Bench- and Pilot-Scale Testing of Ion Exchange and Zero Valent Iron Technologies for Selenium Removal from a Surface Coal Mine Run-Off Water

Bench- and pilot-scale testing was conducted for removal of selenium from runoff water at a surface coal mining operation in 2011. The study focused on two technologies for selenium removal: ion exchange (IX) and zero-valent iron (ZVI). The IX bench- and pilot-scale results showed that IX is a feasible means for treating selenium, provided the selenium is primarily in the selenate [Se (VI)] form and the concentration of sulfate is below 500 mg/L. The IX pilot demonstrated consistent total recoverable selenium reduction to less than the required limit of 4.7 μg/L for the duration of the study. Results also indicated the resin could be regenerated successfully without loss of capacity. The ZVI pilot results confirmed that pH adjustment and tank media configuration were the most critical factors affecting selenium removal by ZVI. With the right media configuration and pH below 6.0, the pilot unit was able to achieve removal below the required limit of 4.7 μg/L.