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 (CO 3 Ap) being a promising candidate for bone regeneration. However, CO 3 Ap cannot be sintered due to thermal decomposition at high sintering temperatures. An alternative method to synthesis CO 3 Ap is via dissolution-precipitation reaction of precursor such as calcium carbonate (CaCO 3 ). This study focuses on the feasibility to synthesis CaCO 3 precursor from natural source material such as limestone. In this study, limestone obtained from the Northern Region of Malaysia were utilized to synthesis CaCO 3 . 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 CaCO 3 , respectively. These were then pressed into pellets and immersed in 1 M sodium hydrogen phosphate (Na 2 HPO 4 ) 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 CO 3 Ap. FTIR analysis identified the synthesized product as AB-type CO₃Ap. Vaterite precursor treated in 1 M Na 2 HPO 4 transform to CO 3 Ap within 3 days with 13.5 wt% of carbonate content while for calcite precursor, the transformation to CO 3 Ap 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 CO 3 Ap by utilizing locally available limestone are feasible.