Purification of Surface Graphite from Passyala, Sri Lanka
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Date
2015
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
Flake graphite occurs as isolated, flat plate-like particles disseminated in lenses or pockets in
metamorphic rocks. Less frequently it occurs in massive accumulations in veins. This is the
geologically most common variety of natural graphite. Surface graphite (flake graphite) deposits
occur at South Western region of Sri Lanka. There were large number of shallow pits in Sri Lanka
had historically been sunk in to the weathered rock or top soil and believed more than 2500
graphite pits and mines were located in the west and central highlands. Graphite exploration from
Matugama, Warakapola, Passyala and Deniyaya are in progress as new sites. Even though there
are various studies on Sri Lankan vein graphite, limited attention was drawn to study the
distribution, chemistry, origin and geology setting of surface graphite deposits in Sri Lanka.
(Wijayananda N.P.,1987).Froth Flotation is versatile mineral processing technique, that utilizes
the difference in surface properties of the valuable minerals and the unwanted gangue
minerals to achieve specific separations from complex ores. Graphite have non-polar surface that
do not readily attach to the water dipoles. Therefore in the separation graphite can be effectively
collected into the froth. (Wills B.A.,2006). considering the chemical purification, recent studies
on flake graphite with alkali roasting proven that the purity can be upgraded over 95%. ( Lu, X.J.,
et al,2002 ) Present research was aimed to study the purification of Sri Lankan flake graphite by
using both chemical and physical purification techniques.
Materials and methodology
Initially collected samples were crushed into chips and prepared powder samples (<250 µm) for
both sample no-01(taken from Wawehena mine) and 02 (taken for Kaluaggala mine). 200g from
each samples were taken into froth flotation. Separated froth was washed to remove the effect of
phenol and dried at 60 C for 24 hours.
3g from each graphite sample was take into alkali roasting, mixed with 10,20,30,40,50,60 vol. %
NaOH (solid: liquid, 1:2) separately and roasted at 250 C under air for one hour. The roasted
sample was acid-leached in 10 vol. % H2SO4 and filtered. The residue was washed to neutral and
vacuum dried at 100 C for 15 hours . (Lu, X.J., et al,2002).Carbon percentage of graphite was
determined according to ASTM - 561 and weighing the residues. Both initial and froth floated
graphite matrix was characterized by Fourier Transform infrared (FTIR) spectrophotometer in 500
- 4000 cm-1 region (Nicolet 6700). The electrical characterization was performed on the dense
graphite pellets by four probe d.c. conductivity in air.
Results and discussion
Table - 4.1 shows the measured carbon content for both sample 01 and 02, before and after froth
flotation. Forth flotation was able to achieve averagely 35% purity enhancement for the collected
flake graphite samples. Therefore it clearly evident that the forth flotation technique is much
effective as an initial purification technique before moving to the chemical or any other
purification method.
Description
Keywords
Mineral Sciences, Materials Sciences, Graphite, Graphite Industry, Chemical, Chemistry, Physical Chemistry