Preliminarily broken-up limestone was addnl. powdered in an eccentric mixer with paddle and disc stirrers in aq. suspension contg. 40-70% by mass of the solid matter (final grain size 1-3 mu m) and used for studying its reactivity in reaction with 1 M H2SO4 at 55 degrees C and pH 5.5 for 60 min in a stirred tank reactor (600 rpm). The limestone conversion decreased with increasing its grain size. The exptl. data were correlated by an exponential equation.