Journal of Scientific & Industrial Research Vol. 60, October 200 I, pp 786-797

Air Pollution due to Opencast Coal Mining and It's Control in Indian Context M K Ghose • and S R Majee

Cen tre of Mining Environment. Indian School of Mines, Dhanbad 826004, India

Received: 29 January 200 I; accepted : 29 June 200 I

Open cast mining dominates the coal production scenario in India . It creates more serious air pollution prob lem in the area. Coal producti on scenari o and its impact on air quality is descri bed. To maint ain the energy demand in opencast mining i~

growing at a phenomenon rate. There is no wcll-clefinccl method for assess ing the impact on air quality clue to mining projects. An investi gati on is conducted to evaluate the impact on ai r environment due to opcncast coa l mining. Emission fac tor dat a arc utili zed for computation of dust generation due to different mining ac ti viti es. Approach for the selecti on of work zo ne and ambient air monitoring stations arc clcscribccl. Work zone air qualit y, ambient air qualit y, and seasonal variations arc di scussed. which shows high po llution potential clue to SPM. The status of air pollution clue to opencast mining is evaluated and its impact on air environment is assessed. Characteristics SPM show a great concern to human hea lth . Air pollu tion control measures involve pl anning and implementati on of a series of preventi ve and suppressive measures in addi ti on to dust extrac tion system. The study reveals that there is a need for wider appli cati on of du st co ntrol chemica ls and an in depth techno-economic survey i ~

essential. Different abatement measures for cont ro l of air pollution arc enumerated . Air pollution cont rol by trees. rrees tolerant to dillerent ai r pollutants and plant species useful for controlling air pollution is di scussed. The methodology adopted could be utili zed on industrial sca le for various sites.

Introduction

Coal is the primary source of energy'. The deve lop­ment of various industries has a cascad ing affect on the demand of coal. With the rapid ra te of growth of industries, the future demand of coal will be very hi gh.2

But th e utili zation of coal would be limited by environmental disruption , including deteri oration of air quality due to the emission of particulate matter and other gaseous pollutants from various mining operati ons , wh ich , in general , have adverse environ mental impacts . The magnitude and significance of air pollution , caused by mining, depends on method of minin g, sca le and co ncentration of minin g activiti es , geo log ical and geomorphological setting of the area. In India, coa l production will have to be increased to meet the energy demand at the rate of 20-25 Mt/y (ref 3). In underground coal mining humans suffer from coal mining inside underground workings but opencast mining creates much more air quality deterioration in res pect of dust and gaseous pollutants in and around the mining complexes . Opencast mining dominates the coal producti on scenario in India due to the techno-economic factor, better safety, etc. At the time of nationali zation in 1973, when the total

· Auti1or for corresponclcncc

coal production was 75 Mt/y the share of opencast mining was 20 per cent. By 2000 AD when the total coal producti on was 4 17Mt the share by opencast mining reached about 70 per cent and the future plan envisages larger share by opencast mining.

In opencast mining, a mass ive overburden will ha ve to be removed to reach the mineral deposits. This may require excavators, transporters, loaders, conveyer belts, etc., which will results in massive discharge of fin e particulate from the overburden materials. Similarl y normal operations will a lso req u ire excava ti on, transportati on, loading, unl oading, size reducti on, stock piling etc4

. All of these will generate particulate matter ' · The vo lume and variety of air borne dust partic les in the ambient air is ever increasing and caus ing air pollution problem in the surrounding areas. Cowherdr' has report ed that vehicul ar traffi c on haul road of mechanized opencast mines can contribute as much as 80 per cent of the du st emitted. Chadwick et of. 7 have estimated that about 50 per cent of total coal dust released during journey time on an unpa ved haul road, while 25 per cent for both during loading and unl oading of dumper. Drilling is perhaps the next important source of fu giti ve dustK. Another major source of fugi tive dust is wind eros ion from coal stockpi les.

