Copper SX-EW Plant Cost: CAPEX and OPEX per Tonne

Last updated: 2026-10-17 · Reviewed by: Senior Metallurgical Engineer, {BRAND}

A 20,000 t/y copper cathode SX-EW plant built alongside a new heap leach operation costs roughly USD 55–85 million, which is USD 2,700–4,200 per annual tonne of cathode capacity, and runs at USD 1,400–2,100 per tonne cash cost before by-product credits. Within that cash cost, sulphuric acid at 4–6 kg per kg of copper and power at 2.2–2.7 kWh per kg of cathode usually account for 55–70% of the controllable spend.

Key Takeaways

• Capacity cost lands at USD 2,700–4,200 per annual tonne of cathode for a greenfield heap leach plus SX-EW project.
• Organic inventory is a capital item, not a consumable: 1,200–2,000 m³ at USD 6–9/L on a 20,000 t/y plant.
• Acid consumption of 4–6 kg per kg copper is the largest single operating cost in oxide heap leaching.
• Electrowinning accounts for 1.8–2.2 kWh/kg of the 2.2–2.7 kWh/kg total power demand.
• Country factors — power tariff, acid logistics, duty — move cash cost by more than plant design does.

What Does a Copper SX-EW Plant Consist Of?

A copper SX-EW plant is a hydrometallurgical route that converts dilute copper-bearing leach solution into 99.99% cathode without smelting, using solvent extraction to concentrate and purify, and electrowinning to recover metal. Four process blocks sit in series, and each has its own cost behaviour.

Thickener vs Filter Press

Pregnant leach solution (PLS) is the copper-bearing liquor that exits the heap leach system or the leach circuit, typically at 1.5–4.0 g/L copper, pH 1.5–2.2, and with an oxidation potential high enough to keep the copper in the cupric state. PLS grade and flow rate set the size of everything downstream, which is why a 10% error in the resource model’s leach recovery propagates into a 10% error in tankhouse capital.

Solvent extraction (SX) is the liquid-liquid separation step that transfers copper from the aqueous PLS into an organic phase containing a hydroxyoxime extractant, and then back into a clean aqueous strip solution, producing a concentrated and purified electrolyte. Extraction and stripping happen in mixer-settlers, each stage a stirred box followed by a settling box, and the number of stages plus the organic-to-aqueous (O/A) ratio set both recovery and capital.

The O/A ratio is a volumetric ratio that sets how much organic is circulated per unit volume of aqueous feed, and it therefore fixes the organic inventory, the pump duty and the mixer-settler size before any equipment is selected. A design at O/A of 1.0 with three extraction stages needs a different inventory and a different settler area from a design at O/A of 1.5 with two stages at the same recovery — the arithmetic is worked through in O/A ratio in solvent extraction.

Electrowinning (EW) is the electrolytic step in which copper is plated from the loaded electrolyte onto stainless steel cathodes at 300–350 A/m², producing a 99.99% cathode. EW is the single largest electrical load in the plant, and its power consumption is governed by current density, acid concentration, temperature and the gap between anode and cathode.

Cathode is the product: a copper sheet of about 45–70 kg, sold against the LME price with a cathode premium or discount that depends on brand registration, geography and freight.

The cost structure follows directly from this flow sheet: capital is dominated by wetted area in the heap, settler area in SX and cathode area in EW, while operating cost is dominated by the chemistry the heap consumes — acid and oxidant — and by the electricity the tankhouse draws.

How Is CAPEX Structured per Annual Tonne?

Table 1 sets out a capital breakdown that can be re-based to any capacity, at AACE Class 4 accuracy of roughly ±30%, in Q3 2026 US dollars, excluding mine fleet, access roads, power line construction and owner’s corporate costs. The copper SX-EW plant cost per annual tonne is then the total divided by cathode output.

Table 1 — Indicative CAPEX breakdown, 20,000 t/y copper SX-EW, heap leach route

Three observations separate a credible estimate from a wish.

First, the heap leach block is not the largest single item even though it handles the most tonnes. The SX and EW blocks together are 45–55% of capital, and the organic inventory alone can exceed the entire reagents and utilities block. Projects that treat the organic as a consumable line item understate capital by 12–18%.

Second, settler area scales with flow, not with copper production. A PLS at 1.5 g/L copper needs twice the flow, twice the settler area and roughly twice the SX capital of a 3.0 g/L PLS at the same cathode output. Two projects with identical nameplate capacity can differ by 30% in SX capital purely because of leach grade, which is why capacity cost per tonne is a poor comparison metric without the PLS grade attached.

