THz spectroscopy of sodium, lithium and potassium montmorillonites

Measurements of the absorption coefficients α of K⁺ -, Li⁺ - and Na⁺ - montmorillonites in the 0.2 to 1.4 THz frequency band are reported. The absorption of THz-radiation by K⁺ - montmorillonite is notably weaker than the absorption of THz-radiation by Li⁺ - and Na⁺ - montmorillonites. The observed difference of THz absorption coefficients is explained by the naturally lower water content of K⁺ - montmorillonite compared to Li⁺ - and Na⁺ - montmorillonites. The results of our experiments provide experimental evidence for the usefulness of THz spectroscopy for the investigation of the interlayer chemistry of clay minerals.