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Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.4, pp 329-338, 2009
jmmce.org Printed in the USA. All rights reserved
Mineralogical Characterization and Beneficiation Studies of Pyrophyllite
from Orissa, India
B. Das and J.K. Mohanty
Institute of Minerals and Materials Technology
(Council of Scientific and Industrial Research)
Contact: firstname.lastname@example.org and email@example.com
Mineralogical and chemical analyses of three textural varieties of pyrophyllite
samples collected from Baliadihi mine of Keonjhar district, Orissa, India are investigated.
Mineralogically they consist of quartz, pyrophyllite, altered feldspar as major minerals and
muscovite, chlorite, tourmaline, hematite etc. as minor minerals. The samples exhibit
compositional variation of SiO
65.56 - 71.66%, Al
18.79- 22.94%, FeO 1.13- 1.68% and
alkalis 3.24 to 6 %. Beneficiation studies using flotation technique has indicated that silica
can be reduced with concomitant increase in alumina and brightness from a raw pyrophyllite
sample which can be suitable for refractory purposes.
Keywords: Pyrophyllite, characterisation, flotation, brightness
Pyrophyllite is one of the most important industrial minerals having manifold uses.
Like talc, it is used in porcelain, building materials, fire-resistant material, insecticide,
textiles, detergents, cosmetics and the filler for rubberising, papermaking, painting etc. Due
to some intrinsic properties such as chemical inertness, high melting point and dielectric
constant and low electrical conductivity, pyrophyllite is useful in ceramic and refractory
applications. It can be used as refractory raw material because of low thermal conductivity
and coefficient of expansion, hot load deformation, excellent reheat stability, corrosion
resistance and low heat shrinkage. It requires lower firing temperature that reduces shrinking
and cracking and improves thermal shock resistance. Massive to coarsely foliated compact
pyrophyllite is suitable for refractory where as finely foliated variety is used in ceramic and
other industries. The massive variety which is marked as grade A is used as wares for
stacking graphite and solvent for the manufacture of synthetic diamond.
B. Das and J.K. Mohanty Vol.8, No.4
Finished product of pyrophyllite has a high degree of vitrification and good
mechanical resistance. It is also used as filler in plastics and rubber, wallboard, paint,
adhesives and roofing resins. Pyrophyllite has a neutral pH and is inert, nonabrasive with
good flowability allowing it to be used as a diluent, extender, carrier for liquids, fungicides,
herbicides and fertilisers. It is used as additive in lubricants and foundry mould coatings.
Pyrophyllite is an early stage metamorphic mineral and is actually quite common
although usually not very abundant as good mineral specimens. It is found as a constituent of
slate, phyllite, schist and other early stage metamorphic rocks. The specifications
recommended for various uses of pyrophyllite are shown in Table-1.
Table. 1 : Specification of pyrophyllite for different industries.
Use Oxide Wt%
Use Oxide Wt%
28 Min. Ceramic Al
60 Max. SiO
Alkalis <0.5 Fe
PCE 28 Min. TiO
Paper LOI 3 Max. MgO 0.5 Max.
15 CaO 0.5 Max.
Moisture 3 Min. Insecticide Fe
CaO 1 Max. LOI 6 Max.
Brightness >80 Acid
Pyrophyllite is a member of phyllosilicates or leaf silicates, which have a sheet-like
structure. The phyllosilicates form stacks of silicate layers that are composed of SiO
tetrahedrons. The sheets are not directly linked above or below to the next silicate sheets. In
Pyrophyllite, two silicate layers are sandwiched between gibbsite layers. Gibbsite is
composed of octahedral coordinated aluminium surrounded by six hydroxides. The gibbsite
layer (G) in pyrophyllite is identical to gibbsite structure except that four of the hydroxides
are replaced by four oxygens from the silicate layers (S). The overall structure of pyrophyllite
can be imagined as stacked S-G-S sandwiches. The bonding between these sandwiches is
nearly nonexistent and gives rise to softness and perfect cleavage in pyrophyllite. It has been
reported that the interlayer bonding forces between [SiO
] and [AlO
are Van der
Waals. Due to this weak force the surface of pyrophyllite is electrically neutral which give
rise to a moderate degree of natural floatability .
