The Sorption of Thorium and Americium onto Fresh and Degraded Ordinary Portland Cement and onto Green Tuff

Abstract

ABSTRACTThe sorption of thorium and americium has been measured onto crushed samples of freshordinary Portland cement (OPC), degraded OPC (DOPC) and green tuff under a range of aqueous conditions as part of research into the disposal of TRU waste in Japan. Sorption onto OPC was measured from deionised water,3 mol dm−3sodium nitrate solution and simulated seawater, and onto DOPC from demineralised water; all solutions were pre-equilibrated with the relevant cement. Sorption onto tuff was measured from pre-equilibrated deionised water, 3 mol dm−3sodium nitrate solution, simulated seawater, OPC leachate and 1 mol dm−3ammonium hydroxide solution. RDvalues were determined from the amount of thorium or americium remaining in solution after centrifugation, 0.45 μm filtration and 10,000 nominal molecular weight cut-off (NMWCO) filtration. Centrifugation gave lower RDvalues than filtration. MeanRDvalues for sorption onto OPC and DOPC were in the range 4 × 104to ≥1 × 106cm3g−1for thorium, and 3 ×103to ≥1 × 105cm3g−1for americium, after filtration through 10,000 NMWCO filters. Mean RDvalues for thorium sorption onto tuff increased from2 × 103cm3g−1in tuff-equilibrated deionised water, to ≥ 4 × 106cm3g−1from ammonium hydroxide solution (10,000 NMWCO-filtration). A similar trend was seen for10,000 NMWCO-iltered americium samples where mean RDvalues increased from 4 × 103cm3g−1in deionised water to 1 × 105cm3g−1in ammonium hydroxide solution.