Adsorption Affinity of Divalent Heavy Metal Ions for Metal Oxides Evaluated by Modeling with the Frumkin Isotherm
✍ Scribed by Hiroki Tamura; Ryusaburo Furuichi
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 194 KB
- Volume
- 195
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
derground water with hazardous heavy metal ions dissolved Adsorption of divalent heavy metal ions, M(II), on metal oxides from waste materials and their migration to the biosphere is important to determine the behavior of ions in waters and soils. are becoming a serious concern.
The amount of adsorbed Pb(II), Cu(II), Zn(II), Co(II), Ni(II),
Modeling of ion adsorption reactions on metal oxides is and Mn(II) ions on the two oxides MnO 2 and Fe 2 O 3 was measured useful to assess the behavior of ions and their concentration as a function of the pH and concentration of the ions under the levels in environments. Also, a model would be applicable conditions where no mono-and polynuclear hydroxo complexes to the design of ion adsorption processes, like the removal play a role in the adsorption. The adsorption affinity of these and disposal of hazardous ions and the recovery and concenions for the oxides was evaluated with a model that considers tration of precious ions, since model calculations may allow simultaneous (1:1) and (1:2) exchange reactions between M 2/ aqua ions and surface hydroxyl protons (surface complexation) us to select the most effective adsorbents for particular ions obeying the Frumkin isotherm. From the model parameters, it was and to optimize solution pH, dose of adsorbents and other found that the affinity order for (1:1) complex formation is Cu 2/ conditions. In the design of waste repositories, where layers ú Mn 2/ ú Zn 2/ ú Co 2/ ú Ni 2/ for MnO 2 and Pb 2/ ú Cu 2/ ú of adsorbents shielding the site can act as barriers to prevent Zn 2/ ú Co 2/ for Fe 2 O 3 . A large affinity of Mn 2/ for MnO 2 was the leakage of dissolved hazardous ions, model calculations ascribed to the oxidation of this ion by MnO 2 . A good correlation could provide information to select the most effective barrier between the stability constants of (1:1) surface complexes and materials for particular ions and to determine the characteristhose of (1:1) hydroxo complexes in solution was obtained. The tics of barrier layers (thickness, density, and others) in theoadsorption affinities of ions here are the affinities for deprotonated retical and efficient ways.
hydroxyl sites with negative charge, since for all the ions the oxides
For modeling interphase reactions like ion adsorption, it are common and the deprotonation properties of hydroxyl sites must be considered that reaction products are localized at the are the same. The good correlation suggests that the two reactions are similar: From electrostatic theory including crystal field correc-interphase, and electrical, geometrical, chemical, and other tions, the both reactions could be regarded as due to ionic bond lateral interactions between them affect the reactions. formation between the positive charge of metal ions and the nega-Among many modeling approaches, the Frumkin isotherm tive charge of deprotonated sites on oxides or hydroxide ions in evaluates the lateral interactions with thermodynamic assolution, as we have suggested previously. ᭧ 1997 Academic Press sumptions (2), and no assumptions of idealized electrical Key Words: divalent heavy metal ions; metal oxides; hydroxo double layers of interphases are required. It can be flexibly complexes; electrostatic contact adsorption; ionic bonding; Frumapplied to ''real'' oxides encountered in environments and kin isotherm; modeling. industry, which are not well defined and which do not necessarily fit the ''idealized'' electrical double layer assumptions used by other models. We have demonstrated the wide appliof divalent heavy metal ions, Pb(II), Cu(II), Zn(II), 241