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Aluminous Chlorite Origin of pH‐Dependent Cation Exchange Capacity Variations
Author(s) -
Villiers J. M.,
Jackson M. L.
Publication year - 1967
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1967.03615995003100050005x
Subject(s) - cation exchange capacity , vermiculite , chemistry , chlorite , alkali metal , deprotonation , ion exchange , base (topology) , clay minerals , inorganic chemistry , dissolution , soil ph , soil water , mineralogy , ion , geology , soil science , organic chemistry , paleontology , quartz , mathematical analysis , mathematics
Abstract Cation exchange capacity (CEC) and K‐fixing power of a micaceous vermiculite were markedly reduced following treatment with solutions of polymeric hydroxy alumina. The partially chloritized product exhibited linear increase in CEC (measured with KCl) from 48 to 95 meq/100 g as the pH of the NaOAc buffer and then KCl washings increased from pH 4 to 8.5; the CEC increased further to 117 meq/100 g upon brief exposure 2 alkali (2% Na 2 CO 3 , pH 11) at 25C. The pH‐dependent CEC appeared to arise from isomorphous substitutional charge (permanent negative charge), blocked by hydroxy Al charged positively by edge — AlOH 2 groups, and restored by deprotonation of the latter on addition of base. The present findings with chloritized vermiculite further establish the mechanism of pH‐dependent CEC of soils since the behavior found is essentially identical to that reported earlier for soil clays containing aluminous, pedogenically formed chlorite, the constituent responsible for pH‐functional variations in CEC in crystalline clays.