Isotopic enrichment of uranium with respect to an isotope

A process for chemical enrichment of uranium with respect to a lighter one of its isotopes. The process consists in contacting uranium of valence state III and uranium of valence state IV, or a compound of uranium of valence state III and a different compound of uranium of valence state III. One of the phases which are contacted or the only phase is liquid. The system should be substantially free of elements which would cause uranium III to oxidize to valence IV.

BACKGROUND OF THE DISCLOSURE 
The present invention relates in general to isotopic exchange by chemical 
route, for isotopic enrichment of uranium with respect to one particular 
isotope thereof. 
As is known, isotopic enrichment of uranium has become or great importance 
and enrichment of natural uranium with respect to 235 U is of particular 
interest. Two methods of enrichment of natural uranium in isotope 235 are 
at the present time used industrially or are about to be so. These are 
gaseous diffusion and centrifugation. The two methods require the uranium 
to be in the form of the hexafluoride, that is to say in the form of a 
very corrosive gas, dangerous and difficult to handle. They are very 
complex and operation of the plants meets with considerable difficulties. 
The first method has additionally the drawback of a high consumption of 
energy. The second becomes of economic value only with a large inventory 
of centrifuges, requires enormous initial investments and is still not 
completely mastered. 
On the other hand, there has been continuing interest in chemical methods 
of isotopic enrichment of uranium. Chemical exchange between ions of 
uranium of valence IV and uranium of valence VI, generally in the form of 
the uranyl ion, has been considerably studied. In particular, it has been 
proposed to effect istopic exchange between U.sup.+4 and UO.sub.2.sup.+2 
in homogenous aqueous solution (for example in U.S. Pat. No. 2,787,587) or 
in aqueous and organic phases brought in contact (U.S. Pat. No. 
2,835,687). It has also been proposed to use ion exchange resins which 
retain one of the isotopes selectively: for example, it has been proposed 
to fix uranium of valence IV on a resin, then to oxidize it and to elute 
it. On this subject, reference may be made to French Pat. Nos. 1,480,129, 
1,600,437, 2,146,462 and 2,546,461. 
While these methods have given some results, they have not achieved 
acceptance. First, the exchange factors per stage are low. Moreover, most 
of them require complex chemical operations. 
Uranium is known to assume valences other than the valences IV and VI, 
which have been until now used in attempts of isotopic separation by the 
chemical route. SAITO has described in particular methods for the 
preparation of acid solutions of uranium salts of valence III (Bull. of 
the Chemical Society of Japan, 1967, Vol. 40, pp. 2107-2110). However, the 
U.sup.+3 ions tend spontaneously to revert, especially in solution, to the 
state of uranous U.sup.+4 ions or even uranyl UO.sub.2.sup.++ ions, which 
phenomenon has often been atributed to atmospheric air. 
This re-oxydation in itself is not surprising if it is recalled that the 
system U.sup.+3 /U.sup.+4 forms an oxidation-reduction system whose normal 
potential is -0.63 volt with respect to a standard hydrogen electrode. The 
U.sup.+3 ions have consequently a reducing character such that they should 
theoretically reduce the water thereby causing the formation of hydrogen. 
It is an object of the invention to provide an isotopic exchange method by 
the chemical route improved with respect to those defined above, 
especially in that it gives high enrichment coefficients per stage, that 
it only uses relatively conventional equipment, easy to operate, that it 
enables the use of non-gaseous phases, preferably liquids, that the 
consumption of energy that it involves compares favorably with that 
required by the majority of known methods and, lastly, that it can be 
carried out in low capacity installations. 
The invention makes use of the observation that it is possible to form 
solutions containing uranium in the valance III state and in which this 
valence state can be preserved in metastable manner, even in acid medium, 
for long durations, in particular sufficient to perform isotopic exchanges 
under industrial conditions, when these solutions are kept out of all 
contact with conducting bodies and when they are practically free--apart 
from the uranium--of metal ions other than the alkali metals and alkaline 
earth metals (or of groups III to VIII of the periodic classification). 
It is clear that, even if the normal potential of the oxidation-reduction 
system U.sup.+3 /U.sup.+4 mentioned above it left out from consideration, 
the species U.sup.+3 cannot escape its oxidation number rising by at least 
one unit under the effect of metallic ions with a less reducing character 
contained in their common solutions. It was however entirely unknown that 
quantities, even very small, of other metallic ions of the above-indicated 
type with respect to the content of U.sup.+3 ions of their common 
solutions had an effect which can be termed as catalytic with respect to 
the rapid oxidation of the U.sup.+3 ions. 
It was noted that it is posible, for each type of metallic ion of groups 
III to VIII of the periodic table (other than uranium), to determine 
experimentally the minimum proportions, called below "catalytic 
proportions" beyond which the rapid conversion of the U.sup.+3 ions 
contained in the solutions concerned, into U.sup.+4 ions is observed. 
These catalytic proportions are very low, for example of the order of one 
ppm (part per million) with respect to the uranium, for ions such as 
nickel, copper or cobalt. 
When, in the remainder of this description, reference is made to solutions 
free of metallic ions of the type concerned, it must be understood that it 
relates to solutions whose contents of these ions are less than the 
corresponding catalytic proportions. 
Not only the phase containing U.sup.+3 must be practically free of certain 
ions, but any aqueous solution containing U.sup.+3 must be kept out of 
contact with the electrically conducting walls. If, for example, an acid 
solution containing U.sup.+3 is in contact with a conducting material, the 
latter can facilitate the reaction between U.sup.+3 and H.sup.+ (which is 
normally very slow in a pure homogeneous phase) by participating in the 
electron exchange between the two participants in the reaction. This 
phenomenon has a catalytic character and is more or less rapid according 
to the relative arrangement of the intensity-potential curves of the 
reactions, U.sup.+3 .fwdarw.U.sup.+4 and H.sup.+ .fwdarw.H.sub.2 in the 
material concerned. In particular, the phenomenon will be all the faster 
as the overvoltage of the hydrogen to this material is lower. 
A process according to one aspect of the invention for effecting uranium 
isotopic exchange, comprises contacting uranium of valence state III and 
uranium of valence state IV, uranium being present in at least one of said 
valences in a liquid phase, under conditions which substantially prevent 
uranium of valence state III from rapidly oxidizing from valence state III 
to valence state IV. 
In a preferred embodiment of the invention, the process comprises forming 
an aqueous phase containing hypo-uranous ions U.sup.+3, the contents of 
said aqueous phase in ions of metals of the groups III to VIII of the 
periodic table being however below the proportions which catalytically 
favor the oxidation of U.sup.+3 into U.sup.+4, and contacting said aqueous 
phase with an organic phase containing uranium in the valence state IV 
under conditions which exclude substantial transfer of uranium in either 
valence state from one phase into the other, while maintaining said 
aqueous phase out of contact with electrically conductive parts. 
Particularly, the contents of the aqueous phase in any of the metals 
selected from the group consisting of nickel, copper or cobalt should be 
maintained below 1 ppm with respect to its content of U.sup.+3 ions. 
According to another aspect of the invention, there is provided a process 
comprising digesting two compounds of uranium of valance state III which 
are not reactive with respect to each other, in a liquid phase and 
separating the two compounds. 
It is not necessary to shield the phases and especially the aqueous phase 
from the atmospheric air, but in most cases, the method will be carried 
out in a closed installation, especially to avoid loss of solvents by 
evaporation. 
In a particular embodiment, the process according to the invention is 
operated as a multistage process which comprises repeating several times, 
particularly a number of times sufficient to produce a substantial 
enrichment of the uranium in the 235 U isotope, and in a corresponding 
number of successive isotopic exchange sections, a cycle which comprises: 
counter-current extraction by an aqueous phase previously depleted of its 
uranium contents, in a zone upstream of a given isotopic exchange section 
with respect to the direction of flow of said aqueous phase, of the U IV 
contained in an organic phase, which U IV already underwent an isotopic 
exchange in the said given section; 
reduction of U IV, extracted as U.sup.+4 in the aqueous phase, and 
production within said given section of an isotopic exchange between the 
aqueous phase containing U.sup.+3 and the organic phase previously loaded 
with U IV, said isotopic exchange being effected under conditions which 
exclude substantial transfer of uranium in either valence state from one 
phase to the other, and 
oxidation of U III into U IV within the aqueous phase, subsequent to the 
isotopic exchange, downstream of said section, and transfer of the 
oxidized uranium into the organic phase previously freed of its U IV 
contents. 
Advantageously, substantial transfer of uranium IV into the aqueous phase 
from the other phase during the isotopic exchange operation is prevented 
by means of a salting-out agent (or relargant) of U IV previously 
introduced into the aqueous phase. 
