A pre-separation process for high hafnium zirconium compound crystallization

Abstract

This invention discloses a pre-separation process for high-hafnium zirconium compound crystallization, belonging to the field of zirconium-hafnium separation and purification technology. Low-hafnium zirconium compound raw materials are pretreated and reacted with sulfuric acid solution to obtain a zirconium-hafnium mixed sulfate precursor. A coordination solubilizing agent composed of phosphate-functionalized β-cyclodextrin and polyethylene glycol is added to the precursor, along with silane-modified nano-yttrium oxide, ultrasonic dispersion, and directional nucleation of hafnium salt seeds, to obtain a high-hafnium crystallization product and a low-hafnium mother liquor. The low-hafnium mother liquor is pH-adjusted to precipitate zirconium compounds and recovered. The clarified mother liquor is purified by nanofiltration after pH adjustment using an ammonium sulfate-sulfuric acid buffer system and then recycled. The high-hafnium crystallization product is washed and vacuum-dried at low temperature to obtain a high-hafnium zirconium compound enriched product. This invention, through the synergistic effect of multiple processes, significantly inhibits zirconium-hafnium co-extrusion, achieving effective enrichment of hafnium components and high-proportion recovery of zirconium resources, and can be used as a pre-separation process for low-hafnium zirconium compounds.

Description

Technical Field

[0001] This invention belongs to the field of zirconium-hafnium separation and purification technology, specifically a pre-separation process for high hafnium zirconium compound crystallization. Background Technology

[0002] With the rapid development of the nuclear industry, military industry, and high-end chip industry, hafnium and hafnium compounds have become a class of rare metal materials of great strategic significance due to their excellent high-temperature resistance and dielectric properties. These materials possess outstanding high-temperature resistance, good neutron absorption capacity, and high-k dielectric properties, which enable them to play an important role in cutting-edge technology fields such as high-end integrated circuit manufacturing.

[0003] In existing industrial production, zircon sand is the main source of hafnium, but its hafnium content is generally low, typically less than 2% hafnium oxide. For the separation of zirconium and hafnium from such low-hafnium feedstocks, mainstream front-end processes mostly employ solvent extraction. These processes typically use methyl isobutyl ketone (MIBK), tributyl phosphate (TBP), tertiary amine extractants (such as N235), and acidic phosphorus extractants (such as P204), along with complex acidity-adjusting environments such as hydrochloric acid-nitric acid, sulfuric acid, or thiocyanate. While solvent extraction technology offers strong continuity in large-scale zirconium-hafnium separation and can produce nuclear-grade zirconium and high-purity hafnium under specific conditions, its efficiency bottleneck becomes increasingly apparent when processing natural low-hafnium feedstocks. Specifically, since the proportion of hafnium in the initial material is very low, in order to ensure that the hafnium produced in the downstream reaches the required purity, the extraction system often needs to be equipped with many extraction stages and large equipment. This not only consumes a lot of reagents and energy, but also leads to a serious mismatch between the processing capacity and output efficiency of the entire production line, which greatly reduces the production efficiency of high value-added hafnium compounds.

[0004] To overcome the limitations of traditional extraction front-end processes, the inventors, considering the material characteristics, attempted to use a chemical co-crystallization method as a front-end process. This involves first converting the zirconium-hafnium mixture into specific salt or oxide precursors, and then using solubility differences for recrystallization separation. Theoretically, this is a low-cost enrichment method. However, in practice, the highly similar physicochemical properties of zirconium and hafnium cause them to precipitate simultaneously during crystallization, making selective enrichment difficult. This has become the core bottleneck restricting its application.

[0005] A more critical contradiction is that if methods such as excessive suppression of crystallization or multi-stage fractional precipitation are used to increase the enrichment ratio of hafnium, a large amount of zirconium components will inevitably remain in the mother liquor or be lost with byproducts, and the increased circulating load will lead to process instability. Correspondingly, traditional crystallization processes often struggle to achieve both "high enrichment" and "high recovery," failing to ensure stable zirconium production while achieving efficient enrichment of trace amounts of hafnium. Furthermore, the random generation of crystal nuclei and the crystal growth rate during crystallization are difficult to control precisely, resulting in uneven composition of the crystallized products. The recovery and treatment of residual mother liquor also becomes extremely complex due to impurity accumulation, significantly limiting the practical application of crystallization pre-separation technology in industrial continuous production.

