Fig. 4 illustrates the changes in the particle size and BET surface area
during mechanical activation as a function of milling time. The mean
particle size of the initial pyrite was about 10 μm. This measure decreased
sharply to 1.92 μm by 20 min mechanical activation and continued
to decrease but more steeply to 1.6 μm in 50 min mechanically
activated pyrite as minimum particle size. The point can be the beginning
for agglomeration phenomena when the particle size has increased
to 1.76 μm in 100 min mechanically activated pyrite. As seen in Fig. 4b,
the granulometric surface area increased rapidly from 0.94 m2
/g in the
initial pyrite to 3.59 m2
/g and 4.43 m2
/g by 20 and 50 min mechanical
activation, respectively, and then dropped to 3.84 m2
/g in the 100 min
mechanically activated pyrite.