Method for solidifying an aqueous solution of thorium nitrate
The process concentrates thorium nitrate solutions to form pentahydrate salt, addressing the need for stable storage and flexible operation by solidifying and storing thorium nitrate directly, reducing space and operational complexity.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ORANO MED MANUFACTURING
- Filing Date
- 2025-11-05
- Publication Date
- 2026-05-15
AI Technical Summary
Existing processes for solidifying thorium nitrate solutions, such as the Krystal process, require transferring solidified crystals and are inflexible, while industrial production of thorium nitrate generates large volumes of aqueous effluents that need stable storage and reduced space requirements.
A process involving concentration of thorium nitrate solution through evaporation to form pentahydrate salt, followed by cooling in a container to solidify it, allowing flexible operation and direct storage in the same container.
Enables stable storage of thorium nitrate in a solid form, reducing space requirements and providing flexibility in operation by adjusting parameters, while avoiding solid transfers.
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Abstract
Description
[0001] Description
[0002] Title: Process for solidifying an aqueous solution of thorium nitrate
[0003] technical field
[0004] The invention relates to the field of solidification of aqueous solutions.
[0005] More specifically, the invention relates to a process for solidifying an aqueous solution of thorium nitrate, Th(NOs)4, enabling the transformation of this aqueous solution into a solid product, essentially consisting of thorium nitrate pentahydrate, which can subsequently be redissolved in water to form a new aqueous solution of thorium nitrate.
[0006] The invention thus makes it possible to store an aqueous solution of thorium nitrate in a solid form, less bulky and more stable over a long storage period than the liquid form, pending later use.
[0007] Prior art
[0008] Lead-212, which is used in the development of radiopharmaceuticals for the treatment of cancers by targeted alpha therapy, is part of the radioactive decay chain of thorium-232, which represents the major component of natural thorium extracted from ores such as monazite or thorite.
[0009] Thus, lead-212 can be obtained by radioactive decay of thorium-232 and / or its descendants.
[0010] The production of lead-212 and, upstream, that of radium-224 and thorium-228 can be carried out using what is called a "generator", that is to say a chromatography column which typically includes a solid stationary phase on which is selectively fixed the radioisotope whose decay is sought (also called parent radioisotope) and which is regularly washed with a liquid phase allowing to elute and, therefore, to recover the radioisotope(s) produced by this decay (also called daughter radioisotope(s)). To prepare a generator for the production of thorium-228 and therefore comprising radium-228 as the parent radioisotope, it is known to circulate an aqueous solution of natural thorium nitrate, comprising both thorium-232 and radium-228, in a column whose solid stationary phase is capable of retaining radium selectively with respect to thorium.
[0011] Thus, radium-228 attaches to the stationary phase while thorium-232 remains in solution and the volume of solution flowing out of the column is unchanged compared to the volume of solution that was put into circulation at the column inlet.
[0012] The production of thorium-228 on an industrial scale therefore generates large volumes of aqueous effluents which it is desirable to retain since they contain all of the thorium nitrate which can still be used, hence the interest in solidifying these effluents so as, on the one hand, to reduce as much as possible the space required for their storage over a long period of time and, on the other hand, to give the thorium nitrate which they contain stability over this same period of time.
[0013] In a completely different context, namely the industrial production of pure thorium nitrate from uranothorianite ore, C. Braun et al. (CEA report no. 1017, 1958, 14 pages, https: / / inis.iaea.org / collection / NCLCollectionStore) described a process for solidifying an aqueous thorium nitrate solution, known as the Krystal process. The principle of this process is to create and then grow thorium nitrate crystals in an upward stream of solution and to extract them from this stream by dewatering as soon as they reach a sufficient size. More precisely, the aqueous thorium nitrate solution is forced into circulation in a crystallizer where it is heated and projected towards the top of the crystallizer, which is under a vacuum of 500 mm Hg. This causes rapid boiling and local supersaturation of the solution.Thorium nitrate crystals form and grow, and an upward flow of solution sorts them by size, with the largest crystals settling at the bottom of the crystallizer where the velocity is higher. The crystal suspension is drawn from the bottom of the crystallizer and forced onto a centrifuge. The centrifuge material is recycled back into the crystallizer to continue the process. Patent application CN 111 024463 A describes a process for preparing a mixed, multi-element standard solution for the analysis of nuclear fuels. During this preparation, some of the raw materials used may undergo purification.For thorium nitrate, the latter includes dissolving commercial thorium nitrate in nitric acid, successive extractions to separate the uranium and transfer the thorium to the organic phase, cleaning the organic phase, aqueous back-extraction, degreasing to remove traces of oil, then concentration and crystallization to obtain high-purity thorium nitrate tetrahydrate.
