Use of hydrous manganese dioxide as a potential sorbent for selective removal of lead, cadmium, and zinc ions from water.

Selective removal of three toxic metal ions, Pb(II), Cd(II), and Zn(II), from aqueous solution by amorphous hydrous manganese dioxide (HMO) was evaluated. Two polymeric exchangers, a polystyrene-sulfonic cation exchanger, D-001, and an iminodiacetic acid chelating exchanger, Amberlite IRC 748, were involved for comparison. Hydrogen ion release is accompanied by metal uptake onto HMO, implying that metal sorption could be generally represented by an ion-exchange process. As compared to both exchangers, HMO exhibits preferable sorption toward the toxic metals in the presence of Ca(II) ions at greater levels. FT-IR of the HMO samples laden with different metals indicate that Ca(II) uptake onto HMO is mainly driven by outer-sphere complexation, while that of three toxic metals might be related to inner-sphere complex formation. In addition, uptake of heavy metals onto HMO approaches equilibrium quickly and the exhausted HMO particles can be regenerated readily for repeated use by HCl solution. The results reported strongly display the potential of HMO as an economic and selective sorbent for removal of toxic metals from contaminated waters.