PREPARATION OF METAL FLUORIDES AND SEPARATION PROCESSES
20220153607 · 2022-05-19
Inventors
- Tobias CHEMNITZ (Garching, DE)
- Florian KRAUS (Penzing, DE)
- Winfried PETRY (Baldham, DE)
- Christian STEYER (Garching, DE)
- Stefan RUDEL (Marburg, DE)
- Riane STENE (Marburg, DE)
Cpc classification
G21G2001/0094
PHYSICS
B01J3/008
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J3/00
PERFORMING OPERATIONS; TRANSPORTING
G21G1/00
PHYSICS
Abstract
Provided is a process which allows uranium and molybdenum fluorides to be efficiently separated, said process comprising a step of providing a mixture containing MoF.sub.6 and UF.sub.6; a step of reducing the UF.sub.6 to UF.sub.5 in the gas phase or in a liquid phase; and a step of separating the UF.sub.5 and the MoF.sub.6 or a conversion product thereof which may be obtained by further converting the molybdenum fluoride to another molybdenum compound. In a further aspect, a process for the fluorination of metals or semimetals is provided.
Claims
1. A process comprising a step of providing a mixture containing MoF.sub.6 and UF.sub.6; a step of reducing the UF.sub.6 to UF.sub.5; and a step of separating the UF.sub.5 and the MoF.sub.6 or a conversion product thereof which may be obtained by further converting the molybdenum fluoride to another molybdenum compound.
2. The process according to claim 1, comprising a step of providing a mixture containing MoF.sub.6 and UF.sub.6 as an initial metal fluoride mixture; a dissolution step, which comprises dissolving MoF.sub.6 and UF.sub.6 in a liquid phase or a supercritical fluid phase to obtain a solution containing both MoF.sub.6 and UF.sub.6 in dissolved form; a precipitation step, which comprises reducing the UF.sub.6 contained in the solution to UF.sub.5 and allowing it to precipitate from the solution; and a separation step, which comprises (i) separating the precipitated UF.sub.5 from the solution; or (ii) removing the liquid phase or supercritical fluid phase of the solution in the presence of the precipitated UF.sub.5 to obtain a solid phase containing the precipitated UF.sub.5 and molybdenum fluoride, and separating the UF.sub.5 and the molybdenum fluoride or a conversion product thereof which may be obtained by further converting the molybdenum fluoride to another molybdenum compound.
3. The process according to claim 2, wherein the mixture containing MoF.sub.6 and UF.sub.6 which is provided as an initial metal fluoride mixture is a gas phase mixture containing MoF.sub.6 and UF.sub.6 mixed in gaseous form.
4. The process according to claim 3, which further comprises a step wherein the gas phase mixture containing MoF.sub.6 and UF.sub.6 is cooled to a temperature where MoF.sub.6 and UF.sub.6 contained in the gas phase are deposited as a mixture containing MoF.sub.6 and UF.sub.6, the mixture is recovered, and is subsequently subjected, optionally after re-evaporation to provide a gas-phase mixture containing MoF.sub.6 and UF.sub.6 in gaseous form, to the dissolution step.
5. The process according to claim 3, which further comprises, prior to the dissolution step, a step wherein the gas phase mixture containing MoF.sub.6 and UF.sub.6 is cooled to a temperature where a portion of the UF.sub.6 contained in the gas phase is deposited and removed from the gas phase.
6. The process according to claim 2, wherein MoF.sub.6 and UF.sub.6 are dissolved in the dissolution step in a liquid phase which comprises or consists of liquid SO.sub.2 as a solvent or in a supercritical fluid phase which comprises or consists of CO in a supercritical state.
7. The process according to claim 2, wherein the separation step comprises separating the precipitated UF.sub.5 from the solution.
8. The process according to claim 7, wherein the separation step further comprises converting MoF.sub.6 contained in the solution to another molybdenum compound prior to or after the separation of the precipitated UF.sub.5 from the solution, and recovering the molybdenum compound from the solution after the separation of the precipitated UF.sub.5 from the solution.
9. The process according to claim 7, wherein the separation step comprises reducing the MoF.sub.6 contained in the solution to obtain a solution containing MoF.sub.5 prior to or after the separation of the precipitated UF.sub.5 from the solution.
10. The process according to claim 2, wherein the separation step comprises (ii) removing the liquid phase or supercritical fluid phase of the solution in the presence of the precipitated UF.sub.5 to obtain a solid phase containing the precipitated UF.sub.5 and molybdenum fluoride, and separating the UF.sub.5 and the molybdenum fluoride.
11. The process according to claim 10, wherein the separation step comprises reducing the MoF.sub.6 contained in the solution to obtain a solution containing MoF.sub.5 prior to removing the liquid phase or supercritical fluid phase of the solution, and wherein the solid phase obtained by removing the liquid phase or supercritical fluid phase of the solution contains the precipitated UF.sub.5 and MoF.sub.5.
12. The process according to claim 11, wherein the precipitated UF.sub.5 and MoF.sub.5 are separated via sublimation of the MoF.sub.5 and its deposition separate from the UF.sub.5.
