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New Method for Stripping Iodine-131 from the Anion Exchange Resin Used to Remove Radionuclides from Milk
New Method for Stripping Iodine-131 from the Anion Exchange Resin Used to Remove Radionuclides from Milk J. P. WALKER, ~ B. F. R~:HNBERG, and I. B. BROOKS Southeastern Radiological Health Laboratory, Montgomery, Alabama
After the milk radionuclide decontamination process, the ion exchangers are prepared for reuse (13). Strontium-90 can be stripped from the cation exchanger with as little as nine bed volumes (by), 60 C, of mixed salt (NAG1, KC1, MgCI2 and CaCl~) regenerating solution (8, 12). The commercial scale project (7, 8) stripped the :~I from the anion exchanger with approximately 50 bv of 2 ~ ttCI at 25 C. The 2-x tiC1 stripping agent has two serious disadvantages. First, it is extremely corrosive to stainless steel equipment used in modern dairies. Second, HC1 is expensive. The purpose of this investigation was to find an efficient stripping agent that would not have acute corrosive action on stainless steel and would be low in price.
Abstract
This investigation was made to find an alternate stripping agent for the removal of ~ I from Dowex 2 X-8 20-50 mesh resin used to remove this nuclide from fluid milk. The agent currently utilized is 2 HC1, which has the disadvantages of causing extreme corrosion to the stainless steel equipment used in nmdern dairies and of being expensive. The chloride: citrate: phosphate charged resin was equilibrated over-night with Na ~ I and 8O-ml portions were placed in 25-ram diameter, jacketed eolmnns. The resin beds were rinsed with six bed volumes of deionized water, 0.25 bed volumes per minute, at 25 C and stripping solutions were passed through. The stripping solutions were NaC1 and a mixed salt containing sodium chloride, sodium citrate and monobasic sodium phosphate. The parameters controlled in this investigation included concentration, temperature, flow rate and total volume. The optimum stripping technique was 30 by of 1 N NaC1 solution at a flow rate of 0.5 bv/min at 71 C. The stripping efficiency was approximately 96%. This technique was calculated to save approximately $1,380.00 in raw materials and operating costs per 45,500 liters of milk processed during each total capacity run at the commercial scale project when compared with the 2 ~ tIC1 stripping method.
Experimental Procedure
A number of laboratory studies (1-4, 9-11) have been made on the removal of radioiodine and radiostrontium from milk using ion exchange techniques. Based on a consideration of these studies, the U.S. Public IIealth Service and the U.S. Department of Agriculture have developed a standby ion exchange system to commercial scale (5-8, 12) for the removal of ~ I and '°Sr from raw whole milk. This system has two fixed bed columns. The first contains approxinmtely 265 liters of Dowex ~ 2 X-8 for iodine removal and the second approximately 1,370 liters of Amberlite IR-120 for strontimn removal.
Received for publication February 2, 1968. ~Present address: Chief Pharmacist, Madison Hospital, Madison, Tennessee.
The approach to these problems is given as follows : 1) Evaluate various inorganic salts or salt mixtures for ~ I stripping efficiencies. 2) Evaluate the effects of volume, temperature, concentration and flow rate on stripping efficiency. 3) Evaluate the ability of the anion exchanger to remove ~ I from milk after being stripped with the new agent, regenerated and rinsed. 4) Compare the chemical, operating and total costs for acceptable stripping agents. Materials. Approximately 500 ml of Dowex 2 X-8 20-50 mesh resin in the chloride form were placed in a column, 7.62-cm in diameter, and regenerated with 25 by, 0.16 bv/min, 25 C, of a infixed salt solution. This salt solution was composed of sodium chloride, sodium citrate and monobasic sodium phosphate (9). The column was rinsed with six bed volumes of deionized water, 25 C, 0.25 by/rain, and the resin was placed in an Erlenmeyer flask. A p proximately 8 t~Ci of ~ I (NaI) were added, mixed well and equilibrated overnight. The following morning 80-rot portions of resin were placed in 25-ram diameter, jacketed columns and rinsed as previously described. The salt stripping solutions were then passed through all the columns except one which was retained
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Mention of commercial products does not imply endorsement by the Public Health Service.
