Process method for preparing superfine medium-heavy rare earth oxide

Abstract

The invention provides a process method for preparing superfine medium and heavy rare earth oxides, and belongs to a rare earth hydrometallurgy separation process. The method comprises the following steps: taking a medium-heavy rare earth salt solution and a carbonate precipitant as raw materials, and carrying out feeding reaction in stages under the conditions of heating and stirring: carrying out first-stage reaction in a manner of synchronously and oppositely adding according to a specific molar feeding ratio, and carrying out heat preservation and aging; after crystals appear, supplementing the raw materials, adjusting the molar ratio, and carrying out a second-stage reaction; and carrying out suction filtration, washing, drying and calcining on the obtained slurry to obtain the superfine medium-heavy rare earth oxide. Wherein the molar feeding ratio of the rare earth ions to the bicarbonate radicals in the first-stage reaction is 1: (4-7), and the molar ratio of the rare earth ions to the bicarbonate radicals in the reaction system is increased to 1: (2.5-3.5) in the second-stage reaction. The method is low in cost, simple in process and small in filtering difficulty in actual operation, and the obtained product is fine in particle, good in dispersion and high in purity and can be industrially produced on a large scale.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of rare earth hydrometallurgy separation process, and particularly relates to a process method for preparing superfine medium and heavy rare earth oxides. BACKGROUND

[0002] Rare earth oxides are compounds formed by lanthanide elements and 17 kinds of rare earth elements such as scandium and yttrium. With its unique optical, electrical, magnetic and catalytic properties, it has become an indispensable strategic functional material in the modern industrial system. Among them, medium and heavy rare earth elements (atomic number ≥ 64, covering gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, ytterbium Yb, lutetium Lu and yttrium Y) have an irreplaceable core value in the fields of new energy equipment, cutting-edge national defense technology and information technology due to their special 4f electron layer configuration and strong spin-orbit coupling effect. Since medium and heavy rare earth elements are less abundant than light rare earth elements in the earth's crust, they are more difficult to mine and refine, so their strategic value is higher, which has given rise to the strategic position of "industrial vitamin". High-dispersion medium and heavy rare earth oxides (particle size 1-500 nanometers) prepared by nanotechnology will have a qualitative leap in their physical and chemical properties. Such materials have deeply empowered the frontiers of permanent magnet motors, solid-state batteries, high-energy lasers and other cutting-edge fields, driving global high-end manufacturing into a new era of "nanoscale precision control". According to the forecast of the International Materials Union, by 2030, the market size of nanosized medium and heavy rare earth materials will account for 35% of the total amount of rare earth applications, and will become a key technology point in the technological competition among major powers.

[0003] Currently, traditional processes usually use oxalate and carbonate precipitation methods to obtain rare earth oxides, which have many shortcomings: the cost of oxalate precipitant is high, and it is toxic, and the cost of acid wastewater treatment is high; although carbonate is economical and environmentally friendly, the instantaneous burst nucleation often generates amorphous or colloidal rare earth carbonate precipitates, which have poor filtration and unstable composition, and the oxides after calcination are prone to agglomeration. In addition, the traditional process has weak targeting for obtaining medium and heavy rare earth oxides, and the process method for obtaining micron-sized to sub-micron-sized and nanosized medium and heavy rare earth oxide particles needs to be developed.

[0004] Therefore, there is an urgent need to provide a new method to easily control the synthesis of superfine medium and heavy rare earth oxide particles to overcome the shortcomings of the prior art. SUMMARY

[0005] The present application aims to provide a process for preparing ultra-fine medium and heavy rare earth oxides to solve the problems of the prior art. The present application is based on the difference in crystallization activity of rare earth carbonate at a specific molar ratio, and uses a staged feeding strategy to achieve the goals of crystallization and particle control: first, a first-stage reaction is carried out at a high molar ratio to induce rapid nucleation; when the crystallization signs of the precipitate are monitored, the raw materials are added in time to the equimolar region to enter the second-stage reaction, which inhibits crystal growth and promotes the formation of fine particle precipitates. The addition of a dispersant can further improve the dispersibility of the particles. The obtained rare earth carbonate precursor is easy to separate solid-liquid, and after washing, drying and calcining, rare earth oxides with low impurity content, small particle size, good dispersibility and high purity are obtained. The method is simple, low in cost and suitable for industrial production.

