Development of Geopolymers from Phosphate By-Products for Thermal Insulation Applications

Abstract

Phosphate mining generates large quantities of waste rock and sludge annually, resulting in significant environmental issues. The large areas of mine sites used to store these wastes limit the availability of usable and agricultural land, alter the topography of the land, and degrade the landscape’s aesthetics. In this study, the acid activation of phosphate by-products to enhance their reactivity and suitability for the development of geopolymer-based thermal insulation materials was investigated. Four formulations of geopolymers were developed using varying ratios of calcined clay by-product and metakaolin as aluminosilicate sources. The activation of precursors was accomplished using a 5M concentration of phosphoric acid (H3PO4). Several analytical techniques, including mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray fluorescence (XRF), were carried out to characterize both the raw clays and resulting geopolymers. Furthermore, the physical and mechanical properties of the synthesized geopolymers have been evaluated. The results demonstrated a notable increase in porosity from 25.63% to 45.56% with the escalation of calcined clay content in geopolymers. This enhanced porosity facilitated the preparation of building insulation materials where mechanical strength is not a main requirement, as the thermal conductivity reached a value of 0.08 W/mK.