E N V I R O N M E N T A L G E O L O G Y N O T E S

APRIL 1970 * NUPBER 34

SULFUR REDUCTION OF ILLINOIS COALS W R S H Q B I L I T Y T E S T S

Roy J. Eielfinstine, Jack A . Simon, Heil Fv Shimp, and M. E . Hopkins

I L L I N O I S S T A T E G E O L O G I C A L S U R V E V

JOHN C. FRYEs Chief Urbana 61801

S U L F U R R E D U C T I O N OF I L L I N O I S COALS

WASHABILITY TESTS

Roy J. Helfinstine, Jack A . Simon, N e i l F. Shimp, and M. E. Hopkins

ABSTRACT

A s s u l f u r i n the coal and o i l burned in power p l a n t s is the major source of s u l f u r dioxide emitted t o the atmosphere, the removal of s u l f u r from coa l before i t i s burned would help to reduce a i r p ~ l l u t i o n . To determine how much the s u l f u r content could be reduced by prepara t ion techniques, 40 coa l samples from 35 I l l i n o i s coal mines were s t u d i e d a t the I l l i n o i s S t a t e Geo l~g - lcal Survey.

Only i n those Illinois coa l s having r e l a t i v e l y low sul- f u r con ten t , as mined, could the s u l f u r content be reduced t o 1 .5 percent or less by washing techniques. Most I l l i n o i s coals, as mined, contain 3 t o 5 percent s u l f u r . Laboratory t e s t s revealed this could be reduced ts about 2.5 t o 4 percent .

INTRODUCTION

When coal is burned under normal conditions, practically all of the sulfur in the coal is released into the atmosphere as sulfur dioxide ( S O 2 ) . Reduction of suZEur dioxide is a major objective of many current pollution control activities. One obvious way to reduce the emission of sulfur dioxide from coal-burning equipment I s to reduce the sulfur content of the c o a l t o

the p r a c t i c a l minimum, b u t more information i s needed t o determine what that p r a c t i c a l minimum is. The I n v e s t i g a t i o n described i n this preliminary report and o t h e r s t u d i e s are being conducted by t h e I l l i n o i s S t a t e Geological Survey t o help provide some of the needed information. Present and projected needs f o r c o a l as f u e l f o r e l e c t r i c power genera t ion make i t imperat ive t h a t we l e a r n everything poss ib l e about our coa l s .

Most of t h e coa l s currently mined i n I l l i n o i s are cleaned before they are so ld . The term "cleaned" (or "washedi') indicates that the coal, as mined, i s processed i n a coa l prepara t ion p l a n t t o reduce the amount of ash and s u l f u r in the coa l and increase i ts hea t ing va lue*

The preparation process is based on the fact that mineral matter (impurities) has a higher s p e c i f i c gravity than the assoc ia t ed coal. Unfor- t una te ly , some of this mineral matter i s in t ima te ly mixed with the c o a l and cannot be r e a d i l y separa ted .

Washability s t u d i e s are conducted i n a l abora to ry t o determine the potential reduction of ash or s u l f u r f o r a c o a l from any given loca t ion . Basically, this is done by p lac ing samples of c o a l i n s o l u t i o n s t h a t have s u i t a b l e specific gravity and determining t h e percentage of the " f loa t " and "sink" f r a c t i o n s . Chemical analyses a l s o are made on t h e f l o a t and s i n k frac- t ions . Five s o l u t i o n s wi th varying s p e c i f i c g r a v i t i e s ranging from 1.23 t o 1.60 were used t o determine t h e r e l a t i o n between t h e chemical ana lyses and the percentage of sink (commonly called "reject" or "refuse") . The r e l a t i o n between the percentage of f l o a t (commonly c a l l e d "recovery") and the chemical analyses were determined i n the same manner. Laboratory f loa t - s ink data generally provide r e s u l t s t h a t r ep resen t the maximum cleaning c a p a S i l i t i e s of a p a r t i c u l a r coal .

This report briefly o u t l i n e s t h e f i r s t phase of a continuing inves- t i g a t i o n of the washability of I l l i n o i s c o a l s and summarizes results. A more comprehensive r e p o r t w i l l be prepared and published a t a later date. Mean- while, d e t a i l e d information is available a t t h e I l l i n o i s S t a t e Geological- Survey f o r those t h o need i t immediate'ly.

