High-Temperature Interactions among Minerals Occurring in Coal

10 High-Temperature Interactions among Minerals Occurring in Coal Donald L . Biggs and Curtis G . Lindsay

1

Ames Laboratory, Iowa State Mining and Mineral Resources Research Institute, and

Downloaded by COLUMBIA UNIV on November 30, 2017 | http://pubs.acs.org Publication Date: April 2, 1986 | doi: 10.1021/bk-1986-0301.ch010

Department of Earth Sciences, Iowa State University, Ames,IA50011

Minerals known to be present in the low temperature ash extracted from coals were heated in a microscope heating stage from 25° to about 1400°C. Mineral types were arranged in homogeneous fields where two fields shared a linear boundary or three fields were in contact at a point. Because of the known reactivity of calcite and pyrite, all specimens contained this pair. Clay minerals, kaolinite, illite and montmorillonite were used as the third component. Reaction temperature between calcite and pyrite is lowered by the presence of clays. Iron was observed to migrate into the clay domain after the formation of pyrrhotite from pyrite and oldhamite was observed forming between the domain of lime formed from calcite and the pyrrhotite.

M i n e r a l i m p u r i t i e s i n c o a l a r e known t o be p r i m a r y c o n t r i b u t o r s t o the s l a g g i n g and f o u l i n g o f u t i l i t y b o i l e r s , f l y a s h and bottom a s h p r o d u c t i o n as w e l l as a t m o s p h e r i c p o l l u t i o n . They a l s o produce u n d e s i r a b l e e f f e c t s i n some p a r t s o f hydrogénation p r o c e s s e s such as l i q u i f a c t i o n and g a s i f i c a t i o n ( 1 , 2 , 3 ) . D e s p i t e a l o n g h i s t o r y o f i n v e s t i g a t i o n prompted by t h e s e o b s e r v a t i o n s , many q u e s t i o n s remain unanswered. Simple e m p i r i c a l r e l a t i o n s h i p s between f u s i o n temperature o f the f u r n a c e d e p o s i t s and t h e m i n e r a l o g y o f c o a l s have been p r o p o s e d (4,5,6). More r e c e n t l y attempts have c o n c e n t r a t e d on a p h y s i c o c h e m i c a l view o f t h e problem comparing a s h f u s i o n temperatures w i t h phase r e l a t i o n s i n three-component c h e m i c a l systems ( 7 , 8 ) . This method o f a t t a c k has y i e l d e d some s i g n i f i c a n t r e s u l t s , b u t a t l e a s t some r e s e a r c h e r s (8) have q u e s t i o n e d t h i s approach, which i s based 1

Current address: Department of Geologic Sciences, Virginia Polytechnic Institute, Blacksburg, VA 24061. 0097-6156/ 86/ 0301 -0128S06.00/ 0 © 1986 American Chemical Society

Vorres; Mineral Matter and Ash in Coal ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

10.

BIGGS A N D LINDSAY

High-Temperature

Interactions

among

129

Minerals

on t h e assumption t h a t these p r o c e s s e s o c c u r under c o n d i t i o n s o f equilibrium. The aim o f t h e r e s e a r c h d e s c r i b e d here i s t o o b s e r v e i n t e r a c t i o n s between m i n e r a l s known t o o c c u r i n c o a l s i n t h e most d i r e c t f a s h i o n p o s s i b l e and i n t h e s i m p l e s t c o n d i t i o n s c o n s i s t e n t w i t h causing the r e a c t i o n s to occur. I t i s considered that observation o f s i m p l e m i x t u r e s o f m i n e r a l s o b s e r v e d t o e n t e r i n t o r e a c t i o n may make p o s s i b l e a b e t t e r a c c o u n t i n g o f t h e p r o c e s s e s by which s l a g and f o u l i n g d e p o s i t s form i n f u r n a c e s .


