Hydroxide, arsenate desorption

Izumi, F. (1993) Rietveld analysis program RIE-TAN and PREMOS and special applications. In Young, R.A. (ed.) The Rietveld Method, Oxford, Oxford University Press, 236-253 Jackson, B.P. Miller, W.P. (2000) Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Sci. Soc. Am. J. 64 1616-1622 Jain, A. Raven, K.P. Loeppert, R.EI. (1999) Ar-senite and arsenate adsorption on ferrihy-drite Surface charge reductions and net OEI-release stoichiometry. Environ. Sci. Techn. 

Jackson, B.P. and Miller, W.P. (2000) Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Science Society of America Journal, 64(5), 1616-22. 

The equation for arsenate desorption by hydroxide (alumina regeneration) is presented in Eq. (2). 

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). 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

A precipitation of the iron hydroxides is also observed. The reddish precipitate in the creek starts right away at the source and contains up to 8 %(w/w) of arsenic. As shown in a previous publication [5] the arsenic is bound only weak to the iron hydroxides. A mobilization is possible by desorption without dissolution of the iron hydroxides. 

Masue, Y., Loeppert, R.H. and Kramer, T.A. (2007) Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum iron hydroxides. Environmental Science and Technology, 41(3), 837-42. 

Foley and Ayuso (2008) suggest that typical processes that could explain the release of arsenic from minerals in bedrock include oxidation of arsenian pyrite or arsenopyrite, or carbonation of As-sulfides, and these in general rely on discrete minerals or on a fairly limited series of minerals. In contrast, in the Penobscot Formation and other metasedimentary rocks of coastal Maine, oxidation of arsenic-bearing iron—cobalt— nickel-sulfide minerals, dissolution (by reduction) of arsenic-bearing secondary arsenic and iron hydroxide and sulfate minerals, carbonation and/or oxidation of As-sulfide minerals, and desorption of arsenic from Fe-hydroxide mineral surfaces are all thought to be implicated. All of these processes contribute to the occurrence of arsenic in groundwaters in coastal Maine, as a result of the variability in composition and overlap in stability of the arsenic source minerals. Also, Lipfert et al. (2007) concluded that as sea level rose, environmental conditions favored reduction of bedrock minerals, and that under the current anaerobic conditions in the bedrock, bacteria reduction of the Fe-and Mn-oxyhydroxides are implicated with arsenic releases. 

Water chemistry patterns in high arsenic wells are not consistent with other geochemical mechanisms of arsenic release. The positive correlation of high arsenic to sulfate and trace metals, and the negative correlation to pH, are not suggestive of desorption or dissolution of iron hydroxides. 

Desorption of arsenic from iron hydroxides is another potential cause of arsenic release, although the data do not indicate that it plays a significant role in the region. However, pH is slightly elevated in wells with low and moderate arsenic as compared with background ground water. Further research is needed to evaluate desorption as a potential mechanism for arsenic release. 

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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