Note: Descriptions are shown in the official language in which they were submitted.
- " ~085068
This invention relates to processes utilizing
ion exchange resin for recovering a concentrated solution
o:E a component of interest from a feed solution relatively
weak in the component of interest and containing an
unwanted impurity component.
In the conventional recovery processes, the
presence of unwanted impurity in the feed solutions
often detracts from the efficiency of the process, as,
firstly, the unwanted component if present in significant
concentrations often tends to initially saturate the
resin in the step of exhaustion of the feed solution
onto the resin, even though the resin has less affinity
for the unwanted component than for the component of
interest, and either longer periods are reguired for
achieving a loading of the component of interest approach-
ing the equilibrium loading, or if a shorter period is
allowed for the absorption step this is at the expense of
achieving lower loadings of the component of interest.
Secondly, the unwanted component tends to be
stripped from the loaded resin in the elution step of
stripping the loaded resin with eluant solution containing
eluant ion, and the unwanted component which is recovered
along with the component of interest in the concentrated
eluate may be of such nature or present in such concen-
trations that it renders the subsequent operation ofseparating the component of interest from the concentrated
r, ~
~085068
eluate more costly than would be the case if a purer eluate
could be recovered.
The present invention provides continuous ion exchange
process wherein batches of ion exchange resin particles pass
successively through an absorption column in contact with a
feecl solution containing an ion of interest and an unwanted
component where they become loaded with the ion and the un-
wanted component, and through an elution column in contact with
an eluant solution where the particles are stripped of the
loaded materials, and wherein uniform batches of loaded resin
particles are withdrawn from the absorption column after the
particles have passed therethrough, and each uniform batch is
isolated in a conditioning chamber wherein the ratio between
the ion of interest and the unwanted component loaded on the
resin particles is increased by flowing a predetermined volume
of a conditioning solution, which is reactive with said loaded
resin particles to increase said ratio, through the isolated
batch at a controlled flow rate before the isolated batch is
moved to the elution column.
The conditioning solution may be capable of
preferentially removing the unwanted component and may be
flowed through the isolated loaded resin for a predetermined
period until equilibrium is essentially complete between the
conditioning solution and the resin, thus maximizing the
removal of unwanted components. By applying a conditioning
solution also containing the component of interest, maximized
loading of the resin can be obtained which increases the
purity of and concentration of the component of interest in
the effluent of the elution step.
---` 1085068
The above process permits the use of a conditioning
solution that will elute the unwanted component more or less
completely. This solution need not necessarily contain any
of the component of interest although it may be found
desirable in some circumstances to have such concentration of
the component of interest in this solution as to maintain
equilibrium thus preventing any significant stripping of the
component of interest from the resin.
Subsequent to the intermediate treatment, the
conditioning solution can be displaced from the resin by a
solution having a high concentration of the component of
interest such as concentrated eluate or any other such
solution.
While the use of such conditioning solutions would be
incompatible with efficient elution if contacted with the
loaded resin in the course of the elution step, or could only
with difficulty be generated by modification of the concentrated
eluate within the confines of the elution column, these
solutions can readily be used in the above treatment without
interfering with the subsequent elution step and may be
generated by addition of a modifying agent or agents to the
concentrated eluate externally of the elution column, or may
be a solution of a material used as an eluant, or can be
derived from concentrated materials containing the component
of interest which are generated
-- 4
108S068
subsequent to the elution step, e.g. from solids precipi-
tated from the concentrated eluate, or can be obtained from
an external source of solution which forms no part of the
exhaustion-elution cycle.
Various exa~ples can be given of the form of
activation of the conditioning solutions: The conditioning
solution can contain an increased ratio of ion of intexest
to eluant ion as compared with the concentrated eluate,
and particularly can contain a greater molar concentration
of the component of interest than of eluant ion, in contrast
to the usual concentrated eluates which normally contain
a greater m~lar concentration of eluant ion than of the
component of interest; where the respective affinities of
the resin towards the component of interest and the unwanted
component are found to vary differentially with pH, the
conditioning solution can be at such pH as to tend to
maximize removal of the unwanted comp~nent and replacement
by the oomponent of interest; and, where the unwanted
component exists in plural oxidation states, the oxidation-
reduction p~tential of the conditioning solution can be
such that the unwanted comp~nent is converted to an
oxidation state for which the resin has lower affinity.
