Circular economy: development of calcium silicate hydrated compounds aimed at the sustainable use of waste from the coal industry

The valorization of industrial by-products is of great importance for the environment and human health. The Circular Economy is an alternative for this scenario, where the concepts of reuse, repurposing, and recycling are applied in the process aiming at a more sustainable production. In this study, sulfated coal ash generated in the desulfurization process of coal burning gases was used as starting material for the synthesis of calcium silicate hydrated compounds (C-S-H) by the two-step method (alkaline fusion followed by hydrothermal treatment). The following parameters that affect the synthesis were evaluated: fusion time, volume of water and agitation time for the alkaline hydrothermal treatment of the samples. The ash and the products obtained were characterized by X-ray fluorescence and X-ray diffraction. The synthesis efficiency was evaluated by the relative intensity of the main tobermorite peak. According to the characterization results, the highest crystallinity was obtained under conditions of fusion time of 1 h; volume of water of 200 mL and agitation time of 6 h. The reuse of ash as raw material for the synthesis of hydrated calcium silicate compounds was effective, meeting the objectives of the sustainable footprint.