Method and apparatus for isotopic lithium separation

Abstract

A method, a use of a distillation column and distillation column for isotopically separating lithium-6 and lithium-7 from a mixture thereof. The method involves using molecular distillation with a molecular distillation column (22) containing a column of structured packing (23).

Description

[0001] METHOD AND APPARATUS FOR ISOTOPIC LITHIUM SEPARATION

[0002] TECHNICAL FIELD

[0003] The disclosure relates to methods and distillation apparatus for isotopically separating lithium-6 and lithium-7 from a mixture thereof, in particular isotopic separation of lithium-7 and lithium-6 from naturally occurring lithium.

[0004] BACKGROUND

[0005] Naturally occurring lithium is a mixture of lithium-7 and lithium-6 in varying proportions due to the geological isotopic separation of the two, with the lithium-6 concentration varying roughly between 2% and 8%, with 5% being the norm.

[0006] Molten salt reactors utilizing lithium fluoride or chloride salts need to have highly enriched lithium-7 due to the large differences in the thermal capture neutron cross sections of lithium-6 and lithium-7, of 941 barn and 0.014 barn, respectively for thermal neutrons, and partly to minimize highly undesirable tritium production from neutron capture by lithium- 6.

[0007] Naturally occurring lithium has a thermal capture crosssection of roughly 65 barn, which is very high when compared to e.g. naturally occurring sodium, with a thermal capture cross-section of 0.5 barn, or naturally occurring potassium, with a thermal capture cross-section of 2 barn. For comparison 99.9% enriched lithium-7 (3N 7Li) has a thermal capture crosssection of 0.95 barn, 99.99% enriched lithium-7 (4N 7Li) has a thermal capture cross-section of 0.11 barn, and 99.999%

[0008] 03693-PCT enriched lithium-7 (5N 7Li) has a thermal capture crosssection of 0.02 barn. This means that 99.99% to 99.999% enriched lithium-7 (4-5N 7Li) is desired for the use of lithium in molten salt reactor salts.

[0009] Examples of lithium fluoride salt that can be used in molten salt reactor salts are 7LiF-BeF2, 7LiF-BeF2-UF4 , 7LiF-ThF4, 7LiF-ThF4 -UF4 , and 7LiF-ThF4-PuF3. Examples of lithium chloride salt that can be used in molten salt fast reactors are 7LiCl-KCl-UC13 , 7LiCl-UC13, 7LiCl-PuC13, 7LiCl-UC13- PuC13.

[0010] Highly enriched lithium-7 is especially important for thermal molten salt breeder reactors, which have the potential to scale much faster than other nuclear technologies given a constrained supply of fissile fuel. For scaling thermal molten salt breeder reactors to meet global energy demand in the coming decades, an annual enrichment capacity of lithium-7 of several tens of thousands of tons would be needed, which is a major challenge for scaling this type of reactor.

[0011] When lithium-6 captures a thermal neutron there is a high probability that it leads to tritium production. The production of tritium from lithium-6 is considered a radionuclide release hazard for nuclear reactors, while it is the goal in some fusion reactor blankets. Thus, nuclear (fission) reactors utilizing lithium need enriched lithium-7 while fusion reactors need enriched lithium-6, and the

[0012] 03693-PCT isotopic separation of lithium can serve both industries synergistically.

[0013] Examples of fluoride salts that can be used in fusion reactor blanket salts are 6LiF-BeF2 and 6LiF-7LiF-BeF2 , where the beryllium also serves as a neutron multiplier, and examples of molten metal alloys that can be used in fusion reactor blankets are Li, Li-Pb, and Li-Bi.

[0014] The predominant method for industrialized isotopic lithium separation is the COLEX process, which is a two-liquid-phase chemical exchange, between lithium hydroxide aqueous solution and a mercury-lithium amalgam, where lithium-6 has a slightly larger affinity for the mercury amalgam. The COLEX process involves large quantities of mercury and mercury compounds, which along with its high energy consumption makes the process unattractive for future isotopic lithium separation.

