,0:$3urfhhglqjv $%&' … · tungstic acid and viewed in hitachi electron microacop;:; at...

STUDY OF ACID MINE DRAINAGE IN NORTH EASTERN COAL MINES OF INDIA

Narendra s. Rawat & Gurdeep Singh

Chemical Laboratories Indian School of Mines

Dha.nbad-826004 India

ABSTRACT

The paper deals with the nature of il'line drainage in the North Eastern Coalfield, Assam /India~/. The drainages from these mines are found to be acidic with high sUphate ranging upto 1500 ppm and iron content rising upto 40 ppm. The total sulphur in coals is upto 7 % out of which 50-80 % is non reactive organically found sulphur. The acidity mainly arises from the oxidation of pyrites of coal. Microscopic studie2 reveal that both the reactive /size 0-5 micron/ as well as stable /50 micron/ pyrites are present in coal samples studied, Leaching studies indicate that oxidation of reactive FJrites followed by dissolution of sulphate sulphur is sufficient to produce the observed acidity and organic sulphur does not seem to play any significant role in acid production in mine drainages. The presence and chemical activity of iron oxidising; sulphur oxidising; w1d iron sulphur oxidising bacteria in minewaters was ascertained by the chemical oxidation of Ferrous iron to Ferric iron; decrease in PH and production of acid. Iron and sulphur axidising bacteria which are having maximum activity were examined under electronmicroscope for morphological study. The rod shaped bacteria with rounded ends, size varying from 1.20 - 3.20 micron in length and 0.51 - 1.25 micron in breadth are identified as Thiobacillus ferrooxidans. This bacteria is found to accelerate the sulphur leaching rate from coal and is indigenous to mine drainages.

INTRODUCTION

One of the major problems encountered by the coal mining industry is of removing the water that percolates into the mines, ~1e mine drainages in some coal mines of North Eastern Coalfield /NEC/, India, are found to be acidic and

~~ :.

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highly con·os1ve [1]. The prc·;:rlems arlS:Ulg out of these acidic drain!5l8es are extremely complex and variable in the region. The well known adveree effects due to ·these e.cirlic mine dr;•.inagefl are potable water supplies, loss of recreC{··· tional Yl:<lues, corcosion of the mining machinery and f:nvir<Jrunata} degradation.

A lot of re!l!larch has already O'·Hm done p~:rtaining to general aspect!!! of acid:!.c mine d:nd.nagea in other countries but no such work has so far been reported about NEG mines. However, etudics on the dietribution of different forms of sulphur in tho high orga."lic sulphur tertiary coals of NEC were report e.' :"ecently [ 2]. This study has been undertaken to un.c~rato.nd the meehar~ism ar1d to st~:dy the various factors reaponsibJ.e for 'ohe acid formation in l'l'"EC, Assam.

Collection and Analysis of Water and Coal S:;>.mp1es:

Original cos.l samples as well as fresh mi.ne water se1nples were obtained from Ledo and Baragoloi Collieries. Sta.TJ.da.c-d methods were employed for estime.tlona of v~~rioue constituents in water samples [3] • The ]if was measured with a Philipe ]if meter. Coal samples were analysed for total sulphur, cyri tic aulph1u· and aulrhate sulphur according to staudard procedures [ 41. The amount of organic sulphur was obtained by deducting the amount of pyri.tic and sulphate sulphur from toal sulphur. Iron was estimated spec-trophotometrically by using VSU2-P spectrophotometer.

Growth of Bacteria:

The culture growth preparation of iron-oxidising, sulphur oxidising, iron and sulphur oxidising bacteria2lere ~~ne as described ~5]. The media were analysed for Fe , Fe iron and development of acid measured by titrating 1 ml of the growing culture against N/100 NaOH solution.

Microscopic Study:

~1e bacteria were observed ~~der ordinary microscope at XlOOO. For electronmicroscopic study, cells of iron and sulpl1ur oxid:tsing bacteria were harvested by centrifuging in refrigeration at 15.000 rpm for half an hour. The her·~ vested cells were negatively s·te.inl!d with 1 '!>phosphotungstic acid and viewed in Hitachi Electron microacop;:; at X9600. Si'l;e of the bacter:i.a were roea-'!lured fr0!1! electronphotomicrographs.

l'yri tes of the co!U sl!llllplee; were mo1.mted on a poliaa€ild i'!ec-tion and viewed with reflected light throue;h an oil irJJ.m3rsion lens attached to micrsc:;p<" at X500. Size of the r\9-rticleie' were measured from the photomicrographs. 134



Leaching Studi.i!B:

Caal samples were crushed to pass a 4 mm sieve retained by a 2 mm sieve. 5 gm of powdered coal sample was taken in 1 litre Erlenmeyer flask and to th:l.s 500 ml of H SO acid leach solution was added. In the microbiological exp,ri~ents, in addition to the above 10 m1 of active culture of iron and sulphur oxidising bacteria containing 107 cell~/ml was added in each set of experiments,

RESULTS AND DISCUSSION

The che!ilical analysis of minewater samples /Table 1/ ahowe that they contain high sulphate, hardness and acidity con-~ tent, coupled with low Jii, This indicates that the wat!lr flowed through coal seams and strata which contain sufficient amount of sulphates and reactive pyrites [§1. The high hardness values coupled with high acidity and low pH infers that the primary cation contributing to it is soluble iron. 'rhe rH of the ground water when p<'l.ased over mine1 coal considerably decreP.aed from 6.9 to 2.7 and 4.1 indi~· eating the variation and difference of reactivity of pyrite~ in the two mines l6, 7].

The distribution of total sulphur and 1 t~ forma in two coal samples ie shown in Fig. l. In these coals, orga."lic Bulp."ttrr ia predominant md this organically bound compommt ia c'!:entlra.lly not chemicaPy reactive 8 , 'l'h.is :1.:! fu.rth<:Jr auppc;.~ted by th.., chemical &ne.l:raee of m].ne wate:re, The difference ~f acidity produc~d in two mines ie mainly because of the 8.Baociated pyr·itic auJpl"mr contl'mt and independ.~:~nt of the a>nourJt of to·tal sul!lfi'll~ prensent in coal.

M:i.C)roecopic ob!!!H''VIlt:ion of e;:oal samples reveale t;hat both ontain "<I'S.ricus types of pyr:!. he shoW!'! in '!ilotogr!i..f.hS 1.-4.

! n photograph 1. th<~~ pyr:l. tea OM\!I' aa s ph'!lroid!!l of t.ne cl·.J.eter!!! of the !iin of 0,5 um .a:1d i.:n ph.otcgr•:ap.I-J. 2, tlrHl®!! !l.f:tlin oceur lUI spheroids of d1f't~'\'en.t aius ioi!l, from 0~5 Util 1 5-50 wn and >50 ik"!l, Among thea® rnotiv~; pyrtl<ll!!i, the f:;:a.mboid!!i.l type /putich '$l.ill~ 0-5 um/ !.11 extremely renctiv® d<~Canpoees rapidly t.c;; produce I!IIV!!Ire e.c:ld m'.Y"'!

, 'l'he other pyrite~ !l.venging 50 urn /phot·oare !'0l<ttivelv st.<<'b1e, Th~~< acid~.ty t:ney ;:rro-~

car~ r.s11d:<.!y neut~·!!.lis"d by the dk!i.:Urd.·t~> ®.V!l.1l1i.ll1 ti :ln rock atTa.ta anCJ in ground. wr.:ter~. Th.s varif):~;i;:o\1 in ·'lhlmica:C charactilr:!.stics of wat~r i<' vs.ricr.J.Il! J.evelB 1ir,rir'J& .are expTained by nl~,fJV~ !act?;,

as oxi-=

115



dati.on of F'e 2 ; iron tP Pe 5 ~ :..ror: /comuJeted ;n 10 to 16 d~Jye/ decrefl.Be ir! Iii /frOtr• 3 .,5 ttJ 1 .. 4? And prodUCtiOn of acJ.d /4.2 to 7,5 ml of l'l/100 NaOH ccms•)JrtPd tJy l ;:,l (\f r;rowin.g culture in 25 days/, ).s more i.n th>l experiments with minewaters as ino2¥lae compared to the con~*ol. With r,·.inewaters ail the Pe iron is oxidieed to Fe- i.ron whereR.S in contr·ol only 25 ;t oxidati.cn took place during the IH'-"le P>·!riod /FJ.g. 1./. Thi.a confinne role of tne bacteria as biocatalyst in AMD pr0ducti.on. • The above reeul ts also ind.icate thtlt sulphur bacteria aJ one do not influene>e the acid formation rate but iron and Aulpl:w.>' ;)Xidising b~tcteri.a !'oxhi,))i t ~>. f~~ter effect in ac,::~~:.f!r2i'~~~-ne the oxidatior-! of Fe"->- tc t~~- · ar.~.d thua corltribut;e &.~~rg~_.f.a.rt cf ar;idity !l.!lc'<Ei.;n:cd ~ith add mir<e dl"ai·na.ges :,c v, Lll •

