CN113072096B - Preparation method of thorium-based molten salt reactor oxygen-free zirconium tetrafluoride applied to nuclear fission energy - Google Patents
Preparation method of thorium-based molten salt reactor oxygen-free zirconium tetrafluoride applied to nuclear fission energy Download PDFInfo
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Abstract
The invention relates to a preparation method of oxygen-free zirconium tetrafluoride applied to a nuclear fission energy thorium-based molten salt reactor. The method solves the problems of environmental unfriendliness and the technical problems that the oxygen content and the purity of the zirconium tetrafluoride produced by a wet method do not reach the standard in the existing methods for producing the zirconium tetrafluoride by the dry method and the sublimation method. With ZrO 2 Taking HF as raw material, regulating material ratio, selecting special feeding mode and reaction temperature and time to ensure that ZrO has uniform grain size 2 Complete reaction and complete conversion into ZrF 4 .H 2 O; then, zrF was obtained by concentration and centrifugation 4 .H 2 O fine product; then ZrF 4 .H 2 Conversion of O to ZrF 4 Generating ZrOF as a by-product 2 (ii) a Then NH is added 4 HF 2 Namely the byproduct can be completely converted into ZrF 4 (ii) a The raw materials adopted by the method are simple and easy to obtain, impurities are easy to remove, the reaction temperature area is low, waste water and waste gas are less generated in the reaction process, and the oxygen content and purity of the final product meet the index requirements of the thorium-based molten salt reactor on fluoride salt.
Description
Technical Field
The invention relates to a preparation method of zirconium tetrafluoride, in particular to a preparation method of oxygen-free zirconium tetrafluoride applied to a nuclear fission energy thorium-based molten salt reactor.
Background
The thorium-based molten salt reactor is a liquid fuel reactor, which uses thorium-uranium nuclear fuel to circulate, takes fluoride salt as a coolant, melts natural nuclear fuel and convertible nuclear fuel in the high-temperature fluoride salt, and carries the nuclear fuel to circulate inside and outside the reactor. Since the coolant is fluoride salt, the coolant becomes solid after cooling, so that the nuclear fuel is not easy to leak, and cannot react with underground water to cause ecological disasters. Meanwhile, the reactor is more freely selected, and can be built in non-coastal areas and underground with the depth of dozens of meters.
The thorium-based molten salt reactor has special strict requirements on the oxygen content of fluoride salt water and the purity of fluoride salt. The oxygen content in typical fluoride salts is required to be in the range of 200-500ppm and the purity is required to be 4.5N-5N. Zirconium tetrafluoride, as one of the fluoride salts, may be used as a coolant for thorium-based molten salt stacks. The prior methods for producing zirconium tetrafluoride include a dry method, a wet method, a sublimation method and the like. The dry method and the sublimation method have serious corrosion to equipment in the production process, generate a large amount of waste gas and cause secondary pollution. The oxygen content and purity of the zirconium tetrafluoride obtained by wet production can not meet the requirements of thorium-based molten salt reactor on the oxygen content and purity of the fluoride salt.
Disclosure of Invention
The invention aims to provide a preparation method of oxygen-free zirconium tetrafluoride applied to a nuclear fission energy thorium-based molten salt reactor, which solves the problems of environmental unfriendliness and the technical problems that the oxygen content and the purity of the zirconium tetrafluoride produced by a wet method do not reach the standard in the conventional method for producing the zirconium tetrafluoride by a dry method and a sublimation method.
