Patent Application
20250034678
The present invention relates to the field of radionuclides. More in particular, the present invention relates to a system and method for separating radionuclides, such as 213Bi radionuclides.
The use of high-purity radionuclides has become increasingly crucial for diagnosis and medical treatment. In particular, targeted alpha therapy is a promising technology to treat various cancers and other diseases via alpha particle emissions. Compared with beta particles and Auger electrons, alpha particles are more effective ionization agents with a lower penetration range (50-100 m) and a higher linear energy transfer (50-230 keV/m), which maximizes the destruction of malignant cells with minimal damage to the surrounding normal tissues.
Recently, 213Bi has emerged as a particularly promising alpha-emitter because of its high specific activity, effective half-life (t1/2=45.6 min), high alpha-decay ratio, and absence of long-lived intermediates. Clinically, 213Bi has been used to investigate the treatment of various cancers such as leukemia, malignant melanoma, brain tumors, and neuroendocrine tumors. In the prior art, the relatively long-lived parent nuclide 225Ac (t1/2=9.92 d) has been applied as the direct source for the production of its short-lived daughter nuclide 213Bi via 225Ac/213Bi generators.
With a radionuclide generator, an effective radiochemical separation of decaying parent and daughter radionuclides may be performed such that the daughter is obtained in high radionuclidic and radiochemical purity. Typically, in a radionuclide generator system, a relatively long-lived radionuclide is used as the parent radionuclide; this decays to a daughter radionuclide with a shorter half-life. There are many advantages related to radionuclide generators, including 1) they may ensure the clinical availability of short-lived daughter radionuclides without relying on the production capability of nuclear reactors or accelerators; 2) they may provide short-lived daughter radionuclides with a high specific activity and in a carrier-free form, at a low cost; and 3) they may provide short-lived daughter radionuclides for medical application in hospitals that are located far away from nuclide production facilities. For example, the radionuclide generator may be present at the hospital, enabling generation of relatively pure samples of daughter radionuclides at the location where they are needed.
Two specific types of radionuclide generators known in the art are the direct radionuclide generators and the inverse radionuclide generators.
In a typical direct radionuclide generator, the column is filled with sorbents, i.e., sorbent material on which the parent isotope is adsorbed and from which the daughter isotope can be eluted at regular time intervals using different eluents. The sorbent material preferably has a high affinity for the parent isotope, and the generator eluate must be free from the parent isotope. Furthermore, the sorbent material in the radionuclide generator should promote a high and reliable (i.e., reproducible) yield, and a high purity of the daughter radionuclide to meet the increasing need for alpha-emitters in clinical studies.
In the inverse radionuclide generator system, the parent radionuclide is stored in a solution—typically a mixture comprising the parent radionuclide and a daughter radionuclide formed by the decay of the said parent radionuclide—, so that the effect of radiolytic damage on the performance of the sorbent material is reduced. As described in MCALISTER, D. R., and HORWITZ, E. P. Automated two column generator systems for medical radionuclides. Applied Radiation and Isotopes, 2009, 67 (11), 1985-1991, in the inverse radionuclide generator system, the solution, i.e., the mixture comprising daughter and parent radionuclides, is typically eluted through a chromatographic column specific for the desired daughter radionuclide (primary separation column, PSC). The daughter nuclide is retained on the PSC, while the parent passes through unretained. A small volume of rinse solution is then passed through the PSC to ensure near-complete recovery of the parent nuclide in an eluate. This eluate comprising the parent nuclide is then stored for further ingrowth of the desired daughter and future processing. The daughter nuclide is stripped from the PSC, and this strip solution is passed through a second column (guard column), which is specific for the parent nuclide. Thereby, the guard column may provide additional decontamination of the parent radionuclide from the daughter product, further improving the separation of the daughter radionuclide from the parent radionuclide, and thus resulting in a higher purity of daughter product.
Several sorbent materials (that are also known in the art as “resins”), are known in the art that may be used in the above described direct and/or inverse radionuclide generator systems. These sorbent materials typically, however, suffer from several disadvantages. For example, the separation properties of organic resins (such as the commercially available AG MP-50 and UTEVA) are affected by radiolytic damage, leading to a short lifetime on the column (the lifetime for AG MP-50 column loaded 100 mCi 225Ac was concluded to be no more than one day) (VASILIEV, A. N., et al. Radiation stability of sorbents in medical 225Ac/213Bi generators. Solvent Extraction and Ion Exchange, 2021, 39 (4), 353-372). Several approaches have been proposed to overcome the (localized) radiolytic damage to the sorbent. US US2005/0008558A1 describes a method to distribute the radionuclide more homogeneously in the volume of packed resin, by adding complexing agents which avoid the concentration of the radionuclide in specific parts of the column. However, this approach is based on the use of highly concentrated acids, which might also impact the properties of the resin.
