Cobalt extraction
Cobalt extraction refers to the metallurgical processes used to recover cobalt from its ores, which occur primarily as a by-product of copper and nickel mining in deposits such as sedimentary-hosted copper-cobalt stratiform ores and nickel-cobalt laterites.[1] The element is rarely mined from primary cobalt-only operations, with global production reaching 238,000 metric tons in 2023 and an estimated 290,000 metric tons in 2024, predominantly through hydrometallurgical techniques like acid leaching, solvent extraction, and electrowinning to yield high-purity cobalt cathode or hydroxide intermediates.[2] Pyrometallurgical methods, including smelting to produce cobalt-enriched matte or slag, are also employed for sulfide ores, often integrated with hydrometallurgy for further refinement.[3] The Democratic Republic of the Congo dominates production, contributing 175,000 metric tons or about 74% of the world's supply in 2023 and an estimated 220,000 metric tons or 76% in 2024, largely from the Central African Copperbelt where cobalt grades can reach 0.85% in high-value deposits like Kisanfu.[2] Other notable sources include magmatic nickel-cobalt sulfide deposits in Canada and Russia, nickel-cobalt laterites in Australia and Cuba, and primary cobalt veins at Bou Azzer in Morocco, though these account for less than 10% each of total output.[1] World reserves stand at approximately 11 million metric tons, with the Congo holding over half at 6 million tons, fueling demand for cobalt in lithium-ion batteries, superalloys, and catalysts amid the global energy transition.[2] Extraction challenges include low cobalt concentrations (often 0.1–0.3% in ores), environmental impacts from acid leaching, and the need for impurity removal during solvent extraction using reagents like Cyanex 272 to achieve >98% recovery rates.[3] Recent advancements focus on sustainable practices, such as bioleaching with microorganisms for lower acid consumption and hybrid pyro-hydrometallurgical flowsheets to minimize losses, supporting projected demand growth to around 400,000 tons annually by the early 2030s.[4]Sources and Ore Types
Primary Cobalt Deposits
Primary cobalt deposits, where cobalt occurs as the dominant metal rather than a byproduct, are relatively rare and primarily classified into two main types: hydrothermal vein deposits and sedimentary stratiform deposits. Hydrothermal vein deposits form through the circulation of mineral-rich fluids in fractured rocks, often associated with ultramafic or mafic host rocks, leading to high-grade cobalt mineralization. A prime example is the Bou Azzer deposit in Morocco, which consists of arsenide-bearing veins within Precambrian serpentinite. Sedimentary deposits, in contrast, occur in layered formations deposited in ancient marine or lagoonal environments, with cobalt concentrated in organic-rich shales and sandstones. While the Katanga system in the Democratic Republic of Congo (DRC), part of the Central African Copperbelt, features such stratiform layers in Neoproterozoic sediments, cobalt here is typically a coproduct of copper mining rather than primary.[1] Key minerals in these primary deposits include sulfarsenides like cobaltite (CoAsS), which is a primary arsenide-sulfide mineral found in veins, and secondary phases such as erythrite (Co₃(AsO₄)₂·8H₂O), a hydrated cobalt arsenate that forms colorful crusts in oxidized zones, and heterogenite (CoO(OH)), a cobalt oxyhydroxide prevalent in weathered supergene enrichments. These minerals typically grade from 0.5% to over 1% cobalt, with cobaltite providing the highest primary concentrations in unaltered ore. In the Copperbelt, heterogenite often caps oxidized portions of the deposits, while erythrite signals underlying arsenide-rich zones. Cobalt in these settings is geochemically linked to copper or nickel, though primary deposits emphasize cobalt as the economic focus.[1][5] Significant cobalt resources are found in the DRC's Central African Copperbelt, contributing to the majority of world cobalt mine production, but primary cobalt deposits remain rare globally, with notable examples including the Bou Azzer mine in Morocco and limited high-grade zones like Kisanfu in the DRC. Smaller but significant primary occurrences include historical vein deposits in Canada's Cobalt-Gowganda district, now largely depleted. As of 2025, world cobalt reserves total approximately 11 million metric tons, with the DRC holding about 6 million metric tons, or roughly 55% of the global total; these estimates highlight the Copperbelt's dominance in overall reserves, while vein deposits like Bou Azzer contribute niche high-grade supplies.