Fan, and three co-authors, reported in 2018 that the extensive mining activities in Shimen realgar mine have generated large amounts of secondary arsenical ferric oxyhydroxides. The reductive dissolution of these tailing sediments at the soil/water interface influences the behavior of arsenic (As). Here, the dynamics of As in these flooded high arsenic tailing sediments at circumneutral pH conditions were investigated by employing a pure culture of a sulfate reducing bacteria (SRB).
Changes in Eh, pH, aqueous Fe(II) and As speciation were monitored over 6 days in batch experiments. Our results demonstrated that SRB was able to reductive dissolve high levels of arsenical ferric oxyhydroxide. The results showed that reactions with aqueous As(III) and As(V) presented different trends, with As(III) (80–100% of total As) being the dominant arsenic species. Aqueous As behavior showed two distinct stages, firstly, the As (V) was released and immediately reduced to As(III) by biogenic sulfide. Next, the released As was removed from the solution by adsorption onto newly formed nano-Fe sulfides (e.g. FeS, FeS2) or co-precipitation with S(-II) to produce nano arsenic sulfide (As3S2).
In addition, the addition of sulfate, calcium and sodium lactate played different roles in the release of As. Addition of sulfate and sodium lactate can trigger the release of arsenic, while calcium caused the opposite effect. The authors concluded that:
1) During the reductive dissolution of the sediment by sulfate-reducing bacteria, the changing trend of As(III) and As(T) were different, As(III) was the dominant arsenic species in sulfidogenic sediment/water interface and determined the change of total As.
2) The change of aqueous As concentration showed two stages, firstly, the reductive dissolution of arsenic iron(hydr)oxide resulted in the release of As and immediately reduced to As(III) by biogenic sulfide. Next, the released As removed from the solution by adsorption with newly formed nano Fe sulfides (e.g. FeS, FeS2) or co-precipitation with S(-II) to produce nano arsenic sulfide.
3) The additional sulfate and calcium played different roles in the release of As, additional sulfate can trigger the release of arsenic, while calcium had the opposite effect. The level of sodium lactate significantly influenced the As behavior, and the release of As increased as the sodium lactate increased.
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