Trace Elements in Fuel - ACS Publications

1 Mineral Matter and Trace Elements in Coal HAROLD J. GLUSKOTER

Downloaded by 120.32.115.112 on February 10, 2016 | http://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch001

Illinois State Geological Survey, Urbana, Ill. 61801 The term, "mineral matter in coal," refers to mineral phases or species present in coal and also to all chemical elements in coal that are generally considered to be inorganic. Most mineral matter occurs in coal as silicates, sulfides, and carbonates. Four coals, separated into series of specific gravity fractions, have been analyzed. The trace elements, germanium, beryllium, and boron, have the greatest organic affinities, whereas Hg, Zr, Zn, As, Cd, Pb, Mn, and Mo are generally inorganically combined in the coal. Each of the other trace elements determined apparently occurs in both organic and inorganic combination. P, Ga, Sb, Ti, and V are more closely associated with the elements having strong organic affinities while Co, Ni, Se, Cr, and Cu are more closely associated with the elements having strong inorganic affinities. ' " p h e t e r m , " m i n e r a l m a t t e r i n c o a l , " is w i d e l y u s e d , b u t its m e a n i n g A

varies a p p r e c i a b l y .

T h e term usually includes a l l inorganic non-coal

m a t e r i a l f o u n d i n c o a l as m i n e r a l phases a n d also a l l elements i n c o a l t h a t are c o n s i d e r e d i n o r g a n i c . T h e r e f o r e , a l l elements i n c o a l except c a r b o n , h y d r o g e n , o x y g e n , n i t r o g e n , a n d s u l f u r are i n c l u d e d i n this b r o a d d e f i n i t i o n . F o u r of these five o r g a n i c elements also a r e f o u n d i n coals i n i n o r g a n i c c o m b i n a t i o n a n d therefore are p a r t of t h e m i n e r a l matter. C a r b o n is, present i n carbonates

[ C a ( F e , M g ) C 0 ] ; h y d r o g e n i n free w a t e r a n d 3

w a t e r of h y d r a t i o n ; o x y g e n i n w a t e r , oxides, carbonates, sulfates, a n d silicates; a n d s u l f u r i n sulfides

(primarily pyrite a n d marcasite) a n d

sulfates. Interest i n m i n e r a l m a t t e r i n c o a l arises p r i m a r i l y because some of the m a t e r i a l s m a y h a v e d e t r i m e n t a l effects d u r i n g c o a l use.

Because

m e t h o d s of u s i n g c o a l are b e c o m i n g m o r e s o p h i s t i c a t e d a n d i n c r e a s i n g l y large amounts of c o a l are b e i n g u s e d at single locations, these d e t r i m e n t a l effects s h o u l d b e c o n s i d e r e d f u r t h e r . 1 In Trace Elements in Fuel; Babu, Suresh P.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

2

TRACE

ELEMENTS

IN

FUEL

A l t h o u g h the a m o u n t of m i n e r a l m a t t e r i n coals varies c o n s i d e r a b l y , i t is n o r m a l l y l a r g e e n o u g h to be significant h o w e v e r the c o a l is used. I n a s t u d y of 65 I l l i n o i s coals, R a o a n d G l u s k o t e r ( J ) f o u n d the m i n e r a l m a t t e r content to r a n g e f r o m 9.4 to 2 2 . 3 % , c o r r e s p o n d i n g to a n

ash

content of 7.3 a n d 1 5 . 8 % , r e s p e c t i v e l y . O ' G o r m a n a n d W a l k e r (2)

found

a n e v e n larger r a n g e ( 9 . 0 5 - 3 2 . 2 6 % )

i n 16

w h o l e c o a l samples

from

i n m i n e r a l m a t t e r content

a w i d e d i s t r i b u t i o n of locations i n N o r t h

A m e r i c a . I f 1 5 % is a reasonable estimate of the average v a l u e of m i n e r a l m a t t e r content i n coals m i n e d i n N o r t h A m e r i c a , t h e n , unless p a r t i a l l y r e m o v e d b y c l e a n i n g , that a m o u n t enters e a c h c o a l u t i l i z a t i o n process. 6


S i n c e a p p r o x i m a t e l y 590 X 1 0 tons of c o a l w e r e p r o d u c e d i n the U n i t e d States i n 1973 i t is e s t i m a t e d that 89 X 1 0

6

tons of this w a s n o r m a l l y

u n w a n t e d m i n e r a l matter. Interest i n m i n e r a l m a t t e r content of c o a l intensified as e l e c t r i c p o w e r plants b e c a m e larger a n d the boilers b e g a n to operate at h i g h e r t e m p e r a tures.

P r o b l e m s of fireside b o i l e r - t u b e f o u l i n g a n d c o r r o s i o n , w h i c h be-

c a m e i n c r e a s i n g l y severe at the h i g h e r temperatures, w e r e r e l a t e d to the sulfur, c h l o r i n e , a l k a l i , a n d ash content of the coals ( 3 ) . W i t h i n the past s e v e r a l years, the g e n e r a l p u b l i c has b e c o m e m o r e interested

in both

a i r a n d w a t e r p o l l u t i o n . T h e r e f o r e , b o t h the c o a l c o n s u m e r a n d the p r o d u c e r n e e d a m o r e t h o r o u g h k n o w l e d g e of the m i n e r a l m a t t e r i n c o a l a n d of the p r o d u c t s a n d b y - p r o d u c t s of the m i n e r a l m a t t e r p r o d u c e d w h e n c o a l is c o m b u s t e d .

M u c h of this interest has b e e n d i r e c t e d to the forms

of sulfur i n c o a l a n d c o a l refuse, to the sulfur oxides f o r m 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 to the sulfates f r o m c o a l o x i d a t i o n . T h e r e has b e e n a c o n s e q u e n t d e m a n d for d a t a r e l a t i n g to t h e o r i g i n , d i s t r i b u t i o n , a n d reactions of sulfur i n c o a l . T h e r e is also m u c h d e m a n d f o r d a t a o n t h e trace elements i n c o a l s : t h e i r concentrations a n d d i s t r i b u t i o n s i n coals, t h e i r v o l a t i l i t y , a n d t h e i r p o t e n t i a l effects o n t h e e n v i r o n m e n t . M o r e r e c e n t l y , there has b e e n m u c h c o n c e r n a b o u t

the

possible

effects of the m i n e r a l m a t t e r i n c o a l o n processes u s e d to c o n v e r t c o a l to other fuels s u c h as gasification, l i q u e f a c t i o n , a n d p r o d u c t i o n o f c l e a n s o l i d fuels.

N o t o n l y is r e m o v i n g a n d d i s p o s i n g of the m i n e r a l m a t t e r

a p r o b l e m , b u t also the p o s s i b l e c h e m i c a l effects s u c h as catalyst p o i s o n i n g , w h i c h m i g h t b e e x p e c t e d i n the m e t h a n a t i o n of gas f r o m c o a l , s h o u l d be considered. N o t a l l of the interest i n m i n e r a l m a t t e r i n coals is s t i m u l a t e d b y its d e t r i m e n t a l effects d u r i n g c o a l use.

I n s e v e r a l instances c o a l is a source

of d e s i r e d elements

U r a n i u m has b e e n p r o d u c e d

a n d materials.

from

l i g n i t e ; g e r m a n i u m a n d sulfur c o u l d be p r o d u c e d f r o m c o a l ; a n d c o a l ash has b e e n u s e d for c o n s t r u c t i o n m a t e r i a l s s u c h as b r i c k , l i g h t w e i g h t aggregate, a n d r o a d p a v i n g m a t e r i a l .

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

1.

Mineral

GLUSKOTER

Minerals

Matter

and Trace Elements

3

in Coal

in Coal

S e v e r a l d o z e n m i n e r a l s are r e p o r t e d i n coals, a l t h o u g h most of these o c c u r o n l y s p o r a d i c a l l y or i n trace amounts. T h e o v e r w h e l m i n g m a j o r i t y of the m i n e r a l s i n c o a l are i n one of f o u r g r o u p s : a l u m i n o s i l i c a t e s , c a r bonates, sulfides, a n d s i l i c a ( q u a r t z )

(Figure 1). C l a y m i n e r a l s are the most

Aluminosilicates—Clay Minerals.

com-

m o n l y o c c u r r i n g i n o r g a n i c constituents of coals a n d of the strata assoc i a t e d w i t h the coals. M u c h of t h e w o r k o n clays r e p o r t e d i n the l i t e r a t u r e is c o n c e r n e d w i t h these strata, not the coals themselves.

M a n y different


c l a y m i n e r a l s h a v e b e e n r e p o r t e d i n coals, b u t t h e most c o m m o n illite

[(OH) K (Si 4

2

6

· Al )Al 0 o], 2

4

2

kaolinite

[(OH) Si Al O 8

4

4

1 0

],

are and

m i x e d - l a y e r i l l i t e - m o n t m o r i l l o n i t e . R a o a n d G l u s k o t e r ( 1 ), i n a n i n v e s t i g a t i o n of 65 coals f r o m the I l l i n o i s B a s i n , r e p o r t e d a m e a n v a l u e of 5 2 % for c l a y i n t h e m i n e r a l m a t t e r . O ' G o r m a n a n d W a l k e r ( 2 ) also f o u n d t h a t t h e c l a y m i n e r a l s m a k e u p the greater p a r t of t h e m i n e r a l m a t t e r i n most of the coals t h a t t h e y s t u d i e d . Sulfides and Sulfates.

