 washes are required when washing with 2L of distilled water based on a 20g sample).

[0069] FeOOH + NaOH → NaFeO2 + H2O

[0070] NaFeO2 + 2H2O → Fe(OH)3 + NaOH

[0071] Furthermore, unlike Fe3O4 and Fe2O3, the formed Fe(OH)3 is not insoluble in ethylene glycol (EG)-maleic acid (MA), and even when roasted, it exhibits a higher leaching rate compared to Fe2O3, inhibiting the selectivity of rare earth elements.

[0072] While NaOH treatment is highly effective for monazite concentrate that does not contain FeOOH, the high FeOOH content of rare earth tailings presents different problems compared to rare earth concentrate treatment.

[0073] The fundamental reason why FeOOH is converted to Fe(OH)3 after immersion in NaOH is that Fe exists in a trivalent state. In the case of NdFeB permanent magnets, which use the same pretreatment process, Fe exists as metallic iron, so after immersion it is converted to Fe3O4.

[0074] Therefore, it is necessary to develop an effective pretreatment process that can selectively leach rare earth elements from rare earth tailings.

[0075] If a reducing agent is added during NaOH immersion to reduce FeOOH during the immersion process and obtain Fe3O4 as the final product, then the formation of Fe(OH)3 can be suppressed, which not only reduces the time required in the washing step after immersion but also lowers the leaching rate of Fe and increases the selectivity of rare earth elements.

[0076] To reduce FeOOH in rare earth tailings, metals with a reduction potential lower than that of FeOOH (Eo = 0.95V), such as Mg, Fe, and Al, or chemical species containing these, can be used as reducing agents. In the following experimental example, metallic Fe and NdFeB permanent magnet powder, composed of elements contained in the rare earth tailings, were used as reducing agents.

[0077] Experimental Example 3 - Fe Used as a Reducing Agent

[0078] The Fe metal powder used as a reducing agent was mixed with tailings in a 1:1 mass ratio, added to a 50% NaOH solution in a 1:10 (w / v) solid-liquid ratio, and then immersed at 145°C for 5 hours.

[0079] The chemical formula for the reaction between FeOOH in rare earth tailings and Fe metal powder to reduce them to Fe3O4 is as follows:

[0080] 2FeOOH + 4Fe + 4H2O → 2Fe3O4 + 5H2

[0081] Unlike before the addition of the reducing agent, when the sample floated with an ochre color, the sample after the reducing agent was added floated with a black color, which indicates that FeOOH was successfully reduced to Fe3O4.

[0082] However, the formation of iron hydroxide was observed during the washing process, and XRD pattern analysis results, as shown in Figure 3, confirmed that the Fe used as a reducing agent remained. The Fe remaining after immersion can increase the iron leaching rate and reduce the selectivity of rare earth elements.

[0083] Experimental Example 4 - Using NdFeB permanent magnet powder as a reducing agent

[0084] NdFeB permanent magnet powder was used as a reducing agent. In the NaOH immersion process, Nd and Fe in the NdFeB permanent magnet are oxidized to Nd(OH)3 and Fe3O4, respectively, and hydrogen gas is released, so it was determined to be an effective reducing agent.

[0085] The chemical formula for the reaction between FeOOH in rare earth tailings and NdFeB magnet powder to reduce them to Fe3O4 is as follows:

[0086] 139FeOOH+Nd2Fe 14 B+OH - → 51Fe3O4 + 2Nd(OH)3 + BO2 - +67H2O

[0087] Based on the above chemical formula, NdFeB was added by chemical equivalent and immersed (1 equivalent of NdFeB = 0.051 g per 1 g of goethite content in tailings).

[0088] The XRD pattern after immersion is shown in Figure 4. Goethite was successfully reduced to Fe3O4, and no iron hydroxide formation was observed during the washing process.

[0089] Furthermore, as the amount of NdFeB added as a reducing agent increases, the final product after immersion also turns black, indicating that NdFeB is effective as a reducing agent in reducing FeOOH.

[0090] The reductively immersed sample was added to EG-MA DES in a solid-liquid ratio of 5:100 (w / w) and leached at 70°C for 5 hours.

[0091] The leaching results of the reductive immersion samples showed an effective reduction in iron leaching, enabling selective leaching of rare earth elements. As shown in Figure 5 and Table 5, a relatively high iron leaching rate was observed at 1 equivalent, but at 5 equivalents or more, approximately 3% of iron leached out even as the equivalent ratio increased.

[0092] The leaching rate of rare earth elements also increased significantly, and beyond 5 equivalents, the leaching rate of rare earth elements did not increase significantly even as the equivalent ratio increased.

[0093] [Table 5]

[0094] Globally, the shift to environmentally friendly energy sources is accelerating in order to achieve carbon neutrality, and this is increasing the demand for core minerals. Rare earth elements are one of these core minerals, and their demand is expected to increase sharply later on in electric vehicle motors and wind power turbines.

