Chromate adsorption

Some differences in arsenate and chromate adsorption on ODA-clinoptilolite and Pb-(Ag-linoptilolites) as well were recorded (Figs. 5 and 6). ODA-clinoptilolite exhibited more efficient arsenate and chromate removal from aqueous solutions than the inorganically exchanged modifications. However, silver exchanged clinoptilolite revealed higher capacity values for both oxyanions uptake than lead exchanged clinoptilolite did. This phenomenon supports preferred silver treated clinoptilolite utilization for specific water purification process even on the base of environmental acceptability. 

Fig. 7 presents partial results of dynamic regime experiments for chromate adsorption and desorption by ODA-clinoptilolite. As shown by breakthrough curves, ODA-clinoptilolite column quantitatively removes chromate species from simulated waste water , apparently more efficiently by lower flow rate. Consequently to similar configuration of chromate and sulfate molecules, such loaded column was more efficient to regenerate with Na2S04 than NaCl solution, as elution curves at the Fig. 7 illustrate. 

In Wedepohl, K.H. (ed.) Handbook of geochemistry. Springer, Berlin, 1 250-271 Weerasooriya, R. Tobschall, H.J. (2000) Mechanistic modelling of chromate adsorption onto goethite. Colloids Surfaces 162 167-175... 

Zachara, J.M. Girvin, D.C. Schmidt, R.L. Resch, C.J. (1987) Chromate adsorption on amorphous iron oxyhydroxide in the presence of major ground water ions. Envir. Sci. Technol. 21 589-594... 

Ainsworth, C. C., Girvin, D. C., Zachara, J. M., and Smith, S. C., 1989, Chromate adsorption ongoethite Effects of aluminum substitution Soil Science Society of America Journal, v. 53, p. 411-418. 

Garman, S. M., Luxton, T. P., and Fick, M. J. (2004). Kinetics of chromate adsorption on goethite in the presence of sorbed silicic acid. J. Environ. Qual. 33, 1703-1708. 

Pressure-jump relaxation was also used by others to study anion adsorption/desorption kinetics on soil constituents. These investigations have included the study of the kinetics and mechanisms of acetic acid adsorption on a silica-alumina surface (Ikeda et al., 1982a) and phosphate (Mikami et al., 1983a) and chromate adsorption (Mikami et al., 1983b), on 7-AI2O3. Double relaxation times on the order of milliseconds were observed in each of these studies. 

De Gioannis G, Muntoni A, Ruggeri R, Zilstra H, Floris M. (2007). Chromate adsorption in a transformed red mud permeable reactive barrier using electrokinesis. 6th Symposium on Electrokinetic Remediation (ed. C CameseUe), June 12-15, Vigo, Spain University of... 

Chromate. Increasing chromate adsorption shifted the PZC of amorphous iron oxide to increasingly lower pH value indicating an inner-sphere adsorption mechanism (54). FTIR analyses of freeze-dried samples containing adsorbed chromate mixed with KBr showed shifts in absorption bands from those... 

S. Mustafa, S. Khan, and M. Iqbal Zaman, Effect of Ni ion doping on the physical characteristics and chromate adsorption behavior of goethite, water research, 44 (2010), 918-926. 

Chromate adsorption onto ferrihydrite was studied by attenuated total reflection IR spectroscopy (ATR-IR) and theoretical frequency calculations (Johnston and Chrysochoou 2012). The calculations were done for several model arranganents, shown in Figure 9.21. It was found that the results are consistent with the formation of monodentate and bidentate surface complexes. Monodentate complexes (Figure 9.21e) are dominaut at low surface coverage aud pH > 6.5, and bidentate complexes (Figure 9.21f) form at high surface coverage aud pH < 6. 

FIGURE 12.3 Chromate adsorption on two B horizons of North American soils. 

Bhutan , M.M. Santosh, A., and Mitra, A.K., Abnormal mode of chromate adsorption on ignited sulphates as carrier surfaces, Adsorpt. Sci. Technol., 8(1). 1-12 (1992). 

Chromate-polyphosphate mixtures were found to be more effective than the individual components. According to Kahler and George (1950) polyphosphates are capable of cleaning the surface, so providing access for the chromate. Polyphosphate can also reinforce the film produced by the chromate (Hatch, 1965 b). Chromate adsorption on the surface makes the potential of the metal more positive, which facilitates the adsorption of negatively charged polyphosphate ions. 

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