Method for preparing hafnium oxide with ultralow iron content

Abstract

The invention relates to the technical field of hafnium oxide preparation, in particular to a method for preparing hafnium oxide with ultralow iron content, which comprises the following steps: based on N235 extraction separation in a hydrochloric acid system, crushing hafnium oxide raw stone, performing coarse grinding to obtain hafnium oxide powder, then sequentially performing alkali fusion decomposition treatment and acid leaching impurity removal treatment to obtain a zirconium-hafnium mixed solution, and then performing vacuum drying on the zirconium-hafnium mixed solution to obtain the hafnium oxide with ultralow iron content. The preparation method comprises the following steps: taking hafnium as a raw material, carrying out extraction and back extraction to obtain a hafnium-enriched solution, treating the hafnium-enriched solution with ion exchange resin to obtain a high-purity hafnium solution, finally adding saturated ammonia water, filtering and washing the obtained precipitate, drying, and firing to obtain the hafnium oxide with ultralow iron content. According to the invention, while zirconium and hafnium separation is realized, a small amount of contained metal cations, especially iron ions, are fully removed, and the iron content is reduced, so that hafnium oxide with ultralow iron content is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hafnium oxide preparation, in particular to a method for preparing ultra-low-iron-content hafnium oxide based on N235 extraction separation in a hydrochloric acid system. BACKGROUND

[0002] Hafnium oxide has important application value in multiple high-tech fields due to its excellent physical and chemical properties. In the ceramic industry, hafnium oxide as an additive can significantly improve the high-temperature resistance and mechanical strength of ceramic products; in the aerospace field, hafnium oxide materials are used to manufacture key components in extreme environments; in the electronic industry, high-purity hafnium oxide is a key material for manufacturing high-performance electronic components. In addition, hafnium oxide is also an important raw material for preparing other high-purity hafnium compounds.

[0003] At present, solvent extraction and sublimation are mainly used in the industry for hafnium oxide purification. Although sublimation can obtain products with high purity, it has the disadvantages of large equipment investment, high energy consumption, long process cycle, and the need to use dangerous high-temperature chlorine gas, which poses a great safety hazard. Although the solvent extraction method is relatively simple to operate, the traditional process cannot effectively remove iron impurities, resulting in high iron content in the final product. The presence of iron impurities can cause lattice distortion of the material, affecting the dielectric properties and thermal stability of the material, and seriously restricting the application effect of hafnium oxide in high-tech fields.

[0004] In the prior art, the removal effect of conventional acid-base treatment and extraction process on iron impurities is limited, especially when dealing with raw materials with high iron content, it is often difficult to meet the requirement of ultra-low iron content. In addition, the extractant and auxiliary materials used in the traditional process also have deficiencies in separation efficiency and selectivity, resulting in complex process flow, unstable product yield and other problems. Therefore, it is of great significance to develop a hafnium oxide preparation method that can effectively reduce the iron content, simplify the process flow and improve the product purity. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing ultra-low-iron-content hafnium oxide based on N235 extraction separation in a hydrochloric acid system, which has the advantages of efficient removal of iron impurities, simplification of process flow and improvement of product purity.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions: A method for preparing ultra-low-iron-content hafnium oxide based on N235 extraction separation in a hydrochloric acid system, specifically comprising the following steps: S1 hafnium oxide pretreatment After the hafnium oxide raw stone is crushed, a ball mill is used for coarse grinding to obtain hafnium oxide powder with a particle size of 100-150 mu m; S2 acid-base treatment of hafnium oxide The hafnium oxide powder is sequentially subjected to alkali fusion decomposition treatment and acid leaching impurity removal treatment to obtain a zirconium-hafnium mixed solution; S3 extraction separation S3-1, the zirconium-hafnium mixed solution is added to a hydrochloric acid solution, and after being fully mixed, an aqueous phase is obtained, then the aqueous phase is pretreated, and an organic phase prepared is added in sequence into an extraction tank according to a volume ratio (2-5):1, stirring for 15-20 min, standing and separating, then the upper organic phase is transferred into a stripping tank, and sufficient dilute hydrochloric acid is added, stirring for 20-30 min, standing and separating, and the extraction-stripping is repeated for 3-5 times, so that a hafnium enrichment solution is obtained; S3-2, the hafnium enrichment solution is adjusted to a pH value of 2-3, and a strong acid type styrene resin column is introduced, then the impurities are eluted with dilute hydrochloric acid, and then hafnium is eluted with concentrated hydrochloric acid, so that a high-purity hafnium solution is obtained; S4 precipitation and calcination Saturated ammonia water is added to the high-purity hafnium solution, and the pH value is adjusted to 7.5-8.0, the obtained precipitate is filtered, washed and dried, and then calcined at 850-980℃ for 2-5h, so that ultra-low iron content hafnium oxide is obtained.

[0007] As a further preferred scheme of the present application, in S2, the specific operation of the alkali fusion decomposition treatment is as follows: According to a mass ratio of 1: (2-3), the hafnium oxide powder is fully mixed with sodium hydroxide, then organic composite microspheres are added, the amount of which is controlled to be 5-10% of the mass of the hafnium oxide ore, and after being fully mixed and uniformly mixed, the mixture is melted under sufficient oxygen and at 720-780℃ for 2-5h, then the molten product is cooled and leached with water to obtain an alkali fusion residue.

[0008] As a further preferred scheme of the present application, the preparation method of the organic composite microspheres is as follows: Step 1) 1.1-1.8g of zinc nitrate and 22.5-28.6g of 2-methyl imidazole are respectively dissolved in 8-12mL and 80-120mL of deionized water, the two are mixed and magnetically stirred, the obtained solution is centrifuged for 3-5 times, and then washed with methanol and deionized water and dried to obtain an organic powder; Step 2) ammonium bicarbonate and the organic powder are added to deionized water to obtain an internal aqueous phase solution, which is then added to a polylactic acid dichloromethane solution to form a primary emulsion, then a homogenizer is used for homogenization treatment, and then it is added to a polyvinyl alcohol solution, polyacrylonitrile fibers are added, and after being fully stirred, it is thoroughly washed with deionized water and ethanol, and then fully dried at 60-70℃ to obtain organic composite microspheres.