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WALKER, REHNBERG. AND BROOKS
as a control a n d deionized w a t e r was p a s s e d t h r o u g h i n s t e a d of salt solution. A p p r o x i m a t e l y 40 liters of r a w s k i m m i l k were p r o c u r e d f r o m t h e local m a r k e t , i n v i t r o spiked w i t h a p p r o x i m a t e l y 8 ~Ci of 1~I a n d e q u i l i b r a t e d o v e r n i g h t a t 5 C. The f o l l o w i n g m o r n i n g 160 by were p a s s e d t h r o u g h each of t h r e e columns c o n t a i n i n g u n l a b e l e d Dowex 2 X-8 a t 0.5 b y / r a i n a n d samples t a k e n f o r removal efficiency d e t e r m i n a t i o n s . Analytical methods. T h r e e 15-ml r e s i n samples were t a k e n f r o m each control a n d two f r o m each s t r i p p e d column. Two 15-ml s a m p l e s were t a k e n f r o m the o r i g i n a l labeled milk a n d the r e s i n t r e a t e d milk f r o m each column. The samples were c o u n t e d f o r ~1I activity, u s i n g the 0.364-mev e n e r g y peak, on a single c h a n n e l g a m m a s p e c t r o m e t e r a n d t h e p e r c e n t a g e s of activity r e m o v e d f r o m the s t r i p p e d ion exc h a n g e r a n d the r e s i n - t r e a t e d milk were computed. Results
Study 1. T h i s s t u d y evaluated the a n i o n e x c h a n g e r r e g e n e r a t i n g s a l t solution (hTaC1, Na~C~H~O~ a n d N a H ~ P O J used b y M u r t h y (9) a n d NaC1 as possible s t r i p p i n g a g e n t s f o r ~ I f r o m Dowex 2 X-8 resin. T h i r t y , f o r t y , a n d fifty bed volumes of the f o r m e r solution were p a s s e d t h r o u g h 80-ml r e s i n beds a t 0.125 b v / rain a t 25 C. The NaC1 was used 0.5, 1.0, 2.0
a n d 4.0 molarities a t 25, 43, 60 a n d 71 C, a t flow r a t e s of 0.125, 0.25 a n d 0.5 b y / r a i n a n d i n 10-, 20-, 30-, 40-, 50-, 60-, a n d 70-by q u a n t i t i e s as s h o w n in T a b l e 1. Study 2. The last s t u d y e v a l u a t e d the ability of the Dowex 2 X-8 to remove 1~1I f r o m r a w skimmilk, 0.5 b v / m i n a t 25 C, a f t e r h a v i n g been s t r i p p e d w i t h 30 b v of 2 ~ NaCI, 0.125 b v / m i n a t 71 C, r e g e n e r a t e d w i t h 25 b y of the a n i o n e x c h a n g e r r e g e n e r a t i n g salt solution a t 25 C, a n d 0.16 b y / r a i n . The r e s i n samples, w h i c h were t a k e n f o r the s t r i p p i n g efficiency d e t e r m i n a t i o n s , were r e t u r n e d to the respective columns b e f o r e r e g e n e r a t i o n f o r t h e n e x t milk run. This p r o c e d u r e was r e p e a t e d t h r e e times u s i n g t h e same identical r e s i n beds. F r e s h cont r o l r e s i n columns were p r e p a r e d as p r e v i o u s l y described f o r each run. The r e s u l t s are s h o w n in Table 2. S t r i p p i n g cost analyses f o r a commercial scale, fixed bed a n i o n e x c h a n g e r 64.8-cm diameter, column c o n t a i n i n g a p p r o x i m a t e l y 265 liters of Dowex 2 X-8 r e s i n a r e p r e s e n t e d i n Table 3. Discussion
T h e d a t a in Table 1 show t h a t ~VaC1 solution can be used to s t r i p 1~I f r o m Dowex 2 X-8 resin. T h e a n i o n e x c h a n g e r r e g e n e r a n t salt solution gave v e r y p o o r s t r i p p i n g efficiencies
TABLE 1. Stripping efficiency of 1~I from Dowex 2 X-8 20-50 mesh resin using anion exchanger regenerating salt and NaC1 solutions. Bed volumes of solution Stripping agent
Flow rate
Molarity Temp
(b v / m i n ) Anion exchanger regeneraat salt solution ~ NaC1 NaC1 ~TaC1 l~aC1 NaC1 I%TaC1 l~aC1 NaC1 :NaC1 NaC1 NaC] NaC1 ~qaC1 NaC1 ~aC1 NaC1
0.125 0.125 0.125 0.125 0.125 0.125 0.125 0.125 0.250 0.500 0.500 0.500 0.500 0.500 0.500 0.500 0.500
10
20
30
50
60
70
~I stripped
( C) . . . 25 . . . .b . . 4.0 43 56.4 88.3 2.0 25 34.2 62.7 2.0 43 60.0 87.1 2.0 60 68.0 95.0 2.0 71 81.1 97.0 1.0 71 ............ 0.5 71 ............ 2.0 71 2.0 25 29.4 53.6 2.0 43 44.5 73.9 2.0 60 63.0 90.4 2.0 71 69.6 94.1 1.0 25 17.6 38.0 1.0 43 30.6 60.1 1.0 60 42.0 78.7 1.0 71 52.5 86.0
40
(% ) 19.1 97.0 80.7 93.5 96.3 97.5 97.0 83.1 99.3 69.3 91.2 97.5 98.4 54.7 78.5 93.2 96.0
-
25.2 31.7 ............ 99.0 99.3 91.0 96.1 97.7 98.4 99.3 99.5 ............ 97.3 97.3 ............ 97.6 97.6 ............ ........................ ........................ 80.7 88.1 92.5 94.8 96.6 98.6 ............ ........................ 67.4 76.5 85.2 88.8 91.7 96.5 ............ ........................ ........................
~Regenerant solution contains a mixture of sodium chloride, sodium citrate and monosodium phosphate (3). b No determination. J. DAIRY SOIENC~ VO~. 51. NO. 9
STI~IPPING IODINE I31 TABLE 2. ~a~I removal from skimmilk and I)owex 2 X-8 20-50 mesh resin. ~ Iodine-
131
x3~I I~emoval
Col~ umn no.
