Note: Descriptions are shown in the official language in which they were submitted.
lOS1~7~
Thi~ invention concerns a ~ethod of recovering uranium
from uranium bearing leach liquors utilizing macroreticular
copolymeric resins of vinylbenzyl chloride (VBC) and a cross-
linker, such as divinylbenzene, as anion exchange resins.
Preferred embodiments of the process utilize gel type strong
base VsC resins or macroreticular weak base VBC resins.
The uranium recovery processes of the prior art
normally use large particle size gelular resins or macroreticular
weak base resins to absorb and purify uranium bearing liquors
and may normally be categorized into two headings, Resin-in-
Pulp Processes and Clarified or Columnar ProcessesO In the
former process the resins are contained in a basket and the
leach liquor is allowed to contact the resin until the resin
becomes saturated with the uranium salt, normally uranyl sul-
fate. At that time the resin undergoes an elution treatment to
recover concentrated uranium salts. The resin particles
normally have a mesh size of 20 plus. (U. S. Standard)
The second category or Columnar Process involves
a prefiltration step after which the uranium bearing liquors
are passed through a resin bed or resin filled column.
Exhausted resins are eluted in generally the same manner.
Resin particle sizes may vary in mesh sizes ranging from 20
to 50. ~lthough these two categories of processes are usually
performed in a discontinuous operation, recently continuous
operations have become commercially attractive.
One important criterion in evaluating such
processes is the elution performance of the resin. Under-
standably, the quicker a resin will elute the uranium salts
- 2 -
1~5~670 ~ ~
the less acid is required and the ~ore economically the process
will operate. Add~tionally, resins having a high physical
stability would also be favorably considered ~or processes such
as uranium recovery where the resins are subjected to a great
deal of physical demand.
The resins utilized in prior art processes have
long been known to suf~er high attrition losses during normal
process conditions.
The life or durability of a resin is usually under-
stood to be directly related to such characteristics as
physical stability, thermal stability, organic fouling, oxidative
stability and reyeneration efficiency. A resin's physical
stability is particularly important as a measure of its
resistance to physical attrition since it is a direct reflection
on the ability of the resin beads to withstand crumbling when
subjected to heavy stresses. Physical stability may readily
be calculated on the basis of results of the "Piston Pump Test",
explained in more detail hereafter.
Another resin characteristic important in deter-
~0 mining durability of a resin is its ability to withstand thermal ~-
degradation. This characteristic is normally termed thermal
stability. Anion exchange resins in the hydroxide form are
particularly susceptible to thermal degradation.
A third characteristic important in evaluating a
resin is its regeneration efficiency which is normally
determined by plotting the ratio of actual column capacity/
theoretical column capacity (~ utilization) versus the ratio
. .~ .
,':
?
~L~5167~
of equivalents of regenerant used/total equivalents available.
It has now been discovered that anion exchange resin
prepared from crosslinked vinylbenzyl chloride has surprisingly
improved elution properties. It has also been discovered that
these anion exchange resins remain suitable whether in gelular
or macroreticular form. Accoraing to the invention there is
therefore provided a process for recovering uranium from
uranium bearing aqueous leach liquors which comprises contacting
the aforesaid liquors with a polymeric crosslinked vinylbenzyl
chloride resin, and thereafter eluting from the resin the
uranium in concentrated salt form. Preferred embodiments
include using a polymeric resin comprising a crosslinked macro- ~ -
reticular copolymer of ~1) at least 90 parts by weight of
monomer containing vinylbenzyl chloride and (2) at most 10
parts by weight of polyvinylidene monomer containing a plurality
of CH2 = C ~ groups in non-conjugated relationship, said
copolymer containing reactive methylene chloride groups as
substituents on the aromatic muclei and being substantially
free of secondary crosslinks. A further preferred embodiment
will utilize sulphuric acid as an eluant. However other suit-
able eluants include brine, acidified brine, nitric acid and
acidified ammonium sulphate~
The invention utilizes an additional advantage of
the VBC resins in that it avoids the toxicity problems common
during the preparation of the prior art resins. For example,
a typical prior art resin is prepared by a process of first
polymerizing or copolymerizing styrene and then chloromethyl-
ating the polymer. For further details of a typical prior art
process, see U.K. Patent 932,i25 and U.S. Patent 3,637,535.
