ANALY’rICA CHIMICA w*rri

DE’L’EI~MINATION OF ZINC IN HIGH YUICITY 13ISMUTH I3Y THERMAL N1;3UTRON AC’L’IVA’I’ION

As appears from the surveys of IJoc:lc-~~~l~‘rr~hli\Ns l --:I, activation analysis of zinc in various s;Lmplcs has been investigated by m;iny workers. From these biblio~- raphics it can be seen tllnt only 2 workers have clcalt with zinc in bismuth srunplcs+l~“. These papers are l~owcvcr not :ivailablc to the general public.

As a non-destructive analysis of truces of zinc in bismuth is not pacticul, iL

scp;iration procedure had to be clcvclol~cd. Various mcthotls have nlreacly been nppliccl for this purpose, c.g. precipitation as zinc mercury thiocy;in;Ltc’i-13 or zinc cluinalclatc”l”llo, organic solvent c.utractions”‘-“‘, ion cscl~~~~~gc~~~~~~~~~~ and the use of ;L column on whicll ditliizonc is rctriincd with an organic solvent on ccllulosc cuzetate”~. The applicability of tlicsc mcthocls is of course prccloniinantly depcnclcnt upon the propcrtics of tlic rilatris and tllc zinc quantity to 1~ dctcrmincd. Accordingly, a special investigation sccmccl necessary for the clctcrmination of traces of Ant in a bismuth rnutrix.

In a first step the matris itself w;Ls pIXXil>iti~tcd ;Ls l~ismutii oxychloriclc, whereas other impurities wcrc scavcn~ccl to a certain cstcnt. Zinc w;~s then estroctccl with hcxonc and stripped into the aclucous phase with dilute ammonia. Precipitation with quinnlclic a&t! finally cave a hi.g!;ly specific racliochcmicnl separation with an escellcnt recovery. ‘I’hc accuracy of the cstablishccl proceclure was tcstccl by an acldi- tion inethocl. The obtnincd sensitivity was 0,og p.p.ni.

Althougll zinc was not cvcn qualitatively detectable in the s;implcs, expcri- mcnts with synthetic snmplcs sliowcd that the proccdurc cstablishccl is adcquntc for the clctcrniinntion of tlic zinc: trnccs in high purity l~ismutli.

From the nuclcnr data (‘l‘ablc I) it is seen that nftcr thermal neutron nctiv;ltion of zinc, 5 nucliclcs iltT nvailahlc for clctcrmining tllis clcmcnt. The small value for the isotopic abundance as well as the small activation cross-section of 7%i restricts tlic USC of 7Lln%jn ancl 71%. If a rapid clwmicnl separation is possible, working near the irrndiation place, fl”Zn is tlic most useful nucliclc, as the activation cross-section is satisfactory and a good saturation factor after a short irradiation can be obtained. Since this work was not performed under these conditions, WZn could not be used. The selection was thus restricted to bin%:, or WZn.

The chemical separation and the transportation time required under the pre- sent working conditions decreased the activity of fiO”lZn far below the activity strength

at the cnci of irradiation. For this I-ciison (‘“%II \vas ciioscn, cvcn though a long irraciin- tion time \vas rcquircd to product an ZltiC!ClUiltC activity.

As tJ1c sample size wits cluite Inrgc (2 g), tiic bismuth \vas first J>rcciJ1itatecl as i+mutll osychioriclc by cliiuting the <olution ~:)~~~1. It was found that many tract cic- mcnts \vcrc more or less scnvengcd into the J>rccipitatc. e.g. copper, selenium, gold, mercury. J>oionium, antimony, siivcr, etc. (a long irradiation of the sample J>roduccs ~101’0 nuciiclc, tiic daughter of z*“mJSi). The coJ>rcciJ>itation of zinc was clctcrmincd with Wn. ‘The results arc shown in Tahic IT.

