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Biomining

Biomining is a biotechnological process that utilizes acidophilic microorganisms to extract valuable metals from low-grade ores, mineral concentrates, and waste materials through mechanisms such as bioleaching and biooxidation, providing an environmentally friendly alternative to traditional pyrometallurgical methods.^[1]^[2] The technique involves the microbial oxidation of sulfide minerals, where bacteria and archaea like Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Sulfolobus metallicus generate ferric iron and sulfuric acid to solubilize metals such as copper, gold, nickel, and zinc.^[1]^[2] In bioleaching, insoluble metal sulfides are converted directly into soluble sulfates, enabling metal recovery from solutions, while biooxidation pretreats refractory ores by removing sulfur and iron layers that encase precious metals like gold in arsenopyrite. These processes typically occur in acidic environments (pH 1.0–2.0) and can operate at temperatures ranging from ambient to 85°C, often in heap, dump, or tank reactors.^[1] Historically, biomining traces its roots to ancient practices at sites like the Rio Tinto mine in Spain, where microbial activity inadvertently aided silver and copper extraction as early as pre-Roman times, but commercial biohydrometallurgy only emerged in the mid-20th century with the identification of key acidophiles in the 1940s and large-scale implementation in the 1970s.^[1] As of 2025, it accounts for more than 20% of global copper production—primarily through heap leaching in Chile—and 5% of gold recovery, particularly for refractory ores, with additional applications in uranium, nickel, and zinc extraction from low-grade sources and e-waste.^[2]^[3] Compared to conventional mining, biomining offers significant advantages, including lower energy consumption, reduced emissions of sulfur dioxide and other pollutants, higher extraction efficiencies (>90% for some metals), and the ability to process ores with grades as low as 0.5% metal content that are uneconomical by smelting.^[1] It also facilitates metal recovery from mine tailings and industrial wastes, minimizing environmental contamination and promoting resource recycling. Recent advancements focus on engineering acidophiles via synthetic biology to enhance tolerance to metal toxicity, high temperatures, and osmotic stress, as well as using microbial consortia for improved efficiency in complex polymetallic ores.^[2]

Fundamentals

Definition and Principles

Biomining is defined as the extraction of metals using microorganisms to facilitate the solubilization of valuable elements from low-grade ores, mine wastes, and electronic waste via biohydrometallurgical processes.^[4] These processes harness the metabolic activities of acidophilic microbes to target sulfide minerals, converting insoluble metal sulfides into soluble forms that can be recovered downstream.^[5] The core principles of biomining revolve around microbial oxidation of sulfide minerals to liberate associated metals, coupled with the production of acids and oxidizing agents that promote metal solubilization through complexation. Acidophilic microorganisms oxidize reduced sulfur and iron compounds, generating ferric iron (Fe³⁺) as a potent oxidant and sulfuric acid to maintain the acidic environment essential for leaching. For instance, iron oxidation proceeds via the reaction \ce{Fe^{2+} -> Fe^{3+} + e^{-}}, primarily mediated by Acidithiobacillus species, while sulfur oxidation yields sulfuric acid according to \ce{S + 1.5 O_2 + H_2O -> H_2SO_4}.^[6] These reactions enable the breakdown of mineral lattices, releasing metals like copper and gold into aqueous solutions.^[4] A fundamental distinction in biomining mechanisms is between direct and indirect action: in direct mechanisms, microorganisms physically attach to mineral surfaces and enzymatically oxidize the sulfides, whereas indirect mechanisms involve the production of lixiviants—such as Fe³⁺ and H₂SO₄—in the bulk solution, which chemically attack the minerals without requiring cell-mineral contact.^[6] Biohydrometallurgy, as a primary subset of biomining, emphasizes these biological pathways and operates with low energy input at ambient or mildly elevated temperatures, contrasting sharply with the high-temperature requirements of pyrometallurgical smelting.^[5]

