WO2011141697A2

WO2011141697A2 - Enrichment of isotopes using substrates

Info

Publication number: WO2011141697A2
Application number: PCT/GB2011/000714
Authority: WO
Inventors: John Fink; Daoyi Chen
Original assignee: John Fink; Daoyi Chen
Priority date: 2010-05-11
Filing date: 2011-05-10
Publication date: 2011-11-17
Also published as: GB2495021A; GB201222251D0; GB2495021B; GB201007877D0; WO2011141697A3

Abstract

The present invention relates to a process for enriching isotopes using colloidal substrates, the specific methodology of using them and to uses therefor. The substrate material of the invention comprises surface ionic groups covering at least part of the substrate. The substrate material of the invention provides a binding mechanism to the isotopes resulting in enrichment in at least one of the isotopes.

Description

DESCRIPTION

Enrichment of isotopes using substrates

BACKGROUND OF THE INVENTION

The present invention relates to an isotope separation effect observed in colloidal substrate materials, to methods of applying them and to uses therefor. In particular the invention concerns such materials, methods and uses for the application of this separation effect for the enrichment of isotopes.

Most elements exist in nature as a mixture of isotopes differing in mass as a result of differences in the number of neutrons in their atomic nuclei. Isotopes of an element have very similar physical and chemical properties that make their separation difficult but some possess distinctly different nuclear properties that make these isotopes particularly useful.

Important needs exist for enriched isotopes of virtually every element in the periodic table, although the required quantities of some may only be on the order of grams per year

(Separated isotopes: Vital tools for science and medicine; Office of chemistry and chemical technology, national research council: Washington, DC. 1982). Some highly enriched stable isotopes are vital to fundamental research in nuclear physics and chemistry, solid state physics, geoscience, and biology and medicine. Many separated non radioactive isotopes are used as nuclear targets in research reactors or particle accelerators to produce particular radioisotopes, which are then used as radiotracers or radiopharmaceuticals. High isotopic enrichment of the target is a key to avoiding possible undesirable physiological side effects because of the presence of other radioisotopes, which may result from isotopic impurities in the target.

Isotopes are also used as tracers in many research areas. Most physical, chemical and biological systems treat isotopes of an element in exactly the same way, so a system can be investigated with the assurance that the method used for investigation does not itself affect the system. Using tracing techniques, research is conducted with various radioisotopes which occur broadly in the environment to examine the impact of human activities. For example, the isotope N-15 is presently used as a tracer in environmental research for studying the origin and fate of nitrogen containing compounds used in agriculture, automobile emissions and marine environments. It is also used in the field of nuclear medicine for the production of certain radionuclides. Low cost schemes for enriching this isotope, therefore, would be of considerable interest.

High isotopic enrichment is a key for most of these applications. Usually, there are several methods available for separation of a given isotope, but choice depends on the enrichment level and quantity required for the separated product, availability of suitable feed material, and numerous other factors. A variety of methods have been developed especially adapted to separating isotopes. Some methods are based directly on mass differences; others result from less obvious mass dependent changes in atomic and molecular properties. Although the common principles underlying isotope separation are relatively few, a large variety of processes have been published as scientific papers and patents. A review of such processes used (or proposed) on the industrial or laboratory scales may be found in Benedict, M;

Pigford, T.H; Levy, H.W; Nuclear Chemical Engineering, 2 ed; McGraw-Hill, New York, (1981). These include; gaseous diffusion, gas centrifugation, laser isotope separation, separation nozzle, electromagnetic separation, thermal diffusion, chemical exchange and distillation. Others include ion exchange resins (U.S.Pat.No.4,280,984) and electromigration (Electrochemistry; Volume 1, p.173-174, Royal Society of Chemistry, 1970). The methods used for the enrichment of isotopes N-15 involve several various techniques. One of these is the use of ion-exchange resins. For, example, Sugiyama et al (Journal of Nuclear Science and Technology, Vol. 39, No. 4, p. 442-446, April 2002) passes a solution of NH4CI in methanol through a glass tube packed with cryptand(2B,2, l) polymer. In this case, however, the levels of enrichment of N-15 is not very high above natural abundance in a single step.