Acknowledgments

The U. S. Public Health Service, Department of Health, Education arid Welfare, through con t rac t No. PH 86-67-206, provided s u b s t a n t i a l support f o r t h i s study. We are a l s o indebted t o the operating coa l companies of l l l i n o i s f o r their invaluable a s s i s t a n c e i n obtaining samples.

PURPOSES OF THE INVESTIGATION

The primary aim of t h i s i n v e s t i g a t i o n was to study the washabi l i ty c h a r a c t e r i s t i c s of I l l i n o i s c o a l s , w i th p a r t i c u l a r emphasis on t h e q u a n t i t y , d i s t r i b u t i o n , and varieties (forms) of sulfur occurr ing i n I l l i n o i s coals. The s t u d i e s could provide a b a s i s f o r determining how much p y r i t i c s u l f u r could be rem6ved from I l l i n o i s coa l s by conventional c o a l cleaning methods and also f o r eva lua t ing the p y r i t i c and total sulfur contents of coal mine r e fuse .

The data developed i n t h i s s tudy supply information required f o r (1) determinat ion of how much s u l f u r can be removed from coal from v a r i a u s seams, or different a reas within the same seam, by conventional p repa ra t ion techniques; (2) eva lua t ion of t h e possibility of recovering p y r i t e from mine refuse t o reduce its p o t e n t i a l as a stream p o l l u t a n t ; and (3) evaluation of the use of I l l i n o i s coa l refuse as a source of p y r i t e f o r s u l f u r recovery o r s u l f u r i c a c i d manufacture.

A secondary o b j e c t of the i n v e s t i g a t i o n has been a comprehensive s tudy of o t h e r chemical and physica l p r o p e r t i e s of I l l i n o i s c o a l s , including trace elements, coal petrography, palynology, and minera l ma t t e r other than s d f ur compounds.

PROCEDURE

Samples

The 40 coa l samples described i n t h i s r e p o r t were taken from 35 Bl l ino i s c o a l mines Located i n most rnin%ng areas of t h e s t a t e * Coal seams sampled were the B a n v i l l e (No. 7), Nerlrin (No. 6 ) , Harrisburg o r Spr ing f i e ld (No. 51, Summum (No. 4 ) , Colches t e r (No. 2) , De Koven, Davis, and Rock Island (No. 1 ) . The number of samples is greater than the number of mines because several mines produced coal from more than one seam. In a l l cases, d i f f e r e n t seams were sampled separa te ly .

An e f f o r t was made to o b t a i n samples t h a t were r e p r e s e n t a t i v e of the coa l processed by the prepa ra t ion plant during one full s h i f t of opera t ion . The ideal sample w a s 2000 pounds of c o a l made up of 20 t o 30 increments taken a t uniform in te rva l s throughout a working s h i f t . However, a t many mines fewer increments were taken because sampling condi t ions were poor. Some samples, therefore, may not be representative of the output for the operating shift and should not be considered r e p r e s e n t a t i v e of t h e output of t h e mine fo r an extended period of t i m e , The samples are, however, s u p e r i o r t o grab samples. A t s e v e r a l s t r i p mines, coals from d i f f e r e n t seams were being mixed at the preparation plan t , and it was not practical t o ob ta in a single-seam sample from t h e t i p p l e , making i t necesary t o c u t them from f resh ly exposed f a c e s i n the p i t s 4

In addi t ion t o t h e 2000-lb sample, a t least three channel samples of about 50 l b s each were cut from the coal f a c e i n different a r e a s of every mine sampled,

Laboratory Prepa ra t ion

The channel samples were crushed and r i f f l e d i n t h e l a b o r a t o r i e s to obtain adequate samples for chemical and phys ica l ana lyses . Chemical analyses included proximate, heating value , total sulfur, forms of sulfur (pyritic, organic, or sulfate), and chlorine analyses. These same analyses , p lus u l t ima te analyses and determinat ions of the f ree-swel l ing index, ash fusion temperature, and Gieseler plasticity were made an a composite of t h e t h r e e face-channel sm.ples.