Experimental

Methods

I s o l a t i o n and I d e n t i f i c a t i o n o f C o a l M i n e r a l s . Two c o a l samples, c o l l e c t e d from d i f f e r e n t c o a l b a s i n s i n t h e U n i t e d S t a t e s (see T a b l e I ) , were s u b j e c t e d t o low-temperature a s h i n g as d e s c r i b e d by Gluskoter (9). T h i s process avoids d e s t r u c t i o n of the m i n e r a l s while o x i d i z i n g the o r g a n i c p o r t i o n o f the c o a l . T h i s ashing procedure o c c u r s a t a much lower temperature than t h a t o f t h e American S o c i e t y f o r T e s t i n g and M a t e r i a l s (ASTM) method i t i s g i v e n t h e name o f "lowtemperature a s h i n g and g e n e r a l l y a b b r e v i a t e d LTA. I n f o r m a t i o n o f a m i n e r a l c o n c e n t r a t e by LTA, a few changes a r e a n t i c i p a t e d ; some c l a y s a r e r e v e r s i b l y d e h y d r a t e d , and h y d r a t e d s u r f a c e s a r e reduced t o t h e hemihydrate form ( f o r i n s t a n c e gypsum i s c o n v e r t e d t o b a s s a n i t e ) . Because these changes a r e known i n advance, due a l l o w a n c e c a n be made f o r them. 11

Table I.

Seam: Locality:

C o a l Samples, L o c a l i t i e s o f O r i g i n , and A n a l y s e s ( a l l samples run-of-mine)

I l l i n o i s #6 S t . C l a i r County, I l l i n o i s

Analysis:

9 mesh χ 0 Raw

M o i s t u r e (%): Ash, ASTM (%): P y r i t i c S u l f u r (%): T o t a l S u l f u r (%): H e a t i n g Value ( B T U / l b . ) : Seam: Locality:

5.31 32.86 2.46 4.57 9,039

9 χ 32 mesh Float 5.44 7.10 0.76 4.57 13,248

9 χ 32 mesh Sink 2.55 68.05 5.08 5.94 3,574

Upper F r e e p o r t Grant County, West V i r g i n i a

Analysis :

M o i s t u r e (%): Ash, ASTM (%): P y r i t i c S u l f u r (%): T o t a l S u l f u r (%): H e a t i n g Value ( B T U / l b . ) :

9 mesh χ 0 Raw 0.30 35.90 1.58 2.18 9,695

9 χ 32 mesh Float 0.68 7.26 0.27 1.06 13,365

9 χ 32 mesh Sink 0.93 72.10 2.62 3.00 3,086


130

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

M i n e r a l c o n s t i t u e n t s o f t h e LTA c o n c e n t r a t e s were i d e n t i f i e d by x-ray d i f f r a c t i o n techniques. I l l i t e , k a o l i n i t e , q u a r t z and p y r i t e a r e u b i q u i t o u s i n t h e m i n e r a l s u i t e s ; c a l c i t e o c c u r s i n most c o n c e n trates. Many o t h e r m i n e r a l s have been i d e n t i f i e d i n c o a l s b u t were not o b s e r v e d i n t h e s e specimens. Heating-Stage M i c r o s c o p i c Observations. F o l l o w i n g the c h a r a c t e r i z a t i o n o f the m i n e r a l s u i t e s by x - r a y d i f f r a c t i o n t e c h n i q u e s , each LTA c o n c e n t r a t e was heated i n a h e a t i n g s t a g e mounted on a m i c r o s c o p e f i t t e d f o r observation i n v e r t i c a l l y incident l i g h t . Concentrates examined i n t h i s way and t h e p r o d u c t phases a r e found i n T a b l e I I .


Table I I .

