Charged filter aid material and ion exchange bed

A method for preparing an improved filter material, together with the improved material prepared thereby and an improved method for removing impurities from a liquid. The filter material comprises a mixture of ion exchange resin particles and treated filter aid material. In the preferred embodiment, the ion exchange resin particles comprise a mixture of anion and cation exchange resin particles, and the filter aid material is treated with a chemical compound to produce a positive surface charge thereon. The filter aid material may be further treated with a second compound to produce an enhanced negative surface charge.

The present invention relates to an improved filter material and to an 
improved method for removing impurities from a liquid. 
In certain water treatment applications, there is a requirement for the 
production of extremely pure water, including the removal of both 
dissolved and suspended or colloidal materials. One area where such a 
requirement is particularly important is in the steam generation of 
electrical power, in both fossil fuel and nuclear power plants. In both 
types of installations, it is common practice to include a filter bed in 
the recycle stream for the steam turbines. In a nuclear power plant, there 
is also a requirement for the highly efficient removal of dissolved and 
undissolved impurities in the so-called "radwaste" systems which are 
associated therewith. These radwaste systems are used to remove both 
radioactive and non-radioactive impurities from liquid streams that are 
employed in connection with the operation of the power plant, including in 
large part liquids that have been used to backwash exhausted filter beds. 
A significant breakthrough in the purification of such liquid streams was 
the invention of Joseph A. Levendusky, which is described and claimed in 
U.S. Pat. Nos. 3,250,702 and 3,250,703, both of which are assigned to the 
assignee of this application. The Levendusky invention is grounded on the 
discovery that when finely divided anion and cation exchange resin 
particles are mixed in aqueous suspension, a volume increase is noted. 
This increase is believed to be the result of an agglomeration or 
"clumping" between the anion and cation exchange resin particles. Such 
resin particles, when used to form a filter bed, produce significantly 
reduced pressure drops across the bed, together with longer run lengths 
and improved efficiency of dissolved and undissolved solids removal. 
Despite these significant advantages of the Levendusky invention, the use 
of mixed anion and cation exchange resin particles as a filter has 
drawbacks. Significant among these is a tendency of these filter beds to 
crack, particularly in the presence of suspended iron oxides. Once a 
filter bed cracks, a complete breakdown of the filtration ability of the 
bed may result. A second disadvantage is that such filter beds have 
sometimes been unsatifactory in the removal of other suspended materials 
such as silica. Such filter beds are also expensive, because of their 
reliance on expensive anion and cation exchange resins, which are not 
regenerated, but which are simply disposed of subsequent to use. A third 
disadvantage of mixed finely divided ion exchange resins is that they 
perform poorly in the removal of oil from water. A fourth problem with 
mixed ion exchange resins is that of "resin bleedthrough". This is 
particularly a problem when the resin particles are precoated onto 
stainless steel filter elements, where the resin particles themselves pass 
through the element and contaminate the liquid stream. Finally, a bed made 
up entirely of ion exchange resins often is not required because the 
primary problem is the removal of suspended and colloidal impurities, 
rather than dissolved materials. 
In an effort to overcome these difficulties, a practice has been adopted of 
placing an "overlay" of conventional filter aid material, such as 
regenerated cellulose, on top of the mixed anion and cation exchange 
resins. The purpose of this overlay is to remove suspended and colloidal 
iron oxides before they can reach the resins, and also to improve the 
removal of colloidal silica. However, such an overlay has the 
disadvantages that it increases the complexity of precoating the filter 
bed onto the filter, and also increases pressure drop across the filter. 
Furthermore, such overlays tend to mat, making the filter bed much more 
difficult to backwash and remove from the filter support. 
As used herein, the term "bed" refers to a layer of filtration material, 
such as a pre-coat layer, which has been deposited on a filter support 
such as a filter screen, an annular filter cartridge, a film, a deep or 
shallow bed, or the like. Such a bed may advantageously be deposited on an 
annular filter cartridge such as those described in U.S. Pat. No. 
3,279,608, which is assigned to the assignee of this application. In 
general, a shallow bed is to be preferred over a deep bed because of the 
desire to minimize the pressure drop, thereby generally increasing the run 
length that is available. 
It is also to be understood in connection with the present application that 
when ratios or percentages of resins or filter aid materials are 
discussed, applicant always refers to the dry weight of the material 
involved. 
