XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1485
higher disorder within the crystal structure (more amor-
phous) has been shown to correlate with a higher gold rob-
bing capacity (Helm et al., 2009 Ng et al., 2022). The gold
robbing capacity, estimated by the gold-rob #,for all four
high carbon samples is highly gold robbing (2.5) which
agrees with the amorphous carbon structure. The four low
carbon samples all have a non gold robbing capacity (0),
which is expected from crystalline carbon.
The Raman data also suggest that there is no correlation
between the physical structure of CM and the delta gold
extractions. The expectation was that the mechanism for
enhanced gold extraction in the presence of activated car-
bon was the type of CM controlling gold robbing. Instead,
all crystalline CM was detected in the low carbon content
samples regardless of the associated delta gold extraction.
This implies that the carbon structure and degree of disor-
der cannot be the sole mechanism for gold extraction and
overcoming gold robbing in carbon containing ores, par-
ticularly for the low CM samples that are expected to be
non gold robbing.
Since the high delta gold extraction in low CM samples
(CM 0.05%) cannot be explained by gold robbing pro-
duced by aggressive amorphous carbon, other mechanisms
must be at play. One factor that can influence the enhanced
recovery in the CIL configuration is the decrease in the con-
centration of gold in solution which drives further dissolu-
tion and results in higher gold extraction following the Le
Chatelier’s principle (Rees and Deventer, 2000). Another
possibility is the reversible adsorption of Au(I) cyanide onto
ore constituents which can be reversed with the addition of
activated carbon that competes for the Au(I) cyanide in all
possible constituents, not only the CM, and therefore leads
to higher gold extraction (Marsden and House, 2006).
In the high CM samples (CM 0.1%) all carbon is
characterized as highly gold robbing amorphous carbon,
but with both high and low delta gold extraction values
(Table 4). The range in delta gold extraction values shows
that the success of overcoming gold robbing in the presence
of activated carbon can be variable. This is not necessarily
unexpected from amorphous carbon but it suggests that the
mechanism of enhanced gold extraction in the presence of
activated carbon could still be explained by the activated
carbon response to gold robbing by amorphous carbon.
More work is needed to evaluate if the large variation in
deltas is simply due to the highly gold robbing nature of
amorphous carbon leading to inconsistent gold recoveries
in the leach. It is worth noting that while it was assumed
that the CM in the head samples was representative of the
CM in the pyrite concentrate (leach feed), it is possible
that a larger portion of the more ordered carbonaceous spe-
cies which are less gold robbing and weakly hydrophobic
reported to the pyrite concentrate thus causing the dis-
crepancies between the gold robbing characteristics iden-
tified on the head samples and the metallurgical response
observed on the pyrite concentrate samples.
Future work should focus on understanding whether
the lower gold concentration in solution, the reversible
adsorption process, or a combination of both are causing
the high delta gold extractions in the low CM samples.
Applying a customized diagnostic leaching procedure to
the leach residues from the CIL and leach tests can aid in
this investigation. Additionally, repeat tests could be con-
ducted to minimize the influence of errors associated with
the experimental methods on the extractions obtained by
both types of leach tests.
CONCLUSIONS
Metallurgical and mineralogical characterization was com-
pleted on several samples from a polymetallic deposit to
assess the impact of carbonaceous matter in the gold extrac-
tion response. Evaluation of the difference in gold extraction
between leach tests completed in the presence and absence
Table 4. Carbon structure of the eight selected samples determined by Raman spectroscopy, compared to the CIL-Leach delta
and gold robbing classification
Sample ID CM, %Carbon Content Carbon Structure
Gold Robbing
Classification
PyCon CIL-Leach Delta,
%
1 0.03 Low Crystalline Non 1.9
2 0.02 Low Crystalline Non 1.9
3 0.01 Low Crystalline Non 13.3
4 0.03 Low Crystalline Non 20.8
5 0.53 High Amorphous Highly 23.7
6 0.37 High Amorphous Highly 24.3
7 0.46 High Amorphous Highly 0.0
8 0.47 High Amorphous Highly 1.3
higher disorder within the crystal structure (more amor-
phous) has been shown to correlate with a higher gold rob-
bing capacity (Helm et al., 2009 Ng et al., 2022). The gold
robbing capacity, estimated by the gold-rob #,for all four
high carbon samples is highly gold robbing (2.5) which
agrees with the amorphous carbon structure. The four low
carbon samples all have a non gold robbing capacity (0),
which is expected from crystalline carbon.
