Mechanical crystallization preparation method of zirconium oxychloride crystal

Abstract

According to the mechanical crystallization preparation method of the zirconium oxychloride crystal, step-by-step cooling is adopted, a proper amount of seed crystal is introduced, a large number of attachment points can be provided for crystallization of zirconium oxychloride, the particle size can be controlled by adopting the method, the zirconium oxychloride crystal with less impurity entrainment is obtained, and the amount of acid used in subsequent pickling is reduced from the source.

Description

Technical Field

[0001] The present invention relates to the technical field of zirconium oxychloride, and specifically to a mechanical crystallization preparation method for zirconium oxychloride crystals. Background Art

[0002] Zirconium oxychloride is an important basic zirconium compound, which can be used to prepare zirconium compounds such as stabilized zirconia, zirconium carbonate, and zirconium sulfate. It can also be used as a raw material for zirconium-hafnium separation to prepare nuclear-grade zirconium and nuclear-grade hafnium, and is used in fields such as structural ceramics, solid oxide fuel cells, papermaking, and nuclear reactors.

[0003] The technological process for preparing zirconium oxychloride products mainly includes processes such as alkali fusion of zircon sand → water conversion → acidification and desilication → evaporation and concentration → cooling crystallization → pickling and impurity removal. Among them, the product preparation mainly obtains zirconium oxychloride crystals by naturally cooling or adding stirring crystallization to the highly concentrated zirconium solution after evaporation and concentration. Usually, only the acidity of the zirconium solution, the concentration of zirconia, and the final temperature of cooling crystallization are controlled, and specific cooling crystallization parameters are generally not controlled. For example, the crystallization conditions given in "Preparation Technology and Application of Zirconium Oxychloride" are: the acidity of the zirconium solution is controlled at 6.5 - 7 mol / L, and the concentration of zirconia is 160 - 180 g / L (Metallurgical Industry Press, P85).

[0004] Currently, there are few relevant studies on the solubility and crystallization mechanism of zirconium oxychloride. During the process of cooling and crystallizing zirconium solution to prepare zirconium oxychloride crystals, supersaturation is extremely likely to occur, causing explosive crystallization, as shown in Figure 1 , that is, a large number of fine crystals are instantaneously generated, with high viscosity, difficult washing and filtration, resulting in entrainment of a large amount of impurities, increasing the difficulty of subsequent pickling and impurity removal, and causing poor consistency of the final zirconium oxychloride product, or even high impurity content. In the field of zirconium oxychloride crystal preparation, during the crystallization process, the conventional operation method is mainly natural cooling crystallization. The cooling crystallization time is about 3 - 4 days, and zirconium oxychloride crystals can be obtained by controlling the acidity of the zirconium solution and the zirconium concentration. However, this natural cooling crystallization method has a long time and low efficiency, and cannot completely control the impurity inclusion in the crystals. Subsequently, pickling is often used for impurity removal. CN 116514163A discloses a method for preparing zirconium oxychloride products using zirconium tetrachloride as a raw material. The proposed acidity of the zirconium solution is 4.5 - 7.5 mol / L, and the concentration of zirconia is 130 - 190 g / L, and natural cooling is used for crystallization. Since the zirconium solution contains more than 20 kinds of impurity ions (such as titanium, aluminum, iron, rare earths, and radioactive toxic elements such as uranium and thorium), the zirconium oxychloride crystals obtained after crystallization will entrain zirconium solution impurities, and only after a large amount of subsequent pickling and impurity removal can zirconium oxychloride products meeting national standards be obtained. Summary of the Invention

[0005] The object of the present invention is to provide a method for mechanically crystallizing zirconium oxychloride crystals. By adopting stepwise cooling and introducing an appropriate amount of crystal seeds, a large number of attachment points can be provided for the crystallization of zirconium oxychloride. Using this method, the particle size and particle length of zirconium oxychloride crystals can be controlled within a certain range, the impurity inclusion amount in the crystals and the viscosity of the crystals can be reduced, making it easy to wash and filter, reducing the entrainment of impurities in the zirconium solution from the source, and saving the amount of acid used in subsequent pickling.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for mechanically crystallizing zirconium oxychloride crystals, comprising the following steps:

[0008] Step 1) Crystal seed preparation:

[0009] Grind zirconium oxychloride crystals to a certain particle size as the crystal seeds for zirconium oxychloride crystallization;

[0010] Step 2) Cooling of zirconium solution:

[0011] Add high-concentration zirconium solution to the crystallization tank and cool it to a certain temperature;

[0012] Step 3) Adding crystal seeds:

[0013] Slowly add the zirconium oxychloride crystal seeds prepared in step 1) to the high-concentration zirconium solution and maintain a certain temperature range for a period of time;

[0014] Step 4) Cooling crystallization:

[0015] Continue cooling crystallization, control the cooling rate and stirring speed. After cooling to a certain temperature, filter to obtain zirconium oxychloride crystals.

[0016] As an improvement of the present invention, in step 1), the grain length of the ground crystal fragments ≤ 30 μm; the zirconium oxychloride crystals used are zirconium oxychloride crystals obtained from the process.

[0017] As an improvement of the present invention, the acidity of the zirconium solution is 6.5 - 7 mol / L, and the zirconium concentration in the zirconium solution is 160 - 180 g / L.

[0018] As an improvement of the present invention, the temperature during adding crystal seeds in step 2) is controlled at 50 - 65 °C.

[0019] As an improvement of the present invention, in step 3), calculated by the zirconia content, the crystal seed addition amount is 0.5 - 3% of the zirconium concentration in the zirconium solution. As an improvement of the present invention, in step 4), the cooling rate of cooling crystallization is 5 - 15 °C / h, the stirring speed ≤ 100 rpm / min, and the final cooling temperature is 25 - 35 °C.

[0020] The grain length of the zirconium oxychloride crystal described in the present invention reaches more than 300 microns.

[0021] When studying the solubility and crystallization mechanism of zirconium oxychloride in the present invention, it is found that in a hydrochloric acid solution with a concentration of 5M - 7M, zirconium oxychloride has a relatively wide metastable zone, which leads to supersaturation and thus easily causes explosive crystallization. Moreover, the crystallization of zirconium oxychloride is relatively dependent on attachments. After dissolving zirconium oxychloride, the crystallization process of zirconium oxychloride was observed under a microscope. As the edge moisture naturally evaporated, a small amount of solid was precipitated. The zirconium oxychloride crystal crystallized in a directional growth manner with the solid at the edge as the attachment point.

[0022] Based on the above theoretical basis, by adding a certain amount of crystal seeds during the cooling crystallization process in the present invention, a large number of attachment points can be provided for the crystallization of zirconium oxychloride. By this method, the crystal particle size and grain length of zirconium oxychloride can be controlled within a certain range, which can achieve a shorter crystallization time and high efficiency, and can also reduce impurity entrainment from the source and save the amount of acid used in subsequent pickling. Brief Description of the Drawings

[0023] Figure 1 It is an electron micrograph of zirconium oxychloride crystals obtained by explosive crystallization. It can be seen from the figure that the grains of this zirconium oxychloride are small and easy to aggregate;

[0024] Figure 2 It is the zirconium oxychloride crystal obtained in Example 1;

[0025] Figure 3 It is the zirconium oxychloride crystal obtained in Example 2;

[0026] Figure 4 It is the zirconium oxychloride crystal obtained in Example 3. Detailed Description of the Invention

[0027] The technical solutions of the present invention will be described in detail below with reference to the drawings and examples.

[0028] Example 1:

[0029] Zirconium oxychloride (ZrO 2 with a content of 36%) was ground to a maximum particle size ≤ 30 μm. The high-temperature zirconium solution after evaporation was added to a jacketed crystallization tank. The zirconium concentration of the zirconium solution was 166 g / L (ZrO 2 ), the acidity was 6.5 mol / L, cold water was introduced for cooling, and it was cooled to 65 °C. Then, ground crystal fragments were added as crystal seeds (4.6 g / L) at 1% of the zirconium concentration, and it was kept warm for 30 min. Then, it was further cooled, and the cooling rate was controlled at 15 °C / h, the stirring rate was 100 rpm / min, and it was cooled to 25 °C. Stirring was stopped and filtration was carried out. The SEM analysis of the obtained zirconium oxychloride crystals is shown inFigure 2 , the crystal length is above 300 microns and the particle size is relatively coarse.

