chemical removal of pyritic sulfur from coal

7/29/2019 Chemical Removal of Pyritic Sulfur From Coal

1/14

1

Chemical Removal of Pyritic Sulfur from CoalJ . W. Hamersma, M . L. & r a f t , E . P . Koutsoukos, and R. A. Meyers

TRW Systems Group, One Space ParkRedondo Beach, California 90278INTRODUCTION

The Meyers Process for the chemical removal of p y r i t i c su lf u r from coali s a TRW propr ie tary process (1 ) which i s cur re n t ly in a bench s ca le develop-ment phase under th e spon sors hip of t h e Demonstration P ro je ct s Branch of theEnvironmental P ro te ct io n Agency. Labo ratory results , which preceded thec u r r e n t b e n c h s c a l e a c t i v i t i e s , are presented here .t h a t 40-75% o f the t o t a l s u l f u r con ten t , co rr es pond ing t o nea r 100% of thep y r i t i c s u l f u r c a n be removed f rom al l coals tes ted u t i l iz ing a mi ld aqueousex tr ac tio n. The background f o r th e process concept and a summary of t h ere su l t s of over one h u n d r e d coal ex t rac t ion s a re presented below.

These resu l ts show

BACKGROUNDThe concept of chemical ly removing p y ri te s from coal has no t h er eto fo re

For example,been advanced as a solution to the s u l f u r o x i d e air po l lu t i on problem as i ti s known t h a t iron p y r i t e s a r e i n s o l u b l e i n any known liquids.the ac id s hyd roch lo r i c , hy d ro f luo r i c , s u l f u r i c o r combinat ions o f thes e ,which di sso lv e many in org ani c s a l t s h a v e l i t t l e o r no e f f e c t on i ro np y r i t e s . On t h e o t h e r h a n d , i t i s wel l known th a t p yr i t es may be oxi dat ive lyconver ted to s u l f a t e s , s o lub le i n s t rong ac id , by s t rong ox id iz ing agen t ssuch as n i t r i c ac id o r hydrogen peroxide .used f o r t h e a n a l y s i s o f the p y r i t i c s u l f u r c o n t e n t o f coa l .reagents have never ser io u sl y been advanced as a method f o r lowering th es u l fu r con ten t of coa l , because even though the y a re str on g enough t od i s s o l v e p y r i t e , t he y a l s o o x i d i z e ( i n the c as e o f n i t r i c a c id , n i t r a t e )the coal matr ix . T h u s , i t was no t though t po s s ib le t o dev i s e a p roces sfo r chemical ly removing o r d iss o lv ing the py r i t i c sulfur con ten t o f coa l .

In fact, they have long beenHowever, these

In ord er to provide an economically vi ab le process f o r the chemicalremoval of pyrites from coal , i t would be necessary to ut i l i ze an oxid iz ingagent (most likely aqueous) which i s a ) s e l e c t i v e t o p y r i t e , b ) r eg e ne ra b le ,and c) h igh ly s o lub le i n both ox idiz ing and reduced form. I t was disco vered


2/14

I .

that e i the r fe r r i c sulfate or ferric chloride meets the above combinationo f requirements, and these reagents form the bas is of the process chemistrywhich i s described i n th i s paper. ;

CHEMISTRVI n the Meyers P rocess, aqueous f e r r i c s ul fa te o r chlori de (mil d but

ef f ec t ive oxid i z in g agents) se le ct ive ly oxidize the pyr i t i c s ul fur content( 2 ) (3) o f coal to form fre e s ul fu r and s ulf ate which dissolves i n t o theaqueous so lution. The free s ul fu r may then be removed from the coa l matr ixby steam o r vacuum vapo riza tion o r solvent e xtrac tion (4) and the oxidiz ingagent may be regenerated and recycled.below.

