1
25-028
Economic Analysis of Alkaline POX: A Review of Costs and
Comparative Viability with Acidic POX
Chulho C. Song
Hatch Ltd., Mississauga, Canada
Liam Coleman
Hatch Ltd., Mississauga, Canada
ABSTRACT
Alkaline pressure oxidation (POX) is an oxidative pre-treat-
ment option that is commercially used for high-carbonate
sulfidic gold ores. The high carbonate grades within the
feed ore shifts the ideal operating pH to a basic regime.
Compared with acidic POX, alkaline POX typically
requires additional steam input due to a lower sulfur oxida-
tion load and a high rate of in-situ carbon dioxide genera-
tion that needs to be vented along with steam. The cost of
this steam addition is the largest differentiator between acid
POX operation and alkaline POX from a cost comparison.
However, alkaline POX can offset these costs through
reduced acid usage for pre-acidulation and decreased alkali
reagent consumption for subsequent neutralization. This
paper reviews the specific operating cost impacts of acid/
base consumption between alkaline and acidic POX with
ores which require pre-acidulation, the overall economics
of alkaline POX, and the regimes in which alkaline POX is
economically favorable.
The findings aim to guide industry professionals in
making informed decisions for alkaline POX adoption by
providing a summary view of its operational benefits and
costs, contributing to the development of cost-effective and
sustainable gold ore processing techniques.
INTRODUCTION
Gold extraction from refractory ores presents unique chal-
lenges due to the finely disseminated nature of gold par-
ticles that are often locked within mineral matrices such
as sulfides, carbonates, or silicates. Conventional cyanida-
tion methods are insufficient for effectively processing these
ores, necessitating pre-treatment techniques. Pressure oxi-
dation stands out as a key technology and can be carried
out under either acidic or alkaline conditions, each with its
specific advantages and challenges. Acidic POX is gener-
ally preferred for ores with low carbonate content, while
alkaline POX is used when the ore contains high carbon-
ate levels to minimize acid costs required in acidulation for
acidic POX operation.
This paper focuses on POX as a treatment method
for high-carbonate sulfidic gold ores, comparing the eco-
nomic implications of alkaline and acidulated acidic POX
processes. High-carbonate ores pose unique challenges in
POX treatment due to the potential for carbonate minerals
to consume reagents and impact process efficiency. In con-
trast to acidic POX, which typically involves higher reagent
consumption in carbonate-rich ores, alkaline POX oper-
ates under conditions that mitigate this issue, potentially
offering economic advantages depending on the specific ore
characteristics and external economic factors such as gold
market trends and fuel logistics.
The analysis presented in this paper aims to provide a
comparative understanding of the cost dynamics between
the two processes, emphasizing the operational trade-offs
and economic viability of alkaline POX for treating high-
carbonate sulfidic gold ores. By offering an overview of the
conditions under which alkaline POX becomes an eco-
nomically favorable option, this study seeks to contribute
valuable insights for the selection of pretreatment strategies
in refractory gold ore processing.
PRESSURE OXIDATION
Pressure oxidation is a hydrometallurgical technique involv-
ing subjecting the ore or concentrate in slurry form to ele-
vated temperature and pressure in the presence of oxygen.
This process oxidizes sulfide minerals, breaking down the
sulfide matrix and liberating the encapsulated gold, making
it available for subsequent leaching.
The POX process can be conducted in either an acidic
or an alkaline medium. Acidic POX is generally used for
ores with low carbonate content, while alkaline POX
is preferred for ores with high carbonate levels, as these
25-028
Economic Analysis of Alkaline POX: A Review of Costs and
Comparative Viability with Acidic POX
Chulho C. Song
Hatch Ltd., Mississauga, Canada
Liam Coleman
Hatch Ltd., Mississauga, Canada
ABSTRACT
Alkaline pressure oxidation (POX) is an oxidative pre-treat-
ment option that is commercially used for high-carbonate
sulfidic gold ores. The high carbonate grades within the
feed ore shifts the ideal operating pH to a basic regime.
Compared with acidic POX, alkaline POX typically
requires additional steam input due to a lower sulfur oxida-
tion load and a high rate of in-situ carbon dioxide genera-
tion that needs to be vented along with steam. The cost of
this steam addition is the largest differentiator between acid
POX operation and alkaline POX from a cost comparison.
However, alkaline POX can offset these costs through
reduced acid usage for pre-acidulation and decreased alkali
reagent consumption for subsequent neutralization. This
paper reviews the specific operating cost impacts of acid/
base consumption between alkaline and acidic POX with
ores which require pre-acidulation, the overall economics
of alkaline POX, and the regimes in which alkaline POX is
economically favorable.
The findings aim to guide industry professionals in
making informed decisions for alkaline POX adoption by
providing a summary view of its operational benefits and
costs, contributing to the development of cost-effective and
sustainable gold ore processing techniques.
INTRODUCTION
Gold extraction from refractory ores presents unique chal-
lenges due to the finely disseminated nature of gold par-
ticles that are often locked within mineral matrices such
as sulfides, carbonates, or silicates. Conventional cyanida-
tion methods are insufficient for effectively processing these
ores, necessitating pre-treatment techniques. Pressure oxi-
dation stands out as a key technology and can be carried
out under either acidic or alkaline conditions, each with its
specific advantages and challenges. Acidic POX is gener-
ally preferred for ores with low carbonate content, while
alkaline POX is used when the ore contains high carbon-
ate levels to minimize acid costs required in acidulation for
acidic POX operation.
This paper focuses on POX as a treatment method
for high-carbonate sulfidic gold ores, comparing the eco-
nomic implications of alkaline and acidulated acidic POX
processes. High-carbonate ores pose unique challenges in
POX treatment due to the potential for carbonate minerals
to consume reagents and impact process efficiency. In con-
trast to acidic POX, which typically involves higher reagent
consumption in carbonate-rich ores, alkaline POX oper-
ates under conditions that mitigate this issue, potentially
offering economic advantages depending on the specific ore
characteristics and external economic factors such as gold
market trends and fuel logistics.
The analysis presented in this paper aims to provide a
comparative understanding of the cost dynamics between
the two processes, emphasizing the operational trade-offs
and economic viability of alkaline POX for treating high-
carbonate sulfidic gold ores. By offering an overview of the
conditions under which alkaline POX becomes an eco-
nomically favorable option, this study seeks to contribute
valuable insights for the selection of pretreatment strategies
in refractory gold ore processing.
PRESSURE OXIDATION
Pressure oxidation is a hydrometallurgical technique involv-
ing subjecting the ore or concentrate in slurry form to ele-
vated temperature and pressure in the presence of oxygen.
This process oxidizes sulfide minerals, breaking down the
sulfide matrix and liberating the encapsulated gold, making
it available for subsequent leaching.
The POX process can be conducted in either an acidic
or an alkaline medium. Acidic POX is generally used for
ores with low carbonate content, while alkaline POX
is preferred for ores with high carbonate levels, as these