MINERAL PROCESSING COURSE

Electrowinning of Metals

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 Electrowinning

> Electrowinning is an
electrolytic technology

> Allows purification of non-

ferrous metals

> Two electrodes – Anode

and Cathode

> Process involves evolution

gases & mist

> Basically electroplating on

a large scale

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 Electrochemical Series

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 Components of Electrowinning

> Rectangular stainless steel

container (1 to 3.5 m3)

> Consist of 14-33 cathodes and

15-35 anodes

> Electrical power derived from

the rectifier

> Copper busbar located outside

> Fitted with stainless steel lids

connected to a gas extraction ELECTROWINNING CELL
fan

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 Operation

> Current causes migration of metal

and other ions
Ionic compound
Hydrogen ion

> Metal deposits on to the cathode

> Cathode is removed for metal

processing when deposition finished
Metal ion

> Oxidation occurs at anode -

+ CATHODE
ANODE (DEPOSITION)

> Cyanide when present, gets oxidised

to cyanate, then to carbon dioxide
and nitrogen gas

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 Copper Electrowinning

> Anodes are made of lead calcium

(Cu anodes for refining)

> Cathode is a copper starter sheet

made of copper plated onto
titanium or stainless steel

> Solution contains 25-60 g/L copper

sulphate (CuSO4), 50-180 g/L
sulphuric acid (H2SO4)

> Temperature maintained at 50-60oC

> Current density is 300A/m2

> Power consumption rate of 2 kWh/kg

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 Nickel Electrowinning

> Extracted from sulphide ores and

laterite

> Using nickel sulphate solution of

concentration 60 g/L

> Sodium sulphate is added to help

deposition process

> Adjusting pH to 3.5 by adding boric

acid

> Temperature is kept at 65oC

> Cathode is a nickel starter sheet, made

of nickel plated on stainless steel

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 Design and Implementation Consideration

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 Electrowinning Plant Design

> Provision of adequate ventilation –

fume hood with exhaust fan

> Materials of construction - stainless

steel hood

> Plant layout issues

― sufficient amount of space
above the cell
― hoist above the cell
― Sludge collection and handling
equipments are essential
― The location of the rectifier

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 Maximising Metal Deposition Rate

> Metal Concentration – applied to concentrated rinse waters

> Current Density – Higher current density = higher rate of deposition

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 Maximising Metal Deposition Rate (cont.)

> Mixing – Agitating the solution disrupts metal depleted layer

allowing metal ions to come into contact with cathode

> Cathode Surface Area – metal deposited is proportional to

cathode’s surface area. Choices between flat plate cathode
and reticulated cathode.

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 Limitations

> Not a stand alone technology and is often combine with

other technology

> Less efficient at low metal ion concentrations

> The applicability and effectiveness varies with metal

― position of the metal on the electrochemical series
― Theoretical rates : 1.09 to 7.35 g/Ah (gold)
― Aluminium near bottom of series
― Nickel electrowinning is sensitive to pH
― Electrowinning for chromium is not practical

> In general, electrowinning is used to remove cations and

not anions

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