YPT Electrowinning Cells

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Transforming Ion to Metal Through Controlled Electrowinning

YPT Electrowinning Cells

An electrowinning cell is an electrolytic device used in hydrometallurgical processes to recover metal from solution by depositing it onto cathodes under the action of an applied current.

In the context of precious-metal recovery (e.g., gold, silver), or base metals (copper, zinc), solution from leaching/elution circuits is passed through a tank containing cathodes and anodes; metal ions migrate and are reduced on the cathode surface, forming a metal deposit that is later removed.

Electrowinning cells are key units in circuits such as 'SX-EW' (solvent extraction – electrowinning) for copper recovery, or in elution/precious metal recovery loops.

Areas of Application

  • In gold and silver processing plants, following elution (for example in carbon-in-leach / carbon-in-pulp circuits) where the barren solution with dissolved gold is treated by electrowinning cells to plate out gold onto steel wool or other cathode media.
  • In base-metal extraction plants, especially with solvent extraction (SX) followed by electrowinning (EW) for copper and zinc, where purified electrolyte is fed to banks of electrowinning cells to produce cathode metal.
  • In generic hydrometallurgical or wastewater treatment applications where soluble metals are to be recovered from solution as a solid metal deposit, thereby reducing discharge or reclaiming value.

Principle of Operation

  • A feed (electrolyte) containing dissolved metal ions (e.g., Au(CN)₂⁻ in gold leach, Cu²⁺ in copper EW) enters the electrowinning cell. At the cathode (negatively charged electrode) metal ions receive electrons and deposit as solid metal. At the anode (positively charged electrode) oxidation reactions occur (often water oxidation producing O₂ or acid generation).
  • The circuit is completed via the external power supply (rectifier) which controls current/voltage, and through the solution which acts as the electrolyte between anode and cathode. The design cell voltage is a function of the cell resistance (electrolyte, electrodes, connections) and decomposition potentials.
  • As metal builds up on the cathode (for example steel-wool or mesh), it is periodically removed (stripped, harvested) for further processing (smelting, refining). The remaining electrolyte is returned or processed further.
  • Efficiency depends on current density (amps per cathode area), electrolyte flow, agitation/mixing, temperature, metal ion concentration, presence of impurities (which can raise over-voltage or reduce current efficiency). For example, iron in solution can reduce current efficiency in copper EW by competing reactions.

Efficient Metal Recovery with Proven EW Design

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Precision Current... Pure Metal...

Design Criteria

Cathode active area:

The area available for metal deposition is critical; for a given production rate, increasing cathode area reduces current density and may improve deposit quality.

Current density and current efficiency:

High current densities increase production rate per area but may reduce current efficiency (because of side reactions, increased over-voltage). The current efficiency is the fraction of current that is effectively used for metal deposition rather than side reactions.

Electrolyte flow and mixing:

Ensures uniform concentration of metal ions, removal of hydrogen bubbles or gas at cathode surface, and reduction of resistive losses. Poor flow may lead to uneven deposition or early termination of the cycle.

Cell voltage and power supply (rectifier):

The voltage is determined by the sum of electrical resistances (electrolyte resistance, electrode resistance, contact resistance) plus the decomposition potentials of reactions. Typical cell voltages in electrowinning may range from ~1.8 V to 2.5 V in certain copper EW circuits.

Material of electrodes:

Cathodes often steel-wool or steel mesh (for precious metals) or stainless steel cathode sheets; anodes may be stainless steel, lead alloys or other inert materials depending on chemistry. Electrode life, corrosion resistance, ease of stripping must be considered.

Cell size, layout and scalability:

Number of cells (in series or parallel) determines total cathode area, throughput, and voltage distribution. Cells must be designed for easy maintenance, sludge/metal removal, and service access.

Impurity control:

Presence of iron, sulphates, cyanide, other metals or gangue can reduce efficiency, plate quality, cause short-circuiting or increase maintenance. For example, iron in copper EW increases undesirable side reaction reducing current efficiency.

Footprint and infrastructure:

Cells require space, power supply (rectifier), electrolyte circulation pump(s), feed and discharge piping, and often ventilation (especially for hazardous solvents or gases). In precious-metal cells, fumes capture (e.g., cyanide fumes) may be necessary.

Technical Specifications

Cell
voltage:

~1.8 V – 3.0 VDepends on chemistry, electrode spacing, solution conductivity

Current
density
(cathode):

~100 - 1000 A/m² (varies widely)Precious metals may use lower density for quality; base metals higher density

Cathode area
per cell

~5 m²-20 m² (depending on design)Scalable for plant size

Deposition
rate

kg metal per hour per cell area – depends on current, efficiency and metal tenorBased on Faraday’s law

Electrolyte
conductivity

~2000-5000 µS/cm (or higher)Higher conductivity reduces resistance and voltage losses

Electrolyte
flow
rate:

Designed to maintain turbulence and refresh boundary layer at cathode surfaceCritical for efficient deposition

Cell
internal
dimensions:

rectangular box ~1 m wide × 1.5-2 m deep × 5-7 m long (for copper EW)

Important Considerations:

  • Electrode spacing and orientation:

    Too close causes shorting; too far increases resistance and decreases plating rate — optimal spacing is often vendor-specified.

  • Hydrogen evolution:

    On the cathode side, hydrogen gas formation can interfere with metal deposition (bubbles reducing effective cathode surface) and can create safety hazards (explosive gas). Hydrogen evolution reduces current efficiency.

  • Fines and sludge accumulation:

    In precious-metal cells, deposition may entrap slimes or gangue; cleaning of cathode media is important to avoid blockages and maintain performance.

  • Power supply harmonics and rectifier efficiency:

    Poor rectifier design or power instability can increase operating cost and reduce metal recovery.

  • Maintenance downtime:

    Cathode removal/cleaning can represent significant operational downtime; designs that minimise this (e.g., in-cell washing) can increase uptime.

  • Metal quality of deposit:

    Poor deposit morphology (due to high current density, impurity poisoning, poor electrolyte flow) may cause difficulties in downstream smelting/refining.

  • Integration with upstream and downstream:

    Electrowinning cell performance is strongly dependent on upstream leach/eluate quality and downstream refining; failings upstream (low metal tenor, high impurity) or downstream (smelting constraints) will impact overall circuit effectiveness.