Method for preparing hafnium oxide from hafnium oxalate feed liquid by oxidation precipitation method

Abstract

The invention discloses a method for preparing hafnium oxide from hafnium oxalate feed liquid through an oxidation precipitation method, and belongs to the technical field of hydrometallurgy. The specific method comprises the following steps: adding an oxidizing agent into hafnium oxalate feed liquid to destroy oxalate ions in hafnium oxalate so as to enable hafnium to form hydroxide precipitates; and separating the generated white precipitate, and roasting at high temperature to obtain hafnium oxide. The strong oxidant used in the method is low in cost, high in precipitation efficiency, green, environmentally friendly, free of large pollution to equipment and the environment and wide in application range. The method is simple in process, does not involve a complex process flow, does not need precise equipment, avoids a large amount of alkali liquor required by metal ion precipitation, is simpler in process flow, higher in efficiency and lower in cost, avoids the generation of a large amount of wastewater, and is very environment-friendly. And meanwhile, the process is wide in application range and suitable for various oxalic acid metal feed liquid.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology and relates to a method for the clean and efficient preparation of hafnium oxide from hafnium oxalate feed solution. Background Technology

[0002] Hafnium has broad application prospects in aerospace, semiconductors, plasma cutting, precision machinery, and military fields. Meanwhile, metallic hafnium possesses excellent neutron absorption capabilities, high temperature resistance, corrosion resistance, and a long service life. It does not produce other radiation after irradiation, making it an indispensable core material for nuclear reactor control rods. Hafnium content in nature is only 1-3% of that of zirconium, and the extremely similar physicochemical properties of zirconium and hafnium make deep separation of the two extremely difficult. Nuclear-grade hafnium separation requires advanced technology and is very challenging to produce. Solvent extraction is the mainstream process for nuclear-grade zirconium-hafnium separation. Oxalate ions ( Hafnium oxalate (HO) is a high-affinity chelating ligand with a strong ability to coordinate with metal ions, and is often used as a stripping agent for metal ions. The traditional method for preparing hafnium oxide from hafnium oxalate feed solution involves obtaining hafnium oxalate crystals through evaporation crystallization, followed by high-temperature calcination to prepare hafnium oxide. This method is inefficient, energy-intensive, and costly. Due to the strong affinity between oxalate ions and hafnium, it is difficult to completely precipitate hafnium from the hafnium oxalate feed solution using NaOH, ammonia, or KOH solutions. Furthermore, the resulting precipitate requires repeated washing, which is complex, consumes a large amount of water, and the wastewater treatment further increases costs. On January 2, 2025, Guangdong Pioneer Rare Materials Co., Ltd. submitted an invention patent application with application number CN202510004244.5 entitled "High-purity hafnium oxide and its preparation method". The patent application mentioned "calcining hafnium oxalate to obtain high-purity hafnium oxide" and also mentioned "dissolving hafnium oxychloride crystals in pure water, filtering and adding oxalic acid solution to precipitate hafnium oxalate". In other words, in this method, oxalic acid is used as a precipitant to obtain hafnium oxalate precipitate, and the hafnium oxalate precipitate is then calcined to obtain high-purity hafnium oxide. Summary of the Invention

[0003] This invention provides a method for the clean and efficient preparation of hafnium oxide from hafnium oxalate solution by oxidation precipitation. The method is characterized by adding an oxidant to the hafnium oxalate solution, reacting it at a certain temperature, separating the resulting white precipitate, and then calcining it at a high temperature to obtain hafnium oxide.

[0004] Furthermore, the hafnium oxalate solution is a solution containing hafnium oxalate, and the solution may also contain oxalic acid and zirconium oxalate; if the hafnium oxalate solution contains zirconium oxalate, the product after high-temperature calcination is a mixture of zirconium oxide and hafnium oxide.

[0005] Furthermore, the oxidant is one or more of hydrogen peroxide or ozone.

[0006] Furthermore, the specified temperature is 0–120 °C, and the high temperature is 350–800 °C, preferably 350–600 °C.

[0007] Furthermore, the method for separating the generated white precipitate is filtration or centrifugation, or the clear liquid is discharged after the precipitate has settled.

[0008] Furthermore, the oxidant hydrogen peroxide or ozone can be replaced by NaClO, NaClO2, NaClO3, KClO, KClO2, KClO3, peracetic acid, ammonium persulfate, sodium percarbonate, etc.

[0009] Furthermore, the oxidation precipitation method is also applicable to the preparation of oxides of other metal ions from oxalate solutions, including but not limited to zirconium oxalate, titanium oxalate, thorium oxalate, scandium oxalate, niobium oxalate, tantalum oxalate, vanadium oxalate, and cobalt oxalate.

[0010] In this invention, the object of treatment is hafnium oxalate solution. An oxidant is added to the hafnium oxalate solution to obtain hafnium hydroxide precipitate. After the hafnium hydroxide precipitate is separated, it is calcined at high temperature to obtain hafnium oxide product. Furthermore, the patent of Guangdong Pioneer Rare Materials Co., Ltd. (High-purity hafnium oxide and its preparation method, CN202510004244.5) describes the process of obtaining high-purity hafnium oxide from hafnium oxide raw materials. Before obtaining hafnium oxalate precipitate, the hafnium-containing material needs to undergo multiple processes such as alkali melting, water leaching, filtration, acid dissolution, hafnium-containing double salt precipitation, acid dissolution, evaporation crystallization, dissolution, evaporation crystallization, dissolution, precipitation, and calcination. The process is very cumbersome, with large reagent consumption, large water consumption, high energy consumption, large wastewater generation, and high cost. In contrast, the present invention obtains hafnium oxide product from hafnium oxalate solution by simply adding an oxidant to obtain hafnium hydroxide precipitate, followed by filtration and calcination to obtain hafnium oxide product. The process has low reagent consumption, simple operation, low cost, high efficiency, and low energy consumption.