[0014] Description of the invention
[0015] The invention aims to propose a process for solidifying an aqueous solution of thorium nitrate Th(NOs)4 based on a principle other than that of the Krystal process.
[0016] The process of the invention comprises the steps of: a) concentration of the aqueous solution by circulation in an evaporator comprising an inlet for supplying it with aqueous thorium nitrate solution, an outlet for removing the aqueous solution from the evaporator, and in which there exists a temperature gradient from a temperature 01 between 50 °C and 70 °C at which the aqueous thorium nitrate solution is brought_at the inlet of the evaporator to a temperature 02 between 130 °C and 160 °C which the aqueous thorium nitrate solution reaches_at the outlet of the evaporator, thereby establishing a concentration gradient of the aqueous solution between the inlet and outlet of the evaporator leading to a concentrated aqueous solution of thorium nitrate pentahydrate of formula Th(NO3)4.5H2O at the outlet of the evaporator; and b) transfer of the aqueous solution thus concentrated from the outlet of the evaporator to a container in which the aqueous solution is allowed to cool, whereby the aqueous solution solidifies in the container by crystallization of thorium nitrate pentahydrate.
[0017] Thus, according to the invention, the solidification of the aqueous solution of thorium nitrate is obtained by concentrating this solution by evaporation until reaching a concentration of thorium nitrate for which it is in the form of pentahydrate salt - salt which is liquid at the highest temperature (62) of the thermal gradient prevailing in the evaporator but which is solid at room temperature - so that the transfer of the aqueous solution thus concentrated in thorium nitrate pentahydrate into a container where it is allowed to cool allows this salt and, consequently, the aqueous solution which contains it to solidify.
[0018] According to the invention, the aqueous solution of Th(NO3)4 can comprise from 150 g / L to 450 g / L of Th(NO3)4. Advantageously, it comprises from 230 g / L to 260 g / L of Th(NO3)4.
[0019] To do this, it can be concentrated beforehand or, conversely, diluted before entering the evaporator.
[0020] Furthermore, depending on its origin, the aqueous solution of Th(NO3)4 may include nitric acid, for example at a level of 0.05 mol / L to 0.5 mol / L.
[0021] When feeding the evaporator, this solution is preferably at ambient temperature, typically between 15°C and 30°C, depending on the temperature in the building where the process is implemented. The temperature of the aqueous Th(NO3)4 solution when it feeds the evaporator, or in other words, when it enters the evaporator, should not be confused with the temperature 0i, which, as previously stated, is the temperature at the evaporator inlet and is between 50°C and 70°C.
[0022] The O2 temperature, which prevails at the outlet of the evaporator, is preferably 145 °C ± 15 °C and, even better, 140 °C ± 5 °C.
[0023] According to the invention, the transfer of the concentrated aqueous solution of Th(NO3)4.5H2O to the container – or step b) – is preferably carried out by means of a pipe that is connected to both the evaporator and the container. Preferably, this transfer includes an overflow of the aqueous solution from the evaporator into the pipe.
[0024] More specifically, this overflow is an overflow of the concentrated aqueous solution of Th(NO3)4.5H2O from the evaporator into the pipe, the evaporator comprising at its outlet a device for creating this overflow. According to the invention, the process advantageously further comprises purging the aqueous solution circulating in the evaporator with dry air, i.e., with a relative humidity between 1% and 10%, ideally between 2% and 5%, the air being purged counter-currently to the aqueous solution. This dry air advantageously has a temperature between 130°C and 160°C, preferably 145°C ± 15°C and, even better, 140°C ± 5°C. The sweeping thus allows the water vapor resulting from the evaporation of the aqueous solution of Th(NOs)4 to be evacuated from the evaporator and, simultaneously, helps to prevent any crystallization of Th(NO3)4.5H2O in the pipe ensuring the transfer of the aqueous solution to the container.
[0025] Preferably, the process also includes depressurizing the evaporator, this depressurization being preferably between 5 hPa and 50 hPa and, even better, 15 hPa ± 10 hPa.