[2][1][5] Mining of primary cobalt deposits varies by deposit type: underground methods, such as cut-and-fill stoping, are employed for deep vein systems like Bou Azzer to access narrow, high-grade ore bodies safely. In contrast, sedimentary layers in the Katanga Copperbelt are often extracted via open-pit operations for near-surface oxidized caps, transitioning to underground mining for deeper stratiform ores to minimize overburden removal and environmental impact. These approaches prioritize selective recovery of cobalt-rich zones while managing associated geotechnical challenges in fractured or layered hosts.[6][7]Byproduct and Associated Ores
The vast majority of cobalt is extracted as a by-product of copper and nickel mining operations, with approximately 98% of global production derived from these sources. Specifically, around 74% originates from copper mines, while 25% comes from nickel mines, leaving only about 1% from primary cobalt deposits.[8][9] In copper-associated ores, cobalt occurs primarily in sulfide minerals such as chalcopyrite (CuFeS_2), which is the dominant copper sulfide, often accompanied by cobalt-bearing minerals like carrollite (CuCo_2S_4). For nickel ores, cobalt substitutes into structures like pentlandite ([Ni,Fe]_9S_8), a key nickel sulfide mineral found in magmatic deposits. These associations drive the economic viability of cobalt recovery, as it is typically a minor component (0.1-0.5% of the ore) but processed alongside the primary metals.[5][10] Global cobalt mine production was estimated at 290,000 metric tons in 2024, following 238,000 metric tons in 2023, with continued growth expected into 2025. The Democratic Republic of Congo (DRC) dominates with roughly 76% of this output, primarily from copper-cobalt sulfide deposits in the Katanga region, while Australia and Indonesia together account for about 15%, mainly through nickel laterite processing.[2][11][12] This by-product dependency creates economic vulnerabilities, as cobalt prices fluctuate in tandem with copper and nickel markets; for instance, the average price in 2025 hovered around $30,000 per metric ton, influenced by oversupply and base metal demand shifts. In the DRC, artisanal and small-scale mining's role has diminished significantly, contributing less than 2% of national production in 2024 amid regulatory pressures and industrial expansion.[13][14]Extraction from Sulfide Ores
Copper-Cobalt Sulfide Concentrates
Copper-cobalt sulfide ores, prevalent in the Democratic Republic of Congo (DRC), are primarily processed through flotation to produce concentrates suitable for downstream hydrometallurgical recovery.[15] Froth flotation employs collectors such as sodium isopropyl xanthate (SIPX) and dithiophosphates at near-neutral pH to selectively recover sulfide minerals like chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄), and carrolite (CuCo₂S₄), achieving copper grades of 25-30% and cobalt grades of 7-8% in bulk concentrates from operations like Kamoto Copper Company.[15] This step typically yields overall metal recoveries of 80-90% for sulfides, with the concentrates filtered and dried prior to further treatment.[16] The concentrates undergo dead roasting in a fluid-bed furnace to convert sulfides to leachable oxides, eliminating sulfur as SO₂ for sulfuric acid production.[17] This oxidative process occurs at 500-600°C under excess oxygen, transforming minerals such as carrolite via the approximate reaction: $2\text{CuCo}_2\text{S}_4 + \frac{31}{2}\text{O}_2 \rightarrow 2\text{CuO} + 4\text{CoO} + 8\text{SO}_2 The resulting calcine contains metal oxides amenable to acid dissolution, with the exothermic reaction generating steam and energy for plant operations.[16] Atmospheric leaching of the calcine follows, using sulfuric acid at 50-80°C to dissolve cobalt and copper oxides, achieving approximately 90% cobalt recovery into solution.[16] The pregnant leach solution (PLS) contains dissolved Co²⁺, Cu²⁺, and impurities like Fe, Ni, and Mn, necessitating purification to isolate cobalt. Purification begins with solvent extraction (SX) to separate copper using aldoxime extractants, transferring cobalt to the raffinate.