Trace Elements in Coal by Neutron Activation Analysis with

8 Trace Elements in Coal by Neutron

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Activation Analysis with Radiochemical Separations J. KENNEDY FROST, P. M. SANTOLIQUIDO, L. R. CAMP, and R. R. RUCH Illinois State Geological Survey, Urbana, Ill. 61801

Procedures for the determination of 11 elements in coal—Sb, As, Br, Cd, Cs, Ga, Hg, Rb, Se, U, and Zn—by neutron activation analysis with radiochemical separation are summarized. Separation techniques include direct combustion, distillation, precipitation, ion exchange, and solvent extraction. The evaluation of the radiochemical neutron activation analysis for the determination of mercury in coal used by the Bureau of Mines in its mercury round-robin program is discussed. Neutron activation analysis has played an important role in recent programs to evaluate and test analysis methods and to develop standards for trace elements in coal carried out by the National Bureau of Standards and the Environmental Protection Agency.

/ C o m b u s t i o n of c o a l a n d o t h e r fossil fuels is a m a j o r source i n t h e e n v i ^

r o n m e n t of trace elements that are h a z a r d s to h u m a n h e a l t h . T o x i c

elements s u c h as H g , A s , S b , F , Se, a n d T I are v o l a t i l i z e d d u r i n g c o a l c o m b u s t i o n a n d are e m i t t e d d i r e c t l y into t h e atmosphere or c o n c e n t r a t e d i n t h e fly a s h ( I , 2, 3).

M o s t elements i n c o a l o c c u r at o n l y parts p e r

m i l l i o n levels, b u t large tonnages of c o a l are c o n s u m e d e a c h y e a r i n t h e U n i t e d States. I n a d d i t i o n , c o a l c o n v e r s i o n processes, w h i c h c o u l d v a s t l y increase c o a l use are n o w b e i n g c o n s i d e r e d seriously. T h e fate of trace elements d u r i n g these processes is l a r g e l y u n k n o w n . T h e r e i s , therefore, m u c h interest i n d e t e r m i n i n g t h e c o n c e n t r a t i o n of v a r i o u s t r a c e elements i n c o a l .

T h e I l l i n o i s State G e o l o g i c a l S u r v e y

r e c e n t l y c o n c l u d e d a s t u d y of the o c c u r r e n c e a n d d i s t r i b u t i o n of p o t e n t i a l l y v o l a t i l e trace elements i n c o a l sponsored b y t h e U . S. E n v i r o n m e n t a l 84 Babu; Trace Elements in Fuel Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

8.

FROST E T A L .

Neutron

Activation

P r o t e c t i o n A g e n c y ( E P A ) (4).

85

Analysis

S e v e r a l t e c h n i q u e s w e r e u s e d to a n a l y z e

101 coals, m o s t l y f r o m I l l i n o i s , for 23 trace elements.

Neutron activation

analysis ( N A A ) was u s e d to d e t e r m i n e several of the elements. T h e γ-ray s p e c t r u m of a c o a l s a m p l e i r r a d i a t e d w i t h t h e r m a l n e u trons is d o m i n a t e d i n i t i a l l y b y the s h o r t - l i v e d isotopes, and and

2 8

6 0

3 8

C1,

5 6

A 1 , a n d s u b s e q u e n t l y b y s u c h l o n g e r - l i v e d isotopes as

Mn, 4 6

2 4

Sc,

5 9

Na, Fe,

C o . B y selection of a s u i t a b l e i r r a d i a t i o n p e r i o d , d e c a y i n t e r v a l , a n d

c o u n t i n g p e r i o d after i r r a d i a t i o n , c h l o r i n e ( 5 ) , s o d i u m (4, 5 ) , a n d m a n ganese (4)

can be determined by instrumental N A A w i t h a N a l ( T l )

detector a n d a 4 0 0 - c h a n n e l , p u l s e - h e i g h t a n a l y z e r . T h i s is the c o u n t i n g e q u i p m e n t a v a i l a b l e at the I l l i n o i s State G e o l o g i c a l S u r v e y a n d is the m i n i m u m e q u i p m e n t i n most N A A laboratories. I f a solid-state G e ( L i ) detector a n d a 1000- to 4 0 0 0 - c h a n n e l a n a l y z e r are a v a i l a b l e , i n s t r u m e n t a l N A A c a n b e extended to m a n y elements.

For

e x a m p l e , R a n c i t e l l i ( 6 ) has a n a l y z e d c o a l a n d fly ash for 25 major, m i n o r , a n d trace elements reduction.

by using instrumental N A A with

Block and Dams (7)

computer

data

u s e d s i m i l a r analysis a n d r e p o r t e d o n

43 elements i n c o a l . C l e a r l y , this is a g o o d m e t h o d for r a p i d l y m o n i t o r i n g the c o m p o s i t i o n of m a n y c o a l samples. R a d i o c h e m i c a l separations are necessary for m a n y elements

when

o n l y a N a l detector is a v a i l a b l e . E v e n w i t h a G e ( L i ) detector, a r a d i o c h e m i c a l s e p a r a t i o n increases t h e s e n s i t i v i t y a n d a c c u r a c y a n d p e r m i t s the d e t e r m i n a t i o n of some elements w h o s e r a d i o a c t i v i t i e s are m a s k e d b y stronger activities i n the m u l t i - e l e m e n t s p e c t r u m of a c o a l s a m p l e .

For

e x a m p l e , m e r c u r y , s e l e n i u m , g a l l i u m , a n d z i n c i n most coals are b e l o w the l i m i t of d e t e c t i o n i n s t r u m e n t a l l y e v e n w i t h the r e s o l u t i o n of a G e ( L i ) c r y s t a l ( 7 ) , b u t c a n b e d e t e r m i n e d after r a d i o c h e m i c a l separations as is d e s c r i b e d later. T h e increase i n a c c u r a c y afforded b y a r a d i o c h e m i c a l s e p a r a t i o n is a b s o l u t e l y necessary i n the d e t e r m i n a t i o n b y N A A of trace elements i n the coals selected as standards. T h e fact t h a t interferences f r o m the c o a l m a t r i x are r e m o v e d b y a r a d i o c h e m i c a l s e p a r a t i o n is the a d v a n t a g e of this m e t h o d of analysis over s u c h i n s t r u m e n t a l m e t h o d s as x - r a y

fluorescence

a n d emission spectroscopy. T h i s a r t i c l e presents a c o m p r e h e n s i v e

v i e w of the present

of-the-art of r a d i o c h e m i c a l separations for the f o l l o w i n g trace

state-

elements

i n c o a l : H g , R b , C s , Se, G a , A s , S b , B r , Z n , C d , a n d U . M o s t of t h e w o r k o n the d e t e r m i n a t i o n of

trace elements

i n c o a l is v e r y

recent.

T h e a c c u r a c y of the analysis m e t h o d s , n e a r l y a l l n e w l y d e v e l o p e d ,

has

b e e n o p e n to q u e s t i o n because of t h e l a c k of standards a n d l a c k of knowledge i n coal.

of

the range

of

concentrations

for

many

trace

elements

F e d e r a l g o v e r n m e n t laboratories h a v e t a k e n the l e a d i n e v a l u

ating methods

of analysis a n d i n d e v e l o p i n g

standards.

B y a round-

Babu; Trace Elements in Fuel Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

86

TRACE

robin

program,

the

Bureau

of

Mines

evaluated

ELEMENTS

analysis

i n c l u d i n g N A A , f o r d e t e r m i n i n g m e r c u r y i n coal.

IN

FUEL

methods,

M o r e recently,

via

a n o t h e r r o u n d - r o b i n p r o g r a m , the N a t i o n a l B u r e a u of S t a n d a r d s ( N B S ) a n d E P A evaluated methods

of

analysis a n d a c c u r a c y

of results

for

s e v e r a l trace elements i n c o a l . N B S is d e v e l o p i n g reference c o a l samples a n d testing m e t h o d s

of

analysis, i n c l u d i n g N A A , to determine

trace

elements i n c o a l . Development and Evaluation by National

of Radiochemical

NAA

Laboratories

Bureau of Mines Round-Robin for Mercury Determination in Coal. M e r c u r y w a s the first trace element i n c o a l to arouse e n v i r o n m e n t a l c o n c e r n , p r o m p t e d b y d a t a s u c h as those of J o e n s u u (8).

