Air Pollution in Mines: Causes and

Control

By

Prof. I.L. Muthreja

Dept. of Mining Eng.

Visvesvaraya National Institute of Technology,

Nagpur

1

AIR POLLUTION

Mining Pollutants

• Particulate

• Gaseous

2

Components of Atmosphere

Troposphere

Stratosphere

Mesosphere

Ionosphere (Reflecting radio

waves)

8Km

50 Km

80 Km

400 Km

Pole equator

16 Km

3

• Troposhere

– High CO2,N2,O2 (Clouds,fog and storms formed )

– Temp reduces with ht -50 deg at 10 Km

• Stratosphere

– Temp increases with height

– Low vapour content (no clouds formation)

– Layer of OZON found

– UV of Sun absorbed

– Temp increases to -10 degrees C

• Mesosphere

– Temp reduces with ht

• Ionosphere

– Density of air is low,

– electrically charged microscopic particles reflect electromagnetic

waves

• Exosphere

4

Particulate Matters:

• Any dispersed mater solid or liquid in which the individual aggregates are larger than single small molecule (0.0002 m m), but smaller than 500 m m. Result of disintegration of solids, if liable to remain in atmosphere, may cause pollution

• Liquid droplets have similar effects, hence included in this category

• Mining: excavation, comminution and transport of solids cause dust pollution.

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• DUST: Solid particles caused by the breakup of larger

masses through grinding, crushing or blasting operations

• Smoke: Fine solid particles resulting from combustion of

organic particles. Size 0.5-1.0 m m • Fumes: Fine solid particles formed by condensation of

vapours of solid materials. Size- 0.03-0.3 m m • Mist: Liquid particles or droplets < 10 m m If mist concentration is high enough to obscure

visibility, it is called as “Fog” • Spray: Liquid particles formed by atomizing of parent

liquids. Size 10-100 m m

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WHAT IS MINE DUST AND WHY DOES IT NEED TO BE CONTROLLED?

Dust is a generic term used to describe fine particles that are suspended in the atmosphere.

The term is non-specific with respect to the size, shape and chemical make-up of the particles.

Particles as small as a few nanometers and as large as 100 microns (μm) have been measured in the atmosphere.

Dust is formed when fine particles become entrained in the atmosphere by the turbulent action of wind, by the mechanical disturbance of fine materials, or through the release of particulate-rich gaseous emissions.

The concentration of particles in the atmosphere can range from a few micrograms to hundreds of micrograms per cubic metre (μg/m3 ) in highly polluted areas.

• Dust associated with mining activity usually

occurs as a result of the disturbance of fine

particles derived from soil or rock.

• Dust formation is initiated by the disturbance

of particles through mechanical action eg

blasting, handling, transporting, in

combination with air movement.

• Where particles are small and light, with a

high surface area relative to their mass, the

upward forces exerted on particles by air

movement may exceed downward

gravitational forces, leading to the formation

of dust.

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• Depending on factors such as climate, geology and the method of mining, the potential exists for greatly increased dust levels in the environment surrounding a mine.

• Modern methods of open cut mining often involve the mining, transport and handling of huge tonnages of material, increasing the potential for dust to be produced.

• The consequences may include visible plumes and haze, the staining and soiling of surfaces, aesthetic or chemical contamination of water bodies or vegetation and, effects on personal comfort, amenity and health.

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• Mine dust may be qualitatively quite different to other types of dust. In an urban environment, dust commonly includes sources from industry, transport, land clearing and wood smoke.

• Mine dust is typically less complex in its make-up, consisting mainly of particles from exposed soil and rock.

• Mine dust can result in a serious nuisance and loss of amenity for populations living in the vicinity of a mine.

• This may be exacerbated by certain types of dust, such as coal and iron ore dust, that are highly visual and may result in a prominent and unsightly coating over surfaces.

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• Fortunately dust rarely presents a serious threat to the wider environment.

• Dust concentrations, and hence deposition rates and potential impacts, tend to decrease rapidly away from the source.

