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The Effects of Wash Solvents on Cation-Exchange Capacity Measurements¹

ABSTRACT

The CEC of a strong acid-exchange resin, four clays, and several soils was determined using various cations for saturation and a wide variety of solvents for removal of the excess electrolyte. Precipitation of the salts in the solvents was avoided by using the more soluble acetates of the monovalent ions and the chlorides of the polyvalent ions, and by diluting the occluded volume of salt solution once with water to reduce its concentration to 0.1N. The CEC of the resin could then be determined equally well by Na, Ca, or Al, using water or any of eight nonaqueous solvents. The CEC of montmorillonite was found to be more dependent on the solvent used: low results with solvents of high dielectric constant could only be prevented by high speed centrifugation, while high results were obtained with acetone, t-butanol, and dioxane owing to salt retention even after extensive washing. No evidence was found for the loss of adsorbed ions due to hydrolysis, or for the formation of basic exchange ions. One additional complication was found with soils: the NH₄⁺ CEC was found to vary owing to the variable solubility of some ammoniated organic matter complex. A method is proposed in which the samples are washed with 0.001N solutions of the salts used for saturation. While high speed centrifugation is required, the introduction of a nonaqueous solvent is avoided, and a clay of known ionic composition results.

¹ Presented before Div. S-2, Soil Sci. Soc. Am., at Ithaca, N.Y., Aug. 12, 1962.

² Assistant Soil Chemist, The Connecticut Agr. Exp. Sta., New Haven.

Received for publication November 4, 1963. Accepted for publication March 11, 1964.