Generally, the present invention relates to an improved filter material. 
The present invention also relates to an improved method for removing 
impurities from a liquid which carries with it virtually all of the 
advantages, and overcomes many of the disadvantages, of the prior art. The 
method of the present invention produces significantly improved removal of 
iron oxides and other suspended and colloidal impurities, and at the same 
time reduces the cost of the precoat material when compared to the use of 
mixed ion exchange resin particles. 
In preparing the filter material of the present invention, a filter aid 
material is first treated in aqueous suspension with an electrolyte-type 
compound that produces a positive surface charge thereon. The filter aid 
material is one that is characterized by a negative surface charge in 
aqueous suspension prior to such treatment. The treated filter aid 
material is then mixed with ion exchange resin particles in the size range 
of 60 to 400 mesh. The mixture of treated filter aid material and ion 
exchange resin particles produces a clumping phenomenon similar to that 
achieved in accordance with the Levendusky invention. 
The present invention also relates to the improved filter material prepared 
by the foregoing method. The material comprises a mixture of ion exchange 
resin particles and filter aid material, the resin particles being in the 
size range of about 60 to 400 mesh. Again, the treated filter aid material 
is characterized by a negative surface charge prior to treatment, and has 
been treated with a chemical compound that produces a positive charge 
thereon. 
The ion exchange resins employed will ordinarily be fifty percent or more 
cation exchange resin particles in the size range of about 60 to 400 mesh. 
In the preferred embodiments of the invention, these cation exchange 
resins are mixed with anion exchange resin particles in the same size 
range. It is also possible to employ resin mixtures that are predominantly 
anion exchange resin particles, or even entirely anion exchange resin. 
However, when the anion exchange resin predominates, it is preferred to 
treat the treated filter aid material a second time with an anionic 
polyelectrolyte in order to produce an enchanced negative surface charge 
thereon. When mixed resin particles are employed, the preferred range of 
mixtures is from about 5 to about 95 percent of one of the two resins, 
based upon the total weight of the resin particles. 
By the term "filter aid material," applicant refers to those materials that 
are conventionally deposited on a filter screen or the like in order to 
aid the filtration which is produced by the filter. Most such materials 
are characterized by an electronegatively charged surface in the presence 
of water. Such materials are well known in the art, and include cellulose 
fibers, diatomaceous earth, charcoal, expanded perlite, asbestos fibers, 
polyacrylonitrile fibers, and the like. Particularly preferred filter aid 
materials for use in accordance with the present invention are cellulose 
fibers, which are available commercially under the trade name Solka-Floc. 
A wide variety of chemical compounds, referred to herein as 
electrolyte-type compounds, may be employed in accordance with the present 
invention in order to produce a positive surface charge on the filter aid 
particles. Such compounds must be miscible with water, and the compounds 
must have a plurality of charge sites in order to form a bond with the 
filter aid material and to have charge sites remaining to produce a 
surface charge that is the reverse of the normal surface charge. Suitable 
non-polymeric cationic-type compounds include 1-carboxymethyl pyridinium 
chloride and cetyl pyridinium chloride. 
The preferred chemical compounds in accordance with the present invention 
is an organic cationic polyelectrolyte. Suitable cationic polyelectrolytes 
include linear polyelectrolytes characterized by little, if any, 
cross-linking. Such polyelectrolytes are well known in the art, and a 
variety are commercially available. Examples of such polyelectrolytes 
include polyalkylene imines, polyalkylene polyamines, polyvinylbenzyl 
quaternary ammonium salts, polyvinylbenzyl tertiary amines, 
vinylbenzylsulfonium polymers, etc. Specific compounds that could be 
employed include, for example, poly(1-butyl-4-vinyl pyridinium bromide), 
and poly(1,2-dimethyl-5-vinyl pyridinium methyl sulfate). A particularly 
suitable cationic polyelectrolyte is one characterized by the repeating 
structure: 
##STR1## 
However, it should be understood that the abovementioned specific 
compounds are not the only ones that can be utilized, as many cationic 
polyelectrolytes are well known in the art, and it would be well within 
the ability of one of ordinary skill in the art to select a suitable 
cationic polyelectrolyte. 
In accordance with the preferred embodiment of the present invention, the 
treated filter aid materials are mixed with a mixture of cation and anion 
exchange resins in the size range of 60-400 mesh. The ratio of cation to 
anion exchange resins that may be employed ranges from about 5% to about 
95% of one of the two resins, based upon the total weight of the resins. 