The uranium of valence IV may be extracted directly from the organic phase 
by the previously adjusted aqueous phase in order that the transfer may be 
practically complete; this adjustment can for example be constituted by a 
reaction in the content of salting-out agent. The extraction of U.sup.+3 
from the aqueous phase may be done, after oxidation to U.sup.+4, by the 
organic phase selected so that the transfer is also practically complete 
for a suitable content of the aqueous phase of salting-out agent. 
The aqueous phase which contains U.sup.+3 in solution must obviously in 
this case: 
be able to contain U.sup.+4 ; 
enable the extraction of uranium of valence IV by the organic phase and for 
this purpose be able to receive a salting-out compound which will 
generally be a halogen ion donor, the uranium then being present in the 
aqueous phase in the form of halogenide, whereby the oxidation and 
reduction operations are greatly facilitated, the hydrogen or hydracid 
obtained on reduction being used to effect the reoxidation. Particularly, 
the Cl.sup.- ion can be used as salting-out agent and UCl.sub.3 can be 
used as the uranium salt in the aqueous phase. Other non-reducing 
salting-out agents may however be used. 
Obviously, the uranium contents of the aqueous and organic phases should be 
as high as possible; however, the following conditions should also be 
fulfilled and limit the contents: precipitation should not occur anywhere 
in the apparatus; the viscosity of the phases should be low enough not to 
impede the flow; the difference between the specific weights should be 
sufficient for separation to be easy. 
In practice, for a complete reflux cascade, the flows of the organic phase 
and of the aqueous phase will be selected as a function of the uranium 
concentrations of the two phases, such that the flows of uranium into 
these two phases, be of the same order. The exchange conditions and 
particularly the content of salting-out agent of the aqueous phase will be 
selected so that less than 5% of uranium of valence IV passes from the 
organic phase to the aqueous phase. Practically passage of uranium of 
valence III from the aqueous phase to the organic phase does not occur in 
almost all cases, since there exist very few complexants of uranium of 
valence III. 
The aqueous phase can only contain UCl.sub.4 in solution it if has a 
minimum acidity (which depends on the concentration of U.sup.+4 ions), 
failing which uranium precipitates in the state of the hydroxide. In 
practice however, it will often be possible to reextract UCl.sub.4 from 
the organic phase with water which is acidified by absorption of the acid 
contained in the organic phase. 
As has been indicated above, the aqueous phase must contain a salting-out 
agent during contact with the organic phase. If it is assumed for 
simplification that this salting-out agent is constituted by Cl.sup.-, the 
U.sup.+3 containing phase must then contain a considerable concentration 
of hydrochloric acid or of a chloride. However, in the latter case, every 
chloride cannot be used. There must be avoided any cation: 
which forms part of a Redox system whose standard potential is greater than 
that of the U.sup.+3 /U.sup.+4 system, if it reacts with noticeable speed, 
this condition having to be respected in homogeneous phase, 
which has the above characteristics, if the second participant of the 
system is a metal. This metal will then be reduced by uranium and 
generally attacked again by the acid. A process of catalytic character 
will take place which will lead to rapid oxidation of U.sup.+3, even if 
the ion responsible for the process is present in very slight amount. This 
is particularly the case of nickel, copper or cobalt ions, the content of 
which must be kept less than 1 ppm (part per million) with respect to the 
uranium. 
The phase containing U.sup.+3 must not only be practically free of certain 
ions, but any aqueous solution containing U.sup.+3 must be kept out of 
contact with electrically conducting walls. As a matter of fact when, for 
example, an acid solution containing U.sup.+3 is in contact with a 
conductive material, the latter can facilitate the reaction between 
U.sup.+3 and H.sup.+ (which is normally very slow in pure homogeneous 
phase) by participating in the exchange of electrons between the two 
participants in the reaction. This process of catalytic character is more 
or less rapid according to the relative disposition of the 
intensity-potential curves of the reactions U.sup.+3 .fwdarw.U.sup.+4 and 
H.sup.+ .fwdarw.H.sub.2 on the material concerned. In particular, this 
process will be all the more considerable as the hydrogen over-potential 
with respect to this material is less. 
Summarizing, content of the aqueous solution with conductive materials must 
be avoided, except in very particular cases (cathode for electrochemical 
reduction kept under voltage) as well as the presence in the aqueous phase 
of ions which could catalyse its decomposition, in particular those having 
an oxidation-reduction potential comparable with that of nickel, copper 
and cobalt, even at very low contents. The only tolerable cations are 
those which cannot be reduced by U.sup.+3 such as ions of alkali metals or 
alkaline earth metals. The chloride containing salting out agents which 
are suitable in addition to HCl, are alkali chlorides or alkaline earth 
chlorides which are sufficiently soluble (such as LiCl or MgCl.sub.2). 
The bringing of the valencies III and IV in contact can be effected by 
extremely various methods. The phases containing the uranium under the two 
valences can be mixable, partially miscible, or non-miscible. One of the 
phases (or the phase in the case of homogeneous phase) will be liquid. The 
other phase can be liquid or solid, especially ion exchange resins in the 
latter case. 
The liquid phase, or each of the liquid phases, can be aqueous, organic or 
mixed, containing uranium in the form of ions or in the state of a complex 
(this case being often that of an organic phase). Solvents which are 
capable of solubilizing uranium IV are well known. 
By aqueous phase, will be understood an aqueous solution of a mineral or 
organic salt of uranium in the dissociated state. The aqueous phase 
containing U.sup.+3 will generally be a solution of a hydracid whose 
halogen ion will play the role of a salting out agent. In any case, only 
non-oxidizing acids will be used. In practice, hydrochloric acid solution 
will generally be used, HCl being the least expensive of the strong acids, 
although use of other hydracids and, to a lesser extent, of non-oxidizing 
strong acids can be contemplated. 
By organic phase, will be understood a solution in an organic solvent (or a 
mixture of such solvents) of a salt or complex of uranium, of valency III 
or IV, as the case may be, in addition a diluent as, for example, when it 
is desired to modify the viscosity, the density and/or surface tension of 
the organic phase and to act on various parameters, such as decantation 
times. Many liquid organic solvents may be used, and the technician 
skilled in the art will have no difficulty in selecting a suitable 
solvent. Recourse will generally be had to the well known solvents which 
are used in the treatment of irradiated nuclear fuels. These organic 
solvents will, as a general rule, be selected from the list below, 
depending on the selected uranium salt; it will often be necessary to add 
thereto a diluent which may be selected among aliphatic or aromatic 
hydrocarbons and their derivatives (such as benzene, toluene, dodecane, 
kerosene, xylene . . . ) which are liquid at ambient temperature. The 
solvents may be for example organic compounds belonging to the families 
below, which do not contain oxidizing impurities, and which are selected 
with regard to their high exchange capacity, their good resistance to 
hydrolysis and to their ability to allow for an easy decantation: 
alcohols 
anionic exchangers, such as tricaprylmethylammonium chloride (sold under 
the trade mark "Aliquat 336" by General Mills, Kankakee, Ill.) 
neutral organophosphorous compounds, bearing the function P.dbd.0 which 
gives with uranium salts complexes generally including several ligands for 
one molecule of uranium. Several families of these may be distinguished: 
phosphates of the type (RO).sub.3 P(O) or RO R'OR"OP (O) (the R,R' and R" 
radicals being linear or branched aliphatic or aromatic carbon chains of 
which two do not contain more than 8 and of which the third can extend up 
to 12 carbon atoms (the number being however preferably 6 at the most for 
each), for example: tributylphoshate (TBP), triisobutylphosphate (TiBP), 
tripropylphosphate (TPP), triethyl-12-butylphosphate (TEBP), 
tri-2-methylbutylphosphate (T2MBP), tri-2-ethylbutylphosphate (TBEP); 
the phosphine oxides RR'R"P(O) in which the radicals are of the same family 
as previously; among the phosphine oxides, there may be indicated a 
particular family in which one of the chains bears the ether oxide 
function and of which the general formula is RO(CH.sub.2)n-P (O)R'R"; R, 
R' and R" are radicals as above and n is an integer at least equal to 1: 
trioctylphosphine oxide (TOPO), tributylphosphine oxide (TBPO), 
di-N-propylmethoxyoctylphosphine oxide, 
di-N-butylethyl-2-methoxyisobutylphosphine oxide, 
di-isobutylmethoxymethyloctylphosphine oxide, triamylphosphine oxide 
(having however the drawback of being soluble in water), trihexylphosphine 
oxide; 
the phosphonates of formula ROR'OR"P(O) which constitute intermediate 
compounds, R, R' and R" having the above indicated meanings, such as: 
dibutylbutylphosphonate (DBBP), di-isobutylphosphonate, 
di-octyloctylphosphonate, di-isobutylbutylphosphonate, 
dibutylisobutylphosphonate, di-isoamylamylphosphonate, 
di-isopropylbutylphosphonate, di-isobutylhexylphosphonate, 
di-isobutylisoamylphosphonate, di-isobutyloctylphosphonate, 
di-isobutylethylhexylphosphonate and di-isobutylmethoxylaurylphosphonate; 
these phosphonates may be diluted for example by dodecane and/or xylene; 
the phosphinates of formula ROR'R"P(O) which are also intermediate 
compounds between the phosphates and the oxides of phosphine, R, R' and R" 
having always the same meaning; among the phosphinates may be mentioned: 
di-isobutylphosphinate (used diluted in toluene), dihexylhexylphosphinate 
(used diluted in kerosene R), dibutylisobutylphosphinate (used diluted in 
toluene), di-isobutylbutylphosphonate (used diluted in toluene), 
dihexylisobutylphosphinate (used diluted in kerosene R), 
dioctylisobutylphosphinate (used diluted in kerosene R). 
