Adsorption of Co 2+, Ni 2+, Cu 2+ and Zn 2+ from 0.5 M NaCl and major ion sea water on a mixture of δ-MnO 2 and amorphous FeOOH

Abstract

The pH pzc values of several mechanical mixtures of amorphous hydrous oxides of iron (amorphous FeOOH) and manganese ( δ-MnO 2) have been determined using the solid addition method. While the pH pzc of δ-MnO 2 remains almost unchanged, the corresponding value for amorphous FeOOH tends to increase with increased proportion of δ-MnO 2 in the mixtures. The adsorption behavior of Co 2+, Ni 2+, Cu 2+, and Zn 2+ with respect to pH on a mechanical mixture of 70% δ-MnO 2 and 30% amorphous FeOOH from 0.5 M NaCl and major ion sea water has been studied. Since δ-MnO 2 is much more active adsorbent than amorphous FeOOH at pH below 6.5, the adsorption data on mixture have not only been normalized with respect to the mass of δ-MnO 2 in the mixture, but also compared with adsorption data on δ-MnO 2 alone. It is interesting to note that though each trace metal behaves in a different way from the other especially with respect to the nature of electrolyte medium, it is generally observed that the adsorption on the mixed oxide system is higher than that on δ-MnO 2 alone under similar condition. It is also observed that adsorption in major ion sea water at a particular pH value is lower than in 0.5 M NaCl solution.