Another example of a sorbent is silica-based materials with impregnated or grafted functional groups. However, silica is leaching at low pH (typically pH<2) and may hence be unstable (YANTASEE, W., et al. Selective capture of radionuclides (U, Pu, Th, Am and Co) using functional nanoporous sorbents. Journal of hazardous materials, 2019, 366, 677-683; ABBASI, W. A., and STREAT, M. Sorption of uranium from nitric acid solution using TBP-impregnated activated carbons. Solvent extraction and Ion exchange, 1998, 16 (5), 1303-1320). Furthermore, silica-based resin structure was found to be slightly more affected by the radiation than resin comprising functional groups (VASILIEV, A. N., et al. Radiation stability of sorbents in medical 225Ac/213Bi generators. Solvent Extraction and Ion Exchange, 2021, 39 (4), 353-372). Finally, the 213Bi yield is relatively low (67-72%) for Isolute SCX-2 and Isolute SCX (MOORE, M. A., et al. The Performance of two silica based ion exchange resins in the separation of 213Bi from its parent solution of 225Ac. Applied Radiation and Isotopes, 2018, 141, 68-72).
As a further example, sorbent material may comprise zirconia-based materials.
Disadvantages comprise leaching of the components of materials, e.g., T-39 (96% ZrO2 and 4% Y2O3) in strong acid solutions (VASILIEV, A. N., et al. 225Ac/213Bi generator based on inorganic sorbents. Radiochimica Acta, 2019, 107 (12), 1203-1211). Furthermore, there may be a decrease of the 213Bi yield due to the accumulation of sorbent dissolution products in the solution: after 25 elutions, 213Bi elution yield decreased to 50%. Such a decrease may not be acceptable for generator applications. In addition, it was found that 0.5-1% of 225Ac per elution were lost with the rinsing solution.
As a final example, PNNL (Pacific Northwest National Laboratory) has disclosed a Bi-generator with organic anion exchange resin (VASILIEV, A. N., et al. Radiation stability of sorbents in medical 225Ac/213Bi generators. Solvent Extraction and Ion Exchange, 2021, 39 (4), 353-372; US005749042A). However, the generated 213Bi sample, i.e., 213Bi eluate, appears to contain an impurity of 225Ac, that is about 0.1% of its initial activity. Furthermore, 2-3% of the 225Ac is lost every milking with washing solution. Finally, the sorbent suffers from radiolytic damage.
There is thus still a need in the art for devices and methods that address at least some of the above problems.
It is an object of the present invention to provide suitable materials, apparatus or methods for separating radionuclides.
The above objective is accomplished by a method and apparatus according to the present invention.
It is an advantage of embodiments of the present invention that the sorbent material may be mechanically, chemically, and radiolytically stable. It is an advantage of embodiments of the present invention that the sorbent material may not suffer from leaching issues. It is an advantage of embodiments of the present invention that the sorbent material may have a long lifetime. It is an advantage of embodiments of the present invention that the sorbent material may be used to separate high activity 225Ac/213Bi. It is an advantage of embodiments of the present invention that the sorbent material may be used to obtain a high 213Bi yield.
In a first aspect, the present invention relates to a radionuclide separating system for separating a daughter radionuclide from a parent radionuclide. The radionuclide separating system comprises an inlet for loading a liquid solution comprising the parent radionuclide onto a column. The radionuclide separating system further comprises the column, which comprises a sorbent material wherein the sorbent material is capable of interacting with the parent radionuclide and daughter radionuclide so as to allow selective desorption of the parent radionuclide and/or the daughter radionuclide at a different moment in time. Herein, the sorbent material is a carbon-based sorbent material. The radionuclide separating system further comprises an outlet for selectively obtaining said daughter radionuclide based on said selective desorption of the parent radionuclide and the daughter radionuclide. It is an advantage of embodiments of the present invention that the carbon-based sorbent material may be formed from an inert carbon material, which may provide good stability for the sorbent material. For example, carbon structures may have a high resistance against strong acid solutions (pH<2) in comparison with inorganic metal oxides. In addition, carbon structures with polycyclic aromatic rings may have higher radiation stability compared with organic resins.
In some embodiments, the carbon structures may have a good radiation stability compared to other organic sorbents, i.e. the carbon structures may have a higher half-value-dose than for most organic sorbents. The half-value-dose may be defined as the radiation dose at which 50% loss of exchange capacity for a given adsorbent occurs. A full definition of the half-value-dose may be found in technical report Radiation effects on ion exchange materials in BNL-50781 by Gangwer T E et al., Brookhaven National Lab., published on 1977 Nov. 1. In some embodiments, the carbon structures may have a half-value-dose of at least 10 MGy.
The inert carbon material may e.g. be inert with respect to radionuclides and solvents. It is an advantage of embodiments of the present invention that separation techniques for radionuclides are obtained wherein the column used in the separation process does not suffer from radiolytic damage or suffers less from radiolytic damage compared to existing columns. It is an advantage of embodiments of the present invention that the carbon-based sorbent material may be used to separate high activity 225Ac/213Bi (e.g., at least 100 mCi 225Ac) to meet the requirements in medical application due to its high radiation stability or the improved separation method.
Where in embodiments reference is made to carbon-based materials, reference may for example be made to inorganic carbon-based materials, for example, the unmodified (initial) carbon structures were produced by the pyrolysis of polymer or a polysaccharide at high temperature degrees, e.g. more than 300° C., e.g, more than 400° C., for example carbon-based materials having an H/C ratio (molar ratio) of less than 1, e.g. less than 0.9.
