FELDSPAR IN RAJAS THAN
Introduction
Feldspars are one of the most abundant among rock forming minerals in the earth's crust.
It comprises group of minerals consisting of aluminium silicate with potassium, sodium
and calcium as mixture. It may also contain small amount of lithium, rubidium and
barium as isomorphous admixtures of alkalies. The formula for feldspars are: Na (Al
Si3O8), K (AI Si3O) and Ca (AI Si2O8) and rarely with barium as Ba (AI Si3 O8),
Feldspars are sub-divided into three broad categories, namely plagioclase, orthoclase and
hyalophanes. The physical properties of all the categories are more or less similar. They
have low refractive indices. Their hardness varies between 6 and 6.5, and specific gravity
between 2.5 and 2.9. They have different colours but pink, brown and grey are common.
Plagioclase feldspars
These feldspars are also called soda-lime feldspar. The end members of the plagioclase
feldspars are albite (NaAl Si3O8) and anorthite (Ca AI2Si2O8) The albite and anorthite
molecules are completely miseible and together form an isomorphous series from pure
albite at one end to oligoclase, andesine, laboradonite, bytownite and to pure calcium
silicate, anorthite at the other end. The plagioclase feldspars usually occur in almost all
igneous rocks. The calcium rich anorthite occurs in basic rocks such as gabbros basalts,
where as soda rich plagioclase feldspars are found in more acidic igneous rocks such as
granites, diorites and quartzporphyries.
Orthoclase feldspars
Orthoclase is a very common mineral. These form a high temperature continuous series
of solid solutions K (AI Si3O8) - Na (AI Si3O8) which gradually change after a process of
slow cooling into potassium rich orthoclase and microcline and sodium-rich components
(anorthoclase). The orthoclase feldspars occurs in acidic rocks particularly granite and
granite pegmatities, where as microcline is more common in intrusive acid rocks such as
granites, granodiorites and syenites. It is also the principal mineral of pegmatites.
Hyalophanes
The hyalophanes are rare orthoclase feldspars containing small quantities of barium.
They form an isomorphous series of K (Al Si3O8) and Ba (A12 Si2O8). Among the three
feldspars,orthoclase are important from commercial point of view. Most of today's
marketed feldspars are mined from pegmatities or feldpathic sand deposits and coarse
grained granites.
India has abundant resources of feldspar mainly of potash and soda feldspar. A number of
occurrences have been noted but the workings of feldspar are confined to the state of
Rajasthan, Bihar, Andhra Pradesh, Karnataka, Tamilnadu, Madhya Pradesh and West
Bengal. The reserves of feldspar in India as on 1-4-1990 are placed at 16137858 tonnes.
About 80% of the total reserves are concentrated in two states i.e. Rajasthan (9867074
tonnes or 61 % of the total), Tamilnadu (2087391 tonnes or 12.93% of the total) and
Andhra pradesh 1947454 tonnes or 12% of the total. Rajasthan continued to be leading
producing state of feldspar accounting for 56% of the total production followed by
Andhrapradesh 31 % Karnataka 8% and Tamilnadu 3%.
Occurrences in Rajasthan :
Rajasthan is the principal feldspar producing state in the country. There are 127 mining
leases for feldspar in the state and about 97724.0 tonnes was produced during the year
1998-99. The description of the deposits in Rajasthan is given below.
Ajmer District:
Large number of feldspar deposits are known to occur in Ajmer district. The principal
occurrences are in Ajmer, Beawar, Nasirabad, Kekri and Kishangarh tehsils, namely at
Lohagal, Banar-Sundri, Foy Sagar-Baro, Piproli, Rajgarh, Nagelao, Kalesara, Makrera,
Beawar, Lohawara, Dhal, Bhodli, Sanod, Basunbani, Kharwa, Lothiana Surajpura,
Soniana, Kishanpura, Jawaja, Kalathera.
The feldspar deposit of district Ajmer are largely potash bearing but a few soada feldspar
occurrences are also known. The quality of feldspar produced in Ajmer- Beawar area is
good with K20 content 11 to 14% and can meet world market standards, The promising
areas of Jawaja Group, Makrera-Rajgarh Group and Ti1ora- Piproli Group of mines are
the most important feldspar producing areas where good quality feldspar is being mined.
The Ajmer district alone produced about 66389 tonnes of feldspar in comparision to the
state's production of 97724 tonns in the year 1998-99.
Bhilwara district:
Feldspar occurs in the mica and beryl mining areas of Jahazpur and Bhilwara. The
production of feldspar from this district was 22700 tonnes during1998-99 there area 56
mining leases of feldspar associated with mica in the district.
Sikar district:
Green variety of feldpar probably microcline has been obtained from Kacharada mines in
Nim-Ka-Thana area and the soda feldspar have been obtained from the granite pegmatites
of Buchara areas. Other areas are Dudawas, Shipur and Sohanpura. About 2231 tonnes of
feldspar has been produced from this district in the year 1998-99.