Microorganisms Involved

Biomining primarily relies on acidophilic prokaryotes that oxidize iron and sulfur compounds to facilitate metal solubilization from ores. Among these, Acidithiobacillus ferrooxidans is a key mesophilic bacterium, thriving at optimal pH 1.5–2.5 and temperatures of 20–40°C, where it oxidizes ferrous iron (Fe²⁺) to ferric iron (Fe³⁺) and elemental sulfur to sulfuric acid.^[7] This Gram-negative, autotrophic chemolithotroph derives energy from the oxidation of reduced inorganic compounds while fixing carbon dioxide (CO₂) via the Calvin-Benson-Bassham cycle.^[8] Its adaptations to extreme acidity and high metal concentrations include efflux pumps, such as those encoded by the ars operon for arsenic resistance, and biosorption mechanisms that sequester toxic ions on the cell surface.^[8] Another prominent primary prokaryote is Leptospirillum ferriphilum, an extreme acidophile (optimal pH ~1.8, temperature ~37°C) that specializes in iron oxidation, contributing to the regeneration of the ferric iron oxidant essential for bioleaching.^[7] Lacking sulfur-oxidizing capabilities, it complements sulfur-oxidizers in microbial communities and exhibits robust tolerance to heavy metals, including up to 30 g/L arsenic, through enhanced efflux systems and metabolic adjustments.^[7] Secondary microbes extend biomining to higher temperatures. Sulfobacillus thermosulfidooxidans, a moderate thermophile (optimal pH 1.9–2.4, temperature up to 60°C), oxidizes both iron and sulfur, supporting processes in warmer environments.^[7] Similarly, the archaeon Sulfolobus metallicus functions as a hyperthermophile (optimal pH ~2.0, temperature 70–80°C), oxidizing sulfur and iron in extreme heat, which is advantageous for refractory ores.^[7] Fungal contributors, such as Aspergillus niger and Penicillium simplicissimum, play a role in bioleaching at near-neutral pH through heterotrophic metabolism, producing organic acids like citric and oxalic acid via glycolysis and the tricarboxylic acid (TCA) cycle to chelate metals.^[9] These fungi operate effectively at pH 3–6, offering alternatives for less acidic conditions, though their application in biomining remains more exploratory compared to prokaryotes.^[9] The metabolic foundation of these prokaryotes is autotrophic chemolithotrophy, where energy is harvested from the exergonic oxidation of Fe²⁺ (via electron transport chains involving cytochromes and rusticyanin) and sulfur (through sulfide:quinone oxidoreductase and other enzymes), coupled with CO₂ fixation for biomass synthesis.^[8] Tolerance to toxic metals is mediated by active efflux pumps (e.g., resistance-nodulation-division transporters) that expel ions like arsenic and mercury, alongside passive biosorption onto extracellular polymeric substances.^[8] In practice, synergistic microbial consortia outperform pure cultures; for instance, mixed communities of A. ferrooxidans with Leptospirillum spp. or heterotrophs like Acidiphilium enhance iron and sulfur oxidation rates, accelerating bioleaching by improving acid production and mineral attachment, with reported efficiency gains in chalcopyrite dissolution.^[10]

Historical Development

Early Observations

Early observations of biomining phenomena date back to ancient civilizations, where unintentional metal extraction occurred through natural processes involving acidic drainage waters. The earliest documented instances of processes akin to biomining in China date to the Song Dynasty (960–1279 AD), where wet copper production via microbial leaching in drainage waters yielded up to 1,000 tons per year to support state coinage needs.^[11]^[12] Similarly, in medieval Europe, silver-copper mines, such as those in the Iberian Pyrite Belt, produced acidic runoffs that naturally dissolved metals from sulfide ores through pyrite oxidation, contributing to inadvertent leaching long before scientific recognition.^[13] In the 19th and early 20th centuries, miners noted "sour liquors"—highly acidic solutions—in tailings from sulfide ore processing, which accelerated metal dissolution beyond expected chemical rates. A prominent example is the Rio Tinto mines in Spain, where intensive pyrite extraction since the mid-19th century generated drainage with pH as low as 1–2 due to natural and mining-induced pyrite oxidation, releasing iron, copper, and other metals into waterways.^[14] These observations highlighted the role of acidic environments in mineral breakdown but were initially attributed solely to abiotic reactions. Scientific identification of microbial involvement began in the mid-20th century. In 1947, researchers reported the presence of bacteria in acid mine drainage (AMD) from coal mines, demonstrating their contribution to sulfuric acid production and iron solubilization.^[15] This was advanced in 1951 by the discovery of the iron-oxidizing bacterium Thiobacillus ferrooxidans (now classified as Acidithiobacillus ferrooxidans) in coal mine drainage waters, where it catalyzed the autotrophic oxidation of ferrous iron to ferric iron under acidic conditions, accelerating AMD formation. By the 1960s, laboratory experiments confirmed that microorganisms like Acidithiobacillus ferrooxidans significantly enhanced the release of metals from sulfide minerals, with dissolution rates 10 to 100 times faster than abiotic processes alone, laying the groundwork for intentional biomining applications.^[16]

