Constant-capacitance surface complexation model, applications

VIBRATIONAL SPECTROSCOPY Infrared and Raman spectroscopies have proven to be useful techniques for studying the interactions of ions with surfaces. Direct evidence for inner-sphere surface complex formation of metal and metalloid anions has come from vibrational spectroscopic characterization. Both Raman and Fourier transform infrared (FTIR) spectroscopies are capable of examining ion adsorption in wet systems. Chromate (Hsia et al., 1993) and arsenate (Hsia et al., 1994) were found to adsorb specifically on hydrous iron oxide using FTIR spectroscopy. Raman and FTIR spectroscopic studies of arsenic adsorption indicated inner-sphere surface complexes for arsenate and arsenite on amorphous iron oxide, inner-sphere and outer-sphere surface complexes for arsenite on amorphous iron oxide, and outer-sphere surface complexes for arsenite on amorphous aluminum oxide (Goldberg and Johnston, 2001). These surface configurations were used to constrain the surface complexes in application of the constant capacitance and triple layer models (Goldberg and Johnston, 2001). [Pg.242]

The intent of this chapter is not to survey noninvasive surface spectroscopy but to illustrate briefly how it is applied to resolve the Stummian issue of whether inner-sphere surface complexes form. For this purpose, the application of electron spin resonance (ESR), electron nuclear double resonance (ENDOR), and electron spin echo envelope modulation (ESEEM) spectroscopies to elucidate metal cation speciation and the use of extended X-ray absorption fine structure (EXAFS) spectroscopy to detect surface anion species will be described. Emphasis will be on the interpretation of spectra. Sample preparation and instrumentation details were reviewed in recent volumes edited by Hawthorne (55) and Perry (27). Because the constant capacitance model was developed in the context of adsorption by hydrous oxides, these... [Pg.45]

The triple layer model is applicable for solutions with a wide range of ionic strength. To use it, it is necessary to know the concentrations of active centres acidity constants and and electric capacitances and of the mineral surface, and also equilibrium constants of all specific and nonspecific complexation reactions. [Pg.196]