A hafnium oxalate and a method for preparing the same

Abstract

The application discloses a kind of fofa oxalate and preparation method thereof, belong to compound synthesis technical field;The preparation method of fofa oxalate provided by the application includes the following steps: (1) ammonium oxalate aqueous solution is added to soluble fofa compound aqueous solution, mixed uniformly after adjusting the pH value of system to 3-6, then heated stirring, aging, obtain colloidal liquid;(2) the colloidal liquid of step (1) is hydrothermally reacted, after reaction, washing, suction filtration, collect filter residue, obtain fofa oxalate.The application is hydrothermally reacted under certain pH value, so that the obtained fofa oxalate has good purity on the basis of ensuring yield, and product crystal particles are uniform;In addition, the method of the application is simple, and the reliability is strong, under the condition of ensuring the quality of fofa oxalate product, also reduce processing cost, and crystal grain size and morphology can be directly controlled by adjusting reaction conditions.

Description

Technical Field

[0001] This invention belongs to the field of compound synthesis technology, and particularly relates to a hafnium oxalate and its preparation method. Background Technology

[0002] Hafnium is a lustrous, silvery-gray transition metal. It does not react with dilute hydrochloric acid, dilute sulfuric acid, or strong alkaline solutions, but it is soluble in hydrofluoric acid and aqua regia. Hafnium constitutes 0.00045% of the Earth's crust and is often found in nature alongside zirconium. Its chemical properties are very similar to zirconium; it exhibits excellent corrosion resistance, is not easily corroded by common acid and alkaline solutions, and readily dissolves in hydrofluoric acid to form fluorine complexes. At high temperatures, hafnium can also directly combine with gases such as oxygen and nitrogen to form oxides and nitrides.

[0003] The precursor of hafnium oxide is mainly hafnium hydroxide, with a solid content generally ranging from 10% to 30%. The process of preparing hafnium oxide from hafnium hydroxide involves direct calcination, which decomposes the hafnium hydroxide to obtain hafnium oxide. However, due to the inherent properties of hafnium hydroxide, the hafnium oxide product produced during calcination exhibits inconsistent particle size and a tendency to agglomerate. Furthermore, the energy consumption for calcining hafnium hydroxide is relatively high, resulting in persistently high production costs and limiting the application of hafnium oxide. Therefore, there is an urgent need to find a low-cost hafnium salt that can be used to directly calcinate hafnium oxide.

[0004] In the field of chemical preparation, the order of ease of preparation of oxide precursors is generally considered to be oxalate particles ≥ carbonate particles ≥ hydroxide particles. Therefore, the preparation of carbonates and oxalates has always been an important topic in hafnium salt preparation, and methods for preparing hafnium oxalate have been continuously explored. However, due to the high solubility of hafnium oxalate at room temperature and pressure, current methods for producing hafnium oxalate using common oxalate preparation methods are not only complex but also difficult to implement on a large scale in actual production. Furthermore, the resulting oxalate has poor crystallinity, and the high-temperature calcination required during preparation can easily lead to hard agglomeration of hafnium oxalate particles during the subsequent calcination preparation of hafnium oxide. In addition, current methods for preparing oxalate are prone to introducing impurities, and the washing and removal effects are poor. Therefore, given that current preparation processes for hafnium oxalate and hafnium oxide are increasingly unable to meet the requirements of modern materials, breakthrough improvements are urgently needed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide hafnium oxalate with high yield, high purity and uniform particle size distribution and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing hafnium oxalate, comprising the following steps:

[0007] (1) Add ammonium oxalate aqueous solution to soluble hafnium compound aqueous solution, mix well, adjust the pH of the system to 3-6, then heat and stir, and age to obtain a colloidal liquid;

[0008] (2) The gelatinous liquid described in step (1) is subjected to a hydrothermal reaction. After the reaction is completed, the liquid is washed and filtered to collect the filter residue and obtain hafnium oxalate.

[0009] The present invention provides a method for preparing hafnium oxalate by mixing soluble hafnium compounds with ammonium oxalate and adjusting the pH value to 3-6, followed by reaction under low-pressure hydrothermal conditions. Heating and aging followed by reheating further facilitates the removal of impurities, ensuring the yield while improving the purity of hafnium oxalate and making the resulting hafnium oxalate particles uniform. At the same time, the technical solution provided by the present invention does not require high-temperature calcination, avoiding the hard agglomeration between powder particles that may occur during the calcination process.

