Method for converting hafnium oxalate feed liquid into hafnium oxychloride feed liquid

Abstract

The invention relates to the field of hydrometallurgy, and discloses a method for converting hafnium oxalate feed liquid into hafnium oxychloride feed liquid, which is characterized by comprising the following steps: adding an HCl solution and an oxidizing agent into the hafnium oxalate feed liquid, and reacting at a certain temperature to obtain a hafnium oxychloride solution. The method has the advantages of simple operation, no introduction of any metal impurity ions, small reagent consumption, low energy consumption, low cost, high efficiency, no physical state change, and realization of continuous production. The method for adding the HCl solution and the oxidizing agent into the oxalate feed liquid is also suitable for converting oxalate solutions of other metal ions into chloride solutions, including but not limited to zirconium oxalate, titanium oxalate, thorium oxalate, scandium oxalate, niobium oxalate, tantalum oxalate, vanadium oxalate, cobalt oxalate, cesium oxalate and rubidium oxalate.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy and relates to a method for converting hafnium oxalate feedstock into hafnium oxychloride feedstock. Background Technology

[0002] Hafnium (Hf), a transition metal element in Group IVB of the 6th period, possesses excellent corrosion resistance, ductility, and high-temperature stability, and is widely used in various technological fields. In the electrical field, its low work function makes it an ideal choice for X-ray tube cathode materials; in the nuclear industry, thanks to its significant thermal neutron capture cross section (thermal neutron absorption cross section), hafnium is widely used as a core material for nuclear reactor control rods and radiation protection components; in the field of metallic materials, hafnium is often introduced as an alloying additive to significantly improve the overall performance of the matrix alloy.

[0003] Zirconium and hafnium often coexist in nature, with hafnium content ranging from 1% to 3% of zirconium. Deep separation of zirconium and hafnium is necessary to obtain nuclear-grade zirconium (requiring a hafnium content in the zirconium <100 × 10⁻⁶). -6 Only those with a purity greater than 99.99% can be used in the nuclear energy industry, while those with a purity greater than 99.99% can be used in the semiconductor industry. Zirconium and hafnium belong to the same group IVB metals, with extremely similar physicochemical properties and nearly identical ionic radii, making separation extremely difficult. It is difficult to obtain high-purity hafnium suitable for semiconductor applications using a single method.

[0004] Solvent extraction is the mainstream method for separating zirconium and hafnium in industry. In the United States, sponge zirconium produced using the methyl isobutyl ketone (MIBK)-HSCN process accounts for approximately two-thirds of the global market share. In addition, the tributyl phosphate (TBP)-HCl-HNO3 method and the trioctyl amine (TOA)-H2SO4 method are also industrialized nuclear-grade zirconium and hafnium separation technologies. However, relying on a single solvent extraction system is insufficient to obtain high-purity hafnium. Oxalate ions ( Hafnium oxalate (HA) is a high-affinity chelating ligand with a strong ability to coordinate with metal ions, and is often used as a back-extraction agent for metal ions. If the hafnium oxalate back-extraction solution obtained in the zirconium-hafnium extraction and separation industry needs further purification of hafnium, it must be converted into a corresponding extraction system. For example, the MIBK system for preferential hafnium extraction needs to be converted into an HCl system before proceeding to the next extraction and separation step. Currently, there are no reports of directly converting hafnium oxalate solution into hafnium oxychloride solution.

[0005] 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 describes a process where "hafnium oxide powder is sequentially subjected to alkali melting, water immersion, and filtration to obtain hafnium hydroxide filter cake; the hafnium hydroxide filter cake is dissolved in sulfuric acid solution to obtain hafnium sulfate solution; sodium sulfate is added to the hafnium sulfate solution to obtain a hafnium-containing double salt; the hafnium-containing double salt is dissolved in sulfuric acid solution, heated to evaporate, and cooled to crystallize to obtain hafnium sulfate crystals; the hafnium sulfate crystals are dissolved in concentrated hydrochloric acid to obtain hafnium oxychloride solution." This method involves multiple steps, including alkali melting, water immersion, filtration, sulfuric acid redissolution, evaporation and crystallization, and further redissolution, to obtain hafnium oxychloride solution from solid hafnium oxide. The operation is extremely complex, energy-intensive, requires large amounts of reagents and water, and is costly. Obtaining hafnium oxide from hafnium oxalate solution using traditional evaporation crystallization or alkaline precipitation methods, and then preparing hafnium oxychloride solution from hafnium oxide further increases reagent consumption and energy consumption, thus increasing costs. Summary of the Invention

