Cation Exchange and Selectivity in Heated Minerals

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Abstract
Various minerals that are commonly present in shales were heated in air as well as hydrothermally and their cation exchange capacity (CEC) and cation exchange selectivity (CES) values were determined. The CEC values of all the heated minerals decreased because of partial or complete collapse of the layers.The CES (KX/Ca1/2X) values of montmorillonites and micaceous vermiculites increased because of wedge site formation by partial collapse after heat treatment to 500 and 750°C in air. The CES values of coarse grained micas, however, decreased by dry heat treatment because of the collapse of frayed edges or wedge zones. Heated illites randomly interstratified with montmorillonite behaved like the specimen montmorillonites, while heated, well crystallized illites behaved similarly to the coarse grained micas. That the wedge zones are enormously selective for potassium was clearly proven here by the collapsed, heated minerals.The CES values of poorly crystalline illites interstratified with montmorillonite increased while those of well crystallized illites with discrete vermiculite impurity decreased upon hydrothermal treatment at 400°C and 500 bar (pressure). The decrease or increase in CES of the hydrothermally heated illite minerals can be explained by the loss or creation respectively of wedge zones just as in the case of air‐heated minerals.

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