What Is Biomining? How Microbes Pull Copper and Gold From Ore

Picture a copper mine and you probably see crushers, furnaces and sulfuric acid. A good share of the work at some of the world’s largest operations is actually done by bacteria. Biomining, the use of microbes to pull metals out of ore, is often linked to about 20% of global copper output, though that figure is contested.

The timing matters. Ore grades are falling, electrification is lifting demand for copper, nickel and cobalt, and miners want processing routes that use less energy than a smelter.

The headline share is less clean than it looks. Popular estimates of 20-25% blend microbial activity with broader acid heap leaching, so how you define the process shapes the number you see.

Here is how biomining works, which metals and ores suit it, where it has decades of commercial history, and where the claims run ahead of the evidence. You will finish able to test any biomining pitch on its own terms.

What is biomining, and how do microbes pull metal out of rock?

Biomining is the umbrella term for using microorganisms to recover metals. Its main working method is bioleaching.

Biomining versus bioleaching Biomining covers any use of microbes in metal recovery; bioleaching is the specific step where microbes help dissolve metal out of ore into solution.

The microbes do not eat metal. They act as chemical catalysts and regenerators, keeping alive the reactions that break sulfide minerals apart. A sulfide mineral is a compound of a metal and sulfur, such as chalcopyrite, the most common copper ore.

A 2025 review in Frontiers in Bioengineering and Biotechnology separates two modes:

1. Direct bioleaching: microbes attach to the mineral surface and speed up its oxidation.
2. Indirect bioleaching: microbes regenerate ferric iron and sulfuric acid, which then attack the mineral chemically, without the microbes touching every particle.

In a real heap, both modes run at once. The split is useful for understanding the chemistry, not for describing what actually happens on site.

You can think of the bioleaching process as a loop: microbes regenerate ferric iron and acid, the oxidant attacks the sulfide, and the dissolved metal moves on to recovery. Reading company reports gets easier once you can follow that loop.

Which bacteria do the work?

The biomining bacteria you will see named most often fall into three groups:

• ***Acidithiobacillus ferrooxidans and Leptospirillum*:** convert ferrous iron to ferric iron, the oxidant that dissolves sulfide minerals.
• ***Acidithiobacillus thiooxidans*:** oxidises sulfur to produce sulfuric acid and clears sulfur layers that can slow dissolution.
• **Thermophiles such as Sulfobacillus, Metallosphaera sedula and Acidianus:** heat-tolerant microbes that help break down stubborn chalcopyrite at higher temperatures.

What conditions do they need?

These organisms are acidophiles, meaning they thrive in strong acid, commonly around pH 1.5-2.0. Gold systems of the BIOX type run at roughly 40-45°C, and one 2025 report described about 42°C as favourable for the bacterial mix.

Thermophilic systems oxidise faster but demand tighter control of heat, aeration and redox potential (a measure of how strongly a solution oxidises). Because microbes regenerate the oxidant rather than work alone, heat, oxygen and acid balance decide whether an operation succeeds. When a startup promises a better microbe, ask whether it also solves those engineering conditions.

Which metals and ores suit biological extraction, and where is it already proven?

Biomining is a family of processes, and ore type picks the route. The evidence is strongest for gold and copper and thinner as you move toward newer applications.

Gold: stirred tanks and refractory ore

Refractory gold ore locks fine gold particles inside sulfide minerals, so cyanide alone cannot reach them. BIOX uses bacteria in stirred tanks to oxidise those sulfides first, then conventional carbon-in-leach recovery takes over.

Ore mineralogy decides the route: on free-milling oxide gold, cyanide leaching recovers over 97%, but on refractory sulfide ore that falls sharply, which is where BIOX pretreatment earns its place.

The process was first commercialised at Fairview in 1986. Metso reported 13 commercial plants by May 2024, some counts reach 14, and a Danfoss/Biomin document cites seven, a gap that probably reflects installed versus operating definitions. No single recovery percentage applies, because results depend on the ore. The Sabodala-Massawa expansion in Senegal shows the process is still being chosen for new gold capacity.

Copper and nickel: heaps and low-grade sulfides

At Escondida, BHP leaches low-grade sulfide ore on heaps with microbial help. Its leach electrowinning circuit has a nameplate of about 350,000 tonnes a year but produces about 200,000 tonnes, according to BHP’s November 2024 site tour material, and the low-grade sulfide stream supplied about 19% of recoverable copper in FY2024. The technology keeps running while its feed quality declines.

Terrafame in Finland extends the model to polymetallic ore, reporting 29,858 tonnes of nickel and 52,192 tonnes of zinc in 2024, plus smaller copper, cobalt and uranium volumes. Its battery-chemicals plant has about 170,000 tonnes a year of nickel sulfate and 7,400 tonnes of cobalt sulfate capacity, according to the company.