[0006] This invention provides a method for converting hafnium oxalate solution into hafnium oxychloride solution, characterized in that HCl solution and oxidant are added to the hafnium oxalate solution, and the reaction is carried out at a certain temperature to obtain hafnium oxychloride solution.

[0007] 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, it is converted into a mixed solution containing zirconium oxychloride and hafnium oxychloride.

[0008] Further, the concentration of the hydrochloric acid solution is 0.01–13 mol / L, and the HCl concentration of the hafnium oxalate feed solution after adding the hydrochloric acid solution is >0.01 mol / L, preferably >0.5 mol / L. Hydrochloric acid provides an acidic environment, inhibiting the formation of hafnium hydroxide and simultaneously generating hafnium oxychloride. If the oxidant is chlorine (Cl2), chlorine monoxide (Cl2O), chlorine dioxide (ClO2), hypochlorous acid (HClO), chlorite (HClO2), or chloric acid (HClO3), HCl will be generated upon reaction with oxalic acid and oxalate ions, thus reducing the amount of hydrochloric acid added. Further, the oxidant is one or more of hydrogen peroxide, ozone, chlorine (Cl2), chlorine monoxide (Cl2O), chlorine dioxide (ClO2), hypochlorous acid (HClO), chlorite (HClO2), or chloric acid (HClO3).

[0009] Furthermore, the specified temperature is 0–120°C, preferably 0–95°C, to provide suitable conditions for the oxidant to oxidize oxalic acid / oxalate.

[0010] Furthermore, the hafnium oxychloride solution can also be obtained by adding hydrogen peroxide or introducing ozone into the hafnium oxalate feed solution and reacting it at a certain temperature to obtain hafnium precipitate, and then dissolving the precipitate with hydrochloric acid solution to obtain the hafnium oxychloride feed solution.

[0011] The key technical point of this invention is: Prior art document CN202510004244.5 describes a process using hafnium oxide as raw material, involving multiple complex steps such as alkali fusion, water leaching, filtration, sulfuric acid redissolution, evaporation crystallization, and further redissolution to obtain a hafnium oxychloride solution. This invention, however, describes a one-step method for obtaining a hafnium oxychloride solution from hafnium oxalate back-extraction solution obtained from the zirconium-hafnium extraction and separation industry.

[0012] The oxidant used in this invention does not introduce metal impurity ions, has no impact on product purity, is simple to operate, requires little equipment investment, has low energy consumption, low reagent consumption, low production cost, and produces almost no wastewater.

[0013] The method of adding HCl solution and oxidant to oxalate solution is also applicable to converting oxalate solutions of other metal ions into chloride solutions, including but not limited to zirconium oxalate, titanium oxalate, thorium oxalate, scandium oxalate, niobium oxalate, tantalum oxalate, vanadium oxalate, cobalt oxalate, cesium oxalate, and rubidium oxalate. Detailed Implementation

[0014] 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.

[0015] Example 1

[0016] The solution to be treated was a hafnium oxalate solution with concentrations of Hf 13.74 g / L and oxalic acid 0.16 mol / L. 10 mL of this solution was placed in a 50 mL centrifuge tube, a magnetic stir bar was added, and the tube was placed in a water bath for heating. Once the temperature reached 95 °C, the magnetic stir bar was turned on, and 1.2 mL of 30% H₂O₂ solution and 2 mL of 37% concentrated hydrochloric acid solution were added dropwise. After reacting for 1.5 h, a hafnium oxychloride solution was obtained.

