posted on 2017-03-27, 00:00authored byNiloofar Karimian, Scott G. Johnston, Edward D. Burton
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.