13. The process according to claim 2, wherein the step of providing a mixture containing MoF.sub.6 and UF.sub.6 as an initial metal fluoride mixture comprises reacting a solid material, which contains elemental uranium and elemental molybdenum, with fluorine radicals, and wherein the reaction comprises exposing the solid material to a gas flow comprising the fluorine radicals, to obtain the mixture containing MoF.sub.6 and UF.sub.6.
14. The process according to claim 13, wherein the step of providing a mixture containing MoF.sub.6 and UF.sub.6 as an initial metal fluoride mixture comprises generating the fluorine radicals from a fluorine containing precursor compound in a plasma source, more preferably in a remote plasma source.
15. The process according to claim 1, comprising a step of providing a gas phase mixture containing MoF.sub.6, UF.sub.6 and a fluorine atom scavenger mixed in gaseous form; a step of irradiating the UF.sub.6 in the gas phase mixture in the presence of the fluorine atom scavenger with light having a wavelength in the range of 340 to 410 nm to reduce the UF.sub.6 to UF.sub.5 and to obtain a mixture comprising UF.sub.5 and MoF.sub.6; and a step of separating the UF.sub.5 and the MoF.sub.6.
16. The process according to claim 15, wherein the light used for irradiation has a wavelength of 380 to 400 nm, more preferably of 395 nm.
17. The process according to claim 15, wherein the fluorine atom scavenger in gaseous form is selected from CO, H.sub.2, Xe and SO.sub.2.
18. The process according to claim 15, which further comprises a step of removing a reaction product of the fluorine atom scavenger and the fluorine formed by the reduction of UF.sub.6 to UF.sub.5.
19. The process according to claim 15, wherein the UF.sub.5 and the MoF.sub.6 are separated by distilling off the MoF.sub.6.
20. (canceled)
21. (canceled)
Description
[0347]
EXAMPLES
Example 1—Preparation of a Mixture or Uranium Fluoride and Molybdenum Fluoride
[0348] a) Reaction System for the Preparation of Uranium and Molybdenum Fluorides
[0349] A mixture of UF.sub.6 and MoF.sub.6 was prepared using the reaction system which is schematically illustrated by the flow chart in
[0350] The system (hereafter referred to as fluorination line) consists of the following subsystems: The gas supply (1), (2), (3), (4), the remote plasma source (RPS, (5)), the reaction tube (6), (7), the pipelines and cold traps, the absorption system (8) and the pumping station (9). In addition, several peripheral devices facilitate the regulation of the process. These include control units for the mass flow controllers (MFC), the readout device for the pressure sensors, the control unit for the oven, the power supply for the microwave as well as PC, keyboard and screen, which is necessary to operate the control software for the RPS. The wiring of the system is housed in a separate control cabinet.
[0351] The use of three MFCs (4) allows the control of the gas flow rate and thus the exact composition of the process gas. The process gas is fed into the RPS (5), where fluorine, hydrogen and oxygen radicals are formed, depending on its exact composition. The (optional) use of oxygen allows the synthesis of oxyfluorides, whereas the (optional) use of hydrogen allows a removal of potential oxide layers on the substrate.
[0352] The actual fluorination takes place in the heatable reaction tube (7). The cold traps are located downstream and allow the deposition of the reaction product. Thereby, the use of the last cold trap as a “getter trap” has itself proven to be advantageous in order to remove residues and impurities from the system. Further downstream the fluorine absorbers (8) are located, which preferably bind unconsumed reactive fluorine species and thereby protect the subsequent pumps (9).
[0353] The use of a Remote Plasma Source advantageously allows the fluorides to be synthesized in a low vacuum. Thus, the use of autoclaves, elevated pressure and/or high temperatures is not necessary.
[0354] Gas Supply with MFCs
[0355] The supply with process gases is controlled by three MFCs (mass flow controllers) manufactured by the Bronkhorst Company. These are driven over an RS232 interface with the Readout and Control System E-8501-0-2A, likewise of the Bronkhorst Company. The MFCs are also equipped with an EtherCAT port. The readout of the pressure takes place by two capacitive sensors CERAVAC Transmitter CTR100N of Oerlikon Leybold with a maximum pressure range of 100 Torr and 10 Torr, respectively. Thereby, the 100 Torr sensor is located directly subsequent to the RPS, whereas the 10 Torr sensor is located downstream of the third cold trap. The usage of capacitive sensors holds the advantage of their independence of the applied gas.
[0356] MFC 1 supplies the RPS with the fluorine containing process gas (fluorine containing precursor compound). In this example NF.sub.3 has been used, but the setup also allows the use of other process gases. In order to ensure a high life time, MFC 1 is equipped with FFKM (Kalrez) gaskets.
[0357] MFC 2 supplies the RPS with Argon, which can be used as a carrier gas and/or for purging the line after the fluorination process and to ensure a counter flow when opening the extraction ports (minimizing the intrusion of oxygen and moisture). The gaskets of MFC 2 are made of Viton.