The chemistry i s o utl in ed i n eqs 1-4

2 Fe+3 + FeS2- Fe+2 + 2s14 Fe+3 + 8 H20 + FeS2,-15 Fe+2 + 2 S + 16H+

3 Fe+2 + 3/2 [Ol-3 Fe+3 + 3/2 IO=]

(1)(2)

S - Coal- + Coal ( 3 )(4)

The aqueous ex tra ct s o lu tio n which co ntains i r o n i n both the ferrousand f e r r i c s tate , may be regenerated, i n any number o f ways, inc luding a i roxidation o f the fe rrous ion to fe rr i c (eq 4) ( 5 ) .aspect o f th i s process l i e s i n the fac t tha t " i ron i s used t o remove iron",s o that o n regeneration it s n ot necessary t o s eparate the ir o n which i sextracted from the coal f r o m a metal oxidizing agent.

Another fortunate

The experimental method i s qu ite s imple, in vo lv in g treatment o f coalwi th aqueous f e r r i c ch lo rid e o r s ul fa te s ol utio n a t approximately 100C t oconvert the p yr i t i c s ul fu r content to elemental s ul fu r and s ulfa te. Theaqueous s olution i s s eparated f r o m the coal and the coal i s washed toremove res idua l fe rr ic s a l t. The elemental s ul f ur which i s d ispersed i nthe coal matrix i s then removed by vacuum d i s ti l l a ti o n o r extrac tion witha so lvent such as toluene o r kerosene. The re s ul ting coal i s ba s ica llyp y r i te fre e and may be used as low s ul fu r f ue l.


3/14

3

RESULTSFour coals were selected fdr process evalu ation whose s u l f u r form

dis t r ibut ion i s typ ica l o f coa ls eas t o f the Miss i ss ipp i R ive r and whichrepresent major U nited S tates coal beds: P ittsburgh, Lower K ittanni ng,I l l i n o i s #5 and H err in 86. The P ittsburgh bed has been described as themost valuable i ndi vid ua l minera l de pos it i n the U nited S tates and perhapsi n the world. ' I ts production accounts f o r approximately 35% o f the to ta lcumulative production o f the A ppalachian bituminous coal bas in t o J anuary 1,1965, and 21% o f the to ta l cumulative production o f the U nited S tates t othat date (6).contains even 1arger.reserves than the. P ittsburgh seam.the most widespread and commercially valuable coal bed i n the Easternin te ri o r coal basin. The He rrin No. 6 bed i s second i n commercial importanceonly t o the No. 5 bed.

The L w e r K i ttanning bed together wi th i t s corre la t ive bedsThe No. 5 bed i s

Analysis f o the fo ur coal samples tha t were used f o r th i s study areshown i n Table 1. The ind ic ate d tolerances a re the standard deviations.F ive o r more coal samples were used f o r s ul fu r, ash and hea t contentanalyses w hi le thre e o r more samples were used f o r s u l fu r forms ana lysis (7).

PyritiSu l fu rSu l fateSu l fu rOrganicSu l fu rTotalSu l fu rAshBtuRank-

LowerKi ttanning3.58 2 .080.04 2 .010.67 2 .104.29 2 .06

20.77 2 .5912,140 5 55

Medium V o l a ti l kBituminous

Table 1Dry Analyses o f Coals

I l l i n o i s #51.57 2 .030.05 f .011.86 .043.48 2 .03

10.96 2 .2612,801 5 58

High Volat i leBituminous

P i ttsburgh~

1.20 2 .070.01 k .010.68 2 .161.88 f .07

22.73 f .4811,493 5 60

i i ah Vo la t i l e IBituminous

H er rin #61.65 f .040.05 2 .012.10 & .063.80 2 .04

10.31 2 .2812,684 5 55

i i g h V o l a ti l e BB i uminous


4/14

I4

Minera l Pyri teLower KittanningI l l i n o i s #5Pi t t sb u rghHerrin #6

Both f e r r i c ch lo r ide and f e r r i c su l f a t e have been used in t h i s s tudywith good results. However, from a pr oc es s st a nd p o in t , f e r r i c s u l f a t e hasthe fol lowing advantages: a ) i t i s l e s s c o rr os iv e , b ) r e g en e rat io n i s l e s scomplicated and expensive in t h a t the i ron su l fa te formed (equat ion 2 ) doesnot have t o be separated from i r o n ch lor id e, and c ) the removal of res idu alle ac h s o lu t i o n i s e a s i e r and therefore more economical.