The technical scheme of the invention is to provide a preparation method of oxygen-free zirconium tetrafluoride applied to a nuclear fission energy thorium-based molten salt reactor, which is characterized by comprising the following steps:
step 1.1, adding 45-50% by mass of hydrofluoric acid into a polytetrafluoroethylene reaction kettle, heating to 65-70 ℃, and firstly adding the hydrofluoric acid into the hydrofluoric acid at one time under stirringx Zirconium dioxide in an amount; whereinx=m/2，mIs the total mass of zirconium dioxide; the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1.8-1;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the temperature at 95-105 ℃, and continuously reacting for 40-60 minutes;
step 1.3, adding the rest zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 95-105 ℃, continuously reacting for 30-60 minutes, and standing for 30-40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 O crude product;
step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 110-120 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, liquid-solid separating in centrifuge while it is hot, removing supernatant, and washing free acid on crystal surface with deionized water to obtain ZrF 4 . H 2 O fine product;
step 3, preparing ZrF 4 And generating a by-product ZrOF 2 ；
ZrF treated in the step 2 4 . H 2 Placing the refined O product into a crucible, placing the crucible into a vacuum drying furnace, drying the refined O product at 350-380 ℃ for 3-4 hours, cooling to room temperature, taking out crystals, wherein the crystals are ZrF 4 And ZrOF 2 A mixture of (a);
step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping NH with the mass being 1.2-1.5% of the mass of the crystals treated in the step 3 4 HF 2 Mixing uniformly; (ZrF in the crystals in this step 4 Does not participate in the reaction) and then the evenly mixed crystal is mixed with NH 4 HF 2 Mechanically pulverizing to 40-60 meshes, putting into a crucible again, paving, putting into a vacuum drying furnace, introducing nitrogen for protection, and performing gradient temperature rise calcination:
a first gradient: calcining at 480-530 deg.C for 3-4 hr; accompanied by NH 4 HF 2 And ZrOF 2 Complete conversion to ZrF 4 Water is generated in the reaction process, and the water generated in the reaction process can be volatilized at the stage, so that the reaction is further promoted to be complete;
a second gradient: calcining again at 550-565 deg.C for 4-5 hr; accompanied by NH 4 HF 2 And ZrOF 2 Complete conversion to ZrF 4 NH is generated during the reaction 4 F, the stage can volatilize NH generated in the reaction process 4 F, the promotion direction is carried out towards the positive direction, so that complete reaction is facilitated;
4.2, in order to prevent the product from contacting air to generate a reverse reaction when the temperature is higher, and the product is taken out after the temperature is reduced to the room temperature, so that the unnecessary oxygen content introduced by the product can be avoided; can be cooled down in a gradient way under the state of nitrogen protection:
a first gradient: reducing the temperature to 30-35 ℃ every half hour to 300-350 ℃;
a second gradient: reducing the temperature to 50-55 ℃ every half hour until the room temperature to obtain an oxygen-free zirconium tetrafluoride product with the oxygen content of 200-500ppm and the purity of more than or equal to 99.99 percent.
Further, in the step 1.1, the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1.
Further, in order to increase the conversion rate of zirconium dioxide, the reaction temperature in step 1.1 is 65 ℃;
in the step 1.2, the reaction temperature is 100 ℃, and the continuous reaction time is 45 minutes;
in the step 1.3, the reaction temperature is 100 ℃; the duration of the reaction was 40 minutes.
Further, the heating temperature in the step 2 is 115 ℃, and the rotating speed of the centrifuge is generally 800-1200r/min.
Further, to more effectively remove the structural water and the crystal water and simultaneously reduce ZrOF 2 The drying temperature in the step 3 is 370 ℃, the drying time is 3 hours, and the interference caused by crystal water in the subsequent deoxygenation process is avoided.
Further, in step 4.1, NH 4 HF 2 The mass of (b) was 1.3% of the mass of the crystals after the treatment in step 3.
Further, in step 4.1, when the gradient temperature-rising calcination is performed:
a first gradient: calcining at 500 deg.C for 4 hr, and volatilizing water produced in the reaction process;
a second gradient: calcining at 555 deg.C for 4 hr to volatilize NH generated during reaction 4 F. The ammonium acid fluoride used for the conversion is in excess, and thus a high-temperature stage is required to remove the excess ammonium acid fluoride by thermal decomposition. Meanwhile, the ammonium fluoride as a byproduct in the conversion of the zirconium oxyfluoride is also removed at high temperature.