[0015] The COLEX process COLEX separation is a mercury-based chemical approach for isotopic separation of lithium-6 and lithium-7, with aqueous lithium hydroxide (LiOH) contacted with lithiummercury amalgam, exploiting greater affinity of lithium-7 than Lithium-6 for the element mercury. The COLEX separation process involves passing a counter-flow of an aqueous lithium hydroxide flow up and a lithium-mercury amalgam flows down through a series of exchange columns containing a cation exchange resin. Mercury drains the lithium-6 fraction preferentially, although lithium-7 primarily flows with the hydroxide. The amalgam is separated from the lithium (enriched with lithium-6) at the bottom of the column, and the mercury is recovered for subsequent use. The lithium-7 fraction is electrolyzed to release the lithium hydroxide solution at the

[0016] 03693-PCT top. The operating temperature, flow rate, and column length all affect the enrichment that can be achieved with this process .

[0017] Facilities at Oak Ridge, Tennessee using the COLEX process were operated between 1955 and 1963 to generate the current US stockpiles of 6Li and 7Li

[0018] The COLEX has several downsides, such as:

[0019] Toxicity of the large amounts of mercury involved.

[0020] Tendency of amalgams to decompose in aqueous solutions. Formation of dangerous mercury-containing waste High energy consumption.

[0021] Potentially disastrous environmental implications since a substantial amount of mercury is required (24 million pounds were used in the U.S. between 1955 and 1963) and many opportunities for leaks into the environment exist.

[0022] Many methods have been researched and developed for the isotopic separation of lithium, including two-liquid-phase chemical exchange, ion exchange resins, ion exchange membranes, laser absorption, thermal diffusion, electromigration, fractional crystallization, microalgal, and molecular distillation. While multiple of these methods have been shown to work, none of them has shown to be an economical replacement for the COLEX process.

[0023] Isotopic separation of lithium metal using molecular distillation has seen limited research, with only a handful of articles published in the late 1950s and early 1960s and

[0024] 03693-PCT was ultimately abandoned. One example of a publication of this period is "SOME EXPERIMENTS ON THE SEPARATION OF LITHIUM ISOTOPES BY MOLECULAR DISTILLATION", by D.B. Trauger, J. J. Keyes, Jr. G. A Kuipers and D. M. Lang, PROCEEDINGS OF THE SYMPOSIUM ON ISOTOPE SEPARATION, AMSTERDAM, 1957.

[0025] CN113750797 discloses a device for separating boron trifluoride with high abundance isotope boron 11 by low- temperature vacuum distillation. The device comprises a low- temperature isotope separation tower which comprises several interior plates, a tower top outlet connected to a condenser, a tower bottom outlet connected to a reboiler, a low- temperature refrigeration system, and an automatic control feeding system which is disposed between the above-mentioned outlets. A top product extraction system is comprised on a reflux line going from a condenser outlet to an inlet on top of the tower. Likewise, a bottom by-product extraction system is comprised on a reflux line going from a reboiler outlet to an inlet on the bottom of the tower. The device also comprises a product storage system, a vacuum system and an exhaust gas treatment system.

[0026] SUMMARY

[0027] It is an object to provide a method and system for isotopic lithium separation that overcomes or at least reduces the problems above.

[0028] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures .

[0029] 03693-PCT Lithium metal melts at 180°C and boils at 1330°C, so simple distillation seems unattractive due to the high boiling point of molten lithium and low separation factor at high temperatures. However, the inventor realized that at temperatures well below the boiling point of lithium, the separation factor is enough that efficient isotopic separation can be performed, due to the high molecular mass difference of molten lithium-6 and lithium-7. The difference in molecular mass between lithium-6 and lithium-7 is enough that a theoretical separation factor of 1.08 can be achieved, with the differences in vapor pressure being small in comparison .