[0026] When the transfer of the concentrated aqueous solution of Th(NO3)4.5H2O to the container is ensured by a pipe connected to both the evaporator and the container, then it is also possible to provide for:
[0027] - on the one hand, a sweep of dry air at the top of the container so as to avoid, there too, crystallization of Th(NO3)4.5H2O during its transfer, in which case this dry air is swept in this duct counter-current to the aqueous solution concentrated in Th(NO3)4.5H2O and preferably has the same characteristics of humidity and temperature as the dry air sweeping the evaporator, and
[0028] - on the other hand, a depressurization of the container and the pipe, in which case this depression is of the same degree as that prevailing in the evaporator.
[0029] Preferably, the evaporator is a double-jacketed tube, that is, comprising an inner jacket through which the aqueous Th(NOs)4 solution circulates and an outer jacket which, together with the inner jacket, delimits a space through which a heat transfer fluid, for example oil, circulates counter-currently to the Th(NOs)4 aqueous solution. The heat transfer fluid has a temperature of between 170 °C and 220 °C at its inlet to the evaporator, and preferably between 185 °C and 195 °C. Also preferably, the container into which the concentrated Th(NO3)4·5H2O solution is transferred also serves to store the solidified aqueous solution. This container is, for example, a drum or barrel, preferably made of stainless steel.
[0030] In addition to enabling the solidification of the aqueous solution of Th(NO3)4 in the form of its pentahydrated salt, the process of the invention offers numerous advantages, including, in particular, those of:
[0031] - to avoid any transfer of a product in solid form, unlike the Krystal process, since, according to the invention, the solidification of the aqueous solution takes place in a container that can also serve as a storage container; and
[0032] - to be flexible in that, on the one hand, it can be easily stopped (by stopping the supply and heating of the evaporator with aqueous Th(NO3)4 solution) and then restarted (by reheating and then refilling the evaporator) according to requirements and, on the other hand, the solidification rate of the aqueous Th(NOs)4 solution can easily be adapted to needs by adjusting the operating parameters. Other characteristics and advantages of the process of the invention will become apparent from the supplementary description that follows and refers to the attached figure.
[0033] It goes without saying that this additional description is given as an illustration of the process of the invention and in no way as a limitation of this object.
[0034] Brief description of the figure
[0035] [Fig.1] schematically represents an example of an installation specifically designed for implementing the process of the invention on an industrial scale.
[0036] In this figure, the different elements of the installation are deliberately represented on a non-uniform scale in order to make the figure more legible.
[0037] Furthermore, aqueous flows are represented by a single line while gaseous flows are represented by a double line.
[0038] Detailed description of a particular implementation method The following relates to an example of an installation specially designed for the implementation of the process of the invention on an industrial scale as well as to an example of implementation of this process.
[0039] Facility :
[0040] As can be seen in Figure 1, the installation, labeled 1 in this figure, comprises the following main components:
[0041] - an evaporation tube 10 to concentrate the aqueous solution of Th(NO3)4 to be solidified;
[0042] - a solidification drum 30 to receive and solidify the aqueous solution of Th(NO3)4 concentrated in Th(NO3)4.5H2O after its exit from the evaporation tube 10, this drum also serving as a storage drum for the solidified aqueous solution;
[0043] - a container 40, for example of the tank type, to supply the evaporation tube 10 with aqueous solution of Th(NO3)4; and
[0044] - a unit 50 for the treatment of gaseous effluents produced during the implementation of the process, this unit being shown in Figure 1 within a dotted frame.
[0045] The evaporation tube 10, the solidification drum 30 and the feeding tank 40 are preferably made of stainless steel.
[0046] The evaporation tube 10, or tube 10, is a double-walled tube, the inner wall 11 being dedicated to the circulation of the aqueous solution of Th(NO3)4 and the outer wall 12 delimiting with the inner wall 11 a space dedicated to the circulation of a heat transfer fluid for the establishment, under operating conditions, of a thermal gradient in the inner wall.
[0047] The inner envelope 11 of the tube 10 has:
[0048] - a first end 13 at which the inner casing 11 is connected to the bottom of the tank 40 by a pipe 14, for supplying the tube 10 with aqueous solution of Th(NOs)4 and which will therefore be called "inlet 13" in what follows, and
[0049] - a second end 15 at which the inner envelope 11 includes a half-dam, which extends perpendicularly to the longitudinal axis of the tube 10 up to the mid-diameter of this envelope, as well as a chute 16 which, under operating conditions, allows the flow of concentrated aqueous ThjNOsh solution, which exceeds the height of the half-dam and which flows out of the tube 10 by overflow, to be conducted into the solidification drum 30; this second end will therefore be called "outlet 15" in what follows.
