A method for preparing a rare earth oxide material with high purity

Abstract

This invention relates to a method for preparing high-purity rare earth oxide materials, belonging to the field of rare earth hydrometallurgy. The method first involves dissolving rare earth concentrate in hydrochloric acid and adjusting the pH to 4.8-5.1, then precipitating with ammonium bicarbonate to obtain mixed rare earth carbonates to pre-remove iron and aluminum impurities. Next, a single rare earth solution is obtained through countercurrent extraction using an extraction system such as P507-kerosene. Subsequently, deep purification is performed at 75±2℃ using macroporous sulfonic acid cation exchange resin with a particle size of 30-60 μm using ion exchange chromatography to remove trace amounts of adjacent rare earth impurities. Finally, precipitation with oxalic acid or ammonium bicarbonate and calcination at 800-1000℃ yields high-purity rare earth oxide powder. This invention fully utilizes the advantages of each method, balancing throughput and ultra-high purity, stably producing single rare earth oxides with a purity of 5N or higher, and effectively avoiding organic phase emulsification, making it suitable for industrial applications.

Description

Technical Field

[0001] This invention relates to the field of rare earth hydrometallurgy, and in particular to a method for preparing high-purity rare earth oxide materials. Background Technology

[0002] Rare earth oxides, especially high-purity single rare earth oxides, are key raw materials for the preparation of high-performance permanent magnet materials, luminescent materials, catalytic materials, and precision polishing powders. With the development of high-end equipment manufacturing and the electronic information industry, the market's requirements for the purity of rare earth oxides have increased from 99.9% (3N) for industrial grade to 99.999% (5N) or even higher. At the same time, strict requirements have also been put forward for physical indicators such as particle size distribution and crystal morphology.

[0003] Currently, the main industrial methods for separating and purifying rare earth elements include solvent extraction, ion exchange, and stepwise precipitation. However, these methods all have significant technical bottlenecks when applied individually to the preparation of high-purity rare earth elements.

[0004] (1) Solvent extraction: This method utilizes the difference in the distribution ratio of rare earth ions between immiscible organic and aqueous phases to achieve separation. Due to its advantages of high throughput, continuous operation, and relatively low cost, it is currently the dominant technology in the rare earth separation industry. However, for adjacent rare earth element pairs with extremely similar chemical properties (such as praseodymium / neodymium, europium / gadolinium), the separation coefficient is often extremely low. It is generally accepted in the industry that if one attempts to increase the purity of a single rare earth element from industrial grade (99.9%) to ultra-high purity (99.999%) solely through solvent extraction, theoretically, the number of extraction stages needs to be increased to several hundred. This not only leads to an exponential increase in equipment investment and floor space, but also the high concentration of impurities such as iron and aluminum can easily cause organic phase emulsification and third phase formation in long processes, forcing frequent production line shutdowns for cleaning. Therefore, although solvent extraction has advantages in throughput and the economics of coarse separation, it has a practically applicable economic purity limit, and it is usually difficult to economically and stably produce products with a purity exceeding 99.9%. However, it remains an irreplaceable core technology for processing rare earth concentrates with complex compositions, achieving rare earth element grouping, and preliminary purification.

[0005] (2) Ion exchange method: This method utilizes the slight difference in affinity between rare earth ions and the active groups of resin to carry out repeated adsorption-desorption processes in the chromatographic column. Due to its extremely high theoretical plate number, the ion exchange method can achieve separation precision that is difficult to achieve by solvent extraction, making it a classic method for preparing ultra-high purity rare earths in the laboratory. However, its fatal flaws are its extremely low throughput, limited resin saturation capacity, long production cycle, discontinuous operation, and large wastewater discharge. If the ion exchange method is used for the entire process starting from rare earth concentrate, its high cost and low efficiency make it completely unsuitable for large-scale industrial production.

[0006] (3) Chemical precipitation method: This method is often used for rare earth enrichment or end product conversion, but a single precipitation method has almost no ability to separate adjacent rare earth elements. If the pH is not properly controlled in the conventional carbonate precipitation process, it is very easy to form amorphous colloidal precipitates such as iron hydroxide and aluminum hydroxide. These colloids will not only encapsulate rare earth and cause losses, but will also seriously affect the filtration performance and product purity of rare earth precipitates.

[0007] In summary, existing technologies lack a method for preparing rare earth oxides that can guarantee low-cost, high-throughput processing while achieving ultra-high purity refining. How to integrate the advantages of various methods and avoid their inherent shortcomings is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The technical problem to be solved by the present invention is: in order to overcome the above-mentioned technical problems, the present invention provides a method for preparing high-purity rare earth oxide materials.

[0009] The technical solution adopted by this invention to solve its technical problem is: a method for preparing high-purity rare earth oxide materials, comprising the following steps:

[0010] a. Raw material pretreatment and preliminary enrichment: After dissolving the rare earth concentrate raw material in hydrochloric acid, the pH of the solution is adjusted to 4.8-5.1. The generated hydrolysis precipitate is removed by filtration, and then ammonium bicarbonate is added as a precipitant, so that the rare earth elements are collectively precipitated in the form of mixed carbonates to obtain mixed rare earth carbonates. In this process, the pH value is controlled to pre-precipitate and remove the hydrolysis precipitate of iron and aluminum impurities, thus avoiding the emulsification of the organic phase in subsequent processes.

[0011] b. Separation and crude purification of the main body: The mixed rare earth carbonate obtained in step a is redissolved and the pH value is adjusted as feed solution and sent to a multi-stage series extraction tank. Through countercurrent extraction and washing process containing the extractant system, washing liquid and back-extraction agent, the rare earth elements are separated one by one to obtain a crude solution of the target single rare earth element with a relative purity of 99.0%-99.9%.

[0012] c. Deep purification: The crude solution of the target single rare earth element obtained in step b is fed into an ion exchange column for ion exchange chromatography separation to remove residual trace impurities or adjacent rare earth elements, thereby obtaining a high-purity single rare earth solution; wherein, the operating temperature of the ion exchange chromatography separation is 75±2℃.

[0013] d. Product conversion: The high-purity single rare earth solution obtained in step c is precipitated with high-purity oxalic acid or ammonium bicarbonate, then filtered, washed, and calcined at 800-1000℃ to finally obtain high-purity rare earth oxide powder products.

