Effect of monovalent and divalent ion solutions as washing agents on the removal of Sr and Cs from soil near a nuclear power plant.

Solutions of monovalent and divalent ions, including calcium, magnesium, ammonium, and potassium, were tested in the removal of Sr and Cs from soil near a nuclear power plant. The Ca and K solutions exhibited removal efficiencies of 68.2% and 81.3% for Sr and Cs, respectively. This high performance was probably due to the physicochemical similarities between 'Ca and Sr' and 'K and Cs'. Alternatively, the Mg and NH solutions performed much worse, despite having the same valences as Ca and K, respectively. Ca and K solutions could also simultaneously remove cationic toxic metals present with the nuclides, albeit much less efficiently (30-40%). For anionic metalloid As and anionic toxic metal Cr, the efficiency was even lower (< 20%). The five-step sequential extraction experiment confirmed that all chemical forms of Sr and Cs, except the residual form, were extensively removed by the Ca and K solutions respectively. For comparison, widely used washing agents exhibited removal efficiencies of 25-30%. Notably, Fe and Mn ions were hardly detected in the Ca solution, while their concentrations were much higher in the common washing agents, suggesting the involvement of an ion-exchange mechanism in Sr and Cs removal, rather than a Fe/Mn oxide dissolution mechanism.