A method for preparing high-purity cerium dioxide

Abstract

The invention discloses a method for preparing high-purity cerium dioxide, using analytical pure cerium nitrate raw material, firstly removing impurities from the raw material, removing metal impurities such as iron, zinc, and lanthanum in cerium nitrate, then continuing to crystallize and remove impurities from cerium nitrate, further removing other metal and non-metallic impurities therein, obtaining cerium nitrate with higher purity, adjusting the pH of the purified cerium nitrate solution and introducing ozone to oxidize trivalent cerium to obtain a tetravalent cerium solution, then adding alkali to the obtained tetravalent cerium to precipitate and collect filter residues to obtain cerium hydroxide precipitate, filtering, washing, drying and crushing the precipitate, and then calcining at 300-600°C for 3-6h in an oxygen atmosphere to obtain high-purity cerium dioxide. The purity of the high-purity cerium dioxide provided by the invention can reach 5N, has broad application prospects, is simple and easy to operate, has low cost, and has stable and reliable product quality, which is conducive to large-scale promotion and utilization.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity cerium dioxide, and belongs to the field of preparation of rare earth oxide products. Background Art

[0002] Rare earth is an important strategic resource in my country. It is widely used in the fields of national defense industry, electronics industry, environmental protection, new energy industry, etc. It is an important raw material necessary for the development of high-tech industry. High-purity rare earth and its compounds have good physical and chemical properties and are constantly being used in new energy vehicles, integrated circuits, new displays, 5G communications and other fields. Cerium, as a rare earth element, is extremely widely used. Cerium oxide CeO2 has a unique oxygen storage and release function and high-temperature rapid oxygen vacancy diffusion ability. It can be widely used in redox reactions and has become a promising automobile exhaust purification catalytic material, high-temperature oxygen-sensitive semiconductor, pH sensor, solid oxide fuel cell SOFC electrode material, electrochemical reaction promoter, metal antioxidant, anti-corrosion coating and additives, and chemical mechanical polishing CMP abrasives, etc. It has great development potential in the high-tech field.

[0003] High-purity rare earth refers to rare earth metals and their compounds with a purity greater than 99.99% (4N). With the development of cutting-edge defense science and technology such as electronics, optics and lasers, the demand for high-purity rare earth materials is increasing. In order to develop advanced materials with higher performance, rare earth metals and their compounds with higher purity are needed. Therefore, the development of high-purity or ultra-high-purity rare earth compounds with a purity of 5N and 6N is gradually increasing. Due to the special outer electron configuration of cerium, cerium can exist stably in positive trivalent and positive tetravalent states, and the purity of cerium dioxide has a significant impact on its properties and uses. High-purity cerium dioxide is necessary for the design and manufacture of various types of optical and electronic devices. When using cerium dioxide as a raw material, internal impurities should be avoided and structural defects in cerium dioxide should be minimized. It is generally believed that the higher the purity of cerium dioxide, the fewer internal defects, the stronger the grain stability, and the higher the corresponding activity. For this reason, the use of simple methods to prepare high-purity or ultra-high-purity cerium dioxide materials is currently a hot topic of research. At present, ordinary cerium dioxide products on the market are mainly yellow cerium dioxide obtained by roasting cerium compounds such as cerium carbonate, cerium oxalate and cerium hydroxide, and white cerium dioxide obtained by roasting cerium sulfate. The above raw materials are usually prepared by a solution method using cerium salts and precipitants. The raw cerium salts used are mostly chemically pure or analytically pure, and the purity is mostly 2N or 3N. There are a certain amount of iron, silicon, calcium, magnesium, aluminum and other compounds, which are not of high purity. In addition, precipitation and sintering treatments are mostly simple heat treatments of cerium precipitates such as carbonates, hydroxides, oxalates, etc. to decompose them, and complete oxidation of trivalent cerium cannot be achieved. A small amount of cerium trioxide will inevitably appear. Although the purity and yield of cerium oxide in the product are high, the cerium dioxide content in cerium oxide and the overall purity of cerium dioxide are not high, and cerium dioxide products with a purity of 5N or 6N or above cannot be obtained, affecting its application in cutting-edge fields.

