Nonexchangeable potassium extraction and associated structural changes of mica dominant clay minerals

Six mica dominant soils representing a landform sequence were used for the present investigation. The effect of extraction of nonexchangeable potassium (K) by boiling 1 M HNO3 treatment and its associated structural changes of micaceous clay minerals was studied by employing x-ray diffraction technique. Potassium release was rapid in the first three extractions and slowed down to a constant rate thereafter in all the clay samples. The first extraction contributed about 45.57-62.69% towards the total K release. The calculated values of rate constant (first order) decreased sharply from 0.065-0.025 min(-1) after third extraction and reached a constant value thereafter. The calculated integral width of first order reflection of mica peak (10 Angstrom) decreased considerably with nitric acid treatment, but no such effect was observed in 5 Angstrom peak. The differential x-ray diffraction (DXRD) traces showed that the HNO3 treatment dissolved finer particles of mica particularly trioctahedral component and mixed layer minerals, smectite, chlorite and vermiculite.