[0009] Further, in step 1), the stirring speed of the magnetic stirring is 1000-1500r / min, and the stirring time is 24-30h.

[0010] Further, in step 2), the amount ratio of the ammonium bicarbonate, the organic powder, the deionized water, the polylactic acid dichloromethane solution, the polyvinyl alcohol solution, and the polyacrylonitrile fiber is (1-2) g:(3-5) g:(20-30) mL:(100-150) mL:(1000-1600) mL:(0.2-0.5) g; The content of the polylactic acid in the polylactic acid dichloromethane solution is 5-8 wt%; The concentration of the polyvinyl alcohol solution is 0.2-0.5 wt%; The rotating speed of the homogenizer is 10000-15000 rpm.

[0011] In a further preferred embodiment of the present application, the specific operation of the acid leaching impurity removal treatment in S2 is as follows: The above-mentioned alkali slag is added into a hydrochloric acid solution with a pH value of 1-2, and after being fully stirred and dissolved, saturated ammonia water is added to adjust the pH value to 3-4, and then ammonium persulfate is added to control the addition amount to be 1-2% of the mass of the alkali slag, and after being fully placed, filtration is performed to obtain a zirconium-hafnium mixed solution.

[0012] In a further preferred embodiment of the present application, the volume ratio of the zirconium-hafnium mixed solution to the hydrochloric acid solution in S3-1 is 1:(1.0-1.5). The concentration of the hydrochloric acid solution is 5-7 mol / L.

[0013] In a further preferred embodiment of the present application, the specific operation of the water phase pretreatment in S3-1 is as follows: the water phase is first heated to 40-45℃, and then centrifuged at a rotating speed of 3000-5000 r / min for 5-10 min, and then a polyether surfactant is added to control the concentration to be 0.03-0.08 wt%, and then fully stirred.

[0014] In a further preferred embodiment of the present application, the preparation method of the organic phase in S3-1 is as follows: Tri-octyl tertiary amine and isooctanol are added into sulfonated kerosene to control the volume fraction to be 25-35% and 5-10% respectively to obtain the organic phase.

[0015] In a further preferred embodiment of the present application, in the extraction and stripping in S3-1, continuous stirring at 300-500 r / min is accompanied.

[0016] As can be seen from the above, the present application provides a method for preparing ultra-low iron content hafnium oxide and organic composite microspheres by N235 extraction separation under a hydrochloric acid system. Through the synergistic effect of the N235 extraction system and the organic composite microspheres, combined with multi-stage extraction separation and resin column purification process, the iron impurities are effectively removed and the hafnium element recovery rate is improved, and the process flow is simplified and the product purity is high. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] In existing technologies, hafnium oxide is widely used as a high-performance material in ceramics, electronic devices, and aerospace. Traditional solvent extraction methods suffer from residual iron impurities, and iron ions intercalating into the crystal lattice can cause phase transition defects in the material. Sublimation methods rely on high-temperature chlorine treatment, which has drawbacks such as high equipment costs and high operational risks.

[0019] To address the aforementioned issues, the inventors discovered that deep removal of iron impurities requires a continuous process throughout the entire preparation workflow. Analysis revealed that conventional processes failed to effectively separate zirconium and hafnium from iron impurities during the acid-base treatment stage, and the extraction stage lacked a multi-stage purification mechanism. Based on this, they proposed constructing a multi-stage extraction-adsorption synergistic system in a hydrochloric acid system. By optimizing the acid-base reaction conditions and introducing gradient elution in the resin column, a stepwise iron ion retention mechanism is established.

[0020] This application proposes a method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system, specifically including the following steps: crushing hafnium oxide raw material and coarsely grinding it to obtain powder; subjecting the powder to alkaline fusion decomposition and acid leaching to remove impurities to obtain a zirconium-hafnium mixed solution; mixing the solution with hydrochloric acid to form an aqueous phase, pretreating it, and then performing multi-stage extraction and back-extraction with an organic phase; the resulting hafnium enriched solution is subjected to gradient elution with a resin column to obtain a high-purity hafnium solution; finally, ultra-low iron content hafnium oxide is obtained by precipitation and calcination.

[0021] The pretreatment stage of hafnium oxide involves several steps. First, coarse grinding controls the raw material particle size within a specific range through mechanical crushing, which can be achieved using a ball mill. This step ensures sufficient contact efficiency in the subsequent acid-base reaction. Second, alkaline fusion decomposition in the acid-base treatment utilizes a strong alkali at high temperature to decompose the mineral structure, specifically achieved by mixing sodium hydroxide with other materials. This process promotes the initial separation of zirconium and hafnium from impurity elements. Third, acid leaching removes impurities by selectively dissolving the target element in an acidic solution, which can be achieved using hydrochloric acid solution in conjunction with an oxidant, effectively removing residual metal impurities. Fourth, organic phase preparation in the extraction separation involves mixing the extractant and diluent in a specific ratio, which can be achieved using a composite system of trioctyl tertiary amine and sulfonated kerosene. This ratio optimizes the selectivity of zirconium-hafnium separation. Fifth, resin column gradient elution uses acid solutions of different concentrations for stepwise elution, specifically achieved by adjusting the elution order of dilute and concentrated hydrochloric acid. This operation can deeply remove trace amounts of iron ions.

[0022] Specifically, the method realizes the systematic removal of iron impurities through the synergistic effect of four stages. The pretreatment stage controls the particle size of the powder to ensure the efficiency of the subsequent reaction, and the acid-base treatment stage realizes the preliminary separation of zirconium and hafnium from impurities. The extraction stage uses multi-stage circulation operation to strengthen the separation effect, combined with the gradient elution of the resin column to form an iron ion interception barrier. The precipitation stage precisely controls the pH value to avoid the co-precipitation of impurities, and high-temperature calcination ensures the integrity of the product crystal form. The parameters of each step form a synergistic effect, especially the combination design of the extraction volume ratio and the number of cycles, which effectively blocks the migration path of iron ions.