LTA Samples and H e a t i n g

LTA Sample Upper F r e e p o r t raw

max (°C) 560 1410

Products

Phases I d e n t i f i e d quartz, i l l i t e , pyrrhotite quartz, m u l l i t e a

Upper F r e e p o r t

1.40 f l o a t

1031 1250

quartz^ quartz^

Upper F r e e p o r t

1.40 s i n k

635 1150

quartz, i l l i t e , pyrrhotite quartz, pyrrhotite, i l l i t e

Illinois

#6 raw

880

Illinois

#6 1.40 f l o a t

625 1370

Illinois

#6 1.40 s i n k

920 1334

d

quartz, i l l i t e , oldhamite(?)

0

pyrrhotite,

quartz, i l l i t e , pyrrhotite, troilite(?) quartz, pyrrhotite quartz, i l l i t e , pyrrhotite, oldhamite quartz, p y r r h o t i t e , oldhamite

XRD peaks o c c u r r e d a t t h e c o r r e c t d i f f r a c t i o n a n g l e s f o r m u l l i t e but were too weak t o p e r m i t a c c u r a t e i n t e n s i t y comparisons. The o v e r a l l p a t t e r n was s i m i l a r t o t h e one f o r t h e i l l i t e k a o l i n i t e p a i r h e a t e d t o 1410°C, except t h a t s t r o n g e r peaks f o r q u a r t z were found i n the LTA XRD p a t t e r n . Peaks were d e t e c t e d a t some o f t h e d i f f r a c t i o n a n g l e s f o r i l l i t e , but t h e i n t e n s i t i e s were n o t comparable w i t h s t a n d a r d p a t t e r n s ; i t i s p o s s i b l e t h a t t h e s e were r e l i c t peaks o f i l l i t e as i t began t o alter. Another sample o f I l l i n o i s #6 raw LTA was heated t o 1421°C; i t formed a h a r d , d a r k - c o l o r e d g l a s s a t about 1400°C; t h i s m a t e r i a l c o u l d n o t be removed from the h e a t i n g - s t a g e c r u c i b l e .


10.

BIGGS A N D LINDSAY

High-Temperature

Interactions

among

Minerals

131


The h e a t i n g s t a g e i s l i m i t e d to i n e r t atmosphere o r vacuum operation. T h e r e f o r e , r e a c t i o n s s e n s i t i v e to a t m o s p h e r i c c o n d i t i o n s , such as p a r t i a l p r e s s u r e o f oxygen, cannot be s t u d i e d . Furthermore, the e x t r e m e l y s m a l l p a r t i c l e s i z e of the sample r e s u l t e d i n i n a b i l i t y to observe changes o c c u r r i n g below the mount s u r f a c e and t o r e s o l v e the s p e c i f i c m i n e r a l s e n t e r i n g i n t o a r e a c t i o n a t any p o i n t i n the run. These d i f f i c u l t i e s were a d d r e s s e d by o b t a i n i n g samples o f the m i n e r a l s i d e n t i f i e d i n the LTA c o n c e n t r a t e b e f o r e h e a t i n g , g r i n d i n g them t o a p p r o x i m a t e l y the same s i z e c o n s i s t as the c o n c e n t r a t e , and mounting them i n s e p a r a t e domains i n the h e a t i n g s t a g e c r u c i b l e . The geometry of these mounts i s shown i n F i g . 1.