[0004] CN110194480B discloses a method for preparing nano cerium oxide, comprising mixing cerium salt and carbonate or oxalate in a molar ratio of 1: (1-3), then adding an alcohol dispersant for sufficient grinding reaction, washing and drying after the reaction to obtain a precursor; and then calcining the precursor to prepare cerium oxide powder. The obtained cerium oxide powder has a small particle size, high purity, good dispersibility, and the whole process is simple, easy to operate, low cost, low equipment requirements, green and environmentally friendly, and a large output of cerium oxide, the operating procedure is continuously adjustable, the experimental process is easy to control, and it is easy to industrialize production. CN1288088C discloses a method for preparing high-purity active nanometer cerium dioxide, which uses cerium salt as cerium source, carbonate, oxalate or oxalic acid as precipitant, adds surfactant, and generates precursor by chemical precipitation reaction under mechanical stirring; the precursor is filtered, washed, dispersed, dried, and roasted in a muffle furnace to obtain high-purity active nanometer CeO2 finished product, which has low raw material price, high product yield, easy operation process, simple equipment and low preparation cost. CN101898782A discloses a method for producing high-purity cerium oxide product, which uses aqueous solution obtained by dissolving crystalline cerium nitrate in deionized water as raw material, industrial grade oxalic acid as precipitant, obtains solid cerium oxalate salt after washing with deionized water and dehydrating in a centrifuge, and obtains high-purity cerium oxide product with purity of 99.99% and impurity iron oxide less than 5ppm after high-temperature calcination in a four-hole kiln. CN1202459A discloses a method for preparing high-purity cerium oxide, which comprises the following steps: introducing a mixed rare earth sulfuric acid solution containing trivalent cerium into the anode chamber of a double-chamber electrolytic cell for direct current electrolytic oxidation to oxidize the trivalent cerium into tetravalent cerium, extracting the trivalent cerium with an organic extractant that can selectively extract the tetravalent cerium, and then reducing and stripping the organic phase loaded with the tetravalent cerium with a stripping solution containing a reducing agent to reduce the tetravalent cerium to trivalent cerium, and finally subjecting the obtained cerium-containing aqueous solution to conventional chemical impurity removal, precipitation, drying, and calcination to obtain a high-purity cerium oxide product. CN106995217A discloses a method for producing nano-scale high-purity cerium oxide powder, and the specific steps are as follows: (1) first prepare a cerium nitrate precursor solution; (2) add the precursor solution prepared in step (1) to an ultrasonic atomization device, and use the cavitation effect of ultrasound to atomize the solution into a smoky gas state to form droplets of micro-nano-scale solution; (3) use a fan to pump the droplets produced in step (2) into a high-temperature atmosphere for spray pyrolysis to produce high-purity, micro-nano-scale cerium oxide powder. CN107416885B discloses a method for producing cerium oxide by electric melting, wherein the cerium oxide raw material is put into an electric arc furnace in batches for melting, and after the melting is completed, it is kept warm for 0 to 2 hours, and then cooled with the furnace to obtain a fused block, and the fused block is crushed, iron-removed, impurity-removed and ground to obtain sand-like or powdery fused cerium oxide of different particle sizes. The process of the present invention is simple, the production cost is low, and other impurities will not be introduced or harmful gases will not be generated during the production process.CN107758719A discloses an environmentally friendly extraction method for high-purity cerium dioxide, comprising the following steps: (1) extraction: mixing cerium chloride liquid and an extractant in a volume ratio of 1:1.2-1.5 for extraction and separation, adding 4-6% by weight of the extractant of hydrotalcite, performing ultrasonic dispersion for 20-30 minutes, standing and separating, recovering the solid phase, and inputting the organic phase into a back extraction procedure; (2) back extraction: taking an oxalic acid solution of 1.5-2.0 times the volume of the obtained organic phase, back extracting it at 50-60°C, performing ultrasonic dispersion for 20-30 minutes, filtering to obtain a precipitate; (3) oxidation: calcining and oxidizing the obtained precipitate at 1000-1100°C for 12-15 hours to obtain high-purity cerium dioxide. CN108928845A discloses a method for preparing high-purity cerium oxide. The method comprises the following steps: treating a sample to be treated with sulfuric acid to obtain a primary treatment liquid and a first solid residue; subjecting the primary treatment liquid to a precipitation reaction to obtain a rare earth precipitate containing cerium hydroxide; neutralizing the rare earth precipitate with hydrochloric acid to obtain a secondary treatment liquid containing rare earth chloride; subjecting the secondary treatment liquid to a first extraction treatment with a first organic extractant, and then subjecting the extracted phase obtained in the first extraction treatment process to a stripping treatment with a stripping agent to obtain a raffinate containing cerium chloride and an extract containing terbium chloride; subjecting the raffinate to a second extraction treatment with a second organic extractant to obtain a cerium chloride solution; and subjecting the cerium chloride solution to precipitation and calcination treatments in sequence to obtain high-purity cerium oxide.

