to above 300 mV, only one semicircle
appears in the Nyquist plot. Comparing
the semicircle at 300 mV with that of at
200 mV, it can be found that the ohm
resistance on the surface of electrode is
increased unproportionately, and the
Warburg impedance line disappeares.
From the CV diagram, it suggests that the
sulfur reaches its highest amount when the
potential is about 300 mV, which could be
the reason why the ohm resistance increases.
From the Nyquist plot we can see that
the ohm resistance at 300 mV is almost 1.6
times than that of 200 mV. This clearly shows
that more sulfur accumulate on the surface
of electrode when the potential is up to 300
mV. From this result, it can be conclude that
the flotability of pentlandite would be
enhanced when the potential is higher than
200 mV. It also can be seen in this plot that
the diffusing control step disappeares and turns
to be an electrochemical polarization process
when the applied potential is above 300 mV.
It was reported that the sulfur formed on
the electrode surface is porous [21], which
allows the dissolved metal ions to the bulk
solution. This may be the reason why the
diffusion control step disappears.
When sodium sulfide is present in the
electrolyte, the Nyquist plot is present in
Figure 4. Comparing the Nyquist plot with
and without sodium sulfide the impedance
when the electrolyte with Na2
S is higher than
that without Na2
S at the same applied potential,
and no Warburg impedance can be identified
in the plot.
As we discussed above, these phenomenon
suggest that plenty of porous sulfur deposit
on the electrode surface. At the same applied
potential, it can be concluded that with the
addition of sodium sulfide more sulfur would
deposit on the electrode, as well as extra sulfur
must come from the sodium sulfide, which
confirms the previous test results.
For all the conditions the impedance
spectra can be described by the same type of
equivalent circuit model, shown in Figure
5. It contains a solution resistance (Rs) in
to above 300 mV, only one semicircleappears in the Nyquist plot. Comparingthe semicircle at 300 mV with that of at200 mV, it can be found that the ohmresistance on the surface of electrode isincreased unproportionately, and theWarburg impedance line disappeares.From the CV diagram, it suggests that thesulfur reaches its highest amount when thepotential is about 300 mV, which could bethe reason why the ohm resistance increases.From the Nyquist plot we can see thatthe ohm resistance at 300 mV is almost 1.6times than that of 200 mV. This clearly showsthat more sulfur accumulate on the surfaceof electrode when the potential is up to 300mV. From this result, it can be conclude thatthe flotability of pentlandite would beenhanced when the potential is higher than200 mV. It also can be seen in this plot thatthe diffusing control step disappeares and turnsto be an electrochemical polarization processwhen the applied potential is above 300 mV.It was reported that the sulfur formed onthe electrode surface is porous [21], whichallows the dissolved metal ions to the bulksolution. This may be the reason why thediffusion control step disappears.When sodium sulfide is present in theelectrolyte, the Nyquist plot is present inFigure 4. Comparing the Nyquist plot withand without sodium sulfide the impedancewhen the electrolyte with Na2S is higher thanthat without Na2S at the same applied potential,and no Warburg impedance can be identifiedin the plot.As we discussed above, these phenomenonsuggest that plenty of porous sulfur depositon the electrode surface. At the same appliedpotential, it can be concluded that with theaddition of sodium sulfide more sulfur woulddeposit on the electrode, as well as extra sulfurmust come from the sodium sulfide, whichconfirms the previous test results.For all the conditions the impedancespectra can be described by the same type ofequivalent circuit model, shown in Figure5. It contains a solution resistance (Rs) in
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