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Flow‐Through and Batch Methods for Determining Calcium‐Magnesium and Magnesium‐Calcium Selectivity
Author(s) -
DeSutter Tom M.,
Pierzynski Gary M.,
Baker Luke R.
Publication year - 2006
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/sssaj2005.0065n
Subject(s) - magnesium , selectivity , chemistry , ion exchange , calcium , gibbs free energy , flow (mathematics) , chromatography , inorganic chemistry , thermodynamics , mathematics , organic chemistry , ion , catalysis , physics , geometry
Conducting binary‐exchange experiments is a common way to identify cationic preferences of exchanger phases and the two most common approaches are the flow‐through and batch methods. The objectives of this research were to provide the materials and methods for both flow‐through and batch equilibration techniques and to compare Ca‐Mg and Mg‐Ca selectivity when using these two methods on a montmorillonitic soil. The methods were evaluated by comparing both the Gibbs free energy values (ΔG ex ) and selectivity diagrams derived from the flow‐through and batch exchange reactions. The ΔG ex values for the Ca‐Mg reaction were 634 and 444 J mol −1 as determined by the flow‐through and batch methods, respectively, indicating an exchanger preference for Ca. Exchanger preference for Ca was also evident in the Mg‐Ca reaction with ΔG ex values of −882 and −784 J mol −1 for the flow‐through and batch methods, respectively. The flow‐through and batch methods worked very well for determining cation selectivity and results indicate no significant differences existed between the two methods.