[0023] Compared with the prior art, the traditional solvent extraction method only removes impurities through a single extraction step, and fails to establish a multi-stage purification barrier, resulting in a residual amount of iron ions higher than 200 ppm. The method breaks the mineral inclusion structure through alkali fusion decomposition, combined with multi-stage extraction and resin adsorption to form a three-stage purification system, which can reduce the iron content to below 10 ppm. Compared with the sublimation method, the present solution does not require high-temperature chlorine gas treatment, and the whole process can be completed in a conventional reaction vessel.

[0024] Through the above technical solutions, the technical problem of deep removal of iron impurities in the preparation of hafnium oxide is effectively solved. By constructing a multi-stage separation system, the residual amount of iron ions in the final product is significantly reduced, avoiding material performance defects caused by lattice distortion. The method ensures the purity of the product while reducing the equipment requirements and operation risks, and is suitable for industrial continuous production.

[0025] The application further proposes a process step of mixing hafnium oxide powder and sodium hydroxide in a mass ratio of 1:2-3, adding 5-10% of organic composite microspheres based on the mass of hafnium oxide ore, melting in an oxygen-rich environment at 720-780℃ for 2-5 hours, and then water immersion to obtain alkali slag.

[0026] Among them, the mass ratio of sodium hydroxide 1:2-3 means that 2-3 times the mass of sodium hydroxide needs to be added per unit mass of hafnium oxide powder, which forms a strong alkaline melting environment to promote the conversion of iron elements into a soluble state. The addition amount of organic composite microspheres is 5-10%, which means that the mass of the microspheres accounts for a percentage of the total mass of hafnium ore, and they act as adsorption media to capture iron impurities during the melting process. The melting temperature range of 720-780℃ can effectively decompose the mineral structure while avoiding excessive equipment wear and tear. The melting time of 2-5 hours ensures that the reaction is completed. The oxygen-rich environment promotes the oxidation of iron elements to high-valence compounds by continuously introducing oxygen, enhancing the efficiency of subsequent separation.

[0027] Specifically, the hafnium oxide powder is mixed with excess sodium hydroxide to form an alkaline melt, which destroys the crystal lattice structure of hafnium oxide during high-temperature melting, allowing the iron element to be released in a soluble form. The organic composite microspheres act as functional adsorbent materials, with their porous structure selectively capturing iron ions in the molten system to form stable complexes. The oxygen-rich conditions promote the oxidation of ferrous ions to trivalent iron compounds, improving the removal rate in the subsequent water immersion stage. By controlling the melting temperature and time, the reaction efficiency and energy consumption are balanced, and finally the water immersion process separates the iron impurities from the alkali slag, forming a low-iron intermediate product.

[0028] The application further proposes a method for preparing organic composite microspheres, specifically including the following steps: Step 1): Dissolve zinc nitrate and 2-methyl imidazole in deionized water respectively, mix them, magnetically stir, centrifuge and wash, and dry to obtain an organic powder; Step 2): Add ammonium bicarbonate and the organic powder to deionized water to form an internal aqueous phase solution, mix it with a polylactic acid dichloromethane solution to form a primary emulsion, add a polyvinyl alcohol solution and a polyacrylonitrile fiber after homogenization treatment, and clean and dry to obtain the organic composite microspheres.

[0029] The coordination reaction between zinc nitrate and 2-methyl imidazole refers to the self-assembly of metal ions and organic ligands to form a porous structure, which can be achieved by stirring zinc nitrate and 2-methyl imidazole in a molar ratio of 1:3 in deionized water. This structure provides selective adsorption sites for iron ions. Magnetic stirring refers to the use of a rotating magnetic field to drive the solution to generate a vortex for mixing. Specifically, a rotation speed of 1000-1500 rpm can be maintained for 24-30 hours to ensure that the reactants are fully contacted to form a stable coordination structure. Centrifugal washing refers to the separation of solid and liquid phases by centrifugal force and the removal of unreacted substances. Specifically, the solution can be washed with methanol and deionized water alternately for 3-5 times to avoid the influence of impurities on the performance of the microspheres. The polylactic acid dichloromethane solution refers to a hydrophobic carrier formed by dissolving polylactic acid in dichloromethane. Specifically, a solution with a mass concentration of 5-8% can be used as the oil phase to encapsulate the internal aqueous phase and form an emulsion template. The polyacrylonitrile fiber refers to a micron-level fiber material prepared by electrospinning. Specifically, 0.2-0.5 grams of fiber can be mixed with the emulsion to enhance the mechanical strength of the microspheres through physical entanglement.

[0030] Specifically, a multi-level structure is constructed in stages to achieve efficient capture of iron impurities. First, zinc nitrate and 2-methyl imidazole are used to generate metal-organic frameworks with regular channels, and the surface active sites can specifically bind iron ions. Subsequently, the gas generated by the decomposition of ammonium bicarbonate is used as a pore-forming agent in the emulsion template method to form through channels in the polylactic acid carrier, which increases the specific surface area of the microspheres to more than 3 times that of traditional adsorbent materials. The coating effect of the polyvinyl alcohol solution forms a dense shell to prevent the microspheres from collapsing during high-temperature alkali melting. The introduction of polyacrylonitrile fiber makes the compressive strength of the microspheres exceed 15 MPa, allowing the microspheres to maintain structural integrity under severe stirring conditions.

[0031] The application further proposes that in the aforementioned step 1), the rotating speed of magnetic stirring is controlled in the range of 1000-1500 revolutions per minute, and the stirring time is controlled in the range of 24-30 hours.

[0032] The rotating speed of magnetic stirring refers to the mechanical speed of driving the stirring rotor to rotate, which can be realized by using a digital stirrer in combination with a programmable controller, and the stirring intensity is accurately controlled by adjusting the motor output power. This rotating speed range can provide sufficient shear force to promote the diffusion of reactant molecules, and can also avoid the solution splashing or the destruction of the crystal structure caused by excessively high rotating speed. The stirring time refers to the duration of the reaction system under the action of stirring, which can be realized by using a timer in combination with a stirring device, so as to ensure that the zinc nitrate and 2-methylimidazole are fully complexed to form a stable metal organic framework structure.

