Particle size
is of the
essence when it
comes to dust
suppression and
its importance
can never be
underestimated.
Wet dust
control in
particular
involves fine
atomized mist
of water used
at elevated
pressures to
coat buoyant
dust
nanoparticles
that are
already
airborne whilst
in the process
enlarging the
particle size
resulting in
settlement
owing to
gravity. We do
mention water
very sparingly
and just as a
common example
as it is not
the only wet
dust
suppressant
available but
can be combined
with other dust
palliatives
such as
surfactants and
amphiphilic
liquid polymers
that can
enhance its
dust control
properties. The
importance of
dust
suppression can
be critically
highlighted in
how respirable
and inhalable
dust
nanoparticles
can by-pass the
respiratory
system and
enter the lower
respiratory
tract.
Depending
length and
frequency of
exposure and
source of dust
nanoparticle it
can scar the
lung tissues
resulting in
pneumoconiosis
(coal) and
silicosis
(silica). The
article will
focus on dust
nanoparticles
and their
effect on
respiratory
system, their
sources,
targeted
methods of dust
suppression of
coal and
silica.
Dust
in the nano
range
The
size range of
particulate
matter varying
between 1 and
100 nanometers
are known as
nanoparticles.
Their very
small size
renders them
susceptible to
dislodgement in
the air and
remain
unnoticed and
dispersed for a
prolonged
period of time
as potential
highly
inhalable and
respirable
particles prone
to attach and
interact on the
alveolar
regions of the
lungs. The role
played by the
pulmonary
surfactant is
critical in
understanding
how exposure to
dust
nanoparticles
can lead to
deterioration
of pulmonary
function as
they are
capable of
reaching the
deepest regions
of the lungs.
Nanoparticle
size, surface
charge and
hydrophobicity
play a key role
in the extent
of damage that
can proliferate
in the
pulmonary
system. The
area of
interest in our
discussion is
alveolar region
consisting of
alveolar ducts
and sacs, which
are covered
with alveoli
that supply
oxygen to the
blood. The
alveoli that
coat the
surface of the
alveoli region
are blanketed
in a thin layer
of pulmonary
surfactant
which reduces
the surrounding
surface tension
and provides a
physical
barrier to
protect alveoli
from collapse
and particle
interaction.
Intricately,
highlighting
the biology of
the lung is to
emphasize the
importance of
why dust
suppression is
not a matter of
choice but a
must because
exposure to
dust
nanoparticles
can lead to
acute,
accelerated and
prolonged lung
disease which
can even lead
to loss of
life.
Reviewing
dust
generation
Origin
of dust can be
related to
larger masses
of the same
material
subjected to
mechanical
deterioration
and breakdown
processes.
Activities such
as stockpiling,
loading,
transportation
and mineral
processing
operations can
result in dust
generation. In
drilling and
blasting
operations air
flush from
drilling and
force of the
blast can
generate dust.
The dropping of
material from
height produces
dust in
loading,
dumping,
draglines and
conveyors. In
mine haulage
roads the dust
is generated
from transit of
mine trucks,
exhaust and
cooling fans
whereas in
storage piles
wind blowing
and high-speed
winds generates
dust particles.
Some processes
are more
prevalent than
the others
depending on
the type of
mine and
mineral that is
being produced.
In general, for
a particle to
be airborne it
is supposed to
have an
aerodynamic
drag force
larger than the
sum of the
particle weight
and the
interparticle
forces. The
smaller
particles such
as
nanoparticles
will behave as
a gas and are
influenced by
molecular
forces however
the larger
particles are
usually
affected by
gravitational
and inertial
forces. From a
health and
safety
perspective the
pivotal factors
chemical
composition of
the dust
particle, the
shape and mass
of particulate
matter in a
unit volume of
air
(mg/m3).
Coal
mining as an
example
They
are 76 known
elements in
coal some of
which are
potentially
hazardous to
human health.
Examples of
some elements
include
arsenic,
mercury and
lead. Coal also
consists of
mineral matter
and there are
about 120
minerals in
coal some of
which have
great impact on
human health.
The chemical
functional
groups found in
coal include
aromatic carbon
backbone
structures and
aromatic
carbon-hydrogen
structures.
Also present
are aliphatic
chains,
hydroxyl,
carboxyl and
carbonyl
groups. The
most important
chemical
component in
coal are free
radicals which
by nature have
great
reactivity
which is
beneficial to
energy
utilization but
at the
detriment of
human health
owing to
diseases such
coal workers
pneumoconiosis.
Effectively,
surfactants are
used to make
water work when
it comes to
coal dust
suppression.
The hydrophobic
nature of coal
requires
improved
wetting ability
of water hence
surfactants
lower the
surface tension
of water thus
enabling the
water particles
to attract coal
dust particles
through the
process of
agglomeration.
Most
importantly the
activated water
droplets should
be equivalent
to the size of
the coal dust
particles so
that the fast
and buoyant
coal dust
particles do
not flow around
them. Making
water work also
comes with the
incentive of
using less
water.
Silica
and
Silicosis
They
are various
forms of silica
and these
silica
nanoparticles
pose
significant
health risks to
the human
respiratory
system leading
to silicosis
and lung
cancer. Silica
toxicity is not
fully
understood but
owing to the
nanoscale size
of some silica
particles
studies
postulate that
interactions
occur between
silica
nanoparticles
and the lung
surfactant. In
order to
achieve
effective
silica dust
suppression it
is key to
determine the
size, surface
charge and
hydrophobicity
given the wide
spectra of the
types of
silica. The
dust
suppression of
silica dust can
be effective on
assessment of
the determinant
factors which
for example a
hydrophobic
surface would
be best
controlled
using an
amphiphilic
dust
suppressant
such as
versatile
liquid polymer
or surfactant.
Given particle
size
considerations
the choice of
dust
suppressant
should also
factor in the
mechanism of
action. If
buoyancy is
what you intend
to tackle then
the particle
size of the
dust
suppressant
should match so
that it can
become
effective. In
cases were the
silica dust
surface is
hydrophilic
then a
hydrophilic
dust
suppressant
will increase
with wetting
capabilities of
the dust
suppressant
therefore
increasing
efficacy of
dust
suppression.
Size,
shape and
charge
Respirable
particles of
dust are a
critical size
that matters
because if
ignored they
have the
potential to
cause pulmonary
damage which
can lead to
silicosis, coal
workers
pneumoconiosis
and eventually
loss of life
due to chronic
ailments such
as lung cancer.
Mining
activities
ranging from
shearing,
excavation,
stock piling,
haul mine
transit just to
mention but a
few contribute
to the
generation of
dust
nanoparticles.
The shape, size
and surface
charge of the
dust particles
govern the mode
of dust
suppression to
be utilized.
The rationale
behind the use
of similar size
molecules to
bind the
suspended dust
nanoparticles
is to enable
the combined
size to force
the particles
to settle under
its own weight
owing to
gravity. Coal
and silica dust
nanoparticles
matter because
failure to
suppress them
using targeted
and effective
dust
suppression
methods can put
mine workers
lives at
serious risk
owing to build
up of inhalable
and respirable
coal dust in
the
lungs.
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