Synthesis and Characterisation of Hydroxyapatite (HAp) from Asiatic Hard Clam (Meretrix meretrix) and Blood Cockle Clam (Anadara granosa) Using Wet Precipitation Process

Hydroxyapatite (HAp) is a bioceramic material having numerous applications in orthopaedic and dental applications. It can be chemically synthesised from materials that are rich in calcium carbonate (CaCO3). Asiatic Hard Clam (Meretrix meretrix) and Blood Cockle Clam (Anadara granosa) are the commercial species in Southeast Asia, resulting in the discharge of abundant waste shells, which further leads to microbial growth, odour and an unhygienic environment. Moreover, shells are the global source of CaCO3. In order to convert the waste into a valuable product, this study aims to synthesise and characterise HAp from Asiatic Hard Clam and Blood Cockle Clam via a wet precipitation process. These clamshells were characterised by X-Ray fluorescence (XRF), and the result revealed that Asiatic Hard Clam contains 97.4 wt% of CaCO3 and Blood Cockle Clam of about 98.8 wt% of CaCO3. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of $-\left(\mathrm{PO}_{4}\right)_{3}^{2-},-\mathrm{CO}_{3}^{2-}$ and -OH functional groups in the synthesised HAp. The X-Ray powder diffraction (XRD) patterns of this powdered HAp showed sharper peaks which indicates better crystallinity. Moreover, the morphology of the HAp before and after sintering was characterised with the help of scanning electron microscope (SEM), which clearly showed the crystalline structure and coalescence of HAp particles. Results have revealed that HAp derived from both natural clamshells using the wet precipitation method displayed similar crystallinity, morphology and chemical characteristics of pure HAp.