Adsorption of Co2+, Ni2+, Cu2+ and Zn2+ from 0.5 M NaCl and major ion sea water on a mixture of δ-MnO2 and amorphous FeOOH

The pHpzc values of several mechanical mixtures of amorphous hydrous oxides of iron (amorphous FeOOH) and manganese (δ-MnO2) have been determined using the solid addition method. While the pHpzc of δ-MnO2 remains almost unchanged, the corresponding value for amorphous FeOOH tends to increase with increased proportion of δ-MnO2 in the mixtures. The adsorption behavior of Co2+, Ni2+, Cu2+, and Zn2+ with respect to pH on a mechanical mixture of 70% δ-MnO2 and 30% amorphous FeOOH from 0.5 M NaCl and major ion sea water has been studied. Since δ-MnO2 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-MnO2 in the mixture, but also compared with adsorption data on δ-MnO2 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-MnO2 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.