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SILICATE ROCKS - A SOURCE OF POTASH FOR FERTILIZERS?
Nikhil Dhawan, Yogendra Pratap Singh, Gulshan Pradhan
Department of Metallurgical Engineering, Indian Institute of Technology, Roorkee-247667
ABSTRACT
Potassium is one of the essential elements for the growth of plants and thereby for humans. In fertilizers,
potash demand has been steadily increasing at ~3.5% annually. Water soluble potash deposits are rare and
highly localized. India is neither present on the world potash production map nor it has adequate potash
richrocks. The K-bearing minerals are recovered either by using conventional underground mining
methods or though solution mining methods. At present, India is importing all its potash demand (about 3.5
million tons per annum) from different countries. However, India possesses a vast resource of silicate rocks
such as glauconitic sandstone (Madhya Pradesh), Feldspar (Rajasthan) and Sericite (Uttar Pradesh). These
rocks are basically a group of alumino silicate of potassium, sodium and calcium (K 2O%: 5-12, Na2O%: 310%, SiO2%: 52-65, Al2O3%: 15-20, Fe2O3%, 5-7, MgO%: 2-3.5). The K extraction from silicate rocks has
received little attention probably due to the slow release of potassium values and the unavailability of
appropriate economic processes & their know-how. The locked structure of alumina-silicate minerals i.e. K
entrapment makes the physical beneficiation futile. In present work, an attempt has been made to identify
the structural and chemical alteration of desired K mineral phase in silicate rock (~K2O%: 10.5, Na2O%:
2%, SiO2%: 55, Al2O3%: 19, Fe2O3%, 5-6, MgO%: 2.5) under different conditions such as acid leaching,
thermal treatment and chemical processing. Different treatments are aimed to increase K availability which
is related to the modifications in mineralogical composition. The modifications in the feed sample and
treated samples are studied through SEM-EDAX, XRD, EPMA and optical microscope. With the
combination of treatments, it is possible to extract more than 90% K and the formation of sylvite phase
(water soluble) confirms the dissolution of potash values.
Chemical
Composition (%)
K2O
10.5
Na2O
2
SiO2
54
Al2O3
19
Fe2O3
6
MgO
2.5
Figure 1 – EDAX spectra of the feed sample and XRD plot showing different phases during different
treatments applied on silicate rock
KEYWORDS
Silicate rocks, Characterization, Potash, Thermal treatment, Leaching