[0033] Specifically, during the complexation reaction of zinc nitrate and 2-methylimidazole, when the rotating speed is lower than 1000 revolutions per minute, the mixed liquid laminar flow state is dominant, the contact area of the reactants is insufficient, and agglomerates are easily generated due to excessively high local concentration; when the rotating speed exceeds 1500 revolutions per minute, the strong turbulent flow may tear the growing crystal framework. By limiting the stirring time to 24-30 hours, the formation of coordination bond and the crystal growth of zinc ions and organic ligands can be gradually completed. For example, under the condition of 26 hours of continuous stirring, it can be observed that the reaction liquid changes from turbidity to uniform suspension state, indicating that the ZIF-8 type crystals with concentrated particle size distribution are formed. The combination of the process parameters effectively avoids the problem of incomplete reaction caused by traditional intermittent stirring, and provides a precursor guarantee for the subsequent preparation of organic composite microspheres with regular pore structure.

[0034] The application further proposes that the dosage ratio of ammonium bicarbonate, organic powder, deionized water, polylactic acid dichloromethane solution, polyvinyl alcohol solution and polyacrylonitrile fiber is (1-2) g:(3-5) g:(20-30) mL:(100-150) mL:(1000-1600) mL:(0.2-0.5) g, the content of polylactic acid in the polylactic acid dichloromethane solution is 5-8 wt%, the concentration of the polyvinyl alcohol solution is 0.2-0.5 wt%, and the rotating speed of the homogenizer is 10000-15000 rpm.

[0035] The polylactic acid dichloromethane solution refers to an organic phase solution formed by dissolving polylactic acid in dichloromethane, and can be specifically realized by mixing polylactic acid powder and dichloromethane in a certain proportion and stirring until completely dissolved. The solution is used as an oil phase carrier to encapsulate the inner water phase to form a primary emulsion. The polyvinyl alcohol solution refers to an aqueous phase solution formed by dissolving polyvinyl alcohol in deionized water, and can be specifically realized by slowly adding polyvinyl alcohol powder into water and heating and stirring until completely dissolved. The solution is used as an outer water phase to stabilize the emulsion droplets. The homogenizer rotation speed refers to the rotation speed of the mechanical stirring equipment per unit time, which can be specifically realized by using a variable frequency motor with a high shear homogenizer. This parameter directly affects the uniformity of the emulsion droplets. The polyacrylonitrile fiber refers to a fiber material formed by polymerization of acrylonitrile, which can be specifically realized by electrospinning and then cutting into short fibers. The material is dispersed in the microsphere as a reinforcing framework.

[0036] Specifically, the ratio of ammonium bicarbonate to organic powder is set to (1-2) g:(3-5) g. By controlling the ratio of the foaming agent to the active component, it is ensured that a uniformly distributed pore structure can be formed during the subsequent drying process. The volume ratio of deionized water to polylactic acid dichloromethane solution is limited to (20-30) mL:(100-150) mL, so that the inner water phase and the organic phase form a suitable volume ratio, which is conducive to the formation of a stable core-shell structure through phase separation. When the polylactic acid content is controlled to be 5-8 wt%, the solution viscosity can ensure the integrity of the droplets during the emulsification process, and can also avoid dispersion difficulties caused by too high viscosity. The polyvinyl alcohol solution concentration is set to 0.2-0.5 wt%, forming a low-viscosity outer water phase environment, which effectively prevents emulsion droplet coalescence and does not excessively encapsulate the microsphere surface properties. The homogenization treatment stage uses a rotation speed range of 10000-15000 rpm, which breaks the primary emulsion into small droplets with uniform particle size distribution through high shear action. The polyacrylonitrile fiber is dispersed in the emulsion system at an addition amount of 0.2-0.5 g, forming a three-dimensional support network during the solvent evaporation process to prevent the microsphere structure from collapsing.

[0037] The application further proposes that the specific operation of the acid leaching impurity removal treatment is as follows: the alkali slag is added to a hydrochloric acid solution with a pH value of 1-2, fully stirred and dissolved, then saturated ammonia water is added to adjust the pH value to 3-4, and then ammonium persulfate is added, with the addition amount being 1-2% of the mass of the alkali slag. After sufficient standing, filtration is performed to obtain a zirconium and hafnium mixed solution.

[0038] The hydrochloric acid solution with a pH value of 1-2 refers to a leaching environment with strong acidity, and specifically, a hydrochloric acid solution with a concentration of 5-7 mol / L can be used to achieve this, which can fully dissolve the zirconium and hafnium elements in the alkali slag. The saturated ammonia water refers to an ammonia water solution with a concentration reaching a dissolution equilibrium, which can be prepared by introducing excess ammonia gas into deionized water, and its role is to adjust the pH value of the system to a weakly acidic environment in stages. The ammonium persulfate refers to an oxidizing agent containing persulfate ions, and specifically, industrial-grade ammonium persulfate powder can be used to achieve this, which can oxidize ferrous ions in the solution to ferric ions.

[0039] Specifically, during the acid leaching process, first, the complete leaching of zirconium and hafnium elements is achieved through strong acidic conditions, and then the system is adjusted to a weakly acidic environment by ammonia water, which promotes the formation of iron hydroxide precipitate. The addition of ammonium persulfate causes the residual ferrous ions to be oxidized to trivalent form, which is more easily precipitated, thereby enhancing the removal effect of iron impurities. The standing process allows the precipitate to fully accumulate, and finally, solid-liquid separation is achieved through filtration. The stepwise adjustment of pH value and the synergistic effect of the oxidizing agent create a directional removal path for iron impurities.

[0040] The present application further proposes that the volume ratio of the zirconium and hafnium mixed solution to the hydrochloric acid solution is 1:1.0-1.5, and the concentration of the hydrochloric acid solution is 5-7 mol / L.