The chloromethylation process, although widely
,.
-
~05 3L~;7~
used to pro~ide polymers and ion exchange resins derived
from such polymers, possesses inherent disadvantages. For
example, the chloromethyl ether used as chloromethylating
agent to provide reactive chloro groups on the polymer is
a substance of great toxicity. Consequently, expensive safety
and protective equipment is required to safeguard operating
personnel. Furthermore, the multi-stage nature of the prior art
process makes it inherently more expensive than the one-step
process utilized to manufacture the polymers of the present
invention. Another disadvantage of the polymers of prior art
process is their vulnerability to metal contamination which may
occur due to the metal-containing catalysts frequently employed
in the manufacturing process. Accordingly the VBC resins use-
ful in the practice of the present invention combine the
advantages of improved physical stability and regeneration
efficiency without loss of column capacity, in addition to the
substantially improved elution performance when compared to
the prior art. It is this combination in one resin which
causes the resin to be highly suitable for uranium recovery~
Furthermore, due to the simplified one-step preparation
process the polymers so produced are inherently more economical
to produce, making the process of the invention even more
commercially attractive.
The desirable elution properties of the resins used
in the present invention are believed to be related to the sub-
stantial absence of secondary crosslinking. The chloromethylated
polymers of the prior art usually possess a considerable degree
of such secondary crosslinking. See
~'~ , '
~)516~7~
Rieman et al, Ion Exchange in Analytical Chemistry,
page 11 (1970) for further details o~ secondary crosslinking.
To determine the elution performance of the resins
they were compared to the prior art chloromethyl ether
resins. These comparative experiments showed that whereas
the elution concentration of the CI~E resins amounted to
7.7 g U38 per liter, the VBC resins showed an elution
concentration of 9.9 g U~Og per liter. S-milarly where an
elution volume of acid of 7.2 bed volumes was required to
elute prior art resins, the VBC resins required no more
than 5.1 bed volumes of acid.
To determine the uranium capacity for strong base
resins suitable for use in the process of the invention
the following test was utilized 1.
Uranium Capacity Test for Strong Base Resins
in Resin-In-Pulp
Screen 20 mls. o~ resin of the type describe~ in
Example I to the following meshes:
Retained
on Mesh Mls. Resin
16
o.5
3-75
18-75
1-75
325
2. Place resin in colu~n and bac~ash and treat ~:ith
1 liter HCl (IN) rollowed by 1 liter o~ ~ater.
3. Pass loadin~ solution for 24 hours at a 1~0 mls.~hr.
.,~,. . .
' ,, . ~ ' . ;~ :
1C~5~67~
rate. Loading solution is as follows:
H2SO4 94.05 g/l9 liters
2 o4 796.5 g~l9 liters
UO2So4 29.0 g/l9 liters
4. Rinse with 1 bed volume of water
5. Elution is performed with 10% H2SO4 at 40 ml/hr.
6. Continue elution until the U3O8 level is 0.04 g/l.
7. Analyze the entire eluate and calculate the
capacity as follows:
g/l U O X liter eluate
Capacity = 3 8
liter resin
Followin~ the test procedure of above the strong base resins
showed a capacity of approximately 58 g/u3o8 liter of resin.
The same resin after undergoing the above test procedure was
tested for elution concentrate. The effluent was collected and
analyzed spectrophotometrically and showed a uranium concen-
tration of 11.4 g U3O8/1.