1

I

I!4

2.4 2 .2a1 .4 5 . 31 . 6 ' 2 . 41 .3 2 . 31 .4 2 . 3

I t has been f o u n d t h a t the e x t e n t of the react ion indica ted by equat ion 2r e l a t i v e t o t h a t of equat ion 1 or t h e s u l f a t e t o s u l f u r r a t i o t o b e 2 .4 2 . 2when rock p y ri te i s used and 1 .4 5 .4 for sedementary pyri te found in thecoals used in th is work .s ta l s t r uc tu re , d i f fer en ces in re a ct iv i t y have been documented which havepossible modes of fo rmat ion (3 a ) . In the case of coa l , no s i gn i f i c an t va r i -a t i o n i n t h i s r a t i o was found with fe r r i c i on concen t ra t ion , ac id concen tra -t i o n , c o a l or reac t ion t ime .

Although both m ate ria ls a r e FeS2 of th e same cry - i

been a t t r i bu ted t p imp ur i t i e s and c rys t a l de fe c t s pecu l i a r t o t he va r ious I

The re su l t s fo r each coa l a r e f o u n d in Table 2.Table 2

Su lf a t e t o Su l fur Ratio fo r Ext rac t ion of Coaland Mineral Py r i t e wi th Fe r r i c Ch lo ride So lu t ionS u b s t r a t e S u l f a t e t o Sul fu r Ra t io(Ave rage All Runs)I

aStandard devia t ionA systemat ic parametr ic s tudy was made i n orde r t o det ermine the e f fe c t

o f ac id concen t ra t ion , coa l p a r t i c l e s i ze , fe r rous and su l f a t e i on concen-t r a t i o n , and rea ct io n t im e, on p y ri te removal. These parameters were studie dus ing cond i tions ( s ee Exper imen tal ) t h a t g ive 40-70% p y r i t i c su l f u r removal


5/14

5

so th a t the e f f ec t s o f parame te r va r ia t ions a re c l ea r and n o t be s o smallas t o be masked by exp erim en tal e r r o r as when removal i s g r e a t e r than85-90%.su lf u r removal with both f e r r i c chlor ide and su l f a t e a s we ll as a se t ofexperiments t h a t were designed p o i n t u p d i f f e re n c e s b etw een f e r r i c s u l f a t eand fe r r ic ch lo r ide .

In addition, s tudies were performed t o demonstrate 90-100% p y r it ic

The effect of added hydrochloric acid concentration was studied inorde r t o determin e w hether or not th e acid had any ef fe c t on p y r i t e andash remova l, s u l fa te / s u l fu r r a t i o , f ina l hea t con ten t and whethe r h i g h HC1concen t ra t ions ch lo r ina ted the coa l .tuents, increased ash removal was expected as well as some suppress ion oft h e s u l f a t e t o s u l f u r r a t i o s i n c e t h e r e a c t i o n t h a t r e s u l t s i n s u l f a t eformat ion a lso yi e l ds e i gh t moles of hydrogen ion per mole of sulfate(common ion e f f e c t ) . Added acid was stu di ed i n th e range of 0.0 t o 1.2Eusing concentra t ions of 0.0, 0.1, 0.3 an d, 1 . 2 l hydrochlor ic ac id i n 0.9if e r r i c ch lor ide . Dup licate runs were made a t each concentration w i t h a l lfour coa l s fo r a t o t a l o f 32 run s. The re s u lt s showed n o c l e a r c u t trendseven ( exc ept one-vide i n f r a ) when the d at a was smoothed v ia computerregre s s ion ana lys i s .enough t o have any subs tant ia l e f fec t on the production o f s u l f a t e o r t ocause the removal of additional ash over t h a t which i s removed by th e pHo f 1M f e r r i c c h l o r id e (pH 2 ) .

