DE1244750B - Process for the enrichment of the isotopes of lithium by chemical isotope exchange between lithium amalgam and a solution, at least one lithium compound - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

PATENT LETTERING

Int. Cl .:

Number:

File number:

Registration date:

Display day:

Issue date:

COId

German class: 121-11 / 02

1,244,750
C20640IV a / 121
January 26, 1960
July 20, 1967
1st February 1968

"atentschrift agrees with the Auelegeschrift

The invention relates to a method for enriching the isotopes of lithium by chemical means Isotope exchange between lithium amalgam and a solution, at least one lithium compound.

Several processes have already become known for the separation of the isotopes of lithium on an industrial scale. Physical methods have proven to be particularly effective. One of these methods consists in carrying out an electrolysis of molten lithium salts, the different migration speeds of the ions or cations of the isotopes being used in a countercurrent of the electrolyte. The countercurrent keeps the heavier and therefore slower migrating isotope ⁷ Li away from the electrode to which it would like to migrate, as a result of which the faster isotope ⁶ Li is enriched in the space of the electrolyser assigned to this electrode.

Another physical separation method is the fractional electrolysis of ionized solutions Lithium compounds using a mercury cathode. Cathodic in electrolysis The deposited lithium combines with part of the mercury to form lithium amalgan and is through the mercury is steadily discharged from the electrolysis apparatus.

In the first method of electrolysis of molten lithium salts in a countercurrent flow of the electrolyte, a relatively high isotope separation effect can be achieved; However, on the one hand the outlay on equipment and on the other hand the energy consumption are very high. In the case of fractional electrolysis of lithium salt or LiOH solutions with a mercury cathode, the enrichment or separation factor is significantly lower; with steady-state equilibrium - depending on the type of anion - it is between 1.06 and 1.07, with the lithium isotope ⁶ Li preferably concentrated in the amalgam. The enrichment or separation factor is given by the quotient of the isotope ratio ⁷ Li: ⁶ Li in the solution and the isotope ratio ⁷ Li: ⁶ Li in the amalgam phase. In order to achieve a further concentration of ⁶ Li, the mixture of the lithium isotopes in the mercury amalgam must be repeatedly converted again into solutions of the ionized lithium compounds, and these must be subjected to further electrolysis.

In this process, too, the energy expenditure is a process for the enrichment of the isotopes of the
Lithium through chemical isotope exchange
between lithium amalgam and a solution,
at least one lithium compound

Patented for:

Commissariat a l'Energie Atomique, Paris

Representative:

Dipl.-Ing. R. Beetz, patent attorney,

Munich 22, Steinsdorfstr. 10

Named as inventor:

Eiichi Saito,

Gif sur Yvette,

Gregoire Dirian,

Palaisseau, Seine-Oise (France)

Claimed priority:

France of January 29, 1959 (785 219)

relatively large for electrolysis, so that the cost is high.

Chemical exchange processes are also known for the enrichment or separation of isotopes, to which the present invention relates; in this process, the separation of the isotopes in the generally carried out either with the help of ion exchange resins, or one uses the chemical isotope exchange between lithium amalgam and the solution of a lithium compound in a solvent.

The use of exchange resins leads to considerable accumulations, but occur in the industrial implementation on great difficulties, so that this process is currently only for isotope separations is useful on a small scale.

The enrichment process in which the chemical isotope exchange between lithium amalgam and the solution of a lithium compound in a solvent, is so far only with solutions of a lithium salt in an organic solvent has been carried out, which is practical

709 754/379

is anhydrous to prevent the lithium amalgam from decomposing to prevent during the exchange reaction.

The desired enrichment effect results from a chemical exchange process when the organic lithium salt solution comes into close contact with the lithium amalgam, which is contained in the mercury in small quantities. During this exchange, the lithium isotope ⁶ Li preferably goes into the lithium amalgam and the lithium isotope ⁷ Li into the organic lithium salt solution.

Even if the static separation factor in this method is only about 1.025, an overall separation effect is achieved which, for example, reaches the value 2, ie the original concentration of the lithium isotope ⁶ Li, which was 8% in the starting lithium increased to twice the value, ie 16% (in the withdrawn lithium amalgam).

This well-known chemical exchange process has several disadvantages:

The apparatus required for its implementation has large dimensions (in the case of the one described above The process uses a column 18 m high) and the transfer of the lithium isotope mixture from the amalgam to the organic solution causes greater difficulties. The direct one Conversion of the lithium from the amalgam into an organic acid solution takes place very slowly and imperfectly, so that you have at least two transmission devices with powerful agitators must be connected in series, which requires a considerable amount of equipment.