Pali district:
In Pali district feldspar deposits are located in Chaondia. Pratapgarh, Dingor, ThandiBeri, Barantkhurd- Girri, Philava areas.
Took district:
Feldspar may be obtained from all the mica mines of Malpura, Tonk, Toda Raisingh and
Duni areas of this district. It is also available from the mica-beryl mines of Kakor area.
About 356 tonnes of feldspar production was reported from this district in the year 199899.
Alwar district:
.
A pink variety of potash feldspar is obtained from huge pegmatite intrusion at a distance
of about 1.5 kms south of village Tatarpur in Bansur tehsil and in Advas, 16 km from
Rajgarh. About 364 tonnes of feldspar was produced during 1998-99. Other occurrences
are located in the area of Khairtal, Kirwar, Gothara, Longarwas, Deotana. Bhatokalan,
Bhanokhar and Gar.
Udaipur district:
Feldspar is found in the mica bearing area of Udaipur district. The mineral is mostly soda
feldspar and contains Na20 from 13 to 18%. It is found near Sai dam area, Malva ka
chorah, Bekariya in tehsil Kotra and Suratpura in tehsil Vallabhnagar. The occurrences
are also found in Loharcha area.
Occurrences of feldspar have also been reported from Baghol, Padasli & GomtiCharbhuja area (Rajsamand); Sheopura (Jhalawar); Bundela Hills (Jhunjhunu district)
Dangarwara, Mundoli, Devapura, Amarpura, Dhagoli, Sakun, Borara, Natata, Barla,
Girot (Jaipur district), Padari as Sarod-ka-para area in Sagwara tehsil (Na2O 11.45%)
(Dungarpur), Lodha, Lodha Geriya, Laloopada, Jagpura, Nal Ganan and Damarwasa.
Industrial Application:Feldspar is traditionally used as a source for alumina and alkali in ceramics & glass
applications which account for 85-90% of total consumption of the mineral. It plays an
important role as fluxing agents in ceramics and glass applications, and are also used as
functional fillers in the paint, plastic, rubber and adhesive industries. Few firms in India
are utilising feldspar as a bonding agent in the manufacture of bonded abrasive like
wheels and discs of garnet, corrundum, emery etc. It is also used in the manufacture of
artificial teeth, fertiliser and white cement. Certain varities of feldspars are used as semi
precious stone e.g. moonstone which is orthocase colourless feldspars with white or
bluish tints.
Ceramics: In ceramics applications, feldspars are used as fluxing agent, softening
melting and wetting other batch constituents. Surface tension pulls the remaining solid
particles together, giving a densification of the ceramic body with rising temperature the
alkalis become more active and first dissolve the clay particles and then the free silica.
The flux controls the degree of vitrification of the ceramic body during firing. As
different ceramic bodies require different degrees of vitrification, the amount of flux
varies accordingly.
Potassium feldspar (K-spar) has technical advantages over sodium feldspar (Na-spar),
as it forms a melt of high viscosity that decreases only slightly with increased
temperature, thereby making ceramics stronger and more refractory K-spars are mainly
used in electrical porcelain applications and porcelain enamels. Na-spars are more often
used in ceramics because they are cheaper.
After clay, feldspar is the biggest ingredient in the raw material batch for ceramic
bodies. Typical feldspar contents are <25% in earthernware, 25-35% in sanitary ware,
15-30% in white ware, 10-55% in floor and wall tiles and 30-55% in electrical
porcelain.
Glass: The alkali content in feldspar acts as a flux, lowering the glass batch melting
temperature and thus cutting production cost. But feldspar are primarity added to glass
batches for their alumina content. Alumina acts as a matrix former by reducing the
tendency for glass to devitrify, and as a stabiliser, which improves the chemical
durability of glass and its physical resistance to scratching, bending, breaking and
thermal shock. Typical feldspar contents of glass range from 0.05% for flat glass and
textile-grade fibreglass, 8% for container glass, 11 % for some speciality glass
application, and up to 18% for insulation fibreglass.
Refractory: In the refractory industry, feldspar is used as one of the batch constituents
in the manufacture of acid proof refractory bricks. It is mixed with fireclay to make the
acid proof refractory bricks.
Abrasives : Fine grained feldspar is used in abrasive industry as mild abrasive material
for incorporation in scouring powders. Although its hardness is around 6, because of its
semiconchoidal fracture, it is used as a mild abrasive. In scouring powder, feldspar is
preferred to silica sand on considered reasons of better health safety as its silica content
is combined and not free. Ground feldspar is used as non-skid dusting agent for city
floors. It is also used as a bond in bonded abrasives. Vitrified wheels with a clayfeldspar bond are preferred because of their high rigidity and dimensional stability.
Electrode :In welding electrode industry, feldspar is used as a flux. Its fluxing
properties make it an ideal ingredient in batch mixes for coating the electrodes.
Feldspar, as a flux, is generally incorporated into the dry blend mix for coating
electrodes used in the manual metal arc process.