Si nc e coal has many b as ic ash con st i-

Apparently, the concentration range was n o t broad

I An impor tan t cons ide ra t ion in any ch em ica l p r o ce ss i s t h e s e l e c t i v i t yf o r t h e d e s i re d r e a c t i o n .f e r r i c i o n , t h e e x t e n t o f the r eac t ion o f the r eagen t w i t h the coal matrixhas a major effect on the process economics.of th i s reac t io n va r ies from small t o subs tan t ia l depending on the ac idconcen t ra t ion , coa l , and fe r r ic an io n . I n o r d e r t o d e f i n e t h i s e f f e c tq ua n t i ta t i v e l y , th e ra t i o of ac tu a l mmoles of fe r rou s ion produced t o themmoles of f err ou s ion necessary t o produce th e su lf a te and elemental s u lf u rt h a t was recovered was c al cu la te d f o r each run (see equa t ions 1 and 2 ) .This r a t io , Fe ( II)[Experimental]/Fe(II)[Calculated], has a value of onefo r 100%s e l e c t i v i t y and a h ig he r v alu e f o r l e s s th an 100% s e l e c t i v i t y .

In the case of oxida t ive leaching o f p y r i t e byW have found t h a t t h e e x t e n t

1

I

t The d a t a , f o r f e r r i c c h lo r i d e , in T ab le 3 were smoothed by linear regressionI


6/14

6

0.9N FeC13O.OM HG1 1.2M HC1

1 .2 1.43.8 6.62.2 3 .43.7 6 .4

ana lys is us ing the va lues genera ted i n t h e a c id matrix w h i l e t h e f e r r i csu l f a t e va lues a re the average of t r i p l i c a te runs .

0 . 4 l Fe2(SO4)O.OM H2 SO4

1 .21 .61 .52 .4

Table 3Varia t ion of Ferr ic Ion Consumption w i t h AcidConcentration and Ferric Anion

Coal~~ ~_ _

Lower K i t t ann ingI l l i n o i s No. 5P i t t s b u r g hHerrin No. 6

I t i s r ea d il y a pp ar en t t h a t the higher ranked Appalachian (LowerKittanning and P i t t s b u r g h ) coa ls r eac t to a l e s s e r e x t e n t w i t h f e r r i c i o nunder a l l exper imenta l cond i t ions t h a n the lower ranked Eas te rn in te r ior( I l l i n o i s #5 and Herrin #6) coals. I n a d d i t i o n , t h e f e r r i c c h lo r id e r un sshow t h a t a very subs tant ia l ac id ca ta lyzed reac t ion occurs i n th i s sys temwhich i s most evident f o r the I l l i n o i s #5 and Herrin #6 coa ls . In th esec o a l s , a reduction of about 42% i n ferric ion consumption is observedwhen the s t a r t in g HC1 co nc en tra tio n i s reduced from 1.2M t o 0.01.correspondin g reduction s f o r Pit tsb urg h and Lower Kittanning coa ls a re 35%and 14% resp ec t iv e ly ,f e r r i c ion consumption ranging from 3% f o r Lower K ittanning coal t o 63% f o rI l l i n o i s #5 coal are observed.f e r r i c s u l f a t e i s t h e p r e fe r re d form o f f e r r i c ion in o rde r t o inc rea ses e l e c t i v i t y .

TheWhen fe r r i c s u lf a t e i s used, fu r th e r r educt ions i n

From t h e s e e a r l y d a t a , i t a pp ears t h a t

The da ta l i s ted i n Table 4 i l l u s t r a t e t he e f f e c t of t o p mesh s i z e onp y r i t i c s u l f u r removal. The coal samples were prepared by th e same comninutiontechniques and ccnsequen tly , t he s iz e d i s t r ib u t io n o f the sample s shou ld be


7/14

7

Table 4Effec t of TO D Mesh Size on Pvrit ic Sulfur Removal

Sulfur Removeda-1 /4 -1 4 -100oa 1I

Lower K itt an ni ng 35 60 65I l l i n o i s No. 5 45 35 50Pi t t sburgh -- 45 60Herrin No . 6 -- 70 50