[0050] The inner envelope 11 also includes three probes, respectively 18a, 18b and 18c, allowing the temperature of the aqueous solution of Th(NOs)4 to be measured very close to the inlet 13 of this envelope, halfway through this envelope and very close to the outlet 15 of said envelope.
[0051] The outer envelope 12 of the tube 10 is also provided with an inlet 19 and an outlet 20 but for the circulation of the heat transfer fluid and whose direction is reversed with respect to that of the inlet 13 and outlet 15 of the inner envelope 11, the heat transfer fluid circulating, in fact, in the tube 10 in the opposite direction to the aqueous solution of Th(NO3)4.
[0052] The heat transfer fluid is, for example, an oil.
[0053] Each of the inlet 19 and outlet 20 of the outer casing 12 is connected by a pipe, respectively 21 and 22, to a system 23, called the heating unit, which heats the heat transfer fluid and regulates the temperature of this fluid according to the temperature that the aqueous solution of Th(NOs)4 must present at the outlet 15 of the inner casing 11. To do this, the pipes 21 and 22 are equipped with probes respectively 25 and 26, which measure the temperature of the heat transfer fluid before its entry and after its exit in the outer casing 12. These pipes can also be equipped with probes (not shown in Figure 1) which measure the pressure and flow rate of the heat transfer fluid.
[0054] Furthermore, the hot group 23 can be connected to a system (not shown in Figure 1), called a cold group, which allows the heat transfer fluid of the hot group to be cooled quickly in the event of degraded operation and thus ensures the safety of the tube 10.
[0055] As seen in Figure 1, the tank 40, which is used to supply, via the pipe 14, the tube 10 with aqueous solution of Th(NOs)4 and which is therefore intended to be filled with this solution, includes a filling mouth 41 which is, for example, connected to a reservoir used to store the aqueous solution of Th(NOs)4, an agitation device 42, for example of the mechanical agitator type, to ensure the homogeneity of the aqueous solution of Th(NOs)4 before its entry into the tube 10 as well as a sampling device 43 to measure the concentration of Th(NO3)4, the acidity and the density of the solution.
[0056] This tank also includes, at its upper part, a vent line 44 which connects to the gaseous effluent treatment unit 50.
[0057] The pipe 14 is equipped not only with a pump 45 to ensure the circulation of the aqueous solution of Th(NO3)4 from the bottom of the tank 40 to the inlet 13 of the tube 10 but also, downstream of this pump (in the direction of circulation of the aqueous solution of Th(NO3)4), with a filter 46 such as a stainless steel mesh filter, for example with a mesh size of 25 LIIYI, to retain impurities that may be present in this solution before it enters the tube 10. A filter (not shown in Figure 1) may also be provided upstream of the pump 45 (in the direction of circulation of the aqueous solution of Th(NO3)4).
[0058] The solidification drum 30, or drum 30, includes, at its top, a lid 31, advantageously with a bellows, allowing it to be closed hermetically but which includes at least two fittings:
[0059] - a first fitting for its connection to the 16mm trunking, and
[0060] - a second fitting for its connection to a pipe 32 intended to carry dry and hot air to the top of the drum from a heater 33, itself supplied with dry air by a pipe 34 connected to a reservoir 35, for example of the tank type, which can, for example, be connected to a compressed air network.
[0061] This configuration allows, under operating conditions:
[0062] - on the one hand, to carry the water vapor, which is produced in the inner shell 11 of the tube 10, towards the inlet 13 of this shell at the level of which this water vapor is evacuated out of the shell by a vent line T1 towards the gaseous effluent treatment unit 50; and
[0063] - on the other hand, to establish a sweep of hot air in the sky of the barrel 30, then from this sky to the entrance 13 of the inner envelope 11 of the tube 10 with a crossing of this tube and, by the same token, to prevent the thorium nitrate from crystallizing in these elements.
