Determination of Radium in Residues Dissolution of Sample i n Condensed Phosphoric Acids C . A. WAMSER, EDWARD B E R N S O H N , R. A. KEELER, AND JOHN ONACKI Vitro Corp. of America, Jersey City, A'. J.
most accurate method for radium assay is the emanation T technique, in which the radon generated by the radium is separated, collected, and measured. However, a much more rapid
precipitation by sulfate. The polyphosphoric acid salts of these metals are undoubtedly formed by the progressive dehydration of the orthophosphoric acid, which yields condensed phosphoric acids ( 2 ) :
HE
method for radium, suitable for much practical work, is based on the coprecipitation of radium on barium chloride carrier followed by alpha counting ( 1 ) . Application of this rapid radiometric method requires the radium in solution, and common practice in the preparation of samples of gangues (which may contain silica, barium, and lead sulfates and other oxides and sulfates) usually involves either A or B:
&Po4
+H4P207 +HjP3010+ (HP03)6
Furthermore, those condensed phosphoiic acids which are formed a t temperatures in the range of the boilingpoint of sulfuiic acid, probably initiate the displacement and eventual volatilization of the sulfate:
+
H6P3Ol0 BaSOl --+Ha[BaP30:0]
-4. Preliminary leaching with hot ammonium acetate (to remove some of the lead sulfate), followed by hydrofluoric acidsulfuric acidltreatmentfor silica removal, fusion:of the ignited residue ~ i t sodium h carbonate, extraction of the melt n-ith water, and separation of the barium-radium-lead carbonates. The thoroughly xvashed carbonates are dissolved in dilute hydrochloric acid and an aliquot portion of the solution is taken for analy5is. B. Ignition of the sample with a n excess of zinc dust (effecting reduction to sulfides), folloffed by leaching with dilute acid, treatment of the insolubles with hydrofluoric acid, and dissolution of the residue in acid (3). An aliquot of the combined solutions is taken for analysis.
+ H2S04t
Although the radium is present in the prepared solution largely as an anionic polyphosphate complex, it was not found necessary to decompose these coinplexes prior to the precipitation of the radium as its chloride-as, for example, by boiling the solution to rehydrate all the phosphates to the ortho form. Presumably, in the presence of a skfold excess of 12 S hydrochloric acid, all the radium is cationically available:
+ 2H+ % R a + + + [ H ~ P ~ O 1 ~ ] - - -
RaP,Olo---
The method described ivas developed to facilitate the preparation of such gangue and residue samples for analysis by the rapid radiometric procedure; in one operation, silica, excess hydrofluoric acid, and sulfate are volatilized and the resultant material is completely ivater-soluble.
RESULTS OBTAINED
The rapid radiometric assay of radium is described ( 1 ) as being sensitive to gram of radium (the specific alpha activity of radium is 2.165 X 1 O I 2 counts per minute per gram) and capable of 3 to 10% accuracy. The method affords separation of radium from all other a-emitting substances accompanying it in nature ( 1 ) ; hence this phase of the determination involves no interfprences. [Data presented by Smes et nl. indicated that less than 0.05% of the following elements are carried on baiium chloride when this procedure is used : uranium, protactinium, thorium, polonium, and bismuth.]
REAGENTS
Orthophosphoric acid, 85%, reagent grade Hydrofluoric acid, 48%, reagent grade Hydrochloric acid-ether solution, 6 volumes of 12 S hvdiochloric acid and 1 volume of ethyl ether Barium chloride solution, 1.5 Jf PROCEDURE
Up to 0.5 gram of the sample is accurately weighed and transferred to a 30-ml. platinum crucible. Approximately 10 ml. of 85% orthophosphoric acid and 3 to 5 ml. of 48% hydrofluoric acid are added, and the crucible is heated gradually so that gentle boiling of the contents is maintained. JVhen silica and most of the excess hydrofluoric acid have been volatilized (volume of the residual charge about 7 ml.), the mixture is gradually brought to a dull red heat and maintained a t this temperature for 15 to 30 minutes, or until a clear viscous, fuming liquid is obtained. The cooled glassy melt is dissolved in about 50 ml. of n a t e r and the solution is diluted to some convenient volume-Le., so that 1 ml. will contain 10-10 to 10-8 gram of radium. A I-ml. aliquot of this solution is transferred to a 15-nil. graduated centrifuge tube, and about 0.05 ml. of 1.5 Jl barium chlolide is added (equivalent to about 10 mg. of barium). If the aliquot taken for analysis contains more than a few milligrams of barium, proportionately less 1.5 AI barium chloride should be added. Then 7 ml. of cold (0' C.) 6 to 1 hydrochloric acid-ether is added, the mixture is stirred, and the precipitated barium-radium chlorides (monohydrates) are handled as described by Ames et al. ( 1 ) . The alpha activity of the barium-radium mixture may conveniently be determined in a parallel plate counter, a methane-argon proportional counter, or the more newly developed scintillation counter.
