When the blue copper sulfate solution surges in the electrolytic tank, the rough anode copper plate
silently melts under the action of electric current, and at the other pole, the clean and pure copper grows
layer by layer like stalactites - this is the magic scene of copper electrolytic refining. Under the traction of direct
current, copper atoms have completed a journey from rough to pure metamorphosis, impurities peeled off, purity
jumped up, the “bloodline” of modern industry is thus unimpeded.
The dance of yin and yang in the electrolyzer
Inside the electrolyzer, the cathode and the anode perform a precise redox reaction:
Anode (rough copper plate): Copper metal loses electrons, oxidizes and dissolves into copper ions
Cu → Cu²⁺ + 2e-
During the process, impurities such as zinc and iron, which are more reactive than copper, are synchronously dissolved
into ions and enter into solution (e.g., zinc: Zn → Zn²⁺ + 2e-), and inert impurities such as gold and silver are simultaneously
dissolved into ions (e.g., Zn → Zn²⁺ + 2e-). The inert impurities such as gold, silver, etc. are difficult to be oxidized and sink
to the bottom of the tank to form valuable “anode mud”.
Cathode (pure copper plate): copper ions in the solution capture electrons, reduction crystallization of high purity copper
Cu²⁺ + 2e- → Cu
active impurity ions exist in the electrolyte, but because of its reduction potential is higher than that of copper ions, can not
be precipitated at the cathode. This “preferential precipitation” mechanism is the core code of purification.
The essence of the reaction: “copper migration” driven by electrical energy
For every copper atom dissolved at the anode, one copper atom is precipitated at the cathode. The total amount of copper
ions in the electrolyte remains unchanged, but impurities are gradually stripped away, resulting in a jump in purity.
Targeted removal of impurities: the underlying logic of industrial-scale
purification
The magic of copper electrolytic refining lies in the triage of impurities:
Reactive metals (Zn, Fe, Ni, etc.):
Priority is given to the dissolution of copper at the anode, but since the cathode only reduces copper ions, such ions remain
in the electrolyte and need to be purified and removed periodically.
Inert metals (Au, Ag, Pt, etc.):
almost insoluble, enriched in anode mud, can extract precious metal resources - each ton of anode mud can be extracted
several kilograms of silver.
Pole distance control:
The distance between cathode and anode is 70~100mm, too small is easy to be short-circuited, too big is a dramatic increase
in energy consumption. Precise plate layout ensures current efficiency and uniform growth of copper crystals.
This “impurity sorting” based on electrode potential allows copper purity to soar from 99% to 99.99%.
Four Process Parameters: The Birth Code of High Purity Copper
Efficient electrolysis requires strict control of technical conditions:
Current Density (200~340 A/m²)
Too high a current density will lead to rough copper cathode crystallization and growth of tumor spurs; too low a current density
will lead to a decrease in production capacity. The industry usually adopts the “dense crystallization threshold” strategy (approx.
300 A/m²) to balance efficiency and quality.
Temperature (55~60℃)
Warming up can reduce the viscosity of the solution and improve the ion migration rate, but overheating will accelerate the escape
of acid mist and energy consumption. Constant temperature magnetic stirring has become the mainstream means of temperature control.
Circulation of electrolyte (top in and bottom out/bottom in and top out)
Circulation eliminates concentration polarization and ensures uniform distribution of copper ions. When the flow rate is insufficient,
“copper dendrite” is easy to appear at the edge of cathode.
Additive control (colloid, thiourea, etc.)
Trace additives are adsorbed on the cathode to inhibit the disordered deposition of copper ions and make the crystallization smooth and dense.
Production reality: the concentration of copper ions in the electrolyte needs to be maintained at 40~50g/L, sulfuric acid 180~200g/L.
Impurities need to be purified after enrichment to avoid cathode precipitation of arsenic, antimony and other hazardous substances.
The industrial soul of copper electrolysis: equipment innovation and
energy-efficiency leap
Electrolysis tank evolution:
from cement lined with lead tank → fiberglass tank → polymer concrete whole tank, corrosion resistance life enhancement to
more than 15 years.
Cathode revolution:
The traditional “starting sheet” (pure copper sheet) is gradually replaced by stainless steel cathode, and the mechanized copper
stripping technology saves 60% of labor.
Energy optimization:
Periodic Reverse Current (PRC) technology disrupts dendrite growth, increasing current density to 640 A/m² without compromising
on quality, and doubling production capacity.
Copper as a cornerstone for every industry
99.99% electrolytic copper is not only the core conductor of cables and motors, but also the lifeline of high-end manufacturing:
Electronics industry: 1 micron electrolytic copper foil has become a key material for chip packaging substrates;
Green energy: photovoltaic welding tape, wind power coils rely on ultra-low oxygen copper;
State-of-the-art equipment: particle gas pedal vacuum chamber needs non-magnetic high purity copper.
Purity challenge: 5N grade (99.999%) copper preparation requires double purification by electrolysis + vacuum melting for
superconducting coils for quantum computers.
From the first electrolysis workshop in St. Petersburg to the flying robotic arms of intelligent factories, copper electrolysis
technology has metamorphosed in its heritage. The coarse anode copper plate, through ionic migration and crystallization
reconstruction, finally becomes a colorful metal scroll. Each beam of accurately controlled current is silently writing the poetry
of metallurgical science - what swirls in the electrolytic cell is not only the blue solution, but also the totem of the spirit of
industrial civilization in pursuit of extreme purity.