A method for preparing hafnium oxide with ultra-low iron content

Abstract

This invention relates to the field of hafnium oxide preparation technology, specifically to a method for preparing ultra-low iron content hafnium oxide. This method is based on N235 extraction and separation under hydrochloric acid. The hafnium oxide ore is crushed and coarsely ground to obtain hafnium oxide powder. Then, it undergoes alkali fusion decomposition treatment and acid leaching to remove impurities, resulting in a zirconium-hafnium mixed solution. Through extraction and back-extraction, a hafnium-enriched solution is obtained, which is then treated with an ion exchange resin to obtain a high-purity hafnium solution. Finally, saturated ammonia is added, and the resulting precipitate is filtered, washed, dried, and then calcined to obtain ultra-low iron content hafnium oxide. In this invention, while achieving zirconium-hafnium separation, other trace metal cations, especially iron ions, are sufficiently removed, reducing the iron content and thus obtaining ultra-low iron content hafnium oxide.

Description

Technical Field

[0001] This invention relates to the field of hafnium oxide preparation technology, specifically a method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system. Background Technology

[0002] Hafnium oxide has significant applications in many high-tech fields due to its excellent physicochemical properties. In the ceramics 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 critical components for extreme environments. In the electronics industry, high-purity hafnium oxide is a key material for manufacturing high-performance electronic components. Furthermore, hafnium oxide is also an important raw material for the preparation of other high-purity hafnium compounds.

[0003] Currently, industrial hafnium oxide purification mainly employs solvent extraction and sublimation methods. While sublimation yields high-purity products, it suffers from drawbacks such as high equipment investment, high energy consumption, and long process cycles, and requires the use of hazardous high-temperature chlorine gas, posing significant safety hazards. Solvent extraction, although relatively simple to operate, is traditionally ineffective at removing iron impurities, resulting in a high iron content in the final product. The presence of iron impurities can cause lattice distortion in materials, affecting their dielectric properties and thermal stability, severely limiting the application of hafnium oxide in high-precision fields.

[0004] In existing technologies, conventional acid-base treatment and extraction processes have limited effectiveness in removing iron impurities, especially when processing raw materials with high iron content, often failing to achieve the required ultra-low iron content. Furthermore, the extractants and auxiliary materials used in traditional processes also have shortcomings in separation efficiency and selectivity, leading to complex process flows and unstable product yields. Therefore, developing a hafnium oxide preparation method that can effectively reduce iron content, simplify the process flow, and improve product purity is of great significance. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing hafnium oxide with ultra-low iron content and its organic composite microspheres by N235 extraction and separation under hydrochloric acid system, which has the advantages of efficient removal of iron impurities, simplified process flow and improved product purity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system includes the following steps:

[0008] S1 Hafnium oxide pretreatment

[0009] After crushing the raw hafnium oxide, it was coarsely ground using a ball mill to obtain hafnium oxide powder with a particle size of 100-150μm.

[0010] S2 hafnium oxide acid-base treatment

[0011] Hafnium oxide powder was subjected to alkali fusion decomposition treatment and acid leaching to remove impurities in sequence to obtain a zirconium-hafnium mixed solution;

[0012] S3 Extraction and Separation

[0013] S3-1, add the zirconium-hafnium mixed solution to the hydrochloric acid solution, mix thoroughly to obtain an aqueous phase, then pretreat the aqueous phase and add it to the extraction tank along with the prepared organic phase at a volume ratio of (2-5):1, stir for 15-20 min, let stand to separate the phases, then transfer the upper organic phase to the back-extraction tank, add sufficient dilute hydrochloric acid, stir for 20-30 min, let stand to separate the phases, repeat the extraction-back-extraction 3-5 times to obtain the hafnium enriched solution;

[0014] S3-2, adjust the pH of the hafnium enrichment solution to 2-3, pass it into a strong acid styrene resin column, then wash off the impurities with dilute hydrochloric acid, and then wash off the hafnium with concentrated hydrochloric acid to obtain a high-purity hafnium solution.

[0015] S4 Precipitation and Incineration

[0016] Add saturated ammonia to a high-purity hafnium solution to adjust the pH to 7.5-8.0. Filter, wash and dry the resulting precipitate, and then calcine it at 850-980℃ for 2-5 hours to obtain hafnium oxide with ultra-low iron content.

[0017] As a further preferred embodiment of the present invention, in S2, the specific operation of the alkali fusion decomposition treatment is as follows:

[0018] Hafnium oxide powder and sodium hydroxide are thoroughly mixed at a mass ratio of 1:(2-3). Then, organic composite microspheres are added, with the amount added controlled to be 5-10% of the mass of raw hafnium oxide. After thorough mixing, the mixture is melted for 2-5 hours under sufficient oxygen and at 720-780℃. The melted product is then cooled and leached with water to obtain alkali slag.