inated materim
Run l'qumber 1
1 2 3 2 3
Milk l~Iilk Milk Resin Resin
97.4 97.4 97.8 99.5 99.5
contam-
2
3
Average
95.2 95.8 94.6 97.8 97.6
95.9
- - ( % ) - -
95.2 95.5 94.5 98.1 97.6
98.4
One hundred sixty bv of in vitro labeled skimmilk were passed through three columns, respectively. Colmnns were rinsed with deionized water, and two were stripped with 2 ~ NaC1. After regeneration with the Cl:PO~:C6H507 mixed salt solution, the columns were rinsed and reused in subsequent milk runs. and, therefore, was deleted f r o m f u r t h e r investigation. The 4 ~ NaC1 solution, 43 C, gave excellent ~ I r e m o v a l d a t a ( 9 7 - 9 9 % ) f o r 30-by q u a n t i ties a n d more, b u t did n o t show a n y p a r t i c u l a r a d v a n t a g e over 2 ~[ f o r equal q u a n t i t i e s of solution a t the same t e m p e r a t u r e . F o r this r e a s o n the 4 ~vx solution was n o t used f o r f u r t h e r investigations. A t room t e m p e r a t u r e (25 C ) , 50 b v of 2 ~ lfaC1, 0.125 b v / m i n , r e m o v e d a p p r o x i m a t e l y 9 6 % of the 1~1I f r o m the resin. The disadv a n t a g e of this p r o c e d u r e is t h a t 6.7 h o u r s
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were r e q u i r e d f o r completion. A t 43 C, 30 b v gave 9 3 . 5 % s t r i p p i n g efficiency; a t 60 C, 20 b y gave 9 5 % , a n d a t 71 C gave 97%. Therefore, i n c r e a s i n g the t e m p e r a t u r e , u s i n g the same c o n c e n t r a t i o n a n d flow rate, reduced the s t r i p p i n g time to 4 h o u r s f o r 30 by a n d 2.7 h o u r s f o r 20 by. A s the t e m p e r a t u r e increased, the a m o u n t of salt solution a n d s t r i p p i n g t i m e decreased. T h i s is i n a g r e e m e n t w i t h the findings of E a s t e r l y , et al. (3) t h a t f e w e r b y of H e 1 are r e q u i r e d f o r ~8~I r e m o v a l f r o m Dowex 2 X-8 with elevated t e m p e r a t u r e s . T h h ' t y bed volumes of 0.5, 1.0 a n d 2.0 NaC1 solution, 71 C, were used a t 0.125, 0.125 a n d 0.250 b y / r a i n flow rates, respectively. The 0.5 ~ gave a p o o r s t r i p p i n g efficiency ( 8 3 % ) . The r e m a i n i n g solutions gave 9 7 % or g r e a t e r removal a n d were, t h e r e f o r e , i n v e s t i g a t e d more extensively. The flow r a t e was increased to 0.5 b y / r a i n a n d 1 a n d 2 ~[ NaC1 solutions were used a t 25, 43, 60 a n d 71 C, respectively. The d a t a show t h a t a p p r o x i m a t e l y 9 4 % of the 1~*I can be s t r i p p e d f r o m Dowex 2 X-8 resin w i t h as little as 20 bv of 2 ~ NaC1 or a p p r o x i m a t e l y 9 6 % w i t h 30 b v o f 1 ~ a t 7 1 C . L o w e r i n g the t e m p e r a t u r e to 60 C caused a small decrease ( 3 - 4 % ) in s t r i p p i n g efficieneies. A t 43 C, 40 b v of 2 ~I or 50 bv of 1 ~t would be r e q u i r e d to achieve a p p r o x i m a t e l y 95.5% efficiency. A t 25 C, 70 by of 2 ~[ solution are r e q u i r e d f o r a p p r o x i m a t e l y 9 5 % efficiency, whereas 1 gives only a b o u t 89%.
TABLE 3. Estimated costs for stripping 131I from a commercial scale fixed bed, 64.8-cm diameter, column containing approximately 265 liters of Dowex 2 X-8 20-50 mesh resin used to process approximately 45,500 liters of raw whole milk. Stripping agent tIC? NaC1 NaC1 NaCI NaC1 NaC1 NaC1 NaC1 NaC1 NaCI NaCI NaCI Na.C1 NaC1
Molarity 2 4 2 2 2 2 2 2 2 2 1 1 1
1
Flow rate
]Bed volnines
(by/rain) 0.200 0.125 0.125 0.125 0.125 0.125 0.500 0.500 0.500 0.500 0.500 0.500 0.500 0.500
47.5 30.0 50.0 30.0 20.0 20.0 70.0 40.0 30.0 20.0 70.0 50.0 30.0 30.0
Stripping Temp time (C) 25 43 25 43 60 71 25 43 60 71 25 43 60 71
(hr) 4.0 4.0 6.7 4.0 2.7 2.7 2.3 1.3 1.0 0.7 2.3 1.7 1.0
1.0
Costs a :s~I stripped (%) 96.3 97.0 96.1 93.5 95.0 97.0 94.8 96.6 97.5 94.1 88.8 96.5 93.2 96.0
Chemical
Operating
Total
1305.00 ~ 554.00 d 461.70 277.00 184.69 184.69 646.39 369.38 277.00 184.69 323.20 230.85 ]38.50 138.50
($) 290.04 290.04 485.82 290.04 195.78 ]95.78 166.77 94.26 72.51 50.76 166.77 123.27 72.51 72.51
1595.04 844.04 947.52 567.04 380.47 380.47 813.16 463.64 349.51 235.45 489.87 354.12 211.01 211.01
Operating COSTS are derived from the commercial scale project (8) and include labor, utilities, depreciation, etc., but not raw materials. b Stripping agent was used by the commercial scale project (8). Includes 8190.25 for NaOtI to neutralize the acid before flushing down the sanitary sewer. d NaCI price estimates were taken from the 64C, Fisher Chemical Index, Fisher Scientific Company for U.S.P. grade material. J. DAISY SCIENCE VOL. 51. NO. 9
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WALKE~,REHNBE~G, AND BEOOKS