H e r e p o r t e d t h a t as

m u c h as 33 p p m m e r c u r y o c c u r r e d i n c o a l a n d i n f e r r e d t h a t c o a l c o m b u s t i o n m i g h t b e a m a j o r source of m e r c u r y i n t h e e n v i r o n m e n t . values w e r e r e p o r t e d b y R u c h et al. (9)

Lower

i n the same year. Sixty-six coals

a n a l y z e d b y t h e m c o n t a i n e d 0.02-1.2 p p m m e r c u r y , a n d t h e m e a n m e r c u r y c o n c e n t r a t i o n of 55 I l l i n o i s coals i n the set w a s 0.18 p p m . I n a n effort to o u t l i n e the p r o b l e m s a r i s i n g i n m e r c u r y d e t e r m i n a t i o n s a n d to e v a l u a t e the m e t h o d s u s e d , the B u r e a u of M i n e s i n 1971 o r g a n i z e d a r o u n d - r o b i n p r o g r a m i n v o l v i n g 11 c o a l samples d i s t r i b u t e d to 20 p a r t i c i p a t i n g laboratories

(10).

N A A w i t h radiochemical separation

and

f o u r a n a l y t i c a l a p p r o a c h e s u s i n g a t o m i c a b s o r p t i o n for d e t e r m i n i n g m e r c u r y i n c o a l w e r e e v e n t u a l l y e v a l u a t e d . A l l five m e t h o d s gave accurate results, b u t a combustion—double

gold amalgamation-atomic

absorption

m e t h o d was c o n s i d e r e d t h e best one a v a i l a b l e because i t a p p e a r e d m o r e a c c u r a t e a n d precise t h a n the others a n d w a s q u i t e s i m p l e , fast, a n d inexpensive.

R e s u l t s f r o m the 14 laboratories r e p o r t i n g w e r e u s e d

to

c a l c u l a t e p r o b a b l e or best v a l u e s of the m e r c u r y contents of the 11 coals, r a n g i n g f r o m 0.05 to 0.41 p p m m e r c u r y . only 3 %

were rejected

as i n a c c u r a t e .

O f 100 N A A results r e p o r t e d , Schlesinger a n d Schultz

com-

m e n t e d t h a t a c t i v a t i o n analysis w a s a r e c o m m e n d e d p r o c e d u r e for d e t e r m i n i n g m e r c u r y i n c o a l i f the n u c l e a r r e a c t o r a n d other necessary e x p e n sive f a c i l i t i e s w e r e a v a i l a b l e a n d i f the r e l a t i v e l y l o n g i n t e r v a l b e t w e e n s a m p l i n g a n d results a n d the associated expense w e r e not serious d i s advantages.

D e t a i l s of a c t i v a t i o n analysis p r o c e d u r e s

used were

not

outlined. N B S Standards and Analysis Methods for Trace Elements in Coal. In November

Material

(SRM)

1630, M e r c u r y i n C o a l , w i t h a p r o v i s i o n a l l y certified m e r c u r y

content

of 0.13 p p m .

1971, N B S i s s u e d S t a n d a r d R e f e r e n c e

L a t e r t h e p r o v i s i o n a l v a l u e of 2.1 p p m s e l e n i u m i n S R M

1630 w a s issued.


8.

FROST E T A L .

Neutron

Activation

87

Analysis

I n m i d - 1 9 7 2 , a n extensive l a b o r a t o r y i n t e r c o m p a r i s o n p r o g r a m w a s i n i t i a t e d b y N B S a n d E P A to d e t e r m i n e the a c c u r a c y of t h e c u r r e n t m e t h o d s of analysis for trace elements i n fuels, w i t h the i n t e n t of i m p r o v i n g the r e l i a b i l i t y of s u c h d e t e r m i n a t o n s . A b o u t 50 laboratories, u s i n g a v a r i e t y of m e t h o d s , p a r t i c i p a t e d i n the analysis of a s a m p l e of c o a l , fly ash, f u e l o i l , a n d gasoline f o r 18 elements, A s , C d , C r , C u , H g , M n , N i , P b , Se, T I , T h , U , V , Z n , F , B e , S, a n d F e . N A A w i t h r a d i o c h e m i c a l separ a t i o n p r o v e d to b e a n i m p o r t a n t t e c h n i q u e for d e t e r m i n i n g a f e w elements, i n c l u d i n g m e r c u r y , arsenic, s e l e n i u m , a n d z i n c . N B S , i n c o n j u n c t i o n w i t h this p r o g r a m , intends to p r o v i d e a n e w S R M for e a c h of the f o u r matrices c o a l , fly ash, f u e l o i l , a n d gasoline, c e r t i f i e d for 15 elements

(II).

F o r a trace element c o n c e n t r a t i o n to be certified b y N B S , it m u s t be d e t e r m i n e d b y at least t w o i n d e p e n d e n t m e t h o d s , the results of w h i c h m u s t agree w i t h i n a s m a l l e x p e r i m e n t a l error r a n g e of ± : 1 % to

±10%,

d e p e n d i n g o n the n a t u r e of the s a m p l e a n d the c o n c e n t r a t i o n l e v e l of the element. fication

S u c h a c c u r a c y i n d e t e r m i n i n g some trace elements for c e r t i of c o a l S R M is a c h i e v e d most easily b y N A A w i t h r a d i o c h e m i c a l

separation. Scientists at N B S h a v e extensively tested a n e u t r o n a c t i v a t i o n m e t h o d t h a t i n v o l v e s a c o m b u s t i o n s e p a r a t i o n p r o c e d u r e o n c o a l as w e l l as o n several other matrices to be certified as s t a n d a r d r e f e r e n c e m a t e r i a l s . T h e p r o c e d u r e s t h e y h a v e thus d e v e l o p e d

to d e t e r m i n e m e r c u r y

s e l e n i u m ( 1 3 ) , a n d arsenic, z i n c , a n d c a d m i u m (14)

(12),

are o u t l i n e d i n a

f o l l o w i n g section o n m e t h o d s f o r d e t e r m i n i n g specific elements i n c o a l .

General Considerations for Determining

Trace Elements in Coal

Volatility of the Elements and Sample Treatment.

A prime

con-

s i d e r a t i o n i n d e v e l o p i n g a n analysis m e t h o d is the v o l a t i l i t y of the element to b e d e t e r m i n e d . C o n t r o l l e d c o m b u s t i o n of t h e c o a l s a m p l e a n d c o l l e c t i o n of t h e v o l a t i l e p r o d u c t s is a g o o d w a y to separate v e r y v o l a t i l e e l e ments

such

as m e r c u r y

and bromine.

The

few

completely

volatile

elements are s u b s e q u e n t l y a n d easily p u r i f i e d . I f the element to b e d e t e r m i n e d is n o t v o l a t i l e , i t is advantageous to r e m o v e the o r g a n i c m a t e r i a l first b y d r y - a s h i n g t h e c o a l at a b o u t 5 0 0 ° C . If the element is v o l a t i l i z e d a b o v e b u t n o t b e l o w 150 ° C , t h e c o a l c a n b e a s h e d at this l o w t e m p e r a t u r e b y a r a d i o f r e q u e n c y , o x y g e n - p l a s m a asher (4).

A l o w - t e m p e r a t u r e asher is expensive, a n d l o w t e m p e r a t u r e a s h -

i n g , i n p a r t i c u l a r , is t i m e - c o n s u m i n g , b u t d r y - a s h i n g is a safe w a y

to

destroy t h e o r g a n i c m a t e r i a l . M o r e o v e r , the r e s u l t i n g ashes are easily brought

into

solution,

either

by

mixed-acid

digestion

or


alkaline

88

TRACE

fusion followed b y dissolution i n acid.