The resins useful in the process of the present
invention may be prepared by any suitable known process. A
preferred polymerization technique, however, is suspension ~`
polymerization, particularly when macroreticular resins are
desired. The term "suspension polymerization" is a term well
known to those skilled in the art and comprises suspending
droplets of the monomer or monomer mixture in a medium in
which the monomer or monomer mixture is substantially in-
soluble. This may be accomplished by adding the monomer or
monomer mixture with any additives to the suspending medium
which contains a dispersing or suspending agent such as, for
instance, in the case of an aqueous suspending medium, the
ammonium salt of a styrene maleic anhydride copolymer, carboxy-
methyl cellulose, bentonite, polyvinylimidazoline, or poly-
(diallyldimethylammonium chloride). The dispersant is pre-
ferably added in an amount o~ .001 to 5%, more preferably from
- 7 -
: . . : - ~, "
l~S~67iO
0.01 to 1~.
Often polymerization processes will utilize additives
or modifiers which have specialized functions. These additives
should of course be chosen such as to be mutually compatible.
For example a pre~erred colloidal stabilizer for the process
of the in~ention is gelatin. Gelatin has an isoelectric point
at about pH 8. It should, therefore, be readily understood
that when gelatin is the stabilizer the p~ of the polymerization
medium should not pass through this point to prevent possible
serious impairment of the bead forming mechanism. Another
stabilizer which may be useful in the process of the invention
is magnesium silicate. Since magnesium silicate is an inorganic
additive, the pH of a polymerization medium containing
magnesium silicate instead of gelatin does not require such
limitation.
Alkalinity of the polymerization mediurn may be main-
tained by one or more additions of a suitable base or the
presence of a sufficient amount of buffering compounds. Other
methods of maintaining an alkaline medium during polymerization
will occur to those skilled in the art~
The polymerization of vinylbenzyl chloride and cross-
linker may be accelerated by a suitable catalyst.
Catalysts which provide free radicals which function
as reaction initiators include benzoyl peroxide, tert-butyl
hydroperoxide, cumene peroxide, tetralene peroxide, acetyl
peroxide, caproyl peroxide, tert-butyl perbenzoate, tert-butyl
diperphthalate, methyl ethyl ketone peroxide. Other suitable
classes of free radical generating compounds include the azo
catalysts.
Another rnethod of effecting copolymerization is
by subjecting the reaction mixture to ultra-violet light in
~51~7(~
the presence o~ suitable catalysts at ambient or slightly
elevated temperatures. Such catalysts include benzoin and
azobisisobutyronitrile.
The amount of catalyst required is roughly proportion-
al to the concentration of the mi~ture of monomers. The usual
range is from 0.01% to 3% by weight of catalyst, with reference
to the total weight of the monomer mixture. The preferred range
is from 0.5% to 1.5%. The optimum amount of catalyst is
determined in lar~e part by the nature of particular monomers
selected, including the nature of the impurities which may
accompany said monomers.
As is known in the art, macroreticular polymers
are prepared by a process which involves the presence of a
phase extender or precipitant. These precipitants vary widely
in nature and are chosen to be particularly suitable with the
monomer mixture used. For example, when employing monomers such -
as divinylbenzene as crosslinking monomers, alkanols with a
carbon atom content of from 4 - 10 will suffice when used in
amounts of from 30 - 50% of total polymer mixture used. Other
suitable precipitants are aliphatic hydrocarbons containing at
least 7 carbon atoms, such as heptane and isooctane. In
general, the amounts of precipitant may vary from as little as
10% to as much as 80% of combined weight of monomer and pre-
cipitant.
A preferred precipitant is methyl isobutyl carbinol,
preferably used in an amount of from 25 - 45% of total
monomex mixture.
The polymerization process may be carried out at
temperatures ranging from 60 to 100C., although preferably
the polymerization is performed between 70 - 90C.
The vinylbenzyl chloride resins of the invention
are hereinafter referred to as VBC resins. The prior art
_ g _
:., '. '
.' . ~
: , . ' . , .: .
lC~S~67(~
chloromethylated resins are re~erred to as CME resins.
