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Deprotonated mineral surface sites

Here, [=SOH2] or [=SO ] represents the concentration of protonated or deprotonated surface sites, respectively, on the mineral surface, and the exponents are constants for each mineral. According to this model, the rate of dissolution of most oxides is slowest in solutions where pH = pHppzc, the pH of the pristine point of zero charge where the surface charge of the mineral of interest equals zero (Figures 3 and 4). Some authors include a separate rate term describing dissolution at near-neutral pH (= h2o[=SOH]). Above and below the pHppzc, oxides are predicted to show enhanced dissolution due to protonated and deprotonated surface sites, respectively. [Pg.2339]

As mentioned earlier, complex formation reactions at hydrous metal oxide surfaces can be treated as an extension of classic coordination chemistry metal centers on mineral surfaces participate in inner-sphere and outer-sphere coordination reactions with molecules adsorbed from overlying solution, including H2O, OH , O, and solute molecules (Schindler, 1981 Schindler and Stumm, 1987). A variety of protonation/deprotonation and complex-formation reactions determine the speciation of surface sites. A few... [Pg.234]

Most oxide and hydroxides, as well as the broken edge sites and basal-plane hydroxyl groups of clay minerals exhibit amphoteric behavior. The formation of eleciric charge can be explained by the acid-base behavior of surface hydroxyl groups. A detailed description can be found in several excellent book chapters and articles [1,2,6,8,13,14,35,45], Charge development on amphoteric surface sites (S—OH) could occur by direct proton transfer. The surface hydroxyl groups can be capable of ionization [8,46], Surface ionization (protonation and deprotonation) reactions can take place on these sites, depending on the pH of the solution ... [Pg.723]

All of the important classes of ligand-directed labilization are represented at mineral surfaces, including the deprotonation of a terminal ti -OH2 site. One therefore expects a similar increase in dissolution of oxide minerals as the surface sites become deprotonated. For a mineral siuface, these deprotonations form negative surface charge [cf Eqs (5) and (10)] and the rates correspondingly increase with pH or charge. The actual location of the deprotonations is unknown, but a likely scenario is that ri -OH2 sites on monomolecular steps deprotonate with increases in pH. [Pg.274]


See other pages where Deprotonated mineral surface sites is mentioned: [Pg.78]    [Pg.78]    [Pg.524]    [Pg.194]    [Pg.33]    [Pg.198]    [Pg.221]    [Pg.29]    [Pg.190]    [Pg.532]    [Pg.306]    [Pg.206]   
See also in sourсe #XX -- [ Pg.78 ]




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