Feasibility study on preparation of hydroxyapatite from calcium-containing construction waste

In response to the environmental issues arising from the increasing volume of urban construction waste, this study utilized waste putty powder as a calcium source to synthesize hydroxyapatite (HAP) via hydrothermal synthesis. The synthesized HAP was characterized using multiple analytical techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscope, scanning electron microscope, energy-dispersive spectrometer (EDS), and BET, to determine the optimal synthesis conditions. The results show that: (1) the diffraction peaks of the synthesized HAP match those of the standard XRD reference card; FTIR analysis confirms the synthesized HAP has characteristic absorption peaks of OH− and PO43−; and EDS scanning shows that the synthesized HAP contains Ca, P, and O elements, confirming the successful synthesis of HAP. (2) The optimal synthesis process conditions for synthesized HAP are pH = 9.5, oscillation temperature 60°C, oscillation time of 3 h, and calcination time of 3 h. (3) The Ca/P molar ratio is 1.62, at which the HAP synthesis rate reaches a maximum of 75.3%. With an aging time of 18 days, the microstructure of HAP achieves its best morphology. This study successfully achieved the efficient synthesis of HAP from waste putty powder, offering a promising strategy for the resourceful utilization and reduction of calcium-source construction waste.