[0019] As a further preferred embodiment of the present invention, the method for preparing the organic composite microspheres is as follows:

[0020] Step 1) Dissolve 1.1-1.8g of zinc nitrate and 22.5-28.6g of 2-methylimidazole in 8-12mL and 80-120mL of deionized water, respectively. Mix the two solutions and stir magnetically. Centrifuge the resulting solution 3-5 times, wash it repeatedly with methanol and deionized water, and then dry it to obtain organic powder.

[0021] Step 2) Add ammonium bicarbonate and organic powder to deionized water to obtain an internal aqueous phase solution, then add it to polylactic acid dichloromethane solution to form a primary emulsion, then homogenize it using a homogenizer, then add it to polyvinyl alcohol solution, add polyacrylonitrile fiber, stir thoroughly, wash thoroughly with deionized water and ethanol, and dry thoroughly at 60-70℃ to obtain organic composite microspheres.

[0022] Furthermore, in step 1), the magnetic stirring speed is 1000-1500 r / min, and the stirring time is 24-30 h.

[0023] Furthermore, in step 2), the 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;

[0024] The polylactic acid dichloromethane solution contains 5-8 wt% polylactic acid.

[0025] The concentration of the polyvinyl alcohol solution is 0.2-0.5 wt%.

[0026] The homogenizer operates at a speed of 10,000-15,000 rpm.

[0027] In a further preferred embodiment of the present invention, in S2, the specific operation of the acid leaching and impurity removal treatment is as follows:

[0028] Add the above-mentioned alkali slag to a hydrochloric acid solution with a pH of 1-2, stir thoroughly to dissolve, add saturated ammonia water to adjust the pH to 3-4, then add ammonium persulfate, controlling the amount added to be 1-2% of the mass of the alkali slag. After sufficient settling, filter to obtain a zirconium-hafnium mixed solution.

[0029] In a further preferred embodiment of the present invention, in S3-1, the volume ratio of the zirconium-hafnium mixed solution to the hydrochloric acid solution is 1:(1.0-1.5).

[0030] The concentration of the hydrochloric acid solution is 5-7 mol / L.

[0031] In a further preferred embodiment of the present invention, in S3-1, the specific operation of the aqueous phase pretreatment is as follows: first, heat the aqueous phase to 40-45℃, and centrifuge it at a speed of 3000-5000 r / min for 5-10 min, then add a polyether surfactant, control its concentration to be 0.03-0.08 wt%, and stir thoroughly.

[0032] In a further preferred embodiment of the present invention, in S3-1, the method for preparing the organic phase is as follows:

[0033] By adding trioctyl tertiary amine and isooctanol to sulfonated kerosene and controlling their volume fractions to be 25-35% and 5-10% respectively, an organic phase can be obtained.

[0034] In a further preferred embodiment of the present invention, in S3-1, the extraction and back-extraction are accompanied by continuous stirring at 300-500 r / min.

[0035] As can be seen from the above, the method provided in this application for preparing hafnium oxide with ultra-low iron content and its organic composite microspheres based on N235 extraction and separation in a hydrochloric acid system effectively removes iron impurities and improves the recovery rate of hafnium through the synergistic effect of the N235 extraction system and the organic composite microspheres, combined with multi-stage extraction and separation and resin column purification process. It has the advantages of simplified process flow and high product purity. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Specifically, this method achieves systematic removal of iron impurities through a four-stage synergistic effect. The pretreatment stage controls powder particle size to ensure subsequent reaction efficiency; the acid-base treatment stage achieves initial separation of zirconium and hafnium from impurities; the extraction stage employs multi-stage circulation to enhance separation, combined with gradient elution of the resin column to form an iron ion retention barrier; the precipitation stage precisely controls pH to avoid impurity co-precipitation, and high-temperature calcination ensures the integrity of the product's crystal form. The parameters of each step create a synergistic effect, particularly the combined design of the extraction volume ratio and the number of cycles, effectively blocking the migration pathways of iron ions.

[0042] Compared to existing technologies, traditional solvent extraction methods remove impurities through a single extraction step, failing to establish multi-stage purification barriers and resulting in iron ion residues exceeding 200 ppm. This method breaks down mineral encapsulation structures through alkali fusion decomposition, combining multi-stage extraction with resin adsorption to form a three-stage purification system, reducing iron content to below 10 ppm. Compared to sublimation methods, this approach eliminates the need for high-temperature chlorine treatment, allowing the entire process to be completed in a conventional reaction vessel.

[0043] Through the above technical solution, this application effectively solves the technical challenge of deep removal of iron impurities during hafnium oxide preparation. 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. This method, while ensuring product purity, reduces equipment requirements and operational risks, making it suitable for industrial continuous production.

[0044] This application further proposes a process in which hafnium oxide powder and sodium hydroxide are mixed at a mass ratio of 1:2-3, 5-10% organic composite microspheres of hafnium oxide raw material are added, the mixture is melted in an oxygen-rich environment at 720-780℃ for 2-5 hours, and then cooled and leached in water to obtain alkali slag.

