Understanding Selenium Mobility by Sorption and Extraction Processes in Surface Coal Mine Spoil

Surface coal mine spoil was studied to evaluate selenium (Se) mobility and solubility using batch experiments, column-Ieachmg 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 concentraton range the sorption mechanism followed the Lanpuir 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 concefltraton 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 emhancd 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.