Nanocomposites and nanomaterials
Synthesis and evaluation of nano manganese dioxide with layered structure as an adsorbent for selective removal of strontium ions from aqueous solution

Yu.V. Bondar, S.V. Kuzenko
State Institution “The Institute of Environmental Geochemistry of National Academy of Sciences of Ukraine”, 34a Palladin ave., Kyiv 03142, Ukraine
E-mail: juliavad@yahoo.com

The selective removal of Sr-90 from liquid radioactive waste and their quantitative determination in the environment have a great importance in recent years. Inorganic adsorbents are the preferred materials for the removal of radionuclides from contaminated waters due to their high selectivity, radiation and thermal stability; and among them manganese dioxide is considered as a promising material for the selective removal of strontium ions from multicomponent contaminated waters.
Nano manganese dioxide with layered structure was prepared through one step experiment in alkaline medium at room temperature. The results of X-ray diffraction method and Fourier transform infrared spectroscopy confirmed the formation of c-disordered hexagonal birnessite. Scanning electron microscopy revealed that birnessite is formed as nanostructured microspheres. 
To determine the efficiency of the synthesized birnessite in selective removal of strontium ions from multicomponent solutions the effect of reaction time, competitive ions (Na, K, Ca) and pH on strontium ions adsorption was investigated in detail. The batch adsorption experiments indicated that birnessite could achieve a fast and efficient adsorption of strontium ions from aqueous solutions. The pH value in the model solutions has a major impact on the adsorption ability of the synthesized birnessite; a higher adsorption efficiency is obtained in an alkaline medium. The presence of alkaline metals ions in the multicomponent solutions had little effect on strontium ions adsorption; however, calcium ions caused considerable decrease in the adsorption parameters. However, taking into account a relatively high adsorption parameters obtained in the model solutions characterizing by a high concentration of calcium ions and a significant excess of calcium over strontium ions, the synthesized nano manganese dioxide with layered structure (c-disordered hexagonal birnessite) can be considered as an adsorbent with a rather high selectivity towards strontium ions. It can be effectively applied for the removal of strontium ions from multicomponent solutions with a high salt content. The synthesized birnessite has lots of additional advantages, such as its simple fabrication process, low cost raw materials, and the ease of desorption.