Selenium-rich mine effluents treatment using zero-valent iron: Mechanism and removal efficiency in the cold climate of Québec, Canada

Abstract

Selenium contamination in mine effluents is a notorious environmental concern due to its toxicity and potential to bioaccumulate. This element is not yet regulated in Canada, and requires the development of sophisticated water treatment technologies at large scale. Increasing evidences suggest that zero-valent iron (ZVI) is an effective reagent for the treatment and removal of selenium from mine water. Accordingly, the results of this study showed that ZVI decreases the selenium concentration below the detection limit (0.0005 mg/L) in a mine effluent containing about 50% selenite and 50% selenate when employed at 1.25% solid: liquid ratio for 8h of contact time. However, for mine effluents having a predominance of selenate (almost 90%), the iron ratio was increased to 2% to reach a final selenium concentration inferior to 0.0005 mg/L. Low temperature (4 °C) decreased ZVI performance to 68% selenium removal for an increased contact time (12 h). These findings allowed us to determine the key operational parameters: ZVI: liquid ratio and the contact time in order to design laboratory columns to further explore this low-cost and effective treatment technology for selenium removal from mining effluents at industrial scale.