Exploring the role of Fe species from biochar-iron composites in the removal and long-term immobilization of SeO42- against competing oxyanions.

Wei, Xue; Li, Xiaodong; Tang, Lin; Yu, Jiangfang; Deng, Jiaqin; Luo, Ting; Liang, Jie; Chen, Xuwu; Zhou, Yaoyu

Carbothermal reduction is a convenient and cost-effective method to produce biochar (BC) supported iron-based nano-particles (INP) for oxyanion contaminants removal. However, considering the possible desorption of the target oxyanion during change of the surrounding environment, the detailed removal mechanisms remain unclear and the long-term efficiency of different INPs cannot be predicted. In this study, different BC/Fe composites were synthesized by controlling the pyrolysis temperatures (500-800 °C). BC/Fe3O4 composite synthesized at 500 °C (BC/Fe500) possessed the strongest surface acidity thus with the best SeO42- removal performance, and BC/Fe0/Fe3O4 composite synthesized at 650 °C (BC/Fe650) possessed the best reducing ability toward SeO42-. Through the co-removal experiments (SeO42- and common competing oxyanions co-existed) and the investigation of Se stability loaded on BC/Fe composites, the removal of SeO42- by BC/Fe500 through highly reversible adsorption could not achieve long-term immobilization of Se, making it an appropriate adsorbent for pre-treatment only, while the efficient reduction of SeO42- to Se0 by BC/Fe650 could largely improve its long-term stability. This study supplies a possible strategy for Se immobilization against common competing oxyanions.