The followin~ table shows the ef~ect of varying the
amount of precipitant - methyl isobutyl carbinol (MIBC) on
Anion Exchan~e Capacity (AEC), precent solids and copolymer
porosity. The VBC resins of the table are typical strong
~ase anion exchange resins of the type shown in Example I
varying an amount of precipitant only and containing 6%
divinylbenzene (DVB) as crosslinker:
- Table I
Copolymer
Resin No. % M~BC AEC (meq/g) Solids ~%) Porosity (%)
1 28 4.31 41.4 3.5
2 30 4.36 38.6 20.2
3 35 4.38 33.6 2g.8
~~ 46.2
While the use of a single precipitant facilitates
recovery, purification and recycling of the precipitant, -
mixtures of precipitants can be used.
A preferred crosslinkin~ monomer is divinyl benzene,
but many alternative crosslinkers are suitable for use in
the process of the invention. Suitable crosslinkers are
divinyltoluenes, divinylnaphthalenes, diallyl phthalate,
éthylene glycol diacrylate, ethylene ~lycol dimethacrylate,
divinylxylene, divinylethylbenzene, divinylsulfone, polyvinyl
or polyallyl ethers of glycol, of glycerol, of pentaeryth-
ritol, of mono-, or dithio- derivatives of glycols, and of
resorcinol; divinylketone, allyl acrylate, diallyl fumarate,
diallyl maleate, trimethylolpropane trimethacrylate,
diallyl succinate, diallyl carbonate, diallyl malonate,
diallyl oxalate, diallyl adipate, diallyl sebacate,
divinylsebacate, diallyl tartrate, diallyl silicate, triallyl
tricarballylate, triallyl aconitate, triallyl citrate, triallyl
phosphate, N,N'-methylene-diacrylamide, N,N'-methylene
dimethacrylamide, N,N'-ethylenediacrylamide, 1,2-di--
-- 10 --
. ' , , ' '.................... . ~ :': : ' , " ,
..
1~5~670
(~-methylme-thylene sulfonamide)ethylene, trivinylbenzene, tri-
vinylnaphthalene, and polyvinylanthracenes.
Other useful crosslinking monomers include the
following: polyvinylaromatic hydrocarbons, such as trivinyl-
benzene, glycol dimethacrylates, such as ethylene glycol
dimethacrylate, and polyvinyl ethers of polyhydric alcohols,
such as divinoxyethane and trivinoxypropane.
The ratio of vinylbenzyl chloride monomer to cross-
linking monomer may vary depending on the use for which the
copolymer is intended and upon the nature of crosslinker,
although generally the crosslinker is present in an amount of
0.1 to 30%. Preferably it is present in an amount of 1 to 10%
and most preferably in an amount of 5 to 8~. It is also
possible to utilize a mixed crosslinking system. The
following Table II illustrates the effects of alternative
crosslinking systems and amounts on anion exchange capacity.
The resins of Table IIare typical strong base anion exchange
resins varying only in crosslinker.
Table II
Resin No. AEC (meq/g) DVB, %*TMPTMA**
4.52 1.5 2
6 4.10 2 12
7 4.02 3 6
*Divinyl benzene activity 79.2~ - reminder primarily
ethylvinylbenzene.
** TMPTMA is trimethylolpropane trimethacrylate.
As mentioned hereinbefore various precipitants or
phase extenders are suitable in the practice of the
invention. Iso-octane (IO) and 2-ethylhexanol(2-EH) were
tested and the results are listed in the following Tables III
and IV. Resins 12 - 15 were converted to weak base resins
by aminolysis with dimethylamine, and are of the type shown ~ ;
in Example II. Resins 7 - 11 are strong base resins containing
6~ DBV, of the type shown in Example I.
