SX-EW Copper: When Leaching Beats Flotation

Say a mine owner asks whether SX-EW copper is the right route for their 1% Cu oxide deposit. Fair question. The answer sits in the mineralogy, not the grade.

Context helps. World mine production of copper reached 21.2 million tonnes in 2021 (USGS 2021). A single month's US output in January 2022 was 110,000 tonnes of recoverable copper (USGS January 2022). Those numbers won't tell you how to treat a 1% Cu deposit. They only remind you that copper is a chemical business.

What SX-EW copper actually is

SX-EW copper is a hydrometallurgical route. You leach copper from ore with acid, then recover it from the solution by solvent extraction and electrowinning. No smelter. No concentrate. You get copper cathode.

Leaching always comes first. Heap leaching stacks crushed ore on a lined pad and irrigates it with dilute sulphuric acid. Agitation leaching does the same in stirred tanks. You get a pregnant leach solution, or PLS, carrying dissolved copper. Solvent extraction then moves copper from that PLS into a clean, concentrated electrolyte. Electrowinning plates it onto cathodes using direct current.

That two-stage SX plus EW sequence gives cathode directly at the mine site. You skip concentrate drying, shipping, smelting and refining. The trade-off? Only certain copper minerals dissolve in acid at a rate and recovery that make money.

Which copper ores fit SX-EW

Acid-soluble oxide copper minerals respond well. Malachite, azurite, chrysocolla and cuprite leach readily in dilute sulphuric acid. Sulphide copper minerals, mainly chalcopyrite, bornite and chalcocite, generally don't leach economically under ambient heap conditions. They need flotation, roasting or pressure oxidation.

Low acid-consuming gangue is essential. The same acid that dissolves copper also attacks carbonates like calcite and dolomite. Clay minerals complicate things. They hold moisture, blind a heap, and can send acid consumption through the roof. A sequential copper assay and mineralogy work tell you the acid-soluble copper share. If most copper is acid-soluble and the gangue is quartz-rich, SX-EW deserves a look. High carbonate or clay? You'll spend more on acid than on copper.

That's why grade alone is a poor decision input. A 1% Cu ore with 90% acid-soluble copper and low acid consumption is a candidate. A 1% Cu ore with 15% acid-soluble copper and heavy carbonate gangue is not.

SX-EW versus sulphidisation flotation for a 1% Cu deposit

Many small mine owners face this decision. Flotation works well on sulphide and mixed ores when you can sell a concentrate. Sulphidisation flotation adds sodium sulphide or sodium hydrosulphide to make oxide surfaces float. It's proven on mixed oxide-sulphide ores and it's flexible. You get a concentrate a smelter buys. You need grinding, flotation cells, thickening and filtration.

SX-EW works well when copper is mostly acid-soluble, acid supply is reliable, and you prefer cathode to concentrate. The tankhouse is power-hungry. The heap needs a lot of area. But you avoid smelter treatment charges and freight deductions. For a small deposit, cathode may fetch better net revenue. That depends entirely on site power, acid logistics and product market.

Mixed deposits sometimes need both. Oxide material can go to leaching, sulphide material to flotation. Separate stockpiles, separate circuits, one flowsheet decision per material type. Industry references suggest small African copper plants typically fall in the 200 to 2,000 t/d band, with 300 to 1,500 t/d being common. That range doesn't decide the route either.

Decision factor	SX-EW route	Sulphidisation flotation
Ore type	Acid-soluble oxide copper, low acid-consuming gangue	Sulphide or mixed oxide-sulphide copper
Product	Copper cathode on site	Copper concentrate for smelter
Reagent focus	Sulphuric acid, solvent extraction reagents	Collectors, frothers, sulphidiser
Power demand	High for electrowinning tankhouse	High for grinding, lower at downstream
Footprint	Heap leach pad large; agitation leach needs tanks and solid-liquid separation	Plant footprint compact; tailings still required
Typical testwork	Sequential assay, bottle-roll leach, column leach, acid consumption	Flotation batch and locked-cycle tests

Testwork that decides the route

You can't decide SX-EW versus flotation from a multi-element assay alone. You need at least four pieces of testwork.

Sequential copper assay

A sequential copper assay separates total copper into acid-soluble, cyanide-soluble and residual fractions. The acid-soluble number is the first gate. Low? SX-EW doesn't get off the ground unless you blend ore or pre-process it.

Bottle-roll leach tests

Bottle-roll tests shake crushed ore with acid for a short time. They tell you leach kinetics, acid consumption and the rough recovery limit. They're cheap and quick. If a bottle roll can't extract a decent share of copper, stop.