The treatment can be applied with particular
advantage in an anion-exchange resin elution system wherein
acidified sulphate is employed as the stripping eluant,
the eluant ion being in this case HS04. ~ highly effective
1085068
conditioning solution can then be obtained by changing the
pH of the concentrated eluate solution by addition of an
acid or a base, to achieve a solution having a pH which is
founcl to optimise removal of the unwanted component and
replacement by a higher loading of the component of interest.
In the case where the feed solution is a sulphate
liquor, and bisulphate ion is employed as eluant, the
efficiency of the process may be improved by mixing the
relatively weak feed solution with a sulphatic solution
relatively rich in the component of interest, to obtain an
enriched feed solution having an enriched molar ratio of
component of interest to the unwanted component, and by
employing the enriched feed solution as the feed to the resin
in the ion-absorption step. This increases the degree of
loading of the component of interest in the exhaustion stage.
The relatively rich sulphatic solution can conveniently be
derived from concentrated eluate, and in the most preferred
form the sulphatic solution is obtained as the effluent from
the above-described treatment of the loaded resin. -
An example of a recovery process embodying the above
aspects of the invention will now be described with reference
to the accompanying drawings wherein:
Figs. 1 to 11 illustrate schematically the successive
steps of a recovery process using continuous counter-current
flow of resin; and
-
1085(~6~
Fig. 12A and 12B together show in greater detail
apparatus employed in carrying out the process.
By way of example only, a process will be described
~!or the recovery of a concentrated solution of uranium from
an acid leach li~uor relatively weak in uranium ion and
containing ferric ion as unwanted impurity. In such case
the component of interest is a complex ion containing -
uranium.
The apparatus as shown in detail in Figs. 12A and
B employs a multiple-compartment continuous downward
counter-current resin flow absorption column A of the type
described in applicant's United States patent no. 4,035,292
dated July 12, 1977, and a continuous upward counter-current
resin flow elution column E, of the type described in
applicant's United States patent no. 4,018,677 dated April
19, 1977 with a measuring chamber M for use in isolating
a predetermined quantity of the resin connected between
column A and the elution column E.
As described in U.S. patent no. 4,035,292 a flow
of pregnant feed at a volumetric flow rate F is passed
upwardly through column A at all times to normally retain
respective batches of resin particles in each compartment
of column A and provision (not shown herein but described in
U.S. patent no. 4,035,292) is made for transferring batches
of resin downwardly from the upper to the lower of any two
selected vertically adjacent compartments of column A.
~08S068
The acid leach liquor is supplied direct to a
feed storage tank 22 through a pipe 23. The pregnant feed
is withdrawn at rate F from the tank 22 and passed upwardly
through the column A by a pump Pl normally through a line 24
connected to the bottom of oolumn A.
Within the column A, uranium and iron in the
ferric state are absorbed on the anion-exchange resin
particles as complexes, e.g.
2-2n
Cuo2(so4)~
3-2n
and ~e(So4)~
e.g. through the reaction
2R2S04 ~ U02(S04)3 --~ R4U02(S4)3 4
and similarly for the complexes containing iron.
Barren solution, typically containing less than
0.001 g/l uranium calculated as U30g, is withdrawn from the
top of column A through a pipe 26, and a proportion is
returned to a barren solution storage tank 27.
The process proceeds as a cycle of steps, and as
a starting point can be taken the conditions prior to the
transfer of a batch of loaded particles from the bottom
compartment of column A to the measuring chamber M.
At this point, the chamber M is empty of particles
and full of pregnant feed liquid. The column E contains
vertically adjacent batches of particles in the levels
indicated from a up to d in Fig. 12B and is full of eluant
~0850~8
liquid. The eluant used in this example is H2S04 supplied
from a tank 28. The molar concentration of the acid is
selected so that it strips the resin efficiently and
typically the eluant may be at 1 to 1.5 molar concentration.
Tbwards the bottom of the column E the eluant
contains progressively increasing concentrations of the
ion of interest, the bottom of the column containing
concentrated eluate.
Fiqure 1 Resin Transfer
Loaded resin is transferred from the bottom
compartment of column A to chamber M through a pipe 29.
