Method for preparing high-purity nanometer rare earth oxide powder

Abstract

The application belongs to the technical field of rare earth materials, and particularly relates to a preparation method of high-purity nanometer rare earth oxide powder. Rare earth carbonate or rare earth oxide raw material is dissolved by nitric acid to obtain a rare earth nitrate solution; a dispersant solution is added into the rare earth nitrate solution to obtain a mixed liquid; liquid carbon dioxide, liquid ammonia and deionized water are pumped into a sieve plate tower in parallel flow to obtain a mixed precipitant; the mixed liquid and the mixed precipitant are pumped into a high gravity reactor in parallel flow to obtain a suspension; the suspension, a crystal form control agent solution and the mixed precipitant are pumped into an ultrasonic wave crystallization reactor in parallel flow to obtain a rare earth oxide precursor slurry; the rare earth oxide precursor slurry is subjected to solid-liquid separation, washing, drying and calcination to obtain the nanometer rare earth oxide powder. The product obtained by the method has narrow particle size distribution, good dispersibility and controllable morphology, and is suitable for industrial production of high-value nanometer rare earth oxide materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth materials, and particularly relates to a preparation method of high-purity nanometer rare earth oxide powder. BACKGROUND

[0002] Nanometer rare earth oxides have a wide application potential in many high-tech fields due to their unique physical and chemical properties, especially in the fields of catalysis, polishing, surface coating, etc. At present, there are various preparation methods for nanometer rare earth oxides, including sol-gel method, hydrothermal synthesis method, combustion method, etc. These methods can prepare nanometer rare earth oxides with different morphologies, such as spherical, flaky and flower-like, etc. However, the above preparation processes have problems such as complexity, high cost, environmental pollution, etc., and the difficulty in accurate control of particle size and morphology, which become key factors restricting the industrial application of nanometer rare earth oxides.

[0003] The sol-gel method and the hydrothermal synthesis method depend on high temperature and high pressure conditions, resulting in high energy consumption, complex equipment and difficulty in scaling up; the conventional chemical precipitation method is prone to particle agglomeration and wide particle size distribution (usually more than 200 nanometers) due to the low mass transfer efficiency of the stirring reactor, and the use of a large amount of alkaline precipitants and organic additives produces high-pollution wastewater, which increases the environmental pressure. Especially for high-end polishing applications, the uniformity of powder particle size and low agglomeration characteristics directly determine the performance, but the existing technology is difficult to achieve precise control of submicron level under the premise of low cost. The core contradiction of current industrial production is that: although the solvent thermal method can improve the uniformity of morphology, its harsh reaction conditions and low yield limit the economic feasibility; and the conventional calcination process based on oxalic acid or ammonium carbonate precipitation produces coarse powder grains (generally greater than 5 microns), and subsequent mechanical grinding will introduce impurities and damage the dispersibility. The performance optimization of rare earth-based polishing materials is highly dependent on the morphology inheritance of the precursor, but the complex process route and impurity residue problems have always hindered the large-scale preparation of high-quality nanometer powder.

[0004] The current preparation of nanometer rare earth oxides faces three technical barriers: purity defects caused by impurities in raw materials, size loss of control caused by low mass transfer efficiency of the reactor, and high pollution and high cost of environmental protection investment. Traditional process relies on commercially available ammonia water, ammonium carbonate or their mixture, which contains sulfate (>200 ppm), chloride (>500 ppm) and organic residues, which are deeply embedded in the lattice during the precipitation process, resulting in a final powder purity of less than 99.99% (4N level), which cannot meet the stringent requirements of K⁺ / Na⁺<10ppm for semiconductor polishing. At the same time, due to the low mass transfer efficiency of the conventional stirred tank, the supersaturation distribution is uneven during the precipitation process, leading to explosive nucleation of crystal nucleus and secondary agglomerates, and the subsequent mechanical crushing introduces wear impurities. On the environmental protection aspect, 1.8 tons of ammonium bicarbonate are consumed per ton of nanometer cerium oxide production, generating 12 tons of ammonia-nitrogen-containing wastewater, although some enterprises try to recover ammonia water, but due to the CO2 absorption rate <70%, the actual production cost increases by 15%. Although hydrothermal method can prepare uniform nanometer sheets, the high-pressure reactor investment exceeds one million yuan, the single batch capacity is less than 100 kg, and the unit energy consumption is 6 times that of traditional precipitation method, forming an industry dilemma of "high performance must be high investment".

[0005] In summary, the preparation technology of nanometer rare earth oxides needs to be innovated to realize efficient, environmentally friendly and low-cost large-scale production.