The column may be any column suitable for comprising the sorbent material. Typically, the sorbent material is comprised in a fluidic path between the inlet and the outlet. In embodiments, the column may be a chromatographic column, as is well-known in the art. The volume of the sorbent material may be any suitable volume and may be selected as suitable for the application envisaged. In some embodiments, a volume of the carbon-based sorbent material may, for example, be from 0.1 to 10 mL. Preferably, the amount of sorbent material that is packed in the column is as small as possible. Typically, the lower the bed volume of the column, the higher the concentration of isotope, i.e., daughter radionuclide, that can be obtained.
In embodiments, the carbon-based sorbent material comprises, e.g., substantially consists of, an active material, e.g., active carbon, with one or more compounds containing one or more functional groups. In embodiments, one or more functional groups may be grafted or impregnated. Preferably, the functional groups are grafted, which may result in good stability of the functional groups in the carbon-based sorbent material. It is an advantage of these embodiments that the sorption affinity may be specifically optimized for the parent radionuclide and/or for the daughter radionuclide. At the same time, these embodiments may also provide high radiolytic stability.
In embodiments, the one or more functional groups are selected from: one or more oxygen-containing groups, e.g., carboxyl, hydroxyl, carbonyl, or epoxide; and/or one or more sulfur-containing groups, e.g., sulfonic acid, sulfoxide, or sulfone; and/or one or more phosphorous-containing groups, e.g., phosphate, phosphinate, phosphonate, or phosphine oxide. In embodiments, the functional groups may be selected from: —COOH, —C—OH, —C═O, —PO4H, and —SO3H. It is an advantage of these embodiments that one or more functional groups can be used for tuning the interaction between the sorbent material and the radionuclides, and thus for tuning the radionuclide separating system. That is, one or more functional groups may be used to optimize the sorbent material for use in a direct radionuclide separating system, or in an inverse radionuclide separating system. Introduction of different functional groups (e.g., —COOH, —C—OH, —C═O, —PO4H, and —SO3H) may be used to tune the mechanism of interaction, e.g., with 213Bi and/or 225Ac metal ions, to obtain a sorbent material with suitable properties for a direct radionuclide separating system and/or for an inverse radionuclide separating system.
For example, functional groups may be used to tune an electrostatic interaction and/or an ion exchange of the carbon-based sorbent material with the nuclide. The electrostatic interaction and/or ion exchange may have a high sensitivity—and therefore, possibly, tunability—to the solution pH, the ionic strength and/or salt concentration. The electrostatic interaction and/or ion exchange mechanisms may be the dominant sorption mechanism for 225Ac, and also 213Bi can interact with such functional groups (e.g., —COOH, —C—OH, —C═O, —PO4H, and —SO3H). With respect to these mechanisms, the following functional groups have been found to have some particularly good properties: sulphonic acid groups, carboxylic acid groups, and bis(2-ethylhexyl) phosphate.
In another example, the functional groups may be used to achieve inner-sphere complexation of a radionuclide (e.g., parent nuclide and/or daughter nuclide) with a phosphate group (—PO4H), a carbonyl (—C═O), hydroxyl group (—C—OH), and carboxylic acid (—COOH). For example, as mainly 213Bi interacts, i.e., forms complexes, with these functional groups, 213Bi may have a stronger affinity, in this respect, compared to 225Ac.
In embodiments, the carbon-based sorbent material comprises one or more of: a pyrolyzed polymer or a polysaccharide, e.g., cellulose, cellulose derivatives, starch or phenolic resins; an activated carbon; a graphitic carbon nitride; a graphite carbon (that is, substantially consisting of carbon); and a carbon molecular sieve. In some embodiments, the carbon-based sorbent material substantially consists of one of these materials and possibly the functional groups. In some embodiments, the carbon-based sorbent material is an activated carbon or a carbon molecular sieve. In particular, polycyclic aromatic structures have higher radiation stability than other materials which are used as supports such as silica and organic resins. In some embodiments, the sorbent material is a polycyclic aromatic carbon structure, preferably with grafted functional groups. It is an advantage of these embodiments that the sorbent material may have a high radiolytic stability. This may be particularly advantageous for use in the radionuclide separating systems.
Examples of functionalized derivatives of carbon-based sorbent materials are sulfonated carbon materials, oxidized carbon materials, and carbon materials with impregnated extractants or cation exchange materials, e.g., bis(2-ehylhexyl)phosphoric acid impregnated activated carbon. Herein, the carbon material is applied as an inert support.
The shape of the sorbent material may impact the structural properties of the sorbent material, which may be a powder, and possibly also the presence of functional groups onto the surface. In embodiments, the carbon-based sorbent material is shaped in beads, or the carbon-based sorbent material is provided as a shell of beads, e.g., of spherical particles. Preferably, the sorbent material is shaped in spherical beads to ensure, for example, a uniform flow pattern in the column and a lower pressure drop over the column. In embodiments, the carbon-based sorbent material is shaped in beads having a size between 5 μm and 1 mm, for example between 10 μm and 500 μm, for example between 10 μm and 250 μm, for example between 10 μm and 150 μm, for example between 50 μm and 150 μm. It is an advantage of these embodiments that the column may be packed rapidly and that rapid purification may be achieved. It is to be noted that also other shapes can be used, aside the beads, such as for example including but not limited to extruded honeycombs, 3D-printed monoliths, tubular structures, non-spherical granules, and others.