GHOSE & MAJEE: AIR POLLUTION DUE TO OPEN CAST MINING 787

O ve r e xpl o it a ti o n o f na ture in th e na m e o f industri alization and development is causing degradation of our environment. At the same time, we do re la li se that we cannot stop the development in the name of saving environment onl y. A balance between susta inable development and environment management is the need of the hour. E nvironmental impact assessment (EIA) pl ays a c rucia l role in resolving the conflicts'1. Thus, it is necessary to assess the impacts on a ir environment due to o pe ncas t coa l minin g so th a t prope r me ti gati ve measures could be implemented . However there is no we ll-de fined method of assess ing the impacts o n a ir environment due to opencast coal projects. To evalu ate the impac t on a ir environment a fact-finding survey is essenti a l. In thi s s tudy atte mpts have been made to develop a meth odo logy to eva luate the statu s o f a ir pollution due to opencast coal mining and to suggest control measures for the control of a ir po lluti on.

Materials and Methods

T he study area was one of the largest opencast coa l projects (OCP) fo r coking coal in Jhari a Coalfie lds (JCF). It has 34.6 Mt quarri able reserve of coal. T he project report was sanct ioned in the year 1982 for a targeted product ion of 2 .5 Mt/y and the li fe of the project was 17 y. The quarry was be in g worked in two patc hes th rough separate box cuts. Working depth during the study peri od was about 60 m in box cut three sec ti ons. Working was going on in X seams hav ing seam thickness of 9.62 m. The project is located in the north-west of JCF in Dhanbad di strict of Jharkhand State. It covers an area of about 6.8 sq km It is located between latitudes 23°46'30"N and 23°47'4"N and long itudes 86° 10'47"E and 86° 13 '3 1 "E. It is surrounded by many open cast and

underground coal mines.

Wo rk zone a ir qu a lity monito rin g sta ti o ns we re selected near the sources of a ir polluti on 111

• T he deta il s of the monitoring stati ons are g iven in Table I and 2. Ambient a ir moni tori ng stat ions were se lected, keeping in view the dom inant wind direct ions preva iling in the area . O ne ambi ent a ir monitoring station was loca ted in the project office of OCP. T he dominant winds d irect ions of the area" ·" were Wand NW. Durin g the selec ti on of ambient a ir mon itoring stations the approach was to put two monitoring instruments at upw ind (W and NW ) and two instruments at downwind (E and SE) di rec tio ns. The approach was a lso to see th at these should cover the industria l, res identia l and sensiti ve area li ke hosp ital as d iffe rent standards have been la id by Centra l Pollu tion

Contro l Board (CPCB ) 13, Governme nt o f Indi a . T he

sampling was continued twice a week for four weeks in a month of each season coverin g winte r (January), summe r (M ay-June), mo nsoon (Au gu st) and pos t­m o nsoo n (O c to be r) seaso ns. 14

· Air sa mpl es we re co llec ted for 24h in three 8h shi fts correspond ing to daytime, evening, and nig httime. Micrometeoro logica l data were collected on sampling days with respect to w ind direc ti o n , w ind ve loc it y, humidit y a nd temperature. 15

· "'. SODAR data were collected from a monostati c and Doppl er SODAR make M/s Ramtech, France in sta ll ed at Central Mining Research Stat ion (CMRI), Dhanbad . The parameters studi ed were wi nd speed and direction, mi xing height, ventilation coefficient (VC).

For the co llec ti on o f samples of suspended parti culate matte r (SPM), g lass fibre ambient (G F/ A) filt e r paper was used in a hi g h vo lume sampl e r (HYS) and fo r respirable du st parti culate matte r (RPM) GF/ A was used in respirable du st sampler (RDS) at a flow rate of 1. 1 to 1.5 m' /min that a llows the SPM to depos it on the filter paper. Particul ate with size range of 0. 1 to I 0011 m was co llec ted by HYS 17

. The cut-po int d iam of RDS was less than I 011 m. Both , HVS and RDS were manu fac tured by M/s Envirotech Ltd, New Delhi . HYS, having impi ngers (bubbl e r tra in s) in se ri es w ith sodium te trac hl o romercurate as abso rb in g so luti o n, were opera ted a t a n average fl ow ra te of 0.5 L /m in fo r collection of SO (as per IS: 5 182, Patt II 1969) fo r 24h.fn the case of co llettion of NO sodium hydrox ide was used as absorbing so lution and co llected at an average flow rate of 0.5L /m in fo r 24h (as per IS: 5 182, Part IV 1976). The impinger samples were put in ice boxes immediately after sa mpling and transferred to a re fri gerator pri or to a na lyse. Th e sa mpl es we re a na lysed spectra­photometrical ly. us in g Wes t a nd Gake methods and Jackob and Hoche iser modi fied meth ods for analysis of SO and Nox , re spec tive ly 17 S PM a nd RPM we re co~puted afte r weighing the fi lter paper before and after sa mp lin g. T he fi lte r paper was cond iti o ned in a dry

atmosphere be fore weighing.