[0006] The synthesis process of the rare earth mixed precipitant optimizes the total concentration of ammonium (3.0-4.0 mol / L) and the proportion of ammonium bicarbonate (60-90%), which significantly improves the product stability (uniform composition and low chloride content) compared with the traditional method, while reducing the consumption of ammonium bicarbonate, reducing wastewater production, and increasing the concentration of ammonium chloride in wastewater to achieve resource utilization. It is worth noting that some enterprises recover wastewater to produce ammonia water (cost reduction of 50%), but because ammonia water is only suitable for extraction saponification and cannot be directly replaced by precipitant, enterprises face the imbalance between supply and demand of excess ammonia water and purchased ammonium bicarbonate. If the regenerated ammonia water can be efficiently converted into a mixed precipitant, it can not only create economic value but also optimize internal material circulation, which is of great significance to the upgrading of the industry and resource recycling. However, the core challenge of this conversion process is that the reaction efficiency of ammonia water absorbing CO2 is limited. This gas-liquid mass transfer process involves multiple intermediate reactions, which are constrained by high CO2 escape rate and low absorption rate. Increasing the reaction temperature or ammonia water concentration can promote CO2 capture, but it will exacerbate ammonia loss. Low-temperature operation requires additional energy consumption, making it difficult to balance efficiency and cost. Current equipment (such as carbonation tower and bubble column) optimizes mass transfer by increasing size, prolonging contact time or intensifying mixing, resulting in equipment height of dozens of meters and high investment, and still has problems such as low CO2 utilization rate and fluctuation of product ratio. More complex is that different types of rare earth carbonate products (such as lanthanum cerium carbonate, praseodymium neodymium carbonate, etc.) have different requirements for the ammonia water concentration and ammonium bicarbonate proportion of the mixed precipitant, and the rigid structure of large-scale towers is difficult to adapt to the production needs of multiple varieties, which lacks economic efficiency and is difficult to achieve precise control. SUMMARY

[0007] To solve the above technical problems, the present application provides a low-cost general-purpose high-purity nano rare earth oxide powder preparation method.

[0008] According to the nano rare earth oxide powder preparation method of the embodiment of the present application, the preparation method comprises the following steps:

[0009] (1) Pump liquid carbon dioxide, liquid ammonia and deionized water into a sieve plate tower respectively to obtain a mixed precipitant;

[0010] (2) Pump a rare earth nitrate solution and the mixed precipitant into a high gravity reactor respectively to obtain a suspension;

[0011] (3) Pump the suspension, a crystal form control agent solution and the mixed precipitant into an ultrasonic wave crystallization reactor respectively to obtain a rare earth oxide precursor slurry;

[0012] (4) Perform solid-liquid separation on the rare earth oxide precursor slurry, and then wash, dry and calcine the rare earth oxide precursor slurry to obtain the nano rare earth oxide powder.

[0013] According to a specific embodiment of the present invention, the method for preparing nano-rare earth oxide powders, wherein the mixed precipitant contains NH4. + CO3 2- HCO3 - The pH of the mixed precipitant is 8-12; among which, NH4 + The concentration is 2.0~4.5 mol / L, CO3 2- HCO3 - The sum of concentrations and NH4 + The concentration ratio is 0.01:1 to 1:1.

[0014] According to the specific embodiments of the present invention, in the preparation method of nano-rare earth oxide powder, in step (1), the purity of the liquid carbon dioxide is ≥99%, and the purity of the liquid ammonia is ≥99.6%;

[0015] And / or, liquid carbon dioxide is added to the sieve tray tower after being filtered through a membrane;

[0016] Liquid ammonia is added to a sieve tray tower after being filtered through a membrane.

[0017] In this invention, membrane filtration refers to a physical technology that uses a selective separation membrane as a medium, driven by pressure difference, to selectively allow certain components in a mixture to permeate while retaining other components, thereby achieving separation, purification, or concentration. For liquid ammonia and liquid carbon dioxide, under high pressure (2-6 MPa) and temperature (-20°C to -30°C) conditions, special membrane materials are used, and the system temperature and pressure are strictly controlled to prevent phase change of the medium and ensure equipment sealing and corrosion resistance.

[0018] The main steps of membrane filtration operation include: selecting and installing a special membrane material resistant to low-temperature corrosion, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or ceramic membrane, according to the separation target; then pre-cooling, pressurizing, and drying the system; and pre-filtering the feed liquid, such as liquid carbon dioxide or liquid ammonia, to reduce membrane fouling; during formal filtration, the liquid is forced through the membrane under pressure to separate and collect the pure permeate from the concentrate rich in impurities; after filtration, the system needs to be backflushed with inert gas to remove sludge and replace the system, and a thorough cleaning procedure is performed to restore membrane performance.

[0019] The traditional preparation method of mixed precipitator in industry is to dissolve solid ammonium bicarbonate with ammonia water of a certain concentration. In this preparation method, ammonium bicarbonate has poor thermal stability (decomposition gas is produced at >40℃), and ammonia water is volatile, resulting in loss of effective ingredients, which requires strict control of temperature and closed operation; at the same time, the precipitation process is easy to entrain ammonium and calcium and magnesium impurities, reducing the purity of rare earth oxides, and the sensitivity of the narrow pH window (8.5-9.5) is easy to cause uneven particles and local crystallization; in addition, the escape of ammonia gas poses a safety and health risk, and the high ammonia nitrogen mother liquor (2000-5000 mg / L) increases the cost of wastewater treatment, and the weak adaptability of colloidal precipitation of heavy rare earth further restricts its application range.

[0020] The present application adopts liquid ammonia-liquid carbon membrane filtration, sieve plate tower synthesis process, and reconstructs the purification path of the precipitator from the source. After liquid ammonia and liquid CO2 are filtered by membrane, electronic grade mixed precipitator is formed, which completely eliminates impurity ions and particles, and then a multi-stage pH gradient is built in the sieve plate tower to avoid side reactions caused by free ammonia. The above treatment method reduces the impurity content in the precipitator to <5 ppm of chloride, undetected sulfate, and <10 ppm of TOC (traditional process >500 ppm / 200 ppm / 100 ppm), and the purity of the obtained precursor rare earth carbonate jumps to 99.9999% (6N grade). When applied to high-end silicon nitride substrate polishing, the surface roughness (Ra) is reduced to 0.14 nm (international advanced level: 0.22 nm), and the micro scratches induced by impurities are reduced by 70%, significantly improving the yield of wafers. This technology realizes the "self-production and self-purification" of the precipitator for the first time, and solves the industry's intractable problem of uncontrollable impurities in purchased raw materials, providing purity guarantee for electronic grade nanometer powder.