I aValues rounded t o neares t 5%

s im i l a r f o r each coal (8) . In genera l , a , increase of pyrite removal isobserved f o r sm alle r top s iz es as expected due t o exposure of p y ri te encap-su la ted wi th in th e coa l ma t r ix . The I l l i no i s #5 an d Herrin #6 coa ls deservespecial comment because reaction of the ferric ion w i t h the coal matrixresul ted in gr ea te r than 75% deple t ion of th e reagent .e f fe c t was approximate ly the same fo r a l l th re e s i ze s a n d t h e r e s u l t i n gdepletion of the reagent may have had a l e v e l i n g e f f e c t on t h e r e s u l t s .the case of the #6 coa l , su bs ta nt ia l ly l es s f e r r i c ion was consumed by the-14 mesh coal (68 vs . >95%)which i s probably the reason f o r th e increasedremoval. Thus, wh ile th e use of a l a r g e r c o al t o p s i ze reduces py r i t erem ov al, i t i s n o t a stro ng fun ctio n of mesh s iz e .in te rna l su r face and permeabi l i ty o f the coa l t o aqueous media are importantfac tors a long with the surface exposure o f pyrite caused by grinding.ad di tio n, th e top mesh s i z e may have an ef f e c t on the ultimate amount o fpyr i te removal , and f u r t h e r r e s ea r ch i s n e ce ss ar y t o c l a r i f y t h e e x ac tna tu re o f the se e f fec t s .

For the #5 c o a l , t h i sI n

I t i s e xp ec te d t h a t t h eIn

An examination of equations 1 and 2 shows that b o t h ferrous ion andsu l f a t e ion could have a r e ta rd ing e f f ec t on py r i t e ex t ra c t i on .a l so be expec ted th a t the r a te i s dependen t on t h e f e r r i c io n c o n c e n tr a ti o n .

I t could


8/14

8

Fer r ic Sul f a t eTreated Cqq.1(0.4N Fe )% w / w S u l f a t e

I n i t i a l F i n a l

Because a commercial process may requ i re the use o f va r ious fe r r i c - fe r rous ionconcent ra t ion mixtures , these are important parameters . Work w i t h mineralpy r i t e has ind ica ted t h a t t h e r e i s no s i g n i f i c a n t r a t e d i f f e r e n c e w i t hferr ic ion concent ra t ion between 0 .5 a n d 3.01 as long a s enough f e r r i cion i s p resen t t o d i s s o lv e a l l t h e m a t e r i a l . R e s ul ts w i t h -100 and -14mesh Lower Kittanning coal using b o t h f e r r i c s u l f a t e and f e r r i c c h l or id ei n d i c a t e v i r t u a l l y (22%)he same removal when th e le ach i s 1 .0 , 2.0 o r2 .5 1 i n f e r r i c i o n . The use of 0.5M ferric chloride seems t o i nc reasep y r i te remova'l by more than 10% . In ad di ti o n , a ser ies of experimentswere pe r f on ed with a s t a r t i n g fe r rous ion concen t ra t ion o f 0 .51 and af e r r i c ion concent ra t ion of 1 .01 . Under th e condi t ions used , a reduct ionof p y r it e removal of 7-8% from a base l ine o f 62% was obs erve d. Thus , thee f fe c t o f fe r rous ion , when p resen t , i s sma l l .

Remov a1Correc t i onbab s %

Since the u se o f f e r r i c s u l f a t e in a p r oc es s has several advantagesover f e r r i c c h lo r id e , a t e s t m a t r i x was' performed, summarized i n Table 5 ,

Table 5Comparison of Ferric Sulfate and Chloride for Pyri te Removala

Coal

ower Kittanningl l i n o i s # 5i t t sbu rghe r r i n #6

P y r i t i c S u lf u rRe4

0.4i Fe++'c1 s0443 38.48 4350 3335 33

lvedI/W

0.91 Fe+++c1 s0443 5450 505 8 --52 64

0.07 0.170.05 0.17 .0.01 0.080.05 0.20

+3+8+7+9

aConditions': 600 ml 0 .4 and 0.91 Fe*3 solut ion, 100 g -100 mesh topb I n cr e a se f e r r i c s u l f a t e e x t r a c t i o n v al ue s by this % t o c o r r e ct f o r

s i z e c o a l , r e f l u x e d a t . 3 0 0 " C fo r 2 hrs .r e t a i n e d s u l f a t e .