[0095] Since primary resources alone are unlikely to meet all demands, the development of processes for recovering rare earth elements from secondary resources is necessary.

[0096] To recover rare earth elements from monazite, where they exist as rare earth phosphates, a pretreatment step must be carried out to convert the acid-insoluble rare earth phosphates into a form that is easily leached. Eutectic solvents, which are environmentally friendly solvents, have unique leaching properties for metal oxides depending on their type, so rare earth elements can be selectively leached using a eutectic solvent that is insoluble in iron oxides.

[0097] As a leaching solvent, an ethylene glycol-maleic acid eutectic solvent can be used, which has excellent light rare earth leaching performance and is insoluble in iron oxides.

[0098] Unlike monazite concentrate, which has a low iron oxide content, tailings containing 10% or more goethite are converted to trivalent iron hydroxide (Fe(OH)3) during the NaOH pretreatment process. This inhibits the selective leaching of rare earth elements, and to suppress the conversion of trivalent iron in goethite to trivalent iron hydroxide (Fe(OH)3) during NaOH immersion, reduction to divalent iron is necessary during the pretreatment process.

[0099] In Experimental Example 4 of the present invention, NdFeB permanent magnet scrap powder was used as a reducing agent, and it was possible to replace the goethite in the rare earth tailings with magnetite (Fe3O4), which is insoluble in ethylene glycol-maleic acid eutectic solvent.

[0100] When a reduction immersion product using an NdFeB permanent magnet as a reducing agent was leached at 70°C for 5 hours using an ethylene glycol-maleic acid eutectic solvent, the results showed that when 5 equivalents or more of NdFeB permanent magnet were added, approximately 3% of iron was leached, while La, Nd, Pr, and Dy showed leaching rates of over 96%, and Ce showed a leaching rate of over 71%, demonstrating the possibility of selective leaching of rare earth elements.

[0101] To selectively recover rare earth elements from rare earth tailings containing both goethite and monazite, we were able to convert rare earth phosphates to rare earth hydroxides via reductive immersion with an added NdFeB permanent magnet as a reducing agent, reduce goethite to magnetite, and selectively leach rare earth elements using a eutectic solvent as the leaching solvent.

Claims

1. A method for recovering rare earth elements from rare earth raw materials, A step of alkali treatment of a mixture of a reducing agent containing a reducing metal with a standard reduction potential lower than that of goethite and the rare earth tailings, A step of leaching the rare earth element from the mixture that has been treated with alkali using a eutectic solvent, Includes, The method wherein the rare earth raw material contains 10% by weight or more of goethite.

2. The aforementioned rare earth raw material contains rare earth tailings, The method according to claim 1, wherein in the rare earth tailings, the rare earth element is contained in a phosphate mineral, and at least a portion of the phosphate mineral is dephosphorylated by the alkali treatment.

3. The method according to claim 1, wherein the phosphate mineral comprises at least one of monazite and floresite, and at least a portion of the goethite is reduced by the alkali treatment.

4. The aforementioned alkaline treatment is carried out in a wet manner. The method according to claim 3, wherein the leaching is performed on the immersion obtained from the alkali treatment.

5. The method according to claim 4, wherein the reducing metal comprises at least one of magnesium, iron, and aluminum, and the reducing agent is used in an amount of 1 to 20 equivalents relative to the goethite content in the rare earth tailings.

6. The method according to claim 5, wherein the reducing agent includes permanent magnet powder.

7. The reducing agent comprises NdFeB permanent magnet powder, The method according to claim 6, wherein the reducing agent is used in an amount of 3 to 10 equivalents relative to the goethite content in the rare earth tailings.

8. The method according to claim 1, wherein the rare earth element comprises one of cerium, samarium, lanthanum, neodymium, praseodymium, and dysprosium.

9. The method according to claim 8, wherein the alkali treatment is carried out using NaOH.

10. The method according to claim 8, wherein the eutectic solvent is a eutectic solvent of ethylene glycol and maleic acid.

11. In the aforementioned rare earth tailings, the total rare earth oxide content is 5 to 20% by weight, and goethite content is 30 to 80% by weight. The aforementioned alkaline treatment is carried out at 100 to 160°C for 1 to 10 hours using an aqueous NaOH solution of 20 to 70% or 40 to 60% concentration with a solid-liquid ratio of 1:5 to 1:20 (w / v). The aforementioned leaching is carried out at a solid-liquid ratio of 1:100 to 50:100 (w / w) at 50 to 85°C for 1 to 24 hours. The method according to claim 10, wherein the reducing agent is used in an amount of 5 to 7 equivalents relative to the goethite content of the rare earth tailings.

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