Parti c le size analysis of SPM was done on the basis of the principle of photo-extinction and sed imen tation techniques w ith a M icron Photos izer manu factured by Seis in Enterprise Co. Ltd , Japan (Mode l S KN I 000) . Attachment of centri fuge with the uni t had made it pos­sible to determine s ize d istri bution up to 0 .02 p. Resp i­rab le dust sampler (RDS) make Envirotcch, New De lhi

788 J SCIIND RES VOL 60 OCTOBER 200 1

Table ! - Location of work zone monitoring stations

Sl No. Station site Location

BW I Feeder breaker Roof of feeder breaker control room at about 3m above the ground

BW2 Haul road (HR I ) At a height of about 2m on the debris at one side of the haul road

BW3 Haul road near box cut On the other of hau l roard near near the hox cut 3 office

3 section (HR2) at about 3 m above the ground

BW4 Dragline secti on At a di stance of I OOm from the draglinne at about 2m above the ground

BWS Shovel/dumper loading On the immed iate above the bench of a working bench

BW6 Workshop Roo f top of a room ncar the workshop area which is about 3m above

the ground

Table 2-Locati ons of different ambient air monitoring stations

Stn No. Station si te Nature of area

BAI Block II OCP Industrial

BA2 Benidih OCP Indust ri al survey offi ce

13A3 Nudkhurkee Res identi al

BA4 M adhuband Residential

BAS Benidih hospital Sens iti ve

was used to determin e resp irab le particul ate matter (RPM). In RDS, the du st-laden air is imparted with a rotating motion by virtue of its tangential entry into the cyc lone. Due to thi s rotati on, dust particles > I 0 1J de­posit on the wa ll s of the cyc lone and settl e be low and the air containing the RPM travels up and is co ll ected over GF/ A fi lter paper. Cascade impactor was also used for particle size analys is (make Graseby, Anderson, UK).

Assessment of Impact on Air Environment

The sources of ai r pollutants were identified and different mining activ iti es were recorded along with producti on of coal and overburden materials. During the study peri od the mine was prod ucing 2500 t coa l /d and overburden removal was 9950 m3/d. Emission factor data

Directi on from Locati on Block II OCP

Centre On the roof top of the Block II pi t oiTice wh ich abou t 4m above the ground level

E On the roof top of the su rvey office at about 4m above the ground

w On the roof top of a vi ll ager 's house which about 7m above the ground

SE On the roo f top of a villager 's house ;ll

about 3m above the ground

NW On the roof top of the hospital at about 4m above the ground

were utilized fo r assess ing dust ge nerati on clu e to different mining act iviti es 1x.20

. It has been estimated that different minin g ac ti viti es ge nerate dust , wh ic h accounted 9 .36t clust/d 21 • The dust generated by eli fferen t activities contributes SPM as well as sett leable fracti ons in the surrounding locations.

Th e data of four seaso ns revealed that SPM concentrati on fo r almost all the mon itoring stati ons exceeded the permi ss ible limit spec ifi ed by Central Pollution Control Board (CPCB) (Table 3) during winter, pre-monsoon and post-monsoon periods. During the monsoon peri od, SPM fe ll withi n the permi ss ible limit due to the remova l of du st particulate with rain water. In fact , they exceeded the permissible li mits spec ified fo r industrial (500 pg/m 3

), res idential (200 pg/m1) and

GHOSE & MAJEE: AIR POLLUTION DUE TO OPEN CAST MINING 789

Tab le 3-Natio nal ambient air quality standards (Central Pollution Control Board, New Delhi )

Po llutant

Sulphur dioxide (S02 )

Oxides of nitrogen as N02 Suspe nded particul ate matter (SPM) Respirable particulate matter (RPM)