[0021] The purity of the liquid carbon dioxide is ≥99%, preferably the purity of the liquid carbon dioxide is ≥99.9%.

[0022] The purity of the liquid ammonia is ≥99.6%, preferably the purity of the liquid ammonia is ≥99.9%.

[0023] The concentration of the mixed precipitator and the ratio of ammonia water to ammonium bicarbonate are slightly different for different rare earth elements. The total concentration of ammonium in the mixed precipitator is 3.0-4.0 mol / L, and the amount of ammonium bicarbonate added is 60-90% of the total concentration of ammonium. Compared with the traditional production of rare earth carbonate by reacting ammonium bicarbonate and rare earth chloride solution, the mixed precipitator has the advantages of stable composition of rare earth carbonate product, less chloride, less ammonium bicarbonate, less wastewater, and high concentration of ammonium chloride in wastewater.

[0024] The mixed precipitator is added to the supergravity reactor at a flow rate of 0.01L / h - 50L / h.

[0025] The rare earth mixed solution is added into the high gravity reactor at a flow rate of 0.01L / h-50L / h; preferably, the mixed precipitant is used in an amount to adjust the pH of the solution to 6-9.

[0026] In step (2), the rare earth mixed solution is a mixture of a rare earth nitrate solution and a dispersant solution,

[0027] The concentration of the rare earth nitrate solution is 25-200g / L;

[0028] The rare earth raw material is dissolved in nitric acid to obtain the rare earth nitrate solution;

[0029] The rare earth raw material is selected from rare earth carbonates or rare earth oxides, wherein the rare earth carbonates or rare earth oxides are one of carbonates and oxides corresponding to lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium and scandium.

[0030] It is worth mentioning that the ordinary commercially available industrial rare earth oxides are all obtained by calcining oxalic acid rare earth or carbonic acid rare earth precipitated by oxalic acid or ammonium carbonate, and the crystal grains of the oxides are coarse, and the particle size is often above 5μm. If the oxides are directly ground to be fine, impurities will be introduced, and the product morphology will be different and the dispersibility will be low. In the present application, the single rare earth compound raw material is dissolved in a nitric acid solution to obtain a rare earth nitrate solution, which can remove the undissolved impurities and will not introduce harmful impurities such as sulfate into the solution.

[0031] In the preparation method of the nano rare earth oxide powder according to the embodiment of the present application, the dispersant solution is a mixed solution of a solvent and water, and the solvent is one or more of ethanol, ethylene glycol, propylene glycol, polypropylene glycol, polyvinylpyrrolidone, glycerol, diethylene glycol monobutyl ether and sodium citrate. In particular, the configuration ratio of the solvent and water is 0.01:1-1:1 by mass. In particular, the mass of the solvent in the dispersant solution is 0.001-15% of the mass of the rare earth raw material.

[0032] In step (2), the high gravity reaction conditions are a high gravity rotation speed of 1000r / min-6000r / min and a reaction temperature of 25-60℃.

[0033] The present application uses a high gravity reactor to carry out a precipitation reaction, realizes rapidization, uniformization and controllability of the reaction process through extremely enhanced mass transfer and micro-mixing, and continuously prepares a nano rare earth oxide product with small particle size, uniform distribution and controllable morphology.

[0034] The preparation method of the nanometer rare earth oxide powder according to the embodiment of the present application, the crystal form control agent solution is a mixture of an organic substance and a non-ionic multi-block solvent;

[0035] The organic substance is one or more of hydroxamic acid, benzohydroxamic acid, salicylic acid, and citric acid;

[0036] The non-ionic multi-block solvent mainly includes one or more of poloxamer and poloxamine.

[0037] The structure general formula of the poloxamer is (EO) a -(PO) b -(EO) c , wherein EO is an oxyethylene group, PO is an oxypropylene group, a and c are the same or different and are integers from 10 to 200, and b is an integer from 20 to 100.

[0038] The poloxamine is a four-arm star-shaped block copolymer with ethylenediamine as the core, and the structure thereof can be represented as [(EO) a -(PO) b )2-N-CH2-CH2-N-[(PO) b -(EO) a ]2, wherein a and b are integers.

[0039] Further, the number average molecular weight of the non-ionic multi-block solvent is 2000-15000 g / mol, and preferably 4000-6000 g / mol.

[0040] The hydrophilic-lipophilic balance (HLB) of the block copolymer is 5-20, and preferably 10-15.

[0041] Some specific examples of the non-ionic multi-block solvent include but are not limited to: Pluronic® P-123, Pluronic® F-127, Pluronic® F-68, Pluronic® L-61, Tetronic® 704, Tetronic® 904, Synperonic™ PE / P series.

[0042] In a most preferred embodiment, the dispersant is Pluronic® P-123, which has a CAS number of 9003-11-6.

[0043] The preparation ratio of the organic substance and the non-ionic multi-block solvent is 0.1:1-1:1 by mass, and the mass of the crystal form control agent solution to the rare earth raw material is 0.001-10%.

