Upcycling industrial residues into tobermorite-bearing calcium silicate hydrates

Abstract

Considering the increasing volume of industrial waste and the gaps in the literature regarding the integrated correlation between the crystalline structure, microstructure, and surface properties of hydrated calcium silicate compounds obtained exclusively from complex waste, this study addresses the valorization of FGD ash for the synthesis of tobermorite-containing materials. The objective was to integratively characterize a C–S–H compound previously synthesized from FGD, focusing on structural, morphological, and textural confirmation for environmental applications. The material was characterized by XRF, XRD, FTIR, Raman, SEM/EDS, TGA, helium pycnometry, particle size distribution, and N₂ adsorption (BET/BJH), in addition to a brief bibliometric analysis for scientific contextualization. The results indicated a composition rich in SiO₂ (26.1%) and CaO (23.1%), with a Ca/Si ratio of ≈0.89 and significant presence of Na, Mg, and Al. XRD confirmed the formation of tobermorite associated with semicrystalline C–S–H compound phases. FTIR and Raman evidenced silicate chains Q¹–Q³, while SEM revealed a typical lamellar morphology. The true density was 2.10 g·cm⁻³, and the specific surface area was 14.85 m²·g⁻¹, with predominantly mesoporous porosity (≈21 nm). TGA demonstrated thermal stability up to ~450 °C. It is concluded that the adopted process enabled the production of a structurally stable and texturally suitable multiphasic material for environmental applications, contributing to circular economy strategies and the valorization of industrial waste.