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MCLEAN E. O.; BITTENCOURT, V. C.
Soil Science: February 1974
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ABSTRACTTri-ionic systems of bentonite and illite clay suspensions were prepared with Ca added at either 90 or 70 percent saturations and various saturations of K and either Na, NH4, or additional Ca added to complete saturation of the clays to pH 7.6. Additional base saturations at 75 and 50 percent were imposed by additions of H-clay. Aliquots of each suspension were prepared by mixing homoionic clays, adding either 0.1 or 0.3 symmetry concentration of BaCl2 or HCl, and diluting to volume. Each suspension was membrane equilibrated with an equal volume of water (50 ml).Marked complementary ion effects on K and Ca displacement occurred when the exchange was from pH-dependent charges. For example, when K plus K-complements totaled 10 percent saturation of the clays (90 percent Ca), the different complementary cations caused twofold difference in the fractions of K displaced with BaCl2 from bentonite clay and more than fourfold difference in fraction displaced from illite. In contrast, when K plus K-complements totaled 30 percent saturation (70 percent Ca), complementary ion effects were much smaller; and when the pH-dependent charges were inactivated by addition of H-clay, the effects were almost completely eliminated.Sodium was so highly hydrolyzed from pH-dependent charges that the complementary ion effect of Na on K (and Ca) displacement by BaCl2 was evidently a result of competition of K with more strongly bonded H ions on the H-preferring charges. The differences in concentrations of electrolyte generated by hydrolysis appeared to account for the differences in complementary ion effect on K and Ca displaced by BaCl2 and HCl.

Tri-ionic systems of bentonite and illite clay suspensions were prepared with Ca added at either 90 or 70 percent saturations and various saturations of K and either Na, NH4, or additional Ca added to complete saturation of the clays to pH 7.6. Additional base saturations at 75 and 50 percent were imposed by additions of H-clay. Aliquots of each suspension were prepared by mixing homoionic clays, adding either 0.1 or 0.3 symmetry concentration of BaCl2 or HCl, and diluting to volume. Each suspension was membrane equilibrated with an equal volume of water (50 ml).

Marked complementary ion effects on K and Ca displacement occurred when the exchange was from pH-dependent charges. For example, when K plus K-complements totaled 10 percent saturation of the clays (90 percent Ca), the different complementary cations caused twofold difference in the fractions of K displaced with BaCl2 from bentonite clay and more than fourfold difference in fraction displaced from illite. In contrast, when K plus K-complements totaled 30 percent saturation (70 percent Ca), complementary ion effects were much smaller; and when the pH-dependent charges were inactivated by addition of H-clay, the effects were almost completely eliminated.

Sodium was so highly hydrolyzed from pH-dependent charges that the complementary ion effect of Na on K (and Ca) displacement by BaCl2 was evidently a result of competition of K with more strongly bonded H ions on the H-preferring charges. The differences in concentrations of electrolyte generated by hydrolysis appeared to account for the differences in complementary ion effect on K and Ca displaced by BaCl2 and HCl.

© Williams & Wilkins 1974. All Rights Reserved.