surface areas exposed to heating. The above effect may be due either to the adsorption and desorption of vapors or to the presence of thermomolecular forces. I n any event, no undue difficulty was encountered in reducing the dip size to the equivalent of 10 to 40 y ; with great care, the remaining dip may be suppressed. APPLICATIONS
The above balance has been utilized in gas adsorption studies for nearly 2 years. At all times it has exhibited reproducible behavior, and has required recalibration only when the magnetic compensation solenoid has been removed and replaced. The balance has been used to study physical adsorption of oxygen and nitrogen on various titanium dioxide powders a t 78” K. A typical ouygen adsorption isotherm on rutile is shown in Figure 6. After 5200 y of oxygen had been adsorbed, the pressure was 1oTYered; this resulted in the desorption of oxygen. The balance ultimately returned t o its original null position within experimental error. Typical isotherms relating to oxygen sorption on commercial titanium dioxide samples a t 504’ C. are presented in Figure 7 . The dots and triangles for the anatase curve were obtained using two aliquot samples from the
same lot. The maximum total uptake on these samples was 23.0 and 61.3 y, respectively; inspection shows that the two runs agree within experimental error. The total uptake for sample melting point 980-5 was 13.8 y. Currently the balance is being utilized to study the composition of praseodymium oxide as a function of temperature and oxygen pressure. KO attempt has been made thus far to increase the sensitivity of the instrument to its limit by raising the center of gravity.
(5) Cini, R., Sacconi, L., J . Sci. Znstr. 31, 56 (1954). (6) Cunningham, B. B., Nucleonics 5 ,
62 (1949). ( 7 ) Dar. A. G.. J . Sci. Znstr. 30, 200 (‘lb53). ‘ Johnston, E. W.
(12) (13)
ACKNOWLEDGMENT
The authors wish to express their appreciation to A. Y. Gerritsen and D. H. Damon, who are undertaking parallel investigations a t the Department of Physics a t Purdue University, for many helpful discussions and suggestions. The authors are likewise indebted to Edward Fagen of the Physics Department for help in the preparation of the tungsten tips. LITERATURE CITED
(1) Barrett, H. 11., Biinie, A. IT., Cohen. 11.. J . .4m. Chem. SOC. 62, 2859 ( 1 h O ) . (2) Beams, J. IT.,Rez). Sci. Znstr. 21, 182 (1950). (3) Bradley, R. S., J . Sci. Znsfr. 30, 84 (1953 ). (4) Carmichael. H.,C a n . J . P h y s . 30, 324 (1952).
(14)
(15)
(16) (17) (18)
krd Ed.. o.-271. Reinhold: New York, 19iK Lowr,B. W., Richards, F. &I.,Yuture 170, 412 (1952). McBain, J. IT.,Bakr, iZ. W., J . Am. Chem. SOC. 48,690 (1920). McBain, J. IT., Tanner, H. Y., Proc. Roy. Soc. (London) A 125, 579 (1929). Partington, J. R., “Advanced Treatise of Physical Chemistry,” Yol. 1, pp. 753-754, Longmans, Sew Tork, 1949. Rodder, J., Microtech Services Co., Berkelev, Calif., personal communication. Simons, J. H., Scheiier, G. L., Jr., Ritter, H. L , Rev. Sei. Znstr. 24, 36 (1953). R’eissberger, A , , ed , “Physical 1Iethods of Organic Chemistrv,” 2nd ed., Vol, 1, pp. 279-280, Interscience, S e w York, 1949.
RECEIVED for review October 11, 1956. Accepted February 23, 1957. Division of Analytical Chemistry, 130th meeting, ACS, Atlantic City, N. J., September 1056. This work was supported by a grant from the Research Corp.
Determination of Low Concentrations Radioactive Cesium in Water BERND KAHN’, DAVID K. SMITH, and CONRAD
P.
STRAUB2
Oak Ridge National laborafory, Union Carbide Nuclear Co., Oak Ridge, Tenn.
b Three methods for determining small amounts of radioactive cesium in water are presented. Radioactive cesium, with milligram quantities of cesium chloride carrier, i s precipitated as cesium ammonium phosphomolybdate, coprecipitated with sodium potassium cobaltinitrite, or concentrated on a cation exchange resin from liter volumes of water, and then purified b y established radiochemical procedures. Studies with radioactive tracers indicate satisfactory chemical yield, tracer recovery, and decontamination from long-lived fission products. After development, the methods were used to determine radioactive cesium in river water in concentrations between 1 O+ and 1 OP8 microcurie per ml. 12 10
ANALYTICAL CHEMISTRY
XXBER of procedures .for determining low concentrations of radio-. active c&um in water have been studied to permit determination of the path of long-livcd cesium-134 and -13i which are discharged into a stream from the Oak Ridgc Sat’ional Laborat,ory. The proccdurrs w r e ncedrd to obtain more accurak analyscs in the concentration range of 10-4 to 10-8 microcurie per i d . than arc possiMc with prcsent methods (S!11. 1 5 ) . Thc nerisitiT-ity of the present methods--\\-hicli are not intended to be uscd for lo^ levcl analys~s-is limited by t8hr small (1- to 10-ml.) sample volumes irnposcd by the relatiwly large solubility of the cc>siumprecipitates used for srparation, and by the small weight of cesium carrier required for efficient beta counting.