Table I.
Recovery of Added Radium
(HF-HIPOI dissolution followed by BaC12. H20 carrier precipitation) Increased a Actirity Due t o Added Radium Added, Counting Rate, Samule Grams X 1010 CounWMiIin. Radium Residue 1 Sone 411 5 733 322 Residue 2
None s
322 622
300
Residue 3
Sone 5
378 675
297
Residue 4
Iione 5
563 864
301
Residue 5
None 5
309 613
301
Residue 6
None 5
150 489
339 Average 310 =k 13
The influence of self-absorption-i.e., absorption of the radium alpha particles within the deposit with a resultant decrease in the counting rate-was also quantitatively estimated by Ameslet al. ( 1 ) . This was accomplished by adding to counting plates a constant amount of radium and variable amounts of barium, preparing the deposits as usual, and counting. A plot of counting rate
DISCUSSION
The glassy melts obtained are soluble in water, and the resultant solutions presumably contain the radium, barium, lead, etc., in the form of anionic complexes-e.g., Ba2PsOls--or BaP3OI0---(4). Thus, the barium in such solutions is found to be masked against 821
828
ANALYTICAL CHEMISTRY
against milligrams of barium, extrapolated to zero barium, enabled the relative self-absorption factor (unity a t barium equals zero) to be estimated as a function of the amount of barium used. The relative self-absorption factor a t 10 mg. of barium corresponds to about 0.85. It was estimated from these data that the variations in counting rate that might be expected from the normal variations of the amount of barium carrier used in a series of determinations, would be negligible when compared with the average error in duplicated analyses.
Table 11. Determination of Radium (By HF-HsPOd dissolution followed by BaC1z.HzO carrier precipitation) Weight of Sample in Aliquot Taken, Gram
Sample Gangue 1l a BaSOa-RaSOr from gangueC BaSOrRaSOrd R a standard 10-9 gram Ra
a
Counting Rate, Counts/Min.
0.002 0.002 0,007 0.002
$}: ):;:
4080
Ra, % X 106
4.0b 33.8 1.0
601 e 612f sanf 5 X 10-0 gram Ra 3011 e 3035’ a 11.8% Basor, 2.2% PbSO4, 17.0% PbCOa, 56.0% SiOz, 5.5% RzOI,etc. Emanation method 3 6 X % Ra. . C Gangue 1 leached h h concentrated HzSO4; solubilized Ba. Ra repptd. by dilution. From BaClr and Bur. Standards RaCIz. coprecipitated as sulfates to contain 10-7 gram Ra per gram BaSOr. IThrough entire procedure. f Through the carrier precipitation only. I--
The method described comprises a rapid preparation of certain samples for the radiometric assay and was found capable of quantitative solution of the radium in a variety of materials. Known amounts of radium (from standard solutions prepared by diluting the contents of National Bureau of Standards radium ampoules) added to various samples, and carried through the entire procedure, were recovered to within 10%.
