AN being oxygen positive, is often used as oxygen supplier in addition to being an explosive base. It forms the explosive base in ANFO (Ammonium Nitrate – Fuel Oil) explosives,which are now widely used.

1. Useful Explosive & Blasting Agent
for modern day Blasting
Author: Partha Das Sharma, B.Tech (Hons.) in Mining Engineering,
E.mail: sharmapd1@gmail.com, Blog/Website: http://miningandblasting.wordpress.com/

2. Needed for an explosion..
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3. Ammonium Nitrate (AN)
An is a weak explosive base, its explosion
temperature being 1130 degree centigrade.
2NH4NO3 → 2N2 + 4H2O + O2 + 378 cal/g.
It being oxygen positive, is often used as
oxygen supplier in addition to being an
explosive base.
It forms the explosive base in ANFO
(Ammonium Nitrate – Fuel Oil) explosives,
which are now widely used.
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4. ANFO
Ammonium Nitrate / Fuel Oil
Ammonium Nitrate Production
Reaction of anhydrous ammonia gas
and concentrated nitric acid.
After the reaction the AN solution is
about 83% concentration.
Excess water is evaporated off to leave
an AN concentration of 95 to 99.9%.
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5. AN Production cont’d
AN Solution is turned into prill.
A small percentage of water
is left in the solution when the
prill is formed.
When the prill is dried the
water is removed and it
leaves voids in the prill.
This is where the diesel fuel
goes when added to the prill.
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6. AN Prill manufacturing Schematic
VAPOURISED AMMONIA 83% - 86% AN solution
AQUOUS NITRIC ACID
Evaporator
Industrial or Blasting grade
Prilling Tower
Prilled at 96 -
97% Melt
Dryer
Pre-Dryer
Cooler
To Storage Coater Screen
Over-size & Fines to
recycle
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7. AN Prill manufacturing
Blasting grade AN prills are made by spraying
molten AN into a prilling tower.
Droplets fall under carefully controlled cooling
conditions.
The AN solidifies while falling, taking on an
approximately spherical shape of relatively
uniform size.
Prilling tower conditions must be such that will
produce a "porous" prill that will absorb the
proper amount of fuel oil (6 percent by weight).
High density prills will not properly absorb the
fuel oil and blasting performance will suffer
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8. Properties of explosive-grade prill
Properties important for explosive-grade AN
prills are:
Low clay content,
Low moisture content,
Free-flow sizing,
Oil absorbency,
Low particle density,
Good friability and
Non-caking consistency.
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9. Temperature Cycling of AN
AN responds to temperature changes by
changing its crystalline structure.
The phenomenon is called Cycling.
The two temperature at which cycling
occur under normal condition are 0 and
32 degree C.
Therefore, product stored over four
seasons or in tropical atmosphere
undergo some degree of cycling.
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10. Thermal and Moisture stability of
AN
In addition, AN is hygroscopic; can attract
moisture from atmosphere and slowly
dissolve itself.
For this reason, blasting grade prills have
some protective coating which offers some
amount of water resistance.
When AN prill has been exposed to both
humidity and temperature, crystalline
structure changes, this is the first cycle.
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11. Thermal and Moisture stability of
AN cont’d…
After AN has undergone more than one
cycle, the waterproof coating is broken;
moisture deteriorates prills.
Therefore, performance of cycled AN prills
will not be consistent.
Some AN prill manufacturers claim to have
technology which gives Thermal stability to
the prills, thereby deterioration is checked.
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12. Thermal and Moisture stability of
AN cont’d…(Storage)
The major problem associated with the storage of Ammonium
Nitrate (AN) are hygroscopicity, thermal stability and caking.
AN must be protected in storage from rain, high humidity, to
prevent caking or in more extreme conditions, total
breakdown of product due to phase transition because of
change in storage temperature.
Caking of AN is prevented by coating the finished product with
inert dust and / or a surfactant and by adding an inorganic salt
or nucleating agent (a stabilizer to prevent the prills
breakdown – Nucleating agents are fine particulate material
which when added to AN melt provide nuclei for crystal
growth and prevent super-cooling which leads to growth of a
small number of large crystals) to the melt prior to prilling.
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13. General specifications of explosive-
grade AN
For good blasting-grade prills size distribution
roughly between 6 and 20 mesh.
Good blasting-grade prill is porous, which
enables it to readily absorb and hold correct
amount of fuel oil (about 5.7%).
Oil is distributed throughout the prill particle,
improving detonability of the ANFO mixture.
The ability of oiled prill to be detonated depends
on the density of prills. Dense prills often are not
detonable, or if initiated, perform at very low rate
of detonation.
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14. AN as blasting agent and AN based
explosives
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15. ANFO Characteristics
ANFO Density ranges from 0.82 - 0.90 g/cc
Oxygen Balanced @ 94.4% AN / 5.6% Fuel
3NH4NO3 + CH2 → 3N2 + 7H2O + CO2.
