Carbonate apatite derived from Northern region limestone of Malaysia: A preliminary evaluation

The global rise in bone reconstructive surgeries necessitates effective artificial bone substitutes, with carbonate apatite (CO3Ap) being a promising candidate for bone regeneration. However, CO3Ap cannot be sintered due to thermal decomposition at high sintering temperatures. An alternative method to synthesis CO3Ap is via dissolution-precipitation reaction of precursor such as calcium carbonate (CaCO3). This study focuses on the feasibility to synthesis CaCO3 precursor from natural source material such as limestone. In this study, limestone obtained from the Northern Region of Malaysia were utilized to synthesis CaCO3. The limestone was subjected to calcination, dissolution in distilled water and dried to produce calcium hydroxide (Ca(OH)2) powder, which was subsequently carbonated at room temperature and 4 °C to produce calcite and vaterite, polymorphs of CaCO3, respectively. These were then pressed into pellets and immersed in 1 M sodium hydrogen phosphate (Na2HPO4) solution at 80 °C for up to 14 days. Characterization using X-ray Diffraction (XRD), Fourier transform infra-red (FTIR), scanning electron microscope (SEM), particle size analyzer and carbon-hydrogen-nitrogen (CHN) analyzer were conducted to examine the formation of CO3Ap. FTIR analysis identified the synthesized product as AB-type CO₃Ap. Vaterite precursor treated in 1 M Na2HPO4 transform to CO3Ap within 3 days with 13.5 wt% of carbonate content while for calcite precursor, the transformation to CO3Ap was within 7 days with 11.8 wt% of carbonate content. This is due to vaterite having higher surface area and solubility when compared to calcite in aqueous solution. These findings suggest the feasibility to obtain high-purity CO3Ap by utilizing locally available limestone are feasible.