[0030] For efficient molecular distillation, the mean free path length of a vapor atom or molecule has to be on the order of or longer than the distance between the evaporation and condensation surfaces. The mean free path length of the lithium atom will depend on the quality of the still's vacuum and lithium vapor pressure, which in turn depends on the temperature of the lithium. The mean free path length of lithium vapor is roughly 50mm at 400°C, 20mm at 500°C, and 15mm at 550°C. Due to the longer free path length at lower temperatures, it is generally more effective to run the molecular distillation at lower temperatures, but the rate of distillation will also be lower due to the lower evaporation rate. Thus, a balance needs to be found between efficient distillation and distillation rate for a particular still. The inventor arrived at an optimum evaporation surface temperature of approximately 500-600°C with the cold side

[0031] 03693-PCT approximately 100°C colder, i.e. approximately 400-500°C for lithium molecular distillation.

[0032] The inventor arrived at the insight that liquid short-path molecular distillation of lithium is attractive since it allows for multiple stages which can have a very short path between the evaporating and condensing surfaces. Furthermore, the inventors arrived at the insight that the still can be constructed using commonly available materials and manufacturing methods since molten lithium is compatible with regular stainless steel, However, this type of still needs simultaneous heating of the bottom of the still while cooling the top of the still at each stage, rendering it energy intensive .

[0033] According to a first aspect, there is provided a method of isotopically separating lithium-6 and lithium-7 from a mixture thereof, comprising: providing a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 to a molecular distillation column or a series of molecular distillation columns, the molecular distillation column comprising packing configured for condensation and evaporation of lithium for isotopically separating lithium-6 and lithium-7, and

[0034] - separating the feed stream into an enriched molten lithium- 6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream in the molecular distillation column or in the series of molecular distillation columns.

[0035] 03693-PCT By providing a distillation column containing a long column of packing that is suitable for molecular isotopic distillation of lithium, a large number of theoretical distillation stages are created allowing for a large separation factor in the packing columns and thus vastly simplifying the construction of the molecular still.

[0036] In a possible implementation form of the first aspect, the method comprises: heating lithium in a lower area of the molecular distillation column to temperatures below the boiling point of lithium and at least partially evaporating the molten lithium in a lower area of the molecular distillation column, and

[0037] - condensing lithium vapor in a condenser that is operably coupled to an upper area of the molecular distillation column, to drive a counterflow of molten lithium and lithium vapor in the molecular distillation column.

[0038] In a possible implementation form of the first aspect, the method comprises isotopically separating lithium-6 and lithium-7 in the packing.

[0039] In a possible implementation form of the first aspect, the method comprises causing a counterflow of molten lithium metal and lithium metal vapor in the packing.

[0040] In a possible implementation form of the first aspect, the method comprises removing an enriched molten lithium-7 stream from the lower area of the molecular distillation column.

[0041] 03693-PCT In a possible implementation form of the first aspect, the method comprises removing an enriched vapor lithium-6 stream from an upper area of the molecular distillation column.

[0042] In a possible implementation form of the first aspect, the method comprises removing an enriched molten lithium-6 stream from the condenser.

[0043] In a possible implementation form of the first aspect, the method comprises applying a high or ultra-high vacuum to the interior of the molecular distillation column.

[0044] In a possible implementation form of the first aspect, the packing comprises structured packing.

[0045] In a possible implementation form of the first aspect, the packing comprises at least one column of packing, preferably at least one column of structured packing that comprises a multitude of theoretical stages.

[0046] In a possible implementation form of the first aspect, the packing comprises evaporation surfaces and condensation surfaces, preferably comprising counterf lowing molten lithium metal and lithium metal vapor over the evaporation and condensation surfaces.

[0047] In a possible implementation form of the first aspect, the method comprises selecting the distance between the evaporation surface and condensation surface area as a function of the operating temperature of the molecular distillation column.

