Deep in the earth's crust, when hot magma meets with oxygen-rich groundwater, or when ancient
ore layers have been weathered and baptized for millions of years, a unique kind of copper resource
is quietly formed - oxidized copper ore. It does not have the dazzling luster of sulfide ore, but with
its environmental friendliness and unique adaptability of hydrometallurgy, it has opened up a green
track full of potential in the global copper resource pattern.
Oxidized Copper Ore: A Gift of Geological Carving Over the Years
Oxidized copper ores, as the name suggests, are deposits in which the element copper exists mainly in the form
of oxidized minerals such as oxides, carbonates, silicates or sulfates. They are the product of long secondary
enrichment of primary copper sulfide ores:
Transformation of oxygen-rich environments: Surface or near-surface copper sulfide minerals (e.g., chalcopyrite
CuFeS2) are exposed to aqueous environments enriched with oxygen and carbon dioxide, where they undergo
complex oxidation, dissolution, migration, and reprecipitation reactions.
Secondary mineral formation: Dissolved copper ions encounter alkaline environments or reducing zones
during downward infiltration and re-precipitate to form new minerals. Typical representatives include:
Malachite [Cu2CO3(OH)2]: bright green, most common, signature banding pattern.
Bluish chalcopyrite [Cu3(CO3)2(OH)2]: dark blue, often symbiotic with malachite.
Silica malachite [CuSiO3-nH2O]: green, blue or cyan, cryptocrystalline.
Hematite [Cu2O]: Bright or dark red.
Black Copper Ore [CuO]: black.
Water chalcopyrite [Cu4SO4(OH)6]: Emerald green.
Distribution characteristics: usually located in the oxidation zone of the deposit, covering the primary
sulfide ore body. The ore body is shallowly buried and easily mined in the open pit.
Core Advantage: Green key to bypassing the fire method
The core value of copper oxide ores is their natural affinity for hydrometallurgy compared to conventional
copper sulphide ores:
Advantage of acid solubility: Copper oxide minerals (especially carbonates, some silicates, and oxides) can **directly
dissolve in dilute acids (e.g., sulfuric acid)** with a mild and rapid reaction:
Malachite: Cu2CO3(OH)2 + 2H2SO4 → 2CuSO4 + CO2↑ + 3H2O
Chalcopyrite: Cu3(CO3)2(OH)2 + 3H2SO4 → 3CuSO4 + 2CO2↑ + 4H2O
Copper ore: Cu2O + H2SO4 → Cu2SO4 + H2O (further oxidized to CuSO4)
Black Copper Ore: CuO + H2SO4 → CuSO4 + H2O
Avoiding high pollution: Wet process (acid leaching-extraction-electrowinning) does not require high temperature
smelting, which completely avoids the problems of large amount of sulfur dioxide (SO2) fumes, high arsenic/lead
fumes, and high energy consumption in pyrometallurgical smelting, and significantly reduces the environmental load.
Economy of processing low-grade ore: Wet process on the ore grade requirements are relatively loose (usually
0.2%-1.0% Cu can be economically processed), can effectively utilize the traditional thermal method is difficult to
profit from the low-grade oxidized ores, complex and difficult to select and even the old mine tailings, greatly
expanding the boundaries of the available resources.
Mild operating conditions: can be carried out at atmospheric pressure, low to medium temperature (<80°C),
equipment investment and operating costs are usually lower than those of large-scale pyrometallurgical smelters.
Wet copper extraction: a green journey from ore to copper cathode
At the heart of the modern utilization of copper oxide ores is the well-established** “Leach-Extraction-Electrowinning”
(LX-SX-EW)** process chain:
Crushing and Heap Leach/Tank Leach:
Heap leaching: Mainstream method for large-scale processing of low-grade ores. The ore is crushed and stacked on
an impermeable pad, and leached by spraying or dripping with dilute sulfuric acid solution (or bacterial-containing
solution). The leaching solution (copper-rich solution, Pregnant Leach Solution - PLS) is collected in a storage tank.
This method is low investment and large scale, especially suitable for open pit mines.
Tank leaching/agitation leaching: Treatment of high-grade or fine-grained ores. The ore is leached in an agitated
tank with an acid solution for several hours, which is highly efficient but relatively expensive and energy consuming.
Solvent Extraction (SX): “purification and concentration” of the solution.
Extraction: PLS (containing impurities such as Cu²⁺, Fe³⁺, Mg²⁺, etc.) is mixed with a specially formulated organic
extractant. The extractant selectively “grabs” the copper ions to form a loaded organic phase, leaving the impurity
ions in the aqueous phase (residue) to be returned to leaching or treatment.
Reverse extraction: The loaded organic phase is mixed with a strong acid solution (e.g., electrolytic lean solution),
and the copper ions are “stripped” down into the aqueous phase, forming a high-purity, high-concentration
copper-rich electrolyte (Rich Electrolyte). The organic phase is regenerated and recycled, and SX is a key step
in obtaining a pure electrolyte.
Electrolytic deposition (EW): Current calling of copper metal.
A high-purity copper-rich electrolyte (Cu²⁺ concentration ~40-50 g/L, H2SO4 ~180 g/L) is pumped into the electrolyzer.
A direct current is applied and a reduction reaction takes place on a permanent cathode (or initiator plate) made
of stainless steel or titanium: Cu²⁺ + 2e- → Cu, and high purity (>99.99%) metallic copper is deposited on the cathode plate.
The anode, which is usually an inert material (e.g. Pb-Ca-Sn alloy), undergoes an oxidation reaction to precipitate
oxygen: 2H2O → O2↑ + 4H⁺ + 4e-.
