An electrokinetic study by the straming potential method of ion exchange at oxide mineral surfaces

Abstract

The streaming potential method has been used to observe changes in the electrical double layer at the surfaces of the minerals Al2O3, SnO2, Fe2O3, and TiO2 in the presence of electrolytes. In addition to the normal effects of preferential physical adsorption of ions, ion exchange involving surface hydroxyl groups offers a useful hypothesis for explaining the results. Anion-exchange mechanisms appeared to be of particular importance in the reactions of phosphate, molybdate, and citrate with the oxide surfaces. In general for the particular samples used, Al2O3 and SnO2 (having basic surfaces) exhibited more pronounced anion exchange than Fe2O3 and TiO2 which had acidic surface.

Catalytic liquid‐phase nitrite reduction: Kinetics and catalyst deactivation

“…In these cases, much higher quantities of ammonium ions were detected in the liquid phase (Figure 3b), which confirms that both reaction kinetics and selectivity are drastically influenced by the increase of pH value of the aqueous solution during the reaction course. One can tentatively suppose that due to the accumulation of hydroxide ions in the liquid phase, there is a certain amount of these species physically adsorbed on the surface of either Pd monometallic or Pd-Cu bimetallic catalyst particles, which is also suggested by other investigators (Johansen andBuchanan, 1957: Vorlop andTacke, 1989). The metal loadings in the catalysts employed are !elatively low and the metallic clusters are less than 50-70 A in diameter, because x-ray analysis did not show the metallic phase.…”

Bulk and Surface Characterization of Distinct Hematite Morphology: Implications for Wettability and Flotation Response

“…However, because the surface of Hematite-1 (ratio Fe/O = 5.6 in Table 5) bears more iron and less oxygen than Hematite-2 (ratio Fe/O = 4.9 in Table 5), one can expect a lower reactivity of (001) surface (more abundant in Hematite-2) as the result of the occurrence of doubly coordinated Fe-OH (Table 2). Since the literature fails to provide information on the surface composition (Fe/O ratio) of other hematite samples used in zeta potential and IEP determinations conducted elsewhere [27,47], some conflicting values of IEP are found for specular hematite from Australia (IEP at pH = 4.2) [47] versus Labrador, Canada, (IEP at pH = 6.6) [27] plus Hematite-2 from Brazil (IEP at pH = 5.6).…”

“…Minerals 2024, 14, x FOR PEER REVIEW 15 of 21 OH (Table 2). Since the literature fails to provide information on the surface composition (Fe/O ratio) of other hematite samples used in zeta potential and IEP determinations conducted elsewhere [27,47], some conflicting values of IEP are found for specular hematite from Australia (IEP at pH = 4.2) [47] versus Labrador, Canada, (IEP at pH = 6.6) [27] plus Hematite-2 from Brazil (IEP at pH = 5.6).…”