[0064] Contrary to the representation given by figure 1, on which the circulation of hot air between the lid 31 of the drum 30 and the outlet 15 of the inner envelope 11 of the tube 10 has been deliberately represented, for reasons of readability, as if it were ensured by a pipe running alongside the chute 16 while being physically isolated from it, this circulation is, preferably, carried out via the chute 16 itself, in which case the hot air circulates in the head of this chute against the current of the aqueous solution of Th(NOs)4, then in the head of the tube 10.
[0065] Alternatively, it is also possible to provide that the chute 16 is included in a coaxial conduit with it, which would be connected, on the one hand, to the cover 31 of the drum 30 and, on the other hand, to the outlet 15 of the inner casing 11 of the tube 10 and in which hot air would circulate, thus surrounding the chute 16 from its junction to the cover 31 to its junction to the inner casing 11.
[0066] In all cases, a probe (not shown in Figure 1), with which the chute 16 is equipped or, where applicable, the conduit in which this chute is included, makes it possible to monitor and regulate the temperature of the hot air which circulates between the lid 31 of the drum 30 and the outlet 15 of the inner jacket 11 of the tube 10.
[0067] The drum 30 is equipped with instrumentation 36 allowing the monitoring of parameters such as its fill level and the pressure and temperature levels prevailing at its top.
[0068] The solidification drum 30 is placed on a roller conveyor 37 equipped at the drum with a weighing device, for example of the balance type, to allow monitoring of the evolution of its mass related to its filling with Th(NOs)4 salt.
[0069] Other connections may be provided at the level of the lid 31 of the drum 30, for example for instrumentation such as an endoscope or videoscope, allowing visual inspection of the inside of the drum, or for any other additional instrumentation.
[0070] As can be seen in Figure 1, the gaseous effluent treatment unit 50, or unit 50, comprises:
[0071] - a demister 51 where the vent line Tl is connected to trap thorium nitrate droplets that may be present in the water vapor brought by this vent line from tube 20;
[0072] - a condenser 53 to condense this water vapor;
[0073] - a container 56, for example of tank type, to collect the condensates from the condenser 53;
[0074] - a bank of filters 63, for example composed of 4 activated carbon filters mounted in series or in parallel, to trap the radon-220 released by the aqueous solution of Th(NO3)4 throughout the installation;
[0075] - a HEPA (High Efficiency Particulate Air) filter 65 to purify the gaseous effluents from the filter bank 63; and
[0076] - a fan 67 to extract the gaseous effluents from the installation and direct them to a chimney 70.
[0077] The demister 51 is connected to the condenser 53 by a pipe 52 while this condenser is itself connected, on the one hand, to the tank 56 by a pipe 54 and, on the other hand, to the filter bank 63 by a pipe 55.
[0078] The tank 56 includes a filling mouth 57, which is connected to the pipe 54, an agitation device 58, for example of the mechanical agitator type, to ensure the homogeneity of the condensates collected in this tank, as well as a sampling device 59 to measure the pH, density, nitrate ion concentration and the activity of radioelements such as thorium-232, radium-228 and thorium-228.
[0079] At its lower part, the tank 56 is connected by a pipe 60 to a pump 61 allowing it to be emptied.
[0080] At its upper part, the tank 56 is connected to the filter bank 63 by a pipe 62 onto which the vent line 44 from the tank 40 is connected. Thus, with this configuration, all the radon-220 released by the aqueous solution of Th(NOs)4 in the various elements of the installation intended to contain this solution is trapped by the filter bank 63.
[0081] This bank of filters is connected to the THE 65 filter by a pipe 64 and the THE 65 filter is itself connected to a fan 67 by a pipe 66.
[0082] An air inlet 68 on the duct 66 ensures that the fan 67 operates at a constant flow rate. The unit 50 also includes, between each piece of equipment, pressure and temperature measuring devices (not shown in Figure 1) allowing these parameters to be monitored under operating conditions.
[0083] As shown in Figure 1, pipes 14, T1, 32, 34, 60, 62, and 68 are fitted with valves, respectively VI, V2, V3, V4, V5, V6, and V7, allowing their opening, closing, or flow rate adjustment. These valves may be, as applicable, two-way or three-way valves, manual or automatic, even though they are all shown in Figure 1 as two-way valves.