However, it has been found that, in the percentage ranges where the anion 
exchange resin predominates, it is often beneficial to employ filter aid 
materials having an enhanced electronegative surface charge rather than a 
positive surface charge. In order to produce this enhanced electronegative 
surface charge, a so-called "double treatment" of the filter aid material 
is employed. In carrying out this double treatment, the filter aid 
material is first treated with a cationic polyelectrolyte of the type 
described above. The material is then treated with an anionic 
polyelectrolyte, which re-reverses the surface charge, producing an 
electronegative surface charge which is enhanced as compared to the 
original negative charge. The anionic polyelectrolytes must be miscible 
with water. Such polyelectrolytes include polymeric acids such as 
polyacrylic acids, polysulfonic acids, etc. Suitable anionic 
polyelectrolytes are again well known to those skilled in the art, and it 
is well within the ability of one of ordinary skill in the art to select a 
suitable material. 
The application of chemical compounds to the filter aid materials is 
carried out in aqueous suspension. In carrying out the preferred method, 
the filter aid material is simply suspended in water using a mechanical 
stirrer or the like, and an adequate amount of chemical compound is added 
to produce an overall positive surface charge. With high molecular weight 
polyelectrolytes (i.e., those having molecular weights in excess of 
100,000), the point at which adequate polyelectrolyte has been added can 
be determined by observing the filter aid material as the polyelectrolyte 
is added. Initially, the suspended filter aid material will be seen to 
expand in volume. This volume expansion will then disappear when a 
reversal of substantially all of the surface charge has been accomplished. 
With nonpolymeric compounds, with lower molecular weight polyelectrolytes, 
and even with some combinations of high molecular weight polyelectrolytes 
and filter aid material, no noticeable volume expansion is produced when 
the polyelectrolyte is added. In those instances, an adequate amount of 
polyelectrolyte must be determined by experience. In this regard, it 
should be borne in mind that it is not possible to employ too much 
polyelectrolyte, as any excess simply will not bond to the surface of the 
filter aid material once the negative charge sites have been used up. 
However, economics obviously dictate that the minimum amount to produce 
the desired result be employed. As a general matter, at least about 5% of 
the chemical compound, whether a polyelectrolyte or nonpolymeric material, 
is required, based upon the dry weight of the filter aid particles. Of 
course, the precise amount required in a particular case depends upon many 
factors, including the nature of the particles being treated and the 
number of positive charge sites that are available on the chemical 
compound being added. 
The foregoing procedure is also employed for the treatment with the anionic 
polyelectrolyte when the so-called "double treatment" is employed. 
In making up filter material in accordance with the present invention, the 
preferred method is to first slurry the ion exchange resin in a relatively 
large volume of demineralized water, say 10 gallons of water per pound of 
resin. The treated filter aid material is then added with continuous 
stirring to ensure homogeneous mixing. It has been found that, when the 
treated filter aid material having a positive surface charge is mixed with 
cation exchange resin, a volume expansion of the suspension is produced, 
similar to the so-called "clumping" phenomenon described in the 
aforementioned Levendusky patents. After a sufficient period of stirring 
to ensure complete mixing, say 5-20 minutes, the anion exchange resin is 
added, and stirring is continued for a similar period to ensure complete 
mixing of all three materials. The addition of the anion exchange resin 
ordinarily produces a reduction in the volume of the suspended material. 
Generally, however, the volume of the suspension will still be larger than 
that desired for precoating onto a filter bed, and the supernate may also 
contain anion exchange resin fines. The volume may be further reduced, and 
the supernate clarified, by the addition of a suitable water-soluble 
polyelectrolyte such as polyacrylic acid in relatively small amount, say 
1-10 ml. per dry pound of anion exchange resin. Such a method of 
controlling the volume of mixed, suspended anion and cation exchange resin 
is well known in the art, and is described in U.S. Pat. No. 3,250,704, 
which is assigned to the assignee of the application. 
When the filter aid material employs a "double-treated" filter aid, the 
filter aid is preferably first mixed with the anion exchange resin 
particles, which will produce a volume expansion of the type described 
above. The cation exchange resin particles are subsequently added to the 
suspension. 
