Oxyanion adsorption mechanisms

Suarez, D. L, Goldberg, S., and Su, C., 1999, Evaluation of oxyanion adsorption mechanisms on oxides using FTIR spectroscopy and electrophoretic mobility in Sparks, D. L., and Grundl, T. J., eds., Mineral-Water Interfacial Reactions, American Chemical Society, p. 137-178. 

Evaluation of Oxyanion Adsorption Mechanisms on Oxides Using FTIR Spectroscopy and Electrophoretic Mobility... 

Adsorption of anions on oxides is usually accompanied by the uptake of protons (or the release of hydroxyl ions). The ratio between the number of protons that are coadsorbed and the level of anion adsorption is not usually stoichiometric. Studies of adsorption of oxyanions on goethite as a function of pH appear to indicate that, provided only one adsorbed species is present, the proton anion ratio is related to the mode of adsorption (Rietra et al., 1999). It follows that oxyanions which adsorb with a similar proton/anion stoichiometry, have a similar adsorption mechanism. 

Much experimental evidence has been adduced in support of the ligand exchange mechanism for oxyanion adsorption. The principal lines of reasoning that lead to this mechanism can be summarized as follows. 

Detailed information on oxyanion bonding mechanism and adsorbed oxide surface species can be obtained by utilizing a combination of spectroscopic techniques and macroscopic measurements, particularly, EM and measurements of net OH change/anion adsorption. ATR-FTIR spectroscopy in suspensions is complemented by DRIFT spectroscopy under conditions where small quantities of adsorbed water are still present. Neither FTIR nor EXAFS provide complete information on surface speciation and bonding. FTIR may not always be... 

A 0.5-gram mass of either the organo-treated or inorganic cation exchanged zeolite and 50 mL of 10 mM/L arsenate or chromate aqueous solutions were placed into Erlenmeyer flasks and mechanically shaken in reciprocating mode to attain equilibrium. Different equilibrium periods for individual zeolite modifications and both aqueous oxyanions species have been established. The adsorption isotherm experiments were conducted using above mass/ volume ratio of samples with an initial metal concentrations ranged from 0.5 to 100 mM/L at laboratory temperature. The... 

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