Effect of grinding on the leaching behaviour of pyrophyllite

The effect of dry grinding on the leaching behaviour of pyrophyllite has been studied by XRD, FT-IR, thermal analysis and N2 adsorption techniques. Pyrophyllite samples were ground for 3, 6, 12 and 18 h. Grinding initially causes the surface area of the pyrophyllite to increase to ∼73 m2 g−1, decreasing with longer grinding because of particle agglomeration. Leaching the ground pyrophyllite with 4 M HCl at 80 °C for 2 h causes depletion of Al3+ and increases the surface area. The highest surface area was recorded in the leached sample ground for 3 h (156.9 m2 g−1 with a pore volume of 0.36 ml g). Structural breakdown by grinding is thought to be the main reason for the enhanced leaching behaviour of the pyrophyllite, but grinding for extended periods decreases the leaching rate without enhancement of the porous properties.