[0005] There are many methods for separating and extracting cerium in current hydrometallurgy, and most of their process principles are based on Ce 4+ With non-CE RE 3+ There are many cerium separation processes that can be roughly divided into two categories: the first is solvent extraction; the second is chemical precipitation. The chemical precipitation method currently used is based on the principle of Ce 4+ With RE 3+ The pH value difference when hydrolyzed in aqueous solution, Ce at a specific acidity 4+ Insoluble and other RE 3+ Rare earth elements are dissolved into corresponding inorganic acid salt solutions and separated by filtering. This process takes a long time to operate, which is 6 to 8 hours, and the filtering process is not easy to complete. The purity of cerium in the filtered precipitate is 85 to 95%, and the appearance color of cerium oxide is dark brown. Therefore, the existing rare earth hydrometallurgical industry to produce more than 99% of cerium oxide is mostly replaced by extraction, but the extraction process is complicated, requires a lot of equipment, and the organic extractant used has certain toxicity. It can be seen from this that it is necessary to develop a method for preparing high-purity cerium dioxide. If a high-purity cerium dioxide material with a purity of at least 5N can be prepared by a simple chemical precipitation method, then this method will have great technical advantages and market prospects. Summary of the invention

[0006] In order to solve the defects in the prior art, the present invention provides a method for preparing high-purity cerium dioxide, using conventional analytical pure cerium nitrate raw material, removing sulfide impurities, removing metal impurities such as iron, zinc, and lanthanum in cerium nitrate, and then removing impurities by crystallization according to the solubility change, further removing other metal and non-metallic impurities therein, obtaining a cerium nitrate raw material with high purity, and ozone oxidation of the purified cerium nitrate to convert the trivalent cerium in the solution into tetravalent cerium, and adjusting the pH by sodium hydroxide solution to hydrolyze and precipitate the tetravalent cerium ion, and finally crushing the cerium hydroxide precipitation product and calcining it in an oxygen atmosphere to obtain high-purity cerium dioxide particles that are almost free of trivalent cerium. The preparation method of the present invention can obtain high-purity cerium dioxide, and the method is easy to operate, low cost, and stable and reliable product quality.

[0007] In order to achieve the above-mentioned object of the invention, the present application provides a method for preparing high-purity cerium dioxide, comprising the following steps:

[0008] 1) Cerium nitrate pretreatment: dissolve cerium nitrate hexahydrate in deionized water to prepare 0.5~1M cerium nitrate solution A, add 0.01~0.1M ammonium sulfide aqueous solution to solution A, continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1%~5% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 105℃~120℃, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution under ice bath conditions, age and centrifuge to obtain cerium nitrate crystals; conventional analytical pure cerium nitrate contains a small amount of impurities containing iron, calcium, silicon, lanthanum and other compounds. By using the difference in the solubility product of the sulfides of the above substances, adding ammonium sulfide to the cerium nitrate solution can further precipitate and remove impurities such as iron, zinc, lanthanum, copper, and lead. For silicon and other metal impurities such as aluminum, the corresponding nitrate solubility changes with temperature are different from cerium nitrate, and crystallization separation is carried out, and cerium nitrate is crystallized and further purified. The pH value of the cerium nitrate solution is controlled at 0.5 and the temperature is controlled at 105°C~120°C, which not only ensures the supersaturation of the cerium nitrate solution, so that the cerium nitrate can be precipitated as much as possible in the later stage, but also ensures that the cerium nitrate crystals carry less non-rare earth impurity elements when precipitating in the supersaturated solution. At the same time, the solution can be quickly cooled under ice bath conditions to have a large supersaturation, so that it exceeds the metastable zone limit and precipitates a large number of crystal nuclei, further improving the yield of the final product. This method is simple and easy to implement, has low equipment requirements, and is low in cost, and is suitable for industrial production.

[0009] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5-1 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0010] 3) Ozone is introduced into solution B under stirring. After 0.5-1h, 0.1M sodium hydroxide solution is added dropwise to solution B until the pH is 6-7. Then, the temperature of solution B is controlled at 50-80°C in a water bath to react for 5-10h until precipitation is complete, and the residue is collected by filtration. Ozone is a strong oxidant and can completely oxidize the trivalent cerium in the solution into tetravalent cerium. Since cerium hydroxide begins to precipitate at a pH of 0.7, in order to avoid the adsorption of cerium hydroxide precipitate on other particles in the solution and reduce impurities in cerium oxide, the pH of the system is controlled before the oxidation reaction to inhibit the precipitation of cerium hydroxide precipitate during the oxidation process. After a period of reaction, the trivalent cerium is basically completely oxidized. At this time, the pH of the system begins to be increased to achieve the precipitation of tetravalent cerium, and the product has a high purity.

[0011] 4) The filter residue is washed, dried, and crushed into powder, and the powder is calcined at 300-600°C for 3-6 hours in an oxygen atmosphere. Washing the precipitate can further remove other ions adsorbed on the surface and improve the purity of cerium oxide. In addition, crushing and then calcining in an oxygen atmosphere can effectively eliminate the appearance of trivalent cerium or oxygen vacancies in cerium oxide during the heat treatment of cerium hydroxide precipitation, thereby improving the purity of the product.

[0012] Furthermore, the cerium nitrate hexahydrate is analytically pure with a purity of 99% to 99.5%.

[0013] Furthermore, the aging time is 0.5~2h.

[0014] Furthermore, in step 3), the flow rate of ozone is 0.1-1 L / min, and the ozone is continuously introduced while stirring during the water bath reaction.

[0015] Furthermore, in step 4), the rinsing is performed by sequentially rinsing with deionized water, anhydrous ethanol, and deionized water; the drying is performed by oven drying at a drying temperature of 60 to 80° C. for a drying time of 1 to 5 hours; and the crushing is performed by crushing the particles into 100 to 400 meshes using a crusher.

[0016] Furthermore, the calcination in step 4) is a staged heat preservation calcination, specifically: heating to 300°C and keeping for 1-2 hours, then heating to 400°C and keeping for 1-2 hours, then heating to 600°C and keeping for 1-2 hours. After a large number of experiments, it was found that the cerium dioxide grains obtained by staged heat preservation calcination are more complete and the particle size is more uniform than that of single temperature calcination, and the internal lattice defects are reduced to a certain extent. As the temperature increases, the grain size gradually increases. During low-temperature calcination, CeO2 particles are in the initial stage of structure formation. At this time, due to the small diffusion capacity of particles, the formed crystal nuclei are difficult to grow, and the CeO2 grains are small; as the calcination temperature increases, the particle diffusion capacity increases exponentially, and the grains gradually grow; and because the relatively small grains have higher surface energy, while the surface energy of larger grains is lower, there is excess surface energy between the interface of small grains and large grains. This excess surface energy becomes a driving force that enables particles inside small grains to jump over the grain boundaries and diffuse into the interior of large grains, causing the grain boundaries to move, so that large grains grow further, accompanied by the annexation and disappearance of some smaller grains. Therefore, with the increase of calcination temperature, the size of CeO2 grains increases. The size of CeO2 grains increases significantly with the extension of calcination time, and the grain growth rate increases significantly. In the early stage of isothermal calcination, the size grows faster: after the calcination time exceeds 3h, the growth rate gradually decreases and gradually tends to be stable. This is because as the isothermal heat treatment process proceeds, the particles continue to grow, the corresponding specific surface area decreases, the surface energy decreases, the structural defects decrease, and the lattice stability increases, then the particle diffusion and grain growth driving forces are reduced, making the grain size growth slower.

