As modern industry demands near-perfect purity levels for copper—99.99% or higher—traditional
pyrometallurgical methods fall short. This is where electrolytic refining emerges as the core technology
bridging the purity gap. This process not only determines purity but also critical properties such as
electrical conductivity and ductility, serving key industries including power transmission, precision
electronics, and high-end equipment manufacturing. So, what precise transformation does the raw
material undergo from crude copper to the rose-colored high-purity cathode copper plate?
Foundation: Strict Raw Material Selection and Pre-Treatment
Electrolytic refining does not begin from scratch; its foundation is high-quality crude copper or anode
copper plates. These raw materials typically originate from preliminary purification through pyrometallurgical
processes, but they still contain various metallic impurities (such as nickel, arsenic, antimony, bismuth, gold,
and silver) and small amounts of non-metallic components. The presence of these impurities poses a threat
to the final product's purity and electrical conductivity.
These raw materials are first cast into anode plates of specific dimensions and thickness. Quality control of
the anode plates is critical: the surface must be as flat and smooth as possible, and the internal structure
must be as dense and uniform as possible to avoid excessive dissolution or premature fracture during the
subsequent electrolytic process. At the same time, another key preparation is the casting of pure starting
plates or the use of specially treated stainless steel mother plates, which will serve as the substrate for
cathode copper deposition and growth.
Core stage: Electrochemical refining within the electrolytic cell
The true core of the electrolytic process occurs within neatly arranged electrolytic cells. These are rectangular
tanks constructed from corrosion-resistant materials (such as concrete lined with plastic or fiberglass) and filled
with continuously circulating electrolyte. The electrolyte primarily consists of a solution of sulfuric acid (H₂SO₄)
and copper sulfate (CuSO₄), with its concentration, temperature, acidity (i.e., free sulfuric acid content), and types
of additives meticulously balanced and strictly controlled—this is the lifeblood of efficient and stable electrolysis.
Within the electrolytic cell, anode plates (composed of crude copper to be refined) and cathode plates/mother
plates are alternately and parallelly suspended in the cell, maintaining precise spacing between them. When a
strong direct current is introduced into the cell via connecting conductors, a silent yet intense electrochemical
transformation immediately begins:
Anode reaction: Under the influence of the current, copper atoms (Cu) on the anode plates lose electrons, oxidize,
and dissolve into the electrolyte, forming copper ions (Cu²⁺). At the same time, more reactive metallic impurities
(such as iron, zinc, and nickel) contained in the anode plate also dissolve into the solution preferentially; while more
inert precious metals (such as gold and silver) and certain insoluble compounds (such as silver selenide and copper
telluride) cannot dissolve effectively and thus precipitate to the bottom of the tank, forming valuable anode sludge.
Cathode reaction: Under the driving force of the electric field, copper ions (Cu²⁺) in the electrolyte migrate to the
cathode surface, gain electrons, and reduce to crystallize into high-purity metallic copper (Cu), which is deposited
in uniform, dense layers on the cathode substrate (initial electrode plate or stainless steel plate). Impurity metal
ions dissolved in the electrolyte, due to their higher precipitation potential than copper (or extremely low concentration),
are difficult to precipitate at the cathode under carefully controlled process conditions, thereby effectively isolating
them from the final product.
The electrolysis process is typically conducted at higher current densities (current intensity per unit cathode area) to
enhance production efficiency. Meanwhile, the electrolyte temperature is strictly maintained within an optimal range
(typically around 50–65°C) to ensure good ion migration speed and crystallization quality. The electrolyte circulation
system is critical, as it ensures uniform composition and temperature throughout the tank, promptly replenishes
copper ions consumed near the cathode, and removes impurity ions and heat accumulated near the anode.
Results: The Birth and Finishing of Cathode Copper Plates
After a predetermined period of continuous electrolytic deposition (typically several days to over ten days), the copper
layer on the cathode reaches the specified thickness (e.g., 5–8 millimeters). At this point, the cathode is carefully lifted
out of the electrolytic cell.
Peeling/Stripping: If a stainless steel substrate is used, the deposited copper plate (now referred to as the cathode
copper) must be completely peeled off. If a thin copper anode plate is used, it may be removed along with the anode plate.
Washing: The peeled-off cathode copper plates are thoroughly washed to remove any remaining electrolyte and trace
impurities from the surface.
Flattening and Trimming: To meet commercial appearance and dimensional requirements, the washed cathode copper
plates are typically subjected to flattening or rolling processes to achieve a smoother surface and remove irregular edges.
Quality inspection, weighing, and bundling: Finally, each cathode copper plate undergoes strict quality inspection
(checking surface quality, physical defects, etc.), precise weighing, and standard-sized bundling and packaging to
become the final product—high-purity cathode copper (typically labeled as Cu-CATH-1, with a purity of ≥99.9935%).
Value extension: By-product recovery and environmental protection
The electrolytic refining process not only produces high-purity cathode
copper but also creates significant added value:
Anode Sludge: The anode sludge settled at the bottom of the tank, though relatively small in total volume, serves as a
valuable raw material for extracting gold, silver, platinum group metals, and rare precious metals such as selenium and
ellurium, possessing extremely high recovery value and requiring complex specialized processes for concentration and
refinement.
Electrolyte Purification: As electrolysis continues, impurity ions (such as nickel, arsenic, antimony, and bismuth) gradually
accumulate in the electrolyte, and the sulfuric acid concentration may also change. Therefore, an electrolyte purification
system must be installed to continuously or intermittently extract part of the electrolyte for impurity removal (such as
crystallization copper removal, extraction, or electrowinning impurity removal), while replenishing fresh acid solution and
returning it to the main circulation system to ensure the long-term stable and efficient operation of the electrolyte.
Environmental protection requirements: Modern electrolytic copper plants place great emphasis on environmental protection.
Wastewater generated during production (such as rinse water and purification wastewater) must undergo strict treatment to
meet standards for reuse or discharge; exhaust gases (primarily acid mist) must be effectively collected and purified through
scrubbers; solid waste (such as purification slag) must be safely disposed of or recycled for resource utilization.
Conclusion: Precision forges the lifeblood of industry
The electrolytic copper production process is a precision engineering endeavor that integrates the wisdom of multiple disciplines,
including materials science, electrochemistry, fluid mechanics, and automatic control. From the meticulous casting of anode plates
to the precise control of ion migration and electron transfer within the electrolytic cell, and finally to the perfect crystallization and
harvesting of cathode copper, every step embodies strict standards and exquisite craftsmanship. It is this mature and efficient
process system that continuously supplies modern industry with high-purity electrolytic copper of exceptional performance,
serving as the indispensable “foundational material lifeblood” that supports the efficient operation of power grids, ensures the
precision and reliability of electronic devices, and drives continuous innovation in advanced manufacturing. In the pursuit of
higher purity, lower energy consumption, and better environmental performance, electrolytic refining technology continues
to advance, further solidifying its position as the cornerstone of the modern copper industry.