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Kinetics of Potassium Release from Biotite¹

ABSTRACT

Data presented suggest that the rate of K release from biotite by leaching with NaCl is independent of the amount of K in the mineral during the depletion of a large proportion of the total K content. Optical and X-ray diffraction data show that weathering of biotite to vermiculite proceeds from the outside edge in toward the center of the particle. The 14Å. layers were found to have about 4 times the diffraction intensity of the 10Å. layers. Observation was made of the actual weathering front. The dependence of rate of K release on leaching rate, NaCl concentration, temperature, time, and particle size was evaluated and an empirical equation derived relating these variables. A theory is presented that the apparent zero-order type of reaction results from the maintenance of a constant concentration of reactive K similar to the principle of a saturated solution of a material in equilibrium with its solid phase. The logarithmic portion of the curve is suggested as the place where a "saturated solution" of reactive K can no longer be maintained and rate of release becomes dependent on the amount of unreacted K.

¹ Contribution from the Department of Soil Science, Michigan State University, and Michigan Agr. Exp. Sta., East Lansing. Journal Article No. 2205. The author wishes to express his appreciation to Mr. N. Yassoglou for the optical work in this paper.

² Associate Professor in Soil Science.

Received for publication February 17, 1958. Accepted for publication May 13, 1958.