Tank Leaching vs Heap Leaching: 2026 Decision Guide

Last updated: 2026-10-19 · By the Lexin Hydromet Process Engineering Team

Tank leaching vs heap leaching is the first flowsheet decision for any ore body that responds to acid or cyanide, because it fixes recovery, capital expenditure (CAPEX) and schedule before a single vessel or liner is ordered. A tank circuit typically recovers 10–25 percentage points more metal than a heap on the same feed, and this guide sets out, with numbers, when that premium is worth paying.

Key Takeaways

• Recovery: agitated tank circuits deliver 85–92% on free-milling gold and 75–90% on oxide copper; heap circuits deliver 60–80% and 60–75% respectively on comparable feed.
• Residence time is the dividing line: 12–48 hours in tanks versus 30–180 days on pads.
• CAPEX: a heap route costs roughly one-third to one-half of a tank route per annual tonne, but it buys lower recovery, not a different process.
• Clays and fines decide more routes than grade does: above about 15–20% fines, a heap needs agglomeration at best and a tank circuit at worst.
• Water balance, climate and altitude constrain heap design more than tank design; only column test work converts these rules of thumb into bankable numbers.

How Tank Leaching Works — and What It Buys You

Tank leaching is a stirred-vessel extraction route that contacts finely ground ore as a 35–45% solids slurry with reagent — dilute sulphuric acid for oxide copper and uranium, dilute sodium cyanide (NaCN) at pH 10.5–11 for gold and silver — in a train of mechanically agitated, baffled vessels. Ore is crushed and milled to a P80 of roughly 45–106 µm (about 140–325 mesh) so that the target mineral is liberated, and residence time per vessel is set so the whole train delivers 12–48 hours of contact. Dissolved oxygen, Eh (oxidation-reduction potential), pH and reagent strength are measured and controlled continuously, which is the route’s defining advantage: the chemistry is under the operator’s command at all times.

how Leaching is decided

What the tanks buy is ceiling recovery and speed. Because every particle is suspended and every surface is wetted, extraction is limited by mineral dissolution kinetics rather than by percolation through a static bed. A well-run agitated leaching tank train on free-milling gold routinely returns 88–92% overall recovery, and on acid-soluble oxide copper 80–90% is achievable where a heap on the same ore would stop at 65–75%. The price is the highest capital intensity of any ambient-pressure route: milling, thickening, tanks, agitators, air or oxygen delivery, and a solid-liquid separation and recovery section downstream, all sized to the full mill throughput.

How Heap Leaching Works — and Where It Wins

Heap leaching is a percolation extraction route that irrigates crushed ore stacked on an engineered, geomembrane-lined pad with the same acid or cyanide reagents, collecting the metal-bearing liquor as pregnant leach solution (PLS) at the pad’s solution collection system. Ore is crushed to a P80 of roughly 12–50 mm (0.5–2 in) — or stacked run-of-mine where permeability allows — often agglomerated with cement or acid to bind fines, stacked in lifts of 4–10 m (13–33 ft), and irrigated at 5–15 L/h/m² (0.12–0.37 gal/h/ft²). Dissolution then proceeds by infiltration and diffusion over 30–180 days of active leach plus rest periods, with leach cycles extending into years for secondary copper sulphides under bacterial action.

ASME VIII Div 1 vs Div 2 in practice

Where the heap wins is cost per tonne and scale. No mill, no thickeners, no agitators: the ore is never ground, so comminution energy — typically 15–35 kWh/t in a milling circuit — is avoided almost entirely. A heap leaching system specified around liner integrity, draindown and agglomeration quality can be built for a fraction of a tank route’s capital cost, which is why heaps dominate low-grade oxide copper in Chile and Peru and treat a large share of the world’s gold below about 1 g/t Au. The corresponding limits are recovery and control: the operator irrigates a static bed and cannot see or adjust the chemistry at the particle surface, so percolation problems — channeling, compaction, fines migration — translate directly into unrecovered metal.

Tank Leaching vs Heap Leaching: Head-to-Head Comparison

The table below collects the parameters that decide the tank leaching vs heap leaching choice in practice. All ranges are typical industry values for well-designed circuits and must be confirmed for the specific ore by test work — treat them as screening numbers, not guarantees.