I:r·on .s,x;,J sulphur a~":ldislng ~oa.cteria used as inoe~4lr.~ in mic! obiclor;ical ;_eaching experimente .. as obse~ed cJ•:er microscope as rods. Fresh Gul ture when obsf!rved under rr,icroSGcp·t:: exhibits th.iJ.t the bat-eria are r1vtilz :.~ccurr-:r::g rnostly single. Electron.photomicrographs /:photogrct;,hB 5, S/ show the morphoJ. ogy of b.!l.ctn:'ia, 'The bacteria g,rc rod shaped with rou.nded ends and co:(rtain single polar .. 'I'iie size of br,,cteria ie 1. 28 - 3. 20 um by 0. whicl-J. is ic'ien·-t:;; fied as tt:i l.lua-ferrnxidaw:"l.£:! as by VP-.ricr,)S reports [9, This bacteria is ha,':tli1ees a.e ic,eiog gran; ~:egati ve ,~

IA~sching experim1mts /Ts.ble IJ:I &: shv•'' that in mi/:ro-t~i.oJ.ogical set•J the a.mow1t of B'l~~-l leached is greater as comparf:d to in absence ba~;t~r:i.,a., Sn.lphu.r le·~J.ched

in. both the coal a_ampl~s i.s J1e.in:~c:·;' p,fY" L tic f~;d sul ph at~ su1p.'HIT /Table V./. The organic <o'.llphur remsin mere or lesr; unaffechd. The bacteria accelerate the leachil'l,l; rate ccnsi.derably aft,;r getting active a;r::l ex pl Ri.ns the nlo•,'f r&.t;e in the initial stage. Sulphur leaching resu: .. ts after 20· .. 25 di:!.ys ia microbiological. experiments inr:lcate some inhibition of act1vit;r of bac~eria. At this st'\1';:', alonzyith sulphur leaching 20me iron also .startc.1 gettine; lencbeCi ,;ut which is fu.rth~r ox1dised to ferric i!tftte by tc'i .• :naspheric oxygen. and bactc:ia, follow:;d by '~itt: ;J:"ecipi·, 1..ati.on t:ts bruoic iron sulp.'la~es on the coal 8urfc:cs in the :~·orn1 of ja:r"csi·::ca /A Fe_2'/so

4/;i,...Oli//',/, whe:c~ A stertGB for

Na, K, and l'l'B, i.ons [l~F 'l'hHl sue;g8sts that fresh culture of bact~ria i~ requ:ired 8.fter 20-25 days ·~o cm1tinue the l·~achine of sulphur. The leaching rnsults are based on the fact that rmlphur content e;'Teater than l. 5 f. is ex pee te.;i tc• produce acidic } eachet~B ic: mi.ne dre.inagc>.:' ! r: . The ;:enc:i.·-a1 1 y acce r;ted chr:micn} reactJ. ons expla u'ti:r..g the oxid2tion of pyri t.:;B /F{~s?/ a:nd the pT·r_,(1;,J.ction of sciz~.i ty /rf+-/ are given by the follo,'ling equati or:s ~

136



2FeS;/S/ + 7 02 + 2 H20 ,., 2Fe 2+

Fe 2+ + 2 o2

+ ~: H+ .. Fe3+ + H20

/1/

/2/

The etoichimetry of ~qn. 1. ah~m> that l mole of 2teS 2 will produce 2 molee of H /acidi ty1 • In turn, 3~he F'-" gi!nerated by Eqn. l can readt!Y oxidise. into Fe and produce an additional 3 moles of H /~qn. 3;. The iron oxidation is the rate limiting step of the reaction in Eqn. 2 and proceeds slowly under sterile condi tiona [1.4] • However, bacteria greatly accelerates this oxidation contributing a major part of acidity formed in acid mine drainage [.10, ll] • Resul1;s obtained in this investigation are also in accordance with the chemical reactions described above.

In actual practice, the rate of acid production is much higher than the reeults obtained in the laboratory. The problem of AMD in NEC commencee with the very high ra:lnfall, about 400 em annually, in the area and its seepage from the hill to the quarry and finally from quarry into the underground mines. Field investigation shows that ave-· rage humidity in these mines is above 90 "· average tempe·· rature inside is about 25-32cC and there is a good percentage of CH , CO and 0 in mine atmosphere which further aid in eas~ pyrfte oxi6ation and aleo help in easy growth of autotropic aerobic bacteria and ultimately lead to rapid rate of acid production, Moreover the trickling of minewater drops from the roof of the galleries and worked out seams makes the pyrites and other substances to get rapidly oxidised by atmospheric air. This aspect is clearly shown by the formation of 2-3 m long tubular structures of hydroxides and <iayey material shown in Pig, A.

