Metal ions, adsorption

J. W. Novak, Jr., R. R. Burr, andR. Bednarik, "Mechanisms of Metal Ion Adsorption of Activated Alumina," Vol. 35, Proc. Int. Symp. on Metals Speciation, Separation, and Recorey, Chicago, lU., July 27—Aug. 1, 1986, Industrial Waste Elimination Research Center of the Illinois Institute of Technology, Chicago, lU. 

The effects on metal ion adsorption of ligands that can themselves adsorb strongly can be quite different from that described above. Many multi-atomic ligands can bond to oxide surfaces through atoms different from those they use to... 

Table 1 summarizes a few properties of the resulting fibers used in studies on their metal ion adsorption abilities. Hereafter, bifucntional fibers derived from PPPE-c and PPPE-f are denoted by symbols FPS-c and FPS-f, respectively, and respective symbols FP-c and FP-f denote monofunctional... 

In a simplified form Eq. (ii) was used, decades ago, to assess metal ion adsorption to surfaces, by plotting log ([Meads] / [Me2+]) vs pH. (Kurbatov et al., 1951). The slope of this curve gives an idea on n. The model for this "Kurbatov-plot" assumes that the adsorbent =S is present in large excess and that the adsorption at constant pH is not affected by surface charge. Fig. 2.11 gives an example for the binding of metal ions to amorphous Si02. 

Such metal ion adsorption effects become relatively significant - especially in very dilute solutions at pH-values above 7. 

Honeyman, B. D., and J. O. Leckie (1986), "Macroscopic Partitioning Coefficient for Metal Ion Adsorption Proton Stoichiometry at Variable pH and Adsorption Density", in J. A. Davis and K. F. Hayes, Eds., Geochemical Processes at Mineral Surfaces, ACS Symposium, Washington, DC. 

If this mechanism is consistent with the experimental relaxation data, then a plot of xp versus the expression in the brackets of Equation 35 will give a straight line with a slope of kjnt and an intercept at the origin. As shown in Figure 11, the data fit this proposed mechanism quite well. Values for i i0, reactant and product concentrations, and K nt input into Equation 35 are from the equilibrium modeling results calculated at each pH value for which kinetic runs were made. Normally a variety of different mechanisms are tested against the experimental data. Several other more complex mechanisms were tested, including those postulated for metal ion adsorption onto y-A O (7) however, only the above mechanism was consistent with the experimental data. Hence it was concluded that the bimolecular adsorption/desorption reaction was the most plausible mechanism for Pb2+ ion adsorption onto a-FeOOH. 

In their description of metal ion adsorption, Benjamin and Leckie used an apparent adsorption reaction which included a generic relationship between the removal of a metal ion from solution and the release of protons. The macroscopic proton coefficient was given a constant value, suggesting that x was uniform for all site types and all intensities of metal ion/oxide surface site interaction. Because the numerical value of x is a fundamental part of the determination of K, discussions of surface site heterogeneity, which are formulated in terms similar to Equation 4, cannot be decoupled from observations of the response of x to pH and adsorption density. As will be discussed later, It is not the general concept of surface-site heterogeneity which is affected by what is known of x> instead, it is the specific details of the relationship between K, pH and T which is altered. 

Metal Ion Adsorption in Mixtures of Multiple Solid Phases. One of the arguments put forth for extending the concepts of solution coordination chemistry to heterogeneous systems is the hypothesis that the mineral components of soils or sediments can be considered as ligands which compete for complexation of adsorbates. To this end, it is important to know the relative ability of different mineral surfaces to complex solutes. 

The results of two sets of computations are shown in Figure 12. Open circles represent calculations for the binary adsorbent systems which used the Kurbatov coefficients for the end-member systems. This is the approach used by Davies-Colley et al., (9) in their examination of metal ion adsorption in mixtures of model... 

At very low adsorption densities, metal ion adsorption exhibits Langmuiriaij behavior. However, above some critical adsorption density, r (i.e., when approximately 0.01% of surface sites are occupied), the intensity of metal lon/interactions decreases with increasing surface-site occupancy. A corollary of this model is that K has a unique value at adsorption densities below r for a specific adsorbate and adsorbent. By extension, 0a[Pg.181]

If the reductant is a metal ion, adsorption may also precede electron transfer ... 

The time-dependent behaviors of metal ions adsorption were measured by varying the equilibrium time between the adsorbate and adsorbent in the range of 30-300 min. The concentration of Pb(ll) and Zn(ll) were kept as 50 ttg/mL while the amount of resin added was 0.5 g. The experiments were performed at pH 4 for Pb L... 

Palmquist, U. Ahlberg, E., Lovgren, L. Sjo-berg, S. (1999) competitive metal ion adsorption in goethite systems using in situ volta-metric methods and potentiometry. J. Coll. Int. Sci. 218 388-396... 

The available nonaqueous reactivity data from Meyer and co-workers [13] and from Schmehl and co-workers [60] on injection and back ET to and from 2 appear to point, instead, to a special role for equilibrium cation adsorption. In the absence of initial alkali metal ion adsorption, injection from MLCT-type chromophores does not occur. In their presence, injection does occur, but in... 

Environmental applications of functional mesostructures metal ion adsorption... 

The oxide, a-quartz, was selected as the substrate for the present and continuing studies of metal ion adsorption. It is of considerable importance in several practical situations—e.g., water purification and ore flotation—and has the important property that it is negatively charged over a wide pH range since its zero-point-of-charge (z.p.c.) is circa pH 2. 

Yiacoumi, SKinetics of Metal Ion Adsorption from Aqueous Solutions Models, Algorithms, and Applications, Kluwer Academic Publishers. Norwell. MA, 1995. 

Vermeer, A. W. P., McCulloch, J. K., van Riemsdijk, W. H., and Koopal, L. K. (1999). Metal ion adsorption to complexes of humic acid and metal oxides Deviations from the additivity rule. Environ. Sci. Technol. 33,3892-3897. 

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