• In the majority of situations dust produced by mining operations is chemically inert, although exceptions may occur where dust particles contain phytotoxic substances such as cement dusts or fluorides

• Damage to vegetation and agriculture is possible through mechanisms such as the blocking of leaf stomata (and the inhibition of gas exchange), or reduced photosynthesis due to smothered surfaces (or in extreme cases lower ambient light levels).

• While such effects on vegetation are likely to be localised and reversible, they can contribute to negative public perceptions of the mining operation's environmental performance.

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• Nevertheless, there does exist the

potential for harmful and more

persistent contamination of the wider

environment from certain types of

material that may be exposed by

mining.

• Dust derived from ore types containing

asbestos, radioactive materials or heavy

metals, for example, are in this

category.

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THE TERMINOLOGY OF DUST

Common terminology used to describe different classes of dust includes:

1) Nuisance dust

• Nuisance dust is a term generally used to describe dust which reduces environmental amenity without necessarily resulting in material environmental harm.

• Nuisance dust comprises particles with diameters nominally from about 1 mm up to 50 μm. This generally equates with 'total suspended particulates' (TSP).

• The TSP range of dust particles is broad, and may be produced from sources such as industrial and mining processes, agricultural practices and, from wind erosion of the natural environment.

• Impacts of mine dust on near neighbours is most often due to nuisance dust.

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2) Fugitive dust:

• Fugitive dust refers to dust derived

from a mixture or not easily defined

sources.

• Examples of fugitive dust include dust

generated from vehicular traffic on

unpaved roads, materials transport

and handling, and unvegetated soils

and surfaces.

• Mine dust commonly is derived from

such non-point sources.

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• Dust is considered to be any solid matter caused by grinding/crushing/blasting operations, which is borne by the air and in which the individual aggregate is larger than single small molecules (0.0002um in diameter, but smaller than 500 um).

• The surface mining activities are associated with dust generation. Hence dust from workings is often considered as significant nuisance. In surface mine sites, dust is said to be one of the major source of irritation. The problems related to dust are not restricted to the mine surroundings itself, but also to the people and vegetation away from it.

• In surface mines dust can be emitted from stack as a plume or it can be picked. up by the wind from ground, the surface of a road or a stockpile.

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Characteristics of dust

A. Physical Characteristics

1) Size

2) Settling properties

3) Optical properties

B. Chemical Characteristics

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A. Physical Characteristics:

1. Size

• Size is one of the most important physical properties of the particulates. The particles of major interest range from 0.01mm -10mm. Particles smaller than these undergo random motion, and through coagulation generally grow to larger sizes and settle out. Particles larger than 10um settle quickly. A 10mm particle has a settling velocity of approximately 20 cm/min.

• The dust particles that are picked up by wind and carried over long distances tend to sort themselves out to the sizes between 0.5 and 50mm.

• The dust particles less than 5mm are considered as respirable dust.

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• < 0.1 mm aerosol resulting from combustion undergo random motion (Brownian) and never settle may coagulate by collision and increase in size

• 0.1-1 mm by condensation of vapours- not affected by Brownian motion settling time measured in months

• > 10 mm resulting from abrasion of solids have definite settling velocity

• Upto 200 mm particles in suspension tend to fall out at uniform speed in calm air (g is countered by friction)

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19

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2. Settling Properties:

• Settling characteristics of particulates are important In the sense that settling is the major natural self-cleansing process for removal of particulates from atmosphere. The particulates can generally be classified as Suspended or Settleable.

• The suspended particles vary in size from less than 1um to approximately 20 mm. They remain suspended for long periods of time.

• The settleable particles or dustfall are larger and heavier and settle out close to their sources. They generally greater than 10 mm in size.