This is accomplished by pumping a flow of pregnant liquid
in a closed path with a pump P2 at a flow rate of 0.5 F
drawn from the chamber M, the flow being withdrawn through
strainers 31 and 32 in chamber M, through the pump P2, and
a line 33 to the side of the bottom compartment of column A
through which the flow F from pump Pl is also temporarily
diverted, and through the line 29. This gives a net down-
ward flow of 0.5 F through the bottom co~partment, which
carries the loaded resin through the line 29 into the chamber
M.
Fiq. 2 Resin Measure
when particles no longer flow through line 29,
the particles in chamber M are allowed to settle and excess
particles are flushed out through a pipe 34 in the top of
column M to the bottom compartment of column A, generally
_ g _
1085068
as described in U.S. patent no. 4,018,677, leaving a pre-
determined quantity of loaded resin particles in chamber M.
Downward transfer of resin within column A can be conducted
after this step.
Fi.q. .~ Condition Loaded Resin
A conditioning liquid is flowed through the quan-
tity of loaded resin in the chamber M. The conditioning
liquid may be modified concentrated eluate withdrawn from a
concentrated eluate tank 36 by a pump P3 and passed through
a line 37 into the top of the chamber ~ through the strainer
31. The effluent from the chamber M is withdrawn through
a strainer 38 at the bottom and passed through a line 39 into
the feed storage tank 22. The flow through the chamber M is
at such flow rate, which may for example be about 3 bed
volumes of the resin in chamber M per hour, as to provide
sufficient time for the loaded resin to substantially
reach equilibrium with the eluate. Unwanted ion is dis-
placed from the resin in chamber M to the feed storage tank
22, and the flow is continued until a desired quantity of
the ion of interest has been added to the feed storage tank
22, to maintain the molar ratio of ion of interest to
unwanted ion in the tank 22 to a desired le~el.
Fiq. 4 Elute in Series
The column E and chamber M are eluted in series
with a predetermined volume of sulphuric acid withdrawn from
the eluant tank 28 by a pump P4 and passed through a line 41
-- 10 --
. . , .
108S068
into the top of column E, eluate withdrawn from the bottom
of column E through a strainer 42 being passed through a
line 43 into chamber ~ and the concentrated eluate from
chamber M being fed into the concentrated eluate tank 36
through a line 44.
The process thereafter follows generally the
scheme described in the above-mentioned U~S. patent no.
4,018,677.
Fiq. S Resin Transfer
The resin in chamber ~ is slurried into the
bottom of column E with concentrated eluate withdrawn from
tank 36 by pump P3 and passed into the chamber M through
the strainers 31 and 32. The resin leaves through a pipe
46. After transferJ the presence of the freshly introduced
resin in the column E results in the resin level in column
E being raised to the level e. In the transfer operation,
any fresh eluant that may be displaced from the top of
column E passes through a line 47 and is collected in the
fresh eluant tank 28.
Fiq. 6 Drain M and displace carrier liquid
Chamber M is drained down into the concentrated
eluate tank through pipe 44, and fresh eluant is pumped
into the top of column E with pump P4 through the line 41,
in order to displace the concentrated eluate which entered
in the previous step. The displaced eluate passes through
a line 48 into the tank 36.
:^ ~
108S068
Fi~. 7 Fill M with eluant
The air in chamber M is displaced with eluant
drawn by pump P4 and passed through a line 49 into the
bottom of chamber M through the strainer 38.
Fiq. 8 Resin transfer
~ esin is flushed from the top of column E by
pumping fresh eluant with pump P4 in a closed cycle through
the line 41 and a line 51 into the top of column E, the
flushed-out particles entering chamber M through a line 52,
and liquid being withdrawn through the strainer 38 and
recirculated to the pump P4 through a line 53.
Fiq. 9 Displace Eluant in series
When particles no longer flow through line 52,
eluant is displaced from the particles in chamber M using
barren solution pumped with pump P4 through a line 54 and
through the line 37 connected to the upper strainer 31 in
chamber M. If the eluant displaced from the chamber M
contains too high a concentration of uranium to be returned
to the fresh eluant tank 28, the outflow from the strainer
38 in chamber M is passed through the line 49 into the
lines 47 and 41 to the top of the elution column E, the
concentrated eluate which is displaced from the bottom of
column E being passed to the concentrated eluate tank 36
through line 48. otherwise, the procedure of Fig. 10 is
followed.