[0006] Therefore, developing a high-hafnium zirconium compound crystallization pre-separation process that can effectively avoid interference from simultaneous zirconium-hafnium crystallization, achieve effective enrichment of hafnium components, and is suitable for industrial continuous production is an urgent technical challenge to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a pre-separation process for high hafnium zirconium crystallization to solve the problems of low zirconium-hafnium separation efficiency, severe zirconium-hafnium co-deposition, and difficulty in achieving both high enrichment and high recovery in existing technologies.

[0008] The objective of this invention is achieved through the following technical solution: A high-hafnium zirconium compound crystallization pre-separation process includes the following steps: S1. Raw material pretreatment: Select low-hafnium zirconium compound raw materials, remove mechanical impurities, and obtain pretreated materials; S2. Chemical conversion: The pretreated material is mixed with sulfuric acid solution, and the reaction temperature is controlled at 80–100℃ and the reaction time is 1.5–2.5h to convert it into a zirconium-hafnium mixed sulfate precursor; S3. Directional crystallization: Add a coordination solubilizing compound to the precursor, stir to dissolve, and crystallize at 40–60℃ for 2–3 hours. Then add silane-modified nano-yttrium oxide and disperse it by ultrasonication. Add hafnium salt seed crystals and continue to crystallize at 40–60℃ for 3–5 hours. Filter to obtain high hafnium crystallization product and low hafnium mother liquor. The coordination solubilizing compound is formed by compounding phosphate-functionalized β-cyclodextrin with polyethylene glycol; the phosphate-functionalized β-cyclodextrin is prepared by modifying β-cyclodextrin with a phosphate esterification agent; S4. Zirconium recovery: Adjust the pH of the low hafnium mother liquor to 8–10 to precipitate the zirconium group. After washing the filtered solid, the recovered zirconium compound is obtained. The clarified mother liquor after filtration is subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system and then purified by nanofiltration before being recycled to step S2. S5. Post-processing: Wash and dry the high hafnium crystal product to obtain a high hafnium zirconium enriched product.

[0009] This invention addresses the technical challenges in existing zirconium-hafnium separation processes, including low hafnium enrichment efficiency, severe zirconium-hafnium co-deposition, the inability of traditional crystallization to simultaneously achieve high enrichment and high recovery, and long solvent extraction processes / high reagent consumption. Through the synergistic effect of multiple steps—raw material pretreatment → sulfuric acid system chemical conversion → selective directional crystallization → zirconium recovery → post-treatment—it achieves hafnium pre-enrichment in low-hafnium zirconium compound raw materials, high-proportion zirconium recovery, and long-term stable circulation of the mother liquor. It can serve as a front-end pre-separation process to reduce the load on back-end purification and is suitable for continuous industrial production. The specific process steps and their effects are as follows: In step S1, the raw material pretreatment process selects low hafnium zirconium compounds to remove mechanical impurities. This avoids solid impurities interfering with crystal nucleation and provides a clean, uniform, and stable raw material system for chemical transformation and directional crystallization, ensuring that the crystallization process is controllable and the product composition is uniform.

[0010] In step S2, the pretreated material is mixed with sulfuric acid solution, and the reaction temperature is controlled at 80–100℃ and the reaction time at 1.5–2.5h. This process converts the low-hafnium zirconium compound into a zirconium-hafnium mixed sulfate precursor, allowing zirconium and hafnium to change from the solid phase to a homogeneous liquid phase ionic form, thus eliminating the interference of solid phase materials on crystallization separation.

[0011] In step S3, directional crystallization, a coordination solubilizing compound (a compound of phosphate-functionalized β-cyclodextrin and polyethylene glycol) is added to the precursor. After stirring and dissolving, the mixture is kept at 40–60℃ for 2–3 hours for crystallization. Then, silane-modified nano-yttrium oxide is added, ultrasonic dispersion is applied, and hafnium salt seed crystals are added. The mixture is kept at 40–60℃ for crystallization for 3–5 hours. The mixture is then filtered to obtain a high-hafnium crystal product and a low-hafnium mother liquor.