The second study (Table 2) shows that exCellent removal (approximately 96%) of in vitro labeled ~ I can be achieved f r o m skimmilk using Dowex 2 X-8 resin that was stripped with 30 by of 2 ~+ N~CI (98.4% efficiency), and regenerated with 25 by of the chloride: citrate: phosphat e mixed salt solution described previously. This removal efficiency is a p p r o x i m a t e l y the same as that found f o r whole milk in the commercial scale system (7). The data in Table 1 show that ~ I can be stripped f r o m Dowex 2 X-8 using NaC] solution at various temperatures, flow rates, concentration and bed volumes. The conditions of choice will be those giving the maximum s t r i p p i n g efficiency at the lowest cost. According to the final r e p o r t f o r the commercial scale p r o j e c t (8), the HC1 cost for a single run, processing 45,500 liters of milk was $1,114.75. A f t e r the s t r i p p i n g procedure, the acid was neutralized with N a O H before flushing into the sanitary sewer. The cost f o r this latter chemical was $190.25. The combined ]:IC1 and N a 0 t T costs ($1,305.00) are a p p r o x i m a t e l y 54% of the total costs ~or all the chemicals used in a single run. Table 3 is an ~s~I s t r i p p i n g cost analysis f o r the agents tiC1 and NaC1. The operating costs were derived f r o m the commercial scale p r o j e c t (8), and include labor, utilities, depreciation, etc., but do not include raw materials. Steam was used to heat the pasteurizer, etc., and was estimated to cost only $14.00 p e r operation. Differences in heating costs for the temperatures used (25, 43, 60 and 71 C) ~or the NaC1 stripp i n g solutions have been considered negligible in this investigation. The H C I has the highest chemical and total costs ($1,595.04). The most economical procedure to provide good s t r i p p i n g efficiency is to use 30 by of 1 )[ NaCl, 0.5 by/rain, 71 C, at a total cost of $211.01. This represents a savings of a p p r o x i m a t e l y $1,380.00 per s t r i p p i n g operation a f t e r processing 45,500 liters of raw whole milk. Conclusion
Sodium chloride has been found to be an effective s t r i p p i n g agent f o r the removal of ~+~I f r o m Dowex 2 X-80 20-50 mesh resin. This agent does not have the acute corrosive p r o p erties o£ HC1 and can be used with existing equipment in modern dairies. Sodium chloride is one of the most readily available and lowest priced salts on the market. This investigation indicates that NaCI is a better s t r i p p i n g agent than HC1. J. DAIRY SCIENCE ~¢+OT~.51, NO. 9
References
(1) Easterly, D. G., J. Y. Harris, L. A. Bunce, and L. F. Edmondson. 1963. Factors affecting the removal of radlostrontium from milk by ion exchange resins. J. Dairy Sci., 46 : 1207. (2) Easterly, D. G., L. F. Edmondson, J. K. Av~nts, and A. M. Sadler. 1964. Effects of type of acid and time between acidification and resiu contact on the removal of radiostrontium from milk. J+ Dairy Sci., 47 : 549. (3) Easterly, D. G., H. E. Walter, and L. ~. Edmondson. 1964. Effect of temperature of regenerant on removal of radionuelides from ion exchange resins. J. Dairy Sei., 47: 1263. (4) :Edmondson, L. ]~. 1964. Ion exehs~ge processes for removing radioactive contamination from milk. J. Dairy Sci., 47: 1201. (5) Fooks, J. IT., J. G. Terrill, Jr., B. H. t![einemann, E. J. Baldi, and H. E. Walter. 1967. Evaluation of full scale strontium removal system for fluid milk. Health Physics., 13: 279. (6) Heinemann, B., E. J. Ba]di, 1~. O. Marshall, E. M. Sparling, H. E. Walter, and J. H. Fooks. 1967. Large scale fixed bed ion exchange system for removi.ng strontimn-99 from fluid milk. II. Compositional studies. J. Dairy Sci., 50:426. (7) tteinemann, B., R. O. Marshall, E. M. Sparling, and R. ]~. Bales. ]967. Large scale combined anion-cation fixed bed system for the removal of radionuclides from milk. Unpublished results. (8) Marshall, R. O., E. M. Sparling, and B. ]~einemann. 1966. Investigation to determine the commercial feasibility and practicaJity of the combined anion-cation fixed resin bed system for the removal of radionuclides from milk. Yinal report. Producers Creamery Company, Springfield, Missouri. (Unpublished.) (9) Murthy, G. K., J. E. Gilchrlst, and J. E. Campbell. 1962. Methods for removing iodine-131 from milk. J. Dairy Sci., 45: 1066. (10) Murthy, G. K., arLd J. E. Campbell. 1964. l~emoval of radionuclides from milk. J. Dairy Sci., 47: 1188. (11) Murthy, G. K. 1965. /~emvoal of iodine-131 from milk. J. Dairy Sci., 48: 1429. (12) Spaxling, E. M., E. C. Baldi, 1~. O. Marshal], B. Heinemaan, H. E. Walter, and J. tI. ~ooks. 1967. Large scale fixed bed ion-exchange system for removing strontium90 from fluid milk. I. Processing results. J. Dairy Sci., 50: 423. (13) Walker, J. P., and B. F. Rehnberg. 1967. Studies on eleanlng techniques for io~ exchange resins used in the remora7 of radionuclides from milk. Unpublished results.
