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ABSTRACT
The proposition that hydrolysis may account for the selective adsorption of heavy metals by clay surfaces is compared with an alternate explanation of specific exchange of the metal with weakly dissociable H+. It is shown that past evidence offered in support of the two hypotheses is somewhat ambiguous. Theoretical treatment is presented for the competition of ions in adsorption reactions which provides a means of distinguishing between the two alternatives through the effect of H+ on the metal-clay reaction in the presence of a competing ion. Experimentally, the effect of H+ on the reaction of Co2+ with montmorillonite is studied in the presence and absence of Mg2+, a weakly competing ion. Ionic strength is held constant, and nonspecific reactions are minimized with an excess of CaCl2. The results are interpreted as favoring the hydrolysis hypothesis. Inherent assumptions are considered.
1 Contribution from the U. S. Plant, Soil and Nutrition Laboratory, Soil and Water Conservation Research Division, ARS, USDA, Ithaca, N. Y., and Department of Agronomy, Cornell University. Agronomy Paper No. 581. Presented before Div. II, Soil Science Society of America, Aug. 23, 1962, at Ithaca, N. Y.
2 Soil Scientist, U. S. Plant, Soil and Nutrition Laboratory; former Research Fellow in Agronomy, Cornell University, now Research Officer, Division of Soils, C.S.I.R.O., Adelaide, South Australia; and Laboratory Technician, respectively.
Received for publication April 15, 1963. Accepted for publication July 23, 1963.
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