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Constt Speed V terminal velocity

• 150-200 mm Newton’s law:

D= particle diameter

m1= specific mass of dust

m2= specific mass of air

• <150 mm : Stokes Law:

N= viscosity of air

5.0

2

1).(..3/8

m

mDgVn

N

mmgDVs

.18

)(. 212

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Falling speed of various sizes of

particulates

Size, micron Falling speed

200 1.2 m/s

100 0.3 m/s

50 70 mm/s

10 3 mm/s

5 0.7 mm/s

1 30 mm /s

0.5 7 mm /s

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3. Optical properties:

Reduction in visibility is one of the most

effect of dust pollution, and the scattering

of light by dust particles is primarily

responsible for that reduction. Particles in

the range of visible light( 0.38 to 0.76mm)

are effective in visibility reduction.

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B. Chemical Properties:

• The effect of dust depends on its chemical

composition. It may consist of many

inorganic and organic compounds which

may have detrimental effects.

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Effects of Dust

A. Effects on Material

B. Effects on vegetation and animals

C. Effects on Human health

D. Miscellaneous effects

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A. Effects on Materials:

• Soiling clothings and textiles

• Corroding materials

• Eroding building surfaces

• Discolouring and destroying painted surfaces

B. Effects on vegetation and animals:

• The increased plugging of stomata reduces plant

growth

• Dust coating on leaves reduces photosynthesis

• Animals eating plants coated with particulates may

suffer some ill effects.

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C. Effects on Human Health:

• Inhalation may lead to respiratory illness (asthama) (40% of the particles between 1 & 2mm are retained in bronchioles and alveoli)

• Irritation of eyes

Human defence mechanism

• > 10 mm =Hairs at the front of the nose remove all particles over 10um

• 2-10 mm Movement of cilia sweeps mucus upward, carrying the particles from windpipe to mouth where they can be swallowed

• <2mm Lymphocytes and the phagocytes in the lung attack some submicron particles

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D. Miscellaneous effects:

1) Visual effects: dust plumes, reduced visibility, coating and

soiling of surfaces leads to annoyance, loss of amenity

2) Need for cleaning surfaces

3) Mechanical/electrical faults

4) Abrasion of moving parts

5) Contamination of laboratory, quality control and standards

room and medical facilities

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Legal Requirements: • United Nations Conference on Human Environment, held in

Stockholm in June 1972, decisions were taken to initiate appropriate steps for the preservation of natural resources of the earth which include the steps for preservation of the quality of air and control of air pollution

• The Air (Prevention and Control of Pollution) Act 1981 and the rules made there under are the laws of the land that ensures the quality of air we breathe.

• The Act defines 'Air Pollutant' as any solid, liquid or gaseous substance present in the atmosphere in such concentration as may be or tend to be injurious to human beings or other living creatures or the plants or property or the environment. Subsequently, with effect from 1st April 1988, Noise has also been declared as an air pollutant. The Act , vide sec 19, has empowered the State Govt to declare any area or areas within the State as “Air Pollution Control Area”.

• The Act has imposed restrictions, vide Sec 21, to establish or operate any industrial plant in such Air Pollution Control Areas without prior consent of State Pollution Control Board. 31

On the basis of Land use and other factors the various areas of a State may be classified into three categories:

a) Industrial and Mixed use areas

b) Residential and rural areas

c) Sensitive areas

Category (a) : having industrial activity in the area and is bounded to have somewhat inferior quality of air compared to other categories

Category(c) : covers hill stations, tourist stations, sanctuaries, national parks, national monuments and other areas where nation would wish to conserve it as clean environment even if that implies some curbs on economic activity.

All areas not classified as a or c, will be classified as category (b)

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• When monitored uniformly over 12 months

of a year with a frequency of not less than

once in a week, with a sampling time of 8

hrs for sample and analysed according to

procedure specified by Central Board, the

concentration of the different pollutants

shall be 95% of the time within the limit as

prescribed in following table

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Pollutants Time-weighted

average

Concentration in ambient air Method of measurement

Industrial Areas Residential, Rural &

other Areas

Sensitive Areas

SulphurDioxide (SO2) Annual Average* 80 µg/m3 60 µg/m3 15 µg/m3 Improved West and Geake F4 - Ultraviolet

Fluorescence

24 hours** 120 µg/m3 80 µg/m3 30 µg/m3

Oxides of Nitrogen as (NO2) Annual Average* 80 µg/m3 60 µg/m3 15 µg/m3 - Jacob & Hochheiser Modified (Na-Arsenite)

Method

24 hours** 120 µg/m3 80 µg/m3 30 µg/m3 - Gas Phase Chemiluminescence

Suspended Particulate Matter

(SPM)

Annual Average* 360 µg/m3 140 µg/m3 70 µg/m3 - High Volume Sampling, (Average flow rate not less

than 1.1 m3/minute).

