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SYNTHESIS OF KAOLINITE FROM MICAS AND K-DEPLETED MICAS

Department of Crop and Soil Sciences and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

^* E-mail address of corresponding author: komarneni{at}psu.edu

The weathering stages of K-depleted biotite, K-depleted phlogopite, and natural biotite were investigated using hydrothermal treatment with AlCl₃ solution at 200°C for 12 to 72 h. Although there were some differences in the degree of weathering of the two K-depleted micas, both first transformed to hydroxy-Al interlayered vermiculite (HIV), which then altered to kaolinite. In case of the natural biotite, the biotite first transformed to a K-depleted mica-like phase, which then altered to kaolinite. The natural biotite had resisted weathering to kaolinite more than did the K-depleted biotite, as expected. The K-depleted phlogopite had less resistance in weathering to kaolinite than the K-depleted biotite. The transformation process changed the color of the micas. The K-depleted biotite changed from greenish-black through yellow to pale gray whereas the natural biotite changed from greenish-black through beige to yellow. However, in the case of K-depleted phlogopite, there was no significant color change during the transformation process. The presence of the interlayer K⁺ ions and the structural Fe²⁺ ions in mica appear to have contributed to the differences in the degree of weathering to kaolinite among the micas investigated.

Key Words: Hydrothermal Treatment • Hydroxy Al-interlayered Vermiculite (HIV) • Kaolinite • K-depleted Biotite • K-depleted Phlogopite • Transformation • Weathering