Eggshell-derived hydroxyapatite/CeO₂ composite for efficient fluoride removal from water

Excessive fluoride ions in water pose a serious threat to human health, and measures should be taken to remove them. A new type of composite material, Es/CeO₂, was prepared by using waste eggshells and a hydrothermal method. The properties of the adsorbent were determined by characterization techniques. When the adsorbent was used to remove F^- ions from wastewater, at room temperature and pH 7, the adsorption capacity reached 17.8 mg g^-1 at an initial fluoride concentration of 30 mg L^-1. The adsorption isotherm model conforms to the Langmuir adsorption isotherm model. The kinetic results show that the pseudo-second-order model can better describe the adsorption process. To gain a detailed understanding of the adsorption mechanism of fluoride, XPS spectral analysis was conducted. It was found that the adsorption mechanism of fluoride by the complex Es/CeO₂ is a dual mechanism of ion exchange and chemical complexation working in concert. It performs well in adsorbing real water samples, can adapt to complex environments, and can withstand up to five adsorption and desorption cycles. The overall results indicate that Es/CeO₂ has great potential in fluoride removal.