[0045] The sodium hydroxide ratio of 1:2-3 means that 2-3 times the mass of sodium hydroxide needs to be added per unit mass of hafnium oxide powder. This creates a strongly alkaline melting environment that promotes the conversion of iron into a soluble state. The organic composite microspheres, added at 5-10%, represent the percentage of their mass relative to the total mass of the raw hafnium oxide. They act as an adsorption medium, capturing iron impurities during the melting process. A melting temperature range of 720-780℃ ensures effective decomposition of the mineral structure while avoiding excessive equipment wear. A melting time of 2-5 hours ensures the reaction is fully completed. The oxygen-enriched environment, through continuous oxygen supply, promotes the oxidation of iron to higher valence compounds, enhancing subsequent separation efficiency.

[0046] Specifically, hafnium oxide powder is mixed with excess sodium hydroxide to form an alkaline melt. During the high-temperature melting process, the hafnium oxide crystal structure is disrupted, releasing iron in a soluble form. Organic composite microspheres, acting as functional adsorbents, selectively capture iron ions in the molten system through their porous structure, forming stable complexes. Oxygen-rich conditions promote the oxidation of ferrous ions to ferric compounds, enhancing the removal rate in the subsequent water leaching stage. By controlling the melting temperature and time to balance reaction efficiency and energy consumption, the final water leaching process separates iron impurities from the alkaline slag, forming a low-iron intermediate product.

[0047] This application further proposes a method for preparing organic composite microspheres, specifically including the following steps: Step 1): Zinc nitrate and 2-methylimidazole are dissolved in deionized water, mixed, magnetically stirred, centrifuged, washed, and dried to obtain organic powder; Step 2): Ammonium bicarbonate and organic powder are added to deionized water to form an inner aqueous phase solution, mixed with polylactic acid dichloromethane solution to form a primary emulsion, homogenized, and then polyvinyl alcohol solution and polyacrylonitrile fiber are added. After washing and drying, organic composite microspheres are obtained.

[0048] The coordination reaction between zinc nitrate and 2-methylimidazole involves the self-assembly of metal ions and organic ligands to form a porous structure. This can be achieved by stirring zinc nitrate and 2-methylimidazole in deionized water at a molar ratio of 1:3. This structure provides selective adsorption sites for iron ions. Magnetic stirring uses a rotating magnetic field to drive eddies in the solution for mixing. A stirring speed of 1000-1500 rpm is maintained for 24-30 hours to ensure sufficient contact between the reactants and the formation of a stable coordination structure. Centrifugal washing separates the solid and liquid phases and removes unreacted substances. Alternating washing with methanol and deionized water 3-5 times is used to avoid residual impurities affecting the microsphere performance. The polylactic acid dichloromethane solution is a hydrophobic carrier formed by dissolving polylactic acid in dichloromethane. A 5-8% (w / w) solution is used as the oil phase to encapsulate the inner aqueous phase, forming an emulsion template. Polyacrylonitrile fiber refers to micron-sized fiber materials prepared by electrospinning. Specifically, 0.2-0.5 grams of fiber can be mixed with an emulsion to enhance the mechanical strength of microspheres through physical entanglement.

[0049] Specifically, efficient capture of iron impurities is achieved through a step-by-step construction of a multi-level structure. First, zinc nitrate and 2-methylimidazole are used to generate a metal-organic framework with regularly spaced pores, whose surface active sites can specifically bind iron ions. Then, using an emulsion template method, the gas generated from the decomposition of ammonium bicarbonate is used as a pore-forming agent to form interconnected channels within a polylactic acid carrier, increasing the specific surface area of ​​the microspheres to more than three times that of traditional adsorption materials. The coating effect of polyvinyl alcohol solution forms a dense shell, preventing structural collapse of the microspheres during high-temperature alkali fusion. The introduction of polyacrylonitrile fibers increases the compressive strength of the microspheres to over 15 MPa, allowing them to maintain structural integrity even under vigorous stirring conditions.

[0050] This application further proposes that in step 1) above, the rotation speed of the magnetic stirrer is controlled within the range of 1000-1500 revolutions per minute, and the stirring time is controlled within the range of 24-30 hours.

[0051] The magnetic stirring speed refers to the mechanical speed at which the stirring rotor rotates. This can be achieved using a digital stirrer in conjunction with a programmable controller (PLC), with the stirring intensity precisely controlled by adjusting the motor's output power. This speed range provides sufficient shear force to promote reactant molecule diffusion while avoiding excessive speed that could lead to solution splashing or crystal structure damage. The stirring time refers to the duration of the reaction system under stirring, which can be achieved using a timer-linked stirring device to ensure that zinc nitrate and 2-methylimidazole fully complex to form a stable metal-organic framework structure.

