3
extent of oxidation. As a result, gold that is dissemi-
nated in sulfide minerals may remain unliberated.
This armoring phenomenon typically results in gold
recovery to be 10% or higher below those achieved
with acidic POX (Thomas &Williams, 2000).
• Gold Price and Gold Grade: Associated with gold
recovery difference, the absolute gold price and
grade directly impact the revenue, ultimately affect-
ing annual cash flows. That is, the higher gold price
and grade lead to acidic POX being favored due to its
higher gold recovery.
• Sulfide Oxidation Extent: Alkaline POX operation
typically has a lower sulfide sulfur oxidation extent
than acidic POX. This provides a partial explana-
tion for the lower typical gold recovery. However,
a secondary effect of the lower sulfide oxidation is
reduced heat generation in the autoclave. This is the
most significant driving factor for additional steam
input required to maintain temperature during auto-
clave operation.
• Capital and Operating Costs: Another critical fac-
tor is the difference in capital and operating costs
between the two processes. Acidic POX requires sig-
nificant acid consumption due to the need for pre-
acidulation to remove carbonates. This leads to addi-
tional neutralization circuits and costs for reagents
to neutralize the acid in subsequent processes. In
contrast, alkaline POX incurs additional costs associ-
ated with additional equipment and fuel expenses for
maintaining the required temperature through steam
generation and potentially larger off-gas treatment
due to carbon dioxide (CO2) generation within the
autoclave. The key cost drivers for both processes are
summarized in Table 1.
Practical Applications and Decision-Making
The practical application of POX technology must take
a holistic view of ore characteristics, reagent availability,
and recovery targets. While alkaline POX may offer cost
savings in certain conditions, the potential reduction in
gold recovery and increased infrastructure requirements
for steam generation and handling CO2 may offset those
advantages. Similarly, acidic POX, though often achieving
higher recoveries, carries its own set of economic challenges
e.g., high operating costs.
In practice, the decision-making process should involve
detailed economic modeling that includes both capital and
operational expenditures (CAPEX and OPEX), along-
side metallurgical testing to evaluate recovery rates. The
Mercur operation is an excellent example of a successful
implementation of alkaline POX, but this was largely pos-
sible due to the unique characteristics of the ore, includ-
ing its high carbonate-to-sulfide sulfur ratio as highlighted
by Thomas and Williams (2000). This ratio, exceeding 10,
made the alkaline POX process economically feasible by
minimizing acid consumption and reducing downstream
reagent costs.
By considering all these economic and operational fac-
tors, mining companies can make more informed decisions
about which POX technology is best suited for their spe-
cific refractory gold ores.
Cost Economics Comparison Case Study—Acidic
Versus Alkaline POX
The following analysis will focus on a case study comparing
the CAPEX and OPEX of acidic versus alkaline POX based
on historical projects and industry standards. Additionally,
a sensitivity analysis was conducted to assess the impact of
key variables on economic feasibility. This will provide a
practical example of how different cost factors influence
the economic decision-making process and help illustrate
the trade-offs involved in selecting between these two POX
methods.
Inputs to Economic Analysis
Table 2 outlines the key inputs used for the economic anal-
ysis of both acidic and alkaline POX processes. It includes
fixed values such as autoclave conditions and reagent costs,
along with variable factors such as sulfide sulfur grade, gold
recovery and gold price fluctuations. These inputs provide
Table 1. Cost Driver Comparison – Acidic POX versus
Alkaline POX
Acidic Pressure Oxidation Alkaline Pressure Oxidation
CAPEX Driver
Acidulation tanks for
handling pre-acidulation
requirements
Bigger boilers to generate
steam for maintaining the
process temperature
Acid storage and unloading
facilities
Larger off-gas systems for
managing higher volume of
in-situ CO
2 generation
Neutralization circuit for
downstream treatment
Increased fuel storage capacity
for steam generation
Less exotic materials of
construction (MOC)
OPEX Driver
Higher demand of sulfuric
acid
Higher fuel demand for
additional steam capacity
Higher demand of
neutralizing agent
extent of oxidation. As a result, gold that is dissemi-
nated in sulfide minerals may remain unliberated.