[0017] Furthermore, the preparation method of high-purity cerium dioxide comprises the following steps: 1) cerium nitrate pretreatment: dissolving cerium nitrate hexahydrate with a purity of 99.5% in deionized water to prepare a 0.5M cerium nitrate solution A, adding a 0.01M ammonium sulfide aqueous solution to the solution A, stirring continuously until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1% of the volume of the solution A, filtering, and collecting the filtrate; adjusting the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heating the filtrate to 110°C, and concentrating to obtain a supersaturated cerium nitrate solution; crystallizing the supersaturated cerium nitrate solution in an ice bath, aging for 2 hours, and centrifuging to obtain cerium nitrate crystals;

[0018] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0019] 3) Ozone was introduced into solution B under stirring at a flow rate of 0.2 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration.

[0020] 4) The filter residue is washed with deionized water, anhydrous ethanol and deionized water in turn; then, it is placed in an oven and dried at 60°C for 3 hours; the dried filter residue is crushed into 400 meshes with a crusher, and the powder is calcined at 600°C for 5 hours in an oxygen atmosphere to obtain the product.

[0021] The present invention also provides a high-purity cerium dioxide, wherein the purity of the cerium oxide is not less than 99.9995%. After measurement and analysis, the product is pure cerium dioxide without the presence of trivalent cerium.

[0022] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0023] 1. The present invention provides a method for preparing high-purity cerium dioxide by chemical precipitation. The method is simple, and adopts existing analytically pure cerium nitrate raw material, and after simple impurity removal, ozone oxidation is carried out to convert trivalent cerium into tetravalent cerium, and the tetravalent cerium ions are hydrolyzed and precipitated. The obtained cerium hydroxide precipitate product is crushed and calcined in an oxygen atmosphere to obtain high-purity cerium dioxide particles that are substantially free of trivalent cerium. This method provides a new idea for the synthesis of high-purity cerium dioxide, and obtains a cerium dioxide product with a relatively high purity.

[0024] 2. The raw materials of the present invention are cheap, the operation process is easy, the required equipment is simple, the preparation cost is low, and it is beneficial to save manpower, material resources and financial resources;

[0025] 3. The method of the present invention does not require the introduction of surfactants, dispersants or other additives, thus avoiding the introduction of excessive impurities, significantly improving the purity of the rare earth compound, and the purity of the product cerium oxide reaches 5N. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the XRD spectrum of cerium dioxide obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0028] It should be noted that the reference to "embodiment" in this document means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0030] For the detection of the purity of cerium dioxide, an inductively coupled plasma mass spectrometer is used to determine the content of rare earth oxides in the sample, and then the purity of CeO2 is calculated.

[0031] The content of trivalent cerium in ceria is measured by ultraviolet-visible spectroscopy, and is characterized by the difference between the actual bandgap width and the theoretical bandgap width of ceria. For details, see Chinese patent CN118275373A.

[0032] Example 1

[0033] A method for preparing high-purity cerium dioxide comprises the following steps:

[0034] 1) Cerium nitrate pretreatment: dissolve 99% pure cerium nitrate hexahydrate in deionized water to prepare 0.5M cerium nitrate solution A, add 0.01M ammonium sulfide aqueous solution to solution A, continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 105°C, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age for 0.5h, and centrifuge to obtain cerium nitrate crystals;

[0035] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0036] 3) Ozone was introduced into solution B under stirring at a flow rate of 0.1 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. Stirring was continued and ozone was continuously introduced during the water bath reaction.

