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Influence of Exchangeable Cations on Water Adsorption by Soil Clays

^a Dep. of Agronomy, Purdue Univ., West Lafayette, IN and USDA-ARS, National Soil Erosion Research Laboratory, West Lafayette, IN
^b School of Natural Resources, The Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210
^c Dep. of Agronomy, Purdue Univ., West Lafayette, IN
^d School of Natural Resources, The Ohio State Univ., Columbus, OH

View larger version (25K): [in a new window]   Fig. 1. Sample Fourier transform infrared (FTIR) spectrum of the Ca-exchanged Fayette sample at 0.02 P/P0.

View larger version (26K): [in a new window]   Fig. 2. (a) Adsorption and desorption isotherms and (b) FTIR spectra in the 2(HOH) region for a Mg-exchanged Blount sample.

View larger version (29K): [in a new window]   Fig. 3. Variability between replicates (solid vs. dashed lines) and hysteresis associated with adsorption (solid markers) and desorption (empty markers) legs of the isotherm for Fayette and Blount samples exchanged with Ca (triangles) and Na (squares).

View larger version (18K): [in a new window]   Fig. 4. Water adsorption isotherms for Ca2+, 50:50 Ca2+/Mg2+, Mg2+, K+, and Na+ exchanged Blount and Fayette soil clays.

View larger version (24K): [in a new window]   Fig. 5. Average values, unnormalized (left axis) and normalized by the clay cation exchange capacity (right axis), for the amount of water adsorbed by Blount and Fayette soil clays at P/P0 0.5 as a function of hydration energy of the exchangeable cations per mole of charge (Table 4). Solid lines correspond to linear regressions for Blount (y = 0.1647x + 7.2470, R2 = 0.99) and Fayette clay (y = 0.2636x – 16.2440, R2 = 0.98) using unnormalized data; the dashed line corresponds to the combined regression for both soil clays using normalized data (y = 0.0063x – 0.0316, R2 = 0.98).

View larger version (19K): [in a new window]   Fig. 6. Water deformation band position for Ca2+, Mg2+, and 50:50 Ca/Mg treatments.

View larger version (36K): [in a new window]   Fig. 7. X-ray diffraction patterns of Ca-exchanged Fayette clay with an increase in partial pressure of water vapor. Clay minerals identified: I—illite, I/S—randomly interstratified illite/smectite, K—kaolinite, and Q—quartz. Peak positions are in nanometers (nm).

View larger version (18K): [in a new window]   Fig. 8. Measured d-spacings of expandable soil clay components as a function of P/P0. Each point corresponds to one x-ray diffraction pattern.