Table 1 — Tank vs heap: head-to-head parameter comparison (typical ranges)

Two readings of Table 1 are worth making explicit. First, the residence-time gap of three orders of magnitude is not a drawback to be engineered away — it is the mechanism by which the heap converts low capital cost into lower recovery. Second, the routes are not competitors for the same ore at the same grade; they are competitors only where the ore is amenable to both, which is precisely why the decision rules later in this guide are stated per scenario.

How Much Recovery Do You Give Up on a Heap?

Recovery is the largest single number in the comparison and the one most often misjudged in early screening. The delta between routes comes from three mechanisms, in roughly equal parts for most ores:

• Liberation. A heap crushes to 12–50 mm (0.5–2 in); metal locked inside coarse particles is never wetted. In an ore where 15% of the gold sits in uncracked sulphide or silicate at heap crush size, that 15% is simply gone.
• Contact efficiency. Irrigation solution follows preferential flow paths. Channeling and local compaction leave dry zones — typically 10–25% of the stacked volume never sees solution at design flow, whatever the lift height.
• Time and passivation. Some minerals (chalcocite, covellite,some jarosite-hosted gold) dissolve too slowly or passivate within a heap’s practical cycle, whereas a tank’s elevated temperature, oxidant addition and fresh solution keep them dissolving.

The counterweights are real but bounded. Agglomeration is a pre-treatment step that binds crushed ore fines into permeable, competent granules with cement and strong acid before stacking, and it restores percolation on moderately clayed feeds. Agglomeration with cement (2–5 kg/t) and curing with strong acid lift percolation efficiency on clayed ores; crush-size optimisation and lift-height tuning add a few points; longer leach cycles buy recovery at the cost of pad inventory. In practice, a well-designed heap closes part of the gap but essentially never all of it: the 10–25 percentage-point recovery discount of Table 1 survives detailed design. On a 2 Mt/a (2.2 million short tons per year) ore at 0.5% Cu, each recovery point is roughly 100 t (110 short tons) of copper per year — at typical copper prices, several tens of millions of dollars of annual revenue. That arithmetic, not the CAPEX table, is what kills marginal heap projects.

The recovery comparison is also ore-specific in a way screening studies blur. Acid-soluble chrysocolla and atacamite respond well in both routes, so the delta may be only 8–12 points; where copper is held in secondary sulphides such as chalcocite, the delta can exceed 25 points and the heap may still not reach economic recovery at any cycle length. The same logic applies to gold: coarse free gold reports well to both routes; gold locked in pyrite reports to neither without pre-oxidation. The leaching pillar page covers how each mineral group behaves across all four industrial routes.

What Do Tank Leaching vs Heap Leaching Cost?

Cost comparison is only meaningful against a fixed ore, throughput and site, but the structure of the two cost bases differs enough to state generally. A tank route concentrates its capital in the grinding circuit, the tank train and the downstream recovery section (carbon adsorption, or solvent extraction and electrowinning (SX-EW) for copper); its operating cost is dominated by grinding energy, fresh reagent and continuous staffing. A heap route concentrates its capital in crushing, pad construction and ponds; its operating cost is dominated by crushing (if any), pumping, liner maintenance and reagent make-up against evaporation losses.

Table 2 — Indicative cost ranges (illustrative; 2026 dollars; Q4 2026 basis; confirm with vendor quotes and a location factor)

Three cautions on Table 2. Ranges are deliberately wide because location factors, reagent logistics and labour rates move individual line items by a factor of two between, say, coastal Chile and a landlocked West African site; the numbers are screening-grade and labelled illustrative for that reason. Second, the tank route’s CAPEX includes equipment that the heap project must replace with something else — most notably water and solution management: a heap without a well-designed drainage and storm system is not cheaper, it is a liability (see heap leach pad design). Third, OPEX per tonne is not the decision variable by itself; OPEX per pound or kilogram of recovered metal is, and the recovery delta of the previous section enters that number directly.

Which Should You Choose? A Numbered Decision Procedure

The choice between routes is a repeatable engineering procedure, not a preference. Applied in order, these seven steps resolve most ore bodies decisively:

1. Characterise the ore mineralogically. Quantify acid-soluble versus sulphide copper (or free versus refractory gold), gangue acid consumption (AEC), clay mineral speciation and fines content below 150 µm (100 mesh). No route discussion is meaningful before this step; a paste-pH and AEC test costs little and eliminates the worst surprises.
2. Establish amenability and kinetics for both routes. Run bottle-roll tests on milled pulp for the tank case and column tests at representative crush size for the heap case, in parallel. Column tests take 2–6 months — start them at the first drill-out, not after the pre-feasibility study.
3. Compare recoveries at equal reagent regimes. Express both routes’ projected recoveries as metal recovered per tonne of ore, using the column and bottle-roll data, corrected for scale-up (columns typically over-predict field recovery by 3–8 points).
4. Compute revenue delta. Multiply the recovery difference by grade, throughput and a conservative long-term price. This is the annual revenue the tank route must buy back with its extra CAPEX and OPEX.
5. Build both cost models. Estimate CAPEX and OPEX per Table 2 for both routes at the same throughput, including downstream recovery, water management and tailings or spent-ore handling. Compare NPV or IRR, not CAPEX alone.
6. Screen the site constraints. Water balance (arid versus tropical), seismicity, altitude, pad area availability, and clay/fines handling all feed back into the routes’ risk profiles differently. A route that is NPV-positive but water-infeasible is not a route.
7. Confirm with pilot work before commitment. Only a pilot-scale campaign — larger columns, agitated pilot tanks, or both — converts screening ranges into design values. Budget for it explicitly; pilot testing and flowsheet verification is the cheapest insurance in hydrometallurgy, typically 0.5–2% of project CAPEX against multi-point recovery risk.

Which Route Wins for Your Ore? Scenario Verdicts

The scenarios below apply the procedure to common situations. They are clearly labelled illustrative: each verdict assumes the stated head grade, mineralogy and site, and each must be re-derived from test work for a real ore body.

Table 3 — Ore-scenario decision table (illustrative verdicts)

Stated as decision rules with the numbers attached:

• For a 2 Mt/a (2.2 million short tons per year) oxidized copper ore at 0.5% Cu with low clay and a multi-decade resource, heap leaching is preferred because the recovery discount (typically 8–12 points on acid-soluble ore) costs less than US$ 10–15 M per year at conservative copper prices, while the tank route’s incremental CAPEX of US$ 20–50 M cannot be amortised over the thin margin per tonne. Ore-by-ore detail for this family is in copper oxide ore processing.
• For the same ore at 0.9–1.2% Cu and 1 Mt/a, tank leaching is preferred because each recovery point is now worth roughly US$ 3–4 M annually; the tank route pays back its premium within 2–4 years and de-risks the grade profile.
• For free-milling gold above about 1.5–2 g/t Au at moderate tonnage, tank leaching is preferred because a 15-point recovery delta on high grade dwarfs the OPEX saving of a heap.
• For free-milling gold below about 1 g/t Au at multi-million-tonne scale, heap leaching is preferred because no alternative recovers the metal at a positive margin — the heap’s low OPEX is the only economic envelope for the grade.
• For any ore with more than about 20–25% fines or dispersive clays, tank leaching is preferred regardless of grade, because percolation — the heap’s entire mechanism — cannot be stabilized reliably even with cement agglomeration.
• For mixed oxide–sulphide copper where neither fraction dominates, a hybrid flowsheet (heap for the oxide, tank or flotation-plus-leach for the sulphide) is preferred to forcing one route to do both jobs badly.

How Do Climate, Altitude and Water Balance Constrain the Choice?

Site physics often decides routes that ore chemistry leaves open, and the constraints bite unevenly.

Water balance. A heap is an open, evaporative system: solution applied to the pad loses water to evaporation and retains inventory in the pore space, and in arid sites such as the Atacama, evaporative losses can exceed 0.2 m³/t of ore, competing directly with process make-up in water-scarce regions. A tank circuit is a closed, pumped system: thickeners recover 70–85% of process water, and make-up is dominated by tailings losses rather than atmospheric losses. Counter-intuitively, the heap can still be the lower-net-water route where its recovery penalty avoids an entire tailings facility. In tropical high-rainfall sites the problem inverts: storm events load the heap’s ponds beyond design freeboard, and dilute, low-grade PLS floods the downstream plant. Both cases argue for sizing ponds against probable maximum precipitation (PMP) events, not average rainfall.

Altitude. Above roughly 4,000 m (13,100 ft) in the Andes, lower atmospheric pressure reduces oxygen partial pressure to about 60% of sea level. For oxide-leaching heaps this matters little; for bacterial (bioleach) heaps and any aerated tank it slows kinetics and inflates blower power. Equipment logistics at altitude — agitator seal performance, reduced human work capacity, freeze-thaw cycling on pad surfaces and ponds — add operating risk to both routes but compound on the heap’s exposed, weather-dependent surfaces.

Climate extremes. Freezing closes heap operations at high-latitude or high-altitude sites unless solution is heated or irrigation is seasonal; tanks housed in buildings continue year-round at the cost of enclosure CAPEX. Conversely, extreme heat accelerates cyanide degradation and evaporation on heaps and raises tank cooling loads. None of these effects is disqualifying alone; all of them shift the risk balance measurably toward the route with enclosed, controllable vessels.

Risk: What Can Go Wrong on Each Route?

The failure modes differ in kind, and procurement should price them in.

Tank-route risks concentrate in single points of failure: an agitator gearbox failure stops a train; liner failure in a tank can shut the whole circuit; a mis-sized thickener starves the recovery section. Mitigation is conventional — spare agitators, redundancy in pumping, robust materials of construction — and largely soluble with money, which is why tank-route risk is mostly a CAPEX problem. Design detail for the vessel itself (impeller selection, gas transfer, materials) is covered in agitated leaching tank design.

Heap-route risks are distributed and slow to detect, which makes them more dangerous per dollar. Liner punctures during stacking leak PLS to groundwater with multi-year remediation liabilities. Fines migration and compaction create perched zones that quietly strand metal for the life of the pad — and the loss surfaces only as an unexplained recovery shortfall, long after the stacking contractor has demobilised. Solution inventory mismatches (pond capacity versus storm events, surge versus draindown) convert weather into process losses. Mitigation is procedural: strict stacking protocols, lift-height control, draindown monitoring per lift, and liner quality assurance during installation. Both routes also carry reagent risk — cyanide management under the International Cyanide Management Code for heaps and tanks alike, and acid mist and handling protocols for tank circuits.

A final risk asymmetry: ramp-up. A tank circuit reaches design recovery within months because each batch is independent — problems are found and fixed per shift. A heap reaches pad-wide steady state over years, because early lifts’ performance is only observable after downstream processing has integrated them; a systematic error in early stacking propagates through the whole production profile. Projects with aggressive schedules or first-time operators should weight this asymmetry heavily in the tank leaching vs heap leaching decision.

FAQ (Frequently Asked Questions)

Can a heap leach project be upgraded to tank leaching later?
Physically yes — a tank train can be added beside an existing heap — but the economics rarely work retroactively. The heap’s recovery discount has already been incurred on years of production, and the tank addition still needs full milling and recovery plant CAPEX. It is far better to size the route correctly at study stage than to plan a conversion. Some operations do run both routes in parallel on different ore types from the start.

What ore grade justifies tank leaching over heap leaching?
There is no universal cut-off, but screening rules exist. For oxide copper, above roughly 0.7–0.8% Cu the recovery delta usually funds the tank route’s premium at moderate tonnages; below about 0.5% Cu the heap usually wins. For gold, 1.5–2 g/t Au marks a similar transition at moderate scale. The correct threshold depends on tonnage, recovery delta from test work, price and site costs — compute it per project.

How much clay can a heap leach pad tolerate?
Below about 10–15% fines, heaps percolate acceptably with standard agglomeration. Between 15 and 25% fines, performance depends on clay mineralogy: kaolinite is manageable with cement and acid curing, whereas smectite and dispersive clays cause collapse and channeling that no agglomeration reliably fixes. Above roughly 25% fines, tank leaching is normally the only dependable route. Confirm with percolation tests on agglomerated columns, not on dry screen fractions.