The methods studied were suggested by those used for determining other radionuclides in small concentrations, such as absorption on ion exchange resin combined with continuous counting of the resin (?), coprecipitation of insoluble hydrouides with aluminum hydroxide (I). and coprecipitation of barium and strontium with calcium carbonate ( I O ) from large volumes of mater. TT’hile concentration by evaporation (6) is common, including the use of ingenious pipetting devices xhich permit evaporation of large volumes on a 1 U. S. Public Health Service, assigned to Oak Ridge National Laboratory. Present address, Robert A. Taft Sanitary Engineering Center, C . S. Public Health Service, Cincinnati, Ohio.
small planchet (14),evaporation was not considered because it is time-consuming, requiring approximately 8 hours to reduce 1 liter of slightly acidified water to 20 ml. b y careful heating. Considered for cesium determination n-ere precipitation from liter volunies of \T ater of relatively insoluble cesium ammonium phosphomolybdate, mixed cesium sodium potassium cobaltinitrite, and cesium and potassium tetraphenj-lborate (9, 19, 16) and the absorption of ccsium on an ion exchange resin and subsequent elution by a small volume of acid. The methods found effective n ere combined n ith a decontaniination and tested procedure in current usf (j), with radioactive cesium tracer and nith a niixturc, of long-lived fission products. They w r e usrd thcn in the analysis of laboratory cfflucnt containing radioactive ccwuni. EXPERIMENTAL
The water samplcls consisted of 1liter volumcs of Oak Ridge tap water or Clinch River tvatcr (cach containing approximately 30 mg. per liter of calcium plus magnesium and 7 mg. per litcr of sodium plus potassium ions), and saniples of a w r y soft water (6.5 nip. per liter of calcium plus magnesium and 12 mg. per liter of sodium plus potassium) and of a v u > -hard water (146 mg. per liter of calcium plus magnesium and 3i-1 mg. per litcr of sodium plus potassium) j the lat,tcr tvio were syntheses of August's, Ga., and Kichita, Kaii.. water, rcqectirel>- ( 2 ) . The water was acidified with 1 ml. of 1 M hydrochloric acid to prcvent absorption of cesium on the container nalls. T o cach water saniplc, were added knorvn quailtitics of radioactive cesium137 traccr (obtained as the chloride from th(1 Opcrations Division, Oak Ridge S:ttion:rl Lalioratory), and of cesium chloridr carriibr (approximately 20 nig.). Tlir ccsiuni carricsr \vas precxipitatcid :it the end of the procedure as cesium perc,hlorate, weighed to determine the fraction of cesium lost during analysis, and counted to determine its activity. The activity of the original sample was then calculated by correcting for the lost cesium. The radioactive cesium was detect'cd with an endwindow Geiger-lluller beta counter or a sodium iodide gamma scint'illation counter. Precipitation of cesium as a phosphomolybdate, cobaltinitrite. or tetraplienylborate vas studied with the intention of obtaining a rapidly settling precipitate using readily available reagents. Rccausr radiochemical analysis includes the dcterminatiori of loss of cmricr in analysis, no attempt was made to recowr ccsium quantitatively, though :t relati\-ely high recovery was desired in order to obtain a satisfactory cesium count rate. The amount of reagents used \vas held to the minimum required for consistent results to aroid contami-
nating the final cesium perchlorate precipitate with other ions, especially other alkalies. Concentration of the cesium on a n ion exchange resin \vas studied to determine the amount of resin, colunin dimensions, and flow rate for efficient retention of cesiuni from 1 liter of water. A number of elutriants kvere tested in order to obtain one which would remove the cesium from the resin in a relatively small volume. After the cesium precipit,atrs had been dissolved or the cesium eluted from the resin. cesium n-as separated from contaminating ions. bot'h radioactive and stable. by silicotungstatc. and perchlorate precipitations and by scavenging precipitations for the cont,aniinants. Decontamination \vas deterniincd b y substituting for thc cesium traccr a mixturc of strontium-90, yttrium-90, cerium-144, ruthenium-106, zirconium95, and niobium-95, each constituent' having approximately thc saiiiC count rate. The perchlorate precipitate \vas also analyzed for sodium. potassium, phosphorusj molybdenum. lcad, and cobalt impurities. The folloxing proccdurrs ~ v c w developed. Phosphomolybdate Procedure. To a 1-liter sample in a 1500-nil. beaker, add cesium carrier, 50 nil. of nitric acid, and 40 ml. of ammonium molybdate solution [lo0 mg. of aninionium molybdate tetrahydratc, (SHI)&oiO?