Other methods involve laser excitation. This involves using lasers to selectively excite one isotope to a higher energy state whereby it dissociates and is collected via a deflection through an electric field. For example, Ambartsumyan et al. (Journal of Experimental and Theoretical Physics Letters, Vol. 17, pp. 63-65, 1973) disclose isotope separation ofN-14 and N-15 by a two-step photodissociation of ^{l 4}NH₃ and ¹⁵NH₃, in which monochromatic radiation of a frequency vl selectively excites a vibrational transition of molecules of only one isotopic composition. The molecules are simultaneously illuminated with light of frequency v2 , the quantum energy of which is sufficient for photodissociation of only the vibrationally excited molecules. Although the separation of nitrogen isotopes with a laser can give high isotopic enrichment factors the yields of those enriched isotopes is not sufficiently large for bulk supplies of these isotopes. It is also a costly process and gives rise to the possibility of isotopic scrambling due to different intermediate chemical reactions.

Current separation of N- 15 is accomplished by NO distillation, or by chemical exchange between NO and HN0₃. Although the former process has a reasonably high separation factor of about 1 .027, the energy consumed by distillation to enrich isotopes is high, making this process not particularly economical. The latter (Nitrox Process) process has an enrichment factor of about 1.055 but yields can be fairly low (grams per day) to adequately satisfy bulk production.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a use of a colloidal substrate and

methodology to enrich isotopes. It is a further object of the invention to provide such a system which is sufficiently versatile to be useful in commercial applications. Another object of the invention is to provide a system which can be applied reproducibly, conveniently and without excessive expense.

According to the present invention there is provided a substrate material comprising:

a colloidal substrate;

a colloidal substrate wherein at least part of the substrate surface comprises surface ionic groups;

a colloidal substrate wherein at least part the substrate surface comprises surface ionic groups capable of binding the isotopes to the surface of the substrate wherein enrichment is effective.

The substrate has been shown to exhibit an enrichment effect between pairs of isotope ions as adsorbate. The substrate of the invention therefore provides a novel technique which may find application as means of enriching isotopes in isotope mixtures instead of the

aforementioned technologies. Furthermore, existing technologies used in the current areas of isotope enrichment could easily be replaced by the present invention. To our knowledge, there are no prior art substrate or other techniques using the substrate for the means described above. Many methods used for isotope enrichment tend to be insufficient for many commercial applications as some are expensive, some are not viable to supply high enrichments or yields of isotopes and most are technically complex.

In the context of this document, "adsorbate" is used to refer to the surface adsorbed isotopes.

The adsorbate may form a bound layer upto any depth on the substrate. Such an layer may comprise, for example, a partial, single, double or diffuse adsorbate layer around the substrate.

Preferably the substrate surface layer is ionic. Preferably the substrate comprises a single material. The substrate of the invention may comprise a material of multiple layers comprising one or more materials, provided that the surface layer is capable of binding to the isotopes.

The enrichment of isotopes is preferably provided by means of controlled deposition onto the surface of the substrate capable of adhering to the isotopes.

The present invention further provides a method for using a colloidal substrate useful for the separation of isotopes that occurs as a result of substrate-isotope contact or interaction comprising the steps of:

a) providing a colloidal substrate capable of binding isotopes to the surface layer;

b) contacting the substrate with the isotopes under conditions effective to enrich at least partially one of the isotopes; and

c) isolation of the substrate in (b) and retrieval of the surface layer isotopes enriched in one isotope.

d) isolation of the supernatant liquid in (b) and retrieval of the isotopes enriched in one isotope.

In a preferred embodiment of the invention there is provided a substrate comprising colloidal silica capable of adhering to the isotopes with properties that results in enrichment of at least one of the isotopes.

Isotopes include atoms, molecules or ions.

Isotopes include NH₄ ⁺ ions.

The substrates, methods and uses of the invention has advantages over other methods used in isotope enrichment. For example, the overall apparatus, procedure embodying the invention would greatly simplify and reduce costs per unit of isotopes enriched and improve yields by using a single-step bulk flocculation of the substrate-adsorbate.

The substrates and conditions of the invention may also be adapted to provide a simple way of enriching a further variety of isotopes, for example isotopes which have a high demand but of are limited supply.

The invention may be beneficial for providing nitrogen isotope tracers for studies of sources and sinks of artificially introduced chemicals to the environment, e.g., fertilizers in cultivated land use as well as providing enrichment of nitrogen isotopes for use in radiopharmaceuticals.