The present invention eliminates the disadvantages of the chemical exchange process described last eliminated and, moreover, the enrichment effect increased and the outlay on equipment decreased.

The inventive method for enriching the isotopes of lithium by chemical Exchange between lithium amalgam and a solution, at least one lithium compound, "is essential characterized in that the lithium amalgam is ionized with an aqueous solution Bringing lithium compounds into contact and those caused by hydrolysis of the lithium of the amalgam Reduction of the lithium concentration in the amalgam either by applying a "decomposition" preventing potential difference between the amalgam phase and the one in contact with it aqueous phase prevented or then compensated for by known electrolysis or cancels.

The essential chemical exchange process in the method according to the invention can be written:

⁷ Li-Hg

«Li — Hg + ⁷ LiX- (1) The hydrolysis reaction can be represented as follows:

Li-Hg + H ₂ O - * LiOH + V ₂ H ₂ / (2)

In contrast to the reaction according to (1), this reaction proceeds slowly and gives lithium hydroxide in the aqueous phase; it extends only to part of the lithium of the amalgam. The content of the Lithium in the amalgam decreases when this reaction occurs; the reaction only increases a portion of the water of the aqueous phase to claim.

If the applied potential difference prevents the reaction according to formula (2), it takes place just a pure exchange reaction in which the amalgam's lithium content remains practically the same and only the percentage ratio of the lithium isotopes in the amalgam and the aqueous phase undergoes a change. This process could be represented as follows:

⁷ Li-Hg (Li content ri) + ⁶ LiX
: £ 6Li-Hg (Li part ri) + ⁷ LiX

If the decomposition reaction according to formula (2) is not prevented in the main contact device and carries out a known electrolysis according to the following in a downstream contact device Formula by:

LiOH

Li ⁺ + OH-

(3)

in which the cathode consists of a lithium amalgam, the lithium content of which had previously decreased somewhat in a first contact device as a result of the decomposition reaction according to formula (2), this electrolysis brings the lithium content of the amalgam back to the normal value η by removing the lithium cation Li ⁺ [Formula (3)] discharges at the cathode and changes into the amalgam phase. In addition, oxygen is released. If ri denotes the reduced proportion of lithium in the partially decomposed amalgam, the processes in the electrolysis cell can be written as follows:

Li + Li-HG (Li part ri) - + Li-Hg (Li part> ri) (4)

2OH -> H ₂ O + V ₂ O ₂ (5)

In this formula, the lithium amalgam is symbolically denoted by Li — Hg, the lithium isotope of mass 7 with ⁷ Li, the isotope of mass 6 with ⁶ Li and the anion which is connected to these cations within the aqueous phase is denoted by X ~. The change in this formula for the case that the anion X is not monovalent can easily be overlooked.

In practice, the enrichment factor is 1.05 in static equilibrium; so it is substantial higher than when using anhydrous organic lithium salt solutions.

It may also be that in the downstream. Contact device another secondary Electrolysis reaction takes place (when the anion X ~ is not the OH anion) if, for example lithium chloride is used in the aqueous phase. In this case, the additional response is:

LiCl

Li ⁺ + CI-

(6)

But also this reaction - just like the reaction according to the formula (5) - has the effect that the original lithium concentration is restored in the amalgam phase, since here too the cation Li ⁺ is after the reaction according to the formula (6) discharges at the cathode and changes into the amalgam phase. In this case, in addition to the evolution of oxygen, there is also a

Development of chlorine on. Of course, the electrolysis reaction according to formula (6) covers only one small part of the soluble lithium salt originally contained in the aqueous phase.

It should be noted that the reactions of the decomposition of the lithium amalgam by the water [formula (2)] and the reactions of electrolysis [formers (3) and (6)] each have an isotope enrichment in the same sense as the reactions according to the formula (1) induce; This results in an increase in the quantity ratio ⁶ Li: ⁷ Li in the amalgam phase. The devices in which this chemical exchange can be carried out are known contact devices for the contact of immiscible liquids; they consist, for example, of a series of slopes or columns, or they represent some other system which, if necessary, can be equipped with sufficiently efficient stirring devices to ensure rapid replacement.