The filter material of the present invention may be prepared as set forth 
above, dewatered, and stored for furture use. Alternatively, the 
components may be mixed immediately prior to being used to form a filter 
bed. When the material is dewatered and stored, it is simply resuspended 
in a suitable volume of water and deposited to form a filter bed according 
to methods that are well known in the art. 
As previously stated, the ratio of cation to anion exchange resins should 
be in the range of 5% to 95%, based upon the total weight of the resin 
particles. Preferably, the amounts of the two resins are about equal or 
the cation exchange resin predominates. Suitable cation and anion exchange 
resins that may be employed in accordance with the present invention are 
of the strong acid and strong base type. Such resins are described in the 
aforementioned Levendusky patents, and are well known in the art. Typical 
solid cation exchange resin particles include those of the 
divinylbenzene-styrene copolymer type, the acrylic type, the sulfonated 
coal type, and the phenolic type. Such resins may be used in the sodium, 
hydrogen, ammonium, or hydrazine form, for example. Typical solid anion 
exchange resin particles that may be employed are the phenolformaldehyde 
type, the divinylbenzene-styrene copolymer type, the acrylic type, and the 
epoxy type. These resins may be used in the hydroxide or chloride form, 
for example. In most cases, the cation exchange resin will be present in 
the hydrogen or ammonium form, and the anion exchange resin will be 
present in the hydroxide form. Such resins are sold in the large bead form 
under the trade names of Amberlite IR-120 and Amberlite IRA-400, 
manufactured by the Rohm & Haas Company, and Dowex HCR and Dowex SBR, sold 
by Dow Chemical Company. 
The amount of treated filter aid material employed in accordance with the 
present invention varies according to a number of factors, primary among 
which is the level of ion exchange capacity that is desired to be retained 
in the filter bed. Generally, the amount of filter aid material may be 
varied within the range of 20-80%, based upon the total weight of the 
anion and cation exchange resins present. 
Once the precoat material has been prepared in aqueous suspension, it is 
precoated onto a filter according to methods which are well known in the 
art. Simply stated, the precoat is formed by recirculating the suspension 
through the filter until a clarified effluent is obtained. The filter is 
then ready for use in the removal of impurities from liquids. 
The following examples are intended to illustrate the present invention, 
and to compare it with the filter beds employed in the prior art. These 
examples should not be considered to limit the present invention, the 
scope of which is determined by the claims.

EXAMPLE I 
500 ml. of demineralized water was placed in a one-liter beaker equipped 
with a magnetic stirrer, and 9 grams of regenerated cellulose, available 
under the trade name Solka-Floc BW-20, were suspended, utilizing the 
stirrer. While stirring was continued, 3 grams of a commercially available 
polyamide-type cationic polyelectrolyte were added. This particular 
polyelectrolyte has a molecular weight in the range of 20,000-100,000, and 
is sold under the trade name "Betz 1175" by the Betz Company, Trevose, Pa. 
Stirring was continued for one hour to insure complete mixing, and the 
treated material was dewatered using a Buchner funnel and set aside. 
In a second one-liter beaker, 4.5 grams cation exchange resin particles was 
suspended in 500 ml. of demineralized water utilizing a magnetic stirrer. 
This cation exchange resin was in the size range 60-400 mesh, was of the 
styrene-divinylbenzene type with sulfonate active groups, and was in the 
hydrogen form. 
The dewatered treated filter aid material was added to the cation exchange 
resin while stirring was continued. A significant expansion of volume was 
observed. Stirring was continued for 10-15 minutes, and 4.5 grams anion 
exchange resin was then added, with continuous stirring. The anion 
exchange resin was also ground in the size range of 60-400 mesh, and was a 
commercially available material having a styrene-divinylbenzene backbone 
chain with quaternary ammonium active groups. The anion exchange resin was 
in the hydroxide form. 4.9 ml. of a 1% solution of polyacrylic acid were 
then added, while stirring was continued, in order to clarify the 
supernate and further reduce the volume of the precoat material. 
The precoat material was then deposited onto a pilot plant filter element, 
which consisted of a single, tubular, stainless steel filter element 
having nominal particle retention rating of 70 microns, and a surface area 
available for filtration of 0.2 ft..sup.2. The filter element was 
precoated with the material by recirculating the slurry through the 
element until a clear recycle stream was produced, indicating that all of 
the material had been precoated onto the element. This procedure produced 
a uniform precoat having a depth of about 1/4 inch. 
