Effect of heat treatment on glass-ceramics covering of SiO2-Al2O3-CaO system using industrial waste as raw material

B.C. Alcantar, J.A. Chavez, G.C. Díaz

On a day to day basis, the demand for goods and services cause environmental damage due to the overuse of natural resources and the increase in residues related to these activities.  The biological treatment of wastewater has become an important source of solid residues.  At the same time, industrial development and technological advances have generated processes that produce a great variety of residues as byproducts.  Some of these residues, because of their inorganic composition and innocuousness, can be incorporated into the production of ceramic materials to substitute traditional or natural raw materials.  The biosolid ashes resulting from the biological treatment of wastewater are rich in CaO, SiO₂, Fe₂O₃ and P₂O₅, while the residues from the anodization process mainly contain Al₂(SO₄)₃ and Al(OH)₃  salts; under this premise, a ceramic system is designed, SiO₂-Al₂O₃-CaO, where biosolid ashes are incorporated as supplementary sources of SiO₂  and the aluminum salts as substitute for Al₂O₃.  The type of thermal treatment applied was a continuous and intermittent system.  Upon examination of the results in the mineral composition and the morphology of the materials obtained through DRX (X-ray Diffraction) and SEM (Scanning Electron Microscopy), it can be observed that the material submitted to both types of thermal treatments show phases of elevated hardness and of highly ordered crystal structures, such as corundum.  Nevertheless the materials that are more homogeneous and have more defined crystals are identified in those samples submitted to a continuous system thermal treatment.