UNIVERSAL LIGANDS FOR THE ISOTOPE SEPARATION OF ELEMENTS

BACKGROUND OF THE INVENTION Field of the Invention

[0001] The present invention relates to methods for isotope separation of elements. More particularly, the present invention relates to methods of isotope separation of elements that employ attachment of ligands to the elements, which allows for the isotopic separation of a large number of elements as well as an increase in the efficiency and cost-effectiveness of the isotope separation. Description of the Prior Art

[0002] Isotope separation has been limited in practice to a few elements due to the fact that the methods commonly available, such as centrifuge or diffusion, require a stable, volatile feed material. The use of laser isotope separation techniques, such as Molecular Laser Isotope Separation (MLIS) and Atomic Vapor Laser Isotope Separation (AVLIS), provides even more limitations.

[0003] For example, the MLIS approach not only requires volatile, stable isotopic compounds, but also requires compounds that possess absorption bands which are isotopically active in order to work.

[0004] The AVLIS approach eliminates the need for stable volatile compounds but has difficulty in making a product that can readily be separated when activated. Additionally, AVLIS operations usually require at least two colors of operation, i.e., IR as well as UV wavelength, which greatly increases the cost of production as well as introduces technical issues with respect to timing and product separation. Typically, the cost of AVLIS separations is much higher than MLIS separations [0005] In addition, before isotope separation can be performed, the usual development path requires a long range screening program to identify candidate molecules that meet the requirements of the separation technology used. This approach dramatically increases the risks and costs associated with developing and implementing any type of isotope separation process.

SLTMMARY OF THE INVENTION

[0006] Accordingly, it is an object of the present invention to provide efficient, effective, economical methods for isotope separation of elements; i.e. metals.

[0007] It is another object of the present invention to provide methods for isotope separation that can be used on a large number of metals

[0008] It is a further object of the present invention to provide methods that allow for the separation of metals in which stable, volatile feed material compounds can be separated

[0009] The aforementioned objectives are met by the present invention, which provides methods of isotope separation of one or more isotopes of a metal, compπsed of selecting a hgand for attachment to one or more isotopes of the metal, chemically attaching the hgand to the one or more isotopes of the metal, and separating the one or more isotopes of the metal by an isotope separation technique

[0010] The methods of the present invention can be performed on isotopes of any metal having a valence of three or more Upon attachment of the hgand to the one or more isotopes of a metal, the metal-hgand forms a volatile, stable complex in which separation of the isotopes of the metal can be performed

[0011] Suitable ligands that are used in the methods of the present invention include, without limitation, boron-containmg ligands, such as BH ₄ , BD ₄ , CH ₃ BH ₃ or CD ₃ BD ₃

[0012] Suitable isotope separation techniques that can be used in the method of the present invention include, without limitation, gas centrifuge, gaseous diffusion, gaseous distillation or molecular laser isotope separation techniques

DESCRIPTION OF THE PREFERRED EMBODIMENTS

|0013] The present invention provides methods of isotope separation of one or more isotopes of a metal, compπsed of selecting a hgand for attachment to the one or more isotopes of the metal, chemically attaching the hgand to the one or more isotopes of the metal, and separating the one or more isotopes of the metal by an isotope separation technique

[0014] The methods of the present invention can be performed on isotopes of any metal having a valence of three or more Upon attachment of the hgand to the one or more isotopes of a metal, the metal-hgand forms a volatile, stable complex in which separation of the isotopes of the metal can be performed

[0015] Suitable hgands that are used in the methods of the present invention include, without limitation, boron-containing ligands, such as BH ₄ , BD ₄ , CH ₃ BH ₃ or CD ₃ BD ₃ [0016] Suitable isotope separation techniques that can be used in the methods of the present invention include, without limitation, gas centπfuge. gaseous diffusion,

gaseous distillation or molecular laser isotope separation techniques. Such isotope separation techniques are well known in the art and are exemplified in U.S. Patent No. 6,726,844; U.S. Patent No. 4,487,629; U.S. Patent No. 5,591,947; and 6,202,440. [0017] In an embodiment of the present invention, isotope separation of a metal is performed by selecting a ligand, attaching the ligand to the metal and using molecular laser isotope separation to separate the isotopes of the metal.

