Systems and Methods for Separating Yttrium and Strontium RELATED PATENT DATA

This application claims priority to U.S. Patent Application Serial No. 16/780,397 filed February 3, 2020, entitled “Systems and Methods for Separating Yttrium and Strontium”, the entirety of which is incorporated by reference herein. STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under Contract DE-AC05-76RL01 830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention. TECHNICAL FIELD

The present disclosure relates to the separation of yttrium and strontium, and in particular embodiments, the present disclosure relates to the separation of yttrium and strontium isotopes and/or the preparation of concentrated forms of yttrium isotopes. BACKGROUND

Yttrium isotopes typically can be fission products along with strontium isotopes and exist in the same solution as strontium isotopes. These fission products are generated by fissioning of actinides. Sr cyclotron targets can produce other isotopes by (p, n) reactions. The present disclosure provides systems and methods for separting yttrium from strontium, isolating yttrium isotopes from a solution of strontium and yttrium isotopes, and/or the preparation of concentrated forms of yttrium isotopes. SUMMARY OF THE DISCLOSURE

Methods are provided for separating yttrium (Y) and strontium (Sr). The methods can include providing a dilute acidic mixture that includes Y and Sr to a vessel having a media therein. The methods can further include while providing the dilute acidic mixture, retaining at least some of Y from the dilute acidic mixture within the first vessel while at least eluting some of the Sr from the dilute acidic mixture to form a dilute acidic eluent.

Additional methods for separating Y and Sr are provided that can include providing a vessel containing a media and a dilute acidic mixture comprising Y. The methods can include providing a concentrated acid mixture to the vessel and while providing a concentrated acid mixture to the vessel recovering a concentrated acid eluent comprising at least some of the Y from within the vessel.

Additional methods for separating Y and Sr are also provided that can include providing a concentrated acidic mixture comprising Y to a vessel having a media therein and while providing that concentrated acidic mixture retaining at least some of the Y from the concentrated acidic mixture within the vessel and forming an eluent.

Further methods are also provided that can include methods for separating Y and Sr. The methods can include providing a vessel containing a media and a concentrated acid mixture that includes Y. The methods can include providing a dilute acid mixture to within the vessel and while providing a dilute acidic mixture to within the vessel recovering a dilute acid eluent that includes at least some of the Y from within the vessel.

Additional methods for separating Y and Sr are also provided that can include providing a first mixture comprising Y and Sr to a first vessel having a first media therein. The methods can include retaining at least some of the Y from the first mixture within the first vessel and providing a second mixture to the first vessel. The methods can further include recovering a first eluent comprising at least some of the Y from within the first vessel and providing the first elute that includes Y to a second vessel having a second media therein. The methods can also include retaining at least some of the Y from the first eluent within the second vessel and providing a third mixture to the second vessel. The method can also include recovering a second eluent that includes at least some of the Y from within the first vessel.

Methods for separating Y and Sr can also include providing a first mixture of at least two components to a first vessel having a first media therein with the first vessel defining a first volume. The method can include retaining at least some of one of the two components within the first vessel and eluting the one of the two components from the first vessel to a second vessel having a second media therein. The second vessel can define a second volume and the first volume can be greater than the second volume. The first media can be different from the second media. The methods can include retaining at least some of the one of the two components within the second vessel and eluting the one of the two components from the second vessel. Additionally, the elution from the first vessel can have a first concentration of the one component and with the elution from the second vessel can have a second concentration of the one component. The second concentration can be greater than the first concentration.

DRAWINGS

Fig. 1 is system for practicing methods according to an embodiment of the disclosure.

Fig. 2 is a system for practicing methods according to an embodiment of the disclosure.

Fig. 3. is distribution coefficient data in accordance with embodiments of the present disclosure. Fig. 4 is a system for practicing methods according to an embodiment of the disclosure.

Fig. 5 is a system for practicing methods according to an embodiment of the disclosure.

Fig. 6 is a system for practicing methods according to an embodiment of the disclosure.

Fig. 7 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 8 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 9 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 10 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 11 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 12 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 13 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 14 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 15 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 16 is data acquired utilizing systems and methods according to an embodiment of the disclosure. Fig. 17 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 18 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

Fig. 19 is data acquired utilizing systems and methods according to an embodiment of the disclosure.