[0012] In the complex solubilizing agent, phosphate-functionalized β-cyclodextrin serves as the core selective coordinating component. Its phosphate groups preferentially coordinate with hafnium ions, reducing the crystallization freedom of hafnium ions and facilitating their directional enrichment. Simultaneously, the β-cyclodextrin matrix exhibits strong acid resistance and stability in sulfuric acid systems, making it less likely to compete with zirconium or hydrogen ions for coordination, thus maintaining the stability of the separation system. Polyethylene glycol, as a dedicated solubilizing stabilizer, utilizes its hydrophilic segments to mitigate the salting-out effect of sulfuric acid systems on the precipitation of the coordinating agent, improving the solubility of phosphate-functionalized β-cyclodextrin in high-salt environments and reducing selective fluctuations caused by local precipitation and adsorption on crystal surfaces, ensuring the coordinating agent remains uniformly dissolved in the system. The synergistic effect of these two components—phosphate-functionalized β-cyclodextrin providing coordination selectivity and polyethylene glycol providing solubility and dispersion stability—allows the complex to maintain stable coordination ability even in high-salt environments.

[0013] Silane-modified acid-resistant nano-yttrium oxide, as an inert crystal-directing agent, maintains its solid particle morphology in sulfuric acid systems without dissolving or reacting. This guides regular crystal growth, reduces crystal distortion and particle agglomeration, and improves product uniformity and filtration performance.

[0014] Ultrasonic dispersion: Physically breaking down the agglomerates of silane-modified nano-yttrium oxide and hafnium salt seed crystals makes the nucleation sites more uniformly distributed, alleviates the concentrated nucleation caused by local supersaturation, and helps stabilize the crystal particle size distribution.

[0015] Hafnium salt seed crystals enable directional nucleation, replacing random spontaneous nucleation, which helps to improve hafnium enrichment and reduce batch-to-batch variation.

[0016] In step S4, zirconium recovery, the pH of the low-hafnium mother liquor is adjusted to 8–10 to allow zirconium components to precipitate. The filtered solid is washed to obtain recovered zirconium compounds, which facilitates the recycling of zirconium resources. The clarified mother liquor after filtration is subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system to maintain stable acidity and reduce the impact of acidity fluctuations on the circulation conditions. It is then purified by nanofiltration to retain the accumulated coordination solubilizing agents in the system, reducing the impact of the accumulation of organic components on the separation selectivity. The purified mother liquor is recycled to step S2 to form a closed-loop production, which is beneficial to improving the utilization rate of raw materials and the stability of continuous process operation.

[0017] In step S5, the high hafnium crystallization product is washed and dried to remove free impurities and residual moisture from the crystal surface, maintain stable product quality, and finally obtain a high hafnium zirconium enriched product, realizing the pre-separation and enrichment of hafnium components in low hafnium raw materials.

[0018] As one possible implementation of this application, in step S1, the raw material pretreatment adopts a combination of sieving for impurities and magnetic removal for iron removal, with a sieve mesh size of 80–200 mesh. This combined impurity removal method can simultaneously remove mechanical impurities and ferromagnetic impurities. The suitable mesh size range can ensure the impurity removal effect while avoiding excessive crushing of the raw materials, thus providing a stable and clean raw material system for subsequent crystallization processes.

[0019] As one possible implementation of this application, in step S3, the amount of the coordination solubilizing compound is 0.5%–1.2% of the total mass of the low hafnium zirconium raw material. This range of addition allows the coordination solubilizing compound to exert a selective coordination effect. Too little addition will affect the hafnium enrichment effect, while too much addition will easily cause system residue and accumulation of mother liquor circulation. This range can balance the separation effect and system stability.

[0020] As one possible implementation of this application, in step S3, the amount of silane-modified nano-yttrium oxide added is 0.3%–0.8% of the total mass of the low-hafnium zirconium oxide raw material. This amount allows the nano-yttrium oxide to play a crystal-directing role, guiding the crystal to grow in a regular manner. If the amount added is too low, the effect of improving the crystal form is limited, and if the amount added is too high, it will easily cause uneven dispersion of the system. This range can improve the crystal quality without introducing excessive impurities.

[0021] As some possible implementations of this application, in step S3, the power of ultrasonic dispersion is 100–300W and the frequency is 20–40kHz.

[0022] As one possible implementation method of this application, in step S3, the amount of hafnium salt seed crystals added is 0.1%–0.5% of the total mass of the low hafnium zirconium raw material. A suitable amount of seed crystals can achieve directional nucleation and reduce the fluctuations caused by random spontaneous nucleation. If the amount added is too low, the nucleation guiding effect is limited, and if the amount added is too high, it will easily cause excess nuclei. This range can improve the hafnium enrichment effect and reduce batch-to-batch fluctuations.