9/14

9

I

t o com pare t h e a D i l i t y o f f e r r i c s u l f a t e t o rem ove p y r i t i c s u l f u r from a l lf o u r c o a ls .s l i g h t l y l e s s sulfur was removed by f e r r i c s u l f a t e than was ind icat ed w i t hf e r r i c ch lor ide . However, when a so lu tio n of 0.9E i n f e r r i c ion was used,i t was found th a t f e r r i c s u lf a t e removed an equa l o r gr ea te r amount ofs u l f u r t ha n f e r r i c c h lo r i d e. A n alys is o f t h e c o a l s a l s o showed t h a t asmall amount of sulfate remains w i t h the coal a f t e r a s imple washingprocedure . Pre liminary res u l t s show th a t this can be reduced t o s t a r t i n gvalu es using more r ig oro us washing procedures. If we a s s u r e t h a t a l l t h esulfate can be removed, t h e n th e v alue s f o r s u l f u r rem oval by f e r r i c s u l -f a t e ex t rac t ion can be ra i sed 3 t o 9% depending on the c o a l .

U t i l i z i n g s o l u t i o n s 0 . 4 8 i n f e r r i c io n, i t was found t h a t

Attempts t o inc reas e py r i te removal by incre as ing the rea c t io n t imem e t w i t h l imi ted success u n d e r o u r s t a n d a r d c o n d i ti o n s du e t o t h e f a c tt h a t r e a c t i o n o f the f e r r i c i on w i t h the coa l matr ix deple ted the f e r r i cion needed fo r ex t ra c t i on of the py r i t e . . T h u s , f o r example , inc rea s ingthe coal reaction t ime from 2 t o 12 hours on ly inc reased p y r i t i c sulfurremoval from 60 t o 80 p e r c e n t f o r P i t t s b u r g h c o a l .o b t a in e d f o r t h e o th e r t h r e e c o a l s .c re ase the amount of leach s olu t io n o r use a cont inuous o r semi-cont inuous( m u l t i p l e b a t c h ) r e a c to r . A multiple batch mode was chosen because i t wasa simple lab ora tor y procedure and a t the same time could approximate con-d it io n s encountered in a commercial p la n t. A 1 hr per batch leach timewas used because our 2 hr results i n d i c a t e d t h a t i n t h e e a r l y s t a g e s o frem oval t h e r a t e b eg in s t o t a i l o f f a f t e r 1 hr and s i x l e aches (o r ba tches )per r u n were used i n o r d e r t o a s su r e t h a t a ny p y r i t e t h a t c ou ld be removedin a rea so na bl e amount of tim e was removed. The pr og re ss of removal wasmonitored by ana lyz ing t he s u lf a te conte nt i n e a c h s p e n t l e a c h s o lu t i o n ,wh ile elemen tal s u l f u r was no t removed u n t i l a l l t h e l e a c h e s were completed.Table 6 shows py r i te ex t ra c t i on a s a func t ion o f success ive le aches a sfol lowed by su l f a t e ana lys i s o f th e l e ach so lu t io n .m ajo r p o rt i on o f p y r i t i c s u l f u r i s removed i n t h e f i r s t two l e ac h eso r two hou rs, followed by l e s s e r amounts i n t h e t h i r d and fourthleaches and only small amounts i n the f ina l two leaches .

S im i l a r r e s u l t s w e r eT h e only a l t e rn a t i ve s were to i n -

N o te t h a t t h e


10/14

10

Table 6Pyr i te Extrac t ion as a Func t ion o f Successive Leaches

[ n i t i a l P y r i t ici u l f u r , m o l[ x t r ac t e d P y r i t i cj u l f u r a s S u l f a t emmol 1

23456

Lower Ki tt an n in q102

31.212.49.2

4 .80 .40 .3

P i t t s b u r g h37.5

13 .56.04 .62.10.60 . 3

I l l i n o i s # 543.4

11.45.53.61.80.70.5

-Herrin #649.7

12.56 . 35.02.11 .o0.6-nominal 40% of th e p y r i t i c su l f u r remains w i t h the coal as e lementals u l f u r . A ll i n d ic a t io n s a r e t h a t t h e s u l f u r t o s u l f a t e r a t i o i s c o n st an t.The results i n terms of f i n a l s u lf u r va lues and py r i te removal a regiven i n Table 7.