[0006] The present application provides a process for preparing ultra-fine medium and heavy rare earth oxides, comprising the following steps:

[0007] S1. Under heating and stirring conditions, a first-stage reaction is carried out by feeding rare earth salt solution and carbonate precipitant as raw materials in a synchronous manner, wherein the molar feeding ratio of rare earth ions to bicarbonate is 1:(4-7). After the reaction is completed, aging is carried out. The rare earth salt solution contains one or more medium and heavy rare earth elements;

[0008] S2. After the rare earth carbonate appears crystallization signs during aging, rare earth salt solution is added to increase the molar ratio of rare earth ions to bicarbonate in the reaction system to 1:(2.5-3.5). After the addition of the material, a second-stage reaction is carried out under certain temperature and stirring conditions. After the reaction is completed, the slurry is collected;

[0009] S3. The slurry obtained in S2 is filtered and washed until there is no chloride ion in the filtrate, and then dried to obtain a rare earth carbonate precursor. The ultra-fine medium and heavy rare earth oxide is obtained by calcining the precursor.

[0010] The ultra-fine medium and heavy rare earth oxide according to the present application refers to a medium and heavy rare earth oxide with a median particle size of less than 2 μm. In the S2 step, the rare earth carbonate appears crystallization signs during aging, specifically, when the precipitate and the solution are clearly layered and the pH value changes from rising to falling. In the S2 step, the molar ratio of the reaction system is controlled by adding raw materials. The rare earth salt solution includes a rare earth salt solution containing one or more medium and heavy rare earth elements, or a salt solution doped with other light rare earth ions with at least one medium and heavy rare earth as the main component.

[0011] In fact, the crystallization activity of rare earth carbonate and the inert region show different nucleation and crystallization growth characteristics. At 50℃, the high ratio (molar ratio of rare earth ions to bicarbonate is 4-7) region is the crystallization active region of yttrium carbonate and other medium and heavy rare earth carbonates, while the equal ratio region or near equal ratio region is non-active, and a long time is needed to realize crystallization. Therefore, the present application adopts a staged feeding reaction, the first stage is carried out at a high ratio, and when it is monitored that the precipitation begins to have certain crystallization signs, the second stage is immediately entered, the rare earth solution is added to the equal ratio reaction, and then continuous stirring and the addition of dispersing agent are carried out, so as to further slow down the crystallization speed of the non-crystallization active region, so that the finally generated precipitation particles are small and have good dispersing performance.

[0012] Optionally, the medium and heavy rare earth elements include yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0013] Optionally, the anions of the rare earth salt solution include at least one of chloride ions, nitrate ions, sulfate ions and acetate ions.

[0014] In fact, the rare earth salt solution can contain other rare earth ions, that is, a soluble inorganic and organic salt solution doped with other light rare earth ions mainly with at least one medium and heavy element.

[0015] Optionally, the carbonate precipitant includes one of sodium carbonate, ammonium carbonate, sodium bicarbonate and ammonium bicarbonate.

[0016] Optionally, the concentration of the rare earth salt solution is 0.1-1.5 mol / L, preferably 0.5-1.0 mol / L.

[0017] Optionally, the concentration of the carbonate precipitant is 0.5-2.0 mol / L, preferably 1.0-1.5 mol / L.

[0018] Optionally, the temperature of the first stage reaction in S1 is 40-70℃.

[0019] Optionally, the temperature of the second stage reaction in S2 is 10-90℃, and the time is 0.1-12 h. In fact, in the staged feeding reaction, after the end of the two-stage reaction, the water content in the precipitation is reduced and the viscosity is lowered, so that the solid-liquid separation is easy, and the agglomeration caused by the generation of a large amount of amorphous colloidal particles at the beginning is avoided, so that the surface is rough and difficult to filter.

[0020] Optionally, in the S2 step, a dispersing agent is added after the completion of feeding, and the dispersing agent includes at least one of PVP-K30, PEG-4000, triammonium citrate, ammonium polyacrylate and sodium hexametaphosphate. The dispersing agent can inhibit the crystallization growth of the particles, so that small particle rare earth oxide powder with better dispersing performance is obtained.

[0021] Optionally, the dispersant is added in an amount of 0.05-2wt%, preferably 1.0-1.5wt%. The mass percentage of the dispersant refers to the mass ratio of the dispersant to the total rare earth carbonate precipitate after the two-stage feeding.

[0022] Optionally, the washing in S3 includes water washing until no chloride ions are present in the filtrate or alcohol washing after the water washing until no chloride ions are present in the filtrate, and the water temperature of the water washing is 20-100℃. The alcohol washing is beneficial to preventing the occurrence of hard agglomeration, and the ultrafine rare earth carbonate precursor is usually obtained by drying in a 55-65℃ oven after the washing by suction filtration.

[0023] Optionally, the calcination temperature in S3 is 400-1100℃, preferably 600-900℃.