[0018] The ligand is selected based on its vibrational frequency so that the metal- ligand bond or a boron bond within the ligand has an absorption wavelength that is close to the emission wavelength of the laser used in the molecular laser isotope separation technique so that little emission tuning of the laser is required. [0019] The ligands of the present invention are large enough in conformation so as to surround a metal completely, resulting in a metal-ligand complex that has a neutral charge with no dipole, and thus is volatile. Ligands that are too large compared to the metal results in a metal not reacting fully with the ligand because of steric hindrance. Incomplete reaction with the ligand results in a metal-ligand-halide complex that has a dipole which results in the complex lacking volatility.

[0020] The ligand is selected based on the ligand's vibrational frequency so that the ligand has an absorption wavelength that is close to the emission wavelength of the laser used in the molecular laser isotope separation technique. The closer the absorption wavelength of the ligand to the emission wavelength of the laser, the less need there is for tuning the laser to the proper emission wavelength, which enhances the efficiency of isotope isolation.

[0021] The present invention is more particularly described in the following non- limiting examples, which are intended to be illustrative only, as numerous modifications and variations therein will be apparent to those skilled in the art. Example 1 - General Reaction of a Multivalent Metal with -BH^or -BDj [0022] A metal halide is reacted with a lithium borohydride compound to form a metal-borohydride complex and a lithium halide salt. [0023] The chemical structure of a lithium-BH ₄ complex is the following:

H

Li+ D

H / _H | \ H

[0024] The boron atom forms a hybridized orbital structure similar to CH ₄ .

[0025] BD ₄ may be used in place of BH ₄ to produce a metal-borodeuterium complex.

[0026] The reactions are illustrated below.

M ⁺ " Z _x + XLiBH ₄ → M(BH ₄ ) _x + xLiZ

M ^+x Z _x + XLiBD ₄ → M(BD _A ) _x + xLiZ where M = metal;

Li = lithium (sodium may be substituted here for lithium);

Z = chlorine, fluorine, iodine or bromine; x = valence of metal, in which valence is > 2.

Example 2 - General Reaction of Multivalent Metal with -BH _j CH _j or -BD _j CH _j [0027] A metal halide is reacted with a lithium methylborolhydride compound to form a metal -methylborohydride complex and a lithium halide salt. [0028]

M ^+I Z _τ + XLiBH ₁ CH ₁ → M (BH £H ₃ ) , + xLiZ

M ⁺¹ Z _x + XLiBD ₁ CH ₁ → M(BD ₃ CH^) _x + xLiZ where M = metal

Li = lithium (sodium may be substituted here for lithium)

Z = chlorine, fluorine, iodine or bromine x = valence of metal, in which valence of metal is > 2.

Example 3 - Calculation of Isotope Shift and Baseline Vibration for Zirconium-BHj and Zirconium-BD ₄ Complexes

[0029] The following indicates the general type of scoring calculations that would be carried out to determine what ligand would be used for each metal. Typical CO: lasers have an infrared emission wavelength ranging from about 800-1600 cm ^" . [0030] In general, calculation for a two-bodied vibration is the following (for δv = 1 i.e., one energy level shift or v = one quantum) (Note: two-bodied calculations are used instead of n ^lh spring-bodied calculations for ease of explanation):

K

δ^ =

2nC \ ,

[0031] where Aε = energy change (when δv = 1 ; i.e., one energy level shift; v = one quantum) k = effective spring constant (dynes/cm) μ = reduced mass (g)

C = speed of light (cm/sec)

[0032] The metal-BH4 complex can be shown as follows:

wherein the atoms within the circle = W ₁ and the H atom outside the circle is W ₂ , and where W = mass;

M = Zirconium (Zr)

[0033] Thus, this illustration shows a metal (Zr) ionically bonded to four BH ₄ molecules.

[0034] The calculation for a two-bodied vibration for the Zr-BH ₄ complex is the following:

The atomic mass unit (amu) of Zr = 90 (base amu); the amu of a Zr isotope = 91 ;

The amu for BH4 = 15

[0035] The wavelength shift between the base Zr and the Zr isotope is calculated as follows:

wavelength shift =

W\xW2

^90 ^~~ „ W,\ + W2 where: W\ = 15 x 3 + 90 + 3 + 1 1 = 149;

Wl = i ;

149x1 therefore: = .99333

149 + 1

150x1 and M _9i = .99338

150 + 1 [0036] The effective spring constant (k) for B-H is ≡ 5 x 10 ⁵ dyne/cm.