Further, in step 4.2, when the temperature is reduced in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature by 30 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature by 50 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product.
The process relates to the influence of reaction temperature on reaction rate, and in the process of cooling from high temperature to low temperature, the inert gas is used for protecting the product atmosphere all the time, so that the occurrence of reversible reaction is reduced, oxygen is prevented from being reintroduced, the temperature is reduced to low temperature, the reaction process is greatly reduced, the oxygen index of the product is not influenced basically, and the product can be bagged as required after being taken out.
Further, in step 4.1, crystallization is carried out with NH 4 HF 2 The thickness of the powder after being spread in the crucible is 3.5-5cm.
Furthermore, in the step 1, the purity of the hydrofluoric acid and the purity of the zirconium dioxide are both more than or equal to 99.99%.
The invention has the beneficial effects that:
1. the invention uses ZrO 2 Taking HF as raw material, firstly, adjusting material ratio and selecting special feeding mode and reaction temperature time to ensure that ZrO is ZrO 2 Complete reaction and complete conversion into ZrF 4 . H 2 O, preventing the zirconium dioxide from reacting with the aqueous acid to generate hexafluorozirconic acid or pentafluorozirconic acid; then, at a lower temperature, zrF is obtained by concentration and centrifugation 4 . H 2 O fine product; then removing the structural water at a determined temperature to obtain ZrF 4 . H 2 Conversion of O to ZrF 4 In the process, only ZrOF by-product is produced 2 (ii) a Then only NH needs to be added 4 HF 2 The byproduct can be completely converted into ZrF 4 (ii) a The method for preparing the oxygen-free zirconium tetrafluoride has the advantages that the adopted raw materials are simple and easy to obtain, the impurity removal is easy, the reaction temperature region is lower, the generation of waste water and waste gas in the reaction process is less, the environment is friendly, the oxygen content of the finally prepared oxygen-free zirconium tetrafluoride product is 200-500ppm, the purity is more than or equal to 99.99%, and the index requirement of thorium-based molten salt pile on fluoride salt is met.
2. The invention is to add NH 4 HF 2 Complete conversion to ZrF 4 In the first stage, water generated in the reaction process is mainly removed at a specific temperature to promote the forward reaction, so that the reaction rate is improved, the reaction tends to be complete, and the quality of an oxygen-free zirconium tetrafluoride product is finally ensured; in the second stage, at a specific temperature, NH formed during the reaction is mainly removed 4 And F, the reaction can be promoted to be complete in the same way, and the quality of the oxygen-free zirconium tetrafluoride product is ensured. Meanwhile, experiments also show that NH is generated when the temperature is directly raised to 550-565 ℃ for calcination 4 HF 2 And ZrOF 2 The reaction was incomplete, further demonstrating the advantages of the gradient calcination of the present invention.
3. After the calcination is finished, the special gradient cooling method is adopted to ensure the quality of the oxygen-free zirconium tetrafluoride product, if not allWhen the temperature is reduced to room temperature, a small amount of water possibly existing can not be evaporated, and a reversible reaction can be carried out to generate a small amount of ZrOF 2 Finally, the purity of the oxygen-free zirconium tetrafluoride product is not up to standard.
Drawings
FIG. 1 shows ZrF in example 1 4 . H 2 XRD pattern of O;
FIG. 2 is a ZrOF doped alloy obtained in example 1 2 ZrF of 4 An XRD pattern;
FIG. 3 is the oxygen-free ZrF of example 1 4 XRD pattern of (a);
FIG. 4 shows ZrF in example 2 4 . H 2 XRD pattern of O;
FIG. 5 is a ZrOF doped alloy obtained in example 2 2 ZrF of 4 An XRD pattern;
FIG. 6 is the oxygen-free ZrF of example 2 4 XRD pattern of (a).
