Hydrous oxides adsorption characteristics

Suzuki, T. M., Tanco, M. L., Tanaka, D. A. P., Yokoyama, T., Matsunaga, H., Yokoyama, T., Adsorption characteristic and removal of oxo-anions of arsenic and selenium on the porous polymers loaded with monoclinic hydrous zirconium oxide, Sep. Sci. Technol., 36, 2001,103-111. 

Some emphasis is given in the first two chapters to show that complex formation equilibria permit to predict quantitatively the extent of adsorption of H+, OH , of metal ions and ligands as a function of pH, solution variables and of surface characteristics. Although the surface chemistry of hydrous oxides is somewhat similar to that of reversible electrodes the charge development and sorption mechanism for oxides and other mineral surfaces are different. Charge development on hydrous oxides often results from coordinative interactions at the oxide surface. The surface coordinative model describes quantitatively how surface charge develops, and permits to incorporate the central features of the Electric Double Layer theory, above all the Gouy-Chapman diffuse double layer model. 

In Skirmer, H.G.W. Fitzpatrick, R.W. (eds.) Biomineralization processes of iron and manganese. Catena Verlag, Cremhngen-Destedt, Catena Suppl. 21 75—99 Ghoneimy, H.F. Morcos.T.N. Misak, N.Z. (1997) Adsorption of Co and Zn ions on hydrous Fe(lll), Sn(lV) and mixed Fe(lll)/ Sn(IV) oxides. Part 1. Characteristics of the hydrous oxides, apparent capacity and some equilibria measurements. Colloids Surfaces A. 122 13-26... 

Sorption on oxides and hydrous oxides has been extensively studied both experimentally and theoretically. In order to define an ideal oxide or hydrous oxide exchanger, we will rely on experiments with well-defined sorbents such as chromatographic alumina (1-4). Briefly, the adsorption characteristics of oxides and hydrous oxides are (1) At high pH, they act as cation exchangers but with less sensitivity to the total salt concentration than clay minerals. This behavior is illustrated in Figure 2, where sorption of strontium on alumina is shown. 

Bowers, A.R. and Huang, C.P., Adsorption characteristics of metal-EDTA complexes onto hydrous oxides, J. Colloid Interf. Sci., 110, 575. 1986. 

Weesner, E.J. and Bleam, W.F., Binding characteristics of Pb + on anion-modified and pristine hydrous oxide surfaces studied by electrophoretic mobility and X-ray adsorption spectroscopy, J. Colloid Interf. Sci., 205, 380, 1998. 

Oxides of four valence metals, titanium, zirconium and cerium, sometimes show selective adsorption characteristics in removing anions from water phases. Hydrous titanium oxide is known to be a selective adsorbent for recovering uranium in seawater, which is present in the form of carbonyl complex in concentrations as low as 3.2 ppb. 

Hydrous titanium oxides are important ion exchangers with different selectivities to different ions, exhibiting certain desirable catalytic and adsorptive properties [1-6]. One particular advantage to these hydrous oxides is their good thermal and radiation stabilities. Studies undertaken by a number of workers have shown that hydrous titanium oxide has ion exchange characteristics that are highly dependent on preparative conditions[7-8], and that the titania surface displayed amphoteric characteristics [9-10]. 

Analysis of the blue reaction product has shown that its composition does not correspond to the formulas just given. Most of the colored material consists of hydrous copper oxide. It is probable that the color reaction involves a chemical adsorption of molecules of the dye on gel particles of Cu(OH)2, whereby the chelate bonds shown in (II) and (III) come into play. Such adsorption compounds belong among the so-called color lakes. It is characteristic of all these lakes that no metal dyestuff compounds arise as a separate phase the metal atoms do not leave their original phase association (compare aluminum-alizarin test, page 96). 

---