Control of

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Control of
FINES DUST
and
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Introduction
Dust is a general term fine particles that are
suspended 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 meter (? g/ m3 ).
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Introduction contd.
There are several sources of mine dust production
and dispersal, which occur during rock breakage,
loading and transport.
Dust emissions by blasting are of concern to both
mine operators and surrounding communities.
Blasting, is one of the operations that is
carried out in most mines, and may produce very
large quantities of dust. The dust cloud can be
raised to substantial heights depending on the
blasting parameters.
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Introduction contd.
The quantity of dust produced, and the effects of
its dispersal depend substantially on geological,
blasting and meteorological conditions.
Most of the dust settles in and around mining
area, although some may be dispersed to long
distances before settling down. Some of the
settled dust is raised again by mining activities
such as moving vehicles.
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Introduction contd.
A limited number of studies only have been
carried out to study the amount of dust produced
during blasting, its dispersal, and the
quantification of the amount of dust reaching a
particular area.
Efforts are needed to understand the process of
dust generation and dispersion, and the steps
that need to be taken to reduce its generation
and the dispersal of fines and dust.
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FINES

• Poorer fragmentation results in boulders and
  also generation of fines thus affecting the
  economy of blasting and
• Excessive fragmentation leads to the generation
  of a significant proportion of fine material.

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• Fines are the finest fraction generated in
  quarries/mines, a material for which there may
  not be much use.
• This fraction often becomes both on environmental
  issue and an economical loss for the producers
• Fine coal is
• Difficult to handle,
• Suffers low yield,
• Carries excessive moisture and
• Often attracts a lower sales price

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DETERIMENTAL EFFECTS OF FINES

• Poor Excess Poor Increased
  Reduced
• blast fines digging
  downtime of production
• shovel-dumper
• operation
• Water spray for dust suppression
• Mix-up with Dust Wet ore
• lumps
• To crushing
• plant
• Reduction in
• price of production Reduction in feed Bridging
  of
• due to poor quality rate to crushing ore at
  grizzly
• plant ore pass
• Tarnish company Reduced overall
• image recovery

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DUST
Dust due to blasting is a major problem
DUST REMAINS SUSPENDED FOR LONGER PERIOD THEN
VISIBLE
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• Dust is a general term-fine particles that are
  suspended 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 meter (? g/ m3 ).

• Dust formation usually occurs with mining
  activity initiated by the disturbance of
  particles e.g. blasting.
• 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.
• If blasting is appropriately designed much of
  dust formation and dispersion can be controlled.

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Dust generation and dispersal can be controlled
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• A sound knowledge of blast mechanism and
  related science is required
• a) to understand the breakage mechanism in the
  immediate vicinity of the charged section of the
  blast hole (the origin of fine particles
  generation)
• b) The influence of explosive properties, priming
  methods, rock properties, blast geometry and
  delay timing on the occurrence and extent of the
  fracture process.
• c) To achieve the goal of reduced fines
  generation, use proper explosive type, blast
  parameters, initiation sequence, charge
  distribution need to be tailored in such a way to
  produce optimum size distribution of fragments

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Correlation Between the Hole Diameter, Charge
Length and the Amount of Fines

• Four blasts were carried out in anorthosite with
  diameters of 76, 89, 102 and 114mm. The specific
  charge was, for all blasts, 0.623 kg/m3 and the
  number of holes varied accordingly. The result
  was an increase of the amount of fines (0-4mm),
  in production scale, by 18 for every half-inch
  increase in borehole diameter. The total increase
  was as high as 53 when the 76mm borehole was
  compared with 114mm one
• (Kristiansen,1995)

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BURDEN

• The quasistatic type of crushing, produced by
  high gas pressures on the walls of adjacent
  redial cracks increases as burden increases
  beyond the optimum burden (for which total
  operating costs are a minimum)
• Close to hole crushing is much higher for very
  small burden

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SPACING

• If the optimum burden is exceeded, then the
  amount of fines is increase
• If the hole spacing is increased and the burden
  kept the same, the fines generation decreases
• increase in burden and decrease in spacing lead
  to more fines

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SUBDRILLING

• If subdrilling is increased beyond the required,
  then the explosive energy is given more time to
  fragment the rock, more fines are produced

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STEMMING

• Stemming influences the fines generation in two
  ways
• Increased stemming length means explosive energy
  has increased time to work and thus produce more
  fragmentation, whereas it also reduces length of
  explosive column thus fines are reduced. However,
  increased stemming length means more boulders