[0017] Take 10 mL of hafnium oxychloride solution in a beaker and perform redox titration using 0.01 mol / L cerium sulfate (Ce(SO4)2), with o-phenanthroline-ferrous sulfate as the titration indicator. The concentration of residual oxalic acid in the solution was found to be approximately 0.003 mol / L.

[0018] Example 2

[0019] The solution to be treated was a back-extraction solution from a factory, with the following concentrations: Hf 12.7 g / L, Zr 1.4 g / L, and oxalic acid 0.43 mol / L. 50 mL of this solution was placed in a 100 mL beaker, 5 mL of 1 mol / L HCl was added, a magnetic stir bar was added, and the beaker was placed in a water bath for heating. Once the temperature reached 45 °C, the magnetic stir bar was turned on, and chlorine gas (Cl2) was continuously introduced. After reacting for 1 h, the gas introduction was stopped, yielding a mixed solution of hafnium oxychloride and zirconium oxychloride.

[0020] Take 10 mL of hafnium oxychloride solution in a beaker and perform redox titration with 0.01 mol / L cerium sulfate (Ce(SO4)2), using o-phenanthroline-ferrous sulfate as the titration indicator. The concentration of residual oxalic acid in the solution was found to be approximately 0.006 mol / L.

[0021] Example 3

[0022] The liquid to be treated was waste liquid from an industrial production process, with the following concentrations of main chemical components: Hf 4.11 g / L, Zr 7.81 g / L, and oxalic acid 0.58 mol / L. 50 mL of this liquid was placed in a 100 mL beaker, 3 mL of 8 mol / L HCl was added, a magnetic stir bar was added, and the magnetic stirrer was turned on. Ozone was introduced at room temperature, and the reaction was stopped after 2 hours, yielding a mixed solution of hafnium oxychloride and zirconium oxychloride.

[0023] Take 10 mL of hafnium oxychloride solution in a beaker and perform redox titration with 0.01 mol / L cerium sulfate (Ce(SO4)2), using o-phenanthroline-ferrous sulfate as the titration indicator. The concentration of residual oxalic acid in the solution was found to be approximately 0.014 mol / L.

[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 converting hafnium oxalate feed solution into hafnium oxychloride feed solution, characterized in that, HCl solution and oxidant are added to hafnium oxalate feed solution, and the reaction is carried out at a certain temperature to obtain hafnium oxychloride solution.

2. The method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution according to claim 1, characterized in that, 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, it is converted into a mixed solution containing zirconium oxychloride and hafnium oxychloride.

3. The method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution according to claim 1, characterized in that, The concentration of the hydrochloric acid solution is 0.01–13 mol / L, and the HCl concentration of the hafnium oxalate feed solution after adding the hydrochloric acid solution is > 0.01 mol / L, preferably > 0.5 mol / L.

4. The method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution according to claim 1, characterized in that, The oxidant is one or more of hydrogen peroxide, ozone, chlorine (Cl2), chlorine monoxide (Cl2O), chlorine dioxide (ClO2), hypochlorous acid (HClO), chlorite (HClO2), or chloric acid (HClO3).

5. The method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution according to claim 1, characterized in that, The specified temperature ranges from 0 to 120 ℃.

6. A method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution according to claim 1 or 5, characterized in that, The specified temperature ranges from 0 to 95°C.

7. The method for converting hafnium oxalate feed solution into hafnium sulfate feed solution according to claim 1, characterized in that, The hafnium oxychloride solution can also be obtained by adding hydrogen peroxide or introducing ozone into the hafnium oxalate feed solution and reacting it at a certain temperature to obtain hafnium precipitate, and then dissolving the precipitate with hydrochloric acid solution to obtain the hafnium oxychloride feed solution.

8. The method for converting hafnium oxalate feed solution into hafnium oxychloride feed solution as described in claim 1, characterized in that, The method of adding HCl solution and oxidant to oxalate solution is also applicable to converting oxalate solutions of other metal ions into chloride solutions, including but not limited to zirconium oxalate, titanium oxalate, thorium oxalate, scandium oxalate, niobium oxalate, tantalum oxalate, vanadium oxalate, cobalt oxalate, cesium oxalate, and rubidium oxalate.