Under fueling leads to:
Greater sensitivity.
Drastic loss of ENERGY.
Orange smoke, inefficient reaction during
detonation.
Over fueling leads to:
Loss of Energy.
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16. Effects of Fueling on Fume
Production
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17. Effects of Fueling on Fume
Production
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18. Effects of Fueling on Energy
Output
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19. ANFO and VOD
ANFO VOD increases as the borehole diameter
increases.
Borehole Velocity of ANFO
16000
14000
V D(ft/sec)
12000
10000
8000
6000
O
4000
2000
0
1 2 3 4 5 6 7 8 9 10 11 12
Borehole Diameter (inches)
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20. ANFO Characteristics
The critical diameter of poured ANFO is
about 2.0 – 2.5 inches.
Under this it will not detonate.
If it is loaded pneumatically the critical
diameter can be increased to 1.0 inch.
ANFO is considered a ‘Blasting Agent”
This means it cannot be detonated with a #8
strength detonator when unconfined.
It requires a primer assembly to be initiated.
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21. ANFO Characteristics
When ANFO detonates it does so
inefficiently.
This produces excess gases from the
reaction.
This is a benefit to blasting due to the rapid
expansion of the gases out into the formation
creating a “heave” effect.
This heave effect allows for easier digging
and better throw.
PARTHA DAS SHARMA
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22. Fertilizer grade VS Explosive grade
AN prills for ANFO
Often Fertilizer grade AN prills are used as ANFO for blasting
purpose.
Blasting prill considered a porous prill which better distributes the fuel
oil and results in much better performance on blasting job.
Difference in properties of Fertilizer and Blasting prill:
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23. ANFO Characteristics cont’d..
ANFO is not waterproof or even resistant.
ANFO can deflagrate if a significant amount
of water has damaged the ANFO.
ANFO can fail to detonate if water has
damaged enough ANFO in the hole.
If the ANFO shoots “low order”, it shoots
inefficiently and produces excess gases.
Orange fumes!
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24. Emulsion
Water solutions of oxidizers in an oil medium (water-in-
oil emulsion).
A mixture of two or more immiscible liquids in which one
is present as droplets, of microscopic size, distributed
throughout the other.
In other words, emulsion explosives are the intimate and
homogenous mixture of two immiscible oxidiser and
fuels phases, stabilized with the help of emulsifier.
The internal phase is composed of solution of oxidiser
salts e.g. Ammonium Nitrate etc. dispersed as
microscopically fine droplets, which are surrounded by a
continuous fuel phase.
The emulsion, thus formed, is stabilized against liquid
separation by an emulsifying agent.
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25. Explosive Emulsion Anatomy
Oil continuous, “external”
phase (green) – 5 to 9%
Mineral oils
Diesel fuels
Recycled oils
Vegetable oils
Aqueous salt discontinuous,
“internal” phase (blue) – 91 to
95%
Ammonium Nitrate
Calcium Nitrate
Sodium Nitrate
Perchlorates
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26. Explosive Emulsion Anatomy cont’d..
A bulking/gassing agent – for density control, is then
dispersed thorough out the basic emulsion matrix.
The gassing agent can either be ultra fine air
bubbles or artificial bubbles from glass, resin or
plastic.
The bulking agents determine and control the
sensitivity of emulsion products – whether emulsion
is cap sensitive or booster sensitive.
Since its micro cell is coated with an oily exterior,
the emulsion has excellent water resistance
property.
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27. Characteristics of Explosive Emulsion
The output energy of emulsion is very near to
the calculated energy.
Viscosity of emulsion can be varied by
changing type of fuel oil used.
Therefore emulsion explosives can be made in
cartridge form of various sizes or can be used
as bulk explosive in opencast as well as in
underground workings.
The ultra fine air bubbles or artificial air
bubbles used as gassing agent acts as
sensitiser.
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28. Initiation of Explosive Emulsion
When initiating shock wave
applies to emulsion explosives
the ultra fine air bubbles gets
heated first and act as ‘Hot-
spots’ in emulsion having
very high temperature (about
1500 -1800 °C).
At this high temperature the
explosive reaction takes
place.
The resulting emulsion can
serve as detonable matrices
to carry solid fuels such as
Aluminium powder, prilled AN
etc.
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29. Properties of Explosive Emulsion
Emulsion explosives are much better water resistant than water
gel slurry or ANFO; as oil phase is at outside i.e., water phase is
enveloped within oil phase (Water – in – Oil emulsion).
Emulsion explosives are much safer to handle, use and store as it
is relatively insensitivity to detonation by friction, impact or fire.
Therefore, it is much safer than NG based explosives and enhances
safety standard of the workings.
High VOD can be obtained. VOD depend upon the oxidixer droplet
size (0.2 to 10 micron). Therefore, toughest rock conditions can
be tackled very effectively and efficiently without compromising
safety standard.
Critical diameter of emulsion explosives again depends upon droplet
size and sensitizer used.