An aqueous suspension containing 500 parts per billion iron as Fe.sub.2 
O.sub.3 was passed through the precoated filter element at a temperature 
of 50.degree..+-.2.degree. C. and at a constant flow rate of 0.8 gallons 
per minute. A portion of the effluent stream was diverted, and iron oxide 
was collected on a 0.45 micron Millipore filter, and was analyzed for iron 
using the o-phenanthroline method. Pressure drop across the filter was 
measured with a mercury manometer attached to the influent and effluent 
lines. The results, expressed in terms of pressure drop across the filter 
versus Fe.sub.2 O.sub.3 loading of the filter are shown in the following 
table: 
Table 1 
______________________________________ 
Fe.sub.2 O.sub.3 loading (g. Fe.sub.2 O.sub.3 /g. 
Pressure Drop (p.s.i.) 
precoat material) 
______________________________________ 
0.234 0.007 
0.252 0.036 
0.288 0.50 
0.342 0.086 
0.360 0.107 
0.378 0.136 
0.432 0.150 
0.468 0.171 
0.540 0.192 
0.540 0.200 
______________________________________ 
In calculating Fe.sub.2 O.sub.3 loading, it is assumed that all of the 
Fe.sub.2 O.sub.3 was deposited on the filter. This assumption could be 
seen to be valid, as the analysis of the effluent showed only 0.62 ppb Fe. 
In order to obtain a comparison with the results set forth above, an 
identical experiment was conducted utilizing mixed anion and cation 
exchange resins without the addition of treated filter aid material, as 
described in the aforementioned U.S. Pat. No. 3,250,702. The procedure 
employed was exactly the same as that discussed in Example I, with the 
exception that 9 grams of anion exchange and 9 grams of cation exchange 
resin were employed. The results are shown in the following table: 
Table 2 
______________________________________ 
Fe.sub.2 O.sub.3 loading (g. Fe.sub.2 O.sub.3 /g. 
Pressure Drop (p.s.i.) 
precoat material) 
______________________________________ 
0.658 0.007 
0.684 0.014 
0.702 0.020 
0.9 0.032 
0.918 0.039 
1.008 0.046 
1.04 0.052 
1.1 0.060 
1.17 0.067 
1.26 0.070 
1.6 0.080 
2.16 0.090 
2.85 0.094 
______________________________________ 
Effluent Fe was estimated at less than 0.1 ppb by a visual examination of 
the effluent. 
The results shown in Tables 1 and 2 were plotted in the drawing which is a 
semi-logarithmic plot of pressure drop versus iron oxide loading of the 
filter material. As can be seen from the graph, the pressure drops 
produced in accordance with the present invention were significantly lower 
than those obtained when operating with anion and cation exchange resins 
alone. These results were highly unexpected, in that the use of mixed 
anion and cation exchange resins already was believed to be a highly 
superior filter material. 
EXAMPLE II 
The following example is based upon a test that was run in the radwaste 
system of a nuclear power plant. In these tests, the improved method and 
filter bed of the present invention were compared with a diatomaceous 
earth filter precoat, as is widely used in the art. The plant employed 
tubular stainless steel filter elements having a surface area of 3.5 
ft..sup.2 each. These elements were of the wedge wire type, having a 
diameter of about 3 inches and slotted openings in the size range of about 
50-100 microns. 
The diatomaceous earth was precoated onto the filters by suspending 11 
pounds of diatomaceous earth in 22 gallons of demineralized water, and 
recirculating the suspension through the filter elements until a clear 
recycle stream was obtained. Thus, the diatomaceous earth was coated onto 
the filter element in an amount of 0.2 lb./ft..sup.2. The radwaste stream 
was then delivered through the filter elements at a flow rate of 0.5 
gpm/ft..sup.2 until a pressure drop of 30 psi was obtained. The average 
number of gallons of water that could be treated before the pressure drop 
was reached was 7,680 gallons. The effluent was passed through a 0.45 
micron Millipore filter, and produced blockage after only 100 ml. had been 
passed, indicating that a substantial amount of suspended solids (probably 
colloidal silica) was present in the effluent. 
A treated filter aid material was then prepared in accordance with the 
present invention by suspending 5.5 lbs. of regenerated cellulose in 22 
gallons of water with stirring. 0.17 lb. of the same organic cationic 
polyelectrolyte used in the previous example was added, and stirring was 
continued for 10-15 minutes. The treated material was then dewatered to 
60-80% moisture. 