P y r i t e is the d o m i n a n t sulfide m i n e r a l i n c o a l .

M a r c a s i t e has also b e e n r e p o r t e d f r o m m a n y different coals.

Pyrite and

m a r c a s i t e are d i m o r p h s , m i n e r a l s that are i d e n t i c a l i n c h e m i c a l c o m p o s i t i o n ( F e S ) b u t differ i n c r y s t a l l i n e f o r m ; p y r i t e is c u b i c w h i l e m a r c a s i t e 2

is o r t h o r h o m b i c .

O t h e r sulfide m i n e r a l s that h a v e b e e n f o u n d i n coals,

a n d sometimes i n significant a m o u n t s , are s p h a l e r i t e ( Z n S )

a n d galena

(PbS). Sulfates are not c o m m o n

a n d often are n o t present at a l l i n coals

that are fresh a n d u n w e a t h e r e d .

P y r i t e is v e r y s u s c e p t i b l e to o x i d a t i o n

a n d d e c o m p o s e s to v a r i o u s phases of i r o n sulfate m i n e r a l s at r o o m t e m p e r a t u r e . T h e f o l l o w i n g i r o n sulfate m i n e r a l phases are associated w i t h I l l i n o i s coals that h a v e b e e n subjected to o x i d i z i n g c o n d i t i o n s ( 4 ) : szomolnokite

FeS0

4

· H 0

rozenite

FeS0

4

· 4H 0

melanterite

FeS0

4

· 7H 0

coquimbite

Fe (S0 )

roemerite

FeS0

jarosite

u s u a l l y a s o d i u m jarosite

2

2

2

2

4

4

* 9H 0

3

2

· Fe (S0 ) 2

4

3

· 12H 0

(Na,K)Fe (S0 ) (OH) 3

4

2

2

6

Sulfides a n d sulfate m i n e r a l s m a k e u p 2 5 % of the m i n e r a l m a t t e r content of I l l i n o i s coals ( 1 ). Carbonates. T h e c a r b o n a t e m i n e r a l s , i n g e n e r a l , v a r y w i d e l y i n c o m p o s i t i o n b e c a u s e of the extensive s o l i d s o l u t i o n of c a l c i u m , m a g n e s i u m , i r o n , manganese, etc. that is p o s s i b l e w i t h i n t h e m . T h e r e is also a w i d e r a n g e of m i n e r a l c o m p o s i t i o n s for the c a r b o n a t e m i n e r a l s i n coals. relatively pure end members, calcite ( C a C 0 ) 3

a n d siderite

The

(FeC0 ),


3


TRACE ELEMENTS


IN FUEL

1.

GLUSKOTER

Mineral

Matter

have commonly been reported.

and Trace Elements

5

in Coal

H o w e v e r the most f r e q u e n t l y r e p o r t e d

c a r b o n a t e m i n e r a l s f r o m t h e m a j o r i t y of t h e coals i n the w o r l d are d o l o m i t e (CaC0

3

· MgC0 )

a n d ankerite ( 2 C a C 0

3

3

· MgC0

3

· FeC0 ). 3

T h e r e are significant differences i n t h e c a r b o n a t e m i n e r a l o g y of coals f r o m different parts of the w o r l d .

C a l c i t e is n e a r l y t h e o n l y

carbonate

m i n e r a l o b s e r v e d i n I l l i n o i s coals ( 1 ) w h e r e a s a n k e r i t e is the d o m i n a n t c a r b o n a t e m i n e r a l i n B r i t i s h coals (5,6), are c o m m o n i n A u s t r a l i a n coals (7).

a n d siderite, a n k e r i t e , a n d c a l c i t e

T h e carbonate minerals make u p 9 %

of the t o t a l m i n e r a l m a t t e r content of coals f r o m the I l l i n o i s B a s i n ( 1 ).


Silica ( Q u a r t z ) . (I)

Q u a r t z is u b i q u i t o u s i n a l l coals. R a o a n d G l u s k o t e r

r e p o r t e d t h a t , o n the average, 1 5 % of the m i n e r a l m a t t e r i n coals

f r o m the I l l i n o i s B a s i n w a s q u a r t z . 1-20%

O ' G o r m a n and W a l k e r (2)

found

q u a r t z i n 16 w h o l e c o a l samples f r o m v a r i o u s parts of the U n i t e d

States. Mineral Matter in Coal and High-Temperature

Coal Ash

T h e m i n e r a l m a t t e r content of c o a l cannot be d e t e r m i n e d q u a l i t a t i v e l y or q u a n t i t a t i v e l y f r o m the ash t h a t is f o r m e d w h e n the c o a l is o x i d i z e d . N o r m a l h i g h - t e m p e r a t u r e a s h i n g of c o a l at 7 5 0 ° C , as d e s i g n a t e d b y A S T M standards ( 8 ) , causes a series of reactions i n v o l v i n g t h e m i n erals i n the c o a l .

O f the f o u r m a j o r m i n e r a l groups o n l y q u a r t z is not

altered d u r i n g high-temperature ashing. Clay Minerals. T h e c l a y m i n e r a l s i n c o a l a l l c o n t a i n w a t e r b o u n d w i t h i n t h e i r lattices. K a o l i n i t e contains 1 3 . 9 6 % , i l l i t e 4 . 5 % , a n d m o n t morillonite 5 %

b o u n d water.

I n a d d i t i o n , t h e m o n t m o r i l l o n i t e i n the

m i x e d - l a y e r clays also contains i n t e r l a y e r or a d s o r b e d w a t e r . A l l of the w a t e r is lost d u r i n g the h i g h - t e m p e r a t u r e a s h i n g . Iron Sulfide Minerals.

D u r i n g h i g h - t e m p e r a t u r e a s h i n g , the p y r i t e

m i n e r a l s are o x i d i z e d to f e r r i c oxide a n d s u l f u r d i o x i d e .

Some of

the

s u l f u r d i o x i d e m a y r e m a i n c o m b i n e d w i t h c a l c i u m i n the ash, b u t m u c h is lost. I f a l l the s u l f u r d i o x i d e w e r e e m i t t e d d u r i n g a s h i n g , t h e r e w o u l d b e a 3 3 % w e i g h t loss w i t h respect to the w e i g h t of p y r i t e or m a r c a s i t e i n the o r i g i n a l sample. Figure 1. Scanning electron photomicrographs of minerals from coals. The minerals were studied and photographed by a Cambridge Stereoscan microscope with an accessory energy-dispersive x-ray spectrometer at the Center for Electron Microscopy, University of Illinois. A. Pyrite framboids from the low-temperature ash of a sample from the DeKoven Coal Member. B. Pyrite: cast of plant cells from the low-temperature ash of a sample from the Colchester (No. 2) Coal Member. C . Kaolinite (left) and sphalente (right) in minerals from a cleat (vertical fracture), Herrin (No. 6) Coal Member. D. Calcite from a cleat in the Herrin (No. 6) Coal Member. E. Kaolinite "books" from a cleat in the Herrin (No. 6) Coal Member. F. Galena: small crystals in the low-temperature ash of a sample from the DeKoven Coal Member.


6

TRACE

Calcite.

ELEMENTS

IN FUEL

T h e c a l c i u m c a r b o n a t e is c a l c i n e d to l i m e ( C a O ) d u r i n g

h i g h - t e m p e r a t u r e a s h i n g , w i t h a loss of c a r b o n d i o x i d e . T h i s results i n a 4 4 % w e i g h t loss. Q u a r t z . T h e stable m i n e r a l q u a r t z ( S i 0 ) is the o n l y m a j o r m i n e r a l 2

f o u n d i n c o a l w h i c h is i n e r t d u r i n g h i g h - t e m p e r a t u r e a s h i n g . T h e changes i n t h e m i n e r a l m a t t e r content i n c o a l d u r i n g a s h i n g h a v e l o n g b e e n r e c o g n i z e d . A n u m b e r of w o r k e r s h a v e suggested schemes for c a l c u l a t i n g t h e t r u e m i n e r a l m a t t e r content f r o m d e t e r m i n a t i o n s m a d e d u r i n g the c h e m i c a l analyses of c o a l . P a r r ( 9 ) r e p o r t e d one of the earliest


of s u c h schemes i n w h i c h o n l y the t o t a l s u l f u r a n d ash contents

were

c o n s i d e r e d i n d e v e l o p i n g the c o n v e r s i o n f o r m u l a e . T h i s is s t i l l the most w i d e l y used procedure. K i n g et al. (10),

A m o r e s o p h i s t i c a t e d m e t h o d w a s suggested

by

w h i c h considers b o t h the c a r b o n d i o x i d e loss f r o m c a r -

bonates a n d the c h l o r i d e d e c o m p o s i t i o n i n a d d i t i o n to t h e factors

con-

s i d e r e d b y the P a r r f o r m u l a . F u r t h e r m o d i f i c a t i o n s of these t e c h n i q u e s h a v e b e e n suggested b y B r o w n et al. (11), a n d M i l l o t (12).

