The velocity, number density and size of representative coal mineral m
atter particles were measured using laser phase Doppler velocimetry su
bsequent to their triboelectrification and while flowing through a con
stant electric field. For 60 mum diameter silica particles, the accumu
lated negative charge, q, could be represented by a normal distributio
n having an average value which was linearly dependent on the gas velo
city in the tribocharger, V, and represented by q(Si) = [2.6V + 4] x 1
0(-14) C. The width of the distribution increased with increasing gas
velocity. Physical mixtures of similar sized silica and glassy carbon,
and coal, were also subjected to electrostatic separation while being
monitored by the non-intrusive laser optical technique. The purity of
the carbon separated from silica was > 90%, and dependent on the accu
mulation of either positive charge or no charge on the silica. For a h
igh volatile A, Elswick seam, Pike County, Kentucky coal, the removal
of mineral matter was comparable to that obtainable by wet processes,
decreasing mineral matter content from 6.4% to 3.7% at a 72% combustib
le recovery.