Kinue Tsunematsu

Zeta potential measurement of muscovite mica basal plane-aqueous solution interface by means of plane interface technique

Abstract The zeta potentials of muscovite mica basal plane were investigated by means of the plane interface technique as a function of pH in the presence of 0.001 M KCl, compared with those of fused silica. For the plane interface technique, the negative zeta potentials of a large muscovite mica sheet, i.e., the mica basal plane, were uniformly higher in magnitude than those of a large silica plate over the pH range from 2 to 11, whereas the zeta potentials of the mica basal plane were markedly dependent on pH in the pH range of 3 to 6. In the pH range of 2 to 3, the zeta potenteials of the mica basal plane showed remarkably negative values of −80 to −60 mV and became more insensitive to the reduction in pH. In particular, we could not observe the presence of an isoelectric point (iep) of the mica basal plane, which has never been encountered normally in the case of pure oxides. For comparison, the electrophoresis measurements were made for both mica and silica particles. The negative mobility zeta potentials of mica particles were smaller in magnitude than those of fused silica particles in the pH range of 3 to 11 even though the positively charged alumina-type sites on the mica particles were neutralized by sodium dodecyl benzene sulfonate (SDBS). This result was quite the reverse of the trend obtained from the plane interface technique. However, the variation in flotation recovery of the muscovite mica with dodecyl ammonium chloride (DAC) as a collector at pH 3 was very consistent with that of crystalline quartz (ζ ∼ −65 mV) with dodecyl trimethyl ammonium bromide (DTAB) at pH 7.4. This observation provided justification for the remarkably negative zeta potential (∼ −75 mV) of the mica basal plane obtained from the plane interface technique at pH 3.

Synthesis of expandable fluorine mica from talc

Expandable fluorine micas were synthesized using talc and Na2SiF6 at 800°C for 2 hours in air, nitrogen, argon, and under vacuum. Gaseous SiF4, generated from Na2SiF6, and the resultant amorphous sodium silicofluoride formed during the reaction between talc and Na2SiF6 below 900°C are taking active part in the formation of expandable micas because the intensity of the 12.5 Å reflection of expandable micas decreases as the gas flow increases in the furnace. Expandable micas seem to be formed by the transformation from talc taking place without the entire disruption of the original atomic arrangement. This takes place with the loss of one Mg2+ from an octahedral site and by the intercalation of every two Na+ into the interlayer site of talc. Infrared absorption and thermal analyses show that expandable micas include a small amount of OH− in their structures.