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Hydroxyl‐Sulfate Exchange Stoichiometry on γ‐Al2O3 and Kaolinite
Author(s) -
He L. M.,
Zelazny L. W.,
Martens D. C.,
Baligar V. C.,
Ritchey K. D.
Publication year - 1996
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/sssaj1996.03615995006000020015x
Subject(s) - stoichiometry , kaolinite , gibbsite , adsorption , chemistry , titration , inorganic chemistry , dissolution , precipitation , ion exchange , mineralogy , ion , organic chemistry , physics , meteorology
There is a release of OH ‐ from soil colloids with the addition of SO 2‐ 4 . The ratio of moles of OH ‐ released per mole of SO 2‐ 4 adsorbed is referred to as the OH/SO 4 exchange stoichiometry. The OH/SO 4 stoichiometry not only provides an important constraint on surface complexation models but also is a critical area of research to explain the effects on soil pH from the application of SO 2‐ 4 amendments such as gypsum. The OH/SO 4 stoichiometry on γ‐Al 2 O 3 and kaolinite was determined by a back titration method with a pH‐stat autotitrator as well as calculated from SO 2‐ 4 adsorption edges at various SO 2‐ 4 concentrations by the thermodynamic approach. The stoichiometry increased with increasing solution pH and SO 2‐ 4 adsorption density. At a low pH, the stoichiometry was low and was similar for γ‐Al 2 O 3 and kaolinite. At higher pH levels, it was higher for γ‐Al 2 O 3 than for kaolinite. The average values of the stoichiometry calculated by the thermodynamic approach were in agreement with those measured by back titration for both γ‐Al 2 O 3 and kaolinite. The thermodynamic approach provides an easier experimental method to evaluate the OH/anion stoichiometry as a function of pH and adsorption density. It also indicated that at low pH levels (<5), the stoichiometry might be overestimated due to dissolution of adsorbents, whereas at higher pH levels (5–8), it might be underestimated because of precipitation of Al hydroxy sulfates and gibbsite.