c.p.m., over a background of 70 c.p.m., which could be lowered to 20 c.p.m. with a suitable anticoincidence arrangement. By using substantially higher neutron fluxes, and counters with lower backgrounds, a sensitivity to about lo-" gram of uranium should be feasible. The lower background counters would in all probability have far less volume than those used in this work, and would entail an additional transfer step from a gas chromatographic trap to the counter. Other Applications. Since the basic technique should work equally well with other rare gases by using appropriate trapping procedures for each gas, activation analysis plus tantalum combustion and 'gas chromatographic purification should be applicable to all substances capable of producing a noble gas radioactivity under irradia-
tion. For example, A r N could be activated and separated by this method for determinations of K4-Ar" for geologic dating. Similar methods have been applied recently to potassiumargon ages (1) and meteorite dating (11). LITERATURE CITED
(1) Armstrong, R., Abstracts of Geo-
chemical Society, Pittsburgh, Pa., Nov. 2-4, 1959. ( 2 ) Bernstein, W., Ballentine, R., Rev. Sa.Instr. 21, 158 (1950). (3) Bvrne. J. T.. ANAL.CHEM.29. 1408 \ - - - .3 -
(4) Ebert, K., Konig, H., Wanke, H.,
2.Nafurforsch. 12a, 763 (1957). (5) Hamamchi. H., Reed, G., Turkevich,
A.. Geoihim.' et .Cosmochim. Acta
12;
337 (1957).
(6) Jervis, R.,.Mackintosh, W., Proc. 2nd United Nations International Confer-
ence on Peaceful Uses of Atomic Energy, 28,470 (1959'). (7) Katcoff, S., Nucleonics 18, No. 11,
201 (1960). (8) Mahlman, H., Leddicotte, G., ANAL. CHFM.27,823 (1965'). (9) Rowland, F. 5. Lee, J. K., White, R. M., U. S. At. hnergy C o r n . , Rept. TID-7578,p. 39 (1960). (10) Smales, A. A., Analyst 7 7 , 778 (1952). (11) Stoenner, R., Zahringer, J., Geochim. et Cosmochim. Acta 15,40 (1958 (12) Tatsumoto, M., Goldberg, lk, Zbid., 17,201 (1959). (13) Zeller, E., Wray, J., Daniels, F., Bull. Am. Assoc. Petrol. Geologists 21, 121 (1957). RECEIVED for review February 23 1961. Accepted May 1, 1961. Research s u p ported by A. E. C. Contract No. At( 11-1)407. Division of Physical Chemistry,
136th Meeting, ACS, Atlantic q t y , N.J., September 1959. Submtted in partial fulfillment of the requirements for the Ph.D. degree by Larry A. Haskin, University of Kansas, 1960.
Radiochemical Determination of Isotopic Thorium in Uranium Process Streams HENRY G. PETROW, BERNARD SO",
and ROBERT J. ALLEN
lonics, Inc., Cambridge, Mass.
b The determination of thorium in uranium mill effluents requires an accurate sensitive method, free of interference from cationic and anionic impurities. The method developed is valuable to the determination of natural thorium and thorium-230, and can be adapted to allow for the determination of other thorium isotopes. Sensitivity and accuracy are good, and only titanium interferes sufficiently to require modification of the procedure. The method can be used for aqueous and solid samples and only conventional counting equipment is required.
I
of interest with regard to radioactive pollution by uranium mill waste streams are thorium-230, and to a lesser degree, natural thorium. There is not available currently a simple reliable method which is applicable t o thorium determination a t tracer levels. The method of Moore (4) is cumbersome when applied to a complex mixture such as uranium mill effluents. Direct extraction by thenoyltrifluoroacetone (TTA) has been recommended (2, 3), but severe inhibition of thorium extraction into TTA by phosphate, fluoride, and even sulfate occurs. SOTOPES
The method described gives satisfactory results on aqueous samples from carbonate and sulfuric acid leach liquors, as well as solubilized ore and residue samples. Excellent separation of thorium from radioactive and stable interferences is effected by a series of solvent extraction steps utilizing primary and tertiary amines. The use of amine extractants has been reviewed by Coleman et al. ( 1 ) . Solvent extraction with a tertiary amine from dilute sulfuric acid removes uranium, zirconium, and molybdenum. Solvent extraction from the same medium with a primary amine removes thorium, but not radium, lead, bismuth, protactinium, actinium, iron (11), vanadium(IV), calcium, magnesium, aluminum, alkali metals, manganese(II), or rare earths. Phosphate, fluoride, and sulfate anions do not inhibit thorium extraction, even when present in large concentrations. The concentration of nitrate, chloride, and perchlorate must be controlled, but concentrations far in excess of those normally encountered can be tolerated. Titanium, if present, follows thorium quantitatively, and special allowance must be made for titanium-bearing samples. After thorium extraction by the primary amine. thorium is re-extracted or
stripped into BM hydrochloric acid. The hydrochloric acid strip solution is scrubbed with a tertiary amine to remove traces of interferences which may have accompanied the thorium. After evaporation of hydrochloric acid, and oxidation to destroy organic material, thorium is taken up in nitric acid. Thorium-230 is then determined by radioassay and natural thorium is determined colorimetrically. APPARATUS AND REAGENTS
The recommended detection equipment consists of a 2~ proportional flow counter, capable of accepting %inch diameter planchets. coupled to a suitable scaler. Alamine 336, tricaprylyl amine, 10% by volume dissolved in benzene. The solution should be washed with an equal volume of 0.5M sulfuric acid prior to use. Alamine 336 can be purchased from the General Mills Co., Kankakee, Ill. Primene JM-T, a mixture of Cta to Czs aliphatic primary amines, 10% b y volume in benzene. This solution should be washed with an equal volume of 0.5M sulfuric acid prior to use. Primene JM-T can be purchased from R o b & Haas, Philadelphia, Pa. Alamine 336, 10% by volume in benzene. This solution is used without prior acid washing. VOL. 33, NO. 10, SEPTEMBER 1961
1301
Aliquat 336, methyl tricaprylylammonium chloride, 30% by volume dissolved in benzene. This solution, used only for titanium-bearing samples, is washed twice with a n equal volume of 12M hydrochloric acid prior to use. Aliquat 336 can be purchased from the General Mills Co. The 100% grade should be specified. Thoron, l-(c+arsonophenylazo)-2naphthol-3,6-disulfonic acid, 0.1% (w./ v.) aqueous solution. PROCEDURE
This procedure is suitable for carbonate or sulfuric acid mill effluents and for perchloric acid solutions resulting from the dissolution of solid samples. The solution should be filtered before analysis, if necessary. Add 200 ml. of the sample to a separatory funnel and adjust the acidity with either sulfuric acid or ammonia so that the p H is no higher than 2 nor lower than 0.5; then add 11 ml. of concentrated sulfuric acid and mix well. Reduce any iron(II1) and vanadium(V) with ascorbic acid. Add 50 ml. of the washed 10% Alamine 336 solvent and shake vigorously for 2 minutes. Allow the phases to disengage, and draw off the aqueous phase into a second separatory funnel containing 50 ml. of the 10% Primene JM-T solvent. Discard the Alamine 336 solvent. Shake the second separatory funnel for 2 minutes, allow the phases to disengage, and draw off the aqueous phase into a third separatory funnel containing 50 ml. of the Primene JM-T solvent. Shake the third funnel for 2 minutes, draw off, and discard the aqueous phase.
Combine the two fractions of Primene JM-T in the second funnel. Wash the combined Primene JM-T solvents twice with 20-ml. portions of 1M sulfuric acid, mixing for 2 minutes in each wash step. Discard both wash solutions. Strip the thorium from the combined Primene JM-T solvents by shaking for 2 minutes with two 15-ml. portions of 9M hydrochloric acid. Transfer both strip solutions to a separatory funnel containing 50 ml. of the untreated 10% Alamine 336 solvent. Discard the Primene JM-T. Shake the funnel for 2 minutes, and draw off the hydrochloric acid into a beaker. Wash the Alamine 336 solvent with 5 ml. of 9M hydrochloric acid, and add the wash solution to the beaker. Discard the Alamine 336 solvent. Evaporate the thorium-bearing strip solution to dryness; sulfuric acid will be evolved and charring of organic material will result. Destroy the charred organic residue by placing the beaker in a muffle furnace adjusted to 600" to 700" C. Bake the sample for 10 minutes, remove the beaker, and cool. Add 10 ml. of concentrated nitric acid and evaporate to a volume of 1 ml. Transfer the thorium-bearing nitric acid solution to a 10-ml. volumetric flask, rinse, and make the solution to volume. For thorium-230 determination, evaporate an aliquot of the 10-ml. sample on a 2-inch diameter stainless steel planchet and then bake the planchet for 2 minutes a t 600" C. Cool the planchet and alpha count. For determination of the thorium-230 content of the initial sample, the followiag calculation is used : Thorium-230, d.p.m./liter
Table
I.
Analysis of Synthetic Thorium230 Solution
(All samples contained 50,000 d.p.m./liter U, 3600 d.p.m./liter Ra, and 5600 d.p.m./
Sample 1A
n n
2A
3A
liter Po) Thorium-230, D.P.M ./Liter Added Found 22,900 22 ,800 22,900 23,100 2 ,290 2 ,270 2.200 2.280 229
'229
J3 4A
B 5A
B 6A B
Table 11.
2.3
0 0
2.9
0
0
Analysis of Nine Mill Effluents
Thorium-230, D.P.M./Liter 628 ,000 627,000 622,000 603,000 604,000 606,000 247 ,000 248,000 247, OOO 337,000 338,000 335,000 133 125 127 5.3 6.2 5.6 4,210 4,280 4,270 33 38 32 2.3 3.9 2.3 1302
ANALYTICAL CHEMISTRY
=
c.p.m. GXAX.2XY -
G
=
Instrument geometry, generally
0.51 for a 2 r counter A = Fraction of final 10-ml. sample
mounted on the planchet Y = Yield factor. For a 1-ml. aliquot, the yield factor is 0.96. If more than 1 ml. if mounted, Y must be decreased by 1% for each additional ml. used. This decrease in apparent yield is the result of alpha particle absorption by the trace of solid material present in the sample T = Correction for the alpha particle contribution from natural thorium present in the sample. For most domestic uranium mills, the natural thorium content is too low to be considered To determine the natural thorium content, add a suitable aliquot of the purified thorium solution to 1 ml. of 70% perchloric acid, and evaporate to dryness. Transfer the thorium perchlorate with 0.33M hydrochloric acid to 10-ml. volumetric flask containing 1 ml. of 0.1% (w./v.) thoron reagent dissolved in water. Make the sample up to volume with 0.33M hydrochloric acid. Measure the absorbance of the sample a t 545 mp, using 0.01% thoron in 0.30M hydrochloric acid as the counter solution. us in^ a 1-cm. cell. the absorbance is 0.0674 absorbance a t
unit per microgram of thorium No more than 80 pg. of thorium can be present in the aliquot, otherwise low answers will result. The concentration of natural thorium can be calculated from the absorbance, the size of aliquot, initial sample volume, and a yield factor of 0.97. The use of thoron for thorium determination is described in detail by Thomason, Perry, and Byerly (6). For the analysis of ores and residues, place a 1-gram sample in a platinum dish, and add 5 ml. of concentrated nitric acid and 2 ml. of 48% hydrofluoric acid. Evaporate just to dryness, and add 2 ml. of concentrated nitric acid, 2 ml. of 48y0 hydrofluoric acid, and 3 ml. of 70y0perchloric acid. Heat to fumes of perchloric acid and continue to heat until the bulk of the perchloric acid has been volatilized. Cool, add 1 ml. of concentrated hydrochloric acid, warm gently, and add water to dissolve all solids. Transfer the sample to a separatory funnel with approximately 200 ml. of water, and add 11 ml. of concentrated sulfuric acid. Analyze for thorium in the manner described above. INTERFERENCES
The decontamination factor for uranium is lo5provided the sample contains no more than 0.2 gram of uranium. For polonium and bismuth the decontamination factor is lo4, while for radium and lead, it is 5 X los. Calcium, magnesium, molybdenum, aluminum, rare earths, actinium, protactinium, iron(II), vanadium(IV), nickel, cobalt, copper, zinc, alkali metals, chromium(II1, VI), and manganese (11, VII) do not interfere. Zirconium does not interfere provided the initial sample contains less than 0.2 gram of ZrOp per liter. Titanium, on the other hand, follows thorium quantitatively. Fortunately, none of the 12 mill effluents treated to date contained any titanium, but several of the ore samples analyzed did contain appreciable titanium. To separate titanium from thorium, two changes were made in the procedure, and these changes should be incorporated if the sample is known to contain titanium. First, the Primene JM-T solvent is stripped with 12M hydrochloric acid rather than the recommended 9M hydrochloric acid. Second, the strip solution is washed with 100 ml. of 30% Aliquat 336 in benzene. The quaternary amine extracts a chlorocomplex of titanium from 12M hydrochloric acid. The yield for the modified procedure is identical to that of the basic procedure. Concentrations of titanium up to 0.1 gram of Ti02 per liter can be tolerated. Several common anions interfere with thorium recovery if present in high enough concentrations. Maximum tolerances for nitrate, chloride, and per-
chlorate are 22, 25, and 30 grams per liter, respectively. Concentrations of phosphate and fluoride of a t least 50 and 10 grams per liter, respectively, are without effect on thorium recovery. Sulfuric acid concentrations up to 300 grams per liter are also without effect on thorium recovery. The sulfuric acid concentration must be a t least 50 grams per liter, otherwise some thorium will be coextracted with uranium by Alamine 336. DISCUSSION
A series of synthetic and actual samples were analyzed by the thorium procedure, and the results are presented in Tables I and 11. The results obtained for the analysis of solid samples also gave excellent precision, and the thorium-230 concentrations were in good agreement with the value calculated from the known uranium content of the mineral. Since none of the actual mill samples contained natural thorium. it was necessary to add a known amount of
Table 111. Analysis of Six Mill Samples Containing Added Natural Thorium
of Natural Thorium Found 98.6 50.3 74.3 24.4 10.1 5 5.3
pg.
Added 100 50 75 25 10
natural thorium to the samples to evaluate the reliability of the procedure for natural thorium. These results are presented in Table 111. The high temperature oxidation of organic residue was investigated thoroughly and no loss of thorium was noted due to formation of refractory thorium oxide. It is possible that samples containing a macro amount of natural thorium will yield a refractory oxide. An alternative method of oxidizing organic material is to heat the solution to dryness and then
oxidize the residue with concentrated nitric acid. Attempts t o remove organic material from the strip solution with organic solvents were unsuccessful. LITERATURE CITED
(1) Coleman, C. F., Brown, K. B.,
Moore, J. G., Crouse, D. J., Znd. Eng. Chena. 50, 1756 (1958). (2) Ebersole, E. R, Harbertson, A., Flygare, J. K., Jr., Sill,C. W., Health and Safety Division, U. S. Atomic Energy Commission, Idaho Falls, Idaho, unnublished data. 1959. (3) c a w , P. G., Brown, E. A., U. 8. Atomic Energy Comm. Doc. NLCO-742 (TID4500-13E. Rev.), (1958). (4) Moore, F. L., ANAL. C ~ M30, . 1020 (1958). (5) Thomason, P. F., Perry M. A., Byerly, W. M., Zbid., 21, 1239 (1949).
RECEIVEDfor review March 15, 1961. Accepted June 26, 1961. Division of Water and Waste Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961. Work ~ ~ p p ~ r by t e dU. S. Atomic Energy Commission, Division of Biology and Medicine, under Contract AT (30-1)2470.
Estimation of the Isotopic Composition of Separated Radium Samples HENRY G. PETROW and ROBERT J. ALLEN lonics, Inc., Cambridge, Mass.
b The isotopic spectrum of radium samples separated from uranium mill effluents i s such that a simple technique capable of estimating the concentration of each nuclide i s required. A technique capable of dete'rmining radium223, radium-224, radium-226, and radium-228 has been developed. Radium-226 i s determined b y differences; the others are determined b y chemical separation and counting of daughter activities. The method is sensitive to low concentrations of activity, approximately 40 d.p.m. per liter, and i s free from interference from other natural activities. The technique permits the rapid estimation of radium nuclides and does not require the use of elaborate or specialized equipment.
A
for the determination of radium in uranium mill ef-. fluents, recently published (4, 6), provides only for the determination of gross alpha radiation originating from radium-226, radium-223 and the equivalent of three daughters, and radiumPROCEDURE
224 and two daughters. No provision is made in the procedure for establishing the isotopic spectrum of the aemitting radium nuclides, or for the estimation of radium-228, a @-emitting nuclide. Normally, one would expect that the ratio of radium-226 activity to radium223 activity in mill solutions would be identical, or a t least similar, to the natural ratio occurring in the uranium ore. Since the equilibrium ratio of radium-226 t o radium-223 in the ore body is about 20, the bulk of separated radium prepared from a mill effluent would be expected to be radium-226. This is seldom the case, and in actual practice, especially with mills using a sulfuric acid leaching process, the bulk of radium activity is due to radium223 and its daughters. This phenomenon was first noted by Ebersole et al. ( 2 ) . The exaggerated ratio of radium223 to radium-226 in mill effluents is a result of the selectivity of the leaching process. Fbdium present in the ore is barely soluble in sulfuric acid, and only a few per cent actually dissolves.
Actinium-227 and thorium-227, both precursors of radium-223, are dissolved to a much greater extent, and radium223 is formed in the aqueous phase by in-growth from these precursors. The effect is that the radium-223 to radium226 ratio in the aqueous phase is greatly increased. If the ore also contains natural thorium, the mixture of radium nuclides becomes even more complex because of the in-growth of radium-224 from its parent, thorium228. Also present would be radium228, bclt the majority would have to be the result of the direct dissolution of that nuclide from the ore. The methods described provide for the direct determination of radium223, radium-224, and radium-228, by chemical separation and radioassay of their respective daughters, lead-211, lead-212, and actinium-228. Radium226 is determined by difference, but it could be determined by the emanation technique, or by chemical separation of bismuth-214 (1). However, the indirect method was chosen since it affords an immediate estimation of the radium-226 content of the sample, VOL. 33, NO. 10, SEPEMBER 1961
1303
