Process for preparing ultra-high-purity rare earth oxide by ion exchange method

Abstract

The invention relates to the technical field of rare earth hydrometallurgy, and discloses a process for preparing ultra-high-purity rare earth oxide by an ion exchange method, which comprises the following steps: loading monodisperse polystyrene sulfonic acid resin into a chromatographic column, and carrying out constant-temperature circulating pretreatment by using a pre-swelling solution containing urea and ammonium nitrate; preparing a rare earth feed liquid containing urea and with anions being nitrate radicals, introducing the rare earth feed liquid into the chromatographic column for adsorption saturation, and then connecting the rare earth feed liquid in series with the retardation column; carrying out displacement leaching by using a composite leaching solution in which ethylenediamine tetraacetic acid, 5-sulfosalicylic acid and urea are dissolved, and collecting target rare earth effluent in sections; and finally, adding a precipitant into the effluent for precipitation, and filtering, washing and firing to obtain the ultra-pure rare earth oxide. According to the invention, a urea swelling driven dynamic compensation system is constructed, and 10%-14% of monodisperse resin with high crosslinking degree is selected to cooperate with urea-ammonium nitrate pretreatment, so that low-pressure-drop operation at a high flow rate of 1.0 BV / h or above is realized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of rare earth hydrometallurgy, in particular to a process for preparing ultra-high-purity rare earth oxide by ion exchange method. BACKGROUND

[0002] Lutetium oxide and ytterbium oxide are key elements in yttrium group heavy rare earths, and are widely used in high-tech fields. For example, yttrium lutetium silicate scintillation crystal is a core component of a positron emission tomography instrument, and the purity of the raw material is extremely high. In addition, they are also important dopants for special laser glass and optical communication devices. These high-end application scenarios usually require the purity of lutetium oxide or ytterbium oxide products to reach 99.999% or above, and the impurity content needs to be strictly controlled at the level of one millionth, so as to ensure the light transmittance and luminous efficiency of the crystal.

[0003] Currently, ion exchange chromatography is mainly used in the industry to prepare high-purity heavy rare earths. This method uses the affinity difference between rare earth ions and ion exchange resin functional groups for separation, and is suitable for processing pairs of elements with extremely similar properties. In order to ensure the flow rate of the liquid in the production process and reduce the operating pressure, the existing process usually selects a polystyrene sulfonic acid resin with a crosslinking degree of 7% to 8% as the stationary phase. The elution system is usually an aqueous solution system with copper ion or hydrogen ion as the retarder. This process route is relatively mature, the operating conditions are mild, and it can meet the continuous production needs of general purity rare earth oxides.

[0004] However, with the increasing demand for product purity, the conventional process has limitations. Although low-crosslinking-degree resins have fast mass transfer, their skeleton structure is relatively loose, and they have insufficient recognition ability for lutetium and ytterbium, which have a very small difference in ionic radius, resulting in a low separation coefficient. If the crosslinking degree of the resin is simply increased to increase the selectivity, the dense network structure will significantly increase the mass transfer resistance, causing the diffusion rate of ions in the resin to decrease sharply, resulting in severe tailing of the chromatographic peak or even the inability to operate at an industrial flow rate. On the other hand, in a pure water solution environment, there is a stable hydration layer around the heavy rare earth ions, which weakens the difference in the small naked ion radius of lutetium and ytterbium, making it difficult for a single ligand to achieve efficient differentiation, resulting in a large overlap range at the interface between the two phases and low single extraction yield. In addition, the traditional high-concentration elution process usually directly discharges or simply neutralizes the waste liquid containing a large amount of organic ligand and inorganic salt, without realizing the closed-loop recovery of high-value complexing agents, resulting in high production costs and environmental pressure. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a process for preparing ultra-high purity rare earth oxide by ion exchange method, so as to solve the technical problems that in the existing heavy rare earth separation process, high separation precision and high industrial flow rate cannot be considered due to the contradiction between resin crosslinking degree and mass transfer resistance, the separation efficiency of adjacent elements is low due to the shielding effect of ion radius difference, and the production cost is high and the environmental protection pressure is large due to the recycling of organic ligand.

[0006] To achieve the above object, the application is implemented by the following technical scheme: a process for preparing ultra-high purity rare earth oxide by ion exchange method, comprising the following steps:

[0007] S1, monodisperse polystyrene sulfonic acid resin is loaded into a chromatographic column, and pre-swelling liquid is circulated through the resin bed layer under constant temperature conditions for pre-swelling treatment; the pre-swelling liquid is an aqueous solution containing urea and ammonium nitrate;

[0008] S2, rare earth raw materials are dissolved and prepared into a feed liquid, the feed liquid contains rare earth ions and urea, and the anion system is nitrate;

[0009] S3, the feed liquid is introduced into the chromatographic column for adsorption, and after saturation, the chromatographic column is connected in series with a blocking column;

[0010] S4, a composite eluent is used for displacement elution, and the target rare earth effluent is collected in sections; the water phase system of the composite eluent dissolves ethylenediaminetetraacetic acid, 5-sulfosalicylic acid and urea;

[0011] S5, a precipitating agent is added to the collected target rare earth effluent for precipitation, and after filtration, washing and calcination, ultra-high purity rare earth oxide is obtained.

[0012] By adopting the above technical scheme, the application realizes efficient separation of heavy rare earth elements by using the physical and chemical field coupling regulation mechanism. The specific action mechanism is as follows:

[0013] Firstly, the chaotropic effect of urea is used for kinetic compensation. In the pre-swelling step, high-concentration urea molecules act as a chaotropic agent to destroy the tetrahedral hydrogen bond network of water clusters, change the polarity and surface tension of the solvent, and promote the penetration of solvent molecules into the dense skeleton of high-crosslinking polystyrene-divinylbenzene resin. The solvent-induced swelling effect expands the microporous structure of the resin, and constructs a mesoscale mass transfer channel, so that the high-crosslinking resin has the mass transfer flux required for industrial high-flow production while maintaining high mechanical strength and high selectivity.

[0014] Secondly, the dehydrated thermodynamic separation environment is constructed. In the feed and elution system, the urea molecules competitively destroy the outer hydration shell of rare earth ions, remove part of the water molecules, and weaken the shielding effect of the hydration effect on the difference in ionic radius. This makes the rare earth ions participate in resin exchange and ligand complexation in a state closer to the naked ion, thereby restoring and amplifying the inherent ionic radius difference between adjacent heavy rare earth elements.

[0015] Finally, the dual-ligand synergy and steric screening. Ethylenediaminetetraacetic acid as the main ligand provides the basic separation ability, and 5-sulfosalicylic acid uses the rigid characteristics of its benzene ring structure as an auxiliary ligand. In the dehydrated environment, 5-sulfosalicylic acid produces a more obvious steric effect on the smaller heavy rare earth ions, inhibiting the tailing and re-adsorption of the difficult-to-elute components in the tail of the chromatographic band, improving the chromatographic peak shape, and improving the separation degree of the two-phase boundary.

[0016] Preferably, in the S1 step, the crosslinking degree of the monodisperse polystyrene sulfonic acid resin is 10% to 14%, the average particle size is 80 μm to 100 μm, and the particle size variation coefficient is less than 3%.

[0017] By adopting the above technical scheme, the high crosslinking degree of 10% to 14% gives the resin a higher sulfonic acid group density and a rigid skeleton, and improves the exchange capacity per unit volume and the selective recognition ability of the heavy rare earth; the monodisperse particle size distribution eliminates the fluid channel blockage caused by small particle filling, ensures the uniformity of the bed void ratio, and can maintain a low column bed pressure drop in cooperation with the pre-swelling process.

[0018] Preferably, in the S1 step, the concentration of urea in the pre-swelling solution is 2.0 to 4.0 mol / L, and the concentration of ammonium nitrate is 0.3 to 0.8 mol / L; the temperature of the constant temperature condition is 50 to 60°C, and the cycle processing time is 12 to 24 hours.