2.7 lbs. of the same cation exchange resin employed in the preceding 
example was then suspended in 22 gallons of demineralized water in a tank 
equipped with a mechanical stirrer. The treated filter aid material was 
added, and stirring was continued for 10-15 minutes. 2.7 lbs. of the same 
anion exchange resin employed in the previous example was added, and 
stirring was continued for another 10-15 minutes. 13.5 ml. of polyacrylic 
acid were then added to clarify the supernate and to decrease the volume 
of the mixture. This mixture was then precoated onto the same filter 
elements, giving a uniform precoat of 0.2 lb./ft.sup.2. 
During this run, it was found that 17,000 gallons of water were passed 
through the filter elements before the 30 psi endpoint was reached. Thus, 
a run length was obtained which was over twice as long as the average run 
length achieved using diatomaceous earth. In addition, when the effluent 
was passed through the same millipore filter used before, it was found 
that 16 liters of water could be passed through the filter without any 
difficulty, indicating that the level of colloidal or suspended particles 
present was far below that present in the effluent in the previous run. 
EXAMPLE III 
The following example is based upon tests that were conducted in the 
radwaste disposal system of a second commercial nuclear power plant. The 
filter elements were of the cylindrical woven wire cloth type. These 
elements are cylindrical stainless steel elements having a length of 36 
inches and a diameter of 1 inch, and are covered with stainless steel 
screen having pore openings of approximately 150-250 microns. The total 
surface area of each element is 1.05 ft..sup.2, and the total filter area 
present was 260 ft..sup.2. 
The plant had been running utilizing plain regenerated cellulose, which was 
precoated onto the filter elements at 0.2 lb./ft..sup.2, using the 
technique described in Example II. The plant was never able to obtain a 
run length in excess of 200,000 gallons utilizing a 30 psi endpoint. 
A mixture of cation exchange resin, anion exchange resin, and treated 
filter acid material, as in the preceding example was coated onto the 
filter elements, again at a level of 0.2 lb./ft..sup.2. The flow rate for 
all of the test runs was 0.5 gpm/ft..sup.2. 
The following results were obtained when utilizing the precoat material of 
the present invention: 
______________________________________ 
Gallons Endpoint Average Turbidity (FTU) 
Treated (psi) Influent Effluent 
______________________________________ 
305,400 0.2 approx. 4.0 less than 0.1 
466,000 2.5 approx. 4.0 less than 0.1 
______________________________________ 
The turbidity is expressed as Formazin Turbidity Units (FTU), which was 
measured in accordance with the method published on p. 350 of the Standard 
Methods for the Examination of Water and Waste Water, 13th ed., published 
by the American Public Health Association, American Waterworks 
Association, and Water Pollution Control Federation. An effluent turbidity 
level of less than 0.1 FTU is considered to be extremely good, and is 
comparable to the results previously obtained utilizing regenerated 
cellulose. As can be seen from the above data, much larger volumes of 
water were passed through the filter, and the pressure drop at the end of 
the run was far below the 30 psi obtained when utilizing plain regenerated 
cellulose. 
EXAMPLE IV 
The following tests were conducted in the radwaste disposal facility of 
still another commercial nuclear power plant employing filter elements of 
the wedge wire type having a total surface area of 130 ft..sup.2. The 
standard of comparison employed was a precoat of the overlay type. This 
precoat material was a mixture of cation and anion exchange resins of the 
type described in the previous examples, which were mixed at a ratio of 
0.78:1 cation to anion exchange resin, and precoated onto the filter 
elements at a dosage of 0.32 lb./ft..sup.2 of filter surface area. This 
precoat of ion exchange resins was then covered with an overlay of 0.07 
lb./ft..sup.2 of regenerated cellulose. 
The precoat material prepared in accordance with the present invention was 
prepared as in the preceding examples, and was precoated onto the filter 
element in an amount of 0.2 lb./ft..sup.2. Data were taken at 2.5, 8.0 and 
15.0 psi pressure drop. 
