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

The recycling of toxic goethite 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 cutlet, 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 degrees 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 degrees 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 degrees C, was found to be influenced by the nucleation period, so that the highest crystalline volume fraction, V-f (0.80-0.85), was obtained for 90-120 min nucleation time at 670 degrees C and 120 min crystallization at 860 degrees C.