1526
INDUSTRIAL AND ENGINEERING CHEMISTRY
Conclusions Should it be desirable to utilize the adsorptive properties of the zoogleal organisms for the removal of radioactive elements in waters relatively devoid of organic nutrients, common foods supplemented with essential minerals can be fed to maintain good control of the activated sludge process.
Literature Cited (1) American Public Health Association, New York, “Standard Methods for the Examination of Water and Sewage,” 9th ed., p. 168, 1946. ( 2 ) Bradney, L., Nelson, W., and Bragstad, R. E., Sewage Workv J . , 22,807 (1950). (3) Heukelekian. H., and Littman, M. L., Ibid., 11, 226 (1939). (4) Horvath, A. A., “The Soy Bean as Human Food,” Peking Union Medical College, 1925.
Vol. 43, No. 7
(5) Ingols, R. S., and Heukelekian, H., Sewage Works J . , 11, 927 (1939). (6) Montagna, S.D., Ibid., 12, 108 (1940). (7) Moore, W. A., Kroner, R. C., and Ruchhoft, C. (”., iinal. Chem., 21, 953 (1949). (8) Morgan, E. H., and Beck, A. J . ,Sewage W a k s J . , 1,46 (1928). (9) O’Shannessy, F. R., and Hewitt, C. H., J. SOC.Chem. I n d . , 54, 167 (1935). (10) Ruchhoft, C. C., Sewage Woiku J., 21, 877 (1949.) (11) Ruchhoft, C. C., and Watkins, J. H., Ibid., 1, 52 (1928). (12) Rudolfs, W., et al., Ibid., 1t o 22 (March 1928-50). (13) Sawyer, C. N., Ibid., 12, 3 (1940). (14) Sawyer, C. S . ,andBradney, L.,Zhid., 17, 1191 (1945). (15) U. S.Dept. Agr., Bull. 28. (16) Waksman, S., “Principles of Soil ,Microbiology,” pp. 50‘3-15, Baltimore, Williams & Wilkins, 1927. (17) Zbid., p. 578. RECEIVED Septembei 13, 1950.
Treatment of Radioactive Waste by Ion Exchange W i t h the installation o f new laboratories for radiochemical research i n populated areas, the treatment of the wastes Presents a Problem- It is desirable to mduce the activity of these wastes to a safe level before discharging them into the ground or sewage systems. This paper describes a preliminary study of the application of ion exchange processes to problems of radioactive waste disposal. The general behavior of the radioactive isotopesand the effect of impurities which might be expected to be present i n general laboratory wastes are discussed. Two general plans for ion exchange treatment of laboratory
wastes are presented. One plan utilizes cation exchange to remove the bulk of the radioactivity a n d give a n effluent free from the ions which usually adsorb or precipitate i n neutral or basic solutions. ~h~ other plan columnsOr io mixed bed to provide complete demineralization a n d give an effluent having a n activity level below the detectable limit. This preliminary study points Out the advantages and limitations of ion exchange procedures for treatment of laboratory wastes and makes it Possible to evaluate such Procedures or suggest further research along these lines.
John A. Ayresl KNOLLS ATOMIC POWER LABORATORY, SCHENECTADY, N. Y,
I
N LABORATORIES using radioactive tracers a large amount of liquid wastes having a low level of activity will be produced. I n many cases it is desirable to reduce the activity t o predetermined levels before discharging the waste into the sewers or in any other manner into the ground or water. Ion exchange is applicable to problems of this type in that it may be used for the removal of small amounts of ions from very dilute solutions. In the deionization of water for industrial purposes all ions in the incoming water are replaced by hydrogen and hydroxyl ions and the effluent is comparable to distilled water. This method is cheaper than distillation since the ion exchanger acts only on the very minor constituents, the impurities, and lets the greater bulk, the water, pass through unchanged. Ion exchange seems attractive for removal of radioactivity, for the wastes from laboratories are expected t o contain 0.1 t o 0.2% solids. A procedure for treating’ nonradioactive laboratory wastes by ion exchange has been described by Beohner and Rfindler (6). The problem of removal of radioactive solids from laboratory wastes is complicated by the fact that the wastes are heterogeneous and vary from day t o day. The wastes will contain solids, organic solvents, oils, and reagents which may form complexes with metallic ions. The research program to evaluate ion exchange was divided into several parts-namely, 1
Present address, Hanford Engineering Works, Richland, rv’ash.
