Process and method for separating rare earth elements from leach solutions

Abstract

Improved method for separating individual and / or groups of rare earth elements from a rare earth-containing leach solution to produce high purity material for further purification. According to a first preferred embodiment, the present invention includes a method comprising the steps of: neutralizing the leach solution, introducing ozone into the solution while controlling the pH to precipitate cerium oxide, removing the precipitated cerium oxide from the solution, adjusting the pH of the solution in the presence of ozone to precipitate the middle / heavy rare earths, removing the precipitated rare earth concentrate from the solution, treating the remaining solution with a precipitating agent to produce a high purity lanthanum precipitate, and removing the solids from the solution.

Description

[Technical field]

[0001] (Related Applications)

[0002] This application claims priority to U.S. Provisional Application No. 63 / 327,477, filed April 5, 2022.

[0003] BACKGROUND AND FIELD OF THE PRESENT ART

[0004] FIELD OF THE PRESENT ART

[0005] The present invention relates to the separation of rare earth elements (REEs), and more particularly to methods for separating rare earth elements from rare earth deposits, leach solutions and concentrates containing rare earth elements. [Background technology]

[0006] BACKGROUND OF THEINVENTION

[0007] Rare earth elements primarily include the lanthanide series of the periodic table, although the term may also include scandium and yttrium. Exemplary rare earth elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (ET), thulium (Tm), ytterbium (Mb), lutetium (Lu), scandium (Sc), and yttrium (Y). Rare earth elements can be classified as light, medium, and / or heavy rare earth elements. Exemplary light rare earth elements include La, Ce, Pr, and Nd. Exemplary medium rare earth elements include Sm, Eu, and Gd, also known as SEG. Exemplary heavy rare earth elements include Sc, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y.

[0008] Most of the known rare earth mineral resources around the world are composed of light rare earth elements, which make up 90-95% of the total rare earth element content by weight, and medium rare earth elements, which make up about 5% of the total rare earth element content. Many deposits contain heavy rare earth elements, which make up less than 1% of the total rare earth element content.

[0009] The related art discloses various methods and apparatus for the extraction of rare earth elements. Some of the methods currently used are very complex, requiring multiple steps to separate the raw materials into the individual elements with high purity, resulting in processes that are capital intensive and difficult to implement. Other methods have proven very difficult to scale up to industrial levels. Significant reductions in the overall process complexity and the amount of material to be processed would allow some of these methods to be implemented more easily.

[0010] Bauer et al., in "Recovery Of Cerium And Lanthanum By Ozonation Of Lanthanide Solutions," disclose a process for oxidizing a mixed lanthanide solution with ozone at pH 4.5 and ambient temperature, precipitating 98 percent of the original cerium. The corresponding purity of the cerium increased from 50 percent to 98 percent. A second ozone oxidation-precipitation step produced 99.9% pure cerium in high yield from the 98% pure material.

[0011] Ozonation at pH 6.5 and 850C also precipitated cerium and the heavier rare earth elements separately, leaving 89% of the original lanthanum in solution at 95% purity. To subsequently recover cerium from the heavier rare earth elements in the precipitate, the precipitate was dissolved in dilute mineral acid and the cerium was reoxidized with ozone at pH 4.5 and ambient temperature. The filtrate contained a concentrated mixture of praseodymium, neodymium, samarium, and europium, which could be separated by ion exchange or solvent extraction.

[0012] WO 2016 / 058007 discloses a method for selectively separating rare earth elements, the method comprising the steps of digesting a rare earth oxide powder with nitric acid to form a first rare earth solution containing solubilized rare earth elements, contacting the first rare earth solution with ammonium hydroxide to precipitate a first precipitation product and form a second rare earth solution, separating the first precipitation product from the second rare earth solution, increasing the pH of the second rare earth solution to precipitate additional rare earth elements from the second rare earth solution as a first intermediate particulate feed, digesting the first intermediate particulate feed with nitric acid to form a third rare earth solution, and contacting the third rare earth solution with ammonium hydroxide to precipitate the second precipitation product and form a fourth rare earth solution.