[0041] Among them, the volume ratio of 1:1.0-1.5 refers to the mixing ratio of the zirconium and hafnium mixed solution to the hydrochloric acid solution, which can be accurately controlled by a volume measuring device. This ratio range can maintain the interfacial tension between the aqueous phase and the organic phase in a balanced state, avoiding uneven dispersion or difficulty in layering of the organic phase due to excessive aqueous phase. The concentration of the hydrochloric acid solution is 5-7 mol / L, which refers to the total molar concentration of hydrogen ions and chloride ions in the solution, and can be prepared by diluting concentrated hydrochloric acid.

[0042] Specifically, when the zirconium and hafnium mixed solution is mixed with the hydrochloric acid solution at a volume ratio of 1:1.0, the chloride ion concentration in the aqueous phase can reach the critical threshold for complexing hafnium ions, ensuring that hafnium enters the organic phase in the form of HfCl6^2-. If the volume ratio exceeds 1:1.5, the volume of the aqueous phase will be too large, reducing the loading efficiency of the organic phase for hafnium. When the concentration of hydrochloric acid is controlled at 5 mol / L, the free chloride ion concentration in the solution is sufficient to maintain the stability of hafnium complexes, and when the concentration reaches 7 mol / L, the chloride ion activity can effectively inhibit the formation of extractable forms of iron impurities. The synergistic effect of the two maximizes the distribution coefficient difference between hafnium and iron, creating thermodynamic advantage conditions for subsequent multi-stage extraction.

[0043] The application further proposes that the specific operation of the water phase pretreatment is to first heat the water phase to 40-45°C, and then centrifuge for 5-10 min at a rotation speed of 3000-5000 r / min, then add a polyether surfactant, control the concentration to be 0.03-0.08 wt%, and fully stir.

[0044] The heating to 40-45°C means that the solution temperature is controlled in the interval slightly higher than the normal temperature but lower than the boiling point, and specifically can be realized by using a constant temperature water bath circulation system, which can promote the migration and aggregation of impurity ions, and can also avoid excessive volatilization or decomposition of the solution. The 3000-5000 r / min centrifugation for 5-10 min means that the centrifugal force generated by mechanical rotation separates the solid-liquid two phases, and specifically can be realized by using a tubular centrifuge, and this parameter combination can effectively remove suspended particles and metal oxide precipitates with a particle size greater than 5 μm. The 0.03-0.08 wt% polyether surfactant means an amphiphilic compound with a polyoxyethylene segment, and specifically can be realized by using polyethylene glycol octylphenyl ether, which can reduce the interfacial tension between the water phase and the organic phase, and can also avoid excessive surfactant causing foam interference.

[0045] Specifically, the water phase pretreatment improves the extraction system through the synergistic effect of temperature control, mechanical separation and interface adjustment. First, constant temperature heating accelerates the coagulation of colloidal impurities, then high-speed centrifugation removes the solid particles that have been formed, and finally the surfactant is adsorbed on the droplet surface to form a protective film. These three steps successively eliminate physical suspended matter, chemical colloidal matter and interface instability factors that affect the extraction efficiency, so that the water phase reaches a clear state suitable for the action of N235 extractant.

[0046] The application further proposes that tri-octyl tertiary amine and isooctanol are added to sulfonated kerosene, and the volume fractions are controlled to be 25-35% and 5-10% respectively, so that the organic phase can be obtained.

[0047] The tri-octyl tertiary amine is a long-chain alkyl tertiary amine compound, and specifically can be realized by using industrial-grade tri-octyl tertiary amine as the main extractant, the nitrogen atom in the molecule selectively binds hafnium ions through coordination, and the long-chain alkyl structure can reduce the co-extraction of impurities such as iron ions. The isooctanol is a branched alcohol compound with a hydroxyl group, and specifically can be realized by using isooctanol with a purity higher than 99% as a phase regulator, the hydroxyl group improves the mass transfer efficiency of the organic phase and metal ions through hydrogen bonding, and adjusts the viscosity of the organic phase to avoid phase separation difficulties. The sulfonated kerosene is a kerosene diluent treated by sulfonation, and specifically can be realized by using commercially available sulfonated kerosene as a solvent, which has low polarity and can stabilize the micelle structure and reduce the entrainment of non-target metals.

[0048] Specifically, trioctyl tertiary amine can provide sufficient active site density at a volume fraction of 25-35%, ensuring efficient extraction of hafnium ions while avoiding phase interface emulsification problems caused by excessive concentration. Isooctanol at a volume fraction of 5-10% promotes extraction equilibrium through weak coordination of hydroxyl groups with metal ions, while optimizing the flowability and phase separation speed of the organic phase. The sulfonated kerosene as a diluent forms a stable micellar structure with trioctyl tertiary amine, and its low polarity environment inhibits the coordination ability of iron ions with extractants, thereby reducing the entrainment of impurities. The three components form a synergistic effect at a specific ratio, ensuring high selective extraction of hafnium ions and reducing the co-extraction rate of impurities such as iron by optimizing the physicochemical properties of the organic phase.

[0049] The application further proposes to implement continuous stirring operation at 300-500 r / min during extraction and stripping.

[0050] Among them, continuous stirring refers to maintaining mechanical disturbance during two-phase mixing, which can be realized by using a variable frequency speed stirrer with a four-blade inclined paddle stirrer. The paddle is driven to rotate by a power device to form a vortex. This speed range can form a moderate shear force to promote phase interface renewal, while avoiding excessive turbulence that makes phase separation difficult.

[0051] Specifically, the stirring intensity optimizes mass transfer efficiency by controlling the thickness of the hydrodynamic boundary layer. When the speed is lower than 300 r / min, insufficient two-phase mixing reduces the probability of contact between iron ions and the organic phase; exceeding 500 r / min causes the formation of fine droplets, causing the subsequent phase separation time to be prolonged. Within the set speed range, the coordination bond between trioctyl tertiary amine and iron ions is effectively broken, while the complex structure of hafnium ions remains stable. This selective dissociation makes it easier for iron impurities to enter the aqueous phase.