ELEMENTS

IN FUEL

Since f u s i o n is r a p i d , i t is p a r -

t i c u l a r l y a t t r a c t i v e i n N A A w h e n s h o r t - l i v e d isotopes are d e t e r m i n e d . A f u r t h e r a d v a n t a g e of s t a r t i n g the N A A w i t h a c o a l ash s a m p l e is that the trace element concentrations i n the ash are as m u c h as 10 or m o r e times greater t h a n i n the c o a l . W h e n the w h o l e c o a l is to be a n a l y z e d , b o m b c o m b u s t i o n m a y

be

safely u s e d to destroy o r g a n i c matter. W e t - a c i d d i g e s t i o n of c o a l is not w i t h o u t safety h a z a r d s . tered i n decomposing methods.

G o r s u c h (15)

discusses the p r o b l e m s

encoun-

organic material b y acid digestion and b y

other

T h e o x i d i z i n g m e d i u m m u s t b e chosen c a r e f u l l y because some

elements are v o l a t i l i z e d f r o m s o m e a c i d m i x t u r e s . A n i t r i c - s u l f u r i c a c i d m i x t u r e is most c o m m o n l y u s e d to w e t - a s h coal. G r e a t e r p r e c a u t i o n s are necessary w h e n p e r c h l o r i c a c i d is one of the oxidants u s e d , a n d i t is u s u a l l y a d d e d after most of the o r g a n i c matter has b e e n d e s t r o y e d

by

another o x i d i z i n g a c i d , e.g., n i t r i c . A f t e r t h e c o a l or c o a l ash s a m p l e has b e e n b r o u g h t i n t o s o l u t i o n , r a d i o c h e m i c a l separations m a y be m a d e b y a n y of several t e c h n i q u e s , s u c h as d i s t i l l a t i o n , p r e c i p i t a t i o n , solvent-extraction, i o n exchange, Common Features of N A A Procedures.

I n a l l of the

etc.

procedures

d i s c u s s e d i n this a r t i c l e , i r r a d i a t i o n s are m a d e i n a h i g h t h e r m a l n e u t r o n flux

(10

1 1

to 1 0

13

neutrons c m "

2

sec" ) s i m u l t a n e o u s l y w i t h the samples 1

a n d s t a n d a r d ( s ) sealed i n p o l y e t h y l e n e containers for a short i r r a d i a t i o n or i n s i l i c a containers for a l o n g i r r a d i a t i o n .

T h e s t a n d a r d is a k n o w n

a m o u n t , or s o l u t i o n of k n o w n c o n c e n t r a t i o n , of a p u r e c o m p o u n d of the element to be d e t e r m i n e d . T h e c o n c e n t r a t i o n of the element i n the s a m p l e is d e t e r m i n e d b y c o m p a r i n g its r a d i o a c t i v i t y w i t h t h a t of the s t a n d a r d , w h i c h is either subjected to t h e same r a d i o c h e m i c a l s e p a r a t i o n as the s a m p l e w i t h a n i n a c t i v e m a t r i x or d i l u t e d . T h e r a d i o a c t i v i t y is c o u n t e d d i r e c t l y i f the s a m p l e is m e a s u r e d i n s o l u t i o n . T h e r a d i o c h e m i c a l y i e l d of p r e c i p i t a t e d samples is d e t e r m i n e d d i r e c t l y b y w e i g h i n g a n d t h a t of s o l u tions of samples b y a l i q u o t r e - i r r a d i a t i o n . Methods for Determining

Specific Elements

Mercury. T h i s is the trace element i n c o a l most s t u d i e d b y r a d i o c h e m i c a l N A A . T h e m e r c u r y v a l u e for S R M 1630 e s t a b l i s h e d b y N B S r e s u l t e d f r o m a specific n e u t r o n a c t i v a t i o n w i t h c o m b u s t i o n that R o o k et al. (12)

procedure

d e v e l o p e d for b i o l o g i c a l samples.

T h e i r r a d i a t e d c o a l s a m p l e is p l a c e d i n a c e r a m i c c o m b u s t i o n b o a t w i t h a d d e d m e r c u r i c o x i d e c a r r i e r a n d b u r n e d i n a s l o w stream of o x y g e n i n a s i m p l e a p p a r a t u s c o n s i s t i n g of a straight q u a r t z c o m b u s t i o n t u b e c o n n e c t e d to a straight c o n d e n s e r s u r r o u n d e d b y a t r a p of l i q u i d n i t r o gen. T h e ash a n d the t u b e are t h e n h e a t e d to a b o u t 800 ° C to d r i v e a l l v o l a t i l e m a t e r i a l i n t o t h e c o l d t r a p . T h e p r o d u c t s are d i s s o l v e d i n n i t r i c


8.

FROST E T A L .

Neutron

Activation

89

Analysis

a c i d . T h e a c t i v i t y of a v i a l c o n t a i n i n g a 2ÎV H N 0 s o l u t i o n of t h e c o l l e c t e d m a t e r i a l is c o u n t e d w i t h a G e ( L i ) detector, measurements b e i n g m a d e at the 0.077 M e V g o l d x-ray a c t i v i t y a r i s i n g f r o m the d e c a y of 65-hr Hg. T h e o n l y interference is f r o m B r w h i c h is, of course, m o r e serious i f c o u n t i n g is d o n e w i t h a N a l detector. B r o m i d e is r e m o v e d b y a d d i n g b r o m i d e c a r r i e r to the n i t r i c a c i d s o l u t i o n of the p r o d u c t s at 40 ° C a n d p r e c i p i t a t i n g w i t h s i l v e r n i t r a t e . M e r c u r i c b r o m i d e is s o l u b l e i n w a r m d i l u t e n i t r i c a c i d a n d is q u a n t i t a t i v e l y r e t a i n e d i n s o l u t i o n . 3

1 9 7

8 2

T r a c e r studies s h o w e d

that m e r c u r y was r e c o v e r e d q u a n t i t a t i v e l y

f r o m b i o l o g i c a l samples. G o o d p r e c i s i o n a n d a c c u r a c y w e r e d e m o n s t r a t e d for the m e t h o d b y analysis of flour standards a n d several N B S b i o l o g i c a l standards. R u c h et al. (9)

u s e d a c o m b u s t i o n p r o c e d u r e to separate the m e r -

c u r y i n t h e i r 1971 s u r v e y of 66 coals for m e r c u r y . T h e irradiated sample, d i l u t e d w i t h A l u n d u m i n a porcelain boat c o n t a i n i n g m e r c u r i c nitrate c a r r i e r , is c o m b u s t e d v e r y s l o w l y i n a slow oxyg e n s t r e a m i n a 9 6 % silica c o m b u s t i o n tube. T h e v o l a t i l e p r o d u c t s are c o l l e c t e d i n t w o consecutive traps, b o t h c o n t a i n i n g a solution of acetic a c i d s o d i u m acetate buffer, b r o m i n e , a n d m e r c u r i c n i t r a t e h o l d - b a c k c a r r i e r . T h e c o l l e c t i o n solutions i n 2N H C 1 are l o a d e d onto D o w e x 2, a n d r a d i o active interferences are e l u t e d w i t h a l i q u o t s of w a t e r a n d 2N H C 1 . T h e r e s i n , i n a s m a l l v i a l , is c o u n t e d for t h e 0.077 M e V p h o t o p e a k f r o m Hg. 1 9 7

T h e o v e r a l l m e r c u r y r e c o v e r y i n the process is 67 ±

1 5 % . The pre-

c i s i o n of the m e t h o d is a b o u t 2 0 % , a n d the d e t e c t i o n l i m i t is a b o u t 0.01 p p m m e r c u r y for a 1-g s a m p l e of coal.