[0013] WO 2016 / 011540 discloses treating the REE water leach solution through a series of purification and precipitation steps to produce high purity mixed rare earth oxides for purification using solvent extraction techniques. An exemplary process for purification uses a pH adjustment step, for example with MgO, MgCO3, or Na2CO3, to remove thorium and iron and other trace impurity elements from the solution. In another embodiment, uranium can be removed from the water leach solution by ion exchange. The purified solution can then be treated with soda ash to precipitate the impurity rare earth carbonates. The rare earth carbonates can then be dissolved in hydrochloric acid (or another acid) and the pH adjusted again to precipitate small amounts of remaining iron and thorium. The purified hydrochloric acid leach solution can then be treated with oxalic acid to precipitate all the rare earths as a mixed rare earth oxalate product. In another embodiment, a two-stage precipitation is performed from the chloride re-leach solution. The two-stage precipitation can be carried out to facilitate recovery of (a) a first precipitate of high purity, e.g., containing at least 90% rare earths, and (b) a second precipitate of lower purity for recycling. The second precipitate can be, for example, a carbonate precipitate, which can be returned directly to the releaching process together with the mineral acid.

[0014] WO 2016 / 025928 discloses a method for extracting and separating rare earth elements, the method comprising the steps of providing a rare earth-containing mineral or tailings, grinding the rare earth-containing mineral to form a powdered mineral; leaching the powdered mineral with at least one mineral acid to form a leach solution containing at least one metal ion, a rare earth element, and a solid material, separating the solid material from the leach solution to form an aqueous metal concentrate, precipitating the aqueous metal concentrate to selectively remove metal ions from the leach solution and obtain a rare earth element precipitate; heating the rare earth element precipitate in air to form an oxide of the rare earth element, mixing the rare earth element oxide with an ammonium salt and heating in dry air / nitrogen, forming a mixture of anhydrous rare earth salts in an aqueous solution, and separating the rare earth element from the aqueous solution using an electrowinning process.

[0015] While useful in some circumstances, the prior art methods are cumbersome and require many steps and reagents. Thus, there is a need for improved methods for separating rare earth elements from leach solutions. Summary of the Invention

[0016] (Summary and Objectives of the Invention)

[0017] From the foregoing, it is apparent that there is a strong need for improved methods for simple, easily scalable, low-cost processes for separating individual and / or groups of rare earth elements from rare earth-containing leach solutions to produce high purity materials that can be more easily purified. Furthermore, there is a need for methods that are particularly suitable for separating light rare earth elements from medium and heavy rare earth elements in order to increase rare earth production worldwide.

[0018] In a first aspect, the present invention relates to a method for separating rare earth elements comprising the steps of: a. neutralizing a leach solution, the leach solution (i) comprising at least two rare earth metal salts and (ii) preferably having a pH of 2 to 6; b. introducing ozone into the solution while controlling the pH to between 2 and 6 to precipitate cerium oxide of greater than 97% purity from the solution; c. removing the precipitated cerium oxide from the solution; d. adjusting the pH of the solution to 6.0-8.0 in the presence of ozone to precipitate the oxyhydroxides / hydroxides of mid / heavy rare earths, Nd and Pr; e. removing the precipitated rare earth concentrate from solution; f. treating the remaining solution with a precipitating agent to produce a high purity lanthanum precipitate; g. Removing the solids from the solution.

[0019] In a second aspect, the present invention relates to a method for separating cerium from a leach solution comprising at least two rare earth metal salts and having a pH of less than 3. According to a preferred embodiment, the method preferably comprises the following steps: a. treating the solution with anhydrous ammonia to raise the pH to 3-5; b. introducing ozone into the solution while controlling the pH at 3-5 by the addition of anhydrous ammonia to precipitate greater than 90% of the cerium oxide from the solution; c. Removing the precipitated cerium oxide from the solution.

[0020] In a third aspect, the present invention relates to a method for separating rare earth elements comprising the steps of: a. slurrying a rare earth concentrate (e.g., rare earth carbonate or oxide) with water and mixing with an ammonium salt, such as a nitrate, halide, or sulfate; b. treating the slurry with ozone to produce a solution containing a high purity Ce concentrate (e.g., preferably >90% or >95%) and other solubilized rare earth elements; c. Removing the cerium solid precipitate from the solution containing other solubilized rare earth elements including La, Nd, Pr, etc.; d. Treating the solution containing the other solubilized rare earths with pH adjustment to produce a separated rare earth concentrate which can be processed to high purity rare earth elements.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a block diagram illustrating a first method according to a first preferred embodiment of the present invention.

[0023] [Diagram 2] FIG. 4 is a block diagram illustrating a second method according to another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Description of the Preferred Embodiments

[0025] For the purposes of promoting an understanding of the principles of the invention, reference will be made to the embodiments illustrated in the drawings and specific language will be used to describe the same, without intending to limit the scope of the invention, it being understood, however, that changes and further modifications of the illustrated devices as would normally occur to one skilled in the art are contemplated.