Third, contingency of 10–15% is not padding at Class 4. Copper SX-EW projects have a documented tendency to overrun on earthworks and electrical bulk materials, and 10% on a project with 40% of capital in civil and electrical work is closer to a minimum than to a cushion.

What Drives OPEX per Tonne of Cathode?

Operating cost in the copper SX-EW plant cost structure splits into a large, chemistry-driven block and a smaller, plant-driven block. Table 2 gives ranges that hold across most oxide heap leach operations, with the calculation basis stated for each line so the numbers can be re-based to a specific site.

MVR vs Multi-Effect Evaporation

Table 2 — Indicative cash cost per tonne of copper cathode, oxide heap leach route

The acid line deserves most attention because it is both the largest and the most frequently mis-estimated. Acid consumption in oxide heap leaching is driven by gangue acid demand — the carbonate, clay and iron content of the ore — rather than by copper grade. An ore with 3% carbonate can consume 80 kg of acid per tonne of ore, which at a 0.4% copper head grade is 20 kg of acid per kg of copper and turns a project from marginal into uneconomic. The most valuable test in the feasibility programme is a column leach test that measures net acid consumption on a representative sample, not a bottle roll.

Power is the second largest line and the most sensitive to country. Electrowinning at 2.0 kWh/kg is a physical constraint set by cell voltage, which is the sum of the reversible copper deposition potential, the anodic oxygen overpotential, the electrolyte resistance and the contact losses. The only meaningful levers are current density, acid concentration, temperature and anode-to-cathode spacing. A tankhouse designed at 320 A/m² and 40 °C will consume about 2.0–2.2 kWh/kg; one at 380 A/m² will consume 5–8% more and require more cathode area maintenance.

Organic loss is small in dollars but diagnostic. A loss of 0.5–0.8 kg/t is normal for a well-run circuit; 1.5 kg/t or more usually indicates crud accumulation, high entrainment from poor phase disengagement, or extractant degradation from prolonged contact with high-chloride or high-manganese liquor. Since the extractant is the most expensive consumable per kilogram, a doubling of the loss rate is worth investigating even though it does not dominate the cost table. The design basis that governs settler behaviour is covered in mixer-settler design.

Which Country Factors Move the Number Most?

Two sites with identical plant design can differ by USD 500 per tonne in cash cost on country factors alone. Table 3 sets out the factors that do the most work, with indicative ranges; all are volatile and should be replaced by current quotations and tariff schedules before any decision.

Mining Equipment Zambia

Table 3 — Country cost factors affecting copper SX-EW cash cost

The acid line is where geography hurts most. A landlocked plant paying USD 210/t for imported acid against USD 130/t for a coastal plant with a smelter next door carries USD 320–480/t of additional cost at 4–6 kg/kg, which is 20–30% of total cash cost. This single factor explains more of the difference between Zambian and Chilean SX-EW cost structures than any process design choice, and it is why several Copperbelt projects have evaluated on-site sulphur burning or acid recovery from concentrate.

Power reliability deserves separate mention because it does not appear in a tariff table. A tankhouse that loses power for two hours requires a controlled shutdown and restart, and a cathode left in a cell without current can re-dissolve or plate unevenly. Sites with load shedding typically carry diesel generation for critical loads, which converts a cheap tariff into an expensive delivered kWh. When comparing tariffs between countries, compare the cost of firm power, not interruptible energy.

Worked Example: 20,000 t/y Plant Economics

Take a 20,000 t/y cathode project with a PLS at 2.5 g/L copper, leach recovery of 85%, 8,000 operating hours per year and 92% tankhouse availability. Annual production of 20,000 t requires about 23,500 t of copper in solution and a PLS flow of roughly 1,170 m³/h at the stated grade.

Capital. Applying the Table 1 mid-points gives approximately USD 70 million, or USD 3,500 per annual tonne. Of that, the SX block including organic inventory is about USD 24 million, and the tankhouse including rectifiers about USD 22 million.