Column leach tests

Column tests often separate a workable heap leach from a failed one. They measure permeability, long-term leach kinetics, acid consumption over time and potential compaction. A column test on a representative sample tells you more than any geological model.

Acid consumption measurement

Acid consumption is the economic gate. You'll measure kilograms of acid per tonne of ore in the bottle-roll and column tests. Then benchmark that against acid supply cost and availability. High carbonate or clay content pushes acid consumption up fast.

What a small mine owner should weigh

Start with product. Cathode is a finished metal you can sell locally or internationally. Concentrate needs a smelter contract, freight, and treatment charges. For a remote site, cathode often wins because you avoid concentrate logistics. Near a smelter or with poor power? Flotation concentrate may be easier. Which product do you actually want to sell?

Acid supply deserves equal weight. Heap or agitation leaching eats acid continuously. Nearest acid plant far away? Your operating cost gets ugly. Look at the ore's carbonate content before you think about acid logistics.

Power is next. The electrowinning tankhouse draws steady direct current. You'll need reliable grid power or a large diesel or gas generation set. Flotation also needs power, mainly for grinding and flotation blowers. But the tankhouse load is continuous and hard to shed.

Footprint matters. A heap leach needs a large lined pad and a solution pond. Agitation leach needs tanks, thickeners and filters. A flotation plant can be much smaller for the same throughput. In mountainous terrain, footprint can decide the route.

Cost modelling is a separate exercise. See the copper processing plant cost guide for the capital and operating cost drivers. The metallurgical route comes first, but the numbers have to close.

Where a full-service EPC contractor fits, and where it does not

Xinhai reports a 1,000 t/d copper flotation plant in Nigeria, a 1,000 t/d oxide-mixed copper project in Bolivia and a 1,100 t/d copper upgrade in Namibia, all using flotation. No published SX-EW project. Its copper materials describe leaching only as an optional route decided by testwork. That's not a criticism. It reflects where the company's published case history sits.

If your ore is a candidate for flotation, a full-service EPC contractor can take it from testwork through plant design, equipment supply, construction and operation. The small-scale copper processing plant page covers that scope. If your ore truly needs SX-EW, ask any supplier for their specific leaching and electrowinning references. Don't accept a flotation vendor claiming to do SX-EW without seeing a plant they've built and operated.

Xinhai's design institute works to JORC, NI 43-101, VALMIN, GB, Eurocodes, US and Australian standards when designing mineral processing facilities. Useful for bankable studies, but it doesn't change the metallurgical decision.

A practical route-selection checklist

Here's the short version of what to do before you commit to SX-EW copper or flotation.

• Confirm the acid-soluble copper share from a sequential copper assay.
• Run bottle-roll and column leach tests before any commitment to SX-EW.
• Benchmark acid consumption against an economic limit based on your acid supply cost.
• Decide cathode versus concentrate based on site power, acid logistics and product market.

If the first two gates fail, flotation or a mixed circuit is your fallback. If they pass, you can start talking to suppliers about a leaching and SX-EW plant. And if you're not sure, ask for testwork before anything else. For broader copper flowsheets, see the copper solutions page. If you have a 1% Cu oxide sample and no test results yet, send it to us.

Frequently asked questions

What is hydrometallurgy with an example?

Hydrometallurgy uses aqueous chemistry to extract metals from ores. A common example? Leach copper oxide ore with dilute sulphuric acid, then recover the copper from solution by solvent extraction and electrowinning. The metal stays in solution for part of the journey, unlike pyrometallurgy which uses heat and smelting.

What are the disadvantages of electrowinning?

Electrowinning needs a continuous, reliable supply of direct current electricity. The tankhouse is energy-intensive and generates acid mist that needs ventilation and scrubbing. It also produces a spent electrolyte stream you must manage. For a small remote mine, that power demand is often the main disadvantage.

What are the five stages of copper extraction?

In a conventional sulphide route, the stages are mining, crushing and grinding, concentration by flotation, smelting to blister copper, and electrorefining to cathode. In a hydrometallurgical route, the five stages are usually mining, crushing, acid leaching, solvent extraction and electrowinning. Your chosen route changes the middle stages.

What is the difference between SX-EW and flotation for copper oxide ore?

Flotation separates copper minerals into a concentrate using bubbles and reagents; the concentrate then goes to a smelter. SX-EW dissolves copper from ore with acid and plates it directly as cathode on site, no smelter needed. SX-EW suits acid-soluble oxide copper with low acid-consuming gangue. Flotation, with sulphidisation, can handle mixed and sulphide ores that don't leach well.