[0037] 4) The filter residue was rinsed with deionized water, anhydrous ethanol and deionized water in turn; then dried in an oven at 60°C for 1 hour; the dried filter residue was crushed to 100 mesh with a crusher, and the powder was calcined at 300°C for 3 hours in an oxygen atmosphere.

[0038] The prepared cerium oxide was tested, and after measurement and calculation, the purity of the cerium dioxide was 99.99951%. The actual band gap width of the cerium dioxide calculated by UV-visible spectroscopy was the same as the theoretical band gap width of the cerium dioxide. It can be seen that the cerium in the cerium dioxide product is all in tetravalent form, without trivalent cerium. The cerium dioxide product has a high purity. Comparing the XRD pattern with the PDF standard card, it can be seen that the peak position and peak intensity of the sample are basically consistent with those of CeO2, and the spectrum shows sharp peaks, indicating that the grains are small and the crystallinity is good.

[0039] Example 2

[0040] A method for preparing high-purity cerium dioxide comprises the following steps:

[0041] 1) Cerium nitrate pretreatment: dissolve cerium nitrate hexahydrate with a purity of 99.5% in deionized water to prepare a 1M cerium nitrate solution A, add 0.1M ammonium sulfide aqueous solution to solution A, and continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 5% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 120°C, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age for 2 hours, and centrifuge to obtain cerium nitrate crystals;

[0042] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0043] 3) Ozone was introduced into solution B under stirring at a flow rate of 1 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. Stirring was continued and ozone was continuously introduced during the water bath reaction.

[0044] 4) The filter residue was rinsed with deionized water, anhydrous ethanol and deionized water in turn; then dried in an oven at 80°C for 5 hours; the dried filter residue was crushed to 400 mesh with a crusher, and the powder was calcined at 600°C for 6 hours in an oxygen atmosphere.

[0045] The prepared cerium oxide was tested, and after measurement and calculation, the purity of the cerium dioxide was 99.99993%. The actual band gap width of the cerium dioxide calculated by UV-visible spectroscopy was the same as the theoretical band gap width of the cerium dioxide. It can be seen that the cerium in the cerium dioxide product is all in tetravalent form, and there is no trivalent cerium.

[0046] Example 3

[0047] A method for preparing high-purity cerium dioxide comprises the following steps:

[0048] 1) Cerium nitrate pretreatment: dissolve 99.5% pure cerium nitrate hexahydrate in deionized water to prepare 0.5M cerium nitrate solution A, add 0.01M ammonium sulfide aqueous solution to solution A, and continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 110°C, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age for 2 hours, and centrifuge to obtain cerium nitrate crystals;

[0049] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0050] 3) Ozone was introduced into solution B under stirring at a flow rate of 0.2 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. Stirring and ozone were continued during the water bath reaction.

[0051] 4) Rinse the filter residue with deionized water, anhydrous ethanol and deionized water in turn; then place it in an oven and dry it at 60°C for 3 hours; crush the dried filter residue to 400 mesh with a crusher, and calcine the powder in an oxygen atmosphere, first heating to 300°C and keeping it for 1 hour, then heating to 400°C and keeping it for 2 hours, and then heating to 600°C and keeping it for 1 hour.

[0052] The prepared cerium oxide was tested, and after measurement and calculation, the purity of the cerium dioxide was 99.99991%. The actual band gap width of the cerium dioxide calculated by UV-visible spectroscopy was the same as the theoretical band gap width of the cerium dioxide. It can be seen that the cerium in the cerium dioxide product is all in tetravalent form, and there is no trivalent cerium.

[0053] Comparative Example 1

[0054] A method for preparing cerium dioxide comprises the following steps:

[0055] 1) Cerium nitrate pretreatment: Dissolve 99.5% pure cerium nitrate hexahydrate in deionized water to prepare 0.5 M cerium nitrate solution A, and adjust the pH of the solution to 0.5 with 1 M dilute nitric acid;

[0056] 2) Ozone was introduced into solution A under stirring at a flow rate of 0.2 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. Stirring was continued and ozone was continuously introduced during the water bath reaction.

