Magnetic manganese dioxide as an amphoteric adsorbent for removal of harmful inorganic contaminants from water

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.