[0019] By adopting the above technical scheme, the urea solution in this concentration range can provide sufficient osmotic pressure and hydrogen bond breaking ability at 50 to 60°C, so that the resin skeleton is fully stretched to reach the swelling equilibrium; the addition of ammonium nitrate maintains the ionic strength of the system, preventing the resin from being damaged due to severe volume mutation during the swelling process.

[0020] Preferably, in the S2 step, the total concentration of rare earth ions in the feed solution is 25 to 40 g / L in terms of total rare earth oxide, the concentration of urea is 2.0 to 4.0 mol / L, and the pH value is 3.5 to 4.0.

[0021] By adopting the technical scheme, the pH value is controlled in the range of 3.5-4.0, which avoids the hydrolysis and precipitation of rare earth ions and ensures the effective adsorption capacity of the resin to the rare earth ions; and the addition of urea increases the solubility of the rare earth salt in the nitric acid system, preventing the local crystallization from plugging the pores when the high-concentration feed is used.

[0022] Preferably, in the S4 step, the specific composition and process conditions of the composite eluent meet the following characteristics: the concentration of ethylenediaminetetraacetic acid is 0.015-0.04 mol / L; the concentration of 5-sulfosalicylic acid is 0.005-0.02 mol / L; the concentration of urea is 2.0-4.0 mol / L; the pH value is adjusted to 8.0-8.8; and the column temperature during elution is controlled to 50-60°C.

[0023] By adopting the technical scheme, the chemical environment and the physical environment are simultaneously optimized by the composite formula. The specific concentration of urea maintains the dehydrated state during the elution process; ethylenediaminetetraacetic acid and 5-sulfosalicylic acid form complex compounds with heavy rare earth ions under weak alkaline and medium-temperature conditions, and the subtle property difference is converted into the macroscopic chromatographic retention time difference through the competitive complex mechanism.

[0024] Preferably, the molar concentration ratio of ethylenediaminetetraacetic acid to 5-sulfosalicylic acid in the composite eluent is 1.5-3:1.

[0025] By adopting the technical scheme, the specific ratio ensures that the dominant complexation of the main ligand and the steric modification of the auxiliary ligand are balanced. If the proportion of 5-sulfosalicylic acid is too low, the tailing cannot be effectively inhibited; and if the proportion is too high, the mixed complex may be too stable, which reduces the elution rate. Under this ratio, the best chromatographic peak symmetry can be obtained.

[0026] Preferably, the monodisperse polystyrene sulfonic acid resin is prepared by the following method: (1) using monodisperse polystyrene microspheres with an average particle size of 36.0-45.0 μm as seeds, swelling in an aqueous solution containing an emulsifier by adding a swelling agent; (2) adding a monomer mixture containing styrene, divinylbenzene and an initiator to continue swelling, wherein the percentage of pure divinylbenzene in the total mass of the monomers is controlled to be 10%-14%; (3) temperature polymerization, curing, washing and drying to obtain white balls; and (4) using concentrated sulfuric acid to perform a sulfonation reaction in the presence of a swelling agent to obtain the finished resin.

[0027] By adopting the technical scheme, the seed swelling method can accurately control the particle size and cross-linking degree distribution of the finished resin, ensure that each resin microsphere has a uniform internal microstructure, eliminate the mass transfer difference between particles, and improve the theoretical plate number of the chromatographic column.

[0028] Preferably, the step S5 further comprises a resource recycling process, specifically: adjusting the pH of the mother liquor after filtration and precipitation to 5.0-6.0, and pumping into a nanofiltration membrane system with a molecular weight cut-off of 100-200 Da for filtration; collecting the retentate of the nanofiltration system, and after supplementing ethylenediaminetetraacetic acid and 5-sulfosalicylic acid, recycling it as the preparation of the eluent in the step S4; and collecting the permeate of the nanofiltration system, and after neutralization, recycling it as a liquid fertilizer raw material.

[0029] By adopting the above technical scheme, the molecular sieving principle of the nanofiltration membrane is utilized to realize the precise separation of organic ligands and inorganic salts. The molecular weights of ethylenediaminetetraacetic acid and 5-sulfosalicylic acid are greater than the cut-off molecular weight, and they are recycled in the concentrated liquid, which significantly reduces the cost of reagents; and the molecular weights of urea and ammonium nitrate are smaller, and they pass through the membrane into the permeate, avoiding the discharge of high-COD wastewater, and realizing the recycling of reagents and the reduction of wastewater discharge.

[0030] Preferably, in the step S5, the precipitant is a saturated oxalic acid solution, and the amount of the precipitant added is 10%-20% more than the stoichiometric ratio, and the precipitation temperature is 55-65 DEG C.

[0031] By adopting the above technical scheme, the precipitation conditions can ensure complete precipitation of rare earth ions, form oxalic acid rare earth precipitates with coarse crystal form and easy filtration and washing, reduce impurity entrainment, and ensure the purity of the final oxide product.

[0032] Preferably, in the step S3, the adsorption flow rate is controlled to be 1.0-2.0 BV / h, and in the step S4, the elution flow rate is controlled to be 0.8-1.2 BV / h, and the pre-column pressure of the chromatographic column during the elution process is controlled to be 0.3-0.8 MPa.

[0033] By adopting the above technical scheme, under the premise of ensuring separation precision, a high flow rate operation is realized, the production cycle is greatly shortened, the productivity efficiency of unit resin is improved, and the advantages of the process in industrial application are embodied.

[0034] The application provides a process for preparing ultra-high-purity rare earth oxides by ion exchange.

[0035] 1. The application constructs a urea swelling driven kinetic compensation system, selects 10%-14% high cross-linking degree monodisperse resin in combination with urea-ammonium nitrate pretreatment, uses a chaotropic agent to expand the dense skeleton of the resin, establishes a mesoscopic transmission channel, realizes low pressure drop operation at a high flow rate of 1.0 BV / h or more, and overcomes the bottleneck of high flow resistance and long production cycle in the industrial application of high cross-linking degree media while ensuring high separation precision, compared with the compromise solution of selecting low cross-linking degree resin in the prior art to reduce mass transfer resistance.

[0036] 2. Adopting the strategy of full nitrate ion dissociation environment and double ligand steric elution, the hydration shielding effect of rare earth ions is weakened by urea, and the rigidity steric hindrance is introduced by 5-sulfosalicylic acid, which sharpens the chromatographic peak shape and inhibits the tailing of difficult elution components, so that the separation coefficient of lutetium / ytterbium is improved to 1.99, the single direct yield is more than 92%, compared with the traditional aqueous single ethylenediaminetetraacetic acid elution process, the problems of serious overlap in the junction area due to small difference in thermodynamic properties of adjacent elements, difficult to meet the product purity standard and need to return repeatedly are solved.