[0014] In this invention, unless otherwise specified, the following terms have the following meanings:

[0015] Relative purity of rare earth elements: refers to the percentage of the mass of a single rare earth element relative to the total mass of all rare earth elements in the sample. This purity index is used to characterize the degree of separation between rare earth elements, without considering non-rare earth impurities.

[0016] Absolute purity of the product: refers to the percentage of the target rare earth oxide product's mass to the total mass of the product. This purity index includes the overall purity of the final product, including non-rare earth impurities, and is commonly referred to as "N-grade" purity.

[0017] In this invention, the purity values ​​involved in step b are relative purity values ​​for rare earth elements; the purity values ​​involved in steps c and d, and the final product, are absolute purity values. All purity values ​​were determined using inductively coupled plasma mass spectrometry (ICP-MS).

[0018] Preferably, in step a, the pH value of the solution is adjusted to 4.8-5.1 by adding ammonia or dilute alkali solution, the concentration of ammonium bicarbonate solution is 5%-10%, the molar ratio of ammonium bicarbonate to the total amount of rare earth oxides in the solution is 2.8-3.5:1, and the precipitation time is 1-2 hours.

[0019] Preferably, in step b, the extractant system is P507-kerosene or naphthenic acid-isooctanol-kerosene, the pH of the extractant solution is 4, the pH of the washing solution is 1.5, the stripping agent is hydrochloric acid or nitric acid, the single-stage mixing and clarification time in the extraction section is 10-12 minutes, the volume ratio of organic phase to aqueous phase is 20:1, and the ratio of the number of stages in the extraction tank, the washing section and the stripping section is 8:10:7.

[0020] Preferably, in step c, macroporous microparticle sulfonic acid cation exchange resin with a particle size of 30-60 μm is used for ion exchange chromatography separation, and aminotriacetic acid (NTA) solution is used as a displacement agent to promote the migration of rare earth ions in the column and achieve separation.

[0021] Preferably, in step d, the pH value of the oxalic acid system is 3-6, the precipitation temperature is 20-80℃, the washing method is multiple washing with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

[0022] Preferably, in step d, the pH value of the ammonium bicarbonate system is 5.2-5.5, the precipitation temperature is 20-80℃, the washing method is multiple washing with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

[0023] Preferably, the ion exchange column is a pressure-resistant stainless steel column, and the operating pressure inside the column is maintained at 2.5-4.0 MPa. Step c specifically includes:

[0024] C1. The produced single rare earth solution is introduced from the top of the ion exchange column. The rare earth ions are adsorbed by the resin and an initial adsorption band is formed at the top of the ion exchange column.

[0025] C2. A solution containing a displacement agent is introduced into the column. The displacement agent combines with the rare earth ions on the resin and promotes the rare earth ions to migrate downward in the ion exchange column. The displacement agent is an NTA solution.

[0026] C3. Collect the outflowing solution at the outlet of the ion exchange column at different time intervals.

[0027] This invention takes a different approach, not attempting to use extraction methods for the final 0.01% purification work that they are not good at, nor attempting to use ion exchange methods for the high-throughput crude separation tasks that they cannot handle. Instead, it lies in discovering a specific relay matching window between solvent extraction in step b and ion exchange in step c. Specifically:

[0028] Positioning of the extraction method: Step b employs a specific 8:10:7 stage configuration and process parameters. Its purpose is not to directly obtain 5N products, but rather to rapidly increase the purity of the target rare earth element to a critical threshold using the lowest possible stage and at the most economical cost. For example, the relative purity of the rare earth element should reach between 99.0% and 99.9%, which is the transition zone between industrial purity and high purity. This purity level is sufficient to separate most non-rare earth impurities with significantly different chemical properties and most light and heavy rare earth elements, while perfectly avoiding the risks of emulsification and huge investments associated with pursuing excessively high purity through 100-stage extraction.

[0029] Positioning of ion exchange chromatography: Step c receives a crude single rare earth solution within the aforementioned critical threshold. At this point, the feed solution contains only trace amounts of adjacent rare earth elements with extremely similar chemical properties and ppm-level non-rare earth impurities, making it ideal for leveraging the extremely high theoretical plate number of ion exchange chromatography. Combined with high-temperature microparticle resin conditions, it is possible to achieve the final 0.01% precision with high throughput, stably realizing 5N-6N level purification.

[0030] If the purity in step b is too low, for example, below 99.0%, the large amount of residual impurities will quickly penetrate the ion exchange column in step c, making it impossible to achieve 5N purity. If one attempts to pursue excessively high purity in step b, one will fall into the cost and stability trap of 100-stage extraction. The 8:10:7 extraction stage ratio and subsequent high-temperature microparticle resin purification step specified in this invention are not arbitrarily chosen, but rather a specific combination selected through extensive experimentation to achieve the optimal balance between overall process economy and product purity. This division of labor—extraction for breadth and ion exchange for depth—and the discovery of a specific parameter window between the two, are the fundamental reasons why this invention can achieve high throughput, low cost, and ultra-high purity.

[0031] The beneficial effects of this invention are that the method for preparing high-purity rare earth oxide materials uses extraction to complete high-throughput basic processing, which significantly reduces costs compared to ion exchange. The ion exchange method is used for refining, which can ensure higher purity compared to extraction. Finally, precipitation not only achieves solid-liquid separation but also shapes the microscopic physical morphology of the product. By combining multiple methods, the goal of low-cost and high-expectation preparation is achieved. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Figure 1 This is a process flow diagram of a method for preparing high-purity rare earth oxide materials in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0035] This invention provides a method for preparing high-purity rare earth oxide materials. Figure 1 The process flow of the preparation method of the present invention is shown, which includes the following steps:

[0036] a. Raw material pretreatment and preliminary enrichment: After dissolving the rare earth concentrate raw material in hydrochloric acid, the pH of the solution is adjusted to 4.8-5.1. The generated hydrolysis precipitate is removed by filtration, and then ammonium bicarbonate is added as a precipitant, so that the rare earth elements are collectively precipitated in the form of mixed carbonates to obtain mixed rare earth carbonates. In this process, the pH value is controlled to pre-precipitate and remove the hydrolysis precipitate of iron and aluminum impurities, thus avoiding the emulsification of the organic phase in subsequent processes.

