Adsorption by goethite

Mechanisms of Sorption Processes. Kinetic studies are valuable for hypothesizing mechanisms of reactions in homogeneous solution, but the interpretation of kinetic data for sorption processes is more difficult. Recently it has been shown that the mechanisms of very fast adsorption reactions may be interpreted from the results of chemical relaxation studies (25-27). Yasunaga and Ikeda (Chapter 12) summarize recent studies that have utilized relaxation techniques to examine the adsorption of cations and anions on hydrous oxide and aluminosilicate surfaces. Hayes and Leckie (Chapter 7) present new interpretations for the mechanism of lead ion adsorption by goethite. In both papers it is concluded that the kinetic and equilibrium adsorption data are consistent with the rate relationships derived from an interfacial model in which metal ions are located nearer to the surface than adsorbed counterions. 

Zinc adsorption by goethite in the absence and presence of phosphate. Aust. J. 

Anion adsorption by goethite and gibbsite. I. The role of the proton in determining adsorption envelopes. J. Soil Sci. 23 177-192... 

Because the various SCM s have different formulations for treating adsorption reactions and the electrostatic terms, parameters fit to one model may not he applicable to other models (Morel et al, 1981). For example, Gao and Mucci (2001) determined different Log K s for As(V) adsorption by goethite when the data were fit to the Constant Capacitance Model, the Basic Stem Model, and the Triple Layer Model. 

Siegel et al. (1992) tested the LAM using mixtures of goethite and montmorillonite day, with quartz as an inert matrix. They modeled adsorption by goethite with the TL model and by montmorillonite using an ion-exchange approach. Adsorption of Ni, Pb, and Sr on the mixtures obeyed the LAM, probably in part because the sorbents were well-defined, crystalline mineral phases. One can tentatively reason that where suspended sorbent phases are relatively crystalline, or occur chiefly in the soil or rock itself, immobile and separate, the LAM approach should work. 

Figure 6.8. Fit of the CD-MUSIC model to cadmium adsorption by goethite. Open symbols represent total dissolved Cd at le-6 mol L. Closed symbols represent total dissolved Cd at le-4 mol L. (From Venema et al., 1996a.)...

Madrid, L. and de Arambarri, P., Adsorption isotherms and hysteresis of proton adsorption by goethite. Geoderma, 21, 199, 1978. 

Fluoride ion is moderately adsorbed by soil minerals. Figure 9.4 shows fluoride adsorption by goethite (FeOOH). Fluoride adsorption conforms to the ligand exchange theory and is probably favored by the close similarity in size of F and OH ions. In acid soils at equal anion concentrations, F adsorption predominates over that of other common anions. This makes F an effective desorbing agent for previously adsorbed anions. 

M.D.A. Bolland, A. M. Posner, and J. P. Quirk, Zinc adsorption by goethite in the absence and presence of phosphate, Aust. J. Soil Res. 15 279 (1977). M. M. Benjamin and N. S. Bloom, Effects of strong binding of anionic adsorbates on adsorption of trace metals on amorphous iron oxyhydroxide, in Adsorption from Aqueous Solutions (P. H. Tewari, ed.). Plenum, New York, 1981. 

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