[0084] Implementation of the process:
[0085] The first step is to establish:
[0086] - on the one hand, a depression, advantageously between 5 hPa and 25 hPa, in the drum 30, in the inner casing 11 of the tube 10, as well as in the tanks 40 and 56, by starting the fan 67 and opening the valves V2 and V6, the airflow necessary for the operation of the fan 67 and the balancing of the depression being ensured by an adjustment of the valve V7; and
[0087] -on the other hand, a sweep of dry and hot air, preferably with a humidity between 1% and 10%, ideally between 2% and 5%, and a temperature between 130°C and 160°C, in the roof of the drum 30, in the roof of the chute 16 (or, where applicable, in the conduit in which this chute is included) and in the roof of the tube 10, by starting the heater 33 and opening the valve V4, the flow rate of the sweep air being regulated by means of the valve V3.
[0088] Opening valve VI and starting pump 45 supply tube 10 with an aqueous solution of Th(NOs)4. Simultaneously, the heat transfer fluid is heated by the heating unit 23 until probe 18c indicates that temperature 02 (which, it should be noted, is the highest temperature in the temperature gradient expected to exist within the inner wall 11 of tube 10 under operating conditions) is reached. This temperature 02 is then maintained throughout the process. The flow rate of pump 45 during tube 10 filling is adjusted to reach 02 before overflow begins. Subsequently, pump 45 is adjusted to achieve the target flow rate of 25 L / h while simultaneously adjusting the temperature 03 of the heat transfer fluid to maintain the target temperature 02 at the outlet of tube 10.
[0089] When the aqueous solution of Th(NO3)4 enters the inner envelope 11 of the tube 10, it is brought to a temperature between 50 °C and 70 °C at the probe 18a, then its temperature increases as it circulates in this envelope until it reaches a temperature between 130 °C and 160 °C, preferably 140 °C ± 5 °C and, ideally, 135 °C at the probe 18c, thereby establishing a concentration gradient of this aqueous solution of ThjNOsh by evaporation in the inner envelope 11 of the tube 10.
[0090] At the outlet 15 of the inner envelope 11 of the tube 10, the flow of concentrated aqueous solution of ThjNOsh thus produced, in which thorium nitrate is in the form of pentahydrated salt, flows out of this envelope and, therefore, out of the tube 10 by overflow and joins the drum 30 via the chute 16, which can be at room temperature but which is preferably equipped with a heat-insulating jacket (not shown in figure 1). Simultaneously, the water vapor resulting from the evaporation of the aqueous solution of Th(NOs)4 is drawn out of the inner jacket 11 of the tube 10 by the hot air flow which sweeps the top of this jacket and the water vapor / air mixture joins the demister 51 via the vent line Tl, then the condenser 53. The condensate resulting from the condensation of the water vapor is collected in the tank 56 while the air joins the filter bank 63, then the THE filter 65 before being extracted from the installation by the fan 67.
[0091] The filling of drum 30 is monitored using instrumentation 36 and the weighing device integrated into the drum. When the maximum fill level of drum 30 is reached, it is replaced with an empty drum. The full drum is conveyed (by means of roller conveyor 37) to a designated cooling area, whereby the concentrated aqueous solution solidifies within the drum through the solidification of the salt.
[0092] To replace the full drum, we stop:
[0093] - the supply of aqueous Th(NOs)4 solution to tube 10 by stopping pump 45 and closing valve VI, which immediately stops the overflow, and - the heating of the purge air from the full drum by stopping heater 33, and
[0094] - heating of tube 10 by modifying the temperature setpoint of the heat transfer fluid of the hot group 23.
[0095] The aqueous solution of Th(NOs)4 present in tube 10 solidifies.
[0096] Once a new drum 30 is in place (using the roller conveyor 37), the process is restarted:
[0097] - heating the heat transfer fluid of the hot group 23 in order to re-dissolve the solidified salt in the evaporator 10;
[0098] - the heating of the sweep air heater 33, and
[0099] - supplying tube 10 with aqueous solution of Th(NOs)4.
[0100] It is therefore possible to implement the process continuously or almost continuously if desired, the only interruptions imposed by this implementation being related to the need to replace the solidification drum 30 when it is full (apart, of course, from interruptions that could be imposed by maintenance operations of the installation).
[0101] The implementation of the process just described involves:
[0102] - an aqueous solution comprising 250 g / L of thorium and 0.1 mol / L of nitric acid,
[0103] - an evaporation tube 110 cm in diameter and 2.4 meters long,
[0104] - a supply flow rate of 25 L / h for this tube with aqueous Th(NOs)4 solution,
[0105] - an O2 temperature of 135 °C,
[0106] - a pressure drop of 15 hPa, and
[0107] - a sweeping air of 140 °C, made it possible to produce 15 kg / h of thorium nitrate pentahydrate or 670 g of thorium nitrate solidified per L of aqueous feed solution of Th(NOs)4.
