ORGANO-BENTONITES WITH QUATERNARY ALKYLAMMONIUM IONS

Three bentonites, from Bavaria, Wyoming and Brazil, were separated into various fractions. The layer charge was determined by alkylammonium ion exchange and increases with particle size from 0.25 Eq/(Si,Al)4O(10) (< 0.06-mu-m) to 0.28 Eq/g/(Si,Al)4O(10) (1-10-mu-m). The charge density corresponds to an interlayer cation density of 0.75-0.80 mEq/g silicate. Total amounts of 0.90-1.0 mEq of different surfactant cations (dimethyl dioctadecylammonium, trimethyl tetradecylammonium, alkylammonium ions) are bound per gram silicate. The difference between the total and the interlayer amount of surfactant ions decreases with increasing particle size. The amounts exceeding the interlayer CEC are bound at the edges. Tetramethylammonium (TM) ions restrict the interlayer adsorption of long-chain quaternary alkylammonium ions such as trimethyl tetradecylammonium (TMTD) ions, and only monolayers of flat-lying surfactants are formed. A ratio of TMTD and TM is attained which leads to densely packed monolayers of organic ions. The collapsing effect is smaller for tetraethylammonium ions so that considerable amounts of TMTD ions are adsorbed in bilayers. When bentonites are reacted with quaternary alkylammonium ions of technical quality some selectivity is observed according to particle size and layer charge. Smaller particles with lower charge density preferentially bind the longer chain compounds, whereas large particles with higher charge density select smaller sized surfactants.