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Fluoro‐Aluminum Complexes on Model and Soil Exchangers
Author(s) -
Anderson M. A.,
Zelazny L. W.,
Bertsch P. M.
Publication year - 1991
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/sssaj1991.03615995005500010012x
Subject(s) - kaolinite , sorption , adsorption , chemistry , ion exchange , phase (matter) , soil water , loam , inorganic chemistry , mineralogy , ion , geology , organic chemistry , soil science
A number of investigators have suggested that complexes may exist as discrete species on the exchange phase and, thus, be important to a complete description of exchange reactions. Little evidence establishing the presence of complexes on the exchange phase has hitherto been provided, however. Adsorption experiments in which µ M F solutions were equilibrated with K‐, Ca‐, and Al‐saturated cation‐exchange resins demonstrated substantial F removal to the Al‐saturated resin, with the adsorbed F quantitatively recovered with a single wash with 1.0 M NH 4 Cl, whereas no F removal was observed when either K or Ca occupied the exchange sites. Removal of both Al and F from Al‐F solutions equilibrated with K‐ and Ca‐saturated resins provided additional evidence for adsorption as fluoro‐Al complexes. Modeling of the competitive complexation‐exchange reactions with MINTEQA2 yielded results that under‐predicted net Al sorption in the presence of F, and thus also inaccurately predicted solution composition, by neglecting potential adsorption of fluoro‐Al complexes. Kaolinite (KGa‐2) samples also sorbed appreciable F, though both surface OH displacement and sorption to exchange‐phase Al were apparently responsible for the observed decrease in F solution concentrations. In the absence of exchange‐phase Al, however, all sorbed F was fixed against displacement by 1.0 M NH 4 Cl. Samples of a Fuquay soil (loamy, siliceous, thermic Arenic Plinthic Paleudult) profile from South Carolina were also extracted with water, 0.01 M CaCl 2 , and 1.0 M NH 4 Cl; no detectable F was found in the water extracts, while considerable F was solubilized in the CaCl 2 and NH 4 Cl extracts, with NH 4 Cl‐extractable F being highly correlated with exchangeable Al ( r 2 = 0.98). These results suggest that part of the Al on the soil exchange phase may in fact exist as fluoro‐Al complexes, and also imply a role of exchange‐phase Al in regulating apparent F solubility within acid soils.