|Imerys purchases of North American mica
plants, Kings Mountain and Suzorite, has added to its
operations in France and Feldspar Corp. in the USA.
The worlds largest industrial minerals group continued
its acquisition trail at the end of 2008 by purchasing two of
the worlds leading mica sources in North America, Kings
Mountain Minerals Inc in the USA, and Suzorite Mining Inc. in
Canada from Zemex Minerals Group (see IM November 08,
Through the acquisitions from Zemex Minerals Group Inc.,
Imerys purchased two of the most significant mica sources in
North America and some of the largest operations outside of its
Kings Mountain and Suzorite were added to mica operations,
The Feldspar Corp in the USA, and the 15,000 tpa Kaolin de
Bretagne and Feldspath du Morvan in France.
Imerys has not hidden its strategy to encourage
organic growth through leveraging process technology,
fundamental research and deep market intimacy, combined with
strategic acquisitions focused on growth in developing regions,
in addition to targeting the acquisition of new minerals
resources in developed countries.
These specific North American acquisitions gave Imerys the
full portfolio of mica grades which add to its present
industrial and specialty minerals such as ground and
precipitated calcium carbonate, hydrous or calcined kaolin,
perlite and diatomite.
Although mica is not nearly the most plentiful mineral used
in industrial applications it offers some unique and beneficial
functionality with excellent value propositions.
Mica is a name for a family of complex hydrous aluminium
silicates that have a sheet structure and exhibit almost
perfect basal cleavage. The two most common and commercially
available micas in use are muscovite and phlogopite micas.
There are other members of the mica family that are very
rarely encountered named Illites (hydrated mica), Sericites
(fine-grained white mica, an ill-defined material that falls
structurally between muscovite and illite) and have notably
been mentioned for use in body ceramics predominantly in
Nearly all economical deposits are mined for an array of
minerals and in most cases mica is a minor component by volume,
but is of key value, Imerys Suzorite phlogopite mica being an
exception to this.
Certain deposits are reported to be mined for mica only and
in these cases mica is encountered in lodes from low
concentration (India), to rather high concentration (China).
These deposits can encounter some drawbacks that make them
difficult to become economically viable and consistent over
The main complexities associated with these deposits is
their reduced size making it difficult to ensure a true
reliable mining plan, the need to use explosives and the
mandatory hand selection to cope with colour variation
generally seen inside the lodes, as well as the need to move to
underground mining in many cases.
Currently Imerys has a total of five deposits (see
map) of both muscovite and phlogopite. As part of Imerys
strategy those deposits are close to their customer base and
located in stable countries. Having such proximity to its end
users offers economies in freight and enables customers to
operate a lean just-in-time supply chain.
|Location of Imerys mica
From a process perspective Imerys uses mainly three routes
to separate and concentrate mica from ore. For altered rocks
the primary process routes used are floatation and wet
concentration (spiral) while hard rock use dry
concentration(crushing and magnetic separation).
To describe the main processes that lead to commercial
grades, the flow sheet provides a summary of various steps to
produce from the coarsest to the finest particle sizes and
their respective outlets on the market.
Deposits based on altered rocks, the run of mine is firstly
blunged, screened to remove the bigger stones and the
subsequent slurry obtained is further cycloned to remove the
fines primarily made of kaolinite or clays.
The overflow of the cycloning process feeds the wet
concentration, a low energy demanding step since it uses
gravimetric forces and is free from any chemicals. This spiral
step allows the concentration of the largest and purest mica as
the feed to floatation made of an assemblage of mica, quartz
and feldspars which ranges typically 200µm to 1mm.
Depending on the mica size liberated from the ore, the
spiral step may not be used and the overflow from cycloning
At this stage the mica obtained is concentrated from pure
muscovite to a grit level of 10-15% depending on the requests
from customers. Some grades named flake or coarse
mica are directly dried and sieved to ensure perfect top
cuts. These are used mainly for sound dampening, decorative
products and oil well drilling.
When final applications ask for a finer mica grade then the
mica concentrate will follow various milling, sieving and
aspect ratio transformations in order to match specifically the
characteristics expected by each market.
This size & shape transformation is either done in wet
(batch and continuous) or dry conditions depending on which
final properties we want to emphasize. Dry and wet ground micas
serve the bulk of the applications as described on the panel,
Some applications looking for very fine minerals (typically
d50 = 5µm) are served with micronised mica obtained
through jet air mill.
Last but not least, for some applications such as the
welding rods industry that are very sensitive to water/vapour
emission (either during their manufacturing step or in the
final end use) a further calcination step can be operated to
remove the natural 4-5% of loss on ignition contained in most
Wet v dry
This wet route, used for altered rocks, is currently being
used at 3 of Imerys 5 deposits, covering all muscovite
The dry route is less encountered worldwide at least when
dealing with industrialized assets. Imerys processes this way
both the muscovite from Burgundy and the Suzorite
The ore rock is crushed in jaw crushers and after having
being dried is further concentrated to obtain blocky mica (non
delaminated mica) and finely delaminated mica. This dry route
generates several different types of mica grades
differentiating themselves principally by their particle size
distribution and their aspect ratio.