At the present time, the phosphates and phosphonates seem to be the 
solvents which give the best results if one takes into account the various 
factors which come into play (speed of extraction, facility of separation, 
etc.). 
When working by liquid-liquid exchange between two phases, they must 
obviously be selected as a function of one another. 
By solid organic phase, is meant any organic ion exchanger having fixed 
ionic compounds of uranium, such as ion exchange resins. Strong cation 
exchange resins are known (for example sulfonic polystyrene resins) weakly 
cationic complexing or chelating agents (for example resins bearing 
carboxylic, phosphate or aminodiacetic groups), strong anionic resins (for 
example quatenary ammonium), moderate or weak anionic resins (for example 
various amines). The above expression may also mean a mineral or organic 
compound deposited or adsorbed on a solid organic support (polystyrene, 
PTFE or Kel F for example) or a solid organic compound used alone. 
Isotopic exchange by the method according to the invention can take place 
between two different compounds of uranium III or between compounds of 
uranium III and uranium IV: it is the latter solution which is by far the 
most interesting. 
Isotopic exchange by the method according to the invention can take place 
either in a monophase liquid system, that is to say the uranium compounds 
are brought in contact in a homogeneous phase, or in a two-phase system, 
that is to say that the uranium compounds are in two different phases, 
like a liquid and a solid or two liquid phases which are not miscible. 
However when the isotopic exchange is effected in a monophase system, it 
is necessary to separate, after enrichment, either the depleted compound, 
or the enriched compound by creating a two-phase system, which complicates 
the method and renders the yield less advantageous. 
Among the methods of applying the invention, exchange in liquid phase seems 
particularly advantageous, especially because it is possible to obtain and 
to maintain the necessary purity without excessive difficulty. Among these 
methods, those which seem most advantageous at the present time use 
exchange between an aqueous phase containing U III and an organic phase 
containing U IV. U III will generally be in the form of a salt dissociated 
in solution. The salt will for example be UCl.sub.3 in an aqueous solution 
of HCl playing the role of a relargent or salting-out agent. 
The concentration of uranium of the aqueous and organic phases of the 
solutions is adjusted as a function of the compounds of uranium used, of 
their crystallisation limits, of the temperature of the clogging limit of 
the contactor selected. It will be chosen as high as possible to reduce 
the volume of the installation, but it must, as indicated above; 
limit the passages of uranium with the valence IV from the organic phase to 
the aqueous phase in the course of the contact, the passage of uranium of 
valence III into the organic phase being negligible with the usual 
solvents; 
enable the almost complete re-extraction by means of simple adjustments 
(elimination of the salting-out agent for example). 
In practice, there is generally used for the exchange: 
an 0.1-2.5 M/l aqueous solution of U III; with UCl.sub.3 in a hydrochloric 
solution, upper limit is preferably limited to 2 M/l; 
a concentration of 1.5 M/l gives good results; 
an 0.1-1 M/l organic phase of U IV. With UCl.sub.4 it will be possible in 
practice to arrive at 0.5 M/l at ambient temperature, by using the 
abovementioned complexants. The contents in the neighborhood of 1 M/l 
require in general working at higher temperatures than ambient, thereby 
reducing the proportion of diluent. 
An isotopic exchange device or installation for enriching uranium in one of 
its isotopes, according to another aspect of the invention, comprises: 
an exchange battery constituted by a plurality of stages each comprising a 
contactor between two phases, one containing U III, the other U IV, and 
means for causing the circulation of one of the phases in counter current 
with the other in the battery, 
an oxidizing reflux circuit comprising means for performing substantially 
complete extraction of U III from the phase which contains it at the end 
of the battery whence this phase emerges, means for oxidizing U III to U 
IV and for transferring the oxidized uranium into the other phase for 
introduction at the same end of the battery, 
a reducing reflux circuit comprising means for substantially complete 
extraction of U IV from the phase which contains it at the other end of 
the battery, for substantially complete reduction of U IV to U III and for 
transfer of the reduced uranium into the other phase for introduction at 
said other end, the whole of the surfaces in contact with U III being 
electrically insulating. 
The means for reducing U IV to U III are advantageously provided to trap 
the troublesome ions: thus, the necessary purity is maintained provided 
that the content in these ions of the uranium solutions to be enriched 
introduced in the system be less than ppm and that the reflux be almost 
complete, that is to say the cascade almost square. 
The uranium can be brought to the cascade at the valence III or IV: but in 
most of cases, the initial loading of the cascade will involve making use 
of particular compounds of U III and U IV. 
Numerous methods for the preparation of uranium compounds with valence IV 
are already well known; there may be mentioned the electrolytic reduction 
of uranyl salts, the chemical reduction of these salts with a suitable 
reducer not permitting U.sup.+3 to be obtained (hydrogen or cracked 
ammonia without impurities), direct attack of a uranium oxide (UO.sub.2 by 
carbon tetrachloride towards 600.degree. C.) or of metallic uranium by an 
acid, followed by filtration. 
Uranium III may be obtained from uranium IV or from its compounds by 
methods which will be described below with regard to reducing refluxes. 
There may for example be used reduction of uranium IV by the electrolytic 
route, by the chemical route (for example by zinc or its amalgam); uranium 
metal may also be attacked with an acid under the specified conditions; or 
by dissolving UCl.sub.3 (or other salts of U with valence III) obtained by 
a dry route. 
It is lastly necessary to note that reduction with zinc of a solution of a 
uranyl salt with a suitable acidity 5 N hydrochloric acid for example) 
enables the obtaining of an equimolecular mixture of uranium III and IV 
which must then be protected against oxidation. In this case, isotopic 
exchange, in a monophase system, is produced at the same time as the 
formation of the two compounds. 
Lastly, various examples of apparatus usable in the installations will be 
described with regard to the various embodiment envisaged below. It is 
however important to note that the speeds of isotopic exchange are very 
high and that, in consequence, the times of contact must be chosen as 
short as possible, to reduce the volume of the solutions, especially in 
the stages or the cascades where the uranium is very enriched. As a 
result, the use of contact apparatuses involving short transit times is 
advantageous in the case of liquid-liquid exchange. It may be noted by way 
of indication that usual mixer-decanters hardly enable dropping below 40 
sec. and pulsed columns rarely below 30 sec., which leads to the 
preference of other equipment such as centrifugal mixer decanter 
assemblies, unfortunately more expensive.

DESCRIPTION OF PREFERRED EMBODIMENTS 
For greater clarity, the flow sheet of a conventional isotopic enrichment 
cascade and the general features of such a cascade modified according to 
the invention will first be described with reference to FIG. 1. 
It will now be assumed that this cascade is intended for isotopic 
enrichment of natural uranium in isotope 235 by a method according to the 
invention of exchange between an aqueous phase containing U III and an 
organic phase containing U IV. 
The exchange battery 11 of the cascade comprises p identical stages which 
will be denoted as 1, . . . , n, . . . , p. At stage n for example, the 
aqueous phase 1 containing U.sup.+3 coming from stage n+1 is mixed with 
the organic phase containing U.sup.+4 coming from stage n-1; after 
separation, the aqueous and organic phases emerge respectively at 3 and 4. 
The phase containing U IV is enriched in light isotope U 235. If .beta. is 
the enrichment coefficient per stage and if R.sub.n is the ratio of the 
richnesses U 235/U 238 (assumed equal at the inputs 1 and 2), the organic 
phase at the output has the richness R.sub.n .multidot..beta. of U 235. 
FIG. 1 also shows diagrammatically, the "rich" reflux 7, where U IV 
enriched in U 235 is reduced to the state of U III and reintroduced at 
stage p in aqueous phase, and the "depleted" reflux which fulfills the 
reverse functions of oxidation, of transferring the uranium from the 
aqueous phase to the organic phase and of reintroduction into stage 1. 
