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Salt Displacement of Acid-Treated Trioctahedral Vermiculites

ABSTRACT

Freshly prepared and 30-day-aged samples of HCl-treated trioctahedral vermiculites from Libby, Montana (L) and northeastern Transvaal, South Africa (S) were leached with 1N or more dilute solutions of NaCl, KCl, CaCl₂, or MgCl₂. The exchange acidity, exchangeable H₃O, Al, and Mg, and the cation-exchange capacity after acid-salt treatment were determined.

With both the L and S minerals, the sum of the salt-displaceable ions after acid treatment corresponded to approximately 90% of the initial CEC. For freshly acidified materials, the exchange acidity (consisting of displaced H₃O and Al ions) comprised the bulk of the exchangeable ions. After 30 days of aging in water at room temperature, exchange acidity had decreased by around one-half, and equivalent amounts of exchangeable Mg had appeared.

The most striking findings concerned: (i) differences between the two minerals with regard to the amounts of H₃O and Al displaced by salts, and (ii) differences in displaced H₃O and Al depending on the exchanging cation and the concentration of the displacing solution. The exchange acidity from fresh HCl-treated S vermiculite consisted of about 60% H₃O and 40% Al when 1N NaCl, CaCl₂, or MgCl₂ was the displacing salt. For L vermiculite, titratable acidity displaced by 1N NaCl, CaCl₂, or MgCl₂ was around three-fourths Al. For both minerals, exchange acidity measured with 1N or 0.05N KCl, 0.05N NaCl, or 0.02N CaCl₂ or MgCl₂ was almost entirely H₃O.

X-ray patterns of K-saturated, acidified samples showed interlayer deposits and reduced collapsibility when the samples were leached with KCl. There were virtually no indications of interlayer material when the samples were leached with 1N CaCl₂ before KCl.

² Postdoctoral Fellow and Professor of Soils and Plant Nutrition, Univ. of California, Riverside.

Received for publication September 19, 1966. Accepted for publication January 16, 1967.