CLAYS IN RAJASTHAN – II
FIRE CLAY
In the last issue we have given a brief account on China clay and ball clay
occurrences in Rajasthan .In continuation of that a brief account of fire clay is given in
the following pages.
Fire clays consist mainly of the mineral kaolinite (Al2O32Sio22H2O) with minor
amounts of other clay minerals, quartzite, iron, titaniam and alkali impurities.
The term has been commonly applied to refractory clays associated with
sedimentary formations and in reality encompasses a wide spectrum of natural kaolinite.
The fire clays, used as refractories are capable of withstanding temperatures
around1700°c.
Fireclays have two modes of occurrence : (i) fairly well defined beds associated
with coal seams and (ii) lenticular beds associated with other coarser sediments. The
colour and other characteristics usually vary depending on the mode of formation. The
chemical parameters determining the suitability in refractory industry include 60 to 62%,
SiO2, 24 to 36% or above A12O3 and less than 5% total fluxes of which the alkali and
iron should be particularly low. Fire clays include both plastic and non plastic varieties. A
good fireclay should have 24 to 26% water of plasticity and shrinkage after firing should
be within 6 to 8%.
Essentially based on chemical composition, fireclays, may be either aluminous or
siliceous and usually burn buff. The aluminous variety burns dense and is more
refractory. Fireclays are usually fissile, practically non magnetic and has a low electrical
conductivity. Based on the capacity to withstand high temperatures, the fireclays are
graded into the following four categories.
Grade
Low duty
Medium duty
Hight duty
Super duty
Cone
19- 28
30
32
35
Oc
1515 -1615
1650
1700
1750
The important deposits of fire clay are located in the state of Bihar, West
Bengal, Madhya Pradesh & Neveli lignite fields of Tamil Nadu.
Occurrences in Rajasthan
Rajasthan contributes about 10% of fire clay to the total country's production.
There are 4 mining leases for fire clay in the state and about 900 tonnes minerals was
produced during the year 1997-98. The description of the deposits in the state is given
below.
Bikaner District
Palana : The fire clay is 0.60 to 0.90 metre thick occurring below the lignite at
depths varying from 39 to 76 metres. It is plastic. The estimated reserves are about two
million tonnes, The fire caly occurring above the lignite seams are upto 2 m. thick, but
these are of inferior quality. It is blackish grey in clour having good slaking
characteristics. The chemical assay is Sio2-39.24%, A12O3 25.40%, Fe2O3-1.25% & LOI12.28%, Water of plasticity 29, dry shrinkage-4% Vitrification buff white fairly vitrified,
PCE is orton cone 31.
Barsingsar : In Barsingsar area clay have been encountered in the bore holes
drilled for lignite exploration. It occurs with an average thickness of 0.5 metres to 0.8
metres at various depths between 30 to 120 mts. The clay beds are found alternately with
the lignite seams. A thick bed of clay (about 10 mts.) is also found as overburden on
lignite seams at 10 mts. depth-from the surface. Studies on these clays have been
conducted in the ceramic & ore dressing laboratory of the department. The impurities of
fme silica and iron oxide & in some cases minor amount of carbonates have been found.
The plasticity is good. The average chemical analysis of crude clays are SiO 2-56.98%.
Al2O3 -28.16%, Fe2O3 -2.40%, TiO2 -0.80%, CaO-0.56%, MgO-0.40%, Na2O -0.67%,
K2O-0.84%, LOI-9.20% and for washed clay it is SiO2 -45.60, Al2O3 -35.82%, Fe2O31.28%, TiO2 -0.48%, CaO-0.28%, MgO-0.20%, Na2O -0.20%, K2O-0.24%, LOI 11.92%. It slakes moderately. On an average the weight recovery of good grade clay in
washing varies from 36% to 58.5% vitrification at 1400°c. to creamish white in colour,
fairly vitrified. large quantities of fire clay will be available from this area when lignite is
mined. About 15 million tonnes of clay may be available from this area.
Den: An extensive deposit of clay at village Deh, distt. Bikaner, under the ball
clay bed has been located during lignite investigations.
Gurha : The clay beds about 1.5 to 3 mts. in thickness have been found above
the lignite seam at village Gurha and on an average 0.3 m. thick. clay will be available
during the mining of lignite.
Alwar District
Kalgoan : A pocket of white, shining clay 10 m. long and thick is intercalated in
a sequence of quartzites and phyllite.
Pharoti : Clay occurs intercalated in steeply dipping, quartzit. It is soft, light grey
and fairly plastic. The deposit appear to be more extensive.
Baswagate: It is a small deposit occurring near Rajgarh town. It is greyish white
in colour and slightly iron stained. Water of plasticiy 15.99%.
Clay deposits also occur at Anandpura, Kuncha and Bigwada areas of Alwar
district.
Jhunjhunu District
Girwari: The deposit is located about 2 km. S.W. of Girwari. In this area
brownish clay occur having moderate plasticity and good vitrification characteristics. The
deposit is not extensive. The fire clay reserves are estimated to be less then ten thousand
tonnes.
