Thermal extraction and physicochemical characterization of nanocrystalline hydroxyapatite from bovine bone waste

This research demonstrated the feasibility of extracting nanostructured hydroxyapatite (HAp) from bovine bone waste through controlled thermal calcination at 600, 800, and 1000 °C. Thermal analysis showed mass losses of 32.50–34.90%, reflecting progressive removal of the organic matrix. Updated XRD analysis confirmed the HAp diffraction fingerprint in all calcined samples but revealed a non-monotonic structural response: H2 (800 °C) produced the largest apparent crystallite size (100.09 nm), the highest crystallinity proxy (96.4%), and the lowest microstrain (2.207 × 10⁻³), whereas H3 and H1 both showed crystallite sizes of 19.91 nm, crystallinity proxies of 92.7%, and microstrain values of 9.211 × 10⁻³. The phase-purity proxy is highest for H3 and H1 (90.6%) and lower for H2 (88.2%), indicating that crystallinity and phase-purity proxies should be interpreted separately. The additional comparative curves for crystallite size, microstrain, crystallinity, and phase purity visualize these temperature-dependent differences. FTIR confirmed characteristic phosphate and structural hydroxyl bands, with H2 showing the clearest overall HAp fingerprint and H1 the lowest prominence of collagen-related bands. DLS identified a small effective hydrodynamic diameter of 15.1 nm and a low polydispersity index of 0.289 for H1, while SEM showed progressive development of granular and faceted morphologies. Overall, 800 °C favored XRD lattice ordering and FTIR definition, whereas 1000 °C favored organic removal and dispersion behavior; therefore, the optimum calcination condition depends on the targeted structural, chemical, or particulate property.