forms an alyse s o r the d i f f e r e n c e i n t o t a l s u l f u r between processed andunt re a ted coal (Eschka ana ly s i s ) r e su l ted i n e s s e n t i a l l y i d e n t i c a l va luesof 93 - 100%. This corresponds to t o ta l su lf u r removal of 40-70%depending on the o r g a n i c s u l f u r c o nt en t of the coa l .g rea te r than 100%removal i s due cumula t ive e r ro r in ana lys i s and theremoval of smal 1 amounts of s u lf a te (0.02-0.04 %). P re se nt ly , the seexpe riments a re being dup l ica ted us ing f e r r i c su l f a t e , and p re l imina rya n a ly s i s i n d i c a t e s t h e s a m e r e s u l t s .

Note t h a t p y r i t i c removal computed from e i th e r su l f u r

The observation of


11/14

11

I

I

w m b hm m m m

w m

0 0 0 0O O Z " 0. . . .

C O O I D I Dh W d *

m U I c O *

0 0 - c u? " ? ?

S0c,v us mm L+c , x

L a )c , Lm a )c,+%m m

.r

L L3 3%I J I Jm m*c,s sa J a ,uL La)a)n nI I I1

mv,

7 -

0%

- 0- 0v -I

VIVIh03Src)VI

0rcL3rc3VIE0-0aJVIm

.r

7

E7

mV


12/14

12

CONCLUSIONThe use of f e r r i c c h l or i d e o r s u l f a t e t o remove pyr i t ic su l fur f rom

coal has been demonstrated t o be a f e a s i b l e p ro c es s t o remove pyritics u l f u r f rom coa l w i t h h i g h s e l e c t i v i t y .th a t th i s removal i s no t af fec t ed t o any gre a t ex te n t by the presence off e r r o u s , s u l f a t e , or hydrogen ions, or coal mesh size. The use o f s i x1 hr leac hes g ives 93-100% p y r i t i c su l f u r removal.

In add it io n, i t has been shown

EXPERIMENTALSampling.

uniform composition.Bureau of Mines (Lower Kittanning and P i t t s b u r g h ) a n d t h e I l l i n o i sGeologica l Survey ( I l l ino is #5 and Herrin #6).( -1 /4 x 0) was coned an d q u ar te re d o r r i f f l e d t o smaller samples andground t o t h e de sir ed mesh s i z e s by the app rop riate ASTM method.analys is in Table 1 are an average of determinations on f i v e or moresamples representing b o t h -14 and -100 mesh samp les taken o r ground ons e v e r al d i f f e r e n t oc c a si o n s.

A de te rmined e f fo r t was made to obtain samples withThe cleaned coal samples were taken by the U . S .

Each gross sampleThe

Standard Runs.was added t o a 1-1. re s i n k e tt le equipped w i t h a s t i r r e r and ref lux con-denser together w i t h 60 0 ml f e r r i c c h lo ri de o r f e r r i c s u l f a t e 1M i n f e r r i cion. The so lu ti on was brou ght t o ref lux (102C) for the des i red t ime( u s u a l l y 2 h r s ) , f i l t e r e d an d washed thoroughly on the f i l t e r funnel . Thiswash ing p rocedure was s u f f i c i e n t fo r runs u sing f e r r i c s u l f a t e , b u t a muchmore thorough washing proced ure i s nece ssary in the f e r r i c c h l o r i d e r u n sto r educe t h e ch lo r ide con ten t to u s ab le l eve l s . Af te r removal of thei r on s a l t s , the coal was r e f luxed w i t h 400 m l t o l u e n e f o r 1 h o u r t o removethe s u l fu r from t h e c o a l, then t he coal was d rie d a t 15OOC under vacuum.All calculat ions are based upon the dry weight o f t he coa l .

