Features of Sr sorption on iron-manganese nodules of the Arctic shelf in natural and barium forms

To assess the potential of using local resources for the emergency response in the area of the Northern Sea Route and the location of the Akademik Lomonosov floating nuclear power plant, a comparative study of the sorption properties towards the radionuclides Sr was conducted on iron-manganese nodules (Fe-Mn nodules) from the Chaun Bay of the East Siberian Sea in natural and barium forms. It was shown that in the absence of competing ions, the sorption of strontium on the natural form of Fe-Mn nodules occurs primarily through ion exchange with calcium and magnesium ions, with a distribution coefficient (K) for Sr of 5.5 · 10 mL/g, and is accompanied by the formation of a SrMnO · xHO phase. Converting the Fe-Mn nodules into the barium form resulted in a significant improvement of their sorption properties in seawater: the K for Sr increased from 5.2 · 10 mL/g to 1.5 · 10 mL/g, and the sorption capacity tripled. It was demonstrated that the increased selectivity of the barium form of Fe-Mn nodules to Sr sorption from seawater is achieved due to the change in the sorption mechanism from ion exchange to the precipitation of Sr with the poorly soluble barium sulfate phase, which is formed in the presence of sulfate ions in seawater. The obtained results allow classification of the barium form of Fe-Mn nodules as one of the most effective inorganic sorbents for Sr immobilization from seawater and seawater-containing liquid radioactive wastes.