After the milk radionuclide decontamination process, the ion exchangers are prepared for reuse (13). Strontium-90 can be stripped from the cation exchanger with as little as nine bed volumes (by), 60 C, of mixed salt (NAG1, KC1, MgCI2 and CaCl~) regenerating solution (8, 12). The commercial scale project (7, 8) stripped the :~I from the anion exchanger with approximately 50 bv of 2 ~ ttCI at 25 C. The 2-x tiC1 stripping agent has two serious disadvantages. First, it is extremely corrosive to stainless steel equipment used in modern dairies. Second, HC1 is expensive. The purpose of this investigation was to find an efficient stripping agent that would not have acute corrosive action on stainless steel and would be low in price.
Abstract
This investigation was made to find an alternate stripping agent for the removal of ~ I from Dowex 2 X-8 20-50 mesh resin used to remove this nuclide from fluid milk. The agent currently utilized is 2 HC1, which has the disadvantages of causing extreme corrosion to the stainless steel equipment used in nmdern dairies and of being expensive. The chloride: citrate: phosphate charged resin was equilibrated over-night with Na ~ I and 8O-ml portions were placed in 25-ram diameter, jacketed eolmnns. The resin beds were rinsed with six bed volumes of deionized water, 0.25 bed volumes per minute, at 25 C and stripping solutions were passed through. The stripping solutions were NaC1 and a mixed salt containing sodium chloride, sodium citrate and monobasic sodium phosphate. The parameters controlled in this investigation included concentration, temperature, flow rate and total volume. The optimum stripping technique was 30 by of 1 N NaC1 solution at a flow rate of 0.5 bv/min at 71 C. The stripping efficiency was approximately 96%. This technique was calculated to save approximately $1,380.00 in raw materials and operating costs per 45,500 liters of milk processed during each total capacity run at the commercial scale project when compared with the 2 ~ tIC1 stripping method.
Experimental Procedure
A number of laboratory studies (1-4, 9-11) have been made on the removal of radioiodine and radiostrontium from milk using ion exchange techniques. Based on a consideration of these studies, the U.S. Public IIealth Service and the U.S. Department of Agriculture have developed a standby ion exchange system to commercial scale (5-8, 12) for the removal of ~ I and '°Sr from raw whole milk. This system has two fixed bed columns. The first contains approxinmtely 265 liters of Dowex ~ 2 X-8 for iodine removal and the second approximately 1,370 liters of Amberlite IR-120 for strontimn removal.
Received for publication February 2, 1968. ~Present address: Chief Pharmacist, Madison Hospital, Madison, Tennessee.
The approach to these problems is given as follows : 1) Evaluate various inorganic salts or salt mixtures for ~ I stripping efficiencies. 2) Evaluate the effects of volume, temperature, concentration and flow rate on stripping efficiency. 3) Evaluate the ability of the anion exchanger to remove ~ I from milk after being stripped with the new agent, regenerated and rinsed. 4) Compare the chemical, operating and total costs for acceptable stripping agents. Materials. Approximately 500 ml of Dowex 2 X-8 20-50 mesh resin in the chloride form were placed in a column, 7.62-cm in diameter, and regenerated with 25 by, 0.16 bv/min, 25 C, of a infixed salt solution. This salt solution was composed of sodium chloride, sodium citrate and monobasic sodium phosphate (9). The column was rinsed with six bed volumes of deionized water, 25 C, 0.25 by/rain, and the resin was placed in an Erlenmeyer flask. A p proximately 8 t~Ci of ~ I (NaI) were added, mixed well and equilibrated overnight. The following morning 80-rot portions of resin were placed in 25-ram diameter, jacketed columns and rinsed as previously described. The salt stripping solutions were then passed through all the columns except one which was retained
1373
Mention of commercial products does not imply endorsement by the Public Health Service.
