XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1895
The presence of scorodite in the ore indicates that the
deposit underwent oxidation. The formation of scorodite
can be depicted by the following reaction (Lattanzi et al.,
2008). As pyrite gets oxidized, Fe ions will react with enar-
gite to leach out arsenic forming scorodite. The ore also
contains pyrite which is the source of Fe to complete the
oxidation process of enargite.
12.5 5H
2 3Cu 6 6H
Cu AsS FeS O O
FeAsO4 H O SO
3 4 2 2 2
2
2+
4
2-
"+++
++++(4)
Based on the arsenic distribution, 67% of arsenic is
from the enargite mineral while the remaining 33% is from
scorodite. The scorodite has a high contribution to the
overall As content due to its higher stoichiometric compo-
sition. Scorodite contains 32% As which is higher than the
19% As of enargite.
Majority of the copper is from enargite at 97%. The
other copper sulfide minerals such as chalcopyrite and born-
ite occur in trace amounts. This implies that the common
process of separating Cu-As-S minerals from Cu-S through
froth flotation with pulp potential adjustments would be
ineffective to this type of ore. Thus, to obtain a high-Cu
but low-As concentrate, arsenic should be removed from
the enargite mineral.
The mineral distribution across particle size fractions is
shown in Figure 1. Enargite, scorodite and pyrite are pres-
ent in various particle size. However, largest proportion of
these minerals occur in the finest size fraction (75 microns).
Blank Leaching
The arsenic dissolution for leaching without the addi-
tion of any solvent was determined to be at 33% As. This
dissolution could potentially be attributed to the arsenic
0
1
2
3
4
5
6
m m m m
Size Fraction
Pyrite Enargite Scorodite
Figure 1. Mineral distribution per size fraction
deportment. It must be noted that at least 33% of the
arsenic is in scorodite. The dissolution of scorodite is rep-
resented by the chemical reaction shown in Eq 5. This
reaction proceeds at pH11.5 which further confirms the
source of the dissolved arsenic (Zhu et al., 2001).
2 4OH
)2H
FeAsO H O
Fe(OH AsO O
4 2
4 4
3-
2
)+
++
-
-(5)
Leached out arsenic is unlikely to be associated with enar-
gite. Li et al. (2018) suggested that leaching of arsenic with
NaOH is possible with the presence of pyrite. The pyrite
is believed to react with NaOH and produce Na2S which
would then leach out arsenic from enargite as shown in Eq
6 and Eq 7
3 6NaOH
3 2Na 3H
FeS
FeS Na SO S O
2
2 3 2 2
)+
+++(6)
xhCu
xhNa
3Na
3
AsS S
Cu S AsS
x
3 4 2
2 3 4
)-+
+-
-
^2
^2 (7)
The measured potential for this leaching system is at
–100 mV. At these conditions, S2– ion is not stable which
supposedly react with enargite to remove arsenic. Instead,
SO3–2 is more favored in these regions. Hence, Eq 6 and
Eq 7 are unlikely to proceed. The current conditions for
this study might not be enough to provide sufficient S2– to
react with the enargite. Additionally, the study by Li et al.
(2018) utilized significantly higher NaOH concentration,
solution temperatures and leaching time. It could also be
inferred that for the succeeding alkaline leaching, at least
33% of the leached As could be potential from the scoro-
dite dissolution.
NaClO-NaOH Leaching
The solution potential and pH of the NaClO-NaOH
leaching at 30°C is shown in Figure 2. The initial solution
pH conditions favored the presence of ClO–. The changes
in potential were also reflected in the amount of arsenic
dissolved in the solution as illustrated in Figure 3. The
decrease in potential in Figure 2 and the increase in arsenic
dissolution in Figure 3 indicates that hypochlorite is gradu-
ally consumed as the reaction progressed. The potential
continued to decrease gradually until a drastic decrease was
observed after 40 minutes in which the condition became
slightly reducing. After 60 minutes, no change in poten-
tial was noted. There was also no change in arsenic disso-
lution possibly indicating that ClO– ions were completely
consumed.