Pyrophyllite is a secondary mineral mostly derived from alteration of feldspar and has a
chemical formula of (Al
)OH. Though silica and alumina are the major constituents,
the common impurities are FeO, CaO, MgO, TiO
and alkalis. It occurs in all shades of
Vol.8, No.4 Mineralogical Characterization and Beneficiation Studies of Pyrophyllite 331
colour, particularly white, light grey, greenish pink, brown, buff and green depending upon
the presence of coloured minerals. Pyrophyllite is identical in physical properties to talc. The
two are isomorphous. Talc has magnesium instead of aluminium and is basically
indistinguishable from pyrophyllite without a chemical test for aluminium. It does not flux
when heated making it an efficient refractory material.
2. MODE OF OCCURRENCE
The pyrophyllite reserve of Orissa is around 10 million tonnes  and Orissa is a
major producer of pyrophyllite. Pyrophyllite occurs as small and large discontinuous
lensoidal to pockety outcrops spatially associated with Singhbhum /Bonai Granite. The
mineral bodies are mostly confined to hill slopes capped by Dhanjori quartzite of variable
thickness. Sometimes they are also seen forming isolated hills/knolls with/without quartzite
capping. Economic deposits of pyrophyllite in Keonjhar district, Orissa, India occur adjacent
to the western hillock stretching over a strike length of 90km from Rebna-Palaspal in south to
Dhobakuchuda-Balabhadrapur in the north more or less along a N-S trending lineament. The
main deposits are at Jaipur, Dhobakuchuda, Balabhadrapur, Anjor, Baliadihi, Madrangajodi,
Dalimpur, Nithigotha, Buriadihi, Sidhamath, Sarasposi, Ukchabeda, Roduna, Bolaniposi,
Rampakot, Rebna and Palaspal, all in Keonjhar district. Occurrences are also reported near
Manada, Joshipur and foothills of Similpal in Mayurbhanj district and Lahunipada in
Sundergarh district. Regular mining activity, mostly manual at a few places are going on.
Pyrophyllite usually occurs in the form of quartz pyrophyllite schist containing pockets of
massive granular pyrophyllite. The pyrophyllite is of lower grade in the lower level and high
grade in the upper level.
A comparison of low and high grade pyrophyllite is given in Table 2.
Table 2. Characteristics of high and low grade pyrophyllites.
Characteristics High grade Low grade
Colour Milky white Greyish white
Texture Massive to Coarse schistose Schistose
(medium to fine grained)
Feel Strongly soapy Moderately soapy
Hardness 1.5-2 2-3
CaO 0.28-0.56 0.28-0.42
MgO 0-0.20 Nil
O 0.38-2.36 0.4-0.51
O 0.04-0.30 0.06-0.12
B. Das and J.K. Mohanty Vol.8, No.4
LOI 2.86-3.90 3.46-3.66
% Pyrophyllite >95 90
%Quartz <2 7-10
%Tourmaline Trace Trace
%Opaque Trace Trace
3. MATERIALS AND METHODS
The pyrophyllite samples of different varieties were collected from a working mine at
Baliadihi, Keonjhar district of Orissa. Each sample was thoroughly mixed and a well
representative sample was drawn in each case for detail characterisation and beneficiation
studies. The run off mine samples were crushed and ground in the laboratory ball mill to
below 75 µm size in which the beneficiation studies were carried out. Chemical analysis of
different size fractions indicates that aluminium values are enriched in the finer fractions. The
grade of aluminium increases with decrease in particle size. Major and minor elements of the
bulk samples and the flotation products were analysed by X-ray florescence technique.