‘L‘AI3I.li I I

COPNKCII’ITATION 01’ ZISC

.__.. .__

IL+eritrrcul %u cctrricr :1 cfivily~ ~clcicd

110. ucidld (mg) (couuls/wi2r) ..-.._____. - . _.. - . . ..-- ._._....- _ ..- I 30 1 I()0 1 20 3S”oO

3 10 3.5500 4 0 .}‘I00 .

a Specific acti\rity is ca. 103 courits/min/pg of xinc.

Activity of .’ filtrafe (corrrrlsltuirr)

_

Many methods are known for liquid-licluid extraction of zincI(~-l”.“~.~(I. None of these mctiiods is however specific and a subsequent separation step is required. To achieve an easy stripJGng of zinc from the organic phssc, a hexonc extraction of the thiocyanatc in hydrochloric acid was choscn”7. Zinc thiocyanate was quantitatively cxtractcd into hcxonc in hydrochloric acid from PH 5 up to x.5 N hydrochloric acid. The extractability as a function of the pi is shown in Fig. I.

After extraction, the organic phase was stripped with ammonium hydroxide. It was found that the ammonium Jlydroxidc concentration for a quantitative striJ>- ping depended on the hydrochloric acid concentration used in the previous extraction. Hence, if zinc was extracted at a certain acidity, quantitative stripping was possible with a somewhat higher ammonium hydroxide concentration. The experimental results are shown in Fig. 2.

Am-d. Clrini. Acta, 35 (I@%) x43-153

150 J. I. KIM, J. HOSTE

Wl/.OH Concantrotmn(N1

Fig. I. IZxtrilct;rbility of zinc thicJCym:ItC into methyl isobutyl Icctonc.

Fig. 2. I3aclc-extraction of zinc. I-ICI concentration of previous cxtrirction: (I) 0.0x N; (2) 0.5 N; (3) 1.0 N; (4) 1.5 N; (5) 2.0 NV; (6) 3.0 N.

As a final step in the separation of zinc, the zinc quinalclate precipitation is often ufjcc\7.‘4, Is.:! H; this gave satisfactory results as far as yield and decontamination

Snn~j.ding n,rztl irradiation A sample of approximately 2 g was taken from three kinds of bismuth (B-2:

and washed with dilute nitric acid purity unknown ; B-3 : gg.ggg%, ; B-4 : gg,gggg”/l) to eliminate surface contamination. The sample was paclcecl in nluminium foil. For the standarcl samples high purity zinc oxide was used, dissolved in 3 A? hydrochloric acid and diluted to a 103.75 pg/rnl solution; 100 ~1 were taken and sealed in 5 qu,artz ampoulc. The sample and standard were packed together in the aluminium irradiation container. The irradiation was performed during 44 days in the Bli-I reactor at the neutron flux of 8 - 1011 n/cm*/sec.

wcrc conccrnccl.

ESP@RIMlIN’I’AI.

After irradiation the sample was washed again with dilute nitric acid to remove surface contamination. Before unsealing the standard sample in the quartz ampoule. it was cooled in liquid air to reduce the vapour pressure which might have arisen inside during the irradiation, and IO ~1 was taken for experiments.

For the preparation of synthetic samples from B-3 and B-4, approximately I g of metallic grains, machined from the metal block, was put into the quartz ampoules. To these, I-S ,ug of zinc, talccn from prepared standard solution, were added, where- after the ampoules were sealed and the contents mixed by shaking. The irradiation of these samples was performecl under the same conditions as described above.

DETERMrNATIOS OF %l IS PURE Bi 151

TABLE III

ANALYSIS OF SYNTHBTIC SAMPIXS

SavrpCc

-_.--

Clreitr. yield

(%I

- .--._- -- %n added %I1 f-OUild .4 clivity n (p.p.nl.) (p.p.tRl.) fcoftntsluriu)

Stilnclarcl sample I.0 (PS) 98.75 ztoJ35 - - IO2I&25

I3-3 O.C$38 94.18 1 .o‘+s I.031 1053 I3-3 I.012 93.97 2.0.$ 2.086 3130

B-4 I .OSO 93.80 2.960 2.915 2976 B-4 I.010 85.61 _I. 102 .$.I80 42G8 B-4 I .023 93.16 g.062 5.160 52G8

._-..- ..__._ --- _... - -.._ - _.^_ .-- ---. __._^_ .__^___.____. _... _..._._- - -- ---_--- a Activity for D r-g sample ant1 IOO~/, chcmicd yiclcl.