[0037] 3. The process integrates the nanofiltration membrane molecular sieving recovery module, which accurately shunts the macromolecular organic ligand and the small molecular inorganic salt according to the difference in molecular weight, realizes the closed loop circulation of expensive reagents such as ethylenediaminetetraacetic acid, the recovery rate is more than 87%, and the high concentration nitrogen-containing waste liquid is converted into fertilizer raw materials, which provides a green solution with resource recycling characteristics for the existing high concentration elution process, which has the problems of high reagent consumption, chemical oxygen demand exceeding standard of discharged waste liquid and other environmental protection and cost difficulties, and greatly reduces the production operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is the performance comparison chart of high crosslinking degree resin under different swelling systems of the test example of the application, wherein (a) is the volume swelling coefficient comparison column chart of the resin, (b) is the flow rate and pre-column pressure relationship curve chart;

[0039] Figure 2 It is the influence column chart of different simulated elution liquid systems on the lutetium / ytterbium separation factor of the test example of the application;

[0040] Figure 3 It is the lutetium / ytterbium separation chromatography flow curve comparison chart of the representative process of the test example of the application, wherein (a) shows the chromatography curve of example 1; (b) shows the chromatography curve of comparative example 3; (c) shows the chromatography curve of comparative example 1;

[0041] Figure 4 It is the single direct yield and production cycle comparison chart of different processes of the test example of the application;

[0042] Figure 5 It is the COD value comparison chart of the discharged liquid before and after nanofiltration treatment of the test example of the application. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the application will be described below in conjunction with the drawings of the application specification. Obviously, the described embodiments are only part of the embodiments of the application, not all. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0044] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0045] Lutetium oxide (CAS No. 12032-20-1), Ytterbium oxide (CAS No. 1314-37-0) and Thulium oxide (CAS No. 12036-44-1) are all rare earth oxide powders with a purity greater than 99.9%; Ethylenediaminetetraacetic acid (CAS No. 60-00-4) is a powder with a purity greater than 99.5%; 5-sulfosalicylic acid dihydrate (CAS No. 5965-83-3) is an analytical reagent with a purity greater than 99.0%; Urea (CAS No. 57-13-6) is an industrial grade product with a biuret content of less than 0.5%.

[0046] Styrene (CAS No. 100-42-5) is a polymerization grade monomer; Divinylbenzene (CAS No. 1321-74-0) is an industrial grade with a total divinylbenzene isomer content of 80%; Benzoyl peroxide (CAS No. 94-36-0) is a wet powder with a water content of about 30%; Polyvinyl alcohol (PVA-1788, CAS No. 9002-89-5); Sodium dodecylbenzenesulfonate (CAS No. 25155-30-0); Dibutyl phthalate (CAS No. 84-74-2); 1,2-Dichloroethane (CAS No. 107-06-2).

[0047] Nitric acid (CAS No. 7697-37-2), ammonia (CAS No. 1336-21-6), ammonium nitrate (CAS No. 6484-52-2), copper nitrate trihydrate (CAS No. 10031-43-3), oxalic acid dihydrate (CAS No. 6153-56-6) and concentrated sulfuric acid (CAS No. 7664-93-9) are all commercially available general reagents.

[0048] Preparation Example 1:

[0049] The present preparation example provides a method for preparing monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 12%, comprising the following steps:

[0050] (1) Seed preparation: uniform polystyrene seed microspheres are prepared by dispersion polymerization, and microspheres with an average particle size of 45.0 μm and a particle size variation coefficient of less than 3% are selected by sieving as seeds;

[0051] (2) Swelling: 10.0 g of the above polystyrene seed microspheres are dispersed in 500 mL of an aqueous solution containing 0.2 g of sodium dodecylbenzenesulfonate, 15.0 g of dibutyl phthalate is added, and the seed microspheres are fully absorbed with swelling agent under stirring at 150 rpm at 30°C for 12 hours;

[0052] (3) Polymerization: a monomer mixture was prepared, containing 85.0 g of styrene, 15.0 g of divinylbenzene (with a purity of 80%, equivalent to 12.0 g of pure divinylbenzene, accounting for 12% of the total mass of monomers), and 1.2 g of benzoyl peroxide; the monomer mixture was added to the emulsion of step (2), and stirring was continued at 30°C for 10 hours; then 500 mL of a 4% polyvinyl alcohol aqueous solution was added, and the temperature was raised to 78°C for constant temperature reaction for 12 hours, and then raised to 95°C for curing for 4 hours; the product was washed with hot water and subjected to ethanol Soxhlet extraction for 24 hours, and then vacuum dried to obtain monodisperse crosslinked polystyrene white balls;

[0053] (4) Sulfonation: 20.0 g of the dried white balls were put into 120 mL of concentrated sulfuric acid with a mass fraction of 98%, and 30 mL of 1,2-dichloroethane was added as a swelling agent, and stirring was continued at 105°C for 9 hours; after the reaction was completed, the product was washed to neutral by using a sulfuric acid concentration gradient dilution method, to obtain a finished resin.

[0054] It was detected that the average particle size of the resin was 100 μm, the particle size uniformity coefficient was 1.05, the crosslinking degree was 12%, and the total exchange capacity was 4.8 mmol / g (dry basis).

[0055] Preparation Example 2:

[0056] The preparation example provides a preparation method of monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 10%, including the following steps:

[0057] (1) Seed preparation: the steps were the same as those in Preparation Example 1;

[0058] (2) Swelling: the steps were the same as those in Preparation Example 1;

[0059] (3) Polymerization: a monomer mixture was prepared, containing 87.5 g of styrene, 12.5 g of divinylbenzene (with a purity of 80%, equivalent to 10.0 g of pure divinylbenzene, accounting for 10% of the total mass of monomers), and 1.2 g of benzoyl peroxide; the subsequent operation steps after adding the monomer mixture were the same as those in Preparation Example 1;

[0060] (4) Sulfonation: the steps were the same as those in Preparation Example 1.

[0061] It was detected that the average particle size of the resin was 100 μm, the particle size uniformity coefficient was 1.05, the crosslinking degree was 10%, and the total exchange capacity was 4.9 mmol / g (dry basis).

[0062] Preparation Example 3:

[0063] The preparation example provides a preparation method of monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 14%, including the following steps:

[0064] (1) Seed preparation: the procedure is the same as that in Preparation Example 1;

[0065] (2) Swelling: the procedure is the same as that in Preparation Example 1;

[0066] (3) Polymerization: a monomer mixture is prepared, containing 82.5 g of styrene, 17.5 g of divinylbenzene (with a purity of 80%, equivalent to 14.0 g of pure divinylbenzene, accounting for 14% of the total mass of monomers), and 1.2 g of benzoyl peroxide; the subsequent operation steps after the addition of the monomer mixture are the same as those in Preparation Example 1;

[0067] (4) Sulfonation: the procedure is the same as that in Preparation Example 1.

[0068] It is detected that the average particle size of the resin is 100 μm, the particle size uniformity coefficient is 1.06, the crosslinking degree is 14%, and the total exchange capacity is 4.6 mmol / g (dry basis).

[0069] Preparation Example 4:

[0070] The present preparation example provides a preparation method of monodisperse polystyrene sulfonic acid resin with an average particle size of 80 μm, including the following steps:

[0071] (1) Seed preparation: uniform polystyrene seed microspheres are prepared by dispersion polymerization, and microspheres with an average particle size of 36.0 μm and a particle size variation coefficient of less than 3% are selected by sieving as seeds;

[0072] (2) Swelling: 10.0 g of the above polystyrene seed microspheres are dispersed in 500 mL of an aqueous solution containing 0.2 g of sodium dodecylbenzenesulfonate, 12.0 g of dibutyl phthalate is added, and emulsification is carried out at 30°C with stirring at 150 rpm for 12 hours;

[0073] (3) Polymerization: a monomer mixture is prepared, containing 85.0 g of styrene, 15.0 g of divinylbenzene (with a purity of 80%, equivalent to 12.0 g of pure divinylbenzene, accounting for 12% of the total mass of monomers), and 1.2 g of benzoyl peroxide; the subsequent operation is the same as that in Preparation Example 1, and only the stirring speed is adjusted to 180 rpm to match the smaller particle size system;

[0074] (4) Sulfonation: the procedure is the same as that in Preparation Example 1.

[0075] It is detected that the average particle size of the resin is 80 μm, the particle size uniformity coefficient is 1.08, the crosslinking degree is 12%, and the total exchange capacity is 4.8 mmol / g (dry basis).