[0026] Where the specification describes advantages of embodiments or other prior art limitations, applicant does not intend to disclaim or disclaim any potential embodiments that may be covered by the appended claims, unless the applicant specifically states that the potential claims are "hereby disclaimed or disclaimed." Moreover, the terms "embodiments of the invention," "embodiments," or "invention" do not require that every embodiment of the invention include every feature, advantage, or mode of operation discussed herein, or that it does not incorporate less than optimal or disadvantageous aspects of the prior art.

[0027] As used herein, the word "exemplary" means "serving as an example, instance, or illustration and illustration." The embodiments described herein are illustrative rather than limiting. It is to be understood that the described embodiments are not necessarily to be construed as preferred or advantageous over other embodiments. Furthermore, the examples and illustrations set forth herein are not to be construed in any way as limiting, restrictive, or explicit definitions of the terms in which they are used. Rather, these examples and illustrations are to be considered for the purpose of illustration only.

[0028] As used herein, the singular forms "a," "an," and "the" are intended to include the plurals unless the context clearly indicates otherwise. Additionally, the word "may" is used in a permissive sense (i.e., meaning "may") rather than a mandatory sense (i.e., meaning "must"). Additionally, throughout this disclosure, where a process or method is shown or described, it should also be understood that the steps of the method may be performed in any order (i.e., repeatedly, iteratively, or simultaneously) and selected steps may be omitted, unless logically required otherwise. Additionally, it is understood that the terms "comprises," "comprising," "includes," and / or "including," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0029] Furthermore, the examples and figures shown herein should in no way be considered as limitations, restrictions, or explicit definitions of the terms used in them. Rather, these examples and figures should be considered for illustrative purposes only. Those skilled in the art will understand that the terms used in these examples or figures are intended to encompass other embodiments, whether described herein or elsewhere, and that all such embodiments are intended to be included within the scope of the terms.

[0030] In order to minimize the limitations found in the prior art, and to minimize other limitations which will become apparent upon reading this specification, preferred embodiments of the present invention may advantageously provide a method for separating rare earth elements from rare earth leach solutions and carbonate concentrates.

[0031] Referring to FIG. 1, according to a first preferred embodiment, the process / method of the present invention can start with a rare earth-containing leach solution. Typically, the source of such a rare earth leach solution is an acid digestion of a rare earth-containing concentrate or ore. Preferably, the rare earth leach solution of the present invention is a rare earth leach solution in which the anion is nitrate (NO3 - ), halides (F - , Cl - , Br - , I - ), or sulfate (SO4 - ) Preferably, the mineral acid of the present invention may be of any concentration and may preferably have a pH of less than 4. According to a further preferred embodiment, the mineral acid may preferably have a pH of less than 1.

[0032] According to a further preferred embodiment, the leaching mixture preferably comprises a leaching solution comprising at least rare earth ions and a solid material. The leaching solution may also comprise at least one metal ion. For example, the at least one metal ion may comprise at least one aluminum ion, at least one zinc ion, at least one copper ion, at least one nickel ion, at least one titanium ion, and / or at least one iron ion. The leaching solution is preferably heated to improve the extraction of rare earths from the rare earth-containing material.

[0033] The rare earth concentrate is preferably composed of about 0.1% REO to 100% REO and is digested with a mineral acid, which may preferably be nitric acid, hydrochloric acid, sulfuric acid or acetic acid. The final pH of the digestion is preferably less than 4. According to a further preferred embodiment, the final pH of the digestion may preferably be less than 2, more preferably less than 1. In a first step 102, the pH of the solution may preferably be adjusted. According to a preferred embodiment, the pH may be adjusted to a range of 3-5 or 3-6. According to a further preferred embodiment, the adjusted pH of the solution may preferably be less than 5, more preferably less than 3.

[0034] After the solution is within the target pH range, a next step 104 may involve introducing ozone while controlling the pH to maintain the pH between 3 and 6. Preferably, treatment of the solution results in precipitation of high purity cerium oxide. According to a preferred embodiment, the purity of the precipitated high purity cerium oxide is preferably in the range of 90% or higher. According to a more preferred embodiment, the purity is preferably 95% or higher, and most preferably 97% or higher.