[0023] As one possible implementation of this application, in step S2, the concentration of the sulfuric acid solution is 1.5–3.0 mol / L.

[0024] As one possible implementation method of this application, in step S4, the continuous flow pH steady-state control stabilizes the acidity of the system within the pH range of 0.5–2.0. Stabilizing the acidity within this range can maintain the ion balance of the mother liquor circulation system, reduce the impact of acidity deviation on the separation state of zirconium and hafnium, and help maintain the stability of the separation effect during continuous production.

[0025] As one possible implementation of this application, in step S4, the nanofiltration membrane used for nanofiltration has a pore size of 0.5–2 nm. This pore size can retain accumulated coordination solubilizing agents while allowing zirconium ions, hafnium ions, and acid radicals to pass through freely, thereby achieving mother liquor purification and retention of effective components, which is beneficial for the long-term circulation stability of the mother liquor.

[0026] As one possible implementation of this application, in step S4, the pH of the low hafnium mother liquor is adjusted using a sodium hydroxide solution or an ammonia solution with a concentration of 10–30 wt%. Using such alkaline reagents can adjust the pH of the mother liquor to the target range, causing the zirconium component to precipitate. The appropriate concentration can avoid local pH being too high, which would cause impurities to be carried into the product, thus improving the purity of the recovered zirconium.

[0027] As one possible implementation method of this application, in step S5, the drying is vacuum low-temperature drying, with a drying temperature of 60–80°C and a relative vacuum degree of -0.06 to -0.09 MPa. Vacuum low-temperature conditions can remove moisture while reducing the impact of high temperatures on crystal form and minimizing product oxidation and tarnishing, thus maintaining the quality stability of the high hafnium zirconium-enriched product and facilitating subsequent storage and further processing.

[0028] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a series of synergistic processes, including raw material pretreatment, chemical conversion in a sulfuric acid system, selective coordination with a coordinating solubilizing compound, silane-modified nano-yttrium oxide crystal shaping, ultrasonic dispersion, directional nucleation of hafnium salt seeds, steady-state pH control of the mother liquor, and nanofiltration purification and circulation. Through the synergistic effect of these processes, selective pre-separation of zirconium and hafnium can be achieved, along with effective enrichment of hafnium components, high-proportion recovery of zirconium resources, improved crystal particle size uniformity, and long-term stable circulation of the mother liquor, ultimately yielding a high-hafnium zirconium compound-enriched product. Specifically, the zirconium recovery rate of the obtained high-hafnium zirconium compound enriched products is ≥93.5%, which can stably achieve efficient recovery of zirconium components; the HfO2 mass fraction in the high-hafnium products is ≥8.9%, and the hafnium enrichment effect is significant; the hafnium oxide / zirconia mass ratio is ≥9.9%, and the zirconium-hafnium pre-separation selectivity is good; the crystal particle size span value is ≤0.72, and the crystal particle size distribution is uniform; the relative increase of TOC in the mother liquor recycling for 5 batches is ≤8.3%, and there is no obvious accumulation of organic components, indicating strong stability of continuous process operation; the product has regular crystals, no agglomeration, and excellent filtration performance, which can fully meet the requirements of high enrichment, high recovery, high stability, and easy industrialization for the front-end pre-separation of low-hafnium zirconium compounds. Detailed Implementation

[0029] Example 1 S1 Select low hafnium zirconium oxide raw material (acid-soluble low hafnium zirconium hydroxide, with hafnium content converted to hafnium oxide of 1.80%), and use a 120-mesh sieve and magnetic removal to remove mechanical and ferromagnetic impurities from the raw material to obtain pretreated material.

[0030] S2 Add 1000g of pretreated material to the reactor, add 4500mL of 2.0mol / L sulfuric acid solution, stir at 200r / min, heat to 85℃ and keep the temperature for 2h to obtain zirconium-hafnium mixed sulfate precursor.

