Salt Displacement of Acid-Treated Trioctahedral Vermiculites
- Malek T. Kaddah and
- N. T. Coleman2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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