[0024] Optionally, in the step S3, the ultrafine medium and heavy rare earth oxide obtained by calcination is subjected to ball milling for 0.5-3h, preferably 1-2h, and then is subjected to dispersion and ultrasonic treatment to obtain highly dispersed nanometer rare earth oxide. The particle size of the highly dispersed nanometer medium and heavy rare earth oxide is 1-500nm.

[0025] Due to the use of the above scheme, the present application has the following beneficial effects:

[0026] (1) The present application realizes the leap of the nucleation and crystallization growth process by the two-stage feeding and the regulation of the crystallization activity, and obtains the ultrafine medium and heavy rare earth oxide under a high reactant concentration, thereby solving the problems of easy agglomeration of the product and difficult solid-liquid separation in the traditional method. In some embodiments, the medium and heavy rare earth oxide prepared by the present application has high purity (>99.998%), small median particle size (less than 1μm), good dispersibility and easy filtration, and has superior comprehensive performance.

[0027] (2) In the process provided by the present application, the carbonic precursor is obtained at normal pressure and low temperature, without the need of relying on high-pressure hydrothermal equipment, and the process is simple and low in cost.

[0028] (3) The method of the present application can further regulate and optimize the particle size and dispersibility of the product by simply adding a dispersant and subjecting the obtained powder to ball milling after calcination. The medium and heavy rare earth oxide particles are reduced from microns to nanometers, and highly dispersed nanometer rare earth oxide is obtained, thereby meeting the requirements of the application fields with more stringent requirements on the particle size of the material. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 FIG. 1 is a diagram showing the changes of the pH values of the different rare earth salt solutions in the aging process in Example 1, wherein (a) is YCl3, (b) is TbCl3, (c) is LaCl3, and (d) is CeCl3.

[0030] Figure 2 SEM images of rare earth carbonates obtained in different stages of Example 1, wherein (a) to (d) are SEM images of rare earth carbonates obtained in the first stage (i.e. during the heat preservation aging until the appearance of crystals) of YCl3, TbCl3, LaCl3, CeCl3, respectively, and (a1) to (d1) are SEM images of rare earth carbonates obtained in the second stage of YCl3, TbCl3, LaCl3, CeCl3, respectively;

[0031] Figure 3 SEM images of oxide products obtained in different molar ratios of YCl3to NH4HCO3in the first stage of Example 2, wherein (a) to (c) correspond to the first stage of YCl3to NH4HCO3in the molar ratio of 1:2.5, 1:5, 1:6, respectively; 3+ SEM images of oxide products obtained in different molar ratios of YCl3to NH4HCO3in the first stage of Example 2, wherein (a) to (c) correspond to the first stage of YCl3to NH4HCO3in the molar ratio of 1:2.5, 1:5, 1:6, respectively; 3+ The molar ratios of YCl3to NH4HCO3are 1:2.5, 1:5, 1:6, respectively;

[0032] Figure 4 SEM images of oxide products obtained in different molar ratios of YCl3to NH4HCO3in the first stage of Example 2, wherein (a) to (c) correspond to the first stage of YCl3to NH4HCO3in the molar ratio of 1:2.5, 1:5, 1:6, respectively; 3+ Particle size distribution of oxide products obtained in different molar ratios of YCl3to NH4HCO3in the first stage of Example 2;

[0033] Figure 5 Particle size distribution of oxide products obtained in different stirring reaction temperatures in the second stage of Example 3;

[0034] Figure 6 Particle size distribution of oxide products obtained in different stirring reaction times in the second stage of Example 4;

[0035] Figure 7 XRD spectra of rare earth carbonates (a) obtained in the first stage of Example 4, rare earth carbonates (b) obtained in the second stage of stirring reaction for 5h, and calcined products (c);

[0036] Figure 8 SEM images and particle size distribution of oxide products obtained in Example 5;

[0037] Figure 9SEM images of oxide products obtained in Example 6, wherein (a) 0.5 mol / L YCl3and 0.5 mol / L NH4HCO3were used as raw materials, (b) 0.8 mol / L YCl3and 0.8 mol / L NH4HCO3were used as raw materials, (c) 1.0 mol / L YCl3and 1.0 mol / L NH4HCO3were used as raw materials, (d) 1.3 mol / L YCl3and 1.3 mol / L NH4HCO3were used as raw materials, (e) 1.5 mol / L YCl3and 1.5 mol / L NH4HCO3were used as raw materials, (f) 0.5 mol / L YCl3and 1.5 mol / L NH4HCO3were used as raw materials, and (g) 1.5 mol / L YCl3and 0.5 mol / L NH4HCO3were used as raw materials;

