Mahtab et al. Ball Milled Bauxite Residue as a Reinforcing Filler In PhosphateBased . 357 Fig. 3. Effects of ball milling on surface area and pH with increasing milling time. Effects of ball milling on the surface area and pH of BR are illustrated in Fig. 3. The unmodified BR has a specific surface area (SSA) of m2/g and a pH of