It will be apparent to the skilled person, that the substrate and methods of the invention can be carried out using materials which are non-toxic to human health. For example, the use of amorphous colloidal silica (Si0₂ - silicon dioxide) is known to be non-toxic to humans.

The substrate may be any dimension. This invention is particularly suited substrates having having at least one dimension which is measurable at the nanometre level, for example a feature which measures from about 1 to about 200 nm, preferably from about 1 to about 150 nm, even more preferably from about 1 to about 100 nm, and most preferably less than about 50 nm in at least one dimension.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be more particularly described with reference to the following Figures and Examples in which:

TABLE. 1 shows the enrichment of levels of ¹⁵NH4⁺ in solution with substrate-isotope interactions in accordance with the invention; the data being generated by a isotope ratio mass spectrometer (IRMS).

FIG. 1 shows graphically the enrichment levels of ¹⁵NH₄ ⁺ with substrate-isotope interactions from examples 1 to 6 in Table. 1 in accordance with the invention;

FIG. 2 shows graphically the enrichment levels ^{l 5}NH₄ ⁺ with substrate-isotope interactions from examples 7 to 9 in Table. 1 in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Colloidal substrates in accordance with the present invention are provided. The colloidal substrate provides support as well as a suitable surface area for the adsorption/enrichment of the isotopes.

A preferred substrate for the invention is silica which is a inorganic polymer comprised of Si- O network macro-structure and advantageously can be in colloidal form, finely ground powder or rigid bulk material whichever is desired for the substrate. Silica is a readily available material common in many materials and uses and is the most abundant mineral in the earth's crust. Advantageously, the substrate of the present invention may utilize silica thus imparting these virtues on the substrate material.

Preferably, the substrate is a clean, purified, well characterised support.

The substrate may also be applied to the isotopes through either immersion or through other application techniques known in the art for applying adsorbates to adsorbents. Furthermore, the isotope concentrations used in the invention are determined by the substrate, isotope type, size, abundances as well as the desired enrichment. Preferably, the isotopic conditions which are chosen should result in the formation of a ionically bound monolayer.

A substrate, methodology carried out from the aforementioned steps may initiate a distinct set of characteristics allowing for a method of enriching isotopes. In order to further illustrate the principles and operation of the present invention, the following examples are provided.

However, these examples should not be taken as limiting in any regard,

EXAMPLE 1

An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing

approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0995 g of ' tCl and 0.1013 g

(Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH₄ ⁺ isotope in solution from 50 N atom % to 39.7033 N atom % as a substrate contact or interaction. In this case the adsorbate ions are predominantly

EXAMPLE 2

In a variant of Example 1 , an aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0435 g of ¹⁴NH₄C1 and 0.0443 g ^NELCl (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ^NH isotope in solution from 50 N atom % to 39.6638 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are predominantly ¹⁴NH₄ ⁺.

EXAMPLE 3

In a variant of Example 1 , an aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0261 g of ¹⁴Νϋ,α and 0.0266 g ¹⁵NrL,Cl (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH₄ ⁺ isotope in solution from 50 N atom % to 39.4088 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are predominantly ^,4NH4⁺.

EXAMPLE 4

In a variant of Example 1, an aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0174 g of ¹⁴NH₄C1 and 0.0177 g ^NRtCl (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH₄ ⁺ isotope in solution from 50 N atom % to 38.6192 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are predominantly ¹⁴NHi⁺.

EXAMPLE 5

In a variant of Example 1, an aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0124 g of ¹⁴NH₄C1 and 0.0127 g ¹⁵ ¾α (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH4⁺ isotope in solution from 50 N atom % to 37.5893 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are predominantly ^,4Nrlt⁺.

EXAMPLE 6

In a variant of Example 1, an aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0062 g of ¹ NH₄C1 and 0.0063 g ^NEUCl (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C overnight. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH4⁺ isotope in solution from 50 N atom % to 36.6442 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are predominantly ¹⁴NH₄ ⁺.

EXAMPLE 7

A further variant of Example 2 was used to investigate isotope separation after 6 weeks in suspension at 4 °C. An aqueous dispersion of silica sol, (Ludox TM-50, Sigma- Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0436 g of ¹⁴NH₄C1 and 0.0443 g ^l5NH₄Cl (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C for 6 weeks. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ^{l 5}NH₄ ⁺ isotope in solution from 50 N atom % to 38.9944 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are

predominantly ¹⁴NH₄ ⁺.