The Raman data also suggest that there is no correlation
between the physical structure of CM and the delta gold
extractions. The expectation was that the mechanism for
enhanced gold extraction in the presence of activated car-
bon was the type of CM controlling gold robbing. Instead,
all crystalline CM was detected in the low carbon content
samples regardless of the associated delta gold extraction.
This implies that the carbon structure and degree of disor-
der cannot be the sole mechanism for gold extraction and
overcoming gold robbing in carbon containing ores, par-
ticularly for the low CM samples that are expected to be
non gold robbing.
Since the high delta gold extraction in low CM samples
(CM 0.05%) cannot be explained by gold robbing pro-
duced by aggressive amorphous carbon, other mechanisms
must be at play. One factor that can influence the enhanced
recovery in the CIL configuration is the decrease in the con-
centration of gold in solution which drives further dissolu-
tion and results in higher gold extraction following the Le
Chatelier’s principle (Rees and Deventer, 2000). Another
possibility is the reversible adsorption of Au(I) cyanide onto
ore constituents which can be reversed with the addition of
activated carbon that competes for the Au(I) cyanide in all
possible constituents, not only the CM, and therefore leads
to higher gold extraction (Marsden and House, 2006).
In the high CM samples (CM 0.1%) all carbon is
characterized as highly gold robbing amorphous carbon,
but with both high and low delta gold extraction values
(Table 4). The range in delta gold extraction values shows
that the success of overcoming gold robbing in the presence
of activated carbon can be variable. This is not necessarily
unexpected from amorphous carbon but it suggests that the
mechanism of enhanced gold extraction in the presence of
activated carbon could still be explained by the activated
carbon response to gold robbing by amorphous carbon.
More work is needed to evaluate if the large variation in
deltas is simply due to the highly gold robbing nature of
amorphous carbon leading to inconsistent gold recoveries
in the leach. It is worth noting that while it was assumed
that the CM in the head samples was representative of the
CM in the pyrite concentrate (leach feed), it is possible
that a larger portion of the more ordered carbonaceous spe-
cies which are less gold robbing and weakly hydrophobic
reported to the pyrite concentrate thus causing the dis-
crepancies between the gold robbing characteristics iden-
tified on the head samples and the metallurgical response
observed on the pyrite concentrate samples.
Future work should focus on understanding whether
the lower gold concentration in solution, the reversible
adsorption process, or a combination of both are causing
the high delta gold extractions in the low CM samples.
Applying a customized diagnostic leaching procedure to
the leach residues from the CIL and leach tests can aid in
this investigation. Additionally, repeat tests could be con-
ducted to minimize the influence of errors associated with
the experimental methods on the extractions obtained by
both types of leach tests.
CONCLUSIONS
Metallurgical and mineralogical characterization was com-
pleted on several samples from a polymetallic deposit to
assess the impact of carbonaceous matter in the gold extrac-
tion response. Evaluation of the difference in gold extraction
between leach tests completed in the presence and absence
Table 4. Carbon structure of the eight selected samples determined by Raman spectroscopy, compared to the CIL-Leach delta
and gold robbing classification
Sample ID CM, %Carbon Content Carbon Structure
Gold Robbing
Classification
PyCon CIL-Leach Delta,
%
1 0.03 Low Crystalline Non 1.9
2 0.02 Low Crystalline Non 1.9
3 0.01 Low Crystalline Non 13.3
4 0.03 Low Crystalline Non 20.8
5 0.53 High Amorphous Highly 23.7
6 0.37 High Amorphous Highly 24.3
7 0.46 High Amorphous Highly 0.0
8 0.47 High Amorphous Highly 1.3