Time weighted

average

Annual * 24 h**

Annual* 24 h**

Annual * 24 h**

Annual* 24 h**

Sensitive Indu strial

15pg/rn' 80pg/m3

30p g/m3 120pg/m .\

15pg/m' 80pg/m3

30pgtm·' 120pg/m3

70pg/rn3 360pg/m 3

I 00pg/rn1

500pg/rn3

50pg/rn.1 120p g/rn.1

75pg/m .1 150pg/m.1

Concentratio n in ambient air

Res idential , Methods of measuremen t Rural 60pg/m3 ! .Improved West and Gake method

80pg/m3 2.Uitra lluorescence

60pg/m3 I Jacob and Hocheiser modified

80pgfm3 method 2 Gas phase chemilluminesencc

140pg/rn 3 - High volume sampling

200pg/rn3

60pg/rn3 - Respirab le particulate matter

100pg/m3 sampler

Lead (Pb) Annua l* 0.50pg/m3 I .Op g/m1 0 .75p g/m3 - AAS method after sampling using

24 h** 0 .75pg/m·' 1.5pglm3 I .Opg/m3 EPM 2000

Carbo n 8 h** I.Omg/rn3 5 .0mg/m3 0.50pg/rn1 - Non-dispersive infrared monox ide (CO) I h 2.0mg/nr' I O.Omg/m.1 0 .75pg/m3 spectroscopy

*A nnual arithmetic mean of minimum I 04 measurements in a year taken twice a week 24 hat uniform interval **24 h /8 h values should be met 98 per cent of the time in a year. However, 2 per cen t of the time. it may exceed but not two consecuti ve days

hospi tal ( I 00 f.lg/m3) areas. During winter, pre-monsoon and post-monsoon periods RPM concentration in the industrial location (BA I) also exceeds the permissible limit ( 150 f.lg/m 3). SO and NOx concentration were also found to exceed th ~ permissible limit at different occasiOns.

Seasonal variation of SPM in work zone air is shown in Figure I . Work zone air quality to be deteriorated during winter season to great extent. SPM and RPM concentrations were found to be very hi gh and exceeded the permissible limits at all locations. Seasonal vari ation of SPM in ambient air at different stations is shown in Figure 2 and status of air pollution in the study area is shown in Figure 3. The data of four seasons revealed that SPM concentration for almost all stations exceeded the permissible limit specified by CPCB. Sett leable dust observed at diffe rent locat ions also exceeded the permi ssible limit ( I 0 mt/km2/month ). The wind rose diagrams at different seasons are shown in Figure 4. Characteri stics of SPM showed the high concentration of respirable fraction , Average particle size distribution of SPM in work zone and ambient air are shown in Figure 5.

Air Pollution Con trol Strategy

The air pollution control measures in volve planning and implementati on of a series of preventive and

suppressive measures so th at the levels of pollution are maintained within certain standard11 . For thi s an air pollut ion strategy is formu lated wh ich refers to the master plan adopted to tackle the air pollution Y Four types of strategy have been distinguished for air po llu tion control. These are:

(i) Air quality management,

(ii) Emission standards ,

(iii) Economic, and

(iv) Cost benefit.

Air quality management is the regulation of the amount, location, and time of pollutant emiss ions to achieve some clearly defined set of amb ient air quality standards. It involves the contro l of pollutant emissions to ensure that these levels do not exceed the acceptable limit. It in volves several steps, which are discussed within a five-fold typology (Figure 6). Emiss ion standards are di stinguished for large number of pollutants and are app li ed to individual or specific group of emitters. If emiss ion standards are derived from consideration of air qua lity standards, this makes the emission strategy, in fact, a part of an air quality manage ment strategy. It is also known as "best ava il ab le and economically feasible control technology". Such an approach could reduce air pollution up to great extent with known methods but these

