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