Minerals used in the Fertilizer Industry
the last four decades, with the
emphasis on agricultural production in India, increased attention was given to
the manufacture of chemical fertilizers. The
fertilizer plants use the raw materials both from natural sources and from the
chemical materials. Gypsum, pyrite
and rock phosphates form the principal mineral sources.
While the first two find extensive use in the manufacture of sulfate
fertilizers, the rock phosphates are mainly utilized in the production of
is a hydrated calcium sulfate (CaSO4.2H20 ) and its anhydrous
is known as anhydrite.
Deposits of gypsum are either of sedimentary origin (bedded type) or of
marine evaporate nature. Gypsum
finds extensive use in the cement, paper, textile and paint industries. The mineral, calcined around 200oC loses 75% of
its water and the product, known by its trade name as 'plaster of paris', is
widely used in building industry as a good finishing material.
It can be moulded into any shape with the addition of water and sets to a
India, gypsum is produced in Rajasthan. Tamil
Nadu, Uttar Pradesh, Gujarat and Maharashtra.
Of these, the first three are the important producers with Rajasthan
possessing around 95% of the total Indian reserves (estimated to be around 1,000
m tonnes). The deposits in
Rajasthan are situated mainly in Bikaner, jodhpur, Nagaur and jaisalmer
districts. The Rajasthan
occurrences are associated with the Vindhyan limestones.
Tamil Nadu the deposits are situated in Tiruchirapalli, Coimbatore and
Ramanathapuram districts and are associated with the shales in Cretaceous
sequence. The gypsum from these
sources is chiefly utilized in the cement and pottery industry.
In Uttar Pradesh, deposits are reported in Dehradun, Garhwal and Nanital
districts. The Majhara deposit in
Dehradun district and Lakshmanjhula in Garhwal district are exploited at
use in fertilizer industry, gypsum with a minimum of 87% CaSO4.2H2O
is preferred. The Sindri
fertilizer plant gets its main supply from the Bikaner deposits.
and pyrite (FeS2) are the principal raw materials in the
manufacture of sulfuric acid which forms the back-bone of many modern industries
such as fertilizers, chemicals, paints and textiles.
Pyrite is either mined as a principal mineral or is recovered from the
sulfide assemblages of copper, lead-zinc, gold and other metallic ore deposits.
India, pyrite deposits occur in Bihar, Karnataka, Rajasthan and Tamil Nadu.
However, the largest deposits are from Amjhore region in Shahabad
district of Bihar where pyrite occurs as a uniform bed of about one metre
thickness in the Bijaigarh black shales of Kaimur series (Vindhyan system).
The deposit (located at nine places within the Amjhore region) has a
remarkable conformity with the overlying and underlying Vindhyan formations and
is confined to a single stratigraphic horizon.
Two types of pyrite occurrences have been reported: the massive
cryptocrystalline variety, which forms the bulk of the deposit and the fine
pyrite grains, disseminated within the black shale.
About 390 million tonnes of pyrite (with 48% S) are estimated to be
available within an area of 120 sq. km in Amjhore region.
Karnataka, pyrite deposits occur around Ingaldahl in Chitaldrug district.
The mineralization is localized in the ferruginous chert bands
interbanded with Dharwarian greenstones in the eastern flank of an anticlinal
structure. It may be noted that
copper mineralization in this region is on the western flank of this structure.
The Ingaldahl pyrite reserves are estimated to be around 2.0 million.
tonnes (of 20-30% S). The deposits in Rajasthan occur at Saladipura and the
inferred reserves are of the order of85 million tonnes (with 22% S).
In Tamil Nadu, the deposits are located around Polur in the Thaniyar
the above occurrences, pyrite is also associated with gold, copper, lead and
zinc deposits as also in Tertiary coals. In
the metallic ores, after the recovery of primary minerals the tailings
containing pyrite are discarded in India. Plans
are underway to recover and utilize pyrite from such tailings, Sizeable deposits
of sulphur have been reported from Puga valley in Ladakh.
India, the requirements of sulphur are of the order of 3,00,000 tonnes per year.
At present the mining activity is at Amjhore by the state-owned Pyrites,
Phophates and Chemicals Ltd. A
sulphuric acid plant of 400 tonnes per day capacity has been set up at Sindri in
deposits of sedimentary origin and of economic importance are known as
phosphorites or rock phosphates. The
formation of these is restricted to marine environments and is a result of
deposition under specific pH conditions from the phosphorus-bearing solutions
derived from the weathering of phosphate minerals like apatite of igneous
source. It is thought that redox
potential does not play any role in their formation.
In all the phosphate minerals, phosphorus exists in its highest valent
India, with the development of superphosphate fertilizer industry, the
exploration for rock phosphate deposits has been accelerated.
Deposits of economic significance are reported from Rajasthan and Uttar
Pradesh. In Rajasthan, they are
located in Udaipur and jaisalmer districts.
The Udaipur deposits occur around Jhamar Kotra area, Kanpur region (Kanpur,
Karbaria Ka Gurha and Maton blocks) and Dakan Kotra area.
The phosphorites are confined to limestone or cherty quartzite and are in
the form of lenticular masses of variable thickness with the P2O5
content between 15 and 25%. However,
the published analyses for Maton deposits indicate P2O5 as
high as 36%. The Jaisalmer deposits
are mainly located in the Fatehgarh area where the phosphorite horizon was
associated with the Mesozoic sandstones. The
varies from 5 to 15%. Two types of
mineral associations are reported from Rajasthan deposits: pellets of collaphane
and black chert in calcareous shaly sandstones and the banded phosphorites (of
alternate collophane with quartz on calcite bands) with limestone bands.
The basic characteristic feature of these phosphorites is their
association with limestones, which distinguishes the same from those of Uttar
Pradesh. Around 80 million tonnes
are estimated to be available in Rajasthan.
Uttar Pradesh, the deposits occur mainly at Mussoorie and Meldeota, although in
all about 10 deposits are located. The
phosphate-bearing zones, thickness varying from a few centimetres to about 15
metres at places, are mainly restricted to chert and carbonaceous shale
formations of Lower Tals or at the contact of the underlying argillaceous
limestones of Upper Krols. Three
varieties of phosphorite -- granular, pelletal and nodular -- have been
reported. The P2O5content
of these deposits varies between 15 and 35%.
The deposits from Uttar Pradesh contain the collophane species of
phosphates together with quartz, calcite, chert, muscovite and clay minerals.
The development of the Mussoorie deposits is beset with several
difficulties such as their complex mineralogy, lack of precise estimates as
regards the quantity and quality of ore available, remoteness of the deposits
and the need for underground mining.
In India, the major share of the requirements for rock phosphates is met from the imports of the order of 5,75,000 tonnes per year while the production is around 6,44,000 tonnes. A beneficiation plant is being set up at Matas near Udaipur by Hindustan Zinc Limited to upgrade the phosphorite from 25% P2O5 to >32% P2O5 with consequent reduction of silica. It is planned to send these concentrates to the superphosphate unit at Debari smelting plant.
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