On the basis of the
particle size distribution, the average particle size (d) was calcu-
lated. The grinding ability index (E
f
) was calculated as a ratio of the
grinding energy to the surface area of the ground material. The
Soko
ł
owski's grinding index (K) was calculated on the basis of the
sizereduction theory described by
Soko
ł
owski(1996)
. Details of the
procedure used in determining these indices can be found in
Dziki
and Laskowski (2010)
. The distribution of the particle size was
evaluated thrice and the values of grinding indices were calculated
from the average particle size