~.4 H 2 0 per ml.]. Heat to 50" C., add 0.5 ml. of phosphoric acid, and stir until dense yellow cesium ammoilium phosphomolybdate precipitates (10 to 15 minutes). Let precipit'atc stand a t least 4 hours, then decant all hut 40 nil. of the supernatant solution. Transfer precipitate t o a 50-nil. gl fuge tube with remaining solution, centrifuge, and discard t'he supernatant solution. K a s h t'he prec+~itatewith trvo 20-ml. portions of 1M nitric acid. Dissolve the prccipitatc in 1 nil. of ammonium hydroxide and 20 nil. of water and add 6M nitric acid dropwise to t,he phcnolphthalcin end point. Stir and let the solution stand several minutes to dissolve the prrc-ipitati. which forms. Heat the solution to boiling and add 1 nil. of acctic acid and 5 nil. of lead acetate solution [150 nig. of lead acet'ate trihydrate, Ph(C?HaO&.3H20 per nil.) ] to precipitate lcad molybdate. Centrifugr: and discard thc precipitate. Seutralize the. solution to the phenolphthalein end point with ammonium hydroxide and add 1 nil. of saturat'ed ammoniuni carbonatc solution to precipitate lcad carbonate. Ccntrifuge and discard the prccipitatc. Dccant, the solution into an Erlrnnieyer flask, heat to dryness, and flanic to rrniov(~ammonia. Take up cesiuni in 2 nil. of n-ater and 5 ml. of 707, perchloric acid. Heat until dense perchloric acid fumes appear, and continue heating for several minutes. Transfer the solution to a glass centrifuge tube and cool in an ice
bath. Add 15 ml. of absolute alcohol, let stand several minutes to precipitate cesium perchlorate, and centrifuge. K a s h the precipitate with two 15-ml. portions of absolute alcohol. Transfer the precipitate to a Hirsch funnel with 5 ml. of absolute alcohol and filter on tared Whatman No. 1 paper. K a s h and dry with three 5-ml. portions of absolute alcohol. Weigh and count the precipitate. Cobaltinitrite Procedure. T o a 1liter sample in a 1500-ml. beaker, add cesium carrier, 10 ml. of acetic acid, 8 ml. of cobaltous chloride solution (500 nig. of cobaltous chloride hexahydrate, CoC'l,. GH20per ml.), 1 ml. of potassium chloride solution (400 mg. of potassium chloride p t r ml.), and 80 ml. of sodium nitritc solution (500 mg. of sodium nitrite pc'r ml.). Cool to 5" C. and stir occasionally until the orange cobaltinitrites of sodium, potassium, and cesium precipitate. Let the precipitate sctt,lv for 3 hours: then decant all but 40 ml. of the supernat,ant solution. Transfer the precipitat'e to a 50-nil. glass centrifuge tube with the remnining solution, centrifugc, and discard the supernatant solution. Wash the prrcipitatc n-ith three 20-1111. portions of cold 1OYo acctic acid. Dissol\-(, thc prccipitate by heating with 20 inl. of 6M h>-drochloric acid. Add 1 nil. of 0.125M silicot,ungsticacid to precipit,atc. cesium silicotungstatc, cool, and centrifugcl. K a s h precipitate with three 20-ml. Tiortione of 6M livdrochloric acid. Dissolve the silicotunestate wrcvinitate b y heating with 2 d o f 6Msodi;m hydroxide and 5 ml. of water. Add 10 ing. of fcrric nitrate to precipitate fcrric hydroxide scavcnger. Centrifuge, and discard thc prccigit,ate. Ilecant solution into a glass cmtrifuge tube, add 20 nil. of 707, pcxhloric acid (white silicon dioxick prccipitatc.s), and heat almost to boiling ( y ~ l l o wtungsten trioxide prrcipitatc3s). Centrifuge and discard the prc,c$it,ate. Decant t'he solution into an Erlcnmcycr flask, heat until dmse perchloric acid fumes appear, and continuc hcating for several minutes. Transfclr thc solution to a glass ccntrifugc tub(. and cool in an ice bath. Add 20 nil. of absolute alcohol and let stand s c ~ c ~ minutes al to precipitate cesium perchlorate (as ~ w l las sodium perchlorat(,)! and centrifuge. Wash the prccipitatr with three 15-ml. portions of cold a1)solute alcohol to dissolve sodium pcrchlorate; filter, wish, and dry the prrcipitatr. Ion Exchange Procedure. JTeigh 5.00 grains (moist weight) of Dolvexj 0 resin (50 t o 100 nicsh. 