LITERATURE CITED
(1) Amiel, S., Welwart, Y. Israel Atomic Energy Comm. Rept. IA-690 (1962).
(2) Analytical Chemistry in Nuclear Reactor Technology (Nov. 4-6, 1957) Gatlinburg, Tenn., U . S. At. Energy Comm. Rept. TID-7555 (1958). (3) Bane, R. W., Brody, J. K., Proc. U . A’. Intern. Conf. Peaceful Uses At. Energy 2nd Geneva 28, 411 (1958). (4) Bate, G. L., Huizenga, J. R., Potratz, H. A Geochem. Cosmochim. Acta 16, 88 (1959). (5) Davis, G., Hubschmann, B., Israel Atomic Energy Comm. Rept. IA-612 (1961). (6) Goldstein, H., “The Attenuation of Gamma Rays and Neutrons in Reactor
Shields,” p. 38, U. S. Govt. Printing Office, Washington, 1957. ( 7 ) Graves, A. G., Froman, 0. K., “Miscellaneous Physical and Chemical Techniques of the Los AIamos Project,” McGraw-Hill, New York, 1952. (8) Henderson, W. J., Tunnicliffe, P. R., Nucl. Sci. Eng. 3, 145 (1958). (9) Hughes, D. J., Schwartz, R. B., “BNL-326 Neutron Cross-sections,” U. S. Govt. Printing Office, Washington, 1958. (10) Jaffey, A. H., Nucleonics 18, No. 11, 180 (1960). (11) Keepin, G. R., Wimett, T. F., Ziegler, R . K., Phys. Rev. 107, 1044 (1957). (12) KO, R., Weiler, M. R., U . S. At. Energy Comm. Res. and Development Rept. HW-66220 (1960).
(13) Mantel, hI., Analytical Laboratory, Israel Atomic Energy Commission/ Laboratories] P. 0. Box 527, Rehovoth, Israel, private communication (19611. (14) Marion, J. B., Levesque, R. J. A., Ludemann, C. A,, Detenbeck, R. W., Nucl. Instr. Methods 8 , 297 (1960). (15) “Reactor Physics Constants,” Argonne Natl. Lab. Rept. ANL-5800 (1958). (16) Sher, R., Floyd, J. J., Phys. Rev. 102, 242 (1956). (17) Stehney, A. F., Perlow, G. J., Proc. U . N . Intern. Conf. Peaceful Uses At. Energy, 2nd Geneva 15, 384 (1958). RECEIVED for revien. July 3, 1961. Resubmitted May 10, 1962. dccepted July 31, 1962.
Anion Exchange Separation and Spectrophotometric Determination of Microgram Quantities of Rhodium in Plutonium-Uranium-Fissium Alloys HAROLD B. EVANS, CAROL A. A. BLOOMQUIST, and JOHN P. HUGHES Argonne National laboratory, Argonne, 111.
b
Microgram amounts of rhodium are separated from the components of an EBR II fuel alloy, using Dowex 1 X 10 anion exchange resin. Uranium, plutonium, palladium, molybdenum, and a portion of the zirconium and ruthenium remain on the column, while rhodium, americium, and the remaining zirconium and ruthenium are found in the eluate. Ruthenium is removed b y fuming with HCIO,. The rhodium is determined spectrophotometrically as the red chloro complex, formed in the presence of hydrochloric acid and tin(ll) chloride. The molar absorptivity of the colored species is approximately 4200.
I
remote pyrometallurgical processing of Experimental Breeder Reactor I1 spent fuel elements, studies have indicated that certain fission products of atomic numbers 40 through 46 are very difficult to remove and reach a n equilibrium concentration after several recycles. At this time, the rate of fission process formation is balanced by losses due t o burnup, decay, and partial loss in processing. These fuel elements, consisting of the natural forms of these elements and whose composition is similar to the equilibrium concentration, comprise the fissium alloy. A typical equilibrium mixture is shown in Table I. I n the manufacture and processing of fuel elements for this reactor, rhodium, as well as the other fission products, N
1692
THE
ANALYTICAL CHEMISTRY
must be determined for control of the process. The reactor will be originally fueled with enriched uranium; however, future operations will use plutonium. In view of the burnup espected in this reactor, much of the analytical work will be performed by remote control procedures using, whenever possible, instrumental methods adaptable to routine procedure and requiring minimum handling and exposure time. The primary problem in the determination of rhodium is separation from the other platinum metals. There is no known specific reagent for rhodium, and most reagents that are used for precipitation or as chromogens are not free from interference from the othpr platinum metals. 117e have been unsuccessful in applying simultaneous spectrophotometry to both aqueous solutions and organic extracts of the platinum metals of this alloy. A variety of
Table I.
