I
WILLIAM J. LACY’ and DON C. LINDSTEN Sanitary Engineerjng Branch, Engineer Research and Development Laboratories, Fort Belvoir, Va.
Removal of Radioactive Contaminants from Water by Ion Exchange Slurry Contaminated water can be made safe for emergency drinking by batch treatment with a mixed bed ion exchange resin
T H E contamination of public water supplies by radioactive materials is a problem of increasing concern, which could arise under many circumstances including use of a nuclear weapon of war and improper disposal of waste from atomic reactor installations, research organizations, or hospitals. Radioactively contaminated water can be decontaminated by various methods, including distillation and conventional water treatment processes (6, 7). Radioactive materials can be removed by ion exchange materials from water by column operation (7, 3, 8, 77) or by a batch slurry process.
Materials
Ion exchange materials used in the test included Amberlite MB-3, Amberlite XE-69, Zeo-Dur, and Permutit Q. Oak Ridge tap water (pH 7.9, hardness 110 p.p.m. calcium carbonate and alkalinity 98 p.p.m. as calcium carbonate) was used in all tests. T h e following radioactive materials were used as contaminants: Ba140La140, Cd115, Ce141,14Lpr144, Cs137-Ba187, 1 1 3 1 , p 3 2 , Sr9OLy90, R~lOLRh106, Tal82, Zr95-Nb95. The analyses of the mixed fission product solutions are given in Table I. All the radioactive contaminants used in the study were obtained from the Operations Division, O R N L (9). Procedure
Oak Ridge tap water was contaminated with the radioactive material to an initial concentration of about 4000 counts per minute per ml. (uncorrected for counter efficiency-about 10%). T o 500 ml. of the contaminated water in a beaker enough ion exchange resin was added to give concentrations of 450, 900, 1350, 1800, and 2700 p.p.m. The contents of the beaker were stirred for 90 minutes at 216 r.p.m. using a Present address, Health Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.
laboratory-type stirring device. Initial samples taken prior to addition of resin were analyzed for p H and for activity count. Samples were taken every 15 minutes throughout the 90-minute cycle, filtered through ,filter paper, and dried and counted using the described procedure. At the end of the 90-minute cycle a final sample was taken and was centrifuged to ascertain any detectable effect. Counting rates, corrected for coincidence, background, and geometry Removal, % =
initial activity
-
material, chemical valence of contaminant, and other factors. T h e p H has an effect upon the basic mechanism of removal. For example, by decreasing the p H of some solutions with hydrochloric acid it is possible to form certain cation-chloride complexes which will be adsorbed on an anion exchanger rather than on a cation exchanger. If the p H of the feed solution is constant, the distribution ratio of cations between resin and solution for a unit volume of
activity of solution after agitation initial activity
(to lOOj,) were used to compute percentage removal of activity in terms of the initial concentration of the contaminant. Results
Results showing the percentage removal of contaminant by the several ion exchange materials investigated and for 15 minutes of contact time are shown in Table 11. Results showing percentage removal of mixed fission product contaminant MFP-2 us. slurrying time a t varying dosages are shown in Figure 1. Results showing percentage removal of contaminant us. concentration of MB-3 at 90 minutes of contact time for various contaminants are shown in Figure 2. I Discussion
The level of contamination used in this study was chosen because of the ease of detection and because it is of the order,of magnitude expected in a water supply after the detonation of a nominal (20KT) atomic bomb (4, 70). T h e estimated concentration of activity from “fallout” and “washin” from an atomic bomb would be about low2pc per cc. (2200 c.p.m. per ml.), However, the initial level of activity for runs using MFP-2 as contaminant was increased by a factor of 5 to 20. Higher initial concentration of contaminants did not affect the percentage removal when MFP-2 was used as the source of radioactive material. The degree of removal of radioactive contamination from water by ion exchange materials is determined by the total dissolved salt content of the water, ionic or colloidal state of the contaminant, type of ion exchange
x
100
solution and a unit mass of resin will be directly proportional to the number of cations per unit mass of resin which are capable of undergoing exchange with the cations in solution. The p H values of the water used in these tests were not necessarily the optimum for removing the particular radioisotopes used but were within the normal range considered safe for potable water. No one type of resin proved to be best for all radioactive contaminants tried. As expected, the mixed bed exchanger MB-3 removed a greater percentage of the contaminants than a single exchanger. In Figure 2, 2700 p.p.m. of MB-3 in contact with contaminated water for 90 minutes removed over 98y0 of all radioactive contaminants tested. Removal of a radioactive contaminant did not increase proportionally with increasing dosage of resin. This was especially noticeable when a cation exchanger was used. No detectable difference in removal of radioactivity was found between filtered or centrifuged samples. Frequently the increased