The flow rate for all runs was 0.7 gpm/ft..sup.2. The results are shown in 
the following table: 
______________________________________ 
Total 
Precoat 
Pressure Gallons Turbidity (FTU) 
Percent 
Material 
Drop (psi) 
Treated Influent 
Effluent 
Removal 
______________________________________ 
overlay-type 
17 36,000 44 33 25 
present 
invention 
2.5 13,500 43 0.8 98 
present 
invention 
8.0 31,000 50 3.0 94 
present 
invention 
15.0 50,000 165 7.1 96 
______________________________________ 
The "percent removal" is one minus the ratio of the effluent to influent 
turbidity multiplied by 100. As can be seen from the foregoing table, a 
dramatic increase in percent removal was achieved when operating in 
accordance with the present invention. Furthermore, the influent turbidity 
levels tend to indicate that material being delivered to the two filter 
beds was comparable in impurity levels. It is noted that run with the 
overlay-type precoat was made at about the same time that the run with the 
precoat material of the present invention was made. 
During the runs set forth above, data were also collected concerning the 
radioactive contaminant levels in the effluents. Specifically, 
measurements were made of the activity of four iodine isotopes and of 
radioactive cobalt isotopes using a germanium-lithium detector. The gross 
gamma activity of the effluent was also measured using a sodium iodide 
detector. The results are shown in the following tables: 
______________________________________ 
Overlay-Type Precoat, 17 psi Pressure Drop 
Gross Gamma 
Specific Activities (microcuries/ml) 
Activity (Total 
I.sup.132 I.sup.135 
I.sup.133 
I.sup.131 
Co.sup.58 
Counts) 
______________________________________ 
Influent 
71 518 1094 1131 11 6.46 .times. 10.sup.6 
Effluent 
0.5 7 20 5 0.3 0.58 .times. 10.sup.6 
D.F. 142 74 55 226 37 11 
______________________________________ 
______________________________________ 
Precoat of the Present Invention, 8 psi Pressure Drop 
Gross Gamma 
Specific Activities (microcuries/ml) 
Activity (Total 
I.sup.132 I.sup.135 
I.sup.133 
I.sup.131 
Co.sup.58 
Counts) 
______________________________________ 
Influent 
83 489 966 1244 26 6.50 .times. 10.sup.6 
Effluent 
0.4 4 9 3 0.2 0.52 .times. 10.sup.6 
D.F. 208 122 107 415 130 13 
______________________________________ 
______________________________________ 
Precoat of the Present Invention, 15 psi Pressure Drop 
Gross Gamma 
Specific Activities (microcuries/ml) 
Activity (Total 
I.sup.132 I.sup.135 
I.sup.133 
I.sup.131 
Co.sup.58 
Counts) 
______________________________________ 
Effluent 
0.4 4 11 4 not found 
0.82 .times. 10.sup.6 
D.F.* 208 122 88 249 -- 8 
______________________________________ 
*Readings were not taken for influent. DF based on assumption that 
influent readings were the same as in preceding table. 
In the foregoing tables, "D.F." indicates the "decontamination factor," 
which is a ratio of the influent contaminants to the effluent 
contaminants. The objective, of course, is to obtain as high a 
decontamination factor as possible. As can be seen from the foregoing 
tables, the decontamination factors produced in accordance with the 
present invention were significantly higher than those obtained when 
employing the mixed resins and overlay material of the prior art. These 
results indicate very significantly improved removal of radioactive 
contaminants from the stream. 
EXAMPLE V 
In the following example, the absence of "bleedthrough" tendency of the 
filter material of the present invention on stainless steel filter 
elements is demonstrated. For comparison purposes, tests were also 
conducted with mixed finely divided ion exchange resins and with untreated 
regenerated cellulose. 
The runs were conducted in a pilot plant having a single, tubular, 
stainless steel filter element having a nominal particle retention rating 
of 150-200 microns and a surface area available for filtration of 0.79 
ft..sup.2. In each case, sufficient filter precoat material was delivered 
to the element to produce a precoat dosage of 0.2 lb./ft..sup.2. The 
filter material was precoated by pumping a 0.5 wt. % aqueous suspension of 
the material through the element with recirculation at a constant flow 
rate of 2.75 gal/min/ft..sup.2. An in-line Hach tubidimeter was used to 
measure turbidity on the downstream or effluent side of the filter 
element. 
RUN NO. 1 
0.08 lb. cation exchange resin was slurried in 4 gal. demineralized water 
in a tank equipped with a stirrer. The resin was in the size range of 
60-400 mesh, and was of the styrenedivinylbenzene type with sulfonate 
active groups in the hydrogen form. 0.08 lb. anion exchange resin was 
added with continued stirring. The anion exchange resin was also in the 
size range of 60-400 mesh and had a styrene-divinylbenzene backbone chain 
with quaternary ammonium active groups. The anion exchange resins was in 
the hydroxide form. 
