Anode plate for electrorefining and electrowinning

01

Control impurities and current density for copper refining anodes

Glencore Technology, owner of the ISA PROCESS permanent stainless steel cathode technology introduced at Mount Isa Mines' Townsville refinery in 1978, explains that copper electrorefining dissolves impure anodes in acidic copper sulphate and replates copper on cathode blanks, and that "commercial operations typically run between 200 and 350 A/m², though some facilities push toward 400 A/m² or higher". Above the limiting current density, deposition becomes mass-transfer limited and cathodes become rough, nodular or dendritic. [1]

Glencore notes that gold, silver, platinum-group metals and lead report to the anode slime, while arsenic, antimony and bismuth are the troublesome soluble impurities: enough arsenic relative to antimony and bismuth helps them form insoluble compounds in the slime, otherwise they co-deposit on the cathode. Nickel dissolves readily and raises the risk of anode passivation. Cathodes next to damaged anodes, or warped and misaligned, develop current hotspots. [1]

Editorial calculation: by Faraday's law, copper deposits at 63.546 / (2 × 26.80) ≈ 1.19 g per ampere-hour, so 300 A/m² for 24 h deposits about 8.5 kg of copper per square metre of cathode face at 100% current efficiency — and dissolves a similar mass from the facing anode. The current density is an assumed example within Glencore's range. [1]

Give the supplier the process (copper electrorefining, zinc or copper electrowinning), cell and electrode dimensions, anode mass or thickness, composition and impurity limits, current density, electrolyte temperature, chloride and manganese levels, lug or hanger bar design, flatness and straightness tolerances, and expected service life.

02

Choose lead-alloy anode composition for electrowinning

Varganov and colleagues at Chelyabinsk Zinc Plant and Chelyabinsk State University, in Tsvetnye Metally (2023), studied rolled lead-alloy anodes with silver, tin, calcium and indium in zinc electrowinning. At current densities up to 400 A/m² and 36 °C, corrosion rate did not depend on alloy composition or cooling mode; but it rose 2–4 times when current density went from 385 to 450 A/m², and 3–5 times when chloride rose from 200 to 600 mg/L, with temperature and manganese also accelerating corrosion. [2]

They found silver the key element: halving surface silver from about 1 to about 0.5 at.% increased corrosion, indium-containing anodes with the coarsest surface crystals corroded fastest, adding 0.6–1.8 at.% tin increased corrosion to a lesser degree, and calcium below 0.1 at.% had no noticeable effect. [2] A supplier linked to this page lists Pb-Sn anode plates among its electrolysis equipment. [3]

Editorial note: because corrosion accelerates sharply just above about 400 A/m² and with chloride, ask the anode supplier for expected life at your actual current density, temperature and chloride level, and for the silver content guaranteed in the alloy.

03

Pb-Sn plates with cells, and anodes with titanium-clad copper hanger bars

Listings include Pb-Sn anode plates with electrolytic cells and anode flattening and cleaning units, and anode plates with titanium-clad copper hanger bars; ask which process each anode is designed for.

04

Ask whether lead anodes are cast or rolled, and how they condition

In a 2003 paper published by The Minerals, Metals and Materials Society (TMS), Andreas Siegmund describes a rolled Pb-Ag-Ca anode for zinc electrowinning developed by RSR Technologies. The abstract says cast lead-silver or lead-silver-calcium anodes can have holes, voids or laps in the surface that start internal corrosion locally, while rolling reduces internal porosity and extends service life. Cast or rolled Pb-Ag anodes need a relatively long time to form a stable protective PbO2/MnO2 layer and may be conditioned mechanically, chemically or electrochemically before use. [4]

The RSR anode has a controlled surface grain structure, with a preferred calcium content of 0.05–0.08% and silver of 0.3–0.4%. In industrial-scale tests at two zinc refineries in North America from May 2001, it formed an adherent protective oxide coating "within a short period of several days" without preconditioning, sludge grew evenly, the anodes stayed dimensionally stable and no short-circuits were observed, says Siegmund. [4]

Editorial note: the abstract is written by the maker of the anode and does not state whether its percentages are by weight or atomic; the Chelyabinsk study above reports silver in at.% and found lower silver increased corrosion. Ask the supplier for the silver and calcium basis, the casting or rolling route, conditioning needs and corrosion data at your current density. [4] [2]

05

Plate body, Ag-Sn-Ca alloying, impurity limits, hanger bar and flatness

06

Anode dimensions, mass, silver content and rated current density

The current density row carries the sharpest limit on this page: lead-alloy corrosion rose 2–4 times between 385 and 450 A/m² in the Chelyabinsk study, so ask for anode life at your own density. [2]

07

Send the process, cell and electrolyte data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Process: [Cu refining; Zn or Cu electrowinning]
Cell: [electrode size; spacing; number]
Anode: [composition; mass; thickness]
Current: [density; total]
Electrolyte: [temperature; Cl⁻; Mn²⁺; acid]
Contact: [lug or hanger bar]
Tolerances: [flatness; straightness]
Life: [expected; recycling of scrap]

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