[0076] Example 1:

[0077] The present example provides a process for preparing ultra-high purity lutetium oxide based on ion exchange method, including the following steps:

[0078] (1) Stationary phase packing and pre-swelling: The monodisperse polystyrene sulfonic acid resin with 12% cross-linking degree and 100 μm average particle size prepared in Preparation Example 1 was packed into a 316L stainless steel middle pressure chromatographic column with a length-diameter ratio of 25:1, and was converted into ammonium type after being treated alternately with 2.0 mol / L nitric acid and 2.0 mol / L ammonia water; an aqueous solution containing 3.0 mol / L urea and 0.5 mol / L ammonium nitrate was prepared as a pre-swelling solution, and the column temperature was controlled at 55°C, and the solution was circulated through the resin bed at a flow rate of 1.5 BV / h for 18 hours to sufficiently open the high cross-linking degree skeleton of the resin;

[0079] (2) Preparation of raw material solution: A heavy rare earth concentrate (containing 60% lutetium oxide, 30% ytterbium oxide, and 10% thulium oxide) was dissolved in high-purity nitric acid, heated to chase the acid to a microcrystalline state, dissolved in deionized water, and urea was added, and the pH value was adjusted to 3.8 with ammonia water, and the chloride ion content was detected by silver nitrate titration to be less than 10 ppm; finally, a feed solution was obtained, in which the total concentration of rare earth ions was 30 g / L (based on the total amount of rare earth oxides), the concentration of urea was 3.0 mol / L, and the anion was a total nitrate system;

[0080] (3) Adsorption and blocking: The raw material solution was pumped into the adsorption column at a flow rate of 2.0 BV / h, and after adsorption saturation, it was connected in series with the blocking column; the blocking column was pre-converted into copper type, and the equilibrium solution was a mixed solution containing 3.0 mol / L urea and 0.03 mol / L copper nitrate trihydrate;

[0081] (4) Double-ligand gradient elution: A composite elution solution was prepared, and the solutes included 0.025 mol / L ethylenediaminetetraacetic acid, 0.01 mol / L 5-sulfosalicylic acid, and 3.0 mol / L urea, and the pH value was adjusted to 8.4 with ammonia water; the column temperature was kept constant at 55°C, the column outlet back pressure valve was adjusted to maintain the pressure before the column at 0.5 MPa, and the displacement elution was carried out at a flow rate of 1.0 BV / h; the online refractometer was used to monitor the effluent, and the effluent was collected in sections, and the section with a purity of lutetium of more than 99.999% was intercepted;

[0082] (5) Post-treatment and recovery: Excess 15% saturated oxalic acid dihydrate solution was added to the collected lutetium elution solution, and stirred at 60°C for 2 hours to precipitate, and after filtration, washing, and calcination at 1000°C, ultra-high purity lutetium oxide product was obtained; the pH value of the precipitate mother liquor was adjusted to 5.5, and after 0.1 μm precision filtration, it was pumped into a nanofiltration system (a roll type membrane module with a molecular weight cut-off of 150 Da was selected), and the operating pressure was controlled at 1.5 MPa; the cut-off liquid (rich in ethylenediaminetetraacetic acid and 5-sulfosalicylic acid) was supplemented with ammonia water and recycled for preparing the elution solution in step (4), and the permeate liquid (rich in urea and ammonium nitrate) was neutralized and used as a liquid fertilizer raw material.

[0083] Example 2:

[0084] The embodiment provides a process for preparing super-high-purity ytterbia based on an ion exchange method, and comprises the following steps.

[0085] (1) stationary phase filling and pre-swelling: the monodisperse polystyrene sulfonic acid resin prepared in the preparation example 2 and having a crosslinking degree of 10% and an average particle size of 100 μm is filled into a chromatographic column and converted into an ammonium type; an aqueous solution containing 2.0 mol / L urea and 0.3 mol / L ammonium nitrate is prepared as a pre-swelling solution, the column temperature is controlled to be 50°C, and the circulation treatment is performed at a flow rate of 2.0 BV / h for 12 hours;

[0086] (2) preparation of a raw material solution: ytterbium concentrate (ytterbia content is greater than 80%) is dissolved in nitric acid, and the treatment process is the same as that in the embodiment 1; finally, a feed solution is obtained, in which the total concentration of rare earth ions is 25 g / L (calculated according to the total amount of rare earth oxides), and the urea concentration is 2.0 mol / L;

[0087] (3) adsorption and blocking: the adsorption flow rate is controlled to be 1.5 BV / h; and the blocking column equilibration solution is a mixed solution containing 2.0 mol / L urea and 0.02 mol / L copper nitrate trihydrate;

[0088] (4) double-ligand gradient elution: a composite elution solution is prepared, the solutes of which include 0.015 mol / L ethylenediaminetetraacetic acid, 0.005 mol / L 5-sulfosalicylic acid and 2.0 mol / L urea, and the pH value is adjusted to 8.0 by using ammonia water; the column temperature is kept at 50°C, the column front pressure is maintained at 0.3 MPa, and the flow rate is controlled to be 1.2 BV / h; and the ytterbium effluent section with a purity greater than 99.999% is collected in sections;

[0089] (5) post-treatment and recovery: the operation steps are the same as those in the embodiment 1, the operation pressure of the nanofiltration system is adjusted to be 1.2 MPa, the cut-off liquid is recycled, and the permeate is recovered as a fertilizer raw material.

[0090] Embodiment 3

[0091] The embodiment provides a process for preparing super-high-purity thulia oxide based on an ion exchange method, and comprises the following steps.

[0092] (1) stationary phase filling and pre-swelling: the monodisperse polystyrene sulfonic acid resin prepared in the preparation example 3 and having a crosslinking degree of 14% and an average particle size of 100 μm is filled into a chromatographic column and converted into an ammonium type; an aqueous solution containing 4.0 mol / L urea and 0.8 mol / L ammonium nitrate is prepared as a pre-swelling solution, the column temperature is controlled to be 60°C, and the circulation treatment is performed at a flow rate of 1.0 BV / h for 24 hours;

[0093] (2) Preparation of feed solution: The terbium concentrate (the content of terbium oxide is greater than 50%) was dissolved in nitric acid, and the treatment process was the same as that in Example 1; finally, the feed solution was obtained, in which the total concentration of rare earth ions was 40 g / L (calculated based on the total amount of rare earth oxides), and the concentration of urea was 4.0 mol / L;

[0094] (3) Adsorption and retardation: the adsorption flow rate was controlled to be 1.0 BV / h; the equilibrium solution of the retardation column was a mixed solution containing 4.0 mol / L urea and 0.05 mol / L copper nitrate trihydrate;

[0095] (4) Double-ligand gradient elution: a composite elution solution was prepared, the solutes of which included 0.04 mol / L ethylenediaminetetraacetic acid, 0.02 mol / L 5-sulfosalicylic acid and 4.0 mol / L urea, and the pH value was adjusted to 8.8 by using ammonia water; the column temperature was constant at 60°C, the pre-column pressure was maintained at 0.8 MPa, and the flow rate was controlled to be 0.8 BV / h; the terbium outflow section with a purity greater than 99.999% was collected in sections;

[0096] (5) Post-treatment and recovery: the operation steps were the same as those in Example 1, and the operation pressure of the nanofiltration system was adjusted to be 2.0 MPa to ensure the permeation flux under a high-concentration solution.

