In the core process of copper smelting—electrolytic refining—the chemical reactions occurring
at the cathode act like precise molecular magic, transforming industrial crude copper into
high-purity material with a purity of 99.99%. The core code behind this transformation is
the copper cathode half-reaction equation. This article will delve into the chemical essence
of this reaction, key process control points, and its critical role in modern industry.
The Scientific Logic Behind the Chemical Equation
The standard expression for the copper cathode half-reaction is:
Cu²⁺ + 2e⁻ → Cu
This seemingly simple equation actually encompasses complex electrochemical mechanisms
at the microscopic level:
Electron transfer: Each copper ion (Cu²⁺) captures two electrons to complete reduction
Lattice formation: Metallic copper deposits in an ordered face-centered cubic structure
Energy balance: The standard electrode potential of the reaction is +0.34V (relative to the standard hydrogen electrode)
In the electrolytic cell, this reaction forms a complete circuit with the anode half-reaction
(Cu → Cu²⁺ + 2e⁻), enabling the purification of copper. Research indicates that for every 1
farad of charge (96,485 coulombs), the cathode can deposit 31.75g of metallic copper,
which serves as the theoretical benchmark for calculating energy consumption and
production in the production process.
Impact of process parameters on reaction efficiency
In actual production, achieving the ideal conversion of the half-reaction requires precise control of three key parameters:
1. Current density (200–350 A/m²)
Below 200 A/m²: Deposition rate is too slow, crystal size > 50 μm
Above 350 A/m²: Dendrite growth increases surface roughness by 25%
Optimal range: 280 A/m² yields a uniform and dense deposition layer
2. Electrolyte composition
Copper sulfate concentration: 160–220 g/L maintains ion mobility
Sulfuric acid content: 40–60 g/L suppresses side reactions
Colloidal additive: 0.5–1.2 g/L gelatin improves crystal morphology
3. Temperature control (50–65°C)
For every 10°C increase in temperature, the reaction rate increases by 15%
Temperatures above 65°C accelerate additive decomposition, producing sulfide inclusions
A large smelter optimized these three parameters, increasing current efficiency from 92% to
97.3% and reducing energy consumption per ton of copper by 18%.
Reaction defects and quality control
In actual operation, deviations from the ideal half-reaction equation can lead to typical quality issues:
Abnormal Phenomena Chemical Mechanism Solutions
Surface Pores H⁺ ions compete for reduction, producing hydrogen gas Adjust pH to 1.8–2.2
Edge Tumors Uneven current distribution causes concentration polarization Improve electrode plate spacing
Coarse Grains Insufficient additive concentration Add 0.3 g/L thiourea
Impurity deposition As/Sb plasma co-reduction Pre-arsenic removal treatment to <0.001%
By monitoring the composition of the deposited layer using an online X-ray fluorescence analyzer, the
impurity excess rate can be controlled below 0.003%.
Reaction formula upgrades in industrial applications
With technological advancements, the basic half-reaction formula has evolved into various improved processes:
1. Periodic Reverse Electrolysis (PRC Technology)
Forward current for 30 seconds (copper deposition)
Reverse current for 0.5 seconds (dissolution of dendrites)
Reduces surface roughness by 60%, particularly suitable for electronic copper foil production
2. Pulse Electrolysis
Using 100 Hz high-frequency pulses
Peak current density reaches 500 A/m²
Grain size reduced to 8–12 μm, tensile strength increased to 260 MPa
3. Magnetic field-assisted electrolysis
Applying a 0.5T steady magnetic field
Enhancing ion migration via the Lorentz force
Increasing deposition rate by 22% and reducing energy consumption by 14%
These innovations have broken through the theoretical limits of traditional reaction-based production
efficiency. In a demonstration project, the line speed for producing 100,000 tons of copper foil annually
reached 15 m/min.
Reactive process restructuring under green metallurgy
Under the carbon neutrality backdrop, the copper cathode half-reaction process is undergoing
environmental innovations:
New energy power supply
Direct connection of photovoltaic DC power to the electrolytic cell
Eliminating AC rectification losses (saving 6% of electricity)
Carbon footprint per ton of copper reduced from 3.1 tons to 1.6 tons of CO₂ equivalent
Closed-loop water system
Electrolyte recycling rate >98%
Copper ion recovery rate from wastewater 99.8%
Achieving “zero liquid discharge” standards
Biological leaching coupling
Pre-treatment of ore with iron(II) sulfide bacteria
Copper leaching rate increased to 95%
Reduced sulfuric acid consumption by 40%
Conclusion: Micro-level reactions driving macro-level industry
As materials science, automatic control, and clean energy technologies converge, this fundamental chemical
reaction is breaking through the boundaries of century-old traditional processes. Understanding and
mastering the precise process of Cu²⁺ + 2e⁻ → Cu is the key to unlocking the treasure trove of high-purity
copper materials.