posted on 2021-01-27, 15:13authored byJingyi Wang, Lei Xie, Sijia Li, Jianmei Wang, Jiansheng Zhang, Hongbo Zeng
The
migration of released selenium because of human activities
can cause many environmental issues. The immobilization of soluble
selenium (i.e., selenite and selenate) on natural pyrite mineral is
believed to be effective for selenium management. In this work, the
redox behavior of immobilized selenium on pyrite has been investigated
using in situ scanning electrochemical microscopy (SECM). The immobilization
of selenium on pyrite (Se-pyrite) was realized through both electrodeposition
and adsorption in selenite solution. The released species from Se-pyrite
surfaces at various potentials were probed using the SECM tip. The
electrodeposited Se-pyrite releases Fe2+ and selenite,
suggesting selenium immobilized on pyrite through electrodeposition
was in the form of both Se0 and FeSe2; while
Se0 was the major form on the adsorbed Se-pyrite, and was
associated with the sulfur sites instead of iron sites. The maximum
amount of released selenium from Se-pyrite was found to be ca. 0.6
V, although the initial potential for selenium release was as low
as around the open circuit potential. The selenium reduction current
distribution was achieved by SECM imaging suggesting an inhomogeneous
adsorption of selenium on pyrite. Because of the change of surface
species, the immobilization of selenium resulted in a decrease of
surface conductivity of pyrite, which was analyzed using SECM tip
approach curves and conductive atomic force microscopy. The surface
conductivity followed the trend of pyrite > electrodeposited Se-pyrite
> adsorbed Se-pyrite. This work provides a new approach for the
in
situ investigation of selenium immobilization on and release from
mineral surfaces (e.g., pyrite), which can be readily applied to similar
systems regarding various environmental issues.