[0044] In the present application, the sieve plate tower is also called a foam tower, which is a kind of staged contact mass transfer equipment for gas-liquid or liquid-liquid systems. It is mainly composed of sieve plates filled with sieve holes, water spraying pipes, tip water plates (also called defoamers), water seal sewage valves and inlets and outlets. The sieve plate is the core component, and a large number of small holes such as slits, circles and squares are uniformly distributed on the sieve plate, and the gas rises through the small holes to contact and mass transfer with the liquid.

[0045] The ultrasonic crystallization reactor is a special equipment combining ultrasonic technology and crystallization process, which is usually composed of an ultrasonic generator, a reaction vessel, an ultrasonic probe, a temperature control / stirring system and the like.

[0046] The high-gravity reactor (HGR) is a new type of equipment that can simulate an environment far exceeding the gravity acceleration of the earth (usually several to several thousand times the gravity acceleration, g) to strengthen the multiphase flow transfer and reaction process.

[0047] According to the preparation method of the nano rare earth oxide powder provided in the embodiment of the present application, in step (3), the ultrasonic power of the ultrasonic crystallization reaction is 0-3500W, the ultrasonic frequency is 0-25KHZ, the stirring speed is 100 rap / min-700 rap / min, the reaction temperature is 25-100℃, and the reaction time is 3h-48h; and / or,

[0048] In step (3), the mixed precipitating agent is pumped into the solution until the pH is 7.5-9.5.

[0049] The precursor slurry is one or a mixture of two or more of rare earth carbonate, basic rare earth carbonate and rare earth hydroxide.

[0050] Through the cavitation effect and physical action (shock wave, microjet, acoustic streaming, thermal effect) of the ultrasonic reaction, the crystallization nucleation is accelerated, the crystal size and morphology are controlled, the particle size distribution and dispersibility are improved, the crystal type selection is affected, and the purity and yield of the product are improved.

[0051] According to the preparation method of the nano rare earth oxide powder provided in the embodiment of the present application, in step (4), the washing is an alternating washing with washing liquid, the washing liquid is one or more of deionized water, ethanol and ethylene glycol, and the washing frequency is 1-8 times; and / or,

[0052] The drying temperature is 40℃-150℃, and the time is 1h-24h.

[0053] According to the preparation method of the nano rare earth oxide powder provided in the embodiment of the present application, in step (4), the calcination temperature is 500℃-1500℃, and the time is 1h-48h.

[0054] The application also provides the high-purity rare earth oxide nanopowder prepared by the preparation method.

[0055] The application has the following advantages:

[0056] The carbonated rare earth or the oxidized rare earth is dissolved in nitric acid, the impurities in the carbonated rare earth or the oxidized rare earth are converted into the liquid phase, and then the rare earth is precipitated and reacted with the mixed precipitant to obtain a precipitate, so that the rare earth and the impurities are separated, the impurities are avoided to be introduced, and the high-purity rare earth alkaline mixed suspension is obtained; then the ultrasonic crystallization reaction is performed to obtain a rare earth precursor crystal, and finally the solid-liquid separation, drying and calcination decomposition are performed to obtain the high-purity rare earth oxide nanopowder.

[0057] The application uses the electronic-grade mixed precipitant, the supergravity precipitation, and the ultrasonic crystallization reaction to synthesize the carbonated rare earth precursor, has the characteristics of easy filtration and easy washing of impurities, and the rare earth oxide particles obtained after calcination have small particle size, can reach the nanometer size, and have uniform size distribution, high specific surface area, no hard agglomeration, loose, good dispersibility, low cost, easy industrialization, and the like, are suitable for the electronic ceramic industry, especially suitable for industrialized production, have strong universality, and have wide application prospect.

[0058] In the application, the supergravity reaction realizes the instantaneous nucleation-controlled growth mechanism through the centrifugal acceleration field, breaks through the mass transfer limitation of the traditional hydrothermal synthesis method and the precipitation method. The liquid flow is torn into micron-level films by using the supergravity reactor, the ion diffusion time is greatly compressed from the second level of the traditional method to the millisecond level, the supersaturation uniformity is significantly improved, the crystal lattice distortion problem caused by high temperature, high pressure and long period (more than 20 hours) in the hydrothermal method is completely solved, and the precision regulation of particle size and crystal form caused by uneven micro-mixing in the precipitation method is solved. In addition, the nucleation density of the crystal is controlled by the supergravity rotation speed, and the adsorbed ions are instantaneously stripped by the ultrahigh shear force, so that the narrow particle size distribution and high dispersibility are realized. The hydrothermal method depends on the surfactant (such as PEG and citrate) to control the morphology, introduces impurities and increases the difficulty of post-processing. The precipitation method causes serious product agglomeration due to the separation of nucleation and growth, and has poor process efficiency and environmental protection. In summary, the reaction period is shortened to minutes by the supergravity method, the energy consumption is reduced to 1 / 3 of the reaction kettle, the equipment height is less than 1 / 4 (<5 meters) of the traditional bubble column, and water is used as the solvent, so that organic modifiers (such as OP-10 and sodium citrate) are not needed, and pollution is avoided. In contrast, the hydrothermal method has high energy consumption and high maintenance cost, and the precipitation method has large three-waste generation and intermittent production rigidity, which has significant industrialization adaptability. The supergravity equipment engineering amplification effect is weak, the production capacity is linearly adjusted through the flow rate and the pipe diameter, the continuous production is supported, and the investment recovery period is significantly shortened. The hydrothermal method is limited by the volume of the high-pressure equipment, and the precipitation method is difficult to scale up due to the decay of stirring efficiency.