790 J SCI IND RES VOL 60 OCTOBER 200 1

1.000

'E ....._ 01 _:. 3000 c 0

Iii -E 2000 <lJ u c 0 u

1000 ~ Q_

VI

Winte r Summer Mo nsoon P-monsoon

UliiiD BW1 I FBI

~ BW4 IDSI

~ BW2 I HR1 l

D sws I SO LI

Clli] BWJ I HR2l

LJ BW6 IWSPI

Figure 1- Seassunal variation or SPM in work zone air

1000,----

BOO

• BA1 ~ BA2 f§l BAJ ffiiiill BA' CJ BA6

Figure 2-Seasonal variation or SPM in ambient air at different stations

should be economica l. Strateg ies, using an economic based approach to air pollution control would prov ide fin ancial incenti ves fo r emi ss ion sou rces to pursue the most cost-effec ti ve means fo r reducing po ll uti on. The emission charges strategy, based on requ iring polluters to pay charges relating to the amount of po llu tion they emit are most frequently used. The purpose is to leave to the choice of polluters not to pollute or to pay fine heav ily with penalties increas ing ex ponentia ll y with the degree of pollut ion. Economic approach to prov ide incentives to a fim1 to find new techniques and new products, which prov ides lower pollutant emi ssions. Cost benefit strategy first attempts to quant ify the costs of all the damage resul ting from air po llu tants and the cost of all known ways of controll ing these po llu tants and then adopt the pollution control options whi ch will minim izes the scene of po llu tion damages and pollution co ntrol costs. In Figure 7. conceptual approach of this form is ill ustrated.

If pollution control expenditure is not made, ambient air polluti on co ncentrati on will be hi g h and po llu tion da mage cost will also go up. As control ex penditure increases, the po ll uti on concentrati on and assoc iated damage costs fa ll.

Strotegy Adopted

As the project area inc ludes the opencast mine, for which no emiss ion stand ards have been proposed and no economic strategies have been devel oped, so th at the strategy adopted here should be the combinat ion of the air quality managemen t and cost benefit strategy. On the basis of collected field data it has been observed that the ma in po llu tion problem in the area is due to the du st. A contro l plan has been fo rmulated for abatement of air po lluti on probl e m. It in vo lves th e planni ng and implementation of a series of prcventi ve and suppressi vc

500

500

,., E ..._ §r L.OO c

c .2 <U 1.... c <lJ u c 0 u

::£ 0... lfl

,., E -..... 0'1 :::l.

.!;

c .2

~ c <lJ u c 0 u N

0 lfl

350

300

200

100 70

100

BO

60

L.O

20 15

GHOSE & MAJEE: AIR POLLUTION DUE TO OPEN CAST MINING

BA1 BA2 BA3 BA 4 BAs

120

100

,., E --§r BO .!: c

.2

~ 60 c <lJ

~ 50 0 u

,., E ..._ Dl :::l.

c

c .2 ..... ~ c QJ u c 0 u X

0 z

L.O

20

100

0

60

L.O

20 15

BA1 BA2 BA3 BA4 BAS

E'3 BAL. D BAs

Fi gure 3-Status of air pollution in the project area (Annual average concentrati on o f a ir pollu tants under study)

79 1

792 1 SCI !ND RES VOL 60 OCTOBER 200 1

WINTER SEASON

N

w ~t===r-----( SE

SW

s

MONSOON SEASON

N NW

w

sw

w

SUMMER SEASON

N

SE

s

Nw'T-MONSOON SEASON

w

SE

s

Seal<.> :- 1 em = 5 '/,

~ 1 7 14 28 Km/hr

Figure 4--Wind rose diagram during differelll seasons

measures, in addition to the dust extraction system1~.

Dust Extraction System

The dust extraction system envisages wet type dust extractors. This includes network of suction heads and ducting connected to wet wall cyclone for separating dust from the air stream. Air outlet of cyclone collectors will have to be connected, so as to discharge clean air to atmosphere and collected dust from the cyclone shall have to be disposed off suitably. It includes the following :

(i) Wet Wall Cyclone Separators

The wet wall cyclone separators mu st include its all required accessories like water spray nozzles, heade rs, water piping hydraulic sca les, solenoid valves, and isolating valves to ensure sufficient separation of coal dust from dust laden air.