[0010] In a preferred embodiment of the preparation method of the present invention, in step (1), the pH value is adjusted to 5.

[0011] The pH range of 3-6 is selected, with pH 5 being preferred, because a uniform and stable gel will be formed in the subsequent reaction process within the above range, especially at pH 5, thereby improving the purity and uniformity of the product particles.

[0012] In a preferred embodiment of the preparation method of the present invention, the heating temperature in step (1) is 55-65°C.

[0013] In a preferred embodiment of the preparation method of the present invention, the heating temperature in step (1) is 60°C.

[0014] Heating to a temperature range of 55-65℃ is beneficial for soluble hafnium compounds to form a gel state with ammonium oxalate under pH conditions of 3-6. In particular, when the reaction temperature is further optimized to 60℃, the gel state formed is excellent, which is beneficial for improving the product yield and obtaining more uniform hafnium oxalate particles.

[0015] In a preferred embodiment of the preparation method described in this invention, the mixture is continuously stirred during the heating process. Continuous stirring during heating helps form a uniform and stable gel-like sample, which is beneficial for the subsequent formation of uniform hafnium oxalate particles.

[0016] In a preferred embodiment of the preparation method of the present invention, the stirring speed in step (1) is 10-20 r / min.

[0017] In a preferred embodiment of the preparation method described in this invention, the stirring speed is 15 r / min.

[0018] Controlling the stirring speed to 10-20 r / min, especially at 15 r / min, can help form a uniform and stable gel sample, which is beneficial for the subsequent formation of uniform hafnium oxalate particles.

[0019] In a preferred embodiment of the preparation method described in this invention, the aging time in step (1) is 26-34 minutes. Further aging after the heating reaction can make the reaction more complete, thereby improving the product yield. Within the aging time range given in this invention, the impact on the yield is not significant, because the preferred aging time of 26-34 minutes can already achieve the optimal yield, and the particle size distribution of hafnium oxalate particles is excellent within this aging time range.

[0020] In a preferred embodiment of the preparation method of the present invention, in step (1), the molar ratio of hafnium to ammonium oxalate in the soluble hafnium compound is 1:(2.0-2.5).

[0021] In a preferred embodiment of the preparation method of the present invention, in step (1), the molar ratio of hafnium to ammonium oxalate in the soluble hafnium compound is 1:2.2.

[0022] An excess of ammonium oxalate ensures that hafnium in soluble hafnium compounds is completely converted into hafnium in hafnium oxalate, thereby increasing the reaction yield. Furthermore, the excess ammonium oxalate can be removed through subsequent reactions without reducing the purity of the product.

[0023] In a preferred embodiment of the preparation method of the present invention, the soluble hafnium compound in step (1) includes hafnium chloride.

[0024] As a preferred embodiment of the preparation method of the present invention, in step (1), the pH value of the system is adjusted by ammonia water, and ammonia water solution is continuously added and stirred during the adjustment process.

[0025] Ammonia is introduced to adjust the pH value because it produces water after the reaction, and its cation is ammonium, which is the same as the cation in ammonium oxalate, so no new impurities are introduced.

[0026] In a preferred embodiment of the preparation method of the present invention, in step (2), the temperature of the hydrothermal reaction is 120-150°C and the time of the hydrothermal reaction is 4.5-6.5 hours.

[0027] In a preferred embodiment of the preparation method of the present invention, in step (2), the temperature of the hydrothermal reaction is 130-140°C and the time of the hydrothermal reaction is 5 hours.

[0028] In a preferred embodiment of the preparation method of the present invention, the pressure of the hydrothermal reaction in step (2) is 1.4-1.6 MPa.

[0029] In a preferred embodiment of the preparation method of the present invention, the hydrothermal reaction pressure in step (2) is 1.5 MPa.

[0030] Heating under pressure can remove unreacted ammonium oxalate from the liquid phase reaction, thereby further improving the purity of the product.

[0031] In addition, the present invention also provides hafnium oxalate, which is prepared by the preparation method described in the present invention.

[0032] In a preferred embodiment of the hafnium oxalate described in this invention, the hafnium oxalate is in granular form, and its D... 50 =2.67-6.79μm, particle size distribution coefficient P≤5.87.