[0052] Specifically, in the complexation reaction of zinc nitrate and 2-methylimidazole, when the rotation speed is below 1000 rpm, the mixed solution is predominantly laminar, resulting in insufficient contact area between reactants and a tendency for localized high concentrations to form aggregates. When the rotation speed exceeds 1500 rpm, excessive turbulence may tear the growing crystal framework. By limiting the stirring time to 24-30 hours, zinc ions and organic ligands can gradually complete the formation of coordination bonds and crystal growth. For example, under continuous stirring conditions for 26 hours, the reaction solution can be observed to change from turbid to a homogeneous suspension, indicating the formation of ZIF-8 type crystals with a concentrated particle size distribution. This combination of process parameters effectively avoids the incomplete reaction problem caused by traditional intermittent stirring, providing a precursor guarantee for the subsequent preparation of organic composite microspheres with regular pore structures.

[0053] This application further proposes that the proportions of ammonium bicarbonate, organic powder, deionized water, polylactic acid dichloromethane solution, polyvinyl alcohol solution, and polyacrylonitrile fiber are (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%, and the speed of the homogenizer is 10000-15000 rpm.

[0054] The polylactic acid dichloromethane solution refers to an organic phase solution formed by dissolving polylactic acid in dichloromethane. Specifically, it can be achieved by mixing polylactic acid powder and dichloromethane in a specific ratio and stirring until completely dissolved. This solution acts as an oil phase carrier to encapsulate the inner aqueous phase, forming a primary emulsion. The polyvinyl alcohol solution refers to an aqueous phase solution formed by dissolving polyvinyl alcohol in deionized water. Specifically, it can be achieved by slowly adding polyvinyl alcohol powder to water and heating and stirring until completely dissolved. This solution acts as an external aqueous phase to stabilize the emulsion droplets. The homogenizer speed refers to the rotational speed of the mechanical stirring equipment per unit time. Specifically, it can be achieved using a variable frequency speed-regulating motor in conjunction with a high-shear homogenizing head. This parameter directly affects the uniformity of emulsion droplet dispersion. Polyacrylonitrile fiber refers to a fibrous material formed by polymerizing acrylonitrile. Specifically, it can be prepared by electrospinning and then cut into short fibers. This material acts as a reinforcing skeleton dispersed inside the microspheres.

[0055] Specifically, the ratio of ammonium bicarbonate to organic powder is set at (1-2) g: (3-5) g. By controlling the ratio of foaming agent to active component, a uniformly distributed pore structure is ensured during subsequent drying. The volume ratio of deionized water to polylactic acid dichloromethane solution is limited to (20-30) mL: (100-150) mL, ensuring a suitable volume ratio between the internal aqueous phase and organic phase, which is beneficial for forming a stable core-shell structure through phase separation. When the polylactic acid content is controlled at 5-8 wt%, the solution viscosity ensures the integrity of droplets during emulsification while avoiding dispersion difficulties due to excessive viscosity. The polyvinyl alcohol solution concentration is set at 0.2-0.5 wt%, creating a low-viscosity external aqueous phase environment, which effectively prevents emulsion droplet aggregation without excessive coating that affects the surface properties of microspheres. The homogenization stage uses a rotation speed range of 10,000-15,000 rpm, breaking the primary emulsion into uniformly distributed microdroplets through high shear. Polyacrylonitrile fibers are dispersed in the emulsion system at an addition amount of 0.2-0.5g, forming a three-dimensional support network during solvent evaporation to prevent the microsphere structure from collapsing.

[0056] This application further proposes the following specific operation for acid leaching to remove impurities: Add the alkali slag to a hydrochloric acid solution with a pH of 1-2, stir and dissolve thoroughly, add saturated ammonia water to adjust the pH to 3-4, then add ammonium persulfate, controlling the amount added to be 1-2% of the mass of the alkali slag, let it stand for a while, and then filter to obtain a zirconium-hafnium mixed solution.

[0057] The hydrochloric acid solution with a pH of 1-2 refers to a strongly acidic leaching environment, specifically achieved using a 5-7 mol / L hydrochloric acid solution. Its function is to fully dissolve the zirconium and hafnium elements in the alkaline slag. Saturated ammonia water refers to an ammonia solution at dissolution equilibrium, prepared by passing excess ammonia gas into deionized water. Its function is to adjust the pH of the system to a weakly acidic environment in stages. Ammonium persulfate is an oxidizing agent containing persulfate ions, specifically achieved using industrial-grade ammonium persulfate powder. Its function is to oxidize ferrous ions in the solution to ferric ions.