Operating cost. Applying Table 2 mid-points with delivered acid at USD 150/t, 5 kg/kg acid consumption and a power tariff of USD 0.09/kWh gives:

Acid 5.0 × 150 = USD 750/t
Power 2.45 × 0.09 × 1,000 = USD 221/t
Organic 1.0 × 7.5 = USD 8/t
Reagents, labour, maintenance, G&A = USD 330/t
Cash cost = USD 1,309/t

At an LME copper price of USD 9,000/t and a cathode premium of USD 40/t, the operating margin is about USD 7,700/t, or USD 154 million per year on 20,000 t, against capital of USD 70 million. That arithmetic explains why SX-EW projects are built when the copper price is strong, and why the same project becomes unfinanceable at USD 6,500/t with the same cost structure.

Sensitivity. Three variables move the outcome more than anything in the design: acid consumption, power tariff and leach recovery. A 1 kg/kg increase in acid consumption adds USD 150/t to cash cost. A USD 0.02/kWh increase in tariff adds USD 49/t. A 5 percentage point drop in leach recovery raises unit cost by roughly 6% because capital is spread over fewer tonnes. Ranking those three in a sensitivity table, rather than reporting a single NPV, is the minimum standard for a credible feasibility study — and the acid number should come from a column test, not a benchmark.

Working capital and sustaining capital are the two items most often left outside the headline number. Working capital covers reagent inventory, cathode in circuit and receivables, and typically runs 8–12% of annual revenue. Sustaining capital covers heap lift expansions, pad repairs, cell lining replacement and organic top-up, and typically runs 3–5% of initial capital per year. A project that reports only initial capital and cash cost is reporting two-thirds of the cash flow picture.

Where Do Cost Estimates Go Wrong?

Seven errors account for most of the gap between a feasibility number and the final copper SX-EW plant cost.

1. Capital comes in 25–40% above the Class 4 estimate. Symptom: the first definitive estimate exceeds the study estimate by more than contingency. Cause: earthworks quantities from a desktop study, electrical bulk materials estimated by ratio rather than take-off, and under-defined EPCM scope. Correction: complete a geotechnical programme and bulk material take-off before the definitive estimate.
2. Organic inventory is treated as working capital and omitted from CAPEX. Symptom: project appears USD 10–16 million cheaper than comparable projects. Cause: the initial organic fill is classified as inventory rather than plant. Correction: include inventory volume at the design O/A ratio and stage count, priced at current extractant and diluent rates.
3. Acid consumption is estimated from copper grade. Symptom: operating cost exceeds the model by USD 300–500/t within the first year. Cause: no column test, and gangue acid demand assumed from a similar project. Correction: run column leach tests with net acid consumption on composited samples from each ore domain.
4. Tankhouse power is estimated at a literature value. Symptom: rectifier load 8–12% above design. Cause: current density, acid strength and temperature differ from the reference case, and cathode contact resistance is not modelled. Correction: calculate cell voltage from component overpotentials for the specific design and verify against the rectifier guarantee.
5. Availability is assumed at 95%. Symptom: nameplate is never reached on an annual basis. Cause: ramp-up curve and tankhouse crane cycle time ignored. Correction: model a 12–18 month ramp to 90–92% availability and treat first-year production as 60–75% of nameplate.
6. Freight and treatment charges are left out of realisation. Symptom: revenue per tonne is below the LME price by more than expected. Cause: cathode premium applied as a constant and freight treated as zero. Correction: model premium by destination plus freight, insurance and any import duty in the buyer’s country.
7. Closure and rehabilitation are excluded. Symptom: NPV looks better than comparable projects with no explanation. Cause: heap rinse, solution neutralisation and pad closure deferred beyond the model period. Correction: include a closure estimate and either discount it or bond it, and include the operating cost of heap rinsing in the final two years.

The common root in five of the seven is that the model was built from ratios rather than from quantities. Ratio-based estimating is legitimate at Class 5 and dangerous at Class 4, and the transition point is exactly when a project starts raising finance.

Case Data: 12,000 t/y Project, Southern Africa

A 12,000 t/y cathode project in southern Africa illustrates how the line items behave in a landlocked, imported-acid setting. The figures are anonymised project data in 2026 US dollars.

Capital. Total installed cost was USD 38.4 million, or USD 3,200 per annual tonne. The heap leach block was USD 7.1 million, the SX block including organic inventory USD 12.9 million, the tankhouse and rectifiers USD 11.2 million, and EPCM, owner’s costs and contingency the balance. Organic inventory was 1,150 m³ at USD 7.2/L, or USD 8.3 million — 22% of total capital and the largest equipment-adjacent line.