Conventional computation of an enrichment cascade shows that it is 
advantageous to adjust at each stage the ascending (from 1 to p) and 
descending flow-rates so as to avoid isotopic remixtures, that is to say 
to bring the uranium arriving at 2 to the same isotopic richness as the 
uranium arriving at 1: this condition is not feasible economically; it is 
therefore convenient to approach as far as possible this ideal condition 
by carrying out partial refluxes between a limited number of so-called 
"square" sub-cascades, such as those of FIG. 1, with a very low flow-rate 
input at N and a very low corresponding flow-rate outputs of enriched 
uranium at E and depleted uranium at D. 
FIG. 2 shows a cascade which comprises an exchange battery, where instead 
of exchange between U III and U IV, there is used exchange between an 
inorganic liquid phase of uranium III and an organic phase of U III. The 
use of those organic solvents mentioned above which cannot complex U III 
is obviously excluded in this case. The exchange battery 11 can have a 
constitution similar to that described in FIG. 1, but the refluxes are of 
different nature. 
The phases are for example the following: 
Organic phase: Uranium in the form of a complex in a dilute organic 
solvent, capable of placing the uranium III in the form of a complex such 
as phosphonate. At ambient temperature, an aliphatic or aromatic inert 
diluent, like for example dodecane, kerosene or xylene, is added to the 
solvent. There can for example be used an organic phase O constituted by: 
______________________________________ 
Phosphonate 
= 50% (for example dibutylbutylphos- 
phonate DBBP) 
O Xylene = 50% 
U III = 0.005 M 
______________________________________ 
Inorganic phase: Uranium at low concentration in the aqueous phase. To this 
phase there must imperatively be added a strong salting out agent intended 
to maintain the uranium complex in the organic phase. If the uranium is in 
the form of UCl.sub.3, the salting out agent may be Cl.sup.- at strong 
concentration in the form of HCl and/or alkali or alkaline-earth chloride. 
There can for example be used as the aqueous phase A: 
______________________________________ 
U.sup.+3 
:0.2 M in the form of UCl.sub.3 
HCl :5 to 8 N, advantageously 7 N. 
______________________________________ 
The aqueous phase enters the exchange battery 11 through 12. In the 
compartment 13, the acidity of this aqueous phase has been raised from 0.5 
to 7 N due to the hydrochloric acid coming from the separator 14 through 
15. 
After isotopic exchange, this aqueous phase goes from the exchange battery 
11 to an extractor 17 through a pipe 16. In this extractor, the aqueous 
phase A is brought in contact with a 50% exhausted DBBP in xylene. The 
uranium III then passes entirely from the aqueous phase into the organic 
phase. The aqueous phase exhausted of uranium then goes into the separator 
14. This separator 14 extracts the hydrochloric acid at 15 and restores an 
aqueous phase whose normality of HCl has passed from 7 N to 0.5 N. The 
hydrochloric acid is sent into 13 through 15 whilst the aqueous phase 0.5 
N, exhausted of uranium, is sent through 18 to a reextractor 19 where it 
is brought in contact with the organic phase O coming from the exchange 
battery 11. The whole of the uranium III passes from the organic phase 
into the aqueous phase, the latter containing practically no more salting 
out agent. The charged aqueous phase A then enters through 21 in an 
apparatus 20, where the uranium, of which a portion has possibly been 
oxidized, is brought back entirely to valence III. Finally, the aqueous 
phase is brought through 22 into the compartment 13 in which HCl, playing 
the role of salting out agent, is introduced. 
The organic phase O, after isotopic exchange in the exchange battery 11, is 
sent through 23 to the extractor 19 where the uranium is extracted by the 
aqueous phase. The exhausted organic phase emerging from 19 through 24 
goes to the extractor 17 where the uranium contained in the aqueous phase 
passes into the exhausted organic phase, owing to the presence of salting 
out agent in the aqueous phase. Finally, the organic phase loaded with 
uranium enters 11 through 25. The supply of natural uranium is effected at 
very low flow-rate through N, the withdrawal of depleted uranium at D and 
the taking off of enriched uranium at E. 
The components of the battery can have the constitution which will be 
described below with regard to FIGS. 3 and 4. 
There will now be described in more detailed manner exchange batteries 
between U III and U IV according to the diagram of FIG. 1. 
The liquid-liquid isotopic exchange between the compounds of U III and 
compounds of U IV in the liquid phase, may be effected under various 
conditions, two of which will be described in the following, i.e.: 
the exchange in homogeneous aqueous phase with extraction of U IV by an 
organic phase; 
exchange between an aqueous phase containing U III and an organic phase 
containing U IV, this condition giving rise to a lower consumption of 
energy and to a simpler apparatus than the first and being generally 
preferable. 
These two embodiments will be described successively by making reference to 
the examples. In all cases, the phase containing the U IV is enriched in 
light isotope (U 235 in the case of enrichment of natural uranium). 
FIG. 3 shows diagrammatically three intermediate stages (of rank n-1, n and 
n+1) of a cascade employing exchange in homogeneous aqueous phase, as well 
as two end stages 1 and p and the refluxes. The number p of stages is 
chosen as equal to the number of theoretical plates to obtain the desired 
enrichment. The poor reflux (that is to say depleted in U 235) and rich 
reflux are constituted by apparatuses enabling the uranium contained 
respectively in the phases containing U III and U IV and emerging through 
one end of the cascade to pass at the other valence before reintroduction 
at the same end of the battery in the other phase. 
The stages are all identical. The stage n for example comprises an 
apparatus 29 in which the aqueous phases are mixed prior to exchange, then 
subjected to extraction by the organic phase. 
The apparatus 29 is for example a pulsed column, a mixer-decanter (which 
has the drawback of not permitting allowing for a contact time of less 
than about 40 seconds in the present state of the art), or a static 
mixer-centrifugal separator assembly. These apparatuses should not have 
any surface which is electrically conducting in contact with the phases 
undergoing exchange and must not introduce catalytic ions. For this 
purpose, recourse should be had to either apparatuses made of plastic 
materials, or apparatuses with surfaces coated with an insulating 
material. 
The apparatus 29 of the stage n receives, through 45, the aqueous phase 
charged with U III coming from the subsequent stage n+1, and, through 41, 
the aqueous phase charged with U IV from the preceding stage n-1. The 
aqueous phase charged with U III and depleted in U 235 emerges from the 
stage at 37 to go to stage n-1, after treatment. 
In the apparatus 29, U IV is extracted entirely by an organic phase 
circulating in counter-current, entering at 34 and emerging at 30. 
One may for example use: 
as input phase charged with U III, an aqueous hydracid solution (generally 
hydrochloric) about 5 N, whose content of U III ranges from 0.1 to 2 M/l; 
as input phase charged with U IV, an aqueous solution of the same hydracid 
(generally hydrochloric) about 5 N, of which the content of U IV ranges 
from 0.1 to 2 M/l; 
as organic phase for the extraction of U IV, capable of extracting the U IV 
entirely from the aqueous phase having the contents of hydracid 
(constituted by HCl) indicated above, various solvents, such as: 
trioctylphosphine oxide (TOPO), diluted in an aromatic organic diluent like 
xylene in the proportion of 10% of trioctylphosphine oxide by weight, if 
one works at ambient temperature, 
triheptylphosphine oxide or THpPo, 
trihexylphosphine oxide or THxPO, 
these solvents being also diluted. 
With the apparatus 29 are associated: 
an assembly for adjusting the acidity of the aqueous solutin of U III, 
before its being sent to the preceding stage, 
an assembly for re-extraction of U IV from the organic phase by an aqueous 
phase and adjustment of the latter before being sent to stage n+1. 
The first assembly comprises a hydrochloric acid concentrator 33, which may 
use electrolysis, osmosis or evaporation (with the addition of a salt to 
avoid the azeotrope H.sub.2 O--HCl with 20% of HCl at atmospheric 
pressure). The latter solution will generally be the most advantageous. 
The concentrator may be one of the well known types for the preparation of 
concentrated HCl, such as those described in U.S. Pat. No. 2,357,095 
(Evans et al) and G.B. Pat. No. 669,671 (Wingfoot Corp.) or in the article 
of M. J. Dehan "Carbon and hydrochloric acid" (Chimie et Industrie, Vol. 
105, No. 23, November 1972, pages 1683-1687), but provided to avoid the 
addition of oxidizing ions and the contact with any conducting surface 
(which implies glass members). 
From the concentrator 33 supplied with hydrochloric aqueous solution 4-9 N 
arriving through 37 emerge: 
at 32, an aqueous solution freed of uranium, very slightly acid (less than 
0.5 N) to be able to extract U IV from an organic phase; the extraction 
can even be effected with water; the TOPO having retained sufficient acid 
to avoid the precipitation of U IV; 
at 38, concentrated acid, generally in the gaseous form, 
at 42, an aqueous solution, containing the whole of U III (depleted in U 
235) which goes to stage n-1. 