[0058] Specifically, in the acid leaching process, zirconium and hafnium are first completely leached out under strongly acidic conditions. Then, ammonia is used to adjust the system to a weakly acidic environment, promoting the formation of ferric hydroxide precipitate from iron ions. The addition of ammonium persulfate oxidizes residual ferrous ions into a more easily precipitated trivalent form, thereby enhancing the removal of iron impurities. The settling process allows the precipitate to fully aggregate, and finally, solid-liquid separation is achieved through filtration. This process, involving stepwise pH adjustment and the synergistic effect of the oxidant, constructs a targeted removal pathway for iron impurities.

[0059] This application further proposes that the volume ratio of the zirconium-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.

[0060] The volume ratio of 1:1.0-1.5 refers to the mixing ratio of the zirconium-hafnium mixed solution to the hydrochloric acid solution, which can be precisely controlled using a volume metering device. This ratio range maintains the interfacial tension between the aqueous and organic phases in equilibrium, preventing uneven dispersion or stratification of the organic phase due to excess aqueous phase. The hydrochloric acid solution concentration of 5-7 mol / L refers to the total molar concentration of hydrogen and chloride ions in the solution, which can be prepared using a concentrated hydrochloric acid dilution method.

[0061] Specifically, when the zirconium-hafnium mixed solution and hydrochloric acid solution are mixed at a volume ratio of 1:1.0, the chloride ion concentration in the aqueous phase reaches 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 hafnium in the organic phase. When the hydrochloric acid concentration is controlled at 5 mol / L, the concentration of free chloride ions in the solution is sufficient to maintain the stability of the hafnium complex, while at a concentration of 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 difference in partition coefficients between hafnium and iron, creating thermodynamically advantageous conditions for subsequent multi-stage extraction.

[0062] This application further proposes the following specific operation for aqueous phase pretreatment: first, heat the aqueous phase to 40-45℃, centrifuge at 3000-5000 r / min for 5-10 min, then add a polyether surfactant, control its concentration to 0.03-0.08 wt%, and stir thoroughly.

[0063] Heating to 40-45℃ refers to controlling the solution temperature slightly above room temperature but below the boiling point. This can be achieved using a constant-temperature water bath circulation system. This temperature range promotes the migration and aggregation of impurity ions while preventing excessive evaporation or component decomposition. Centrifugation at 3000-5000 r / min for 5-10 min refers to separating the solid and liquid phases through centrifugal force generated by mechanical rotation. This can be achieved using a tubular centrifuge. This parameter combination effectively removes suspended particles larger than 5 μm and metal oxide precipitates. The 0.03-0.08 wt% polyether surfactant refers to amphiphilic compounds with polyoxyethylene segments. Polyethylene glycol octylphenyl ether can be used. This concentration range reduces the interfacial tension between the aqueous and organic phases while avoiding foam interference caused by excessive surfactant.

[0064] Specifically, aqueous phase pretreatment improves the extraction system through the synergistic effects of temperature control, mechanical separation, and interface regulation. First, isothermal heating accelerates the aggregation of colloidal impurities. Then, high-speed centrifugation removes the formed solid particles. Finally, surfactants are directionally adsorbed onto the droplet surface to form a protective film. These three steps sequentially eliminate physical suspended matter, chemical colloidal substances, and interfacial instabilities that affect extraction efficiency, bringing the aqueous phase to a clear state suitable for the action of the N235 extractant.

[0065] This application further proposes to add trioctyl tertiary amine and isooctanol to sulfonated kerosene, controlling their volume fractions to be 25-35% and 5-10% respectively, to obtain an organic phase.

[0066] Among them, trioctyl tertiary amine refers to a long-chain alkyl tertiary amine compound. Specifically, industrial-grade trioctyl tertiary amine can be used as the main extractant. Its nitrogen atoms selectively bind hafnium ions through coordination, while the long-chain alkyl structure reduces the co-extraction of impurities such as iron ions. Isooctol refers to a branched-chain alcohol compound with hydroxyl groups. Specifically, isooctol with a purity higher than 99% can be used as a phase modifier. Its hydroxyl groups improve the mass transfer efficiency between the organic phase and metal ions through hydrogen bonding, while also adjusting the viscosity of the organic phase to avoid phase separation difficulties. Sulfonated kerosene refers to a kerosene-based diluent that has undergone sulfonation treatment. Specifically, commercially available sulfonated kerosene can be used as a solvent. Its low polarity stabilizes the micelle structure and reduces the entrainment of non-target metals.

[0067] Specifically, trioctyl tertiary amine, at a volume fraction of 25-35%, provides sufficient active site density to ensure efficient extraction of hafnium ions while avoiding phase interface emulsification problems caused by excessive concentration. Isooctol, at a volume fraction of 5-10%, promotes extraction equilibrium through the weak coordination of hydroxyl groups with metal ions, while optimizing the fluidity and phase separation rate of the organic phase. Sulfonated kerosene, as a diluent, forms a stable micelle structure with trioctyl tertiary amine; its low polarity environment inhibits the coordination ability of iron ions with the extractant, thereby reducing impurity entrainment. The three components, in a specific ratio, form a synergistic effect, ensuring both 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.