DESCRIPTION

The systems and methods of the present disclosure will be described with reference to Figs. 1 -19. Referring first to Fig. 1 a system 10 is disclosed that includes at least two vessels 12 and 14 that can be in fluid communication via conduit 16 as well as another conduit 18. As for all vessels and conduits described in this description they can likewise be refered to as containers or holders or really any form of apparatus that can retain liquid or solid particles, and/or mixtures thereof within a confined or predefined space. Conduits 16 and 18 are represented as continuous here but throughout the specifications should be recognized that they can be valve operable to be opened or closed as desired to provide or not provide fluid communication between one vessel and another. The conduits can also be configured to provide the solution that is being exchanged or provided through them. Therefore, by example, the conduits can be resistant to acid or organic acids or resistant to organics themselves as needed. In accordance with example implementations the methods for separating Y and Sr can include providing a dilute acidic mixture including Y and Sr. This dilute acidic mixture of Y and Sr can be in vessel 12 for example and this dilute acidic mixture can include nuclides of Y (for example ⁹⁰ Y, ⁸⁹ Y, ⁸⁸ Y, or ⁸⁶ Y) as well as nuclides of Sr (for example "Sr, ⁸⁹ Sr, ⁸⁸ Sr or ⁸⁶ Sr). This dilute acidic mixture can be sourced from Sr- bearing nuclear material stockpiles which can be a biproduct of nuclear processing. For example, ⁸⁶ Y is a 14.7 hr half-life isotope produced by the (p, n) reaction onto an isotopically enriched ⁸⁶ Sr target. In the case of ⁸⁶ Y/ ⁸⁶ Sr, it can be a result of proton bombardment onto a ⁸⁶ Sr cyclotron target.

General recipes for the preparation of solutions that can simulate Sr-bearing stockpile materials are provided in Table 1.

Table 1. General recipe to prepare a simulant solution containing Group II elements and Y that approximate those found in an example product solution.

Spiked solutions can also be prepared with reference to Table 2 below as well.

Table 2. activities that were spiked into each column load solution prior to purification. In accordance with example implementations acidic reagents can be utilized such as solutions of dilute acidic mixtures and concentrated acidic mixtures prepared with the reagents disclosed below for example.

Concentrated hydrochloric acid (HCI) can be ACS Certified grade or higher (Fisher Scientific, Waltham, MA). Dilutions of HCI can be prepared from deionized water (>18 MW-crm) using a Barnstead E-Pure water purification system (Dubuque, IA). Scintillation cocktail was UltimaGold AB (PerkinElmer, Billerica, MA).

A supply of ~5 mCi ⁹⁰ Sr in ~2% HNO3 can be obtained and this solution can be evaporated to nitrate salt, then transformed to formate salt. The ⁹⁰ Sr residue can be evaporated and transformed to chloride salt prior to use. An infrared lamp can be used to evaporate metered volumes of the transformed "Sr stock solution to Teflon vials (7 ml_ round-bottom vial, Savillex, Eden Prairie, MN).

Single element solutions containing concentrates of Ca(ll), Sr(ll), Ba(ll), and Y(lll) in 0.1 M HCI can be prepared, as briefly described below:

• Ca solution can be prepared by dissolving calcium metal chips in concentrated. HCI. After evaporation of excess acid, the CaCl2 salts can be brought up in 0.1 M HCI. Prepared Ca(ll) cone. = 99.26 mg/mL.

• Sr solution can be prepared from strontium(ll) carbonate salt. The salt can be saturated with cone. HCI to destroy carbonate and convert the salts to strontium chloride. The excess acid can be evaporated off overnight, and then the dried salts were brought up in 0.1 M HCI. Prepared Sr(ll) cone. = 260.21 mg/mL.

• Ba solution can be prepared from barium(ll) chloride salt. The salt can be dissolved directly in 0.1 M HCI. Prepared Ba(ll) cone. = 8.55 mg/mL. Y solution can be prepared from yttrium(lll) chloride salt. The salt can be dissolved directly in 0.1 M HCI. Prepared Y(lll) cone. = 3.42 mg/mL.

Aliquots of these solutions can be added to ⁹⁰ Sr-spiked solutions in order to simulate the dissolved solids present in ⁹⁰ Sr stocks.

In accordance with example implementations, and with reference to Fig. 1 , this dilute acidic mixture can include Y and Sr can be provided to vessel 14 having a first media 20 therein. The dilute acidic mixture can have a pH less than 7 and the dilute acidic mixture can also have a pH less than 3. The dilute acidic mixture can have a concentration of acid that is less than 0.1 M, for example, but must include sufficient acid to remain acidic. As described herein the dilute acidic mixture can additionally include elemental Sr, Ca and/or Ba and the dilute acid mixture can include stockpiled Sr-bearing nuclear material for example.