Detailed Description
The conception of the invention is as follows:
the method aims to solve the problems of environmental unfriendliness and the technical problems of substandard oxygen content and purity of the zirconium tetrafluoride produced by a wet method in the prior method for producing the zirconium tetrafluoride by a dry method and a sublimation method. The invention uses ZrO 2 Taking HF as raw material, firstly, adjusting material ratio and selecting special feeding mode and reaction temperature time to ensure that ZrO is ZrO 2 Complete reaction and complete conversion into ZrF 4 . H 2 O, preventing the zirconium dioxide from reacting with the aqueous acid to generate hexafluorozirconic acid or pentafluorozirconic acid; then, at a lower temperature, zrF is obtained by concentration and centrifugation 4 . H 2 O fine product; then removing the structural water at a determined temperature to obtain ZrF 4 . H 2 Conversion of O to ZrF 4 In the process, only ZrOF by-product is produced 2 (ii) a Then only NH needs to be added 4 HF 2 The byproduct can be completely converted into ZrF 4 。
The specific reaction equation is as follows:
ZrO2+4HF⇋ZrF4.H2O+H2O（1）
2ZrF4.H2O⇋ZrF4+ZrOF2+HF↑+H2O（2）
ZrOF2+2NH4HF2⇋ZrF4+2NH4F↑+H2O（3）
the invention is further described with reference to the following figures and specific embodiments.
Example 1
This example prepares oxygen-free zirconium tetrafluoride by:
step 1.1, adding 45-50% by mass of hydrofluoric acid with the mass concentration of 3000 g into a polytetrafluoroethylene reaction kettle, heating to 65 ℃, and rapidly adding 750 g of zirconium dioxide into the hydrofluoric acid at one time under a stirring state; wherein the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1;
step 1.2, waiting for the boiling of a reaction solution, maintaining the reaction temperature at 100 ℃, and continuously reacting for 45 minutes;
step 1.3, adding 750 g of zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 100 ℃, continuously reacting for 40 minutes, and standing for 30 to 40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 And (4) crude O product.
Step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 115 ℃, and concentrating; concentrating to obtain crystals, taking out the crystals, and performing liquid-solid separation in a centrifuge while the crystals are hot, wherein the rotation speed of the centrifuge is set to 1200r/min. Removing supernatant, washing free acid on the surface of the crystal with deionized water to obtain ZrF 4 . H 2 The XRD spectrum of the refined product is shown in figure 1.
Step 3, preparing ZrF 4 And generating a by-product ZrOF 2 ；
Putting the crystal treated in the step 2 into a crucible, putting the crucible into a vacuum drying furnace, drying the crucible at 370 ℃ for 3 hours, cooling the dried crystal to room temperature, and taking out the crystal, wherein the crystal is ZrF 4 And ZrOF 2 A mixture of (a); the XRD spectrum is shown in FIG. 2, from which ZrF can be seen 4 . H 2 O drying process at 370 deg.CIn the medium, partially converted to zirconium oxyfluoride ZrOF 2 。
Step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping NH with the mass being 1.3% of the mass of the crystals treated in the step 3 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 mesh, placing into crucible again, spreading to 3.5-5cm, placing into vacuum drying furnace, introducing nitrogen gas for protection, and performing gradient heating calcination:
a first gradient: calcining at 500 deg.C for 4 hr, and volatilizing water produced in the reaction process;
a second gradient: calcining at 555 deg.C for 4 hr to volatilize NH generated during reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature by 30 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature by 50 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product. The product was zirconium fluoride by XRD qualitative analysis, without other peaks, see FIG. 3.
Through Agilent 5110-ICP-OES detection, the zirconium ion content of the oxygen-free zirconium tetrafluoride product is 544912ppm (corresponding to 54.5 percent in table 1), the iron ion content is 1.1ppm, and other heavy metals are less than 1ppm.
The fluorine content of the oxygen-free zirconium tetrafluoride product was 455089ppm (corresponding to 45.5% in table 1) as determined by Lei Ci PXSJ-216F ionometer, see table 1.
