Abstract:
Biological shells with simple components result in outstanding properties compared to the
man-made materials. Bivalve shells can be reused as a low-cost raw material for different
industrial applications. This study was focused on the characterization of Saccostrea
cucullata (Rock Oyster) shells collected from the Southern coastal zone in Sri Lanka and
identification the potential of synthesizing commercial products from oyster shells.
Collected oyster shells from Dickwella coastal belt were subjected to prepare shell
powder after sieving the crushed shells using a metal sieve with 600 micron of mesh size.
Shell powder samples were sintered at 1000◦C for two hours in the muffle furnace for
removal of moisture, gases, and other remnants. Raw oyster shells and prepared shell
powder samples were characterized using Fourier Transform Infrared Radiation (FT-IR),
X-ray Diffraction (XRD) and X-Ray Fluorescence (XRF) Spectroscopy. After analysis of
shell structure, functional groups, and composition, two wet precipitation techniques were
employed to synthesize Hydroxyapatite (HA): (Ca10(PO4)6(OH)2). The first method
includes converting shell CaCO3 into CaO as starting material, reacting with Nitric acid,
Phosphate provider & NH4OH at pH 10 and sintering. The second method consists of
converting calcined shell CaCO3 into Ca(OH)2, reacting with Phosphoric acid & NH4OH
at pH 10, and sintering. Based on characterization results, the oyster shell is mainly
composed of CaCO3 (98%), and extracted CaCO3 powder is compatible with properties of
commercial CaCO3 product. Based on XRF, the oyster shell also consists of trace
elements such as Zr, MgO, SO3, SiO2, and Sr. CaO level of shell powder was 97.9 % after
thermal decomposition of CaCO3 during firing. HA produced from the second method
recorded characteristic peak with high intensity at 2 theta value of 31.79◦ by signifying
the crystalline phase only for HA compound in XRD analysis. XRD and XRF results
revealed that HA powder which was produced from the second method using Ca(OH)2 as
starting material & sintering at a temperature of 900oC recorded similar composition
(CaO>77%, P2O5>20%) to the commercially available HA. In conclusion, rock oyster
shells act as environmentally friendly, value-added by-products to manufacture HA for
medical applications with the technical possibility to replace commercial HA.
Keywords: Bivalve shells, Shell characterization, Fourier transform infrared radiation, Xray diffraction, X-Ray fluorescence, Industrial applications, Hydroxyapatite
