Phosphate Adsorption on Hematite, Kaolinite, and Kaolinite–Hematite (k–h) Systems As Described by a Constant Capacitance Model
✍ Scribed by A. Ioannou; A. Dimirkou
- Book ID
- 102580898
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 159 KB
- Volume
- 192
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
The constant capacitance model was used to describe phosphate adsorption on hematite, kaolinite, and a kaolinite-hematite syswhere s o is the permanent structural charge resulting from tem (k-h). The model assumes a ligand exchange mechanism isomorphous substitutions in soil minerals, s H is the net and considers the charge on both adsorbate and adsorbent. The proton charge, s IS is the inner-sphere complex charge, s OS model is shown to provide a quantitative description of phosphate is the outer-sphere complex charge, and s d is the associated adsorption on these, including the effect of varying pH values.
charge.
The computer program Ma-Za 2, a program that fits equilibrium
Oxide minerals except in very acid soils (3, 4), do not constants to experimental data using an optimization technique, have any structural charge, so that the balance of surface was used to obtain optimal values for the anion surface complexation constants on hematite, kaolinite, and a kaolinite-hematite charge reduces to system, while the PC program Ma-Za 1 in Q-Basic language was used for the application of the constant capacitance model. The s H / s IS / s OS / s d Å 0.
[2]
model represented adsorption of phosphate anions well over the entire pH range studied (3.8-9.0). The main advantage of the The surface hydroxyl groups on the oxides are the phosmodel is its ability to represent changes in anion adsorption ocphate-reactive functional groups considered in the models.
curring with changes in pH. Extension of the model to describe
Phosphate adsorption occurs via a complex formation mechphosphate adsorption in a mixed system, such as the kaoliniteanism with these hydroxyl ions.
hematite system, using the surface protonation-dissociation con-Chemical modeling of phosphate adsorption at the oxidestant of hematite was qualitatively successful. In mixed system solution interface has been successful using surface comthe model reproduced the shape of the adsorption isotherms well over the pH range 3.8-9.0. However, phosphate adsorption was plexation models. These models are designed to calculate overestimated. The hematite and the kaolinite-hematite system values for the thermodynamic properties mathematically and were synthesized and identified by X-ray, NMR, and FT-IR specconstitute a family of models having similar characteristics.
troscopy.