Coal, 100 g , of the desired mesh ( -14 x 0 or - 00 x 0)


13/14

13

Mult iple Pass R u n s were performed the same way except that thef e r r i c chlorid e was changed every hour f o r tot a l rea ct io n t ime of 6 hoursand the f e r r i c su l f a t e was changed a t 1 , 2.5 , 4 .5 hrs wi th a to ta l re act iontime of 8.5 hrs. A f t e r t h e f i n a l f i l t r a t i o n a nd wash, t h e s u l fu r wasremoved by toluene extraction and the coal d ri ed in th e normal manner.

Coal a nal yse s were performed by Commercial T est in g and EngineeringCo., Chicago, I l l inois .TRW Timeshare/CDC 6500 computer system.

Data handling and curve f i t t i n g were done on the

REFERENCES AND NOTES1. Pa ten t pending.2. Oxidation o f py r i t e and copper su l f id e o res by fe r r i c s a l t s is known (3 )b u t the scope and se le c t i v i t y of the re act io n have not been invest ig a ted .In Refe rence 3b ) , however, t he au tho rs s t a t e (w i thou t d i r e c t p roof ) t ha ti r o n p y r i t e i n copper ore concent ra tes is not a t tacked i n a period ofhours a t 100C.mesh top size iron pyr i t e minera l w i t h 15 aqueous fe r r i c ch lo r ides o l u t i o n a t 100C r e s u l t s i n 49% d i s s o l u t i o n a f t e r 2 hrs, 96% n 8 hr and99.5% i n 16 h r .

Cont ras t ing ly , we have found that t reatment of -200

3. a ) J . W. Mellors , "A Comprehensive Tr e a ti s e on In org ani c and T he or eti ca lChemistry", Vol. XIV, John Wiley and Sons, New York, 1961, p.221-232

b ) F. P . Haver and M . M. Wong, J . Met. , 5 February 1971.4 . I t was no t obvious a t t he s t a r t o f ou r work th a t e lemental su l f u r c ou ldbe removed from the coal matrix, as previous reports had indicated thatcoal heated w i t h e le m en ta l s u l f u r r e s u l t e d i n recombination and elimina-t ion of hydrogen su l f ide (e .g . , B . K. Mazumdor, Fuel, 41, 121 (1962).5 . E . J . Sercombe and J . K . Gary, Bri t . Pat . 1 ,143,139 (1969). V . V . Ernilov,

Y . P . Romanteev and Yu. A. Shchurouski i , Tr. I n s t . Met. Obogashch.,Akad. Nauk K9z, SSR, 30, 55-64 (1969); L . Liepna and B. Macejevskis,Dokl. Akad. Nauk SSR, 173 (61, 1336-8 (1967).6 . P . Averi t t , "Coal Resources of the U.S.", U. S. Geological Survey B u l l .1257, January 1 , 1967.

7 . All an al y si s and sampling were done acco rding t o ASTM pr oc ed ur es ; c f ."Annual Book of ASTM S ta nd ar ds ", P a rt 1 9, Gaseous Fu el s; Coal and Coke" ,American Soc iety fri r Te st in g and M ate ria ls, Ph ila de lph ia, 1971.8. P . Rosin, and E. Rammler, Jo ur . I n s t. Fu el. , vol 7 , October 1933, p 29-36; J . G . Ben nett , Jour. I n s t . Fu el , vol 10 , October 1936, pp 22-39;

M . R . geer and H . F . Yancy, Trans . A.I.M.E., vol 130, 1938, pp 250-269.A . S . Scott, Bureau of Mines Rept. of Investigations 3732, 1943, 9 pp;Bertrand A. Landry, Bureau of Mines B u l l . 454, 194 4, 127 pp.


14/14

14

ACKNOWLEDGEMENTThe authors wish t o acknowledge the support o f the Environmental

P rotection Agency (a fte r i n i t i a l f e a s ib i l i t y demonstration) under ContractEHSD 71-7, and the encouragement o f Messrs. T. K. J anes and L. Lorenzio f tha t agency and J . Blumenthal, E. R. Bol ler , E. A. Burns, B. Dubrow,W. Krawitz, A. A. Lee, C. A. Flegal, and L. J . Van Nice o f TRW Systems,and the technica l ass istance o f Messrs. J. M. Horn, D. R. Moore and0. B. Kilday.

chemical removal of pyritic sulfur from coal

Documents