CATION EXCHANGE PROPERTIES OF MICAS

Abstract

SummaryThe abilities of 10 trioctahedral and 3 dioctahedral micas to release K by cation exchange were compared by repeatedly extracting the micas with NaCl solutions.For a chosen solution concentration and pH, the quasi‐equilibrium concentration of K in a solution in contact with a mica is largely independent of the fraction of mica K exchanged. The solution concentration ratio cK/cNa ranges from 1×10‐5 for dioctahedral micas to 1·2×10‐3 for a very reactive biotite and seems to depend on the number of mica structural‐hydroxyl groups orientated so that the OH transition moment is perpendicular to the mica basal plane. In the phlogopite‐biotite series, the most important single constituent of a mica that determines its K release is the F content.Micas that lose much negative charge when the K is exchanged release K more readily to acidic solutions. The pH of unbuffered solutions increases during the exchange of K from these micas, confirming the view that sorption of protons decreases the negative charge of the aluminosilicate layers.