[16] Cobalt is then selectively extracted from this raffinate using Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) at pH 4.5-5.5, which preferentially binds Co²⁺ over residual Cu²⁺, Ni²⁺, and Fe²⁺ due to its organophosphorus chemistry, enabling >95% cobalt loading.[18] Stripping with sulfuric acid produces a purified cobalt electrolyte. Final recovery occurs via precipitation as cobalt hydroxide (Co(OH)₂) using lime or magnesia at pH 9-10, or as cobalt sulfide (CoS) with sodium hydrosulfide for high-purity applications.[16] In DRC operations like the Mutanda mine, operated by Glencore, copper-cobalt sulfide concentrates are processed via a roast-leach flowsheet integrated with SX-EW, recovering cobalt as hydroxide at rates supporting annual production of approximately 15,000-20,000 tonnes as of 2023, though recent export restrictions in the DRC (lifted in 2025) have influenced operations; the mine emphasizes oxide heap leaching alongside concentrate treatment for mixed feeds.[19][20]Nickel-Cobalt Sulfide Concentrates
Nickel-cobalt sulfide concentrates are primarily obtained from pentlandite-bearing ores, which are magmatic sulfide deposits containing approximately 1-2% cobalt alongside 10-20% nickel.[21] These concentrates are produced through froth flotation, where pentlandite ((Fe,Ni)9S8) is selectively recovered, often with associated pyrrhotite and chalcopyrite, yielding a mixed sulfide product suitable for hydrometallurgical processing.[22] The cobalt occurs mainly as a substitute for nickel in the pentlandite lattice, making co-extraction feasible during downstream treatment.[23] The Sherritt-Gordon process, a pressure hydrometallurgical method, is widely applied for recovering nickel and cobalt from these concentrates in Canadian and Australian operations. In this process, the concentrate undergoes oxidative ammonia leaching in autoclaves at temperatures of 80-100°C and pressures of 500-700 kPa, using an ammonia-ammonium sulfate solution with oxygen as the oxidant.[24] The sulfides are oxidized to soluble metal ammine complexes, represented simplistically as: \text{MSO}_4 + n\text{NH}_3 \rightarrow \text{M}(\text{NH}_3)_n^{2+} + \text{SO}_4^{2-} where M denotes Ni or Co.[25] This step achieves over 95% co-leaching of both nickel and cobalt, with impurities like iron precipitating as hematite.[26] Following leaching, the pregnant solution undergoes separation of nickel and cobalt, typically via solvent extraction using organophosphorus extractants such as Cyanex 272 or PC-88A, which selectively load cobalt over nickel in the ammoniacal medium.[27] The cobalt-rich strip solution is then processed to recover metal, either by hydrogen reduction under pressure to form cobalt powder—proceeding through a transient carbonyl intermediate (Co2(CO)8)—or by precipitation as cobalt hydroxide using reagents like magnesia.[28] Nickel is similarly recovered as powder via hydrogen reduction after purification. Key advantages of the Sherritt-Gordon process include its tolerance for high magnesium content in the feed, which does not interfere with ammonia complexation, and lower energy requirements compared to traditional roasting methods that demand high temperatures and generate SO2 emissions.[29] Commercial examples include Sherritt International's Fort Saskatchewan refinery in Canada, with operations supporting a cobalt production of approximately 3,500 tonnes annually as of 2025.[30][31]Extraction from Oxide Ores
Copper-Cobalt Oxide Ores
Copper-cobalt oxide ores occur predominantly in the oxidized supergene zones of sediment-hosted deposits in the Democratic Republic of the Congo (DRC), where weathering has enriched secondary minerals. These ores typically contain heterogenite (CuCoO₂·6H₂O) as the primary cobalt-bearing phase, alongside malachite and other copper oxides, with cobalt grades ranging from 1% to 3%. The presence of acid-soluble gangue such as dolomite and silica influences processing economics, but the ores' friable nature and solubility in acids make them suitable for low-cost heap and dump leaching operations without prior concentration or smelting.[32] The extraction process begins with direct sulfuric acid heap leaching conducted at ambient temperatures, typically 20–30°C, to dissolve the oxide minerals into sulfate solutions. Ore is crushed to a P₈₀ of around 625 μm and stacked into heaps irrigated with dilute H₂SO₄ (5–10 g/L), with cycles lasting 60–120 days depending on ore permeability and mineralogy. The dissolution follows simplified reactions for the oxide components, such as: \text{CoO} + \text{H}_2\text{SO}_4 \rightarrow \text{CoSO}_4 + \text{H}_2\text{O} Similar reactions occur for copper oxides and heterogenite, yielding pregnant leach solutions (PLS) containing 5–15 g/L Cu and 0.5–2 g/L Co. Cobalt recovery rates typically reach 80–90%, with higher efficiencies (up to 95%) achievable under optimized conditions like reductive addition of SO₂ to enhance heterogenite dissolution.