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 (CaCO<inf>3</inf>) powders, which were then used as the renewable material to synthesize calcium acetate monohydrate (Ca(CH<inf>3</inf>COO)<inf>2</inf>·H<inf>2</inf>O) via acetic acid reaction. After that, cockle-derived calcium acetate monohydrate was subsequently prepared as a solution to synthesize calcium pyrophosphate (Ca<inf>2</inf>P<inf>2</inf>O<inf>7</inf>·xH<inf>2</inf>O) via a simple precipitation process with tetrasodium pyrophosphate decahydrate (Na<inf>4</inf>P<inf>2</inf>O<inf>7</inf>·10H<inf>2</inf>O). 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 (CaCO<inf>3</inf>) is a potentially renewable source for the preparation of triclinic calcium acetate with the chemical formula of Ca(CH<inf>3</inf>COO)<inf>2</inf>·H<inf>2</inf>O, which was further used as the precursor to form value-added amorphous calcium pyrophosphate with the chemical formula of Ca<inf>2</inf>P<inf>2</inf>O<inf>7</inf>·4H<inf>2</inf>O. 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.