Selenium in the soil-plant system exposed to mine effluent

This work investigated the behavior of selenium from mining effluents (65 ± 0.9 μg/L) in the soil-plant system. Exposed sediments had a mean total selenium concentration of 321 mg/kg, and exposed Typha latifolia plants accumulated 534 and 92 mg/kg in their roots and leaves respectively. Typha latifolia had a strategy of phytostabilization and selenium accumulation mainly in the roots. Selenium speciation results showed that the selenium species most accumulated by Typha latifolia roots were selenite and selenomethionine with mean concentrations of 2.68 and 2.04 mg/kg respectively, while the other species were the most translocated (mean translocation factor of 1.89). Several technologies (biological, chemical, physical, physico-chemical, electrochemical, floating plant islands) were evaluated for selenium treatment of mine effluents. Among these options, zero-valent iron reduced the selenium concentration below 0.5 μg/L in a mine effluent containing approximately 50% selenite and 50% selenate when used at a solid:liquid ratio of 1.25% for 8 h contact time.  For mine effluent containing 90% selenate, the solid:liquid ratio was increased to 2% to achieve a final selenium concentration of less than 0.5 μg/L. These results are encouraging for further exploration of zero-valent iron for selenium removal from mining effluents on a field scale.