Glass-ceramics prepared from sludge generated by a water purification plant

Abstract Glass-ceramics were prepared from sludge generated in a water purification process. The main constituents of this sludge were SiO 2 and Al 2 O 3 , with considerable amounts of Fe 2 O 3 and MnO also present. The batch composition of the parent glass was adjusted to be close to the composition of the eutectic point in the CaO–Al 2 O 3 –SiO 2 system by mixing the sludge with CaCO 3 and waste soda-lime glass. The samples were melted at 1300 °C for 2 h and quenched in water. The resulting glass cullet was ground to 850 °C, forming gehlenite (Ca 2 Al 2 SiO 7 ) and wollastonite (CaSiO 3 ) above 900–950 °C. The color of the sample changed from black to yellow-brown upon crystallization. The average four-point bending strength and Vickers microhardness of the glass-ceramics heated at 1000 °C (99 MPa and 5.2 GPa) was comparable with the values of commercial glass-ceramics. The chemical durability in acid and alkali solutions was 17.7 and 0.23 mg/cm 2 , respectively, showing excellent durability in alkali solution.