[0068] This application further proposes to implement continuous stirring at 300-500 r / min during the extraction and back-extraction processes.

[0069] Continuous stirring refers to maintaining mechanical disturbance during the two-phase mixing process. This can be achieved using a variable frequency speed-regulating stirrer in conjunction with a four-bladed inclined impeller, with the impeller rotated by a power unit to create vortices. This speed range can generate appropriate shear force to promote phase interface renewal while avoiding excessive turbulence that could hinder phase separation.

[0070] Specifically, the stirring intensity optimizes mass transfer efficiency by controlling the hydrodynamic boundary layer thickness. When the rotation speed is below 300 r / min, insufficient mixing between the two phases reduces the probability of iron ions contacting the organic phase; above 500 r / min, fine droplet formation is triggered, resulting in a prolonged subsequent phase separation time. Within the set rotation 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.

[0071] Example 1

[0072] A method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system includes the following steps:

[0073] S1 Hafnium oxide pretreatment

[0074] After crushing the hafnium oxide ore, it was coarsely ground using a ball mill to obtain hafnium oxide powder with a particle size of 100 μm.

[0075] S2 hafnium oxide acid-base treatment

[0076] First, hafnium oxide powder and sodium hydroxide are thoroughly mixed at a mass ratio of 1:2. Then, organic composite microspheres are added, and the amount added is controlled to be 5% of the mass of hafnium oxide raw material. After being thoroughly mixed, the mixture is melted for 2 hours under sufficient oxygen and at 720°C. The melted product is then cooled and leached with water to obtain alkali slag.

[0077] Then, the above-mentioned alkali slag is added to a hydrochloric acid solution with a pH of 1. After stirring and dissolving thoroughly, saturated ammonia water is added to adjust the pH to 3. Then, ammonium persulfate is added, and the amount added is controlled to be 1% of the mass of the alkali slag. After standing for a while, the mixture is filtered to obtain a zirconium-hafnium mixed solution.

[0078] S3 Extraction and Separation

[0079] S3-1: A zirconium-hafnium mixed solution was added to a 5 mol / L hydrochloric acid solution at a volume ratio of 1:1. After thorough mixing, an aqueous phase was obtained. The aqueous phase was then heated to 40°C and centrifuged at 3000 r / min for 5 min. Fatty alcohol polyoxyethylene ether was then added at a concentration of 0.03 wt%, and the mixture was stirred thoroughly to obtain a pretreated aqueous phase. This pretreated aqueous phase was then added to the extraction tank along with the prepared organic phase at a volume ratio of 2:1. The mixture was stirred for 15 min, allowed to stand for phase separation, and then the upper organic phase was transferred to the back-extraction tank. Sufficient dilute hydrochloric acid was added, and the mixture was stirred for 20 min. The mixture was allowed to stand for phase separation, and the extraction-back-extraction process was repeated 3 times. During the extraction and back-extraction, continuous stirring at 300 r / min was maintained to obtain the hafnium enriched solution.

[0080] In the preparation of the organic phase, trioctyl tertiary amine and isooctanol are added to sulfonated kerosene, and their volume fractions are controlled to be 25% and 5% respectively.

[0081] S3-2, adjust the pH of the hafnium enrichment solution to 2, pass it into a strong acid styrene resin column, then wash off the impurities with dilute hydrochloric acid, and then wash off the hafnium with concentrated hydrochloric acid to obtain a high-purity hafnium solution.

[0082] S4 Precipitation and Incineration

[0083] Add saturated ammonia to a high-purity hafnium solution to adjust the pH to 7.5. Filter, wash and dry the resulting precipitate, and then calcine it at 850°C for 2 hours to obtain hafnium oxide with ultra-low iron content.

[0084] The preparation method of the organic composite microspheres is as follows:

[0085] Step 1) Dissolve 1.1g zinc nitrate and 22.5g 2-methylimidazole in 8mL and 80mL of deionized water, respectively. Mix the two solutions and stir magnetically. Centrifuge the resulting solution three times and wash it repeatedly with methanol and deionized water before drying to obtain organic powder.

[0086] Step 2) Add 1g of ammonium bicarbonate and 3g of organic powder to 20mL of deionized water to obtain an internal aqueous phase solution. Then add it to 100mL of polylactic acid dichloromethane solution with a polylactic acid content of 5wt% to form a primary emulsion. Then homogenize it using a homogenizer at 10000rpm. After that, add it to 1000mL of polyvinyl alcohol solution with a concentration of 0.2wt% and add 0.2g of polyacrylonitrile fiber. After stirring thoroughly, wash it thoroughly with deionized water and ethanol, and dry it thoroughly at 60℃ to obtain organic composite microspheres.

[0087] Example 2

[0088] A method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system includes the following steps:

[0089] S1 Hafnium oxide pretreatment

[0090] After crushing the raw hafnium oxide, it was coarsely ground using a ball mill to obtain hafnium oxide powder with a particle size of 100-150μm.