R e l i a b i l i t y of the m e t h o d

was

d e t e r m i n e d b y the accurate analysis of t w o c o a l samples u s e d i n the B u r e a u of M i n e s s t u d y of the p r o b l e m s i n v o l v e d i n d e t e r m i n i n g m e r c u r y i n coal (9)

a n d t h e n b y the agreement w i t h i n e x p e r i m e n t a l error of the

results f r o m t h e 11 B u r e a u of M i n e s r o u n d - r o b i n c o a l samples a n d t h e i r p r o b a b l e m e r c u r y contents

(4).

M o r e r e c e n t l y m e r c u r y has been l o g i c a l S u r v e y (16)

d e t e r m i n e d at the I l l i n o i s G e o -

b y a m o d i f i c a t i o n of the m e t h o d of R o o k et al.

(12).

T h e c o a l s a m p l e is b u r n e d as d e s c r i b e d a b o v e , a n d the v o l a t i l e p r o d ucts are c o l l e c t e d i n the straight t u b e condenser c o o l e d b y s o l i d c a r b o n d i o x i d e . T h e c o l l e c t e d m a t e r i a l is d i s s o l v e d i n n i t r i c a c i d , a n d B r is removed b y silver bromide precipitation. T h e resulting sample solution is c o u n t e d for the 0.077 M e V a c t i v i t y of Hg. 8 2

1 9 7

R a d i o c h e m i c a l y i e l d s are 8 0 - 9 0 % . v i a t i o n for t h e m e t h o d is ± 1 5 % .

T h e average r e l a t i v e s t a n d a r d d e -

T h e v a l u e of 0.14 p p m m e r c u r y was o b -

t a i n e d o n S R M 1630. T h e m e r c u r y contents of m o r e t h a n 100 c o a l samples f r o m the U n i t e d States h a v e b e e n d e t e r m i n e d at t h e I l l i n o i s State G e o l o g i c a l S u r v e y . V a l u e s r a n g e f r o m 0.01 to 1.73 p p m (9, P i l l a y et al. (17)

16).

determined mercury by radiochemical N A A i n a

v a r i e t y of e n v i r o n m e n t a l samples, i n c l u d i n g c o a l .


90

TRACE

ELEMENTS

IN

FUEL

T h e i r r a d i a t e d s a m p l e a n d the p o l y e t h y l e n e c o n t a i n e r i n w h i c h i t w a s i r r a d i a t e d , a l o n g w i t h m e r c u r y c a r r i e r , are w e t - a s h e d w i t h a m i x t u r e of n i t r i c , s u l f u r i c , a n d p e r c h l o r i c acids u n d e r g o o d reflux c o n d i t i o n s . T h e m e r c u r y is i s o l a t e d f r o m the digest b y p r e c i p i t a t i o n as m e r c u r i c sulfide a n d is p u r i f i e d b y e l e c t r o d e p o s i t i o n as e l e m e n t a l m e r c u r y o n g o l d f o i l , w h i c h is t h e n c o u n t e d for H g a n d 24-hr H g x- a n d γ-ray a c t i v i t y w i t h a t h i n N a l detector. 1 9 7

1 9 7 r a

C h e m i c a l yields were generally 7 5 - 9 0 % . c e d u r e w a s d e t e r m i n e d b y tracer studies. the 0.01 p p m l e v e l a n d less t h a n 5 %

T h e a c c u r a c y of the p r o

E r r o r s are less t h a n 1 5 %

at

at the 2 p p m l e v e l of m e r c u r y i n

b i o l o g i c a l tissues. P r e c i s i o n ranges f r o m less t h a n 1 7 % r e l a t i v e s t a n d a r d d e v i a t i o n at the 0.01 p p m l e v e l to less t h a n 5 %

at the 5 p p m

level.

E l e v e n c o a l samples f r o m O h i o a n d P e n n s y l v a n i a a n a l y z e d b y this m e t h o d h a d m e r c u r y concentrations of 0.32-1.20 p p m , w i t h a n average v a l u e of a b o u t 0.5 p p m

(18).

O ' G o r m a n et al. (19)

u s e d r a d i o c h e m i c a l N A A as a referee m e t h o d

i n e v a l u a t i n g the d e t e r m i n a t i o n of m e r c u r y b y a t o m i c a b s o r p t i o n niques.

A

commercial

testing

laboratory

d i d the

neutron

tech

activation

analyses. I r r a d i a t e d c o a l samples w e r e d i g e s t e d w i t h m e r c u r y c a r r i e r i n a n a c i d s o l u t i o n , a n d the m e r c u r y w a s d i s t i l l e d as m e r c u r i c c h l o r i d e . T h e m e r c u r y w a s e l e c t r o p l a t e d f r o m t h e d i s t i l l a t e , a n d the a c t i v i t y w a s c o u n t e d b y m u l t i c h a n n e l γ-ray s p e c t r o m e t r y . O n l y one

N A A d e t e r m i n a t i o n w a s m a d e o n e a c h of the 10 coals

s t u d i e d b y O ' G o r m a n et al. s e n s i t i v i t y is g i v e n .

N o estimate of the method's

Combustion-double

p r e c i s i o n or

gold amalgamation-atomic

ab

s o r p t i o n results a g r e e d w e l l w i t h the n e u t r o n a c t i v a t i o n results, a n d t h e former

method

w a s therefore

combustion-solution-atomic Weaver

considered

to be

more reliable than a

a b s o r p t i o n m e t h o d that gave l o w e r results.

and von Lehmden

(20),

u n d e r sponsorship

evaluated two instrumental N A A methods

of the E P A ,

a n d one w i t h r a d i o c h e m i c a l

separation for determining mercury i n coal. I n the r a d i o c h e m i c a l p r o c e d u r e the i r r a d i a t e d c o a l s a m p l e a n d m e r c u r i c o x i d e c a r r i e r are d i g e s t e d w i t h s u l f u r i c a c i d , f o l l o w e d b y n i t r i c a c i d . W a t e r a n d p o t a s s i u m b i s u l f a t e are a d d e d to d r i v e off a n y n i t r i c a c i d r e m a i n i n g . T h e m e r c u r y is separated b y a s t a n d a r d d i t h i z o n e extraction, a n d t h e extract is c o u n t e d for the 0.077 M e V p h o t o p e a k of H g with the N a l detector. 1 9 7

T h e three m e t h o d s w e r e e v a l u a t e d b y a n a l y z i n g the 11 c o a l samples from

the B u r e a u of

Mines round-robin program.

The

radiochemical

m e t h o d p r o v e d to b e r e l i a b l e , b u t W e a v e r a n d v o n L e h m d e n n o t e d t h a t it is t i m e - c o n s u m i n g , r e q u i r e s a large a m o u n t of l a b o r a t o r y

equipment

a n d f u m e h o o d space, a n d m a y h a v e r e c o v e r y errors. I n s t r u m e n t a l N A A u s i n g a l a r g e - v o l u m e (36 c c ) G e ( L i ) detector d i d not g i v e accurate results b e c a u s e of m a t r i x interferences

o n the

1 9 7

H g p e a k at 0.077 M e V .


The

8.

FROST E T A L .

Neutron

Activation

91

Analysis

other i n s t r u m e n t a l m e t h o d i n w h i c h c o u n t i n g was d o n e o n t h e n e w l y developed

10 m m G e ( L i ) l o w energy p h o t o n detector w h i c h has g o o d

r e s o l u t i o n i n the l o w e n e r g y r e g i o n of the γ-ray s p e c t r u m a n d a 400c h a n n e l a n a l y z e r , gave g o o d , fast results. O a k R i d g e is also u s i n g N A A extensively i n its s t u d y of t r a c e ele ments i n c o a l a n d t h e i r d i s p o s i t i o n i n p o w e r p l a n t c o m b u s t i o n ( 2 ) .

