The interaction of water with the clay fractions (<2 μm) from two midwestern soils was studied using Fourier transform infrared (FTIR) spectroscopy and gravimetric methods. The soil clay fractions were obtained from a Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and a Fayette silty clay loam (fine-silty, mixed, mesic, superactive Typic Hapludalfs). These clay fractions were exchanged with Mg2+, 50:50 Ca2+/Mg 2+, Ca2+, Na+, and K+ to determine the influence of the exchangeable cation on their water sorption behavior. Water sorption isotherms and FTIR spectra of the clays were collected simultaneously using a gravimetric-spectroscopic cell. Overall, the amount of water sorbed by the samples increased as the ionic potential of the exchangeable cation increased and was strongly correlated to the hydration energy of the cations (P > F < 0.0001). The position of the H-O-H bending band (v2 mode) also increased with increasing ionic potential of the exchangeable cation indicating strengthening of water II bonds. In addition, it was observed that the position of this band decreased with increasing water content for the Mg-exchanged clays compared with an overall increase for the Ca-exchanged samples. X-ray diffraction patterns indicated an expansion of the phyllosilicate clay minerals as the water activity increased; howeveir, no differences were observed between the Ca- and Mg-exchanged samples. This study shows that the molecular properties of water on Ca- and Mg-exchanged soil clays are similar to that on specimen clays and provides new insight about the role of exchangeable cations in soils.
ASJC Scopus subject areas
- Soil Science