Pb alleviates As mobilization during the biological reductive dissolution of Pb-As jarosite.

The biological dissolution of jarosite accelerates As mobilization in acid mine drainage environments, which can be influenced by coexisting metals. However, few studies have focused on the effects of coexisting Pb on this biogeochemical process. Here, we investigated the behavior of As during the reductive dissolution of Pb-As jarosite (PbFe3(SO4, AsO4)2(OH)6) by a sulfate-reducing bacterium (SRB) of Desulfovibrio desulfuricans. Pb incorporation inhibited jarosite dissolution and As mobilization. One reason was that Pb incorporation caused lattice distortion of jarosite, decreasing its solubility. Another reason was that S2- produced via anaerobic respiration of D. desulfuricans was partially captured by Pb2+ to form PbS, which negatively affected the reduction of Fe3+ in jarosite to aqueous Fe2+, slowing down the reductive dissolution of Pb-As jarosite and As release. Furthermore, the dissolved As5+ was reduced and quickly precipitated by forming As2S3 or being absorbed on the formed amorphous secondary minerals, resulting in only trace amounts of As being retained in the aqueous environment. Transcriptomic analysis provided additional evidence for As reduction, sulfate reduction, and extracellular electron transfer mediated by SRB. These findings offered new sights for understanding the geochemical cycling of As in acid mine drainage, and provided a reference basis for the treatment of Pb and As co-contaminated environment.