[0097] Example 4:

[0098] The embodiment provides a process for preparing ultra-high-purity rare earth oxide based on an ion exchange method, which comprises the following steps:

[0099] (1) Stationary phase packing and pre-swelling: the resin selection and pre-swelling operation parameters are completely the same as those in Example 1;

[0100] (2) Preparation of feed solution: the same as Example 1;

[0101] (3) Adsorption and retardation: the same as Example 1;

[0102] (4) Double-ligand gradient elution: a composite elution solution was prepared, the ligand concentration of which was adjusted to be 0.03 mol / L ethylenediaminetetraacetic acid and 0.015 mol / L 5-sulfosalicylic acid (the molar proportion of the auxiliary ligand 5-sulfosalicylic acid was improved), and the urea concentration was maintained at 3.0 mol / L, and the pH value was adjusted to 8.5 by using ammonia water; the column temperature was constant at 55°C, the pre-column pressure was maintained at 0.5 MPa, and the flow rate was controlled to be 1.0 BV / h; under this formula, the space steric hindrance effect of 5-sulfosalicylic acid is used to further sharpen the boundary chromatographic band of lutetium and ytterbium;

[0103] (5) Post-treatment and recovery: the same as Example 1.

[0104] Example 5:

[0105] The embodiment provides a process for preparing ultra-high purity rare earth oxide based on ion exchange method, comprising the following steps:

[0106] (1) Stationary phase packing and pre-swelling: the monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 12% and an average particle size of 80 μm prepared in Preparation Example 4 is packed; the pre-swelling liquid formula and temperature are the same as in Example 1, and the flow rate is adjusted to 1.0 BV / h for 20 hours of circulation treatment;

[0107] (2) Preparation of raw material liquid: the same as in Example 1;

[0108] (3) Adsorption and blocking: the same as in Example 1;

[0109] (4) Double-ligand gradient elution: the eluent formula is completely the same as in Example 1; due to the increase of bed resistance caused by the decrease of resin particle size, the pre-column pressure is increased to 0.65 MPa to maintain a constant flow rate of 1.0 BV / h, and the rest of the temperature control and pH parameters are the same as in Example 1;

[0110] (5) Post-treatment and recovery: the same as in Example 1.

[0111] Comparative Example 1:

[0112] Compared with Example 1, the existing industrial conventional ion exchange process is simulated, and the difference lies in that:

[0113] Stationary phase: replaced with a commercially available conventional polystyrene sulfonic acid resin with a crosslinking degree of 7% and a Gaussian distribution (non-uniform particle size) of particle size;

[0114] System environment: no urea is added in the pre-swelling liquid, raw material liquid and eluent, and only deionized water system is used;

[0115] Ligand: no auxiliary ligand 5-sulfosalicylic acid is added in the eluent, and only 0.025 mol / L ethylenediaminetetraacetic acid (EDTA) is used as a single complexing agent;

[0116] Feed concentration: due to the lack of urea solubilization, in order to prevent the precipitation of ethylenediaminetetraacetic acid rare earth complex from causing column plugging, the rare earth concentration of the raw material liquid is reduced to 8 g / L, and the rest of the flow rate and temperature control remains the same.

[0117] Comparative Example 2:

[0118] Compared with Example 1, the difference lies in that: no urea is added in the pre-swelling liquid, raw material liquid and eluent, and only deionized water is used as a solvent, and an equivalent amount of ammonium nitrate is added in the eluent to maintain the ionic strength, and the rest of the resin parameters and process steps are the same.

[0119] Comparative Example 3:

[0120] The difference compared with Example 1 is that: no auxiliary ligand 5-sulfosalicylic acid is added in the eluent, only 0.035 mol / L of ethylenediaminetetraacetic acid is used as a single complexing agent (the total ligand concentration is kept roughly the same), and the rest is the same.

[0121] Comparative Example 4:

[0122] The difference compared with Example 1 is that: the nitric acid / nitrate in the whole system is replaced by hydrochloric acid / chloride; specifically, hydrochloric acid is used to dissolve the raw materials, ammonium chloride and copper chloride are used to replace ammonium nitrate and copper nitrate, and ammonia / hydrochloric acid buffer system is used to adjust the pH, and the rest is the same.

[0123] Comparative Example 5:

[0124] The difference compared with Example 1 is that: the resin used is replaced by a common polystyrene sulfonic acid resin with a crosslinking degree of 12% but a Gaussian distribution of particle size (non-uniform particle size), with an average particle size of about 100 μm and a particle size uniformity coefficient greater than 1.5, and the rest is the same.

[0125] Comparative Example 6:

[0126] The difference compared with Example 1 is that: the resin used is replaced by a monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 7%, and the rest is the same.

[0127] Comparative Example 7:

[0128] The difference compared with Example 1 is that: the nanofiltration fractionation in step (5) is cancelled, and the mother liquor after precipitation is directly discharged after simple neutralization without ligand recovery and recycling, and the rest is the same.

[0129] Test Example 1:

[0130] Test purpose: By comparing the swelling properties and hydrodynamic characteristics of high crosslinking degree resins under different pretreatment systems, the effectiveness of urea-ammonium nitrate system in improving resin mass transfer performance and realizing high flow rate and low pressure drop operation is verified.

[0131] The test steps are as follows:

[0132] 1. Two portions of dry monodisperse polystyrene sulfonic acid resin with a crosslinking degree of 12% prepared in Preparation Example 1 were selected, and each portion was accurately weighed 50.0 g.

[0133] 2. The first batch of resin, corresponding to the pretreatment conditions of Example 2, was placed in a constant temperature water bath shaker, 500 mL of deionized water was added, the temperature was controlled at 55°C, and it was shaken and soaked for 18 hours. The second batch of resin, corresponding to the pretreatment conditions of Example 1, was placed in the same constant temperature device, 500 mL of an aqueous solution containing 3.0 mol / L urea and 0.5 mol / L ammonium nitrate was added, and it was treated at 55°C for 18 hours.

[0134] 3. After treatment, the average particle size of the wet resin under both conditions was measured using a laser particle size analyzer, and the wet apparent volume was calculated based on the bulk density. The volume swelling coefficient is based on the dry basis volume, and its calculation formula is: (wet volume after swelling - dry volume) / dry volume × 100%.

[0135] 4. Pack the two portions of resin after swelling equilibrium into a 316L stainless steel high-pressure chromatography column with an inner diameter of 50 mm and a column height of 1250 mm, and control the packing height to be consistent.

[0136] 5. Connect the high-pressure constant flow pump to the column pressure sensor, and place the entire chromatography system in a 55℃ constant temperature chamber.

[0137] 6. Pass pure water through the first resin column, and pass a mobile phase containing 3.0 mol / L urea and 0.5 mol / L ammonium nitrate through the second resin column. Gradually adjust the flow rate, setting the flow rate gradient sequentially to 0.5 BV / h, 0.8 BV / h, 1.0 BV / h, 1.2 BV / h, 1.5 BV / h, and 2.0 BV / h.

[0138] 7. Run the test for 30 minutes at each flow rate point, and record the pressure data before the column after the pressure reading stabilizes. If the system pressure exceeds the safety threshold of 2.5 MPa or a flow path blockage occurs, stop the test and record it as system overpressure.

[0139] The test data is shown in Table 1:

[0140] Table 1: Comparison of swelling properties and hydrodynamic data of highly crosslinked resins under different pretreatment systems

[0141]

[0142] Conclusion: Based on Table 1 and Figure 1The volume swelling coefficient of the resin swollen only by pure water is only 12.4% under the same high cross-linking degree matrix, while the volume swelling coefficient of the resin treated by the urea-ammonium nitrate system reaches 38.6%. This shows that in a pure water environment, the 12% high cross-linking degree leads to strong binding force of the polystyrene skeleton, and it is difficult for water molecules to penetrate into the deep layer of the microspheres, and the resin is in a relatively dense shrinkage state. In the system constructed in the present application, high-concentration urea as a strong ionizing agent destroys the tetrahedral hydrogen bond structure of water molecules, reduces the surface tension of the solvent, and interacts with the polar sulfonic acid groups in the resin skeleton, generating an osmotic pressure difference that overcomes the elastic shrinkage force caused by high cross-linking degree, so that the dense resin microspheres undergo significant physical volume expansion.

