Adsorption of uranium ions on nano-hydroxyapatite and modified by Ca and Ag ions

Adsorption of uranium ions on nano-hydroxyapatite modified by silver (Ag-HAP) and calcium (Ca-HAP) ions was examined. Composites or studied adsorbents were studied by means of XRD, ASAP and DLS molecules sizes. The Langmuir, Freundlich, and Dubinin-Radushkevich models were applied to describe the adsorption isotherms. The maximum adsorption capacity ( q m ) was found to be 8.1 mmol/g for Ca-HAP and 7.2 mmol/g for Ag-HAP at 293 K. The mean free energy values evaluated from the D-R model indicated that the adsorption of U(VI) ions on the adsorbents proceeds as the chemisorption mechanism. The adsorption equilibrium was reached for both sorbents after 120 min. The adsorption kinetics followed the pseudo-second-order model. There were determined basic parameters characterizing the double electrical layer at the nano-HAP/electrolyte and Ag-HAP/electrolyte, Ca-HAP/electrolyte inters faces: density of the surface charge and zeta potential.