RU2538700C2 - Method of producing silicon tetrafluoride and uranium dioxide from uranium tetrafluoride - Google Patents

Abstract

FIELD: physics, atomic power.

SUBSTANCE: invention relates to nuclear material engineering and can be used in uranium tetrafluoride conversion. Silicon tetrafluoride and uranium dioxide are obtained from uranium tetrafluoride. Silicon dioxide is subjected to mechanical activation followed by homogenisation thereof with uranium tetrafluoride in stoichiometric ratio. The homogenised mixture is granulated, dried at 250-300°C and heat treated in a medium of a dry inert gas.

EFFECT: invention enables uranium tetrafluoride conversion with high output of highly pure silicon tetrafluoride, which is not contaminated with volatile uranium compounds, at temperature not higher than 600°C.

1 dwg, 1 tbl, 7 ex

Description

The invention relates to the field of nuclear material technology and can be used in the conversion of uranium tetrafluoride, including depleted, to uranium dioxide to obtain a valuable polycrystalline silicon precursor - silicon tetrafluoride

$${\text{Uf}}_{\text{4 (tv)}}+{\text{SiO}}_{\text{2 (tv)}}\to {\text{UO}}_{\text{2 (tv)}}+{\text{SiF}}_{\text{4 (gas)}}\text{(one)}$$

Closest to the proposed method for producing (prototype) silicon tetrafluoride and uranium dioxide from uranium tetrafluoride is a method that includes machining in a disintegrator at a relative speed of 5-15 thousand rpm for 7-20 minutes, a mixture of uranium tetrafluoride and silicon dioxide in a molar ratio (1.05-1.10): 1, heat treatment of the mixture at 600-650 ° C in a tube furnace (without phase mixing) in air for 1-2 hours and subsequent defluorination of the solid product with steam at 500-550 ° C for 1 h while stirring the solid phase (Pa ent of the Russian Federation 2412908 C1, IPC C01G 43/01, C01B 33/107).

The disadvantages of the prototype are:

- the possibility of contamination of silicon tetrafluoride with uranium due to the oxidation of UF ₄ in an oxygen-containing medium to UF ₆ ;

- the use of non-stoichiometric ratios of reactants, resulting in contamination of the resulting fluorine-uranium oxide (~ 1,3% F ^- in the form of uranyl fluoride), resulting in the need for high-temperature operation defluorination solid;

- low yield of SiF ₄ when using crystalline forms of silicon dioxide (quartz, cristobalite, tridymite, etc.), especially when carrying out the conversion process in the absence of mixing of the mixture of reagents (boat, crucible) at a temperature below 600 ° C;

- high temperatures of the process, at which it is necessary to use expensive nickel-based alloys as the structural material of the apparatus.

The technical result of the invention is to increase the yield of high-purity, not contaminated with volatile compounds of uranium, silicon tetrafluoride at a stoichiometric ratio of UF ₄ : SiO ₂ (1: 1), lowering the temperature of the process, allowing the use of cheaper structural materials for instrumentation of the process.

The technical result is achieved by the fact that in the method for producing silicon tetrafluoride and uranium dioxide, uranium tetrafluoride is mixed with silicon dioxide, followed by heat treatment, the silicon dioxide being subjected to mechanical activation, homogenized with uranium tetrafluoride in a stoichiometric ratio, the homogenized charge is granulated, dried at a temperature of 250-300 ° C, the heat treatment of the granules is carried out in a dry inert gas environment for 1-2 hours at a temperature not exceeding 600 ° C.

The invention is implemented as follows (Figure 1). The mechanical activation of silicon dioxide in order to increase its specific surface and increase its reactivity is carried out in a grinder (attritor, planetary, vibration, ball mill or other devices). The duration and conditions of mechanical activation of silicon dioxide are determined by the type of grinder and the form of silicon dioxide (crystalline or X-ray amorphous SiO ₂ ). Next, for a specified time, the operation of homogenizing the mixture of reagents is carried out in any suitable device (turbulent type mixer, disintegrator, etc.), then granulation (granule size ~ 1 mm) of the homogenized mixture (mixture) is carried out in any known manner to improve contact between reagent particles and reducing pyleunos. After granulation, the material enters the drying apparatus, which is carried out in a stream of dry inert gas (nitrogen, argon, helium) or in vacuum at a temperature of 250-300 ° C, or by any other known method. Drying the granules allows you to minimize the water content in the system, and thereby reduce the likelihood of adverse reactions, in particular, with the formation of hydrogen fluoride. After drying, the granules are sent to the conversion stage, which can be carried out both in the apparatus with the absence of mixing of the material (for example, a crucible), and with mixing (for example, a rotary tube furnace). The conversion of uranium tetrafluoride to triuran octoxide is carried out in a stream of dried inert gas (nitrogen, argon, helium) at a temperature below 600 ° C for 1-2 hours. The high-purity gaseous silicon tetrafluoride released is removed from the purge gas reactor and captured by cryocondensation, or sorption (absorption) on sodium fluoride (potassium), or by any other known method.

The solid product, uranium dioxide, is collected in any suitable containers.

Compliance with the stoichiometric ratio of reactants at the reaction completeness flow eliminates the need for additional high temperature defluorination solid (UO _2). Carrying out the process in an inert environment eliminates the formation of volatile UF ₆ and thereby ensures that SiF _{4 is} not contaminated with uranium.

The invention is illustrated by the following examples.

Example 1 (prototype). Silicon dioxide in the form of a quartz concentrate (98.5% SiO ₂ ) weighing 9.0 g is mixed with 46.3 g of uranium tetrafluoride in a disintegrator for 15 minutes (10,000 rpm). The resulting mixture is placed in the apparatus without stirring (boat, tube furnace), through which the dried inert gas is blown. The apparatus is heated at a rate of 10 ° C / min to 650 ° C and the mixture is kept for 2 hours. The SiF ₄ yield is 40%.