In those contact devices in which one If the hydrolysis reaction is to be prevented practically completely, the amalgam is negative Brought potential and the solution to a positive potential; a known electrolysis device, which consists, for example, of a direct current source and a voltage regulating device as well as a voltage and ammeter, allows adjustment and maintenance of the necessary Potential difference. These contact devices are still called type A. .

In the second case one leaves contact devices in which the chemical exchange reaction takes place and the contactors are called Type A ', a partial decomposition of the amalgam. But one arranges further contact devices behind these devices, the Type B contact devices are mentioned. In these last-mentioned contact devices B a regeneration of the part of the amalgam that is in the contact devices is carried out Type A 'has been decomposed, thereby offsetting the effects of this hydrolysis reaction and the initial relationship

/ Lithium of the amalgam

\ Mercury of the amalgam

is restored.

It is therefore necessary that in the devices of type B the electrolysis current through a potential difference which makes the solution positive and the amalgam negative.

In type B devices, the intended purpose is not the chemical isotope exchange, but above all a compensation of the hydrolysis reaction that takes place in the devices of the Type A 'played. Now, however, neither the partial decomposition nor the regeneration of the amalgam can occur repeal, do not even lead to a reduction in the effect of isotope enrichment, which in Type A 'devices. It's not just the electrolysis of a lithium salt in aqueous solution associated with an isotope separation of lithium; it was found; that too the secondary or hydrolytic reaction of the attack of the lithium on the amalgam by the solution also leads to a separation of the isotopes of lithium according to the attack conditions, whose separation factor is 0.96 and in which the isotope with atomic mass 6 is also preferably in concentrated in the amalgam.

It follows that all processes of decomposition and subsequent regeneration of the amalgam reinforce the enrichment effect obtained in type A or A 'devices, but with an additional consumption of energy

ίο in the form of electrical energy is necessary.

The type B devices are in principle smaller than the devices in terms of their dimensions the type A '.

The method according to the present invention can also be used with three types of devices carry out: devices of type A with prevention of hydrolysis, others of type A ', in which one can play the decomposition reaction, and finally others of type B, which the Type A 'devices must be connected downstream.

The potential difference and the current density; which are necessary to the decomposition reaction of the Avoid amalgams in Type A devices or in Type B devices To regenerate amalgam that has been partially decomposed in type A 'devices hang on several factors, in particular the respective concentrations of lithium in the amalgam and in the solution.

Either of the two phases that circulate in or through the assembly of the contact devices Devices passing through may have a separate circulation. Some amount of the amalgam - which has been produced without enrichment of isotopes - as well as a certain amount of aqueous solution of lithium salts, which was also prepared independently of the amalgam without an enrichment effect of the isotopes, are in this Case in countercurrent or in parallel flow by the process according to the invention in contact with one another brought.

For reasons of efficiency, it proves to be advantageous to circulate the aqueous solution and to couple that of the amalgam in the following way: The one coming from a contact device Amalgam enriched with one of the isotopes of lithium is completely decomposed and according to the classical converted to chemical methods in order to obtain directly or indirectly the aqueous phase; this is then fed to the inlet of a contact device which is fed with an aqueous phase must be whose enrichment corresponds to that of the amalgam from which the aqueous phase originated. The amalgam can decompose through contact with certain substances, such as Graphite, cast iron or certain alloys, or finally accelerated by electrolytic means will; in the latter case the atnal yarn is brought to a positive potential.

The coupling also results from an opposing transition of the phases, i. H. during preparation of the amalgam starting from an aqueous solution; the aqueous solution of the electrolyzed Lithium compound with a mercury cathode. So allows the aqueous solution, which is already at one of the Isotopes of lithium is enriched and comes from a contact device, the restoration

or setting of an amalgam, its degree of lithium enrichment corresponds to that of the solution; this amalgam can be placed in another contact device, z. B. be introduced into a contact device located before this stage.