NAA

w i t h r a d i o c h e m i c a l s e p a r a t i o n is one m e t h o d u s e d for d e t e r m i n i n g m e r c u r y i n c o a l a n d c o a l ash. I r r a d i a t e d c o a l samples are w e t - a s h e d w i t h a m i x t u r e of H C 1 0 , H N 0 ,

H S 0 , C r 0 ~ , and monochloroacetic

acid,

a n d c o a l ash w i t h a m i x t u r e of H C 1 , H 0 , H F , H N 0 , a n d H C 1 0 .

Mer

4

3

2

4

2

4

2

2

3

4

c u r y is separated as the sulfide, a n d its g a m m a a c t i v i t y is m e a s u r e d . M e t h o d r e l i a b i l i t y was d e t e r m i n e d b y analysis of the 11 B u r e a u of M i n e s r o u n d - r o b i n c o a l samples. T h e concentrations of some other elements i n c o a l a n d c o a l ash d e t e r m i n e d b y other m e t h o d s are b e i n g c h e c k e d at O a k R i d g e b y r a d i o c h e m i c a l n e u t r o n a c t i v a t i o n as w e l l (2).

T h e samples are

w e t - a s h e d as d e s c r i b e d above, a n d e a c h e l e m e n t is s e p a r a t e d specifically. Rubidium and Cesium. T h e earliest s t u d y of trace elements i n c o a l b y r a d i o c h e m i c a l n e u t r o n a c t i v a t i o n was b y Smales a n d S a l m o n , w h o r e p o r t e d o n r u b i d i u m a n d c e s i u m i n 12 coals f r o m C o u n t y D u r h a m , E n g l a n d i n 1955

(21).

T o d e t e r m i n e r u b i d i u m , the i r r a d i a t e d c o a l s a m p l e a n d a d d e d r u b i d i u m c a r r i e r are d i g e s t e d a n d the o r g a n i c m a t t e r d e s t r o y e d b y h e a t i n g w i t h n i t r i c a n d s u l f u r i c acids, f o l l o w e d b y n i t r i c a n d p e r c h l o r i c acids. T h e r u b i d i u m is s e p a r a t e d f r o m the gross a c t i v i t y of the s a m p l e b y p r e c i p i t a t i o n w i t h f e r r i c h y d r o x i d e . T h e r u b i d i u m is t h e n p r e c i p i t a t e d as the c o b a l t i n i t r i t e a n d finally as the c h l o r o p l a t i n a t e . T h e a c t i v i t y of the c h l o r o p l a t i n a t e c a u s e d b y the 1.8 M e V β~ p a r t i c l e of 18.7-day R b is c o u n t e d w i t h a G e i g e r counter. I n the d e t e r m i n a t i o n of c e s i u m , the c o a l s a m p l e a n d c e s i u m c a r r i e r are d i g e s t e d , a n d t h e p e r c h l o r a t e s e p a r a t i o n a n d f e r r i c h y d r o x i d e scav e n g i n g p r e c i p i t a t i o n are m a d e as i n t h e p r o c e d u r e for r u b i d i u m . C e s i u m is t h e n separated f r o m the r e m a i n i n g s o l u t i o n b y p r e c i p i t a t i o n of c e s i u m b i s m u t h i o d i d e . T h e final s e p a r a t i o n is m a d e b y p r e c i p i t a t i o n of c e s i u m c h l o r o p l a t i n a t e , w h i c h is c o u n t e d w i t h a G e i g e r counter for the 0.66 M e V β" d e c a y of C s (t = 2.1 y r ) , or c o u n t e d for t h e 0.13 M e V γ-ray associ a t e d w i t h the i s o m e r i c t r a n s i t i o n of C s ( t% = 2.9 h r ). 8 6

1 3 4

h

1 3 4 m

T h e c h e m i c a l y i e l d of e a c h e l e m e n t w a s u s u a l l y a b o u t 7 0 % .

The

r u b i d i u m content of the 12 C o u n t y D u r h a m coals w a s 6 - 3 0 p p m , a n d t h e c e s i u m content i n 10 of the coals was 0.8-3.7 p p m .

Reproducibility

of results was v e r y g o o d for c e s i u m ; the r e l a t i v e s t a n d a r d d e v i a t i o n of the m e a n result w a s u s u a l l y less t h a n 5 % .

R u b i d i u m results w e r e s l i g h t l y

less r e p r o d u c i b l e , the largest r e l a t i v e s t a n d a r d d e v i a t i o n b e i n g 2 2 % . Selenium.

I n 1969, P i l l a y et al. (22)

d e t e r m i n e d the s e l e n i u m c o n

tent of 86 coals f r o m v a r i o u s c o a l - p r o d u c i n g areas of t h e U n i t e d States b y N A A c o m b i n e d w i t h extractive s e l e n i u m d i s t i l l a t i o n .


92

TRACE

ELEMENTS

IN FUEL

T h e i r r a d i a t e d c o a l s a m p l e w i t h s e l e n i u m c a r r i e r a d d e d is w e t - a s h e d w i t h a n i t r i c - p e r c h l o r i c a c i d m i x t u r e u n d e r g o o d reflux. D e t a i l e d tracer experiments w e r e r u n to s h o w that trace levels of s e l e n i u m are not lost f r o m the s a m p l e d u r i n g a s h i n g a n d e q u i l i b r a t i o n of the c a r r i e r w i t h t h e s a m p l e . T h e s e l e n i u m ( V I ) is r e d u c e d to s e l e n i u m ( I V ) a n d d i s t i l l e d i n t o 2 M H C 1 , w i t h t w o a d d i t i o n s of h y d r o c h l o r i c a n d h y d r o b r o m i c acids. E l e m e n t a l s e l e n i u m is p r e c i p i t a t e d , d i s s o l v e d i n n i t r i c a c i d a n d h y d r o g e n p e r o x i d e , a n d r e p r e c i p i t a t e d . T h e S e a c t i v i t y of t h e p r e c i p i t a t e w a s counted w i t h a N a l crystal. T h e s e l e n i u m r e c o v e r y is u s u a l l y a b o u t 8 0 % . T h e authors ( 2 2 ) h a d 7 5

g o o d p r e c i s i o n i n t h e i r results. S e l e n i u m concentrations i n t h e 86 coals r a n g e d f r o m 0.5 to 11 p p m b u t u s u a l l y w e r e f r o m 1 to 5 p p m ; t h e m e d i a n w a s 2.8 p p m . A s i m i l a r p r o c e d u r e has b e e n u s e d at the I l l i n o i s State G e o l o g i c a l S u r v e y to d e t e r m i n e s e l e n i u m , b u t l o w - t e m p e r a t u r e c o a l ash w a s a n a l y z e d b e c a u s e it w a s d e t e r m i n e d that the a m o u n t of s e l e n i u m that m i g h t b e lost f r o m c o a l o n a s h i n g at 1 5 0 ° C ( s o m e t i m e s u p to 4 - 5 % ) w a s w i t h i n the a c c u r a c y a n d p r e c i s i o n of the e x p e r i m e n t a l m e t h o d

(4).

T h e i r r a d i a t e d c o a l ash samples are d i g e s t e d u n d e r reflux w i t h a m i x t u r e of h y d r o c h l o r i c , n i t r i c , a n d p e r c h l o r i c acids. T h e s e l e n i u m is t h e n s e p a r a t e d b y the h y d r o b r o m i c a c i d d i s t i l l a t i o n a n d c o l l e c t e d i n w a t e r at 0 ° C . E l e m e n t a l s e l e n i u m is p r e c i p i t a t e d f r o m the d i s t i l l a t e w i t h sulfurous a c i d , a n d t h e a c t i v i t y of the p r e c i p i t a t e is c o u n t e d . T h e p h o t o p e a k a r i s i n g f r o m the 0.121 a n d 0.136 M e V γ-rays of Se is m e a s u r e d . 7 5

R a d i o c h e m i c a l y i e l d s are q u a n t i t a t i v e . T h e r e l a t i v e s t a n d a r d d e v i a t i o n of a m e a s u r e m e n t is u s u a l l y better t h a n ± 1 0 % . 1630 gave 2.0 ±

A n a l y s i s of S R M

0.13 p p m s e l e n i u m , a n d results for the N B S - E P A r o u n d -

r o b i n c o a l a n d fly ash samples a g r e e d w i t h i n e x p e r i m e n t a l error w i t h the p r o b a b l e certified values of s e l e n i u m i n those samples.