100r-~

20~ ~ ---'---'~ J s 10 20 1.0 60 eo 100

Particle size (IJ)

- Work zone -1- Ambi ent ton e-

Figure 5-Average particle size di stributi on o r SPM in ambien t and work zone air

GHOSE & MAJEE: A IR POLLUTION DUE TO OPEN CAST MI NING

SPECIFY AI R QUALITY COMPILE AN MONIT OR MONIT OR STANDARD S INVENT ORY OF METEOROLOGICAL AIR POLLUTION

OR GOALS SOURCE EMISSIONS CONDITIONS CONC ENT RATION

I I J

l APPLY MODEL TO J CALCULATE AIR O.UAUTY

DEVISE A SET OF EMISSION CONTROL TACTIC S TO ACHIEVE

AIR QUALITY STANDARDS

J ENF ORSE EMISSION _j l CONTROL TACTICS

1 l AIR-QUA L!TY AIR- QUALIT Y STANDARDS STANDARDS ACHIEVED NOT ACHIEVE D

Figure 6-Stages involved in the ambient ai r-quality management strategy

"' 0 u

POLLUTIO N CONTROL EXPENDITURE I OR COST l

TOTAL OAHAGf +C ONTROL 1/cosT I I \ /.

' OPTI HUH / , .... I ------/ ' / ............ ____ .....

Ambient ai r pollution concentration

\ POLLUTION

DAHAGf COS\

Figure 7-Schematic representation of the rela tionship between po ll ut ion control expend i ture, pollution damage cost and polluiant concentration

793

794 J SCIIND RES VOL 60 OCTOBER 200 1

(ii ) Air Exhaust Fan

Air ex hau st fan should be of centrifugal type with radial bladed impe ll er. The fan s should be of robust. The

fan assoc iated with dust ex traction should be des igned

for adequate duty keeping of approx. 25 per cent on pressure rating. The fan must be vibration-free during

operation and des igned to limit noi se level to 90 elBA.

The fan and motor are to be observed for continuous

operation. Relevant IS code of engineering practices has to be e mployed for the des ig n and const ructi on of

impe ll er, shaft and bearings.

(iii) Dust Collection Hood

Necessary dust co llecting hoods and MS sheet ducting

of adequ ate size and des ign must be provided for guiding

dust laden a ir fro m the generating points to wet wa ll

cyc lone separators and dust-free air from cyc lo ne to atmosphere via ex tract ion fan s. The c lean air from the

fan has to be taken to a su itable he ight (not less th an 2 m or I .5 m above height of roof in the vici nity, which ever

is more) befo re discharging into a tm osp he re. Th e

fo ll owing points should be considered while des igning hood and ducting system. Centre line of hoods is to be

located at the points of generati on of maximum pressure . The hood connection has to be des igned for collecting

the dusty a ir from various dust generation sources. The hoods are to be adequate ly s ized to co llect all du sty a ir

generated at the point. Ve loc ity in the hood should not be too hi gh as to draw the large size parti c le . The ducts

fo r convey ing dusty air are to be of should have round

shape, hav ing stream line appea rance.

(iv) Dust Arrester

The dust prod uced duri ng drilling and blasting could be minimi zed by arresting and filtering the du st-l aden

air before it is thrown into the work ing env ironment. Dust arreste rs commonl y used w ith clown the ho le drill s

at the co ll ar of the ho les being drill ed.

(v) Dust Extractors with a Filtering or a Porous Layer

The fi lter in g unit m ay be made of so lid a nd continuous cons isting of pape r, which gives a very hi gh efficie ncy. T he f ilte ring layer may co mpri se fr iab le materi a l such as loose powder, sand or granular material, in a horizontal or vertical bed, cotton, woo l, g lass c loth with silicon and other synthe tic fibres.

Dust Suppressive Measures

(i) Water Spraying

The regul ar spray ing of water over coal inc reases

the free moisture content of the coal and a lso provides quantity of wa ter needed to bind th e du st a nd to

agg lomerate into a semi solid conditi on .

(ii) Water Spraying by Ultrasonk Dry Fogging System hy Means

nf Service Nozzle

In thi s system, wa ter drople ts are set between 0.3 to 5.0-mm diam with the he lp of compressed a ir. Wi th

inc reas ing fineness of droplets , the su rface area affinity

for dust increases, along with the number of droplets per

unit volume. It is clue to the fact that the droplets roughly hav ing the same size as that of the dust parti c les and as

they a re charged, the affinit y requ ired fo r wetting the

dust is achieved and the dust part ic les agg lomerate and

suppresses at the source . This requ ires no wetting agent.

(iii ) Chemicals for Dust Control

Water spraying requires huge quantity of wate r but

clue to the scarc ity of wate r in most of the coal mines it is required to redu ce wate r consumpt io n fo r du s t

suppress ion. It is poss ible o nl y if sui tab le chemicals. whi ch act as wett ing agents, are added to water. It he lps

in proper wetting of the fine r sizes of dust and inc reases

the effic iency of we ttin g.