The second assembly comprises a re-extractor 31 (which can be very similar 
to the apparatus 29) in which U IV is entirely extracted by the very 
slightly acid aqueous phase coming through 32 from the concentrator 33. 
The aqueous solution charged with U IV goes through 35 to the stage n+1 
where it will be reacidified before introduction into the exchange 
apparatus of the stage. 
At each stage (n, for example), the aqueous solution coming through 40 from 
the re-extractor of the preceding stage (n-1 for example) is acidified 
before introduction into the apparatus 29: this operation is effected in a 
mixing acidifier 39 supplied with hydrochloric acid by the concentrator 
33, by means of 38. 
The U IV uranium enriched in U 235 emerging in concentrated aqueous phase, 
very slightly acid, from the re-extractor of stage p is reduced to the U 
III state and reintroduced at stage p through a reducing reflux. This 
reducing reflux comprises an apparatus 46, supplied through 47 from the 
re-extraction of stage p, which restores U IV to the state U III. It can 
be very similar to that which will be described below with reference to 
FIG. 4 and it suffices here to note that this apparatus 46 may be: 
a reactor in which U IV is reduced to U III in the aqueous phase by a 
reducing solid product such as metallic zinc or a zinc amalgam, recovery 
of the zinc having then to be provided for. 
an electrolysis tank with a diaphragm in which the uranium is reduced by 
the electrochemical route. The tank can be of the type used for the 
manufacture of chlorine, but with non-metallic walls or covered with 
insulation (except for the electrodes) and a porous diaphragm of sintered 
glass, PVC, PTFE, or an ion exchange membrane insulating the cathode 
compartment. 
The cathode can for example be of a metal or alloy whose hydrogen 
overpotential is sufficient, such as mercury or an amalgam, of lead for 
example. The anode may be of graphite. Lead, cadmium, tin can also be 
contemplated. 
The solution in the cathode compartment is brought to between 1 and 2 N by 
addition of HCl from the concentrator 52 of the stage 1 to improve the 
Faraday yield. The chlorine which is released at the anode is 
fractionated: a part is recombined with hydrogen formed at the cathode; 
the rest is used in the oxidizing reflux, as will be seen below. In 
practice, 0.25 A/cm.sup.2 is not exceeded in the course of the 
electrolysis. 
The aqueous solution of U III taken up through 48 in the apparatus 46 
supplies the last stage p of the cascade, after having been acidified by a 
delivery of HCl coming through 51 from the concentrator 52 of stage 1. 
The reducing reflux, when a mercury cathode is used, also effects the 
elimination of troublesome cations (such as Ni, Cu, . . . ) and enables 
the maintenance of their content at a very low value (less than one ppm) 
which is necessary: these cations are amalgamated and then retained by an 
auxiliary mercury purification system. 
The oxidizing reflux is provided on the other hand to oxidize the uranium 
emerging through 53 from the concentrator 52 from the first stage in 
slightly acid concentrated aqueous phase from the U III form to the U IV 
form, and to reintroduce it through 54 in to the apparatus 29.sub.1 of 
this first stage. 
The reflux comprises a reactor 50 in which U III is restored to U IV, for 
example by one of the following operations: 
electrolysis; 
bubbling of an oxidizing gas (Cl.sup.2 for example, coming through 49 from 
the tank 46 as indicated in FIG. 3). 
The operational conditions must be obviously selected to avoid bringing the 
uranium to valency VI. 
In the case of the refluxes indicated in FIG. 4, there is a double 
interaction between the refluxes: 
The chlorine serving for the oxidizing reflux comes through 49 from the 
anode compartment of the electrolyser 46 used for the reducing reflux; 
the acid coming from the deacidifier 52 at stage 1 (corresponding to the 
oxidizing reflux) is used before and after the electrolysis at 46 to 
enable good electrolysis and adjust the acidity of the emerging solution. 
The table below brings together the results of a certain number of trials 
in flasks for which the uranium salts were 0.2 M UCl.sub.4 and UCl.sub.3 
chlorides in an HCl medium of 4 to 9 N. 
__________________________________________________________________________ 
N.degree. 
1 2 3 4 5 G 7 8 9 
__________________________________________________________________________ 
N HCL Medium 
7 7 7 7 5 4 5 5 5 
Extraction agent 
TOPO 
TOPO 
TOPO 
TOPO 
TOPO 
TOPO 
TOPO 
TOPO TOPO 
Duration 3 m 5 m 5 m 10 s 
30 s 
30 s 
1 m 3 m 7 m 
.alpha. -1 .times. 10.sup.4 
38 40 40 38 39 38 37 36 35 
Diluent Tol Tol Tol Tol Tol Tol Tol Tol Tol 
Temperature 
Amb -20.degree. 
-20.degree. 
Amb Amb Amb Amb Amb Amb 
-25.degree. 
-25.degree. 
__________________________________________________________________________ 
N.degree. 
10 11 12 13 14 15 16 17 18 
__________________________________________________________________________ 
N HCL Medium 
5 7 7 9 5 6 5 5 5 
Extraction Agent 
TOPO 
TOPO 
EH TBPO 
EH EH 3H TH.sub.p PO 
TH.sub.x PO 
Duration 15 m 
2 m 1 m 4 m 1 m 1 m 1 m 1 m 1 m 
.alpha. - 1 .times. 10.sup.4 
32 37 39 35 35 40 41 36 37 
Diluent Tol Tol Ker Tol Ker Ker Ker Tol Tol 
Temperature 
Amb Amb Amb Amb Amb Amb Amb Amb Amb 
__________________________________________________________________________ 
where: 
EH=di2ethylhexylphosphoric acid or D2EHPA 
Tol=Toluene 
Ker=Kerosene 
Amb=Ambient (temperature in .degree.C.) 
Particularly satisfactory results are obtained under the following 
conditions: 
acidity of the aqueous medium in mixer-decanters around 5 N HCl; 
extraction agent: dilute trioctylphosphine (TOPO). 
The enrichment coefficient .alpha. is all the higher as the extraction is 
rapid; it diminishes with the duration of contact to reach an ultimate 
value corresponding to the reversible exchange and which corresponds to 
values of .alpha. of the order of 1.0027. 
After the example of exchange in the homogeneous aqueous phase illustrated 
in FIG. 3, there will now be described the exchange between the 
hydrochloric aqueous phase of UCl.sub.3 and organic phase (for example 
UCl.sub.4 in TBP diluted in dodecane) with reference to the examples 
illustrated in FIGS. 4 and 5. 
In FIG. 4, the battery of isotopic exchange stages is again denoted by 11. 
Each stage is constituted by an apparatus for bringing two phases in 
contact and, subsequently, for separating them, similar to the apparatuses 
29 of FIG. 3. For example, use can be made of: 
pulsed columns for liquid-liquid extraction, such as those marketed under 
the name PSE by Stahl Apparate and Geratebau, Viernheim, Hessen, R.F.A.; 
multiple mixer-decanters or mixer settlers (which have however the drawback 
of long duration of contact) such as those marketed under the name LTE by 
Lurgi Ges. fur Warmetechnik mbH, Frankfurt, West Germany; 
continuous Podbielniak centrifugal contacters for liquid-liquid extraction, 
marketed by Baker-Perkins Inc. Saginaw, Mich., U.S.A.; 
Lurgi Westfalia drum extractors with counter-current circulation, marketed 
by Westfalia Separator AG, Oelde, West Germany, which enable flow-rates 
going up to 7m.sup.3 /hour; 
Alfa-Laval counter-current centrifugal extractors; 
rotary disc contactors; 
extraction centrifuges, such as those marketed by Liquid Dynamics, Chicago, 
U.S.A., under the trade mark "QUADRONIC". 
All the above-mentioned apparatuses, such as are available in commerce, 
comprise numerous metallic parts in contact with the liquid: they must 
obviously be modified and the parts concerned must be constituted or 
coated with electrical insulation. This can be glass or plastics. However 
plastics must be selected to resist at the same time concentrated acids 
(the hydrochloric aqueous phase) and constituents of the organic phase 
(especially phosphates and aromatic hydrocarbons). 
With the battery 11 are associated: 
a rich or reducing reflux, comprising a re-extractor 71, an apparatus 72 
for reducing U.sup.4+ to U.sup.3+, an acidifier 69, an apparatus 73 for 
the possible extraction of UCl.sub.4 and the associated pipes and 
equipment. 
a poor or oxidizing reflux, comprising an apparatus 68 for oxidation of 
U.sup.3+ to U.sup.4+, an apparatus 74 for increasing the acidity, an 
extractor 66 and the associated pipes and equipment; 
lastly apparatuses 70 and 75 for purification and recycling of the aqueous 
and organic phases. 