1374
WALKER, REHNBERG. AND BROOKS
as a control a n d deionized w a t e r was p a s s e d t h r o u g h i n s t e a d of salt solution. A p p r o x i m a t e l y 40 liters of r a w s k i m m i l k were p r o c u r e d f r o m t h e local m a r k e t , i n v i t r o spiked w i t h a p p r o x i m a t e l y 8 ~Ci of 1~I a n d e q u i l i b r a t e d o v e r n i g h t a t 5 C. The f o l l o w i n g m o r n i n g 160 by were p a s s e d t h r o u g h each of t h r e e columns c o n t a i n i n g u n l a b e l e d Dowex 2 X-8 a t 0.5 b y / r a i n a n d samples t a k e n f o r removal efficiency d e t e r m i n a t i o n s . Analytical methods. T h r e e 15-ml r e s i n samples were t a k e n f r o m each control a n d two f r o m each s t r i p p e d column. Two 15-ml s a m p l e s were t a k e n f r o m the o r i g i n a l labeled milk a n d the r e s i n t r e a t e d milk f r o m each column. The samples were c o u n t e d f o r ~1I activity, u s i n g the 0.364-mev e n e r g y peak, on a single c h a n n e l g a m m a s p e c t r o m e t e r a n d t h e p e r c e n t a g e s of activity r e m o v e d f r o m the s t r i p p e d ion exc h a n g e r a n d the r e s i n - t r e a t e d milk were computed. Results
Study 1. T h i s s t u d y evaluated the a n i o n e x c h a n g e r r e g e n e r a t i n g s a l t solution (hTaC1, Na~C~H~O~ a n d N a H ~ P O J used b y M u r t h y (9) a n d NaC1 as possible s t r i p p i n g a g e n t s f o r ~ I f r o m Dowex 2 X-8 resin. T h i r t y , f o r t y , a n d fifty bed volumes of the f o r m e r solution were p a s s e d t h r o u g h 80-ml r e s i n beds a t 0.125 b v / rain a t 25 C. The NaC1 was used 0.5, 1.0, 2.0
a n d 4.0 molarities a t 25, 43, 60 a n d 71 C, a t flow r a t e s of 0.125, 0.25 a n d 0.5 b y / r a i n a n d i n 10-, 20-, 30-, 40-, 50-, 60-, a n d 70-by q u a n t i t i e s as s h o w n in T a b l e 1. Study 2. The last s t u d y e v a l u a t e d the ability of the Dowex 2 X-8 to remove 1~1I f r o m r a w skimmilk, 0.5 b v / m i n a t 25 C, a f t e r h a v i n g been s t r i p p e d w i t h 30 b v of 2 ~ NaCI, 0.125 b v / m i n a t 71 C, r e g e n e r a t e d w i t h 25 b y of the a n i o n e x c h a n g e r r e g e n e r a t i n g salt solution a t 25 C, a n d 0.16 b y / r a i n . The r e s i n samples, w h i c h were t a k e n f o r the s t r i p p i n g efficiency d e t e r m i n a t i o n s , were r e t u r n e d to the respective columns b e f o r e r e g e n e r a t i o n f o r t h e n e x t milk run. This p r o c e d u r e was r e p e a t e d t h r e e times u s i n g t h e same identical r e s i n beds. F r e s h cont r o l r e s i n columns were p r e p a r e d as p r e v i o u s l y described f o r each run. The r e s u l t s are s h o w n in Table 2. S t r i p p i n g cost analyses f o r a commercial scale, fixed bed a n i o n e x c h a n g e r 64.8-cm diameter, column c o n t a i n i n g a p p r o x i m a t e l y 265 liters of Dowex 2 X-8 r e s i n a r e p r e s e n t e d i n Table 3. Discussion
T h e d a t a in Table 1 show t h a t ~VaC1 solution can be used to s t r i p 1~I f r o m Dowex 2 X-8 resin. T h e a n i o n e x c h a n g e r r e g e n e r a n t salt solution gave v e r y p o o r s t r i p p i n g efficiencies
TABLE 1. Stripping efficiency of 1~I from Dowex 2 X-8 20-50 mesh resin using anion exchanger regenerating salt and NaC1 solutions. Bed volumes of solution Stripping agent
Flow rate
Molarity Temp
(b v / m i n ) Anion exchanger regeneraat salt solution ~ NaC1 NaC1 ~TaC1 l~aC1 NaC1 I%TaC1 l~aC1 NaC1 :NaC1 NaC1 NaC] NaC1 ~qaC1 NaC1 ~aC1 NaC1
0.125 0.125 0.125 0.125 0.125 0.125 0.125 0.125 0.250 0.500 0.500 0.500 0.500 0.500 0.500 0.500 0.500
10
20
30
50
60
70
~I stripped
( C) . . . 25 . . . .b . . 4.0 43 56.4 88.3 2.0 25 34.2 62.7 2.0 43 60.0 87.1 2.0 60 68.0 95.0 2.0 71 81.1 97.0 1.0 71 ............ 0.5 71 ............ 2.0 71 2.0 25 29.4 53.6 2.0 43 44.5 73.9 2.0 60 63.0 90.4 2.0 71 69.6 94.1 1.0 25 17.6 38.0 1.0 43 30.6 60.1 1.0 60 42.0 78.7 1.0 71 52.5 86.0
40
(% ) 19.1 97.0 80.7 93.5 96.3 97.5 97.0 83.1 99.3 69.3 91.2 97.5 98.4 54.7 78.5 93.2 96.0
-
25.2 31.7 ............ 99.0 99.3 91.0 96.1 97.7 98.4 99.3 99.5 ............ 97.3 97.3 ............ 97.6 97.6 ............ ........................ ........................ 80.7 88.1 92.5 94.8 96.6 98.6 ............ ........................ 67.4 76.5 85.2 88.8 91.7 96.5 ............ ........................ ........................
~Regenerant solution contains a mixture of sodium chloride, sodium citrate and monosodium phosphate (3). b No determination. J. DAIRY SOIENC~ VO~. 51. NO. 9
STI~IPPING IODINE I31 TABLE 2. ~a~I removal from skimmilk and I)owex 2 X-8 20-50 mesh resin. ~ Iodine-
131
x3~I I~emoval
Col~ umn no.
