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

Abstract

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 Ca2+ 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 Mg2+ and NH4+ solutions performed much worse, despite having the same valences as Ca2+ and K+, respectively. Ca2+ 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 fivestep sequential extraction experiment confirmed that all chemical forms of Sr and Cs, except the residual form, were extensively removed by the Ca2+ and K+ solutions, respectively. For comparison, widely used washing agents exhibited removal efficiencies of 25?30%. Notably, Fe2+ and Mn2+ ions were hardly detected in the Ca2+ 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.