Enhancing thermal insulation with phosphate washing sludge waste as an inorganic foaming agent in porous acid-based geopolymers: Formulation and processing optimization

Abstract

This study explores the potential utilization of phosphate washing sludge (PWS), a calcium carbonate-rich by-product of phosphate mining, as an inorganic foaming agent in the production of porous acid-based geopolymers. The investigation focused on evaluating the impact of various factors, including phosphoric acid concentration (ranging from 8 M to 12 M), liquid/solid (L/S) ratio (0.8 to 1.2), and the amount of PWS added (ranging from 0 wt% to 50 wt%), on the properties of the resulting geopolymers, such as porosity, density, thermal conductivity, and compressive strength. To optimize the formulation and processing parameters of porous acid-based geopolymers, a surface response methodology using statistical modeling was employed. This approach facilitated a systematic examination of the different factors influencing the properties of geopolymers. The raw materials involved in the study, namely kaolinitic clay, PWS, and the produced geopolymers, were characterized using various techniques such as X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscope coupled with Energy Dispersive X-Ray (SEM/EDX), laser particle size analysis, and mapping. The results revealed that the combination of a phosphoric acid concentration of 10 M, a L/S ratio of 0.88, and the addition of 16 wt% PWS yielded the best performance in terms of porosity, compressive strength, and thermal conductivity, with values of 29.4 %, 13.8 MPa, and 0.0931 W/m.K, respectively. Additionally, a mathematical model was developed to predict optimal parameter combinations for desired performance characteristics. This research holds promise for the development of cost-effective thermal insulation materials for building applications.