Table I. Radiochemical Analysis of Fission Product Mixtures
Contribution to Activity, % -
Total
Radioactive Element Total trivalent earths Ruthenium Cesium Cerium Strontium Zirconium Niobium Barium Others in traces
MFP-1
MFP-2
rare 10.0 16.0
40.0 5.0 10.5 5.0 5.0 5.0 3.5
48.5 3.0 7.0 20.4 8.9 1.1 1 .o 7.0
3.1 - 100.0
100.0
VOL. 49, NO. 10
OCTOBER 1957
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and the Sanitary Engineering Branch of ERDL, Fort Belvoir, Va., for their cooperation. Radiochemical analyses were carried out by Bernd Kahn, USPHS. literature Cited
30
I5
60
45
75
90
TIME S L U R R Y l h G i l k MINUTES)
Figure 1 . Effect of increased contact time and concentration of ion exchange resin on removal of MFP-2
removal by increased resin dosage was negligible. T h e amount of radioactive substance in water contaminated to concentrations well above drinking water tolerances is negligible on a gravimetric basis ( 2 ) Batch-type treatment, used in these tests, is less efficient than column-type operation. However, in a batch treatment, equilibrium is reached very rapidly, and under certain conditions is more readily accomplished. According to Gustavson (5)the batch operation under nonequilibrium conditions has
and nonionic chromium complexes is slurried with a cation exchange resin to assure a quantitative uptake of chromium cations without reaching the final complex equilibrium, so the contact time is short enough to prevent appreciable shift in equilibrium between the complexes Provided no transformation of nonionic o r anionic complexes into cations has occurred, the amount of cationic chromium can be calculated bv analyzing either the solution or the ion exchange resin. Using the slurry or dispersed contact
certain advantages over the column method for solutions containing cationic, anionic, and nonionic (unchanged or colloidal) materials For example, a solution containing cationic, anionic,
method described here. water decontamination factors of 10 can be achieved by using simple inexpensive equipment. T h e rate of treatment is not limited by maximum flow rate through a column or depth of the resin bed.
(1) Ayres, J. A., IND.END. CHEW.43, 1538-40 (1951). (2) Bale, W. F., “Levels of Radioactivity in Water and Food That Can Be Permitted Under Emergency Conditions in Wartime,” Biophysics Branch, Division of Biology and Medicine, U. S. Atomic Energy Commission (1949). (3) Friend, A. G., M.Sc. thesis, Virginia Polytechnic Institute, June 8, 1952. ( 4 ) Glasstone, Samuel, ed., “Effects of Atomic Weapons,” U. S. Government Printing Office, Washington, D. C., 1950. (5) Gustavson, K. H , J . SOC.Leather Trades’ Chemists 35, 160 (1951) (6) Lacy, W. J., Lindsten, D. C . , “Purification of Water Contaminated with Radioactive Material,” ERDL, Fort Belvoir, Va., Rept. 1275 (Dec. 24, 1952). ( 7 ) Lacy, W J , Lindsten, D. C., Lowe, H. N., “Removal of Radioactive Materials from Contaminated Water by Thermocompresqion Distillation,” ERDL, Fort Belvoir, Va , Rept. 1313 (Aug 28, 1953). (8) Idauderdale, R . ’4, J , pvater Works Assoc. 43,327 (1 951 ). (9) Oak Ridge Nationdl Laboratory, Oak Ridge, Tenn., “Isotopes Catalogue and Price List,” January 1955. (10) Sullivan, TY. H., .‘Problem of Radioactive Water Contamination in TVarfare,” U . S Atomic Energy Commission, ‘Tech. Information Div.. Oak Ridge, Tenn , ADZ-83. (11) Thompson, J., McGarvey, I?. X , J . Am. Mhter Vl’orks Assoc. 45, 145 (1953).
RECEIVED for review October 15, 1956 ACCEPTED January 25, 1957
Acknowledgment
I
The? authors are i?debted to personnel of the Health Physics Division of O R K L
Table !I.
Removal of Radioactive Contaminants from Water b y Slurrying with Ion Exchange Resin“
Radioactive Contaminant
MFP-2
Chemical Foim Waste concentration in NazCOs Nitrates in “03 Chlorides in HCl
5,000
7.7
48,000
7.6
4,100
7.7
RU’06-Rh’06
*
90-minute contact time
INDUSTRIAL AND ENGINEERING CHEMISTRY
yo Removal Exchange Resin Used; Perniutit ZeoAmberP P &!I Q. Dur lite XE-69
Resin Dosage
~
450 2700 450 2700
61.3 76.3 50.7 83.9
46.3 62.7 52.5 66.2
54.0 64.9 57.4 89.5
450 2700
77.7 92.7
68.0
77.0
92.5 93.0
2,000
7.6
450 2700
92.3 93.7
96.3 97.7
93.7 95.1
Tantalate in K O H
2,600
7.7
450 2700
27.0 27.9
16.1 17.9
23.1 24.2
8,400
7.6
450 2700
53.1 53.8
69.5 72.9
70.2 73.7
3,600
7.2
450 2700
40.1 65.4
47.3 69.5
58.2 77.3
QESIN (FPV’
Figure 2. Decontamination of radioactively contaminated water b y slurrying with ion exchange resin MB-3
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Initial C.P.M./Ml. pH of Initial Stock Activity Soh.
Oxalates in HzCzOa
Pri44 Chlorides in HC1 COlVCEITRfi- O h O F
Division of LVater, Sewage, and Sanitation Chemistry, 130th Meeting, ACS, Atlantic City, N. J , September 1956.
in HC1
15-minute contact time Uncorrected for counter efficiency (approx 10%).
