Brushite(CaHPO4·2H2O) prepared by spontaneous precipitation with different phosphate salts and calcium lactate derived from scallop shell wastes

The utilization of food waste as a starting material is a green strategy for producing calcium hydrogen phosphate dihydrate (CaHPO 4 · 2 H 2 O, brushite) through spontaneous precipitation using calcium lactate (CL, Ca(CH 3 CHOHCOO) 2 ·H 2 O) derived from scallop shell waste with M 2 HPO 4 (M = Na, K, and NH 4 ). The prepared brushite samples were designated Brushite Na, Brushite K, and Brushite NH4, respectively, based on the phosphate source. The highest production yield (97.32%) was observed for Brushite Na, while the highest purity (86.28%) was observed for Brushite NH 4 . The thermal behaviors of all obtained brushites are very similar, confirming the dehydration reaction and the presence of water crystals (2.5 mol H 2 O) in the structure. The factor group splitting analysis was used to illustrate the vibrational spectra of the HPO 4 2− and H 2 O functional groups. For the HPO 4 2− unit, the correlation field splitting analysis of type C 3v −C s −C s 4 was calculated and had 48 internal modes, whereas H 2 O in the above hydrate was symbolized as C 2v −C s −C s 4 and had 12 modes. The synthesized brushite crystallized in the monoclinic crystal system without detectable impurity phases, as revealed by XRD patterns. The highest diffraction peak (∼11.65°, hkl = 020) indicated the plate-like brushite particles, which are consistent with the plate-like morphology revealed by the SEM result. The brushite precipitations reported in this work provide useful information for large-scale industrial synthesis to obtain low-cost products and are expected to serve as an alternative for the removal and value-added processing of scallop shells, reducing enormous waste in the future.