[0038] Figure 10 Particle size distribution of oxide products obtained in Example 7 using different dispersants;

[0039] Figure 11 Particle size distribution of oxide products obtained in Example 8 using different mass ratios of ammonium citrate to Y2(CO3)3, wherein the mass ratios were 0.5:100, 1.0:100, 1.5:100, and 2.0:100, respectively;

[0040] Figure 12 Changes in pH of the system during aging of different rare earth salt solutions in Example 9, wherein (a) is GdCl3, (b) is DyCl3, (c) is ErCl3, and (d) is YbCl3;

[0041] Figure 13 Particle size distribution of oxide products obtained in Example 9 using different rare earth salt solutions as raw materials;

[0042] Figure 14 Changes in pH of the system during aging of mixed rare earth solutions in Example 10;

[0043] Figure 15 Particle size distribution of oxide products obtained in Example 10 using different calcination temperatures, wherein the temperatures were 600°C (a), 700°C (b), 800°C (c), 900°C (d), 1000°C (e), and 1100°C (f), respectively;

[0044] Figure 16 Particle size distribution of products obtained in Example 11 using different ball milling times;

[0045] Figure 17 Particle size distribution of products obtained in Example 11 after 1 h of ball milling and addition of different amounts of ammonium citrate dispersant;

[0046] Figure 18TEM image of the product obtained by ball milling for 1 h in Example 11. DETAILED DESCRIPTION

[0047] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings thereof by those skilled in the art to which the present application belongs. The present application will be specifically described below in conjunction with the embodiments, but the embodiments and the protection scope of the present application are not limited to the following embodiments.

[0048] Example 1

[0049] Under the condition of stirring in a water bath at 50℃, 15 mL of 1 mol / L YCl3, TbCl3, LaCl3 and CeCl3 solution respectively and 75 mL of 1 mol / L ammonium bicarbonate solution (the molar ratio of rare earth to ammonium bicarbonate is 1:5) were added to four beakers in a synchronous manner, and after the addition was completed, the solution was aged until the crystallization of rare earth carbonate occurred, that is, the precipitation and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing (see Figure 1 ), the morphology of the rare earth carbonate precipitate at this time was observed by electron scanning microscopy, which is shown in Figure 2 (a) to (d); and 10 mL of 1 mol / L YCl3, TbCl3, LaCl3 and CeCl3 solution was added to the rare earth solution respectively to make the molar ratio of rare earth to ammonium bicarbonate 1:3, and after the addition was completed, the solution was continuously stirred at 50℃ for 1 h. After the reaction was completed, the solid was washed by filtration with deionized water until the filtrate was clear when it was added dropwise into 1 mol / L AgNO3 solution (that is, there was no obvious chloride ion in the filtrate), and the solid was dried in a 60℃ oven to obtain the rare earth carbonate precursor, the morphology of which is shown in Figure 2 (a1) to (d1).

[0050] The crystallization conversion of rare earth carbonate can be judged by measuring the pH change of the solution during the precipitation process. The above results prove that for terbium and yttrium which are medium and heavy rare earths, the above method can obtain rare earth carbonate precipitate particles with obviously reduced morphology and size, and the median particle size is less than 1 μm, while for lanthanum and cerium which are light rare earths, the above method cannot obtain fine particle products.

[0051] Example 2

[0052] 50℃ water bath stirring conditions 30 mL, 15 mL, 12.5 mL 1 mol / L YCl3 solution respectively with 75 mL 1 mol / L ammonium bicarbonate solution (Y 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:2.5, 1:5, 1:6, respectively, and was added to three beakers in a synchronous manner. After the addition was completed, the solution was aged until the yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing. At this time, 15 mL of 1 mol / L ammonium bicarbonate solution, 10 mL of 1 mol / L YCl3 solution, and 12.5 mL of 1 mol / L YCl3 solution were added to the solution, respectively. 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:2.5, 1:5, 1:6, respectively, and was added to three beakers in a synchronous manner. After the addition was completed, the solution was aged until the yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing. At this time, 15 mL of 1 mol / L ammonium bicarbonate solution, 10 mL of 1 mol / L YCl3 solution, and 12.5 mL of 1 mol / L YCl3 solution were added to the solution, respectively. Figure 3 、 Figure 4 .

[0053] The results prove that: the one-stage reaction is set in the low ratio region of Y 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:2.5, 1:5, 1:6, respectively, and was added to three beakers in a synchronous manner. After the addition was completed, the solution was aged until the yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing. At this time, 15 mL of 1 mol / L ammonium bicarbonate solution, 10 mL of 1 mol / L YCl3 solution, and 12.5 mL of 1 mol / L YCl3 solution were added to the solution, respectively.

