Influence of pH and Chloride-Based Metal Salts on Coagulation/Dispersion Behavior of Talc Suspension

Abstract

In this study, the coagulation behavior of talc suspensions in the presence and absence of chloride-based metal salts (NaCl, CaCl₂ and AlCl₃) at a constant (pH 4) and different pHs was assessed by sedimentation tests and zeta potential (ZP) measurements. In addition, the pH-dependent dissolution experiments were performed on the talc powder in water. To evaluate the results of the sedimentation tests, the turbidity of supernatant liquid was considered. The isoelectric point (iep) of the talc sample was determined at around pH 1.9. Even though the talc suspension used in this work has a sufficient ZP at neutral pHs to provide a better dispersion in suspension, the sedimentation tests and also the viscosity measurements showed that the powdered talc coagulated easily, even at these pHs without the metal salt. This was attributed to the hydrophobic attraction between the basal surfaces of talc particles. At acidic pHs (i.e., pH 4) the effect of metal salts on the coagulation of talc suspension was marginal.

Keywords:

• coagulation
• dispersion
• hydrophobic
• talc
• zeta potential

Notes

*LOI: Loss on ignition.

†: The amounts of the minerals were calculated semi-quantitatively by the Rietveld method.

*ppm: part per million (mg/l); **ppb: part per billion (µg/l).