Sparks, D L

3 items:

Arsenate Adsorption Mechanisms at the Allophane−Water Interface We investigated arsenate (As(V)) reactivity and surface speciation on amorphous aluminosilicate mineral (synthetic allophane) surfaces using batch adsorption experiments, powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). The adsorption isotherm experiments indicated that As(V) uptake increased with increasing [As(V)]o from 50 to 1000 ?M (i.e., Langmuir type adsorption isotherm) and that the total As adsorption slightly decreased with increasing NaCl concentrations from 0.01 to 0.1 M. Arsenate adsorption was initially (0?10 h) rapid followed by a slow continuum uptake, and the adsorption processes reached the steady state after 720 h. X-ray absorption spectroscopic analyses suggest that As(V)... Categories: Publication; Types: Citation
Effects of Dissolved Carbonate on Arsenate Adsorption and Surface Speciation at the Hematite−Water Interface Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite?water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [PCO2 = 10-3.5 atm and ?0; CO2-free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L-1, [As(V)]0 = 1.5 mM and I = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in... Categories: Publication; Types: Citation
Arsenic Speciation and Reactivity in Poultry Litter Recent U.S. government action to lower the maximum concentration levels (MCL) of total arsenic (As) (10 ppb) in drinking water has raised serious concerns about the agricultural use of As-containing biosolids such as poultry litter (PL). In this study, solid-state chemical speciation, desorbability, and total levels of As in PL and long-term amended soils were investigated using novel synchrotron-based probing techniques (microfocused (?) synchrotron X-ray fluorescence (SXRF) and ?-X-ray absorption near-edge structure (XANES) spectroscopies) coupled with chemical digestion and batch experiments. The total As levels in the PL were as high as ≈50 mg kg-1, and As(II/III and V) was always concentrated in abundant needle-shaped... Categories: Publication; Types: Citation

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