[0358] MFC 3 supplies the line with either oxygen (synthesis of oxyfluorides) or hydrogen (removal of potential oxide layers on the substrate), if desired.
[0359] Remote Plasma Source (RPS)
[0360] The plasma is burning inside the Remote Plasma Source. The plasma is created using microwave radiation with a frequency of 2.45 GHz. The radiation provides the energy to break the fluorine bonds of the fluorine containing process gas (fluorine containing precursor compound). In doing so, a high concentration of fluorine radicals (degree of dissociation greater 95%) can be created, which allows a highly efficient fluorination.
[0361] Due to its relatively weak bond, NF.sub.3 is advantageously used as the process gas. The RPS is the model MA3000C-193BB of the MUEGGE Company. According to the technical specifications, the model requires high flow rates of the process gas of at least 500 sccm. However, it could be shown during operation that the RPS can be operated safely at much smaller flow rates of as low as 2 sccm. The RPS is powered by the microwave power supply MX3000D-117KL (MPS) with a maximum power output of 3000 W also of the MUEGGE Company. It is controlled via PC, which runs the Windows-based control software. However, the input signal for the MPS is based on CAN bus, so a signal converter is interposed between PC and MPS.
[0362] The cooling water monitoring of both components is automated. As soon as the temperature leaves a precisely defined window or the cooling water flow rate becomes too low, an interlock shuts down the MPS. If the pressure of the cooling water exceeds a threshold value, magnet valves at the entry switch of the cooling water in order to protect the system from damage and/or leakage.
[0363] Reaction Tube
[0364] The actual fluorination takes place in the reaction tube. The reaction tube is made from nickel, which has been passivated before. It is located inside an oven, which can be heated up to 1000° C. Due to the high reactivity of the fluorine radicals, the distance from the plasma to the substrate should be held as short as possible in order to reduce losses because of recombination. Therefore, only a short reducing 4-way cross is located between the RPS and the reaction tube. Here, one of the pressure sensors as well as a viewport equipped with a sapphire glass window on the opposite side are located. The viewport on one hand allows to confirm whether the plasma is burning and on the other side allows a direct evaluation of the reaction process of the substrate
[0365] Pipelines and Cold Traps with Bypass
[0366] The pipelines lead from the reaction tube further downstream to the cold traps, in which a deposition can take place.
[0367] The pipelines are made from stainless steel 1.4404 with a diameter of ½ inch. All of the valves used are membrane valves of the type 6L-ELD8-77X-P of the Swagelok Company. These valves are hallmarked by a high corrosion resistance.
[0368] The cold traps are made from PFA and feature a simple U-tube design. They are being passivated before use at a pressure of 1 bar for 24 hours with pure fluorine in order to remove non-fluorinated constituents and thereby to guarantee the chemical inertness of the material. Each cold trap can be bypassed. This allows the purging of the system before the resublimation process with Argon on one hand and on the other hand switching to another could trap, if the deposited product negatively affects the gas flow rate leading to an increased pressure. In addition, it has proven useful to utilize the cold trap furthest downstream as a “getter trap” in order to remove residues and residual humidity, which is left after heating and evacuation in the system and thereby to further increase the purity of the synthesized products.
[0369] Absorption System
[0370] The absorption system consists of two tubes made of stainless steel 1.4435 filled with a fluorine absorber. This can be Soda lime, Al.sub.2O.sub.3 or TiO.sub.2. They protect the pumping unit from non-deposited reactive fluorine species. The absorber tubes are connected with valves in a way that they can be used either in row or that the front tube can be bypassed. Three thermocouples on each tube allow the monitoring of the reaction front. Thereby, they allow measuring the level of exhaustion of the absorber material. The absorber tubes are connected to the line via DN 40 CF flanges.
[0371] Pumping Unit
[0372] As pumping system, a rotary vane pump TRIVAC D40BCS with PTFE oil of the Leybold Company was used as the first stage, boosted with a roots pump RUVAC WSU 251 as a second stage. On this stage, a SECUVAC valve is placed, which automatically vents the pumps and shuts off the system on the vacuum side, when the rotary vane pump is switched off. The rotary vane pump is equipped with chemical filter CFS 40-65, which consists of porous Al.sub.2O.sub.3 and removes residues from the oil. It is also equipped with the exhaust filter with lubricant return ARS 40-65.
[0373] Synthesis Product Extraction
[0374] The synthesis product is extracted from the cold traps by recondensing it into sample cylinders. These cylinders are equipped with a membrane valve and connected to the extraction ports. The sample cylinder is cooled with liquid nitrogen, whereas the cooling agent of the cold traps is removed at the same time. This recondensing step increases the purity of the synthesis product even more.