[0031] S3 The above precursor was cooled uniformly at a rate of 2℃ / h, and the system temperature was stabilized to 45℃ under stirring. Then, 1.0wt% of a coordination solubilizing compound (a mixture of phosphate-functionalized β-cyclodextrin and polyethylene glycol 200 in a 9:1 mass ratio) of the total mass of the low hafnium zirconium raw material was added to the precursor, and the mixture was stirred at 200 r / min for 15 min until completely dissolved. Then, the mixture was kept at 45℃ for 2.5 h for crystallization. Subsequently, 0.5wt% of silane-modified nano-yttrium oxide with a purity ≥99.9% of the total mass of the low hafnium zirconium raw material was added, and the mixture was ultrasonically dispersed at a low power of 200W and a frequency of 30kHz for 5 min. Finally, 0.3wt% of the total mass of the low hafnium zirconium raw material with a purity ≥99.5% was added. Hafnium salt seed crystals (hafnium sulfate, which were pulverized by air jet to a median particle size D50 of 1-5 μm before addition) were crystallized at 45℃ for 4 hours and then filtered through a 300-mesh filter cloth to obtain high hafnium crystallized products and low hafnium mother liquor.

[0032] The preparation method of phosphate ester-functionalized β-cyclodextrin is as follows: Weigh 100g of β-cyclodextrin and add 800mL of deionized water, stirring until completely dissolved. Adjust the pH of the system to 10-11 with 10wt% NaOH solution, heat the system to 50℃, add 25g of sodium tripolyphosphate dropwise, and stir for 3 hours. After the reaction is complete, add 1200mL of anhydrous ethanol for precipitation, and filter through a 300-mesh filter cloth. Wash the filter cake twice with deionized water and vacuum dry at 70℃ for 4 hours to obtain phosphate-functionalized β-cyclodextrin. The obtained phosphate-functionalized β-cyclodextrin has a phosphorus content of 5.0-5.8%, an average degree of substitution (DS) of 0.4-0.5, and an infrared spectrum at 1250cm⁻¹. -1 A P=O stretching vibration peak appears at this location.

[0033] The preparation method of silane-modified nano-yttrium oxide is as follows: 10 g of nano-yttrium oxide (particle size 20–50 nm, purity ≥99.9%) was weighed and added to 100 mL of an ethanol-water mixture (volume ratio 9:1). The mixture was ultrasonically dispersed for 30 min to form a uniform suspension. 0.3 g of KH-550 aminosilane coupling agent was added, and the pH of the system was adjusted to 4.0–5.0 with acetic acid. The mixture was stirred at 50 °C for 2 h. After the reaction, the mixture was centrifuged, washed twice with ethanol, and vacuum dried at 80 °C for 3 h to obtain silane-modified nano-yttrium oxide. Testing showed that the obtained silane-modified nano-yttrium oxide, after soaking in 2.0 mol / L sulfuric acid for 24 h, exhibited a dissolution loss of <0.5%, demonstrating its stable crystal-directing effect.

[0034] S4. Take the low-hafnium mother liquor and adjust the pH of the system to 9.0 using a 20wt% ammonia solution. Stir for 20 min to allow the zirconium group to precipitate. Filter with a 300-mesh filter cloth, and wash the filter cake twice with deionized water to obtain the recovered zirconium. The clarified mother liquor after filtration is subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system (ammonium sulfate concentration 0.2mol / L, sulfuric acid concentration 0.1mol / L). (i.e., real-time control using an online pH meter, and the frequency of the buffer feed pump is adjusted in real time according to the online pH meter reading through a PID feedback control system to ensure that the pH fluctuation deviation is ≤±0.1). The acidity is stabilized at pH 1.0, and then purified through a 1nm nanofiltration membrane (a negatively charged acid-resistant nanofiltration membrane with a molecular weight cutoff of 800–1200 Da). All purified mother liquor is recycled to step S2 for reuse.

[0035] S5 The high hafnium crystal product was washed twice with deionized water at room temperature, with the amount of water used each time being three times the mass of the product. After washing, it was placed in a vacuum drying oven and dried for 4 hours at a temperature of 70°C and a relative vacuum of -0.07MPa to obtain a high hafnium zirconium enriched product.

[0036] Example 2 S1 Select low hafnium zirconium raw material (same as in Example 1), use 80 mesh sieve and magnetic removal to remove mechanical and ferromagnetic impurities from the raw material to obtain pretreated material.

[0037] S2 Add 1000g of pretreated material to the reactor, add 4500mL of 2.0mol / L sulfuric acid solution, stir at 180r / min, heat to 80℃ and keep the temperature for 1.5h to obtain zirconium-hafnium mixed sulfate precursor.

