Comparative structural screening of calcium phosphate powders recovered from Labeo rohita fishbone and fish-scale waste under a common calcination schedule

Fishbone and fish-scale residues offer related but structurally distinct feedstocks for calcium-phosphate recovery. This study compares Labeo rohita bone and scale processed by source-adapted pretreatments and a common calcination schedule of 820°C for 2 h at 5°C min⁻¹. The objective was to examine whether a shared thermal treatment produces comparable structural and morphological outcomes. X-ray diffraction showed apatite-compatible reflections in both powders, with additional β-tricalcium-phosphate-compatible reflections in the scale-derived product. Fourier-transform infrared spectra supported phosphate-containing structures and showed a carbonate-associated feature in the bone-derived powder. Scanning electron microscopy revealed rough, fused agglomerates in both products, with compact aggregates in the bone field and larger hierarchical clusters in the scale field. This preliminary structural and morphological screening provides a same-species comparison of two complete processing routes. Its engineering significance is that a common calcination schedule does not by itself ensure equivalent calcium-phosphate products; precursor architecture and pretreatment must be considered together when selecting routes for subsequent application testing.