TABLE 1 -- PYRITIC SULFUR^ REDUCTION I N FLOAT CORLS

80 percent recovery

0 1

02

0 3

0 4

0 5

06

0 7

0 A

09

10

1 1

1 2

13

14

1 5

1 C

17

1 8

1 9

2 0

2 1

2 2

2 3

2 4

2 5

T 6

2 7

2 8

29

30

3 P

3 2

3 3

3 4

3 5

36

3 7

3 1)

3'3

46:

AVERAGE

l~hsrnlccsl data on dry baris, 2 ~ e r c e n t reduction from original sample,

The 1-ton sample of raw coal was crushed to a maximum s i z e of 1% i n . wi th a j a w crusher. A r ep resen ta t ive portion (about 200 l b s ) of t h i s 1% in. x 0 coal was crushed to a top s i z e of 3/8 i n . , then screened into 3/8 i n . x 14 mesh, 1 4 mesh x 100 mesh, and 100 mesh x 0 fractions. Washability studies were made on t h e 1% in* x 0, 3 f 8 i n . x 14 mesh, and 1 4 mesh x 100 mesh f r a c t i o n s .

Gravi ty sepa ra t ions of very f ine coal (less than 100 mesh) are dif- f i c u l t with any coal and a r e p a r t i c u l a r l y d i f f i c u l t wi th I l l i n o i s coals, which are q u i t e porous. The l i q u i d used f o r the sepa ra t ion rapidly p e n e t r a t e s the pores and thereby exerts a major influence on the r e s u l t s . Although some tests were made w i t h the 100 mesh x 0 c o a l s , the results were R O ~ s a t i s f a c t o r y .

Chemical Analyses

Chemical analyses, which determined percentages of ash, sulfate s u l f u r , p y r i t i c s u l f u r , o rganic sulfur, and t o t a l sulfur, were made on a l l f l o a t f r a c t i o n s and on some s i n k fractions. Grindab i l i t y and f u s i b i l i t y of t he ash were also determined f o r the l i g h t e s t , intermediate, and heav ies t (1.60 s p e c i f i c gravity) f l o a t f r a c t i o n s of the 1% in. x 0 coal, although t h e va lues a r e no t presented i n this report. The proximate analyses and derer- minations of t o t a l s u l f u r , forms of sulfur, heating value, and free-swelling index were made f o r t h e raw coa l , as received, and on the sized f r a c t i o n s .

A l l chemical values presented in t h i s r e p o r t are on t h e dry basis .

RESULTS

Sul fu r Removal

Three forms of su l fu r - su l f a t e , organic, and pyritic-were determined by chemical analyses. The s u l f a t e sulfur content is q u i t e low, wi th an average of only 0.08 percent f o r t h e 40 samples tested. The organic s u l f u r i s in complex combination with o t h e r organic matter i n the coal and cannot be

TABLE 2-EFFECT OF COAL SIZE ON SULFUR REDUCTION*

x 100 mesh

- - - - -

* Sulfur values are given on the dry b a s i s and a r e averages o f 40 samples.

Original sample

l~h@rnicarl date on dry bar1

removed from the coal by physical means. The pyritic sulfur, which can be p a r t l y sepa ra t ed from the c o a l by g r a v i t y methods, is t h e Eom of s u l f u r of particular interest i n this study.

A s pyrite i s about f o u r times heavier than the associated coa l , g r a ~ r i t y methods of s e p a r a t i o n can be used. Nowever, some of t h i s s u l f u r is generally f inely disseminated throughout t h e c o a l and cannot be readily sepa- ra ted . Table 1 shows the percentage of p y r i t i c s u l f u r m o v e d from the samples i n this i n v e s t i g a t i o n wi th 40 and 80 percent recoveries (1% i n . x O s i z e ) . Although 78.4 percent of the p y r i t i c sulfur was removed from sample 24 with SO percent recovery of the r a w coa l sample, t h e average removal of p y r i t i c s u l f u r from a l l samples was only 53.9 percent. Even w i t h 40 percent clean c o a l recovery, which i s Ear less than the commerciaLly acceptable recovery level, an average of only 76.8 percent of the p y r i t i c s u l f u r was removed.