Within vessel 14 can be a first media 20 that includes a resin. This resin can include Bis(2-ethylhexyl) hydrogen phosphate (HDEHP). The first media can also include alkylphosphorus extractants. Alternatively, the first media can also include Si. In accordance with example implementations the media 20 can be considered a first media.

The Y purification method can employ two columns or vessels in tandem. First vessel 14 can have media 20 that includes a Di- (2- ethylhexyl)phosphoric acid (HDEHP)-based extraction chromatography resin, sold under the trade name Ln Resin (Eichrom Technologies, Ltd, Lisle, IL). The particle size distribution used was 100-150 pm, but other size distributions such as 50-100 pm or 20-50 pm are contemplated.

The Ln Resin can be packed into a column having a -0.25 cc internal volume in a 1 cc SPE tube kit (Supelco) that can be cut to the appropriate dimension. The columns can be polypropylene, with 20 pm pore size polyethylene frits. The column can be fitted with a custom- made plastic cap (with female luer fitting) that can be inserted into the top of the trimmed column. In accordance with example implementations, while providing the dilute acid mixture comprising Y and Sr the method can provide for retaining at least some of the Y from the dilute acidic mixture within vessel 14 while eluting some of the Sr from the dilute acidic mixture to form a dilute acidic eluent which would be provided to conduit 18. In accordance with example implementations the method can also include providing the dilute acidic mixture from reservoir 12 and then providing the dilute acidic eluent to reservoir 12 via conduit 18 for example.

In accordance with example implementations, the dilute acidic mixture can further comprise Zr and the method can also include while providing the dilute acidic mixture, retaining at least some of the Zr from the dilute acidic mixture within vessel 14. The method can also include further retaining at least some of the Fe from the dilute acidic mixture within vessel 14. The dilute acidic mixture can include HCI for example, an organic acid for example, such as formic acid for example.

Referring next to Fig. 2 a system 25 is depicted that can include a vessel 14 containing a media 20 and a dilute acidic mixture 22 that includes Y. In accordance with example implementations vessel 14 can be the vessel of system 10 after the providing of the Y/Sr mixture 12 to vessel 14 for example. In accordance with example implementations a concentrated acid mixture contained in vessel 24 can be provided via conduit 26 to vessel 14. While providing the concentrated acid mixture of vessel 24 to vessel 14 an acid eluent comprising at least some of the Y from within vessel 14 can be recovered in vessel 30 as eluent 32 via conduit 28.

In accordance with example implementations, vessel 14 can include one or both of Zr and Fe and while providing the concentrated acid mixture from vessel 24 to vessel 14 at least some or both of the Zr and Fe can be retained. In accordance with example implementations this concentrated acid mixture can include HCI, an organic acid, such as formic acid for example. In further embodiments the method can provide the concentrated acid eluent of 32 from within vessel 30 to another vessel containing another medium. This additional embodiment will be described with more detail herein. Additionally the media 20 remains as the media 20 as described in system 10 for example.

In accordance with an example embodiment, tandem column- based ⁹⁰ Y purification methods are contemplated and described herein. Referring to Fig. 3, the affinity for Y on Ln Resin drops approximately as a negative power function with increasing HCI concentration. At 0.1 M HCI, the distribution coefficient ( K _d ) for Y exceeds 10 ⁵ mL/g; by the time HCI concentration has increased to 8 M HCI, Y K _d drops by -6 orders of magnitude. This substantial change in Y affinity between the two HCI concentrations can dictate what is considered a dilute acidic or concentrated acidic mixture. In accordance with example implementations and with respect to the systems and methods of the present disclosure, a dilute acidic mixture, for example, can be an acid mixture that provides for a K _d of at least 10, while a concentrated acidic mixture, for example, can provide for a K _d of less than 10; each of which with regard to Y on a HDEHP resin such as Ln Resin.

Further, with reference to Fig. 3, Zirconium-90 is a contaminant of concern in aged ⁹⁰ Sr-bearing stockpiles, as it is the stable decay product of ⁹⁰ Y. Therefore, it accumulates in the "Sr stocks over time. The data in Fig. 3 demonstrates that Zr(IV) affinity for Ln Resin is >10 ⁴ mL/g across the entire range of HCI concentration. Therefore, a primary Ln Resin column is capable of ⁹⁰ Zr removal during the ⁹⁰ Y load step. Furthermore, ⁹⁰ Zr is retained on the column while ⁹⁰ Y is eluted and may pass to column 2 (see Table 3).