[0037] The main purpose here is to transform the complex rare earth concentrate into a relatively simple mixed rare earth carbonate, while removing a large number of acid-insoluble impurities, such as silicon and iron, through preliminary separation.

[0038] b. Separation and crude purification of the main body: The mixed rare earth carbonates obtained in step a are redissolved and the pH value is adjusted as feed solution and sent to a multi-stage series extraction tank. Through countercurrent extraction and washing process containing an extractant system, washing liquid and back-extraction agent, the rare earth elements are separated one by one to obtain a crude target single rare earth element solution with purity within the critical threshold range; in this embodiment, the crude target single rare earth element solution has a relative purity of 99.0%-99.9%.

[0039] c. Deep purification: The crude solution of the target single rare earth element obtained in step b is sent into an ion exchange column for ion exchange chromatography separation to remove residual trace impurities or adjacent rare earth elements, and a high-purity single rare earth solution is obtained.

[0040] d. Product conversion: The high-purity single rare earth solution obtained in step c is precipitated with high-purity oxalic acid or ammonium bicarbonate, then filtered, washed, and calcined at 800-1000℃ to finally obtain high-purity rare earth oxide powder products.

[0041] Preferably, in step a, adjusting the solution pH to 4.8-5.1 is achieved by adding ammonia or dilute alkali solution. The concentration of ammonium bicarbonate solution is 5%-10%, the molar ratio of ammonium bicarbonate to the total amount of rare earth oxides in the solution is 2.8-3.5:1, and the precipitation time is 1-2 hours. Here, the molar ratio is set to 2.8-3.5:1, slightly higher than the theoretically required molar ratio (approximately 2.5:1). The inventors found that when using the theoretical ratio or a ratio slightly lower than this range, rare earth precipitation is incomplete, with a precipitation yield of only 92-95%. However, when the molar ratio is increased to 2.8-3.5:1, the rare earth precipitation rate can stably reach over 99.5%. More importantly, within this specific excess range, the mixed rare earth carbonate particles generated by the precipitation exhibit loose, porous spherical aggregates rather than amorphous colloidal precipitates. This significantly improves the efficiency of subsequent filtration and washing and effectively avoids the risk of co-precipitation of ferric hydroxide and aluminum hydroxide caused by local pH fluctuations due to insufficient precipitant. If the amount of ammonium bicarbonate used is further increased beyond the upper limit of this range, it will not only cause material waste and increase the burden of ammonia nitrogen wastewater treatment, but also easily lead to excessively fine precipitate particles and difficulty in filtration, without any additional technical benefits.

[0042] The pH value of hydrochloric acid should be selected between 4.8 and 5.1. If the pH value is too high, a large amount of impurities such as iron and aluminum will hydrolyze and precipitate into the product. If the pH value is too low, rare earth elements will not precipitate completely.

[0043] This pH value is lower than the critical hydrolysis pH value of rare earth elements. At this pH value, rare earth elements do not form hydroxide precipitates, but only react with carbonate ions to form carbonates. Furthermore, at this pH value, most of the iron and aluminum have already hydrolyzed and precipitated or remain in the acid-insoluble residue, effectively preventing colloidal impurities from being mixed into the rare earth carbonate mixture.

[0044] In ordinary production processes, the pH value is generally controlled at 6-7. This leads to a large amount of ferric hydroxide and aluminum hydroxide colloids co-precipitating with rare earth elements, resulting in organic phase emulsification and a third phase, which often forces the production line to frequently stop for cleaning.

[0045] The ratio of rare earth content to ammonium bicarbonate mass is set at 1:3, mainly to ensure thorough precipitation.

[0046] Compared to direct extraction of the raw ore solution, this step significantly reduces the processing load of the subsequent extraction tank and the risk of organic phase emulsification, because high concentrations of ferric ions are easily extracted into the organic phase and form a third phase.

[0047] Preferably, in step b, the extractant system is P507-kerosene or naphthenic acid-isooctanol-kerosene, the pH of the extractant solution is 4, the pH of the washing solution is 1.5, the stripping agent is hydrochloric acid or nitric acid, the single-stage mixing and clarification time in the extraction section is 10-12 minutes, the volume ratio of organic phase to aqueous phase is 20:1, and the ratio of the number of stages in the extraction tank, the washing section and the stripping section is 8:10:7.

[0048] In this step, the extraction stage actually uses 8 stages, mainly to ensure that rare earth ions are fully captured by the organic phase. The washing stage uses 10 stages, using a washing solution with a pH of 1.5 to backwash the light rare earths with weak binding in the organic phase back to the aqueous phase, retaining only the target rare earths with strong binding, thereby achieving the cleavage of adjacent elements and also improving the utilization rate of hydrochloric acid. The back-extraction stage uses 7 stages, mainly to use higher acidity to completely strip the target rare earths from the organic phase back to the aqueous phase.

[0049] Preferably, in step c, macroporous microparticle sulfonic acid cation exchange resin with a particle size of 30-60 μm is used for ion exchange chromatography separation. The ion exchange operation is carried out at a temperature of 75±2℃, and nitric acid triacetic acid solution is used as the displacement agent to promote the migration of rare earth ions within the column and achieve separation. The column operating pressure is 2.5-4.0 MPa, and a high-pressure stainless steel ion exchange column with a rated pressure of not less than 15.0 MPa is used. The displacement agent is a 0.015-0.03 mol / L nitric acid triacetic acid solution, and its pH is adjusted to 6.0-6.5 using ammonia water.

[0050] The principle behind using a high-temperature operation of 75±2℃ is that the affinity of sulfonic acid groups for rare earth ions weakens with increasing atomic number. High temperature can reduce solution viscosity and accelerate the mass transfer rate of rare earth ions in resin micropores. At the same time, the highly cross-linked macroporous resin selected in this invention exhibits good dimensional thermal stability at 75℃, and its swelling rate is controlled at an extremely low level, without negatively affecting bed permeability. Under the combined effect, the theoretical plate height is significantly reduced and the chromatographic peak shape is significantly narrowed.

