Topotactic cation exchange in transformed micas under hydrothermal conditions

The formation of hydroxylated phases was investigated using K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) under hydrothermal treatment with alkali (Li⁺, K⁺, NH₄⁺, Rb⁺ and Cs⁺), alkaline earth (Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺), and aluminum (Al³⁺) cations at 200°C for 1 and/or 3 days. The K-depleted biotite treated with alkali cations produced anhydrous hydroxylated phases, while the K-depleted muscovite did not significantly exchange alkali cations but dehydrated to form Na-muscovite in all cases. The alkaline earth cations, however, produced hydrous hydroxylated phases with both K-depleted micas. The degree of hydration energy of cations and the charge density of micas were found to influence the formation of anhydrous and hydrous phases from the K-depleted micas. This type of topotactic cation exchange potentially could be used for fixation and immobilization of radioactive species such as Cs, Sr, Ra, etc. in the transformed micas. The K-depleted biotite and muscovite treated with Al³⁺ were transformed to hydroxy-Al interlayered vermiculites (HIV) because of hydrolysis and polymerization of Al³⁺. These HIV phases could also serve as useful adsorbents for soil and groundwater contaminants.