posted on 2019-04-23, 00:00authored byZong-Sheng Liang, Bao-Dong Song, Yong-Ling Liu, Yong Liu, Hai-Tao Ren, Song-Hai Wu, Shao-Yi Jia, Xu Han
Natural pyrite has a strong ability
to immobilize Ni(II) impurities.
However, the differences in the oxidation reactivity between Ni(II)-adsorbed
pyrites [Py*-Ni(II)] and Ni(II)-structurally incorporated pyrites
[Py-Ni(II)] are still not clearly understood. In this study, Ni(II)-free
pyrite (Py-free), Py*-Ni(II), and Py-Ni(II) were prepared, and their
oxidation reactivity were compared. Our results show that Ni(II) can
be successfully incorporated into the crystalline structure of Py-Ni(II)
by replacing structural Fe(II) with the formation of sulfur defects
on the surface of Py-Ni(II). The oxidation reactivity of different
pyrites depends on how Ni(II) is immobilized in pyrite and follows
the order of Py-0.08 > Py-0.02 > Py-free > Py*-Ni(II) [Py-0.02
and
Py-0.08 are named according to the Ni(II):Fe(II) molar ratios in the
starting material for the synthesis of Py-Ni(II)], indicating that
structurally incorporated Ni(II) enhances the oxidation rate of pyrite,
whereas adsorbed Ni(II) does the opposite. Differences in the electrochemical
properties also indicate that structurally incorporated Ni(II) enhances
the electron-transfer rates at the Py-Ni(II) surface, thus increasing
the oxidation rates of pyrite. Variations in H2O2 concentrations confirm that the high electron-transfer rates induced
by structurally incorporated Ni(II) enhance the reaction rates between
dissolved oxygen and the pyrite surface, producing H2O2 at pHs 2.5 and 7.0. The presence of Fe(III)-S(-II) defects
also significantly contributes to the production of H2O2. Variations of cumulative ·OH indicate
that structurally incorporated Ni(II) improves the production of ·OH at pHs 2.5 and 7.0. The significantly higher concentrations
of ·OH than those of H2O2 at
pH 2.5 indicate that ·OH plays an important role
in pyrite oxidation under acidic condition. The comparable concentrations
of H2O2 and ·OH at pH 7.0
suggest that H2O2, ·OH, and
even Fe(IV) formed between pyrite and H2O2 contribute
to pyrite oxidation under pH-neutral condition.