24 hours** 500 µg/m3 200 µg/m3 100 µg/m3

RespirableParticulate Matter

(RPM) (size less than 10

microns)

Annual Average* 120 µg/m3 60 µg/m3 50 µg/m3 - Respirable particulate matter sampler

24 hours** 150 µg/m3 100 µg/m3 75 µg/m3

Lead (Pb) Annual Average* 1.0 µg/m3 0.75 µg/m3 0.50 µg/m3 - ASS Method after sampling using EPM 2000 or

equivalent Filter paper

24 hours** 1.5 µg/m3 1.00 µg/m3 0.75 µg/m3 .

Ammonia1 Annual Average* 0.1 mg/ m3 0.1 mg/ m3 0.1 mg/m3 .

24 hours** 0.4 mg/ m3 0.4 mg/m3 0.4 mg/m3 .

CarbonMonoxide (CO) 8 hours** 5.0 mg/m3 2.0 mg/m3 1.0 mg/ m3 - Non Dispersive Infra Red (NDIR)

1 hour 10.0 mg/m3 4.0 mg/m3 2.0 mg/m3 Spectroscopy

* Annual Arithmetic mean of minimum 104 measurements in a year taken twice a week 24 hourly at uniform interval.

** 24 hourly/8 hourly values should be met 98% of the time in a year. However, 2% of the time, it may exceed but not on two consecutive days.

NOTE:

National Ambient Air Quality Standard: The levels of air quality with an adequate margin of safety, to protect the public health,, vegetation and property.

Whenever and wherever two consecutive values exceeds the limit specified above for the respective category, it would be considered adequate reason to institute regular/continuous

monitoring and further investigations.

The standards for H2S and CS2 have been notified seperately vide GSR No. 7, dated December 22, 1998 under Rayon Industry - for details please see Sl. No. 65 of this document.

[S.O. 384(E), Air (Prevention & Control of Pollution) Act, 1981, dated April 11, 1994 ]

[EPA Notification: GSR 176 (E), April 02, 1996]

1. Included vide Notification SO. 955 (E), Air (Prevention & Control of Pollution) Act, 1981 dated October 14, 1998)

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Whenever and wherever, three

consecutive measurements spaced by

atleast the week apart, or any three out of

10 consecutive meaurements spaced

atleast one week apart, are found to

exceed limits, it would be considered

adequate reason to institute regular

weekly continuous monitoring and further

investigations

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Generation of Dust

• There are a number of mechanisms which produce dust in mlnes.

• It can occur naturally, as in sand or soil or it can be produced by fracturing larger particles or aggregations.

• Small particles can be picked up by the wind from exposed soil surfaces and carried long distances in suspension.

• Wind over a stockpile or through a stream of falling material, as off conveyor, can also remove fine particles. A falling stream of material itself can create an air current with a similar effect.

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Three main dust sources in surface mines

1) Piont Source:

Drilling, blasting, loading, 'tipping, draglines, dozers, chutes, crushers, screens, exhaust from dust control systems, unsheeted trucks, conveyor transfer points.

2) Line source:

Well defined haul-roads, open conveyors

3) Area or Dispersed Source:

Top/soil stripplng and dumping when dry and friable, mine floors, unsurfaced haul-roads, waste dumps, stockpiles, spillages.

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a) DRILLING:

This is one of the main source of dust production in mines.

Dust production will be higher if:

i. Bits are not sharp enough.

ii. There is insufficient thrust on bits.

iii. Suitable arrangement for clearance of cuttings from the hole is not provided.

Large diameter blast holes drilled in surface mines produce huge quantity of fine dust which get dispersed in the mine atmosphere and its neighboring places by natural ventilation.