[0375] b) Preparation of UF.sub.6 and MoF.sub.6
[0376] Using the reaction system described above, a mixture containing UF.sub.6 and MoF.sub.6 was provided in line with the following protocol. [0377] Cleaning of a metal substrate comprising 99 wt % U and 1 wt % Mo with 7 M HNO.sub.3 in order to remove oxide layer, afterwards removal of HNO.sub.3 with aqua dest. and acetone (total weight after cleaning: 1504.8 mg). [0378] Placing substrate on Monel carrier and inserting it at argon counterflow into the reaction chamber. [0379] Purging the entire system three times with argon and evacuating afterwards in order to remove any oxygen or humidity which entered the system during the introduction of the carrier and substrate. During the purging process, the absorbers are bypassed in order to avoid unnecessary dust of the absorber material accumulate in the downstream valves. [0380] Filling the Dewar vessels of the cold traps with the different frigorific mixtures (in the last experiments isopropanol-dry ice at a temperature of −82° C. for cold trap 1, isopropanol-dry ice at a temperature of −85° C. for cold trap 2 and liquid nitrogen at a temperature of −190° C. for the third cold trap) [0381] Closing all MFC bypass valves. [0382] Closing all bypass valves of the cold traps [0383] Closing the bypass of the absorber and open the absorber valves [0384] Switching on the cooling water for the RPS (Remote Plasma Source) and the MPS (Microwave Power Supply), checking that it exceeds 4 I/min [0385] Setting the value for the Ar MFCs at the MFC Control Panel to 20 sccm [0386] Starting the RPS at the control computer, setting it to 3000 W [0387] Setting the value for the NF.sub.3 MFCs at the MFC Control Panel to 20 sccm [0388] Controlling through the sapphire window, whether the plasma ignited correctly [0389] Fluorination over 45 minutes until the target is dissolved (controlled through the sapphire glass window) [0390] Pressure sensor 1: between 3.70 (start of process) and 4.15 mbar (end of process) [0391] Pressure sensor 2: between 3.04 (start of process) and 3.28 mbar (end of process) [0392] Maximum Temperature of the reaction chamber 74.6° C. (no forced cooling of the tube required) [0393] Shutting off the cold traps by closing their valves [0394] Removing the frigorific mixtures and letting the fluorides in the cold traps heat up [0395] Extracting the fluorides via the extraction ports and transferring them into a FEP tube cooled with liquid nitrogen. The highest concentration of MoF.sub.6 is in cold trap 3 and therefore will be extracted via port 3. [0396] The amount of MoF.sub.6 recovered from cold trap 3 accounts to about 35% of the total amount of MoF.sub.6 produced during the reaction and has been enriched from 1:99 to 3:2 (mass ratio of MoF.sub.6 to UF.sub.6). Another 20% of the MoF.sub.6 were deposited in cold trap 1. The amount of UF.sub.6, which has been recovered, was not recorded.
Example 2—Gas-Phase Separation with UV Light Using CO as Fluorine Scavenger
[0397] A 1:1 (weight) mixture of UF.sub.6 and MoF.sub.6 was placed into a quartz vessel. Onto this mixture, about 100 kPa (1 bar) of CO (gaseous) was added and the UF.sub.6/MoF.sub.6/CO mixture was irradiated with ultraviolet light having a wavelength of 395 nm for 12 hours. The following reactions takes place:
##STR00001##
[0398] After 12 hours of irradiation, the reaction mixture was cooled using liquid nitrogen (−196° C.) and the volatile COF.sub.2 was pumped off. An additional 100 kPa (1 bar) of CO (gaseous) was added to the quartz vessel and the mixture was irradiated again with 395 nm light for an additional 12-24 hours.
[0399] After this additional irradiation cycle, the reaction mixture was cooled to −196° C. and the volatile COF.sub.2 was pumped off. A mixture of UF.sub.5 (solid, non-volatile) and MoF.sub.6 (liquid, volatile) remained. The MoF.sub.6 was then be separated from the UF.sub.5 via distillation. Both UF.sub.5 and MoF.sub.6 are collected in quantitative amounts at the end of the separation. Analysis with MP-AES (microwave plasma atomic emission spectroscopy) showed the molybdenum sample to be pure, with no detectable amounts of uranium. Analysis of the UF.sub.5 sample showed that over 99% of the molybdenum had been removed.
[0400] Similarly, this reaction can be done using hydrogen gas (H.sub.2). The separation was done in the same way as the CO separation, except the corresponding reactions are:
##STR00002##
[0401] However, attention must be paid to choosing an appropriate reaction vessel. Quartz should not be used because it will react with the HF gas formed. Perfluorinated plastic is also not recommended due to the solubility of MoF.sub.6 in such plastics.
[0402] Procedures
[0403] 1. 200 mg UF.sub.5 and 200 mg of MoF.sub.6 were distilled into a quartz vessel (which was previously flame dried; the volume of the quartz vessel was approximately 30 mL).
[0404] 2. 100 kPa (1 bar) of CO (gas) was added to the vessel.
[0405] 3. The UF.sub.6/MoF.sub.6/CO mixture was irradiated with 395 nm light for about 12 hours.
[0406] 4. The mixture was cooled to −196° C. (using liquid nitrogen) and the volatile COF.sub.2 was pumped off.
[0407] 5. 100 kPa (1 bar) of fresh CO was placed into the vessel and the mixture was irradiated again with 395 nm light for an additional 12 to 24 hours.