R e c e n t l y G i v e n (13)

Pringle and Bradburn (5),

discussed i n d e t a i l the p r o b l e m of

c o n v e r t i n g r a w c h e m i c a l a n a l y t i c a l d a t a to a p u r e c o a l basis b y s u b t r a c t i n g the c a l c u l a t e d m i n e r a l m a t t e r content. Analyses of Minerals in Coal Separation of Minerals from Coal. T h i s section concerns m i n e r a l s i n t h e strict s e n s e — n a t u r a l l y o c c u r r i n g , i n o r g a n i c substances w i t h definite c h e m i c a l c o m p o s i t i o n a n d o r d e r e d a t o m i c a r r a n g e m e n t — a n d not

indi-

v i d u a l c h e m i c a l elements. T h e r e h a v e b e e n m a n y studies i n w h i c h w o r k ers h a v e a n a l y z e d m i n e r a l s t h a t w e r e p i c k e d b y h a n d f r o m c o a l seams, f r o m c o a l p a r t i n g s , or f r o m cleats or t h a t w e r e s e p a r a t e d f r o m t h e c o a l b y a m e t h o d b a s e d o n differences i n specific g r a v i t y b e t w e e n the c o a l a n d the m i n e r a l s c o n t a i n e d i n i t . A s a first step, these studies w e r e i m p o r t a n t c o n t r i b u t i o n s , b u t i t q u i c k l y b e c a m e a p p a r e n t that the large a m o u n t of i n s e p a r a b l e m i n e r a l m a t t e r i n coals r e s u l t e d i n i n c o m p l e t e a n a l y t i c a l d a t a . I n the next stage i n this r e s e a r c h the coals w e r e ashed at 3 0 0 ° - 5 0 0 ° C , t e m p e r a t u r e s b e l o w that of n o r m a l c o m b u s t i o n , or at r o o m t e m p e r a t u r e s i n an oxygen

stream.

This provided additional information, but

l i m i t e d because m a n y of the m i n e r a l s w e r e o x i d i z e d a l o n g w i t h

was the

organic fraction. W i t h i n the past d e c a d e the t e c h n i q u e of e l e c t r o n i c ( r a d i o f r e q u e n c y ) l o w - t e m p e r a t u r e a s h i n g has b e e n u s e d to investigate m i n e r a l m a t t e r i n coal.

I n a l o w - t e m p e r a t u r e asher, o x y g e n is passed t h r o u g h a r a d i o f r e -

q u e n c y field, a n d a d i s c h a r g e takes p l a c e . A c t i v a t e d o x y g e n thus f o r m e d passes over the c o a l s a m p l e , a n d the o r g a n i c m a t t e r is o x i d i z e d at r e l a t i v e l y l o w t e m p e r a t u r e s — u s u a l l y less t h a n 1 5 0 ° C

(14).


1.

GLUSKOTER

Mineral

Matter

and Trace Elements

7

in Coal

T h e effects of l o w - t e m p e r a t u r e a s h i n g a n d of the o x i d i z i n g gas stream o n the m i n e r a l s i n c o a l are m i n i m a l .

N o o x i d a t i o n of m i n e r a l phases

present has b e e n r e p o r t e d , a n d the o n l y phase changes o b s e r v e d

were

those e x p e c t e d at 150 ° C a n d 1 torr. T h e r e f o r e , most of t h e m a j o r m i n e r a l constituents of coals, i n c l u d i n g p y r i t e , k a o l i n i t e , i l l i t e , q u a r t z , a n d c a l c i t e , are unaffected b y the r a d i o f r e q u e n c y a s h i n g . R e c e n t studies of mineral matter i n coal w h i c h used radiofrequency low-temperature ashing i n c l u d e G l u s k o t e r ( 1 5 ) , E s t e p et al. (16), Walker (2), and Rao and Gluskoter

Wolfe (17), O'Gorman and

(1).


Identification of Minerals in Coal. O n c e the l o w - t e m p e r a t u r e m i n e r a l m a t t e r r e s i d u e has b e e n o b t a i n e d b y r a d i o f r e q u e n c y a s h i n g , the m i n e r a l s c a n b e i d e n t i f i e d , a n d t h e i r concentrations c a n be d e t e r m i n e d b y a v a r i e t y of i n s t r u m e n t a l t e c h n i q u e s .

T h e best d e v e l o p e d ,

most

inclusive, and

p r o b a b l y most r e l i a b l e m e t h o d u s e d thus f a r i n d i s t i n g u i s h i n g m i n e r a l s i n c o a l is x - r a y d i f f r a c t i o n analysis. It has b e e n u s e d extensively G l u s k o t e r (15),

W o l f e (17),

by

O'Gorman and Walker (2), and Rao and

G l u s k o t e r ( I ) a n d has b e e n s o m e w h a t successful i n q u a n t i f y i n g m i n e r a l analyses. E s t e p et al. (16) 200 c m "

1

u s e d i n f r a r e d a b s o r p t i o n b a n d s i n the r e g i o n 6 5 0 -

to a n a l y z e q u a n t i t a t i v e l y as w e l l as q u a l i t a t i v e l y for m i n e r a l s

i n l o w - t e m p e r a t u r e ash.

O'Gorman and W a l k e r (2)

also a p p l i e d this

t e c h n i q u e i n t h e i r investigations. D i f f e r e n t i a l t h e r m a l analyses ( D T A ) of m i n e r a l s i n a h i g h - t e m p e r a ture c o a l ash h a v e b e e n r e p o r t e d b y W a r n e (18, 19).

T h e method was

a p p l i e d to the m i n e r a l m a t t e r f r a c t i o n of f o u r samples b y O ' G o r m a n a n d Walker (2). E l e c t r o n m i c r o s c o p y , e v e n t h o u g h it has r a p i d l y i n c r e a s e d i n p o p u l a r i t y as a m i n e r a l o g i c a l r e s e a r c h t o o l , has not b e e n u s e d extensively to i d e n t i f y m i n e r a l s i n coals.

D u t c h e r et al.

(20)

reported on a limited

i n v e s t i g a t i o n w h i c h u s e d the e l e c t r o n p r o b e to a n a l y z e m i n e r a l m a t t e r i n coal.

S c a n n i n g electron m i c r o s c o p y w i t h a n e n e r g y - d i s p e r s i v e x - r a y

system accessory has b e e n u s e d to a l i m i t e d extent to s t u d y m i n e r a l s o b t a i n e d f r o m 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 (21, 22, 23). of

5 7

F e M o s s b a u e r spectra i n coals b y L e f e l h o c z et al. (24)

A study

demonstrated

t h e v a l i d i t y of a p p l y i n g this t e c h n i q u e to c o a l a n d suggested the presence of h i g h - s p i n i r o n ( I I )

i n s i x - f o l d c o o r d i n a t i o n i n several of the samples

studied. M a s s s p e c t r o m e t r i c investigations of isotopes i n c o a l a n d c o a l m i n erals h a v e also b e e n v e r y l i m i t e d i n scope. R a f t e r ( 2 5 ) p u b l i s h e d s u l f u r isotope d a t a o n 27 N e w Z e a l a n d c o a l samples b u t d i d n o t d r a w a n y c o n c l u s i o n s f r o m these d a t a . S m i t h a n d B a t t s (26)

d e t e r m i n e d the iso-

t o p i c c o m p o s i t i o n of s u l f u r i n a n u m b e r of A u s t r a l i a n coals a n d c o n c l u d e d that, f r o m this t y p e of d a t a , one m i g h t d e d u c e the o r i g i n of the o r g a n i c a l l y


8

TRACE ELEMENTS

IN FUEL

c o m b i n e d s u l f u r , the d e p t h of p e n e t r a t i o n of sea w a t e r i n t o u n d e r l y i n g c o a l measures, a n d the factors c o n t r o l l i n g r e d u c t i o n of sulfates to sulfides b y b i o g e n i c residues. Investigation of Minerals in Coal in Situ. T h e c o a l p e t r o g r a p h e r uses t h e o p t i c a l m i c r o s c o p e , u s u a l l y i n reflected l i g h t m o d e , to c h a r a c t e r i z e the o r g a n i c f r a c t i o n ( m a c é r a i s ) i n coals. T h e science of c o a l p e t r o g r a p h y has d e v e l o p e d a h i g h degree of p r e c i s i o n , p a r t i c u l a r l y d u r i n g the last 25 yrs.

H o w e v e r , these t e c h n i q u e s h a v e not b e e n n e a r l y as successful i n

investigating m i n e r a l matter i n coal.

P y r i t e , because of its h i g h reflect-

ance a n d its a b u n d a n c e i n coals, is the most l i k e l y m i n e r a l to b e s t u d i e d Downloaded by 120.32.115.112 on February 10, 2016 | http://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch001

microscopically. microscopes

Several automated

have been developed

M c C a r t n e y a n d E r g u n (27)

microscopes

and

image-analyzing

that c o u l d be u s e d i n s u c h a s t u d y .

r e p o r t e d o n a n a u t o m a t e d reflectance s c a n -

n i n g m i c r o s c o p e system of t h e i r o w n d e s i g n a n d i n c l u d e d results of p y r i t e analyses. Geochemistry of Mineral Matter in Coal A s p r e v i o u s l y discussed the m a j o r p r o b l e m of o b t a i n i n g a n u n a l t e r e d m i n e r a l - m a t t e r r e s i d u e has b e e n a l l e v i a t e d s o m e w h a t b y u s i n g r a d i o f r e q u e n c y l o w - t e m p e r a t u r e a s h i n g . A n o t h e r serious p r o b l e m , a n d one less a m e n a b l e to s o l u t i o n , is the c o m p l e x i t y of this system of m i n e r a l m a t t e r i n c o a l . T h e c o m p l e x i t y results f r o m the v a r i e t y of p h y s i c a l a n d c h e m i c a l c o n d i t i o n s i n w h i c h the c o a l - f o r m i n g m a t e r i a l s w e r e d e p o s i t e d a n d i n w h i c h the c o a l f o r m e d .