After deposition for a certain period of time, the cathode plate is stripped to obtain A-grade copper cathode that
can be directly sold or further processed. The electrolysis-poor liquid returns to the anti-extraction section for
recycling.
Challenges and breakthroughs: the key to unlocking complex deposits
Despite the significant advantages, the development and utilization of oxidized copper ore still faces challenges
that drive technological innovation:
The “hard nut to crack”: difficult to process oxidized/mixed ores
Silicon malachite conundrum: slow acid dissolution rate and low leaching of silicon malachite.
Combined Copper Trouble: Copper is tightly encapsulated in vein minerals (e.g., iron oxides, clays), making it
difficult to access the acid.
Mixed ore complexity: oxidized ore and sulfide ore coexistence, a single acid leaching can not effectively dissolve copper sulfide.
Breakthrough Program:
Enhanced leaching: Increase temperature (hot acid leaching), fine grinding, add co-solvents (e.g., fluoride, chloride salts).
Ammonia leaching system: For highly alkaline veins or mixed ores containing copper sulfides, use ammonia-ammonium
carbonate solution to leach, forming a stable copper-ammonia complex.
Bioleaching: Using acidophilic microorganisms (e.g. Thiobacillus ferrooxidans) to oxidize sulfide minerals, releasing encapsulated
copper or directly dissolving part of the oxidized minerals. Environmental protection, low energy consumption, promising.
Pretreatment activation: calcine, microwave treatment, etc. to destroy the parcel structure, improve the mineral reaction activity.
Impurity elements: the test of purification process
Iron (Fe³⁺): present in large quantities, consumes acid and extractant, affects electrolyte quality.
Manganese (Mn²⁺): may oxidize to MnO2 at the anode during electrolysis and contaminate the cathode.
Aluminum (Al³⁺), Magnesium (Mg²⁺): Excessive concentrations can cause an increase in the viscosity of the electrolyte,
affecting copper deposition and current efficiency.
Breakthrough program:
Optimize SX: Develop a highly selective extractant that specifically grabs copper ions and effectively separates impurities
such as iron and manganese.
Control leaching conditions: Adjust pH and redox potential (Eh) to selectively dissolve copper and inhibit impurity leaching.
Precipitation/Ion Exchange: Adding removal steps (e.g., neutralization and precipitation to remove iron and aluminum) before
the leach solution enters the SX.
Environmental Footprint: The Quest for Continuous Optimization
Wastewater management: Leach and extraction solutions contain acids and impurities that need to be neutralized or recycled.
Tailings safety: Leached tailings need to be properly stockpiled to prevent acid and heavy metal contamination.
Breakthrough Programs:
Closed Loop Water Recycling: Minimize fresh water consumption and wastewater discharge.
Neutralization and solidification of tailings: Add neutralizing agents such as lime and solidify and stabilize the tailings,
and build a high-standard impermeable tailings storage.
Resource utilization: Research on the recovery of associated elements (e.g. cobalt) from tailings or waste liquid, or the
use of waste residue to make building materials.
Strategic Value: Green Growth Pole on the Resource Map
The value of copper oxide ores goes beyond their copper content:
Revitalization of “stagnant” resources: A large number of low-grade oxide ores, old mine tailings and complex
mixed ores around the world have been revitalized by the maturity of the wet process technology, which significantly
extends the service life of mines.
Environmental pressures: Increasingly stringent environmental regulations, particularly SO2 emissions, are making
wet copper extraction the preferred option for new or retrofit projects.
Regional resource rebalancing: In regions where high quality sulphide ores are scarce or energy costs are high, the
development of hydrometallurgy based on local oxidized ore resources can achieve regional resource self-sufficiency.
Supporting green industry: Grade A copper cathode produced by wet process is a high-quality raw material for
manufacturing high-conductivity wires (wind power, photovoltaic, electric vehicles), high-efficiency radiators, and
precision electronic components, and is itself an important part of the green supply chain.
Light of the future: technological innovation drives a broader world
Oxidized copper ore hydrometallurgical technology is still evolving at a high speed:
Efficient and green leaching and extraction agents: Research and development of chemicals with stronger
solvency capacity, higher selectivity and easier biodegradation.
Process Enhancement and Intelligence: Apply sensors, big data and AI to optimize leach pad management,
SX process control and electrolysis parameters to improve efficiency and reduce costs.
Low-grade/ultra-low-grade ore processing revolution: Improve heap leaching technology (e.g., thin-layer heap
leaching, segmente heap construction), combined with bioleaching or in-situ leaching, to make lower-grade
resources economically viable.
Development of “urban mines” from abandoned mines/tailings: Wet technology is a key means of recovering
copper and other valuable metals from historical mine wastes, realizing a win-win situation for both resource
recycling and ecological restoration.
Conclusion: The awakening of the green vein
Oxidized copper ore, this green vein sleeping on the surface, is no longer a metallurgical “chicken ribs”. With
its natural fit with hydrometallurgy, it is taking an unprecedented position at the center of the resource stage.
From the vast heap leach fields in Chile to the emerging wet plants in Africa, from revitalizing the historical
tailings to supporting the future of green power, copper oxide ore copper extraction technology has not only
reshaped the landscape of the copper industry with its core competitiveness of being environmentally friendly,
resource efficient and cost controllable, but has also become a key path for the sustainable development of the
mining industry.
This is a green revolution with still waters running deep. When the dilute sulfuric acid solution trickles through
the low-grade ore heap, when the high-purity copper cathode grows silently in the electrolysis tank, the oxidized
copper mine is in its unique way, conveying the inexhaustible copper flow for the human industrial civilization,
and at the same time guarding the green water and green mountains under the feet to live on. This is copper
oxide ore - a green treasure hidden in the oxidized zone, the key to unlocking a sustainable future.