-- 11 --
: - . : , . . , ;
: - : . . :
-.. , . .. . .. , . . ; .,, , . . ~. ; :
~51~
' Tab'le'I'II
Resin %IO* Porosity, ~ ) AEC _meg/g) %'Solids
7 20 ~~ 4'43 43.0
8 25 32.6 4.34 35.5
9 30 46.4 _- __
65.0 -- --
11 55 69.0 - --
Tab'l'e''IV
Product
Vol. AEC % Porosity,
Resin 2-E~I,'%* Por'osity,'( ~_ ) (meg/q) Solids (Vol%)
12 25 2.6 4.63 5~.1 ---
13 30 2.5 5.09 53.5 ---
14 35 27.5 4.90 5~.4 24.9
40 48.8 4.78 35.3 48.9
*The precentages of precipitants are based on total
monomer mixture weight.
A wide variety of amines can be employed in the
amination reaction. Thus, primary, secondary, and tertiary
alkaliamines or arylamines can be employed. Polyalkylene-
polyamines include ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine, dimethylamine,
trimethylamine, propylenediamine, and the like. Aminoalcohols
such as dimethylaminoethanol can also he used successfully.
A preferred resin of the process of this invention
employs a trialkylamine as the aminating agent, thus pro~
ducing strong base, quaternary ammonium anion exchangers.
The aklyl radical does not generally contain more than 4 carbon
atoms, with trimethylamine being the preferred amine.
The following examples I and II illustrate methods
of preparing the resins used in the practice of the invention
They should not be construed as limiting the scope of the
invention. All percentages throughout the specification and
claims are by weight unless otherwise indicated. Example III
illustrates a known process of preparing a typical CME resin
- 12 -
, ,
105~6~7al
which corresponds in type to a resin prepared according to
Example I.
'Example I
..
Preparation of a Macroreticular Type I Strong
' Ba'se'Re'sin'
. _. _:A_._ . __ __ _ ____ .._
680 grams of water are placed in a flask. To the
stirred aqueous phase, is added 4.4 gO o~ gelatin dissolved
in 50 ml of water, 6.4 g. poly(diallyldimethylammonium chloride)
dispersant, 8.3 g. of boric acid, and 10.0 g. of 50~ sodium
hydroxide. The resulting solution is stirred for 30 minutes.
To the aqueous phase is added a solution of 475 g.
of vinylbenzyl chloride, 39.0 g. of divinylbenzene (79.2% active),
276.7 g. of methyl isobutyl carbinol and 5.1 g. of benzoyl
peroxide. The resulting mixture is heated with stirring to
80C. and is held at that temperature for lO hours. The inert
solvent is removed by steam distillation and the resulting
copolymeric beads are dried in a steam oven.
82.5 g. of beads and 400 g of water are placed in ' '
a flask and stirred for 30 minutes. To the resulting slurry is
added 34 gm. of anhydrous trimethylamine and the mixture is
stirred for 4 hours at 60C. The temperature is increased
slowly to 100C. in order to remo~e the excess amine. The
resulting mixture is cooled and the beads are washed and
bottled. The resulting strong base resin has an anion exchange
capacity of 4.36 meq/g, a solids content of 34%, and a porosity
of 0.4 cc/cc.
Example II
Preparation'of'a Macroreticular_Weak Base Resin
680 grams of water are added to a flask. To the
stirred aqueous phase is added 5.8 g. of poly~diallyldimethyl-
ammonium chloride), 4.0 g. of gelatin, 9.4 g. of boric acid,
and 9.2 g. of 50% sodium hydroxide. The resulting solution is
- 13 -
,; ' ' .
. . , :
~35~67~
stirred and the monomer phase consisting o~ 410 g. o~ vinyl-
benzyl chloride, 40 g. of divinylbenzene (79.2% active), 264 g.
o~ methylisobutyl carbinol, and 6.4 g. of benzoyl peroxide is
added to the flask. The resulting mixture is heated to 80C.
for 10 hours and ~he inert solvent is removed by steam
distillation. The resulting beads are washed with water and
are dried in a steam oven overnight.
