Adsorption of Pb2+, Zn2+, and Cd2+ from waters by amorphous titanium phosphate

In the current study, amorphous titanium phosphate (TiP) was prepared as an adsorbent for heavy metals from waters. Uptake of Pb2+, Zn2+, and Cd2+ onto TiP was assayed by batch tests; a polystyrene–sulfonic acid exchanger D-001 was selected for comparison and Ca2+ was chosen as a competing cation due to its ubiquitous occurrence in waters. The pH-titration curve of TiP implied that uptake of heavy metals onto TiP is essentially an ion-exchange process. Compared to D-001, TiP exhibits more preferable adsorption toward Pb2+ over Zn2+ and Cd2+ even in the presence of Ca2+ at different levels. FT-IR analysis of the TiP samples laden with heavy metals indicated that the uptake of Zn2+ and Cd2+ ions onto TiP is mainly driven by electrostatic interaction, while that of Pb2+ ions is possibly dependent upon inner-sphere complex formation, except for the electrostatic interaction. Moreover, uptake of heavy metals onto TiP approaches equilibrium quickly and the exhausted TiP particles could be readily regenerated by HCl solution.