[0054] Table 1 Comparison of the filtration performance of the precursors under different reaction conditions

[0055]

[0056] Example 3

[0057] 50℃ water bath stirring conditions 30 mL, 15 mL, 12.5 mL 1 mol / L Y(NO3)3 solution respectively with three 75 mL 1 mol / L sodium bicarbonate solution (Y 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:2.5, 1:5, 1:6, respectively, and was added to three beakers in a synchronous manner. After the addition was completed, the solution was aged until the yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing. At this time, 15 mL of 1 mol / L ammonium bicarbonate solution, 10 mL of 1 mol / L YCl3 solution, and 12.5 mL of 1 mol / L YCl3 solution were added to the solution, respectively. 3+The molar ratio of the ammonium bicarbonate was 1:2.9, and after the feeding was completed, the reaction system was transferred to a 30°C, 50°C, and 90°C water bath, respectively, and stirred for 1 hour. After the reaction was completed, the solid was washed by filtration with deionized water (the washing speed of the precursor by filtration is shown in Table 1) until the mixed solution remained clear (i.e., no obvious chloride ions in the filtrate) when the filtrate was added dropwise into a 1 mol / L AgNO3 solution. The solid was dried in a 60°C oven to obtain the rare earth carbonate precursor. The precursor was calcined at 700°C for 3 hours to obtain the oxide. The morphology and particle size of the oxide are shown in Figure 5 .

[0058] The results prove that: after the yttrium solution is added and the reaction is continued at different temperatures, the particle size of the product is slightly affected. At a medium temperature of 50-60°C, the filtration performance is poor. In comparison, at a high temperature or at room temperature of 30°C, the particle size is smaller, the energy consumption is lower, and the filtration performance is better, especially at room temperature or at a low temperature, the median particle size is less than 1 μm.

[0059] Example 4

[0060] Three 15 mL 0.5 mol / L Y2(SO4)3 solutions were added to three 75 mL 1 mol / L ammonium bicarbonate solutions (Y 3+ The molar ratio of the ammonium bicarbonate was 1:5, and after the feeding was completed, 10 mL of 0.5 mol / L Y2(SO4)3 solution was added to the Y 3+ The molar ratio of the ammonium bicarbonate was 1:3.1, and after the feeding was completed, the reaction system was transferred to a 30°C water bath and stirred for 1, 5, and 12 hours. After the reaction was completed, the solid was washed by filtration with deionized water until the mixed solution remained clear (i.e., no obvious chloride ions in the filtrate) when the filtrate was added dropwise into a 1 mol / L AgNO3 solution. The solid was dried in a 60°C oven to obtain the rare earth carbonate precursor. The precursor was calcined at 500°C for 3 hours to obtain the oxide. Specifically, the particle size of the oxide products obtained when the one-stage reaction was completed and the two-stage stirring reaction time was 1 hour, 5 hours, and 10 hours is shown in Figure 6 ; the XRD spectra of the precursor (a) before the one-stage reaction was completed, the precursor (b) after the two-stage stirring reaction for 5 hours, and the calcined product (c) are shown in Figure 7 .

[0061] The results show that: after adding yttrium solution, the small particle product can be obtained after a period of stirring. The particle size of the product at the end of the reaction is larger than 10 μm; the particle size of the product is significantly reduced after stirring for 1 h, and the median particle size is less than 1 μm; the particle size of the product is not significantly reduced and tends to be stable by continuing to extend the stirring reaction time. XRD analysis shows that the phase of the precipitate in the reaction system is always yttrium carbonate of water-rhombic yttrium type, and the phase of the calcined product is yttrium oxide.

[0062] Example 5

[0063] Under the condition of 50 °C water bath stirring, 15 mL of 1 mol / L YCl3 solution and 75 mL of 1 mol / L ammonium bicarbonate solution (Y 3+ : ammonium bicarbonate = 1:5) are added to a beaker in a synchronous manner, and after the addition is completed, the reaction system is aged until the yttrium carbonate crystals appear, i.e., the precipitate and the solution are obviously layered, and the pH value of the reaction system changes from increasing to decreasing, then 10 mL of 1 mol / L YCl3 solution is added to Y 3+ : ammonium bicarbonate = 1:3, and after the addition is completed, the reaction system is transferred to a 30 °C water bath and aged for 5 h. Filtration is performed, and the filtrate is washed with deionized water until the mixed solution of the filtrate and 1 mol / L AgNO3 solution remains clear (i.e., there is no obvious chloride ion in the filtrate), and then the solid is dried in a 60 °C oven to obtain the rare earth carbonate precursor. The oxide is obtained by calcining the precursor at 600 °C for 3 h, and the morphology and particle size of the oxide are shown in Figure 8 .

