Determination of the Processing Route for Obtaining Calcium Acetate from Eggshell Waste

Eggshell waste represents an underutilized biogenic resource, rich in calcium carbonate and organic components, whose increasing generation poses significant environmental and economic challenges. It is estimated that more than 8 million tons of eggshells are produced worldwide annually, most of which are disposed of in landfills, leading to landfill overload and increased waste management costs. In this context, the main objective of this study was to develop and compare three processing routes for converting calcium carbonate derived from eggshell waste into calcium acetate, using commercial vinegar (4–5% acetic acid) as a low-cost, sustainable acid source. The proposed routes were systematically evaluated based on processing efficiency, product characteristics, and operational simplicity. The materials obtained were characterized by X-ray fluorescence, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), X-ray photoelectron spectroscopy (XPS), particle size analysis, and zeta potential measurements. The results indicated that the eggshells contained approximately 95.39% calcium, confirming their suitability as an efficient calcium precursor. Among the routes evaluated, the process using a spherical condenser under reflux at 90 °C showed superior performance, achieving shorter reaction times and maintaining comparable yields of membrane byproducts compared to the other methods. This approach differs from conventional routes by eliminating the need for high-purity reagents, reducing processing time, and using exclusively food-grade acetic acid, thus increasing sustainability and cost-effectiveness. Morphological, chemical, and thermal analyses confirmed the quality and stability of the synthesized calcium acetate. In general, these results demonstrate that eggshell waste can be efficiently valorized into calcium acetate through a scalable, straightforward process, thereby reducing landfill disposal and supporting circular economy strategies, with potential applications in the production of calcium-based biomaterials.