Potassium retention in montmorillonites

The amounts of potassium retained, after exchange with normal ammonium acetate solution at pH 7, were measured with six montmorillonite-beidellite minerals, whose interlayer charge ranged 0·72-1·00 M + /Si 8 O 22 and where tetrahedral substitution of Al for Si ranged 0·14-0·93 M + /Si 8 O 22 . The amount of potassium retained increased with increasing interlayer charge, but there was no correlation between the amount of potassium retained and the tetrahedral charge.