[0051] This step uses a combination of macroporous microparticle resin, 75℃ high-temperature operation, and a displacement agent. Compared with conventional processes, which rely solely on the extraction tank, some elements with extremely low separation coefficients require up to 100 extraction stages to barely separate them, resulting in very high equipment investment and acid and alkali consumption.

[0052] To ensure uniform distribution of the particulate resin and prevent its loss, the upper and lower distributors of the high-pressure stainless steel ion exchange column are made of sintered porous titanium plates with a pore size of 10-15 μm; the top and bottom of the resin bed are respectively filled with a quartz sand protective layer with a height of 5-8 cm and a particle size of 80-100 μm to ensure uniform fluid distribution and intercept any particulate resin fragments that may escape.

[0053] Preferably, in step d, the pH value of the oxalic acid system is 3-6, the precipitation temperature is 20-80℃, the washing method is multiple washing with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

[0054] The oxalic acid system is used for product conversion, resulting in larger precipitate particles with good crystallization and a high removal rate of non-rare earth impurities. The decomposition temperature of rare earth oxalate is about 800℃, and that of rare earth carbonate is about 600℃. The range of 800-1000℃ is set here to ensure complete decomposition into oxides while allowing the crystals to grow initially, which is convenient for subsequent grinding and processing.

[0055] This utilizes the crystallization effect of oxalate precipitation. Rare earth oxalate is a needle-shaped large crystal. During calcination, gas escapes uniformly from the internal pores of the crystal, which plays a role in in-situ pore creation. The final product has a narrow D50 distribution, high loose density and no hard agglomerates, which is a decisive quality advantage for laser crystal growth and precision polishing powder.

[0056] Preferably, in step d, the pH value of the ammonium bicarbonate system is 5.2-5.5, the precipitation temperature is 20-80℃, the washing method is multiple washing with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

[0057] The ammonium bicarbonate system is used here. Compared with the oxalic acid system, it has a lower cost and a higher precipitation rate, but it is very easy to form amorphous colloids, which makes filtration and washing slower and more prone to trapping impurities.

[0058] Oxalic acid systems, on the other hand, are more expensive and have more difficult wastewater treatment. The appropriate choice can be made based on the actual production needs.

[0059] Preferably, the ion exchange chromatography separation is carried out in a pressure-resistant stainless steel column, with the operating pressure maintained at 2.0-5.0 MPa. The macroporous microparticle sulfonic acid cation exchange resin in step c has a particle size of 30-60 μm. The specific steps include:

[0060] C1. The produced single rare earth solution is introduced from the top of the ion exchange column. The rare earth ions are adsorbed by the resin and an initial adsorption band is formed at the top of the ion exchange column.

[0061] C2. A solution containing a displacement agent is introduced into the column. The displacement agent combines with the rare earth ions on the resin and promotes the rare earth ions to migrate downward in the ion exchange column. The displacement agent is an NTA solution.

[0062] C3. Collect the outflowing solution at the outlet of the ion exchange column at different time intervals.

[0063] This step can remove the ppm-level non-rare earth impurities and adjacent element pairs that are extremely difficult to separate from the residue in step b, and improve the purity from 3N to 5N-6N level.

[0064] Conventional industrial resins have a particle size of about 300-1200μm, while micro-particle resins of 30-60μm are used here. The particle size is reduced by nearly 10 times, which will increase the theoretical plate number exponentially. The diffusion path of ions in the resin is extremely short, and the mass transfer resistance is greatly reduced, thus enabling the effective separation of adjacent rare earth elements.

[0065] NTA, or aminotriacetic acid, is a strong complexing agent. When an NTA solution flows through the rare earth zone, a complexation reaction occurs, and rare earth ions are pulled off the resin by NTA and encapsulated in a water-soluble complex. NTA is used here primarily because there are slight differences in the stability of the complexes formed between NTA and rare earth elements. As the column flows downwards, weaker light rare earth impurities are preferentially recaptured by the resin, while the target rare earth elements tend to remain in the mobile phase. This micro-cycle of countless adsorption-re-adsorption cycles amplifies minute differences in chemical properties into separation at physical distances.

[0066] In the entire preparation process, step a is a pretreatment step, which mainly utilizes the pH difference of hydrolysis to remove 99% of impurities and protect the extractant; step b is an extraction and separation step, which utilizes the slight affinity difference of the extractant and washes it in the extraction tank to amplify the separation effect; step c is an ion exchange step, which utilizes the high theoretical plate number of the resin and the high temperature of 75℃ to accelerate the kinetics and achieve ppm-level separation; step d is a product conversion step, which uses oxalic acid or ammonium bicarbonate system to obtain large-particle crystals, and then performs temperature-controlled calcination to prevent abnormal crystal growth.

[0067] The present invention will be further described in detail below through specific embodiments and comparative examples, but the present invention is not limited to these embodiments. In each embodiment and comparative example, the content of rare earth elements and impurities were determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0068] To address the high-temperature operating conditions of 75±2℃ required by this invention, the inventors conducted long-term hydrothermal mechanical stability tests on the selected macroporous sulfonic acid-type styrene-divinylbenzene cation exchange resin (crosslinking degree 12%) with a particle size of 40-60μm. The resin was packed into a pressure-resistant stainless steel column with an inner diameter of 100mm, and operated continuously for 720 hours at an operating pressure of 3.0MPa and a temperature of 75℃, using deionized water as the mobile phase.

[0069] After operation, the resin bed height changed from the initial 1800 mm to 1792 mm, with a bed volume shrinkage rate of only 0.44%; the bed pressure drop changed from the initial 2.5 MPa to 2.7 MPa, an increase of 8.0%, with no significant increase; no resin fragments or abnormally high organic carbon content (TOC < 2 ppm) were detected at the outlet; electron microscopy after drying showed that the resin particles had intact morphology, with no obvious breakage or cracks, and its exchange capacity retention rate was ≥ 96%.

[0070] The experiment proves that the high cross-linking macroporous resin selected in this invention can effectively control the swelling within an acceptable range at a high temperature of 75°C due to the sufficient structural rigidity of the resin skeleton. Combined with the advantage of short mass transfer paths brought by the particle size, it can fully meet the requirements of long-term industrial operation.