Radiochemical sebavation After 5 days cooling, in order to reduce the activity of the matrix and of the

short-lived nuclidcs, the sample was dissolved, with addition of 10.Sg mg of zinc carrier, in IO ml of 7 N nitric acid. The solution was evaporntcd almost to dryness and nitric acid was removed by evaporating in the presence of 3 ml of concentrated hydro- chloric acid. Boiling was continued for another IO min and the sample solution diluted with 50 ml of water. A white bismuth-oxychloricle prccipitatc was formed, and filtered off through a glass filter.

The filtrate was evaporated to 20 ml. To this solution IO ml of IO’>/, ammonium thiocyanatc were added and zinc was extracted twice with 20 ml of hcxone. From the combined organic phase, zinc was stripped with IO ml of 3 N ammonia solution.

The solution was boiled to reduce the ammonia concentration and after cooling, IO ml of buffer solution (200 g of’ sodium acetate trihydratc dissolved in 300 ml of glacial acetic acid and diluted to I 1) and 5 ml of quinaldic acid (3 g of quinalclic acid dissolved in xoo ml of water and neutralized with sodium hydroxide to pH 7) wcrc added. A white precipitate was quantitatively formed within romin.

The precipitate was separated by centrifugation in a weighed counting vial. The precipitate was washed with water and alcohol. After evaporation of the last tracts of alcohol under the infrared lamp the precipitate was dried for I bin the oven at a temperature of x00’. Then it was weighed to determine the yield.

The standard samples were also precipitated as zinc quinaldate. For the synthetic samples, the unscaled quartz ampoules were transferred to a

beaker and the samples dissolved in 5 ml of 7 N nitric acid. After complete dissolution, the quartz picccs were removed, washed with dilute nitric acid and discarded. The separation procedure was then followed as stated above.

The racliochcmical purity of the separated zinc was checked by y-spectrometry (4oo-channel analyzer coupled with the scintillation detector of 3” x 3” NaI(T1) crystal). Only 04% could be detected.

For quantitative measurements the photopeak at 1.11 MeV was selected and counted for 30 min, starting 6 days after the end of irradiation. A I-,ug portion of Zn standard gave rise to 102x+ 25 counts/min under the x.x1-MeV photopeak, whereas the background was 50 + 3 counts/min.

.4 ?zaC. Chim. Ada, 35 (x966) 148-153

J. I. ICII\I, J. HOST13

The accuracy of the proccdurc bus tcstccl by an addition method. Scvcn samples bvcrc: prelxuxxl by placing I g of bismuth grains (B-2) into a quartz ampculc. These wcrc spiked with rcslxctivcly 0.47, 0.8r). x.95, 4.15, 6.38, 8.89 and x3.51 ppm. of zinc, out of the standard solution. Tbc quartz ampoulcs wcrc scalccl and their contents thoroughly mixed by shaking. After irradiation they wcrc submitted to the chcrnical scpuration and counting clcscribccl above. The results wcrc calculated by the mctlmd of lcast squares for fitting a straight lint to the cxpcrimental points”“. ‘l’hc results arc given in Fig. 3, X is tbc concentration of the component to lx clctcrmincd in the spcci- mcns, Y the mcasurccl activity, n the slope of the straight lint (specific activity) and

6 the intcrccpt with the ordinate. l‘hc original zinc content of the samples is of course given by 6/a. ‘Ihc negative vuluc of b= -60 counts/min indicates that no zinc is prc- sent. lirorn the addition proccdurc the stnnclnrd clcviation was cstimatcd as _I x.zOj,. ‘I’lrc specific activity of tlic acldition mctbod, compared with that of the standard mctbocl also nllowcd an appraisal of the accuracy. These two values were respectively 1026 f x0 counts/niin/p.p.m. ancl 102x* 25 counts/min/p.p.m. If a count rate equal to tbc background is taken as the limit, the method slioulcl allow clctcrmination of 0.05 1xp.m. of zinc in a 2-g bismuth snmplc.