T h e system of m i n e r a l m a t t e r i n c o a l is a r e l a -

t i v e l y l o w - t e m p e r a t u r e , l o w - p r e s s u r e system w i t h m a n y c o m p o n e n t phases. It is a n o p e n system w i t h m a n y m o b i l e components.

T h e r e is also the

f u r t h e r c o m p l i c a t i o n t h a t t h e system has b e e n active a n d m a y h a v e b e e n c h a n g i n g at a n y t i m e since its genesis ( a p p r o x i m a t e l y 300 m i l l i o n yrs f o r coals of the P e n n s y l v a n i a n system ). A l t h o u g h the system is c o m p l i c a t e d , i n t e r p r e t i n g i t s h o u l d not b e i m p o s s i b l e , for the m i n e r a l s associated w i t h c o a l a n d w i t h a l l other s e d i m e n t a r y rocks are not the results of r a n d o m d e p o s i t i o n . T h e y are the p r e d i c t a b l e e n d p r o d u c t of a definite set of b i o logical, chemical, a n d physical conditions, w h i c h provided an environment i n w h i c h the m i n e r a l s c o u l d b e d e p o s i t e d or i n w h i c h t h e y c o u l d f o r m . T h e m i n e r a l m a t t e r a n d the ash i n c o a l h a v e often b e e n i n f o r m a l l y classified as i n h e r e n t ( s t e m m i n g f r o m the p l a n t m a t e r i a l i n t h e

coal

s w a m p ) or as a d v e n t i t i o u s ( a d d e d after the d e p o s i t i o n of the p l a n t m a t e r i a l i n the s w a m p ) .

T h i s classification is m i s l e a d i n g a n d difficult to

a p p l y , e s p e c i a l l y f o r those m i n e r a l s that are c o n t e m p o r a n e o u s

w i t h the

p e a t s w a m p b u t w e r e not i n c o r p o r a t e d b y the plants. T h e r e are s t a n d a r d terms a p p l i e d to sediments a n d s e d i m e n t a r y rocks that c a n b e u s e d w i t h c o a l m i n e r a l s . T h o s e m i n e r a l s w h i c h w e r e t r a n s -


1.

GLUSKOTER

Mineral

Matter

and Trace Elements

9

in Coal

p o r t e d b y w a t e r or w i n d a n d d e p o s i t e d i n the c o a l s w a m p are a l l o g e n i c or d e t r i t a l . A l l of the m i n e r a l s w h i c h f o r m e d w i t h i n the c o a l s w a m p , i n the peat, or i n the c o a l are a u t h i g e n i c . T h e t e r m syngenetic a p p l i e s to the m i n e r a l s that w e r e c o n t e m p o r a n e o u s

w i t h the c o a l f o r m a t i o n , a n d e p i -

genetic refers to those w h i c h w e r e f o r m e d later, s u c h as cleat Chemical

fillings.

Analyses of Mineral Matter and Trace Elements in Coal

I n a s m u c h as m i n e r a l m a t t e r has b e e n defined b r o a d l y to i n c l u d e a l l


i n o r g a n i c elements

i n coals, the c h e m i c a l c h a r a c t e r i z a t i o n of m i n e r a l

m a t t e r i n v o l v e s the d e t e r m i n a t i o n of m a n y elements. ical

analyses

of

chemical methods

geological

materials have

I n general, chem-

progressed

from

to s o p h i s t i c a t e d i n s t r u m e n t a l m e t h o d s .

the

The

wet major

elements i n the m i n e r a l constituents of c o a l , S i , A l , T i , C a , M g , F e , P , S, N a , K , are the same as those i n silicate rocks a n d are often d e t e r m i n e d b y x-ray

fluorescence

spectroscopy

and

flame

photometry.

T h e m i n o r a n d trace elements i n coals are c u r r e n t l y d e t e r m i n e d b y several t e c h n i q u e s , the most p o p u l a r of w h i c h are o p t i c a l e m i s s i o n a n d a t o m i c a b s o r p t i o n spectroscopy.

N e u t r o n a c t i v a t i o n analysis is also a n

excellent t e c h n i q u e for d e t e r m i n i n g m a n y elements, b u t it r e q u i r e s a n e u t r o n source, u s u a l l y a n a t o m i c reactor. I n a d d i t i o n , x - r a y spectroscopy,

e l e c t r o n spectroscopy

s p a r k source mass spectroscopy

fluorescence

for c h e m i c a l analyses ( E S C A ) , a n d

h a v e b e e n successfully a p p l i e d to the

analyses of some m i n o r a n d trace elements i n coal. U n t i l r e c e n t l y , c h e m i c a l analyses of coals w e r e d o n e o n ash p r o d u c e d f r o m t h e c o a l at r e l a t i v e l y h i g h temperatures.

T h i s w a s the s t a n d a r d

a p p r o a c h for m a n y years, a n d analyses of trace elements i n coals d o h a v e a l o n g h i s t o r y . A n e a r l y a r t i c l e o n a n element as rare as c a d m i u m i n c o a l w a s p u b l i s h e d 125 yrs ago

(28).

O n e l i m i t a t i o n of

high-temperature

ash s a m p l e is that v o l a t i l e elements m a y b e lost d u r i n g c o m b u s t i o n a n d w i l l not be detected.

A n o t h e r p r o b l e m w h i c h a p p l i e s e s p e c i a l l y to a n a l y -

ses for trace a n d m i n o r elements is that there h a v e not b e e n a n y c o a l standards a v a i l a b l e u n t i l v e r y recently. Recent comprehensive

investigations i n v o l v i n g a large n u m b e r

of

c o a l samples a n d d e t e r m i n a t i o n s of m a n y elements i n c l u d i n g trace elements h a v e b e e n u n d e r t a k e n b y the U . S . G e o l o g i c a l S u r v e y (29), U . S . B u r e a u of M i n e s (30), and

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

T h e P e n n s y l v a n i a State U n i v e r s i t y

Literature

the (23),

(2).

of Trace Elements and Mineral Matter in Coal

A d e t a i l e d r e v i e w of the w o r l d l i t e r a t u r e c o n c e r n e d

with mineral

m a t t e r a n d trace elements i n c o a l is w e l l b e y o n d t h e scope of this c h a p -


10 ter.

TRACE

ELEMENTS

IN FUEL

S u c h a r e v i e w w o u l d i n v o l v e the d i s c u s s i o n of several t h o u s a n d

books, j o u r n a l articles, a n d other p u b l i c a t i o n s a n d w o u l d itself c o m p o s e at least a modest v o l u m e .

H o w e v e r , the a n n o t a t e d b i b l i o g r a p h y at t h e

e n d of this c h a p t e r lists several r e v i e w articles that m a y be of h e l p to anyone

interested i n o b t a i n i n g f u r t h e r i n f o r m a t i o n o n trace

elements

a n d m i n e r a l matter i n coal. Occurrence

of Trace Elements in Coal

T h e m o d e r n investigations of trace elements i n coals w e r e p i o n e e r e d b y G o l d s c h m i d t , w h o d e v e l o p e d the t e c h n i q u e of q u a n t i t a t i v e c h e m i c a l Downloaded by 120.32.115.112 on February 10, 2016 | http://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch001

analysis b y o p t i c a l e m i s s i o n spectroscopy these earliest w o r k s , G o l d s c h m i d t (31)

a n d a p p l i e d it to c o a l ash. I n

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

c o m b i n a t i o n s of the trace elements i n coals.

I n a d d i t i o n to i d e n t i f y i n g

trace elements i n i n o r g a n i c c o m b i n a t i o n s w i t h the m i n e r a l s i n c o a l , h e p o s t u l a t e d the presence of m e t a l o r g a n i c complexes observed

a n d a t t r i b u t e d the

concentrations of v a n a d i u m , m o l y b d e n u m , a n d n i c k e l to the

presence of s u c h complexes i n coal. Goldschmidt

(32)

also i n t r o d u c e d the c o n c e p t of a

geochemical

classification of elements, i n w h i c h the elements are classified o n the basis of t h e i r affinities a n d tendencies to o c c u r i n m i n e r a l s of a single group. fides.

T h e c h a l c o p h i l e elements are those w h i c h c o m m o n l y f o r m s u l I n a d d i t i o n to sulfur, t h e y i n c l u d e Z n , C d , H g , C u , P b , A s , S b ,

Se, a n d others. W h e n present i n coals, these elements w o u l d b e

expected

to o c c u r , at least i n p a r t , i n sulfide m i n e r a l s . Sulfides other t h a n p y r i t e a n d m a r c a s i t e h a v e b e e n n o t e d i n coals, b u t , except i n areas of l o c a l c o n c e n t r a t i o n , t h e y o c c u r i n trace or m i n o r amounts. T h e l i t h o p h i l e elements

are those t h a t g e n e r a l l y o c c u r

i n silicate

phases a n d i n c l u d e a m o n g others: S i , A l , T i , K , N a , Z r , B e , a n d Y .