The selenium

concentrations of 101 coals a n a l y z e d b y the a b o v e m e t h o d r a n g e f r o m 0.45 to 7.7 p p m a n d h a v e a m e d i a n v a l u e of 1.9 p p m

(16).

A t N B S , the n e u t r o n a c t i v a t i o n w i t h c o m b u s t i o n s e p a r a t i o n m e t h o d u s e d for d e t e r m i n i n g m e r c u r y i n c o a l (12) d e t e r m i n i n g s e l e n i u m b y R o o k (13).

was f u r t h e r i n v e s t i g a t e d for

T h e same p r o c e d u r e is u s e d except

that the s a m p l e is h e a t e d finally to 1000 ° C .

M e r c u r i c o x i d e is also u s e d

as c a r r i e r for the s e l e n i u m b e c a u s e s e l e n i u m oxides are difficult to d i s solve i n m i n e r a l acids. T h e m e r c u r i c s e l e n i d e f o r m e d carries the s e l e n i u m effectively, a n d , as i t is s o l u b l e i n n i t r i c a c i d , the d i s s o l u t i o n p r o c e d u r e d e v e l o p e d f o r the m e r c u r y s e p a r a t i o n c a n be u s e d so that m e r c u r y a n d s e l e n i u m c a n b e d e t e r m i n e d i n the same s a m p l e . R o o k c o u n t e d the a c t i v i t y of his p r o d u c t solutions w i t h a G e ( L i ) d e t e c t o r a n d 2 0 4 8 - c h a n n e l a n a l y z e r , m e a s u r i n g the 0.265 M e V γ-ray p e a k of 120-day

75

S e , as

1 9 7 m

H g interferes w i t h the m o r e c o m m o n l y u s e d 0.136

M e V peak. T r a c e r studies s h o w e d t h a t s e l e n i u m is r e c o v e r e d q u a n t i t a t i v e l y i n


8.

FROST E T A L .

Neutron

Activation

93

Analysis

the separation. T h e m e t h o d is fast, a n d its p r e c i s i o n a n d a c c u r a c y are g o o d . T h e a c c u r a c y of a m e a n r e s u l t is r e p o r t e d to b e better t h a n

±10%

r e l a t i v e at the 9 5 % confidence l e v e l . T h e p r o v i s i o n a l v a l u e of 2.11 ±

0.09

p p m s e l e n i u m i n S R M 1630 w a s e s t a b l i s h e d b y this m e t h o d . Gallium.

S i n c e i n v e s t i g a t i o n s h o w e d t h a t g a l l i u m is not lost w h e n

c o a l is a s h e d i n a l o w - t e m p e r a t u r e p l a s m a asher not e x c e e d i n g 150 ° C , S a n t o l i q u i d o a n d R u c h (4, 23)

determined gallium i n the low-tempera

ture ash of c o a l . T h e i r r a d i a t e d ash s a m p l e a n d a d d e d g a l l i u m a n d z i n c carriers are f u s e d w i t h s o d i u m h y d r o x i d e . T h e m e l t is t a k e n u p i n w a t e r , the m i x t u r e is filtered, a n d z i n c h y d r o x i d e , w h i c h carries the g a l l i u m , is t h e n p r e c i p i t a t e d . T h e p r e c i p i t a t e is d i s s o l v e d i n 8 M H C 1 s o l u t i o n , a n d the g a l l i u m is extracted w i t h i s o p r o p y l ether a n d b a c k - e x t r a c t e d w i t h water. T h e a c t i v i t y of the aqueous s o l u t i o n is c o u n t e d b y m e a s u r e m e n t of t h e 0.832 M e V γ-ray p h o t o p e a k of 14-hr G a . 7 2

Radiochemical

yields

are w i t h i n

46-74%.

s t a n d a r d d e v i a t i o n of the m e t h o d is ± 8 % .

The

average relative

T h e a c c u r a c y of the m e t h o d

w a s c h e c k e d b y analysis of a U . S. G e o l o g i c a l S u r v e y r o c k s t a n d a r d . G a l l i u m concentrations i n 101 coals, c a l c u l a t e d f r o m t h e c o n c e n t r a t i o n i n the c o a l ash a n d the p e r c e n t a g e of l o w - t e m p e r a t u r e ash i n t h e c o a l , r a n g e f r o m 1.1 to 7.5 p p m , the m e d i a n v a l u e b e i n g b e t w e e n 2.9 a n d 3.0 p p m (16). Arsenic.

A t the I l l i n o i s G e o l o g i c a l S u r v e y , arsenic has also b e e n

d e t e r m i n e d i n l o w - t e m p e r a t u r e c o a l ash, a n d the c o n c e n t r a t i o n is c a l c u l a t e d to a w h o l e c o a l basis because i t w a s f o u n d that n e g l i g i b l e a m o u n t s of arsenic are lost i n the l o w - t e m p e r a t u r e a s h i n g of c o a l

(4).

T h e i r r a d i a t e d ash s a m p l e , w i t h arsenic c a r r i e r a d d e d , is d i g e s t e d u n d e r reflux w i t h h y d r o c h l o r i c , n i t r i c , a n d p e r c h l o r i c acids. A r s e n i c ( I I I ) is t h e n d i s t i l l e d f r o m the m i x t u r e w i t h h y d r o b r o m i c a c i d a n d c o l l e c t e d i n w a t e r . E l e m e n t a l arsenic is p r e c i p i t a t e d w i t h s o d i u m h y p o p h o s p h i t e , a n d the a c t i v i t y of the p r e c i p i t a t e is c o u n t e d . T h e 0.559 M e V γ-ray p h o t o p e a k of 26.5-hr A s is m e a s u r e d . R a d i o c h e m i c a l y i e l d s are quantitative. 7 6

T h e m a x i m u m r e l a t i v e s t a n d a r d d e v i a t i o n of a m e a s u r e m e n t was ± 1 2 % .

found

R e s u l t s b y this m e t h o d for the N B S - E P A r o u n d - r o b i n c o a l

a n d fly ash samples a g r e e d w i t h i n e x p e r i m e n t a l error w i t h the p r o b a b l e certified values f o r the t w o samples.

T h e arsenic concentrations i n 101

coals a n a l y z e d r a n g e d f r o m 0.52 to 93 p p m

(16).

T h e d i s t i l l a t i o n s e p a r a t i o n p r o c e d u r e was the p r i n c i p a l m e t h o d u s e d for t h e arsenic d e t e r m i n a t i o n s , b u t m o r e r e c e n t l y S a n t o l i q u i d o (24)

has

d e v e l o p e d a m e t h o d for t h e carrier-free s e p a r a t i o n of arsenic f r o m l o w temperature

coal

ash i n v o l v i n g r e t e n t i o n o n

an inorganic

exchanger

column. T h e i r r a d i a t e d c o a l ash s a m p l e is f u s e d w i t h s o d i u m h y d r o x i d e . A 7 M H N 0 s o l u t i o n of the m e l t is passed t h r o u g h a s m a l l c h r o m a t o g r a p h i c 3


94

TRACE

ELEMENTS

IN

FUEL

c o l u m n filled w i t h a c i d a l u m i n u m o x i d e or h y d r a t e d m a n g a n e s e d i o x i d e . T h e c o l u m n is r i n s e d w i t h 7 M H N 0 . T h e A s a c t i v i t y o n the c o l u m n is t h e n c o u n t e d . 7 6

3

A n a l y s e s of six coals gave results i n agreement w i t h those o b t a i n e d e a r l i e r b y the d i s t i l l a t i o n m e t h o d .

T h e p r e c i s i o n of b o t h i n o r g a n i c ex

c h a n g e r m e t h o d s is g o o d , w i t h average r e l a t i v e s t a n d a r d deviations less t h a n ± 8 % .

