Fulvic Acid Influence on Arsenic Immobilization During Jarosite Bioreduction and Transformation

Acid mine drainage (AMD) is enriched with arsenite (As(III)), arsenate (As(V)), and jarosite. While jarosite can immobilize arsenic (As) through adsorption and other mechanisms, it dissolves and transforms into other minerals under near-neutral and reducing conditions via microbial mediation, thereby altering As fate. Fulvic acid (FA), a ubiquitous natural organic matter in the environment, has been proven to exhibit complex interactions with various iron minerals, Fe/S-metabolizing microorganisms, and As. However, the role of FA in the bioreduction and transformation of jarosite, as well as its subsequent impact on As mobility and fate, remains unclear. This study aims to elucidate the regulatory effect of FA on the biodissolution and transformation of jarosite, and the corresponding changes in As speciation. The results showed that FA exerted contrasting effects depending on arsenic speciation. In the As(III) treatments, FA intensified the inhibition of microbial dissimilatory sulfate reduction, suppressed sulfide production, and consequently limited orpiment formation. In contrast, in the As(V) treatments, FA enhanced the association of As(V) with jarosite surfaces, reduced aqueous As stress, and supported the persistence of As-tolerant sulfate-reducing populations. This promoted jarosite transformation toward mackinawite and facilitated As immobilization through orpiment precipitation. This study reveals the critical role of FA in the migration and transformation of As in mining areas, providing novel insights for optimizing AMD remediation strategies such as soil capping.