[0064] The results show that: after adding yttrium solution in the second stage, no stirring is performed, but direct aging is performed, which can form crystalline bodies with large particle sizes, and the particle size is larger than 10 μm.

[0065] Example 6

[0066] Under the condition of 55 °C water bath stirring, 15 mL of 0.5 mol / L, 15 mL of 0.8 mol / L, 15 mL of 1.0 mol / L, 15 mL of 1.3 mol / L, 15 mL of 1.5 mol / L, 15 mL of 1.5 mol / L, and 15 mL of 0.5 mol / L YCl3 solution are added to 75 mL of 0.5 mol / L, 75 mL of 0.8 mol / L, 75 mL of 1.0 mol / L, 75 mL of 1.3 mol / L, 75 mL of 1.5 mol / L, 75 mL of 1.5 mol / L, and 75 mL of 0.5 mol / L ammonium bicarbonate solution (Y 3+molar ratio of 1:5) were added to five beakers in a synchronous manner. After the addition was completed, the reaction system was aged until yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously separated, and the pH value of the reaction system changed from increasing to decreasing. At this time, 10 mL of 1 mol / L YCl3 solution was added to Y 3+ The molar ratio of yttrium chloride and ammonium bicarbonate was 1:3. After the addition was completed, the reaction system was transferred to a 40°C water bath and stirred for 5 h. After the reaction was completed, the solid was washed by filtration with deionized water until the mixed solution remained clear after the filtrate was added dropwise to 1 mol / L AgNO3 solution (i.e., there was no obvious chloride ion in the filtrate). The solid was dried in a 60°C oven to obtain a rare earth carbonate precursor. The precursor was calcined at 400°C for 3 h to obtain an oxide. The morphology of the oxide is shown in FIG. 1. Figure 9 .

[0067] The results show that when the yttrium chloride solution and the precipitant ammonium bicarbonate are at a relatively low concentration, large particle agglomerates are generated, which is not conducive to the preparation of fine particles. When the yttrium chloride solution and the precipitant ammonium bicarbonate are at a relatively high concentration, fine particles are also not prepared. The relatively suitable concentration range is that the concentration of the precipitant is 1.0-1.5 M, and the concentration of the yttrium chloride solution is 0.5-1.0 M.

[0068] Example 7

[0069] Five 15 mL 1 mol / L YCl3 solutions and five 75 mL 1 mol / L ammonium bicarbonate solutions (Y 3+ The molar ratio of yttrium chloride and ammonium bicarbonate was 1:5. After the addition was completed, the reaction system was aged until yttrium carbonate crystals appeared, i.e., the precipitate and the solution were obviously separated, and the pH value of the reaction system changed from increasing to decreasing. At this time, 10 mL of 1 mol / L YCl3 solution was added to Y 3+The molar ratio of YCl3 and ammonium bicarbonate was 1:5, and 10 mL of 1 mol / L YCl3 solution was added to the reaction system when the pH value of the reaction system changed from increasing to decreasing. Figure 10 .

[0070] These results show that adding dispersants immediately after adding yttrium solution can inhibit subsequent growth and obtain smaller particles, and the median particle size can be less than 0.5 μm.

[0071] Example 8

[0072] Four 15 mL 1 mol / L YCl3 solutions and four 75 mL 1 mol / L ammonium bicarbonate solutions (Y 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:5, and 10 mL of 1 mol / L YCl3 solution was added to the reaction system when the pH value of the reaction system changed from increasing to decreasing. 3+ The molar ratio of YCl3 and ammonium bicarbonate was 1:5, and 10 mL of 1 mol / L YCl3 solution was added to the reaction system when the pH value of the reaction system changed from increasing to decreasing. Figure 11 .

[0073] The results show that too much dispersant will cause bridging flocculation and re-agglomeration of particles, and too little dispersant will not have a significant effect due to insufficient wrapping of the particle surface. The best effect is obtained when the mass ratio of TAC to Y2(CO3)3 is 1.0:100, the product D50 is less than 500 nm, has the characteristics of high dispersion and nanometerization, and the product purity is high.

[0074] The relative purity of rare earth and the content of impurities of the product with the mass ratio of ammonium citrate:Y2(C03)3 of 1.0:100 were detected according to GB 12690 series, and the results are shown in Table 2. The purity of Y2O3 of the product is >99.998%.

