WWRC 95-09
Effects of Redox Potential on the Speciation of Selenium in Ground Water and Coal-Mine Backfill Materials, Wyoming
Abstract
Determining redox potential (Eh) effects on selenium speciation is important in assessing the potential
mobility of selenium in ground water and coal mine backfill. Although, general trends for redox potential conditions
controlling selenium speciation have been observed, experimental data establishing specific redox potentials
controlling selenium speciation is lacking. The objective of this research was to investigate the effects of redox
potential on selenium speciation in ground water and coal-mine backfill material suspension. A redox controlling
apparatus was designed to control redox potential of ground water and coal-mine backfill suspension. Samples of
ground water and coal-mine backfill suspension were placed in a reaction chamber and were reacted to varying redox
potentials. A syringe was used to obtain samples from the reaction chamber, through a sample port. Samples were
analyzed for selenite and selenate with ion chromatography. The redox controlling apparatus was successful in
controlling and maintaining the redox conditions of the samples. Reduction of selenate to selenite in ground-water
samples was not observed in a Eh range of 444 to -280 mV. Concentrations of selenite in ground water gradually
decreased at 213 mV and decreased sharply at -106 mV. Selenate concentrations in the backfill-material suspension
decreased slightly at a Eh of 455 mV and by 80% at a Eh of -106 mV. Selenite in the backfill-material suspension
was adsorbed to below detectable limits, possibly by iron and manganese oxides; therefore, speciation changes due
to redox potential could not be determined.
Additional Key Words: Selenium speciation, selenium toxicity, selenium mobility
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