7
previously noted. A carbonate-to-sulfide sulfur ratio above
this threshold indicates alkaline POX is more advantageous
economically.
The recovery difference (acidictalkaline POX) showed
a negative impact on NPVD. As the recovery efficiency
increased, the NPVD decreased (i.e., alkaline POX was
more favoured). The EBV for recovery difference was found
to be 4.7%, which is significantly lower than the 10.0%
used in the base case and reported in the above-mentioned
literature (Thomas &Williams, 2000). This result also
aligns with trend for gold prices being higher than indus-
trial inflation during the period from 2000 to 2024.
Gold price and gold grade directly impact revenue, and
thus both showed a negative relationship with NPVD. As
either the gold price or gold grade increased, the NPVD
decreased (i.e., acidic POX was more favoured). The EBV
for gold price and grade was identified at $1,166 and
2.3%, respectively, indicating the point where acidic POX
becomes economically viable compared to alkaline POX.
Fuel prices exerted a negative influence on the NPVD,
with rising fuel costs correlating to decreasing NPVD (i.e.,
acidic POX is more favoured). The EBV for fuel price was
calculated to be –2.2 USD/L, suggesting that even under
negative fuel costs, the alkaline POX process struggles to
achieve economic competitiveness. However, this find-
ing is contingent on the assumptions within the base case
remaining constant. For a different feed material with other
parameters changed the fuel price may influence the eco-
nomic choice of alkaline or acidic POX.
Figure 3 presents a bar chart comparing the relative
sensitivity of the key parameters to the NPVD impact. The
slopes of the NPVD versus parameter lines, derived from
Figure 1, were normalized by designating the CO3/SS slope
as 1 and proportionally adjusting the other slopes. This
normalization provides a clear and standardized assessment
of each parameter’s effect on economic outcomes.
The results show that the gold grade exhibited the high-
est sensitivity at 1.62, followed by gold price and recovery
difference at 1.48 each. Sulfide sulfur grade also demon-
strated relatively high sensitivity at 1.37, while fuel price
had the lowest sensitivity at 0.24. These findings indicate
that other key parameters display greater sensitivity than
the previously emphasized CO3/SS ratio, underscoring the
wide variability in their influence on NPVD. As a result,
implementing strategies that carefully manage changes and
interactions among these critical variables becomes essen-
tial for economic evaluation of acidic or alkaline POX.
The compounding effects of these sensitivities must
also be considered. As individual parameters change, their
interactions can significantly impact the overall economic
feasibility of the alkaline POX process. For instance, if both
sulfide sulfur grade and carbonate-to-sulfide sulfur ratio
increase, the external heat requirements decrease, while the
net benefit from acidulation and neutralization is enhanced,
making alkaline POX economically more attractive.
Conversely, an increase in gold grade combined with higher
recovery efficiency may widen the revenue gap between
acidic and alkaline POX, ultimately reducing the financial
advantage of alkaline POX compared to acidic POX.
This analysis illustrates the necessity of considering not
only individual parameter sensitivities but also their inter-
actions under different scenarios. This approach enables
more effective economic decision-making when selecting
the appropriate POX process.
CONCLUSION
This study thoroughly evaluated the economic feasibil-
ity of alkaline POX compared to acidic POX, supported
by sensitivity analyses focusing on key variables: sulfide
sulfur grade, carbonate-to-sulfide sulfur ratio, fuel price,
gold price, grade, and recovery. The analysis reveals that
while the carbonate-to-sulfide sulfur ratio remains a foun-
dational metric in determining the suitability of alkaline
$(1,000)
$(800)
$(600)
$(400)
$(200)
$0
0
2
4
6
8
10
1 2 3 4 5 6 7 8 9 10
SS Grade,%
Sensitivity Analysis -SS Grade at Fixed CO 3 (10%)
CO /SS NPVD
Acid Cost
Dominant
Acid Cost
Dominant
Fuel Cost
Dominant
3
Figure 2. Sensitivity analysis: effect of SS grade with
carbonate grade fixed at 10%
Figure 3. Relative Sensitivity Analysis by Normalized Slope
NPV
Impact,
M
USD
CO3/
SS
Ratio
previously noted. A carbonate-to-sulfide sulfur ratio above
this threshold indicates alkaline POX is more advantageous
economically.
