Correlation Between Fe/S/As Speciation Transformation and Depth Distribution of and in Simulated Acidic Water Column.

It is well known that speciation transformations of As(III) vs. As(V) in acid mine drainage (AMD) are mainly driven by microbially mediated redox reactions of Fe and S. However, these processes are rarely investigated. In this study, columns containing mine water were inoculated with two typical acidophilic Fe/S-oxidizing/reducing bacteria [the chemoautotrophic and the heterotrophic ], and three typical energy substrates (Fe, S, and glucose) and two concentrations of As(III) (2.0 and 4.5 mM) were added. The correlation between Fe/S/As speciation transformation and bacterial depth distribution at three different depths, i.e., 15, 55, and 105 cm from the top of the columns, was comparatively investigated. The results show that the cell growth at the top and in the middle of the columns was much more significantly inhibited by the additions of As(III) than at the bottom, where the cell growth was promoted even on days 24-44. dominated over in most samples collected from the three depths, but the elevated proportions of were observed in the top and bottom column samples when 4.5 mM As(III) was added. Fe bio-oxidation and Fe reduction coupled to As(III) oxidation occurred for all three column depths. At the column top surfaces, jarosites were formed, and the addition of As(III) could lead to the formation of the amorphous FeAsO⋅2HO. Furthermore, the higher As(III) concentration could inhibit Fe bio-oxidation and the formation of FeAsO⋅2HO and jarosites. S oxidation coupled to Fe reduction occurred at the bottom of the columns, with the formations of FeAsO⋅2HO precipitate and S intermediates. The formed FeAsO⋅2HO and jarosites at the top and bottom of the columns could adsorb to and coprecipitate with As(III) and As(V), resulting in the transfer of As from solution to solid phases, thus further affecting As speciation transformation. The distribution difference of Fe/S energy substrates could apparently affect Fe/S/As speciation transformation and bacterial depth distribution between the top and bottom of the water columns. These findings are valuable for elucidating As fate and toxicity mediated by microbially driven Fe/S redox in AMD environments.