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Effect of Precipitation of Alkaline Earth Carbonates and Magnesium Hydroxide on Na‐Ca‐Mg Exchange in Wyoming Bentonite
Author(s) -
Levy Rachel,
Tanji K. K.,
Whittig L. D.
Publication year - 1983
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/sssaj1983.03615995004700050013x
Subject(s) - bentonite , precipitation , magnesium , alkaline earth metal , ionic strength , chemistry , hydroxide , sodium hydroxide , inorganic chemistry , mineralogy , geology , alkali metal , aqueous solution , paleontology , physics , organic chemistry , meteorology
Wyoming bentonite saturated with Ca and Mg at five different ratios was equilibrated with NaCl solution. It was found that the preference of the bentonite for Ca over Mg was not affected by the presence of exchangeable Na. The separation factor, α Na Ca+Mg , of the bentonite equilibrated with NaCl was compared to that of bentonite in which alkaline earth carbonates and magnesium hydroxide precipitated. It was found that in the presence of alkaline earth precipitation only, α Na Ca+Mg was a function of ionic strength and equivalent fraction of soluble Na. However, precipitation of the carbonates caused a different distribution of the exchangeable ions in the bentonite crystallite compared to the distribution in the absence of precipitation. Where carbonates precipitated, Na was found between the interlayers and Ca and Mg occupied the outside surfaces of the clay. As the pH of the equilibrium solution increased and additional precipitation of alkaline earth carbonates and magnesium hydroxide occurred, α Na Ca+Mg increased with decrease in ionic strength. Apparently this increase in the preference for Na was due to the restriction on Na, occupying the internal surface of the bentonite, to diffuse into the equilibrium solution because of hydroxide coating of the crystallites.