Feldspar incorporated into the mix carries out two important functions namely (i) It acts
as an arc stabiliser, & (ii) helps in weld pool protection. In the case of weld pool
protection, slag formers such as felspar form a molten/solid barrier to protect the weld
pool and new weld metal. Feldspar can form between 5 and 10% of the total dey blend
mix. In India, mostly potassium felspar is used though in other countries both potassium
and sodium bearing feldspar are used. There is an increasing trend for using high
potassium bearing feldspar because they give a smoother arc which is important in
certain applications. Each type of feldspar gives a unique slag viscosity, but finally it is
the manufacture's experience, rather than chemical understanding, that dictates' which
felspar affects the viscosity in a particular way.
Fillers & extenders: Physical properties, such as good dispersibilty, chemical inertness
and stable pH. low free silica content and brightness of 89-95% lend fine ground
feldspathic materials excellent filler qualities. However, in this field of application,
feldspar complete with other, cheepoo and geographically more converient minerals,
including baryter, calcium carbonate kaolin, mica and tale. As aresult a this, feldspathic
materials are often considered the second choice in filler & extender applications.
On the whole, fillers still represent a small market for feldsparthic minerals, but demand
in the paint, plastic and rubber industries is increasing because in paint application that
are subject to acidic environment (e.g.out door paints, anti corrosive paint, grout &
plasters).
Feldspathic minerals provided good film integrity, resistance to abrasion, chemical attack
and chalking. In paints, filler-grade feldspars also achieve maximum colour strength
through their low tint strength. Other beneficial properties of feldspar in paints and
coatings include low viscosity at high pigment loading, low vehicle demand and
exceptional resistance to frosting.
In plastics, feldspar offer the same physical properties that in paint application. They
provide resistance to staining, and their index to refraction is similar to most of the
common resins. This refractive index also allows the production of adhesives which dry
clear on wood and translucent on glass.
Processing:
The processing of Fledspars usually involves flotation or magnetic seperation to remove
accessory minerals, such as mica, garnet, illmenite and quartz. Silica (SiO 2) occurs as a
co-product in the mining of feldspar ores, present as quartz in pegmatite deposits and
silica sand in feldspathic sand deposits. In some feldspar applications, however, the
presence of silica can be advantageous. Other uses require extremely pure and finely
ground
grades.
The
degree
of
feldspar
grinding
depends
on
end-product
requirements.Glass grade feldspar is usually the coarsest material, where as filler
application demand finely ground feldspars.
Statistical Information for fellspar in Rajasthan
Year
Production
Revenue
No. of leases.
(thous. tons)
(thous. Rs.)
1994-95
70.470
4190.0
92
1995-96
71.060
6093.00
98
1996-97
103.320
2825.70
99
1997-98
126.810
3435.05
117
1998-99
97.724
1811.50
127
District wise Production of feldspar (Year:1998-99)
S.No.
District
Production
Leases
(thous. Rs.)
1
Ajmer
66.389
54
2
Bhilwara
22.700
56
3
Sikar
2.231
5
4
Pali
3.000
3
5
Tonk
0.356
2
6
Jaipur
0.167
6
7
Alwar
0.364
1
8
Rajsamand
1.517
-
97.724
127
Total of Rajasthan
Specification:
There is no ISI specification for feldspar. Specifications of feldspar in various industries
as prescribed by them is as below :Abrasives : Feldspar is used in the form of powder and lumps which have Si02-60% min;
A1203- 18% min, and K2O/ Na2O- 10% minimum. While CaO, Fe203 should below 0.6%
and 0.45% respectively, LOI should not be more than 2%.
Ceramics: It is mainly used as a fluxing agent and white wares contain good proportion
of feldspar. There are two grades used, Gr. I should have S102-68% maximum, Fe203
should be below 0.1 % while ratio of K/Na should be 2: 1. In Gr I Si02 is 72% maximum
and Fe203 is same as that of Gr. I i.e. 0.1 % max. CaO should be in traces while MgO
should not be present.
Glass Industry: In glass industry potash felspar is preferred as it introduces potash for
clarity and alumina for durability and also controlling viscocity of molten glass. It should
contain 1% to 13% of Na2O and K2O combined, 15 to 18% of A1203 65 to 68% of Si02
and Fe2O3 below 0.3% while the size should be 30 to 80% mesh.
Refractory: As already mentioned earlier feldspar is added as one of the batch
constituents for refractory. Here also 11 to 12 % of combined Na2O and K2O are
preferred while Si02 should be within 60&65%, A1203 should be 18 to 19% Fe2O3 should
be below 1.5%, PCE=4 orton cone and LOI should be below 0.8% size preferred is 2.5 to
10 cms.
Electrodes: Feldspar finds use in electrode manufacture as it acts as a flux and forms
slag which protects molten metal from oxidation. For this potash feldspar having 13 to
14% of K2O, I to 3% of Na2O, 63 to 67% Si02, 17 to 20% of A1203 and Fe2O3 upto 0.3%
is preferred. LOI should be maximum upto 1 % Size 0.2 to 0.06 mn.