inated materim
Run l'qumber 1
1 2 3 2 3
Milk l~Iilk Milk Resin Resin
97.4 97.4 97.8 99.5 99.5
contam-
2
3
Average
95.2 95.8 94.6 97.8 97.6
95.9
- - ( % ) - -
95.2 95.5 94.5 98.1 97.6
98.4
One hundred sixty bv of in vitro labeled skimmilk were passed through three columns, respectively. Colmnns were rinsed with deionized water, and two were stripped with 2 ~ NaC1. After regeneration with the Cl:PO~:C6H507 mixed salt solution, the columns were rinsed and reused in subsequent milk runs. and, therefore, was deleted f r o m f u r t h e r investigation. The 4 ~ NaC1 solution, 43 C, gave excellent ~ I r e m o v a l d a t a ( 9 7 - 9 9 % ) f o r 30-by q u a n t i ties a n d more, b u t did n o t show a n y p a r t i c u l a r a d v a n t a g e over 2 ~[ f o r equal q u a n t i t i e s of solution a t the same t e m p e r a t u r e . F o r this r e a s o n the 4 ~vx solution was n o t used f o r f u r t h e r investigations. A t room t e m p e r a t u r e (25 C ) , 50 b v of 2 ~ lfaC1, 0.125 b v / m i n , r e m o v e d a p p r o x i m a t e l y 9 6 % of the 1~1I f r o m the resin. The disadv a n t a g e of this p r o c e d u r e is t h a t 6.7 h o u r s
1375
were r e q u i r e d f o r completion. A t 43 C, 30 b v gave 9 3 . 5 % s t r i p p i n g efficiency; a t 60 C, 20 b y gave 9 5 % , a n d a t 71 C gave 97%. Therefore, i n c r e a s i n g the t e m p e r a t u r e , u s i n g the same c o n c e n t r a t i o n a n d flow rate, reduced the s t r i p p i n g time to 4 h o u r s f o r 30 by a n d 2.7 h o u r s f o r 20 by. A s the t e m p e r a t u r e increased, the a m o u n t of salt solution a n d s t r i p p i n g t i m e decreased. T h i s is i n a g r e e m e n t w i t h the findings of E a s t e r l y , et al. (3) t h a t f e w e r b y of H e 1 are r e q u i r e d f o r ~8~I r e m o v a l f r o m Dowex 2 X-8 with elevated t e m p e r a t u r e s . T h h ' t y bed volumes of 0.5, 1.0 a n d 2.0 NaC1 solution, 71 C, were used a t 0.125, 0.125 a n d 0.250 b y / r a i n flow rates, respectively. The 0.5 ~ gave a p o o r s t r i p p i n g efficiency ( 8 3 % ) . The r e m a i n i n g solutions gave 9 7 % or g r e a t e r removal a n d were, t h e r e f o r e , i n v e s t i g a t e d more extensively. The flow r a t e was increased to 0.5 b y / r a i n a n d 1 a n d 2 ~[ NaC1 solutions were used a t 25, 43, 60 a n d 71 C, respectively. The d a t a show t h a t a p p r o x i m a t e l y 9 4 % of the 1~*I can be s t r i p p e d f r o m Dowex 2 X-8 resin w i t h as little as 20 bv of 2 ~ NaC1 or a p p r o x i m a t e l y 9 6 % w i t h 30 b v o f 1 ~ a t 7 1 C . L o w e r i n g the t e m p e r a t u r e to 60 C caused a small decrease ( 3 - 4 % ) in s t r i p p i n g efficieneies. A t 43 C, 40 b v of 2 ~I or 50 bv of 1 ~t would be r e q u i r e d to achieve a p p r o x i m a t e l y 95.5% efficiency. A t 25 C, 70 by of 2 ~[ solution are r e q u i r e d f o r a p p r o x i m a t e l y 9 5 % efficiency, whereas 1 gives only a b o u t 89%.
TABLE 3. Estimated costs for stripping 131I from a commercial scale fixed bed, 64.8-cm diameter, column containing approximately 265 liters of Dowex 2 X-8 20-50 mesh resin used to process approximately 45,500 liters of raw whole milk. Stripping agent tIC? NaC1 NaC1 NaCI NaC1 NaC1 NaC1 NaC1 NaC1 NaCI NaCI NaCI Na.C1 NaC1
Molarity 2 4 2 2 2 2 2 2 2 2 1 1 1
1
Flow rate
]Bed volnines
(by/rain) 0.200 0.125 0.125 0.125 0.125 0.125 0.500 0.500 0.500 0.500 0.500 0.500 0.500 0.500
47.5 30.0 50.0 30.0 20.0 20.0 70.0 40.0 30.0 20.0 70.0 50.0 30.0 30.0
Stripping Temp time (C) 25 43 25 43 60 71 25 43 60 71 25 43 60 71
(hr) 4.0 4.0 6.7 4.0 2.7 2.7 2.3 1.3 1.0 0.7 2.3 1.7 1.0
1.0
Costs a :s~I stripped (%) 96.3 97.0 96.1 93.5 95.0 97.0 94.8 96.6 97.5 94.1 88.8 96.5 93.2 96.0
Chemical
Operating
Total
1305.00 ~ 554.00 d 461.70 277.00 184.69 184.69 646.39 369.38 277.00 184.69 323.20 230.85 ]38.50 138.50
($) 290.04 290.04 485.82 290.04 195.78 ]95.78 166.77 94.26 72.51 50.76 166.77 123.27 72.51 72.51
1595.04 844.04 947.52 567.04 380.47 380.47 813.16 463.64 349.51 235.45 489.87 354.12 211.01 211.01
Operating COSTS are derived from the commercial scale project (8) and include labor, utilities, depreciation, etc., but not raw materials. b Stripping agent was used by the commercial scale project (8). Includes 8190.25 for NaOtI to neutralize the acid before flushing down the sanitary sewer. d NaCI price estimates were taken from the 64C, Fisher Chemical Index, Fisher Scientific Company for U.S.P. grade material. J. DAISY SCIENCE VOL. 51. NO. 9
1376
WALKE~,REHNBE~G, AND BEOOKS