[0059] In the crystallization stage, the present application constructs a ternary synergistic system of ultrasonic field-electronic grade precipitator-crystal face selective adsorbent. Micro-jet is generated by ultrasonic wave, which instantaneously destroys the van der Waals force between particles, reduces the agglomeration index of rare earth compounds; the crystal form control agent preferentially adsorbs on the surface of rare earth compound particles, blocks the growth rate of the surface, and promotes the directional development of particles into controllable morphology; the electronic grade mixed precipitator provides uniform CO3 2- or OH - release, delays nucleation, and realizes monodisperse growth. The above-mentioned ternary synergistic coupling strategy makes the controllable rate of crystal morphology increase to 98% (the controllable rate of crystal morphology of the traditional method is <70%), and the product can be customized. Among them, the nano cerium oxide is used for silicon wafer CMP polishing, the material removal rate (MRR) is increased to 450 nm / h, and the surface scratch is reduced by 60%, which meets the requirements of 3nm node; the present application realizes the triple effects of "cavitation anti-agglomeration-crystal face directional growth-precipitation synergistic modification", and solves the industry technical bottlenecks of uniformity and functional directional regulation of nano powder morphology. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0061] Figure 1 is the SEM of the nano cerium dioxide prepared in embodiment 1 of the present application.

[0062] Figure 2 is the XRD of the nano cerium dioxide prepared in embodiment 1 of the present application.

[0063] Figure 3 is the SEM of the nano lanthanum oxide prepared in embodiment 2 of the present application.

[0064] Figure 4 is the XRD of the nano lanthanum oxide prepared in embodiment 2 of the present application.

[0065] Figure 5 is the SEM of the nano yttrium oxide prepared in embodiment 3 of the present application.

[0066] Figure 6 is the XRD of the nano yttrium oxide prepared in embodiment 3 of the present application.

[0067] Figure 7 is the SEM of the nano cerium dioxide obtained in embodiment 4.

[0068] Figure 8SEM image of the nanometer cerium dioxide obtained in Example 5.

[0069] Figure 9 SEM image of the nanometer cerium dioxide obtained in Example 6.

[0070] Figure 10 SEM image of the nanometer cerium dioxide obtained in Comparative Example 1. DETAILED DESCRIPTION

[0071] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0072] The preparation method of the high-purity nanometer rare earth oxide powder of the present application comprises the following steps:

[0073] 1) Dissolving the rare earth raw material with nitric acid to obtain a rare earth nitric acid solution; the rare earth raw material is selected from rare earth carbonate or oxide;

[0074] 2) Adding a dispersant solution into the rare earth nitric acid solution obtained in step 1) to obtain a rare earth mixed solution;

[0075] 3) Pumping the mixed solution obtained in step 2) and the electronic-grade mixed precipitant into a high-gravity reactor in parallel flow to obtain a suspension; wherein,

[0076] Pumping liquid carbon dioxide, liquid ammonia and deionized water into a sieve plate tower in parallel flow to obtain a mixed precipitant;

[0077] 4) Pumping the suspension obtained in step 3), a crystal form control agent solution and the mixed precipitant into an ultrasonic crystallization reactor in parallel flow to obtain a rare earth oxide precursor slurry by reaction;

[0078] 5) After the crystal nucleus reaction is completed, performing solid-liquid separation on the rare earth oxide precursor slurry obtained in step 4), washing, drying and calcining to obtain the nanometer rare earth oxide powder.

[0079] In the preferred examples, in step 1), the rare earth carbonate is one of the carbonates corresponding to lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium or scandium; the rare earth oxide is one of the oxides corresponding to lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium or scandium; the relative purity of the rare earth raw material is greater than 99.9%, and preferably, the purity is greater than 99.99%.

[0080] The concentration of the rare earth nitric acid solution is 25-200 g / L, more preferably, the concentration of the rare earth nitric acid solution is 70-140 g / L, or the concentration is 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135 or 40 g / L, or the concentration of the rare earth nitric acid solution is selected from any value in the range of 25-200 g / L, which is not described here.

[0081] In step 2), the dispersant solution is a mixed solution of solvent and water, the solvent is one or more of ethanol, ethylene glycol, propylene glycol, polypropylene glycol, polyvinylpyrrolidone, glycerol, diethylene glycol monobutyl ether, and sodium citrate, and the solvent and water in the dispersant solution are configured in a ratio of 0.1:1 to 1:1.

[0082] The mass of the solvent in the dispersant solution is 0.001-15% of the mass of the rare earth raw material.

[0083] The dispersant in the application can wrap the subsequently generated rare earth precursor compound crystals, prevent grain growth, form a large amount of gas during the calcination of the rare earth precursor crystals, have a partitioning effect, prevent the agglomeration of rare earth oxides, and be conducive to obtaining rare earth oxide powders with good dispersibility and high specific surface area.

[0084] In the preferred examples, in step 3), the purity of the liquid carbon dioxide is ≥99%, preferably ≥99.9%; and the purity of the liquid ammonia is ≥99.6%, preferably ≥99.9%.

[0085] The liquid carbon dioxide and the liquid ammonia are respectively filtered through a membrane, and then pumped into the sieve plate tower together with the deionized water.

[0086] The electronic mixed precipitant is a mixed solution of NH 4+ , CO3 2- , and HCO3 - , wherein the concentration of NH 4+ is 2.0-4.5 mol / L, preferably 2.0-3 mol / L, or the concentration of NH 4+ is 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5 mol / L, or the concentration of NH 4+ is selected from any value in the range of 2.0-4.5 mol / L, which is not described here.