Microscopic and X-ray diffraction studies were carried out for the identification of
mineral phases present in the samples. A Leitz orthoplan transmitted light microscope was
used for the microscopic studies. The XRD study was carried out by automatic Philips PW
1750 unit using a scanning speed of 2
/min. in the range of 2Ø from 10 to 70
. The brightness
of the raw pyrophyllite and pyrophyllite roasted at 1200
C was measured by reflectance
meter taking MgO powder as standard (100 units).
subaeration flotation machine with one litre capacity was used for batch
flotation studies. Dodecylamine, a cationic reagent was used as the collector for the flotation
of pyrophyllite. All the flotation studies were carried out after stage crushing in jaw and roll
crusher followed by grinding in the laboratory ball mill. The flotation tests were carried out
after conditioning the sample with required amount of reagents for a predetermined time. The
agitation intensity, the pulp density and pH were controlled during the experiments. pH of the
slurry was maintained before the addition of the collector and monitored through out the
experiment. Dilute NaOH or HCl was added to regulate the pH value. All the flotation tests
were carried out at a fixed pulp density. The concentrates and tailings were collected
separately, dried, weighed and analysed for different constituents to assess the product
Pyrophyllite is a product of hydrothermal alteration of granite. The mineralogy of
pyrophyllite bearing rocks is almost similar to granite/altered granite. The results of
mineralogical study of different varieties of pyrophyllite bearing rocks carried out under
microscope are as follows.
Vol.8, No.4 Mineralogical Characterization and Beneficiation Studies of Pyrophyllite 333
4.1. Granular Variety
This variety exhibits a granular texture (Fig. 1). Irregular and anhedral coarse grains of
quartz and subhedral grains of altered feldspars are embedded in a matrix of pyrophyllite.
Comparatively coarse flakes constitute the matrix whereas the flakes of pyrophyllite within
altered feldspars are very fine grained. Finely pyrophyllitised subhedral grains are
pseudomorphs after feldspar. Orthoclase as relics within pyrophyllite is less altered. Both
quartz and feldspar grains are veined by pyrophyllite. Minor amounts of secondary biotite,
tourmaline, opaques and rutile are present. Pyrophyllitised feldspar grains near the margin are
rimmed by coarser muscovite. The mineral assemblage of granular variety can be put as
pyrophyllite + quartz + altered feldspar + muscovite + tourmaline + opaques.
Fig. 1. Irregular and anhedral coarse grains of quartz and subhedral grains of altered
feldspars are embedded in a matrix of pyrophyllite.
4.2. Schistose Variety
Minerals constituting the rock are pyrophyllite, quartz and muscovite ± chlorite.
Opaques are common in form of minute prismatic, skeletal and dusty forms. Accessory
minerals include secondary biotite, illite (yellowish coloured minute prismoids interfolial to
pyrophyllite), rutile (brownish/reddish coloured small euhedra and subhedra showing thick
borders), anatase (subhedral bluish coloured), tourmaline (prismatic) and sphene (rhombic
shaped). Pyrophyllite as coarse to medium flakes/laminae along with flaky muscovite imparts
pronounced schistosity (Fig.2). Quartz showing undulose extinction occurs as dilated,
elongated eye shaped, granulated/fractured grains in interfolial planes of flaky minerals.
Quartz grains when drawn elongated are aligned subparallel to the schistosity plane. Their
borders are denticulated due to replacement by pyrophyllite.
B. Das and J.K. Mohanty Vol.8, No.4
Fig. 2. Pyrophyllite as coarse to medium flakes/laminae along with flaky muscovite imparts
4.3. Slaty Variety
It is a cryptoscaly variety that forms a large bulk of the valley deposit, being
concordant with the schistose variety. Although in naked eye, very fine lamellae are
indistinct, under microscope cryptoscaly flakes are clearly visible. It is a pyrophyllite +
muscovite + quartz + tourmaline ± chlorite in which pyrophyllite and muscovite constitute
around 90% of the bulk. Secondary biotite, illite, rutile and opaques are present in minor
proportions. Pyrophyllite and muscovite are concordantly arranged to impart fine laminations
that are megascopically identified as crude slaty cleavages (Fig.3). They are characterised by
Fig. 3. Pyrophyllite and muscovite are concordantly arranged to impart fine laminations that
are megascopically identified as crude slaty cleavages.
The modal analysis data of three different petrographic varieties of pyrophyllite are
presented in Table 3.