[0048] 03693-PCT In a possible implementation form of the first aspect, the method comprises keeping the molten lithium in its free molecular flow regime with the mean free path of molecules preferably being less than the distance between the evaporation condensation surfaces of the packing material.

[0049] In a possible implementation form of the first aspect, the distance between evaporation and condensation surfaces of the still, preferably the evaporation and condensation surfaces of the packing, is equal to or shorter than the mean free path length of the lithium atoms.

[0050] In a possible implementation form of the first aspect, the method comprises keeping the temperature of the evaporation surfaces at approximately 600°C.

[0051] In a possible implementation form of the first aspect, the method comprises keeping the temperature of the condensation surfaces at approximately 500°C, preferably in combination with a distance between the evaporation surfaces and the condensation surfaces of 20 mm or less.

[0052] In a possible implementation form of the first aspect, the distillation column is operably coupled to one or more of:

[0053] - an evaporator,

[0054] - a condenser,

[0055] - a source of the mixture of the molten lithium stream,

[0056] - a reflux,

[0057] - a vacuum system for pulling a high or ultra-high vacuum.

[0058] 03693-PCT In a possible implementation form of the first aspect, the distillation column comprises one or more of:

[0059] - a first upper outlet port for enriched vapor lithium-6,

[0060] - a second lower outlet port for enriched molten lithium-7,

[0061] - trace heating elements,

[0062] - thermal insulation.

[0063] According to a second aspect, there is provided a use of a distillation column that comprises packing to perform molecular distillation of lithium for isotope separation of lithium-6 and lithium-7.

[0064] In a possible implementation form of the second aspect, inert gas is recirculated through the molecular distillation column, from a lower position in the distillation column to a higher position in the distillation column, to provide an advection flow to carry the lithium vapor in a counter flow direction to the condensed molten lithium moving from the higher position in the distillation column to the lower position in the distillation column under the influence of gravity .

[0065] According to a third aspect, there is provided a lithium distillation apparatus for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the distillation apparatus comprising:

[0066] - a distillation column comprising: a source of molten lithium metal feed material containing a mixture of lithium-6 and lithium-7,

[0067] - an upper outlet port for enriched vapor lithium-6, - a lower outlet port for enriched molten lithium-7,

[0068] 03693-PCT an inlet for receiving a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 from the source, the inlet being disposed between the upper outlet port and the lower outlet port, packing configured for condensation and evaporation of lithium for isotopically separating of lithium-6 and lithium-7 , wherein the distillation column is operably coupled to:

[0069] - an evaporator,

[0070] - a condenser having an inlet coupled to the upper outlet port, the condenser having an outlet that is outlet coupled to a reflux port of the distillation column and to an outlet of enriched molten lithium-6, and a vacuum system for pulling a high or ultra-high vacuum.

[0071] In a possible implementation form of the third aspect, the packing comprises structured packing.

[0072] In a possible implementation form of the third aspect, the packing comprises evaporation surfaces and condensation surfaces .

[0073] In a possible implementation form of the third aspect, the packing comprises at least one column of packing, preferably at least one column of structured packing that comprises a multitude of theoretical stages.

[0074] In a possible implementation form of the third aspect, the distance between evaporation and condensation surfaces of the still, preferably the evaporation and condensation surfaces

[0075] 03693-PCT of the packing, is equal to or shorter than the mean free path length of the lithium atoms, preferably the mean free path length of the lithium atoms when the temperature of the evaporation surfaces is approximately 600°C.

[0076] In a possible implementation form of the third aspect, the distance between evaporation and condensation surfaces of the still, preferably the evaporation and condensation surfaces of the packing, is 20 mm or less than 20 mm.

[0077] These and other aspects will be apparent from the examples and embodiments described below.

