3012 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
the rapid oxidation of grinding media and sulfide mineral
surfaces depleted the original DO in aqueous system dur-
ing the process of grinding. However, the flotation pulp
system was usually an open system so a certain amount of
oxygen in the air unavoidably dissolved in the pulp under
the action of mechanical stirring, which soon resulted in
a small increase of DO (Figure 3B). After that, the DO
varied a little while the Eh gradually increased from about
–300 mV to –180 mV in the following process of pyrite/
pyrrhotite depression and marmatite activation, which
indicated that mechanical stirring in fact had little effect on
the Eh and DO of the pulp.
Scenario 2: Pyrite/pyrrhotite depression with CaO
and pulp redox potential regulation by aeration, fol‑
lowed by marmatite activation with CuSO4, using BX as
collector. Maintaining the same test conditions and proce-
dure, a significant change had taken place in flotation results
when the Eh of the pyrite/ pyrrhotite depression stage was
regulated just by aerating the flotation pulp with air (involv-
ing parameter 8.84 L/min aeration rate and 3 min aeration
time). The Zn grade and recovery of the obtained rougher
concentrate increased to 23.86% and 86.88%, respec-
tively, while the S grade decreased to 38.13% (Figure 2).
Apparently, the separation of marmatite from pyrite and
pyrrhotite was strengthened remarkably, and under this
scenario, the pulp pH was also maintained above 12.0 with
slight variations while the Eh rapidly decreased from ini-
tial 65 mV to –300 mV after adding 6500g/t CaO, but
then Eh rapidly increased from about –300 mV to 0 mV
then to 50 mV as pulp aeration performed and CuSO4 was
added to pulp (Figure 3A), which was different from that
in scenario 1. During the Eh regulation in pyrite/pyrrhotite
depression stage, the DO of pulp experienced an appar-
ent decline rather than a presumed increase when the Eh
rapidly increased from about –300 mV to 0 mV, showing
a negative correlation between each other further, the DO
decreased to near 0 mg/L at about 2.5 minutes and then
started to recover (Figure 3B). Therefore, it was assumed
that the increase of Eh in the stage of pyrite/pyrrhotite
depression with lime mainly resulted from the decrease of
reducing substances in the pulp caused by oxidation, which
consumed the DO and led to the DO depletion in the
pulp, and the DO didn’t increase until the reducing sub-
stances in the pulp were exhausted by oxidation. After that,
the addition of CuSO4 was responsible for a small increase
in DO and Eh but without Eh regulation by aeration, the
DO always remained at a low level while the Eh recovered
to pre-descent levels after decreasing to a minimum.
Scenario 3: Pyrite/pyrrhotite depression with lime,
followed by marmatite activation with CuSO4, using
BX as collector and with two-step pulp redox potential
regulation by aeration. The Zn grade and recovery of the
obtained zinc rougher concentrate reached 37.01% and
94.58%, respectively, while the S grade further decreased
to 33.21% (Figure 2). What differentiated scenario 3 from
scenario 2 was that marmatite activation with CuSO4 was
also carried out with Eh regulation by aeration with air, and
the DO thus experienced an apparent growth from 2 mg/L
to 5.5 mg/L while Eh increased from 50 mV to 100 mV
(Figure 3).
It was found that the pulp redox potential dominated
the flotation separation of marmatite from pyrite and pyr-
rhotite. In order to further investigate the influence of
Eh on pyrite/pyrrhotite depression, Eh was changed via
varying aeration time with constant aeration rate of 8.84
L/min. As illustrated in Figure 4, the Eh in the stage of
pyrite/ pyrrhotite depression rapidly increased from about
–300 mV to 75 mV when we prolonged the aeration with
air correspondingly, zinc rougher concentrate experi-
enced a dramatic increase in its Zn grade and recovery and
an obvious decrease in its S grade, which was towards a
desired depression effect for pyrite and pyrrhotite by lime
and promised an ever-improving Zn-S separation result.
However, Zn grade and recovery declined when Eh reached
73 mV. Therefore, Eh had a noticeable effect on pyrite/pyr-
rhotite depression with lime and thus it should be given a
suitable Eh range, for example 0 to 50 mV, to achieve an
optimal Zn-S separating result.
Characterisation of Dissolved Components
ICP-OES was used for the full-spectrum scanning analysis
of the dissolved elements of the pulp filtrate before and after
pyrite/pyrrhotite depression with lime. The results indi-
cated that the major detectable elements in the fresh pulp
filtrate without lime (pH 6) were Fe, S and Ca after the
action of lime, the concentration of Fe in the alkaline pulp
filtrate (pH12) was small enough to be negligible, while
the levels of S and Ca significantly increased from 549 and
307 mg/L to 2076 and 994 mg/L, respectively. The increase
in the concentration of Ca was mainly originated from the
added CaO moreover, soluble sulfur-containing anions,
except SO
4
2- ,were produced in the pulp during pyrite/
pyrrhotite depression with lime in view of the fact that
SO
4
2- would be mainly precipitated as CaSO4 (Ksp=10–6)
under high concentration of Ca2+, hardly resulting in a
notable increase in S. Therefore, S
n
2- seemed to be one of
the most suitable options because CaSn easily dissolves in
an aqueous system. The chemical phases of the dissolved
components in the pulp stirred for 3 min without or with
lime were characterized by Raman spectrum. The samples
the rapid oxidation of grinding media and sulfide mineral
surfaces depleted the original DO in aqueous system dur-
ing the process of grinding. However, the flotation pulp
system was usually an open system so a certain amount of
oxygen in the air unavoidably dissolved in the pulp under
the action of mechanical stirring, which soon resulted in
a small increase of DO (Figure 3B). After that, the DO
varied a little while the Eh gradually increased from about
–300 mV to –180 mV in the following process of pyrite/
pyrrhotite depression and marmatite activation, which
indicated that mechanical stirring in fact had little effect on
the Eh and DO of the pulp.