Results b y the m e t h o d u s i n g h y d r a t e d manganese

of

dioxide

are s l i g h t l y h i g h e r t h a n those b y the d i s t i l l a t i o n a n d a c i d a l u m i n u m o x i d e exchanger

methods,

w h i c h m a y reflect the fact that m o r e metals

r e t a i n e d b y t h e h y d r a t e d manganese d i o x i d e

are

exchanger.

A t N B S , the neutron activation method w i t h combustion

separation

step a p p l i e d to the d e t e r m i n a t i o n of m e r c u r y a n d s e l e n i u m i n c o a l has b e e n m o d i f i e d a n d e x t e n d e d to analysis for arsenic, z i n c , a n d c a d m i u m b y O r v i n i et al.

(14).

A f t e r c o m b u s t i o n of the s a m p l e a n d carriers i n a n o x y g e n s t r e a m , r e d u c i n g c o n d i t i o n s are a c h i e v e d b y a flow of c a r b o n m o n o x i d e o v e r the s a m p l e ash. A r s e n i c , z i n c , c a d m i u m , a n d a n y r e m a i n i n g s e l e n i u m a n d m e r c u r y are r e d u c e d to e l e m e n t a l f o r m . W h e n the s a m p l e is h e a t e d to 1150°C i n a slow carbon monoxide stream i n a quartz tube i n a furnace, r e c o v e r y of a l l five elements i n the l i q u i d n i t r o g e n t r a p is c o m p l e t e i n 30 m i n . T h e r e c o v e r y t r a p is w a s h e d w i t h n i t r i c a c i d to dissolve a l l t h e m e t a l s , a n d t h e r a d i o a c t i v i t y of a n i t r i c a c i d s o l u t i o n of the p r o d u c t s is c o u n t e d w i t h a G e ( L i ) detector. T h e m e t h o d w a s tested b y tracer experiments o n several m a t r i c e s , i n c l u d i n g c o a l a n d c r u d e o i l . R e c o v e r i e s w e r e q u a n t i t a t i v e or n e a r l y so (97.8%).

T h e m e t h o d gave g o o d results for z i n c , c a d m i u m , m e r c u r y ,

s e l e n i u m , a n d arsenic i n N B S o r c h a r d leaves a n d b o v i n e l i v e r a n d is c u r r e n t l y b e i n g u s e d to d e t e r m i n e these elements i n n e w Antimony.

SRMs.

I n the d e t e r m i n a t i o n of a n t i m o n y i n c o a l , the i r r a d i a t e d

c o a l s a m p l e m i x e d w i t h b e n z o i c a c i d a n d a n t i m o n y t r i o x i d e c a r r i e r is burned in a Parr bomb

(4).

T h e b o m b contents are d i g e s t e d w i t h c o n c e n t r a t e d h y d r o c h l o r i c a c i d , a n d m a t e r i a l s t i l l u n d i s s o l v e d is t h e n d i g e s t e d w i t h p o t a s s i u m h y d r o x i d e a n d h y d r o g e n p e r o x i d e . A c r u d e separation is m a d e b y a sulfide p r e c i p i t a t i o n f r o m the c o m b i n e d d i g e s t i o n solutions. T h e sulfides are d i s s o l v e d i n a q u a r e g i a , the s o l u t i o n is e v a p o r a t e d , a n d a n t i m o n y i n t h e r e s i d u e is r e d u c e d to a n t i m o n y ( I I I ) w i t h h y d r o x y l a m i n e h y d r o c h l o r i d e . T h e s a m p l e , i n a m m o n i u m t h i o c y a n a t e — h y d r o c h l o r i c a c i d m e d i u m , is l o a d e d onto a D o w e x 2 c o l u m n ( S C N " f o r m ). A r s e n i c a n d other i m p u r i t i e s are e l u t e d w i t h a l i q u o t s of m o r e d i l u t e a m m o n i u m t h i o c y a n a t e - h y d r o c h l o r i c a c i d solutions. A n t i m o n y is e l u a t e d w i t h s u l f u r i c a c i d a n d fixed i n s o l u t i o n b y a d d i t i o n of h y d r o c h l o r i c a c i d . T h e a c t i v i t y of the s o l u t i o n c a u s e d b y the 0.56 M e V γ-ray of 2.8-day S b is c o u n t e d . 1 2 2

Dissolution

of

t h e oxides

and/or

other

compounds

of

antimony

present after c o m b u s t i o n of t h e c o a l s a m p l e p r o v e d difficult. R a d i o c h e m i c a l y i e l d s are r a t h e r l o w , r a n g i n g f r o m 30 to 5 5 % .

T h e average relative


8.

Neutron

FROST E T A L .

Activation

s t a n d a r d d e v i a t i o n of a n analysis is ±20%. 101 coals a n a l y z e d w a s 0.1-8.9 p p m

95

Analysis T h e a n t i m o n y content

of

(16).

Bromine. A N A A m e t h o d for b r o m i n e i n c o a l w a s d e v e l o p e d i n o r d e r to h a v e a n interference-free

(4)

method.

T h e irradiated coal sample, m i x e d w i t h A l u n d u m i n a porcelain boat c o n t a i n i n g b r o m i d e c a r r i e r , is b u r n e d i n the same m a n n e r as i n the m e t h o d for m e r c u r y ( 4 ) , a n d t h e c o m b u s t i o n p r o d u c t s are t r a p p e d i n t w o s o d i u m or p o t a s s i u m h y d r o x i d e solutions. T h e a l k a l i s o l u t i o n , i n a l a r g e c o u n t i n g v i a l , is c o u n t e d d i r e c t l y for the 0.56 M e V γ-ray p h o t o p e a k of 3 6 - h r B r . C h e m i c a l y i e l d s are 4 9 - 7 7 % . T h e average r e l a t i v e s t a n d a r d d e v i a 8 2

t i o n is ± 1 0 % . 4 to 29 p p m (4,

B r o m i n e concentrations i n 23 coals a n a l y z e d r a n g e d f r o m 16).

Zinc and Cadmium.

A radiochemical method was developed

(4)

f o r s e p a r a t i n g of z i n c a n d c a d m i u m f r o m l o w - t e m p e r a t u r e c o a l ash. T h e i r r a d i a t e d c o a l ash s a m p l e w i t h z i n c a n d c a d m i u m carriers is f u s e d w i t h s o d i u m h y d r o x i d e . T h e m e l t i n 2 N H C 1 s o l u t i o n is l o a d e d onto a D o w e x 1 a n i o n e x c h a n g e c o l u m n ( C I " f o r m ) . T h e c o l u m n is r i n s e d w i t h 2N H C 1 , a n d c a d m i u m a n d z i n c are s i m u l t a n e o u s l y e l u t e d w i t h d i s t i l l e d w a t e r . T h e a c t i v i t y of t h e e l u a t e c a u s e d b y the 0.438 M e V γ-ray of 13.8-hr Z n is c o u n t e d i m m e d i a t e l y , a n d after a o n e - w e e k d e c a y p e r i o d c a d m i u m is m e a s u r e d b y the 0.530 M e V γ-ray a c t i v i t y of 54-hr Cd. 6 9 m

1 1 5

R a d i o c h e m i c a l y i e l d s are 8 0 - 9 5 % cadmium.

for

zinc and quantitative

T h e average r e l a t i v e s t a n d a r d d e v i a t i o n w a s ± 2 5 %

a n d better t h a n ± 1 0 %

for

for z i n c

for c a d m i u m . T h e d e t e c t i o n l i m i t of the m e t h o d

is 50 p p m c a d m i u m i n the ash. A n a l y s i s of t w o I l l i n o i s coals w i t h u n u s u a l l y h i g h c a d m i u m content agreement

(17 a n d 21 p p m )

g a v e results i n g o o d

w i t h those o b t a i n e d b y a t o m i c a b s o r p t i o n

stripping voltammetry (4). radiochemical method

for

T h e recent d e v e l o p m e n t the

d e t e r m i n a t i o n of

a r s e n i c i n c o a l a n d fly ash, b y O r v i n i et al. (14),

and by

anodic

a n d testing of

zinc, cadmium,

a

and

has a l r e a d y b e e n d i s

cussed i n t h e section o n arsenic. Uranium.

