Copper Electrowinning Equipment

What is copper electrowinning equipment used for?

Copper electrowinning equipment recovers copper from a solution by passing direct current through a purified copper sulphate electrolyte and reducing the cupric ion onto a cathode blank as metallic copper. It is the final stage of a leach, solvent extraction and electrowinning circuit, and it is the route to cathode metal for feed that no smelter will take: oxide and mixed ore leach solutions, tailings and stockpile leachate, mine water, secondary copper and electronic scrap leach liquors, spent etching and plating solutions, and refinery bleed streams. A cellhouse sits downstream of solvent extraction, which lifts the copper into a clean high-acid strip liquor and rejects iron, manganese and chloride to the raffinate, and its output is a full sheet of cathode copper at 99.99% that is shipped and sold as metal rather than as a concentrate.

What cathode purity does copper electrowinning achieve?

Cathode copper at 99.99%, meeting the Cu-CATH-1 chemical composition that LME Grade A recognises, with lead held below 5 ppm and sulphur below 15 ppm. The same grade is described by BS EN 1978 as Cu-CATH-1, by ASTM B115 as Grade 1 and by GB/T 467 as high-purity copper cathode, and the four designations are used interchangeably in the market for the same deliverable chemistry. What makes the grade achievable is not the cell itself but the discipline around it: solvent extraction upstream to strip the impurities, chloride and cobalt held inside their windows, iron below about 3 g/L, no entrained organic reaching the cathode, close contact temperature control at the electrodes, and a wash that removes entrained electrolyte before the sheet is bundled. Purity is verified on the customer’s own metal, by sampling and assay per lot, rather than accepted from a specification sheet.

What is the difference between copper electrowinning and copper electrorefining?

The anode. In electrorefining the anode is impure copper metal that dissolves as the cell operates, so the copper comes from the anode, anode scrap and anode slime are part of the flowsheet, and the cell runs at only about 0.25–0.3 V because the dissolution potential offsets most of the deposition cost. In electrowinning the anode is insoluble — a lead-calcium-tin plate that never dissolves — and the copper comes entirely from the solution, with oxygen rather than copper evolved at the anode. That is why an electrowinning cell runs at 1.8–2.5 V and consumes roughly ten times the electrical energy per tonne, and it is also why electrowinning can accept a dilute and relatively dirty leach liquor that an electrorefining line could not touch, and why it generates no anode scrap and no meaningful anode slime to be re-melted. If your feedstock is metallic copper, you need electrorefining; if your feedstock is a solution, electrowinning is the only route to cathode metal without a smelter.

What cathode current density does the cellhouse run at, and why is it capped?

The design band for a cellhouse fed by solvent extraction and filtration is 250–300 A/m² of cathode area. Permanent-cathode tankhouses average about 330 A/m² against about 240 A/m² for starter-sheet operations, modern plants operate up to 350–400 A/m², and the 2025 world tankhouse survey averages 265 A/m² across all plants. The cap exists because current density is limited by the rate at which copper ions can be delivered to the cathode surface, not by the rectifier. Push past that rate and the surplus current is consumed by hydrogen evolution instead, the deposit grows nodular and dendritic, nodules bridge the electrode gap and short-circuit the cell, and current efficiency falls away faster than the tonnage rises. One documented case is instructive: a plant designed for 275 A/m² on purified feed achieved only about 75–110 A/m² on un-purified leach solution before the deposit became unmanageable, which is the practical reason filtration and solvent extraction are treated as part of the cellhouse design rather than as upstream conveniences.

What is the cell voltage made up of, and why does it matter more than the current?

The cell voltage is a budget of four terms: about 0.89 V of thermodynamic potential that the chemistry fixes, the anodic overpotential needed to evolve oxygen on a lead alloy surface, the resistive drop across the electrolyte gap and the cell hardware, and the loss to stray currents and short circuits. Only the first term is immovable. The other three are design variables — the anodic term is addressed by anode composition and cobalt addition, the ohmic term by the 95–106 mm electrode pitch and the 45 mm anode-to-cathode gap, and the hardware term by machined contacts, correct busbar section and insulated supports. A cell running at 1.9–2.1 V is converting almost all of its electrical input into copper; a cell running above 2.5 V is buying water decomposition with the same current, which shows up directly in the energy per tonne and in the roughness of the deposit.

What electrolyte composition does the cellhouse run, and why is the acid held below 170 g/L?

