scholarly journals Mineral reaction kinetics constrain the length scale of rock matrix diffusion

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
R. A. Wogelius ◽  
A. E. Milodowski ◽  
L. P. Field ◽  
R. Metcalfe ◽  
T. Lowe ◽  
...  
Keyword(s):  
Reaction Kinetics ◽  
Matrix Diffusion ◽  
Length Scale ◽  
Rock Matrix ◽  
Mineral Reaction

Diffusion Measurements on Crystalline Rock Matrix

1994 ◽  
Vol 353 ◽  
Author(s):  
Kari Hartikainen ◽  
A. HautojÄrvi ◽  
H. Pietarila ◽  
J. Timonen
Keyword(s):  
Power Law ◽  
Gas Flow ◽  
Crystalline Rock ◽  
New Technique ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Model Calculations ◽  
Short Time ◽  
Drill Cores

AbstractA new gas flow technique is introduced such that experiments on very long samples are possible. This new technique together with increased accuracy of the measurements, allows the observation of power law tails in the break-through curves. Dispersion in these experiments can be controlled in great detail, and therefore the power law tails can be used to determine very accurately the parameters relevant in matrix diffusion. Results for rock and metal samples are shown, and they are fitted with model calculations which include both dispersion and matrix diffusion. The introduced technique, which is designed for ordinary drill cores, is suitable for scanning a large number of samples in a very short time.

Study of the Uranium Heterogeneous Diffusion through Crystalline Rocks and Effects of the “Clay-Mediated” Transport

2003 ◽  
Vol 807 ◽  
Author(s):  
U. Alonso ◽  
T. Missana ◽  
M. García-Gutiérrez ◽  
A. Patelli ◽  
J. Ravagnan ◽  
...  
Keyword(s):  
Surface Area ◽  
Bentonite Clay ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Mineral Surface ◽  
Transport Models ◽  
Actual Surface ◽  
Disturbed Areas ◽  
High Level ◽  
Preferential Pathways

ABSTRACTRock matrix diffusion is one of the possible mechanisms for radionuclide retardation in a deep geological high-level radioactive waste repository, and it is usually considered that radionuclides diffuse as solutes through the rock. Nonetheless, the potential effects that clay, from the bentonite barrier, may induce on the radionuclides migration should be taken into account. Furthermore, transport models generally assume that the whole mineral surface is accessible to transport, whereas transport is highly conditioned by the heterogeneous mineral distribution, since different minerals may act as preferential pathways, while others may present higher sorption capability. It is therefore necessary to determine the actual surface area accessible to transport.The aim of the present work is the identification of the uranium preferential pathways to the granite, both in presence or absence of bentonite clay. Results showed that uranium as solute diffused in specific mineral areas, indicating that the actual surface area accessible to matrix diffusion, and/or sorption on the surface, is significantly lower than the whole mineral surface. By the other hand, the uranium in presence of the clay was randomly distributed on the surface, and penetrated into the granite mainly through “defects” (as fractures or grain boundaries); its migration being enhanced on specially fractured or disturbed areas.

Brownian Simulation of Matrix Diffusion

2000 ◽  
Vol 663 ◽  
Author(s):  
Sofie Andersson ◽  
Allan T. Emrén
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Boltzmann Distribution ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Dissolved Species ◽  
Apparent Diffusion ◽  
Wide Variability ◽  
Far From Equilibrium ◽  
Solid Piece

ABSTRACTThe commonly used approach in dealing with matrix diffusion is to assign an effective diffusion constant for the radionuclide in the rock matrix. The idea behind this approach is that, on a scale much larger than the pore size, the irregularities tend to cancel out. Although it might look plausible at first sight, this approach has been questioned both for theoretical and experimental reasons.Here, Brownian simulation has been used to investigate the transport of dissolved material in a rock matrix modeled as a system of pores with a wide variability in size and shape. The Boltzmann distribution is used locally, although the system globally is far from equilibrium.The simulation consists of two main parts. First, the model rock is formed by precipitation of irregular mineral grains from a liquid phase. As the grains grow, they tend to form a mostly solid piece of rock.In the second part of the simulation, a dissolved species is introduced at one side of the rock and allowed to diffuse through its pore system. It is found that no apparent diffusion constant, D, can explain the properties of the system. Rather, D is found to be a function of both distance and time.

Postglacial Matrix Diffusion in a Boulder Sample

1995 ◽  
Vol 412 ◽  
Author(s):  
K. Rasilainen ◽  
J. Suksi ◽  
K.-H. Hellmuth ◽  
A. Lindberg ◽  
S. Kulmala
Keyword(s):  
Strong Mixing ◽  
Matrix Diffusion ◽  
Fracture Face ◽  
Rock Matrix ◽  
Land Uplift ◽  
Last Glaciation ◽  
Low Concentrations ◽  
Content Analyses ◽  
Activity Ratios ◽  
Possible Cause

AbstractA boulder sample was studied for its unusual U content. Analyses of U-series nuclides within the rock matrix perpendicular to an assumed fracture face show abrupt pulse-like concentration distributions with very low concentrations of U daughters. Both Th-230/U-234 and Pa-231/U-235 activity ratios are low, indicating recent U accumulation into the rock. Matrix diffusion is tested as a possible cause for the experimental observations. We assume that the diffusion process was triggered and controlled by rock expansion, strong mixing of different water types and rapid land uplift at the end phase of the last glaciation.

Investigation of the Influence of Heterogeneous Porosity on Matrix Diffusion: a Novel Approach Using Adaptive Tree-Multigrid Technique and Real Porosity Data

1996 ◽  
Vol 465 ◽  
Author(s):  
P. Simbierowicz ◽  
M. Olin
Keyword(s):  
Matrix Diffusion ◽  
Two Dimensional ◽  
Rock Matrix ◽  
Empirical Parameter ◽  
Heterogeneous Model ◽  
Novel Approach ◽  
The Standard Model ◽  
Leaching Experiments ◽  
Heterogeneous Matrix ◽  
Infiltration Experiment

ABSTRACTLast year we developed a two-dimensional deterministic heterogeneous matrix diffusion model, which is capable of utilising porosity information originating from real drill-core samples. The results of numerical infiltration experiment we had performed with the model displayed substantial spatial variations in the penetration depth. Because it is practically impossible to verify experimentally those two-dimensional penetration profiles we had computed, this time we decided to try modelling of measured leaching curves. Unfortunately we have not succeeded in acquiring such curves for the exact same samples, which we have used in numerical leaching experiments. Nevertheless it can be seen, that the shape of leaching curves computed with the heterogeneous model is clearly closer to the shape of measured curves, than the shape of curves provided by the standard model. These differences can be utilised as a basis for an approximate numerical method of assessing the geometric factor, which has traditionally been a purely empirical parameter.The results of the new numerical experiments agree with our older results from last year: the heterogeneity of the rock matrix has highly significant impact on the diffusion. However, when interpreting the results, one must not neglect numerous limitations of the model, and hence, one should not attempt to overgeneralise the conclusions.

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