[33] Post-leaching, the PLS undergoes impurity removal to prepare it for metal recovery. Iron and manganese, introduced from gangue dissolution, are removed by oxidation and precipitation; for example, iron as goethite or jarosite, and manganese as MnO₂, typically after copper solvent extraction to avoid interference. Additional impurities like aluminum may require neutralization or precipitation steps. The purified solution then proceeds to solvent extraction (SX) using reagents like LIX 84 for copper separation, producing high-purity copper electrolyte for electrowinning. The cobalt-rich raffinate is further processed via SX with Cyanex 272 or precipitation as cobalt hydroxide using magnesia or NaOH, yielding cobalt cathode via electrowinning or intermediate salts for sale. These downstream steps mirror those used for sulfide-derived solutions but operate at lower temperatures.[34][35] This hydrometallurgical route is a significant contributor to the DRC's cobalt production, supporting major operations at sites like Tenke Fungurume and Kakanda, where annual outputs exceed 20,000 tons of cobalt equivalent from oxide feeds. A primary challenge is elevated acid consumption, often 50–100 kg H₂SO₄ per ton of ore, driven by carbonate gangue like dolomite (CaMg(CO₃)₂), which reacts to form gypsum and consumes up to 20–30% of the applied acid. Mitigation strategies include selective mining to minimize gangue and pre-neutralization of fines.[32]Laterite Ores
Laterite ores, primarily found in tropical regions such as Indonesia and Australia, consist of weathered layers including limonite (iron-rich oxide horizons) and saprolite (magnesium-rich silicate horizons), with cobalt grades typically ranging from 0.1% to 0.2%.[36] These ores are nickel-dominant, where cobalt occurs as a valuable byproduct associated with manganese oxyhydroxides in the limonite layer and silicates in the saprolite.[37] Extraction from these low-grade deposits is economically viable through hydrometallurgical methods, particularly high-pressure acid leaching (HPAL), which targets the limonite fraction due to its amenability to acid dissolution.[38] The HPAL process involves slurrying the ore and subjecting it to sulfuric acid leaching in an autoclave at approximately 250°C and 40 atm pressure, facilitating reactions such as the dissolution of cobalt oxide:\ce{CoO + H2SO4 -> CoSO4 + H2O}
This yields a pregnant leach solution containing nickel, cobalt, and impurities like iron and aluminum, with cobalt recovery rates around 90-93%.[39][40] Following leaching, the solution undergoes neutralization to precipitate iron and other impurities, producing a mixed hydroxide precipitate (MHP) rich in nickel and cobalt (typically 30-40% Ni and 1-6% Co).[41] Solvent extraction (SX) then separates cobalt from nickel, enabling further purification via electrowinning or precipitation into battery-grade products.[37] Key operational facilities processing laterite ores via HPAL include the Ramu mine in Papua New Guinea, which produced 3,072 tonnes of contained cobalt in 2023 and 2,625 tonnes in 2024, with ongoing operations expected to contribute similarly in 2025, and the Coral Bay facility in the Philippines, with an annual capacity of 2,500 tonnes of cobalt.[42][43] HPAL operations from laterite ores are projected to contribute over 30,000 tonnes of cobalt globally in 2025, driven by expansions in Indonesia and Australia.[44] However, the process faces significant drawbacks, including high capital expenditures (often exceeding $500 million for a mid-sized plant) due to the need for robust autoclaves and acid plants, as well as operational challenges from silica in saprolitic ores, which can form gels that clog equipment and reduce efficiency.[45] Emerging technologies aim to address these limitations, such as carbon-negative leaching of serpentine-rich laterites using bioleaching or enhanced weathering processes, which integrate microbial acid production or CO₂ mineralization to extract cobalt while sequestering carbon; pilot studies in 2025 demonstrate potential for sustainable recovery from ultramafic sources.[46][47]