By Alan H. Welch, Kenneth G. Stollenwerk
Offers an outline of the elemental strategies that have an effect on arsenic prevalence and delivery via delivering adequate history details on arsenic geochemistry and outlines of high-arsenic flooring water. Of curiosity to scientists operating within the box of arsenic, healthiness execs attracted to arsenic publicity, and water-resource managers and regulators.
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7 . g. Krupp, 1990; Spycher and Reed, 1989). We had believed this controversy to have been settled recently by Helz et al. (1995) who utilized spectroscopy, molecular orbital calculations, and the solubility studies to arrive at the conclusion that the principal aqueous species in excess-sulfidic solutions are and Helz et al. 9 for the reaction: They also This value leads to Clarke and Helz (2000) analyzed phase behavior in the copper + arsenic + sulfur+ water system and obtained a somewhat different value for the equilibrium constant for eq 11.
Peak positions are calibrated by reference to an appropriate standard (usually gold) collected under identical conditions as the sample. A background function is subtracted from the photopeaks of interest, and peak fitting using appropriate lineshape functions is applied. Details of XPS data collection and analysis procedures as applied to arsenic can be found in Nesbitt et al. (1998; 1995; 1999). Similar to IR spectroscopy, XPS analysis is not an ideal technique for the study of arsenic in complex, heterogeneous natural materials due to peak overlap from all the elements present.
Nickel (Ni) is typically assigned a valence of +2 in oxides, hydroxides, and silicates; however, the XPSdetermined valence of Ni in niccolite (NiAs) is +1, and the valence of arsenic is –1 (Nesbitt and Reinke, 1999). , 2000). Light or electron microscopic identification of As-hosting sulfides in aquifer sediments is usually precluded by the low modal abundance of sulfide phases and/or As concentrations below detection limits of conventional energy dispersive detectors. However, identification of Asbearing minerals is relatively simple using XAFS spectroscopy (when one type of mineral is the predominant host).