Glass-ceramic proppants from sinter-crystallisation of waste-derived glasses

The present investigation aims at evidencing the feasibility of glass-ceramic spheres by sinter-crystallisation of fine glass powders (<100 μm), in turn obtained by the melting of inorganic waste, such as red mud from Bayer process or municipal solid waste incinerator fly ash, or low-cost minerals. While dense and highly crystallised monoliths may be achieved by sintering pressed glass powders just at the glass crystallisation temperature (T_C), applying fast heating and short holding times, dense glass-ceramic beads could be obtained only by firing well above T_c (T_c + 100°C). An increased sintering temperature was applied in order to enhance the viscous flow and promote the spheroidisation of powder clusters, previously formed by casting fine powders on a rotating drum. The high degree of crystallinity and the uniform microstructure were found to contribute positively to the mechanical properties (compressive strength exceeding 120 MPa, for beads with a diameter of 1 mm, approximately).