[0078] BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In the following detailed portion of the present disclosure, the aspects, embodiments, and implementations will be explained in more detail with reference to the example embodiments shown in the drawings, in which:

[0080] Fig. 1 is a diagrammatic representation of a system according to an embodiment comprising a molecular distillation apparatus and a nuclear reactor,

[0081] Fig. 2 is a diagrammatic representation of a system according to another embodiment comprising a molecular distillation apparatus and a nuclear reactor, and

[0082] Fig. 3 is a diagrammatic representation of yet another system according to another embodiment comprising a molecular distillation apparatus and a nuclear reactor.

[0083] 03693-PCT DETAILED DESCRIPTION

[0084] Fig. 1 shows an embodiment of a system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. The system comprises a molecular distillation apparatus and a nuclear reactor 1 for providing heat for the distillation process. However, it is understood that the nuclear reactor 1 could be replaced by another source of heat, such as a burner or a geothermic heat source. The molecular distillation apparatus comprises at least one still 20 configured for isotopically separating a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream. The molecular distillation apparatus may comprise several stills 20 in series. In the embodiment shown in Fig. 1, the still 20 comprises a vertical molecular column 22, a vacuum port 29 for connection to a vacuum system 40 for pulling a high or ultra-high vacuum, a feed port 24 for receiving the mixture of molten lithium, a reflux port 26, a first upper outlet port 27 for enriched vapor lithium-6, a second lower outlet port 28 for enriched molten lithium-7, structural packing 23, trace heating elements 31, and thermal insulation 32.. Molten lithium metal feed material containing the mixture of lithium- 6 and lithium-7 is fed to the vertical molecular distillation column 22 by a feed conduit that leads to the feed port 24, preferably as a substantially constant stream, but this could also be an intermittent stream. The vacuum port 29 is connected to a vacuum pump 4 that creates a high or ultra- high vacuum in the interior of the vertical molecular distillation column 22. An evaporator 25 is operably coupled to still 20 at two separate positions by an evaporator conduit

[0085] 03693-PCT 29 that has an inlet at the lowest area of the vertical molecular distillation column 22 and an outlet slightly above the lowest area of the vertical molecular distillation column 22. In the present embodiment, the inlet of the evaporator conduit 29 is connected to the second lower outlet 28, but it should be understood that the evaporator 25, may just as well have its own port into the lowest area of the vertical molecular distillation column 22. Enriched molten lithium-7 is circulated through the evaporator conduit 29 and the evaporator 25 by a circulation pump (not shown) .

[0086] The packing material 23, preferably structured packing 23, provides a large surface area with counterflowing molten lithium metal and lithium metal vapor. The structured packing material 23 is preferably optimized for short-path molecular distillation of lithium, taking the operating temperature of the still 20 into consideration in the design of the structured packing 23. One or more relatively long columns of packing 23 serve as multiple theoretical stages allowing for a large separation factor in the one or more packing columns 23. The distillation process happens above the melting point of molten lithium.

[0087] In an embodiment the packing 23 comprises capillary material for transporting molten lithium through the packing 23 by capillary effect of the capillary material. This capillary material acts like a wick for molten lithium.

[0088] The first upper outlet 27 connects to the inlet of a condenser 30 and the outlet of the condenser 30 is split into a reflux 26 and an off-stream 21 of enriched molten lithium-6.

[0089] 03693-PCT The condenser 30 is operably coupled to the still 20 for removing heat from the stream of enriched vapor lithium-6 coming from the upper outlet 27 to thereby condense at least partially the stream of enriched vapor lithium-6 coming from the upper outlet 27 in the condenser 30. The condenser 30 is cooled with a heat exchange medium to remove heat from the condenser 30. The exchange medium is in an embodiment a molten salt, preferably a nitrate, fluoride, or chloride salt.

[0090] The system comprises a heat exchange arrangement for transferring heat from the nuclear reactor 1 to the evaporator 25 using at least one heat exchange medium, the heat exchange arrangement being configured for supplying heat to the evaporator 25 with a heat exchange medium having a temperature of at least 400°C.

