HR: 1340h
AN: H13G-1671    [Abstracts]
TI: Effects of Chlorine Promoted Oxidation on Arsenic Release from Sulfide Minerals
AU: * West, N
EM: nrenwest@vt.edu
AF: Virgina Tech Department of Geosciences, 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Schreiber, M
EM: mschreib@vt.edu
AF: Virgina Tech Department of Geosciences, 4044 Derring Hall, Blacksburg, VA 24061, United States
AU: Gotkowitz, M
EM: mbgotkow@wisc.edu
AF: Wisconsin Geologic and Natural History Survey, 3817 Mineral Point Rd, Madison, WI 53705, United States
AB: High arsenic concentrations (>100 ppb) have been measured in wells completed in the Ordovician St. Peter sandstone aquifer of eastern Wisconsin. The primary source of arsenic is As-bearing sulfide minerals within the aquifer. Periodic disinfection of wells by chlorination may facilitate arsenic release to groundwater by increasing the rate of sulfide mineral oxidation. During typical well disinfection procedures, aquifer solids exposed along uncased portions of wells remain in direct contact with chlorine disinfection solutions for up to twenty-four hours. Due to the redox sensitivity of arsenic mobility in groundwater, it is important to evaluate the effect of repeatedly adding oxidizers to an arsenic impacted aquifer system. This study focuses on abiotic processes that mobilize arsenic from the solid phase during controlled exposure to chlorinated solutions. Two St. Peter samples with As concentrations of 21 and 674 ppm were selected for the experiments. Before reaction, the aquifer mineralogy is characterized using scanning electron microscopy (SEM) and electron microprobe analysis (EMPA). The samples are then reacted with solutions of 60 mg/L free chlorine, 1200 mg/L free chlorine, or nanopure water (control) at pH 7.0 and pH 8.5. These parameters represent typical solution chemistries present within the wells after disinfection. Solutions are sampled periodically during the experiments and analyzed for As, Fe, other trace metals such as Co, Mo, Cr, and Ni, and sulfate. Analysis of the post-reaction solids using SEM, EMPA, laser ablation ICP-MS and Raman techniques are used to document the changes in mineralogy due to chlorination and to document which solid phases contain As.
DE: 1065 Major and trace element geochemistry
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting