Removal of oxovanadium(IV) from aqueous solutions by using commercial crystalline calcium hydroxyapatite.

The interaction of oxovanadium(IV) (VO(2+)) in aqueous solution with commercial calcium hydroxyapatite (CAP) has been studied. VO(2+) ions are adsorbed on the surface of CAP by coordination to OH groups, without modification of the crystalline lattice. The extent of the adsorption is followed by chemical analysis, ESR and IR spectroscopy. Results are compared with those obtained for VO(2+)/synthetic calcium hydroxyapatite (HAP), reported by us in previous works. The uptake is better than the observed for HAP. The maximum adsorption is observed at pH 3.5 and 288 K. We conclude that VO(2+) is indeed adsorbed on CAP and the extent of adsorption depends on the pH and temperature.