Sawai Madhopur District
Phalodi : Clay occuring at Phalodi is plastic, brownish in colour. The
average thickness of the clay band is 1.5 mts. The reserve is about twenty thousand
tonnes. The other deposits are located at Naranli and Tatwara. The depostis at
Bhatpura, Ghat, Ghadi & Nirapur are being mined for clay.
Barmer District
Botia clays: The deposits at Botia distt. Barmer is fairly large with estimated
reserves of about 1.2 million tons. The clay is soft & gritty and is grelyish white in
colour. It analyses to SiO2 -59.68%, Al2O2 -25.66%, Fe2O3-1.17%, K2O & Na2O3
0.36% LOI-9.98. It is suitable for making fire clay insulation bricks, sewer pipes ect.
Bhadres : The clay band about 1 m. thick occurs 5 km. from Bhadres. It is
suitable for refractory.
Nimla : The clay is fine grained; occurring 1 km south of this village it is
suitable for stoneware & fire clay insulation bricks.
Bharatpur District
In this district fire clay occurs associated with red ochre near village
Chhuntri and Vilong. The clay is suitable for the production of stoneware and fire
clay insulation bricks.
Reserves & Grade
The Known recoverable reserves of different clays viz. ball clays, china
clays and fire clays are placed at about 35 millions tonnes, 208 million tonnes and
17.8 million tonnes respectively. However, additional rserves of 20 million tonnes
of fire clay will be also available form Barsingsar, Palana, and Gurha area of distt.
Bikaner.
The clay deposits of Rajasthan can be classified in terms of their use in various
industries. Ball clays of Bikaner are plastic, white burning and can be used to have better
green strength in the body of Ceramic items. Fire clays available interbedded with lignite
seams could be used in the production of saggars & refractories. Other clay deposits in
various districts are the china clays. Grade of china clay of Rajasthan varies depending
upon the impurities present in it and hence they are being used in different ceramic
industries. The clay deposits of Chittorgarth & nearby area generally contain a higher
percentage of SiO2, CaO and iron. They are suitable for cement manufacture as they have
the property of good lime reactivity. The other deposits of china clay in the distt. of
Bhilwara, Sikar, Jaipur, Sawaimadhopur, Alwar and Bundi are suitable for the
manufacture of white ware, electrical insulator, glazed tiles, sanitary ware, potteries, and
fine ceramies.
Specification for fire clay in various industries
The name fire clay is given to a group of refractory clays which can stand
temperatures above POE 19. Fire clay is generally sedimentary in origin and is mainly
found in coal measures as bedded deposits. In nature fire clay is usually found to contain
Al2O3, SiO2, oxides of calcium, iron titanium and magnesium, and alkalies Refractories
and Plasticity are the two main properties needed in fire clay for its suitability in the
manufacture of refractory bricks. However, all lfireclays are not necessarily plastic clays.
Depending upon the refractoriness, fire clay can be used for manufacture of low duty,
intermediate duty, high duty or super duty fire bricks.
(1) Present status of specification of fire clay for different and use industries and
the likely future trend (Item (1) of the terms of reference:
The only industry in which fire clay is used is refractory industry. The I.S.I. has not
standardized andy specification. Recently, the Sub-committee on Refractory raw
materials appointed by the Directorate General of Technical Development (DGTD) has
recommended the following seven specifications.
Gr.I
Gr.II
Gr.III
32-25% 1.0
30-32% 1.5a) Non-plastic/ Semi- Al2O3 : 35-40% Fe2O3: 1.0% (max)
1.5% 32 (min) 2% 30(min)
plastic caly
PCE: 33 (min) (Orto)
b) Plastic caly
Gr.I
Gr.II
Gr.III
Gr.IV
A12O3:30-32%
28-30% 2-3% 22-28% 1-2% 18-20% 1.5Fe233: 1-1.5% PCE:
28 (min)
26 (min)
2% 18-21
30 (min) (Orton)
(2) Present status of classification of reserves according to its industial
applications (Item(ii) of the terms of reference) :
In the inventory as on 1.1. 85 (as also in earlier inventories), no attempt has been
made to classify the reserves according to different grades.
(3) Recommendations for standardization fo grades for different end-use
applicatio1l for purpose fo reserve estimation keeping in view the broad limitations of the
exploration agencies.
(Item (iii) of the terms of reference) :
After examining the specifications prescribed by the Sub-committee on Refractory
Raw Materials of the D.G.T.D., the Group recommends the following end-use
classification of reserves:
Refractory industry
a) Non-plastic/
Semi plastic
type
b) Plastic
type
A12O3
Fe2O3
PCE
A12O3
Fe2O3
PCE
:
:
:
:
:
:
30% (min)
2% (max)
Orton cone 30 (min)
18% (min)
3% (max)
Orton cone 18 (min)