[0033] It can be observed that the hafnium oxalate provided by the present invention has a small and uniform particle size and does not exhibit agglomeration.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The method of this invention utilizes aqueous solutions of soluble hafnium-containing compounds, ammonium oxalate, and ammonia to regulate the mixed solution environment. Through hydrothermal reaction, the resulting hafnium oxalate products are more conducive to the removal of impurity elements, resulting in uniform hafnium oxalate crystal particles and good washing effect. This ensures that hard agglomeration between powder particles is avoided during the subsequent calcination preparation of hafnium oxide. Furthermore, high-temperature calcination is unnecessary, avoiding hard agglomeration that may occur during calcination. Simultaneously, this method allows for control of crystal size and morphology by adjusting reaction conditions, resulting in well-crystallized, agglomerated powder. Moreover, the method of this invention is simple, reliable, and reduces processing costs while ensuring the quality of hafnium oxalate products. The crystal size and morphology can be directly controlled by adjusting reaction conditions. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] Example 1

[0038] This invention provides a hafnium oxalate, and the preparation method of the hafnium oxalate is as follows:

[0039] (1) Take 1000L of hafnium chloride aqueous solution with a mass concentration of 60g / L and add it to the reactor. Add ammonium oxalate aqueous solution to it. The molar ratio of hafnium chloride to ammonium oxalate is hafnium chloride:ammonium oxalate = 1:2.2. Stir the two evenly. Then, continuously add ammonia solution to the evenly stirred solution while stirring continuously until the pH value of the system is 5. Then turn on the steam switch of the reactor and heat the mixed solution to 60℃. Stir at a speed of 15r / min. When the mixed solution becomes transparent gel, stop stirring and let it stand for 30min.

[0040] (2) Transfer the transparent gel-like substance after standing and aging in step (1) to the autoclave, turn on the steam switch of the autoclave and close the valve at the same time, slowly heat and pressurize. When the temperature inside the autoclave rises to 130°C, control the pressure inside the autoclave to 1.5 MPa, maintain this temperature and pressure for 5 hours. After the reaction is completed, filter and wash with pure water 3 times, then vacuum dry, collect the filter residue, dry it, and obtain hafnium oxalate.

[0041] Example 2

[0042] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the pH value of the system is adjusted to 3.

[0043] Example 3

[0044] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the pH value of the system is adjusted to 6.

[0045] Example 4

[0046] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the aging time is 26 minutes.

[0047] Example 5

[0048] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the aging time is 34 minutes.

[0049] Example 6

[0050] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the steam switch of the reaction vessel is turned on, the mixed solution is heated to 60°C, and stirred at a speed of 20 r / min.

[0051] Example 7

[0052] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that the steam switch of the reactor is turned on, the mixed solution is heated to 60°C, and stirred at a speed of 10 r / min.

[0053] Example 8

[0054] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that when the temperature inside the reactor rises to 150°C, the pressure inside the reactor is controlled at 1.5 MPa, and the reaction is maintained at this temperature and pressure for 5 hours.

[0055] Example 9

[0056] This invention provides a hafnium oxalate, the only difference from the hafnium oxalate preparation process in Example 1 is that when the temperature inside the reactor rises to 120°C, the pressure inside the reactor is controlled at 1.5 MPa, and the reaction is maintained at this temperature and pressure for 5 hours.

[0057] Comparative Example 1

[0058] The present invention provides a hafnium oxalate comparative example, the only difference between which is the preparation process of hafnium oxalate in Example 1 is that the pH value of the system is adjusted to 1.

[0059] Comparative Example 2

[0060] The present invention provides a hafnium oxalate comparative example, the only difference between which is the preparation process of hafnium oxalate in Example 1 is that the pH value of the system is adjusted to 7.

[0061] Comparative Example 3

[0062] The present invention provides a hafnium oxalate comparative example, the only difference from the hafnium oxalate preparation process in Example 1 is that the steam switch of the reaction vessel is turned on, the mixed solution is heated to 40°C, and stirred at a speed of 15 r / min.

[0063] Comparative Example 4

[0064] The present invention provides a hafnium oxalate comparative example, the only difference from the hafnium oxalate preparation process in Example 1 is that the steam switch of the reaction vessel is turned on, the mixed solution is heated to 80°C, and stirred at a speed of 15 r / min.

[0065] Comparative Example 5

[0066] The present invention provides a comparative example of hafnium oxalate, the only difference of which is that when the temperature inside the reactor rises to 130°C, the pressure inside the reactor is controlled at 1.1 MPa, and the reaction is maintained at this temperature and pressure for 5 hours.

[0067] Comparative Example 6

[0068] The present invention provides a comparative example of hafnium oxalate, the only difference of which is that when the temperature inside the reactor rises to 100°C, the pressure inside the reactor is controlled at 1.5 MPa, and the reaction is maintained at this temperature and pressure for 5 hours.

