SYNTHESIS OF HECTORITE

Abstract

Hydrothermal reaction of slurries made from homogeneous Si-Mg precipitates, lithium hydroxide and sodium hydroxide yielded hectorite-like smectite products. The transmittance measured on 1% dispersions and the rheological properties of a 2.5% gel solution were easily controlled by adjusting the chemical composition of the slurry, the hydrothermal synthesis temperature, and the reaction time. The transmittance and rheological properties attained their maxima for materials synthesized at 200°-225°C in 2 h and at a system composition of Si: Mg: Li: Na =8: 5.4: 0.6: 0.7. The hectorite produced from a composition of Mg/Si=5.5/8 showed optimum transparency and apparent viscosity, whereas transmittance and rheological properties decreased with increasing amount of Mg in the Mg/Si range (5.5-6.5)/8. Additional Li and Na improved both properties. The average particle size of the products correlates well with the transmittance (r=-0.883) and apparent viscosity at a high shear rate of 1022/s (r=-0.714), and the apparent viscosity at a low shear rate of 10.2/s correlates well with gel strength after 600 s (r=0.949), which is apparently controlled by the total alkali metals (Li+Na) content.