EXAMPLE 8

A further variant of Example 5 was used to investigate isotope separation after 6 weeks in suspension at 4 °C. An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0124 g of

and 0.0127 g ¹⁵NH₄C1 (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C for 6 weeks. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH₄ ⁺ isotope in solution from 50 N atom % to 34.1839 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are

predominantly ¹⁴NH₄ ⁺. EXAMPLE 9

A further variant of Example 6 was used to investigate isotope separation after 6 weeks in suspension at 4 °C. An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 40% w/w silica in a 100 cm3 volumetric flask. To 5 ml of this dispersion, 0.0062 g of ¹⁴NH C1 and 0.0063 g ¹⁵NH₄C1 (Cambridge Isotopes) was added with gentle mixing for 1 minute. The sample was then stored in a refrigerator at 4 °C for 6 weeks. 1.5 ml of this mixture was then transferred to a 2 ml centrifuge tube and stored in ice water. These were then centrifuged at 16,000 rpm for 30 minutes. Then, 0.5 ml of the supernatant liquid was removed and made up to 1 ml with distilled water and the sample sent off for IRMS analysis (Isoanalytical Ltd). TABLE. 1 shows the results of this experiment and clearly show a depletion of the ¹⁵NH4⁺ isotope in solution from 50 N atom % to 31.5142 N atom % as a result of substrate contact or interaction. In this case the adsorbate ions are

predominantly ¹⁴NH₄ ⁺.

Claims

CLAIMS What is claimed is:

1. A enrichment of isotopes using a substrate comprising: a colloidal material; a surface adsorbing layer covering at least part of the colloid; the surface adsorbing layer providing the colloid with a binding layer for binding isotopes to the colloid wherein isotope enrichment is effective.

2. The substrate according to claim 1, wherein the colloidal particles comprise nano- particulate material.

3. The substrate according to claim 1, wherein the colloidal particles are from about 5 nm to about 80 nm in diameter.

4. The substrate according to claim 1, wherein the material of the colloid is formed from a material selected from the group consisting of polymers, glasses, ceramics, carbon, metals, composites and combinations thereof.

5. The substrate according to claim 1, wherein the colloid comprises silica.

6. The substrate according to claim 1 , wherein at least part of the surface adsorbing layer comprises surface ionic groups.

7. The substrate according to claim 1, wherein at least part the surface adsorbing layer comprises surface ionic groups capable of binding the isotopes to the surface of the colloid wherein the enrichment is effective.

8. The substrate according to claim 1 wherein isotope enrichment is effective.

9.The substrate according to claim 8, wherein the isotopes comprise atoms, molecules or ions.

10. The substrate according to claim 8, wherein the isotopes further comprise metals, metals and metalloids and combinations thereof.

1 1. The substrate according to claim 8, wherein the isotopes comprise nitrogen ions.

12. The substrate according to claim 8, wherein the isotopes comprise ammonium ions.

13. A method for using a colloidal substrate for enriching of isotopes comprising the steps of: a) providing a colloidal material with a surface adsorbing layer suitable for forming a binding layer between the colloid and isotopes; b) enriching isotopes on the surface adsorbing layer of the colloid.

14. The method of claim 13 wherein step b) further comprises enriching isotopes in solution.

15. The method according to claim 13, wherein the colloidal particles comprise nano- particulate material.

16. The method according to claim 13, wherein the colloidal particles are from about 5 nm to about 80 nm in diameter.

17. The method according to claim 13, wherein the material of the colloid is formed from a material selected from the group consisting of polymers, glasses, ceramics, carbon, metals, composites and combinations thereof.

18. The method according to claim 13, wherein the colloid comprises silica.

19. The method according to claim 13, wherein at least part of the surface adsorbing layer comprises surface ionic groups.

20. The method according to claim 13, wherein at least part the surface adsorbing layer comprises surface ionic groups capable of binding the isotopes to the surface of the colloid wherein isotope enrichment is effective.

21 . The method according to claim 13, wherein isotope enrichment is effective.

22. The method according to claim 13, wherein the isotopes comprise atoms, molecules or ions.

23. The method according to claim 13, wherein the isotopes further comprise metals, non- metals and metalloids and combinations thereof.

24. The method according to claim 13, wherein the isotopes comprise nitrogen ions.

25. The method according to claim 13, wherein the isotopes comprise ammonium ions.