WWRC 95-08
Understanding Selenium Mobility by Sorption and Extraction Processes in Surface Coal Mine Spoil
Abstract
Surface coal mine spoil was studied to evaluate selenium (Se) mobility and solubility using batch
experiments, column-leaching techniques, and sequential and individual extraction processes. Both selenite and
selenate followed linear isotherm patterns at relatively lower Se treatments, whereas over a broader solution Se
concentration range the sorption mechanism followed the Langmuir model. The variation in the isotherm patterns
with change in Se concentrations suggested that mechanisms for selenite-selenate sorption would be a function of
the concentration of solution-phase Se. Greater isotherm slope for selenite sorption suggested higher affinity of this
specie for the mine spoil, while selenate was the more labile aqueous specie. In the exchangeable phase, selenite was
the predominant specie. The results also indicated that adsorbed Se may be transformed into plant-available Se with
time. Cationic presence enhanced selenite immobilization, with Fe being the most effective followed by Mn and Ca.
The column leaching study indicated selenate had a faster mobilization rate, and there was a probable antagonistic
relationship between Se species and sulfate in mine spoil solutions.
Additional Key Words: Selenite, Selenate, Adsorption, Extraction, Aqueous Phase, Exchange Phase, Batch and
Column Studies.
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