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 (TC), applying fast heating and short holding times, dense glass-ceramic beads could be obtained only by firing well above Tc (Tc + 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).