Fig. 3 also provides a K _d map for Fe(lll) on the first media such as Ln Resin. During the column 1 load step (0.1 M HCI), Fe may have a K _d of -10 ³ mL/g. Accordingly, most, if not all, of this contaminant can be retained on column 1 during the ⁹⁰ Y load/wash (i.e., the Y/Sr dilute acid mixture is provided to the first vessel). Additionally, Fe can have a K _d of -1300 mL/g at 8 M HCI. Accoringly, Fe can be retained on the column during the ⁹⁰ Y transfer step (see Table 3 below, and in accordance with system 25).

Table 3. Example behavior of Y(III) and Sr(II) through the tandem column process. While not exclusively evaluated during the present study, the behavior of Fe(III) and Zr(VI) are also shown.

Referring next to Fig. 4 system 35 is provided that includes a vessel 36 having a media 38 therein in fluid communication via conduit 44 to vessel 40 having a mixture 42 therein and operatively coupled to another conduit 46 for retrieving any eluent from vessel 36. In accordance with example implementations methods are provided for separating Y and Sr that can include providing a concentrated acid mixture 42 with this acid mixture comprising Y to vessel 36 having media 38 therein. This concentrated acid mixture can be provided from the methods and systems of Fig. 2 as described herein and vessel 36 can be aligned with system 25 for example to receive an acidic eluent therefrom.

In accordance with example implementations media 38 can include a resin such as diglycolimide resin, for example (diglycolamide)-based extraction chromatography resin, sold under the trade name DGA-Normal Resin (Eichrom Technologies, Ltd.). The particle size distribution used can be 20-50 pm, 50-100 pm, and/or 100- 150 pm Example extraction media can include N,N,N ^’ ,N ^’ -tetra-n- octyldiglycolamide.

The concentrated acid mixture can include at least some of the Sr for example as radioactive and stable isotopes of Sr such as ⁹⁰ Sr, ⁸⁹ Sr, ⁸⁸ Sr, or ⁸⁶ Sr. The method can include while providing the concentrated acid mixture retaining at least some of the Y from the concentrated acid mixture within vessel 36 and forming an eluent that can include at least some of the Sr in conduit 46. At least some of the concentrated acid mixture can include Zr and the method can include, while providing the concentrated acid mixture to vessel 36, retaining at least some of the Zr from the concentrated acid mixture. Additionally or separately, at least some of the concentrated acid mixture can include Fe and the method can include, while providing in the concentrated acid mixture, retaining at least some of the Fe from the concentrated acid mixture within vessel 36.

Referring next to Fig. 5 system 50 is provided that can include vessel 36 having media 38 therein as well as a concentrated acid mixture 42 that includes Y. In accordance with example implementations vessel 54 can include a dilute acid mixture 56. This dilute acid mixture can be provided to within vessel 36. The method can provide for, while providing dilute acid mixture 56 to within vessel 36, recovering a dilute acid eluent in conduit 52 that can include at least some of the Y from within vessel 36. The media within vessel 36 can be as described with reference to Fig. 4 for example.

The vessel 36 can include at least some of the Y for example as radioactive and stable isotopes of Y such as of ⁹⁰ Y, ⁸⁹ Y, ⁸⁸ Y, or ⁸⁶ Y, for example. The vessel can also cntain one or more of Zr or Fe and the method can further include for providing dilute acid mixture 56 to vessel 36 eluting at least some of one or both of Zr and/or Fe within vessel 36. As described herein the dilute acidic mixture can include HCI and the mixture can include an organic acid such as formic acid for example. Additionally while providing the dilute acid mixture to vessel 36, the method can include eluting at least some of the Sr within the vessel.

Referring next and with reference to Fig. 6 a system 60 is provided wherein vessels 14 and 36 are provided in tandem and embodiments of the systems of 10, 25, 35, and 50 described herein are utilized together to prepare an eluent 52 comprising Y. In accordance with example implementations and with reference to Fig. 6 a first mixture 12a comprising Y and Sr can be provided to a first vessel 14 having a first media 20 therein. This first mixture can be a dilute acidic solution and the first media can be an alkylphosphorus extractant resin such as HDEHP resin. At least some of the Y from first mixture 12a can be retained within vessel 14 utilizing media 20 for example.

In accordance with example implementations a second mixture 24a can be provided to first vessel 14 and the method can further include recovering a first eluent 28 and providing first eluent 28 that includes Y to a second vessel 36 having a second media 38 therein. The second mixture can be a strong acidic or concentracted acidic solution such as HCI and the second media can be a diglycolamide resin such as N, N, N\ N’-tetra-n-octyldiglycolamide. The method can further include retaining at least some of the Y from first eluent 28 within second vessel 36 utilizing media 38 for example and providing a third mixture 42 to second vessel 36 and, when providing third mixture 42, recovering a second eluent 52 that includes at least some of the Y from the first vessel. This third mixture can be a weak or dilute acid mixture such as HCI.

