Surface charge 438 carbonates

Carbon Surface area (m-7g) Pore volume (cm Vg) pH v< Carbon surface charge" (mmol/g) Adsorbent/adsorbate complex charge (rnmo)/g) Adsorbed NOM charge" (mmol/g)... 

However, these workers did not mention the pH of the solution that determine the carbon surface charge. 

The adsorption of natural organic matter such as humic acid and lipids that have large molecular dimensions but also have polar groups in their molecule, has been attributed to the pore-size distribution in carbons and to the nature of the carbon surface charge. The former determines the availability of the pore for adsorption, and the latter determines the electrostatic interactions between the carbon surface and the adsorbate molecule. Many natural organic materials have molecular diameters of about 3 nm so that only activated carbons with a large proportion of mesopores will be more suitable for their adsorption. 

Phospha.te Treatment. Calcium phosphate is virtually insoluble in boiler water. Even small levels of phosphate can be maintained to ensure the precipitation of calcium phosphate in the bulk boiler water, away from heating surfaces. Therefore, the introduction of phosphate treatment eliminates the formation of calcium carbonate scale on tube surfaces. When calcium phosphate is formed in boiler water of sufficient alkalinity, a particle with a relatively nonadherent surface charge is produced. This does not prevent the development of deposit accumulations over time, but the deposits can be controlled reasonably well by blowdown. 

Apart from reactions with the electrolyte at the carbon surface, the irreversible specific charge is furthermore strongly affected by the possible co-intercalation of polar solvent molecules between the graphene layers of highly graphitic matrices [139]. This so-called "solvated intercalation reaction" depends (i) on the crystallinity and the morphology of the parent carbonaceous material, which will be discussed in Sec. 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

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