THERMODYNAMICS AND THERMOCHEMISTRY OF THE EXCHANGE REACTION BETWEEN NH4+ AND Mn2+ IN A MONTMORILLONITE CLAY |
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Authors: | M. GILBERT R. VAN BLADEL |
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Affiliation: | (The Agricultural Institute, Johnstown Castle, Wexford, Ireland;) |
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Abstract: | The exchange reaction between NH4+ and Mn3+ was studied on a montmorillonite clay at several temperatures and different ionic strengths. Manganese was preferred to ammonium; this preference increased with the temperature and dilution of the dialysate. Comparison with published data concerning exchanges involving NH4+ and the alkaline-earths showed that in the sequence of increasing selectivity: Mg2+ < Ca2+ < Sr2+ < Ba2+, Mn2+ lies between Mg2+ and Ca2+. The enthalpy change was measured calorimetrically and calculated by application of the van't Hoff law to the temperature coefficient of the equilibrium constants. Both values were in good agreement. The excellent recoveries of Mn2+ at the end of the exchange reaction and the constancy of the cation exchange capacity over the whole range of surface composition ruled out the possibility of significant adsorption in the MnOH+ form. The behaviour of manganese was very similar to that of the alkaline-earth cations. |
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