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Large volumes of neutral or alkaline medium-level liquid radioactive wastes with high salinity accumulate as a result of the operation of nuclear power plants. Specifically, the wastes include bottom residues from evaporators and recovery solutions from block desalinization setups. These solutions, whose radioactivity is due mainly to cesium, are all stored on-site at nuclear power plants. Since the reserve storage space is constantly decreasing and the construction of new storage sites requires enormous capital investments, the problem of reprocessing liquid radioactive wastes is becoming acute. A promising method is selective sorption of radionuclides in a flow on synthetic inorganic ion exchangers.From the standpoint of selectivity for cesium and the degree to which the physicochemical and sorption properties have been studied, three groups of synthetic inorganic ion exchangers stand out: zeolites (aluminosilicates), insoluble bisalts heterovalent metals and hexacyanoferrates of metals [1][2][3][4]. Of the first group, individual zeolites exhibit enhanced selectivity to cesium in the presence of sodium and potassium salts [5][6][7]. Examples of the use of synthetic zeolites to remove 137Cs from different technological waters are presented in the literature [2, 4,[7][8][9]. At the same time, it should be noted that the selectivity of some zeolites to cesium decreases substantially in the presence of sodium ions and especially ammonium ions [5]. Moreover, as far as we know, selective zeolites are not produced in Russia on a commercial scale. Natural zeolites (clinoptilolite, hydrobiotite, and others) are not as effective as the synthetic analogs, both with respect to selectivity and exchange rate, which makes it impossible to achieve in a column a high degree of purification and sufficiently long service life of the fill.Of the second group of inorganic ion exchangers, phosphates of tetravalent metals, specifically, zirconium and titanium phosphates, have been most studied [1, 3, 10]. Spherogranular samples of these sorbents, obtained by the sol-gel method, have been tested in columns at the stand level and have been shown to be effective for decontamination of the water coolant of a research reactor [11] and a simulant of the coolant in the holding basin [12] and wastewater of the Beloyarsk nuclear power plant [13].Finally, inorganic ion exchangers of the third group, based on insoluble hexacyanoferrates (II) of transition metals (zinc, copper, nickel, cobalt, iron, and others) or heavy metals (titanium, zirconium, thorium, molybdenum, and others) [2-4, 7. 14, 15], are most highly cesium-selective. Hexacyanoferrate (II) sorbents are more cesium selective than phosphate inorganic ion exchangers [7, 16]. At the same time, the scientific and technical literature contains little information about the practical testing of such inorganic sorbents in a prolonged filtration regime. Thi~ is due mainly to the fact that the synthesized bexacyanoferrate ion exchangers are obtained mainly by the gel (precipitation) metho...

Several zirconium phosphate (ZrP) gels of various water contents produced by a sol - gel method were investigated. They were found to be the polymer-class gels using the method of small-angle neutron scattering. X-ray diffraction analysis revealed that their solid-phase framework was formed from branched fragments (layers and blocks) of -ZrP crystal structure. These gels are strongly fluctuating systems when they are on the scale of . Their fluctuation character is shown to be described by two parameters: a correlation radius and a fractal dimension D. It was found that and almost did not depend on the water content and that D increased from to when the water content decreased from 50% to 0% as the gels were dried to a temperature of . Simultaneously, substantial shrinkage of granules, a decrease in porosity and ion-exchange capability, and formation of blocks from -phosphate layers occurred with decrease in the water of the hydrogel as it dried. A probable description of the evolution of the ZrP-gel structure with variation in the water content during drying is suggested on the basis of the data obtained.

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