[0087] The sum of the concentrations of CO3 2- , HCO3 - , and NH 4+The concentration ratio is 0.01:1-1:1, preferably, the concentration ratio is 0.01:1-0.5:1, more preferably, the concentration ratio is 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or any value in the range of 0.01:1-1:1, which is not listed here.

[0088] The pH of the mixed precipitant is 8-12, preferably 11.

[0089] In the preferred examples, in step 3), the mixed precipitant is injected into the supergravity reactor at a flow rate of 0.01L / h-50L / h, more preferably 0.1-5L / h, or the flow rate is 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0L / h, or any value in the range of 0.01L / h-50L / h, which is not listed here.

[0090] The mixed solution is injected into the supergravity reactor at a flow rate of 0.01L / h-50L / h, more preferably 0.1-5L / h, or the flow rate is 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0L / h, or any value in the range of 0.01L / h-50L / h, which is not listed here.

[0091] In particular, the amount of mixed precipitant is used to adjust the pH of the solution to 6-9, more preferably 7-8.

[0092] The concentration, addition rate and amount of the electronic grade mixed precipitant are controlled in the above range, which is beneficial for the transformation of rare earth nitric acid solution to rare earth precursor crystal form. Changing the concentration of the electronic grade mixed precipitant will make the crystal grain larger or agglomerate, changing the titration rate of the electronic grade mixed precipitant will change the nucleation rate and growth rate of the grain, and changing the amount of the electronic grade mixed precipitant will increase the loss of rare earth or increase the impurity content, which is not easy to wash and filter.

[0093] By controlling the concentration, addition rate and amount of the electronic grade mixed precipitant in the above specific range, the precipitation behavior of rare earth ions from nitric acid solution can be effectively regulated, the precipitation process is changed from amorphous to good crystal form of rare earth precursor, and high purity and high consistency products are obtained. Specifically, changing the concentration of the electronic grade mixed precipitant will make the crystal grain larger or agglomerate, changing the titration rate of the electronic grade mixed precipitant will change the nucleation rate and growth rate of the grain, and changing the amount of the electronic grade mixed precipitant will increase the loss of rare earth or increase the impurity content, which is not easy to wash and filter.

[0094] In a preferred example, in step 4), the crystal form control agent is a mixture of an organic substance and a non-ionic multi-block solvent, the organic substance is one or more of hydroxamic acid, benzohydroxamic acid, salicylic acid, citric acid, and the non-ionic multi-block solvent mainly includes one or more of poloxamer and poloxamine. The general structure of poloxamer is (EO) a -(PO) b -(EO) c , wherein EO is an oxyethylene group, PO is an oxypropylene group, a and c are the same or different integers of 10-200, and b is an integer of 20-100.

[0095] The poloxamine is a four-arm star-shaped block copolymer with ethylenediamine as the core, and its structure can be represented as [(EO) a -(PO) b )2-N-CH2-CH2-N-[(PO) b -(EO) a ]2, wherein a and b are integers.

[0096] Further, the number average molecular weight of the non-ionic multi-block solvent is 2000-15000 g / mol, preferably 4000-6000 g / mol.

[0097] The hydrophilic-lipophilic balance (HLB) of the block copolymer is 5-20, preferably 10-15.

[0098] Some specific examples of non-ionic multi-block solvents include, but are not limited to: Pluronic® P-123, Pluronic® F-127, Pluronic® F-68, Pluronic® L-61, Tetronic® 704, Tetronic® 904, Synperonic™ PE / P series.

[0099] In a most preferred embodiment, the dispersant is Pluronic® P-123, which has a CAS number of 9003-11-6.

[0100] The mass ratio of the organic substance to the non-ionic multi-block solvent is 0.1:1-1:1; the mass of the crystal form control agent solution to the rare earth raw material is 0.001-10%.

[0101] The present application finds that, by using the non-ionic multi-block copolymer with the above specific structure as a dispersant, the hydrophobic segment (PPO) thereof can be firmly anchored on the surface of nano cerium oxide precursor particles, while the hydrophilic segment (PEO) extends into the aqueous phase to form a steric hindrance, which can effectively inhibit the Ostwald ripening and agglomeration of the particles during the synthesis process, thereby obtaining nano cerium oxide particles with uniform particle size distribution and high dispersion stability. Compared with traditional small molecule dispersants (such as sodium citrate), the block copolymer provides more durable and stable steric stabilization.

[0102] The crystal form control agent precisely manipulates the nucleation and growth process of rare earth crystallization through complex physicochemical effects (adsorption, complexation, templating, and kinetic regulation), ensuring that the final product is formed and stabilized on the target crystal form. This is crucial for realizing the excellent application performance of rare earth nanomaterials in the fields of luminescent display, biological imaging, magnetism, catalysis, sensing, and others.

[0103] In preferred examples, in step 4), the mass of the crystal form control agent is 0.01-10% of the mass of the rare earth raw material in step 1), more preferably 2%-5%. Preferably, the mass of the crystal form control agent is 2%, 2.5%, 3.5%, 4%, 4.5%, or 5% of the mass of the rare earth raw material, or the mass of the crystal form control agent is any value within the range of 0.01-10% of the mass of the rare earth raw material, which is not listed here.