These

w o u l d be e x p e c t e d to o c c u r i n coals i n some c o m b i n a t i o n w i t h the silicate m i n e r a l s : k a o l i n i t e , i l l i t e , other c l a y m i n e r a l s , q u a r t z , a n d stable h e a v y detrital minerals. T h e carbonate m i n e r a l s i n coals o c c u r p r i m a r i l y as e p i g e n e t i c f r a c ture

fillings

(cleat

filling).

M a g n e s i u m , i r o n , a n d m a n g a n e s e are often

associated w i t h the s e d i m e n t a r y c a r b o n a t e m i n e r a l s a n d w o u l d r e a s o n a b l y b e e x p e c t e d to be associated w i t h the cleat fillings i n c o a l . A large n u m b e r of silicate, sulfide, a n d c a r b o n a t e m i n e r a l s h a v e b e e n i d e n t i f i e d f r o m c o a l seams, a n d the elements c o m p o s i n g t h e m necessarily o c c u r i n coals i n i n o r g a n i c c o m b i n a t i o n .

However, mineralogical investi-

gations of coals h a v e not g e n e r a l l y b e e n q u a n t i t a t i v e , a n d w h e t h e r a n element occurs o n l y i n i n o r g a n i c c o m b i n a t i o n or p e r h a p s is also present i n o r g a n i c c o m b i n a t i o n has not c o m m o n l y b e e n N i c h o l l s (33)

approached

considered.

this p r o b l e m b y p l o t t i n g the a n a l y t i c a l

d a t a f o r the c o n c e n t r a t i o n of a s i n g l e element i n c o a l or i n c o a l ash


1.

GLUSKOTER

Mineral

Matter

and Trace Elements

11

in Coal

against the ash content of t h e c o a l . D i a g r a m s d e p i c t i n g a n u m b e r of s u c h p o i n t s for a single c o a l seam or for a g r o u p of c o a l seams i n a single geographic

area w e r e

affinity of the element.

i n t e r p r e t e d for d e g r e e of i n o r g a n i c or Nicholls concluded

organic

(33):

. . . one element, b o r o n , is l a r g e l y , almost e n t i r e l y , associated w i t h the o r g a n i c f r a c t i o n i n coals; some elements, s u c h as b a r i u m , c h r o m i u m , c o b a l t , l e a d , s t r o n t i u m , a n d v a n a d i u m are, i n the m a j o r i t y of cases, asso c i a t e d w i t h the i n o r g a n i c f r a c t i o n ; a n d a t h i r d g r o u p i n c l u d i n g n i c k e l , g a l l i u m , g e r m a n i u m , m o l y b d e n u m , a n d c o p p e r , m a y be associated w i t h either of b o t h fractions.


H e t h e n s u b d i v i d e d t h e t h i r d g r o u p i n t o n i c k e l a n d c o p p e r , w h i c h are i n i n o r g a n i c c o m b i n a t i o n w h e n f o u n d i n l a r g e concentrations, a n d g a l l i u m , g e r m a n i u m , a n d m o l y b d e n u m , w h i c h are l a r g e l y i n o r g a n i c c o m b i n a t i o n w h e n f o u n d strongly concentrated. H o r t o n a n d A u b r e y ( 34 ) h a n d p i c k e d p u r e v i t r a i n samples f r o m coals a n d s e p a r a t e d t h e m i n t o five different specific g r a v i t y fractions. t h e n a n a l y z e d these for 16 m i n o r elements.

They

T h e y c o n c l u d e d that for the

three v i t r a i n s t h e y s t u d i e d , b e r y l l i u m , g e r m a n i u m , v a n a d i u m , t i t a n i u m , a n d b o r o n w e r e c o n t r i b u t e d almost e n t i r e l y b y the i n h e r e n t ( o r g a n i c a l l y combined)

m i n e r a l m a t t e r a n d that manganese,

phosphorus,

and tin

w e r e associated w i t h t h e a d v e n t i t i o u s ( i n o r g a n i c a l l y c o m b i n e d ) m i n e r a l matter. A m u c h m o r e a m b i t i o u s series of investigations of the o r g a n i c - i n o r g a n i c affinities of trace metals i n coals w a s u n d e r t a k e n a n d r e p o r t e d o n b y Z u b o v i c a n d c o - w o r k e r s at the U . S . G e o l o g i c a l S u r v e y (35, 36, 37, 38, 39). I n the most recent a r t i c l e , Z u b o v i c ( 3 9 ) l i s t e d the f o l l o w i n g 15 elements i n o r d e r of percent o r g a n i c affinity: G e ( 8 7 ) , B e ( 8 2 ) , G a ( 7 9 ) , T i (78), Β (77), V (76), N i (59), C r (55), C o (53), Y (53), M o (40), C u ( 3 4 ) , S n ( 2 7 ) , L a ( 3 ) , a n d Z n ( 0 ) . H e c o n c l u d e d that this series w a s a p p a r e n t l y r e l a t e d to the c h e l a t i n g properties of the metals. 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 has r e c e n t l y b e e n extensively i n v e s t i g a t i n g trace elements i n c o a l (23, 40). A s a p a r t of this s t u d y f o u r sets of float-sink samples w e r e a n a l y z e d for a n u m b e r of trace a n d m i n o r elements. T h r e e coals, c r u s h e d a n d s i z e d to % i n . b y 28 m e s h , w e r e s e p a r a t e d i n t o six specific g r a v i t y fractions b y floating t h e m i n m i x t u r e s of p e r c h l o r o e t h y l e n e a n d n a p h t h a . T h e heaviest of these six fractions (1.60 s i n k ) was t h e n separated i n t o t w o parts u s i n g b r o m o f o r m (specific g r a v i t y 2.89). T h e f o u r t h c o a l w a s also separated i n p e r c h l o r o e t h y l e n e a n d n a p h t h a , b u t o n l y t w o fractions w e r e a n a l y z e d , one w i t h specific g r a v i t y of less t h a n 1.25 a n d one w i t h specific g r a v i t y h e a v i e r t h a n 1.60. B y use of a t e c h n i q u e s i m i l a r to that of Z u b o v i c ( 3 9 ) , the trace elements d e t e r m i n e d i n these samples are l i s t e d i n o r d e r of d e c r e a s i n g affinity for t h e c l e a n c o a l fractions, o r d e c r e a s i n g o r g a n i c affinity ( T a b l e I ) . T h e sequence was d e t e r m i n e d b y c o m p a r i n g ratios of the a m o u n t of a n ele-


12

TRACE

ELEMENTS

IN

FUEL

m e n t i n the lightest float f r a c t i o n ( a l w a y s less t h a n 1.30 specific g r a v i t y ) to the a m o u n t of the element i n the 1.60 s i n k f r a c t i o n . T h e n u m e r i c a l values thus d e t e r m i n e d are not g i v e n because they v a r y w i t h the p a r t i c l e size d i s t r i b u t i o n of the c o a l , the specific g r a v i t y of the l i q u i d u s e d to m a k e t h e first ( l i g h t e s t ) s e p a r a t i o n , a n d the size d i s t r i b u t i o n of the m i n e r a l fragments i n a single c o a l . H o w e v e r , the sequence g i v e n i n T a b l e I does i n d i c a t e w h i c h elements

are p r i m a r i l y

i n organic

combination,

w h i c h are i n i n o r g a n i c c o m b i n a t i o n , a n d w h i c h are, a p p a r e n t l y , b o t h i n o r g a n i c a l l y a n d o r g a n i c a l l y c o m b i n e d i n coals of t h e I l l i n o i s B a s i n .


Table I.

Affinity of Elements for Pure Coal and Mineral Matter as Determined from Float—Sink Data Davis Coal

DeKoven Coal

Β Ge Be Ti Ga Ρ V Cr Sb Se Co Cu Ni Μη Zr Mo Cd Hg Pb Zn As

Ge Ga Be Ti Sb Co Ρ Ni Cu Se Cr Μη Zn Zr V Mo Pb Hg As

Clean coal—lightest specific g r a v i t y f r a c t i o n (elements i n " o r g a n i c combination ) ,,

M i n e r a l matter—specific g r a v i t y greater t h a n 1.60 (elements i n " i n o r g a n i c combination")

Colchester (No. 2) Coal

Herrin (No. 6) Coal

Ge Β Ρ Be Sb Ti Co Se Ga V Ni Pb Cu Hg Zr Cr Mn As Mo Cd Zn

Ge Β Be Sb V Mo Ga Ρ Se Ni Cr Co Cu Ti Zr Pb Mn As Cd Zn Hg

T h e sequences s h o w n i n T a b l e I c a n be d i v i d e d i n t o several g e n e r a l groups.

F i r s t , there are those elements w h i c h are a l w a y s i n t h e

most closely associated w i t h the c l e a n c o a l a n d w h i c h , therefore, t h e greatest o r g a n i c

affinities.

These

group have

are g e r m a n i u m , b e r y l l i u m , a n d

b o r o n , w h i c h are three of the t o p five elements l i s t e d b y Z u b o v i c

(39).

A t the other e n d of the list are the elements w i t h t h e least affinity f o r t h e o r g a n i c p o r t i o n of the c o a l . T h e elements m e r c u r y , z i r c o n i u m , z i n c , arsenic, a n d c a d m i u m are n e a r the b o t t o m i n a l l f o u r coals s t u d i e d , a n d l e a d , manganese, a n d m o l y b d e n u m are near the b o t t o m i n three of the four.

