Effect of moisture content and soil type on self diffusion of ⁸⁶Rb in soils

Abstract

Self-diffusion coefficients (D) for Rb+ have been measured in a heteroionic Lower Greensand soil over a wide range of moisture contents at three different compactions. The moisture content is shown to have a considerable effect on the value of the self-diffusion coefficient, a rapid rise in the value of D taking place between 5 and 10% moisture content. It is shown that this effect is not simply due to the increased volume of water-filled pore space at higher moisture contents, and other possible factors which could influence the shape of the diffusion coefficient/moisture content curve are discussed. Diffusion coefficients for Rb+ in eight other soils at pF 2 are also reported, but no simple correlation with any of several soil properties measured could be found. A value of 1·0 × 10−7cm2/sec. would seem to be a reasonable generalization for the self-diffusion coefficient of Rb+ in moist calcium-dominated soils.

Flow, Transport, and Reaction in Porous Media: Percolation Scaling, Critical‐Path Analysis, and Effective Medium Approximation

“…When solute diffusion coefficients obtained from a large number of experiments (Barraclough & Nye, ; Barraclough & Tinker, ; Conca, ; Graham‐Bryce, ; Jurinak et al, ; Klute & Letey, ; Mehta et al, ; Olesen & Kemper, ; Patil et al, ; Porter et al, ; Rökens & Bruce, ; Rowell et al, ; Sadeghi et al, ; Schaefer et al, ; So & Nye, ; Warncke & Barber, ; Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) , ; Conca & Wright, ; Hu & Wang, ; Haggerty, ; Haggerty et al, ; Letey & Klute, ; Klute & Letey, ; Sallam et al, ; Mehta et al, ; Rinaldi & Cuestas, ) were compared with the moisture content directly with no attempt to estimate a threshold Hunt, Ghanbarian, & Ewing (), the result, shown in Figure , was that D pm / D w ≈ θ 1.96 , an exponent very close to 2. When the data for each porous medium were analyzed separately, however, in the same fashion as the gas diffusion coefficient Ghanbarian et al, , the result obtained followed equation .…”

Magnesium Diffusion in Soils at Different Water and Magnesium Contents

“…A change of soil water content leads t o a change of diffusive flux because the cross sectional area available for diffusion is restricted t o the water filled pore space, and the effective path length (depending o n tortuosity and continuity of pores) is also a function of water content ( Rowell et al 1967, Va"aidyanathan et al 1968, Graham-Bryce 1963. But in these experiments the contribution of tortuosity and continuity of pores to the change of diffusive flux with water content cannot be separated from that of cross sectional area.…”

Interaction of K concentration in the soil solution and soil water content on K diffusion

“…The diffusion measurements were carried out at four K levels and four different water contents in order to evaluate the interaction between K concentration and soil water content on diffusive flux. It has already been established that soil water content influences K diffusion in soils (Graham-Bryce 1963, Rowell et al 1967, Vaidyanarhan et al 1968, Grirnme et al 1971 because the cross sectional area available for the passage of K as well as the tortuosity and continuity of the diffusion path (Porter et al 1960, Rowell at al. 1967) is determined by it.…”