Effect of Goal Size on Su l fu r Reduction

The effect of coal s i z e upon the washabi l i ty c h a r a c t e r i s t i c s of the coal may be important. Table 2 lists t h e average percentages of total and pyritic s u l f u r (dry b a s i s ) a t f i v e recovery values and three s i z e ranges for the 40 coals t e s t ed . The percentages of t o t a l and p y r i t i c s u l f u r were usua l ly lower i n the f iner c o a l sizes, bur t h e d i f f e r e n c e s were not g r e a t enough t o cons ider fine gr inding of these coa l s a s an e f f e c t i v e procedure for sulfur reduct ion. However, a f e w exceptions t o t h i s average t r end i n d i c a t e t h a t fine gr inding might produce a beneficial e f f e c t on some coa l s .

Su l fu r vs. Recovery

One of the basic aims of these washabi l i ty s t u d i e s i s to provide information t h a t shows the potential of Illinois coals as a source of f u e l w i th certain sulfur limits and wi th p r a c t i c a l l i m i t s of recovery of the raw coal. Although the percentage of al lowable s u l f u r may be regulated by govern- ment bodies, a p r a c t i c a l recovery L i m i t w i l l vary with every mine and from day to day at any mine.

Table 3 gives the percentages of total sulfur, pyritic s u l f u r , and ash i n the o r i g i n a l c o a l samples a t both 40 and 80 percent recover ies . The d a t a a r e based on analyses obtained from the 1% in. x 0 c o a l samples. The samples a r e arranged i n ascending orde r of total s u l f u r percentages. The data were ca lcu la t ed by an IBN 360 computer, which was programmed t o cons t ruc t "bes t f i t t i n g " curves and t o i n t e r p o l a t e t o o b t a i n the s u l f u r and ash percentages a t any desired recovery percentage.

Table 3 shows t h a t f ive of t h e 40 coals t e s t e d could be f l o a t e d wi th an 80 percent recovery and a maximum of 1-50 percent s u l f u r (dry basis) . These f ive coals were n a t u r a l l y occurr ing low-sulfur coa l s t h a t ranged from 1.18 t o 1 . 7 1 percent s u l f u r , as sampled. Three a d d i t i o n a l coals could be reduced t o a s u l f u r content of 1.5 percent or less with 40 percent recovery. O f a l l t h e coals tested, only 10 samples at 80 percent recovery and 19 samples at 40 per- cent recovery had s u l f u r percentages of 2.5 o r less.

Central Illinois Southwestern l l linois Western I l linois

0 0 0

8 Percent recovery of f loat coal

Fig. 1 - Sulfur. distribution calculated for b~nqmsite samples from three geological areas.

Frankl in -Jef ferson Counties No. 6 Coal - Low. Sul fur Area lV2 inch X 0 size

Pig. 2 - Sulfur df tribntion chcu la ted for composite samples.

Sul fur and recovery for

5 s u l f u r ranges based on 40 I l l i n o i s c o a l s ~ m p l e s

u s u o / r e c o v e r y range

6 . 5 Sulfur and recovery

for 2 samples with

6.0 d i f f e r ent woshobil i ty chorocter ist ics

5 . 5

5 .O

0 0

5' 4.0 0 Y

L 3 - - 3.5 Q)

- 0 -, 3.0 C

I .O

0.5

0 10 20 3 0 40 50 60 70 80 90 I00

P e r c e n t r e c o v e r y of f l o o t c o o l

Fig. 4 - Relationship of sulfur and recovery for 2 samples.

These data should n o t be extended from number of samples t o r e l a t i v e quan t i ty of c o a l being mined o r coa l r e se rves a v a i l a b l e , Some of the samples are E r o m areas with very l o w coal r e se rves , while the reverse is t r u e of o the r s . The annual product ion from the mines sampled a l s o v a r i e d g r e a t l y . It u l t f - mately may be practical t o make q u a n t i t a t i v e e s t ima tes for t o t a l coa l r e se rves by sulfur ca t egor i e s , but a t present this c a p a b i l i t y i s limited by l a c k of available sampf..es from a reas wi th no ope ra t ing mines, Available information leads t o the conclusfon, however, t h a t less than 3 percent of the t o t a l Illi- nois coal r e se rves can be cleaned t o less than 1.5 percent s u l f u r wi th a normal recovery.