CONCLUSIONS

The oxidation and decomposition of reactive pyrites in coal and associated strata followed by sulphate dissolution is mainly responsible for acid formation in NEG mines. The organic sulphur component is found to be chemically inert. Thiobacillus ferrooxidans /the iron and sulphur oxidising bacteria/ accelerate the acid formation step to a greater extent as compared to sulphur oxidising bacteria.

ACKNOWLEDGEMENT

The authors are thankful to Dr. A.C.Shipstone of Central Drug Research Institute, I~cknow for electromicroscopic work of bacteria. and to Dr. S.G.Choudhry, Geologist, Central Fuel Research Institute, Dhanbad for taking photomicrographs

137



of pyrites i.n coal. One of the authors /G.S./ is grateful to ProL G.S.Marwa."la, Di.rector, Indian School of M~nes, Dhanbad for awarding fellowship.

Ref,crences

:1J Rawat, N.S, Saxena, A.K., Gurdeep Singh and Su.'ldriyal, A.K. ,"Pbysico-chemica.l Cha.ract<erietics of Underground Minewa.ters and X-ray lmaJ.yeia of Corrosion Products," J. Mines, Metals & Fuels, 29/5/, 108-114, May 1981

2] Debabrata Chandra, Swapw1 Gobinda Choudhari and Subrata Ghose, "Distribut].on of Sulphur in Coal Seams with Spe-· cial Refilrence ot the Tertiary Co<>.ls of North-Eastern India", Fuel 59. 3:i7-359, May 1980

[3] Water and Wastewater A.nalyeie - A Course Manual, NEERI, Nagpur /India/, 1979

1-_41 .J Indian Standards, IS 1350 /Part III/, 5-13, 1962

[5 J ~'hakur, D.N., Saroj, KK. and Gupra, A., "Presence of Iron and Sulphur Oxidising Bacteria in Indian Minewaters and their Chemical Activity", Ind. ,T. of Expt. Biology, 14/2/, 380-382, May 1976

Caruccio, T. FrarLk and Parizek R. Hichard, "An Evalua·· tion of Factors Affecting AMD Production and the Groundwater Interactions in Selected Areas of West Penn.", Proc. Second Symp< on Coal Mine Drainage, Res. Monroeville, Penn., 107-151, 1968

[7 J Caruccio, j_', Frank, Geidel, G, Wendelyn and Pelletier, PJike, "Occurence and Prediction of Acid Drainages''!_ J. of Energy Div., Proc. ASCE, 107, No. EYl, May l9til

[s] Caruccio, T. Frank, "The Quantification of Reactive Pyrite by grain size", 3rd Symp. on Coal Min!! Drainage Res, Mellen Inet. Pittsburgh, Penn. P, 123, 1970

Brumett, J, C. and Tri butech, H., "Il<>c ter,•.al Leaching Patterns on Pyrite Crystal Surface",, J, Bacteriology, 310-317, April 1978

. 1 LlOJ Ashmead, Douglas, "Tho!! Influence of Bacteria in the

Fonnation of Acid Minewa.tere", Colliery Guardian, 694-697, June 2, 1955

[nJ Mal.ouf, E.E., "T'ne Role of Ml.croor~anims in Chemical Mlning", Mining Engineering, 23/ll,, 43-46, November 19'71

l2,i Water PoHnt:i.on 11!1crotiology E:x. by Ralph Mitchel}, Wiley Inte:::"' Scie:n-:_::o;, Chapter 4~ ·rne IYlicrrJbiolcc:v· of Min·~ Dr:\in~~~~ Po11~;.ti.,:>r~~ r.g, J.·~J72



Brimhall, B. Daniel and Wadsworth, E. Milton, "Oxygen Consturlption in Dump Leaching, Soc. of Min.Eng. AIME Trans. 254, 68, March 1973

,-14-, Singer, C. Philip and Stumen, Werner, "Acidic Mine L 1 Drainage: The Rate Determinine Step", Science, 167,

1121-1123, Feb. 1970

139



1-'

.j

>.

TAB

LE

I.

0

Ch

emic

al

An

aly

sis

of

Min

e W

ater

Sam

ple

s

Ph

ysi

cal

app

eare

nce

, A

cid

ity

so

2 -M

ine

wate

r sa

mp

le 1

/w

ith

su

spen

sio

n/

4

Led

o /T

irap

/ L

Y

ello

w

2.9

59

6 19

46

850

2.0

1

2.6

·-d

O-

L

Yel

low

3

.1

198

14

12

33

0 1

.86

1

7.4

-do

-L

Cle

ar

6.5

20

52

6 fi

76

0.