Copper is held at 30–50 g/L in the rich electrolyte with the cell allowed to bite 2–5 g/L out of it per pass, and the lean liquor is kept above about 30 g/L because below that figure hydrogen evolution begins to share the deposition current and cathode quality falls away. Sulphuric acid runs at 150–180 g/L, and the lean stream is deliberately held below 170 g/L. Acid is not a free variable: it is what drives acid mist generation at the cell surface, and it affects the deposit roughness and the solubility balance. Because the cell generates 1.98 g of sulphuric acid for every gram of copper plated, the acid concentration rises as the cell works, and holding it below the ceiling is an operating constraint as much as a design one. Temperature runs at 45–50 °C, which lowers the electrolyte resistance and improves ion mobility without driving evaporation and mist losses up.

Why is chloride added to the electrolyte rather than removed?

Chloride at 30–40 mg/L is a deliberate additive, not a contaminant. It acts as a deposit-smoothing agent at the cathode, producing a dense coherent sheet that releases cleanly at stripping instead of a rough one that tears. It does interact with the hardware, which is why the material selection responds to it: above about 40 mg/L, chloride begins to pit 316L stainless steel blanks, and South American tankhouses handling more than 30 mg/L of chloride all run 316L rather than a cheaper grade. The chloride window is therefore narrow in both directions — too little and the deposit is rough, too much and the blank is attacked — and it is controlled by measured addition and periodic titration rather than by trusting the feed analysis.

What does cobalt do in a copper electrowinning cell?

Cobalt is held at 100–150 mg/L to protect the lead anodes. Lead-calcium-tin anodes corrode and polarise in sulphuric acid service as the oxide film on their surface forms and breaks down, and cobalt in the electrolyte stabilises that film, which suppresses both the corrosion rate and the anodic overpotential. The benefit shows up twice: the anodes last longer, moving towards the upper end of their five-to-ten-year service life and holding their consumption towards the lower end of the 1–12 kg per tonne range, and the cell voltage stays lower because a stable oxide film is a lower-resistance surface. Cobalt also reduces the amount of lead that reports to the cathode, which is what keeps the lead figure in the cathode assay below 5 ppm and keeps the product inside the Grade A composition.

Why are permanent cathodes used instead of starter sheets?

Because a starter sheet is a second plating operation. A conventional starter-sheet tankhouse has to plate a thin copper sheet on a titanium or stainless mother blank, strip it, hang it as a cathode, harvest the copper that grows on it, and then deal with the starter sheet itself. Permanent cathodes remove that loop entirely: a 316L blank is dressed, charged, plated and stripped, and it returns directly to the cell. The consequences are visible in the industry data — permanent cathodes now stand in about 80% of tankhouses and carry roughly 94% of hydrometallurgical cathode production, with starter-sheet plants concentrated among installations built in the twentieth century. The trade-off is capital: a permanent cathode set is a significant material cost, but it is a long-lived asset rather than a consumable, and its rated life depends on the blank repair and edge strip discipline being maintained.

How thick is a 316L cathode blank, and how long does it last?

A standard permanent cathode blade is 316L austenitic stainless steel, containing 10–14% nickel and 2–3% molybdenum, at roughly 3–3.25 mm thick and of the order of 1 m by 1–1.2 m of deposit surface, giving 2.0–2.04 m² of plating area counting both faces. The surface finish matters as much as the thickness: a machined 2B finish in the 0.2–0.3 µm Ra range is what allows the copper sheet to release cleanly without tearing the edges. On life, the practical figures are wide, which is why the design details matter — standard permanent cathodes are rated for up to ten years without repair in well-run tankhouses, against less than three years reported for some alternative designs, and the copper-clad hanger bar, its cladding thickness and the moulded edge strips are the components that decide which end of that range a plant reaches. Relying on a cheap blade to save capital is the single most common way to increase the real cost of a cellhouse.

Why is the anode cut narrower and shorter than the cathode?

To reject edge growth. Copper does not plate only on the flat faces of the blank: it also grows around the edges and the bottom, and if the anode extends as far as the cathode, that growth is deposited at a very high local current density because the geometry concentrates the field there. The result is a thick, rough, dendritic bead along the cathode edge that eventually reaches the neighbouring cathode across the busbar gap and short-circuits the cell. Cutting the anode roughly 3 cm narrower and shorter than the cathode is a cheap geometric decision that removes the driver for that growth, and it complements the moulded edge strip on the blank. It is also why anode straightness is enforced: a bowed anode has the same effect as an anode that is too large, because part of its face ends up closer than the design gap.

How is the cathode harvested without stopping the tankhouse?