Operating. Acid was imported at USD 205/t delivered and consumption ran at 5.4 kg/kg, giving USD 1,107/t — 63% of cash cost. Power at 2.4 kWh/kg and USD 0.075/kWh cost USD 180/t, of which about 12% was diesel generation during load shedding. Organic loss averaged 1.2 kg/t in year one, falling to 0.9 kg/t after a crud removal programme, worth about USD 2.3 million over three years at 12,000 t/y.

Performance. Ramp-up to nameplate took 14 months, with tankhouse availability at 89% in year one and 92% in year two. Unit cash cost in year one was USD 1,860/t against a model of USD 1,620/t, with the gap split between acid consumption (USD 140/t) and diesel generation (USD 100/t).

The three numbers worth carrying into a comparable study are USD 3,200 per annual tonne, acid at 63% of cash cost in an imported-acid setting, and a 14-month ramp to nameplate. All three are site-specific, and the acid share in particular will halve for a coastal project with a smelter next door. Country-specific logistics for this type of project are covered under Zambia.

FAQ

What is the typical copper SX-EW plant cost per annual tonne of capacity?
For a greenfield heap leach, SX and EW project, USD 2,700–4,200 per annual tonne at Class 4 accuracy, excluding mine fleet, power line and owner’s corporate costs. Brownfield expansions that reuse ponds and infrastructure can come in 30–40% lower.

How much of the capital is the solvent extraction circuit?
SX equipment plus initial organic inventory is typically 32–44% of total capital, with the organic inventory alone at 12–18%. The share rises with PLS flow and falls with PLS grade, because settler area scales with flow.

Why is acid such a large part of the operating cost?
Because oxide heap leaching consumes 4–6 kg of sulphuric acid per kg of copper in a typical ore, and 2–10 kg/kg in ores with high carbonate or clay content. At USD 110–190/t delivered, that is USD 440–1,140 per tonne of cathode before any other cost.

How much power does electrowinning use per kilogram of copper?
Typically 1.8–2.2 kWh/kg at 300–350 A/m² and 38–42 °C, with total plant demand at 2.2–2.7 kWh/kg once pumps, SX mixers and utilities are included. Higher current density and wider anode-cathode spacing both increase specific consumption.

What organic loss rate should a new plant expect?
0.5–0.8 kg per tonne of cathode in a well-run circuit after commissioning, and 1.0–1.5 kg/t during the first year while crud is being managed. Sustained losses above 1.5 kg/t indicate an entrainment or degradation problem rather than normal consumption.

How long does it take to reach nameplate capacity?
Twelve to eighteen months for a greenfield plant, with tankhouse availability typically at 88–90% in year one and 92–94% by year three. Models that assume 95% availability from month one overstate first-year revenue by 15–20%.

Does a higher copper price change the design?
It changes the cut-off grade and the ore reserve, not the plant design. The plant is sized on PLS flow and grade, and a higher copper price typically extends the reserve life rather than increasing the flow through an existing SX-EW circuit.

Conclusion

Copper SX-EW plant cost is set by four numbers before any quotation is requested: PLS flow and grade, which fix SX and tankhouse capital; acid consumption, which fixes cash cost; power tariff, which fixes the second-largest operating line; and leach recovery, which fixes the denominator that all unit costs are divided by. Get those four from test work rather than benchmarks, and a Class 4 estimate becomes defensible.

If you are sizing an SX-EW circuit and want the capital and operating structure rebuilt against your PLS analysis, send the leach test data through our turnkey plant engineering route, or start from the copper SX-EW process page for the flow sheet and design basis.

References

1. USGS Mineral Commodity Summaries — copper production, reserves and price context by country. usgs.gov
2. SME Mineral Processing Handbook — heap leaching, solvent extraction and electrowinning practice and cost structure. smenet.org
3. MetSoc Conference of Metallurgists (COM) proceedings — copper SX-EW operating and cost papers, including Copperbelt case studies.
4. CSIRO Mineral Resources — heap leach hydrology and copper SX chemistry. csiro.au
5. Hydrometallurgy (Elsevier) — hydroxyoxime extractant degradation and electrowinning energy consumption papers.
6. ASME Boiler and Pressure Vessel Code, Section VIII — pressure vessel requirements for pressure leach equipment referenced in the capital estimate.

Changelog

• 2026-10-17 — First publication. CAPEX breakdown per annual tonne, OPEX table with calculation basis, country factor comparison, worked 20,000 t/y example, 12,000 t/y case data.

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