[0075] Table 2 Relative content of rare earth and content of impurity ions (%)

[0076]

[0077] Example 9

[0078] Under the condition of stirring in a water bath at 50°C, 15 mL of 1 mol / L GdCl3, DyCl3, ErCl3 and YbCl3 solution and 75 mL of 1 mol / L ammonium bicarbonate solution (the molar ratio of rare earth to ammonium bicarbonate is 1:5) were added to four beakers in a synchronous and opposite manner. After the addition was completed, the solution was aged until the crystallization of rare earth carbonate occurred, i.e. the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing (pH=9.5) Figure 12 ). Then, 10 mL of 1 mol / L GdCl3, DyCl3, ErCl3 and YbCl3 solution was added to the solution to make the molar ratio of rare earth to ammonium bicarbonate 1:3, and 0.0444 g of ammonium citrate (the mass ratio of ammonium citrate to RE2(C03)3 is about 0.7:100) was added. Then, the solution was stirred in a water bath at 30°C for 5 h. After the reaction was completed, the solid was filtered and washed with deionized water until the mixed solution of the filtrate and 1 mol / L AgNO3 solution remained clear (i.e. there was no obvious chloride ion in the filtrate). The solid was dried in a 60°C oven to obtain a rare earth carbonate precursor. The precursor was calcined at 600°C for 3 h to obtain an oxide. The particle size of the oxide is shown in Table 3. Figure 13 .

[0079] These examples further prove that under the same conditions, all middle and heavy rare earths can be prepared into fine particle rare earth oxides with D90 less than 700 nm and D50 less than 400 nm.

[0080] Example 10

[0081] Under the condition of stirring in a water bath at 50°C, 15 mL of 1 mol / L mixed rare earth solution (14.85 mL of 1 mol / L YCl3+0.15 mL of 1 mol / L CeCl3) and 75 mL of 1 mol / L ammonium bicarbonate solution (the molar ratio of rare earth to ammonium bicarbonate is 1:5) were added to a beaker in a synchronous and opposite manner. After the addition was completed, the solution was aged until the crystallization of rare earth carbonate occurred, i.e. the precipitate and the solution were obviously layered, and the pH value of the reaction system changed from increasing to decreasing (pH=9.5) Figure 14), 10 mL of mixed rare earth solution (9.9 mL of 1 mol / L YCl3+ 0.1 mL of 1 mol / L CeCl3) was added to the reaction system to make the molar ratio of rare earth to ammonium bicarbonate 1:3, and 0.0444 g of ammonium citrate was added (the mass ratio of ammonium citrate to RE2(CO3)3 was about 1.0:100), and then the reaction system was transferred to a 30°C water bath for stirring reaction for 5 h. After the reaction was completed, the solid was washed by filtration with deionized water until the mixed solution of the filtrate and 1 mol / L AgNO3 solution remained clear after dropwise addition (i.e., there was no obvious chloride ion in the filtrate), and the solid was dried in a 60°C oven to obtain a rare earth carbonate precursor. The precursor was calcined at different temperatures (600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C) for 3 h to obtain oxides, and the particle size thereof was observed by SEM as shown in FIG. 1. Figure 15 .

[0082] The results prove that: adding a small amount of light rare earth cerium to the yttrium solution can also prepare highly dispersed nanometer rare earth oxide particles. It is inferred that: a small amount of light rare earth is added to the medium and heavy rare earth, and this method can also be used to prepare ultrafine particle doped rare earth oxides or their composite oxides. At the same time, with the increase of calcination temperature, the particles first become more dense and uniform, and the primary particle size is significantly reduced. When the temperature is higher than 1000°C, the particle size increases significantly, which is due to the sintering and fusion between the particles. The best calcination temperature is about 900°C, and the median particle size of the product is less than 400 nm.