The apparatus 70 is intended to remove all or part of the hydrochloric acid 
from a 5-7 N aqueous hydrochloric phase free of uranium which it receives 
at 76; there emerges therefrom; at 77, a solution containing between 0.2 
and 2 N HCl and, at 78, HCl gas containing little water. This apparatus is 
for example a still. 
In the re-extraction apparatus 71, the solution coming from 77 re-extracts 
completely the uranous chloride UCl.sub.4 contained in an organic phase 
arriving at 79. 
U.sup.4+ contained in the aqueous loaded with UCl.sub.4 emerging from the 
re-extractor 71 is reduced in the electrolyser 72 containing a 
semi-permeable membrane and of which the cathode is constituted either of 
mercury, or of lead, or of lead amalgam, or of metals whose hydrogen 
overpotential is sufficient, for example Cd, Sn; there is formed 
hypo-uranous chloride UCl.sub.3 in the cathode compartment. 
The electrolyser 72 may be of one of the types currently used in the 
preparation of chlorine by electrolysis, such as described for example in 
"Chlorine-- Its Manufacture, Properties and Uses" J. S. Scance, Robert E. 
Krieger Publishing Company, Chapters 5 and 6. There may also for example 
be used: 
cells with horizontal cathode, with forced or gravity flow; in particular, 
one may use cells operative with co-currents of the aqueous phase and of a 
thin layer of mercury, the cathode compartment being surmounted by a 
diaphragm of sintered glass provided with evacuation ducts for the 
hydrogen, and the anode compartment provided with pipes for the exit of 
chlorine; 
vertical cathode cells constituted by a film of mercury falling by gravity, 
provided with diaphragms not capable of introducing impurities, for 
example of PTFE, PVC, fluon, grafted PTFE (the diaphragms may be of 
purified ion exchange resins or sintered glass), such as described at 
Chapter 15 pages 575-596 of the work. "Industrial Electrochemical 
Processes" of A. T. Kuhn, Observer Publ. Co.; 1971; the mercury also 
serves as a heat carrier and is cooled before being returned to the cells; 
cells with rotary horizontal cathode. 
The aqueous phase emerging from the cathode compartment through 80 is 
acidified at 69 by HCl gas arriving through 78a until an aqueous solution 
containing more than 2 N HCl is obtained which emerges at 81. If residual 
UCl.sub.4 subsists, it is extracted in a contact apparatus 73 by a portion 
of the exhausted organic phase brought in through a by-pass 82. 
The aqueous phase then enters at 83 the exchange battery 11 where it 
circulates in counter-current with an organic phase entering at 84 and 
containing UCl.sub.4. At 68, the uranium from the aqueous phase is 
oxidized by the chlorine arriving through 85 of the anode compartment of 
the electrolyser 72: UCl.sub.3 is converted into UCl.sub.4. The acidity of 
the aqueous phase is brought to 5-7 N at 74 by a portion of the HCl gas 
arriving from 70 through 78b. Then UCl.sub.4 is extracted in the apparatus 
66 (a battery of pulsed columns for example) by the organic phase arriving 
at 86, almost entirely, because of the high content of salting out HCl of 
the aqueous phase. The aqueous phase freed of its uranium then feeds the 
deacidifier 70 and 76. 
The organic phase which is loaded with UCl.sub.4 at 66 emerges at 84 and 
circulates in 11 in counter-current with the aqueous phase entering at 83: 
the organic phase is enriched in 235 U whilst the aqueous phase is 
depleted in 235 U. UCl.sub.4 is re-extracted at 71. 
The organic phase freed of its uranium is then washed at 75 by a current of 
sodium carbonate which retains the hydrolysis products of the solvents as 
well as the possible oxidizing metals which precipitate. The purified 
organic solution is then recycled through 86. A small fraction is drawn 
off through 82 to extract residual U IV from the aqueous phase. 
The assembly thus described will constitute a total reflux battery; 
production is ensured by introducing at N a flow of organic phase loaded 
with UCl.sub.4 very small with respect to the circulating flow; this flow 
is compensated by portions taken off at E on the enriched uranium and at D 
on the depleted uranium. 
Other modifications of this system are possible, for example as regards 
deacidification. It is possible for example to replace HCl gas arriving at 
78b by a concentrated aqueous solution of depleted UCl.sub.4 and to 
regulate the extraction battery 66 such that only a predetermined fraction 
of UCl.sub.4 be extracted; the solution 76 which then contains UCl.sub.4 
is concentrated at 70 to liberate slightly acid water at 77, HCl gas at 78 
and a concentrated solution of UCl.sub.4 at 78b. HCl may be replaced by 
MgCl.sub.2 or LiCl, at least partly, to increase the content of salting 
out agent without increasing the acidity. 
The embodiment illustrated at FIG. 5 differs from the preceding one only by 
the constitution of the refluxes. For greater simplicity, the apparatuses 
corresponding to those of FIG. 4 bear the same reference numerals. 
In FIG. 5, the counter-current exchange battery 11 receives through 90 the 
8 N hydrochloric aqueous solution of UCl.sub.3 to be enriched. This 
solution is mixed with an aqueous phase of UCl.sub.3 coming from a 
reducing reflux constituted by an extractor 71, an electrolyser with a 
mercury cathode 72, an acidifier 69, and entering the battery 11 through 
the supply pipe 83. In the battery 11, this aqueous phase encounters, in 
countercurrent, an organic phase entering through 84, constituted by TBP 
diluted to 30% in dodecane and loaded with UCl.sub.4, which emerges from 
the battery through 79. The 8 N hydrochloric aqueous phase, emerging from 
the battery 11, is divided into two fractions. The first fraction, of 
slight flow-rate is rejected at D. The other is sent through 92 to the 
oxidizing reflux. It is oxidized in a bubbler 68, by a current of chlorine 
entering through 85, and UCl.sub.3 thus passes to the state of UCl.sub.4. 
The aqueous phase charged with UCl.sub.4 leaves the bubbler through the 
pipe 93 and enters an extractor 66. In this extractor 66, UCl.sub.4 passes 
from the 8 N hydrochloric medium into the organic phase entering 66 
through the pipe 86. 
The organic phase, charged with UCl.sub.4, leaves the extractor 66 through 
84 and supplies the exchange battery 11. The 8 N hydrochloric aqueous 
phase exhausted of UCl.sub.4 leaves the extractor 66 through 76. A portion 
of this hydrochloric solution is directed to a distillation apparatus 70 
and the remainder (to which their is added through 71 water coming from 
the still 70, in order to bring its normality of about 3 N) enters through 
102 re-extractor 71, wherein the 3 N hydrochloric phase encounters in 
counter-current the organic phase loaded with UCl.sub.4 coming, through 
the pipe 79, from the exchange battery 11. The acidity conditions are such 
that almost the whole of the UCl.sub.4 passes into the 3 N hydrochloric 
aqueous phase. The organic phase, freed of UCl.sub.4, leaves the 
re-extractor 71 through the pipe 94 and is introduced into a separator 95, 
where the degradation products of the TBP are removed through 96. This 
separator may be a chamber for washing by Na.sub.2 Co.sub.3. 
The degradation products of the TBP comprise vigorous complexants and can 
entrain a portion of the enriched UCl.sub.4. The fraction of these 
products which retain UCl.sub.4 corresponding to the production is removed 
through E. The other fraction is treated to recover the uranium which is 
reintroduced into the aqueous phase in the installation through 98. 
The 3 N hydrochloric aqueous phase containing UCl.sub.4 emerges from the 
re-extractor 71 through the pipe 99. After mixing with UCl.sub.4 recovered 
from 95, it is lead through the pipe 100 to the electrolyser 72 in which 
uranium IV is brought back to valence III. 
The distillation apparatus 70 separates the 8 N hydrochloric solution 
emerging from the extractor 66, on the one hand into concentrated 
hydrochloric acid 78 which serves to restore to about 8 N the normality of 
the UCl.sub.3 solution emerging from the electrolyser 72, before its entry 
into the exchange battery 11 and, on the other hand, into water 101 used 
to reduce the normality of the 8 N hydrochloric solution arriving through 
76 before its entry into the re-extractor 71. 
In FIGS. 6 to 9 are described various examples in which are to be found the 
same functions of enrichment and of oxidizing reflux on the depleted side 
(which is not shown), but where the reduction on the rich reflux side is 
ensured by an amalgam, according to various alternatives: the same 
reference numerals will again be used to denote the corresponding members. 
FIG. 6 shows the same devices to be used in connection with the method as 
in FIG. 5. However UCl.sub.4 is reduced by zinc amalgam. The plate column 
71 receives, besides the organic and aqueous phases, as in FIG. 5, a third 
phase constituted by zinc amalgam coming from the electrolyser 103 through 
the pipe 104. This amalgam is recycled from the column 71 to the 
electrolyser 103 through the pipe 105. Since a small amount of zinc is 
being entrained by the organic phase, a supplementary washer 106 is 
provided in the return pipe 86 of the aqueous phase. 