[0071] Example 1

[0072] This embodiment uses fluorocarbon cerium ore concentrate (REO content of about 55%, with the main impurities being Fe2O3 3.2%, Al2O3 2.8%, and CaO 5.1%) from a certain place in Sichuan as raw material, and the target product is neodymium oxide with a purity of ≥99.999% (5N).

[0073] Step a, Raw material pretreatment and preliminary enrichment:

[0074] 100 kg of rare earth concentrate was dissolved in 6 mol / L industrial hydrochloric acid at 80 °C with stirring for 2 hours. The solution was filtered to remove acid-insoluble residue, mainly silicates and barite. Dilute ammonia was slowly added to the filtrate to adjust the pH to 5.0. A small amount of precipitate formed; this was removed by filtration. The reddish-brown flocculent precipitate mainly consisted of ferric hydroxide and aluminum hydroxide. An 8% ammonium bicarbonate solution was added to the resulting clear solution, with the amount added controlled according to a molar ratio of ammonium bicarbonate to the total rare earth oxides in the solution of 2.8-3.5:1. The solution was stirred to precipitate for 1.5 hours and then allowed to stand for 1 hour. The mixture was filtered to obtain a mixed rare earth carbonate filter cake. Testing showed that this step achieved a 97.2% removal rate of iron and aluminum impurities. The inventors unexpectedly discovered that when the molar ratio of ammonium bicarbonate to rare earth oxides was strictly controlled at 2.8-3.5:1, the microstructure of the precipitate underwent a qualitative change. Below a ratio of 2.8:1, the product is a typical amorphous gel, making filtration difficult; above a ratio of 3.5:1, excess ammonium bicarbonate forms partially soluble complexes with rare earth elements, leading to a decrease in yield. Only within the narrow window of 2.8-3.5:1 does the generated rare earth carbonate precursor exhibit loose, porous, spherical aggregates (SEM images attached), with a 40% reduction in specific surface area and a more than 3-fold increase in filtration speed. This characteristic has a decisive impact on ensuring the clarity of the feed solution in subsequent step b and the calcination activity in step d.

[0075] Step b, Separation and Crude Purification:

[0076] The mixed rare earth carbonates obtained in step a were redissolved in hydrochloric acid, and the pH of the feed solution was adjusted to 4.0, with the rare earth concentration controlled at 1.2 mol / L. This feed solution was then fed into a multi-stage series extraction tank at a flow rate of 10 L / h. The extraction tank was specifically configured with: 8 extraction stages, 10 washing stages, and 7 back-extraction stages. The organic phase was a 1.5 mol / L P507-kerosene solution, the washing solution was a hydrochloric acid solution with pH=1.5, and the back-extraction agent was 4 mol / L hydrochloric acid. The single-stage mixing contact time in the extraction stage was 10 minutes, and the organic phase to aqueous phase flow ratio (O / A) was 20:1. Through countercurrent extraction and washing operations, a neodymium chloride solution was collected at the outlet of the back-extraction stage. ICP-MS analysis showed that the relative purity of neodymium in this solution was 99.5% (i.e., the mass percentage of neodymium in the total rare earth elements), with praseodymium (Pr) as the main adjacent rare earth impurity, accounting for approximately 0.3%. At this point, any remaining non-rare earth impurities in the solution (such as Ca, Na, etc.) are not included in the purity calculation in this step.

[0077] Regarding the O / A ratio setting of 20:1, conventional rare earth extraction ratios are mostly 1:1 to 5:1. The high ratio used in this invention is not to increase throughput, but to solve a specific background technical problem—organic phase emulsification and third phase formation.

[0078] When separating feed solutions containing trace amounts of Fe and Al, if the ratio is too low (high proportion of aqueous phase), the trace impurities in the aqueous phase will rapidly reach their saturation solubility in the organic phase due to excessively high local concentrations, thus precipitating a colloidal third phase. This invention significantly reduces the absolute amount of aqueous impurities in contact with a unit volume of organic phase by increasing the O / A ratio to 20:1. This ensures that the impurities are always dispersed in the organic phase as unsaturated molecules and discharged with the washing liquid, thereby fundamentally preventing the formation of third-phase nuclei.

[0079] If the O / A ratio is reduced to 5:1, with other conditions remaining the same as in this embodiment, a visible emulsion band appears in the clarification chamber of the extraction tank after 24 hours of continuous operation. Therefore, O / A = 20:1 is a non-obvious structural parameter that ensures the continuous and stable operation of this long-process technology for more than 120 hours.

[0080] Step c, Deep Refining:

[0081] The neodymium chloride solution obtained in step b was concentrated to a rare earth concentration of approximately 50 g / L, and the pH was adjusted to 3.5 as the feed solution for ion exchange. A jacketed, insulated, high-pressure stainless steel ion exchange column with an inner diameter of 100 mm and a height of 2000 mm was used, packed with macroporous sulfonic acid-type cation exchange resin with a particle size of 40-60 μm, and the resin bed height was 1800 mm. Hot water at 75℃ was circulated through the column jacket to maintain the column operating temperature at 75±2℃. The feed volume was 5% of the resin bed volume. After feeding, a 0.02 mol / L nitric acid solution with a pH of 6.2 was introduced at a flow rate of 0.8 L / h as a displacement agent for elution and development. The operating pressure inside the column was controlled between 2.5-3.0 MPa, and a high-pressure constant flow pump with a rated pressure of 20 MPa was used. The effluent was collected in segments at the column outlet, and the effluent from the main neodymium peak region was combined to obtain a high-purity neodymium chloride solution. According to ICP-MS analysis, the absolute purity of neodymium in the solution (relative to the total solids mass after drying) reached 99.9993% (i.e., 5N3 level), and the total amount of major non-rare earth impurities was <10ppm.

[0082] Step d, Product Conversion:

[0083] To the high-purity neodymium chloride solution obtained in step c, a 10% high-purity oxalic acid solution was slowly added while stirring at 60°C, controlling the pH value at the precipitation endpoint to be 4.5. After complete precipitation, stirring was continued for 30 minutes, and the mixture was allowed to stand for aging for 2 hours. The mixture was then filtered, and the filter cake was washed 5 times with high-purity water. The filter cake was placed in a muffle furnace and heated to 900°C at a rate of 5°C / min, held at that temperature for 4 hours, and then cooled to room temperature with the furnace to obtain high-purity neodymium oxide powder.