This armoring phenomenon typically results in gold
recovery to be 10% or higher below those achieved
with acidic POX (Thomas &Williams, 2000).
• Gold Price and Gold Grade: Associated with gold
recovery difference, the absolute gold price and
grade directly impact the revenue, ultimately affect-
ing annual cash flows. That is, the higher gold price
and grade lead to acidic POX being favored due to its
higher gold recovery.
• Sulfide Oxidation Extent: Alkaline POX operation
typically has a lower sulfide sulfur oxidation extent
than acidic POX. This provides a partial explana-
tion for the lower typical gold recovery. However,
a secondary effect of the lower sulfide oxidation is
reduced heat generation in the autoclave. This is the
most significant driving factor for additional steam
input required to maintain temperature during auto-
clave operation.
• Capital and Operating Costs: Another critical fac-
tor is the difference in capital and operating costs
between the two processes. Acidic POX requires sig-
nificant acid consumption due to the need for pre-
acidulation to remove carbonates. This leads to addi-
tional neutralization circuits and costs for reagents
to neutralize the acid in subsequent processes. In
contrast, alkaline POX incurs additional costs associ-
ated with additional equipment and fuel expenses for
maintaining the required temperature through steam
generation and potentially larger off-gas treatment
due to carbon dioxide (CO2) generation within the
autoclave. The key cost drivers for both processes are
summarized in Table 1.
Practical Applications and Decision-Making
The practical application of POX technology must take
a holistic view of ore characteristics, reagent availability,
and recovery targets. While alkaline POX may offer cost
savings in certain conditions, the potential reduction in
gold recovery and increased infrastructure requirements
for steam generation and handling CO2 may offset those
advantages. Similarly, acidic POX, though often achieving
higher recoveries, carries its own set of economic challenges
e.g., high operating costs.
In practice, the decision-making process should involve
detailed economic modeling that includes both capital and
operational expenditures (CAPEX and OPEX), along-
side metallurgical testing to evaluate recovery rates. The
Mercur operation is an excellent example of a successful
implementation of alkaline POX, but this was largely pos-
sible due to the unique characteristics of the ore, includ-
ing its high carbonate-to-sulfide sulfur ratio as highlighted
by Thomas and Williams (2000). This ratio, exceeding 10,
made the alkaline POX process economically feasible by
minimizing acid consumption and reducing downstream
reagent costs.
By considering all these economic and operational fac-
tors, mining companies can make more informed decisions
about which POX technology is best suited for their spe-
cific refractory gold ores.
Cost Economics Comparison Case Study—Acidic
Versus Alkaline POX
The following analysis will focus on a case study comparing
the CAPEX and OPEX of acidic versus alkaline POX based
on historical projects and industry standards. Additionally,
a sensitivity analysis was conducted to assess the impact of
key variables on economic feasibility. This will provide a
practical example of how different cost factors influence
the economic decision-making process and help illustrate
the trade-offs involved in selecting between these two POX
methods.
Inputs to Economic Analysis
Table 2 outlines the key inputs used for the economic anal-
ysis of both acidic and alkaline POX processes. It includes
fixed values such as autoclave conditions and reagent costs,
along with variable factors such as sulfide sulfur grade, gold
recovery and gold price fluctuations. These inputs provide
Table 1. Cost Driver Comparison – Acidic POX versus
Alkaline POX
Acidic Pressure Oxidation Alkaline Pressure Oxidation
CAPEX Driver
Acidulation tanks for
handling pre-acidulation
requirements
Bigger boilers to generate
steam for maintaining the
process temperature
Acid storage and unloading
facilities
Larger off-gas systems for
managing higher volume of
in-situ CO
2 generation
Neutralization circuit for
downstream treatment
Increased fuel storage capacity
for steam generation
Less exotic materials of
construction (MOC)
OPEX Driver
Higher demand of sulfuric
acid
Higher fuel demand for
additional steam capacity
Higher demand of
neutralizing agent