[0091] S2 hafnium oxide acid-base treatment

[0092] First, hafnium oxide powder and sodium hydroxide are thoroughly mixed at a mass ratio of 1:2.5. Then, organic composite microspheres are added, and the amount added is controlled to be 7% of the mass of hafnium oxide raw material. After being thoroughly mixed, the mixture is melted for 3 hours under sufficient oxygen and at 750°C. The melted product is then cooled and leached with water to obtain alkali slag.

[0093] Then, the above-mentioned alkali slag is added to a hydrochloric acid solution with a pH of 1.5. After stirring and dissolving thoroughly, saturated ammonia water is added to adjust the pH to 3.5. Then, ammonium persulfate is added, and the amount added is controlled to be 1.5% of the mass of the alkali slag. After standing for a while, the mixture is filtered to obtain a zirconium-hafnium mixed solution.

[0094] S3 Extraction and Separation

[0095] S3-1: A zirconium-hafnium mixed solution was added to a 6 mol / L hydrochloric acid solution at a volume ratio of 1:1.2. After thorough mixing, an aqueous phase was obtained. The aqueous phase was then heated to 42°C and centrifuged at 4000 r / min for 8 min. Fatty alcohol polyoxyethylene ether was then added at a concentration of 0.05 wt%, and the mixture was stirred thoroughly to obtain a pretreated aqueous phase. This pretreated aqueous phase was then added to the extraction tank along with the prepared organic phase at a volume ratio of 3:1. The mixture was stirred for 18 min, allowed to stand for phase separation, and the upper organic phase was transferred to the back-extraction tank. Sufficient dilute hydrochloric acid was added, and the mixture was stirred for 25 min. The mixture was allowed to stand for phase separation, and the extraction-back-extraction process was repeated 4 times. During the extraction and back-extraction, continuous stirring at 400 r / min was maintained to obtain the hafnium enriched solution.

[0096] In the preparation of the organic phase, trioctyl tertiary amine and isooctanol are added to the sulfonated kerosene, and their volume fractions are controlled to be 30% and 8% respectively.

[0097] S3-2, the pH of the hafnium enrichment solution was adjusted to 2.5, passed into a strong acid styrene resin column, and then impurities were eluted with dilute hydrochloric acid, followed by hafnium elution with concentrated hydrochloric acid to obtain a high-purity hafnium solution.

[0098] S4 Precipitation and Incineration

[0099] Add saturated ammonia to a high-purity hafnium solution to adjust the pH to 8.0. Filter, wash and dry the resulting precipitate, and then calcine it at 900℃ for 3 hours to obtain hafnium oxide with ultra-low iron content.

[0100] The preparation method of the organic composite microspheres is as follows:

[0101] Step 1) Dissolve 1.5g zinc nitrate and 25.5g 2-methylimidazole in 10mL and 100mL of deionized water, respectively. Mix the two solutions and stir magnetically. Centrifuge the resulting solution 4 times and wash it repeatedly with methanol and deionized water before drying to obtain organic powder.

[0102] Step 2) Add 1.5g of ammonium bicarbonate and 4g of organic powder to 25mL of deionized water to obtain an internal aqueous phase solution. Then add it to 120mL of polylactic acid dichloromethane solution with a polylactic acid content of 7wt% to form a primary emulsion. Then homogenize it using a homogenizer at 13000rpm. After that, add it to 1200mL of polyvinyl alcohol solution with a concentration of 0.3wt% and add 0.3g of polyacrylonitrile fiber. After stirring thoroughly, wash it thoroughly with deionized water and ethanol, and dry it thoroughly at 65℃ to obtain organic composite microspheres.

[0103] Example 3

[0104] A method for preparing ultra-low iron content hafnium oxide based on N235 extraction and separation in a hydrochloric acid system includes the following steps:

[0105] S1 Hafnium oxide pretreatment

[0106] After crushing the hafnium oxide ore, it was coarsely ground using a ball mill to obtain hafnium oxide powder with a particle size of 150 μm.

[0107] S2 hafnium oxide acid-base treatment

[0108] First, hafnium oxide powder and sodium hydroxide are thoroughly mixed at a mass ratio of 1:3. Then, organic composite microspheres are added, and the amount added is controlled to be 10% of the mass of hafnium oxide raw material. After being thoroughly mixed, the mixture is melted for 5 hours under sufficient oxygen and at 780°C. The melted product is then cooled and leached with water to obtain alkali slag.

[0109] Then, the above-mentioned alkali slag is added to a hydrochloric acid solution with a pH of 2. After stirring and dissolving thoroughly, saturated ammonia water is added to adjust the pH to 4. Then, ammonium persulfate is added, with the amount added controlled at 2% of the mass of the alkali slag. After standing for a while, the mixture is filtered to obtain a zirconium-hafnium mixed solution.

