Nanosize crystalline selective sorbents for sorption of long-lived radionuclides

Selective sorption-reagent materials on the basis of amorphous xerogels of barium silicate, titanate and zirconate form nanoparticles of barium sulfate stabilized by the xerogel matrix during the reaction with sulfates contained in initial solution. It was shown that sorption properties of such nanoparticles are principally different from those of barium sulfate microcrystals. Such nanoparticles are principally different from those of barium sulfate microcrystals. Such nanosorbents do not virtually undergo the ageing processes characteristic of regular microcrystals. Their selectivity in regard to strontium radionuclides is so high that allows removing strontium-90 selectively from 1N calcium chloride solutions with decontamination factors > 1000. In such solutions, conventionally used sorbents selective to strontium have decontamination factors close to 1. Presently, the Institute of Chemistry FEDRAS is building a pilot for producing such sorption-reagent materials(nanosorbents) for decontamination of LRW at the Russian Ministry of Atomic Energy facilities in the Russia Far East. The main problem of a purposeful synthesis of crystalline nanosorbents stabilized by xerogel matrices was discussed. It is concerned with instability of their structure during the chemical reaction of the precipitate formation in a homogeneous mesoporous medium. This fact is related to a possibility of parallel reactions yielding different forms of particles that could be defined as 'nanoparticles in mesopore volume', 'surface chemical compounds' or 'microcrystals at outer surface of xerogel particles'. The reaction direction is determined by the interfacial tension forces: nanoparticle-solution, nanoparticle-mesopore surface and mesopore surface-solution. By changing the respective values through application of surface-active and polymer additives, one could obtain materials with a preference of the form 'nanoparticle in mesopore volume' which is characterized by the highest stability and selectivity in regard to radionuclides. The calculations are presented that illustrate contributions of the mentioned values in the process of a purposeful synthesis