Fig. 10 DisPlace Eluant
- 12 -
108S068
The outflow from strainer 38 of chamber M
displaced by the barren solution is passed direct to the
fxesh eluant tank 28 along the line 49 and a line 56,
until the concentration of the outflowing eluant is ~oo
dilute for recovery.
Fiq. 11 Resin Transfer
-
The particles are then slurried out of chamber M
with barren solution pumped by pump P4 from the barren
solution tank 27 through the lines 54 and 37 to the strainers
31 and 32 in chamber ~. The particles slurried out of the
chamber pass to the uppermost compartment of the absorption
column A through a line 57 extending from the bottom of
chamber M.
The cycle of operation can then be repeated.
It will be appreciated that the above-described
example is merely illustrative of one sequence of operations
that may be employed, and that other forms of process can
be used instead. Thus, for example, in the step of draining
chamber M and displacing eluate from column E, as illustrated
in Figure 6, the eluate may be displaced from column E
either by pumping fresh eluant into the top of the column -
or by opening an air inlet at the top of the cDlumn E and
allowing eluate to drain from the column under gravity.
Instead of transferring an eluted batch of resin
25- from the upper part of column ~ to the intermediate measur-
ing chamber M before returning it to the absorption column
108S068
A, the batch may instead be transferred direct to the
absorption column A. In such case, after draining chamber M
and displacing eluate from column E as illustrated in Figure
6 or as described ab~ve, the air in chamber M is displaced
with pregnant feed liquor drawn by a line (not shown)
connecting the tank 22 to the pump P4 and passed by the
pump P4 to the bottom of chamber M through the line 49 and
the strainer 38. The transfer of eluted particles from
column E to column A is then carried out by flushing the
particles from the top of column E by pumping barren
solution drawn from tank 27 along line 53 with pump P4, the
solution being passed into the top of column E through the
lines 41 and 51. The flushed-out particles enter the top
of column A through a line (not shown) connecting the outlet
line 56 direct to the uppermost compartment of column A.
This operation is conducted while the-liquid level in column
A is low to avoid loss of resin particles, as described in
U.S. patent 4,035,292. When particles no longer flow through
the line to the uppermost compartment of column A, the pump
P4 is stopped and a gravity flow of barren solution is
allowed to continue through the line from chamber E until
the flow ceases. The cycle of operations commencing at
Figure 1 can then be repeated.
The step of conditioning the batch of loaded resin
that is isolated in chamber M can be carried out at or prior
to the stage indicated in Figure 3.
- 14 ~
10850~8
In the example illustrated in Figure 3, the
loaded resin is contacted with concentrated eluate which is
modified in its chemical composition or in its pH by
adldition of reagents through an addition line 58.
Other conditioning solutions may, however, be
employed and the conditioning solution need not necessarily
contain any or any significant quantity of the component
of interest.
With a strong base ion exchange resin loaded with
uranium and with ferric iron as an unwanted component, it
has been found that a significant degree of removal of
the iron loading can be obtained employing a-sulphuric
acid solution.
The conditioning solution may thus be clean water
or feed liquor to which sulphuric acid has been added,
preferably in an amount to produce a concentration of
approximately 0.3 lar acid~ The stronger the acid
solution, the faster and more complete is the elution of
iron but this is accompanied by a disproportionate increase
in the amount of uranium which is lost in the strip liquor.
This loss can be reduced by adding uranium to the
conditioning solution along with the acid, but this results
in an increased utilization or recycling of uranium. The
optimum concentrations can be determined for any particular
set o~ conditions by those experienced in the art and under
typical conditions the acid concentration w~uld be in the
'
108S068
region of 0.2 to 0.5 M. After the treatment with the acid -
solution, the loaded resin may be contacted with a rich
uranium-containing solution, e.g. concentrated eluate which
i~s adjusted in pH. This treatment can serve to significantly
increase the uranium loading. The conditioned resin can
thereafter be subjected to elution.