[0408] 6. The mixture was cooled to −196° C. and the remaining CO and COF.sub.2 were pumped off. A mixture of MoF.sub.6 (liquid, volatile) and UF.sub.5 (solid, non-volatile) was left.
[0409] 7. The MoF.sub.6 was then distilled to a new quartz vessel.
[0410] 8. MP-AES analysis was performed on the molybdenum-containing (MoF.sub.6, read below) and uranium-containing (UF.sub.5) samples to check for purity. [0411] To allow for easier handling of the MoF.sub.6 sample for MP-AES measurements, the MoF.sub.6 was reduced to MoF.sub.6 by light with a wavelength of 252 nm using the following reaction:
##STR00003## [0412] The results of the MP-AES measurements for the uranium-containing (UF.sub.5) sample can be found in Table 1. The results of the MP-AES measurements for the molybdenum-containing (MoF.sub.6) sample can be found in Table 2.
[0413] Results
TABLE-US-00003 TABLE 1 MP-AES results of the uranium sample (UF.sub.5) obtained after the UV separation of MoF.sub.6 from UF.sub.6 using 395 nm light and carbon monoxide. All trials were measured in triplicates. Trial 1 (U) Trial 2 (U) Trial 3 (U) Mo, mg/L 0.16 ± 0.01 0.16 ± 0.01 0.13 ± 0.00 % Mo 0.30 ± 0.01 0.32 ± 0.01 0.26 ± 0.00 U, mg/L 39.31 ± 2.27 35.62 ± 0.77 35.52 ± 0.95 % U 73.52 ± 1.41 68.61 ± 1.70 68.89 ± 1.05 Mo/U ratio 1.70 1.63 1.61 before separation Mo/U ratio 0.01 ± 0.00 0.01 ± 0.00 0.01 ± 0.00 after separation % Mo 99.41 ± 0.02 99.30 ± 0.03 99.42 ± 0.01 removed
[0414] Table 1 shows the analysis of the UF.sub.5 sample obtained after the gas phase separation using CO as fluorine scavenger. The separation was performed three times, Trials 1-Trail 3. The measurements were run in triplicates and an average value of the results is reported along with standard deviations. The amount of Mo is reported, along with its percentage in the sample. Similarly, the amount of U is reported along with its percentage in the sample. The Mo/U ratios before and after separation are given, along with the % of Mo removed.
TABLE-US-00004 TABLE 2 MP-AES results of the molybdenum sample obtained after the UV separation of MoF.sub.6 from UF.sub.6 using 395 nm light and carbon monoxide. A single sample was prepared for each trial. Trial 1 (Mo) Trial 2 (Mo) Trial 3 (Mo) Mo, mg/L 29.14 26.29 28.95 % Mo 39.99 36.34 40.02 U, mg/L n.d. n.d. n.d. n.d. = not detected
[0415] Table 2 shows the analysis of the MoF.sub.5 sample obtained after the gaseous CO separation. The Trials 1-3 listed in Table 2 correspond to Trials 1-3 listed in Table 1. The entire MoF.sub.5 sample was dissolved for the MP-AES measurement, therefore, only one sample was prepared for each measurement. Reported are the amounts of Mo found in the sample along with the percentage of Mo. Uranium was not detected.
Example 3—Separation Using Liquid Sulfur Dioxide (SO.SUB.2.) with UV Light
[0416] A 1:1 (weight) mixture of UF.sub.6 and MoF.sub.6 was placed in an FEP or PFA reaction vessel. Onto this mixture, 3-5 mL of SO.sub.2 (liquid) were distilled. The reaction mixture was then irradiated with 395 nm light. Irradiation time can be suitable selected, depending on how much UF.sub.6 is present in the sample. With 200 mg UF.sub.6, an irradiation time of 1 hour and 30 minutes was more than sufficient. The separation of MoF.sub.6 from UF.sub.6 is achieved through the following reactions/conditions:
##STR00004##
[0417] Since MoF.sub.6 is not affected by UV light of this wavelength (395 nm) and because its reaction with SO.sub.2 is so slow, after irradiation a mixture of UF.sub.5 (solid, non-volatile), MoF.sub.6 (liquid, dissolved, volatile), SO.sub.2 (liquid, volatile) and SO.sub.2F.sub.2 (gas, volatile) was obtained. MoF.sub.6 and the remaining SO.sub.2+SO.sub.2F.sub.2 were removed from UF.sub.5 through distillation. MoF.sub.6 may be extracted from the SO.sub.2 solution after a few days (4 to 7 days) as solid MoOF.sub.4, generated by the reaction of MoF.sub.6 with SO.sub.2 described above.
[0418] Analysis of the MoOF.sub.4 sample using MP-AES showed no detectable amounts of uranium. Measurement of the UF.sub.5 sample showed that more than 99% of the molybdenum had been removed.
[0419] Procedures
[0420] 1. 200 mg UF.sub.6 and 200 mg MoF.sub.6 were distilled into an FEP or PFA reaction vessel. The reaction vessel contained a 1 cm stir bar coated with PTFE.
