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

Abstract

The selective removal of 90Sr from natural waters and technological effluents is an important issue to ensure radiation safety. Manganese dioxide with layered structure was prepared through the reaction of potassium permanganate with manganese chloride 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 the synthesized birnessite is formed as agglomerated microspheres. Scanning electron microscopy and adsorption–desorption method revealed that birnessite is formed as agglomerated microspheres with mesoporous texture and external surface area of 207 m2/g. To determine the efficiency of the synthesized birnessite in selective removal of strontium ions from multicomponent solutions, the effect of contact time, competitive ions (Na, K, Ca) and pH on strontium ions adsorption was investigated in detail. Strontium ions adsorption has demonstrated a fast initial adsorption followed by a much slower sorption process. It was found that the synthesized birnessite can effectively remove strontium ions from monocomponent solution. The presence of alkaline metals ions in the model solutions (up to ~ 0.3 mol/l) 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 characterized by a high concentration of calcium ions and a significant excess of calcium over strontium ions, the synthesized birnessite can be considered as an adsorbent with a rather high selectivity toward strontium ions. It can be effectively applied for the removal of strontium ions from multicomponent solutions with a high salt content. The alkaline medium is preferable for selective removal of strontium ions. The synthesized birnessite has lots of additional advantages, such as its simple fabrication process, low-cost raw materials and the ease of desorption.