Modern Commercialization

The commercialization of biomining accelerated in the 1970s with pioneering pilot-scale bioleaching operations for copper recovery from low-grade sulfide ores. At the Bingham Canyon Mine in Utah, USA, Kennecott Copper Corporation initiated early commercial bacterial leaching in the late 1950s, but expanded efforts in the 1970s demonstrated practical recoveries of 20-30% metals from waste dumps using naturally occurring acidophilic bacteria such as Acidithiobacillus ferrooxidans.^[17]^[18] The 1980s and 1990s marked widespread industrial adoption, particularly for heap bioleaching of copper and biooxidation of refractory gold ores. In Chile, the Quebrada Blanca mine commissioned a fully bioleaching-based operation in 1994, processing heaps of 100,000 to 500,000 tons of mixed oxide-sulfide ores and producing over 80,000 tons of copper annually by the mid-2000s.^[19]^[20] For gold, Gencor launched the world's first commercial biooxidation plant at the Fairview Mine in South Africa in 1986, treating refractory sulfide concentrates to liberate encapsulated gold particles through bacterial oxidation.^[21]^[22] By the 2000s, biomining had achieved global scale, contributing approximately 20% of the world's copper production, with major operations at sites like the Escondida mine in Chile, which integrated bioleaching for secondary sulfide ores. Tank-based biooxidation for gold also expanded, as exemplified by the Ashanti Goldfields Company's Sansu plant in Ghana, commissioned in 1994 and scaled to reactors exceeding 1,300 m³ by the early 2000s, enabling treatment of over 790 tons of concentrate per day. Key innovations included Mintek's development of the BIOX® process in South Africa during the 1980s, a patented bacterial oxidation method for refractory gold that facilitated multiple commercial plants worldwide. Complementing this, BacTech advanced moderately thermophilic bacterial oxidation technologies in the 1990s, achieving over 90% sulfide oxidation in pilot and full-scale gold recovery operations, such as at the Youanmi mine in Australia.^[23]^[24]^[25] In the 2010s, biomining increasingly integrated with hydrometallurgical processes like solvent extraction and electrowinning, enhancing overall efficiency and achieving recovery rates up to 90% in optimized copper and gold operations, as seen in expanded Chilean heap systems and advanced BIOX® facilities.^[26]^[27] In the 2020s, biomining continued to expand, with Quebrada Blanca Phase 2 achieving initial production in 2023 and ramping up, contributing to bioleaching's share of approximately 20% of global copper production as of 2025.^[28]^[29]

Biomining Techniques

Biooxidation

Biooxidation serves as a critical pretreatment method in biomining for refractory ores, where valuable metals such as gold are encapsulated within sulfide matrices that resist conventional extraction techniques. The process involves the aerobic microbial oxidation of these sulfide minerals, primarily pyrite (FeS₂) and arsenopyrite (FeAsS), converting them into soluble sulfates and thereby liberating the entrapped metals for subsequent recovery, often via cyanidation. This biological approach employs acidophilic bacteria to catalyze the oxidation, producing ferric ions (Fe³⁺) that chemically attack the sulfide structure, enhancing metal accessibility without the high energy demands of pyrometallurgical alternatives.^[30] Operationally, biooxidation is performed in a series of agitated tank reactors, with commercial-scale volumes reaching up to 1,500 m³ per reactor to handle substantial ore throughputs. The process typically maintains a retention time of 4-6 days at temperatures of 30-40°C and a low pH range of 1.5-2.0 to optimize microbial activity. Oxygen sparging is essential, as it supports the bacterial oxidation of ferrous iron (Fe²⁺) to ferric iron (Fe³⁺), which drives the breakdown of sulfide minerals; air or pure oxygen is introduced to achieve dissolved oxygen levels sufficient for efficient reaction kinetics. Key microorganisms involved include species like Acidithiobacillus ferrooxidans, which thrive under these acidic, aerobic conditions.^[31]^[21]^[32] The fundamental chemistry of pyrite biooxidation can be represented by the following equation:

$4\text{FeS}_2 + 15\text{O}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{Fe}_2(\text{SO}_4)_3 + 2\text{H}_2\text{SO}_4

This reaction illustrates the complete aerobic oxidation to soluble iron(III) sulfate and sulfuric acid, facilitated by microbial regeneration of the oxidant.^[33] Biooxidation offers distinct advantages for processing sulfide refractory ores, often containing 10-30% sulfides, achieving up to 95% sulfide oxidation and enabling effective pretreatment where direct leaching fails. It is particularly suited for ores rich in gold, uranium, and nickel, providing a cost-effective, lower-emission alternative to roasting by minimizing SO₂ emissions and energy use. Notable commercial implementations include the BIOX® process, which has treated refractory gold concentrates to yield recovery rates up to 90% post-cyanidation, and the ASTER™ process, which integrates biooxidation for similar high-efficiency sulfide destruction in gold extraction.^[34]^[35]^[36]^[30]

Dump and Heap Leaching

Dump and heap leaching represent scalable, low-cost biomining methods for extracting metals, particularly copper, from low-grade ores by percolating acidic solutions through large piles, facilitated by acidophilic microorganisms that oxidize sulfide minerals. In dump leaching, the process utilizes existing waste rock dumps, often exceeding 100 m in height and containing low-grade ore with less than 0.5% metal content, where dilute sulfuric acid (pH 1.5–2.5) is irrigated at rates of 5–10 L/m²/h to promote microbial activity and metal solubilization.^[37]^[38] This method is inherently slow, typically requiring years to achieve recoveries of 50–70%, due to the heterogeneous nature of the uncrushed material and limited control over environmental variables.^[37]^[39] Heap leaching, in contrast, involves purpose-built engineered stacks of ore, typically 3–10 m high, with the material crushed to less than 10 mm to enhance permeability and microbial access, placed on lined impermeable bases for efficient collection of the pregnant leach solution (PLS).^[39]^[38] Aeration is facilitated through embedded pipes to supply oxygen, supporting microbial oxidation, while irrigation with acidified water maintains optimal conditions; the process is faster, often completing in months with copper recoveries of 70–90%.^[37]^[38] Key parameters include temperature gradients from ambient to 50°C, which influence microbial consortia, and initial inoculation with acidophiles like Acidithiobacillus species to accelerate startup.^[37] Unlike dumps, which repurpose mining waste with minimal preparation, heaps are actively constructed for optimized flow and recovery.^[39] The overall process flow begins with the introduction of acidified water and air to the pile, enabling microbial oxidation of sulfides to produce ferric ions that solubilize metals, resulting in PLS containing dissolved metals such as Cu²⁺, which is then processed via solvent extraction and electrowinning to recover pure metal.^[37] For chalcopyrite (CuFeS₂), the primary copper sulfide, microbial oxidation follows the simplified reaction under acidic conditions:

\text{CuFeS}_2 + 4\text{O}_2 + 2\text{H}^+ \rightarrow \text{Cu}^{2+} + \text{Fe}^{2+} + 2\text{SO}_4^{2-}

This step generates ferrous iron, which bacteria reoxidize to ferric for continued leaching.^[37] Notable examples include the large-scale heaps at Chuquicamata in Chile, covering over 1 km², where bioleaching of low-grade sulfides has produced significant copper output, demonstrating the commercial viability of these surface-based techniques.^[39]

In Situ Biomining

In situ biomining represents an innovative underground extraction technique that solubilizes metals directly within ore deposits without the need for excavation, relying on microbial catalysis to target sulfide minerals in deep or inaccessible formations. The process begins with the injection of oxygenated, acidic lixiviant solutions—typically sulfuric acid-based with dissolved oxygen and ferric iron—into the ore body, often through flooded underground mine workings or fractured strata. Acidophilic microorganisms, such as those from the Acidithiobacillus genus, colonize the subsurface environment and oxidize the sulfides, liberating metals into a soluble form as part of the pregnant leach solution (PLS). This PLS is subsequently pumped to the surface via recovery wells for further processing and metal precipitation. Ongoing pilots, such as the EU's BIOMOre project at Rudna mine in Poland (2015-2020) and subsequent studies as of 2023, continue to test indirect bioleaching at depths up to 1 km.^[40]^[41]^[42] Technical implementation requires strategic borehole drilling to enhance ore permeabilization through hydraulic fracturing or natural fissure exploitation, ensuring efficient lixiviant distribution. Injection occurs at controlled flow rates of 5-20 L/min per well, maintaining a highly acidic pH below 2 and temperatures of 20-50°C to optimize microbial activity and reaction rates; these conditions are often achieved naturally via the exothermic oxidation process, with recirculation of regenerated ferric iron from surface bioreactors. The general microbial-mediated dissolution of metal sulfides follows the adapted reaction:

\text{MS} + 2\text{O}_2 + 2\text{H}^+ \rightarrow \text{M}^{2+} + \text{SO}_4^{2-} + \text{H}_2\text{O}

where MS denotes the metal sulfide and the process generates sulfuric acid in situ, sustaining the low pH. Recovery involves pumping the PLS to surface solvent extraction and electrowinning plants, where metals are stripped and purified.^[43]^[41] One key advantage of in situ biomining is its reduced surface footprint, avoiding large-scale earthmoving and infrastructure typical of conventional mining, which minimizes ecosystem disruption and land rehabilitation needs. Capital costs are substantially lower than those for open-pit operations due to eliminated excavation and milling requirements, making it viable for deep-seated or low-grade deposits that are otherwise uneconomic. For instance, conceptual and pilot applications target deep copper sulfides, such as in Poland's Rudna mine, where the method suits uneconomic remnants below 1 km depth.^[40]^[44] Despite these benefits, in situ biomining is constrained by slow leaching kinetics, often requiring 1-5 years for substantial metal mobilization due to limited subsurface flow and microbial colonization rates. Groundwater contamination poses a significant risk, as acidic, metal-bearing leachates could migrate beyond the ore zone if permeability barriers fail, necessitating robust monitoring and containment strategies. To date, the approach remains largely at the pilot scale, highlighting scalability hurdles for broader commercialization.^[41]^[40]

