Premium
ISOTOPIC EXCHANGE OF FIXED AMMONIUM
Author(s) -
NEWMAN A. C. D.,
OLIVER S.
Publication year - 1966
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1966.tb01463.x
Subject(s) - sorption , chemistry , ammonium , isotope dilution , isotope , diffusion , inorganic chemistry , kinetic isotope effect , saturation (graph theory) , dilution , chromatography , thermodynamics , organic chemistry , adsorption , mass spectrometry , physics , mathematics , quantum mechanics , deuterium , combinatorics
Summary The isotope 15 N was used to study the rate of exchange between unlabelled NH 4 ‐hydrobiotite and labelled solution NH 4 . Most of the isotopic dilution occurred within 10 minutes of adding the solution to the solid, but even after 13 days less mineral‐NH 4 had exchanged with isotope than was removed by several extractions with KC1 solution. NH 4 remaining in the mineral after extraction with KC1, conventionally named ‘fixed ammonium’, contained some isotope which was sorbed without release of unlabelled NH 4 ; the fixed ammonium was, therefore, not isotopically exchangeable. The sorption was shown to result from incomplete ammonium saturation of hydrobiotite, isotope slowly replacing interlayer cations trapped by lattice collapse. The rate of sorption was initially controlled by a temperature‐dependent diffusion process for which the activation energies were between 9 and 13 kcal/ mole. In the later stages of the reaction the rate became progressively slower than predicted by the diffusion equation, and analysis of the kinetics suggested that, ultimately, exchange of cations at the sorption sites was the rate‐limiting process.