Minerals surface coverage

The adsorption appears to be into the Stem layer, as was illustrated in Fig. V-3. That is, the adsorption itself reduces the f potential of such minerals in fact, at higher surface coverages of surfactant, the potential can be reversed, indicating that chemical forces are at least comparable to electrostatic ones. The rather sudden drop in potential beyond a certain concentration suggested to... 

The amount of collector used is necessarily very small because surface coverages of a monomolecular layer or less are required to impart sufficient hydrophobicity to the mineral. The usages typically range from 1—100 g of collector per ton of ore treated for sulfide flotation (typically 0.2—10% value metal content ia the ore) and 100—1000 g/1 for nonsulfide flotation (1—20% value mineral content) (10). 

In surface precipitation cations (or anions) which adsorb to the surface of a mineral may form at high surface coverage a precipitate of the cation (anion) with the constituent ions of the mineral. Fig. 6.9 shows schematically the surface precipitation of a cation M2+ to hydrous ferric oxide. This model, suggested by Farley et al. (1985), allows for a continuum between surface complex formation and bulk solution precipitation of the sorbing ion, i.e., as the cation is complexed at the surface, a new hydroxide surface is formed. In the model cations at the solid (oxide) water interface are treated as surface species, while those not in contact with the solution phase are treated as solid species forming a solid solution (see Appendix 6.2). The formation of a solid solution implies isomorphic substitution. At low sorbate cation concentrations, surface complexation is the dominant mechanism. As the sorbate concentration increases, the surface complex concentration and the mole fraction of the surface precipitate both increase until the surface sites become saturated. Surface precipitation then becomes the dominant "sorption" (= metal ion incorporation) mechanism. As bulk solution precipitation is approached, the mol fraction of the surface precipitate becomes large. 

McCarron et al. (1990) used the X-ray photoelectron spectroscopy to analyze chalcopyrite and pyrite surface after being conditioned in sodium sulphide solutions. They found that multilayer quantities of elemental sulphur were produced at the surface of both minerals in 3 x 10 and 3 x 10" mol/L sulphide solutions although for a given sulphide concentration, the surface coverage of elemental sulphur for p)uite was greater than that for chalcopyrite under open circuit conditions. Eliseev et al. (1982) concluded that elemental sulphur was responsible for the hydrophobicity of pyrite and chalcopyrite treated with sodium sulphide. Luttrell and Yoon (1984a, b) observed a shoulder due to elemental sulfixr near 164 eV in the S (2p) spectra from relatively pure chalcopyrite floated after being conditioned at different pulp potential established by different hydrosulphide concentration. 

Mayer, L. M. (1999). Extent of coverage of mineral surfaces by organic matter in marine sediments. Geochim. Cosmochim. Acta 63,207-215. 

The adsorption of surfactant on a mineral surface is generally an exothermic process and at a constant surfactant concentration in the solution its adsorbed amount decreases with increasing temperature. Using the partial derivation 31n c/3T for a constant number of CH2 groups n of an hydrocarbon chain of a surfactant and constant values of the surface coverage a, we arrive to an equation for calculation of the total adsorption energy E. From the relation E = Ep + Ea, Richter and Schneider74 derived an equation which is valid for all isotherms ... 

Thus, were the xanthate ion itself to adsorb and retain its charge, lateral repulsion would make it impossible for the surface coverage on the mineral to be a high one, and the desired hydrophobicity of the surface would not be achieved. In the electrochemical mechanism described by Salami and Nixon, the adsorption can become a charge-transfer reaction, continuing by the participation of oxygen until the surface is fully covered with dixanthate (and hence wettable). The mechanism is thus an electrochemical oxidation. 

In summary, the efficiency of (-)-ephedrine supported on inorganic MTS in the model reaction is determined by two factors firstly, the activity of the mineral surface towards the formation of racemic 1-phenyl-propan-l-ol wich depends on the coverage of the surface by organics and secondly, the accessibility to the catalytic sites wich depends on the mesopore diameters of the support. 

In surface precipitation, cations (or anions), which adsorb to the surface of a mineral, may form a precipitate of the cation (anion) with the constituent ions of the mineral at high surface coverage. Figure 13.28 shows schematically the surface precipitation of a cation Me " to hydrous ferric oxide. This model, suggested by Farley et al. (1985), allows for a continuum between surface complex formation and bulk solution precipitation of the sorbing ion that is. 

Summary. Ion beam techniques such as KBS are a good analytical tool for studying interface phenomena due to their multielement capability and the possibility of working on whole rock sections. Interesting information on the sorption mechanisms can be obtained from these studies the colloid surface coverage is low (less than one monolayer) the retention mechanisms are partly controlled by the electric charges developed at the surfaces (colloid, mineral) the colloid detachment rate is very low indicating an irreversible character with... 

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