Bio-Based Calcium Phosphate from Cow, Pig, Fish and Chicken Waste: Rietveld Refinement, Morphology, Optical Properties and Effects on Seed Germination

The conversion of animal waste into calcium phosphate (CaP) materials offers opportunities for biomass valorization, although feedstock-dependent differences require systematic assessment. This study compared CaPs obtained from bovine, porcine, and chicken bones, and pirarucu fish scales under identical thermal-treatment conditions at 700 °C for 7 h, combining structural, textural, optical, and preliminary seed-germination analyses. Mineral yields ranged from approximately 22% for CaP_Fish to 51% for CaP_Cow. X-ray diffraction and Rietveld refinement identified hydroxyapatite as the dominant crystalline phase in CaP_Cow and CaP_Fish, with the latter containing 99.36% hydroxyapatite and 0.64% CaO. CaP_Chicken and CaP_Pig exhibited multiphase compositions containing Ca9MgK(PO4)7 and NaCaPO4, respectively, alongside hydroxyapatite. FTIR and Raman spectroscopy supported the identification of phosphate-containing structures, while SEM revealed source-dependent particle morphologies. Specific surface areas ranged from 0.570 m2 g−1 for CaP_Cow to 8.318 m2 g−1 for CaP_Chicken. Photoluminescence measurements revealed distinct emission profiles, although assignment to specific defects or carbon quantum dots remained unconfirmed. Germination assays were conducted at 50 mg L−1 using three independent Petri dishes containing ten seeds per species and treatment. After seven days, CaP_Fish exhibited the highest mean maize germination percentage (83.33 ± 5.77%), but no CaP treatment differed significantly from the control. For tomato, only CaP_Cow showed significantly lower germination than the control. These findings demonstrate source-dependent differences in CaP properties while highlighting the need for further investigation before establishing optical applications, plant-growth benefits, or broader phytotoxic effects.