INFLUENCE OF THE MONTOMORILLONITE STRUCTURAL PECULIARITIES ON TRITIUM SORBTION

Rada Pushkareva

34, Palladin av., Kiev, 252680, Ukraine, Tel. (380.44) 444-23-95, Fax (380.44) 444-00-60,

Keywords: tritium, montmorillonite, structural hydroxyls, interlayer water, free water, isotopic exchange, compensation of the surplus charge, radiolysis.

Tritium accumulation in the rock formed montmorillonite was established in the radioactive waste repository site during the fieldwork. The main rock-forming minerals of containing rocks are quartz, feldspar and montmorillonite. To find out the structural position of tritium thermal analysis of the main rock-forming minerals was performed. Quartz and feldspar holds moisture in the temperature range to 1000⁰C. Dehydration and dehydroxylation of montmorillonite cause moisture losses resulting from heating of researched clayey rocks from 16 to 700⁰C.

The water extracts distilled off clayey rocks according the data of the differential thermal analyses: in the temperature intervals 16-120⁰C (free water); 120-240⁰C (interlayer molecular water); 240-450⁰C (water of hydrogetite admixture, 3-6% from sum total moisture distilled) and 450-700⁰C (the structural water - constitutional hydroxyls). Tritium activity in extracts increased in two orders upon interaction of the samples with heavy tritium water having activity 4000 Bq/l during 180 days.

Heavy isotope of the hydrogen entry in the interlayer or free water occurs by the hydration with tritium contained water. The entry of this radionuclide in the structure hydroxyls is possible as a result of the isotopic exchange.

Montmorillonite of the containing rocks characterized by high degree of the heterovalent isomorphism of the both octahedral Al and tetrahedral Si. Surplus negative charge compensates at the expense of, except exchange cations, the substitution for O by OH-groups in the break of the structural sheet and octahedral position. Montmorillonite interaction with tritium content water create conditions for the formation OT-groups instead of OH.

Tritium radioactive decay forms H*, T*, OH* and OT* hot radicals in the radionuclide content water as a result of radiolysis. These radicals characterized by abnormally high reactionary ability.

Thus the structural peculiarities of the montmorillonite and radiochemical properties of tritium create the auspicious conditions for isotopic exchange in different structural positions of the montmorillonite.