Estimation of Calcium Diffusion Coefficients from Electrical Conductance1
- B. L. Conkling and
- R. W. Blanchar2
Diffusion coefficients for Ca in various horizons of the Bardley, Lebanon, Marshall, and Putnam soils were calculated from electrical conductivity measurements. A diffusion model which separates ion movement in solution from that along soil surfaces provided estimates of Ca movement that agreed with estimates of self-diffusion measured using 45Ca. The equation has the form dq/dt = (ΛC/Λα) Dliq (dC/dx) + Dsur (dCe/dx), where dq/dt is the flux, ΛC/Λα the ratio of molar conductivities at the given concentration divided by that at infinite dilution, Dliq the diffusion coefficient in the liquid phase at infinite dilution, dC/dx the solution gradient, Dsur the diffusion coefficient along the soil surface, and dCe/dx the gradient of exchangeable concentration. Values of Dliq varied from 0.95 to 1.60 × 10−6 m2s−1 and Dsur from 0.61 to 1.18 × 10−6 m2s−1. Values of Dliq estimated at 0.01 mol/L CaCl2 concentration were 5 to 6% higher than those measured in 1 mol/L CaCl2 and values of Dsur are independent of salt concentration. The ratio of the quantity of Ca diffusing through solution to that along the particle surfaces was < 1 to 4 at 0.01 mol/L salt and approximately 4 to 1 at a 1 mol/L salt level. The estimated Ca diffusion coefficient along the particle surface was in all cases lower in the surface horizon samples than in those from a lower depth in the soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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