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A first step in refining traditional holistic models is to In this paper, the acid-base properties of illite/water suspen-isolate and analyze the surface reaction mechanisms of difsions are examined using the constant capacitance surface com-ferent components in natural particles. Of particular interest plexation model. On the basis of results of potentiometric titrations are clays, since they are the dominant components in natural and solubility experiments, we conclude that the proton reactions minerals. As to what has already been done in this area, and montmorillonite (a 2:1 layer-type clay mineral). For the Evaluation of these two models indicates that both of them cangive good descriptions of the experimental data of systems with study of kaolinite (8), in addition to the amphoteric surface different illite concentrations and ionic strengths and that the one hydroxyl group, GSOH, they postulate a second surface site-one pK a model can be considered as a simplification of the functional group, GXH, which is weakly acidic and can two sites-two pK a s model. Since both models assume only depro-undergo ion exchange with cations from the background tonation reactions at the illite surfaces, they suggest that the sur-electrolyte. For the study of montmorillonite (9), besides face behavior of the illite is similar to that of amorphous SiO 2 .GSOH and GXH, another surface hydroxyl group GTOH, Model assumptions, experimental procedures, and evaluative cri-which undergoes one deprotonation reaction, is incorporated teria are detailed in the paper. ᭧ 1997 Academic Press to evaluate the surface acid-base behaviors. Wieland and

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Adsorption of diphenyl-, phenyl-and orthophosphate on γ-Al2O3 was studied with a combination of macroscopic and 31 P solid-state NMR measurements. Results for adsorption suggest that diphenyl phosphate was bound largely as an outer-sphere complex, while phenyl phosphate was held largely as inner-sphere surface complexes with an outer-sphere complex present only at higher pH values. Both the adsorption edge and the cross polarization magic angle spinning NMR spectra were consistent with the interaction between the surface and phenyl phosphate being driven by electrostatic forces. Adsorption of orthophosphate was more complex, with evidence of outer-and inner-sphere complexes and surface precipitation. Increasing the orthophosphate concentration and equilibration time tended to increase the fraction bound as a surface precipitate.

The chemically active phosphorus surface sites defined as PO(x), PO(x)H, and PO(x)H2, where x = 1, 2, or 3, and the bulk phosphorus groups of PO4(3-) at synthetic carbonate-free fluorapatite (Ca5(PO4)3F) have been studied by means of single-pulse 1H,31P, and 31P CP MAS NMR. The changes in composition and relative amounts of each surface species are evaluated as a function of pH. By combining spectra from single-pulse 1H and 31P MAS NMR and data from 31P CP MAS NMR experiments at varying contact times in the range 0.2-3.0 ms, it has been possible to distinguish between resonance lines in the NMR spectra originating from active surface sites and bulk phosphorus groups and also to assign the peaks in the NMR spectra to the specific phosphorus species. In the 31P CP MAS NMR experiments, the spinning frequency was set to 4.2 kHz; in the single-pulse 1H MAS NMR experiments, the spinning frequency was 10 kHz. The 31P CP MAS NMR spectrum of fluorapatite at pH 5.9 showed one dominating resonance line at 2.9 ppm assigned to originate from PO4(3-) groups and two weaker shoulder peaks at 5.4 and 0.8 ppm which were assigned to the unprotonated PO(x) (PO, PO2-, and PO3(2-)) and protonated PO(x)H (PO2H and PO3H-) surface sites. At pH 12.7, the intensity of the peak representing unprotonated PO(x) surface sites has increased 1.7% relative to the bulk peak, while the intensity of the peaks of the protonated species PO(x)H have decreased 1.4% relative to the bulk peak. At pH 3.5, a resonance peak at -4.5 ppm has appeared in the 31P CP MAS NMR spectrum assigned to the surface species PO(x)H2 (PO3H2). The results from the 1H MAS and 31P CP MAS NMR measurements indicated that H+, OH-, and physisorbed H2O at the surface were released during the drying process at 200 degrees C.

The potential possibility of the surface complexation models to describe the sorption of trace metals on natural sediments has been suggested since the late 1980s, which should be of natural importance to predict the bioavailability of trace metals in aquatic sediments. This possibility was tested based on 11 geographically and hydrologically diverse natural aquatic sediment samples. The sorption of Cu(II), Zn(II), Pb(II), and Cd(II) on these sediments was studied by both sorption isotherm and pH−edge sorption experiments. The experimental sorption data were fit well by the surface complexation model (the double-layer model). The linear free energy relationship (LFER) between the surface complexation constants (K s) of trace metals on the sediments and the corresponding first-hydrolysis constants (*K 1) was observed, which could be expressed as log K s = a log *K 1 + b. The slope of the linear regression, a, was dependent on the sediment composition:  a = 0.19TOC − 0.09Oxides + 1.31 (n = 11), where TOC (%) is the total organic carbon and Oxides (%) include reactive iron oxide, amorphous iron oxide, cryptocrystalline manganese oxide, and aluminum oxide. The results strongly suggest that the sorption of trace metals on natural sediments could be described reasonably by the surface complexation model and predicted potentially from the relationships between Ks and *K1 and the sediment composition.

Sediments are primarily made up of clay minerals, which In this paper, we conducted potentiometric titrations, batch ad-are sheet silicates constructed of tetrahedral sheets (silica sorption experiments and FT-IR analysis to study the uptake of tetrahedra, SiO 4 ) and octahedral sheets (gibbsite structure, copper in illite/water suspensions and then applied the constant g-Al(OH) 3 ). The three most common clay minerals in soil capacitance surface complexation model to interpret the reaction systems are kaolinite, montmorillonite, and illite. mechanism at the aqueous illite surfaces. Our research shows thatThe adsorption of heavy metals at the kaolinite/water the copper adsorption at these surfaces is strongly dependent on and montmorillonite/water interfaces has been studied by pH and that the adsorption causes a deprotonation of surface Schindler and Stadler et al. using the constant capacitance groups. We propose that the uptake of copper in the carbonatefree illite suspensions can be explained by the formation of mono-surface complexation model (1, 2). They account for the nuclear surface complexes, GSOCu / and GSOCuOH, and a surface adsorption behavior of kaolinite and montmorillonite multinuclear surface complex, GSOCu 2 (OH) / 2 , followed by the by postulating a combined ion exchange-surface complexformation of a bulk precipitate, Cu(OH) 2 (s), or a surface precipi-ation model that assumes two kinds of binding sites on the tate, GSOCu 2 (OH) 3 (sp). For the illite suspensions containing clay mineral surfaces: (a) weakly acidic groups (GXH), carbonates, we propose that the copper-illite interaction can be which undergo ion exchange, and (b) amphoteric surface depicted by the formation of mononuclear surface complexes, hydroxyl groups (GSOH), which form inner sphere com- as a function of pH, the concentration of the substrate, and