In embodiments, the sorbent material may have a porosity between 0% and 70%. In embodiments, the pore size may be from 0 to 100 nm. In embodiments, the surface area of the sorbent material is smaller than 100 m2/g, for example less than 50 m2/g, for example, less than 25 m2/g, for example, less than 10 m2/g. It is an advantage of these embodiments that, due to the limited surface area, rapid purification may be achieved. A smaller surface area is desirable to avoid capture of isotopes inside the sorbent structure, which improves the elution efficiency by reducing the elution path.
For forming the carbon-based sorbent material, a carbon material for further functionalization may be selected. Functionalisation, in particular by grafting, may be easier for some carbon materials than for others. Preferably, the carbon material may have many defects in the carbon structure, or the carbon material may already have particular functional groups on its surface (e.g., activated carbon), which can be converted into the functional groups in accordance with embodiments of the present invention. Furthermore, functionalization via grafting imposes different requirements on the carbon material than impregnation. Next, the materials and processes used for radionuclide generation may be selected depending on the type of generator (i.e., inverse radionuclide separating systems or direct radionuclide separating systems). In particular, the sorption performance may be tuned by ionic strength and/or pH.
Although the invention is, in this description, mainly described with respect to 225Ac as the parent radionuclide and 213Bi as the daughter radionuclide, the present invention is by no means to be interpreted as being limited to these embodiments. In embodiments, the radionuclide separating system is based on a decay of: 225Ac to 213Bi; 113Sn to 113mIn; 87Y to 87mSr; 232U to 228Th and/or to 224Ra and/or to 220Rn and/or to 216Po and/or to 212Pb; and 227Ac to 211Pb, or possibly of 191Os to 191mIr. Herein, as understood by the skilled person, the decay is of the parent compound to the daughter compound. Preferably, the radionuclide separating system is based on a decay of 225Ac to 213Bi for separating 213Bi radionuclides. It is an advantage of embodiments of the present invention that the technology can be applied for the generation of a plurality of radionuclides. It is an advantage of embodiments of the present invention that, for example, an elution of 213Bi radionuclides can be high, compared to, e.g., elution of 213Bi radionuclides using columns comprising sorbent materials according to the state of the art, e.g., silica-based materials. It is an advantage of embodiments of the present invention that the carbon-based sorbent material may be used to separate high activity 225Ac/213Bi, e.g., at least 100 mCi 225Ac.
The affinities of the sorbent material for the parent radionuclide and daughter radionuclide may be dependent on pH and/or ionic strength of a solvent in contact with the sorbent, e.g., of the mixture or of an eluent. In embodiments, the sorbent material is capable of interacting with the parent radionuclide and daughter radionuclide so as to allow selective desorption of the parent radionuclide and/or the daughter radionuclide at a different moment in time comprises that the sorbent material has at least different affinities within a particular pH range and within a particular range of ionic strengths and/or salt concentrations, as is the case for carbon-based sorbent materials according to embodiments of the present invention.
In some embodiments, the radionuclide separating system is a direct radionuclide separating system, and the carbon-based sorbent material has a strong affinity for both the parent radionuclide and the daughter radionuclide, so as to selectively desorb the daughter radionuclide. In some embodiments, the mixture comprises parent nuclides and daughter nuclides, preferably at a low salt concentration, for example, the salt concentration less than 1.0 M, for example, the salt concentration less than 0.5 M. Preferably, the pH of the mixture is at least more than the pKa of the functional groups, for example, the pH is more than 1.47 for bis(2-ethylhexyl)phosphoric acid impregnated activated carbon, for examples, the pH is better more than 2 for bis(2-ethylhexyl)phosphoric acid impregnated activated carbon, so the parent nuclide would be adsorbed via electrostatic attraction and/or ion exchange.
Herein, the daughter radionuclide may be selectively desorbed using a first elution solution due to the daughter radionuclide more preferably interacts with elution ions than with the sorbent material, whereafter the parent radionuclide may be eluted by an acid solution for reuse and reduce the radiolytic damage to the sorbents.
The elution solution for the daughter radionuclide may comprise, preferably at least 0.1 M, such as at least 0.2 M, preferably at least 0.4 M, of NaI, NaCl, HI, HCl, or a combination thereof. In embodiments, the pH value of the elution solution may be at least, or more than, the pKa of main active sites. For examples, the elution solution may contain at least 0.45 M NaI at a pH of at least 2 for bis(2-ehylhexyl)phosphoric acid impregnated activated carbon.
The parent radionuclide may desorb from the generator column using the acidic solution, e.g., a HNO3 solution or a HCl solution. The concentration of HNO3 in said solution may be at least 0.1 M, preferably at least 0.2 M, such as from 0.1 to 0.5 M, preferably from 0.2 M to 0.3 M. It is an advantage of embodiments of the present invention that a reduced contact time of 225Ac with the carbon-based sorbent material, and an even distribution of the 225Ac over the column may be achieved, which may improve the lifetime of the column. It is an advantage of embodiments of the present invention that the parent isotope 225Ac is able to be eluted by relatively weak acid solution from the column to reuse next time.