[0057] 3) Rinse the filter residue with deionized water, anhydrous ethanol and deionized water in turn; then place it in an oven and dry it at 60°C for 3 hours; crush the dried filter residue to 400 mesh with a crusher, and calcine the powder in an oxygen atmosphere, first heating to 300°C and keeping it for 1 hour, then heating to 400°C and keeping it for 2 hours, and then heating to 600°C and keeping it for 1 hour.

[0058] The prepared cerium oxide was tested, and after measurement and calculation, the purity of the cerium dioxide was 99.84%. The difference between the band gap of the product and the theoretical band gap of cerium dioxide calculated by UV-visible spectroscopy was 0.7 eV. It can be seen that there are certain rare earth and non-rare earth impurities in the cerium dioxide product, and a small amount of cerium in the cerium dioxide exists in the form of trivalent cerium, indicating that there are certain oxygen vacancies in the cerium dioxide.

[0059] Comparative Example 2

[0060] A method for preparing cerium dioxide comprises the following steps:

[0061] 1) Cerium nitrate pretreatment: dissolve 99% pure cerium nitrate hexahydrate in deionized water to prepare 0.5M cerium nitrate solution A, add 0.01M ammonium sulfide aqueous solution to solution A, continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 105°C, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age for 0.5h, and centrifuge to obtain cerium nitrate crystals;

[0062] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid;

[0063] 3) Oxygen was introduced into solution B under stirring at a flow rate of 0.1 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. Stirring was continued and oxygen was continuously introduced during the water bath reaction.

[0064] 4) The filter residue was rinsed with deionized water, anhydrous ethanol and deionized water in turn; then calcined at 300°C for 3h in an oxygen atmosphere.

[0065] The prepared cerium oxide was tested. After measurement and calculation, the purity of the cerium dioxide was 99.9992%. The difference between the actual band gap width of the cerium dioxide calculated by UV-visible spectroscopy and the theoretical band gap width of the cerium dioxide was 1.1 eV. It can be seen that the cerium dioxide product has a high purity, but some cerium exists in the form of trivalent cerium. After analysis, the reason is that the oxidation ability of oxygen is worse than that of ozone, and complete oxidation takes longer. In addition, some oxygen vacancies may also exist in the direct calcination of samples that have not been crushed.

[0066] Comparative Example 3

[0067] A method for preparing high-purity cerium dioxide comprises the following steps:

[0068] 1) Cerium nitrate pretreatment: dissolve 99.5% pure cerium nitrate hexahydrate in deionized water to prepare 0.5M cerium nitrate solution A, add 0.2M ammonium sulfide aqueous solution to solution A, and continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 10% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 110°C, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age for 2 hours, and centrifuge to obtain cerium nitrate crystals;

[0069] 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5M cerium nitrate solution B, introducing ozone into solution B under stirring at a flow rate of 0.2L / min, and after 1 hour, adding 0.1M sodium hydroxide solution dropwise into solution B until the pH value is 7, and then controlling the temperature of solution B at 80°C in a water bath to react for 6 hours until precipitation is complete, filtering and collecting the residue, and continuously stirring and introducing ozone during the water bath reaction;

[0070] 3) The filter residue was rinsed with deionized water, anhydrous ethanol and deionized water in turn; then dried in an oven at 60°C for 3 h; the dried filter residue was crushed to 400 mesh using a crusher, and the powder was calcined at 600°C for 5 h in an oxygen atmosphere.

[0071] The prepared cerium oxide was tested, and after measurement and calculation, the purity of the cerium dioxide was 99.9996%. The difference between the band gap of the product and the theoretical band gap of cerium dioxide calculated by UV-visible spectroscopy was 0.2 eV. Only a very small amount of trivalent cerium was present in the cerium dioxide product, but it was calculated that the yield of cerium dioxide was low. The reason is that excessive ammonium sulfide caused part of the cerium to precipitate, affecting the yield of cerium dioxide.