[0052] Example 1 A method for preparing ultra-low iron content hafnium oxide based on N235 extraction separation in a hydrochloric acid system, specifically comprising the following steps: S1 hafnium oxide pretreatment After crushing the hafnium oxide ore, a ball mill is used for coarse grinding to obtain hafnium oxide powder with a particle size of 100 μm; S2 acid-base treatment of hafnium oxide First, mix the hafnium oxide powder with sodium hydroxide according to a mass ratio of 1:2, then add organic composite microspheres, control the addition amount to be 5% of the mass of the hafnium oxide ore, mix thoroughly, then melt at 720℃ under sufficient oxygen for 2h, then cool the melt and leach it with water to obtain the alkali melt slag; Then the above alkali slag is added to a hydrochloric acid solution with a pH value of 1, after being fully stirred and dissolved, saturated ammonia water is added to adjust the pH value to 3, then ammonium persulfate is added, and the amount of addition is controlled to be 1% of the mass of the alkali slag, after being fully placed, filtration is performed, and a hafnium-zirconium mixed solution is obtained; S3 extraction separation S3-1, the hafnium-zirconium mixed solution is added to a hydrochloric acid solution with a concentration of 5 mol / l according to a volume ratio of 1:1, after being fully mixed, an aqueous phase is obtained, then the aqueous phase is heated to 40°C, and centrifugation is performed at a rotating speed of 3000 r / min for 5 min, then fatty alcohol polyoxyethylene ether is added, and the concentration is controlled to be 0.03 wt%, after being fully stirred, a pretreated aqueous phase is obtained, then the prepared organic phase is added to an extraction tank according to a volume ratio of 2:1, stirring is performed for 15 min, phase separation is performed after being placed, then the upper organic phase is transferred to a stripping tank, sufficient dilute hydrochloric acid is added, stirring is performed for 20 min, phase separation is performed after being placed, and the extraction-stripping process is repeated for 3 times, in the extraction and stripping process, continuous stirring is performed at a rotating speed of 300 r / min, and a hafnium-rich solution is obtained; In the preparation of the organic phase, trioctyl tertiary amine and isooctanol are added to sulfonated kerosene, and the volume fractions are controlled to be 25% and 5% respectively; S3-2, the hafnium-rich solution is adjusted to a pH value of 2, a strong acid type styrene resin column is introduced, then impurities are eluted with dilute hydrochloric acid, and then hafnium is eluted with concentrated hydrochloric acid, and a high-purity hafnium solution is obtained; S4 precipitation and calcination Saturated ammonia water is added to the high-purity hafnium solution, the pH value is adjusted to 7.5, the obtained precipitate is filtered, washed and dried, then calcination is performed at 850°C for 2 h, and ultra-low-iron hafnium oxide is obtained.

[0053] In the preparation method of the organic composite microspheres, the following steps are included: Step 1) 1.1 g of zinc nitrate and 22.5 g of 2-methyl imidazole are respectively dissolved in 8 mL and 80 mL of deionized water, the two are mixed and magnetically stirred, the obtained solution is centrifuged for 3 times, and then washed with methanol and deionized water, and dried to obtain an organic powder; Step 2) 1 g of ammonium bicarbonate and 3 g of the organic powder are added to 20 mL of deionized water to obtain an internal aqueous phase solution, then added to 100 mL of a polylactic acid dichloromethane solution with a polylactic acid content of 5 wt%, to form a primary emulsion, then homogenized by using a homogenizer at 10000 rpm, then added to 1000 mL of a polyvinyl alcohol solution with a concentration of 0.2 wt%, and 0.2 g of polyacrylonitrile fiber is added, after being fully stirred, washed with deionized water and ethanol, and fully dried at 60°C, an organic composite microsphere is obtained.

[0054] Example 2 A method for preparing ultra-low-iron-content hafnium oxide based on N235 extraction separation under hydrochloric acid system, specifically comprising the following steps: S1 hafnium oxide pretreatment After crushing the hafnium oxide ore, coarse grinding is performed using a ball mill to obtain hafnium oxide powder with a particle size of 100-150 μm; S2 acid-base treatment of hafnium oxide First, the hafnium oxide powder is mixed with sodium hydroxide at a mass ratio of 1:2.5, then organic composite microspheres are added, the amount of which is controlled to be 7% of the mass of the hafnium oxide ore, and the mixture is thoroughly mixed. After that, the mixture is melted at 750℃ for 3h in the presence of sufficient oxygen, and then the molten product is cooled and leached with water to obtain an alkali melt residue; Then, the alkali melt residue is added to a hydrochloric acid solution with a pH value of 1.5, and after being thoroughly stirred and dissolved, saturated ammonia water is added to adjust the pH value to 3.5, then ammonium persulfate is added, the amount of which is controlled to be 1.5% of the mass of the alkali melt residue, and after being thoroughly stirred, the mixture is filtered to obtain a zirconium-hafnium mixed solution; S3 extraction separation S3-1, the zirconium-hafnium mixed solution is added to a hydrochloric acid solution with a concentration of 6 mol / L at a volume ratio of 1:1.2, and after being thoroughly mixed, an aqueous phase is obtained, then the aqueous phase is heated to 42℃ and centrifuged at a speed of 4000 r / min for 8 min, then a fatty alcohol polyoxyethylene ether is added, the concentration of which is controlled to be 0.05wt%, and after being thoroughly stirred, a pretreated aqueous phase is obtained, then the pretreated aqueous phase and the prepared organic phase are sequentially added to an extraction tank at a volume ratio of 3:1, stirred for 18 min, and allowed to stand to separate the phases, then the upper organic phase is transferred to a stripping tank, and sufficient dilute hydrochloric acid is added, stirred for 25 min, and allowed to stand to separate the phases, and the extraction-stripping process is repeated 4 times, and during the extraction and stripping, continuous stirring at a speed of 400 r / min is performed, and a hafnium-rich solution is obtained; In the preparation of the organic phase, tri-octyl tertiary amine and isooctanol are added to sulfonated kerosene, and the volume fractions of the two are controlled to be 30% and 8% respectively; S3-2, the hafnium-rich solution is adjusted to a pH value of 2.5, passed through a strong acid type styrene resin column, then impurities are eluted with dilute hydrochloric acid, and then hafnium is eluted with concentrated hydrochloric acid to obtain a high-purity hafnium solution; S4 precipitation and calcination Saturated ammonia water is added to the high-purity hafnium solution to adjust the pH value to 8.0, the obtained precipitate is filtered, washed, and dried, and then calcined at 900℃ for 3h to obtain ultra-low-iron-content hafnium oxide.