In accordance with other example implementations and with reference to Fig. 6 a first mixture 12a comprising Y and Sr can be provided to a first vessel 14 having a first media 20 therein. At least some of the Y from first mixture 12a can be retained within vessel 14 utilizing media 20 for example. In accordance with this embodiment the first mixture can be a strong acidic or concentracted acidic solution such as HCI and the first media can be diglycolamide resin such as N, N, N’, N’-tetra-n-octyldiglycolamide.

Continuing with this embodiment, a second mixture 24a can be provided to first vessel 14 and the method can further include recovering a first eluent 28 and providing first eluent 28 that includes Y to a second vessel 36 having a second media 38 therein. This second mixture can be a dilute or weak acidic solution that can include HCI and the first media can be an alkylphosphorus extractant resin such as HDEHP resin.

The method can further include retaining at least some of the Y from first eluent 28 within second vessel 36 utilizing media 38 for example and providing a third mixture 42 to second vessel 36 and, when providing third mixture 42, recovering a second eluent 52 that includes at least some of the Y from the first vessel. This third mixture can be a strong or concentrated acid mixture such as HCI. Additionally the method can provide that vessels 14 and 36 are of substantially different sizes with vessel 14 being at least as large but can be larger than vessel 36. In such a configuration, the Y recovered from the systems and methods of the process can be in a concentrated form and suitable for industrial use. Accordingly, the volume of vessel 14 can be larger than the volume of vessel 36.

Table 3 above also indicates the behavior of the four selected ions on the second media (DGA Resin) during the ⁹⁰ Y transfer, secondary wash, and ⁹⁰ Y elute steps.

An example system schematic 60 is shown in Fig. 6, and the labels are defined in Table 4 below. System 60 includes three pumps (PP, SP1 , and SP2). These pumps are provided as one or more of many potential fluid delivery systems, that can also include gravity.

Table 4. Listing of schematic labels presented in Figure 6. System 60 can be programmed to perform the series of steps outlined in Table 5 below. Delivered reagent volumes and flow rates through the columns may be set, as described below.

The reagent volumes programmed to be delivered to system 60 can be a function of the fluid delivery systems displacement volume, for example wherein one (or two) syringe volumes were delivered for a particular step. The delivered volumes can be deliberately programmed to be excessive (i.e., many bed volumes of reagent delivered through the columns).

Table 5. Tandem column purification method steps as tested. a. As tested; other concentrations, amounts delivered, and/or flow rates are contemplated. b. unretained; the -depleted load/wash solution was returned to a reservoir for eventual reuse. c. The bulk of the product is in the first -0.5 to -0.7 mL elute fraction. d. Water was flushed through all fluid transport lines and then the lines were purged with air. This included a water flush through the SL using thePP.

The flow rates may be ultimately limited by a number of factors, which may include the following: the back-pressure generated by the fluid pathways (primarily the columns); the amount of back-pressure the columns or fittings or pumps can handle prior to leaking; the amount of back-pressure the extraction chromatography resin can handle prior to bleeding excessive extractant; and the adsorption / desorption rate of the analytes on the column resins. The flow rate range indicated in Table 5 represents the two example rate values assessed. The lower flow rate may be performed for Runs 1 -4, and the higher flow rate may be performed for Run 5. The elapsed times required to perform the protocol described in Table 5 are shown in Table 6.

Table 6. Approximate, non-optimized elapsed times required to perform the isolation and purification process. ^a a. Indicated times include line blow-outs at each step and manual fraction collection activities (which introduced some additional time) b. Approximate values; elapsed times not closely tracked.

An example product solution, which had a ⁹⁰ Sr activity concentration of 1.25 Ci/mL, contained the stable Group II element concentrations listed in the 2nd column of Table 7 for Ca, Sr, and Ba. The Y concentration was based on the approximate mass concentration of ⁹⁰ Y present in a "Sr solution of this activity concentration. The element and activity concentrations in Table 7 are but one example of a "Sr product composition, and may not be representative of other "Sr batches.