[0421] 2. About 3-5 mL of SO.sub.2 were distilled into the reaction vessel using liquid nitrogen as a cooling agent.
[0422] 3. The reaction mixture was warmed to room temperature and stirred using a stir plate to ensure complete solution of MoF.sub.6 and UF.sub.6 in SO.sub.2.
[0423] 4. Under constant stirring, the sample was irradiated with 395 nm light for 1 hour and 30 minutes.
[0424] 5. After irradiation, a mixture of UF.sub.5 (solid, non-volatile), MoF.sub.6 (liquid, dissolved, volatile), SO.sub.2 (liquid, solvent, volatile), and SO.sub.2F.sub.2 (gaseous, somewhat dissolved, volatile) was obtained.
[0425] 6. The MoF.sub.6 was removed by distilling all volatile compounds (MoF.sub.6, SO.sub.2, and SO.sub.2F.sub.2) into a new FEP or PFA reaction vessel.
[0426] 7. Molybdenum can then be extracted from the SO.sub.2 solution (SO.sub.2/SO.sub.2F.sub.2 mixture) by allowing the MoF.sub.6 to completely react with the SO.sub.2 solvent to form MoOF.sub.4, see equation below.
##STR00005##
[0427] This reaction is slow and takes about a week.
[0428] 8. After one week, the MoOF.sub.4 is extracted by pumping off the SO.sub.2 solution.
[0429] 9. MP-AES analysis was preformed on the uranium-containing (UF.sub.5) and molybdenum-containing (MoOF.sub.4) samples. [0430] Results for the MP-AES analysis of the uranium-containing (UF.sub.5) sample are given in Table 3. Results for the MP-AES analysis of the molybdenum-containing (MoOF.sub.4) sample are given in Table 4.
[0431] Results
TABLE-US-00005 TABLE 3 MP-AES results of the uranium sample (UF.sub.5) obtained after the SO.sub.2/UV separation of MoF.sub.6 from UF.sub.6 using 395 nm light and SO.sub.2 as a solvent. All trials were measured in triplicates. Trial 4 (U) Trial 5 (U) Trial 6 (U) mg Mo/L 0.08 ± 0.00 0.28 ± 0.03 0.10 ± 0.01 % Mo 0.15 ± 0.01 0.50 ± 0.02 0.17 ± 0.00 mg U/L 37.44 ± 0.25 34.78 ± 2.54 36.22 ± 3.77 % U 73.01 ± 2.35 62.82 ± 0.42 63.11 ± 0.43 Mo/U ratio 1.64 1.68 1.65 before separation Mo/U ratio 0.01 ± 0.00 0.02 ± 0.00 0.01 ± 0.00 after separation % Mo removed 99.69 ± 0.02 98.81 ± 0.04 99.58 ± 0.01
[0432] Table 3 shows the analysis of the UF.sub.5 sample obtained after the liquid SO.sub.2 separation. The separation was performed three times, Trial 4-Trial 6. The measurements were run in triplicates and an average value of the results is reported along with standard deviations. The amount of Mo is reported, along with its percentage in the sample. Similarly, the amount of U is reported along with its percentage in the sample. The Mo/U ratios before and after separation are given, along with the % of Mo removed.
TABLE-US-00006 TABLE 4 MP-AES results of the molybdenum sample (MoOF.sub.4) obtained after the SO.sub.2/UV separation of MoF.sub.6 from UF.sub.6 using 395 nm light and SO.sub.2 as a solvent. All trials were measured in triplicates. Trial 4 (Mo) Trial 5 (Mo) Trial 6 (Mo) Mo, mg/L 54.24 ± 2.55 55.90 ± 3.71 55.92 ± 1.11 % Mo 54.65 ± 1.23 50.59 ± 1.33 49.96 ± 0.83 U, mg/L n.d. n.d. n.d. n.d = not detected
[0433] Table 4 shows the analysis of the MoOF.sub.4 sample obtained after the liquid SO.sub.2 separation. The separation was performed three times, Trial 4-Trial 6, which correspond to Trials 4-6 in Table 3. The measurements were run in triplicates and an average value of the results is reported along with standard deviations. The amount of Mo is reported, along with its percentage in the sample. No uranium was detected in these samples.
Example 4—Separation Using Liquid SO.SUB.2 .with Filtration
[0434] A mixture of UF.sub.5/MoF.sub.5 can be made from the following reactions (using the indicated wavelength):
##STR00006##
[0435] This 1:1 (weight) mixture of UF.sub.5 and MoF.sub.5 was then be separated by placing the mixture into a filtration vessel (a glass H-tube was used, but any appropriate filtration vessel is also suitable). Onto the mixture, 5-10 mL of SO.sub.2 (liquid) were distilled. MoF.sub.5 is soluble in SO.sub.2 while UF.sub.5 is insoluble in SO.sub.2. Separation was then achieved via filtration through a glass frit. After filtration/separation, analysis of the MoF.sub.5 sample showed less than 0.25% uranium to be present. Analysis of the UF.sub.5 sample showed the sample to contain about 2% molybdenum. The amount of molybdenum in the UF.sub.5 sample is, naturally, dependent on the quality of the filtration and the repetitions of filtration.