The oxygen content in the oxygen-free zirconium tetrafluoride product is 289ppm by the measurement of a force-measuring OHN836 oxygen nitrogen hydrogen combined measuring instrument, and the standard is met.
TABLE 1
Example 2
In the present example, oxygen-free zirconium tetrafluoride was prepared by the following steps, except that the mass ratio of the total mass of zirconium dioxide to the mass concentration of 45% to 50% hydrofluoric acid was 1:
step 1.1, adding 45-50% by mass of hydrofluoric acid with the mass concentration of 3000 g into a polytetrafluoroethylene reaction kettle, heating to 65 ℃, and rapidly adding 682 g of zirconium dioxide into the hydrofluoric acid at one time under a stirring state; wherein the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the reaction temperature at 100 ℃ and continuously reacting for 45 minutes;
step 1.3, adding 682 g of zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 100 ℃, continuously reacting for 40 minutes, and standing for 30 to 40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 And (4) crude O product.
Step 2, zrF preparation 4 . H 2 O, fine products;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 115 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, liquid-solid separating in centrifuge while it is hot, setting rotation speed of centrifuge at 800-1200r, removing supernatant, washing free acid on crystal surface with deionized water to obtain ZrF 4 . H 2 The XRD spectrum of the O fine product is shown in figure 4 and is similar to that of figure 1.
Step 3, zrF preparation 4 And generating a by-product ZrOF 2 ；
Putting the crystal treated in the step 2 into a crucible, putting the crucible into a vacuum drying furnace, drying the crucible at 370 ℃ for 3 hours, cooling the dried crystal to room temperature, and taking out the crystal, wherein the crystal is ZrF 4 And ZrOF 2 A mixture of (a); the XRD pattern is shown in FIG. 5, which is consistent with FIG. 2.
Step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping the crystals with the mass of the crystals treated in the step 3NH of 1.3% crystal mass 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 meshes, placing into a crucible again, paving to 3.5-5cm, placing into a vacuum drying furnace, introducing nitrogen for protection, and performing gradient heating calcination:
a first gradient: calcining at 500 deg.C for 4 hr to volatilize water generated during the reaction;
a second gradient: calcining at 555 deg.C for 4 hr to volatilize NH generated during reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature by 30 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature by 50 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product. The XRD pattern is shown in FIG. 6, which is consistent with FIG. 3. The product was determined to be zirconium fluoride and no other miscellaneous peaks.
Detecting by an Agilent 5110-ICP-OES to obtain an oxygen-free zirconium tetrafluoride product with the zirconium ion content of 544895ppm, the iron ion content of 1.1ppm and the other heavy metals content of less than 1ppm;
detecting the fluorine content in the oxygen-free zirconium tetrafluoride product to be 455289ppm by a Lei Ci PXSJ-216F ion meter;
the oxygen content of the oxygen-nitrogen-hydrogen combined analyzer measured by a force-measuring OHN836 oxygen-nitrogen-hydrogen combined analyzer is 355ppm and meets the standard.
Example 3
In the embodiment, oxygen-free zirconium tetrafluoride is prepared by the following steps, which are different from the embodiment 1 in that the mass ratio of the total mass of zirconium dioxide to hydrofluoric acid with the mass concentration of 45% -50% is 1.8:
step 1.1, adding hydrofluoric acid with the mass concentration of 45-50% and the mass of 3000 g into a polytetrafluoroethylene reaction kettle, heating to 65 ℃, and quickly adding 833 g of zirconium dioxide into the hydrofluoric acid at one time under a stirring state; wherein the mass ratio of the total mass of the zirconium dioxide to the hydrofluoric acid with the mass concentration of 45-50% is 1.8;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the reaction temperature at 100 ℃ and continuously reacting for 45 minutes;
step 1.3, adding 833 g of zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 100 ℃, continuously reacting for 40 minutes, and standing for 30 to 40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 And (4) crude O product.