[0035] In the next step 106, the process continues until the cerium is removed from the solution as precipitated cerium. According to another preferred embodiment, the removal of the cerium can then be achieved by any solid-liquid separation means. According to a preferred embodiment, the pH of the solution is then adjusted to 6.0-7.0. At the desired pH, preferably greater than 6, the medium / heavy rare earth elements precipitate together with Nd and Pr.

[0036] According to a further preferred embodiment, the process of the present invention is preferably continued until a desired amount of the target rare earths (e.g., mid / heavy rare earths plus Nd and Pr) have been removed from solution as precipitant. In a next step 108, the precipitant / solids can be removed from solution by any desired solid-liquid separation method.

[0037] In a next step 110, the remaining solution is preferably treated with a precipitating agent (i.e., carbon dioxide, hydroxide or oxalate) or evaporated to produce a high purity lanthanum concentrate, preferably with a lanthanum purity of 95% or greater, more preferably 98% or greater. In a preferred next step 112, the La-containing solids are preferably removed from the solution by further solid-liquid separation techniques.

[0038] According to a preferred embodiment, in a next step 114, the solids produced in the above process are preferably redigested with mineral acid and reprocessed as described above to produce higher purity rare earth elements. For example, the La concentrate produced can be digested with mineral acid and the resulting solution can be further reprocessed / treated according to the conditions disclosed for the medium / heavy / neodymium-praseodymium stage to further upgrade and purify the La.

[0039] A second embodiment will now be described with reference to FIG. 2. In a first step 202, a rare earth concentrate (such as a rare earth carbonate) is preferably slurried with water and mixed with an ammonium-containing salt (such as a nitrate, halide or sulfate). The rare earth concentrate is a mixture of two or more rare earth elements, one of which is Ce. According to a preferred embodiment, in the first step 202, a slurry may be formed by mixing 1 part carbonate to 1-20 parts water, together with 0.5-4 parts ammonium salt to 1 part rare earth concentrate. In a next step 204, the slurry may be treated with ozone to produce a high purity cerium concentrate and to solubilize other rare earth elements. In a next step 206, the cerium solids may be removed by solid-liquid separation techniques. According to a preferred embodiment, in a next step 208, the resulting solution is preferably treated with stepwise pH neutralization techniques (as described above) to produce a separated rare earth precipitate, which is then reprocessed into high purity rare earth elements. Preferably, the solution is pH neutralized to a pH of 6.0 to 8.0, most preferably 6.0 to 7.0.

[0040] It is preferred to precipitate the mid / heavy rare earths (along with Nd and Pr) within the desired pH range, and the pH is maintained to continue precipitation. According to a preferred embodiment, this process is continued until the solution is depleted of the desired amount of Nd and Pr. Then, in the next step 210, the precipitate / solids are preferably removed from the solution by solid-liquid separation techniques.

[0041] In a next step 212, the remaining solution is treated with a precipitating agent (such as a base, carbonate, or chelating agent) to produce a high purity lanthanum concentrate. This concentrate may contain greater than 95% lanthanum, preferably greater than 98% lanthanum. In a next step 214, solids are preferably removed from the solution. In a next step 216, the solids produced can be redigested with mineral acid and reprocessed as described above to produce higher purity rare earth elements.

[0042] The following examples are offered for illustrative purposes and should not be construed as limiting the scope of the invention. EXAMPLES

[0043] [example]

[0044] A rare earth concentrate containing 50% Ce, 30% La, 19% Nd-Pr, and 1% Sm-Lu in carbonate form is digested with hydrochloric acid to produce a rare earth chloride solution with a final pH of 1. The pH of this solution is adjusted to 3 and ozone is introduced. The pH is then maintained at 2.5-6 until the desired amount of Ce is removed from the solution at the desired purity (preferably 95-98%). The cerium-containing solids are then preferably removed from the solution. The remaining dissolved rare earths are preferably further processed by adjusting the pH to a value of 6-8 and preferentially precipitating the mid / heavy rare earths together with NdPr. This mid / heavy rare earth / Nd-Pr concentrate is preferably removed from the solution by solid-liquid separation. According to a preferred embodiment, the remaining leach solution should preferably contain only high purity La (preferably >97%). This material may be further precipitated to produce high purity La compounds.

[0045] If the desired purity of Nd-Pr, La, or Ce is not achieved, the purified material can then be digested with hydrochloric acid and the pH treatment repeated as above to target specific impurity elements. Purities as high as 99.9% can be achieved by this method.