[0038] S3 The above precursor was cooled at a constant rate of 2℃ / h, and the system temperature was stabilized to 45℃ under stirring. Then, 0.5wt% of the total mass of low hafnium zirconium raw material and a coordination solubilizing compound (same as in Example 1) were added to the precursor and stirred at 180r / min for 15min until completely dissolved. Then, the mixture was kept at 45℃ for 2.5h for crystallization. Subsequently, 0.3wt% of the total mass of low hafnium zirconium raw material and ≥99.9% purity of silane-modified nano-yttrium oxide (same as in Example 1) were added and ultrasonically dispersed at 100W power and 20kHz frequency for 5min. Then, 0.1wt% of the total mass of low hafnium zirconium raw material and ≥99.5% purity of hafnium salt seed crystals (same as in Example 1) were added and the mixture was kept at 45℃ for 3h for crystallization. The mixture was filtered through a 300-mesh filter cloth to obtain a high hafnium crystal product and a low hafnium mother liquor.

[0039] In step S4, the low-hafnium mother liquor was taken, and the pH of the system was adjusted to 8.0 using a 10wt% sodium hydroxide solution. The mixture was stirred for 20 minutes to allow the zirconium group to precipitate. The precipitate was then filtered through a 300-mesh filter cloth, and the filter cake was washed twice with deionized water to obtain the recovered zirconium. The clarified mother liquor after filtration was subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system (ammonium sulfate concentration 0.2mol / L, sulfuric acid concentration 0.1mol / L) to stabilize the acidity at pH 0.5. The mother liquor was then purified through a 0.5nm nanofiltration membrane (a negatively charged acid-resistant nanofiltration membrane with a molecular weight cutoff of 800–1200 Da). All purified mother liquor was recycled to step S2 for reuse.

[0040] S5 The high hafnium crystal product was washed twice with deionized water at room temperature, with the amount of water used each time being three times the mass of the product. After washing, it was placed in a vacuum drying oven and dried for 4 hours at a temperature of 60°C and a relative vacuum of -0.06MPa to obtain a high hafnium zirconium enriched product.

[0041] Example 3 S1 Select low hafnium zirconium raw material (same as in Example 1), use a 200-mesh sieve and magnetic removal to remove mechanical and ferromagnetic impurities from the raw material to obtain pretreated material.

[0042] S2 Add 1000g of pretreated material to the reactor, add 4500mL of 2.0mol / L sulfuric acid solution, stir at 220r / min, heat to 100℃ and keep the temperature for 2.5h to obtain zirconium-hafnium mixed sulfate precursor.

[0043] S3 The above precursor was cooled at a constant rate of 2℃ / h, and the system temperature was stabilized at 45℃ under stirring. Then, 1.2wt% of the total mass of low hafnium zirconium raw material and a coordination solubilizing compound (same as in Example 1) were added to the precursor, and the mixture was stirred at 220r / min for 15min until completely dissolved. Then, the mixture was kept at 45℃ for 2.5h for crystallization. Subsequently, 0.8wt% of the total mass of low hafnium zirconium raw material and ≥99.9% pure silane-modified nano-yttrium oxide were added, and low-power ultrasonic dispersion at 300W and 40kHz was turned on for 5min. Then, 0.5wt% of the total mass of low hafnium zirconium raw material and ≥99.5% pure hafnium salt seed crystals (same as in Example 1) were added, and the mixture was kept at 45℃ for 5h for crystallization. The mixture was filtered through a 300-mesh filter cloth to obtain a high hafnium crystal product and a low hafnium mother liquor.

[0044] In step S4, the low-hafnium mother liquor was taken and the pH of the system was adjusted to 10.0 using a 30wt% ammonia solution. The mixture was stirred for 20 minutes to allow the zirconium group to precipitate. The precipitate was then filtered through a 300-mesh filter cloth, and the filter cake was washed twice with deionized water to obtain the recovered zirconium. The clarified mother liquor after filtration was subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system (ammonium sulfate concentration 0.2mol / L, sulfuric acid concentration 0.1mol / L) to stabilize the acidity at pH 2.0. The mother liquor was then purified through a 2nm nanofiltration membrane (a negatively charged acid-resistant nanofiltration membrane with a molecular weight cutoff of 800–1200 Da). All purified mother liquor was recycled to step S2 for reuse.

[0045] S5 The high hafnium crystal product was washed twice with deionized water at room temperature, with the amount of water used each time being three times the mass of the product. After washing, it was placed in a vacuum drying oven and dried for 4 hours at a temperature of 80℃ and a relative vacuum of -0.09MPa to obtain a high hafnium zirconium enriched product.