A ncutrcln activation analysis for the determination of zinc in bismuth was

dcvclopccl. After irradiating the samples for 44 clays at 4 - 1011 n/cm”/scc, zinc was separatccl quantitatively by hexone estraction and precipitation as quinaldate. The sensitivity of the method was cstimatcd as 0.05 pp.m. No zinc could be detected in the high purity bismuth samples. An addition method of analysis showed that the precision was 1.20/, .

Atd. ClGm. AC&Z, 35 (rgG6) 14%1.53

DETERMINATIOK 01: %n IN PURE Isi

Unc analyst par activation

153

au moycn de neutrons est cEvelopp& pour lc dosage du zinc dans le bismuth. Apr&s irradiation des &hantillons pendant 44 jours A 4 * 1011 n/cm2/scc, lc zinc est sGparf.2 quantitativcmcnt par extraction avec l’hesone et pr6cipitation sous formc de qninaldatc. La scnsibilitd de 1a mdthodc est cstimdc A 0.05 p.p.m. I’rtkision 1.2’);.

Mit dcr Ncutroncnaktivierungsanalysc wurdc Zink in \Vismut bestimmt. Die Proben wurden 44 ‘I’age mit 4 - IO*’ n/cm$/scc lxzstralllt und clas Zink quantitntiv durch Extraktion mit Mexon und l%llung als Chinalclat abgctrcnnt. In hochrcincn Wismutproben konnte kcin Zink nachgewiescn wcrclcn. Die Enq~fincllicl~kcit dcr hic- thodc bctriigt ctwa 0.05 p.p.m., illrc Genauigkeit 1.2’yo.

I7 I8

I9 20 ZLL

1 ‘2

2.3

=+

25

26

;;:

29

Copes, 4 (1959) 22r. W. A. ~~HOOKSLIANK. JIM., c;. W. IADIMC~TTE AND J, A. DEAN, .4nftl. Cluw., 30 (1958) I 785. RI. KAWAIIAIBA, fI. XIOCHIZUKI ANI) T. !UISAKI, J(~pctrl .-l)~dy.d. 16 (~#a) .1.#8. I-1. .A. ~~Alll.~lAN. G. \v. ~.I?I>DICO’~TlS AND P. 1.. >rOORE. cl,lCll. C/WHl.. 26 (1954) Ig.39. IX. H. FILI~Y, .-ltzctl. C/rem., 36 (rg64) 1597. I<. SAnlsIlAL AND I<. SOI<EnlARK, Modem 7‘rl!rld.s ijr Activfr/iorr Aurtlysis, illt. COllf. in Activatioll Amdysis, Collcgc Station. Texas, rgGr. T. u. PIERCE AND 1’. P. I’ECK. .~~rIn~~~St. 87 (Ig62) 360. N. H. FuRniAN, Stroldard ~VJcfllods of Cllmlicul ~l~lllIy.sis, (5th Ed.. Van Nostrand. New York, 1962. G. 12. F. LUNDELI., I-I. A. DRIGIXT ASD J. 1. HOPIZMAN, Applied /~aorpllic Antllysis, 2nd Ed., John Wiley, New York, 1953. G. N. MORRISON AND I-I. FREISRR, Sohwt Evfrnctio~a ill A rlulyticcll Ckcrtristry, John Wiley, New York, 1957. 13. l3. SANDRLL, Colorinrcfric Dcferr~rimfion of Trctccs of Mctnls, lntcrscicncc. New York. 1959. J. 1ilNNUNrsN AND B. WDNNERSTRAND, Chemist-/lnalysl. .+z (1953) 80.

Ia. I,OWSN AND 11. I,. CORNEG. f~?ln~. C/lC)lI., “-7 (1958) 1965. W. J, YOUUEN, Sfdisficd Mefhods for Ckcntisfs, John Wiley. New York. rg5r.

A rrd. Ckirtl. Acln, 35 (rg6G) 148-153