The upper p a r t of f i g u r e 1 shows t h e average r e l a t i on between the t o t a l sulfur and the float coal recovery for t h e coa l s sampled i n c e n t r a l I l l i n o i s , southwestern I l l i n o i s , and western Illinois. The average sulfur content i n the c o a l , as mined (100 percent recovery) , was s l i g h t l y less than 5 percent f o r a l l t h r e e areas. The sulfur i n the coa l s sampled from south- western I l l i n o i s and western I l l i n o i s was reduced t o about 3 percent with a 70 percent recovery. The average s u l f u r i n the c e n t r a l Illinois coals sampled was reduced t o about 3.5 percent a t 70 percent recovery.

The lower p a r t of f i g u r e 1 shows the r e l a t i o n between t h e p y r l t i c sulfur and recovery for the same coa l s . A remarkable s i m i l a r i t y is shown among t h e coals from the t h ree a r e a s , w i th a reduct ion from about 2 .5 percent p y r i t i c s u l f u r , as mined, t o about 1 percent p y r i t i c s u l f u r w i t h 70 percent recovery.

The average s u l f u r content f o r the c o a l s sampled i n t h e low-sulfur coa l area of F rank l in and J e f f e r s o n Counties is shown i n f i g u r e 2, The coa l s , as sampled, had an average of l e s s than 1.5 percent t o t a l s u l f u r . This was read i ly reduced t o 1.25 percent with a 90 percent recovery. The p y r i t i c s u l f u r va r i ed from about 40 t o 50 percent of the t o t a l s u l f u r .

Figure 3 summarizes the r e l a t i o n between the percentages of t o t a l s u l f u r and f l o a t c o a l r ecove r i e s i n five sulfur ranges f o r t h e 40 I l l i n o i s coals sampled f o r t h i s s tudy . All the coa l s tested t h a t contained between 1 and 2 percent s u l f u r , as sampled, were considered as a group, and t h e average values were p l o t t e d . The same was done with t h e 2 t o 3, 3 t o 4 , 4 t o 5 , and p lus 5 ranges. The p a t t e r n of reduct ion of s u l f u r is q u i t e similar i n each range.

It i s important t o no te that f i g u r e s 1, 2, and 3 represent average d a t a from s e v e r a l mines. The d a t a from i n d i v i d u a l mines sometimes v a r i e d considerably E r o m the average. T e s t results from s e v e r a l coa l samples obtained from a s i n g l e mine might a l s o show some v a r i a b i l i t y ,

F igure 4 illustrates t h e extreme variability o f r e s u l t s between mines. The mine represented by sample 37 had more than 6 percent sulfur i n the r a w coa l sample, y e t the 80 percent float f r a c t i o n had about 3 percent s u l f u r . The mine represented by sample 29 had less s u l f u r (about 5 pe rcen t ) i n the raw coal than sample 37, but t h e f l o a t coal had more than 4 percen t s u l f u r a t 80 percent recovery. The l i g h t e s t 10 percent f r a c t i o n of sample 29 s t i l l contained more than 3 percent s u l f u r .

Sulfur i n the Sink Fraction

The r e j e c t m a t e r i a l from some I l l i n o i s c o a l preparation plants i s a poss ib l e source of recoverable sulfur. For example, t h e 1.60 s p e c i f i c g rav i ty sink material (refuse) from one of the 40 samples t e s t e d dur ing the present i n v e s t i g a t i o n contained about 26 percent s u l f u r . Four other coals sampled had more than 20 percent sulfur in t h e 1.60 sink f r a c t i o n .

The Illinois coals sampled from ac t ive mines and tested f o r t h i s study indicated t h a t only a few could be prepared t o a s u l f u r content of 1 .5 percent o r less. These samples were r e l a t i v e l y low i n sulfur when mined.

