Professor John Ralston - Summit Speaker Series - September 6, 2016

Professor John Ralston                              

Emeritus Laureate Professor University of South Australia

September 6, 2016 2:00 pm

8-207 Donadeo Innovation Centre for Engineering

“Selective Surface Chemistry- Inorganic and Organic Tailoring of Mineral Interfaces for Separation”

Inorganic and organic reagents can selectively alter the surfaces of metal oxide and metal sulfide surfaces. The basic ideas and concepts of the interaction of inorganic and organic reagents with mineral surfaces, along with their subsequent influence on dispersion stability are explored.

We classify mineral surfaces according to their surface charge and intrinsic hydrophobicity, illustrating how techniques ranging from wettability determinations and surface spectroscopy to atomic force microscopy and rheology may be used as classification tools.

Metal oxide surfaces develop surface charge and potential, as do metal sulphides. However the latter also respond to oxidation-reduction potential and, upon exposure to an aqueous environment, their surface chemistry changes with time. pH, the presence of dissolved oxygen, the influence of sulfoxy species, low MW xanthates, sulphide ions, cyanide  and metal ion hydrolysis products can all have a significant influence on the surface chemistry and separation behaviour of metal sulphides. We reveal how   knowledge of the surface chemistry can be used to achieve exquisite selective separations.

The surface chemistry of metal oxide and silicate surfaces may be manipulated by pH and the presence of low and high MW reagents. We focus on high MW organic reagents in this lecture, illustrating the mechanisms by which they interact with mineral surfaces, coupled to a thermodynamic summary.

Application of these concepts to the control of talc wettability through the adsorption of specific polymers is dealt with, including considerations of adsorbed layer density, morphology, contact angle measurements and underlying solid surface structure. For kaolinite, we place particular emphasis on the importance of temperature in flocculation. Adsorbed layer thickness, electrokinetic potential, hydrodynamic diameter, yield stress, separation energy and ‘goodness of solvent’ are all shown to play a major role in the ability to build compact floc structures and efficient flocculation.