SELECTIVE REMOVAL OF RADIONUCLIDES FROM NUCLEAR WASTE EFFLUENTS USING INORGANIC ION EXCHANGERS

摘要

The development of ion exchange processes and materials focuses on selective separation. R&D on inorganic materials for selective separation processes has been strong for several years. The superior selectivity of some inorganic ion exchangers compared to other sorption materials presently used in the separation processes has been the major initiative for continuing research. High selectivity is the key to fulfilling the strict regulations concerning waste effluents and to enhancing the energy efficiency of separation processes. Several selective inorganic ion exchange materials have been developed at the Laboratory of Radiochemistry for decontamination of low and intermediate radioactive waste solutions, and some of those materials have found industrial applications. One of them is extremely cesium selective (k_(Cs/Na)=1,500,000) a transition metal hexacyanoferrate (CsTreat~®) which is granular and has a wide operational pH range (pH 1 to 13). These physical properties are one of the key factors for ion exchange materials in their conventional separation processes and are atypical for the most of selective inorganic materials. About 900 m~3 of high-salt (～240 g/L NaNO_3) evaporator concentrates have been decontaminated with only 112 liters of CsTreat~® at Loviisa nuclear power plant, Finland, in ten years. For the second most important fission product, strontium, a granular sodium titanate (SrTreat~®) material has been developed. It has a high selectivity (k_(Sr/Na)=200,000) but rather limited pH range (above 9) and it is also sensitive to calcium. Large numbers of metal oxides with various doping elements have been developed for selective separation of activated corrosion products. For radioactive cobalt and nickel very effective materials have been found: titanium oxide, (CoTreat~®) and tin antimonates, respectively.