[0084] Product testing results:

[0085] The obtained neodymium oxide product has an absolute purity of 99.9994% (i.e., 5N4 level), with the following main non-rare earth impurities: Fe 5ppm, Al 3ppm, Si 8ppm, Ca 12ppm; the adjacent rare earth impurity Pr content is 4ppm. The product has a D50 particle size of 3.2μm, a loose packing density of 1.45g / cm³, and a spherical morphology.

[0086] Example 2

[0087] This embodiment uses mixed rare earth carbonates obtained by preliminary enrichment of ion-adsorption type rare earth ore leaching solution from a certain place in Jiangxi as raw material, and the target product is high-purity europium oxide with a purity of ≥99.99% (4N).

[0088] Step a, Raw material pretreatment and preliminary enrichment:

[0089] The raw material, a mixture of rare earth carbonates, contains approximately 92% REO and small amounts of iron, aluminum, calcium, and magnesium impurities. After dissolving the raw material in hydrochloric acid, the pH of the solution is adjusted to 5.1. A 5% ammonium bicarbonate solution is then added for recrystallization over 2 hours to further remove impurities, yielding refined mixed rare earth carbonates.

[0090] Step b, Separation and Crude Purification:

[0091] The product from step a was redissolved and separated using a naphthenic acid-isooctanol-kerosene extraction system. The extraction tank configuration included an 8-stage extraction section, a 10-stage washing section, and a 7-stage back-extraction section. The pH of the feed solution was 4.0, the pH of the washing solution was 1.5, and the back-extraction agent was 4 mol / L nitric acid. The single-stage contact time in the extraction section was 12 minutes. The europium-rich fraction solution was collected, and the relative purity of europium in rare earth elements was determined to be 99.1%, with the main impurities being adjacent gadolinium (Gd) and samarium (Sm).

[0092] Step c, Deep Refining:

[0093] The same high-pressure ion exchange apparatus as in Example 1 was used, but the resin was replaced with the same type of macroporous sulfonic acid cation exchange resin with a particle size of 30-50 μm. The operating temperature was 75±2℃, and the column operating pressure was 3.5-4.0 MPa. The substitution agent was a 0.025 mol / L NTA solution with pH=6.0. After separation by ion exchange chromatography, the europium main peak region solution was collected, and the absolute purity of the europium product was increased to 99.995% (4N5).

[0094] Step d, Product conversion (ammonium bicarbonate system):

[0095] A 10% high-purity ammonium bicarbonate solution was added dropwise to the above high-purity europium solution at 40°C, controlling the pH value to remain stable at 5.3 during the precipitation process, with a precipitation time of 1 hour. The precipitate was filtered and washed with high-purity water until the conductivity of the filtrate was <10 μS / cm. The filter cake was calcined at 850°C for 3 hours to obtain high-purity europium oxide powder.

[0096] Product testing results:

[0097] The resulting europium oxide product has an absolute purity of 99.995% (4N5), with a total non-rare earth impurity content of <50ppm. This example uses an ammonium bicarbonate precipitation system, which results in a high precipitation rate and reduces costs by approximately 30% compared to the oxalic acid system, although the washing time is slightly longer.

[0098] Comparative Example 1

[0099] This comparative example illustrates the importance of the pretreatment process in step a for avoiding organic phase emulsification and improving product purity.

[0100] The same bastnaesite concentrate as in Example 1 was used. The difference was that the pH adjustment and ammonium bicarbonate precipitation enrichment process in step a were omitted. Instead, the solution after dissolving the mineral powder in hydrochloric acid was simply filtered to remove insoluble matter, and then the pH was directly adjusted to 4.0 as the extraction solution for step b.

[0101] Process description:

[0102] After filtering 100 kg of concentrate dissolved in hydrochloric acid, the solution contained Fe. 3+ Approximately 2.8 g / L, Al 3+ Approximately 2.5 g / L. This feed solution was fed into the P507-kerosene extraction system under the same extraction conditions as in Example 1. After only about 8 hours of extraction operation, a distinct brownish-yellow flocculent third phase began to appear in the clarification chamber of the extraction tank. The interface between the organic and aqueous phases was blurred, and severe emulsification occurred. Continuing operation for 12 hours further exacerbated the emulsification, resulting in significant entrainment of the organic phase in the aqueous phase. The extraction efficiency dropped sharply, forcing a shutdown for cleaning.

[0103] Result comparison:

[0104]

[0105] The results of Comparative Example 1 clearly demonstrate that step a, by controlling the pH to 4.8-5.1 to pre-precipitate and remove easily hydrolyzable impurities such as iron and aluminum, is crucial for ensuring the stable operation of subsequent solvent extraction processes. Without this pretreatment step, high concentrations of Fe... 3+ Entering the extraction system will quickly trigger third-phase emulsification, causing the entire separation process to be unable to continue.

[0106] Comparative Example 2

[0107] This comparative example is used to illustrate the criticality and synergistic effect of the combination of high-temperature operation and particulate resin in step c.

[0108] Using the exact same raw materials and steps a and b as in Example 1, a neodymium chloride solution with a purity of 99.5% was obtained as the feed liquid. The only difference was the ion exchange operating conditions in step c.

[0109] Comparative Example 2-1:

[0110] The operating temperature in step c was adjusted from 75±2℃ to room temperature 25±2℃, and the other conditions were exactly the same as in Example 1: the particle size of the microparticle resin was 40-60μm and the NTA concentration was 0.02mol / L.

[0111] Comparative Example 2-2:

[0112] Replace the resin in step c with a commercially available industrial-grade macroporous sulfonic acid cation exchange resin with a particle size of 300-500 μm. The operating temperature is still maintained at 75±2℃, and the other conditions are the same as in Example 1.

[0113] Comparative Examples 2-3:

[0114] The operating temperature in step c was adjusted to room temperature (25±2℃), and the resin was replaced with a conventional resin with a particle size of 300-500μm. The other conditions were the same as in Example 1.