Because of the intimate mixture between oxidizer and fuel, emulsion
explosives have higher energy than water gel slurries or ANFO
and it matches with energy level of Nitroglycerine based explosives.
Since Emulsion explosives are well oxygen-balanced, generates a
minimum of noxious fumes and far less smoke.
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30. Bulk Emulsion Characteristics
Typical density of a sensitized emulsion runs about
1.20 g/cc.
Loaded in diameters between 1and 12 inches.
VOD increases with Borehole Diameter.
Sensitivity/density can vary with the addition of
microballoons or chemical gassification.
Can be dead pressed when sensitized with
microballoons.
Can be classified as Oxidizer of Blasting Agent.
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31. Heavy ANFO Blends
Blends of ANFO and Emulsion
This is an attempt to increase bulk density of
ANFO and making the mixture a ‘repumpable’
consistency.
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32. Heavy ANFO Blends
Why blends are used?
Increase the density of ANFO; hence, increase
energy in the borehole
Provide water resistance to ANFO
Economic (price range between that of ANFO and
emulsion)
Reduce mining costs
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33. Heavy ANFO Blend Benefits
Longer sleep times with heavy blends.
Water resistance for ANFO in wet formations.
Pattern expansions.
Maximize energy in hole.
Drill cost savings potential.
More production per hole.
Less shots per cut.
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34. Heavy ANFO Blend Trucks
Bulk trucks for loading
of Heavy ANFOs are
designed to blend
components prior to
loading and provide
loading of emulsion or
ANFO alone, or a
combination of the two,
in varying proportions.
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35. Heavy ANFO Blend Densities
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36. Heavy ANFO Blend
Experiment has shown that the performance of Heavy
ANFO becomes sluggish as more emulsion is added
unless the emulsion has been sensitized by gassing or
microballoons.
It appears that in hard-rock performance will suffer when
there is more than 30 percent of un-sensitized emulsion in
the mix.
In softer formations greater percentages of un-sensitized
product can usually be employed because suitable
fragmentation of the rock depends to a greater degree on
heave energy.
The degree of non-ideal detonation introduced by the lack
of sensitization means that a greater degree of the total
energy is released as heave energy.
PARTHA DAS SHARMA
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37. Bulk Heavy ANFO explosives
A waterproof product is typically produced at
50 percent emulsion addition.
However, to obtain a product that can be
pumped reliably it is common to use a
waterproof Heavy ANFO containing 60 to 70
percent emulsion.
Such products should always be made with a
sensitized emulsion, or performance will
suffer.
PARTHA DAS SHARMA
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38. Bulk Heavy ANFO cont’d..
When waterproof heavy ANFO blend is loaded into
wet holes it should always be loaded from the
bottom up.
This is achieved using a bulk truck with a hose that
can extend to the bottom of the blasthole.
The product is pumped through the hose.
The hose is retracted as loading proceeds, but is
always kept in the explosive.
The water rises on top of the advancing column of
more dense explosive.
Mixing does not occur if the loading is carefully
performed.
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39. Bulk Heavy ANFO cont’d..
When Heavy ANFO is augured into wet holes it
spatters on impact with the water, and prill goes into
the solution.
Water is mixed into the explosive column.
Bridging may occur with portions of the explosive
column separated by a water gap.
Since the gap sensitivity of these products is not
large this may lead to the failure of a portion of the
explosive column to detonate unless it happens to
be primed on both sides of the water gap.
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40. Specifications of the ANFO and
the Heavy ANFO Blend
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41. Author’s Bio-data
Author’s Bio-data:
Partha Das Sharma is Graduate (B.Tech – Hons.) in Mining Engineering from IIT,
Kharagpur, India (1979) and was associated with number of mining and explosives
organizations, namely MOIL, BALCO, Century Cement, Anil Chemicals, VBC Industries,
Mah. Explosives etc., before joining the present organization, Solar Group of Explosives
Industries at Nagpur (India), few years ago.
Author has presented number of technical papers in many of the seminars and journals on
varied topics like Overburden side casting by blasting, Blast induced Ground Vibration and
its control, Tunnel blasting, Drilling & blasting in metalliferous underground mines,
Controlled blasting techniques, Development of Non-primary explosive detonators (NPED),
Hot hole blasting, Signature hole blast analysis with Electronic detonator etc.
Author’s Published Book: "Acid mine drainage (AMD) and It's control", Lambert Academic
Publishing, Germany (ISBN 978-3-8383-5522-1).
Currently, author has following useful blogs on Web:
http://miningandblasting.wordpress.com/
http://saferenvironment.wordpress.com
http://www.environmentengineering.blogspot.com
www.coalandfuel.blogspot.com
Author can be contacted at E-mail: sharmapd1@gmail.com, sharmapd1@rediffmail.com,
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Disclaimer: Views expressed in the article are solely of the author’s own and do not
necessarily belong to any of the Company.
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42. PARTHA DAS SHARMA
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