907, nioisture, hydrogcn c!-c.lc), and fill a 1.0-cm. (inner diamclter) glass column. Wash t h r rcsin ivitli 20 nil. of 1JI hydrochloric acid and n-ith 100 ml. of distilled n-at,er. Add ccsiuni cwrier to a 1-liter saniplc of \ v a t u and let the saniplc run through the rcsin ( d u n i n a t rate of 5 ml. per minute. Slowly clutc cesium from the colunin xvith 20 ml. of 6-V hvdroohloric acid. ,4dd 1ml. of 0.125M s thc eluate to precipitate cesium silicoVOL. 29, NO. 8, AUGUST 1957
1211
tungstate, and then follon- the procedure given in the cobaltinitrite method. RESULTS
Seither cesium nor a combination of cesium and potassiuni tetraphenylboron settled under the conditions reported to be most favorable for precipitation (8); hence this precipitation was not considered further. Although the phosphomolj bdate settled completely in approYimatelJ- 12 hours. decanting after 4 hours resulted in a cesium loss of only l5Y0, and \vas considered feasible. The phosphoinolybdate precipitate does not form in thc absmce of cesium, and appears to have a consistent cesium -ammonium -phosphorus -molybdenuin ratio of 1.S: 1 2 : 1 0: 12.0. The cobaltinitrite precipitate was well settlpd after 3 hours, and the supernatant solution could be readily decanted. The cesium-potassium-sodium-cobalt ratio !vas 0.1 :2.0:0.9: 1.0 and the constancy of its potassium-sodium-cobalt ratio in the absence of cesium ,uggested that the cesium is carried on tlic potassium and sodium. The cobaltiriitrite preciyitate
Table I.
Radionuclide Cesium-l3T
\f-ater Sample Oak Ridge
carried 9 i % of the cesium in the sample, and the phosphomolybdate contained 93%. The 5 grams of ion exchange resin retained more than 99.9% of the cesium in 1 liter of mater, but no additional cesium after 1200 ml. of t a p water had passed through the column. Varying the amount of calcium chloride in the influent water indicated t h a t cesium breakthrough occurred because of displacement by calcium, and that the capacity of the resin for cesium was inversely proportional to the calcium concentration in the lyater. Elution of the resin column \\as 99 7% complete with 20 ml. of 6M hydrochloric acid. The results of cesium tracer studies lvith the various m t e r samples are listed in Table I. The differences betn-een recovered and added tracer, after the foriner had been corrected for carrier yield (60 to io%), were xithin the probible error of counting (1% for each count rate) and 11-eighing (0.5%), indicating good interchange of carrier and tracer, and little contamination of the final precipitate by stable substances.
Tracer Study of Cesium Procedures
Method Phosphomolybdate Cobaltinitrite Ion exchange
ilctivity -4ctivity Added, Recovered Counts/ Counts/ Minute Minute Deviation, % 6,750 6,630 -1 8 6,750 6,830 +I2 92,800 91,300 -1 6
\Tic hi ta Phosphomolybdate ( s p t het ic ) Cobaltinitrite
20,000 20,000
20,400 19,700
$2.0 -1.5
Augusta Phosphomolybdate (synthetic) Cobaltinitrite
20,000 20,000
19,800 20,400
-1.0 $2.0
102,000 99 700 102,000 99,100 102,000 104,600
-2.3 -2.8 $2.5
Clinch River Phosphomolybdate Cobaltinitrite Ion eschange Mixed fission Oak Ridge products
Table 11.
Phosphomolybdate Cobaltinitrite Ioneschange
59,200,000 25,900,000 59,200,000
2,200 260 2,100
... ...
Cesium Concentrations in Effluent Water
Sample Settling basin
Procedure Phosphomolybdate Cobaltinitrite Ion exchange
White Oak Lake
Phosphomolybdate Cobaltinitrite
Clinch River Mile 14.4 (6.4 miles belonwaste entrance)
Phosphomolybdate Cobaltinitrite
Clinch River Mile 4.5 (16.3 miles below waste entrance) Ratio of count rate
Phosphomolybdate Cobaltinitrite Ion exchange
1212
~
Gross Beta Count, Counts per Minute per Ml. 37 i 2
to disintegration rate is 0.07.
ANALYTICAL CHEMISTRY
13
i3
1 7 f 0.7
