Conversion of Bivalve Shells to Monocalcium and Tricalcium Phosphates: An Approach to Recycle Seafood Wastes

The search for sustainable resources remains a subject of global interest and the conversion of the abundantly available bivalve shell wastes to advanced materials is an intriguing method. By grinding, calcium carbonate (CaCO₃) powder was obtained from each shell of bivalves (cockle, mussel, and oyster) as revealed by FTIR and XRD results. Each individual shell powder was reacted with H₃PO₄ and H₂O to prepare Ca(H₂PO₄)₂·H₂O giving an anorthic crystal structure. The calcination of the mixture of each shell powder and its produced Ca(H₂PO₄)₂·H₂O, at 900 °C for 3 h, resulted in rhombohedral crystal β-Ca₃(PO₄)₂ powder. The FTIR and XRD data of the CaCO₃, Ca(H₂PO₄)₂·H₂O, and Ca₃(PO₄)₂ prepared from each shell powder are quite similar, showing no impurities. The thermal behaviors of CaCO₃ and Ca(H₂PO₄)₂·H₂O produced from each shell were slightly different. However, particle sizes and morphologies of the same products obtained from different shells were slightly different-but those are significantly different for the kind of the obtained products. Overall, the products (CaCO₃, Ca(H₂PO₄)₂·H₂O, and Ca₃(PO₄)₂) were obtained from the bivalve shell wastes by a rapidly simple, environmentally benign, and low-cost approach, which shows huge potential in many industries providing both economic and ecological benefits.