Step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 115 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, liquid-solid separating in centrifuge while it is hot, setting rotation speed of centrifuge at 800-1200r to remove supernatant, and washing free acid on crystal surface with deionized water to obtain ZrF 4 . H 2 The XRD spectrum of the refined product O is the same as that of figure 1.
Step 3, preparing ZrF 4 And generating a by-product ZrOF 2 ；
Putting the crystal treated in the step 2 into a crucible, putting the crucible into a vacuum drying furnace, drying the crucible at 370 ℃ for 3 hours, cooling the dried crystal to room temperature, and taking out the crystal, wherein the crystal is ZrF 4 And ZrOF 2 A mixture of (a); the XRD spectrum is the same as that of FIG. 2.
Step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping NH with the mass being 1.3% of the mass of the crystals treated in the step 3 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 mesh, placing into crucible again, spreading to 3.5-5cm, placing into vacuum drying furnace, introducing nitrogen gas for protection, and performing gradient heating calcination:
a first gradient: calcining at 500 deg.C for 4 hr, and volatilizing water produced in the reaction process;
a second gradient: calcining at 555 deg.C for 4 hr to volatilize NH generated during reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature by 30 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature by 50 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product. The XRD spectrum of the product is consistent with that of figure 3, and the product is proved to be zirconium fluoride.
Detecting by an Agilent 5110-ICP-OES to obtain an oxygen-free zirconium tetrafluoride product with the zirconium ion content of 545012ppm, the iron ion content of 1.3ppm and the other heavy metal content of less than 1ppm;
detecting the fluorine content in the oxygen-free zirconium tetrafluoride product to be 454922ppm by a Lei Ci PXSJ-216F ion meter;
the oxygen content of 366ppm, determined by a force-applicable OHN 836O-N-H combination meter, meets the standard.
Example 4
This example prepared oxygen-free zirconium tetrafluoride by the following steps, differing from example 1 in the temperature and time during the reaction:
step 1.1, adding 45-50% by mass of hydrofluoric acid with the mass concentration of 3000 g into a polytetrafluoroethylene reaction kettle, heating to 70 ℃, and rapidly adding 750 g of zirconium dioxide into the hydrofluoric acid at one time under a stirring state; wherein the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the reaction temperature at 105 ℃, and continuously reacting for 40 minutes;
step 1.3, adding 750 g of zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 105 ℃, continuously reacting for 30 minutes, and standing for 30 to 40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 And (4) crude O product.
Step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 120 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, centrifuging while it is hotLiquid-solid separation in the machine, setting the rotation speed of a centrifuge to 800-1200 turns, removing supernatant, and cleaning free acid on the surface of the crystal by deionized water to obtain ZrF 4 . H 2 The XRD spectrum of the refined product O is the same as that of figure 1.
Step 3, preparing ZrF 4 And generating a by-product ZrOF 2 ；
Putting the crystal treated in the step 2 into a crucible, putting the crucible into a vacuum drying furnace, drying the crucible at 380 ℃ for 3 hours, cooling the crucible to room temperature, and taking out the crystal, wherein the crystal is ZrF 4 And ZrOF 2 A mixture of (a); the XRD spectrum is the same as that of FIG. 2.
Step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping NH with the mass being 1.2% of the mass of the crystals treated in the step 3 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 mesh, placing into crucible again, spreading to 3.5-5cm, placing into vacuum drying furnace, introducing nitrogen gas for protection, and performing gradient heating calcination:
a first gradient: calcining at 530 ℃ for 3 hours, and volatilizing water generated in the reaction process;
a second gradient: calcining again at 565 deg.C for 4 hr to volatilize NH generated during the reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature to 35 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature to 55 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product. The XRD pattern was consistent with that of FIG. 3.
Detecting by an Agilent 5110-ICP-OES to obtain the oxygen-free zirconium tetrafluoride product with the zirconium ion content of 544935ppm; the content of iron ions is 1.3ppm, and the content of other heavy metals is less than 1ppm.