Table 7. Stable elements added to simulated working stock, considering a target activity concentration of 1.25 Ci/mL. a. Sr mass concentration includes contributions from b. Per 7.5 Ci of example c. Based on Y specific activity and activity concentration of 1.25 Ci/mL. Given the example 1.25 Ci/mL ⁹⁰ Sr activity concentration, it was approximated that 6.4 ml_ of this solution would be required to obtain a synthetic 8 Ci ⁹⁰ Sr solution. A 6.0 mL sample injection loop can be installed in system 60 (“SL”, Figure 6), which can allow for routinely injecting a simulated "Sr solution, the salt content of which would be equivalent to ~7.5 Ci "Sr. Based on this 6.0 mL injection, the total (and pmoles) of the Group II elements are listed in Table 7.

"Sr / ⁹⁰ Y-bearing solutions that closely simulated the elemental composition of a stock Sr bearing solution was prepared. The solution stable element compositions are listed in Tables 1 and 7 and the spiked "Sr activity values are listed in Table 2.

The isolated ⁹⁰ Y produced by this (or any) purification method for medical purposes oftentimes requires a ⁹⁰ Y: "Sr activity ratio of >1 x10 ⁶ :1. Accordingly, for every 1 Ci ⁹⁰ Y in an isotope product, a maximum of 1 x10 ⁶ Ci (1 pCi) "Sr may be allowable. Based on the molar specific activities in Table 8, 1 pCi "Sr is equivalent to 4.7x1 O ⁴ pmoles (0.47 nmoles) of Group II elements (see, for example, simulated "Sr stock solution that is described in Table 7).

Table 8. Molar specific activity calculations for pure and as well as + Group II elements in simulated aged stock. a. 3523 Ci of ( Table 7).

Using the ⁹⁰ Y isolation and purification processes of the present disclosure, at least a 10 ⁶ -fold activity enrichment of ⁹⁰ Y over "Sr may be attainable. Based on the starting "Sr activity levels present in the five test runs (1 -5), the maximum "Sr activity levels in the ⁹⁰ Y product fractions are shown in Table 9. Table 9. activities that were spiked into each column load solution prior to purification (as replicated in Table 2), and the required maximum activity levels in the product fraction to achieve a Y activity enrichment factor. a. Mean and (±ls) values obtained from replicate measurements taken throughout the study interval. b. Maximum activity after a product enrichment factor.

The ⁹⁰ Y isolation and purification method (Table 5) can be performed using the system 60 shown in Fig. 6. The process can be performed five times, with ⁹⁰ Sr solution injections containing elevated Ca, Sr, Ba, and Y levels to simulate the levels in ~7.5 Ci of an example 90Sr product solution. "Sr activity levels in each of the five solutions is presented in Table 9; these activities can be dissolved in 6 ml_ of solution, and can be injected into the fluidic system using a sample injection loop (SL, Fig. 6).

The tandem column process can include a Ln resin and a DGA resin column, respectively. Once the ⁹⁰ Sr/ ⁹⁰ Y solution is loaded into the sample injection loop, in semi-automated fashion, for example, with a peristaltic pump, the ⁹⁰ Y isolation and purification process can be fully automated.

For Run 1 , which contained the least ⁹⁰ Sr/ ⁹⁰ Y activity of the five runs, a fraction collector can be employed to collect fractions of ~2 ml_ volume across the entire process (except for the ⁹⁰ Y elution step, during which <1 mL fractions were collected). The ⁹⁰ Y activity chromatogram is shown immediately after the conclusion of the run, and once the samples achieved secular equilibrium (Fig. 7). The first three ⁹⁰ Y elution fractions, representing 0.85 mL, can contain 83% of the ⁹⁰ Y in the injected sample.

When the "Sr in the fractions reach equilibrium with ⁹⁰ Y, the profile of the unretained "Sr, traveling from the sample injection loop and through the load/wash of column 1 can be determined. Example fractions shown can each be 2 mL in volume. The "Sr can be in the first 6 mL volume; the next 2 mL fraction can contain the bulk of the residual "Sr. This ~30 of may be carried from the sample injection loop as a segment of wash solution trapped between two air segments, for example. With the passing of the air segments, the "Sr activity may be at baseline for the remainder of the column wash. Overall, 97% of the "Sr in the load/wash fraction may be accounted for.

Runs 2 through 5 can contain approximately double the ⁹⁰ Sr/ ⁹⁰ Y activity of Run 1. Some fractions (the "Sr load effluent and the early ⁹⁰ Y elution), can be split into two. For the "Sr load, the first and second 10 mL fractions can be collected (except for Run 2, in which the first 18.2 mL and the second 2.35 mL were collected). For the ⁹⁰ Y elution, the first 0.72 to 0.84 mL can be collected in one fraction, and the remainder of the 2.5 mL ⁹⁰ Y elution volume in the second fraction.