The harvest is a scheduled operation inside a continuing shift rather than a shutdown. Half or one third of a cell’s cathodes are pulled at a time — which is why practical cathode counts are divisible by two or three — and the remaining electrodes continue to plate while the crane works its way along the cell row. The loaded blanks go to the stripping machine, the copper sheet is separated from the blank, the blank is inspected and returned to the cells on a conveyor pitched at three times the electrode pitch, and the sheet goes forward to washing, drying, weighing and bundling. The stripping machine is sized to the cellhouse’s real peak rate rather than to the largest available: for a 10,000 tonnes per year cellhouse a machine rated around 250 plates per hour occupies about two and a half hours of the day, while continuous machines above 600 cathodes per hour exist for very large electrorefining tankhouses where the daily cathode count is far higher.

How is the number of cells and the rectifier rating calculated for a target tonnage?

The calculation starts from the electrochemical equivalent of copper, 0.02846 kg per ampere-day. Take the target annual tonnage, divide by the yearly operating days to get daily output, and the daily copper per cell follows from the deposit area of one cathode, the cathode count in the cell, the design current density, the current efficiency and the time efficiency. From that, the cell count is the daily target divided by the daily output of one cell, rounded up to a practical arrangement, and the rectifier is sized at the maximum current the cellhouse can draw — deposit area per cathode, times cathodes per cell, times the number of cells, times the highest current density the plant will ever run — with the voltage set from the design cell voltage multiplied by the number of cells in the string. The rectifier is then specified at the next standard size above that maximum, which is why the published rating of a cellhouse rectifier is always slightly higher than the calculated duty. YuSai supplies this arithmetic with the quotation so the buyer can check it against their own balance.

Where does the acid generated in the cell go, and why does it matter to the leach plant?

Every gram of copper plated generates 1.98 g of sulphuric acid, and the cellhouse is the largest single acid source in a hydrometallurgical copper circuit. That acid is not a waste product; it is the leach reagent. In a heap leach operation the lean electrolyte leaving the cellhouse at 150–180 g/L sulphuric acid is returned to the solvent extraction strip stage, and between 20% and 40% of the lean flow goes back there to carry the acid balance, with the remainder bled to the impurity purge. The plant’s entire acid balance therefore depends on how much copper the cellhouse plates, and the consequence for design is that a cellhouse cannot be sized in isolation: the acid it generates, the acid the leach consumes and the acid the raffinate carries are one coupled system, and the whole mass balance is built as a single calculation.

How is acid mist controlled in the cellhouse?

Acid mist is generated at the anode, where oxygen evolution breaks the electrolyte surface and carries sulphuric acid into the atmosphere as a fine aerosol. The response is suppression plus capture. At the cell surface, a floating layer of polypropylene balls covers the electrolyte and knocks down the mist mechanically; where the site requires close control, cell covers or hoods are held at negative pressure and the headspace is ducted through a mist eliminator to a scrubber. Close capture is what makes the system economical, because an open cellhouse under general ventilation has to be diluted with a far larger air volume to reach the same working atmosphere, and the scrubber and fan have to be sized for that diluted volume. The scrubber liquor is analysed and logged, so the emission record is produced as a by-product of operating the plant rather than as a separate compliance exercise.

Can copper electrowinning treat a leach solution without solvent extraction?

It can, and the design changes in a predictable way. Direct electrowinning of an un-purified leach solution is feasible, but the iron, manganese, aluminium and chloride that solvent extraction would have rejected all remain in the cell feed, and the deposit tolerates a much lower current density as a result. The documented experience is that a cellhouse designed for about 275 A/m² on purified feed achieved only roughly 75–110 A/m² on a raw pregnant leach solution before the deposit became unacceptable. The practical consequence is that direct electrowinning works best on a clean or a high-tenor liquor, such as spent etching solution or a well-conditioned leachate, and that where solution purification is not used the cellhouse has to be sized with a materially larger electrode area, and therefore a larger capital cost, to reach the same tonnage. That comparison is what normally decides the question, and it is settled in the test campaign rather than on the drawing board.

What capacity can you supply, and how is the cellhouse configured?

Capacity is engineered to your solution assay and your monthly copper volume rather than taken from a catalogue of fixed models. What matters is the copper tenor of the feed, the impurity load that sets the achievable current density, the target cathode grade, and the electrode area needed to carry the target current at that current density — so two cellhouses quoted at the same daily copper output can require rather different cell counts and rectifier ratings depending on what is in the solution. YuSai sizes the cell count, the cathode area, the electrode pitch, the rectifier rating, the busbar section, the circulation rate, the cooling duty, the exhaust and scrubber duty and the scavenger capacity from your analysis and your target copper volume, and states the resulting figures in the process design package. The cellhouse is laid out modularly, so a line that proves the route at a modest tonnage can be extended by adding cells and rectifier capacity in parallel rather than by being replaced.