Adsorbed calcite-oleate

Fig. 2.4b shows the flotation of scheelite, fluorite and calcite using sodium oleate and trisodium phosphate. The flotation of fluorite and calcite can be depressed by sodium phosphate at pH < 9.5 and pH < 10.0, respectively, but not that of scheelite. Since the PZC of scheelite, fluorite and calcite are pH = 1.5, 9.5, and 10.0, respectively (Wang, 1983), anionic species H2POJ, HPO ", and PO " which are predominant, will not be adsorbed on the negatively charged surface of scheelite, and thus will have no depression effect at pH > 2.2 below pH 9.5, fluorite surface is positively charged and the anionic phosphate species can be adsorbed on fluorite, leading to its depression. A similar depression mechanism can be formulated for calcite at pH < 10.0. 

Oleate has been observed to adsorb on calcite and apatite, electrostatically below their points of zero charge, and chemically above these points. 

The IRRAS spectra of ultrathin films can also be measured in the region of phonon absorption of the substrate. Figure 2.13 shows results of / -polarized ex situ IRRAS of calcite (CaCOs) after adsorption of oleate for 5 min in a 3.3 X 10 M oleate solution at pH 10, measured by Mielczarski and Miel-czarski [41] at different angles of incidence. It is important that although the absorption bands of adsorbed oleate at 1575, 1538, and 1472 cm lie within the region of the reststrahlen band of calcite (1600-1400 cm ), they have sufficient... 

The monolayers with different occupancy (25-100%) of all the calcium sites available on the surface (i.e., one oleate molecule adsorbed on each calcium site) were modeled. The structures of most stable oleate SAMs—that is, 67%, 100%, and 75% occupancy on fluorite 111, calcite 104, and fluorapatite 100 surfaces, respectively—are presented in Figure 2.11. Some of the characteristic properties of these SAMs are summarized in Table 2.5. It is evident form these results that the... 

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