Eurosoil 2012 edition:4th location:Bari, Italy date:02-06 july 2012
Cement based waste disposal is the most important option to provide safe storage of the non-recyclable often highly
toxic waste fraction remaining at the end of today’s waste processing chain. Despite all engineering efforts and safety
investments ultra-alkaline, concrete derived, pore waters (pH 12 – 14) will always remain associated with cement based waste
disposal. To avoid contamination of the environment due to slow leeching of the metals from these waste forms, engineered
barriers are built around the waste disposal sites in order to provide containment of the metals leeching out. Upon
consideration of a concrete-based storage scenario for 137Cs containing radioactive waste, care must be taken to provide
buffer materials that ensure the retention of this cation in presence of concrete pore water with changing composition. Since
the applicability of organic ion exchangers in ultra-alkaline, radioactive conditions is limited to a fairly short timeframe, such a
buffer sink should include inorganic materials combining long-term stability in such conditions with a high selectivity for the
monovalent Cs+ cation, thereby enabling its efficient sorption in the saline, alkaline conditions imposed by the concrete.
Zeolites (natural and synthetic) represent a family of crystalline framework materials typically formed at high pH from different
starting materials such as clays, fly ash, high purity silicon sources (TEOS, aerosil,…), etc. The combination of their stability in
alkaline aqueous conditions with their cation exchange capacities makes them highly promising candidates for the application
as a buffer material in a cement based storage scenario for radioactive waste.