Clay Retention, Activities, and Excised Root Uptake of Ions in Bentonite Suspensions and Dialyzates
1968
Snyder, G. H. | Reicosky, D. C. | McLean, E. O. | Franklin, R. E.
Suspensions of bentonite clay saturated with varying Ca and K or Rb ratios and containing several concentrations of CaCl₂ or KCl were membrane equilibrated with equal volumes of water. Activities and concentrations of Ca and K or Rb, and Cl ions in both suspension and dialyzate phases were determined with electrode and radioactive tracer techniques. The “suspension effect” (greater activity of cations and lesser activity of anions in the suspension than in the dialyzate phase) increased with increased K saturation (decreased Ca saturation) and with decreased electrolyte concentrations. Permanent charge cation exchange sites appeared to contribute most to the suspension effect, while the pH-dependent charges favored hydrolysis of the metallic cations and thus tended to mask the suspension effect. A given concentration of electrolyte was many times more effective in causing changes in cation retention by the clay phase when the clay was predominantly saturated with Ca rather than with Rb. Higher retention of cations at high Rb saturations generally paralleled the electrode-measured activities and excised root uptake (corn and soybeans) of cations. Addition of 0.2 S of CaCl₂ decreased the differences in cationic activities between phases and generally eliminated significant differences in uptake between phases.
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