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Development of Sustainable Hydrometallurgical Technologies for
Critical Minerals and Precious Metals
J.J. Eksteen and E.A. Oraby
Western Australian School of Mines: Minerals, Energy &Chemical Engineering Curtin University, Perth, Australia
ABSTRACT: For most of the 20th century, our metallurgical focus has been on metallurgical bulk commodities
that could be concentrated, smelted, converted, and refined under less stringent constraints imposed by
communities, water availability, safety, and governments. As ore grades decreased and ores also became more
polymetallic, and as the risks around Critical Minerals became clear, particularly insofar they are used in the
renewable energy transition, and compliance to ESG targets became essential, a sea change has been required
in how we extract and refine metals. The high-grade requirements imposed by smelters (or pressure leach
operations) have become hard to satisfy without significant recovery loss at the mine and concentrators. As the
value of water increased in many mining jurisdictions and the industry have become more focused on Circular
Economy drivers, the reuse, repurpose and recycle of water and reagents and wastes have become essential. Dry
disposal of tailings has also become a major driver to recycle the water and chemicals back to the metallurgical
operations. Conventional hydrometallurgical operations, which mostly used either mineral acids such as sulfuric
acid, ammonia, or sodium cyanide for metal recovery, has become problematic due to their lack of selective
dissolution, the need for expensive post-treatment (neutralization and detoxification) and the poor ability to
recover, recycle and reuse the reagents have become problematic and often not sustainable. Development of
suitable alternative and selective lixiviants therefore offers a compelling research focus.
INTRODUCTION
Metallurgical process technology research and develop-
ment in the 20th century led to multiple orders of mag-
nitude increase in productivity, increased recoveries, yields
and process intensification but mostly in the form of a
linear and carbon-based economy, without much focus
on waste valorization, or reagent recovery, water recycling,
etc. Economically, the emphasis was on bulk mineral com-
modities and precious metals. In contrast, the 21st century
has seen a transition to circular economies, a major shift
towards water recovery and reuse, critical minerals, and met-
als crucial for the green energy transition, decarbonization,
and, where feasible, a move towards “green” reagents. Our
hydrometallurgical approaches must develop in step with
these megatrends and some developments have become
important enablers. In addition, the available of renewable
energy, major geopolitical shifts, supply chain constraints,
as well as the closure of many oil and gas refineries that co-
produced by-products like sulfur (in the case of Australia)
has changed the economic and risk drivers of many conven-
tional metallurgical reagents such as sulfuric acid, sodium
cyanide, burnt and slaked lime, and reducing agents derived
from fossil fuels.
Conventionally the capital intensity of high tempera-
ture and pressure operations, such as smelting and pressure
Development of Sustainable Hydrometallurgical Technologies for
Critical Minerals and Precious Metals
J.J. Eksteen and E.A. Oraby
Western Australian School of Mines: Minerals, Energy &Chemical Engineering Curtin University, Perth, Australia
ABSTRACT: For most of the 20th century, our metallurgical focus has been on metallurgical bulk commodities
that could be concentrated, smelted, converted, and refined under less stringent constraints imposed by
communities, water availability, safety, and governments. As ore grades decreased and ores also became more
polymetallic, and as the risks around Critical Minerals became clear, particularly insofar they are used in the
renewable energy transition, and compliance to ESG targets became essential, a sea change has been required
in how we extract and refine metals. The high-grade requirements imposed by smelters (or pressure leach
operations) have become hard to satisfy without significant recovery loss at the mine and concentrators. As the
value of water increased in many mining jurisdictions and the industry have become more focused on Circular
Economy drivers, the reuse, repurpose and recycle of water and reagents and wastes have become essential. Dry
disposal of tailings has also become a major driver to recycle the water and chemicals back to the metallurgical
operations. Conventional hydrometallurgical operations, which mostly used either mineral acids such as sulfuric
acid, ammonia, or sodium cyanide for metal recovery, has become problematic due to their lack of selective
dissolution, the need for expensive post-treatment (neutralization and detoxification) and the poor ability to
recover, recycle and reuse the reagents have become problematic and often not sustainable. Development of
suitable alternative and selective lixiviants therefore offers a compelling research focus.
INTRODUCTION
Metallurgical process technology research and develop-
ment in the 20th century led to multiple orders of mag-
nitude increase in productivity, increased recoveries, yields
and process intensification but mostly in the form of a
linear and carbon-based economy, without much focus
on waste valorization, or reagent recovery, water recycling,
etc. Economically, the emphasis was on bulk mineral com-
modities and precious metals. In contrast, the 21st century
has seen a transition to circular economies, a major shift
towards water recovery and reuse, critical minerals, and met-
als crucial for the green energy transition, decarbonization,
and, where feasible, a move towards “green” reagents. Our
hydrometallurgical approaches must develop in step with
these megatrends and some developments have become
important enablers. In addition, the available of renewable
energy, major geopolitical shifts, supply chain constraints,
as well as the closure of many oil and gas refineries that co-
produced by-products like sulfur (in the case of Australia)
has changed the economic and risk drivers of many conven-
tional metallurgical reagents such as sulfuric acid, sodium
cyanide, burnt and slaked lime, and reducing agents derived
from fossil fuels.
Conventionally the capital intensity of high tempera-
ture and pressure operations, such as smelting and pressure