Calculated Equilibrium Fission Product Concentration
(5 wt. yo new metal per cycle) Weight yo Element Zirconium 0.10 0.01 Niobium Molybdenum 3.42 0.99 Technetium 2.63 Ruthenium 0.47 Rhodium Palladium 0.30
chromogenic and other reagents has been used in spectrophotometric methods for rhodium, including organic sulfides (18, 25, 26), sodium hypochlorite @), and stannous chloride (1, IS), and recently Jacobs reported a sensitive spectrophotometric method using .t’,N‘ - bis - (3 - dimethylaminopropyl) dithio-oxamide to determine rhodium (15)and palladium (14). Meinke and Anderson (24) have determined rhodium by activation analysis. The method has great potential for application t o irradiated fuel elements, as one niay be able to eliminate lengthy wet-chemical methods and analyze the entire alloy by radiochemical techniques and gamma spectrometry (12).
Several methods (5, 8, 9) were available for the gravimetric approach, but were abandoned because of the high alpha activity, time factor, or the close control required. The platinum metals in milligram quantities are easily reduced by other metals or by titanous or chromous solutions. However, it was difficult to dissolve the precipitates and obtain quantitative recovery. Volumetric methods (18) require separation and larger amounts of sample than encountered here. Syrokomsky and Proshenkova (SI)oxidized rhodium (111) t o the quinquevalent state and used the method as a basis for the volumetric determination of rhodium in the presence of other platinum metals. We used argentic oside as a n oxidant
ancl, in a study of the spectrum, observed a broad peak with maximum Absorption at 515 nip. The molar absorptivity was very low and the color was stable for approximately one hour after filtration. Palladium did not interfere. Paper chromatography has been used for separation of the platinum metals (4, 6, 1 7 ) and many other metal ions and acid radicals. The method used for uranium-fissium alloys (6) was timeconsuming and not adaptable t o plutonium-bearing alloys. I n a majority of the published methods, cation exchange resins are used t o separate rhodium from nonradioactive solutions (16, 20-22, SO). Most of such methods are not quantitative and usually require close control of feed preparation and large elution volumes. Many authors (3, 20, 22) have observed the unpredictable behavior of rhodium, which may exhibit either anionic or cationic properties, according t o the method of preparation. The platinum metals form chloride anion compleves of the general type MeC16-2. Often, absorbability or elution properties can be controlled b y changes in the ligand. Kraus, Nelson, and Smith (19) studied the absorbability of the elements from hydrochloric acid solution on the anion exchange resin, Dowex 1. Berman and McBryde (3) extended the equilibrium data of Kraus et al. t o include all the platinum metals, and found good agreement with other data. This work (3, 19) forms the basis of our present method of separation. The rhodium is subsequently determined using tin(I1) rhloride ( I , 13). Direct addition of a c>hromogen to an aliquot of the untreated eluate would be an idealized condition and would simplify ion exchange analytical procedures. The method described here consists essentially of three steps: sample preparation, ion exchange separation, and spectrophotometric determination. It is readily adapted to routine procedure and is elementary and less time-consuming than the cation application (16), as it requires only one fuming instead of three, control of the acid in the feed is not so critical, prior removal of uranium is not necessary, and separation from plutonium is efficient. Ion exchange separation techniques are easily adaptable t o high-level hazardous material, such as plutonium. The handling and operations involving this element are carried out in a wellventilated, open-gloved-type hood, equipped with special filters for removal of contamination from exhaust air. Proper protective clothing should also be worn. The radiation here is principally alpha and shielding is not necessary. With subsequent application of this method at the facility, in addition to the usual precautions in handling the
------F1
Figure 1. Side view of column vacuum apparatus
extremely toxic plutonium (0.65 pg. of Pu239 = maximum permissible body level) very high-level beta and gamma radiation will require remote handling. Radiation levels of the order of 106 roentgens per hour are expected in the remote processing and fabrication facility. EXPERIMENTAL
Apparatus. ,411 absorbance measurements were made with a Beckman Model DU spectrophotometer, equipped with a photomultiplier attachment a n d line-operated power supply. Matched set of 50-mm. Corex cells. Column vacuum atmaratus (see I. Figure 1). Reagents. RHODIUM CHLORIDE STOCKSOLUTION.Dissolve approximately 0.3 gram of pure rhodium metal according t o t h e method developed by Wichers et al. (10, 12, 32, 8). Follow t h e procedure carefully. (We suggest opening the sealed tubes in a shielded area while wearing protective gloves.) Transfer the dissolved metal to a tared volumetric flask, and dilute to volume with 8 X hydrochloric acid.