[0091] The nuclear reactor 1 comprises reactor core 2, a primary heat exchange loop 3 containing a primary heat exchange medium, the primary heat exchange loop 3 passes through the reactor core 2 and through a primary heat exchanger 4. The primary heat exchange loop 3 comprises a primary circulation pump 5 for circulating the primary heat exchange medium in the primary heat exchange loop 3.

[0092] The system comprises a secondary heat exchange loop 1 containing a secondary heat exchange medium, the secondary heat exchange loop 12 passes through the primary heat exchanger 4 and through the evaporator 25, for transferring heat from the nuclear reactor 1 to the evaporator 25. A

[0093] 03693-PCT circulation pump (not shown) is provided in the secondary heat exchange loop 12.

[0094] To provide the necessary heat for the molecular distillation process, the secondary heat exchange medium is heated to a temperature of approximately 400°C or more, e.g. using a nuclear reactor or other suitable source of heat.

[0095] The nuclear reactor may be a gas-cooled reactor, such as a high-temperature gas-cooled reactor (HTGR) or a very-high- temperature reactor (VHTR) , a liquid metal cooled reactor (LMR) , a heat pipe cooled reactor (HPR) , or a molten salt reactor (MSR) . Accordingly, the first heat exchange medium can be gas, liquid metal, or molten salt, and the second heat exchange medium can be gas, liquid metal, or molten salt, and any combinations of the material used for the first and second heat exchange medium are possible.

[0096] Accordingly, the heated secondary heat exchange medium is supplied to the molecular distillation apparatus, where it is utilized in the evaporator 25, to drive the isotopic separation process.

[0097] The secondary heat exchange medium utilized in the evaporator 25 comprises or is in an embodiment a molten salt with a suitable melting and boiling point, such as NaNO3-KNO3 eutectic salt with a melting point of approximately 250°C. The evaporator 25 is heated to at least approximately 400°C, preferably to approximately 550°C.

[0098] 03693-PCT The secondary heat exchange medium utilized in the evaporator 25 comprises or is in another embodiment LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°

[0099] The secondary heat exchange medium utilized in the evaporator 25 comprises in yet another embodiment a LiF-NaF-KF eutectic salt, with a melting point of approximately 450°C, to heat the evaporator to approximately 600°C, preferably to approximately 700°C.

[0100] Fig. 2 shows another embodiment of the system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that the secondary heat exchange loop 12 passes both through the evaporator 25 and the condenser 30. Accordingly, the components and elements of the system that are the same and their functionality are not described again, instead, reference is made to the embodiment above .

[0101] At least one intermediate heat exchanger 50 is placed between the evaporator 25 and the condenser 30 to increase the temperature drop between the evaporator 25 and the condenser 30. The at least one intermediate heat exchangers 50 preferably comprise a counterflow recuperator. The heat that is removed from the intermediate heat exchanger 50 / counterf low recuperator can be used for other purposes,

[0102] 03693-PCT e.g. power generation or district heating. Another heat exchanger 52 can be arranged downstream of the condenser 30. The heat that is removed from the heat exchanger 52 can be used for other purposes, e.g. power generation or district heating .

[0103] For cooling the condenser 30 the heat exchange medium may be a molten salt, such as the LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°C, which allows cooling down the condenser to approximately 150°C, preferably approximately 130°C.

[0104] Alternatively, a LiF-NaF-KF eutectic salt, with a melting point of approximately 450°C, can be used to heat the evaporator to approximately 600 °C, preferably to approximately 700°C, and the LiF-NaF-KF salt or a LiNO3-NaNO3- KNO3 eutectic salt can be used to cool down the condenser to approximately 550°C, preferably to approximately 400°C.

[0105] In some embodiments, an organic coolant can be used to cool the condenser 30 while maintaining the high temperature required for isotopic separation.