In alternative embodiments, the radionuclide separating system may be an inverse radionuclide separating system, the carbon-based sorbent material being adapted for having a higher affinity for the daughter radionuclide than for the parent radionuclide. In embodiments, the carbon-based sorbent material comprises one or more of a phosphate group, a phosphonic group, a phosphinic group, carbonyl, a hydroxyl group, or a carboxylic acid group. These functional groups may result in the sorbent material having a higher affinity for the daughter radionuclide than for the parent radionuclide. In embodiments wherein the radionuclide separating system is the inverse radionuclide separating system, the radionuclide separating system may comprise a second column having a sorbent material, e.g., AG MP-50 or Ac resin, with higher affinity for the parent radionuclide than for the daughter radionuclide, an inlet, and an outlet. In embodiments, the outlet of the column may be configured to be fluidically coupled to an inlet of the second column when a strip solution, comprising the daughter radionuclide released from the column, is let out of the column. The sorbent material of the second column may not need a carbon-based sorbent material, as the daughter solution (that may cause most radiolytic damage) has a relatively short retainment time in the second column. However, also the sorbent material of the second column may comprise a carbon-based sorbent material, for which features may be independently as correspondingly described for carbon-based sorbent material of the column. It is an advantage of embodiments comprising the second column that a higher purity daughter radionuclide elution may be obtained, that is, comprising substantially no parent radionuclide.
Any features of any embodiment of the first aspect may be independently as correspondingly described for any embodiment of the second aspect of the present invention.
In a second aspect, the present invention relates to a method for separating radionuclides, the method comprising: loading a mixture of a parent radionuclide and a daughter radionuclide to a column comprising a carbon-based sorbent material; allowing the sorbent material to selectively interact with the parent radionuclide and the daughter radionuclide, the sorbent material having an affinity for interacting with the parent radionuclide and daughter radionuclide so as to allow selective desorption of the parent radionuclide and the daughter radionuclide; and selectively desorbing the parent radionuclide and the daughter radionuclide after said interaction, so as to selectively obtain the daughter radionuclide. In embodiments, the method may be performed using a radionuclide separating system as described with respect to the first aspect of the present invention.
In embodiments, the mixture may comprise the parent radionuclide and the daughter radionuclide dissolved in water. It is an advantage of water that its pH may be easily adjusted, and furthermore, that ions may be dissolved efficiently and at high concentrations.
In embodiments, the different moments in time may comprise that selective desorption of the parent radionuclide and/or the daughter radionuclide may be performed subsequently in time.
These embodiments may relate to a direct radionuclide generator, e.g., using a direct radionuclide separating system. The sorbent material is adapted so that the sorbent material has a strong affinity for both the parent radionuclide and the daughter radionuclide, so as to selectively desorb the daughter radionuclide, wherein said selectively obtaining the daughter radionuclide comprises, eluting the daughter radionuclide from the column using an eluent having a pH of at least more than the pKa of the functional groups on sorbents, after the parent radionuclide was bound to the sorbent material. Finally, the parent radionuclide, e.g., 225Ac, can be eluted by a solution comprising HNO3, such as by a solution comprising HNO3 at a concentration of from 0.1 to 0.5 M. Then the solution comprising the parent radionuclide may be stored and/or used as the mixture in a subsequent cycle. This step may also reduce the radiolytic damage for the sorbent via decreasing the contact time between the isotopes and sorbent, and it is easy to recycle and reuse the parent radionuclide, e.g., 225Ac.
These embodiments may relate to inverse radionuclide generation, e.g., using an inverse radionuclide separating system. In embodiments, the sorbent material is adapted so that the sorbent material has a higher affinity for the daughter radionuclide than for the parent radionuclide so as to preferably bind the daughter radionuclide, wherein said selectively obtaining the daughter radionuclide comprises rinsing the column, and thereafter stripping the daughter radionuclide from the column into a strip solution
In embodiments, the mixture may comprise NaNO3 and HNO3, preferably at a total concentration of NaNO3 and HNO3 higher than the ionic concentration of the strip solution, such as at least 2 M, preferably at least 3 M. The mixture may have a pH of less than 2, preferably less than 1.
The rinsing may, for example, be performed using an elution comprising NaNO3 and HNO3, preferably at a total concentration of NaNO3 at least 2 M, preferably at least 3 M. The elution for the rinsing may have a pH of less than 2, preferably less than 1. The pH of rinsing solution may be less than the pH of mixture solution in the prior step. Preferably, the pH of rinsing solution may be same as the pH of mixture solution in the prior step. This may result in good sorption of the daughter radionuclide, e.g., 213Bi, but not of the parent radionuclide, e.g., 225Ac.
In embodiments, the strip solution may comprise, for example, at a concentration of from 0.1 to 3.0 M, NaI, NaCl, HI, HCl or HNO3 or a combination thereof. Preferably, the strip solution has a pH of at most 2. In embodiments, the strip solution may comprise from 0.1 to 3.0 M NaI at a pH of at most 2, or from 0.1 to 3.0 M NaCl at a pH of at most 2, or from 0.1 to 3.0 M HCl. Herein, HNO3 may be used to adjust the pH value of the solution.