400 grams of the above copolymer are slurried in
390 ml. o~ water and 360 g. of 50% sodium hydroxide. To
10 this mixture is added 610 ml. of 40% dimethylamine. The mixture
is heated to 65C. and is held at that temperature for 4 hours.
At the end of that period the excess amine is removed by
distillation and the product is washed to neutrality and bottled.
The resulting weak base resin has a capacity of 5.28 meq/g and
a solids content of 42.8%.
The following additional step, if desired, is optional.
To 136 g. of the above weak base resin in 195 g. of water is
added 18.1 g. of 30% hydrogen peroxide to convert the resin
to the amine oxide form to the extent of 19.7%. The mixture
is stirred at 50C. for 4 hours, and the beads are washed with
water and bottled.
The resulting weak base resin in the amine oxide
form has a capacity of 5.11 meq/g and a solids content of
38.5%. The porosity is 0.46 cc/cc of beads.
Example III
.
Preparation of Comparative Resin A
To 750 g. of water is added 4.4 g. of gelatin
dissolved in 50 ml. of water, 6.4 g. of polyvinylimidazoline
dispersant, 4.0 g. of boric acid, and 5.0 g. of 50% sodium
hydroxide. The resulting aqueous phase is stirred for
30 minutes.
- 14 -
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" ~ '~ : .; . . ,' ,.: '' :' '' ' ~ ' . ,: ' ' ', ::' , . ' , , , :, .
~Sil670
To the aqueous phase is added a solution consisting
o~ 447 ~. of styrene, 35 g. (55% active) of DVB, 318 g. of
MIBC, and 4.8 g. of benzoyl peroxide. The resulting mixture
is stirred rapidly at 80 for 10 hours and the inert solvent is
removed by steam distillation. The resulting copolymeric beads
are dried in a steam oven.
To 318 g. of the above copolymer is added 1260 g.
of CME and 660 g. of ethylene dichloride. The resulting mixture
is stirred at 35~40C for two hours. The mixture is cooled
to 0-5C. and 275 g. of aluminum chloride is added over a two
hour period while maintaining the temperature below 25C. The
reaction mixtureis then heated at 47-50C. for a four hour
period. -
The resulting bead slurry is cooled to 0-5 5C . and is
quenched into 1500 ml. of cold water. The quenched mixture is
drained and washed four times with 1500 ml. portions of water.
The last wash is not removed and is adjusted with 20% solution
of sodium carbonate to pH 8. The resulting product is drained
and packed out.
To one third o~ the above chloromethylated inter-
mediate slurry is added 290 g. of 25% aqueous trimethylamine
(TMA) over a 1 - 1.5 hour period while maintaining the temper- ;
ature at 10 - 15C. After the amine addition is complete, the
mixture is stirred for four hours at 10 - 15C. The excess `
amine and solvent are removed by steam distillation and the
beads are washed with water to give the final product.
The uranium recovery process of the present invention
places a premium on the physical stability of an ion exchange
resin. The piston pump test is an accelerated test developed
to measure an ion exchange resin's resistance to attrition
under simulated and exaggerated conditions.
, ,
- - 15 - ~
~- : . , , , .: . .
.. . . ..
.
' - : ' ' ~ ' . '':
.: . .. : . ::
1~51~70
Piston Pump Test
.
The test ~s performed in 200 ml. o~ resin ln one
inch diameter columns operating under constant pressure
(40 lbs/psi). The resin is subjected to repeated cycles of
treatment with 1.2 N-H2SO4 and 3.5 N-NaOH with water rinses
between each solution. The acid and base solutions are passed
upflow through the resin bed and the water rinses are passed
downflow. Cycling is controlled au-tomatically by a programmer,
and the flow rates during exhaustion (acid) and regeneration
~base) are measured every five cycles. The test is stopped
after 50 cycles, since a good correlation has been developed
between field performance and piston pump test performance
at this level. The change in flow rate from the initial reading
to that following ~0 cycles is an excellent measure of the resin's
physical stability. If breakd~wn occurs, smaller resin particles
tfines) are being formed, and at constant pressure, a drop in
flow rate would be observed. Conversely, if the resin exhibits
no physical breakdown, the particle size remains essentially
constant and hence the flow rate stays constant.