1. The efficiency of ion cxchangt resins for this type of process. 2. Determination of operating curves under set conditions for typical types of ions. 3. Determination of amount of leakage or efficiency of ion eschange resin in order to estimate decontamination factors, 4. Effect of reagents which might cause precipitation or complexing. 5 . Effect of solvents, greases, detergents, or precipitatcs. 6. Possible concentration by incineration.
From these data it is possible to suggest possible installations which might be used for treatment of the liquid wastes by ion exchange.
Materials Several types of ion excliangc. resins mere used. Amberlitc IR-100H (9), a low capacity cation exchange resin; hmberlitc IR-4B (7, 8),an amine-type anion pxchange resin; and Amberlite XE81 (IO),a mixture of fully regmerated cation and anion exchange resins, were obtained from Resinous Products and Chemical Go., Philadelphia, Pa. Bmherlite IR-100H was chosen for the preliminary cation exchange experiments because it could be easily regenerated and a complete cycle couId be carried out in a relatively short time. In some experiments Dowes 50 ( 4 ) or Nalcite HCR, a high capacity cation exchange resin obtained from National Aluminate Corp., Chicago, Ill., was used in order to determine the maximum concentration factors. The cation exchange resins were screened and only the fraction which would pass through a 20-mesh screen but would not pass through a 40-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July 1951
I %
80
9
-
I
I
0
x
I
I
I
I
AMBERLITE IR-100H DOWEX 5 0
ks 4
may be determined. The data for two curves showing the replacement of sodium ion by hydrogen ion by means of two typical resins are presented in Tables I and 11; these curves are shown in Figure 1. As it is very desirable to have a high concentration factor, the resin having the highest capacity is the most desirable for treatment of radioactive wastes.
-
W
60-
-
40-
-
20-
-
W
+
1527
3
22
1"
z
I?
; 0
z 200
300
400
500
600
700
VOLUME OF E F F L U E N T IN MILLILITERS
Figure 1. Removal of Sodium Ions from Solution by Ion Exchange Columns mesh screen wtts used. The resins were then slurried in water, poured into the column, and classified for approximately 20 minutes by backwashing at the recommended flow rate of 6 gallons per square foot per minute in order to remove the fines. The anion exchange resins and the mixed resins were not screened or classified. The radioactive tracem used to determine the decontamination factors were all obtained from the Oak Ridge National Laboratory, Oak Ridge, Tenn.
Evaluation of Different Cation Exchange Resins Since a continuous process would require a series of columns, all the preliminary investigations were made using a laboratory size glass column 1.5 cm. in diameter and filled with resin to a depth of 60 cm. In order to determine the relative capacities of the different cation exchange resins, a dilute sodium chloride solution was poured through a column filled with the resin in the hydrogen form and fractions of the effluent were titrated t o determine the displaced hydrogen ion. The results were then plotted in the form of the regular Schumann (4,lW)curve where the ratio of the concentration of the sodium ion in the effluent to that in the feed solution is plotted against milliliters of effluent. I n the first portions of the effluent the ratio C/C,is substantially zero, but a point is soon reached at which the value suddenly rises. The end point, or breakthrough, is taken as that point a t which this ratio is equal to 0.02. From the number of milliequivalents of hydrogen ion displaced, the breakthrough capacity of the resin
Table I. Titration of Effluents from Amberlite IR-lOOH Column
Total Vol. of Effluent, M1.
311. NaOH Required to Titrate 15 M1. of Effluent
...
22.5 29.75 29.75 29.9 29.75 29.6 29.4 28.35 26.15 22.6 17.8 12.8 4.4
yo of Original Na. Appearing in Effluent
.. .. .. ..
..
