With goethite, interaction

Farquhar ML, Chamock JM, Livens FR, Vaughun DJ (2002) Mechanisms of arsenic uptake from aqueous solution by interaction with goethite, lepidocrocite, mackinawite and pyrite as X-ray absorption spectroscopy study. Environ Sci Tecnol 36 1757-1762... 

Cohen, D. R., Waite, T. D. (2004). Interaction of aqueous Au species with goethite, smectite and kaolinite. 

Interaction of phosphate solutions with goethite may lead to surface precipitation of phosphates if the concentration of P in solution exceeds the mineral solubility (Jo-nasson et al., 1988). A combined Auger, XPS, scanning SIMS and electron diffraction study showed that after 90 days at 60 °C, crystals of griphite (an Fe hydroxy phosphate) precipitated out of a phosphate solution onto crystals of goethite (Martin et al., 1988). 

A total of nine possible types of surface sites on goethite can occur when it is suspended in a solution containing the major ions of seawater. These are the negative, neutral, and positive surface sites caused by the ionization of the surface functional groups and the six surface complexes caused by the interactions of the six (Na, Mg, Ca, K, Cl, SOi ) major ions of seawater with goethite. The distribution of these surface sites will vary with the pH and concentrations of the individual ions in the solution. 

Moyes LN, Parkman RH, Chamock JM, Vaughan DJ, Livens FR, Hughes CR, Braithwaite A (2000) Uranium uptake from aqueous solution by interaction with goethite, lepidocrocite, muscovite, and mackinawaite An X-ray absorption spectroscopy study. Environ Sci Technol 34 1062-1068 Muller F, Besson G, Manceau A, Drits V-A (1997) Distribution of isomorphous cations within octahedral sheets in montmorillonite from Camp-Bertaux. Phys Chem Minerals 24 159-166 Muller J-P, Manceau A, Calas G, Allard T, Ildefonse P, Hazemann, J-L (1995) Crystal chemistry of kaolinite and Fe-Mn oxides relation with formation conditions of low temperature systems. Am J Sci 295 1115-1155... 

Correcting for Coulombic Interaction. The surface speciation as a function of solution variables can be computed if we can correct our equibrium constants for electrostatic attraction or repulsion. Westall (21, 22, 23) has developed a computer program that permits one to compute iteratively the composition of the surface and its charge from a set of equilibrium constants. Figures 12 and 13 illustrate the application of this computation to the interaction of o-phosphate with goethite ( -FeOOH). This interaction is rather involved because various mono-dentate and bidentate surface species have to be assumed to account for the experimental observations (18, 24) ... 

Figure 12. Interaction of phosphate with goethite (a-FeOOH). Extent of adsorption is predicted with the help of the equilibrium constants given in Table I (IS), (a) (-) calculated curve (O) experimental measure-...

Table I. Equilibria on the Interaction of Phosphate with Goethite (a-FeCX)H)...

Celi, L., Presta, M., Ajmone-Marsan, F. and Barberis, E. (2001) Effects of pH and electrolyte on inositol hexaphosphate interaction with goethite. Soil Science Society of America Journal 65, 753-760. 

Sigg, L., and W. Stumm (1981), The Interaction of Anions and Weak Adds with the Hydrous Goethite (a-FeOOH) Surface", Colloids and Surfaces 2, 101-117. 

Like X-ray diffraction patterns, neutron and electron diffraction patterns provide averaged information about the structure of a compound. Details of these techniques are given in works by Hirsch et al. (1965) and West (1988). Neutron diffraction involves interaction of neutrons with the nuclei of the atoms. As the neutrons are scattered relatively evenly by all the atoms in the compound, they serve to indicate the positions of the protons in an oxide hydroxide. This technique has been applied to elucidation of the structure and/or magnetic properties of goethite (Szytula et al., 1968 Forsyth et al., 1968), akaganeite (Szytula et al., 1970), lepidocrocite (Oles et al., 1970 Christensen Norlund-Christensen, 1978), hematite (Samuelson Shirane, 1970 Fernet et al., 1984) and wiistite (Roth, 1960 Cheetham et al., 1971 Battle Cheetham, 1979). A neutron diffractogram of a 6-line ferrihydrite was recently produced by Jansen et al. (2002) and has helped to refine its structure (see chap. 2). 

The interaction of phosphate with d and Na is shown in Figure 11.11. Upon adsorption of phosphate onto goethite, d adsorption dropped to zero, whereas adsorption of Na increased substantially (Nanzyo and Watanabe, 1981, 1982). It was suggested that adsorption of phosphate is followed by adsorption of additional cations at pH >7. 

---