Antimony and Arsenic Behavior during Fe(II)-Induced Transformation of Jarosite

Jarosite can be an important scavenger for arsenic (As) and antimony (Sb) in acid mine drainage (AMD) and acid sulfate soil (ASS) environments. When subjected to reducing conditions, jarosite may undergo reductive dissolution, thereby releasing As, Sb, and Fe²⁺ coincident with a rise in pH. These conditions can also trigger the Fe²⁺-induced transformation of jarosite to more stable Fe(III) minerals, such as goethite. However, the consequences of this transformation process for As and Sb are yet to be methodically examined. We explore the effects of abiotic Fe²⁺-induced transformation of jarosite on the mobility, speciation, and partitioning of associated As(V) and Sb(V) under anoxic conditions at pH 7. High concentrations of Fe²⁺ (10 and 20 mM) rapidly (<10 min) transformed jarosite to a green rust intermediary, prior to the subsequent precipitation of goethite within 24 h. In contrast, lower concentrations of Fe²⁺ (1 and 5 mM) led to the formation of lepidocrocite. As K-edge XANES spectroscopy revealed some reduction of As(V) to As(III) at higher concentrations of Fe²⁺, while Sb L₁-edge XANES spectroscopy indicated no reduction of Sb(V). The transformation processes enhanced Sb mobilization into the aqueous phase, while As was instead repartitioned to a surface-bound exchangeable phase. The results imply that Fe²⁺-induced transformation of As/Sb-jarosite can increase Sb mobility and exert major influences on As partitioning and speciation.