T h e r e m a i n i n g elements, those that are a p p a r e n t l y associated


to

1.

GLUSKOTER

Mineral

Matter

and Trace Elements

13

in Coal

v a r y i n g degrees w i t h b o t h the o r g a n i c a n d i n o r g a n i c p o r t i o n s of the coals, c a n also be d i v i d e d i n t o t w o g r o u p s : those elements t h a t t e n d to b e m o r e g e n e r a l l y a l l i e d to the elements

with

organic

gallium, antimony, titanium, and vanadium) t e n d to be

more

i n o r g a n i c a l l y associated

affinities

(phosphorus,

a n d those elements

(cobalt,

that

nickel, chromium,

s e l e n i u m , a n d c o p p e r ) . T h i s s u m m a r i z e d sequence g e n e r a l l y agrees w i t h that g i v e n b y Z u b o v i c ( 3 9 )

w i t h o n l y a f e w m i n o r discrepancies.

elements l i s t e d i n T a b l e I i n c l u d e 12 of the 15 elements discussed

The by

Z u b o v i c ( 3 9 ) as w e l l as n i n e a d d i t i o n a l elements. A l t h o u g h a n element is l i s t e d a m o n g those w i t h the highest o r g a n i c Downloaded by 120.32.115.112 on February 10, 2016 | http://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch001

affinities, its o c c u r r e n c e cluded.

i n i n o r g a n i c c o m b i n a t i o n i n coals is not p r e -

B o r o n , w h i c h is a m o n g those f o u n d i n h i g h concentrations i n

the cleanest c o a l fractions, occurs i n amounts u p to 200 p p m i n t h e c l a y m i n e r a l i l l i t e f r o m I l l i n o i s coals (41).

S i m i l a r l y , a p o r t i o n of those ele-

ments u s u a l l y c o n c e n t r a t e d most h e a v i l y i n the h i g h specific g r a v i t y f r a c tions m a y also be i n o r g a n i c c o m b i n a t i o n .

This d u a l occurrence

p o s t u l a t e d for the m e r c u r y content of I l l i n o i s coals b y R u c h et al.

was (42),

a n d m e r c u r y is i n c l u d e d here w i t h the elements h a v i n g the l o w e r o r g a n i c affinities. The

float-sink,

o r w a s h a b i l i t y , d a t a c a n be d i s p l a y e d as w a s h a b i l i t y

curves a n d as histograms. W a s h a b i l i t y curves a n d histograms for a series of elements are g i v e n i n F i g u r e s 2 - 5 .

T h e figures are p r e s e n t e d i n order

of the i n c r e a s i n g tendencies of the elements to b e c o n c e n t r a t e d i n the heavier fractions

(decreasing

organic affinity).

T h e washability curve

is a t y p e of c u m u l a t i v e c u r v e f r o m w h i c h one c a n r e a d t h e

expected

c o n c e n t r a t i o n of a n element at a n y g i v e n r e c o v e r y rate of a c o a l , a s s u m i n g s e p a r a t i o n b a s e d o n specific g r a v i t y differences. scissa is " r e c o v e r y of float c o a l — p e r c e n t "

T h e r e f o r e , the a b -

a n d s h o u l d be a p p l i c a b l e to

a n y specific g r a v i t y s e p a r a t i o n w i t h o u t r e g a r d to the m e d i u m i n w h i c h it is d o n e or the m e t h o d used. T h e r a w c o a l c o n c e n t r a t i o n of a n element is r e a d at the 1 0 0 % r e c o v e r y p o i n t , a n d c o n c e n t r a t i o n i n the cleanest coals ( m o s t m i n e r a l m a t t e r - f r e e ) is r e a d at the l o w r e c o v e r y e n d of the c u r v e (20-30%

recovery).

F i g u r e 2 shows the w a s h a b i l i t y c u r v e a n d h i s t o g r a m for g e r m a n i u m i n a s a m p l e f r o m the D a v i s C o a l M e m b e r .

G e r m a n i u m is the

element

w i t h the highest o r g a n i c affinity i n the coals s t u d i e d . T h e n e g a t i v e slope of the c u r v e i n d i c a t e s that g e r m a n i u m is c o n c e n t r a t e d i n the c l e a n c o a l fractions; this is also a p p a r e n t f r o m the h i s t o g r a m . T h e h i s t o g r a m i n d i cates that there is a h i g h e r c o n c e n t r a t i o n of g e r m a n i u m i n the 1.60-2.79 specific

g r a v i t y f r a c t i o n t h a n i n the greater-than-2.79

specific

gravity

f r a c t i o n . A p p a r e n t l y , a greater p o r t i o n of the g e r m a n i u m is c o n c e n t r a t e d w i t h the c l a y m i n e r a l s t h a n w i t h the sulfide m i n e r a l s , w h i c h c o m p o s e the m a j o r i t y of the 2.79 sink f r a c t i o n .



14

TRACE

0

20 Recovery

2.79 1.29 1.31 1.40 1.60 2.79 S p e c i f i c gravity of coal fraction

Figure 2. Germanium in specific gravity fractions of a sample from the Davis Coal Member. Upper: washability curve. Lower: distribution of germanium in individual fractions. A l l of t h e w a s h a b i l i t y curves s h o w n a r e d r a w n w i t h t h e ordinates the same l e n g t h a n d t h e o r i g i n at zero c o n c e n t r a t i o n so t h a t t h e slopes c a n b e c o m p a r e d a n d i n t e r p r e t e d . F i g u r e 3, w h i c h shows b e r y l l i u m i n the D a v i s C o a l M e m b e r , presents a flat w a s h a b i l i t y c u r v e a n d also a r e l a t i v e l y u n i f o r m h i s t o g r a m . B e r y l l i u m i s , therefore, r a t h e r e v e n l y d i s t r i b u t e d i n the c l e a n c o a l samples a n d is also present, i n s o m e w h a t lesser a m o u n t s , i n t h e h e a v i e r sink fractions. N i c k e l i n a s a m p l e f r o m the C o l c h e s t e r ( N o . 2 ) C o a l M e m b e r ( F i g u r e 4 ) is d e f i n i t e l y c o n c e n t r a t e d i n the h e a v i e r specific g r a v i t y fractions. H o w e v e r , t h e w a s h a b i l i t y c u r v e r e m a i n s w e l l a b o v e t h e abscissa a n d does n o t a p p e a r t o a p p r o a c h t h e o r i g i n i n t h e cleanest f r a c t i o n ( p u r e s t


GLUSKOTER


1.

Mineral

Matter

and Trace Elements

in Coal

15

Figure 3. Beryllium in specific gravity fractions of a sample from the Davis Coal Member. Upper: washability curve. Lower: distribution of beryllium in individual fractions. coal).

T h i s p a t t e r n m a y be i n t e r p r e t e d as s h o w i n g n i c k e l i n o r g a n i c as

w e l l as i n i n o r g a n i c c o m b i n a t i o n . T h e final w a s h a b i l i t y c u r v e a n d h i s t o g r a m ( F i g u r e 5 ) are of arsenic i n a s a m p l e f r o m the H e r r i n ( N o . 6 )

Coal Member.

The washability

c u r v e shows a n intense c o n c e n t r a t i o n of arsenic i n the h e a v i e r fractions. T h e c u r v e approaches

the abscissa a n d i f e x t r a p o l a t e d w o u l d intersect

the o r d i n a t e near the o r i g i n . A r s e n i c is one of the least o r g a n i c a l l y r e l a t e d elements i n a l l f o u r of the coals s t u d i e d . F i g u r e s 2 - 5 present examples of g r a p h i c representations of the org a n i c - i n o r g a n i c affinities of several elements i n coals.

A larger number


16

TRACE

ELEMENTS

IN

FUEL

/

NICKEU


Colchester

20 Recovery

r

40 of float

1.26

1I

Specific

gravity

I

1.24-

Coal

60 coal (percent)

Member

80

1

60

2.89

2.89

of c o a l fraction

Figure 4. Nickel in specific gravity fractions of a sample from the Colchester (No. 2) Coal Member. Upper: washability curve. Lower: distribution of nickel in individual fractions. of s u c h curves f o r the e l e m e n t a l d i s t r i b u t i o n of these coals a n d statistical s u m m a r i e s of major, m i n o r , a n d trace element d i s t r i b u t i o n s i n 101 coals f r o m the U n i t e d States are g i v e n i n R u c h et al. (40). Conclusions M i n e r a l m a t t e r i n c o a l , as t h e t e r m is g e n e r a l l y u s e d , i n c l u d e s t h e m i n e r a l phases ( s p e c i e s ) present i n t h e c o a l seam as w e l l as those elements g e n e r a l l y t h o u g h t to b e i n o r g a n i c , e v e n i f t h e y are present i n coals i n organic combination.

T h e m a j o r m i n e r a l s f o u n d i n coals a r e silicates


1.