A second measure of resin stability in the piston
pump test is the change in perfect bead count in the resin
sample after 50 cycles. Representative resin samples
taken before and after the test are examined microscopically
for cracked beads. Obviously, the higher the perfect bead
count after the test, the more stable the resin.
Macroreticular, strong base anion exchange resins
prepared from vinylbenzyl chloride according to Example I
exhibit excellent physical stability in the piston pump test
compared to resins prepared from chloromethylated styrene
according to comparative Example III~ Typical results obtained
for a CME resin and for a VBC resin are given below.
- 16 -
'.:
: . : : . ;: . . . . ..
..:
i~l67~ %
AEC Flow Rate, liter/hr. Change ~ Per'fect beads
Resin me~ Init'i'al Final 'F'lo~ Before A-ter
_ _ .
VBC
(Ex.l) 4.36 100 100 0 99 99
C~E(Comp.
Ex.
II) 4.40 100 70 30 99 85
The test results were obtained on resin samples
that were screened to the exact same particle size, therefore, '
the marked improvement in performance exhibited by the VBC
resin can be directly attri~uted to its manner of preparation
and not to variance in particle size distribution.
Quaternary ion exchange resins may be somewhat liable
to decomposition particularly when in the hydroxide form. This
instability is greatly enhanced by increased temperature. Two
routes are followed by this decomposition reaction. ;
(1) Resin-CH2-N-(-CH3)3+ OH~ Resin-CH2OH + N(CH3)3
(2) Resin-CH2-N-(-CH3)3 + OH Resin-CH2N-(-CH3)
In order to test the useful ion exchange resins for
thermal stability, strong base anion exchange vinyl benzyl
chloride resins o~ the type described in Example I and a '
corresponding chloromethylated resin as described in comparative
Example III are subjected to the ~ollowing test.
The resin as received is converted completely to the ;
hydroxide form using approximately 1000 mls. of 1 N NaOH for
15 mls. of resin. The resin is rinsed with D.I. water and
placed in an appropriate container containing excess D.I. water ~;
(at least a 20 to 1 water to resin ratio) and the container
is placed in an oven o~ appropriate temperature. Periodically
the sample is removed, completely converted to the HCl form and
evaluated for solids content~ and true strong base capacity.
After this, the resin is reconverted to the hydroxide form
using 1 N-HCl followed by 1 N-NaOH and replaced in the same
- 17 -
:. . .. : , : . ., ~
167all
temperature environment. Several spot checks are made at all
temperatures to con~irm that the resins are completely in the
hydroxide form during the testing periods. The results indicate
that the VBC resins have consistently greater thermal stability
than the corresponding CME resins.
A further advantage that the strong base V~C resins
have over prior art CME resins is improved regeneration
efficiency. The true regeneration efficiency of a strong base
resin is determined by plotting the ratio - actual column
capacity~theoretical column capacity (% utilization~, versus
the ratio - equivalents of regenerant used/total equivalants
available~ A typical VBC resin when tested for regeneration
efficiency as defined above and in accordance with known
analytical procedures showed a significant improvement when
compared to the regeneration efficiency of a typical and
corresponding CME resin. The improved regeneration efficiency
of VBC over the CME resins at normal use levels or regenerant
is in the range of at least about 10~ and may be as high as
30% for some embodiments under preferred conditions. The
significance of this improved regeneration efficiency is that
the end user can use less regenerant to achieve a desired column
capacity when using VBC resins than he can when using the CME
resins, thereby, greatly reducing his overall regenerant costs.
- 18 -
-, . ~ ~ . '. . ' , ' . ' . :
.. - .. . . : .
.