Applications in Metal Recovery

Base Metals Extraction

Biomining plays a dominant role in the extraction of base metals, particularly copper, where it accounts for approximately 15% of global production. This process is especially effective for low-grade chalcopyrite ores containing 0.4-0.6% copper, which are uneconomical for traditional smelting. Through heap leaching, microorganisms such as Acidithiobacillus ferrooxidans oxidize sulfide minerals, producing sulfuric acid and ferric iron that facilitate the dissolution of copper into soluble copper sulfate (CuSO₄). Recovery efficiencies in these operations typically reach 80-90%, enabling the processing of vast ore volumes that would otherwise be discarded.^[40]^[30] A prominent example is the Escondida mine in Chile, the world's largest copper producer, which has utilized bioleaching since the 1990s to recover over 500,000 tons of copper annually from low-grade oxide and sulfide ores. At Bingham Canyon in the USA, bioleaching contributes to the mine's total output of around 300,000 tons of copper per year (as of 2025), supporting approximately 25% of production through enhancement of solvent extraction-electrowinning (SX-EW) processes for secondary minerals.^[45]^[46] The Talvivaara mine in Finland (now operated as Terrafame since 2017 following environmental challenges and bankruptcy) demonstrates integrated nickel-copper biomining, where bioheap leaching recovers copper alongside primary nickel targets from polymetallic black schist ores, despite past controversies involving groundwater contamination. These operations integrate biomining with downstream electrowinning to produce high-purity cathode copper.^[19]^[47]^[48] Nickel extraction via biomining targets both laterite and sulfide ores, with biooxidation achieving recovery rates of 70-85% through heap or tank leaching methods. For saprolite laterites, hybrid processes like roasting followed by bioleaching enhance accessibility of nickel by partial sulfation before microbial oxidation. The Talvivaara operation exemplifies this, yielding about 70% nickel recovery after 13-14 months of primary heap bioleaching, with co-recovery of copper at lower rates due to mineral associations. These approaches are particularly viable for low-grade deposits, integrating with precipitation or electrowinning for metal refinement.^[49]^[48] Other base metals, such as zinc and cobalt, benefit from biomining in pilot and commercial scales. Zinc recovery from sphalerite ores reaches up to 70% in bioleaching pilots, leveraging acidophilic bacteria to oxidize zinc sulfides in stirred-tank or heap configurations. For cobalt, bioleaching of sulfide-rich tailings achieves extractions of around 90%, as demonstrated in mini-pilot studies using iron- and sulfur-oxidizing consortia. These processes often recover multiple metals simultaneously and culminate in electrowinning for pure metal production, offering a sustainable alternative to pyrometallurgy.^[50]^[51] Biomining for base metals provides notable environmental advantages, including a reduction in smelting-related emissions by up to 50% through avoidance of high-temperature processes and lower energy demands. At sites like Escondida, this translates to decreased SO₂ releases and minimized waste generation compared to conventional methods.^[47]

Precious Metals Recovery

Biomining plays a crucial role in recovering precious metals, particularly gold and silver, from refractory ores where the metals are encapsulated within sulfide minerals such as pyrite and arsenopyrite. Approximately 60-70% of global gold reserves are refractory, requiring pretreatment to liberate the gold for subsequent extraction via cyanidation. Biooxidation processes oxidize these sulfide matrices, exposing the precious metals and enabling high recovery rates, typically achieving 90-95% gold extraction during cyanidation following treatment.^[52]^[53] For gold recovery, established biooxidation methods like the BIOX® process utilize acidophilic bacteria to break down refractory sulfides in agitated tanks, followed by conventional cyanidation. The Albion Process™ complements this by combining ultrafine grinding with atmospheric oxidative leaching, further enhancing liberation of encapsulated gold particles. These techniques are particularly effective for low-grade ores containing less than 1 g/t Au, making economic extraction viable where traditional methods fail. Silver is often co-extracted alongside copper or gold, with bioleaching targeting minerals like acanthite (Ag₂S) in heap operations, yielding 60-80% recovery rates.^[54]^[55]^[56] The integrated biomining workflow for precious metals typically involves bioleaching and oxidation to pretreat the ore, followed by cyanide leaching to dissolve the liberated metals and carbon adsorption to recover them from solution. Notable commercial examples include the São Bento mine in Brazil, operational from 1991 to 2013, which produced up to 100,000 ounces of gold annually using BIOX® pretreatment on refractory sulfide ores. Similarly, Newmont's Carlin operations in the USA implemented heap biooxidation for whole-ore treatment starting in 2000, processing Carlin Trend refractory deposits to achieve viable gold recovery. These processes also reduce cyanide consumption by up to 30% compared to direct cyanidation of untreated refractory ores, minimizing environmental risks while improving overall efficiency.^[57]^[58]^[59] In some sandstone-hosted deposits, biomining facilitates co-recovery of uranium alongside precious metals, with bioleaching achieving approximately 70% uranium recovery in Wyoming's roll-front deposits through microbial oxidation of organic matter and reduction zones. This approach leverages acid-tolerant bacteria to enhance solubility in situ or heap configurations, supporting multifaceted metal extraction from complex geological settings.^[60]