Chemicals, useful as wett ing agents a re the followin g:

(a) Aqueous so luti on of CaCI , MgCI , hydrated time, ::! ~

sod ium s ilicate. etc. ,

(b) Teepol- laboratory grade product of Burmah Shel l,

(c) Kodak wetti ng agent - product of Kodak Ltd ,

(d) Lessapol - product ofT mperia l Che mical Industri es ,

(e) F ilset 50 - product of F ill e r Group of Company,

(f) Jalasakti - A hygroscop ic so lid.

(iv) Haul Road Dust Consolidation

Surface mine haul road is the most prolific source of

dust in surface mines25 . Watering of the haul roads is the most common method of cont roll ing dust emi ss ion. The

frequency of watering has to be related to the c limatic

conditi ons. Va rious products are avai lab le in the market

for consolidati on of hau l road dust as the water is qui ck ly evaporated if the water spray ing is no t done at frequent

GHOSE & MAJEE: AIR POLLUTION DUE TO OPE CAST MINING

Dust Source

Blasting

Loading and unloading

Mobile equipment

Fixed plant (Crushers, screen conveyors. etc.)

Dust blow

Table 4--Abatement measures for control of ai r pollution at the source

Control measures

2 Dust suppression by water and I or detergent

3 Use of dust arrester

I Dust may be suppression by water sprays

Before charging and blasting considerat ion of expected atmospheric condit ion

I Suppress dust by automatic or mannual water sprays (with detergent)

2 Enclose of the loading and unloading area, wherever possible

I Internal roads to be surfaced

2 Exhausts fan to be directed upwards

3 Dust suppression by water sprays

4 Selection of proper routes

5 Sheeting of loads of fine materi als

6 Green barrier along mine road

I Provision of enclosers

2 Use of water sprays to suppress dust

3 Use of dust collectors (bag, wet or dry centri fu gal, electrostatic, etc.)

4 Green barrier all around

I Enclosure of stock piles

2 Vegetation of waste dumps

3 Water spraying to suppress dust

4 Establishment of green barriers of trees

Air Pollution Control by Trees

795

intervals. The raised dust causes the problem of visibility on the haul road, which, in turn , affects the average vehicle speed in addition to the pollution problem. The health of the workers would be affected due to high respirable dust concentration. Various products are available in the market for the consolidation of haul road dust. Hygroscopic salts extract moisture from the atmosphere and keep the road surface damp . Most common examples are calcium chloride, sodium si licate, magnesium chloride, and hydrated lime. Surfactants/ wetting agents could reduce the surface tension of water helping wetting of dust particles and thus economize the watering costs. Monitoring of SPM was done with the help of high volume air samplers. SPM was measured before and after application of the chemical (Filset-50) and found that SPM level of 263 I 11g/m3 came down to about 780 11g/m3 after one month of application. The study reveals that there is a need for wider application of dust control chemicals on the haul roads of Indian coal mines.

Plantation of trees is one of the best measures for checking the air pollution. Trees are to be selected, based on the type of pollutants, their intensity, location , easy availabi lity and sustainability to the climate. For arresting dust pollution, trees having compact branching, closely arranged leaves, broad leaves of simple elliptical and hairy structure, shiny or waxy leaves and high proline content are suitable. A list of trees tolerant to different air pollutants is given in Table 5

Control of Air Pollution

Different abatement measures for control of dust generated from different mining operations are given in

Table 4.

A wide green belt of fast growing trees should be raised around the coal project. New colonies and residential building should be created at a considerable distance from the project. To create green barrier around roadsides, fixed plants, stockpiles of OB dumps the following guidelines may be useful in increasing the efficiency:

(i) Trees s hould be planted in beds arranged perpendicular to the direction of prevailing wind,

(ii) Trees should be planted in a concentric fashion around the source of pollution ,

(iii ) Peripheral plantations may also be used as wind brakes on dry tailings ,

7% .I SCI IND RES VOL 60 OCTOBER 200 1

(iv) A judicious mixture of open and permeable planting with dense planting should be made to achieve max imum beneficial effect,

(v) Plants and trees of different heights should be planted on both sides of the traffic lanes,

(v i) A wide green belt of I 0-m width with 6 rows of tall fast growing trees will have to be rai sed around the CHP and mine complex.