[0046] Comparative Example 1 Compared to Example 1, no coordination solubilizing compounding agent is added in step S3, while the remaining steps and parameters are exactly the same as in Example 1.

[0047] Comparative Example 2 Compared to Example 1, the polyethylene glycol 200 is removed from the coordination solubilizing compound in step S3, while the remaining steps and parameters are exactly the same as in Example 1.

[0048] Comparative Example 3 Compared to Example 1, silane-modified nano-yttrium oxide is not added in step S3, while the remaining steps and parameters are exactly the same as in Example 1.

[0049] Comparative Example 4 Compared to Example 1, the phosphate ester functionalized β-cyclodextrin in step S3 is replaced with sulfonated modified β-cyclodextrin, and the remaining steps and parameters are exactly the same as in Example 1.

[0050] Comparative Example 5 Compared to Example 1, except for the absence of hafnium salt seed crystals in step S3, the other steps and parameters are exactly the same as in Example 1.

[0051] Comparative Example 6 Compared to Example 1, except that the mother liquor is directly circulated without nanofiltration purification in step S4, the other steps and parameters are exactly the same as in Example 1.

[0052] Experimental Example To verify the technical effect of the high hafnium zirconium compound crystallization pre-separation process of the present invention, the products obtained in Examples 1-3 and Comparative Examples 1-6 were tested under the same experimental conditions; three parallel samples were taken from each batch, and three repeated tests were performed on each sample, and the average value of the results was taken.

[0053] The specific testing items and methods are as follows (the test results are shown in Table 1): (1) Zirconium recovery rate: Based on the total mass of zirconium in the raw material, the proportion of the total mass of zirconium in the high hafnium product and the recovered zirconium compound is calculated, in %. (2) Mass fraction of HfO2 in high hafnium product (determined by ICP-MS inductively coupled plasma mass spectrometry, in %. (3) Mass ratio of hafnium oxide / zirconia: calculated from the mass fraction of HfO2 and ZrO2 in the product, in %.

[0054] It is worth noting that the above conversion of zirconium and hafnium components into corresponding oxides for content characterization is only used as a quantitative comparison basis and does not restrict the actual existence form of the product. (4) Crystal particle size uniformity: The high hafnium crystal product was measured by a laser particle size analyzer and characterized by the span value (D90–D10) / D50. The smaller the span value, the more uniform the particle size distribution. (5) Mother liquor circulation stability: Five batches were continuously circulated, and the total organic carbon content in the mother liquor was measured by a TOC analyzer. The relative increase in TOC was used to characterize the degree of accumulation of organic components. A relative increase in TOC ≤ 10% indicates stable circulation, while a relative increase in TOC > 10% indicates significant accumulation and decreased stability.

[0055] Table 1: Test Results of Examples and Comparative Examples As can be seen from Table 1: Examples 1-3 utilize raw material pretreatment, chemical conversion of sulfuric acid system, selective coordination of coordination solubilizing compounding agent, silane-modified nano-yttrium oxide crystal form guidance, ultrasonic dispersion, directional nucleation of hafnium salt crystals, steady-state control of mother liquor pH and nanofiltration purification circulation as the main synergistic processes to achieve selective pre-separation of zirconium and hafnium, effective enrichment of hafnium components, high-proportion recovery of zirconium resources, improved crystal particle size uniformity, and long-term stable circulation of mother liquor, resulting in a high-hafnium zirconium compound enriched product. Under the above process, the zirconium recovery rate is ≥93.5%, and the zirconium component can be stably recovered; the HfO2 mass fraction in the high hafnium product is ≥8.9%, and the hafnium enrichment effect is significant; the hafnium oxide / zirconia mass ratio is ≥9.9%, and the zirconium-hafnium pre-separation selectivity is good; the crystal particle size span value is ≤0.72, and the crystal particle size distribution is uniform; based on the TOC of the first batch of mother liquor, the relative increase of 5 batches is ≤8.3%, the organic components have no obvious accumulation, and the process is stable and continuous; the product has regular crystals, no agglomeration, and good filtration performance, which meets the requirements of high enrichment, high recovery, high stability, and easy industrialization for the front-end pre-separation of low hafnium zirconium compounds.

