388 ANALYTICA CHIMICA ACTA

S E P A R A T I O N OF R A D I O C O B A L T F R O M N I C K E L

R. MILLS AND M. J. VERNON

Department o] Radiochemistry, Research School o/Physical Sciences, Australian National University Canberra, A.C.T. (Australia)

(Received May 23rd, 196o)

INTRODUCTION

A reinvestigation of the classical cobaltinitrite method for the separation and esti- mation of cobalt in the presence of nickel is described in this study. This work was undertaken in conjunction with experiments in the nuclear physics field by CARVER AND TURCHINETZ 1 a n d PURSER AND TITTERTON 2, wh ich i m p o s e d ce r t a i n l im i t i ng

conditions on the separation. The nuclear problem involved the irradiation of nickel metal with both high energy

~, radiation and fast neutrons. In the former case it was required to determine the ratios of the SaNi (7,p)57Co and aSNi (7,n)57Ni yields and in the latter, the 58Ni (n,np)57Co and 58Ni (n,2n)aTNi yields. Since the decay product from the 36 h 57Ni is also 270 day 57Co, it is apparent that separation of 57Co immediately after irradiation enables measurement of both the (7,p) and (n,np) yields respectively and another separation after one or two weeks measures the corresponding (7,n) and (n,2n) yields. The critical requirements for these determinations were, therefore, fairly rapid separation ( < I h) and at the same time reasonably complete cobalt removal ( > 99 %), immediately following the irradiations.

The quanti ty of nickel irradiated ( ~ io g) and the requirement for the separated cobalt to be in a suitable physical form for analysis by scintillation spectrometry indicated that the cobaltinitrite separation was the most suitable one. However, in analytical textbooks, it is usually stated that the precipitation step in this method takes an appreciable period of time. For example, SCOTT 3 states that the precipitating solution should be left for 6 h or preferably overnight, KOLTHO~r AND SANDELL a not less than 12 hours, HILLEBRAND, LUNDELL, BRIGHT AND HOFFMAN 5 24 hours, and TREADWELL AND HALL 6 24 hours. The methods described in these textbooks also differ in the respect that Scott recommends that the solution be brought to the boiling point immediately before the precipitation step and retained at this temperature for a 3o-min period during precipitation. The other texts do not mention this require- ment.

RESULTS AND DISCUSSION

A series of experiments was performed therefore in which the completeness of cobalt removal was determined as a function of standing time. The effect of heating the solution was also examined. In these experiments an accurately measured aliquot of

Anal. Chim. Acta, 23 (196o) 388-39o

SEPARATION OF RADIO-Co FROM N i 389

cobalt nitrate solution, containing 5 mg Co, was added to a solution of AnalaR nickel nitrate ( < o.ooo5% Co) containing I O g Ni. The standard separation procedures, as given in the above references, were then used to precipitate cobalt as potassium cobaltinitrite. After measured time intervals the precipitates were filtered, washed, dissolved iD 2O ml 6 N H2SO4 and made up to 5o ml in standard flasks. These samples were analyzed colorimetrically by the method of YOUNG AND HALL 7 at 625 m# with a Unicam SP 500 spectrophotometer. The results obtained are given in Table I.

T A B L E I

T I M ~ D E P E N D A N C E OF P R E C I P I T A T I O N I N C O B A L T I N I T R I T E S E P A R A T I O N

Standing Cobalt recovery

time Hot solution Cold solution (minJ (%) (%)

IO - - 86.27 I O - - 85.29 15 50.98 98.63 15 37.25 97.65 3 ~ 41.18 98.63 3 ~ 75.49 99 .02 45 85.88 99.61 45 93.14 99.61 60 88.23 - - 60 94.71 - -

These results clearly indicate that the cobaltinitrite method meets the requirements of the nuclear physics problem very satisfactorily, provided a standing time of about 45 min is used and the precipitating solution is not heated. I t is also indicated that for many analytical applications longer standing times are unnecessary.

The method modified in this manner was successfully applied to the determination of relative nuclear reaction yields described in the second paragraph. Standard carrier techniques were used and the percentage recovery of carrier determined in each pre- cipitation. The reproducibility of the procedure can be inferred from the fact that > 99% recovery was obtained in all cases. Although the cobalt was precipitated only once, contamination by radioactive nickel was quite small and in anTy case is rendered negligible by the scintillation spectrometric technique of analysis.

SUMMARY

A reinvest igat ion of the classical cobaltinitri te method for the separat ion of cobalt f rom nickel has shown t h a t the s tanding t ime can be reduced to less t han 6o min wi th > 99% recovery. The method is suitable for the separat ion of some of the shor t lived cobalt isotopes.

