Reaktionen von Ca‐Montmorillonit und Ca‐Vermiculit mit Kohlensäure

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Abstract
Reaction of Ca‐Montmorillonite and Ca‐Vermiculite with CO2The treatment of Ca‐montmorillonite and Ca‐vermiculite with carbonic acid (Pco2 = 2 atm) has shown the following results:In the pH range of ± 3.9–6.0 Ca is exchanged by H directly only on pH dependent (variable) charge sites (Cav), whereas, Ca on permanent charge sites (Cap) is exchanged only by lattice cations mainly Al released by proton attack. Therefore, with regard to proton uptake from carbonic acid the two Ca‐clays behave as extremely weak acids.The exchange of Cav proceeds rapidly that of Cap much more slowly, the first one is essentially reversible the latter at least not within a short period of time. The proportion of Cav is found from a graphical extrapolation of the Ca saturation‐pH‐function (fig. 3).Al released during the initial stage of the reaction is non exchangeable, prevents the expandable minerals partly from collapsing on K tratement (verm. much more than mont.) and has an OH/Al ratio of about 2. On treating the same clay sample several times or at low suspension concentrations exchangeable Al with OH/Al = O occurs. Exchangeable hydrogen was never detected. Vermiculite is less resistent against carbonic acid than montmorillonite.The results were discussed in respect to the mechanism of release of lattice constituents and in respect to Al release under the influence of CO2‐concentrations of soils.