Most Illinois raw coals appear t o con ta in t o t a l s u l f u r ranging from 3 t o 5 percent . Our s t u d i e s i n d i c a t e most of these coals w i l l r e t a i n from 2.5 to 4 percent s u l f u r w i t h 80 percent recovery.

T h e f l o a t coal fractions (c lean coa l ) usually had l e s s sulfur when t h e coal was crushed t o finer sizes. However, the d i f f e rences were not g r e a t enough t o make f i n e gr inding a p r a c t i c a l means of s u l f u r reduction f o r most of the c o a l s t e s t e d .

The sulfur in the 1.60 specific gravity s i n k f r a c t i o n s ( r e fuse ) f o r the 40 samples included i n this study indicated t h a t f i ve samples had a sulfur content of 20 t a 26 percent and mlght be suitable f o r processing as a source of s u l f u r .

EWVIROMENTAL GEOLOGY NOTES SERIES

Controlled Dr i l l ing Program i n Northeastern I l l i n o i s . 1965. aata from Controlled Dr i l l ing Program i n Du Page County, I l l i n o i s . 1965. Act iv i t ies i n Environmental Geology i n Northeastern I l l i n o i s . 1965. Geologica3. and Geophysical Znves t i ga t ions f o r a Ground-Water Supply a t Macomb, I l l i n o i s . 1965, Problems i n Providing Minerals for an Expanding Population. 1965. Data from Controlled Dr i l l i ng Program i n Kane, Kendall, and De Kalb Counties, I l l i n o i s , J-965. Data from Controlled Dr i l l ing Program i n McHenry County, I l l i n o i s . 1965. An Application of Geologic Information to Land Use i n the Chicago Metropolitan Region. 1966. Data from Controlled Drilling Program i n Lake County and the Northern Part of Cook County, I l l i n o i s . 1966. Data from Controlled Dr i l l ing Program i n W i l l and Southern Cook Counties, I l l i n o i s . 1966. Ground-Water Supplies Along the I n t e r s t a t e Highway System i n I l l i n o i s . 1966. Effects of a Soap, a De&?rgent, and a Water Softener on the P l a s t i c i t y of Earth Materials, 1966. Geologic Factors i n Dam and Reservoir Planning. 1966. Geologic Studies as an Aid t o Ground-Water Management, 1967. Hydrogeology a t Shelbyville , Illinois-A Basis fo r Water Resources Planning. 1967. Urban Expansion-An Opportunity and a Challenge t o Indus t r i a l Mineral Producers. 1967. Select ion of Refuse Disposal S i t e s i n Northeastern I l l i n o i s . 1967. Geological Information f o r Managing the Environment. 1967. Geology and Engineering Charac ter i s t ics of Some Surface Materials i n McHenry County, I l l i n o i s . 1968. Disposal of Wastes: Sc ient i f ic and Administrative Considerations. 1968. Mineralogy and Petrog~aphy of Carbonate Rocks Related to Control of Sulfur Dioxide i n Flue Gases-A Preliminary Report. 1968. Geologic Factors i n Community Development a t Naperville, I l l i n o i s . 1968. Effects of Waste Effluents on the P l a s t i c i t y of Earth Materials. 1968. Notes on the Earthquake of November 9 , 2968, i n Southern I l l i n o i s . 1968. Preliminary Geological kraluat ion of Dam and Reservoir S i t e s i n McHenry County, I l l i n o i s . 1969. Rydrogeologic Data from FQUP Landf i l l s i n Northeastern I l l i n o i s . 1969. Evaluating Sanitary Landf i l l Sites i n I l l i n o i s . 1969. Radiocarbon Dating a t the I l l i n o i s State Geological Survey. 1969. Coordinated Mapping of Geology and Soi l s f o r Land-Use Planning. 1969. Preliminary Stratigraphy of Unconsolidated Sediments f rom the Southwestern Part of Lake Michigan. 1970. Geologic I n v e s t i g a t i ~ n of the S i t e fo r an Environmental Pollut ion Study. 1970. Distr ibutf on of Major , Minor, and Trace Constituents i n Unconsolidated Sediments from Southern Lake Michigan . 1970. Geology f o r Planning i n De Kalb County, I l l i n o i s . 1970.

* Out of print