R]~SUM]~

Les au teurs ont repris la m6thode classique au cobaltinitr i te pour la s@ara t ion du cobalt d 'avec le nickel. Ce proc6d6 peu t ~tre utilis6 pour la s6parat ion d ' isotopes du cobalt de courtes p6riodes.

ZUSAMMENFASSUNG

Eine neue Un te r suchung der klassischen Xobal tn i t r i tmethode zur Trennung yon Kobal t und Nickel wird beschrieben. Durch die erzielte Zeitersparniss eignet sich die Methode zur T rennung kurzlebiger Kobal t - Isotope.

Anal . Chim. Acta, 23 (196o) 388-39 o

39 ~ R. MILLS, M. J. VERNON

R E F E R E N C E S

1 j . H. CARVER AND W. E. TURCHINETZ, Proc. Phys. Soc., 73 (1959) 585 . 2 K. H. PURSER AND E. W'. TITTERTON, Australian J. Phys., 12 (1959) lO3. 3 W. W. SCOTT, Scotts Standard Methods o/Chemical Analysis, Van Nostrand, New York, Vol. i,

1939, p. 312. 4 I. M. I4_OLTHOFF AND E. ]3. SANDt~LL, Textbook o] Quantitative Inorganic Analysis, Macmillan,

London, 195 o, p. 603. W. F. J-IILLEBRAND, G. E. F. LUNDELL, H. A. BRIGHT AND J. I. HOFFMAN, Applied Inorganic Analysis, John Wiley & Sons, New York, 1953, p- 420.

8 F. P. TREADWELL AND ~vV. T. HALL, Analytical Chemistry, John Wiley & Sons, New York, 1942, p. 218.

7 R. S. YOUNG AND A. J. HALL, Ind. Eng. Chem., Anal. Ed., 18 (1946) 264.

Anal. Chim. Acta, 23 (196o) 388-39 ~

A R E A E F F E C T S IN A L U M I N U M E L E C T R O D E S

WILLIAM M. MACNEVIN AND RICHARD M. WILSON

McPherson Chemical Laboratory, The Ohio State University, Columbus, Ohio (U.S.A.)

(Received March i8th, 196o)

BAKER AND )/[ORRISON 1 reported the observation of a current in a short-circuited cell consisting of an aluminum and a platinum electrode in 0.2 N acetic acid. BAKER 2 later applied this electrode system to the determination of microgram quantities of fluoride in fuming nitric acid. Repetition of the BAKER AND MORRISON work in this laboratory led to the observation that the magnitudes of current and potential were affected by the area of the aluminum electrode. This observation led in turn to the prediction that a cell consisting of two aluminum electrodes of different areas would develop potential and current. The only comparable observation is a report by GREENE AND FONTANA ~, made after the completion of the experimental work reported here, that a potential and a current develop between a small "artificial pit" and a larger area of stainless steel.

T h i s p a p e r d e s c r i b e s e x p e r i m e n t s t h a t e s t a b l i s h t h e r e a l i t y of t h e o b s e r v a t i o n , t h a t

d e f i n e f a c t o r s c o n t r o l l i n g t h e m a g n i t u d e of c u r r e n t a n d t h a t e s t a b l i s h t h e f r a m e w o r k

of t h e p r o b a b l e e l e c t r o d e m e c h a n i s m .

P r e l i m i n a r y a t t e m p t s to r e p e a t t h e BAKER AND MORRISON w o r k b y HOLLAND 4

r e s u l t e d in c u r r e n t - t i m e c u r v e s in w h i c h a c u r r e n t n e a r l y c o n s t a n t for as m u c h as

one h o u r w a s o b t a i n e d in c o n t r a s t t o t h e p e a k - s h a p e d c u r v e of BAKER AND MORRISON.

A f t e r t h e a r e a e f fec t w as r e a l i z e d i n t h e p r e s e n t w o r k a n d t h e a r ea s of t h e e l e c t r o d e s

c o n t r o l l e d , t h e c u r r e n t - t i m e c u r v e s cou ld b e d u p l i c a t e d .

U s e of t h e r o t a t i n g a l u m i n u m e l e c t r o d e for m e a s u r e m e n t of f l uo r ide or e l e m e n t s

t h a t r e a c t w i t h f l uo r ide h a s b e e n r e p o r t e d b y HOWARD, WEBER AND WEBER 5, Jo - HANNESSON ~, KABANOV AND POLYAK 7, KOLTHOFF AND SAMBUCETTI 8 a n d b y OVSEPYAN

AND TARSYAN 9.

Anal. Chim. Acta, 23 (196o) 390-395