Arsenic removal from water/wastewater using adsorbents—A critical review

Preservation of elemental and isotopic source identification of sedimentary organic matter

Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes

Calculated Mn(2p3/2) X-ray photoelectron spectra (XPS) of Mn 21 ,M n 31 , and Mn 41 free ions are strikingly similar to Mn(2p 3/2) spectra of Mn 21 -, Mn 31 -, and Mn 41 -oxides and oxyhydroxides, indicating that these ions adopt high spin states in MnO, manganite, and birnessite. The Mn(2p) peak structures reveal the presence of only Mn 31 in manganite, but Mn 21 ,M n 31 , and Mn 41 are present in the near-surface of synthetic birnessite at about 5, 25, and 70%, respectively. Precipitation of birnessite by reaction of Mn 21 (aq) with an

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Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation

Concentrations of naturally occurring arsenic in ground water vary regionally due to a combination of climate and geology Although slightly less than half of 30,000 arsenic analyses of ground water in the United States were 1 μg/L, about 10% exceeded 10 μg/L At a broad regional scale, arsenic concentrations exceeding 10 μg/L appear to be more frequently observed in the western United States than in the eastern half Arsenic concentrations in ground water of the Appalachian Highlands and the Atlantic Plain generally are very low ( 1 μg/L) Concentrations are somewhat greater in the Interior Plains and the Rocky Mountain System Investigations of ground water in New England, Michigan, Minnesota, South Dakota, Oklahoma, and Wisconsin within the last decade suggest that arsenic concentrations exceeding 10 μg/L are more widespread and common than previously recognized

Arsenic release from iron oxide appears to be the most common cause of widespread arsenic concentrations exceeding 10 μg/L in ground water This can occur in response to different geochemical conditions, including release of arsenic to ground water through reaction of iron oxide with either natural or anthropogenic (ie, petroleum products) organic carbon Iron oxide also can release arsenic to alkaline ground water, such as that found in some felsic volcanic rocks and alkaline aquifers of the western United States Sulfide minerals are both a source and sink for arsenic Geothermal water and high evaporation rates also are associated with arsenic concentrations 10g/L in ground and surface water, particularly in the west

Arsenic in Ground Water of the United States: Occurrence and Geochemistry

Ni2p3/2 X-ray photoelectron spectral peak binding energies of Ni metal, NiS, and NiAs (all conductors) span a range of about 0.5 eV and are, consequently, insensitive to formal Ni oxidation state and to the nature of the ligand to which Ni is bonded, relative to other metals (e.g., Fe). Ni2p3/2 peak structures and binding energies reflect two energetic contributions. The major contribution is that associated with the electrostatic field produced by ejection of the Ni(2p) photoelectron, the minor contribution is the relaxation energy associated with filling unoccupied, conduction band 3d9 and 4s Ni metal orbitals. These conduction band orbitals become localized on the Ni photoion (and sometimes filled) in response to the field created by the photoemission event. Because only the core Ni2p electron and nonbonding orbitals of predominantly metallic character are affected, the main peak of all three conductors are affected similarly, leading to similar Ni2p3/2 main peak binding energies. NiO, Ni(OH)2, and NiSO4 are insulators in which Ni is divalent and is bonded to oxygen. Although Ni is bonded to oxide in these phases, Ni2p binding energies differ substantially, and reflect primarily the nature of the ligand (O2−, OH−, SO4
2−) to which Ni is bonded. The influence of the ligand is the result of charge (electron) transfer from valence band bonding orbitals of dominantly ligand character, to unoccupied conduction band orbitals localized on Ni photoions. Relaxation energy resulting from charge transfer is acquired by the emitted photoelectron, thus Ni2p3/2 photopeak binding energies of these insulators reflect the nature of the ligand to which Ni is bonded. The Ni2p main peak binding energy of these conductors and insulators is a poor guide to Ni oxidation states. The Ni2p3/2 binding energies of insulators reflect, however, the nature of the ligand in the first coordination sphere of Ni. The intensity of the Doniach–Sunjic contribution to Ni2p XPS spectra of NiS and NiAs is dependent on the nature of the ligand. The Doniach–Sunjic contribution to ligand XPS core-level photopeaks (e.g., S2p of NiS and As3d of NiAs) has not been explained and is poorly understood.

Interpretation of Ni2p XPS spectra of Ni conductors and Ni insulators

Mössbauer spectroscopy : an introduction for inorganic chemists and geochemists

Abstract Pyrite has a poor {001} cleavage. Unlike most other minerals with a rocksalt-type structure, pyrite typically fractures conchoidally, demonstrating that parting surfaces are not constrained to the {001} crystallographic plane. Cleavage along {001} require rupture of only Fe-S bonds, but pyrite consists of both Fe-S and S-S bonds. Analysis of bond energies indicates that S-S bonds are the weaker bonds and they are likely to be ruptured when pyrite is fractured. With each ruptured S-S bond, two mononuclear species (formally S1-) are produced, one bound to one fracture surface and the second to the opposite fracture surface. This monomer is reduced to S2- (monosulfide) during relaxation through oxidation of surface Fe2+ ions to Fe3+. These surface relaxation processes explain the surface states observed in S(2p) and Fe(2p3/2) X-ray photoelectron spectra (XPS) of pyrite. The S(2p) XPS spectrum is interpreted to include bulk disulfide contributions at 162.6 eV and two surface state contributions at 162.0 and 161.3 eV. The monosulfide (S2-) emission is near 161.3 eV, as observed in S(2p) spectra of pyrrhotite, and the 162 eV peak is interpreted to result from the surface-most sulfur atom of surface disulfide ions. The Fe(2p3/2) XPS spectrum includes three contributions, a bulk Fe2+ emission near 707 eV and emissions from two Fe surface states. One surface state is interpreted to be Fe2+ surface ions. Their coordination is changed from octahedral before fracture to square pyramidal after fracture. The consequent stabilization of the antibonding Fe d2z orbital yields unpaired electrons in the valence band resulting in multiplet peak structure in the Fe(2p3/2) spectrum. Similarly, each surface Fe3+ ion, having contributed a non-bonding 3d electron to the valence band (bonding orbital), contains unpaired 3d electrons, resulting in multiplet splitting of its Fe(2p3/2) signal. The high-energy tail observed in the Fe(2p3/2) spectrum of pyrite is the product of emissions from both surface states with Fe2+ multiplet peaks centered near 708 eV and the surface Fe3+ multiplets spanning the binding energies from 708.75 to about 712 eV.

G. M. Bancroft

Papers

Interpretation of Ni2p XPS spectra of Ni conductors and Ni insulators

Mössbauer spectroscopy : an introduction for inorganic chemists and geochemists

Sulfur and iron surface states on fractured pyrite surfaces

XPS study of reductive dissolution of 7Å-birnessite by H3AsO3, with constraints on reaction mechanism

Applications of the Mössbauer effect to silicate mineralogy—I. Iron silicates of known crystal structure