RHODIUM CHLORIDE ST.4NDaRD
SOLE-
TIOX;. Using a weight buret, weigh out the required amount of standard rhodium stock solution which, when diluted to volume, will give a solution 8 M in hydrochloric acid and will contain approximately 35 pg. of rhodium per gram of solution. SIhlUL.4TED FISSION ALLOY STOCK SOLUTION.Prepare this solution from the metal chlorides, assuming the following alloy composition: 70% uranium, 20y0 plutonium, 4.12% ruthenium, 2.51y0 molybdenum, 1.99% palladium, and zirconium. For each 5 ml. of solution, standard rhodium was varied from 50 to 150 pg.
STANNOUS CHLORIDE(1M in 2.5M hydrochloric acid). Dissolve 225.6 grams of analytical reagent grade stannous chloride dihydrate in 208 ml. of concentrated hydrochloric acid. Dilute t o 1 liter in a volumetric flask. Insert a stick of tin metal into the reagent bottle for storage stability. DOWEXh I O 3 EXCHANGE RESIN. Bio-Rad, analytical grade, AG 1 X 10, 200-400 mesh, chloride form, anion exchange resin (1.4 meq. per ml. wet bed). Other chemicals were C.P. or reagent grade quality. Resin Column Preparation. BioR a d analytical grade resins have been previously processed and are ready for use. Commercial resins should be cycled with t h e appropriate organic solvent and electrolyte before use. T h e stock resin is qtored, covered with distilled water, in a polyethylene bottle. The glass column is fitted with a small glass-~ool plug. and filled with distilled water up to the mid-point of the reservoir. -An aqueous slurry of resin is poured into the column and the particles are allon-ed to settle and reclassify thcmselres by gravity flow. The resin height i s adjusted to 7 inches and thc column is n-ashed alternatPly with successive 10-nil. volumes of 8M hydrochloric acid, water, and 8-11 hydrochloric acid before use. The pressure drop is directly proportional to the resin size and is also related to thc eize of the glass-wool plug used for rctrntion of the resin in the column. Rest results wrre obtained with a drop rate of 35 i 5 drops per minute. The resin capacity is more than adequate for the separation and. +ice the columns have reservoirs attached, two or three banks of four samples each can be handled convenientlv. PROCEDURE
Dissolution of Sample. Uraniumplutonium-fissium alloys are conveniently dissolved b y heating a mixture of hydrochloric and perchloric or nitric acids in a sealed quartz tube. The analyst should be thoroughly familiar with the detailed study of the method reported by Wichers et al. (20, 11, 32, 33). Transfer a 0.5-gram sample (or less) of the alloy as turnings to a quartz tube, 12 mm. in outside diameter by 8 mm. in inside diameter and approximately 15 inches in length, which has been sealed and carefully annealed at one end. Slowly add, in small increments, 5 ml. of 12M hydrochloric acid. After the evolution of gases has ceased, add 2 drops of 72% perchloric acid. (The volume of liquid should never be greater than one half of the volume of the tube.) Seal off the tube at a length of approximately 10 to 12 inches, using a gas-oxygen torch and annealseal in a gas flame. Place the tube in a steel shell which has been previously hydrostatically tested and'x-rayed, and
VOL. 34, NO. 13, DECEMBER 1962
1693