When this coupling is carried out, the one enriched in one of the isotopes is withdrawn Lithium from the aqueous phase or from an amalgam at the point where the enrichment

hydrolysis occurs in the first of these devices; however, the effects of this reaction will be compensated in the second device,

F i g. 3 a system in which the transition or the conversion of the lithium, which is in an aqueous Lithium salt solution is contained in the amalgam state,

F i g. 4 a system in which the transition or the

preferably at a temperature of a few deca degrees C (normal room temperature is quite Cheap). Although a higher temperature could result in better energy efficiency, 5 because a higher concentration makes it possible to work with a smaller volume of the phases, it proves Nevertheless, it is advantageous not to exceed the above-mentioned limits, because the decomposition reaction the aqueous phase by the lithium of the Amal-

tion of the istopes is highest. The feeding of the io gams shows a tendency to occur to a greater extent, entire arrangement of contact devices when the temperature rises, follows in the form of an aqueous solution of lithium With reference to the schematic figures

salt or - what comes to the same thing - the drawing are now some examples of Anin Shape of amalgam; the feeding is carried out using the method according to the invention, that the addition or mixture wrote at the 15. It shows

Insertion point with preferably the same isotopic F i g. 1 is a type A contact device in which

concentration or at least close to one another chemical isotope exchange takes place and the low isotope concentrations. Hydrolysis can be prevented

also another removal of the enriched F i g. 2 a combination of two contact

Provide lithium in a different location where the 20 directions are highest, the first of which is an isotopic enrichment device; this second type A 'and the second one of type B, subtracting it gives lithium which is enriched ^{in 7 Li,
if lithium enriched at 6} Li was withdrawn from the first withdrawal point.

In a special way of carrying out the present invention, the aqueous phase is a solution of lithium oxide, the mean concentration of which is at most equal to the solubility limit, ie approximately 5 η at normal temperature and somewhat higher

at a higher temperature (6 η at 8O ⁰ C); 30. Conversion of the amalgam lithium into the aqueous, however, this concentration should preferably take place between solution,

F i g. 5 is a schematic diagram illustrating the interaction of a device, the one Contact device according to FIGS. 1 and

is equal to the solubility limit, ie about 0.8 η at 35 includes two additional systems, as they are in normal temperature; Incidentally, this limit is also F i g. 3 and 4, variable with temperature. F i g. 6 a detailed representation of a single

In another application of the invention, the device according to FIG. 5, is the lithium compound in aqueous solution. 7 an interconnection of equipment

dung the lithium chloride; the concentration of the gene, which is shown in detail in FIGS. 5 and 6 shown LiCl should be at most approximately equal to 10n, what they are.

Solubility limit of this compound at normal The Fig. 1 shows a contact device 1, which in

Temperature corresponds to; if one works at higher temperatures from a pipe or a column, one could use a stronger concentration. The aqueous layer or phase 2, which ionitration contains, since the solubility limit contains lithium strongly acidified with 45, flows through the tube or the temperature rises (it is about 30 η with the column of the device 1 in countercurrent 100 ^p C); in this case, the conversion to the lithium amalgam 3 requires an additional elek-lithium amalgam in lithium chloride. Supply from trische device, which is a direct current source 4, chlorine or hydrochloric acid. The reverse voltage regulator 5, a voltmeter 6, reversed conversion generated during the electrolysis at 50 and an ammeter 7, allows the anode chlorine, this chlorine can be reused or maintain a potential difference that can be detected around the first Conversion through- is required to lead the decomposition reaction of the. . To prevent amalgams.

The other halogen salts of lithium, e.g. B. The negative electrode consists of the layer of

Lithium sulfide and lithium nitrate are also 55 amalgams 3; the positive electrode 8 expands for suitable for carrying out the invention. Your within the liquid layer 2 over the entire However, it is less convenient to use; the loading length of the contact device 1. Creation costs are higher, the hydrolytic re- The F i g. 2 shows a contact device 9 of FIG

Actions that can occur, or Reaction Type A ', in which, at the same time as the chemical functions for the transition of the isotope exchange in the aqueous phase 60, a decomposition contained lithium into the amalgam state and reaction of the water or the amalgam occurs ; The contact device 10 is a device of the riger, while these processes are particularly simple type B, their dimensions are much smaller than if one used the lithium. the dimensions of the contact device 9. The

At normal pressure one works in a tem- 65 potential difference, that in 10 between the two temperature interval, the lower limit of which is applied by the phase, leads to regeneration Solidification of the aqueous phase is given, so with the initially (in the device 9) partially zerder Concentration varies and its upper limit is set by amalgams; the electrical one used for this

see 0.5 η and 2.5 η lie. Very good results were achieved with a concentration of 2η. The amalgam contains a lithium content that is at most

Additional device is not shown; it corresponds to that of the additional device in FIG. 1.

As in FIG. 2 already indicated, several devices A ', B, A' ... can alternate successive.