Imerys produces one of the lowest bulk density (<200 g/l)
commercial grade available worldwide by utilising this dry
process with selected Imerys deposits, this can also generate
particularly high aspect ratio products also.
Imerys provides the suitable surface treatment needed to
enhance compatibility with certain polymer families. However
the trend is to see this processed being captured by
compounders as part of the know-how and their way to
differentiate from each other in their respective markets.
Imerys big five
The mineral specificity of each of Imerys five
deposits combined with a careful selection of the most
appropriate and state-of-the-art processing
equipments allows Imerys to cover any mica demand
Imerys global research and process development teams
are collaborate to leverage and develop new technologies and
Experience gained from recent product innovations, such as
Barrisurf, a high aspect clay for improved barrier properties
in water based coating, allows the group to expand the mineral
product portfolio and performance around key functional
With mica, perlite and vermiculite Imerys has a suite of
minerals for niche applications including fire protection and
Imerys Suzorite operation in Boucherville, Quebec
which produces phlogopite mica, by a process of continued
investment is described by the company as one of the most
modern and efficient mineral processing plants in the
As displayed in the panel, the applications where mica finds
an interest are numerous and thanks to the broad particle size
range and its unique delamination behaviour mica has few cost
|Different mica processing for different
Selecting mica for markets
Any particular markets or applications using mica in their
formulations to impart one or more of the properties, will
select one grade rather than another on the best cost
performance ratio of the expected technical benefit at the best
value (See Selection criteria panel).
Amongst criteria that contribute to usage value, all
applications have in common a high demand with regards to
particle size distribution: sharp top cut, limited to no fines
and steep distribution (tend as much as possible to
monodisperse). This not mentioning the utmost cleanliness and
consistency from one batch to the other.
However, against what is most often perceived, poor brightness
is not a definite barrier to any mica use. The vast majority of
paints & coatings applications - which is the largest
outlet for mica not considering the well-known US specificity
of mica into joint compound - is claiming for highest
brightness mica such as some very unique muscovite.
|Micas 2009 global market
Marine and anticorrosive paints, however, are not so
sensitive and many of the others applications will not take
into account this characteristic but will be very demanding on
the bulk density (sound dampening, fire retardant) or the
chemistry (welding rods) or the aspect ratio (plastics),
The bulk of plastic for automotive are dark to black colour
hence fully satisfied with phlogopite that complement ideally
fiber glass in a compounded formulation, not only by reducing
significantly the price per kg but also since its platy
structure reduces the presence of fibre at the plastic surface
as a source of possible defect once a paint layer is sprayed
onto the plastic piece.
Mica is not an easy mineral to sell due to the numerous
final applications and it requires a strong customer technical
support to match market needs.
Delivering a cost effective, high performance mica requires
close cross functional cooperation ranging from geologists,
process engineers, research and development scientists and
This additional support is where Imerys believes it
has the edge in the mica market and after adding Kings Mountain
and Suzorite is now the worlds leading producer.
Contributors: Julian Danvers, Doug Smith
and Richard Enos of Imerys SA.
As an overview, below is a listing of Imerys main
operations, the mica type mined and processing routes commonly
used to concentrate and mill micas.
Imerys mica locations
| Acid igneous rock : granite,
| pegmatites, alaskite, aplite.
| Appalachian Mountains (US)
|| Imerys Spruce Pine
| Burgundy (France) Imerys Feldspath du
| Liberated during the kaolinization
| of granite. Brittany (France)
|| Imerys Kaolins de Bretagne
| Kings Mountain (US)
|| Imerys Kings Mountain
| Georgia (US)
|| Imerys North America
| (Alkaline ultrabasic rocks)
| Suzor (Canada)
|| Imerys Boucherville
Muscovite v phlogopite mica
When comparing the two main grades of mica, muscovite and
phlogopite, the primary differences are:
- Muscovite is considerably more white and flexible than
phlogopite and as a consequence typically is used for more
colour sensitive applications
- Phlogopite is darker in shade and offers better heat
resistance than muscovite. It lends itself to high
temperature less colour sensitive applications. Of particular
interest is the unique very low bulk density and larger PSD
spectrum of Imerys Suzorite mica than any other
This being said, muscovite mica in particular can exhibit a
variety of different properties:
- Particle sizes are available across a very broad range
within a deposit, this determines what process is needed to
match the mineral purity and which particle sizes are
achievable in commercial products
- Lattice substitutions often vary from deposit to deposit
and as such can impart different behaviours in delamination,
flake flexibility, colour, etc
- Interlayer cations (primarily K) that are not evenly
bonded to both cleavage plan generate different levels of
- Associated minerals (kaolin, feldspar, quartz) within a
deposit contribute to the final properties of mica
The various substituting atoms have effects on the physical
properties of mica however Imerys technical expertise can
bring support to customers formulators when attempting to
substitute one mica for another, to ensure that functionality
is maintained or even improved in the application.
- Flexible & toughness
- lsotropic reinforcement, anti-cracking
- Thermal stabilty and LCTE
- Chemical inertness
- Barrier to gas, electrolytes and UV
- Vibration damping
- Electrical & Fire insulation
- Rheology, lubricity
- Whiteness, Brightness
- Aspect ratio & bulk density
- Particle size distribution
- Clear top cut