Preparation and properties of glass-ceramic materials obtained by recycling goethite industrial waste

The recycling of toxic geothite waste, originated in the hydrometallurgy of zinc ores, in glass-ceramic matrices has been studied. Oxide compositions suitable to form glasses were prepared by mixing the goethite waste with granite scraps and glass cullet, yielding the following oxide composition (wt%): SiO2, 44.6; Al2O3, 3.3; Fe2O3, 25.5; MgO, 1.6; CaO, 4.5; Na2O, 5.9; PbO, 3.1; ZnO, 6.5; K2O, 1.0; TiO2, 2.0; other 2.0. By proper addition of carbon powder, the initial Fe3+/Fe2+ ratio (12) of glasses melted in air at 1450 °C was approximated to the stoichiometric value of magnetite (2) to obtain high nucleation and crystallization rates. The heat treatment of iron supersaturated goethite glasses above 630 °C led to the formation of magnetite nuclei with a high tendency to grow and coalesce with time. The crystallization of pyroxene, occurring on the magnetite crystals above 800 °C, was found to be influenced by the nucleation period, so that the highest crystalline volume fraction, Vf(0.80-0.85), was obtained for 90-120 min nucleation time at 670 °C and 120 min crystallization at 860 °C.