In some embodiments, sometimes the strip solution is further added to a second column having a sorbent material with a higher affinity for the parent radionuclide, that is, higher than for the daughter radionuclide, and eluting the daughter product, i.e., daughter radionuclide, from the second column, after interaction between the sorbent material of the second column and remaining parent radionuclide in the strip solution was allowed.
Any features of any embodiment of the second aspect may be independently as correspondingly described for any embodiment of the first aspect of the present invention.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
Although there has been constant improvement, change, and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable, and reliable devices of this nature.
The above and other characteristics, features, and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.
In the different figures, the same reference signs refer to the same or analogous elements.
The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term “comprising” therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. The word “comprising” according to the invention therefore also includes as one embodiment that no further components are present. Thus, the scope of the expression “a device comprising means A and B” should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noticed that the term “coupled” should not be interpreted as being restricted to direct connections only. The terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression “a device A coupled to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
The following terms are provided solely to aid in the understanding of the invention.
As used in the context of the present invention, grafting functional groups, means that the chemical species are covalently bonded onto the solid surface, e.g., the surface of a sorbent material. As used in the context of the present invention, impregnation of functional groups means that the chemical species are physically distributed in the internal surface of the porous material.
As used in the context of the present invention, CMS is an abbreviation for carbon molecular sieve, and CNT is an abbreviation for carbon nanotube.
In a first aspect, the present invention relates to a radionuclide separating system for separating a daughter radionuclide from a parent radionuclide. The radionuclide separating system comprises an inlet for loading a liquid solution comprising the parent radionuclide onto a column. The radionuclide separating system further comprises the column, which comprises a sorbent material wherein the sorbent material is capable of interacting with the parent radionuclide and daughter radionuclide so as to allow selective desorption of the parent radionuclide and/or the daughter radionuclide at a different moment in time. Herein, the sorbent material is a carbon-based sorbent material. The radionuclide separating system further comprises an outlet for selectively obtaining said daughter radionuclide based on said selective desorption of the parent radionuclide and the daughter radionuclide.
In a second aspect, the present invention relates to a method for separating radionuclides, the method comprising: loading a mixture of a parent radionuclide and a daughter radionuclide to a column comprising a carbon-based sorbent material; allowing the sorbent material to selectively interact with the parent radionuclide and the daughter radionuclide, the sorbent material having an affinity for interacting with the parent radionuclide and daughter radionuclide so as to allow selective desorption of the parent radionuclide and/or the daughter radionuclide; and selectively desorbing the parent radionuclide and the daughter radionuclide after said interaction, so as to selectively obtain the daughter radionuclide.
By way of illustration, embodiments not being limited thereto, a schematic overview of a direct and inverse radionuclide separating system is shown in
Several carbon-based sorbent materials, both for use in an inverse radionuclide separating system, and for use in a direct radionuclide separating system, in accordance with embodiments of the present invention, have been prepared and tested, as described below. Herein, although La3+ (as a substitute for a parent radionuclide) and Bi3+ (as daughter radionuclide) are used in the exemplary mixture, comprising water as a solvent, it is to be understood that, in particular, other parent and/or daughter radionuclides could be used as well. In particular, La3+ may be assumed to be replaceable by Ac3+ without considerably changing the results obtained and described below.
In the following examples, reference is made to R (%), which is a removal percentage. Furthermore, reference is made to D (%), which is a desorption percentage. Finally, reference is made to Kd (mg/L), which is a distribution coefficient, defined as the concentration ratio of a chemical between two media (e.g., between the sorbent material and the mixture of the parent radionuclide and the daughter radionuclide) at equilibrium. The removal percentage R (%), distribution coefficient Kd (mL/g), and desorption percentage D (%) may be calculated as follows:
wherein m (g) is the mass of the adsorbents (i.e., the sorbent material). V (mL) is liquid phase volumes in the adsorption process, and Co (mol/L) and Ce (mol/L) represent the initial concentration and equilibrium concentration of La3+ or Bi3+ in the adsorption process, respectively. ns1 (mol) and ns2 (mol) represent the amount of La3+ or Bi3+ adsorption on the sorbent after the adsorption process and desorption process, respectively.
In what follows, examples are provided of carbon-based sorbent materials for use in an inverse radionuclide separating system. In the inverse radionuclide separating system, there is first selective adsorption of the daughter radionuclide (in the following examples, Bi3+) over the parent radionuclide (in the following examples, a substitute for the parent radionuclide, i.e., La3+) on the sorbent material. Next, desorption of the daughter radionuclide is performed from the sorbent material.
In this example, the sorbent material is activated carbon Norit CA1, with additional grafting by H2SO4 or HNO3 treatment. Herein, the grafting results in an increase in oxygen content (both for H2SO4 and HNO3 treatment), i.e., in the formation of carboxylic (and other) groups, and in an increase in sulphur content (for H2SO4 treatment), i.e., in the formation of sulphonic acid groups. For example, the sulfonated Norit CA1 (150° C.) was fabricated using concentrated H2SO4. Briefly, 15 g of Norit CA1 was mixed with 150 mL of concentrated sulfuric acid (95.0-98.0%) in a 500 mL round-bottomed flask and stirred for 10 min at room temperature. Then, the suspension was heated to 150° C. with continuous agitation and kept at that temperature for 3 h. After the suspension was cooled at room temperature, the obtained black products were filtered and intensively washed with deionized water until sulfate ions were no longer detected with barium chloride (addition of 5 drops of 1.0 M BaCl2 to 1 mL of filtrate). Finally, the sample was dried in an oven at 70° C. The prepared product was designated sulfonated Norit CA1 (150° C.).