0:5 1.2 4.7 12.1 24.1 40.0 57.3 85.2
Determination of Operating Curves Operating curves for various ions using column procedures have been determined by many investigators (6). However, it was desirable to obtain these curves under set conditions for various representative ions. Cations. The curves for the sodium ion, a typical monovalent cation, were presented in Figure 1. To complete the picture the curves for typical di- and trivalent cations, barium and lanthanum, were determined. The data are listed in Tables I11 and IV and the curves are shown in Figure 2. As was expected these curves are very similar and the capacities of the resin for these different ions are practically the same.
Table 11. Titration of Effluent from Dowex 50 Column (Replacement of N a + by H using Dowex 50) Flow rate, ml./min. 3.3 *0.3 Column Internal diameter, om. 0.8 Bed height, om. 60 30 Vol. of resin, cu. om. 20-30 mesh Size of resin 0.1135 M NaOH Original solution 1.2%NaCl VOl. of Fraction, MI. 25 10
(Replacement of Na + by H + using Amberlite IR-100H) Flow rate, ml./min. 20 * 2 Column Internal diameter, om. 1.6 Bed height, om. 63 126 Vol. of resin, cu. cm. 20-30 mesh Size of resin NaOH 0.0782 M Original solution 1% NaCl Vol. of Fraction, M1.
V O L U M E OF E F F L U E N T IN M I L L 1 L I T E R S
Figure 2. Removal of Barium and Lanthanum Ions from Solution by Ion Exchange Columns
10
10 10 10 11.5 10 10 +
10
10 10 10
10 10 10 10 10
10
10 10
10 10
10 10 10 10
Total Vol. of Effluent, M1. 25 35 45 55 75 95 116.5 136.5 156,5 178 198 218 238 278 318 358.5 898.5 439 479 520 540 560 580 600 620 640 650
Ml. SJaOH Required to Titrate Effluent 15.10 17.00 16.93 16.89 16.88 17.00 20.80 17.00 17.35 17.26 17.46 17.40 17.25 17.20 17.55 17.19 17.54 17.16 17.65 17.43 17.72 17.83 17.46 17.04 15.85 12.63 10.32
a
of 0rigin.al + Appearing in Effluent
..
.. .. ..
.. .. .. .. .. .. .. I .
. I
.. . I
.. .. .. .. ..
..
2:4
9.2 27.7 40.9
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1528
Table 111. Titration of EfWuents from Amberlite IR-IOOH Column ,Replacement of B a - + b y H - using .4niherlite IR-100H) Flow rate, nil. j m i n . 20 A 2 Column Internal diameter, cm. 1 5 Bed height, cm. 61 1-01. of resin, cu. cm. 118 Size of resin 20-30 mesh SaOH 0.0782 ,I4 Original solution '2yoBaClz
7-01. of Fraction, 111.
Total Yo]. uf Effluent, 511.
111. S a O H Required t o Titrate Effluent
yo of Oiiginai B a A +.ippearing in Effluent
Table IV. Titration of Effluents from Amberlite IR-100R Column (Replacement of L a + & *by H' using Amberlite IR-100H) Flov rate, ml./min. 20 1 2 Column Internal diameter, c m . 1.5 Bed height, om. 61 1-01, of resin, cu. c m . 118 Size of resin 20-30 mesh SaOH 0.0782 M Original solution 1% LaCla 1-01 of Traction, 311. 75 25 25 25 25 25 25 25 25 25 25
Total 101 of Effluent, 111.
--
311. S a O H of Orlglnni Required to L a i + ' Appearing Titrate Effluent in Effluent
iJ
100 200 313 863 413 463
si?
563 613 i63
'24 20
2.5.85 25.80 23.30 19.75 10.45 4.60 2.20 1.20 0 30
..