[0083] Example 11

[0084] 50℃ water bath stirring conditions 15 mL 1 mol / L mixed rare earth solution (14.85 mL 1 mol / L YCl3+0.15 mL 1 mol / L CeCl3) and 75 mL 1 mol / L ammonium bicarbonate solution (rare earth and ammonium bicarbonate molar ratio of 1:5) in a beaker, after adding, aging to the appearance of rare earth carbonate crystallization, namely the precipitation and solution has obvious stratification, pH value of the reaction system from rising to decline, add 10 mL mixed rare earth solution (9.9 mL 1 mol / L YCl3+0.1 mL 1 mol / L CeCl3) to the molar ratio of rare earth and ammonium bicarbonate is 1:3, and then add 0.0444 g of ammonium citrate (ammonium citrate: RE2(CO3)3 mass ratio of about 1.0:100), then the reaction system is transferred to a 30℃ water bath and stirred for 6h. After the reaction, the solid is washed with deionized water until the filtrate is clear when added to 1 mol / L AgNO3 solution (i.e. no obvious chloride ions in the filtrate). The solid is dried in a 60℃ oven to obtain a rare earth carbonate precursor. The precursor is calcined at 900℃ for 3h to obtain an oxide. The oxide is ball milled using 0.5mm milling beads with a ball to material mass ratio of 10:1 (100g milling beads, 10g oxide sample) and a material to water ratio of 1:10 (10g sample, 100mL H2O). The particle size of the product after different milling times is shown in Table 1. Figure 16 . The 1h milled product is further added with different amounts of ammonium citrate (ammonium citrate: RE2O3 mass ratio of 0.5-3.0:100) and the particle size of the product after ultrasonic dispersion is shown in Table 2. Figure 17 .

[0085] The results show that the particle size of the calcined product decreases after ball milling and the distribution is more uniform. The particle size of the product milled for 1h is significantly reduced, with a D50 of less than 200nm and a D90 of less than 400nm. However, further prolonging the milling time increases the particle size, which is due to the increased surface energy of the powder after long time milling, leading to re-agglomeration. Adding ammonium citrate to the milling slurry can further improve the dispersion of the particles, with the best dispersion effect when the ammonium citrate: RE2O3 mass ratio is 2.0:100, with a D50 value of less than 100nm. TEM is shown in Figure 18 , with a single particle diameter of 50-80nm.

[0086] Although the embodiments of the present application have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to the embodiments. However, it should be understood that such modifications and changes are within the scope and spirit of the present application as described in the claims. Moreover, the present application described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A process for the preparation of ultrafine medium rare earth oxides, characterized in that, The method comprises the following steps: S1, under heating and stirring, a first-stage reaction is carried out by adding a rare earth salt solution and a carbonate precipitant as raw materials in a synchronous mode, and after the reaction, the system is aged, wherein the molar ratio of rare earth ions to bicarbonate is 1:(4-7), and the rare earth salt solution comprises one or more kinds of medium and heavy rare earth elements; S2, after the system is aged until the rare earth carbonate begins to crystallize, a rare earth salt solution is added to increase the molar ratio of medium and heavy rare earth ions to bicarbonate to 1:(2.5-3.5), and then a second-stage reaction is carried out under a certain temperature and stirring, and after the reaction, the slurry is collected; S3, the slurry obtained in S2 is filtered and washed until there is no chloride ion in the filtrate, and then the rare earth carbonate precursor is obtained by drying, and then the ultrafine medium and heavy rare earth oxide is obtained by calcination.

2. The process of claim 1, wherein, The medium and heavy rare earth elements include yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium; and / or the anions of the rare earth salt solution include at least one of chloride ions, nitrate ions, sulfate ions and acetate ions; and / or the carbonate precipitant includes one or more of sodium carbonate, ammonium carbonate, sodium bicarbonate and ammonium bicarbonate.

3. The process of claim 1, wherein, The concentration of the rare earth salt solution is 0.1-1.5 mol / L, preferably 0.5-1.0 mol / L; and / or the concentration of the carbonate precipitant is 0.5-2.0 mol / L, preferably 1.0-1.5 mol / L.

4. The process of claim 1, wherein, The temperature of the first-stage reaction in S1 is 40-70℃; and / or the temperature of the second-stage reaction in S2 is 10-90℃, and the time is 0.1-12 h.

5. The process of claim 1, wherein, In the step S2, a dispersant is added after the addition is completed, and the dispersant includes at least one of PVP-K30, PEG-4000, triammonium citrate, ammonium polyacrylate and sodium hexametaphosphate.

6. The process of claim 5, wherein, The addition amount of the dispersant is controlled to be 0.05-2 wt%, preferably 1.0-1.5 wt%.

7. The process of claim 1, wherein, The washing in S3 includes water washing until there is no chloride ion in the filtrate or alcohol washing after the water washing until there is no chloride ion in the filtrate, and the water temperature of the water washing is 20-100℃.

8. The process of claim 1, wherein, The calcination temperature in S3 is 400-1100℃, preferably 600-900℃.

9. The process of claim 1, wherein, In the step S3, the ultrafine medium and heavy rare earth oxide obtained by calcination is ball milled and dispersed, the ball milling time is 0.5-3 h, preferably 1-2 h, and then high-dispersion nano rare earth oxide is obtained by dispersion and ultrasonic treatment.

Images