FIG. 7 shows again the same devices to be used in connection with the 
method as in FIG. 4, but the electrolyser is replaced by a contactor 107 
in which the reduction of the uranium IV to uranium III is effected by 
zinc amalgam coming through 108 of the electrolyser 109. 
In the case of FIG. 8, the reflux 71 and reducing 107 apparatuses are 
replaced by a single apparatus 110 in which the three phases circulate: 
organic, aqueous and zinc amalgam. The two aqueous and organic phases 
circulate in counter-current whilst the direction of flow of the zinc 
amalgam is immaterial. UCl.sub.4 is re-extracted and reduced in a single 
operation. 
For an aqueous phase highly concentrated in salting out agent (HCl or 
chloride), the apparatus 110 constitutes by itself the whole of the 
reducing reflux. 
In FIG. 9, there is shown an alternative of the method which is convenient 
for aqueous phases with low contents of salting out agent (0.5 N). In this 
case, it is advantageous to combine the apparatuses 107-110 and 71 into a 
single tower, the flow of ZnHg arriving at mid-height of the tower. 
The aqueous solution then contains zinc chloride; it passes through the 
apparatuses 69-73-67-68-74-66 without disturbing their operation. 
In FIGS. 7 to 9, the addition at 74 of HCl gas may be advantageously 
replaced by the addition of a concentrated solution of salting out agent 
111 (LiCl or MgCl.sub.2 for example) emerging from the deacidifier 70. The 
flow-rate is adjusted so that the concentration of salting out agent in 
the solution 112 emerging from 74 is such that the uranium is extracted at 
66 in a suitable number of stages. 
The solution 76 exhausted of uranium is electrolysed at 109, the cathode 
being constituted by a film if amalgam 113 depleted of zinc coming from 
the reactors 107 and 110. The solution 114 which emerges from the 
electrolyser is not completely depleted of ZnCl.sub.2 to maintain a 
suitable Faraday yield in the electrolyser. 
In the deacidifier 70 which is, in these examples, a group of rectifying 
columns, there is removed at 115 steam containing little HCl, at 78 HCl 
containing little water, and at 111 a concentrated more or less acid 
solution of LiCl or MgCl.sub.2 containing also ZnCl.sub.2. 
After condensation, the solution 115 serves to re-extract at 71, not only 
UCl.sub.4 from the organic phase, but also the amount of ZnCl.sub.2 which 
might also be contained therein. It will be noted that with this system it 
is advantageous to minimise attack by the hydrochloric acid on the zinc 
dissolved in the mercury, to replace a portion of the hydrochloric acid of 
115 by a chloride not reduceable by the zinc amalgam and having a good 
salting out effect (MgCl.sub.2 or LiCl already mentioned may be suitable). 
This is obtained by by-passing part of the flow 114 directly to 115. Some 
ZnCl.sub.2 however remains in the organic phase emerging from 71; this 
ZnCl.sub.2 must be removed or not by washing with acidified water 
according as the washing with carbonate 75 is run or not. In this case, 
the zinc electrolyser may, if necessary, be placed after the by-pass 
proposed hereabove. 
ZnCl.sub.2 can again be extracted by an organic phase which forms a complex 
of the ZnCl.sub.2 (TBP for example), independent of the principal organic 
phase, at the level of 76, this ZnCl.sub.2 being then re-extracted by 1 N 
hydrochloric acid in order to reduce the zinc in the amalgam with a good 
Faraday yield. 
The following examples (of unit exchange for the examples 1 to 9) enable 
the magnitude of the separation factor to be appreciated. 
EXAMPLE 1 
Uranium III--Uranium IV Exchange in a two-phase system 
U III: in 0.4 M aqueous solution, 7 N hydrochloric medium 
U IV: 0.4 M in benzene and TBP organic phase 
Temperature: 21.degree. C. 
Time of Exchange: 15 seconds 
Separation factor: .alpha.=1.0030. 
EXAMPLE 2 
Liquid-liquid exchange in a counter-current mixer-settler 
______________________________________ 
III = 0.2 M 
Aqueous Phase 
HCl = 7 N 
U IV = 0.2 M 
Organic Phase: 50% TBP in a dodecane-toleune mixture 
40%-10% 
______________________________________ 
Contact time variable from 49 to 132 seconds. 
Separation factor: .alpha.=1.0012 to 1.0026 according to the contact time 
and agitation. 
EXAMPLE 3 
Liquid-liquid Exchange using as organic solvent an alkyl phosphate 
UCl.sub.3 =0.4 M in 7 N aqueous hydrochloric solution 
UCl.sub.4 =0.4 M complexed by TBP (40%) diluted in kerosene R (60%) 
Temperature: 21.degree. C. 
Contact time: 15 seconds 
Separation factor: .alpha.=1.0025. 
EXAMPLE 4 
Liquid-liquid Exchange using an alkyl phosphate as organic solvent 
UCl.sub.3 =2.35 M+UCl.sub.4 =0.13 M in 1.55 N HCl solution 
UCl.sub.4 =0.42 M in tri-isobutylphosphate (42% by volume) diluted in 
xylene (58% by volume) 
Temperature: 35.degree. C. 
Contact time: 30 seconds 
Separation factor: .alpha.=1.0028 
EXAMPLE 5 
Liquid-liquid Exchange using a phosphonate as solvent 
UCl.sub.3 =1 M+0.125 M UCl.sub.4 in 4.6 N HCl solution 
UCl.sub.4 =0.55 N in n-butyl di-isobutylphosphonate at 40% in dodecane 
Ratio volumes organic/aqueous=2 
Temperature: 20.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0025. 
EXAMPLE 6 
Liquid-liquid Exchange using a phosphine oxide as solvent 
UCl.sub.3 =0.11 M+UCl.sub.4 =0.01 in 5 N HCl 
UCl.sub.4 =0.12 M in trioctylphosphine oxide (TOPO) diluted to a content of 
10% in toluene 
Temperature: 25.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0024 
EXAMPLE 7 
Liquid-liquid Exchange using a sulfoxide as solvent 
UCl.sub.3 =0.42 M+UCl.sub.4 =0.16 M in 4.5 N HCl 
UCl.sub.4 =0.44 M in an organic phase containing 2 M/l of 
di-n-amylsulfoxide diluted in a mixture of equal volumes of 
tetrachlorethane and tetrabromethane 
Temperature: 25.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0020 (which corresponds at least to 1.0025 if 
account is taken of the UCl.sub.4 remaining in the aqueous phase) 
EXAMPLE 8 
Liquid-liquid exchange using an amine as solvent 
UCl.sub.3 =0.08 M in 6 N HCl 
UCl.sub.4 =0.08 M in the aliquat 336 diluted in the proportion of 17% in 
toluene (the aliquat 336 is an industrial mixture of quaternary ammoniums 
manufactured by GENERAL MILLS, Kankakee, Ill.) 
Temperature: 22.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0026 
EXAMPLE 9 
Aqueous phase-cruanic phase liquid-liquid exchange 
UCl.sub.3 =0.7 M in 7.35 N hydrochloric aqueous solution 
UCl.sub.4 =0.68 M complexed by 50% tri-isobutylphosphate in kerosene R 
Temperature: 25.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0027 
EXAMPLE 10 
Aqueous phase-organic phase liquid-liquid exchange 
UCl.sub.3 =0.7 M in 8.2 N hydrochloric aqueous solution 
UCl.sub.4 =0.67 N complexed by 50% tri-2-methylbutylphosphate in dodecane 
Temperature: 30.degree. C. 
Contact time: 1 minute 
Separation factor: .alpha.=1.0027 
EXAMPLE 11 
Aqueous phase-organic phase liquid-liquid exchange 
UCl.sub.3 =0.08 M in 6 N hydrobromic acid 
UCl.sub.4 =0.08 M in D.sub.2 EHPA (diethyl.sub.2 hexylphosphoric acid) 
diluted to 30% in toluene 
Ambient temperature 
Contact time: 5 minutes 
Separation factor: .alpha.=1.0020 
EXAMPLE 12 
Cascade of the Woodward type with four stages according to the system of 
FIG. 10 
Aqueous phase A: UCl.sub.3 =0.42 M, HCl=8 N 
Organic phase O: UCl.sub.4 =0.42 M, 50% TEP-50% toluene 
The ratio of the richnesses of U 235 was measured at the different steps 
(see diagram); in particular, the ratio between the richness of the 
richest product in U 235 and the richness of the poorest product in U235 
is equal to 1.0109, which corresponds to an average separation factor of 
1.0027 per stage. 
Right hand branch: The uranium contained in the organic phase O is divided 
into two parts; half is brought to valence III and subjected to the 
previously indicated conditions for the aqueous phase; the remainder is 
kept in the organic phase and a fresh contact is effected; the operation 
is repeated at each stage. 
