Martin Richard Houchin

Surface titrations and electrokinetic measurements on stannic oxide suspensions

The electrokinetic and surface charge behavior of stannic oxide (SnO2) in KNO3 electrolyte solutions is reported as a function of pH and ionic strength. Potentiometric titrations of the surface groups showed that the point of zero charge occurred at pH 4.3 ± 0.1. The isoelectric point obtained from microelectrophoresis was at pH 4.5 ± 0.15. Stannic oxide behaved similarly to other insoluble metal oxides with respect to the effect of pH on its surface charge and zeta potential. Intrinsic equilibrium constants, which describe the ionization of surface hydroxyl groups and the ion-binding of electrolyte, were calculated using various estimates of the total hydroxyl site density and three different methods of calculation. The preferred values are NS = 11.2 OH groups per nm2, pKa1int = 0.7, pKa2int = 7.9, and p*KK+int = 6.3.

Siderite (FeCO3): Its dissolution and interaction with stannic oxide in aqueous suspensions

Abstract The dissolution rates of a magnesium-rich siderite and an iron-rich magnesite were measured as a function of pH. Electrophoretic measurements were performed on siderite (IEP = pH 7.9), stannic oxide (IEP = pH 4.5), as well as on stannic oxide suspended in solutions of Fe(II), Fe (III), Mg(II) and carbonate. Whilst MG(II) and carbonate had little effect on the isoelectric point (IEP) of stannic oxide, FE(II) and FE(III) adsorbed strongly, shifting the IEP to considerably higher pH values. Electrophoretic mobilities were also measured on stannic oxide particles suspended in filtrates derived directly from siderite suspensions. Under certain circumstances, the surfaces of stannic oxide and siderite became indistinguishable from each other with respect to measured zeta potentials. The significance of these results for selective flotation of cassiterite from siderite is discussed.

Surface titrations and electrokinetic measurements on australian cassiterites

Abstract Fragments of crystals of cassiterite from four Australian ore deposits were cleaned and finely ground. Their points of zero charge were measured by potentiometric titration of the surfaces in aqueous solutions of KNO3. Isoelectric points were obtained from microelectrophoresis measurements. The values were compared with those for synthetic stannic oxide. It was found that, despite a range of trace element concentrations in the natural samples, the points of zero charge and isoelectric points were similar to each other and to stannic oxide.

Surface studies on aqueous suspensions of tourmaline (dravite)

Abstract Tourmaline (dravite) from Western Australia was characterized and its surface properties studied by techniques including potentiometric titrations, microelectrophoresis, X-ray diffraction, microprobe analysis, secondary ion mass spectrometry and ion exchange. Results showed that, when suspended in aqueous solution, dravite released lattice ions into solution. The zeta potential of the dravite surface could be manipulated by exchanging ions from the tourmaline lattice with ions of different valency from solution. The significance of these results to tourmaline flotation are discussed with particular reference to selective cassiterite flotation from tourmaline.