Eggshell waste valorization into CaO/CaCO₃ solid base catalysts

One of the main challenges of a circular economy is the reuse of waste into value-added products. In this context, the large amounts of food waste generated globally have become a great renewable resource for recycling and transformation, increasing the sustainability of the supply chain. In particular, 7.2 million tons of hen eggshell waste are produced annually, which is converted into a source of environmental pollution. However, eggshell is a biodegradable residue composed of more than 90% CaCO₃ and thus can be exploited as a catalyst, adsorbent, composite, and functional material, among other uses. The aim of the present work is the valorization of eggshell waste to obtain CaO/CaCO₃ materials with applications as heterogeneous catalysts.
Domestic hen eggshells were first washed with tap water to eliminate impurities, and then the inner membrane was manually removed. Afterward, the eggshells were dried in an oven at 80 °C for 24 h under air. The dried eggshells were calcined in a muffle at different temperatures, times, and heating speeds to achieve diverse compositions. The crystalline structures achieved were characterized by X-ray diffraction (XRD), while their textural properties were obtained through N₂ adsorption–desorption (the BET method). Thermogravimetric analyses (TGA) were used to study the thermal stability of the obtained samples. The physicochemical changes and properties observed were correlated with the treatments applied, evidencing the transformation from CaCO₃ to CaO. Considering these preliminary results, the prepared solids could be useful as base catalysts in different heterogeneous reactions.