1898 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
45°C due to the potential decomposition of hypochlorite
at higher temperatures.
According to Figure 5, the leaching rate of arsenic
reached a high value in a short duration at room tempera-
ture, thus it is expected that the leaching curve would not
conform to the typical shrinking core model. In this study,
kinetic modelling was done using the Avrami model in Eq
10 which can be converted to a linear expression in Eq 11.
ln^1 x kt n --=h (10)
ln ln^1 ln ln x k n t --=+h@ 6 (11)
where x is the fraction, k is the rate constant for the reac-
tion, t is the reaction time and n is the Avrami exponent.
This model was originally proposed to describe the
kinetics of crystallization but was used successfully to
explain the leaching kinetic data of multiple solid-liquid
reactions (Faraji et al., 2022) This model was used to
describe the kinetics of arsenic leaching fr copper smelter
dust using Na2S-NaOH (Tian et al., 2021), dissolution of
tellurium and antimony from tellurium-bearing materials
in alkaline sulfide solutions (Xu et al., 2020) and leaching
of copper from waste printed circuit boards (Hao et al.,
2022).
NaClO-NaOH leaching has a fast initial dissolution
rate followed by a drastic decrease which generates a linear
plot for ln(-ln(1-x)) against the natural logarithm of time
as shown in Figure 6. The leaching kinetics of this study
deviated from other investigations conducted on As leach-
ing from enargite using NaClO-NaOH media. Authors
reported that this type of leaching was diffusion controlled
in which diffusion of ClO– to the copper oxide product
layer formed on the surface of the ore was the controlling
step (Mihaljovic et al. 2011 Viñals et al., 2003).The devia-
tion in the behavior is mainly affected by the ore miner-
alogy. Mihaljovic (2011) and Vinals (2003) investigated
Cu-As-S concentrates including enargite and tennantite. In
contrast, the ore in the present study contained scorodite,
an arsenic oxide, which was observed to dissolve readily in
alkaline conditions.
The leaching rate can also be influenced by the physical
properties of the ore. The arsenic minerals occur in various
particle size fractions, but greater proportion is in the finer
size fraction based on the MLA data. Furthermore, enargite
is highly liberated but still has a significant proportion that
is associated with other minerals. The highly liberated and
fine particles are expected to be easily leached out. On the
other hand, the presence of the other minerals locked with
the arsenic minerals could slow down the dissolution rate.
CONCLUSION
This study investigated the selective removal of arsenic
from enargite and scorodite ore via alkaline leaching. The
high-arsenic ore contains 1.06% As and 1.9% Cu. The
arsenic occurs as 4% enargite (Cu3AsS4) and 1% scorodite
(FeAsO4·2H2O). The presence of scorodite indicates that
the enargite has undergone oxidation. Results also show
that 97% of the copper is from enargite with no other cop-
per sulfide minerals observed. The arsenic dissolution with-
out the addition of solvent is attributed to the dissolution
of scorodite at alkaline conditions which contributes to at
most 33% As. In NaClO leaching, conditions are initially
oxidizing favoring the ClO– as the dominant species which
would react with the As from the ore The highest dissolu-
tion is at 85% As at high concentration (0.6M NaClO), low
temperature (30°C) and fine particle size (P80 of 37µm).
The initial leaching rate is fast as more soluble forms of
arsenic is dissolved. But as reaction progresses, rate signifi-
cantly decreases due to the consumption of more refractory
form of arsenic. The Avrami model typifies this behavior
and produces a more linear fit for the plot of ln(-ln(1-x)
against natural logarithm of time. The NaClO-NaOH
R² =0.9571
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 1 2 3 4 5 6
ln time, mins
Figure 6. Kinetic modeling of As leaching in NaClO-NaOH using the Avrami equation
ln(-ln(1-x)
45°C due to the potential decomposition of hypochlorite
at higher temperatures.
According to Figure 5, the leaching rate of arsenic
reached a high value in a short duration at room tempera-
ture, thus it is expected that the leaching curve would not
conform to the typical shrinking core model. In this study,
kinetic modelling was done using the Avrami model in Eq
10 which can be converted to a linear expression in Eq 11.
ln^1 x kt n --=h (10)
ln ln^1 ln ln x k n t --=+h@ 6 (11)
where x is the fraction, k is the rate constant for the reac-
tion, t is the reaction time and n is the Avrami exponent.
This model was originally proposed to describe the
kinetics of crystallization but was used successfully to
explain the leaching kinetic data of multiple solid-liquid
reactions (Faraji et al., 2022) This model was used to
describe the kinetics of arsenic leaching fr copper smelter
dust using Na2S-NaOH (Tian et al., 2021), dissolution of
tellurium and antimony from tellurium-bearing materials
in alkaline sulfide solutions (Xu et al., 2020) and leaching
of copper from waste printed circuit boards (Hao et al.,
2022).
NaClO-NaOH leaching has a fast initial dissolution
rate followed by a drastic decrease which generates a linear
plot for ln(-ln(1-x)) against the natural logarithm of time
as shown in Figure 6. The leaching kinetics of this study
deviated from other investigations conducted on As leach-
ing from enargite using NaClO-NaOH media. Authors
reported that this type of leaching was diffusion controlled
in which diffusion of ClO– to the copper oxide product
layer formed on the surface of the ore was the controlling
step (Mihaljovic et al. 2011 Viñals et al., 2003).The devia-
tion in the behavior is mainly affected by the ore miner-
alogy. Mihaljovic (2011) and Vinals (2003) investigated
Cu-As-S concentrates including enargite and tennantite. In
contrast, the ore in the present study contained scorodite,
an arsenic oxide, which was observed to dissolve readily in
alkaline conditions.
The leaching rate can also be influenced by the physical
properties of the ore. The arsenic minerals occur in various
particle size fractions, but greater proportion is in the finer
size fraction based on the MLA data. Furthermore, enargite
is highly liberated but still has a significant proportion that
is associated with other minerals. The highly liberated and
fine particles are expected to be easily leached out. On the
other hand, the presence of the other minerals locked with
the arsenic minerals could slow down the dissolution rate.
CONCLUSION
This study investigated the selective removal of arsenic
from enargite and scorodite ore via alkaline leaching. The
high-arsenic ore contains 1.06% As and 1.9% Cu. The
arsenic occurs as 4% enargite (Cu3AsS4) and 1% scorodite
(FeAsO4·2H2O). The presence of scorodite indicates that
the enargite has undergone oxidation. Results also show
that 97% of the copper is from enargite with no other cop-
per sulfide minerals observed. The arsenic dissolution with-
out the addition of solvent is attributed to the dissolution
of scorodite at alkaline conditions which contributes to at
most 33% As. In NaClO leaching, conditions are initially
oxidizing favoring the ClO– as the dominant species which
would react with the As from the ore The highest dissolu-
tion is at 85% As at high concentration (0.6M NaClO), low
temperature (30°C) and fine particle size (P80 of 37µm).
The initial leaching rate is fast as more soluble forms of
arsenic is dissolved. But as reaction progresses, rate signifi-
cantly decreases due to the consumption of more refractory
form of arsenic. The Avrami model typifies this behavior
and produces a more linear fit for the plot of ln(-ln(1-x)
against natural logarithm of time. The NaClO-NaOH
R² =0.9571
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 1 2 3 4 5 6
ln time, mins
Figure 6. Kinetic modeling of As leaching in NaClO-NaOH using the Avrami equation
ln(-ln(1-x)