Rare Earth Elements and E-Waste

Biomining has emerged as a promising method for recovering rare earth elements (REEs) from secondary sources such as mine tailings and phosphogypsum, leveraging acidophilic bacteria like Acidithiobacillus ferrooxidans to solubilize metals including neodymium (Nd) and lanthanum (La). In a two-step bioleaching process using co-cultures of A. ferrooxidans and Acidiphilium cryptum, recoveries reached 70.7% for Nd and 84.5% for La from phosphogypsum, demonstrating enhanced solubilization through biological acid production and jarosite formation. Similarly, single-step bioleaching with A. ferrooxidans from phosphate rock achieved 32.5% recovery for Nd and 37.0% for La under optimized conditions of pH 2 and 1% pulp density. These microbial processes reduce reliance on external chemical acids compared to traditional hydrometallurgy, promoting lower environmental impact through in situ acid generation via sulfur oxidation.^[61]^[62]^[61] In e-waste recycling, biomining targets printed circuit boards (PCBs) to extract REEs alongside precious metals like gold (Au), palladium (Pd), and copper (Cu), using fungi such as Aspergillus niger to produce organic acids like citric and gluconic acid for metal solubilization. Bioleaching with A. niger and mixed cultures has yielded up to 100% Cu recovery and 48% Au recovery from PCBs over 28-30 days, while REE recoveries, including cerium (Ce), europium (Eu), and yttrium (Y), reached 80-99% in optimized fungal and bacterial systems. Processes adapted for urban mining, such as bioleaching variants inspired by commercial technologies like BioX, enable selective recovery from complex e-waste matrices without high-energy smelting.^[63]^[63]^[63] Key mechanisms in REE biomining include biosorption, where microbial cell surfaces bind REE ions, and bioaccumulation, involving intracellular uptake facilitated by specialized proteins like lanmodulin (LanM) in methylotrophic bacteria. LanM exhibits picomolar affinity for lanthanides, enabling selective binding and separation of REEs from mixed solutions with high specificity. For instance, Lawrence Livermore National Laboratory (LLNL) research in 2024 utilized engineered LanM proteins for biosorption from coal byproducts, achieving high selectivity for light REEs in low-grade feedstocks like coal fly ash.^[64]^[65]^[66] These approaches offer advantages in handling heterogeneous waste matrices, recovering critical REEs such as dysprosium essential for magnets and electronics, while minimizing toxic outputs compared to pyrometallurgical methods. Projections indicate that biomining could contribute significantly to REE supply diversification by 2025, potentially meeting a growing share of demand amid geopolitical supply constraints. A notable case is the EU-funded DEMETER project (2022-2025), which concluded in 2025 having developed bioleaching protocols for REE extraction from e-waste, integrating microbial consortia to achieve scalable urban mining with reduced chemical inputs and demonstrating improved recovery efficiencies in pilot tests.^[67]^[68]^[69]^[70]

Economic and Environmental Considerations

Economic Feasibility

Biomining exhibits a favorable cost structure compared to traditional smelting and pyrometallurgical methods, primarily due to its reliance on microbial processes that eliminate the need for high-temperature furnaces and extensive infrastructure. Capital expenditures (CAPEX) for commercial-scale biomining operations typically range from USD 100-500 million for large-scale heap or tank setups, representing a substantial reduction—often 30-60% or more—of the costs associated with equivalent pyrometallurgical facilities.^[71] Operating expenditures (OPEX) for biomining, such as heap or dump leaching, are estimated at USD 0.5-2 per kg of copper recovered, lower than the USD 3-6 per kg for pyrometallurgical processing of low-grade ores, enhancing viability for uneconomical deposits.^[23] Revenue generation in biomining is driven by its applicability to low-grade ores containing less than 0.5% metal content, achieving recovery rates of 60-88% through bioleaching processes, which extends the economic life of deposits otherwise unviable for traditional extraction. Payback periods for biomining projects are typically 1-5 years, supported by steady metal output and lower ongoing costs once operational. The global biomining market, valued at USD 2.1 billion in 2024, is estimated at USD 2.3 billion in 2025, reflecting growing adoption for sustainable metal recovery amid depleting high-grade reserves. In 2025, U.S. policy reports emphasize investing in biomining for domestic critical mineral supply, potentially boosting market growth.^[71]^[72]^[73]^[74] In comparisons to conventional methods, biomining offers energy savings of up to 30%, consuming around 250 kWh per ton of ore processed without the high-heat roasting required in pyrometallurgy. Water usage is also reduced, at approximately 0.3 tons per ton of ore in heap bioleaching, about 50% less than typical hydrometallurgical processes, enhancing return on investment (ROI) particularly for remote or water-scarce sites where infrastructure costs are prohibitive.^[75]^[72] Economic viability of biomining is influenced by ore mineralogy, with sulfide ores particularly suited due to microbial affinity, optimal scales exceeding 1 million tons of ore per year for heap operations, and sensitivity to metal prices—such as copper exceeding USD 3 per pound to ensure profitability. A notable case is the Talvivaara mine in Finland, with total investments exceeding €1 billion (approximately USD 1.1 billion) and targeting 50,000 tons of nickel production annually, but it filed for bankruptcy in 2014 due to environmental overruns, production shortfalls, and fluctuating nickel prices.^[76]^[71]^[77]^[78]

