Rheological investigations of galena particle interactions

The rheological behaviour of ultrafine (<5 mu m) galena particle slurries has been studied using a concentric cylinder rheometer. The influence of solids content and pH on viscosities and extrapolated yield values are reported and discussed in the context of the level of particle interaction. These studies, coupled with microflotation, microelectrophoresis and X-ray photoelectron spectroscopy (XPS) surface chemical analysis, have furthered our understanding of the role of interparticle forces in controlling the collectorless floatability of galena. In the pH range 6-10, the rheological behaviour of oxidized and effectively hydrophilic galena particles is controlled by electrostatic repulsive forces and the yield values scale with the zeta potentials squared. At pH values less than 6 this relationship breaks down and yield values cannot be predicted by electrostatic and van der Waals considerations alone. A non-DLVO contribution to the extrapolated yield value tau(B)' is required to describe the observed rheological behaviour. The magnitude of tau(B)' is influenced by pH, hydrodynamic conditions, the particle volume fraction and time scale of any conditioning periods. tau(B)' is controlled to a minor degree by hydrodynamic, gravitational and inertial forces, but is mainly due to an attractive hydrophobic force between galena particle surfaces. This attractive hydrophobic particle interaction has been probed by microflotation. XPS has confirmed a pH-controlled surface cleaning mechanism which is responsible for the formation of hydrophobic galena surfaces. (C) 1997 Published by Elsevier Science B.V.