The average arsenic dissolution per treatment in the fac-
torial experiment is shown in Table 2. The dissolution from
Mineral
Distribution,
wt%
The presence of scorodite in the ore indicates that the
deposit underwent oxidation. The formation of scorodite
can be depicted by the following reaction (Lattanzi et al.,
2008). As pyrite gets oxidized, Fe ions will react with enar-
gite to leach out arsenic forming scorodite. The ore also
contains pyrite which is the source of Fe to complete the
oxidation process of enargite.
12.5 5H
2 3Cu 6 6H
Cu AsS FeS O O
FeAsO4 H O SO
3 4 2 2 2
2
2+
4
2-
"+++
++++(4)
Based on the arsenic distribution, 67% of arsenic is
from the enargite mineral while the remaining 33% is from
scorodite. The scorodite has a high contribution to the
overall As content due to its higher stoichiometric compo-
sition. Scorodite contains 32% As which is higher than the
19% As of enargite.
Majority of the copper is from enargite at 97%. The
other copper sulfide minerals such as chalcopyrite and born-
ite occur in trace amounts. This implies that the common
process of separating Cu-As-S minerals from Cu-S through
froth flotation with pulp potential adjustments would be
ineffective to this type of ore. Thus, to obtain a high-Cu
but low-As concentrate, arsenic should be removed from
the enargite mineral.
The mineral distribution across particle size fractions is
shown in Figure 1. Enargite, scorodite and pyrite are pres-
ent in various particle size. However, largest proportion of
these minerals occur in the finest size fraction (75 microns).
Blank Leaching
The arsenic dissolution for leaching without the addi-
tion of any solvent was determined to be at 33% As. This
dissolution could potentially be attributed to the arsenic
0
1
2
3
4
5
6
m m m m
Size Fraction
Pyrite Enargite Scorodite
Figure 1. Mineral distribution per size fraction
deportment. It must be noted that at least 33% of the
arsenic is in scorodite. The dissolution of scorodite is rep-
resented by the chemical reaction shown in Eq 5. This
reaction proceeds at pH11.5 which further confirms the
source of the dissolved arsenic (Zhu et al., 2001).
2 4OH
)2H
FeAsO H O
Fe(OH AsO O
4 2
4 4
3-
2
)+
++
-
-(5)
Leached out arsenic is unlikely to be associated with enar-
gite. Li et al. (2018) suggested that leaching of arsenic with
NaOH is possible with the presence of pyrite. The pyrite
is believed to react with NaOH and produce Na2S which
would then leach out arsenic from enargite as shown in Eq
6 and Eq 7
3 6NaOH
3 2Na 3H
FeS
FeS Na SO S O
2
2 3 2 2
)+
+++(6)
xhCu
xhNa
3Na
3
AsS S
Cu S AsS
x
3 4 2
2 3 4
)-+
+-
-
^2
^2 (7)
The measured potential for this leaching system is at
–100 mV. At these conditions, S2– ion is not stable which
supposedly react with enargite to remove arsenic. Instead,
SO3–2 is more favored in these regions. Hence, Eq 6 and
Eq 7 are unlikely to proceed. The current conditions for
this study might not be enough to provide sufficient S2– to
react with the enargite. Additionally, the study by Li et al.
(2018) utilized significantly higher NaOH concentration,
solution temperatures and leaching time. It could also be
inferred that for the succeeding alkaline leaching, at least
33% of the leached As could be potential from the scoro-
dite dissolution.
NaClO-NaOH Leaching
The solution potential and pH of the NaClO-NaOH
leaching at 30°C is shown in Figure 2. The initial solution
pH conditions favored the presence of ClO–. The changes
in potential were also reflected in the amount of arsenic
dissolved in the solution as illustrated in Figure 3. The
decrease in potential in Figure 2 and the increase in arsenic
dissolution in Figure 3 indicates that hypochlorite is gradu-
ally consumed as the reaction progressed. The potential
continued to decrease gradually until a drastic decrease was
observed after 40 minutes in which the condition became
slightly reducing. After 60 minutes, no change in poten-
tial was noted. There was also no change in arsenic disso-
lution possibly indicating that ClO– ions were completely
consumed.
The average arsenic dissolution per treatment in the fac-
torial experiment is shown in Table 2. The dissolution from
Mineral
Distribution,
wt%