Influence of a backfilling material on borosilicate glass leaching

The results of the leaching tests in different types of paste have shown that the presence of an absorbing medium around the glass tends to eliminate the saturation conditions that are present in water or water solution. It is conceivable that such an effect is transitory. When the clay surrounding the glass is saturated, the composition of the leachate will begin to evolve toward saturation and will probably be diffusion-controlled. However, at least for the first period, a model is dissolution in large amounts of water fits the experimental data better than a model based on satural effects. Tests performed with addition of Fe2O3 show that the influence of corrosion products is not negligible. Their presence partially saturates the absorptive center of the clay, altering the leaching conditions. The use of Fe2O3 to simulate corrosion products is probably a crude approximation. A more realistic approach is needed. If a similarity exists between leaching data tests in paste and in large amounts of water, the surface composition in the two cases is largely different. In the first case, in the external part of the film, silicon precominates while in the second case iron is prevalent. At 800C the surface composition does not seem to affect the capacity of the surface layer of reducing the leaching rate with time. At 500C tests with the highest iron content present lower values of weight losses