75

4.0

·-dO

·-L

Yel

low

2

.59

53

0 18

00

490

1.5

2

30

.8

;...

ao

-M

ain

su

mp

Yel

low

3

.0

32

2

1488

9

Hl

1.0

6

.36

,0

,Bar

38

olo

i 8L

O

rang

e ·-

Red

die

h

2.9

7

386

1825

90

0 1

.24

2

0,0

i -d

o-

51

Cle

ar

8.4

0

-51

2 ]0

6

0.7

5

6.0

8

' i -d

o-

61

Lig

ht

Yel

low

3

.58

19

4 1

51

0

5'10

1

.00

1

8.4

5

I 1~..

:to-

llla

in

sum

p L

____

Cle

ar

4.1

25

7 12

35

980

0.6

2

l1L

O



TABLE II.

Total sulpimr /'fo.4 and distril:n.~.t.Um ·)f differl!lni; formll l.n t"tal Bu1phur of coat !Hlt-:;>l"!a

1

Collier1'/ ! Total Distri~tlon ~~':1' eu~~:J Goal aampl!l 1Sul):lhur r . c nu eh r--organrc·---~ ,- -- ----~--·--~·-.1.. ---------·-~"-'"'1 !Ledo /Tiraw' 4.42 n.o 18.5 70.5 I

I'Baragoloi 6.05 2,3 17.5 :30.2 ! ~~-..,--~-"""",.,r.""""~---,_,, ____ ~_._J



..... .,.. t\

)

TAB

LE

III

• T

ota

l su

lph

ur

leac

hed

at

dif

fere

nt

tim

e in

terv

ale

I 'Tim

e /d

ay

s/

I 5

1.7

5

1.2

0

1.5

4

1.2

9

0.9

5

o.a

10

6

.5

6.0

4

.46

4

.4

4.2

4

.3

15

14

.4

11

.1

11

.2

10

.0

12

.0

6.5

20

21

.1

14

.6

16

.6

12

.3

15

.6

9.7

25

23

.6

17

.2

18

.3

14

.6

17

.1

10

.3

30

2

5.1

2

0.7

1

9.0

1

6.9

1

9.0

1

5.0

WB

• S

ulp

hu

r le

ach

ed w

ith

bacte

ria

WOB

= S

ulp

hu

r le

ach

ed w

ith

ou

t b

acte

ria

0.9

5

0.6

8

3.9

4

.0

10

.0

8.8

12

.4

10

.3

16

.2

11

.7

17

.7

12

.1



.... .,.. ""'

. =

3.0

Py

riti

c

sulp

hu

r .3

8

.33

.12

Su

lph

ate

su

lph

ur

.58

.5

5

.89

Org

an

ic

sulp

hu

r .1

5

.04

.1

4

, To

tal

sulp

hu

r 1

.11

.9

2

1.1

5

'IB

= S

ulp

hu

r le

ach

ed

wit

h b

acte

ria

WOB

=

Su

lph

ur

leach

ed

wit

ho

ut

bacte

ria

TAB

LE

IV

.. 4

.0

.12

.3

0

.30

.1

2 .1

1

.84

.48

.3

6 .8

2 .6

0

.05

.06

.0

03

.12

.0

2

1.0

1

.84

.663

1

.06

.7

3



LISTE OF FIGlTHES

.t'hotomic.rc•graph l

Reactive Pyrite in clay minorals /framboids.l ty-pe/ size 0-5 MID

25-50 )JJD.

Pho" orci c1·ograph 2

Heactive Pyrites size 5-50 ).ill!

>50 ,um

Photomicrograph 3

Stable Pyrite size >50 Jli'll

l'hotor,,icrograph 4

::,;tabli:! l'yrtte size > 500 f-'"'11

S.\.edronmicrograph 5 Iron- and sulphur-oxidiein& bacteria /Thiobacillus ferrooxidans; X 9 600

t:lectr<;nmicrograph 6

lron- and sulphur-oxidising bacteria /L'hi o bac i.llus fe rrooxidansl X 9 600

sae 1.20 - ).20 pm long 0, 52 - 1.25 p wide

Fit;. A

144

2-3 m long tubular structures of hydroxides and clayey material formed in walls of worked out seams



146



~i' ',, ,

~\-, .,..,j

""; "?'

·~'~'"" f'!

I· '·



7:::/G A



,0:$3urfhhglqjv $%&' … · tungstic acid and viewed in hitachi electron microacop;:; at...

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