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Shape and Size of Blast

• The length to width ratio should be at least 3.0
  if possible, because the blast has to be given
  the space to move forward without sealing the
  back rows. If a row is not allowed to move
  forward, the explosion gases are trapped for a
  longer time and unnecessary fines are generated.
• The bench should be wide and shallow, not short
  and deep

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SPECIFIC CHARGE

• Generally an increase in specific charge would
  yield an increase in fines.
• By decreasing the charge factor to an optimum
  value, fines could be reduced to 36.5 whereas a
  higher charge factor increased fines production
  to 64.45

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DECOUPLING

• The amount of fines can be reduced by decoupling
  (by providing an annulus of air between the
  charge and blasthole wall) because the borehole
  pressure becomes lower
• Decoupling can be achieved either by using
  cartridged explosives or by placing the bulk
  explosives inserted in the hole

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DECKING AND STEM PLUGS

• Charges are decked by separating portions of the
  explosive columns with drill cuttings or air
  pocket deck charges.
• When air decked, considerable reduction can be
  observed in the amount of fines generated
• Stem plug makes considerable
• difference

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DELAY TIME

• If fines are to be minimized, the rock in front
  of a row must be loosened before the next row
  behind it starts to move.
• The amount of fines rises with shorter delay
  times and a greater number of boreholes

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INITIATION SEQUENCE

• In a V-type initiation effective burden is
  considerably less than drilled burden distance.
• The reduction allows displacement of rock with
  ease. Because of lower inertia of the smaller
  burden, less crushing.
• The effective burden also effectively changes
  delay interval thus causing easy movement of rock
  between holes thus does not allow increase in
  fines

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Dust generation and dispersion Controlled by
Blast design and execution Stemming
material Down the hole initiation
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FRAGMENTATION PHOTO ANALYSIS

• Input Image
• Automatic Edge Detection
• Net Creation
• Block Unfolding Sizing and Counting
• Histogram
• Cumulative Size Distribution Curve

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• Fragmentation Analysis Information
• Data from Fragmentation Analysis Software
• Field Photographs
• Fragmentation Analysis Photographs
• Digging Condition at Face

Blast No. 3
Blast No. 3
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India Blasting video
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Introduction contd.
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.
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Design
If blasting is appropriately designed much of
dust formation and dispersion can be controlled.
This requires a sound knowledge of blast
mechanism and related science

• The breakage mechanism in the immediate vicinity
  of the charged section of the blast hole (the
  origin of fine particles generation).
• (b) The influence of explosive properties,
  priming methods, rock properties, blast geometry
  and delay timing on the occurrence and extent of
  the fracture process.