Table 5-Trees tol erant to air pollu tant s

Dust pol luti on

Alswnia scholoris

Cassia sia111ea

Dalbe1gia sissoo

Ficus henghalensis

F. in{t'c/oria

i\1/an gifi'm indiu 1

Pt'lloii!IOrtllll fe iTI I.f!.ill l'l /111

Polwt!thia logn ifl' lia

Shm •ea rolmsta

'l i'clontl gmndis

Alnus l' iridis

OI.O ne

Accr Ncgunda

Accr Plwllanoides

Quercus palustris

Aar J!Iatanoides

A. negunda

Qut' IY" IIS palustris

Sulph ur dioxide

Alhi:ialehheck

A ilw111111s e.rcd1·11

Alstonia sclwlaris

A:adimchw indica

Fims religiosa

Lagestm<'lllia

Miiiii iSOIIS clw1gi

Polmlthia lognift'm

Tl'llrinalia m:jw w

A en f'latanoides

Quacus fWius tri.l·

Q. mhra

Oxides or nitrogen

Cagus orit'lllalis

Quercus m hmr

Nohinia f!Sellllocacia

Lead

Cassia silllllt'S

Zi~.1pl111s n1t111ritiww

Maiti and Banerjee21' have found that the plants can

act as li vi ng filters of dust polluting in mining areas. It is reported that a 8 m wide green belt between roads and buildings can red uce the dust fall by 2-J times coni fe r reduce dust fa ll up to 42 per cent in temperate urban areas. The stud y indicates these evergreen plants with simple, pol ish surface like -Alstonia scholaris , Ficus lun ea, F. henghalensis and Mognifem indica are best dust catchers. Plant spec ies useful for cont ro lli ng air pollution are given in Table 6.

Conclusions

Ma in air po llution prob lem due to opencast mining is cl ue to the dust. Work zone and ambient ai r quality data also reveal the hi gh pollution potenti al in the project area and surrounding locations . The respirab le frac ti on in SPM is fou ncl to be hi gh and ala rming to human hea lth. Air pollution control measures involve planning and implementation of a series of preventi ve and suppression measures in add iti on to dust extraction system. The re is a need for wider app li cation of dust control chemi ca ls on haul roads for which an in depth technoeconomic sur vey is esse nt ial. By proper impl e mentati on of suggested abatement measures, ai r pollu tion in opencas t mi ne and its envi ronment can be suitably controlled and also a ri g ht kind of ba lance between susta inable development and environmental manage ment can be mai ntained . The methodology adopted rnay have formed guidelines wh ich could be utili zed on industrial scale fo r var ious sites

Acknowledgements

The authors are th ankful to the Ministry of Env ironmental and Forests, Government of India for financial grants for infrastructral facili ties at Centre of Mining Environ ment, Indian School of Mines. Financial

Table 6 -Useful plant spcci(;s rnr controll in g :~ ir polluti on along with their ch:1rac teristics

Speci:t l properties

(i) Puhe~cence on leaves t0 entrap : and hold dust panicle'

(i i) Leaves and branches to slow winll .

(iii ) Blossoms and foliage that prmidc plca~a n t smell to mask: ndnur.

(il) Lca1·cs and br;111chc' to slow the act1on of r;Jill \:

(v) Plants th;ll absorb SO

NdlllC or spec ies

Cua:ama, Putrwrjil '£1, N1·ctantlll's, Trenw , llolof!i'leliu. Tem1inalia

A lhi::ia. Smnan ia, PellmJ Jiw mlll. h1111arindus /)ei!Jagio

Morinda. Cl'sllwn. Locntmw, Anona, /11iclll'litl, .laslllilllt ll l (itm s, Plu1ncritt, !11ognoliu.

A:an!ichw. Nelia. Acacia a,, ,·icn!twfrnm is . /)c/oni.r Ca.Hw

Lir·lll't ts. Fagus , Acer

GHOSE & MAJEE: AIR POLLUTION DUE TO OPEN CAST MINING 797

support in th e form fe llowship rece ived from th e University Grants Commiss ion to S R Majee is grateful ly acknow I edged.

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