[0011] In this invention, the added strong oxidant H2O2 and ozone do not introduce any impurities and have no impact on product purity. Furthermore, the cost is low and the risk factor is minimal. The oxidation products are mainly CO2 and H2O, which are essentially non-polluting to the environment, and the clarified liquid can be directly reused.

[0012] This invention employs a precipitation method using H2O2 and ozone, which produces no wastewater and avoids the problems of equipment corrosion and product contamination associated with traditional alkaline precipitation methods. The working environment is also safer, with less harm to human health.

[0013] In this invention, an oxidation precipitation method is used to oxidize oxalate and excess oxalate into H2O and CO2 using H2O2 or ozone. The zirconium-hafnium precipitation rate can reach over 99%, which is highly efficient.

[0014] In summary, this method is clean, efficient, simple to operate, low in cost, produces no wastewater, has high product purity, and results in virtually no loss of metal ions. Attached Figure Description

[0015] Figure 1 This is a SEM image of hafnium oxide products.

[0016] Figure 2 This is the XRD pattern of hafnium oxide products. Detailed Implementation

[0017] The method of the present invention will be further illustrated below with reference to embodiments. These embodiments are for illustrative purposes and do not constitute an undue limitation of the invention.

[0018] Example 1

[0019] The hafnium oxalate feed solution contained 16.68 g / L Hf, 1.32 g / L Zr, and 0.3 mol / L oxalic acid. 10 mL of this feed solution was placed in a 50 mL centrifuge tube, a magnetic stir bar was added, and the tube was heated in a water bath. Once the temperature reached 95 °C, the magnetic stir bar was turned on, and 1.2 mL of 30% H₂O₂ solution was added dropwise. After reacting for 2 h, the mixture was centrifuged, the supernatant was removed, and the white solid was dried at 80 °C and then calcined in a muffle furnace at 500 °C for 2 h to obtain a white, lumpy solid. This solid was ground to obtain hafnium oxide powder, with a hafnium recovery rate of 99.22%.

[0020] Example 2

[0021] The solution to be treated was the back-extraction liquid from a multi-stage back-extraction process in a zirconium-hafnium separation industry at a certain factory, containing 28.8 g / L Zr, 8.75 g / L Hf, and 0.5 mol / L oxalic acid. 100 mL of this solution was placed in a 500 mL three-necked flask, heated to 80 °C, and then 15 mL of 50% H₂O₂ solution was added in batches. Heating and stirring were stopped after no more bubbles were generated. After the temperature cooled to room temperature, the solution was filtered, and the filter cake was calcined at 800 °C for 1 h. After grinding, a mixed powder of zirconium oxide and hafnium oxide was obtained. The filtrate contained 0.15 g / L Zr and 0.11 g / L Hf, with a Zr precipitation rate >99% and an Hf precipitation rate >98.5%.

[0022] Example 3

[0023] The solution to be treated was the Hf back-extraction solution from the zirconium-hafnium extraction and separation process, with an Hf concentration of 10.49 g / L, a Zr concentration of 0.26 g / L, and an oxalic acid concentration of approximately 0.28 mol / L. 250 mL of this solution was placed in a 500 mL beaker, and ozone was introduced into the solution at room temperature. After reacting for 3 h, the ozone introduction was stopped, and the solution was allowed to stand for at least 12 h. The supernatant was poured off, and the precipitate was placed in a crucible and calcined at 400 ℃ for 3 h. After grinding, hafnium oxide powder was obtained. The hafnium precipitation rate was 99.07%.

[0024] The above description is merely an example of the implementation of this invention and is not intended to limit the invention. Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing hafnium oxide from hafnium oxalate feed solution by oxidation precipitation, characterized in that, An oxidant is added to a hafnium oxalate solution, and the reaction is carried out at a certain temperature. The resulting white precipitate is separated and then calcined at a high temperature to obtain hafnium oxide.

2. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 1, characterized in that, The hafnium oxalate solution is a solution containing hafnium oxalate, and the solution also contains oxalic acid and zirconium oxalate; if the hafnium oxalate solution contains zirconium oxalate, the product after high-temperature calcination is a mixture of zirconium oxide and hafnium oxide.

3. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 1, characterized in that, The oxidant is hydrogen peroxide or ozone.

4. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 1, characterized in that, The specified temperature is 0–120 °C, and the specified high temperature is 350–800 °C.

5. A method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 1 or 4, characterized in that, The high temperature mentioned is 350~600℃.

6. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 1, characterized in that, The method for separating the generated white precipitate is filtration or centrifugation, or the clear liquid is discharged after the precipitate has settled.

7. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation according to claim 3, characterized in that, The hydrogen peroxide or ozone can be replaced by NaClO, NaClO2, NaClO3, KClO, KClO2, KClO3, peracetic acid, ammonium persulfate, or sodium percarbonate.

8. The method for preparing hafnium oxide from hafnium oxalate solution by oxidation precipitation as described in claim 1, characterized in that, The oxidation precipitation method is also applicable to the preparation of oxides of other metal ions from oxalate solutions, including but not limited to zirconium oxalate, titanium oxalate, thorium oxalate, scandium oxalate, niobium oxalate, tantalum oxalate, vanadium oxalate, and cobalt oxalate.

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