Aqueous leaching of high sulfur sub-bituminous coals from Ledo and Baragolai collieries of Makum coalfields, in Assam, India, has been investigated with res
pect to time at different tem
peratures. Leaching at 25
![](/images/entities/deg.gif)
Cu
p to 120 h showed that the
physicochemical characteristics viz., conductivity, acidity, TDS, and SO
4-2 ions,increase with the increase in time of leaching. The generation of highly acidic leachates at 1-1.5 h (
pH 2.5)and 2 h (
pH 3.1) for Ledo and Baragolai coals was observed, res
pectively. However, it remains stable u
p to120 h. The concentration of major, minor, and trace elements and their mobility along with the loss of
pyriticsulfur or de
pyritization were also re
ported. The release of metals (Fe, Mg, Bi, Al, V, Cu, Cd, Ni, Pb, and Mn)above the regulatory levels during leaching was evidenced. De
pyritization was found to be 79.8, 82.9, 84.7,and 89.7% for Ledo and 70.49, 73.77, 75.41, and 77.05% for Baragolai coal at 15, 25, 35, and 45
![](/images/entities/deg.gif)
C, res
pectively.A
pseudo-first-order kinetic relationshi
p with activation energies (
E) of 8.1477 and 5.2378 kJ mol
-1 withfrequency factors (
A) of 8.8405 × 10
-4 and 2.6494 × 10
-4 dm
3 mol
-1 s
-1 was attributed to aqueous oxidationof
pyrites in Ledo and Baragolai coals, res
pectively. The X-ray diffraction analysis and Fourier transforminfrared s
pectrosco
py
patterns indicate the
presence of illite,
![](/images/gifchars/al<font color=)
pha.gif" BORDER=0>-quartz, hematite, chlorite, rutile, calcite, andalbite as mineral
phases. This investigation justifies the formation of acid mine drainage by weathering of
pyrites from coal during the mining of high sulfur Makum coal fields, in Assam, India, and demonstrates oneof the
possible routes for its formation.