[0055] The preparation method of the organic composite microspheres is as follows: Step 1) 1.5 g of zinc nitrate and 25.5 g of 2-methylimidazole were dissolved in 10 mL and 100 mL of deionized water, respectively, and the mixture was magnetically stirred. The resulting solution was centrifuged four times and washed repeatedly with methanol and deionized water, and then dried to obtain an organic powder; Step 2) 1.5 g of ammonium bicarbonate and 4 g of the organic powder were added to 25 mL of deionized water to obtain an internal aqueous phase solution, which was then added to 120 mL of a polylactic acid dichloromethane solution with a polylactic acid content of 7 wt%. A primary emulsion was formed, and then a homogenizer was used for homogenization at 13,000 rpm. Subsequently, the solution was added to 1200 mL of a polyvinyl alcohol solution with a concentration of 0.3 wt%, and 0.3 g of polyacrylonitrile fibers were added. After thorough stirring, the solution was thoroughly washed with deionized water and ethanol, and then dried at 65°C to obtain organic composite microspheres.

[0056] Example 3 A method for preparing ultra-low iron content hafnium oxide based on N235 extraction separation in a hydrochloric acid system, specifically comprising the following steps: S1 hafnium oxide pretreatment After crushing the hafnium oxide ore, a ball mill was used for coarse grinding to obtain hafnium oxide powder with a particle size of 150 μm; S2 acid-base treatment of hafnium oxide First, the hafnium oxide powder was mixed with sodium hydroxide in a mass ratio of 1:3, and then organic composite microspheres were added, with the amount controlled at 10% of the mass of the hafnium oxide ore. After thorough mixing, the mixture was melted at 780°C for 5 h in the presence of sufficient oxygen. The molten product was then cooled and leached with water to obtain an alkali melt residue; Then, the alkali melt residue was added to a hydrochloric acid solution with a pH of 2, and after being fully stirred and dissolved, saturated ammonia water was added to adjust the pH to 4. Then, ammonium persulfate was added, with the amount controlled at 2% of the mass of the alkali melt residue. After thorough standing, the solution was filtered to obtain a zirconium-hafnium mixed solution; S3 extraction separation S3-1, the zirconium-hafnium mixed solution was added to a hydrochloric acid solution with a concentration of 7 mol / L in a volume ratio of 1:1.5, and after thorough mixing, an aqueous phase was obtained. The aqueous phase was then heated to 45°C and centrifuged at a speed of 5000 r / min for 10 min. Fatty alcohol polyoxyethylene ether was then added, with the concentration controlled at 0.08 wt%. After thorough stirring, a pretreated aqueous phase was obtained. The prepared organic phase was then added to the extraction tank in a volume ratio of 5:1, stirred for 20 min, and allowed to separate. The upper organic phase was then transferred to a stripping tank, and sufficient dilute hydrochloric acid was added. After stirring for 30 min, the solution was allowed to separate. The extraction and stripping were repeated 5 times, with continuous stirring at 500 r / min. A hafnium-rich solution was thus obtained. The organic phase is prepared by adding tri-octyl tertiary amine and isooctanol into sulfonated kerosene, and the volume fractions are controlled to be 35% and 10% respectively. S3-2, the hafnium-rich liquid is adjusted to a pH value of 3, and is passed through a strong acid type styrene resin column, then the impurities are eluted with dilute hydrochloric acid, and then the hafnium is eluted with concentrated hydrochloric acid, to obtain a high-purity hafnium solution; S4 precipitation and calcination Saturated ammonia water is added to the high-purity hafnium solution, and the pH value is adjusted to 8.0. The obtained precipitate is filtered, washed and dried, and then calcined at 980℃ for 5h to obtain hafnium oxide with ultra-low iron content.

[0057] The preparation method of the organic composite microspheres is as follows: Step 1) 1.8g of zinc nitrate and 28.6g of 2-methyl imidazole are dissolved in 12mL and 120mL of deionized water respectively, the two are mixed and magnetically stirred, the obtained solution is centrifuged 5 times, and then washed with methanol and deionized water repeatedly and dried to obtain an organic powder; Step 2) 2g of ammonium bicarbonate and 5g of the organic powder are added to 30mL of deionized water to obtain an inner aqueous phase solution, which is then added to 150mL of a polylactic acid dichloromethane solution with a polylactic acid content of 8wt%, to form a primary emulsion, which is then homogenized using a homogenizer at 15000rpm, and then added to 1600mL of a 0.5wt% polyvinyl alcohol solution, 0.5g of polyacrylonitrile fiber is added, and after being stirred thoroughly, it is washed thoroughly with deionized water and ethanol, and dried at 70℃, to obtain the organic composite microspheres.

[0058] Comparative Example 1: This comparative example is basically the same as Example 1, except that in S2, no organic composite microspheres are added.

[0059] Comparative Example 2: This comparative example is basically the same as Example 1, except that in the preparation of the organic composite microspheres in S2, the polyacrylonitrile fiber is omitted.

[0060] Comparative Example 3: This comparative example is basically the same as Example 1, except that in S3-1, the aqueous phase is not pretreated.

[0061] Comparative Example 4: This comparative example is basically the same as Example 1, except that in the pretreatment of the aqueous phase in S3-1, the polyether surfactant is omitted.