[0106] Fig. 3 shows another embodiment of the system for isotopically separating lithium-6 and lithium-7 from a mixture thereof by molecular distillation. In this embodiment, structures, and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. This embodiment is essentially the same as the first embodiment, except that inert gas is recirculated

[0107] 03693-PCT through the molecular distillation column 22, from a lower position in the distillation column 22 to a higher position in the distillation column 22, to provide an advection flow to carry the lithium vapor in a counter flow direction to the condensed molten lithium moving from the higher position in the distillation column 22 to the lower position in the distillation column 22 under the influence of gravity.

[0108] The distillation column 22 is operated with an atmosphere of inert gas, preferably helium or argon around atmospheric pressure, and a blower 36 recirculates the gas from bottom to top in the distillation column 22 giving the evaporated lithium an upward draft while molten lithium flows downwards, driven by gravity, thereby improving the efficiency of the molecular distillation column 22. Instead of a vacuum pump, a blower or pump 44 is provided to maintain the pressure in the distillation column 22 to a desired pressure, which could for example be a pressure that is substantially equal to atmospheric pressure, e.g. approximately 1 bar absolute. However, the inert gas atmosphere in the distillation column 22 can be any pressure from close to high vacuum to above atmospheric pressure, but if operated at atmospheric pressure and purged with inert gas at the beginning of operations, instead of pulling a vacuum, the distillation column 22 has much lower requirements to withstand pressure differences and is thus cheaper to construct.

[0109] The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in

[0110] 03693-PCT practicing the claimed sub ect-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0111] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g. , cross-hatching, arrangement of parts, proportion, degree, etc. ) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0112] 03693-PCT

Claims

CLAIMS1. A method of isotopically separating lithium-6 and lithium- 7 from a mixture thereof, comprising: providing a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 to a molecular distillation column (22) or a series of molecular distillation columns (22) , the molecular distillation column (20) comprising packing(23) configured for condensation and evaporation of lithium for isotopically separating lithium-6 and lithium-7, and separating the feed stream into an enriched molten lithium-6 stream and an enriched molten lithium-7 stream by molecular distillation of the feed stream in the molecular distillation column (22) or in the series of molecular distillation columns (22) .

2. The method of claim 1, comprising: heating lithium in a lower area of the molecular distillation column (22) to temperatures below the boiling point of lithium and at least partially evaporating the molten lithium in the lower area molecular distillation column (22) , and condensing lithium vapor in a condenser (30) operably coupled to an upper area of molecular distillation column(22) , to drive a counterflow of molten lithium and lithium vapor in the molecular distillation column (22) .03693-PCT3. The method of claim 1 or 2, comprising isotopically separating lithium-6 and lithium-7 in the packing (23) .

4. The method of claim 3, comprising causing a counterflow of molten lithium metal and lithium metal vapor in the packing(23) .

5. The method of any one of claims 1 to 4, comprising removing an enriched molten lithium-7 stream from the lower area of the molecular distillation column (22) .

6. The method of any one of claims 1 to 5, comprising removing an enriched vapor lithium-6 stream from an upper area of the molecular distillation column (22) .

7. The method of any one of claims 3 to 6, when depending on claim 2, comprising removing an enriched molten lithium-6 stream from the condenser (30) .

8. The method of claim 1 or 2, comprising applying a high or ultra-high vacuum to the interior of the molecular distillation column (22) .

9. The method of any one of claims 1 to 8, wherein the packing (23) comprises at least one column of packing, preferably at least one column of structured packing (23) that comprises a multitude of theoretical stages.

10. The method of any one of claims 1 to 9, wherein the packing (23) comprises evaporation surfaces and condensation surfaces, preferably comprising counterf lowing molten lithium03693-PCTmetal and lithium metal vapor over the evaporation and condensation surfaces.

11. The method of claim 10, comprising selecting the distance between the evaporation surface and condensation surface area as a function of the operating temperature of the molecular distillation column (22) .