The F i g. 3 shows the inflow 11 of the Li + ions containing Solution and drain 12 of the amalgam; the solution is partially in an evaporator 13 evaporated, the removal of the water is completed in the electrolytic cell 14 from which the Water enters the line 15 in vapor form, together or simultaneously with the oxygen (or the chlorine) that are formed during electrolysis, as well as the hydrogen that is produced by a weak decomposition of the amalgam. The electrolytic cell 14 has a mercury cathode 16. The inlet of the mercury takes place via an inlet line 17; the lithium from the aqueous solution goes into the amalgam state.

The in the F i g. The system shown in FIG. 4 consists of a column 18 which is filled with a filler material 19 and is fed via the line 20 at its upper part with lithium amalgam; about the Line 21 at the lower part is supplied with pure water; the counterflow of the two liquids and the presence of the filler 19 causes the amalgam to be finely dispersed and accelerated its decomposition. Hydrogen is separated out and the lithium hydroxide solution can over the upper drain line 22 can be fed to a contact device. That in the lower drain 23 itself accumulating mercury can expediently be used to feed a system, such as it in Fig. 3 is shown. If the salt used in this case is lithium chloride, one leads in the lower part of the column, dilute hydrochloric acid is added instead of pure water.

The F i g. 5 shows a contact device 24. its electrical accessory for simplicity because is not shown. The device 25 serves to transfer the in the aqueous solution contained lithium in the amalgam state and the device 26 for transferring the amalgam lithium into the aqueous phase or solution. The circulation of the amalgam is through a coherent, Strong line symbolizes the circulation of the aqueous phase by a dashed line.

The withdrawal or removal of the ^{lithium enriched in 6} Li takes place either at point 27 in the form of the amalgam or at 28 from the aqueous phase; the withdrawal or removal of the ^{lithium enriched in the 7} Li isotope takes place either at 29 (amalgam) or at 30 (aqueous phase). The solution is fed in at arrow 31; this feed corresponds - taking into account the total existing lithium content - the respective withdrawals.

In FIG. 6, a contact device 24 is shown, which again without the additional device drawn for the prevention of the hydrolysis reaction or for the compensation of the decomposition effects is; there is also an evaporator 13 and an electrolytic cell 14; Besides that this figure shows a condenser 32 and the column for the decomposition of the atnalgam; that on the ground The mercury that collects in this column is fed into the electrolytic cell 14 by a pump 33 conveyed in to form the amalgam again using the lithium of the aqueous solution; Finally, lines 28 and 30 are for the removal of the lithium and a line 31 for the supply of the system is provided. Water is supplied via line 34; as by-products

ίο hydrogen (or chlorine) or oxygen (O ₂ ) are obtained as by-products at the points marked by arrows.

The F i g. 7 illustrates how two units according to FIG. 5 can be interconnected.

The lithium is fed into the aqueous phase at 35; ^{a fraction enriched in 6} Li is removed at the point indicated by 36 - from the aqueous phase - and at the point indicated by 37 - likewise from the aqueous phase

ao phase - a fraction enriched ^{in 7 Li;} this figure thus shows a coupling of two circulations or recirculations via the aqueous phase.

In general, the connection between different units of an overall facility or cascade can be carried out according to known models; Fig. 7 represents only a selected one Example.

Claims (2)

Patent claims: 1. Process for enriching the isotopes of lithium by chemical isotope exchange between lithium amalgam and a solution, at least one lithium compound, characterized in that the Bringing lithium amalgam with an aqueous solution of ionized lithium compounds and the decrease in lithium concentration due to hydrolysis of the lithium of the amalgam in the amalgam either by applying a potential difference that prevents decomposition between the amalgam phase and the aqueous phase in contact with it prevented or subsequently compensated or reversed by known electrolysis power. 2. The method according to claim 1, wherein the enrichment of the isotopes is carried out in a multi-stage contact process and before each new stage a transition of the lithium contained in the aqueous phase into the amalgam state and the lithium contained in the amalgam into the state of the aqueous solution is effected , characterized in that the aqueous phase consists of a lithium hydroxide solution, the concentration of which is between 0.5 η and 2.5 η and the lithium concentration in the amalgam is at most 0.8 η . Considered publications: Zeitschrift für Elektrochemie, 44 (1938), pp. 111 to 115; Journ. Chem. Phys., 5 (1937), p. 597; J. am. Chem. Soc, 58 (1936), p. 2519. 1 sheet of drawings 709 754/379