Experiments

w i t h Known M i n e r a l s

Experiments w i t h I n d i v i d u a l M i n e r a l s . S i n g l e m i n e r a l mounts i n the h e a t i n g - s t a g e c r u c i b l e y i e l d e d the expected p r o d u c t s , t h a t i s , p y r i t e y i e l d e d p y r r h o t i t e and t r o i l i t e , c a l c i t e gave l i m e and c a r b o n d i o x i d e , and c l a y s r e a c t e d under h i g h temperature c o n d i t i o n s t o y i e l d a s i l i c a t e glass. Experiments w i t h P a i r s and T r i p l e t s o f Known M i n e r a l s . In these e x p e r i m e n t s , known m i n e r a l s were ground and p l a c e d i n the h e a t i n g s t a g e c r u c i b l e i n s e p a r a t e domains as p a i r s or t r i p l e t s o f m i n e r a l s . The p a i r s and t r i p l e t s were heated and the b e h a v i o r a t t h e i r bounda r i e s observed. T a b l e I I I l i s t s the m i n e r a l s used i n p a i r mounts and the r e a c t i o n p r o d u c t s o b t a i n e d by h e a t i n g . Because the most r e a c t i v e phases found i n the experiments w i t h p a i r s o f m i n e r a l s were c l a y s , c a l c i t e , and p y r i t e , t h e s e were p r e p a r e d i n t r i p l e t mounts. In t r i a l s u s i n g e i t h e r m o n t m o r i l l o n i t e or i l l i t e w i t h c a l c i t e and p y r i t e , a l i q u i d formed a t the mutual boundary o f the l a t t e r p a i r a t 600-650°C. P y r i t e and c a l c i t e had, of c o u r s e , p r e v i o u s l y r e a c t e d and t h i s l i q u i d t h e r e f o r e o c c u r r e d between the p r o d u c t phases p y r r h o t i t e and l i m e . Subsequent x - r a y a n a l y s i s showed the p r e s e n c e o f p y r r h o t i t e , l i m e , and o l d h a m i t e . In b o t h i n s t a n c e s , the temperature o f t h i s r e a c t i o n was lower than t h a t o b t a i n e d i n the p a i r mount o f c a l c i t e and p y r i t e , 1140°C. When k a o l i n i t e was i n the mount w i t h c a l c i t e and p y r i t e , the same r e a c t i o n o c c u r r e d a t 750-760°C. Though the mechanism by w h i c h the c l a y s reduce the r e a c t i o n temperature i s not y e t u n d e r s t o o d , the d i f f e r e n c e s i n r e a c t i o n temperature w i t h and w i t h o u t c l a y i s considered s i g n i f i c a n t . The most o b v i o u s change i n the c l a y s themselves d u r i n g t h e s e experiments was a d a r k e n i n g b e g i n n i n g w i t h p y r i t e d e c o m p o s i t i o n . T h i s was more marked i n the case o f i l l i t e and m o n t m o r i l l o n i t e . I t i s c o n s i d e r e d t h a t i n a l l t h e s e c a s e s , the c l a y m i n e r a l s t r u c t u r e was d e s t r o y e d and p o s s i b l y formed a s i l i c a t e g l a s s , much l i k e those found i n f u r n a c e s l a g s but h a v i n g , perhaps, l e s s oxygen.




132

Figure

1.

Geometric arrangement o f m i n e r a l p a i r s and t r i p l e t s used i n the h e a t i n g s t a g e e x p e r i m e n t s and s u p p o r t i n g e x p e r i ments. I n a l l t r i p l e t mounts, p o s i t i o n 3 was o c c u p i e d by a clay mineral.


10.

BIGGS A N D LINDSAY

Table I I I .

High-Temperature

among

133

Minerals

M i n e r a l P a i r s and H e a t i n g P r o d u c t s

Mineral Pair Calcite-illite Calcite-kaolinite Calcite-montmorillonite Calcite-pyrite


Interactions

Calcite-quartz Illite-kaolinite Illite-montmorillonite Illite-montmorillonite Illite-pyrite Illite-quartz Kaolinite-montmorillonite Kaolinite-pyrite Kaolinite-quartz Montmorillonite-pyrite Montmorillonite-quartz Pyrite-quartz

max (°C) 1310 1322 1285 1253 1467 1410 662 1212 1519 1450 1403 1445 1220 1053 1492 1571