Fluorine 455016ppm was detected by Lei Ci PXSJ-216F ionometer.
The oxygen content measured by a force-measuring OHN836 oxygen-nitrogen-hydrogen combined analyzer is 422ppm and meets the standard.
Example 5
This example prepared oxygen-free zirconium tetrafluoride by the following steps, differing from example 4 in the temperature and time during the reaction:
step 1.1, adding 45-50% by mass of hydrofluoric acid with the mass concentration of 3000 g into a polytetrafluoroethylene reaction kettle, heating to 65 ℃, and rapidly adding 750 g of zirconium dioxide into the hydrofluoric acid at one time under a stirring state; wherein the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the reaction temperature at 95 ℃, and continuously reacting for 60 minutes;
step 1.3, adding 750 g of zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 95 ℃, continuously reacting for 60 minutes, and standing for 30 to 40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 And (4) crude O product.
Step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 110 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, liquid-solid separating in centrifuge while it is hot, setting rotation speed of centrifuge at 800-1200r, removing supernatant, washing free acid on crystal surface with deionized water to obtain ZrF 4 . H 2 The XRD spectrum of the O fine product is the same as that of figure 1.
Step 3, zrF preparation 4 And generating a by-product ZrOF 2 ；
Putting the crystal treated in the step 2 into a crucible, putting the crucible into a vacuum drying furnace, drying the crucible at 350 ℃ for 4 hours, cooling the crucible to room temperature, taking out the crystal, wherein the crystal is ZrF 4 And ZrOF 2 A mixture of (a); the XRD spectrum is the same as that of FIG. 2.
Step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystal treated in the step 3 inInto a polytetrafluoroethylene container, NH was added in an amount of 1.5% by mass based on the mass of the crystals after the treatment in step 3 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 mesh, placing into crucible again, spreading to 3.5-5cm, placing into vacuum drying furnace, introducing nitrogen gas for protection, and performing gradient heating calcination:
a first gradient: calcining at 480 ℃ for 4 hours, and volatilizing water generated in the reaction process;
a second gradient: calcining at 550 deg.C for 5 hr to volatilize NH generated during the reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature to 35 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature to 55 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product. The XRD pattern was consistent with that of FIG. 3.
Detecting by an Agilent 5110-ICP-OES to obtain the oxygen-free zirconium tetrafluoride product with the zirconium ion content of 544851ppm; the content of iron ions is 1.2ppm; the content of other heavy metals is less than 1ppm.
The fluorine content was 455198ppm as determined by Lei Ci PXSJ-216F ionometer.
The oxygen content measured by a force-measuring OHN836 oxygen-nitrogen-hydrogen combined analyzer is 332ppm, and the standard is met.
From the above 5 examples, it can be seen that all the data of the produced product are within the acceptable range and the preparation process is very stable as long as the feeding proportion, the temperature and the adding amount of the ammonium bifluoride are within the given ranges.