Table 3. Modal analysis data of different petrographic varieties of pyrophyllite.
Variety Pyrophyllite Quartz Muscovite Chlorite Tourmaline Opaque
Granular 49-65 17-28 7-9 Nil 1-2.6 0.54-2
Schistose 56-61 17-26 8-18 2-10 0.25-1 2-3
Slaty 65-68 6-8 15-19 2 0.23-0.46 3-6
Vol.8, No.4 Mineralogical Characterization and Beneficiation Studies of Pyrophyllite
Petrographically the pyrophyllite bearing rocks are divisible into three major varieties.
Major minerals are pyrophyllite, quartz, muscovite with/without chlorite and tourmaline.
Minor to trace amounts of rutile, tourmaline, anatase, sphene, illite and kaolinite are present.
Modal analysis data reveal that slaty variety contains high amount of pyrophyllite compared
to the granular and schistose varieties. This variety also contains more muscovite (15-19%)
and lesser amount of quartz compared to the other two varieties. The granular variety contains
more free quartz that may be easily separated from pyrophyllite. Hence this sample was taken
for beneficiation study.
Brightness of pyrophyllite plays a key role in deciding its utility and value in different
industries. The brightness data of the different varieties are shown in Table 4.
Table 4. Brightness of different varieties of pyrophyllite .
Samples Sp.Gr. Brightness
Room temp 1200
Granular 1.62 69 80
Schistose 1.60 62 72
Slaty 1.61 54 66
From the study it is observed that by only firing the powder sample at 1200
C, there is
an increase in the brightness. The brightness of the sample depends on the impurity content in
the sample. The presence of quartz and coloured minerals such as iron-oxide-hydroxide,
opaques, chlorite, and micaceous minerals decreases the overall brightness of the material. So
it is important to reduce the coloured minerals and opaques from the raw sample to enhance
the brightness of the material.
4.5. Chemical Composition
As pyrophyllite is derived from granitic rocks by metasomatism/ low temperature
hydrothermal activity, the chemical composition of pyrophyllite is broadly similar to granitic
composition with slight variation depending on the degree of hydrothermal alteration. The
chemical analyses of the different varieties are given in Table 5.
Table 5. Major element composition (wt%) of pyrophyllite types (N=5).
FeO CaO MgO Na
Granular 67.88 20.87 1.59 0.64 0.67 0.96 3.98 2.66
67.12 19.32 1.68 1.55 1.50 1.40 4.60 2.20
Slaty 65.74 22.83 1.46 1.55 0.86 0.90 4.27 2.02
N= No of samples from each variety
B. Das and J.K. Mohanty Vol.8, No.4
From the above table it is observed that silica and alumina are two major constituents
of pyrophyllite. The samples contain 19 to 23% Al
and 65 to 68% SiO
and have 2 to 3%
LOI. Potassium is more than sodium indicating that it is derived from K-bearing feldspars
especially orthoclase. FeO, CaO and MgO are present in minor to trace amount.
5. BENEFICIATION STUDIES
In order to meet the specifications of various industries the quality and brightness of
pyrophyllite has to be upgraded by removing the undesirable and coloured minerals. From the
three varieties of pyrophyllite, based on petrographic study (modal analysis), the granular
variety was found suitable for beneficiation. Out of the various beneficiation methods,
flotation may be an ideal one as other methods such as gravity and magnetic methods are
unsuitable because (i) the density difference between the pyrophyllite and quartz is not
significant to attempt gravity separation and (ii) quantum of the magnetic materials in the
sample is very less.