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b) Blasting:

Heavy dust concentration is produced by blasting due to shattering and disintegration of strata.

Amount of dust produced depends upon pattern of holes, quantity and strength of the explosive used, brittleness characteristics of rock, rock strength distribution etc.

A good proportion of dust is made up of particles below 5mm.

c) Loading ,unloading and transfer points:

Much amount of dust is raised by loading and unloading of dry material.

Loading of coal/overburden in dumper/railway wagon/ conveyor produces dust.

Similarly dust is raised by unloading and transfer points.

It is generally estimated that 0.02% of coal loaded for transportation is converted into fugitive dust and similar percentage is converted into fugitive dust at unloading points.

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d) Hauling:

Often dust deposited on the floor of haulage road can become air-borne by movement of men, mobile equipments, dumpers, vehicles etc.

Chance of dust production is more with dry unsurfaced haul-roads.

e) Grading Roads and other surfaces:

Considerable amount of dust is produced by heavy earth moving equipment, essentially when they are used for the purpose of grading roads and other surfaces.

Dust produced depends on the moisture present in the material and severity of wind.

f) Handling of dusty material

Portland cement and similar material are easily rendered airborne during handling and batching.

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g) Fixed plants:

ROM of mine is sent to crushing and

screening plant for required size reduction.

Because of crushing and vibratory motions

large amount of dust is produced.

The in-pit crushing system with conveyor

transport adds substantial amount of dust

to mine atmosphere.

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h) Dust blow:

The refuse heap, stockpiles and overburden dumps cause dust production due to wind.

High air velocity is contributing factor for creating airborne dust clouds.

Once dust has been formed or in the event of naturally fine particle materials such as clays being present, the environmental nuisance from dust depends upon the opportunity it has to react with air flows of a velocity sufficient to carry it from the point of origin.

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Pick-up velocities of dry dusts

Particle

Size, mm

Air velocity, m/s

Coal Silica Granite

75-105 5 6 7

35-75 4 5 6

10-35 3 3 4

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It is found experthan 5 m/s, dust of above 100 mm will be raised from stationary dry sufaces and carried down wind for 250 m.

Wind speeds of 9 mls can transport dust over 800 m.

On haul roads velocity is imparted to the dust by machinery and hence lower wind speeds suffice to transport the dust and prevent rapid settling out.

imentally that at wind speeds of more

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Air pollution factors and air quality

data due to mining operation The magnitude and significance of the environmental

pollution caused by mining operations depend on:

- Type of mineral

- Method of mining and beneficiation

- Smoke and gas from beneficiation plants

- Processing plant scale

- concentration of mining activity

- Geological and geomorphologic settings of the area

- Land use pattern before and after mining

- Natural resources existing in the area

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Dust factors:

A. Overburden Excavation: i. Scraper loading-

ii. Shovel excavation- 1.0-3.0 Kg/t

iii. Bucket wheel excavation- 0.7-2.0 Kg/t

iv. Loading in vehicles – 0.07-0.4 Kg/t

B. Transportation:

Conveyor Belt - 0.5-1.0 Kg/t(each transfer point)

Dumper - 1.5-3.0 Kg/Km of earthen dry surface

- 0.1 – 0.5 Kg/Km of soiled surface

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C. Unloading :

Conveyor system -- 0.8-1.5 Kg/t

Dumper- Bull Dozer -- 1.5 – 4.0 Kg/t

D. Mineral Excavation:

Bucket wheel excavator- 0.5-1.0 Kg/t

Shovel - 0.8-1.5 kg/t

Loading conveyor belt- 0.05-0.1 Kg/t each travel point

Loading Dumper - 0.07-0.3 Kg/t

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E. Transport:

Conveyor Belt - 0.05-0.1 Kg/t each transfer point

Dumper/truck - 1.5-3.0 Kg/Km travel on dry surface

- 0.2-0.5 Kg/Km travel on solid road

F. Stock Piling/Loading:

Conveyor - 1.0 – 2.5 Kg/t

Dumper/manual - 1.5-4.0 Kg/t

G. Size Reduction:

Jaw Crusher - 1.5-2.5 Kg/t

Screening - 2.5-5.0 Kg/t

Loading - 0.8-1.5 Kg/t

Stock piling/retrieval - 1.0-4.0 Kg/t 48

Dispersion of Dust

• Dust produced is mixed thoroughly with the surrounding air and diluted by atmosphere dispersion. The dispersion is due to turbulence and bulk air flow. The adverse meteorological conditions may give rise to problems of air pollution

• Factors Affecting Dispersion of Dust:

The following meteorological parameters may affect dispersion of dust in atmosphere: 1. Rate of change of temperature with altitude (Laps rate)

2. Pressure

3. Wind

4. Moisture

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1. Rate of change of temperature with altitude:

The temperature change of atmosphere with altitude affects the plume

dispersion.

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Looping plume condition will arise during unstable atmospheric conditions. There will be rapid mixing of dust and wind causing high eddies may carry the entire plume to the ground causing high concentration of dust close to the source before dispersion is complete.

In a Neutral plume, the plume may rise directly into atmosphere. If wind velocity is more than 32 Km/hr and when cloud cover blocks solar radiation by day and terrestrial radiation by night, the neutral plume will be converted into coning plume.

In stable atmospheric conditions also, there will be Coning plume formation. In coning plume conditions there is limited vertical mixing and probability of air pollution problem in the area may be increased as the fine dust particles will remain in the atmosphere for longer duration.

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2. Effect of Pressure:

• High pressure systems are related to clear skies, light winds, atmospheric stability. If such system prevails over an area for several days, dust can build up to cause pollution problems.

• Low pressure systems are commonly associated with unstable atmospheric conditions and brings wind and rain. Hence contaminant build up are less likely to occur under such conditions. However in the absence of rain, deposited dust will be raised and carried for longer distances.

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3. Effect of wind

It is an important vehicle in the distribution, transport and dispersion of dust in air. Hence wind rose diagrammes are essential to know the direction and speed of wind in an area over long periods of time.

4. Moisture:

It has profound effect on air quality of the region. With high humidity conditions dust problems are less likely.

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55

Gaussian steady-state

dispersion model

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It provides a steady-state solution to the transport and diffusion

equations (transport plus diffusion = dispersion).

The basic Gaussian diffusion equations assumes:

The degree of dilution is inversely proportional to the wind

speed.

Pollutant material reaching the ground level is reflected

back into the atmosphere.

The pollutant is conservative, i.e., not undergoing any

chemical reactions, transformation or decay.

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The accuracy of predicting the plume rise since that

affects the emission height used in the Gaussian

dispersion equation.

The accuracy of the dispersion coefficients used in the

Gaussian dispersion equation

Wind speed and wind direction are constant from the

source point to the receptor (for a wind speed of 2 m/s

and a distance of 10 km, 80 minutes of constant

conditions would be needed).

Atmospheric turbulence is also constant throughout the

plume travel distance.

Only vertical and crosswind dispersion occurs (i.e., no

downwind dispersion).

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The model equations

The spatial dynamics of pollution dispersion is described by the

following type of equation in a Gaussian model:

C(x,y,z,t)= (Q/2πuσyσz ) *exp{-(y2/2σy2 )}*exp{-(z+Heff)

2/2σz2)}

+exp{-(z+Heff)2/2σz

2}

where

C(x, y, z,t) :- pollutant concentration at point ( x, y, z );

u :- wind speed (in the x "downwind" direction, m/s)

σy, σz:- represents the standard deviation of the concentration in the y

and z direction, i.e., in the wind direction and cross-wind, in meters;

Q:- is the emission strength (g/s)

Heff is the effective stack height.