[0104] In preferred examples, in step 4), the ultrasonic crystallization reaction has an ultrasonic power of 0-3500W, more preferably 2500W-3000W; an ultrasonic frequency of 0-25KHz, more preferably 15-KHz; a stirring speed of 100 rap / min-700 rap / min, more preferably 600 rap / min; a reaction temperature of 25-100℃, more preferably 25-60℃; and a reaction time of 3h-48h, more preferably 24h-48h.

[0105] Further, in step 4), the electronic-grade mixed precipitant is used in an amount sufficient to adjust the ph of the solution to 7.5-9.5, more preferably 7.8-9.

[0106] In preferred examples, in step 5), the washing is alternating washing with washing liquids, and the washing liquids are one or more of deionized water, ethanol, and ethylene glycol, preferably ethanol or deionized water; the washing is performed 1-8 times, preferably 3-4 times; the drying temperature is 40℃-150℃, preferably 100-150℃; and the drying time is 1h-24h, preferably 6h-12h.

[0107] In the preferred examples, in step 5), the calcination temperature is 500-1500℃, preferably 600-1200℃; the time is 1-48h, preferably 3-36h.

[0108] The application further provides the high-purity rare earth oxide nanopowder prepared by the preparation method.

[0109] Embodiment

[0110] The preparation method of the high-purity rare earth oxide nanopowder comprises the following steps:

[0111] 1) dissolving rare earth raw materials with nitric acid to obtain rare earth nitrate;

[0112] 2) adding a dispersant solution into the rare earth nitrate solution obtained in step 1) to obtain a rare earth mixed solution;

[0113] 3) pumping liquid carbon dioxide and liquid ammonia through membrane filtration into a sieve plate tower in parallel with deionized water to obtain an electronic-grade mixed precipitant;

[0114] 4) pumping the mixed solution obtained in step 2) and the mixed precipitant obtained in step 3) into an ultra-gravity reactor in parallel until the pH is 7-8 to obtain a suspension;

[0115] 5) pumping the suspension obtained in step 4), a crystal form control agent solution and the electronic-grade mixed precipitant obtained in step 3) into an ultrasonic crystallization reactor in parallel until the pH is 8-9, and reacting to obtain a rare earth oxide precursor slurry;

[0116] 6) after the crystal nucleus reaction is completed, performing solid-liquid separation on the rare earth oxide precursor slurry obtained in step 5), washing, drying and calcining to obtain the nanopowder of rare earth oxide.

[0117] The process parameters of examples 1-6 are shown in table 1.

[0118] Table 1 Process parameters of examples 1-6

[0119]

[0120] Table 2 Test items and detection basis

[0121]

[0122] The SEM image of the nanometer cerium dioxide obtained in example 1 is shown in Figure 1 . Figure 2The XRD pattern of the nano ceria is shown in Figure 1. Characteristic diffraction peaks appear at about 28.5°, 33.1°, 47.5°, 56.3°, etc. These characteristic peaks are consistent with the (111), (200), (220), (311) crystal planes of cubic fluorite structure ceria, respectively. The pattern shows that the prepared ceria is pure cubic crystal system, in which the (111) crystal plane diffraction peak at 28.5° is the strongest peak. No diffraction peaks of other impurities are detected, indicating that the product has high purity.

[0123] The SEM image of the nano lanthana obtained in Example 2 is shown in Figure 2. Figure 3 Figure 4 The XRD pattern of the nano lanthana is shown in Figure 3. Characteristic diffraction peaks appear at about 26.1°, 29.1°, 39.5°, 46.0°, 52.2°, etc. These characteristic peaks are consistent with the (100), (002), (101), (102), (110) crystal planes of hexagonal lanthana, respectively. This shows that the prepared lanthana is of hexagonal crystal structure. The diffraction peaks in the pattern are sharp and the base line is flat, indicating that the product has good crystallinity. No diffraction peaks of other impurities are detected, indicating that the product has high purity.

[0124] The SEM image of the nano yttria obtained in Example 3 is shown in Figure 4. Figure 5 Figure 6 The XRD pattern of the nano yttria is shown in Figure 5. Characteristic diffraction peaks appear at about 20.5°, 29.1°, 33.8°, 48.5°, 57.6°, etc. These characteristic peaks are consistent with the (211), (222), (400), (440), (622) crystal planes of cubic yttria, respectively. This shows that the prepared yttria is of cubic structure. No other impurity peaks appear in the pattern, indicating that the product is a pure phase.

[0125] The SEM image of the nano ceria obtained in Example 4 is shown in Figure 6. Figure 7

[0126] The SEM image of the nano ceria obtained in Example 5 is shown in Figure 7. Figure 8

[0127] The SEM image of the nano ceria obtained in Example 6 is shown in Figure 8. Figure 9

[0128] Examples 1, 4, 5 and 6 all prepared nano ceria products, but there are significant differences in size and morphology. In combination with the parameters listed in Table 1, it can be seen that the variation of the key parameters in each example has a decisive influence on the morphology and size of the product.

[0129] Example 1 and Example 4 differ in the amount of dispersant: in Example 1, the dispersant is 0.5% of the amount of cerium nitrate, while in Example 4, the dispersant is 1% of the amount of cerium nitrate. 3+ ​​​​​The molar ratio of dispersant to Ce

[0130] Example 1 and Example 5 both use dispersant and Ce 3+ The molar ratio of dispersant to Ce

[0131] Example 1 and Example 6 also differ in the type and ratio of crystal form control agent: Example 1 uses hydroxamic acid and Pluronic® P-123 at a ratio of 0.5:1, while Example 6 uses salicylic acid and Pluronic® P-127 at a ratio of 0.2:1. The different combinations of control agents result in a significant difference in morphology, with the product of Example 1 being round particles and the product of Example 6 being a flaky structure.