Left hand branch: Identical operations but applied to the aqueous phases. 
EXAMPLE 13 
Successive exchanges in a cascade of Hutchinson & Murphy type 
A cascade with four plates was formed and four equilibrating operations 
were carried out, each being followed by a rotary transfer to approach 
equilibrium. 
The aqueous phase has the following characteristics: 
0.4 M in U III and 8 N in HCl 
The organic phase: 
0.4 M in U IV, 50% TBP in benzene 
The contact time of each operation was 5 minutes 
Separation factor: .alpha.=1.0026. 
EXAMPLE 14 
Successive exchanges in a cascade of the total reflux counter current type 
that is to say a "square" cascade with four stages according to FIG. 1, 
each of the contacts as well as the refluxes being effected step by step. 
Three rotations were effected. 
Isotopic analyses enabled the rise to equilibrium of such a cascade in 
total reflux to be followed, filled uniformly at the start with natural 
uranium. The phases had the following characteristics: 
Aqueous phase: UCl.sub.3 =0.4 M, HCl=8 N 
Organic phase: UCl.sub.4 =0.4 N, TBP=50% in benzene 
Contact time for each operation: 5 minutes. 
The various steps certainly resulted in enrichment according to theory, in 
particular the ratio of the end richnesses was 1.0080, which corresponds 
to .alpha.=1.0026. 
All the particular embodiments described until raw use liquid phase 
exchange. The invention may also use exchange between a solid phase and a 
liquid phase. The isotope exchange reaction is advantageously the same as 
in the preceding cases, that is to say that one of the phases contains 
preferentially valence III uranium and the other valence IV uranium; it is 
the latter which is enriched in light isotope. 
The operational technique using solid supports (ion exchange resins for 
example) and enabling multiplication of the exchange is that of band 
displacement. The band displacement may be considered as being the meeting 
of two frontal analyses, one called direct at the head of the band, the 
other called reverse at the tail of the band. These two operations being 
symmetrical, there will be given an example of a direct frontal analysis. 
It is assumed that the conditions are such that U IV is fixed on the solid 
mass. Before any introduction of uranium, a compound capable of oxidizing 
U III to U IV is fixed on the solid phase in a quantitative manner and a 
solution of U III is introduced at the top of the column. In a short 
height of the solid phase, which is similar to a plate, U III in solution 
arriving in contact with the oxidizing compound will be fixed on the solid 
phase at the U IV state, provided that it has more affinity for the solid 
phase than the product obtained as a result of the reduction of the 
initial oxidizing compound. If the choice is suitable, a displacement in 
the first plate is effected. If, by transfer of solution, there is brought 
into this plate a new fraction of the supply solution, there will be 
isotopic exchange between the U.sup.+4 fixed on the solid phase and the 
U.sup.+3 in solution. Under such conditions of operation, it will be noted 
that, for a given height of solid phase, the first drop of uranium 
emerging will be depleted in U 235 all the more as the column is greater, 
whilst the last drop emerging will have the initial isotopic composition. 
If the supply of uranium is interrupted once all the solid phase is 
saturated with U IV and if a reducer is supplied which converts U IV into 
U III and whose oxidation product has more affinity for the solid phase 
than U III, the phenomena which occur at the level of the theoretical 
plate can again be considered. It will thus be appreciated that, as the 
pasage of the solution progresses, the U IV will emerge from the column in 
a more and more enriched form. A reverse frontal analysis will thus be 
effected. 
Four types of frontal analysis can be considered in respect of the 
invention according as said analysis is direct or reverse and as the 
reflux which corresponds to the passage of uranium from one phase to the 
other by means of the oxidation-reduction reaction is of the oxidizing or 
reducing type. 
Direct frontal analysis (DFA) with oxidizing reflux 
Reverse frontal analysis (RFI) with reducing reflux 
Direct frontal analysis (DFA) with reducing reflux 
Reverse frontal analysis (FRA) with oxidizing reflux. 
To effect a displacement as a band, two opposite frontal types are opposed, 
one oxidizing, the other reducing. There are hence two possibilities 
according as the oxidizing front is at the head or at the tail of the 
band: 
DFA ox+RFI red 
DRA red+RFI ox 
the choice of one or other of the two systems being made depending on 
practical reasons. 
There must hence be used: 
a medium wherein one of the valences is preferentially fixed; 
two Red/ox compounds whose reaction product displaces uranium (reverse 
front) or is displaced by it (direct front) and whose reaction speed with 
the uranium is of the order of magnitude of the isotopic exchange speed. 
Oxidation-reduction reactions may be carried out outside of the solid phase 
and the two operations in the reflux, i.e.: 
the oxidation-reduction reaction, 
the passage of the uranium from one phase to the other, can be accomplished 
separately. 
One then has a method called an external reflux, which is necessarily 
discontinuous. The phases coming into play in the method are liquid and 
solid phases, as previously described. The concentrations in the aqueous 
phase may vary between 0.01 and 1 mole/liter and in the resin phase 
between 0.1 and 1.5 mole per kg of dry resin. 
There will now be described an example of a method with an external reflux. 
FIG. 11 shows diagrammatically an elemental cascade and its auxiliary 
elements in the case of an anionic resin. 
The exchange section 116 is constituted by columns in series, the length of 
each resulting from optimisation taking into account the height of the 
theoretical plate, of the route of the enriched band brought into play. 
The solid phase loaded with U IV emerging from the exchange section 116 
goes into the rich reflux 117. In the case of a strong anionic resin (FIG. 
11), a slightly acid aqueous phase (0.5 N HCl) displaces uranium IV from 
the resin. The solid phase freed of uranium IV goes through 118 into the 
poor reflux 119 where it is loaded with uranium IV before returning to the 
exchange section 116. The liquid phase emerging from the rich reflux 117 
is acidified through 120 before passing into the reducer 121. The 
reduction of the valence IV to the valence III is effected by chemical or 
electrochemical route. After acidification through 122, the liquid phase 
passes through the exchange section 116. It is then oxidized at 123 by any 
known method, such as previously described, for example by chlorine coming 
through 124 of the electrolyser 121. This liquid phase passes through the 
poor reflux 119 where it yields its uranium to the solid phase. The liquid 
phase then goes into the deacidifier 125. There emerges therefrom on one 
hand, a slightly acid aqueous solution which is sent through 126 to the 
rich reflux and on the other hand, a solution of HCl through 127. 
A solution of U III being very sensitive to the presence of any substance 
capable of oxidizing it, it is necessary not only that the purity 
conditions of the solution with respect to dangerous substances be ensured 
to preserve the stability of the U III. The resin should be maintained in 
such a purity condition as well. Should commercial resins be used, they 
should be carefully freed of the oxidizing groups which they contain 
peroxides which have served as polymerisation catalysts as well as 
impurities fixed on the resin, particularly products resulting from attack 
of metallic components of the installation, etc. in the course of the 
manufacture of acid resins. 
The following example shows the unitary effect obtained: 
Uranium IV was fixed on a strong anionic resin in a 8 N HCl medium. This 
resin, similar to DOWEX 2.times.10 resins, has been manufactured from a 
matrix obtained by copolymerisation of styrene and divinylbenzene and 
fixation thereon of exchange groups bearing quaternary ammonium groups, 
and has been purified. The resin with U IV fixed thereon was then 
contacted with a solution of uranium III in the same medium and in equal 
amount. The uranium was recovered separately from each of the phases, the 
uranium IV being eluted from the resin by weakly acidified water. The 
ratio of the isotopic richnesses of each of the two fractions obtained is: 
1.0024. 
There can also be used, at least for unitary exchanges, a cation exchange 
resin with moderate cross-linking, constituted by a polystyrene structure 
cross-linked with divinyl-benzene, with active sulphonic groups grafted 
thereon. The resin obtained is comparable to the DOWEX 50 WX8 resin, but 
is free of oxidizing impurities. U.sup.+3 was fixed on the resin in 
H.sub.2 SO.sub.4 medium of 0.5 acidity. This resin was placed in contact 
for about two hours with a solution of uranium IV in equal amount, then 
the uranium was recovered separately from each of the phases; the ratio of 
the richnesses was measured; the value found was .alpha.=1.0020. 
Industrial installations can have generally the same constitution as 
certain of those using the exchange U.sup.+4 -U.sup.+6, already described 
in the documents mentioned above. 
In the Figures and in the examples, it is not always specified if the 
supply, the production and the removal are ensured through the aqueous or 
organic phase. In fact this is immaterial. In the same way, the points of 
introducing and withdrawing rich and poor materials can be differently 
placed. 
In general, it must be understood that the scope of the present patent 
extends to modifications of all or part of the features described within 
the scope of equivalents.