[0072] The above is a detailed description of a method for preparing high-purity cerium dioxide. The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, its architecture can be flexible and can derive a series of products. Just making a few simple deductions or substitutions should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. A method for preparing high-purity cerium dioxide, characterized in that: The steps include: 1) Cerium nitrate pretreatment: dissolve cerium nitrate hexahydrate in deionized water to prepare 0.5~1M cerium nitrate solution A, add 0.01~0.1M ammonium sulfide aqueous solution to solution A, continue stirring until precipitation is complete, wherein the amount of ammonium sulfide solution added is 1%~5% of the volume of solution A, filter, and collect the filtrate; adjust the pH of the filtrate to 0.5 with 1M dilute nitric acid, then heat the filtrate to 105℃~120℃, and concentrate to obtain a supersaturated cerium nitrate solution; crystallize the supersaturated cerium nitrate solution in an ice bath, age, and centrifuge to obtain cerium nitrate crystals; 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5-1 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid; 3) Ozone was introduced into solution B under stirring. After 0.5-1h, 0.1M sodium hydroxide solution was added dropwise to solution B until the pH value was 6-7. Then, the temperature of solution B was controlled at 50-80℃ in a water bath for 5-10h until precipitation was complete. The residue was collected by filtration. 4) Rinse and dry the filter residue, then crush it into powder, and calcine the powder at 300-600°C in an oxygen atmosphere for 3-6 hours.

2. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: The cerium nitrate hexahydrate is analytically pure with a purity of 99% to 99.5%.

3. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: The aging time in step 3) is 0.5~2h.

4. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: The flow rate of ozone in step 3) is 0.1-1 L / min, and the ozone is continuously introduced while stirring during the water bath reaction.

5. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: In the step 4), the rinsing is performed by sequentially rinsing with deionized water, anhydrous ethanol and deionized water; the drying is performed by oven drying at a temperature of 60 to 80° C. for a drying time of 1 to 5 hours; and the crushing is performed by crushing with a crusher to 100 to 400 meshes.

6. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: The calcination in step 4) is a staged heat preservation calcination, specifically: heating to 300° C. and keeping it for 1-2 hours, then heating to 400° C. and keeping it for 1-2 hours, then heating to 600° C. and keeping it for 1-2 hours.

7. The method for preparing high-purity cerium dioxide according to claim 1, characterized in that: The method comprises the following steps: 1) pretreatment of cerium nitrate: dissolving cerium nitrate hexahydrate with a purity of 99.5% into deionized water to prepare a 0.5M cerium nitrate solution A, dropping a 0.01M ammonium sulfide aqueous solution into the solution A, and continuously stirring until precipitation is complete, wherein the amount of the ammonium sulfide solution added is 1% of the volume of the solution A, filtering, and collecting the filtrate; adjusting the pH of the filtrate to 0.5 with 1M dilute nitric acid, and then heating the filtrate to 110°C, and concentrating to obtain a supersaturated cerium nitrate solution; The supersaturated cerium nitrate solution was crystallized in an ice bath, aged for 2 hours, and centrifuged to obtain cerium nitrate crystals; 2) dissolving the cerium nitrate crystals obtained in step 1) into deionized water to prepare a 0.5 M cerium nitrate solution B, and adjusting the pH of the solution B to 0.5 with 1 M dilute nitric acid; 3) Ozone was introduced into solution B under stirring at a flow rate of 0.2 L / min. After 1 h, 0.1 M sodium hydroxide solution was added dropwise to solution B until the pH value was 7. Then, the temperature of solution B was controlled at 80°C in a water bath and reacted for 6 h until precipitation was complete. The residue was collected by filtration. 4) The filter residue is washed with deionized water, anhydrous ethanol and deionized water in turn; then, it is placed in an oven and dried at 60°C for 3 hours; the dried filter residue is crushed into 400 meshes with a crusher, and the powder is calcined at 600°C for 5 hours in an oxygen atmosphere to obtain the product.

8. The high-purity cerium dioxide prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The purity of the cerium oxide is not less than 99.9995%.

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