Which route uses less water per tonne of ore?
It depends on the site, not the route. Tank circuits recycle 70–85% of water through thickeners, losing most make-up to tailings. Heaps lose water to evaporation and pore retention — large in deserts, small in wet climates — but avoid tailings entirely. In arid regions a heap can consume more make-up water per tonne than a tank circuit; in wet regions the opposite holds. Model the full site water balance before claiming either route is “drier”.

How long from decision to first metal for each route?
A heap route typically reaches first metal 12–24 months after construction decision: pad construction and stacking can begin early and PLS appears weeks after first irrigation. A tank route usually takes 24–36 months, dominated by mill and tank-train construction. However, the heap then needs months to pad-wide steady-state recovery, while the tank route reaches design recovery within its first months of operation — schedule comparisons must include ramp-up, not just first PLS.

Is tank leaching always higher recovery than heap leaching?
On amenable ore, yes — typically by 10–25 percentage points — because full liberation and controlled chemistry beat static-bed percolation. The exceptions are coarse-gold ores where gravity recovery outside either route captures metal a mill would smear, and ores where very long heap cycles (bioleaching of secondary sulphides) eventually match tank recoveries. For the standard comparison — same ore, same reagent regime, realistic cycles — the tank route wins on recovery essentially always.

Does altitude affect the choice between routes?
Above about 4,000 m (13,100 ft), yes, modestly. Reduced oxygen partial pressure slows bacterial action in bioleach heaps and raises aeration power in tanks; freeze-thaw and intense UV weather pad surfaces, geomembranes and pond covers. Neither effect alone disqualifies a route, and Chilean and Peruvian operations run heaps above 4,000 m (13,100 ft) routinely. Altitude shifts operating cost and maintenance risk more than it changes the fundamental ore-based decision.

Conclusion: Tank Leaching vs Heap Leaching in One Paragraph

The tank leaching vs heap leaching decision reduces to three questions with numerical answers: what recovery delta does test work show for your ore, what is each recovery point worth at your grade and throughput, and can your site support percolation, water balance and ramp-up risk? When the delta is small, the grade low and the site dry and permeable, the heap’s cost structure wins decisively. When the delta is large, the grade is high, clays are present, or the schedule cannot absorb a multi-year ramp-up, the tank route’s premium buys back its cost many times over. Neither route is the “better” one — the correct answer is the one your ore’s numbers point to, and the only way to get those numbers is column and bottle-roll test work, scaled up through pilot verification before the CAPEX is committed.

If you are weighing these routes for a live project, send the Lexin Hydromet process engineering team your ore characterisation data — or start with a scoping conversation — and we will help you frame the route decision with design-grade numbers rather than screening averages. The full library of route, design and application guides is collected in the Lexin Hydromet resource hub.

References

1. Fuerstenau, M.C. & Han, K.N. (eds.), Principles of Mineral Processing, Society for Mining, Metallurgy & Exploration (SME), Littleton, Colorado.
2. Wills, B.A. & Finch, J.A., Wills’ Mineral Processing Technology, 8th edition, Butterworth-Heinemann, Oxford.
3. Marsden, J.O. & House, C.I., The Chemistry of Gold Extraction, 2nd edition, Society for Mining, Metallurgy & Exploration (SME), Littleton, Colorado.
4. Davenport, W.G., King, M., Schlesinger, M. & Biswas, A.K., Extractive Metallurgy of Copper, 5th edition, Elsevier, Oxford.
5. U.S. Geological Survey, Mineral Commodity Summaries (copper and gold chapters), Reston, Virginia — annual editions.
6. Kappes, D.W., “Precious Metal Heap Leach Design and Practice,” in Mineral Processing Plant Design, Practice, and Control, SME, Littleton, Colorado.
7. Havlík, T., Hydrometallurgy: Principles and Applications, Woodhead Publishing, Cambridge.

Changelog

• 2026-10-19: First published.

Related reading

• The Process Flowsheet guide
• Stage Efficiency: selection rules