Separation of valuable or harmful chemical trace components (radionuclides, metals, metalloids) from solution is difficult because they often exist in the presence of overwhelming majority of other, mainly harmless chemical species of much higher concentrations. We have successfully developed highly selective inorganic ion exchange materials that are of have been used in more than 60 industrial applications worldwide in the nuclear industry and produced scientific knowledge understanding on the origin of selectivity to tailor new materials for the nuclear field. Research for applications and knowledge is also underway for the separation of natural radionuclides, in hydrometallurgy and for metal recycling.
A suite of commercial inorganic ion exchange materials was developed together with Fortum in the 1990s (then Imatran Voima Oy) comprised CsTreat®, SrTreat® and CoTreat®. The first industrial application was that of CsTreat® at Loviisa nuclear power plant (NPP) in 1991 continuing still today after 26 years of highly efficient operation. Early industrial application sites in 1990s included Olkiluoto NPP (TVO, Finland), Callaway NPP (Union Electric, USA), Paldiski naval base (Estonia), Murmansk naval base (Russia) and Tokaimura (JAERI, Japan). In the 2000s the new major industrial application were at Savannah River R-105 Reactor (USDOE), Sellafield Nuclear Reprocessing Plant (BNFL, UK), Dounreay Prototype and Demonstration Fast Reactors (NDA,UK). The major operations at Bradwell Magnox NPP (ElectricSolutions) at Fukushima NPP accident site started in 2012-2013 are still underway. At Fukushima, more that 700 000 m3 heavily contaminated highly radioactive waste water has been purified of Cs-137 and Sr-90 below detectable level which indicates a purification factor in the order of 107.
The removal of oxoanionic metal or metalloid species such as arsenate, ruthenate, pertechnetate and antimonate is often difficult due to their high mobility and lack of sorbents of high selectivity for anionic species. The key here is to develop multifunctional materials with the capability to reduce the oxoanionic metal(loid) to a cationic form and to sorb it into the material by selective cation exchange. Pilot scale testing of SbTreat material has been carried out at Loviisa NPP during 2012-13 for Sb-124 removal. Similar difficulties are encountered in the removal of organometallic complexes (e.g. Co-60-EDTA) due to the neutral or anionic nature of the complex. For this multifunctional materials with photocatalytic and sorptive properties have been developed and studied. Antimony oxide based materials have been found most effective to strip and sorb cobalt from its EDTA complex.
The high demand of rare earth elements (REE) has turned the attention to recycling of REE from spent products or hydrometallurgical waste. The challenge in the separation of individual REEs comes from their very similar chemical properties. REE recycling and separation is currently studied in two EU Marie Curie doctoral training networks. Here, very promising results have been obtained using zirconium oxide and titanium oxide sorbents with simple mineral acids as eluants.
While having the advantage of high selectivity compared to organic ion exchange resins, the diffusion of ions in the crystalline inorganic materials is often low which means that the volumetric operating capacities are low. To overcome this limitation research is underway to develop inorganic ion exchange materials in nanofibre formats. Here, Na-titanates and other materials with high kinetic performance have been prepared.