Determination of Diffusion Coefficients Based on Ficks Second Law for Various Boundary Conditions
Christian Wolfrum, H. Lang, H. Moser, W. JORDAN · Radiochimica Acta · 1988
Based on Ficks second law the evaluation of diffusion experiments leads to two distinct apparent diffusion coefficients for each of the ions Cs+, Rb+, and Pb+. On the other hand, only one diffusion coefficient was found for Sr2+, I-, TcO4 - and SeO4 2-. To get an insight into these results diffusion experiments with rock plates were carried out which were equilibrated for several weeks with the corresponding natural groundwater. Either the water-saturated plates were fixed immediately between two volumes of groundwater, one of them spiked with a tracer, or the equilibrated plates were additionally contacted with a tracer solution and then installed into the diffusion cells. The transfer of the diffusing substances through the rock material was evaluated by the non-steady state estimate based on Ficks second law and compared with the steady state evaluation based on Ficks first law. The results are discussed for the two types of experiments.