Mg and K exchange cation effects on the XRD analysis of soil clays

Abstract

The changes detected by Mg‐ and K‐saturation and ethylene glycol and glycerol solvation of a modern fluvial soil from the Mississippi River floodplain can be explained by the predictable behavior of smectite and vermiculite layers of variable charge. Simulated patterns based on NEWMOD were used to identify discrete layer types and varieties of two-component mixed layered clays present. Phases detected include several two-component varieties of R0 and R1 ordered mixtures of illite, smectite, or vermiculite and minor quantities of smectite, illite, kaolinite, chlorite, and clay-sized quartz. Major differences in the coarse (<2 µm) and fine clay (<0.2 µm) fractions are associated with smectite/illite in the Mg-treated material that appears to be illite/vermiculite in the K-saturated sample. A high-charged smectite or vermiculite is the most abundant expandable material in this soil. Observed differences between Mg and K saturation illustrate the general complexity of the varieties of expandable layer sequences in soils, which can be identified by the application of the approach described in this paper.

Keywords:

• K and Mg cation saturation
• clay mineral quantification
• XRD

Acknowledgements

This work was partially supported by the Junta de Andalucía (Spain) through Research Group RNM135 “Applied Mineralogy”.