Swelling of sericite by LiNO₃-hydrothermal treatment

The swelling of sericite by a LiNO₃ hydrothermal treatment and the effect of dehydroxylation of sericite prior to hydrothermal treatment are investigated in this study. We demonstrate that a well-swelled sericite with 80% exchangeable K and a cation exchange capacity of 1.10 meq/g can be prepared from a fully dehydroxylated sample under 270 °C hydrothermal treatment. Some Li⁺ ions were found to permanently migrate into the sericite but without a total charge reduction of sericite after hydrothermal treatment. Accordingly, some octahedral hydroxyls transform into "-OLi" forms, a transformation that may be promoted by dehydroxylation. The hydrothermal treatment reconstitutes the hydroxyl groups of sericite lost during dehydroxylation. However, OH groups of pyrophyllite released during dehydroxylation are not regained after hydrothermal treatment. Finally, the pyrophyllite in the original sericite ore is not affected during hydrothermal treatment. Consequently, pure sericite particles in hydrothermally treated sericite ore can be easily separated from pyrophyllite particles by hydrodynamic sedimentation due to the selective swelling of sericite.