Mechanisms of cesium sorption onto magnetite

One of the current options for the final disposal of high level radioactive wastes is the deep geological repository (DGR). The metal canisters represent the first physical barrier to radionuclide migration towards the geosphere and their corrosion products may play a significant role in sequestering radionuclides by sorption and/or (co)precipitation phenomena. In this work, the sorption of 137Cs on pure nanocrystalline magnetite has been experimentally studied in a wide range of pH, ionic strength, and radionuclide and sorbent concentration. The magnetite was synthesized in laboratory under controlled conditions and its main physico-chemical properties as microstructure, surface area and surface charge were analysed previous to sorption experiments. Sorption was negligible up to pH 8.5 and maximum sorption values were reached around pH 12. A significant increase in Cs sorption was observed when decreasing the ionic strength. Linear sorption isotherms were observed within the range of Cs concentration used (up to 10-6 M). As expected, Cs showed very small sorption onto the oxide, but the whole experimental results could be satisfactorily fit with a simple model. In addition, the model developed in the oxide-electrolyte system was able to reproduce fairly well the sorption of Cs onto magnetite in two more complex waters (synthetic bentonite and cement porewaters). All the possible effects on sorption that could increase the uncertainties on the (small) sorption values were analysed in depth. In addition, the possible influence of mineral trace impurities on the sorption (for example silicates from experimental vessels), already discussed in the literature, was avoided.

[1]  Marmier,et al.  Surface Complexation Modeling of Yb(III) and Cs(I) Sorption on Silica. , 1999, Journal of colloid and interface science.

[2]  F. Clarens,et al.  Sorption of Caesium on Commercial Magnetite with low Silica Content: Experimental and Modelling , 2003 .

[3]  F. Morel,et al.  Surface Complexation Modeling: Hydrous Ferric Oxide , 1990 .

[4]  B. Allard,et al.  Sorption of strontium and cesium on rocks and minerals , 1982 .

[5]  Werner Stumm,et al.  Specific adsorption of cations on hydrous γ-Al2O3 , 1973 .

[6]  Marmier,et al.  Surface Complexation Modeling of Yb(III), Ni(II), and Cs(I) Sorption on Magnetite. , 1999, Journal of colloid and interface science.

[7]  D. Sparks.  Environmental Soil Chemistry , 1995 .

[8]  T. Missana,et al.  Uranium (VI) sorption on colloidal magnetite under anoxic environment: Experimental study and surface complexation modelling , 2003 .

[9]  H. Hahn,et al.  Magnetite seeded precipitation of phosphate. , 2004, Water research.

[10]  U. Schwertmann,et al.  Iron Oxides , 2003, SSSA Book Series.

[11]  R. M. Cornell.  Adsorption of cesium on minerals: A review , 1993 .

[12]  Werner Stumm,et al.  Specific Chemical Interaction Affecting the Stability of Dispersed Systems , 1970 .

[13]  J. A. Ritter,et al.  Adsorption of Cesium, Strontium, and Cobalt Ions on Magnetite and a Magnetite−Silica Composite , 2001 .

[14]  B. Venkataramani,et al.  Sorption properties of oxides: III. Iron oxides , 1978 .

[15]  R. J. Hunter.  The interpretation of electrokinetic potentials , 1966 .

[16]  J. Dumonceau,et al.  Sorption of cesium, barium and europium on magnetite , 1998 .