Challenges and Drawbacks

One of the primary technical challenges in biomining is the slow kinetics of the bioleaching process, which typically requires weeks to months for metal extraction, in contrast to the days or hours needed for pyrometallurgical methods. This delay arises from the biological nature of microbial oxidation, where acidophilic bacteria like Acidithiobacillus ferrooxidans gradually oxidize sulfide minerals, limiting throughput in industrial operations. Another key issue is passivation, where iron precipitates such as jarosite form layers that block mineral pores and hinder microbial access, particularly in chalcopyrite leaching. To mitigate passivation, the addition of chloride ions has been shown to enhance dissolution rates by preventing sulfur layer formation and catalyzing copper release, though concentrations must be carefully controlled to avoid microbial toxicity. Biomining microorganisms are also highly sensitive to variations in temperature and pH, with optimal ranges typically between 30–45°C and pH 1.5–2.5; deviations can inhibit growth and reduce efficiency. Environmental risks associated with biomining include the potential generation of acid mine drainage (AMD) when leachates are unmanaged, leading to soil and water acidification. Re-processing of mine tailings through biomining can mobilize heavy metals like arsenic and cadmium, exacerbating leakage into surrounding ecosystems if containment fails. Mitigation strategies involve using impermeable liners in heap setups to prevent percolation and adding lime for neutralization of acidic effluents, which raises pH and precipitates metals for safer disposal. Operationally, heap and dump leaching in biomining are weather-dependent, as excessive rainfall can dilute the acidic lixiviant and slow microbial activity, while arid conditions may limit irrigation. High salinity levels exceeding 50 g/L, often from seawater or brine recycling, inhibit microbial growth by disrupting cell membranes and enzyme function in most acidophiles, though halotolerant strains like Acidihalobacter prosperus offer partial adaptation. Biomining generally poses lower health and safety risks than traditional mining due to reduced need for explosives and heavy machinery, but biohazards from extremophilic microbes, such as aerosolized Acidithiobacillus species, require protective measures like biosafety protocols. Scalability remains limited for complex, low-grade ores containing multiple sulfides, as microbial consortia struggle with inhibitory impurities, necessitating pre-treatment or strain optimization. To address these hurdles, brief applications of genetic engineering have enhanced strain robustness; for instance, CRISPR-Cas9 editing of Acidithiobacillus ferridurans improves tolerance to metals and chloride, boosting leaching efficiency. Closed-loop systems, which recycle process water and minimize evaporation, can significantly reduce overall water loss, promoting sustainability in water-scarce regions.

Bioremediation Applications

Biomining microbes, particularly sulfate-reducing bacteria (SRB) such as Desulfovibrio species, play a key role in remediating mine waste by precipitating heavy metals as insoluble sulfides in acid mine drainage (AMD), which typically has a pH of 3-5. These bacteria reduce sulfate to sulfide under anaerobic conditions, enabling the removal of metals like zinc and copper with efficiencies ranging from 80% to over 95% in laboratory and field settings. For instance, Desulfovibrio strains tolerate metal concentrations up to 100 mg/L while maintaining high sulfate reduction rates, facilitating in situ precipitation without extensive chemical inputs.^[79]^[80] In tailings treatment, bioleaching processes recover residual metals from mining wastes while stabilizing the material through microbial activity, reducing environmental mobility. At the Berkeley Pit in Montana, USA—an abandoned copper mine site flooded since the 1990s—pilot-scale applications of bacterial sulfate reduction have demonstrated ongoing microbial neutralization of acidic waters laden with metals like iron and manganese. These efforts integrate SRB to promote sulfide precipitation, mitigating AMD generation and enabling partial metal recovery as a secondary benefit.^[81]^[82] Beyond mining contexts, microbes similar to those in biomining contribute to oil spill cleanup through biosurfactant production, which enhances hydrocarbon emulsification and bioavailability for degradation. Pseudomonas species produce rhamnolipids, glycolipid surfactants that disperse oil into microdroplets, accelerating microbial breakdown. In the 1989 Exxon Valdez spill, which released approximately 42 million liters of crude oil into Alaska's Prince William Sound, bioremediation efforts incorporating such biosurfactants aided in achieving up to 70% biodegradation of spilled hydrocarbons within the first year, as nutrients and surfactants boosted indigenous microbial populations.^[83]^[84] Additional applications include e-waste detoxification via fungal biosorption, where metal-accumulating fungi bind heavy metals like copper and iron from electronic scraps. Fungi such as Pleurotus florida exhibit high biosorption capacities, removing over 95% of copper (up to 97 mg/g) through cell wall binding and enzymatic activity, offering a low-energy method to detoxify leachates from discarded devices. Similarly, uranium bioremediation in groundwater leverages dissimilatory metal-reducing bacteria at sites like the Old Rifle facility in Colorado, where 2000s pilot tests injected electron donors like ethanol to stimulate U(VI) reduction to immobile U(IV), lowering soluble uranium concentrations from 5 μM to below 1 μM over months.^[85]^[86] These bioremediation strategies are inherently in situ and cost-effective, with operational costs for microbial metal removal estimated at $1-5 per kg compared to over $10 per kg for conventional chemical precipitation methods, while simultaneously integrating resource recovery with environmental stabilization.^[87]^[88]