Example 2. Silica in the form of a quartz concentrate (98.5% SiO ₂ ) weighing 20.0 g is subjected to mechanical activation in a centrifugal planetary mill for 60 minutes, after which it is mixed with 103.1 g of uranium tetrafluoride, the homogenized charge is dried in inert gas flow at 250 ° C for 2 hours and placed in an apparatus without stirring (boat, tube furnace), through which the dried inert gas is blown. The apparatus is heated at a rate of 10 ° C / min to 575 ° C and the mixture is kept for 2 hours. The SiF ₄ yield is 85%.

Example 3. Silicon dioxide in the form of a quartz concentrate (98.5% SiO ₂ ) weighing 30.0 g is subjected to mechanical activation in a centrifugal planetary mill for 60 minutes, after which it is mixed with 154.7 g of uranium tetrafluoride, the homogenized charge is granulated, dried in a stream of inert gas at 250 ° C for 2 hours, after which it is placed in the apparatus without stirring (crucible, tube furnace), through which the dried inert gas is blown. The apparatus is heated at a rate of 10 ° C / min to 575 ° C and the mixture is kept for 2 hours. The SiF ₄ yield is 100%.

Example 4 (prototype). Silica in the form of X-ray amorphous SiO ₂ (89%) weighing 30.5 g is mixed with 142.2 g of uranium tetrafluoride in a disintegrator for 10 minutes (8000 rpm), after which it is placed in the apparatus without stirring (boat, tube furnace) through which drained inert gas is blown. The apparatus is heated at a rate of 15 ° C / min to 600 ° C and the mixture is held for 1 hour. The SiF ₄ yield is 75%.

Example 5. Silicon dioxide in the form of X-ray amorphous SiO ₂ (89%) weighing 31.3 g is subjected to mechanical activation in a vibration mill for 15 minutes, after which it is mixed with 145.6 g of uranium tetrafluoride, the homogenized charge is dried for 3 hours at 270 ° C in vacuum, after which it is placed in the apparatus without stirring (boat, tube furnace), through which the dried inert gas is blown. The apparatus was heated at 15 ° C / min to 500 ° C and held for 1 h. Yield of SiF ₄ is 92%.

Example 6. Silicon dioxide in the form of x-ray amorphous SiO ₂ (89%) weighing 80.0 g is subjected to mechanical activation in a vibration mill for 15 minutes, after which it is mixed with 372.6 g of uranium tetrafluoride, the homogenized charge is granulated, dried in vacuum at 270 ° C for 3 hours, after which they are placed in an apparatus without stirring (crucible, tube furnace), a reactor through which dried inert gas is blown. The reactor is heated at a rate of 15 ° C / min to 500 ° C and held for 1 hour. The SiF ₄ yield is 100%.

Example 7. Silicon dioxide in the form of cristobalite (99.5% SiO ₂ ) weighing 40.0 g is subjected to mechanical activation in a centrifugal planetary mill for 30 minutes, after which it is mixed with 208.3 g of uranium tetrafluoride, the homogenized charge is granulated, dried in a stream of inert gas at 300 ° C for 1 h, after which it is placed in the apparatus without stirring (crucible, tube furnace), through which the dried inert gas is blown. The apparatus is heated at a speed of 10 ° C / min to 575 ° C and incubated for 1 h. The yield on SiF ₄ is 100%).

The process conditions and the output of SiF ₄ are summarized in table 1.

Table 1 Example No. ₂ * SiO Mechanical Activation Conditions Mixture preparation conditions Temperature and process time Yield of SiF _4.
% 1 (prototype) Quartz Without MA 15 min, 10,000 rpm 650 ° C, 2 h 40 2 Quartz MTC, 60 min 250 ° C, 2 h 575 ° C, 2 h 70 3 Quartz MTC, 60 min 250 ° C, 2 h, granulation 575 ° C, 2 h 95 4 (prototype) X-ray amorphous Without MA 10 min, 8000 rpm 600 ° C, 1 h 75 5 X-ray amorphous BM, 15 min 270 ° C, 3 h 500 ° C, 1 h 92 6 X-ray amorphous BM, 15 min 270 ° C, 3 h, granulation 500 ° C, 1 h one hundred 7 Cristobalite MTC, 30 min 300 ° C, 1 h, granulation 575 ° C, 1 h one hundred * main impurities in silicon dioxide: Al, Fe, Ca, Mg, Ti, K, Na, Mn, Sr, Cr, Ni, Zn, Cu.
CPM - planetary mill; BM - vibratory mill.

As can be seen from the above examples, the claimed method for producing high-purity silicon tetrafluoride and uranium dioxide from uranium tetrafluoride:

- provides a high (up to 100%) yield of high-purity silicon tetrafluoride, not contaminated with volatile uranium compounds, at a temperature not exceeding 600 ° C even in an apparatus without stirring when using both X-ray amorphous and crystalline forms of silicon dioxide;

- does not require additional operations for high-temperature defluorination of the solid reaction product, since the process is carried out at a stoichiometric ratio of the reactants;

- allows you to use cheaper, compared with nickel alloys, structural materials.

Claims (1)

A method of producing silicon tetrafluoride and uranium dioxide from uranium tetrafluoride by mixing it with silicon dioxide followed by heat treatment, characterized in that the silicon dioxide is subjected to mechanical activation, homogenized with uranium tetrafluoride in a stoichiometric ratio, the homogenized charge is granulated, dried at a temperature of 250-300 ° C moreover, the heat treatment of the granules is carried out in a dry inert gas environment for 1-2 hours at a temperature not exceeding 600 ° C.

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