In Fig. 8 and with reference to Tables 11 and 14, for Run 2, the ⁹⁰ Y yield can be determined in the primary elute fraction can be 95%; the "Sr recovery in the equilibrated primary load fraction can be 98%. In Fig. 9, for Run 3, the ⁹⁰ Y yield in the primary elute fraction can be 86%; the "Sr recovery in the equilibrated primary load fraction can be 97%. In Fig. 10, for Run 4, the ⁹⁰ Y yield in the primary elute fraction can be 86%; the "Sr recovery in the equilibrated primary load fraction can be 100%. In Fig. 11 , for Run 5, the ⁹⁰ Y yield in the primary elute fraction can be 89%; the "Sr recovery in the equilibrated primary load fraction can be 104%. Additionally, a 2 mI_ aliquot of the Run 5 primary column load/wash fraction effluent can be sampled immediately upon collection. The aliquot can be added to scintillation cocktail and the resulting sample counted by liquid scintillation analyzer (LSA). This sample can be periodically counted until the sample approaches ⁹⁰ Sr/ ⁹⁰ Y secular equilibrium. The LSA pulse height spectra at time “near-zero” and beyond are shown in Fig. 12. The high-energy ⁹⁰ Y b emission region is apparent above the lower-energy "Sr b emission region beyond ~1000 channels. The time “zero” spectra indicates virtually no ⁹⁰ Y is present in the sample - it has been adsorbed onto the primary Ln Resin column. As time progresses, ⁹⁰ Y ingrowth from the "Sr parent is observed.

Example performance of the tandem purification process is shown in Table 10 for ⁹⁰ Y. The table provides the total injected ⁹⁰ Sr/ ⁹⁰ Y into system 60, and the determined ⁹⁰ Y activity across all the collected fractions. Table 11 uses the Table 10 data to calculate the total ⁹⁰ Y recovery across all fractions (% activity balance), and the ⁹⁰ Y recovery in the column 2 elution.

Table 10. Determined activities ( i) obtained immediately after completion of the tandem column purification process, including fluidic system rinses and spent columns. Column 2 elution activities are in bold. a. Elapsed time at which activity fractions were calculated. b. Small aliquot of the original Y column load solution, extrapolated to total load volume. c. Mean and (±ls) values obtained from replicate measurements taken throughout the study interval. d. Activity sum across all collected / analyzed column effluent fractions, system rinses, and spent columns.

Across all five runs, 97.2±5.0% of the activity injected into the system can be accounted for. This ±5.0% was assessed as the uncertainty in the measurement approach. Consequently, this same relative uncertainty can be used to assign uncertainties to the individual ⁹⁰ Y elution yields. Across all five runs, it can be determined that the mean ⁹⁰ Y elution fraction was 87.8±4.3% of the total injected ⁹⁰ Y. The ⁹⁰ Y yields for Run 5, which was performed at higher flow rates (for example doubled) than Runs 1 -4, can result in ⁹⁰ Y product yields that can be statistically indistinguishable from the other runs. Table 11. Assessment of Y radiochemical yields in the Col. 2 product fractions following the tandem column purification process. Percentages calculated from values in Table 10. a. Elapsed time at which activity fractions were calculated. b. Ratio of activity in sum of fractions / activity in injected activity reference sample. c. Ratio of activity in C2 elute fractions / activity in injected activity reference sample. d. ± uncertainty values in ( ) were assigned based on the standard deviation for the Run 1-5 activity balance” (shaded cell).

The decay of each primary ⁹⁰ Y elution fraction for the five runs can be periodically monitored radiometrically. The activity of the initial ⁹⁰ Y sample can be normalized at time near-zero to “1 ”, then calculate the activity fraction across the next ~60 days. The charts in Fig. 13 through Fig. 17 show the decaying ⁹⁰ Y elution fraction overlaid atop the theoretical ⁹⁰ Y decay rate. In all cases, the decaying ⁹⁰ Y elution fraction can remain atop the theoretical curve. Should any "Sr have been present in these ⁹⁰ Y product fractions, the data would have begun to rise above the theoretical curve.

Upon approaching ~60 elapsed days of counting, the ⁹⁰ Y activity in the ⁹⁰ Y product fractions can became too low to accurately measure by the radiometric detector. At that point, some of the volume of the primary ⁹⁰ Y elution fractions may be sacrificed to inject into scintillation cocktail. The samples can then be counted across several more days by LSA. Because of the low activity levels, the samples may be counted for extended periods of time (2 h each) to obtain count rates, which may then converted to net count rates and ultimately decay units (Bq).