[0056] In Comparative Example 1, due to the absence of a coordinating solubilizing compound, the selective coordination effect on hafnium ions was lost, resulting in severe zirconium-hafnium co-deposition, a significant decrease in hafnium enrichment efficiency, a HfO2 mass fraction of only 3.2%, a hafnium oxide / zirconia mass ratio of 3.3%, a reduced zirconium recovery rate, a significantly worsened crystal particle size distribution, and noticeable accumulation of organic matter in the mother liquor, leading to decreased process stability. In Comparative Example 2, because polyethylene glycol 200 was not added to the compound, the solubility of the coordinating agent in the high-salt system decreased, weakening selectivity and dispersibility, reducing hafnium enrichment and zirconium recovery effects, worsening crystal uniformity, and decreasing mother liquor circulation stability. In Comparative Example 3, because silane-modified nano-yttrium oxide was not added, the crystal form guiding effect was lacking, resulting in irregular crystal growth, a wider particle size distribution, a reduced hafnium enrichment efficiency, an increase in the span value to 2.13, and poorer product uniformity. In Comparative Example 4, replacing phosphate-functionalized β-cyclodextrin with sulfonated modified β-cyclodextrin weakened the selective coordination ability for hafnium, reduced the separation efficiency of zirconium and hafnium, significantly decreased the HfO2 mass fraction and the hafnium oxide / zirconia mass ratio, and exacerbated the accumulation of organic matter in the mother liquor. In Comparative Example 5, due to the lack of hafnium salt seed crystals, crystallization was mainly based on random spontaneous nucleation, reducing the controllability of hafnium enrichment, decreasing the HfO2 content in the product, and worsening batch stability. In Comparative Example 6, because the mother liquor was directly circulated without nanofiltration purification, organic coordinating agents continued to accumulate, disrupting the coordination balance of the system, reducing the hafnium enrichment effect, worsening the circulation stability of the mother liquor, and making long-term operation prone to separation effect degradation.

Claims

1. A pre-separation process for high hafnium zirconium compound crystallization, characterized in that, The process includes the following steps: S1. Raw material pretreatment: Select low hafnium zirconium raw materials, remove mechanical impurities, and obtain pretreated materials; S2. Chemical conversion: The pretreated material is mixed with sulfuric acid solution, and the reaction temperature is controlled at 80–100℃ and the reaction time is 1.5–2.5h to convert it into a zirconium-hafnium mixed sulfate precursor; S3. Directional crystallization: Add a coordination solubilizing compound to the precursor, stir to dissolve, and crystallize at 40–60℃ for 2–3 hours. Then add silane-modified nano-yttrium oxide and disperse it by ultrasonication. Add hafnium salt seed crystals and continue to crystallize at 40–60℃ for 3–5 hours. Filter to obtain high hafnium crystallization product and low hafnium mother liquor. The coordination solubilizing compound is formed by compounding phosphate-functionalized β-cyclodextrin with polyethylene glycol; the phosphate-functionalized β-cyclodextrin is prepared by modifying β-cyclodextrin with a phosphate esterification agent; S4. Zirconium recovery: Adjust the pH of the low hafnium mother liquor to 8–10 to precipitate the zirconium group. After washing the filtered solid, the recovered zirconium compound is obtained. The clarified mother liquor after filtration is subjected to continuous flow pH steady-state control using an ammonium sulfate-sulfuric acid buffer system and then purified by nanofiltration before being recycled to step S2. S5. Post-processing: Wash and dry the high hafnium crystal product to obtain a high hafnium zirconium enriched product.

2. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S3, the amount of the coordination solubilizing compound is 0.5%–1.2% of the total mass of the low hafnium zirconium raw material.

3. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S3, the amount of silane-modified nano-yttrium oxide added is 0.3%–0.8% of the total mass of the low hafnium zirconium raw material.

4. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S3, the ultrasonic dispersion power is 100–300W and the frequency is 20–40kHz.

5. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S3, the amount of hafnium salt seed crystals added is 0.1%–0.5% of the total mass of the low hafnium zirconium raw material.

6. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S2, the concentration of the sulfuric acid solution is 1.5–3.0 mol / L.

7. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S4, continuous flow pH steady-state control stabilizes the acidity of the system within the pH range of 0.5–2.

0.

8. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S4, the nanofiltration membrane used for nanofiltration has a pore size of 0.5–2 nm.

9. The high hafnium zirconium compound crystallization pre-separation process according to claim 1, characterized in that, In step S5, the drying is a vacuum low-temperature drying, with a drying temperature of 60–80℃ and a relative vacuum degree of -0.06 to -0.09 MPa.

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