Claims (10)
1. A preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor is characterized by comprising the following steps:
step 1, preparing ZrF 4 . H 2 O crude product;
step 1.1, adding 45-50% by mass of hydrofluoric acid into a polytetrafluoroethylene reaction kettle, heating to 65-70 ℃, and firstly adding the hydrofluoric acid into the hydrofluoric acid under stirringIs added at one timex Zirconium dioxide in an amount; whereinx=m/2，mIs the total mass of zirconium dioxide; the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1.8-1;
step 1.2, waiting for the boiling of the reaction liquid, maintaining the reaction temperature at 95-105 ℃, and continuously reacting for 40-60 minutes;
step 1.3, adding the rest zirconium dioxide into the reaction solution again, maintaining the reaction temperature at 95-105 ℃, continuously reacting for 30-60 minutes, and standing for 30-40 minutes after the reaction is completed; filtering and collecting filtrate to obtain ZrF 4 . H 2 O crude product;
step 2, preparing ZrF 4 . H 2 O fine product;
adding the filtrate collected in the step 1.3 into another polytetrafluoroethylene reaction kettle, heating to 110-120 ℃, and concentrating; concentrating to obtain crystal, taking out crystal, liquid-solid separating in centrifuge while it is hot, removing supernatant, and washing free acid on crystal surface with deionized water to obtain ZrF 4 . H 2 O fine product;
step 3, preparing ZrF 4 And generating a by-product ZrOF 2 ；
ZrF treated in the step 2 4 . H 2 Placing the refined O product into a crucible, placing the crucible into a vacuum drying furnace, drying the refined O product at 350-380 ℃ for 3-4 hours, cooling the dried refined O product to room temperature, taking out crystals, wherein the crystals are ZrF 4 And ZrOF 2 A mixture of (a);
step 4, preparing oxygen-free ZrF 4 ；
Step 4.1, placing the crystals treated in the step 3 into a polytetrafluoroethylene container, and doping NH with the mass being 1.2-1.5% of the mass of the crystals treated in the step 3 4 HF 2 Mixing uniformly; then evenly mixing the crystal and NH 4 HF 2 Mechanically pulverizing to 40-60 meshes, putting into a crucible again, paving, putting into a vacuum drying furnace, introducing nitrogen for protection, and performing gradient temperature rise calcination:
a first gradient: calcining at 480-530 deg.C for 3-4 hr, and volatilizing water produced in the reaction process;
a second gradient: calcining at 550-565 deg.C for 4-5 hr, and volatilizing NH generated during reaction 4 F；
Step 4.2, then, reducing the temperature in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature to 30-35 ℃ every half hour to 300-350 ℃;
a second gradient: reducing the temperature to 50-55 ℃ every half hour until the room temperature to obtain an oxygen-free zirconium tetrafluoride product with the oxygen content of 200-500ppm and the purity of more than or equal to 99.99 percent.
2. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 1, characterized in that: in the step 1.1, the mass ratio of the total mass of the zirconium dioxide to the mass concentration of 45-50% hydrofluoric acid is 1.
3. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 1 or 2, characterized in that:
in the step 1.1, the reaction temperature is 65 ℃;
in the step 1.2, the reaction temperature is 100 ℃, and the continuous reaction time is 45 minutes;
in the step 1.3, the reaction temperature is 100 ℃; the duration of the reaction was 40 minutes.
4. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 3, wherein the method comprises the following steps: the heating temperature in step 2 was 115 ℃.
5. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 4, characterized in that: in the step 3, the drying temperature is 370 ℃ and the drying time is 3 hours.
6. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 5, wherein the method comprises the following steps: NH in step 4.1 4 HF 2 The quality of (2) is the quality of the crystal after the treatment of the step (3)1.3% of.
7. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 6, wherein the method comprises the following steps: in step 4.1, when the gradient temperature rise calcination is carried out:
a first gradient: calcining at 500 deg.C for 4 hr, and volatilizing water produced in the reaction process;
a second gradient: calcining at 555 deg.C for 4 hr, volatilizing NH generated during reaction 4 F。
8. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 7, wherein the method comprises the following steps: in step 4.2, when the temperature is reduced in a gradient manner under the nitrogen protection state:
a first gradient: reducing the temperature by 30 ℃ every half hour to 350 ℃;
a second gradient: reducing the temperature by 50 ℃ every half hour until the temperature reaches the room temperature to obtain the oxygen-free zirconium tetrafluoride product.
9. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 8, characterized in that: in step 4.1, crystallization is carried out with NH 4 HF 2 The thickness of the powder after being spread in the crucible is 3.5-5cm.
10. The preparation method of oxygen-free zirconium tetrafluoride applied to nuclear fission energy thorium-based molten salt reactor according to claim 9, wherein: in the step 1, the purity of the hydrofluoric acid and the purity of the zirconium dioxide are both more than or equal to 99.99 percent.
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