[0143] The difference in fluid mechanics data further confirms the influence of the above-mentioned mechanism on the process feasibility. The pressure of Comparative Example 2 has reached 0.42 MPa at a low flow rate of 0.5 BV / h, and the pressure increases exponentially as the flow rate increases. When the flow rate reaches 1.2 BV / h, the pressure has broken through 2.0 MPa, which cannot meet the requirements of continuous high flux for industrial production. This is because the resin is not fully swollen, the porosity is low, and the effective mass transfer channel is narrow, so the shear resistance of the fluid in the resin bed is too large. In contrast, Example 1 shows good linear fluid mechanics characteristics within the full flow rate range, and even at a high flow rate of 2.0 BV / h, the pre-column pressure is still stable within a controllable range of 0.84 MPa. This shows that the swelling effect induced by urea successfully constructs a mesoscale fluid transport channel inside the resin and between particles, achieving dynamic compensation of the mass transfer resistance of high cross-linking degree resin. Through the pre-swelling process of the present application, the inherent contradiction between high selectivity and high flow resistance of high cross-linking degree resin is solved, and the physical basis for stable operation of high cross-linking degree resin under industrial high flow rate conditions is established.

[0144] Test Example 2:

[0145] Test purpose: Through static equilibrium experiments, the distribution coefficients and separation factors of lutetium and ytterbium ions in different simulated elution systems are determined to verify the effectiveness of the urea-biligand cooperative system in the present application in amplifying the property differences of adjacent heavy rare earths from the thermodynamic point of view.

[0146] The test steps are as follows:

[0147] 1. The ammonium type monodisperse polystyrene sulfonic acid resin prepared in Preparation Example 1 was selected and dried to constant weight under vacuum.

[0148] 2. Four different simulated elution systems were prepared:

[0149] Example 1 simulated system: containing 0.025 mol / L ethylenediaminetetraacetic acid, 0.01 mol / L 5-sulfosalicylic acid, 3.0 mol / L urea, and adjusting the pH to 8.4 with ammonia water.

[0150] Comparative Example 3: This system was used to study the effect of the bidentate ligand and contained 0.035 mol / L ethylenediaminetetraacetic acid and 3.0 mol / L urea, and the pH was adjusted to 8.4 using ammonia water.

[0151] Comparative Example 2: This system was used to study the effect of urea and contained 0.025 mol / L ethylenediaminetetraacetic acid and 0.01 mol / L 5-sulfosalicylic acid, but did not contain urea, and the pH was adjusted to 8.4 using ammonia water.

[0152] Comparative Example 1: This system was a conventional aqueous single-ligand control and contained 0.025 mol / L ethylenediaminetetraacetic acid, but did not contain urea or 5-sulfosalicylic acid, and the pH was adjusted to 8.4 using ammonia water.

[0153] 3. A single rare earth nitrate stock solution containing 1.0 g / L of lutetium oxide and 1.0 g / L of ytterbium oxide was prepared, respectively.

[0154] 4. A number of conical flasks with stoppers were prepared, and 1.00 g of dry resin was accurately weighed into each flask, and 50.0 mL of one of the four simulated elution solutions described above was added to each flask, respectively.

[0155] 5. 5.0 mL of the lutetium oxide stock solution or the ytterbium oxide stock solution was accurately transferred into the conical flasks corresponding to each system, respectively, to form eight series of experiments.

[0156] 6. After all the conical flasks were sealed, they were placed in a constant temperature shaker at 55°C and shaken at a speed of 150 rpm for 48 hours to ensure that the solid-liquid two phases reached exchange and complexation equilibrium.

[0157] 7. After the equilibrium was reached, the conical flasks were taken out and allowed to stand until they were clear. The supernatant was filtered through a 0.22 μm filter membrane, and the concentration of the rare earth ions remaining in the liquid phase was determined by inductively coupled plasma mass spectrometry.

[0158] 8. According to material balance calculations, the distribution coefficient (Kd) and the separation factor (a) were calculated. The definition of the distribution coefficient is: Kd = (the amount of rare earth ions in the resin phase / the mass of the resin) / (the amount of rare earth ions in the liquid phase / the volume of the solution). The definition of the separation factor is: a = the distribution coefficient of ytterbium / the distribution coefficient of lutetium.

[0159] The test data are shown in Table 2:

[0160] Table 2: Distribution coefficients of lutetium / yterbium and separation factors in different simulated elution solution systems

[0161]

[0162] Conclusion: According to Table 2 and Figure 2The data show that in the conventional aqueous single-ligand system (Comparative Example 1), the distribution coefficients of lutetium and ytterbium are both low and close to each other, and the separation factor obtained is only 1.15, indicating that the difference in the thermodynamic properties of the two elements cannot be effectively amplified under this condition. When 5-sulfosalicylic acid is introduced into the aqueous phase (Comparative Example 2), the separation factor is increased to 1.27, indicating that the double ligand has a certain synergistic effect, but the increase is limited.

[0163] The core mechanism of the present application is reflected in the comparison between the system of Example 1 and the other systems. Comparing the system of Comparative Example 2 with the system of Example 1, both of which use double ligands, but after the introduction of urea in the system of Example 1, the separation factor jumps from 1.27 to 1.99. This is because high-concentration urea as a chaotropic agent destroys the outer hydration shell of lutetium and ytterbium ions, weakens the shielding effect of the hydration effect on the difference in ionic radii, and makes rare earth ions participate in complexation in a state closer to bare ions, thereby amplifying their inherent property differences. At the same time, the distribution coefficient of ytterbium ions is significantly improved, while the distribution coefficient of lutetium ions decreases slightly, indicating that the dehydrated environment is conducive to the recognition of the property differences by the resin.

[0164] Comparing the system of Comparative Example 3 with the system of Example 1, both of which contain urea, but the system of Example 1 uses double ligands, while the system of Comparative Example 3 only uses single EDTA. The separation factor of the system of Example 1 (1.99) is significantly higher than that of the system of Comparative Example 3 (1.48). This proves that in the dehydrated environment, the rigid benzene ring structure of 5-sulfosalicylic acid produces a more effective steric hindrance effect on the smaller lutetium ions, further inhibiting their interaction with the resin, thereby reducing the distribution coefficient of lutetium and sharpening the separation effect.

[0165] In summary, the urea-double ligand synergistic system constructed in the present application significantly increases the separation factor of adjacent heavy rare earth elements from a thermodynamic point of view through the dual effects of dehydrating and steric hindrance, providing a chemical basis for efficient chromatographic separation.

[0166] Test Example 3:

[0167] Test purpose: Through dynamic chromatographic separation experiments, the chromatographic parameters of lutetium / ytterbium separation under different process conditions are compared to comprehensively evaluate the actual effects of the present application in terms of separation efficiency, peak symmetry, and reduction of component overlap.

[0168] The test steps are as follows:

[0169] 1. Perform complete ion exchange chromatographic separation operations according to the process conditions of Examples 1 to 5 and Comparative Examples 1, 3, 4, 5, and 6, respectively. All experiments use a chromatographic column with a length-diameter ratio of 25:1, and the same heavy rare earth concentrate is used as the raw material liquid.

[0170] 2. In the S4 elution step, an online refractive index detector and a UV-Vis spectrophotometer are connected at the outlet of the chromatographic column, continuously recording the refractive index and absorbance at a specific wavelength of the effluent, and a chromatographic effluent curve is plotted in real time.

[0171] 3. At the same time, an automatic fraction collector is used to collect the effluent in separate parts at fixed time intervals (e.g., every 5 minutes).

[0172] 4. After the separation is completed, samples are taken from each part of the collected effluent, and the concentrations of lutetium and ytterbium are analyzed by ICP-MS.

[0173] 5. Based on the obtained chromatographic curve and the concentration data of each part of the effluent, the following parameters are calculated:

[0174] Resolution (Rs): calculated according to the retention times and peak widths of the two main peaks of lutetium and ytterbium, with the formula: Rs = 2 x (retention time of ytterbium - retention time of lutetium) / (peak width of lutetium + peak width of ytterbium).