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Assessment & Monitoring

• Air quality monitoring integral part of air pollution control program

• Through monitoring current trends in air quality can be evaluated by comparing the data with the regulated standards

• information so obtained is helpful in implementing control measures for reducing pollutant concentration to acceptable levels and in assessing the effect of air pollution control strategies

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• Data to be collected: – Meteorological data (Weather monitoring station)

• wind speed, turbulence and wind direction

• Temperature & Relative humidity

• Rainfall

• Pressure

• Sunshine

• Dust fall measurement

• Suspended Particulate matter & Respirable particulate measurement

• Concentration (High Volume Samplers, Respirable Dust Samplers)

• Size analysis (Particulate Size Analyser, Particulate counters)

• Dust characterisation (mineralogical) (X-ray Diffraction)

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SAMPLING:

1. Objectives:

The strategy for sampling the atmosphere and the extent of a survey governed by the objective, which should be defined before planning and undertaking a sampling program

a) To Assess Health Hazards

b) To Determine Background Pollution Levels

c) To Determine The Degree Of Air Pollution Control

d) To Identify Specific Source Of Air Pollution

e) To Collect Data For Formulation And Testing Of Pollution Models

f) For Scientific investigations

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2. Preliminary information required for planning the survey:

In addition to objective of a sampling program, information to be collected:

– Local sources of dust

– Topography

– Population distribution

– Land use pattern

– Climatology

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3. Planning for survey

It includes:

a) Selection of sampling procedures

b) Location of samplers

c) Period of sampling, frequency of sampling

and duration of survey

d) Processing of data

e) Auxiliary requirements

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a. Selection of sampling procedures:

Objective of any sampling program to

obtain genuine and representative

sample

Sampling to be carried out long

enough and at a rate that allows

collection of an analytically measurable

sample.==> requires an appropriate

sampling procedure High Volume

samplers (SPM or RDS)/ Particle size

analysers etc.

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b. Location of sampling stations:

Factors governing location: – Objectives

– Method/instrument to be used for sampling

– Resources available

– Physical access and security against loss or tempering

– Representativeness

– Should fulfill physical requirement

Objectives

i. Health hazard as close as possible to specific locations where effects are to be studied

• Population centre for healt hazards

• Critical areas- schools, hospitals etc

ii. Material damage vegetation at foliage level (near leaves)

iii. Background level determination grid form location & sampling in all location simultaneously requires considerable amount of effort, resources & manpower

Contribution from specific sources of pollution level upwind and downwind locations

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Sampling equipment:

To be provided with proper security against theft and temper

Representativeness:

Site should be representative of the area

Physical requirement:

Availability of the site, accessibility, power availability etc

Comparability:

Location to be standardized from the comparison point of view ( 3-4 m above ground, 1-1.5 m from the nearest vertical surface, HVS on the roof of low buildings etc)

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c. Period, frequency and duration of sampling:

Length of time over which a single sample or set of samples is collected

Frequency: depending on objective of sampling: samples are collected during a given time ( sampling of three hours – 8 times a day)

Duration of sampling: total length of time for which entire sampling program is carried out ( one year ( all seasons))

Period should be such that measurable quantities of dust are trapped in the sample at the end of sampling

Period and frequency should be such that statistically reliable averages over long periods or over the duration of sampling may be obtained from the data.

One 24 hr sample collected daily, once weekly, once monthly will give unreliable estimate of annual average

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d. Processing of data

e. Auxiliary requirement

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Control of dust:

- Forecasting the problem & avoiding them

- Preventing its escape into the

atmosphere

- Recapturing it once it is in the air

“TO AVOID CREATING IS EASIER THAN

SUBSEQUENT CONTROL”

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1) Dust blown from surface excavations, dumps etc:

- simple water sprays at active locations

- revegetation or use of surface stabilisation

2) Drilling:

- Dry collection of dust (Cyclone & filter)

- Wet drilling (water or foaming agents)

- Use of sharp bits

- Use of proper thrust and flushing system

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73

The air and water flow during drilling operation to demonstrate water

flushing of the drill cuttings. The water flows through the center of the

drill steel and out the end of the drill bit to remove the cuttings from the

drill hole.

74

Internal workings of a water separator sub.

75

A basic dry dust collection system on a drill.