The recovery difference (acidictalkaline POX) showed
a negative impact on NPVD. As the recovery efficiency
increased, the NPVD decreased (i.e., alkaline POX was
more favoured). The EBV for recovery difference was found
to be 4.7%, which is significantly lower than the 10.0%
used in the base case and reported in the above-mentioned
literature (Thomas &Williams, 2000). This result also
aligns with trend for gold prices being higher than indus-
trial inflation during the period from 2000 to 2024.
Gold price and gold grade directly impact revenue, and
thus both showed a negative relationship with NPVD. As
either the gold price or gold grade increased, the NPVD
decreased (i.e., acidic POX was more favoured). The EBV
for gold price and grade was identified at $1,166 and
2.3%, respectively, indicating the point where acidic POX
becomes economically viable compared to alkaline POX.
Fuel prices exerted a negative influence on the NPVD,
with rising fuel costs correlating to decreasing NPVD (i.e.,
acidic POX is more favoured). The EBV for fuel price was
calculated to be –2.2 USD/L, suggesting that even under
negative fuel costs, the alkaline POX process struggles to
achieve economic competitiveness. However, this find-
ing is contingent on the assumptions within the base case
remaining constant. For a different feed material with other
parameters changed the fuel price may influence the eco-
nomic choice of alkaline or acidic POX.
Figure 3 presents a bar chart comparing the relative
sensitivity of the key parameters to the NPVD impact. The
slopes of the NPVD versus parameter lines, derived from
Figure 1, were normalized by designating the CO3/SS slope
as 1 and proportionally adjusting the other slopes. This
normalization provides a clear and standardized assessment
of each parameter’s effect on economic outcomes.
The results show that the gold grade exhibited the high-
est sensitivity at 1.62, followed by gold price and recovery
difference at 1.48 each. Sulfide sulfur grade also demon-
strated relatively high sensitivity at 1.37, while fuel price
had the lowest sensitivity at 0.24. These findings indicate
that other key parameters display greater sensitivity than
the previously emphasized CO3/SS ratio, underscoring the
wide variability in their influence on NPVD. As a result,
implementing strategies that carefully manage changes and
interactions among these critical variables becomes essen-
tial for economic evaluation of acidic or alkaline POX.
The compounding effects of these sensitivities must
also be considered. As individual parameters change, their
interactions can significantly impact the overall economic
feasibility of the alkaline POX process. For instance, if both
sulfide sulfur grade and carbonate-to-sulfide sulfur ratio
increase, the external heat requirements decrease, while the
net benefit from acidulation and neutralization is enhanced,
making alkaline POX economically more attractive.
Conversely, an increase in gold grade combined with higher
recovery efficiency may widen the revenue gap between
acidic and alkaline POX, ultimately reducing the financial
advantage of alkaline POX compared to acidic POX.
This analysis illustrates the necessity of considering not
only individual parameter sensitivities but also their inter-
actions under different scenarios. This approach enables
more effective economic decision-making when selecting
the appropriate POX process.
CONCLUSION
This study thoroughly evaluated the economic feasibil-
ity of alkaline POX compared to acidic POX, supported
by sensitivity analyses focusing on key variables: sulfide
sulfur grade, carbonate-to-sulfide sulfur ratio, fuel price,
gold price, grade, and recovery. The analysis reveals that
while the carbonate-to-sulfide sulfur ratio remains a foun-
dational metric in determining the suitability of alkaline
$(1,000)
$(800)
$(600)
$(400)
$(200)
$0
0
2
4
6
8
10
1 2 3 4 5 6 7 8 9 10
SS Grade,%
Sensitivity Analysis -SS Grade at Fixed CO 3 (10%)
CO /SS NPVD
Acid Cost
Dominant
Acid Cost
Dominant
Fuel Cost
Dominant
3
Figure 2. Sensitivity analysis: effect of SS grade with
carbonate grade fixed at 10%
Figure 3. Relative Sensitivity Analysis by Normalized Slope
NPV
Impact,
M
USD
CO3/
SS
Ratio