[0046] Although the above description of the present invention contains many specific details, these should be construed as examples rather than as limitations on the scope of the present invention. Many other variations are possible. Thus, the scope of the present invention should be determined not by the illustrated embodiments, but by the appended claims and their legal equivalents.

Claims

1. 1. A method for separating rare earth elements, comprising the steps of: a. treating a leach solution, the leach solution comprising at least two rare earth metal salts, the leach solution being treated with a neutralization process to achieve a pH of 2-6; b. introducing ozone into the solution while controlling the pH to between 2 and 6 to precipitate cerium oxide from the solution; c. Removing the precipitated cerium oxide from the solution; d. Removing the solids from the solution containing the remaining rare earth elements; e. adjusting the pH of the solution to between 6.0 and 8.0 to precipitate the mid / heavy rare earths along with the hydroxides of Nd and Pr; f. Removing the precipitated Nd-Pr and mid / heavy rare earths from the solution; g. Treating the remaining solution with a precipitating agent or evaporating it to produce a high purity lanthanum concentrate; h. Removing the precipitated solid from the solution; A method comprising:

2. 10. The method of claim 1, further comprising redigesting the solids produced in step (h) with mineral acid and reprocessing according to steps (a) through (h).

3. 2. The method of claim 1 , wherein the rare earth leach solution comprises an aqueous rare earth salt.

4. The aqueous rare earth salt is nitrate (NO ３ － ), halides, or sulfates (SO ４ ２－ 4. The method of claim 3, wherein

5. 10. The method of claim 1, further comprising digesting the rare earth-containing material with at least one mineral acid to form the leach solution of step (a).

6. 6. The method of claim 5, wherein the pH of the at least one mineral acid is less than 1.

7. 10. The method of claim 1 , wherein the rare earth leach solution of step (a) further comprises a solid material.

8. 2. The method of claim 1, wherein the rare earth leach solution of step (a) further comprises at least one non-rare earth metal ion.

9. 9. The method of claim 8, wherein the non-rare earth metal ions comprise non-rare earth metal ions selected from the group of non-rare earth metal ions including aluminum, zinc, copper, nickel, titanium and iron.

10. 6. The method of claim 5, further comprising the step of heating the leach solution to improve extraction of rare earths from the rare earth-containing material.

11. 2. The method of claim 1, wherein the purity of the cerium oxide is greater than 90%.

12. 1. A method for separating cerium from a leach solution containing at least two rare earth metal salts and having a pH of less than 3, the method comprising: a. adjusting the pH of the solution to raise the pH to 3-5; b. introducing ozone into the solution while controlling the pH between 3 and 5; c. precipitating the cerium oxide from the solution; d. Removing the precipitated cerium oxide from the solution; A method comprising:

13. 1. A method for separating rare earth elements, comprising the steps of: a. slurrying a rare earth concentrate, the slurry being formed by mixing 1 part carbonate salt to 1-20 parts water, together with 0.5-4 parts ammonium salt to 1 part rare earth concentrate; b. treating the slurry with ozone to produce a solution containing a high purity cerium concentrate and other solubilized rare earths; c. Removing the cerium solids from the solution containing the other solubilized rare earth elements; d. sequentially adjusting the pH of the solution containing the other solubilized rare earth elements to produce a separated rare earth concentrate that can be processed into high purity rare earth elements; A method comprising:

14. The method of claim 13 , wherein the rare earth concentrate comprises a rare earth carbonate or a rare earth oxide.

15. 15. The method of claim 14, wherein the ammonium salt is a nitrate, halide, or sulfate.

16. 16. The method of claim 15, wherein the ammonium salt comprises an aqueous solution of ammonium chloride.

17. 17. The method of claim 16, wherein the step of treating the solution comprises adjusting the pH to between 6.0 and 7.

0.

18. 18. The method of claim 17, further comprising precipitating the mid / heavy rare earths, neodymium, and praseodymium from solution at a pH in the range of 6-8.

19. 20. The method of claim 18, further comprising continuing the process until the desired amount of Nd:Pr as the precipitating agent is depleted from the solution.

20. 20. The method of claim 19, further comprising treating the remaining solution from which the solids have been removed with a precipitating agent to produce a solution containing a high purity lanthanum concentrate.

21. 21. The method of claim 20, further comprising removing the solids from the solution.

22. 22. The method of claim 21, further comprising redigesting any solids produced with mineral acid and reprocessing the solution to produce purer rare earth elements.

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