The functional groups of sulfonated Norit CA1 (150° C.) were investigated by XPS. The two main oxygen environments could be assigned to O═C (531.3 eV) and O—C (533.1 eV), representing a potential mixture of hydroxyl, carbonyl and carboxylate functional groups. In addition, this lower binding energy component becomes sharper, and more intense, which can then be assigned to overlapping sulfate/sulfonate and carbonyl environments. The sulfur 2p spectrum of sulfonated Norit CA1 (150° C.) showed a mixture of two overlapping sulfur environments that we have tentatively assigned to a mixture of sulfonate or sulfate (S 2p3/2 at 168.5 eV) and a lower oxidation state species such as sulfite or sulfinic acids (167.5 eV).
Reference is made to
The radiation stability of sulfonated Norit CA1 (150° C.) was also investigated by exposing the sorbent to radiation and investigating the impact on the sorption performance. Briefly, the 200 mg sulfonated Norit CA1 (150° C.) was mixed with 2 mL of 1 M HCl solutions into 4 mL glass vials and irradiated by 60Co. The received doses were from 0.5 to 11 MGy. References samples in 2 mL of 1 M HCl solutions without radiation treatment were also done. Finally, the samples were washed and dried in an oven and then used to study the sorption properties. Herein, the mixture of solution comprised 10 μmol/L of La3+ and 10 μmol/L of Bi3+. The amount of sorbent material was 10 mg and the amount of the mixture was 10 mL. Herein, the experiments for
In this example, the sorbent material comprised graphitized carbon black (Carbopack X) and sulfonated graphitized carbon black. Herein, the reaction conditions for the sulfonization are 5 g of Carbopack X in 50 mL 97% H2SO4 at 80° C. for 180 min, thereby forming the sulfonated graphitized carbon black, i.e., sulfonated Carbopack X.
Reference is made to
In this example, the sorbent material is a Carbon Molecular Sieve [Carboxen 572]. Herein, sulfonated Carboxen 572 was synthesized using 2.5 g of Carboxen 572 in 25 mL of 97% H2SO4, at 150° C. for 240 min.
Reference is made to
It may be observed that there is no sorption of La3+ for Carboxen 572. Furthermore, there is low capacity for Bi3+ and La3+ due to insufficient functional groups, but there is selectivity towards Bi3+ over La3+. After sulfonation, the sorption capacity for Bi3+ increased with the increase of sulfur and oxygen contents on the surface of sulfonated Carboxen 572. A similar explanation for these observations may be assumed as with respect to Example 2 above. A NaNO3 solution could be employed to avoid La3+ adsorption on sulfonated Carboxen 572, as was also observed in the results of Example 1.
In this example, the sorbent material is sulfonated carbonized methyl cellulose (SCMC). Herein, the carbonized methyl cellulose is formed by carbonization of methyl cellulose at a range of temperatures. Below and in the figures, SCMC-[T] is used, wherein [T] indicates the temperature at which the methyl cellulose was carbonized. Herein, sulfonation was performed in 97% H2SO4, at 150° C. for 600 min.
Reference is made to
In this example, the sorbent material is activated carbon Norit CA1 (without additional functionalization, e.g., through grafting). Reference is made to
It may be observed that at pH≤1.0, a high selectivity in La3+/Bi3+ sorption may be achieved (i.e., no sorption capacity for La3+, and high removal percentages for Bi3+). An explanation for this observation may be found in that this kind of activated carbon has different kinds of functional groups on its surface, allowing different interaction mechanisms with La3+ and Bi3+. XPS oxygen is spectra for Norit CA1 was shown in
In this example, the sorbent material comprised HDEHP-AC, i.e., bis(2-ethylhexyl)phosphate modified activated carbon. Bis(2-ethylhexyl)phosphate has the following chemical structure:
Reference is made to
Further reference is made to
Thereby,
Reference is made to
Step 0 (preparation phase, not indicated): Based on the density of active sites for 225Ac and 213Bi, the optimal ionic strength and pH range may be chosen. The column 10 is typically conditioned with HNO3 (e.g., 0.1 M), which may be introduced through an inlet of the column.
Step 1: Then, the mixture of a parent radionuclide and a daughter radionuclide, comprising 225Ac (parent radionuclide) and 213Bi (daughter radionuclide), is passed through the column 10, e.g., comprising introducing in the column 10 via an inlet. The mixture may further comprise, for example, NaNO3, which may increase the ionic strength, and HNO3, for reducing the pH. This may result in selective adsorption of 213Bi on the sorbent material in the column 10, which is a carbon based sorbent material in accordance with embodiments of the present invention. An elution comprising 225Ac, HNO3, and NaNO3 may be removed through an outlet of the column 10.
Step 2: Subsequently, a small volume of a solution containing HNO3 and NaNO3 would be applied, e.g., through the inlet, to rinse residual 225Ac from the column 10, while 213Bi remains adsorbed. The elutes of step 1 and 2, possibly after evaporation of the solvent of the elute of step 2, may be regenerated for use in the mixture in a step 1 of a subsequent cycle, thereby reducing waste of the process.