[0132] Comparative Example

[0133] Comparative Example: An experiment was conducted using a non-electronic grade precipitant prepared by mixing 25%-28% concentrated analytical pure ammonia water with ≥99% pure analytical pure ammonium bicarbonate. The ammonia water and ammonium bicarbonate were mixed in a certain ratio and dissolved in deionized water, and stirred until completely dissolved and uniform, to obtain the desired precipitant. The sum of the concentrations of CO3 2- and HCO3 - and the ratio of NH4 + concentration were both 0.01:1.

[0134] The parameters of the comparative example and Example 1 are compared as follows:

[0135] Table 3 Comparison of parameters of comparative example and Example 1

[0136]

[0137] The SEM image of the nanometer ceria obtained in the comparative example is shown in Figure 10 .

[0138] When Example 1 uses an electronic grade precipitant, the nanometer ceria product obtained has high phase purity, regular round morphology, uniform particle size distribution, a median particle size of about 200 nm, and good dispersibility.

[0139] In comparison, the use of a non-electronic grade precipitant in the comparative example adversely affects various properties of the product:

[0140] First, lattice formation is doped with defects, and the chemical purity of the product decreases;

[0141] Secondly, the heterogeneous nucleation and non-uniform growth occur in the homogeneous nucleation process, causing the particle size distribution to be broadened and the morphology to be irregular, and the particles with different sizes and shapes appear in the product, and the rod-shaped and sheet-shaped precipitates due to the growth inhibition of specific crystal faces also appear;

[0142] Thirdly, the agglomeration tendency of the particles is intensified, resulting in the decrease of the dispersion stability.

[0143] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing high-purity nano-rare earth oxide powder, characterized in that, The preparation method includes the following steps: (1) Liquid carbon dioxide, liquid ammonia and deionized water are pumped into a sieve plate tower respectively to obtain a mixed precipitant; (2) The rare earth nitrate solution and the mixed precipitant were pumped into a high gravity reactor to obtain a suspension; (3) The suspension, crystal form control agent solution and the mixed precipitant are pumped into the ultrasonic crystallization reactor respectively to react and obtain rare earth oxide precursor slurry; (4) The rare earth oxide precursor slurry is subjected to solid-liquid separation, washed, dried and calcined to obtain the nano rare earth oxide powder; The mixed precipitant contains NH4 + CO3 2- HCO3 - The pH of the mixed precipitant is 8-12; among which, NH4 + The concentration is 2.0~4.5 mol / L, CO3 2- HCO3 - The sum of concentrations and NH4 + The concentration ratio is 0.01:1 to 1:1; In step (1), the liquid carbon dioxide is pumped into the sieve tray tower after being filtered through a membrane. The liquid ammonia is filtered through a membrane and then pumped into a sieve tray tower; The crystal form control agent is a mixture of organic compounds and nonionic multiblock solvents; The organic compound is one or more of hydroxamic acid, benzohydroxamic acid, salicylic acid, and citric acid; The nonionic multiblock solvent includes one or more of poloxamer and poloxamine; In step (3), the ultrasonic power of the ultrasonic crystallization reaction is 0~3500W, the ultrasonic frequency is 0~25KHZ, the stirring speed is 100rap / min~700rap / min, the reaction temperature is 25~100℃, and the reaction time is 3h~48h.

2. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (1), the purity of the liquid carbon dioxide is ≥99%, and the purity of the liquid ammonia is ≥99.6%.

3. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (2), a dispersant solution is first added to the rare earth nitrate solution to obtain a rare earth mixture, and then the rare earth mixture is pumped into a high-gravity reactor; and / or Rare earth raw materials are dissolved in nitric acid to obtain a rare earth nitrate solution; The concentration of rare earth nitrate solution is 25~200g / L; The rare earth raw materials are selected from rare earth carbonates or rare earth oxides, wherein the rare earth carbonates or rare earth oxides are one of the carbonates and oxides corresponding to lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium.

4. The method for preparing high-purity nano-rare earth oxide powder according to claim 3, characterized in that, The dispersant solution is a mixture of solvent and water in a mass ratio of 0.1:1 to 1:1; wherein, The solvent is one or more of ethanol, ethylene glycol, propylene glycol, polypropylene glycol, polyvinylpyrrolidone, glycerol, diethylene glycol monobutyl ether, and sodium citrate; The mass ratio of the dispersant solution to the rare earth raw material is 0.001-10%.

5. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (2), the hypergravity reaction conditions are a hypergravity rotation speed of 1000rap / min to 6000rap / min and a reaction temperature of 25 to 60℃.

6. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, The ratio of organic compounds to nonionic multiblock solvents is 0.1:1 to 1:1; The mass ratio of crystal form control agent to rare earth raw material is 0.001-10%.

7. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (3), the mixed precipitant is pumped in until the solution pH is 7.5~9.

5.

8. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (4), the washing involves alternating washing with washing solutions, wherein the washing solutions are one or more of deionized water, ethanol, and ethylene glycol, and the number of washing cycles is 1 to 8; and / or, The drying temperature is 40℃~150℃, and the time is 1h-24h.

9. The method for preparing high-purity nano-rare earth oxide powder according to claim 1, characterized in that, In step (4), the calcination temperature is 500℃~1500℃ and the time is 1h-48h.

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