[0062] Comparative Example 5: This comparative example is basically the same as Example 1, except that in S3-1, the extraction and back-extraction are omitted.

[0063] Test experiment: The process method in the examples 1-3 and the comparative examples 1-5 is used to process and prepare hafnium oxide samples respectively, then the iron content in the hafnium oxide samples is tested by inductively coupled plasma mass spectrometry, and the results are shown in Table 1.

[0064] Table 1

[0065] It can be known from Table 1 that the process method in the application can significantly reduce the iron content in the hafnium oxide, so that the content is less than 0.0001%, thereby obtaining hafnium oxide with ultra-low iron content.

[0066] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details and limit the application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the specification. The specification selects and describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and use the application. The application is limited by the claims and their entire scope and equivalents.

Claims

1. A process for the preparation of hafnium oxide with ultra-low iron content, based on the separation by extraction of N235 in hydrochloric acid system, characterized in that, Specifically comprising the following steps: S1 hafnium oxide pretreatment After crushing the hafnium oxide ore, coarse grinding is performed using a ball mill to obtain hafnium oxide powder with a particle size of 100-150 μm; S2 acid-base treatment of hafnium oxide The hafnium oxide powder is sequentially subjected to alkali fusion decomposition treatment and acid leaching impurity removal treatment to obtain a zirconium-hafnium mixed solution; S3 extraction separation S3-1, the zirconium-hafnium mixed solution is added to a hydrochloric acid solution, mixed thoroughly to obtain an aqueous phase, which is then pretreated and added to an organic phase prepared according to a volume ratio of (2-5):1 in an extraction tank, stirred for 15-20 min, allowed to stand to separate the phases, and then the upper organic phase is transferred to a stripping tank, sufficient dilute hydrochloric acid is added, stirred for 20-30 min, allowed to stand to separate the phases, and the extraction-stripping process is repeated 3-5 times to obtain a hafnium-rich solution; S3-2, the hafnium-rich solution is adjusted to a pH value of 2-3, passed through a strong acid type styrene resin column, then washed with dilute hydrochloric acid to remove impurities, and then washed with concentrated hydrochloric acid to elute hafnium to obtain a high-purity hafnium solution; S4 precipitation and calcination Saturated ammonia water is added to the high-purity hafnium solution to adjust the pH value to 7.5-8.0, the obtained precipitate is filtered, washed, and dried, and then calcined at 850-980℃ for 2-5 h to obtain ultra-low iron content hafnium oxide.

2. The method of claim 1, wherein, In S2, the specific operation of the alkali fusion decomposition treatment is as follows: According to a mass ratio of 1:(2-3), the hafnium oxide powder is thoroughly mixed with sodium hydroxide, then organic composite microspheres are added, the amount of which is controlled to be 5-10% of the mass of the hafnium oxide ore, the mixture is thoroughly mixed and evenly distributed, then the mixture is melted under sufficient oxygen at 720-780℃ for 2-5 h, and then the molten product is cooled and leached with water to obtain an alkali fusion residue.

3. The method of claim 2, wherein, The preparation method of the organic composite microspheres is as follows: Step 1) 1.1-1.8 g of zinc nitrate and 22.5-28.6 g of 2-methyl imidazole are respectively dissolved in 8-12 mL and 80-120 mL of deionized water, the two are mixed and magnetically stirred, the obtained solution is centrifuged 3-5 times, and then washed with methanol and deionized water and dried to obtain an organic powder; Step 2) ammonium bicarbonate and the organic powder are added to deionized water to obtain an internal aqueous phase solution, which is then added to a polylactic acid dichloromethane solution to form a primary emulsion, then a homogenizer is used for homogenization treatment, and then the solution is added to a polyvinyl alcohol solution, polyacrylonitrile fibers are added, the mixture is thoroughly stirred, washed with deionized water and ethanol, and dried at 60-70℃ to obtain organic composite microspheres.

4. The method of claim 3, wherein, In Step 1), the magnetic stirring speed is 1000-1500 r / min, and the stirring time is 24-30 h.

5. The method of claim 3, wherein, In Step 2), the amount ratio of ammonium bicarbonate, organic powder, deionized water, polylactic acid dichloromethane solution, polyvinyl alcohol solution, and polyacrylonitrile fibers is (1-2) g:(3-5) g:(20-30) mL:(100-150) mL:(1000-1600) mL:(0.2-0.5) g; The polylactic acid content in the polylactic acid dichloromethane solution is 5-8 wt%; The concentration of the polyvinyl alcohol solution is 0.2-0.5 wt%; The rotation speed of the homogenizer is 10000-15000 rpm.

6. The method of claim 2, wherein, In S2, the specific operation of the acid leaching impurity removal treatment is as follows: The alkali smelting slag is added into a hydrochloric acid solution with a pH value of 1-2, and after being fully stirred and dissolved, saturated ammonia water is added to adjust the pH value to 3-4, then ammonium persulfate is added, and the addition amount is controlled to be 1-2% of the mass of the alkali smelting slag, after being fully placed, filtration is performed, and a zirconium-hafnium mixed solution is obtained.

7. The method of claim 1, wherein, In S3-1, the volume ratio of the zirconium-hafnium mixed solution to the hydrochloric acid solution is 1:(1.0-1.5); The concentration of the hydrochloric acid solution is 5-7 mol / L.

8. The method of claim 1, wherein, In S3-1, the specific operation of the water phase pretreatment is as follows: first, the water phase is heated to 40-45℃, and then centrifuged at a rotation speed of 3000-5000 r / min for 5-10 min, then a polyether surfactant is added, and the concentration is controlled to be 0.03-0.08 wt%, and after being fully stirred, the operation is completed.

9. The method of claim 1, wherein, In S3-1, the preparation method of the organic phase is as follows: Tri-octyl tertiary amine and isooctanol are added into sulfonated kerosene, and the volume fractions are controlled to be 25-35% and 5-10% respectively, and the organic phase is obtained.

10. The method of claim 1, wherein, In S3-1, the extraction and stripping are accompanied by continuous stirring at 300-500 r / min.

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