76

Dust collector dump point prior to shroud installation (A). Two men

installing the shroud onto the dust collector dump point (B). The dust

collector dump point after installation of the shroud (C).

77

Typical dust collection system used by small crawler or "buggy‖ drills.

3. Haul Road Dust:

- To water all haul roads

- Tankers

- Water sprinkler system

Water alone may not be effective:

- Water retention on haul road is skin deep

- High heat, low humidity and high wind speed may affect retention of water on roads

- Dust binding capacity of water is poor

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Alternative to water:

- Use of Hygroscopic salts

Retains water for long duration thus reduce water requirements

Salt brines- effective but cause problems with vegetation, ground water or surface water

Calcium/Magnesium Chloride powder

- Use of Oil-Water emulsions:

Help to consolidate dust but do not penetrate deep and may cause slipping of equipment on roads

- Starch based absorbents:

More effective

- Absorbs water 100-150 times its weight

- Swells in water and gets immobilized on road surfaces for a period of 3-6 months

79

80

Example of haul road dust from a typical mine haul truck

81

Cross section of haul road

82

Water truck equipped with a front water cannon and rear water sprays

83

Various types of manufactured fan spray nozzles for use on a water truck.

84

Respirable dust concentrations measured from haul road after water

application occurred at 10:00 a.m.

4. Transport:

- Use enclosed vehicles for dry material

- Use of rigid fiber glass covers/ tarpaulins

- Use of chemical binder sprays to form resistant surface crust

85

86

Types of fugitive dust emissions from conveyor belts.

87

Typical dust curtain used at the entrance and exit of the chute

enclosure.

5. Crushing, handling etc:

- Use of water sprays

- Reduce height of fall material

- Enclose transfer points

- Use of dust collectors: Principles of dust collection:

- Gravity

- Centrifugal force

- Inertia

- Filtration

- Electrostatic attraction

88

89

Illustration of a wet dust control approach with partial enclosure at a crusher

dump loading operation. Note the blue "fan patterns" signifying water sprays.

90

Illustration of a dry (exhaust) dust control system with a partial

enclosure at a crusher dump loading operation.

91

Illustration of a dry (exhaust) dust control system at the discharge of a

jaw crusher onto a belt conveyor.

92

Illustration of a dry (exhaust) dust control system on a vibrating

screen.

CONCLUSION:

• The nature of mining involves disturbing the ground,

removing and handling soil and rock, and the

subsequent transport, dumping, crushing and processing

of this material. At all stages there is some potential to

produce dust. Best practice environmental management

requires considering this issue during mine planning,

operations and at mine closure.

• The dual concerns of occupational health and the air

quality near the mine require careful management. For

mines located in dry or windy environments, the issue

becomes more challenging.

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• In some situations the dust produced during mining may

contain hazardous substances and this clearly requires

special consideration. Even where dust does not contain

harmful constituents, it may still represent a potential

threat to the health of mine workers if concentrations in

the work environment are allowed to exceed certain

levels.

• From the standpoint of environmental impact, the main

concern is the potential of dust to be released off-site

and to affect the surrounding environment and general

environmental amenity. The impact on environmental

amenity is the most common issue relating to dust

generated from mining operations.

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• In recent years, tools have become widely available that can greatly

assist in the control and management of dust. Modelling techniques

can predict dust impacts at the planning stage. The various mine

dust emission sources can be estimated quantitatively, thus allowing

control efforts to be applied systematically.

• Technological developments in monitoring techniques have

provided the means to accurately measure ambient dust levels. So-

called 'real-time' dust monitors are able to supply rapid feedback on

dust levels to the mine operators. This information can alert mine

personnel to high dust events in a timely manner, allowing

adjustments to mine operations. Such information can also be

directly linked to wind information, giving an indication of

contributing dust sources .

• Clearly, the level of effort and expense that is applied in the control

of dust will vary depending on circumstances. Each mine will have a

unique set of conditions, and the appropriate solutions are not

necessarily available 'off the shelf'. Nevertheless, success can be

achieved using a wide range of methods, and the range of available

of dust control techniques continues to develop and improve. 95