[0069] Comparative Example 7

[0070] The present invention provides a comparative example of hafnium oxalate, the only difference of which is that when the temperature inside the reactor rises to 170°C, the pressure inside the reactor is controlled at 1.5 MPa, and the reaction is maintained at this temperature and pressure for 5 hours.

[0071] Example of effect

[0072] This example records the purity, yield, impurity elements, and particle size data of hafnium oxalate prepared in Examples 1-9 and Comparative Examples 1-7. Specific statistics are shown in Table 1.

[0073] Table 1

[0074]

[0075] As can be seen from Table 1, when the technical solution of the present invention is adopted, the purity of the obtained product is above 99.32%, the yield is above 63.33%, and the particle size distribution is uniform with P below 5.87.

[0076] As can be seen from Examples 1-3 and Comparative Examples 1-2, the pH value adjusted with ammonia water affects whether gelation can be effectively achieved and the uniformity of particle size and particle size distribution of the formed product. In Comparative Examples 1-2, due to the pH value being too acidic or neutral, gelation could not be achieved during the reaction, and thus hafnium oxalate products could not be formed. As can be seen from Examples 1-3, when the pH value is adjusted within the range given in this invention, it affects the yield and purity of the product as well as the particle size and particle size distribution uniformity of the product.

[0077] As can be seen from Examples 1 and 4-5, when the aging time is changed within the aging time range of the present invention, the effect on yield and purity is not significant, but the particle size and particle size distribution uniformity of the product will be affected. Whether the aging time is reduced or increased to a certain extent, the particle size distribution uniformity of the product will decrease to a certain extent.

[0078] As can be seen from Examples 1 and 6-7, when the rotation speed is increased within the rotation speed range given by the present invention, the particle size of the obtained product decreases, but the uniformity of particle size distribution shows a decreasing trend; when the rotation speed is decreased within the rotation speed range given by the present invention, the particle size of the obtained product increases, and the P value reflecting the uniformity of particle size distribution also shows an increasing trend, that is, the uniformity of particle size distribution decreases.

[0079] As can be seen from Examples 1, 8-9 and Comparative Examples 6-7, when the heating temperature after aging is changed within the scope of the present invention, it has a certain impact on the purity and yield of the product, and also has a slight impact on the particle size and particle size distribution uniformity of the product. However, when the heating temperature after aging is not within the range given by the present invention, such as when the heating temperature after aging in Comparative Example 6 is too low, the yield of the product will be significantly reduced. When the heating temperature after aging in Comparative Example 7 is too high, the particle size of the product will increase and the particle size distribution uniformity will decrease.

[0080] As can be seen from Example 1 and Comparative Examples 3-4, when the temperature during initial heating and stirring is not within the range given in this invention, the yield shows a significant decreasing trend, the purity also decreases significantly, and the particle size uniformity also decreases.

[0081] As can be seen from Example 1 and Comparative Example 5, when the second heating is carried out at atmospheric pressure instead of pressure, the purity of the obtained product decreases, and the uniformity of particle size distribution also shows a decreasing trend.

[0082] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing hafnium oxalate, characterized in that, Includes the following steps: (1) Add ammonium oxalate aqueous solution to soluble hafnium compound aqueous solution, mix well, adjust the pH of the system to 3-6, then heat and stir, and age to obtain a colloidal liquid; (2) The gelatinous liquid described in step (1) is subjected to a hydrothermal reaction. After the reaction is completed, the liquid is washed, filtered, and the filter residue is collected to obtain hafnium oxalate. In step (1), the heating temperature is 55-65℃; In step (1), the molar ratio of hafnium to ammonium oxalate in the soluble hafnium compound is 1:(2.0-2.5). In step (1), the pH value of the system is adjusted by ammonia water. During the adjustment process, ammonia water solution is continuously added and stirred continuously. In step (2), the temperature of the hydrothermal reaction is 120-150℃; the pressure of the hydrothermal reaction is 1.4-1.6MPa. The soluble hafnium compound is hafnium chloride.

2. The preparation method according to claim 1, characterized in that, In step (1), the stirring speed is 10-20 r / min.

3. The preparation method according to claim 1, characterized in that, In step (1), the aging time is 26-34 minutes.

4. The preparation method according to claim 1, characterized in that, In step (2), the hydrothermal reaction takes 4.5-6.5 hours.

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