[0030] Example 2

[0031] Grind zirconyl chloride (ZrO 2 with a content of 36%) until the maximum particle size ≤ 30 μm. Add the high-temperature zirconium solution after evaporation to a crystallization tank with a jacket. The zirconium concentration of the zirconium solution is 161 g / L (calculated based on ZrO 2 ), the acidity is 6.8 mol / L, and cool it by passing cold water. Cool it to 50 degrees, then add the ground broken crystals as crystal seeds in an amount of 0.5% of the zirconia content of the zirconium solution. After maintaining the temperature for 30 min, continue to cool down, control the cooling rate at 10 °C / h, and control the stirring speed at 80 rpm / min. When the material in the kettle drops to 32 °C, stop stirring and filter. The SEM analysis of the zirconyl chloride crystals is shown in Figure 3 , the crystal length reaches above 300 microns and the particle size is relatively coarse.

[0032] Example 3

[0033] Grind zirconyl chloride (ZrO 2 with a content of 36%) until the maximum particle size ≤ 25 μm. Add the high-temperature zirconium solution after evaporation to a crystallization tank with a jacket. The zirconium concentration of the zirconium solution is 178 g / L (calculated based on ZrO 2 ), the acidity is 7 mol / L, and cool it by passing cold water. Cool it to 56 degrees, then add the ground broken crystals as crystal seeds in an amount of 3% of the zirconia content of the zirconium solution. After maintaining the temperature for 1 h, continue to cool down, control the cooling rate at 5 °C / h, and control the stirring speed at 50 rpm / min. When the material in the kettle drops to 34 °C, stop stirring and filter. The SEM analysis of the zirconyl chloride crystals is shown in Figure 4 , the crystal length reaches above 500 microns and is significantly thicker.

[0034] Based on the data of the above examples, the mechanical crystallization preparation method of the present invention has a short time, and the entire crystallization process does not exceed 24 h. Compared with the traditional natural crystallization method, the time is shortened by 2 - 3 days and the efficiency is high. Moreover, the crystals obtained by the present invention have a long enough length, all reaching above 300 microns, and even above 500 microns. Compared with the crystals obtained by explosive crystallization, the crystals of this length have a small amount of entrained impurities and low viscosity. In the subsequent pickling process, a small amount of pickling acid can achieve a good pickling effect, saving the pickling amount and reducing costs.

[0035] The upper and lower limits and interval values of the process parameters (such as temperature, time, etc.) of the present invention can all implement this method, and the examples are not listed one by one here.

[0036] The content not detailed in the present invention can all adopt the conventional technical knowledge in the field.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A mechanical crystallization preparation method for zirconium oxychloride crystals, the mechanical crystallization preparation method comprising the following steps: Step 1) Seed preparation: Grinding zirconium oxychloride crystals to a certain particle size to serve as seeds for zirconium oxychloride crystallization; Step 2) Cooling of zirconium liquid: Add high concentration zirconium liquid into the crystallization tank and cool it to a certain temperature; Step 3) Adding seed crystals: Slowly adding the zirconium oxychloride seed crystals obtained in step 1) into the high concentration zirconium solution, and maintaining a certain temperature range for a period of time; Step 4) cooling crystallization: Continue cooling and crystallizing, control the cooling rate and stirring speed, and after cooling to a certain temperature, filter to obtain zirconium oxychloride crystals.

2. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: In step 1), the grain size of the ground zirconium oxychloride fragments is ≤30 μm.

3. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: The acidity of the zirconium solution is 6.5-7 mol / L, and the zirconium concentration in the zirconium solution is 160-180 g / L.

4. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: In step 3), the temperature when adding the seed crystals is controlled at 50-65°C.

5. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: In step 3), the amount of seed crystal added is 0.5-3% of the zirconium oxide concentration in the zirconium liquid according to the zirconium oxide content. After the seed crystal is added, the residence time is maintained for 30 min-60 min.

6. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: In step 4), the cooling rate of the cooling crystallization is controlled to be 5-15°C / h, the stirring speed is ≤100rpm / min, and the final cooling temperature is 25-35°C.

7. The method for preparing zirconium oxychloride crystals by mechanical crystallization according to claim 1, characterized in that: The length of the zirconium oxychloride crystals is more than 300 microns.

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