[0175] Tailing factor (Tf): taking the lutetium peak as an example, the ratio of the width of the latter half to the former half at 10% of the peak height is measured.

[0176] Theoretical plate number (N): also taking the lutetium peak as an example, with the formula: N = 5.54 x (retention time of lutetium / half-peak width) 2 .

[0177] Overlap ratio of the boundary region: the region where the relative purities of lutetium and ytterbium are both less than 99.9% is defined as the boundary region, and the percentage of the volume of this region to the total elution liquid volume is calculated.

[0178] The test data are shown in Table 3:

[0179] Table 3: Comparison of chromatographic separation performance parameters under different process conditions

[0180]

[0181] Conclusion: According to the data in Table 3 and Figure 3 , the resolutions of Examples 1-5 are all above 1.7, which is much higher than all the comparative examples, especially compared with Comparative Example 1 (0.96) of the conventional process, a leap from partial overlap to baseline separation is achieved. This is directly attributed to the fact that the system of the present application amplifies the component differences in thermodynamics.

[0182] The comparison of the tailing factor can particularly explain the effect of the dual ligand. The tailing factor of Example 1 is 1.06, close to the ideal symmetrical peak (Tf = 1.0), while the tailing factor of Comparative Example 3 using only single EDTA is 1.38, and the peak shape presents obvious asymmetric tailing. This confirms that the steric hindrance effect generated by the rigid structure of 5-sulfosalicylic acid effectively inhibits the non-ideal adsorption-desorption process of the difficult-to-elute components (such as lutetium) at the trailing edge of the chromatographic band, thereby sharpening the peak shape.

[0183] The comparison of the theoretical plate number reflects the superiority of the stationary phase. The monodisperse resin used in Example 1 has a theoretical plate number of 3580, while the theoretical plate number of Comparative Example 5 using the same crosslinking degree but Gaussian distribution of particle size is only 1860. This shows that the monodisperse resin eliminates the vortex diffusion and mass transfer path difference caused by uneven particle size, ensuring the homogeneity of the bed and significantly improving the column efficiency.

[0184] The overlap ratio of the junction zone is a key indicator of process economy. The overlap ratio of Example 1 is only 7.8%, meaning that more than 92% of the eluent can directly enter the product collection or retarder recovery stage. While the overlap ratio of Comparative Example 1 is as high as 23.4%, meaning that a large amount of raw materials need to be recycled for further processing, greatly reducing the single-pass yield and production efficiency. Comparative Example 4 of the chloride ion system (18.2%) and Comparative Example 6 of the low crosslinking degree resin (13.1%) also show a higher overlap ratio, further highlighting the advantages of the full nitrate ion liquid environment combined with high crosslinking degree resin of the present application.

[0185] In summary, the dynamic chromatography experimental data systematically prove the advancement of the process of the present application from four dimensions of resolution, peak shape symmetry, column efficiency and component overlap. Through the synergistic effect of kinetic compensation driven by urea swelling, thermodynamic separation environment of dehydrating and dual ligand steric washing, the present application successfully solves the problems of peak tailing and serious overlap in the junction zone commonly existing in the separation of heavy rare earths, and realizes the unity of high separation efficiency and high production efficiency.

[0186] Test Example 4:

[0187] Test purpose: By comparing the product quality indicators and key efficiency parameters in the production process of different processes, the comprehensive advantages of the present application in preparing ultra-high purity rare earth oxides are verified from the perspective of industrial application.

[0188] The test steps are as follows:

[0189] 1. According to the process conditions of Examples 1 to 3 and Comparative Examples 1 and 6, respectively, complete ion exchange chromatography separation, precipitation, filtration, washing and full-flow operation of burning to prepare the final rare earth oxide product. All experiments use an equal amount of the same batch of heavy rare earth concentrate as the starting material.

[0190] 2. Sampling the final oxide product prepared in each batch, using high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for full element analysis, focusing on the main content of target rare earth elements and the content of adjacent rare earth impurities (such as ytterbium and thulium in the lutetium product, lutetium and thulium in the ytterbium product, etc.) and other non-rare earth impurities, and finally calculating the product purity.

[0191] 3. According to the results of the segmented collection in step S4, the mass of the effluent part corresponding to the rare earth oxide that can be directly used for precipitation, calcination and finally obtained as a product of qualified purity is accurately weighed. The ratio of this mass to the total mass of target rare earth elements in the input raw material solution is the single direct yield.

[0192] 4. Record the total time from the start of adsorption in step S3 to the complete flow-out of the target component at the end of the elution in step S4 for each experimental group. This time is defined as a complete production cycle.

[0193] The test data are shown in Table 4:

[0194] Table 4: Comparison of product quality and production efficiency indicators of different processes

[0195]

[0196] Conclusion: According to the data in Table 4 and Figure 4 , the process proposed in the present application shows obvious superiority in product quality and production efficiency.

[0197] In terms of product purity, the product purity prepared in Examples 1-3 all reached more than 99.999%, and the total amount of adjacent rare earth impurities was controlled within 10 ppm, meeting the application requirements of ultra-high purity materials. In contrast, the product purity of Comparative Example 1 using the conventional process was only 99.96%, and the impurity content far exceeded the target specification, which could not be used for high-end applications. Even if Comparative Example 6 used a monodisperse resin but with a lower crosslinking degree, the product purity could only reach 99.995%, and the impurity content was nearly 10 times that of the examples. This shows that the high crosslinking degree resin used in the present application combined with the dehydrated-resistance cooperative elution system has higher selectivity and separation precision for heavy rare earth elements with very similar properties.

[0198] The advantages of the present application are more prominent in terms of the key indicators of production efficiency, namely single-pass recovery rate and production cycle. The single-pass recovery rate of Example 1 reaches 94.2%, while the low-crosslinking degree of Comparative Example 6 and the conventional process of Comparative Example 1 are only 85.3% and 71.7%, respectively. The improvement in yield is essentially a direct reflection of the improvement in the efficiency of chromatographic separation. Less overlap of the boundary zone means less backflow material, thereby reducing the waste of material and time. In terms of production cycle, Example 1 only takes 76 hours to complete a cycle, while Comparative Example 1, which runs at a low flow rate, takes 124 hours. The present application realizes stable operation of high-crosslinking degree resin at high flow rate through urea swelling technology, thereby improving the production efficiency by more than 60% under the premise of ensuring separation precision.

[0199] In summary, this series of data confirms that the process of the present application can stably produce ultra-high purity rare earth oxides that meet the needs of high-end applications. By combining the high selectivity of high-crosslinking degree resin with the high mass transfer flux brought by the urea system, the present application not only solves the technical bottleneck of product purity not meeting the standards, but also significantly improves the overall economic efficiency of the process by improving the single-pass yield and shortening the production cycle.

[0200] Test Example 5:

[0201] Test purpose: By analyzing the chemical composition and cost-effectiveness of the eluate mother liquor before and after nanofiltration treatment, the effectiveness of the resource recovery system in Step S5 of the present application is verified, and its role in reducing production costs and environmental load is evaluated.

[0202] The test steps are as follows:

[0203] 1. Collect the mother liquor obtained after oxalic acid precipitation and filtration in Step S5 of Example 1 and Comparative Example 7. The initial volume and chemical composition of the two mother liquors are theoretically similar.

[0204] 2. For the mother liquor of Example 1, follow its process description: first adjust the pH value to 5.5, then pump into the nanofiltration system with a molecular weight cut-off of 150 Da after 0.1 μm precision filtration, and concentrate and separate at an operating pressure of 1.5 MPa.

