Eggshells from agro-industrial waste for the recovery of lime, portlandite, and calcite nanoparticles through the lime cycle: A circular economic approach

Abstract

This work focused on the study the lime cycle for samples obtained from agro-waste of chicken eggshells, mainly composed of calcite (CaCO3), in the context of circular economy concept and for nanotechnological applications. The thermal analysis (TGA/DSC) analyzed the transformation temperatures of the individual phases. Based on these results, the eggshells were calcined at 850 °C to ensure the complete conversion of calcite into lime (CaO). The lime was then hydrated with distilled water to convert it into portlandite (Ca(OH)2). The samples belonging to this cycle were structurally characterized using X-ray diffraction, and the vibrational states were identified using Fourier transform infrared spectroscopy. Scanning Electron Microscopy was used to study the changes in morphology and crystallite size. This showed that all compounds along the cycle are microparticles consisting of nanocrystals, which correlated with the Dynamic Light Scattering results. The Zeta potential was used to determine the surface charge of the samples and shown a variety of results due to the different transformations during the cycle and the mineral content of the eggshells as shown by the results of the ICP technique.

Keywords

• Lime cycle
• Circular economy
• Temperatures of calcination
• Mineral content