12. The method of claim 10 or 11, comprising keeping the molten lithium in its free molecular flow regime with the mean free path of molecules preferably being less than the distance between the evaporation condensation surfaces of the packing material.

13. The method of any one of claims 10 to 12, wherein the distance between evaporation and condensation surfaces of the still (20) , preferably the evaporation and condensation surfaces of the packing (23) , is equal to or shorter than the mean free path length of the lithium atoms.

14. The method of any one of claims 10 to 13, comprising keeping the temperature of the evaporation surfaces at approximately 600°C.

15. The method of claim 14, comprising keeping the temperature of the condensation surfaces at approximately 500°C, preferably in combination with a distance between the evaporation surfaces and the condensation surfaces of 20 mm or less.03693-PCT16. The method according to any one of claims 1 to 15, wherein the distillation column (22) is operably coupled to one or more of :- an evaporator (25) ,- a condenser (30) ,- a source of the mixture of the molten lithium stream,- a reflux (26) ,- a vacuum system (40) for pulling a high or ultra-high vacuum.

17. The method according to any one of claims 1 to 16, wherein the distillation column (22) comprises one or more of:- a first upper outlet port (27) for enriched vapor lithium-6,- a second lower outlet port (28) for enriched molten lithium-7,- trace heating elements,- thermal insulation (32) .

18. The method according to any one of claims 1 to 17, wherein the packing (23) comprises capillary material for transporting molten lithium through the packing (23) by capillary effect of the capillary material.

19. Use of a distillation column (22) that comprises packing (23) to perform molecular distillation of lithium for isotope separation of lithium-6 and lithium 7.

20. Use of a distillation column (22) of claim 19, wherein inert gas is recirculated through the molecular distillation column (22) , from a lower position in the distillation column03693-PCT(22) to a higher position in the distillation column (22) , to provide an advection flow to carry the lithium vapor in a counter flow direction to the condensed molten lithium moving from the higher position in the distillation column (22) to the lower position in the distillation column (22) under the influence of gravity.

21. A lithium distillation apparatus for isotopically separating lithium-6 and lithium-7 from a mixture thereof, the distillation apparatus comprising: a source of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7,- a distillation column (22) comprising:- an upper outlet port (27) for enriched vapor lithium- 6 ,- a lower outlet port (28) for enriched molten lithium-7 , an inlet (24) for receiving a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 from said source, the inlet (24) being disposed between the upper outlet port (27) and the lower outlet port (28) ,- packing (23) configured for condensation and evaporation of lithium for isotopically separating of lithium-6 and lithium-7, wherein the distillation column (22) is operably coupled to:- an evaporator (25) ,- a condenser (30) having an inlet coupled to the upper outlet port (27) , the condenser (30) having an outlet that is outlet coupled to a reflux port (26) of the03693-PCTdistillation column (22) and to an outlet of enriched molten lithium-6, and- a vacuum system (40) for pulling a high or ultra-high vacuum.

22. The distillation apparatus of claim 21, wherein the packing (23) comprises structured packing (23) .

23. The distillation apparatus of claim 21 or 22, wherein the packing (23) comprises evaporation surfaces and condensation surfaces .

24. The distillation apparatus of claim 23, wherein the distance between evaporation and condensation surfaces of the still (20) , preferably the evaporation and condensation surfaces of the packing (23) , is equal to or shorter than the mean free path length of the lithium atoms, preferably the mean free path length of the lithium atoms when the temperature of the evaporation surfaces is approximately 600°C.

25. The distillation apparatus of claim 23, wherein the distance between evaporation and condensation surfaces of the still (20) , preferably the evaporation and condensation surfaces of the packing (23) , is 20 mm or less than 20 mm.

26. The distillation apparatus of any one of claims 21 to 25, wherein the packing (23) comprises capillary material for transporting molten lithium through the packing (23) by capillary effect of the capillary material.03693-PCT

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