Control of FINES DUST and

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 ).

Dust emissions by blasting are of concern to both mine operators and surrounding communities. Introduction contd. There are several sources of mine dust production and dispersal, which occur during rock breakage, loading and transport. 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.

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.

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.

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.

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

Poor Excess PoorIncreased Reduced blast fines digging downtime of production shovel-dumper operation Water spray for dust suppression Mix-up with DustWet ore lumps To crushing plant Reduction in price of productionReduction in feedBridging of due to poor qualityrate to crushingore at grizzly plantore pass Tarnish companyReduced overall imagerecovery DETERIMENTAL EFFECTS OF FINES

DUST Dust due to blasting is a major problem DUST REMAINS SUSPENDED FOR LONGER PERIOD THEN VISIBLE

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.

Dust generation and dispersal can be controlled

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

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, 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)

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

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

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

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

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

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

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

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

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

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

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

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

Blast No. 3 Fragmentation Analysis Information  Data from Fragmentation Analysis Software  Field Photographs  Fragmentation Analysis Photographs  Digging Condition at Face

India Blasting video

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.

If blasting is appropriately designed much of dust formation and dispersion can be controlled. (a)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. This requires a sound knowledge of blast mechanism and related science : Design

Sampling Results What points need to be mentioned regarding these? These are aditya data.

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.

Jaisalmer video

Details of Experimental Blast Explosive UsedRAJBLAST + ANFO RAJBLAST + ANFO RAJBLAST + ANFO + WATER BAG + SAW DUST Average Burden (m) Average Spacing (m) Max. Charge Per delay Average Throw (m) Average Back break(m) Average over On side break (m) Average Fragments size (mm) Powder factor FragmentationNot Good Good

Blast observations Blast No Average burden (m) Average spacing (m) Max. charge per delay Explosive chargeRajblast* +ANFO Rajblast* + ANFO Rajblast* + ANFO with sawdust + water bag Average fragment size (mm) Powder Factor FragmentationLarge boulders and finely crushed Uniform fragmen- tation Uniform fragmen- tation * Rajblast is cap sensitive aluminised slurry

Fragmentation Analysis Blast No. 1: Cartridged slurry Rajblast charge

Fragmentation Analysis Blast No. 2: Cartridged slurry Rajblast charge

Fragmentation Analysis Blast No. 4: Cartridged slurry Rajblast bottom charge and ANFO as column

Fragmentation Analysis Blast No. 5: Cartridged slurry Rajblast bottom charge and ANFO mixed with saw dust as column and with water bags in stemming

Sampling Results

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.

Water ball in stemming Placing ball filled with water in a blasthole The balls have been filled with water; when the ball breaks it sprays water, which moistens dust and thus reduces dust dispersion.

Placing the water filled ball

Water filled ampoule in stemming Diameter : 89 mm Length : 0.8 m The blasthole liner is filled with water and formed into cartridge shape. Effective in providing confinement as water is incompressible and also in reducing dust.

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.

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.

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.

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.

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  L H

Software Details Blast data, atmospheric data and ground contour data

Software Details Temperature, Pressure, Humidity parameters and coefficient of ground profile

Software - One

Software - Two

Software - Three

Software - Four

Software - Five

Experiment Site Details Sites: Birla, Aditya and Jaisalmer. MineralUnit of Quantity No. of Mines QuantityLabour Limestone000 t

Layout of Instruments for measurement Blast point Wind Direction

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.

Birla video Mining operations are very close to the residential areas.

Sampling Results Answer awaited: What points need to be mentioned regarding these? What do these measurement show?

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. Distance of power supply to the instruments (> 100 m) then the voltage reaching is quite weak. Incorrect rate of suction leading to erroneous dust weight.

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. Blast point Wind Direction

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.

Aditya Cement Works Variable Strata

Aditya video