, _{t u} - _r 3.75x10 ^"9 wavelength shift

Yl .όόxlO ^"24 1-99666 .99338,

= 2.91 x 10 ³ (2.47 x 10 ^"5 ) = 0.072cm ^"1

[0037] Thus, for Zr with an amu = 90 the δε ₉₀ = 2.91 x 10 ³ = 2920 cm ^'1

[0038] This is the absorption wavelength for the base Zrgo metal.

[0039] Thus, the absorption wavelength for the isotope Zrgi metal is 2920 cm ^'1 +

0.072 = 2920.072 cm ^"1 .

|0040] Based on these calculations, the emission wavelength of the laser needs to be close to approximately 2920 cm ^"1 and no wider than 0.072 cm ^"1 so that it can effectively isolate the two Zr isotopes.

[0041] Calculation of the wavelength shift and absorption wavelength of the ligand

BD ₄ is as follows:

// ₉₀ = ^ ^4x2 í = 1.97590 ^ 164 + 2 U ₉ 1 = 165x2 = 1 . _r yπ/6zrπ05r

^ 165 + 2 wavelength shift = 2.91 x 10 ³

1.9759 Vl .97605

= 0.0775 cm

[0042] Thus, for Zr with an amu = 90 the As ₉₀ = 2.91 x 10 ³ = 2063 cm ^"1

[0043] Thus, the absorption wavelength for the isotope Zr ₉ i metal is 2063 cm ^"1 + 0.0775 = 2063.0775.

[0044] Based on these calculations, the emission wavelength of the laser needs to be close to approximately 2063 cm ^"1 and no wider than 0.0775 cm ^{" 1} so that it can effectively isolate the two Zr isotopes.

Example 4 - Calculation of Second Isotope Shift and Baseline for Zr-BH ₄ and Zr-BD ₄ [0045] Where amu for M (Zr) = 90 and amu for ligand (BH ₄ ) = 15:

(90 ₊ 4S)xlS ₌ 15 + 135

^ ₉₀ = 2.91 x lO ³ U ₇ =L= = 792 cm ^"1 \ -J\3.5 J

( i i A

|0046] The wavelength shift for Zrgo to Zrgi =

_. /13.5 V13.6 J = 0.291 cm ^"1 [0047] Where amu for M (Zr) = 90 and amu for ligand (BD ₄ ) = 19:

^ ₉₀ = 2.91 x 10 ³ f — !— 1= 709 cm ^"1 9 ⁰ U 6.83 J

10048] The wavelength shift for Zr9o to Zr9i =

_. /16.83 Vl 6.84 ) = Q21λ cm ^"1 Example 5 - Determination of Ligand Molecular Weight (amu) for a Particular Laser

U ( l ) v 2*3x10'° \ 1.66*1 ⁽ T ²⁴ U^ J where v = vibrational frequency of a laser

|0049] Solve for μ: μ = f - 2*(3xl O ¹⁰ )( _λ 1.66x10 ^"24 )

1

M = — v

.2427

K

« ^■ 16.97 μ ⁼ -^- where μ = general formula for reduced mass.

[0050] We now look for the difference in molecular weight (amu) among a metal

(M), boron (B) and H or D.

|0051] For H: M^[B(H)J _x

|0052] For D: M ^+x [D(H)v] _x

where the numerator and the denominator are the same and = A [0053] Thus: μ H + μM + μA = HM + HA [0054] Solve for M: μU + μA = M(H-//) [0055] When M >0, then H > μ

[0056] Therefore, in picking an active atom on a ligand: ligand (L) > — 16.97 v

[0057] An alternate approach is to begin with the available laser emissions line (v) and determine what the reduced mass and, therefore, what ligand is to match. |0058] Therefore, if the specific laser of interest has an emission frequency of approximately 800 cm ^" , then with a spring constant of approximately 5 x 10 , the molecular weight of the ligand would need to be at least 13.3 grams/mole. Thus, a ligand such as -BH ₄ could be used. However, more specific calculations would have to be carried out to determine the specific ligand for a particular metal, as described hereinabove.

|0059] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications that are within the spirit and scope of the invention, as defined by the appended claims.