Mineral

GLUSKOTER

Matter

and Trace Elements

in Coal

17

ARSENIC Herrin (No. 6) C o a l

Ε 7.0

V


_

Member

20

40 Recovery

3

of float

60 coal

__u

80

100

(percent)

1.25- 1.28- 1.33- 1.40- 1.60- : 1.28 1.33 1.40 1.60 2.89 Specific gravity of coal fraction

Figure 5. Arsenic in specific gravity fractions of a sam ple from the Herrin (No. 6) Coal Member. Upper: washability curve. Lower: distribution of arsenic in individual fractions. ( k a o l i n i t e , i l l i t e , m i x e d - l a y e r c l a y m i n e r a l s , a n d q u a r t z ) , sulfides marily pyrite a n d marcasites), ankerite, or ferroan

a n d carbonates

(calcite,

(pri

siderite, a n d

dolomite).

T h e t w o major p r o b l e m s e n c o u n t e r e d i n i n v e s t i g a t i n g m i n e r a l m a t t e r i n c o a l are that the m i n e r a l m a t t e r a n d c o a l are so i n t i m a t e l y m i x e d that p h y s i c a l separation of the t w o is not feasible i n a q u a n t i t a t i v e s t u d y a n d that t h e g e o c h e m i c a l

system is extremely c o m p l i c a t e d

a n d difficult t o

c h a r a c t e r i z e . T h e first p r o b l e m is o v e r c o m e i n p a r t b y r e f i n i n g the t e c h -


18

TRACE

ELEMENTS

n i q u e s u s e d to p r e p a r e samples for analyses ( r a d i o f r e q u e n c y

IN FUEL

low-tem-

p e r a t u r e a s h i n g , for e x a m p l e ) , b u t the s e c o n d p r o b l e m is a n i n h e r e n t p a r t of the system a n d is less a m e n a b l e to s o l u t i o n . T h e literature c o n c e r n e d w i t h trace elements a n d m i n e r a l s i n coals has i n c r e a s e d i n q u a n t i t y as the interest i n these m a t e r i a l s , c a u s e d b y c o n c e r n a b o u t e n v i r o n m e n t a l q u a l i t y a n d energy a v a i l a b i l i t y , has i n creased.

A n u m b e r of excellent r e v i e w articles, p a r t i c u l a r l y t h a t b y

W a t t (43),

have been published and provide comprehensive summaries

of the e x i s t i n g literature. F o u r I l l i n o i s coals, separated i n t o series of specific g r a v i t y fractions, Downloaded by 120.32.115.112 on February 10, 2016 | http://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch001

h a v e b e e n a n a l y z e d for 21 trace a n d m i n o r elements.

T h e degree to

w h i c h a n element is associated w i t h the lightest specific g r a v i t y f r a c t i o n a n d therefore w i t h the purest c o a l is a measure of t h a t e l e m e n t s o r g a n i c affinity i n c o a l .

I f the element is c o n c e n t r a t e d i n the heaviest specific

g r a v i t y f r a c t i o n , it is t h e n i n i n o r g a n i c c o m b i n a t i o n . G e r m a n i u m , b e r y l l i u m , a n d b o r o n h a v e b e e n d e t e r m i n e d to h a v e t h e greatest

organic

affinities, a n d H g , Z r , Z n , A s , C d , P b , M n , a n d M o are g e n e r a l l y i n o r ganically combined.

T h e o t h e r elements t h a t w e r e d e t e r m i n e d a l l s h o w

degrees of i n o r g a n i c a n d o r g a n i c associations, w i t h P , G a , S b , T i , a n d V t e n d i n g to b e a l l i e d w i t h t h e other elements h a v i n g o r g a n i c affinities a n d C o , N i , C r , Se, a n d C u m o r e closely associated w i t h the i n o r g a n i c a l l y c o m b i n e d elements. T h i s series is v e r y s i m i l a r to a series of elements i n coals p r e s e n t e d i n o r d e r of d e c r e a s i n g o r g a n i c affinities b y Z u b o v i c

(39).

Acknowledgments T h e c h e m i c a l a n a l y t i c a l d a t a o n w h i c h T a b l e I a n d F i g u r e s 2 - 5 are b a s e d w e r e d e t e r m i n e d b y the A n a l y t i c a l C h e m i s t r y S e c t i o n of 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 . T h e S u r v e y research r e p o r t e d is sponsored, i n p a r t , b y G r a n t N o . R-800059 a n d C o n t r a c t N o . 68-02-0246 f r o m the U . S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , D e m o n s t r a t i o n Projects B r a n c h , C o n t r o l Systems L a b o r a t o r y , R e s e a r c h T r i a n g l e P a r k , N . C . Annotated 1.

Bibliography

W a t t , J . D . , " T h e Physical, and Chemical Behaviour of the M i n e r a l Matter in C o a l U n d e r Conditions M e t i n Combustion Plant. Part I, The Occurrence, O r i g i n , Identity, Distribution, and Estimation of the M i n e r a l Species in British Coals," British C o a l Utilization Research Association, Literature Survey, 121 p., Leatherhead, Surrey, E n g l a n d , 1968. This excellent review of minerals i n coal and the chemical composition of coals does not, as the title may suggest, limit itself to British coals. The literature of the rest of Europe and of North America is generously cited. A large section devoted to the various methods of determining the amount of mineral matter is included. There is also a section concerned with the methods of identifying mineral species i n coals.


1.

GLUSKOTER

Mineral

Matter and Trace Elements

in Coal


2.

19

Nicholls, G . D . , " T h e Geochemistry of Coal-bearing Strata" i n " C o a l and Coal-bearing Strata" ( D . G . Murchison and T. S. Westoll, E d s . ) , p. 2 6 9 307, Oliver and B o y d , E d i n b u r g h and L o n d o n , 1968. M a n y data on trace elements i n coal are included i n the chapter. The emphasis is on the geochemistry of the trace elements, w i t h discussions of the concentration levels of trace elements i n coals, the organic (or inor ganic) affinities of the trace elements, and the geochemical controls of associations of elements. This and the following significant review article are contained w i t h i n a single volume. 3. Mackowsky, M . T h . , " M i n e r a l Matter in C o a l " i n " C o a l and Coal-bearing Strata" ( D . G . Murchison and T. S. Westoll, E d s . ) , p. 309-321, Oliver and B o y d , E d i n b u r g h and London, 1968. Mackowsky discusses the mineral phases found i n coals and differenti ates those phases w i t h geologically different genetic histories. A number of the mineral phases are shown i n a series of photomicrographs of p o l ished sections of coals. 4. W i l l i a m s , F . Α., Cawley, C . M . , "Impurities i n C o a l and Petroleum" i n " T h e Mechanism of Corrosion by F u e l Impurities" ( H . R. Johnson and D . J . Littler, E d s . ) , p. 2 4 - 6 7 , Butterworths, L o n d o n , 1963. In addition to discussing the major minerals and the elemental com position of coals, the authors discuss methods of removing impurities from coal and the effects of the impurities on several aspects of coal utilization. 5. Magee, E . M . , H a l l , H . J . , Varga, Jr., G . M . , "Potential Pollutants i n Fossil Fuels," Environmental Protection Technology Series, E P A - R 2 - 7 3 - 2 4 9 , 293 p., U . S . Environmental Protection Agency, 1973. The data on sulfur, nitrogen, and trace elements i n coal and i n oil are summarized. Emphasis is placed on the geographic and geologic distribution of the trace elements. 6. Abernethy, R. F . , Gibson, F . H . , "Rare Elements i n C o a l , " Information Circular 8163, 69 p., U . S . Bureau of Mines, 1963. This circular reviews the occurrence of 34 trace elements i n coal and the occurrence and distribution of chlorine, phosphorus, titanium, and manganese, w h i c h are not considered rare i n coal. Separate chapters are devoted to germanium, gallium, and uranium i n coal. 7. Averitt, Paul, Breger, I. Α., Swanson, V . E . , Zubovic, Peter, Gluskoter, H . J . , " M i n o r Elements i n C o a l — A Selected Bibliography, July 1972, Pro fessional Paper 800-D, p. D - 1 6 9 - D - 1 7 1 , U . S . Geological Survey, 1972. This bibliography lists 65 selected references to articles on trace ele ments i n coals. Most articles cited are i n English and are concerned w i t h North American coals. 8. Swaine, D . J . , "Trace elements i n C o a l " (originally written i n E n g l i s h ) . Published i n Russian as S vein, D . D z h . , "Mikroelementy ν ugliakh" i n " O c h e r k i sovremonnoï geokhimii i analiticheskoï k h i m i i " ( Symposium v o l ume i n honor of the 75th anniversary of Academician A . P. Vinogradov) ( A . I. Tugarinov, E d . ) , p. 482-492, M o s k v a : " N a u k a " Publishers, 1972. This review contains sections on the occurrence of 13 trace elements in coals and a summary of trace element distribution i n coals. 9. Thiessen, Gilbert, "Composition and Origin of the M i n e r a l Matter in C o a l " i n "Chemistry of C o a l Utilization" ( H . H . L o w r y , E d . ) , v. 1, p. 4 8 5 - 4 9 5 , John W i l e y and Sons, Inc., N e w York, 1945. The relationships of mineral matter to ash content are discussed. C o n centrations of chemical elements are mentioned, and the mineral matter contents of pétrographie components are summarized. 10. Ode, W . H . , " C o a l Analysis and Mineral Matter" i n "Chemistry of C o a l Utlization, Supplementary V o l u m e " ( H . H . L o w r y , E d . ) , p. 202-231, John


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W i l e y a n d Sons, Inc., N e w York, 1963. Methods of coal analysis are given more attention than i n most other reviews. D a t a on mineral matter a n d trace elements are reviewed, and 116 references to them are included. 11. Breger, Irving Α., "Geochemistry of C o a l , " Econ. Geol. (1958) 53, 8 2 3 841. This introduction to the geochemistry of coal includes discussions of the origin a n d the physical a n d chemical structure of coal i n addition to a discussion of the composition of coal.