Scenario 2: Pyrite/pyrrhotite depression with CaO
and pulp redox potential regulation by aeration, fol‑
lowed by marmatite activation with CuSO4, using BX as
collector. Maintaining the same test conditions and proce-
dure, a significant change had taken place in flotation results
when the Eh of the pyrite/ pyrrhotite depression stage was
regulated just by aerating the flotation pulp with air (involv-
ing parameter 8.84 L/min aeration rate and 3 min aeration
time). The Zn grade and recovery of the obtained rougher
concentrate increased to 23.86% and 86.88%, respec-
tively, while the S grade decreased to 38.13% (Figure 2).
Apparently, the separation of marmatite from pyrite and
pyrrhotite was strengthened remarkably, and under this
scenario, the pulp pH was also maintained above 12.0 with
slight variations while the Eh rapidly decreased from ini-
tial 65 mV to –300 mV after adding 6500g/t CaO, but
then Eh rapidly increased from about –300 mV to 0 mV
then to 50 mV as pulp aeration performed and CuSO4 was
added to pulp (Figure 3A), which was different from that
in scenario 1. During the Eh regulation in pyrite/pyrrhotite
depression stage, the DO of pulp experienced an appar-
ent decline rather than a presumed increase when the Eh
rapidly increased from about –300 mV to 0 mV, showing
a negative correlation between each other further, the DO
decreased to near 0 mg/L at about 2.5 minutes and then
started to recover (Figure 3B). Therefore, it was assumed
that the increase of Eh in the stage of pyrite/pyrrhotite
depression with lime mainly resulted from the decrease of
reducing substances in the pulp caused by oxidation, which
consumed the DO and led to the DO depletion in the
pulp, and the DO didn’t increase until the reducing sub-
stances in the pulp were exhausted by oxidation. After that,
the addition of CuSO4 was responsible for a small increase
in DO and Eh but without Eh regulation by aeration, the
DO always remained at a low level while the Eh recovered
to pre-descent levels after decreasing to a minimum.
Scenario 3: Pyrite/pyrrhotite depression with lime,
followed by marmatite activation with CuSO4, using
BX as collector and with two-step pulp redox potential
regulation by aeration. The Zn grade and recovery of the
obtained zinc rougher concentrate reached 37.01% and
94.58%, respectively, while the S grade further decreased
to 33.21% (Figure 2). What differentiated scenario 3 from
scenario 2 was that marmatite activation with CuSO4 was
also carried out with Eh regulation by aeration with air, and
the DO thus experienced an apparent growth from 2 mg/L
to 5.5 mg/L while Eh increased from 50 mV to 100 mV
(Figure 3).
It was found that the pulp redox potential dominated
the flotation separation of marmatite from pyrite and pyr-
rhotite. In order to further investigate the influence of
Eh on pyrite/pyrrhotite depression, Eh was changed via
varying aeration time with constant aeration rate of 8.84
L/min. As illustrated in Figure 4, the Eh in the stage of
pyrite/ pyrrhotite depression rapidly increased from about
–300 mV to 75 mV when we prolonged the aeration with
air correspondingly, zinc rougher concentrate experi-
enced a dramatic increase in its Zn grade and recovery and
an obvious decrease in its S grade, which was towards a
desired depression effect for pyrite and pyrrhotite by lime
and promised an ever-improving Zn-S separation result.
However, Zn grade and recovery declined when Eh reached
73 mV. Therefore, Eh had a noticeable effect on pyrite/pyr-
rhotite depression with lime and thus it should be given a
suitable Eh range, for example 0 to 50 mV, to achieve an
optimal Zn-S separating result.
Characterisation of Dissolved Components
ICP-OES was used for the full-spectrum scanning analysis
of the dissolved elements of the pulp filtrate before and after
pyrite/pyrrhotite depression with lime. The results indi-
cated that the major detectable elements in the fresh pulp
filtrate without lime (pH 6) were Fe, S and Ca after the
action of lime, the concentration of Fe in the alkaline pulp
filtrate (pH12) was small enough to be negligible, while
the levels of S and Ca significantly increased from 549 and
307 mg/L to 2076 and 994 mg/L, respectively. The increase
in the concentration of Ca was mainly originated from the
added CaO moreover, soluble sulfur-containing anions,
except SO
4
2- ,were produced in the pulp during pyrite/
pyrrhotite depression with lime in view of the fact that
SO
4
2- would be mainly precipitated as CaSO4 (Ksp=10–6)
under high concentration of Ca2+, hardly resulting in a
notable increase in S. Therefore, S
n
2- seemed to be one of
the most suitable options because CaSn easily dissolves in
an aqueous system. The chemical phases of the dissolved
components in the pulp stirred for 3 min without or with
lime were characterized by Raman spectrum. The samples