Valorization of Skipjack Tuna (Katsuwonus pelamis) Bone Waste into Tunable Calcium Phosphates: Empirical Modeling of Thermal Transformation

Skipjack tuna (Katsuwonus pelamis) bone waste is an abundant, underutilized resource that poses significant environmental disposal challenges. Here, calcium phosphate (CaP) nanopowders were synthesized via controlled calcination (600–1000 °C, 1–4 h) to valorize this byproduct. The effects of calcination temperature and duration on phase composition, lattice parameters, Ca/P ratio, particle size, and trace metal concentrations were evaluated using regression models incorporating temperature–duration interactions, with quadratic models used to assess nonlinear responses. XRD and FTIR confirmed the formation of B-type carbonated nano-hydroxyapatite at 600 °C, followed by its progressive transformation into biphasic HAp/β-TCP above 800 °C. The regression models exhibited strong empirical performance, identifying calcination temperature as the dominant factor governing phase evolution and lattice contraction. Particle size increased from approximately 36 to 214 nm and was the only response variable requiring a quadratic model, indicating nonlinear growth during calcination. Trace metal concentrations (As, Cd, and Pb) remained well below the limits specified by ASTM F1185. These findings demonstrate that K. pelamis bone waste can be converted into tunable biphasic CaP biomaterials and provide an empirical framework for minimizing energy consumption and reducing trial-and-error experimentation during sustainable waste valorization.