The Synergetic Effect of Hydrogen Ions on the Cation Exchange of Potassium in Micas

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Abstract
Interlayer K in eleven trioctahedral micas, with compositions ranging from fluorphlogopite to biotite, was replaced by treating cut flakes with aqueous solutions of Na salts at controlled pH values. Replacement in natural micas was faster at pH 4·5 than at pH 9, and there is a co-operative action or synergy of H+ and Na+ in replacing K+. The synergetic effect of H+ tends to be greatest in micas that lose most net negative charge when K is replaced, and increases when Fe2+ in biotite is oxidized by heating. Possible relationships between the synergetic effect and the chemical composition of micas are discussed in relation to the structure and chemical changes in the aluminosilicate layers when K is exchanged, and it is concluded that incorporation of protons into the structure is responsible for the synergetic effect.

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