.. i'g 23 4 59 5 82 2 91 5 95.3 PF 8
Because in actual operation laboratory wastes will consist of ail types of ions in solution, one experiment n-as performed in which the feed solution consisted of a mixture of sodium, barium, and lanthanum ions. The effluent was analyzed for these ions t o determine the different breakthrough points. The data are lieted in Tables V and 1-1. In Table V are shown the milliliters of sodium hydroxide required to titrate a definit,e volume of the effluent. From the t.otal amount of hydrogen ion replaced, the total capacity of t'he coluilln can be calculated. After 300 mi. have been poured through the column, the sodium ion starts T O appear in the effluent. The effluent fractions were analyzed for barium by precipitation as sulfate and for lanthanum by precipit.ation as oxalat,e after renioval of the barium. The concentrat,ion of these ions is shown in columns 5 and 6 of Table V. The amount of sodium ion in 50 ml. of the effluent after the brealithrough (300 ml.) equals: 0.0956 (80.00 - nil. of S a O H required to titrate .50 ml. of effluent) - meq. Ba++/50 ml. of effluent meq. La+++,'50 ml. of effluent
In Table 1-1are listed the milliequivalents per milliliter and per cent, of original appearing in effluent for each of the ions-sodium, barium, and lanthanum-for various volumes of the effluent. These data represent, to a degree the theoretical performance in which the hydrogen ion on the resin is replaced by sodium, then the sodium is replaced by barium, and finally the barium is replaced by lanthanum. Anions and Amphoteric Ions. If the main radioactive com-
Vol. 43, No. 1
ponents of laboratory waste are the fission products, the only negative or amphoteric ions of importance are molybdenum, tellurium, and ruthenium. These exist to some extent &s positive ions so some removal by cation exchange resins can be expected, but the most efficient remol-a1 n-ill be with the anion exchange resins. TELLURIUM. 9 solution containing 1.5 grams of tellurium in a hydrochloric acid solution ITas passed through a column filled with the cation exchange resin, hmberlit,e IR-100H. About 90% of the tellurium was removed. The results show that the capacity of these resins for tellurium is very low, approximately 0.4 millimole per liter of resin. This is due to the equilibrium bet,ween the positive and negative valence states of tellurium in the solution. After the resin in the column had been saturated with the tellurium salt and backwashed, it was allowed to stand for a fev hours before regeneration. However, before the column was act,ually regenerated, a m-hite precipitate formed and settled in the interstices of the column. This was probably due to the equilibrium Te02++
+ 2Hp0e TeOd-- + 4 H +
-4s t,he tellurium separates it' hydrolyzes and precipitates. The hydrogen ion formed by the hydrolysis reaction displaces more Tellurium and the reaction proceeds until the tellurium is completely removed from the column. Because of this behavior a cation exchange resin would be of little value for removal of amphoteric ions since these ions would be only partially removed and would not remain on the resin for any period of time, The behavior of tellurium anion in the presence of an anion exchange resin was tried with more success. A solution containing 24 millimoles of tellurium, 24 millimoles of sodium hydroxide, and 122 millimoles of sodium chloride per liter was poured through an anion exchange column at a flow rate of approximately 15 milliliters per minute. The column had been prepared by filling a glass tube, 1.6 em. in diameter, to a depth of 60 cm. with hmberlite IR-4B and regenerating this resin with hydrochloric acid. The reeiii vias deep orange in color but changed to a very light orange as the feed solution passed through and the chloride was replaced by the hydroxyl and tellurate ions. .kfter 510 ml. had passed t,hrough the flow was stopped. An analysis showed that the effluent contained no tellurium. The exhausted portion of the resin n-as 22 em. in length. The following calculations give an approximate capacity of the -4iiiberlite IR-4B resin for tellurium: J-oluine of exhausted resin: 22 X (1.6)2 X 0.7854 = 45.0 cc, Tellurium adsorbed:
24 X 510 X 0.1276 = 1,56 grams 1000
Capacity of Amberlite IR-4B: 1.56 X
1000
=
34 7 grams Te
SIOLYBDEWM.;\Iolybdenuni behaved just like the tellurium. From a solution of sodium molybdate the molybdenum was removed only partially by a cation exchange resin but completcly and satisfactorily by an anion exchange resin. RUTHEXIUM.Preliminary studies have shown that tracer iuthenium in nitric acid solutions is removed only to a very ehght degiee with cation exchange resins but can be removed with anion exchange resins. Some batch studies using Ru'O' as tiacer in nitrir acid solutions gave 98% removal with anion exchange resin (hmbeilite IR-4B) and