Products I d e n t i f i e d l i m e (CaO) l i m e (CaO) (indeterminate)* lime, pyrrhotite ( F _ S ) , o l d h a m i t e (CaS) q u a r t z ( S i 0 ) , l i m e (CaO) mullite ( A l ^ i o O ^ ) ( i n d e te rminate;b (indeterminate) p y r r h o t i t e , t r o i l i t e (FeS) quartz mullite (poorly-crystalline) mullite quartz ^ (indeterminate) quartz quartz e i

x

2

Only those p r o d u c t s a r e l i s t e d which c o u l d be p o s i t i v e l y i d e n t i f i e d by XRD; no attempt i s made here t o deduce the c o m p o s i t i o n o f amorphous p r o d u c t s . XRD p a t t e r n s f o r t h e s e h e a t i n g p r o d u c t s d i d not match any s t a n d a r d p a t t e r n c l o s e l y ; attempts t o match w i t h computer r o u t i n e s produced r e s u l t s o f low r e l i a b i l i t y . " P o o r l y c r y s t a l l i n e " means t h a t d i f f r a c t i o n maxima were found c o r r e s p o n d i n g t o the i n d i c a t e d phase, but peaks were not sharp d i d not have the c o r r e c t r e l a t i v e i n t e n s i t i e s i n a l l c a s e s .

and

Supporting Experiments. To examine the e f f e c t o f o x i d i z i n g and r e d u c i n g atmosphere on t h e s e m a t e r i a l s , g r a p h i t e c r u c i b l e s 10mm i n d i a m e t e r and 2mm deep were packed i n the manner d e s c r i b e d above and h e a t e d i n a f u r n a c e f i t t e d t o p e r m i t i n t r o d u c t i o n o f s p e c i f i e d gases d u r i n g h e a t i n g . A f t e r h e a t i n g , the samples were examined by s c a n n i n g e l e c t r o n m i c r o s c o p y and energy d i s p e r s i v e x - r a y s p e c t r o s copy (SEM/EDS) ( F i g u r e 2 ) . Samples t r e a t e d i n t h i s way are l i s t e d i n T a b l e IV. In a l l t h e s e c a s e s where p y r i t e was used w i t h a c l a y , i r o n was found t o have m i g r a t e d from the i r o n s u l f i d e i n t o r e g i o n t h a t was originally clay. E l e m e n t a l mapping showed the p r e s e n c e o f i r o n t o have c o m p l e t e l y pervaded the r e g i o n f o r m e r l y o c c u p i e d by c l a y . In a l l mounts c o n t a i n i n g c a l c i t e and p y r i t e , the c a l c i u m and s u l f u r peaks were p r e s e n t i n the r e g i o n o r i g i n a l l y o c c u p i e d by c a l c i t e and sometimes found i n the r e g i o n t h a t had been p y r i t e - f i l l e d .


134

MINERAL

MATTER

A N D A S H IN C O A L

α 500 Pyritef

All

] pKaolinite


3 Ο Ο

0.000

5.000 10.000 15.000 ENERGY (KEV)

20.000

Al 500

Pyrite

Kaolinite

ζ ο ο

0.000

I500h

1000

5.000

C

10.000 15.000 ENERGY (KEV)

20.000

Pyrite ^J>)

Kaolinite

Fe

-

CD h-

I

500

Ο

Al | i

S i

"0.000

F i g u r e 2.

5.000

Γ,

1

1

•

ι

10.000 15.000 ENERGY (KEV)

ι 20.000

E n e r g y - d i s p e r s i v e s p e c t r a from a p y r i t e - k a o l i n i t e mount h e a t e d to 1200°C. L o c a t i o n s o f the s p e c t r a w i t h r e s p e c t to the sample are i n d i c a t e d by the s m a l l squares i n the circles.


BIGGS A N D LINDSAY

High-Temperature


1500 V

Interactions

among

Minerals

|Fe Pyrite

Koolinite

£ 1000 ζ Z> Ο

ο 500 Ι

0.000

1000 h

5.000

10.000 15.000 ENERGY (KEV)

20.000

e

Fe Pyrite

3 Ο

Kaolinite

500

Fe

0.000

5.000

10.000

15.000

20.000

ENERGY ( K E V ) Figure

2.