Some examples applied to uranium extraction
are given below:
Example 1
A volume of strong base ion exchange resin loaded
with uranium and with ferric iron was contacted over a
period of 60 mins. with five v~lumes of 0.3 molar sulphuric
acid (pH approx. o.6). The acid was then displaced over a
period of 10 mins. with one vDlume of concentrated eluate
containing 16.5 g/l. U adjusted with sulphuric acid at
approx. pH o.6.
The results were indicated in Table 1
Table 1
. . . .
Resin before Resin after %
Conditionina Conditionin~ Chanqe
_ _
Uranium (U) 59.6 g/l. 60.4 g/l. + 1.34
.
Iron (Fe3 ) 9.9 g/l. 2.88 g/l. ~70.9
. . ..
Fe3 as % of U 16.6~ 4.7~ -71.7
Example 2
A volume of strong base ion exchange resin
~ 16 -
108506~
loaded with uranium and with ferric iron was oontacted
over a period of 39 mins. with 3.6 volumes of an aqueous
solution containing 44.3 g/l. U and adjusted to approx,
pH 1 with H2S04.
The results were indicated in Table 2
Table 2
Resin before Resin after
Conditionin~ Conditioninq Chan~e
, U 70.6 g/l. 130 g/l. +84
Fe3+ 4.22 o . g8 - 77~
Fe3 as ~ of U 5.98~ o.75% -87.5
In the procedures of both Example 1 and Example 2
it was noted that the majority of the iron came off the
resin while the first two volumes of conditioning solution
were being passed through the loaded resin.
The results obtained in Example 2 indicate that
a commercially pure yellow cake could be precipitated
directly from the eluate of the resin without the need for
further purification.
The uranium loadings that are obtained are
strikingly high and may indicate that the uranium is being
loaded as a divalent complex rather than as the tetravalent
complex form which uranium is normally assumed to adopt.
The above Examples have referred to treatments
in which a conditioning liquid is employed of pH lower
- 17 -
- 108S068
than the eluate.
In alternative procedures, conditioning liquids
of increased pH may be employed.
E~amPle ~
Employing a recovery process generally as
described with reference to the drawings, the pH of concen-
trated eluate recovered in the concentrated eluate tank 36,
normally about pH 0.7, can be adjusted to a pH in the
range of a~out pH 1 to 3, more typically about pH 1.5 to
2.5, to provide an activated eluate, by addition of a base,
e.g. ammonia, or sodium or magnesium hydroxide, or calcium
hydroxide if precipitated solids are re ved, through the
addition line 58, as indicated in Fig. 3 prior to flowing
the concentrated eluate through the loaded resin in the
measuring chamber M.
In the resin saturation step of Fig. 3, unwanted
Fe3 ion is eluted to the pregnant feed tank 22. However,
as the effluent from the chamber ~ is rich in uranium, the
flow can be continued until such time as the flow adds to
the tank 22 suffi-cient uranium to diminish the Fe3+ ~U
ratio to a level, as low as practical and preferably below
about 12:1, at which the disadvantages associated with
initial saturation of the resin with Fe3+ complexes are
avoided, or significantly reduced.
In this way, greatly reduced initial loadings of
Fe3 can be obtained on the loaded resin passed to the
- 18 -
108S068
chamber ~, and these relatively low loadings of Fe3 can
be alm~st entirely displaced from the loaded resin in the
saturation step of Fig. 3 prior to recovering concentrated
eluate from the loaded resin to the concentrated eluate
tank, thus achieving an eluate which is substantially
free of Fe3 ion.
Table 3 shows compositions of streams that may be
achievable with this process.
Table 3
Molar weight
Uranium Fe3+ so~2 Ratio Ratio
Stream gm.U308/1 gm/l gm/l Fe /U S04 /U308
.
Feed
(through line 23) 1.00 6.oo. ~o.oo 30 1 40:1
M~dified feed
(contents of 22) 1.518 6.071 41.08 20:1 27 1
Eluate
(contents of 36) 45.83 <0.4 84.oo 0.044:1 1.8:1
In one example of the practice of the process,
with stream compositions as in Table 3, when NaOH is used
as the addition 58 to raise the pH of the eluate to pH 2,
about 10.11 g of H2S04 would be consumed per gram of U308
recovered and about 0.97 g of NaOH would be added per gram
of recovered U308.