The decay rates from the LSA samples described above can be converted to decay rates for each analysis date; ⁹⁰ Y product fraction activity (Bq) results are displayed in Fig. 18. The elapsed time between the ⁹⁰ Y purification runs and the LSA analyses are shown in Table 12. As shown in Fig. 18, the decay rates for the samples continue to diminish over time; this is indication that the primary source of activity in the samples remains as ⁹⁰ Y. As such, these decay rates should continue to fall until ⁹⁰ Y achieves secular equilibrium with the trace levels of "Sr present in the samples.

Table 12. Elapsed time between LSA count results shown in Figure 17 and initiation of the tandem column purification.

The LSA data in Fig. 18 can be used to calculate the ⁹⁰ Sr decontamination factors in the primary ⁹⁰ Y product fractions. As activity levels continue to drop in the LSA samples, the "Sr decontamination factors continue to rise with time, as shown in Fig. 19.

Stocks of ⁹⁰ Sr bearing material can be considered a consumable item in the described process; some losses of ⁹⁰ Sr will be anticipated with each ⁹⁰ Y milking cycle. However, it is desirable to retain as much ⁹⁰ Sr as possible at the conclusion of the ⁹⁰ Y separation process. High ⁹⁰ Sr recoveries can be beneficial for at least two reasons: 1 ) unrecovered ⁹⁰ Sr will require additional purchases to replace losses in the stockpile, and 2) ⁹⁰ Sr activity levels in process effluents and peripheral components will increase the cost of waste disposal. Therefore, in addition to obtaining a high-purity ⁹⁰ Y product with high yields, a method that would result in high recoveries of ⁹⁰ Sr at the conclusion of each purification cycle would be beneficial. Ideally, virtually all of the "Sr would be recoverable in the effluents of the primary ⁹⁰ Y extraction column.

Activity results of fractions collected during the tandem column purification process (Fig. 7 through Fig. 11). Each figure presents the fractional activities near time “zero” (left-side), and near 50-60 elapsed days (right-side) following the performance of the ⁹⁰ Y purification process. While the left-side figures provided fractional ⁹⁰ Y activities, the right-side figures provided fractional "Sr activities.

The distribution of "Sr recovered from all the dual-column effluents and peripheral components involved in the tandem column purification process are listed in Table 13. The top shaded row provides the determined spiked activity of "Sr injected into each of the five runs; they range between ~400 and ~770 pCi. The row in bold reports the "Sr activity recovered in the column 1 ⁹⁰ Y load/wash effluents. The bottom shaded cell provides the sum of all "Sr accounted for during the tandem column purification process. Table 13. Determined r activities ( in each portion of the tandem column purification process, including fluidic system rinses and spent columns. Recovered activity in Col. 1 load/wash is in bold. a. Elapsed time at which activity values were obtained. b. Small aliquot of the original column load solution, extrapolated to total load volume. c. Mean and (±ls) values obtained from replicate measurements taken throughout the study interval. d. Activity sum across all collected and analyzed column effluent fractions, system rinses, and spent columns.

The data in Table 13 illustrates that virtually all of the "Sr activity was accounted for in the column 1 load/wash fraction. The fractions with the next-highest "Sr activities contained levels that were <1 .8x1 O ³ relative to the load/wash fraction (see “system rinses” in Run 5).

The data in Table 14 summarizes the ⁹⁰ Sr yields across each of the five runs. First, the fraction of ⁹⁰ Sr accounted for in the Table 13 “sum of fractions” vs. the “injected activity reference” values. Overall, it can be possible to account for 99.4 ± 3.2% of the "Sr relative to the reference aliquots that may be sampled prior to initiating the ⁹⁰ Y purification process. The relative uncertainty of ±3.2% can be employed to assign uncertainties to the "Sr activities accounted for in the “column 1 load/wash” fraction. Based on this, a mean "Sr recovery of 99.3 ± 3.1% in the column 1 load/wash effluents across all five runs can be obtained. Virtually all of the "Sr injected into the ⁹⁰ Y purification process may be recoverable in the fluids emerging from the primary Ln Resin column. Table 14. Assessment of radiochemical recoveries following the tandem column method. Percentages calculated from values in Table 13. a. Elapsed time at which activity fractions were calculated. b. Ratio of activity in sum of fractions / activity in injected activity reference sample. c. Ratio of activity in Cl load & wash effluents / activity in injected activity reference sample. d. ± uncertainty values in ( ) were assigned based on the standard deviation for the Run 1-5 activity balance” (shaded cell).