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Estimation of Calcium Diffusion Coefficients from Electrical Conductance
Author(s) -
Conkling B. L.,
Blanchar R. W.
Publication year - 1986
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1986.03615995005000060015x
Subject(s) - dilution , diffusion , chemistry , analytical chemistry (journal) , conductance , electrical resistivity and conductivity , flux (metallurgy) , phase (matter) , mineralogy , thermodynamics , chromatography , physics , organic chemistry , quantum mechanics , condensed matter physics
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 45 Ca. The equation has the form dq/dt = (Λ C /Λα) D liq ( dC/dx ) + D sur ( dC e /dx ), where dq/dt is the flux, Λ C /Λα the ratio of molar conductivities at the given concentration divided by that at infinite dilution, D liq the diffusion coefficient in the liquid phase at infinite dilution, dC/dx the solution gradient, D sur the diffusion coefficient along the soil surface, and dC e / dx the gradient of exchangeable concentration. Values of D liq varied from 0.95 to 1.60 × 10 −6 m 2 s −1 and D sur from 0.61 to 1.18 × 10 −6 m 2 s −1 . Values of D liq estimated at 0.01 mol/L CaCl 2 concentration were 5 to 6% higher than those measured in 1 mol/L CaCl 2 and values of D sur 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.