[0110] S3 Extraction and Separation

[0111] S3-1: A zirconium-hafnium mixed solution was added to a 7 mol / L hydrochloric acid solution at a volume ratio of 1:1.5. After thorough mixing, an aqueous phase was obtained. The aqueous phase was then heated to 45°C and centrifuged at 5000 r / min for 10 min. Fatty alcohol polyoxyethylene ether was then added at a concentration of 0.08 wt%, and the mixture was stirred thoroughly to obtain a pretreated aqueous phase. This pretreated aqueous phase was then added to the extraction tank along with the prepared organic phase at a volume ratio of 5:1. The mixture was stirred for 20 min, allowed to stand for phase separation, and then the upper organic phase was transferred to the back-extraction tank. Sufficient dilute hydrochloric acid was added, and the mixture was stirred for 30 min. The mixture was allowed to stand for phase separation, and the extraction-back-extraction process was repeated 5 times. During the extraction and back-extraction, continuous stirring at 500 r / min was maintained to obtain the hafnium enriched solution.

[0112] In the preparation of the organic phase, trioctyl tertiary amine and isooctanol are added to sulfonated kerosene, and their volume fractions are controlled to be 35% and 10%, respectively.

[0113] S3-2, adjust the pH of the hafnium enrichment solution to 3, pass it into a strong acid styrene resin column, then wash off the impurities with dilute hydrochloric acid, and then wash off the hafnium with concentrated hydrochloric acid to obtain a high-purity hafnium solution.

[0114] S4 Precipitation and Incineration

[0115] Add saturated ammonia to a high-purity hafnium solution to adjust the pH to 8.0. Filter, wash and dry the resulting precipitate, and then calcine it at 980℃ for 5 hours to obtain hafnium oxide with ultra-low iron content.

[0116] The preparation method of the organic composite microspheres is as follows:

[0117] Step 1) Dissolve 1.8g zinc nitrate and 28.6g 2-methylimidazole in 12mL and 120mL of deionized water, respectively. Mix the two solutions and stir magnetically. Centrifuge the resulting solution 5 times and wash it repeatedly with methanol and deionized water before drying to obtain organic powder.

[0118] Step 2) Add 2g of ammonium bicarbonate and 5g of organic powder to 30mL of deionized water to obtain an internal aqueous phase solution. Then add it to 150mL of polylactic acid dichloromethane solution with a polylactic acid content of 8wt% to form a primary emulsion. Then homogenize it using a homogenizer at 15000rpm. After that, add it to 1600mL of polyvinyl alcohol solution with a concentration of 0.5wt% and add 0.5g of polyacrylonitrile fiber. After stirring thoroughly, wash it thoroughly with deionized water and ethanol, and dry it thoroughly at 70℃ to obtain organic composite microspheres.

[0119] Comparative Example 1: This comparative example is basically the same as Example 1, except that no organic composite microspheres were added in S2.

[0120] Comparative Example 2: This comparative example is basically the same as Example 1, except that polyacrylonitrile fiber is omitted in the preparation of organic composite microspheres in S2.

[0121] Comparative Example 3: This comparative example is basically the same as Example 1, except that the aqueous phase was not pretreated in S3-1.

[0122] Comparative Example 4: This comparative example is basically the same as Example 1, except that in S3-1, polyether surfactants are omitted in the aqueous phase pretreatment.

[0123] Comparative Example 5: This comparative example is basically the same as Example 1, except that in S3-1, continuous stirring is omitted during extraction and back-extraction.

[0124] Test experiment:

[0125] Hafnium oxide samples were prepared using the process methods described in Examples 1-3 and Comparative Examples 1-5, respectively. The iron content in the hafnium oxide samples was then tested using inductively coupled plasma mass spectrometry, and the results are shown in Table 1.

[0126] Table 1

[0127]

[0128] As shown in Table 1, the process method of the present invention can significantly reduce the iron content in hafnium oxide to less than 0.0001%, thereby obtaining hafnium oxide with ultra-low iron content.

[0129] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full 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, and 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, 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, and then organic composite microspheres are added, with the amount of addition controlled at 5-10% of the mass of the hafnium oxide ore, the mixture is thoroughly mixed and evenly distributed, then melted at 720-780℃ under sufficient oxygen for 2-5 h, and then the molten product is cooled and leached with water to obtain an alkali fusion residue, 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 dissolved in 8-12 mL and 80-120 mL of deionized water respectively, 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, thoroughly stirred, washed with deionized water and ethanol, and dried at 60-70℃ to obtain organic composite microspheres, 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.

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

3. The method of claim 1, wherein, In S2, the specific operation of the acid leaching impurity removal treatment is as follows: The above 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, and after being fully placed, filtration is performed, and a zirconium-hafnium mixed solution is obtained.

4. 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.

5. 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 rotating 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.

6. 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.

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

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