Continued.


136



T a b l e IV.

Subjects of Supporting

Assemblage Calcite-kaolinite Calcite-quartz Pyrite-quartz Pyrite-quartz Pyrite-calcite Pyrite-kaolinite Pyrite-kaolinite Pyrite-montmorillonite Pyrite-montmorillonite Py.-calc.-kao. Py.-cale.-mont. Py.-cale.-mont. Note:

Atmosphere inert inert oxidizing reducing reducing oxidizing reducing inert reducing reducing inert reducing

Experiments Τ

(°C) 1400 1400 1200 1200 1200 1200 1200 800 800 1200 800 800

Duration 60 60 30 30 30 30 30 15 15 30 15 15

(min)

The i n d i c a t e d temperature was the s t e a d y - s t a t e temperature f o r the t r i a l . The i n d i c a t e d d u r a t i o n was the p e r i o d o f time f o r which t h a t s t e a d y - s t a t e temperature was m a i n t a i n e d .

D i s c u s s i o n and C o n c l u s i o n s I t i s apparent t h a t the phenomena d e s c r i b e d here a r e not complete p r o c e s s e s t e r m i n a t i n g i n e q u i l i b r i u m assemblages. The times o f r e a c t i o n are too s h o r t f o r many o f the p r o d u c t s o f s i l i c a t e s such as c l a y s and q u a r t z t o come to thermodynamic e q u i l i b r i u m a t the new temperature. That t h i s i s i n d e e d the case i n o p e r a t i o n of powerp l a n t b o i l e r s i s o b v i o u s from the c o n s i d e r a t i o n o f the amount o f g l a s s found i n f u r n a c e s l a g s and f l y - a s h . I l l i t e and m o n t m o r i l l o n i t e a r e s i m i l a r i n s t r u c t u r e and d i f f e r s l i g h t l y from k a o l i n i t e i n t h i s r e g a r d . The f i r s t two a r e composed of two s i l i c o n - o x y g e n l a y e r s p e r o c t a h e d r a l l a y e r c o n t a i n i n g i r o n , magnesium and aluminum and i n k a o l i n i t e the r a t i o o f t e t r a h e d r a l and o c t a h e d r a l l a y e r s i s 1. In c l a y s t h e r m a l m o d i f i c a t i o n o c c u r s a t lower temperature t h a n s i l i c a because the bonds formed between the A l , Fe, and Mg atoms and oxygen a r e weaker than the S i - 0 bonds. C l a y s , t h e r e f o r e , a r e e x p e c t e d to be more r e a c t i v e than the s i l i c a crystals. There i s e v i d e n c e of d r a s t i c s t r u c t u r a l m o d i f i c a t i o n s , i f not v i t r i f i c a t i o n , i n the c l a y m i n e r a l domains d u r i n g t h e r m a l t r e a t ment and t h a t i r o n e n t e r s the r e g i o n . F u r t h e r i n q u i r i e s are i n p r o g r e s s t o answer t h e s e q u e s t i o n s . C a l c i t e appears l a r g e l y i n e r t a t temperatures a p p r o a c h i n g 600°C i n the p r e s e n c e of some o f the c l a y m i n e r a l s and i n e r t u n t i l about 900°C i n t h e i r absence. The cause o f t h i s f l u x i n g i s not w e l l under s t o o d a t t h i s time, but i n v e s t i g a t i o n s a r e p l a n n e d t o e x p l a i n t h i s behavior. At whatever temperature, the r e a c t i o n o b s e r v e d i s the d e c o m p o s i t i o n o f c a l c i t e to l i m e (CaO) and c a r b o n d i o x i d e . The e x t e n t to which c a r b o n d i o x i d e i n f l u e n c e s f u r t h e r r e a c t i o n i s n o t known but must be c o n s i d e r e d as an i m p o r t a n t s t e p i n a complete explanation. L i k e c a l c i t e , p y r i t e i s q u i t e r e a c t i v e and i t s t h e r m a l b e h a v i o r i s i n f l u e n c e d by the p r e s e n c e o f c l a y m i n e r a l s . The i n i t i a l r e a c t i o n temperature o f p y r i t e a l o n e o r i n the p r e s e n c e o f c a l c i t e a l o n e i s to


10.

