Utilization of waste phosphogypsum to prepare hydroxyapatite nanoparticles and its application towards removal of fluoride from aqueous solution

In the present study, waste phosphogypsum (PG) was utilized firstly to prepare hydroxyapatite nanoparticles (nHAp) via microwave irradiation technology. The nHAp derived from PG exhibited a hexagonal structure with the particle size about 20 nm × 60 nm and high purity. Meanwhile, the adsorption behaviour of fluoride onto the nHAp derived from PG was investigated to evaluate the potential application of this material for the treatment of the wastewater polluted with fluoride. The results indicate that the nHAp derived from PG can be used as an efficient adsorbent for the removal of fluoride from aqueous solution. The maximum adsorption capacities calculated from Langmuir–Freundlich model were 19.742, 26.108, 36.914 and 40.818 mg F−/g nHAp for 298, 308, 318 and 328 K, respectively. The pseudo-second order kinetic model was found to provide the best correlation of the used experimental data compared to the pseudo-first order and the adsorption isotherm could be well defined by Langmuir–Freundlich equation. The adsorption mechanism investigation shows that electrostatic interaction and hydrogen bond are the main driving force for fluoride uptake onto nHAp derived from waste PG.