ExamPle 4
A sample of IRA 400 anion exchange resin in the
sulphate form was placed in a column and a pregnant feed
solution in the fo~m of a sulphatic feed solution at pH
~08S068
2.2 containing uranium and ferric ion at a m~lar ratio of
Fe /U of 10:1 was flowed through the column until the resin
was in equilibrium with the feed solution. The loading
achieved on the resin was 83 g/l U30g.
Thereafter, the loaded resin was treated with a
conditioning solution rich in uranium ion. The conditioning
solution was obtained by dissolving yellow cake from a
conventional uranium recovery plant in sulphuric acid and
was adjusted to pH 1.5 by addition of sodium hydroxide.
The conditioning solution contained 22 g/l
U308, and a volume of the conditioning solution equal to
three bed volumes of the loaded resin was flowed through
the loaded resin over a period of twenty minutes.
After the treatment, the resin loadings were
analysed and were found to be 130 g U308/1 bçd volume
of the resin and 0.7 g Fe /1 bed volume.
In the step of eluting this loaded resin with
lM H2S04, the first bed volume of eluate contained
26 g/litre U308 and 0.7 g/litre Fe3+. Substantially the
whole of the Fe3+ was stripped from the resin in the first
bed volume of eluate.
In counter current elution of the loaded resin,
six batches of the loaded resin could be substantially
completely stripped with about 12 to 15 bed volumes of
lM H2S04, i.e. one bed volume of the resin could be stripped
with ~out 2 to 2~ bed volumes of the acid.
- 20 -
~;
~08S068
The resulting strong eluate accordingly has a
concentration of U308 of approximately 50 to 65 g
U308/1 and a ferric ion concentration of less than 0.4 g/l.
Instead of using adjustment of the pH of the
5 concentrated eluate to produce a conditioning solution
a similar result may be achievable by dissolving in the
eluate additional uranium recycled from the recovery
processing conducted on the strong eluate.
Further, examples of conditioning liquids include
solutions derived from the subsequent uranium recovery
operations which need not have uranium contents as high
as are encountered in the concentrated eluate.
Moreover, the conditioning solution may instead
be a uranium rich solution at such oxidation-reduction
potential, achieved by dosing with a reducing agent such
as metallic iron particles or sulphur dioxide, that the
Fe3 is reduced to the Fe state, which is incapable of
forming complexes for which the resin has affinity.
Example ~
Independently of the advantages achievable by
using the loaded resin conditioning step, an increased
initial loading of uranium onto the resin can be achieved
by recycling concentrated eluate to the pregnant feed
storage tank in an amDunt sufficient to significantly
diminish the Fe3+/U ratio present in the feed supplied
through the inlet line 23. For this purpose, only small
- 21 -
10~35068
quantities of concentrated eluate need to be recycled,
relative to the flow of pregnant feed liquor.
Table 4 shows the stream compositions that may
be achievable, where the process described above with
reference to the drawings was conducted with the omission
of the resin conditioning step of Fig. 3, and with a small
volume of concentrated eluate being pumped directly from
the eluate tank 36 to the feed storage tank 22 for each
unit volume of acid leach liquor added through the line 23.
Table 4
Molar weight
Uranium ~e3 S0~ Ratio Ra~io
Stream gm U308/1 gm /l gm /l Fe3~/U S04 2/U308
.
Feed
(through line 23) 1.00 6.oo 40~00 30 1 40 1
Modified Feed
15 (contents of 22) 1.l~95 5.982 l~o.67 20:1 27:1 -
Eluate
(contents of 36) 28.33 5.00 77.00 0.88:1 2.7:1
While the above-described process has referred
to separation of uranium from uranium and ferric ion-
containing liquors, it will be appreciated that the same
processing steps may be applied with other feed solutions
e.g. solutions containing copper as the ion of interest,
and with feed solutions containing ferric ion and other
unwanted components that may load on the resin.
Moreover~ the principles of pre-treatment of
the loaded resin to reduce unwanted ion loadings and of
- 22 -
1085068
enriching the feed solution to obtain higher initial
:Loadings are not restricted in their application to anion-
exchange processes but may be appLied in cation-exchange
processes.