[0436] Procedures
[0437] 1. 50 mg UF.sub.5 and 50 mg MoF.sub.5 were placed in a glass filtration apparatus (an H-tube was used).
[0438] 2. To this mixture, 5 to 10 mL of SO.sub.2 was distilled at −196° C. Afterwards, the mixture was allowed to warm to −30° C. The part of the filtration apparatus containing UF.sub.5 was maintained at −30° C. for the duration of the filtration procedure.
[0439] 3. The solution was manually agitated by shaking the filtration apparatus lightly to dissolve the MoF.sub.5 in the SO.sub.2 solvent. Solution of MoF.sub.5 in SO.sub.2 produces a yellow solution. (SO.sub.2 alone is colorless)
[0440] 4. The SO.sub.2 solution containing MoF.sub.5 was then filtered to the other side of the filtration apparatus via a glass frit.
[0441] 5. The side of the filtration apparatus was maintained at −30° C. while the side containing the newly filtered S02/MoF.sub.5 solution was allowed to warm. Consequently, the SO.sub.2 was slowly distilled back to the original (UF.sub.5) side of the filtration apparatus.
[0442] 6. Steps 4 and 5 were repeated 7 to 10 times, or until the SO.sub.2 solution above the UF.sub.5 sample remained colorless.
[0443] 7. The SO.sub.2 was distilled out of the filtration apparatus. MoF.sub.5 was found on one side of the apparatus while UF.sub.5 was found on the other side.
[0444] 8. The MoF.sub.5 and UF.sub.5 samples were controlled for purity using micro X-ray fluorescence spectroscopy. [0445] Results are given below. The uranium sample showed about a 2% impurity of molybdenum, while the molybdenum sample showed about a 0,25% impurity of uranium.
[0446] Results
TABLE-US-00007 unn. C norm. C Atom. C Fehler (1 Sigma) E1 OZ Serie [Gew. %] [Gew. %] [At. %] [Gew. %] Mo 42 K-Serie 1.95 99.81 99.92 0.00 U 92 0.00 0.19 0.08 0.00 W 74 L-Serie 0.00 0.00 0.00 0.00 Summe: 1.95 100.00 100.00
[0447] The above table shows the results of the micro X-ray fluorescence spectroscopy of the MoF.sub.5 sample. This shows less than 0.25% uranium is left in the sample after filtration.
TABLE-US-00008 unn. C norm. C Atom. C Fehler (1 Sigma) E1 OZ Serie [Gew. %] [Gew. %] [At. %] [Gew. %] U 92 16.40 97.74 94.56 0.00 Mo 42 K-Serie 0.38 2.26 5.44 0.00 W 74 L-Serie 0.00 0.00 0.00 0.00 Summe: 16.78 100.00 100.00
[0448] The above table shows the of the micro X-ray fluorescence spectroscopy of the UF.sub.5 sample. This shows about 2% of Mo to be left in the sample.
Example 5—Separation Using Supercritical CO
[0449] As the critical point of CO is defined by a pressure of 34.5 bar and a temperature of 132.9K, all experiments with supercritical CO were performed in a high-pressure vessel. The pressure hull of the vessel contained a mixture of UF.sub.6 and MoF.sub.6, which was cooled by a cold finger in its bottom. The bottom itself was sloped in order to ensure that no shaded regions exist, which may not be irradiated. A sapphire window allowed UV light to pass and was sealed to the pressure hull with an FFKM O-ring. The pressure necessary for safe sealing was applied by a steel-lid tightened to the pressure hull with six screws. Both, pressure hull and cold finger have a bore for the insertion of thermocouples for temperature measurement.
[0450] The pressure hull was wrapped with heating tape to ensure that both MoF.sub.6 and UF.sub.6 actually condense on the cold finger and not at the walls of the pressure hull.
[0451] The high-pressure container was connected via a bellow-sealed valve to a storage container for CO as well as a pressure gauge. Pressure gauge and storage container were also connected via a bellow-sealed valve. A third bellow-sealed valve connected the high-pressure section and a low pressure section. Two storage containers, one for UF.sub.6 and one for MoF.sub.6, may be connected to one port of the low pressure section. This was done one after another. A measuring cell for IR- and UV/VIS spectroscopy was connected to another extraction port. The pressure in this part of the system was determined by a piezo-resistive pressure sensor. This low-pressure section can be sealed off from the pumps, the argon inlet and the CO inlet by a bellow-sealed valve.
[0452] For the experiments, a mixture of MoF.sub.6 and UF.sub.6 was condensed into the measuring cell and characterized by IR-spectroscopy. Thereby, the exact composition and the ratio of MoF.sub.6/UF.sub.6 before the experiment was known. After the spectroscopic analysis, the measuring cell was reconnected to the line and its content resublimated into the high-pressure container, which was cooled with liquid nitrogen at the cold finger to a temperature of −33° C., whereas the wall temperature was held at a temperature of 1° C. via the heating tape. Thereby it was ensured that MoF.sub.6 and UF.sub.6 only condense at the cold finger. The high-pressure container was subsequently sealed off.