[0108] Reference cited
[0109] C. Braun et al., CEA report no. 1017, 1958, 14 pages, https: / / inis.iaea.org / collection / NCLCollectionStore Patent application CN 111 024463 Published on April 17, 2020
Claims
Demands 1. A process for solidifying an aqueous solution of thorium nitrate Th(NO3)4, comprising the steps of: a) concentrating the aqueous solution by circulation in an evaporator (10) comprising an inlet (13) for supplying it with aqueous thorium nitrate solution, an outlet (15) for removing the aqueous solution from the evaporator, and in which there exists a temperature gradient from a temperature 0i between 50 °C and 70 °C at which the aqueous thorium nitrate solution is brought to the inlet of the evaporator to a temperature 02 between 130 °C and 160 °C which the aqueous thorium nitrate solution reaches at the outlet of the evaporator, thereby establishing a concentration gradient of the aqueous solution between the inlet and outlet of the evaporator, leading to a concentrated aqueous solution of thorium nitrate pentahydrate of formula Th(NO3)4.5H2O at the outlet of the evaporator; and b) transfer of the aqueous solution thus concentrated from the outlet of the evaporator (10) to a container (30) in which the aqueous solution is allowed to cool, whereby the aqueous solution solidifies in the container by crystallization of thorium nitrate pentahydrate.
2. A process according to claim 1, wherein the aqueous thorium nitrate solution comprises from 150 g / L to 450 g / L and, preferably, from 230 g / L to 260 g / L of thorium nitrate at its inlet to the evaporator.
3. A process according to claim 1 or claim 2, wherein the aqueous thorium nitrate solution comprises from 0.05 mol / L to 0.5 mol / L of nitric acid.
4. A method according to any one of claims 1 to 3, wherein the aqueous thorium nitrate solution is at room temperature when it feeds the evaporator.
5. A method according to any one of claims 1 to 4, wherein the temperature 02 is 140 °C ± 5 °C.
6. A method according to any one of claims 1 to 5, wherein the transfer of the concentrated aqueous solution of thorium nitrate pentahydrate to the container (30) is carried out by means of a conduit (16) which is connected to both the evaporator (10) and the container (30).
7. A method according to claim 6, wherein the transfer of the concentrated aqueous solution of thorium nitrate pentahydrate to the container (30) includes an overflow of the aqueous solution from the evaporator into the conduit (16).
8. Method according to claim 7, wherein the overflow of the concentrated aqueous solution of thorium nitrate pentahydrate is an overflow of this solution from the evaporator (10) into the conduit (16).
9. A method according to any one of claims 1 to 8, further comprising a dry air sweep of the aqueous solution circulating in the evaporator (10), the dry air being swept in the opposite direction to the aqueous solution.
10. A method according to any one of claims 6 to 8, further comprising a dry air sweep at the top of the container (30) and in the conduit (16), the dry air being swept in the conduit counter-current to the concentrated aqueous solution of thorium nitrate pentahydrate.
11. A method according to claim 9 or claim 10, wherein the dry air has a temperature between 130 °C and 160 °C, preferably 140 °C ± 5 °C.
12. A method according to any one of claims 1 to 11, further comprising depressurizing the evaporator (10).
13. A method according to any one of claims 6 to 8 and 10, further comprising depressurizing the container (30), the pipe (16), and the evaporator (10).
14. A method according to claim 12 or claim 13, wherein the depressurization is between 5 hPa and 50 hPa, preferably 15 hPa ± 10 hPa.
15. A method according to any one of claims 1 to 14, wherein the evaporator (10) is a tube which includes an inner shell (11) in which the aqueous thorium nitrate solution circulates and an outer shell (12) delimiting with the inner shell a space in which a heat transfer fluid circulates counter-currently to the circulation of the aqueous thorium nitrate solution, the heat transfer fluid having a temperature 03 between 170 °C and 220 °C and, even better, between 185 °C and 195 °C at its inlet into the evaporator.
16. A method according to any one of claims 1 to 15, wherein the container (30) serves as an additional storage container for the solidified aqueous solution.