Selenite sorption

Su, C. Suarez, D.L. (2000) Selenate and selenite sorption on iron oxides An infrared and electrophoretic study. Soil Sci. Soc. Am. J.101-111... 

Dynes, J. J., and Huang, P. M. (1997). Influence of organic acids on selenite sorption by poorly ordered aluminum hydroxides. Soil Sci. Soc. Am. J. 61, 772-783. 

Monteil-Rivera, F., Masset, S., Dumonceau, J., Fereroff, M. Jeanjf.an, J. 1999. Sorption of selenite ions on hydroxyapatite. Journal of Materials Science Letters, 18, 1143-1145. 

Monteil-Rivera, F., Fedoroff, M., Jeanjean, J., Minel, L., Barthes, M.-G. Dumonceau, J. 2000. Sorption of selenite (SeOf ) on hydroxyapatite an exchange process. Journal of Colloid and Interface Science, 221, 291-300. 

Baur, I. Johnson, C. A. 2003a. Sorption of selenite and selenate to cement minerals. Environmental Science and Technology, 37, 3442-3447. 

Figure 9. Logarithmic plots of sorption of phosphate, selenite and selenate by a soil at the indicated pH values. To permit plotting on a common scale, the concentrations of selenite and selenate have been multiplied by factors to account for their lower affinity. For example, the values at pH=6 for selenite were 0.05 and for selenate 0.008. The lines indicate the fit of a model based on the heterogeneity of the reacting surfaces [44].

Subject to limitations discussed in section 4.1., the effects of pH on anions are similar to those observed using iron oxides. Thus, the sorption of phosphate and of selenite generally decrease with increasing pH (Fig. 12.) for the reasons discussed earlier. Similar principles apply for borate. However sorption increases with increasing pH because the pK for borate dissociation is near 9. The concentration of borate ions therefore increases 10-fold for each... 

Figure 13 illustrates the fit of the model to the effects of time and solution concentration for selenite and for selenate sorption by a soil. 

While the sorption curves are almost linear on a log log scale, the model fits a gentle curve as this is consistent with a bigger body of information (Fig. 9.). At any given level of sorption, the concentration of selenite in solution decreases with time and with increasing temperature. It is this decrease that is modelled as due to diffusive penetration. Selenate differs in that the sorption curves are steeper (as also shown in Fig. 9.) and, importantly, that the effects of time, though detectable, are much smaller. These two species therefore provide a test for the argument that apparent non-reversibility of sorption occurs because of the continuing reaction. 

Figure 14. Desorption of selenite (a) and selenate (b), after incubation for 10 days at 60°C with selenite or selenate respectively at the levels indicated by the arrows on the vertical axis. Different levels were used so that the concentration range would be similar. The broken lines show the sorption curves [80].

Figure 14. shows that selenite desorption did not follow the same track as sorption. This is because it takes time to reverse the diffusive penetration. This was tested from the fit of the model. When the model which had been fitted to sorption data, some of which is shown in Fig. 13., was used to predict desorption, the prediction was close to the observation. In contrast, desorption of selenate was greater. This is consistent with its much slower continuing sorption reaction. The greater desorption was also predicted... 

Vlll. The effects of time and temperature of incubation on the sorption and subsec]uenl desorption of selenite and selenate by a soil. /. Soil Sci. 40, 29-37. 

Panak PJ, Booth CH, Caulder DL, Bucher JJ, Shuh DK, Nitsche H (2002) X-ray absorption fine structure spectroscopy of plutonium complexes with bacillus sphaericus. Radiochim Acta 90 315-321 Papelis C, Brown GE Jr, Parks GA, Leckie JO (1995) X-ray absorption spectroscopic studies of cadmium and selenite adsorption on aluminum oxides. Langmuir 11 2041-2048 Papelis C, Hayes KF (1996) Distinguishing between interlayer and external sorption sites of clay minerals using X-ray absorption spectroscopy. Colloids and Surfaces A 107 89-96 Parise J (1999) New opportunities for microcrystalline and powder diffractometiy at synchrotron sources. In Schulze DG, Stucki JW, Bertsch PM (eds) Synchrotron X-ray Methods in Clay Science, Clay Minerals Society Workshop Lectures 9. The Clay Minerals Society, Boulder, Colorado, p 115-145 Park SH, Sposito G (2002) Structure of water adsorbed at a mica surface. Phys Rev Lett 89 085501-1-085501-3... 

Suarez et al. (36) use a combination of FTIR spectroscopy, electrophoretic mobility and pH titration data to deduce the specific nature of anionic surface species sorbed to aluminum and silicon oxide minerals. Phosphate, carbonate, borate, selenate, selenite and molybdate data are reviewed and new data on arsenate and arsenite sorption are presented. In all cases the surface species formed are inner-sphere complexes, both monodentate and bidentate. Two step kinetics is typical with monodentate species forming during the initial, rapid sorption step. Subsequent slow sorption is presumed due to the formation of a bidentate surface complex, or in some cases to diffusion controlled sorption to internal sites on poorly crystalline solids. 

XPS is one of the most widely used non-in-situ surface-sensitive techniques. It has been used to study sorption mechanisms of inorganic cations and anions such as Cu, Co, Ni, Cd, Cr, Fe, selenite, and uranyl in soil and aquatic systems (19-28). The disadvantage of invasive non-in-situ techniques is that they often must be performed under adverse experimental conditions, e.g., desiccation, high vacuum, heating, or particle bombardment. Such conditions may yield data that are misleading as a result of experimental artifacts (2,29,30). Review articles on XPS, AES, and SIMS are available (29,31,32). 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

Borate sorption investigated by Toner and Sparks [99] shows the maximum values at about pH 8.5 with a slow decrease to lower pH values and a strong decrease to higher ones. Saeki and Matsumoto [100] discuss selenite adsorption onto various adsorbents. a-A Os (y4g = 5.3m /g) evidently had too small a surface to give meaningful results, with Al(OH)3 (A = 126 m /g) the maximum adsorption (80%) was found at pH 6, decreasing to 20% at both pH 3 and pH 10. 

The sorption of Se" ions in single crystals of stilbite and on clinoptilolite-containing tuffs, in dependence on the concentration and pH of a selenite solution, was studied by IR speetroscopy [11Z2]. The sorption of Se" ions takes place with considerable changes in the spectrum of clinoptilolite tuff. It was assumed that the sorption on clinoptilolite tuff from 0.1 M solution of sodium selenite with pH = 9 occurs in the form of selenite and pyroselenite anions forming a hydrogen bond with zeolite water moleeules. 

Monteil-Rivera, F., M. Fedoroff, J. Jeanjean, L. Minel, M.-G. Barthes, and J. Dumonceau. 2000. Sorption of selenite Se03 on hydroxyapatite An exchange process. J. Colloid Interface Sci. 221 291-300. 

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