Step 3: 213Bi may be eluted, by introducing through the inlet, an elution solution, i.e., strip solution, comprising NaCl, NaCl or HCl with lower ionic strength than that used for the sorption process 1. Indeed, if even a small mass of 225Ac from the high ionic strength solution is sorbed onto the column 10, it would be also difficult to elute this 225Ac when eluting the 213Bi. The elute comprising 213Bi may be collected through an outlet of the column 10, whereby the daughter radionuclide 213Bi has been separated from the parent radionuclide 225Ac.
Step 4: To reuse the column 10, any Cl− or I− ions on the column may be eluted, i.e., removed, by rinsing the column 10 with, for example, H2O or 0.1 M NH3·H2O.
To further ensure high purity of the eluted Bi (as preferably no Ac may be present in the elution), a second column 20 (guard column) may be introduced, comprising a sorbent material with higher affinity for the parent radionuclide than for the daughter nuclide, e.g., AG MP-50 or Ac resin. The presence of the second column 20 may not increase the separation time for 213Bi. An example of an inverse 225Ac/213Bi separating system comprising the second column 20 is shown in
For several of the carbon-based sorbent materials of the above Examples 1 to 7, the characteristics of the sorbent materials have been analysed using elemental analysis, to determine the carbon, sulphur and oxygen content in the respective materials. The results are summarized below in Table A.
In the above Examples 1 to 7, a range of sorbent materials, in combination with mixtures, were used. The present invention is, of course, not limited to these examples. Indeed, a range of optional technical features may be used to provide good properties to the sorbent material, as described elsewhere in this description.
In what follows, examples are provided of carbon-based sorbent materials for future use in a direct radionuclide separating system. In direct radionuclide separating system, there is first co-adsorption of the parent (in the following examples, a substitute for the parent radionuclide, i.e., La3+) and daughter radionuclide (in the following examples, Bi3+) on the sorbent material. Next, selective desorption of the daughter radionuclide (in the following examples, Bi3+) is performed from the sorbent material.
In this example, the sorbent material comprised HDEHP-AC.
Reference is made to
In combination with
In combination with
Reference is made to
Step 0 (preparation phase): The sorbent materials may be conditioned with HNO3 (e.g., at a concentration of at least 0.01 M). The mixture (that is, of a parent radionuclide and a daughter radionuclide) may be prepared with HNO3 (e.g., >0.01 M) containing 225Ac and 213Bi.
Step 1: The mixture may be introduced into the column 10, e.g., through an inlet. Both 225Ac and 213Bi may be sorbed on the sorbent material of the column 10.
Step 2: An elution solution comprising NaI (e.g., at least 0.45 M) and HNO3 (e.g., 0.01 M) may be introduced into the column 10 so as to elute 213Bi. That is, the selectivity of the sorbent material may be increased by the elution solution having a large ionic strength.
Step 3: To increase the lifetime of the column 10, the 225Ac can be eluted by HNO3 (e.g., a solution comprising HNO3 at a concentration of from 0.1 to 0.5 M). Removing the 225Ac may reduce the contact time between 225Ac and the sorbent material.
Step 4: The pH of the 225Ac solution obtained in step 3 is preferably at least 2. This obtained 225Ac solution may be reused in step 0 of a next cycle for forming the mixture.
It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope of this invention. For example, any formulas given above are merely representative of procedures that may be used. Steps may be added or deleted to methods described within the scope of the present invention.
By way of illustration, embodiments not being limited thereto, an example of how spherical carbon materials can be synthesized is given. In this example, the spherical sulfonated carbon material was fabricated by pyrolysing the cellulose beads at 400° C. and then via a sulfonation process. The sulfonation temperature and sulfonation time was 150° C. and 180 min, respectively.
Reference is made to
Reference is made to
Further by way of illustration, the present invention not being limited thereto, an example of an experimental separation is described below. An 225Ac/213Bi column was prepared with 100 mg of SCMC-500. The prepared 5 mL starting solution was composed of 200 kBq 225Ac, 0.055 mol L−1 HNO3 and 3.0 mol L−1 NaNO3. The columns were rinsed with H2O (10 mL) and then 0.01 mol L−1 HNO3 solution (2 mL). Subsequently, the prepared 225Ac solution (5 mL) in a Falcon tube was passed through the column under a sorption flow rate of 1.4±0.1 mL min−1. Thereafter, 1 mL of 0.02 mol L−1 HNO3/3 mol L−1 NaNO3 solution was applied to wash the Falcon tube, and then 2.5 mL of 0.02 mol L−1 HNO3/3 mol L−1 NaNO3 was utilized to wash the column-100. Finally, 1 mL of 1 mol L−1 HCl was employed to elute the 213Bi with an elution flow rate of 1.4±0.1 mL min−1. The 225Ac impurity in the elution was 0.03±0.01% (the activity ratio of 225Ac to 213Bi at the end of separation). The total separation time was 6.5±0.3 min. The 213Bi yield was 94±3%.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21218490.7 | Dec 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/087876 | 12/27/2022 | WO |
