Abstract

Manganese dioxide (δ-MnO₂) with magnetic properties has been synthesized by precipitation of MnO₂ in the presence of magnetite. The resulting material has a particle size distribution between 0.5 and 5 μm. Magnetization of the material is in the order of magnitude of that of magnetite. Therefore a solid–liquid separation by means of moderate magnetic fields is possible.

Due to the properties of δ-MnO₂ the point of zero charge of the surface is about 2.5. Therefore, the adsorbent is almost exclusively a cation exchanger although sorption of oxoanions is also possible. Sorption experiment with Cd²⁺, Ni²⁺, and Pb²⁺ ions revealed a preferred sorption. Alkaline earth ions such as Ca²⁺ affect the uptake only at high concentrations. Because of the small particles and the respective large specific surface, sorption is fast.