The mixed resins were recirculated through the filter element, and the 
following results were obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
1 50.0 
2 37.0 
3 10.0 
4 3.0 
5 1.1 
6 0.5 
7 0.28 
8 0.16 
9 0.1 
______________________________________ 
RUN NO. 2 
Run number 1 was repeated, except that 0.16 lb. regenerated cellulose was 
substituted for the mixed ion exchange resins. The following results were 
obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
1 100 
2 100 
4 100 
6 10 
8 3 
10 1.2 
12 0.52 
14 0.3 
______________________________________ 
RUN NO. 3 
In this run, 0.08 lb. of the same regenerated cellulose used in the 
previous run was suspended in 0.3 gal. water containing 0.038 oz. "Betz 
1175," a cationic polyelectrolyte described in Example I. The regenerated 
cellulose was dewatered using a Buchner funnel. 0.04 lb. of the cation 
exchange resin employed in Run No. 1 was suspended in 4 gal. water, and 
the treated regenerated cellulose was added with continued stirring. 0.04 
lb. of the anion exchange resin employed in Run No. 1 was then added, and 
the entire mixture was stirred to ensure uniform mixing. The resulting 
mixture contained 50% of the ion exchange resins used in Run No. 1 and 50% 
of the regenerated cellulose used in Run No. 2, which had been treated in 
accordance with the present invention. The mixture was delivered through 
the filter element, and the following results were obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
1 2.3 
2 2.5 
3 0.44 
4 0.21 
5 0.12 
______________________________________ 
A comparison of Run No. 3 with Runs Nos. 1 and 2 shows a dramatic decrease 
in effluent turbidity with the filter material of the present invention 
when compared with mixed ion exchange resins or with regenerated cellulose 
used alone. These data demonstrate a significant decrease in the tendency 
of the filter material of the present invention to "bleed through" the 
filter element during a filtration run. 
EXAMPLE VI 
The following example demonstrates the superior and unexpected oil removal 
ability of the filter material of the present invention. For comparison 
purposes, tests were also conducted with mixed finely divided ion exchange 
resins and with untreated regenerated cellulose. 
These runs were conducted in the same pilot plant used in the preceding 
example using a tubular stainless steel filter element having a nominal 
particle retention rating of 76 microns and a surface area available for 
filtration of 0.2 ft..sup.2. 
In each instance the filter material was precoated onto the filter element 
at a constant dosage of 0.2 lb/ft..sup.2. A suspension of SAE 10 pneumatic 
pump oil having a turbidity of 100 FTU was delivered to the precoated 
filter element at a flow rate of 4.0 gal/min/ft..sup.2, and samples were 
periodically removed from the effluent stream for turbidity measurements. 
These measurements were made with a Hach turbidimeter. 
RUN NO. 1 
In this run the filter element was precoated with a 50--50 mixture of the 
same ion-exchange resins employed in the preceding example. The following 
results were obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
15 0.38 
30 0.38 
45 1.75 
60 2.75 
75 4.5 
90 5.5 
______________________________________ 
RUN NO. 2 
Run No. 1 was repeated, except that the filter element was precoated with 
untreated regenerated cellulose. The following results were obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
15 1.5 
30 2.5 
45 5 
60 11 
75 10 
90 10 
105 30 
120 40 
135 40 
150 39 
165 39 
______________________________________ 
RUN NO. 3 
The filter element was precoated with a filter material identical to that 
employed in Run No. 3 of the preceding example. The following results were 
obtained: 
______________________________________ 
Time (min.) Effluent Turbidity (FTU) 
______________________________________ 
15 0.35 
30 0.65 
45 1.4 
60 1.9 
75 2.5 
90 1.25 
105 1.75 
120 2.05 
______________________________________ 
As can be seen from a comparison of Run No. 3 with Runs Nos. 1 and 2, the 
filter material of the present invention produces dramatically improved 
oil removal when compared to mixed ion exchange resins or regenerated 
cellulose used alone. Such results were totally unexpected. 
Obviously, many modifications and variations of the invention as 
hereinbefore described will occur to those skilled in the art, and it is 
intended to cover in the appended claims all such modifications and 
variations as fall within the true spirit and scope of the invention.