Nonexchangeable Potassium in a 1.4-Nanometer Mineral and Mica in a Korean Ultisol

Abstract

Eleven cations, Na+, NH+4, Cs+, Ag+, Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Pb2+, and Al3+, were used individually to extract K from clay fractions of a Korean Ultisol in order to provide information on nonexchangeable K in a 1.4-nm mineral and mica. The 1.4-nm mineral and mica. The 1.4-nm mineral exhibited x-ray diffraction patterns of partially interlayered vermiculite. The associated change in mineral structure following K extraction was determined by x-ray diffraction analysis to improve the understanding of the 1.4-nm mineral structure. Potassium extraction conducted with solutions containing 0.5 M Mg2+ and Ba2+ at 25 and 100 °C showed that nonexchangeable K was extracted only with Ba2+ at 100 °C. The associated intensity increase of the 1.4-nm reflection after K extraction suggested that more than one-half of the K was present in the 1.4-nm mineral. The cumulative amount of nonexchangeable K extracted with 0.5 M Pb2+ at 100 °C (10.5, 40.5, and 75 cmol kg-1) and its proportion to the total K (35, 69, and 89%) increased in the order <0.2-µm < 0.2–0.5-µm < 0.5–2-µm fractions. There was little effect of the interlayer material on the K extraction from the 1.4-nm mineral. The associated intensity increase of the 1.4-nm reflection and no change in its d spacing suggest that the nonexchangeable K resides at the opened interlayer surface rather than as mica layers in the 1.4-nm mineral. Single extractions of nonexchangeable K at 100 °C for 50 h showed that Ag+, Ba2+, and Pb2+ were effective, whereas Na+, NH+4, Cs+, Mg2+, Ca2+, Sr2+, Cu2+, and Al3+ were not, indicating that the atomic weight and hydration energy of a cation are important in determining its K-extraction ability.