[0115] Summary of experimental results:

[0116]

[0117] Results analysis:

[0118] Comparative Example 2-1 demonstrates that by simply lowering the temperature to room temperature, under the same particulate resin conditions, the product purity drops from 5N4 to 4N2, and the residual impurities in adjacent Pr particles increase by more than 15 times. This proves that a high temperature of 75℃ can significantly reduce mass transfer resistance, which is a key non-obvious characteristic for achieving ultra-high purity above 5N.

[0119] Comparative Example 2-2 demonstrates that even with the use of conventional large-particle resin, the purity still decreases to the 4N5 level at high temperatures. This proves that the high theoretical plate number provided by the 30-60μm microparticle resin is the hardware foundation for achieving ppm-level impurity removal. The absolute purity of the product in Comparative Example 2-2 is only 99.94%, and the residual amount of the adjacent rare earth impurity Pr is 38ppm, failing to meet the product specification requirement of 99.999% (5N). This fully demonstrates that simply introducing high temperature without providing a high theoretical plate number as a separation basis with microparticle resin cannot achieve the final purity target of this invention.

[0120] Comparative Examples 2-3 demonstrate that if both high temperature and particulate resin are missing, the product purity degrades drastically to near the level at the exit of step b, and the ion exchange step almost loses its ability to achieve deep purification.

[0121] Through comparative experiments, the inventors unexpectedly discovered that achieving a leap in absolute product purity from 99.9% (3N) to 99.999% (5N) could not be accomplished by using high temperature alone or by using particulate resin alone. Data from Comparative Example 2-1 shows that even with particulate resin, the product purity at room temperature could only be increased to 99.99% (4N), with adjacent impurities remaining at the tens of ppm level, failing to meet the ultra-high purity requirements. Comparative Example 2-2 shows that even with conventional large-particle resin at high temperature, the limited number of trays could only increase the purity to around 99.94%, still orders of magnitude lower than 5N. Only when both the operating temperature of 75±2℃ and the particulate resin with a particle size of 30-60μm were simultaneously met was a stable production of purity above 5N achieved for the first time. This indicates that high temperature and particulate resin are not simply additive, but rather two indispensable conditions for achieving ultra-high purity, their combination constituting a complete and non-obvious solution.

[0122] Comparative Example 3

[0123] This comparative example illustrates the synergistic matching relationship between the extraction stage ratio in step b and step c, demonstrating the economic and technical necessity of a specific stage configuration.

[0124] The same raw materials and steps a, c, and d were used as in Example 1. The only difference was the adjustment of the number of extraction tank stages in step b; all other operating parameters were exactly the same.

[0125] Comparative Example 3-1:

[0126] The extraction tank stage ratio was adjusted from 8:10:7 to 3:4:2, reducing the washing and back-extraction sections. The resulting neodymium chloride solution had a purity of 95.2%, and then proceeded to step c for the same ion exchange purification.

[0127] Comparative Example 3-2:

[0128] The extraction stage ratio in step b was adjusted from 8:10:7 to 20:40:20 to simulate a purification process entirely reliant on extraction. Under this configuration, the total residence time of the material in the extraction tank was extended to more than 2.5 times that of Example 1, leading to oxidative degradation of the P507 extractant. Infrared spectroscopy of the circulating organic phase detected decomposition peaks of the POC bonds, and the organic phase color changed from light yellow to brownish-yellow. The degradation products exhibited surfactant properties, which in turn caused new interfacial emulsification problems in the clarification chamber. Furthermore, the equipment footprint and initial investment were 3-4 times higher than in Example 1. This comparative example demonstrates that simply increasing the number of extraction stages is neither technically nor economically feasible.

[0129] Comparative Example 3-3

[0130] This comparative example illustrates a critical purity matching threshold between steps b and c.

[0131] The same raw materials and steps a, c, and d were used as in Example 1. The difference was that the ratio of the extraction tank stages in step b was adjusted from 8:10:7 to 6:8:5, while the other operating parameters remained exactly the same.

[0132] The results showed that after using a 6:8:5 stage configuration, the purity of the Nd:C chloride solution at the outlet of step b decreased from 99.5% to 98.8%, with a slight increase in the content of the main impurities Pr and Sm. When this solution entered the same ion exchange column in step c, to maintain a product purity of 5N, the feed flow rate had to be reduced to 0.24 L / h, only 30% of the original throughput; simultaneously, the consumption of the NTA replacement agent increased by 45%. If the original flow rate of 0.8 L / h was maintained, the final product purity could only reach 99.98% (4N8), with Pr impurity residue reaching as high as 120 ppm, far from meeting the 5N requirement.

[0133] This demonstrates that once the outlet purity of step b falls below a threshold of approximately 99.0%, the load of residual impurities on step c increases non-linearly, leading to a sharp decline or even collapse in the efficiency of the ion exchange purification process. The 8:10:7 series ratio specified in this invention is a unique design that locks the purity of the feed solution above this threshold window at the lowest cost.

[0134] Summary of experimental results:

[0135]

[0136] Results analysis:

[0137] Comparative Example 3-1 demonstrates that if the purity of the feed provided in step b is below a threshold, for example, <99%, even with the efficient purification in step c, the final product purity cannot reach 5N. This indicates that although step c is efficient, its processing capacity has a limit, and step b must provide a "clean" feed solution of a certain purity. The 8:10:7 series ratio of this invention precisely finds and limits this economically and technically optimal feed purity window, approximately 99.5%.

[0138] Comparative Example 3-2 demonstrates that attempting to improve purity solely by increasing the number of extraction stages is economically impractical. Excessive stages lead to prolonged material residence time, causing extractant degradation and the generation of new interfacial contaminants. Furthermore, the equipment investment and floor space required increase exponentially. This confirms the technical limitations of the single extraction method.

[0139] The specific matching relationship between step b (specific extraction configuration) and step c (ion exchange purification) of this invention enables the highest product purity to be achieved at the lowest overall cost with a light extraction burden and acceptable ion exchange flux.

[0140] Comparative Example 4

[0141] The same raw materials and process conditions as in Example 1 (steps a, b, and c) were used, with the only difference being the type of eliminator used in step c.

[0142] Comparative Example 4-1: The replacement agent was changed from an NTA solution with a concentration of 0.02 mol / L (pH=6.2) to an EDTA solution with the same concentration and pH value.

