Premium
Ammonium‐calcium exchange equilibria in soils and weathered pumices that differ in cationexchange materials
Author(s) -
OKAMURA Y.,
WADA K.
Publication year - 1984
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.1365-2389.1984.tb00295.x
Subject(s) - allophane , chemistry , vermiculite , ammonium , imogolite , cation exchange capacity , inorganic chemistry , ion exchange , humus , montmorillonite , selectivity , partition coefficient , soil water , clay minerals , mineralogy , ion , geology , soil science , paleontology , biochemistry , organic chemistry , chromatography , catalysis
SUMMARY The retention of NH 4 + and Ca 2 + on soil and weathered pumice samples containing constant and/or variable charge components was measured in different NH 4 CI‐CaCl 2 solutions. The NH 4 +/Ca 2 + selectivity of each sample was evaluated using a quotient of the partition of NH 4 + on the exchange sites and in the solution relative to that of Ca 2 +. It increased with decreasing pH and increasing NH 4 Cl‐CaCl 2 concentration for a given equivalent fraction of NH 4 + in the solution. These effects were quantitatively explained in terms of the changes of NH 4 + and Ca 2 + concentrations in the solution and in the diffuse double‐layer of the ion‐exchange material as predicted by the law of mass action and the electric double layer theory. The NH 4 +/Ca 2 + selectivity of different exchange materials showed a similar variation among their exchange sites and increased in the order humus, allophane and imogolite (Si/Al ratio 0.5) < allophane (Si/Al ratio 1.0), montmorillonite < vermiculite, illite < halloysite. The origin of negative charge, the steric features around the exchange sites and clay‐humus interaction are suggested as being important in determining the NH 4 +/Ca 2 + selectivity.