Diffusion kinetic modeling of strontium leaching from cementotious matrices

Radioactive waste management is a serious endeavor to modern societies, with grave implications for future generations. In this vast and rapidly growing field, leaching experiments of hazardous materials from engineered matrices and natural geological barriers are an important tool for assessing the dispersion of contaminants into the environment. These small scale leaching experiments emulate real life dispersion of buried waste. One of the main challenges that one faces in this field, is the huge gap between the experimental leaching time (weeks or months, and seldom a few years), and the actual time materials should be contained within an intact matrix (hundreds or thousands of years before they are rendered practically unhazardous). In order to bridge this gap computer simulations and chemical physics modeling are introduced to simulate leaching experiments and estimate physical constants, which in turn are used for long-time leaching predictions with reasonable confidence bounds. In this work we present a diffusion-kinetic modeling of strontium leaching from carbonated and uncarbonated Portland cement paste. We have developed a model that allows us to fit the strontium diffusion constant and the kinetic pseudo 1st order rate constant that appear in the analytical expression for the cumulative leached strontium, with experimental results.This approach differs from most of the common geophysical leaching models, in which a thermodynamically induced concentration change via a vast set of chemical equilibria (quasi steady state), separately follows a diffusion induced concentration change