The second study (Table 2) shows that exCellent removal (approximately 96%) of in vitro labeled ~ I can be achieved f r o m skimmilk using Dowex 2 X-8 resin that was stripped with 30 by of 2 ~+ N~CI (98.4% efficiency), and regenerated with 25 by of the chloride: citrate: phosphat e mixed salt solution described previously. This removal efficiency is a p p r o x i m a t e l y the same as that found f o r whole milk in the commercial scale system (7). The data in Table 1 show that ~ I can be stripped f r o m Dowex 2 X-8 using NaC] solution at various temperatures, flow rates, concentration and bed volumes. The conditions of choice will be those giving the maximum s t r i p p i n g efficiency at the lowest cost. According to the final r e p o r t f o r the commercial scale p r o j e c t (8), the HC1 cost for a single run, processing 45,500 liters of milk was $1,114.75. A f t e r the s t r i p p i n g procedure, the acid was neutralized with N a O H before flushing into the sanitary sewer. The cost f o r this latter chemical was $190.25. The combined ]:IC1 and N a 0 t T costs ($1,305.00) are a p p r o x i m a t e l y 54% of the total costs ~or all the chemicals used in a single run. Table 3 is an ~s~I s t r i p p i n g cost analysis f o r the agents tiC1 and NaC1. The operating costs were derived f r o m the commercial scale p r o j e c t (8), and include labor, utilities, depreciation, etc., but do not include raw materials. Steam was used to heat the pasteurizer, etc., and was estimated to cost only $14.00 p e r operation. Differences in heating costs for the temperatures used (25, 43, 60 and 71 C) ~or the NaC1 stripp i n g solutions have been considered negligible in this investigation. The H C I has the highest chemical and total costs ($1,595.04). The most economical procedure to provide good s t r i p p i n g efficiency is to use 30 by of 1 )[ NaCl, 0.5 by/rain, 71 C, at a total cost of $211.01. This represents a savings of a p p r o x i m a t e l y $1,380.00 per s t r i p p i n g operation a f t e r processing 45,500 liters of raw whole milk. Conclusion
Sodium chloride has been found to be an effective s t r i p p i n g agent f o r the removal of ~+~I f r o m Dowex 2 X-80 20-50 mesh resin. This agent does not have the acute corrosive p r o p erties o£ HC1 and can be used with existing equipment in modern dairies. Sodium chloride is one of the most readily available and lowest priced salts on the market. This investigation indicates that NaCI is a better s t r i p p i n g agent than HC1. J. DAIRY SCIENCE ~¢+OT~.51, NO. 9
References
(1) Easterly, D. G., J. Y. Harris, L. A. Bunce, and L. F. Edmondson. 1963. Factors affecting the removal of radlostrontium from milk by ion exchange resins. J. Dairy Sci., 46 : 1207. (2) Easterly, D. G., L. F. Edmondson, J. K. Av~nts, and A. M. Sadler. 1964. Effects of type of acid and time between acidification and resiu contact on the removal of radiostrontium from milk. J+ Dairy Sci., 47 : 549. (3) Easterly, D. G., H. E. Walter, and L. ~. Edmondson. 1964. Effect of temperature of regenerant on removal of radionuelides from ion exchange resins. J. Dairy Sei., 47: 1263. (4) :Edmondson, L. ]~. 1964. Ion exehs~ge processes for removing radioactive contamination from milk. J. Dairy Sci., 47: 1201. (5) Fooks, J. IT., J. G. Terrill, Jr., B. H. t![einemann, E. J. Baldi, and H. E. Walter. 1967. Evaluation of full scale strontium removal system for fluid milk. Health Physics., 13: 279. (6) Heinemann, B., E. J. Ba]di, 1~. O. Marshall, E. M. Sparling, H. E. Walter, and J. H. Fooks. 1967. Large scale fixed bed ion exchange system for removi.ng strontimn-99 from fluid milk. II. Compositional studies. J. Dairy Sci., 50:426. (7) tteinemann, B., R. O. Marshall, E. M. Sparling, and R. ]~. Bales. ]967. Large scale combined anion-cation fixed bed system for the removal of radionuclides from milk. Unpublished results. (8) Marshall, R. O., E. M. Sparling, and B. ]~einemann. 1966. Investigation to determine the commercial feasibility and practicaJity of the combined anion-cation fixed resin bed system for the removal of radionuclides from milk. Yinal report. Producers Creamery Company, Springfield, Missouri. (Unpublished.) (9) Murthy, G. K., J. E. Gilchrlst, and J. E. Campbell. 1962. Methods for removing iodine-131 from milk. J. Dairy Sci., 45: 1066. (10) Murthy, G. K., arLd J. E. Campbell. 1964. l~emoval of radionuclides from milk. J. Dairy Sci., 47: 1188. (11) Murthy, G. K. 1965. /~emvoal of iodine-131 from milk. J. Dairy Sci., 48: 1429. (12) Spaxling, E. M., E. C. Baldi, 1~. O. Marshal], B. Heinemaan, H. E. Walter, and J. tI. ~ooks. 1967. Large scale fixed bed ion-exchange system for removing strontium90 from fluid milk. I. Processing results. J. Dairy Sci., 50: 423. (13) Walker, J. P., and B. F. Rehnberg. 1967. Studies on eleanlng techniques for io~ exchange resins used in the remora7 of radionuclides from milk. Unpublished results.