Chelating Adsorbent for Heavy Metal Ions Prepared by Loading Anion-Exchange Resin with Thiacalix[4] arenetetrasulfonate

A chelating adsorbent for heavy metal ions has been prepared by loading an anion-exchange resin with thiacalix[4]arenetetrasulfonate (TCAS). Batchwise extraction studies have revealed a high adsorption ability of the TCAS-loaded resin toward heavy metal ions with high selectivity. The present resin strongly retained the heavy metal ions tested here [Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)] in a slightly acidic to neutral pH region, while no adsorption was observed for alkaline earth metal ions, Mg(II) and Ca(II), in this pH region. These adsorption characteristics of the present resin should be ascribed to the contribution of the bridging sulfur of the loaded TCAS to selectively coordinate to metal ions categorized to be soft to intermediate Lewis acids by the Hard and Soft Acids and Bases (HSAB) rule. A continuous column adsorption system with the present resin allowed the selective and almost quantitative (more than 99.98%) removal of heavy metal ions.