40 grniiis of solid C&I'hCJIl tliosidi~. Iniinediatc~lys c r e ~ von tho r a p ~ r i t ltest for Irakage by inimcrsing the shell iintlcr watw. Placc the. sholl in n inufne furriaccl niaint:riiicd at a1)i)rositiiatvly 300" i 10' C. for 4 hours. (This furnaco is q w i n l l y cqiiiliiietl witli tc~riil)c~i~:it~iro control saft.ty dcvicrs to ob\.iate elwtricsl failuws or 1iruii:iii :itlti
crrlll's. 1
Rcnio\.e tlie shcll froni tlic, futnaci.. cool to rooiii t c m p ( ~ r a t u r c ~anti . reniovc' tlic tiil~cl. 1iislicc.t for caoiriplctc, tiissolutioii. cool tlic. tube in solid carlion rlim i t l c ~ .ant1 iip(1ii. Tr:in4(>1,thc contents to n 50-ml. volumetric flask and niakc~ thc find solution 8.11 in liydroi~hlorir acicI. Separation of Rhodium Using Anion Exchange. Sclect froni the stock solution :in :ilicquot that caont:iino 50 to 150 gg. of rliodiiiiii. and transfer it to :i 40-nil. l)oriisilicatt. glaw graduat,ed ccnt~rifugrtub. .\tljurt tlir \~olumrto 5 nil. and ni:ikr thr final solution 8.U in hydrochloric acid. .\tltl 0.5 nil. of concentrated nitric nciel. and lieat the sohition 011 a sand h t h until gas evolution ocrurs. Diecoiitinuc hcating t,he ssnililc and pcrmit it to ~t:indfor allout 2l ' 2 hours brforc tranofcwing to the rcsin c d r i n i i i , p r q i x c ( l as Iireviously tlew4wtl. l\.heii thcs Ii~\.ol of the ~saiiililc soliitiiin iicarn thc toll of the iwin 1 ) d . LISP thrc~e5-1111.Ijortions of the c~lutingsolution to n-:isli out t,lie saniple c>ont:rincrs. and ~ i t l t lto the, cnliinin n-hrn tht. lc\.c~lof thc, iirwcltliiig ~iort,ionof clutnt nears t l i P top of the rrsin t)cd. Pas.: t,lir soliitioni through tlie c.oliinin. n.ith the aid of g m t l c suction, iiit,o :I 50-mi. volmi~ctric fl:isk. a t a tlrol) rat(, of 35 = 5 drnps pcr niinutc. 110 not allon. the cdiinins to reach drynws. (Too much \.aciiiini n-ill give a fait tlroi' rat(, anti lcntl t o channeling in tlic rcxsin c ~ c i l u m i i . v-it,li si~t)sequcnt 1 mor scl)ar:i t i OII.1 ( 'oii t i i i u i ~ wa sliirie the coiuniii i\-ith S.l/ liytlrocliloric~acid iuitil a total volurnr, of 15 to 30 nil. has Iicoii collectc~tlin the> flask. I:lute the I)lutonium froni tlic column with 0.30.11 liyilroclilori fer to u-astcs. Traiisf~r rltiatc along \vith the 8.ll liydrocliloric~acitl \vashings cr. S l o ~ l yadd 2 inl. ilfiiric :wid. c o \ w the ~ i ~ ~ l ~(m'rrs - i ~ ianti p ovaiiorztc to funiw. .itld 500 p1. of pt~rc.liloric~ acid slowly to t,lie lint sulfuric. aciil :mtl continue funling for 1 to 2 niiniitrs. ('ool. anti rinw th(, cover with a minimum of \rat,cr and thc sides of tht. heakw with 8.l! liydroc~hloric acid. .[gain heat to copious fmiics of sulfiuic acid for IO miniitcs. add 2 drop.: of perchloric acid, a i d ccintinuc* fuming for 10 minutes. Cool, repeat tlic rinsing 017cwtion with water anti Kll Iiytlrochloric acid. and continlie funiing until an c~stiniat~ctl volurnc of 0.5 nil. of sdfuric acid rcinains. Do not allow the acid to funic t,o clryiiess and, if niwssary, add 0.5 nil. of sulfuric :rc*id between the second antl tlie t,hirtl fuming stelis. (Thc fuming opcration \\-ill eliminate organic niattcr. ruthenium, and nit,ratc ions, which n-oultl interfere (luring thcolordevrlopnient stagc.) 1694
ANALYTICAL CHEMISTRY
.5 Effect of HCI concentration on rhodium chloro I'IAVELtZC'-
Figure 2. complexes
$rn
r
~
Cary 14, 5 - c m . cells
DISCUSSION AND RESULTS
LlTERATVRi CITED
VOL 34
NO 13,
DECEMBER 1962
1695