[0453] In a next step, dried CO was condensed into a storage container using liquid nitrogen and then heated to room temperature, thereby becoming supercritical. The CO was allowed to enter into the high-pressure container by opening the connecting valve. The pressure gauge showed 56 bar, so the CO in the high-pressure container was in the supercritical state. The high-pressure-container was again sealed off by closing the connecting valve, heated to 20° C. and its content was irradiated for 60 minutes with 395 nm wavelength. During that time, the storage container was evacuated again.
[0454] After that time, all constituents which were volatile at room temperature were condensed into a storage container using liquid nitrogen. The storage container was kept at liquid nitrogen temperature and evacuated, removing CO and COF.sub.2, but leaving MoF.sub.6 and unreacted UF.sub.6 in the solid phase. The storage container was then disconnected from the line, vented and filled with water, dissolving UF.sub.6 and MoF.sub.6 and the solution was analyzed using MP-AES.
[0455] The solid residues of the high-pressure chamber (mainly UF.sub.5) were dissolved in diluted HNO.sub.3 and also measured using MP-AES.
[0456] The results are shown in the following table:
TABLE-US-00009 Content storage Content high-pressure Mixture before container chamber U [mg] 26.8 2.98 20.96 Mo [mg] 8.5 7.35 0.08
[0457] Thus, the uranium content could be reduced by 89% and at the same time, 86% of the molybdenum content could be recovered. What is additionally important is the very small amount of Mo left in the high-pressure chamber, proving MoF.sub.6 to be virtually unaffected by the irradiation process.
Example 6—Preparation of OsF.SUB.6
[0458] Using the reaction system described in Example 1, OsF.sub.6 was prepared using the following materials and reaction conditions. [0459] Placing osmium powder on Monel carrier (total mass 206.8 mg) [0460] Inserting the substrate under argon counterflow into the reaction chamber [0461] Slowly evacuating the system in order to avoid the powder to be swirled up and slowly flushing it again with argon, repeating this process two more times, last time only evacuating without refilling the chamber with argon [0462] Heating the chamber to 100° C. in order to remove humidity absorbed on the surface of the osmium powder (the increased temperature and low pressure efficiently dry the powder) [0463] Switching off the heating and let the chamber cool down again to about 40° C. [0464] Filling the last Dewar vessel with liquid nitrogen first in order to bind remaining humidity [0465] Filling the first two Dewar vessels with liquid nitrogen (only cold trap one and two are used to recover the product of the reaction to increase its purity) [0466] Closing all MFC bypass valves. [0467] Closing all bypass valves of the cold traps [0468] Closing the bypass of the absorber and open the absorber valves [0469] Switching on the cooling water for the RPS (Remote Plasma Source) and the MPS (Microwave Power Supply), checking that it exceeds 4 l/min [0470] Setting the value for the Ar MFCs at the MFC Control Panel to 8 sccm [0471] Starting the RPS at the control computer, setting it to 3000 W [0472] Setting the value for the NF.sub.3 MFCs at the MFC Control Panel to 2 sccm [0473] Controlling through the sapphire window, whether the plasma ignited correctly [0474] Fluorination for about 75 minutes, after that time the osmium powder is completely consumed [0475] Pressure sensor 1: 1.60 mbar [0476] Pressure sensor 2: 1.242 mbar [0477] Maximum Temperature of the reaction chamber 74.1° C. (no forced cooling of the tube required) [0478] Shutting off the cold traps by closing their valves [0479] Removing the frigorific mixtures and letting the fluorides in the cold traps heat up [0480] Extracting the fluorides via the extraction ports and transferring them into a FEP tube cooled with liquid nitrogen.
Examples 7 to 16
[0481] Using similar conditions as set forth in Example 2, except for changes indicated in the table, the metal fluorides listed in the following were prepared:
TABLE-US-00010 Mass flow for obtained F containing mass flow Ex. Metal Fluoride Heating of Metal precursor carrier gas remarks 7 Mo MoF.sub.6 no heating 35 sccm 35 sccm 8 Ru RuF.sub.5 190° C. 2 sccm 14 sccm 9 Rh RhF.sub.3 2 sccm 8 sccm for RhF.sub.6 rapid RhF.sub.6 cooling necessary 10 W WF.sub.6 no heating 60 sccm 100 sccm 11 Re ReF.sub.6 no heating 60 sccm 100 sccm both substances ReF.sub.7 form simulta- neously at the given gas ratios. Separation by cold traps of different temperature possible. 12 Os OsF.sub.6 no heating 2 sccm 8 sccm 13 Ir IrF.sub.6 no heating 60 sccm 0 sccm (although heating may be beneficial) 14 Pt PtF.sub.4 no heating 54 sccm 10 sccm Use of PtF.sub.6 nickel/Monel sample holder favored due to atomic fluorine spillover effect; for PtF.sub.6 rapid cooling necessary 15 U UF.sub.6 no heating 25 sccm 25 sccm 16 Te TeF6 no heating 8 sccm 8 sccm