Cockle-shell biowaste as a low-cost renewable source for synthesis of calcium acetate monohydrate as a precursor of quasi-amorphous calcium pyrophosphate hydrate

Abstract

Calcium-rich seashell wastes can be used as renewable materials to prepare value-added compounds. This work proposed an eco-environmental preparation of calcium pyrophosphate by using cockle-shell biowaste as a low-cost renewable calcium source for the first time. Cockle shell was first ground, obtaining calcium carbonate (CaCO3) powders, which were then used as the renewable material to synthesize calcium acetate monohydrate (Ca(CH3COO)2·H2O) via acetic acid reaction. After that, cockle-derived calcium acetate monohydrate was subsequently prepared as a solution to synthesize calcium pyrophosphate (Ca2P2O7·xH2O) via a simple precipitation process with tetrasodium pyrophosphate decahydrate (Na4P2O7·10H2O). The physicochemical characteristics of the synthesized calcium acetate precursor and its calcium pyrophosphate product were investigated by X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy. The characterization results demonstrate that cockle shell powder (CaCO3) is a potentially renewable source for the preparation of triclinic calcium acetate with the chemical formula of Ca(CH3COO)2·H2O, which was further used as the precursor to form value-added amorphous calcium pyrophosphate with the chemical formula of Ca2P2O7·4H2O. This approach not only demonstrates the feasibility of using biogenic Ca-sources for material synthesis but also offers an environmentally friendly process with potential long-term benefits in reducing environmental issues, promoting sustainable chemical production, and increasing value to the underused biowaste.