Literature Cited 1. Rao, C. Prasada, Gluskoter, H. J.,"Occurrenceand Distribution of Min erals in Illinois Coals," Ill. StateGeol.Surv. Circ. (1973) 476, 56 pp. 2. O'Gorman, J. V., Walker, P. L., Jr., "Mineral Matter and Trace Elements in U.S. Coals," Office of Coal Research, U.S. Department of the Interior, Research and Development Report No. 61, Interim Report No. 2 (1972) 184 pp. 3. Crossley, Η. E., "A Contribution to the Development of Power Stations," J. Inst. Fuel (1963) 36, 228-239. 4. Gluskoter, H. J., Simon, J. Α., "Sulfur in Illinois Coals," Ill. State Geol. Surv. Circ. (1968) 432, 28 pp. 5. Pringle, W. J. S., Bradburn, E., "The Mineral Matter in Coal. II—The Composition of the Carbonate Minerals," Fuel (1958) 37, (2), 166-180. 6. Dixon, K., Skipsey, E., Watts, J. T., "The Distribution and Composition of Inorganic Matter in British Coals. Part 3: The Composition of Carbonate Minerals in the Coal Seams of the East Midlands Coalfields," J. Inst. Fuel (1970) 43, (354), 229-233. 7. Kemežys, M., Taylor, G. H., "Occurrence and Distribution of Minerals in Some Australian Coals," J. Inst. Fuel (1964) 37, (284), 389-397. 8. "Annual Book of ASTM Standards," Part 19, pp. 438-439, ASTM Std. D1374-73, American Society for Testing and Material, Philadelphia, 1973. 9. Parr, S. W., "The Classification of Coal," Univ.Ill.Eng. Exp. Sta. Bull. (1928) 180, 62 pp. 10. King, J. G., Maries, M. B., Crossley, H. E., "Formulae for the Calculation of Coal Analyses to a Basis of Coal Substance Free of Mineral Matter," J. Soc. Chem. Ind. London (1936) 57, 277-281. 11. Brown, R. L., Caldwell, R. L., Fereday, F., "Mineral Constituents of Coal," Fuel (1952) 31, (3), 261-273. 12. Millot, J. O., "The Mineral Matter in Coal. I—The Water of Constitution of Silicate Constituents," Fuel (1958) 37, (1), 71-85. 13. Given, P. H., "Problems of Coal Analysis," Pennsylvania State Univ. Rept. SROCR-9, submitted to the U.S. Office of Coal Research under Contract No. 14-01-0001-390, 40 pp., 1969. 14. Gluskoter, H. J., "Electronic Low-temperature Ashing of Bituminous Coal," Fuel (1965) 44, (4), 285-291. 15. Gluskoter, H. J., "Clay Minerals in Illinois Coals," J. Sediment Petrology (1967) 37, (1), 205-214. 16. Estep, P. Α., Kovach, J. J., Karr, C., Jr., "Quantitative Infrared Multicomponent Determinations of Minerals Occurring in Coal," Anal. Chem. (1968) 40, (2), 358-363. 17. Wolfe, D. F., "Noncombustible Mineral Matter in the Pawnee Coal Bed, Powder River County, Montana," M.S. Thesis, Montana College of Mineral Science and Technology, 1969.



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Matter

and Trace Elements

in Coal

21

18. Warne, S. St. J., "Identification and Evaluation of Minerals in Coal by Differential Thermal Analysis,"J.Inst. Fuel (1965) 38, (292), 207-217. 19. Warne, S. St. J., "The Detection and Identification of the Silica Minerals Quartz, Chalcedony, Agate, and Opal, by Differential Thermal Analysis," J. Inst. Fuel (1970) 43, (354), 240-242. 20. Dutcher, R. R., White, E. W., Spackman, W., "Elemental Ash Distribution in Coal Components—Use of the Electron Probe," Proc. 22nd Ironmaking Conf., Iron Steel Div., Metallurgical Soc., Amer. Inst. Mining Eng., New York (1964) 463-483. 21. Gluskoter, H. J., Ruch, R. R., "Iron Sulfide Minerals in Illinois Coals," Geol. Soc. Amer. Abstr. 3, 582. 22. Gluskoter, H. J., Lindahl, P.C.,"Cadmium: Mode of Occurrence in Illinois Coals," Science (1973) 181, (4096), 264-266. 23. Ruch, R. R., Gluskoter, H. J., Shimp, N. F., "Occurrence and Distribution of Potentially Volatile Trace Elements in Coal," Ill. StateGeol.Survey Environ. Geol. Note (1973) 61, 43 p. 24. Lefelhocz, J. F., Friedel, R. Α., Kohman, T. P., "Mössbauer Spectroscopy of Iron in Coal," Geochim. Cosmochim. Acta (1967) 31, (12), 22612273. 25. Rafter, Τ. Α., "Sulfur Isotope Measurements on New Zealand, Australian, and Pacific Islands Sediments," Proc. Nat. Sci. Found. Symp., Yale Uni versity (April 1962) 42-60. 26. Smith, J. W., Batts, B. D., "The Distribution and Isotopic Composition of Sulfur in Coal," Geochim. Cosmochim. Acta (1974) 38, 121-133. 27. McCartney, J. T., Ergun, S., "An Automated Reflectance Scanning Micro scope System for Study of Coal Components. Application to Analysis of Pyrite Distribution," U.S. Bureau of Mines, unpublished data. 28. Liebig, J., Kopp, H., "Jahresbericht über die Fortschritte der Reinen, Pharmaceutischen, und Technischen Chemie," "Physic, Mineralogie, und Geologie für 1847-1848," p. 1120, Giessen, 1849. 29. Swanson, V. E., "Composition of Coal, Southwestern United States," U.S. Geological Survey, Southwest Energy Study, Coal Resources Work Group, Part II, 61 pp., 1972. 30. Kessler, T., Sharkey, A. G., Jr., Friedel, R. Α., "Analysis of Trace Elements in Coal by Spark-source Mass Spectrometry," U.S. Bur. Mines Rept. Invest. (1973) 7714, 8 pp. 31. Goldschmidt, V. M., "Rare Elements in Coal Ashes," Ind. Eng. Chem. (1935) 27, 1100-1102. 32. Goldschmidt, V. M., in "Geochemistry" (A. Muir, Ed.), 730 pp., Clarendon, Oxford, 1954. 33. Nicholls, G. D., "The Geochemistry of Coal-bearing Strata," "Coal and Coal-bearing Strata" (D. G. Murchison and T. S. Westoll, Eds.), pp. 267-307, Oliver and Boyd, Edinburgh and London, 1968. 34. Horton, L., Aubrey, Κ. V., "The Distribution of Minor Elements in Vitrain: Three Vitrains from the Barnsley Seam," J. Soc. Chem. Ind., London (1950) 50 (suppl. issue 1), 541-548. 35. Zubovic, P., "Minor Element Content of Coal from Illinois Beds 5 and 6 and Their Correlatives in Indiana and Western Kentucky," U.S. Geo logical Survey, openfilereport, 79 pp., 1960. 36. Zubovic, P., Stadnichenko, T., Sheffey, Ν. B., "The Association of Minor Elements with Organic and Inorganic Phases of Coal," U.S. Geol. Survey Prof. Paper (1960) 400-B, B84-B87. 37. Zubovic, P., Stadnichenko, T., Sheffey, Ν. B., "Chemical Bases of Minor Element Associations in Coal and Other Carbonaceous Sediments," U.S. Geol. Surv. Prof. Pap. (1961) 424-D (Article 411) D345-D348.



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38. Zubovic, P., Stadnichenko, T., Sheffey, Ν. B., "Distribution of Minor Ele ments in Coal Beds of the Eastern Interior Region," U.S. Geol. Surv. Bull. (1964) 1117-B, 41 pp. 39. Zubovic, P., "Physiochemical Properties of Certain Minor Elements as Con trolling Factors of Their Distribution in Coal," ADVAN. CHEM. SER. (1966) 55, 221-246. 40. Ruch, R. R., Gluskoter, H. J., Shimp, N. F., "Occurrence and Distribution of Potentially Volatile Trace Elements in Coal," Ill. State Geol. Surv. Environ. Geol. Note (1974) 72, 96. 41. Bohor, B. F., Gluskoter, H. J., "Boron in Illite as a Paleosalinity Indicator of Illinois Coals," J. Sediment. Petrology (1973) 43, (4), 945-956. 42. Ruch, R. R., Gluskoter, H. J., Kennedy, E. J., "Mercury Content of Illinois Coals," Ill. State Geol. Survey Environ. Geol. Note (1971) 43, 15 pp. 43. Watt, J. D., "The Physical and Chemical Behaviour of the Mineral Matter in Coal under the Conditions Met in Combustion Plant, Part I. The Occurrence, Origin, Identity, Distribution and Estimation of the Mineral Species in British Coals," Literature Survey, 121 pp., British Coal Utiliza tion Research Association, Leatherhead, Surrey, England, 1968. RECEIVED April 11, 1974


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