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Sampling Results
What points need to be mentioned regarding
these? These are aditya data.
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Experiments at Jaisalmer
Diameter 120 mm
Depth 4.0 5.0 m
Spacing 3.0 m
Burden 2.5 m
Charging ANFO a column charge and aluminized
slurry explosive as bottom charge.
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Jaisalmer video
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Details of Experimental Blast
Explosive Used RAJBLAST RAJBLAST RAJBLAST ANFO RAJBLAST ANFO RAJBLAST ANFO WATER BAG SAW DUST
Average Burden (m) 2.27 1.93 2.44 2.42 2.62
Average Spacing (m) 2.83 2.10 2.19 2.85 2.08
Max. Charge Per delay 103.80 66.48 53.56 298.32 44.30
Average Throw (m) 5.80 7.43 6.00 9.00 5.95
Average Back break(m) 1.37 1.66 1.64 1.85 1.01
Average over On side break (m) 0.65 0.85 1.77 1.80 1.66
Average Fragments size (mm) 727 755 275 317 106
Powder factor 6.42 5.00 6.81 8.23 6.48
Fragmentation Not Good Not Good Good Good Good
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Blast observations
Blast No. 1 2 3 4 5
Average burden (m) 2.27 1.93 2.44 2.42 2.62
Average spacing (m) 2.83 2.10 2.19 2.85 2.08
Max. charge per delay 103.8 66.48 53.56 298.32 44.20
Explosive charge Rajblast Rajblast Rajblast ANFO Rajblast ANFO Rajblast ANFO with sawdust water bag
Average fragment size (mm) 727 755 275 317 106
Powder Factor 6.42 5.00 6.81 8.23 6.48
Fragmentation Large boulders and finely crushed Large boulders and finely crushed Uniform fragmen-tation Uniform fragmen- tation Uniform fragmen- tation
Rajblast is cap sensitive aluminised slurry
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Fragmentation Analysis
Blast No. 1 Cartridged slurry Rajblast charge
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Fragmentation Analysis
Blast No. 2 Cartridged slurry Rajblast charge
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Fragmentation Analysis
Blast No. 4 Cartridged slurry Rajblast bottom
charge and ANFO as column
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Fragmentation Analysis
Blast No. 5 Cartridged slurry Rajblast bottom
charge and ANFO mixedwith saw dust as column and
with water bags in stemming
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Sampling Results
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Sampling Results
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Sampling Results
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Ball filled with water
High tensile, non-brittle plastic balls were used
in the stemming column.
Ball filled with water
The ball works as a lock or obstruction to the
blow out of stemming material for a little while
longer.
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Water ball in stemming
The balls have been filled with water when the
ball breaks it sprays water, which moistens dust
and thus reduces dust dispersion.
Placing ball filled with water in a blasthole
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Placing the water filled ball
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Water filled ampoule in stemming
The blasthole liner is filled with water and
formed into cartridge shape.
Diameter 89 mm Length 0.8 m
Effective in providing confinement as water is
incompressible and also in reducing dust.
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Water filled ampoule in stemming
These are placed as the last ½ m of stemming.
This is done to avoid damage to ANFO in case of
incidental breakage of ampoule and damage in the
column.
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Water filled ampoule in stemming
In this blast five blastholes were without water
ampoules and five blastholes were with water
ampoules.
The ejection of detonation gases was reduced when
water ampoules were used, which resulted in
better and uniform fragmentation.
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Water sprinkling of area surrounding the blast
If soil, fines and dust is moist then it may not
get airborne easily.
The area surrounding the blast were thoroughly
sprinkled with water before charging the
blastholes.
This dust prevents dust settled out during
previous operations from becoming airborne.
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Conclusions
Measurement of dust falling from moving plume is
difficult task, which is affected by wind
direction, velocity and other parameters.
The atmospheric carries dust much longer then the
visible dust plume.
Several steps can be taken to reduce generation
of fines and dust by optimizing blasting
parameters.
Dust dispersal can be controlled to some extent
by use of water filled ampoules and water filled
plastic balls in the stemming.
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Dust Dispersal After Surface Mine Blasting

• Dust released after blasting and its dispersal
  needs to be studied
• Modelling of Near Source Dispersal of SPM in
  Planetary Boundary Layer
• Respirable dust sampling and meteorological
  conditions

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Software Details
Blast data, atmospheric data and ground contour
data
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Software Details
Temperature, Pressure, Humidity parameters and
coefficient of ground profile
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Software - One
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Software - Two
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Software - Three
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Software - Four
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Software - Five
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Experiment Site Details
Sites Birla, Aditya and Jaisalmer.
Mineral Unit of Quantity No. of Mines Quantity Labour
Limestone 000 t 557 145552 19621
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Layout of Instruments for measurement
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Birla Cement Works
Diameter 165 mm
Depth 8.0 m
Spacing 6.0 m
Burden 5.0 m
Charging 25 cap sensitive explosive and 75.
Bottom initiation using Excel or Raydet systems
are adopted and air decking techniques practiced.
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Birla video
Mining operations are very close to the
residential areas.
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Sampling Results
Answer awaited What points need to be mentioned
regarding these? What do these measurement show?
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Difficulties with field measurement
Incorrect identification of central line of plume.
Uneven surface levels of instruments 1,2,3,4 and
5.
Incorrect assumption of uniform dust distribution
in the vertical column.
Incorrect rate of suction leading to erroneous
dust weight.
Distance of power supply to the instruments (gt
100 m) then the voltage reaching is quite weak.
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Difficulties with field measurement
Wind direction, may sometimes, suddenly change at
the last moment, after the entire set of
instrument have been laid.
This may result in either partial dust capture or
no dust, at all, may reach to any of the five
instruments.
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Aditya Cement Works
Diameter 114 mm
Depth 9.0 m
Spacing 7.0 m
Burden 4.5 m
Charging ANFO a column charge and slurry
explosive as bottom charge.
Bottom initiation using signal tube method and
air decking techniques practiced.
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Aditya Cement Works
Variable Strata
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Aditya video