5.1. Flotation Studies
The basic objective of beneficiation studies is to investigate the response of flotation
performance for the recovery of pyrophyllite from the associated minerals. The collector used
for flotation studies is dodecylamine due to its satisfactory collecting power for the
aluminosilicate minerals at certain pH ranges. More over the crystal structure analysis of the
pyrophyllite shows that it has most cleavable planes and due to its lower aluminium silica
ratio responds more favourably to cationic collectors (1). The cationic flotation has been
extensively studied and practised in kaolinite purification and iron ore processing [3, 4]. The
surface properties and flotation behaviour of kaolinite, illite and pyrophyllite using
dodecylamine as a collector have been investigated extensively . SEM studies have
indicated that pyrophyllite takes the thin slice shape without any pores and hence taking the
same reagent could easily float 96% of pyrophyllite. The collector molecules may be
adsorbed both on internal and external surface leading to better flotation of the pyrophyllite
compares to illite and kaolinite. Similarly flotation of pyrophyllite using N-dodecyl-1 and 3-
diaminoprpopane was carried out where the recovery of the mineral was found to be more
than 80% . The effect of dry grinding on flotation recovery of pyrophyllite was also
studied using an alcohol type frother. It was observed that dry grinding for longer duration
negatively affects the pyrophyllite flotation . The complete chemical analysis of the
granular variety pyrophyllite sample for flotation study is shown in Table 6.
Table 6. Chemical analysis of the pyrophyllite sample.
Oxide Wt% Oxide Wt%
Vol.8, No.4 Mineralogical Characterization and Beneficiation Studies of Pyrophyllite 337
The sample contains 21.4% Al
, 63.6% SiO
and 5.5% K
O as the major
constituents. Besides that, it also contains traces of CaO, MgO, TiO
. The sample
is greyish white in colour. The results of flotation studies as a function of pH are shown in
Fig. 4. It has been seen that the collector shows a satisfactory collecting power for the
pyrophyllite mineral. The aluminosilicate mineral exhibits a better flotatbility in a mild acidic
medium of around pH 4.5. At a reagent concentration of 100 gms/tonne an alumina
concentration of 29.5% with 54% recovery could be obtained. The flotability decreases at
alkaline pH. The relationship between the contact angle and zeta potential for flotation point
of view of pyrophyllite is well studied . The contact angle of water on pyrophyllite is >40
over a wide pH range from 2-12. The contact angle has increased to >65
when treated with
0.2mM DDA solution suggesting the flotability of this mineral. The zeta potential of
pyrophyllite mineral suggests that it exhibits iep at pH 2.4 . Below this iep, the
aluminosilicate mineral is highly negative. Hence when dodecylamine is introduced into the
pulp at the acidic pH, it may be attracted due to electrostatic force at the mineral surface. In
the alkaline pH range the flotatbility of pyrophyllite mineral may be due to precipitation of
DDA molecules and weak hydrogen bonding between NH
group and aluminosilicate
resulting in a decrease in recovery. A typical analysis of the flotation products is given in
Table - 7.
Table 7. Chemical analyses of flotation products .
MgO 0.01 0.02
CaO 0.04 0.05
O 7.84 3.15
O 0.14 0.05
From the above table it is observed that the assay of alumina has gone up from 21.4%
to 29.35% and silica has come down from 63.62% to 55.71% in the concentrate. The effect of
dodecylamine concentration at natural pH has also been studied. The results are shown in
Fig.5. The weight of the concentrate has increased with increase in reagent concentration and
the levels of Al
vary between 26.2 to 29.5%
It was observed that around 100 gm/tonne of
the reagent is sufficient for the flotation of minerals present in the ore. The improvement in
the grade of pyrophyllite in respect of Al
and curtailment of SiO
contents by flotation
technique has confirmed well to the recommended specification of refractory grade. The
alkali content in the concentrate product however could not be brought down to the desired
B. Das and J.K. Mohanty Vol.8, No.4
limit. Therefore, attempts need to be taken to optimally bring down the alkali content by
resorting to suitable chemical techniques for which the efforts are afoot.
Pyrophyllite samples of Keonjhar district, Orissa are used in many industries. Of the
three varieties, granular variety is in demand but because of less brightness, presence of
coloured minerals and quartz, the utility is restricted. Hence the sample needs beneficiation.
Beneficiation by flotation technique using dodecylamine as collector is found suitable to
reduce the quartz content, coloured minerals and enhance the brightness of the product.
The authors are thankful to Director, IMMT, Bhubaneswar for his permission to
publish this paper. We are grateful to the authorities of Baliadihi mines for kindly providing
the sample for the investigations.
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