Influence of the Titanium Dioxide Addition in Matrix Formulation on the Radwaste-Mortar Matrix Characteristics

Abstract

The rutile form of titanium dioxide (TiO₂) was added to mortar matrix preparations with the objective to improve the mechanical and physico-chemical characteristics of the radwaste-mortar matrix mixtures, in particular the leach-rate of the immobilized radionuclide. The final solidified radwaste form was made with high water-to-cement ratio (0.36) for easy leaching of the immobilized radionuclide, ³⁷Cs. TiO₂was added to the mortar formulation, replacing the appropriate amount of cement, in the amounts of 1,2,5,8 and 10 weight percents of total cement weight. In the highly basic environment of the mortar (pH ≅ 12), the titanium will form a HTiO-type membrane, which is semi-permeable and selective for the cations like Cs⁺ in the pH range above 5.5. Only the rutile form of TiO₂was observed in the prospected radwastemortar mixture samples, using X-ray Fluorescence Spectrometry. Nevertheless, ¹³⁷Cs leach-rate for the matrix formulations prepared with TiO2 was notably lower than the normally prepared (TiO₂ free) samples. Furthermore, the mechanical strength of the samples prepared with TiO₂ was higher than that of the TiO ₂-free samples, and the correlation between the mechanical strength and TiO₂ content appears to be exponential over the composition range explored here. Improvement of the physico-chemical properties of the titanium prepared formulations, is a topic of further investigations.