Future Directions

Sustainability Enhancements

Recent advances in biomining technologies during the 2020s have focused on minimizing energy and water demands, with bioleaching processes demonstrating lower energy consumption than conventional pyrometallurgical methods by eliminating the need for energy-intensive roasting steps.^[89] Closed-circuit heap leaching systems further enhance resource efficiency by recycling approximately 80-85% of process water, reducing reliance on freshwater sources and mitigating risks of water scarcity in arid mining regions.^[90] Emissions from biomining are notably lower than traditional methods that rely on fossil fuel combustion.^[91] Additionally, certain acidophilic microbes employed in these processes facilitate CO₂ fixation, enabling carbon-neutral operations by converting atmospheric CO₂ into biomass and carbonates during metal oxidation.^[92] In support of circular economy principles, biomining enables the reprocessing of mine tailings to recover residual metals such as copper, nickel, zinc, and cobalt, transforming waste into valuable resources and reducing the environmental burden of legacy mining sites.^[89] Regulatory frameworks have increasingly favored biomining through standards like the Initiative for Responsible Mining Assurance (IRMA) certification, which emphasizes low-impact extraction methods including biological processes to meet environmental and social benchmarks set by the EU and UN.^[93] For instance, Mintek's green bioleaching initiatives in South Africa leverage microbial oxidation to avoid sulfur dioxide release during sulfide mineral processing, offering substantial reductions in SO₂ emissions compared to smelting.^[94] Life-cycle assessments (LCAs) of biomining operations reveal lower global warming potential than pyrometallurgical alternatives, primarily due to reduced energy inputs and emissions.^[95] Integration with renewable energy sources, such as solar-heated heaps to maintain optimal microbial activity temperatures, further lowers the carbon footprint and enhances overall sustainability in remote mining operations.^[96] As of 2025, pilot projects integrating biomining with recycling have shown promise in supplying critical metals for renewable energy technologies.^[97]

Emerging Innovations

Recent advancements in biomining are pushing the boundaries of microbial applications beyond traditional terrestrial ore processing, incorporating fungi, extraterrestrial environments, engineered biomaterials, genetic modifications, and computational optimizations to enhance efficiency and expand resource recovery. Fungi offer promising alternatives for leaching metals from e-waste and neutral pH ores through the production of organic acids such as citric and oxalic acids, which solubilize metals without requiring extreme acidity. For instance, Penicillium expansum has been utilized in bioleaching rare earth elements (REEs) from electronic waste, where mechanisms including pH control, organic acid biosynthesis, and phosphate bioavailability enable effective extraction under milder conditions compared to bacterial methods.^[98] In a 2024 study, this fungus achieved substantial REE recovery from phosphor-containing waste, demonstrating up to 80-90% solubilization of key elements like europium and terbium after optimization of culture conditions.^[99] These fungal approaches are particularly suited for urban mining scenarios, where low-grade, neutral-pH materials predominate. Biomining concepts are extending to extraterrestrial resource utilization, with NASA and ESA exploring microbial extraction from lunar and Martian regolith to support in-situ resource utilization for future missions. Acidithiobacillus species, known for iron and sulfur oxidation on Earth, have been tested in microgravity on the International Space Station, successfully extracting iron and aluminum from regolith simulants by forming biofilms that enhance mineral dissolution despite reduced sedimentation.^[100] These experiments simulate Mars gravity conditions and indicate that biomining could yield essential metals like Fe and Al for habitat construction. As of November 2025, with Artemis II delayed to 2026, such innovations remain in conceptual and ISS testing phases, addressing the logistical challenges of transporting materials from Earth toward potential self-sustaining colonies.^[101] Hybrid biomaterials are emerging as selective tools for REE recovery, leveraging engineered proteins like lanmodulin (LanM) for high-affinity binding. LanM, derived from methylotrophic bacteria, exhibits exceptional selectivity for REEs over competing ions, achieving binding efficiencies exceeding 95% in low-pH environments through its unique beta-hairpin structure that coordinates lanthanides.^[102] When immobilized on magnetic nanoparticles, LanM forms bio-nano hybrids that integrate microbial leaching with targeted adsorption, accelerating overall metal recovery by up to twofold compared to free microbial systems by enhancing mass transfer and specificity.^[64] These hybrids show promise for processing complex ores or e-waste streams. Genetic engineering via CRISPR-Cas systems is tailoring microbes for harsher biomining conditions, such as elevated temperatures and metal toxicities. For example, CRISPR editing of Acidithiobacillus ferridurans has introduced genes mitigating toxic ion release while boosting tolerance to heavy metals, allowing sustained activity in high-stress leachates.^[103] Engineered strains now exhibit optimal performance at 60°C, expanding applicability to refractory ores that require thermal pre-treatment, with projections of 50% efficiency improvements in leaching rates by 2030 through iterative synthetic biology refinements.^[104] Microbial consortia for enhanced biomining, particularly for urban mining of battery wastes, have shown improved performance. In lithium-ion battery recycling, bioleaching consortia recover up to 95% of lithium and 96% of cobalt using acid-producing bacteria in multi-step processes, minimizing energy inputs while targeting specific electrode metals.^[105] Such optimizations could revolutionize closed-loop recovery from electronic discards, aligning with circular economy goals.^[106]

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(PDF) Urban biomining: lithium recovery from spent batteries ...
Aug 9, 2025 · The first step consisted of lithium extraction from spent batteries, using bacterial and fungal acid extrolites. The second step explored lithium recovery.<|control11|><|separator|>