Fig. (4) Concentrations of SO3vs. CaO and Fe2O3 in each particle-size fraction of FA studied. The fractions were numbered in the order of decreasing particle size: (1) >0.1 mm, (2) 0.09-0.1 mm, (3) 0.08-0.09 mm, (4) 0.071-0.08 mm, (5) 0.063-0.071 mm, (6) 0.056-0.063 mm, (7) 0.053-0.056 mm, (8) 0.050-0.053 mm, (9) 0.045-0.050 mm, (10) 0.036-0.045 mm, (11) 0.032-0.036 mm and (12) <0 0.32 mm.