P e r r i c o s a n d B e l k a s (25)

have determined u r a n i u m i n

six coals b y n e u t r o n a c t i v a t i o n f o l l o w e d b y s e p a r a t i o n of the u r a n i u m daughter neptunium-239 b y carrier-free extraction chromatography.

The

coals, f r o m m i n e s i n n o r t h e r n G r e e c e , h a d v e r y h i g h u r a n i u m c o n c e n t r a tions ( 0 . 0 1 2 - 0 . 0 3 7 % ) .

H o w e v e r , u r a n i u m at the f e w parts p e r m i l l i o n

l e v e l f o u n d i n m o s t coals c o u l d n o d o u b t b e d e t e r m i n e d b y a m o d i f i c a t i o n of this m e t h o d . T h e c o a l samples are a s h e d at 6 0 0 ° C , a n d the a s h is d i s s o l v e d b y d i g e s t i o n w i t h n i t r i c a n d h y d r o f l u o r i c acids. T r a c e s of h y d r o f l u o r i c a c i d are e v a p o r a t e d , a n d d i l u t e n i t r i c a c i d solutions of t h e ash samples are i r r a d i a t e d . T h e i r r a d i a t e d ash s o l u t i o n , w i t h n i t r i c a c i d a d d e d , is h e a t e d to dryness, a n d the r e s i d u e is t a k e n u p i n h y d r o c h l o r i c a c i d . T h e s o l u t i o n


96

TRACE

ELEMENTS

I N FUEL

is t r e a t e d w i t h h y d r o x y l a m i n e h y d r o c h l o r i d e to r e d u c e t h e n e p t u n i u m q u a n t i t a t i v e l y t o t h e extractable n e p t u n i u m ( I V ). T h e s a m p l e i n h y d r o x y l a m i n e h y d r o c h l o r i d e — h y d r o c h l o r i c a c i d s o l u t i o n is passed t h r o u g h a c o l u m n o f t h e n o y l t r i f l u o r o a c e t o n e i n x y l e n e as s t a t i o n a r y phase o n b o r o silicate glass p o w d e r as s u p p o r t , a n d the c o l u m n is r i n s e d w i t h h y d r o c h l o r i c a c i d - h y d r o x y l a m i n e h y d r o c h l o r i d e s o l u t i o n . T h e n e p t u n i u m is e l u t e d w i t h 6 M H C 1 , followed b y ethyl alcohol a n d 6 M H C 1 , a n d the activity of the s o l u t i o n is c o u n t e d b y m e a s u r i n g the 0.106 M e V p h o t o p e a k o f N p . 2 3 9

T h e average

c h e m i c a l y i e l d o f this s e p a r a t i o n h a d a l r e a d y

s h o w n to b e 9 9 . 5 % , so n o y i e l d c o r r e c t i o n is necessary.

been

T h e m e t h o d is

fast a n d has a n error o f a b o u t ± 5 % . T h e a c c u r a c y o f t h e m e t h o d w a s c h e c k e d b y analysis o f t w o r o c k standards. Summary N e u t r o n a c t i v a t i o n w i t h r a d i o c h e m i c a l s e p a r a t i o n affords a r e l i a b l e m e t h o d f o r a n a l y z i n g 11 trace elements i n c o a l .

B u r n i n g the coal a n d

t r a p p i n g t h e p r o d u c t s is a s i m p l e w a y to separate c e r t a i n elements f r o m t h e o r g a n i c m a t r i x . T h e c o n c e n t r a t i o n o f some elements i n c o a l m a y b e d e t e r m i n e d b y analysis o f t h e l o w - t e m p e r a t u r e a s h o f t h e c o a l . A v a r i e t y of r a d i o c h e m i c a l s e p a r a t i o n m e t h o d s c a n b e used. T h e r e is also t h e p o s s i bility of developing methods

o f analysis f o r s e v e r a l other elements i n

c o a l . F o r e x a m p l e , i o n e x c h a n g e separations m a d e w i t h t h e n e w l y d e v e l o p e d i n o r g a n i c exchangers present a l a r g e l y u n e x p l o r e d

field.

Literature Cited 1. Billings, C. E., Matson, W. R., Science (1972) 176, 1232. 2. Bolton, Ν. E., van Hook, R. I., Fulkerson, W., Lyon, W. S., Andren, A. W., Carter, J. Α., Emery, J. F., "Progress Report," June 1971-Jan. 1973, Contract W-7405-eng-26, Oak Ridge National Laboratory, March 1973. 3. Swanson, V. E., Appendix J-II, "Report of the Coal Resources Work Group, Southwest Energy Study," U.S. Geological Survey, Jan. 1972. 4. Ruch, R. R., Gluskoter, H. J., Shimp, N. F., Ill. StateGeol.Surv. Environ. Geol. Note (1973) 61, 43 pp. 5. Gluskoter,H.J., Ruch, R. R., Fuel (1971) 50, 65. 6. Rancitelli, L. Α., "Pacific Northwest Laboratory Annual Report for 1972 to U.S. Atomic Energy Commission, Division of Biomedical and Environ mental Research," Vol. II, Pt. 2, pp. 56-57, April 1973. 7. Block, C., Dams, R., Anal. Chim. Acta (1974) 68, 11. 8. Joensuu, Ο. I., Science (1971) 172, 1027. 9. Ruch, R. R., Gluskoter, H. J., Kennedy, E. J., Ill. State Geol. Surv. Environ. Geol. Note (1971) 43, 15 pp. 10. Schlesinger, M. D., Schultz, H., Bur. Mines Rept. Invest. (1972) 7609, 11 pp. 11. von Lehmden, D. J., Jungers, R. J., Lee, R. E., Jr., Anal. Chem. (1974) 46, 239. 12. Rook, H. L., Gills, T. E., LaFleur, P. D., Anal. Chem. (1972) 44, 1114. 13. Rook, H. L., Anal. Chem. (1972) 44, 1276. 14. Orvini, E., Gills, T. E., LaFleur, P. D., Trans. Amer. Nucl. Soc. (1972) 15, 642.


8.

FROST E T A L .

Neutron

Activation

Analysis

97

15. Gorsuch, T. T., "The Destruction of Organic Matter," Pergamon, England, 1970. 16. Ruch, R. R., Gluskoter, H. J., Shimp, N. F., "Illinois State Geological Sur vey Final Report," Contract No. 68-02-0246 and Grant No. R-800059, Mar. 1974. 17. Pillay, K. K. S., Thomas, C. C., Jr., Sondel, J. Α., Hyche, C. M., Anal. Chem. (1971) 43, 1419. 18. Pillay, K. K. S., Thomas, C. C., Jr., Sondel, J. Α., Hyche, C. M., Environ. Res. (1972) 5, 172. 19. O'Gorman, J. V., Suhr, Ν. H., Walker, Jr., P. L., Appl. Spectrosc. (1972) 26, 44. 20. Weaver, J. N., von Lehmden, D. J., Amer. Chem. Soc., Div. Fuel Chem. Preprint 16(3), 16 (1972). 21. Smales, Α. Α., Salmon, L., Analyst (1955) 80, 37. 22. Pillay, K. K. S., Thomas, C. C., Jr., Kaminski, J. W., Nucl. Appl. Technol. (1969) 7, 478. 23. Santoliquido, P. M., Ruch, R. R., Radiochem. Radioanal. Lett. (1972) 12, 71. 24. Santoliquido, P. M., Radiochem. Radioanal. Lett. (1973) 15, 373. 25. Pericos, D. C., Belkas, E. P., Talanta (1969) 16, 745. RECEIVED April 24, 1974


Trace Elements in Coal by Neutron Activation Analysis with

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