[0205] 3. Collect the nanofiltration retentate and nanofiltration permeate obtained after treatment of Example 1, respectively. The mother liquor of Comparative Example 7 is used as the control group for direct discharge without any treatment.

[0206] 4. The concentrations of ethylenediaminetetraacetic acid (EDTA) and 5-sulfosalicylic acid (5-SSA) in the initial mother liquor and nanofiltration retentate are determined by high performance liquid chromatography (HPLC). The formula for calculating the ligand recovery rate is: recovery rate = (retentate volume x retentate ligand concentration) / (initial mother liquor volume x initial mother liquor ligand concentration) x 100%.

[0207] 5. According to the national standard method (such as potassium dichromate method), the chemical oxygen demand (COD) values of the nanofiltration permeate obtained after the treatment of Example 1 and the direct discharge mother liquor of Comparative Example 7 are determined respectively.

[0208] 6. Based on the current market price (assuming the price of EDTA is 10 yuan / kg and the price of 5-SSA is 35 yuan / kg), combined with the measured recovery rate of the ligand, the reagent cost saved for producing one kilogram of ultra-high purity lutetium oxide product is calculated. Cost saving = (EDTA consumption x recovery rate x price) + (5-SSA consumption x recovery rate x price).

[0209] The test data are shown in Table 5:

[0210] Table 5: Resource recovery and environmental protection benefit data of nanofiltration recovery process

[0211]

[0212] Conclusion: According to the data in Table 5 and Figure 5 , the nanofiltration recovery process adopted in the application has achieved obvious results in resource utilization and environmental protection.

[0213] In terms of resource recovery, the nanofiltration system is used to treat the precipitation mother liquor in Example 1, achieving efficient recovery of expensive organic ligands. The recovery rate of ethylenediaminetetraacetic acid reaches 97.4%, and the recovery rate of 5-sulfosalicylic acid reaches 96.8%. This means that most of the ligands can be recycled for the preparation of subsequent batches of eluent, greatly reducing the amount of fresh reagents. Based on this recovery rate, the cost calculation shows that the production of one kilogram of lutetium oxide product can directly save reagent cost of about 185.3 yuan. In contrast, Comparative Example 7 directly discharges the mother liquor containing all ligands, resulting in complete waste of resources.

[0214] In terms of environmental protection, the effect of nanofiltration treatment is also obvious. The COD value of the mother liquor directly discharged by Comparative Example 7 is as high as 52,600 mg / L, which belongs to high-concentration organic wastewater. If it is directly discharged, it will cause serious pollution to the water body, and subsequent deep treatment will need to be invested at a high cost to meet the standards. After nanofiltration treatment in Example 1, most of the organic ligands are intercepted and recovered, and the COD value of the permeate finally discharged is reduced to 8,500 mg / L. Although this permeate (rich in urea and inorganic salts) still needs to be further treated or used as a fertilizer, its main organic pollution load is reduced by about 84% compared with the original mother liquor. This proves that the nanofiltration step is not only a key link in resource recovery, but also an effective means of wastewater pretreatment and reducing the pressure of end-of-pipe treatment.

[0215] In summary, the data of Test Example 5 verifies the necessity and superiority of the step S5 of the present application from both economic and environmental dimensions. The introduction of the nanofiltration recovery system converts the expensive ligand consumed once in the traditional rare earth separation into recyclable production materials, constructing a closed-loop green process route, which not only significantly reduces the production cost, but also greatly reduces the environmental footprint of the process, in line with the requirements of sustainable industrial development.

[0216] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications, changes, omissions, substitutions, and equivalents will now occur to one of ordinary skill in the art having the benefit of this disclosure. Therefore, the scope of the application is not to be limited to the preferred embodiments. Rather, the scope of the application is to be defined as by the following claims and their equivalents.

Claims

1. A process for the preparation of ultra-high purity rare earth oxides by ion exchange method, characterized in that, The method comprises the following steps: S1, loading monodisperse polystyrene sulfonic acid resin into a chromatographic column, and performing pre-swelling treatment by circulating a pre-swelling solution through the resin bed under constant temperature conditions; the pre-swelling solution is an aqueous solution containing urea and ammonium nitrate; S2, dissolving rare earth raw materials to prepare a feed solution containing rare earth ions and urea, and the anion system is nitrate; S3, feeding the feed solution into the chromatographic column for adsorption, and connecting the chromatographic column with a blocking column in series after saturation; S4, performing displacement elution using a composite elution solution, and collecting target rare earth effluent in sections; the water phase system of the composite elution solution dissolves ethylenediaminetetraacetic acid, 5-sulfosalicylic acid and urea; S5, adding a precipitating agent to the collected target rare earth effluent for precipitation, and obtaining ultra-high purity rare earth oxide through filtration, washing and calcination.

2. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In the step S1, the cross-linking degree of the monodisperse polystyrene sulfonic acid resin is 10% to 14%, the average particle size is 80 μm to 100 μm, and the particle size variation coefficient is less than 3%.

3. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In the step S1, the concentration of urea in the pre-swelling solution is 2.0 to 4.0 mol / L, and the concentration of ammonium nitrate is 0.3 to 0.8 mol / L; the temperature of the constant temperature condition is 50 to 60 ℃, and the circulation treatment time is 12 to 24 hours.

4. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In the step S2, the total concentration of rare earth ions in the feed solution is 25 to 40 g / L in terms of total rare earth oxide, the concentration of urea is 2.0 to 4.0 mol / L, and the pH value is 3.5 to 4.

0.

5. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In the step S4, the specific composition and process conditions of the composite elution solution meet the following characteristics: The concentration of ethylenediaminetetraacetic acid is 0.015 to 0.04 mol / L; The concentration of 5-sulfosalicylic acid is 0.005 to 0.02 mol / L; The concentration of urea is 2.0 to 4.0 mol / L; The pH value is adjusted to 8.0 to 8.8; The column temperature during elution is controlled to be 50 to 60 ℃.

6. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 5, characterized in that, The molar concentration ratio of ethylenediaminetetraacetic acid to 5-sulfosalicylic acid in the composite elution solution is 1.5 to 3:

1.

7. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 2, characterized in that, The monodisperse polystyrene sulfonic acid resin is prepared by the following method: (1) using monodisperse polystyrene microspheres with an average particle size of 36.0 to 45.0 μm as seeds, swelling in an aqueous solution containing an emulsifier by adding a swelling agent; (2) adding a monomer mixture containing styrene, divinylbenzene and an initiator for continuous swelling, wherein the percentage of pure divinylbenzene in the total mass of monomers is controlled to be 10% to 14%; (3) warming polymerization, curing, washing and drying to obtain white balls; (4) using concentrated sulfuric acid to perform sulfonation reaction in the presence of a swelling agent to obtain the finished resin.

8. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, The step S5 further includes resource recovery treatment, specifically: Adjusting the pH value of the mother liquor after filtration and precipitation to 5.0 to 6.0, and pumping into a nanofiltration membrane system with a molecular weight cut-off of 100 to 200 Da for filtration; Collecting the cut-off liquid of the nanofiltration system, adding ethylenediaminetetraacetic acid and 5-sulfosalicylic acid, and then recycling it for the preparation of the elution solution in the step S4; Collecting the permeate of the nanofiltration system, neutralizing it, and recycling it as a liquid fertilizer raw material.

9. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In step S5, the precipitant is saturated oxalic acid solution, the amount of which is 10% to 20% more than the stoichiometric ratio, and the precipitation temperature is 55 to 65 ℃.

10. The process for preparing ultra-high purity rare earth oxide by ion exchange method according to claim 1, characterized in that, In step S3, the adsorption flow rate is controlled to be 1.0 to 2.0 BV / h, and in step S4, the elution flow rate is controlled to be 0.8 to 1.2 BV / h, and the pre-column pressure of the chromatographic column during the elution process is controlled to be 0.3 to 0.8 MPa.

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