Mobilization of arsenic during reductive dissolution of As(V)-bearing jarosite by a sulfate reducing bacterium

Microbial sulfidization of arsenic (As)-bearing jarosite involves complex processes and is yet to be fully elucidated. Here, we investigated the behavior of As during reductive dissolution of As(V)-bearing jarosite by a pure sulfate reducing bacterium with or without dissolved SO₄^2- amendment. Changes of aqueous chemistry, mineralogical characteristics, and As speciation were examined in batch experiments. The results indicated that jarosite was mostly replaced by mackinawite in the system with added SO₄^2-. In the medium without additional SO₄^2-, mackinawite, vivianite, pyrite, and magnetite formed as secondary Fe minerals, though 24.55 % of total Fe was in form of an aqueous Fe²⁺ phase. The produced Fe²⁺ in turn catalyzed the transformation of jarosite. At the end of the incubation, 41.99 % and 48.10 % of As in the solid phase got released into the aqueous phase in the systems with and without added SO₄^2-, respectively. The addition of dissolved SO₄^2- mitigated the mobilization of As into the aqueous phase. In addition, all As⁵⁺ on the solid surface was reduced to As³⁺ during the microbial sulfidization of As-bearing jarosite. These findings are important for a better understanding of geochemical cycling of elements As, S, and Fe in acid mine drainage and acid sulfate soil environments.