Then there is the share dispute. Mining Technology puts bioleaching at up to about 20% of world copper, while Discovery Alert cites 20-25% for heap bioleaching.

A stricter count Analyst Aaron Blotnick, quoted by Discovery Alert, places strictly microbial biomining below 10%, with broader leaching near 20%.

All three figures come from secondary sources. A headline claiming a fifth of copper comes from biomining is a broad heap-leaching estimate, not a measure of what microbes alone produce.

Why is the industry paying attention, and where does the hype outrun the evidence?

Commercial history explains why biomining works. The pressure on the mining industry explains why interest is growing now.

What is driving the interest

• Falling grades: EY’s 2025 analysis found planned copper greenfield projects averaging about 0.5% copper or lower, against about 0.8% in 2010.
• Electrification demand: copper, nickel, cobalt and zinc feed batteries and grids, and Terrafame links leaching directly to battery chemicals.
• Tailings reprocessing: waste rock and stockpiles become potential resources where flotation or smelting would not pay.
• Lower energy: skipping the furnace can cut energy use and sulfur dioxide emissions.
• E-waste: microbes are being tested on electronics, though the material needs sorting and shredding first.

Capital is following. Endolith raised a $13.5 million Series A led by Squadra Ventures on 13 November 2025, with a further $3 million tranche expected, after validation through BHP’s Think & Act Differently programme, and it is preparing mine-site pilots. Rio Tinto had gathered more than 2,500 samples through its Mining Microbiome Analytics Platform by June 2025. A reported Rio Tinto and BioleachTech tailings pilot appears only in a market report and remains unconfirmed.

Behind the funding headlines sits a mix of established operators and venture-backed biomining companies, and you can judge each one by whether its results come from a mine-site, a pilot or a laboratory.

Energy claims need the same care. Terrafame says its process uses about 90% less energy than alternatives, and a 2025 market analysis cites 0.8-1.2 MJ/kg for bioleaching against 13-16 MJ/kg for smelting. Both depend on the baseline and system boundary chosen.

Proven, promising or promotional?

No specific 2024-2026 microbial project was found for Freeport-McMoRan, Moa Nickel or Metals Biotech. When you meet a funding or energy claim, ask whether it rests on a mine-site result or a laboratory test, and what it is compared against.

What limits biomining, and what do the numbers say about speed, cost and risk?

The trade-off becomes clear when you line up the clocks.

Speed, recovery and cost

For e-waste, a 2026 secondary comparison put bioleaching at 50-85% recovery for $300-700 per tonne, against smelting at 85-98% for $800-1,500. Cheaper, but less complete.

Hours versus months is the whole story. Biomining wins on cost and energy for low-grade or refractory material, and loses where speed and predictability on high-grade concentrate count most.

Technical, environmental and financial risks

• Passivation: sulfur-rich layers can coat chalcopyrite and stall recovery.
• Temperature: cold slows microbes, so sites like Terrafame need heat management.
• Acid drainage: the same biology can create acidic, metal-laden runoff; Finnish Minerals Group flags solution circulation and water management as key risks.
• Scale-up: laboratory recoveries rarely transfer cleanly to heaps.
• Capital: Terrafame’s secondary leach area carries more than €200 million in commitments.
• Regulation: acidic solutions and closure liabilities attract heavy permitting.
• Price exposure: low energy use does not protect margins.

Technical success is not financial immunity Terrafame’s 2024 EBITDA fell to €16.1 million from €36.2 million on net sales of €544.5 million, as nickel and nickel-sulfate prices weakened.

Past performance does not guarantee future results, and reported recovery figures vary with ore, scale and operating conditions.

For readers wanting to go further on passivation and ramp-up timing, our deep-dive into sulphide ore bioleaching risks explains why chalcopyrite resists standard bacteria.

Where biomining fits, and what to check before trusting a claim

Biomining is a proven family of processes, strongest in low-grade copper sulfide heaps, heap-suited nickel and polymetallic ores, refractory gold and selected waste streams. It does not replace smelting or pressure oxidation across the board.

Before you trust a claim, run four checks:

1. Share definition: does the figure count strictly microbial output or all heap leaching?
2. Data stage: is the recovery result from a laboratory, a pilot or a commercial plant?
3. Energy baseline: what process and system boundary does the saving compare against?
4. Price exposure: how sensitive is the project to the commodity it sells?

Next, watch Terrafame’s secondary leaching area, planned for 2026, and whether startups such as Endolith move from column tests to mine-site results. These statements are speculative and subject to change based on market developments and company performance.

This article is for informational purposes only and should not be considered financial advice. Investors should conduct their own research and consult with financial professionals before making investment decisions.