Arsenate sorption-desorption

Pigna M, Krishnamurti GSR, Violante A (2006) Kinetics of arsenate sorption-desorption from metal oxides Effect of residence time. Soil Sci Soc Am J 70 2017-2027... 

Arsenate is readily adsorbed to Fe, Mn and Al hydrous oxides similarly to phosphorus. Arsenate adsorption is primarily chemisorption onto positively charged oxides. Sorption decreases with increasing pH. Phosphate competes with arsenate sorption, while Cl, N03 and S04 do not significantly suppress arsenate sorption. Hydroxide is the most effective extractant for desorption of As species (arsenate) from oxide (goethite and amorphous Fe oxide) surfaces, while 0.5 M P04 is an extractant for arsenite desorption at low pH (Jackson and Miller, 2000). 

Residence time effects on arsenate ad-sorption/desorption mechanisms on goethite. Soil Sci. Soc. Am. J. 65 67-77... 

Pfeifer, H.-R., Gueye-Girardet, A., Reymond, D. et al. (2004) Dispersion of natural arsenic in the Malcantone watershed, southern Switzerland Field evidence for repeated sorption-desorption and oxidation-reduction processes. Geoderma, 122(2-4 SPEC. IIS.), 205-34. 

The first seven cycles of an in situ iron removal project in The Netherlands were simulated with the hydrogeochemical transport model PHREEQC (version 2). The concentration changes of CH4, NH/, Mn, Fe , P04 and As are discussed in detail. Arsenic shows concentration jumps in pumped groundwater which are related to oxidation/reduction and sorption/desorption reactions resulting from the water quality variations. 

H.R. Pfeifer, A. Gueye-Girardet, D. Reymond et al.. Dispersion of Natural Arsenic in the Malcantone Watershed, Southern Switzerland Field Evidence for Repeated Sorption-Desorption and Oxidation-Reduction Processes, Geoderma. 122(2-4), 205-234, Oct. (2004). 

Dissolved arsenic concentrations can be limited either by the solubility of minerals containing arsenic as a constituent element (or in solid solution) or by sorption of arsenic onto various mineral phases. For both the precipitation-dissolution of arsenic-containing minerals and sorption-desorption of arsenic onto solid phases, equilibrium calculations can indicate the level of control over dissolved arsenic concentrations that can be exerted by these processes. However, neither of these types of reactions is necessarily at equilibrium in natural waters. The kinetics of these reactions can be very sensitive to a variety of environmental parameters and to the level of microbial activity. In particular, a pronounced effect of the prevailing redox conditions is expected because potentially important sorbents (e.g., Fe(III) oxyhydroxides) are unstable under reducing conditions and because of the differing solubilities of As(V) and As(III) solids. 

Chapter 2 Sorption and Desorption of Arsenic by Soil Minerals... 

O Reilly et al. (2001) studied the effect of sorption residence time on arsenate desorption by phosphate (phosphate/arsenate molar ratio of 3) from goethite at different pH values. Initially, desorption was very fast (35% arsenate desorbed at pH 6.0 within 24 hrs) and then slowed down. Total desorption increased with time reaching about 65% total desorption after 5 months. These authors found no measurable effect of aging on desorption of arsenate in the presence of phosphate. Furthermore, desorption results at pH 4.0 were similar to the desorption behaviour at pH 6.0. On the contrary, Arai and Sparks (2002) demonstrated that the longer the residence time (3 days-1 year), the greater was the decrease in arsenate desorption by phosphate from a bayerite. 

Whereas studies have been carried out on the factors (surface coverage, residence time, pH) which influence the desorption of arsenate previously sorbed onto oxides, phyllosilicates and soils (O Reilly et al. 2001 Liu et al. 2001 Arai and Sparks 2002 Violante and Pigna 2002 Pigna et al. 2006), scant information are available on the possible desorption of arsenate coprecipitated with iron or aluminum. In natural environments arsenic may form precipitates or coprecipitates with Al, Fe, Mn and Ca. Coprecipitation of arsenic with iron and aluminum are practical and effective treatment processes for removing arsenic from drinking waters and might be as important as sorption to preformed solids. 

Fig. 10. Sorption of phosphate (P04) (A) and desorption of arsenate (As04) (B) from two samples formed at pH 7.0 and R = 0.1, obtained coprecipitating aluminum and arsenate (7R0.1) or by adding arsenate (7AR0.1) immediately after the precipitation of aluminum. Reaction time was 24 hours. Redrawn from Violante et al. (2006).

Myneni, S. C. B., Traina, S. J., Logan, T. J. Waychunas, G. A. 1997. Oxyanion behaviour in alkaline environments sorption and desorption of arsenate in ettringite. Environmental Science and Technology, 31, 1761-1768. 

He has contributed to research on the interface between soil chemistry and mineralogy and soil biology. His special areas of research include the formation mechanisms of aluminum hydroxides and oxyhydroxides, the surface chemistry and reactivities of short-range-ordered precipitation products of Al and Fe, the influence of biomolecules on the sorption and desorption of nutrients and xenobiotics on and from variable charge minerals and soils, the factors that influence the sorption and residual activity of enzymes on phyllosilicates, variable charge minerals, organomineral complexes, and soils and the chemistry of arsenic in soil environments. 

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