[0143] Comparative Example 4-2: The excretion agent was replaced with HEDTA solution of the same concentration and pH value.

[0144] The experimental results are as follows:

[0145]

[0146] The results showed that when EDTA was used as a replacement agent, under high-temperature conditions of 75±2℃, the solubility of the complex formed by EDTA and trace amounts of alkaline earth metal ions that might remain in the solution decreased, leading to a local increase in turbidity within the column. The pressure drop of the ion exchange column abnormally increased from the normal 2.5-3.0 MPa to 4.5-5.0 MPa, indicating that its chemical compatibility under the specific high-temperature conditions of this invention was inferior to that of NTA. Although HEDTA's effect was close to that of NTA, its commercial price was about 3-5 times that of NTA, and the wastewater treatment difficulty was comparable. NTA exhibited excellent thermal stability and separation selectivity under the high-temperature system defined in this invention, while also taking into account the economics of industrial applications. This specific combination produced unexpected technical effects.

[0147] The inventors further investigated the effect of column operating pressure on the separation effect. While keeping other conditions the same as in Example 1, experiments were conducted by changing only the operating pressure of the ion exchange column. The results are as follows:

[0148]

[0149] Experiments show that when the pressure is below 2.0 MPa, it is insufficient to overcome the inherent resistance of the 30-60 μm particulate resin bed, easily leading to channeling and a sharp decrease in separation efficiency. When the pressure exceeds 5.0 MPa, some of the weaker mechanical resin particles rupture, and the fragments block the flow path and contaminate the product. Therefore, the preferred operating pressure range of 2.5-4.0 MPa in this invention is the key range to ensure high separation efficiency and long-term stable operation of the resin.

[0150] Compared with existing technologies, this method for preparing high-purity rare earth oxide materials uses extraction to complete high-throughput basic processing, which significantly reduces costs compared with ion exchange. Ion exchange is used for refining, which can ensure higher purity compared with extraction. Finally, precipitation not only achieves solid-liquid separation, but also shapes the microscopic physical morphology of the product. By combining multiple methods, the preparation goal of low cost and high expectations is achieved.

[0151] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing high-purity rare earth oxide materials, characterized in that, Includes the following steps: a. Raw material pretreatment and preliminary enrichment: After dissolving the rare earth concentrate raw material in hydrochloric acid, the pH of the solution is adjusted to 4.8-5.

1. The generated hydrolysis precipitate is removed by filtration, and then ammonium bicarbonate is added as a precipitant, so that the rare earth elements are collectively precipitated in the form of mixed carbonates to obtain mixed rare earth carbonates. In this process, the pH value is controlled to pre-precipitate and remove the hydrolysis precipitate of iron and aluminum impurities, thus avoiding the emulsification of the organic phase in subsequent processes. b. Separation and crude purification of the main body: The mixed rare earth carbonate obtained in step a is redissolved and the pH value is adjusted as feed solution and sent to a multi-stage series extraction tank. Through countercurrent extraction and washing process containing the extractant system, washing liquid and back-extraction agent, the rare earth elements are separated one by one to obtain a crude solution of the target single rare earth element with a relative purity of 99.0%-99.9%. c. Deep purification: The crude solution of the target single rare earth element obtained in step b is fed into an ion exchange column for ion exchange chromatography separation to remove residual trace impurities or adjacent rare earth elements, thereby obtaining a high-purity single rare earth solution; wherein, the operating temperature of the ion exchange chromatography separation is 75±2℃. d. Product conversion: The high-purity single rare earth solution obtained in step c is precipitated with high-purity oxalic acid or ammonium bicarbonate, then filtered, washed, and calcined at 800-1000℃ to finally obtain high-purity rare earth oxide powder products.

2. The method for preparing high-purity rare earth oxide materials as described in claim 1, characterized in that, In step a, the pH value of the solution is adjusted to 4.8-5.1 by adding ammonia or dilute alkali solution. The concentration of ammonium bicarbonate solution is 5%-10%, the molar ratio of ammonium bicarbonate to the total amount of rare earth oxides in the solution is 2.8-3.5:1, and the precipitation time is 1-2 hours.

3. The method for preparing high-purity rare earth oxide materials as described in claim 1, characterized in that, In step b, the extractant system is P507-kerosene or naphthenic acid-isooctanol-kerosene, the pH of the extractant solution is 4, the pH of the washing solution is 1.5, the stripping agent is hydrochloric acid or nitric acid, the single-stage mixing and clarification time in the extraction section is 10-12 minutes, the volume ratio of organic phase to aqueous phase is 20:1, and the ratio of the number of stages in the extraction tank, the washing section and the stripping section is 8:10:

7.

4. The method for preparing high-purity rare earth oxide materials as described in claim 1, characterized in that, In step c, macroporous micro-sulfonic acid cation exchange resin with a particle size of 30-60 μm is used for ion exchange chromatography separation, and aminetriacetic acid solution is used as a displacement agent to promote the migration of rare earth ions in the column and achieve separation.

5. The method for preparing high-purity rare earth oxide materials as described in claim 1, characterized in that, In step d, the pH value of the oxalic acid system is 3-6, the precipitation temperature is 20-80℃, the washing method is multiple washings with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

6. The method for preparing high-purity rare earth oxide materials as described in claim 1, characterized in that, In step d, the pH value of the ammonium bicarbonate system is 5.2-5.5, the precipitation temperature is 20-80℃, the washing method is multiple washing with high-purity water, the calcination temperature is 800-1000℃, and the calcination tool is a muffle furnace.

7. The method for preparing high-purity rare earth oxide materials as described in claim 4, characterized in that, The ion exchange chromatography separation is carried out in a pressure-resistant stainless steel column, with the operating pressure maintained at 2.5-4.0 MPa. Step c specifically includes: C1. The produced single rare earth solution is introduced from the top of the ion exchange column. The rare earth ions are adsorbed by the resin and an initial adsorption band is formed at the top of the ion exchange column. C2. A solution containing a displacement agent is introduced into the column. The displacement agent combines with the rare earth ions on the resin and promotes the rare earth ions to migrate downward in the ion exchange column. The displacement agent is an NTA solution. C3. Collect the outflowing solution at the outlet of the ion exchange column at different time intervals.

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