A review on preparation raw materials, synthesis methods, and modifications of hydroxyapatite as well as their environmental applications

Hydroxyapatite (HAP) is an environmentally friendly material with good biocompatibility and bioactivity as well as excellent ion exchange and adsorption properties, which has potential application prospects in the environment. In this paper, the preparation raw materials (e.g., mineral resources, industrial waste, and biological waste, especially for eggshell biowaste) and synthesis methods (e.g., precipitation, hydrothermal, sol-gel, biomimetic, mechanical, and high-temperature calcination, especially for eggshell treatment and eggshell-based HAP preparation) of HAP are systematically reviewed. HAP modifications (e.g., metal doping, non-metal recombination, and organic substances composite) and their environmental applications (e.g., adsorption of inorganic anions, metal ions, and organic substances, as well as catalytic degradation of pollutants) in the environment are summarized. At the same time, the factors affecting adsorption efficiency and the desorption and regeneration properties of HAP and its derivatives were discussed. Finally, the directions of research and application on HAP in the future are pointed out. This review provides a scientific basis for the research and application of HAP in adsorption removal and catalytic degradation of pollutants.