BIGGS A N D LINDSAY

High-Temperattire

Interactions

among Minerals

137

produce p y r r h o t i t e , ( F e ^ ^ S ) and t r o i l i t e ( F e S ) . The l o s s o f s u l f u r i s o b v i o u s and c o n t i n u e s over an a p p r e c i a b l e temperature range. The most i m p o r t a n t r e a c t i o n p r o d u c t s a r e those o f t h e i r o n enrichment o f t h e c l a y m i n e r a l r e s i d u e s , p r o b a b l y a p r e c u r s o r o f t h e i r o n o x i d e and g l a s s m i x t u r e s commonly o b s e r v e d i n s l a g s and f l y a s h e s , and t h e f o r m a t i o n o f t h e s u l f i d e o f c a l c i u m , o l d h a m i t e . Oldhamite i s o b s e r v e d i n a l l experiments where c a l c i t e and p y r i t e i n t e r a c t , whereas a n h y d r i t e i s o b s e r v e d o n l y where they have r e a c t e d i n t h e p r e s e n c e o f an o x y g e n - r i c h atmosphere. T h i s behavior suggests t h a t o l d h a m i t e , formed i n t h e r e d u c i n g p a r t o f a f l a m e , i s a n e c e s sary p r e c u r s o r t o the formation o f a n h y d r i t e .


Acknowledgments T h i s m a t e r i a l i s based, i n p a r t , on work s u p p o r t e d by t h e U.S. Bureau o f Mines, Department o f t h e I n t e r i o r , under Grant No. Gl106002. Any o p i n i o n s , f i n d i n g s , and c o n c l u s i o n s o r recommendations e x p r e s s e d i n t h i s p u b l i c a t i o n a r e those o f t h e a u t h o r s and do n o t n e c e s s a r i l y r e f l e c t t h e views o f t h e U.S. Bureau o f Mines, Department of t h e I n t e r i o r . Work on o t h e r p a r t s o f t h i s p u b l i c a t i o n was performed i n Ames L a b o r a t o r y and was s u p p o r t e d by t h e A s s i s t a n t S e c r e t a r y o f F o s s i l Energy, D i v i s i o n o f C o a l U t i l i z a t i o n t h r o u g h t h e P i t t s b u r g h Energy Technology C e n t e r , C o a l P r e p a r a t i o n Branch. Ames L a b o r a t o r y i s o p e r a t e d f o r t h e U.S. Department o f Energy by Iowa S t a t e U n i v e r s i t y under C o n t r a c t W-7405-Eng-82.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Mukkherjee, D. K.; Chowdhury, B. Fuel 1976, 55, 4-8. Wakely, L. D.; Davis, Α.; Jenkins, R. G.; Mitchell, G. D.; Walker, P. L., Jr. Fuel 1979, 58, 379-385. Gray, D. Fuel 1978, 57, 213-216. Moody, A, H.; Langan, D. D. Combustion 1935, 6, 13-20. Gauger, A. W. Procedures of the American Society of Testing Materials 1937, Part I, 376-401. Palmenburg, O. W. Industrial and Engineering Chemistry 1939, 31, 1058-1059. Electric Power Research Institute (EPRI) Report CS-1418, Research Project 736; prepared by Battelle, Columbus Labora tories, 1980. Huggins, F. E . ; Kosmack, D. Α.; Huffman, G. P. Fuel 1981, 60, 577-584. Gluskoter, H. J . Fuel 1965, 44, 285-291.

RECEIVED June 13, 1985


High-Temperature Interactions among Minerals Occurring in Coal

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