Because the geometry and influence of self-absorption and back-scattering are dependent on the type of counting instrument and planchet used, the counting rates of samples were related to radium content by means of a factor determined under the same conditions for known amounts of radium. Typical results obtained are summarized in Tables I and 11. Although hot polyphosphoric acids are highly corrosive, no difficulty with platinum ware was experienced. Over 200 hydrofluoric acid-phosphoric acid fusions were effected during the project without injury to any of the platinum ware. It is recommended, however, that residues containing both organic matter and lead sulfate be pretreated with nitric acid-sulfuric acid before the addition of hydrofluoric acid and phosphoric acid. Mechanical losses of radium during the vigorous volatilization operations were found to be negligible in comparison to the observed duplicability of determinations. This was established in a series of experiments in which a constant amount of radium was added to three samples of a residue. These were treated with a mixture of hydrofluoric, sulfuric, and phosphoric acids, and fluorine and sulfur were expelled by volatilization after one, three, and five such treatments. The amount of radium recovered from the final melts was constant within 5 % . LITERATURE CITED
(1) Ames, D. P., Sedlet, J., Anderson, H. H., and Kohlman, T. P., “Rapid Radiometric Assay for Radium and Application to Uranium Ore Process Solution,” Paper 22.70, pp. 1700-16 in “The Transuranium Elements,” Part 11, IV-14B, New York, McGraw-Hill Book Co., 1949. (2) Bell, R., Ind. Eng. Chem., 40, 1464 (1948). (3) Fineman, P., Weissbourd, B. B., Anderson, H. H., Sedlet, J . , Ames, D. P., and Kohlman, T. P., “An Emanation Method for Radium Analysis,” Paper 16.7, pp. 1206-25 in “The Transuranium Elements,” Part 11,IV-14B, New York, McGraw-Hill Book Co., 1949. (4) Yost, D., and Russell, H., “Systematic Inorganic Chemistry,” p. 221, Sew York, Prentice-Hall, Inc., 1944. RECEIVEDfor review September 23, 1952. Accepted January 30, 1953. Presented before the Division of Analytical Chemistry at the 122nd Meeting of the AMERICAX CHEMICAL SOCIETY, Atlantic City, N. J.
Determination of Deuterium CLYDE A. DUBBS, Veterans Administration Center, Los Angeles 25, c a l i f . simplified apparatus was designed to improve the A speed and reliability of deuterium determination, particuHIGHLY
larly when only very small samples of material are available for analysis. The elongated train usually employed in the hot zinc reduction of water to hydrogen-deuterium gas mixtures, although permitting mass spectrometric assay on less than 5 mg. of weakly deuterated water or biological fluid without preliminary purification, has persistently shown serious memory effects. The new approach has been able to eliminate most of the large internal surface that has been responsible for these effects. PREVIOUS APPARATUS
This laboratory initially used the well-known Graaf and Rittenberg reduction train ( 3 )as modified by Alfin-Slater and associates ( 1 , 2 ) , It includes the following succession of major components: ( I ) water sample tube; (2) reduction tube, packed with granulated zinc and surrounded by a microcombustion furnace held a t 400” C.; (3) dry ice trap; (4) Toepler pump, to which is attached ( 5 ) manometer and ( 6 ) gas sample tube; ( 7 ) drying tube; and (8) vacuum pump. I n use, the aqueous sample, previously frozen in the liquid sample tube, is allowed to evaporate into the evacuated system and, after complete reduction, a sufficient amount of t h e resultant hydrogen-deuterium gas is Toeplered into the gas sample tube for mass spectrometric assay.
The elongated train presents a large internal glass surface which apparently contains numerous OH groups (presented by the silicate glass or a water film absorbed thereon) that can eschange hydrogen and deuterium with the adjacent gas phase ( 3 ) . This extensive exchange surface, equilibrated from one run, can introduce appreciable isotope contamination in subsequent runs, giving rise to the obstinate difficulty known as memory effect or holdup, Graaf and Rittenberg ( 3 ) state that they have been unable to eliminate this holdup with their apparatus; and, after trying and discarding several simple gas-flushing techniques, their experience has been confirmed. As a result, it has been common practice either to make one or two preliminary runs with each new sample merely to condition the apparatus ( 3 , L, 6 ) , or to provide separate trains for different levels of deuterium concentration. Both expedients are wasteful of sample, time, and effort. NEW APPARATUS
The present approach has been to eliminate every unnecessary component-especially the dry ice trap and Toepler pump-and to minimize the surface area of essential components. The resulting apparatus (Figure 1) consists basically of the liquid sample tube attached directly to the gas sample tube. A series of such tube pairs can be attached to a common manifold for mul-
