Copper, an ancient and everlasting metallic luster, has long been deeply embedded in the veins
of human civilization. From the wires and cables that light up thousands of homes to the core components
that drive intelligent manufacturing; from the huge power grid that guarantees clean energy transmission
to the precision medical equipment that guards health, copper has become the indispensable “bloodline”
that supports the modern industrial system with its excellent electrical conductivity, thermal conductivity,
ductility and corrosion resistance. A key step in giving copper materials their outstanding quality is the
sophisticated and complex copper refining process.
From ore to refined copper: the core mission of refining
Copper ores in nature are far from pure. They usually coexist with iron, sulfur, arsenic, antimony, bismuth,
lead, nickel, gold, silver and many other elements. The core objective of copper refining is to efficiently
separate the impurities through a series of physical and chemical processes, ultimately producing refined
copper that is extremely pure (usually 99.99% Cu or higher, i.e. Grade A copper), stable and fully compliant
with the standards of various demanding industrial applications. This process is not only about the quality
of the copper, but also has a direct impact on the performance, reliability and service life of downstream
products.
Fire Refining: The Art of Purification at High Temperatures
Fire refining is the mainstream process for rough copper with high copper content (e.g. anode copper), the core
of which is to utilize the differences in physical and chemical properties of different elements at high
temperatures for separation and purification.
Anode furnace refining:
Oxidation slagging: Air or oxygen-enriched air is drummed into the molten crude copper, and impurities such
as iron, lead, zinc, tin, arsenic, antimony, etc. are preferentially oxidized. Generated oxides and add the quartz
sand (SiO2) flux reaction to form slag floating, be effectively skimmed.
Reduction deoxygenation: After the end of the oxidation stage, a small amount of oxygen may remain in the
copper liquid. Natural gas, liquefied petroleum gas (LPG) or wood reduction (traditional method) is used to
reduce cuprous oxide (Cu2O) to metallic copper and to prevent porosity in the final product.
Critical Steps - Fire Refining De-Antimony:
Arsenic and Antimony Removal: Arsenic and antimony are common and very harmful impurities in copper
(reduced electrical conductivity, thermal embrittlement). By precisely controlling the oxidizing atmosphere
and temperature, it forms volatile oxides (As2O3, Sb2O3) which are either discharged with the flue gas or
form stable compounds into the slag.
Lead and bismuth removal: Lead and bismuth have low melting points. Control the appropriate temperature
and add specific flux (such as soda, fluorite), so that the formation of low melting point slag or part of the
volatile removal.
Sulfur and oxygen removal: Desulfurization in oxidation stage and oxygen removal in reduction stage are the
standard process.
Casting of anode plates: After refining, the pure copper liquid is cast into thick anode plates ready for the next
step of electrolytic refining. The physical specifications of the anode plates (e.g. flatness, uniformity of thickness)
are critical to the efficiency of electrolysis.
Electrolytic refining: the ultimate in current-driven purification
Electrolytic refining is the decisive step in obtaining ultra-high purity refined copper (copper cathode), often with a
purity of more than 99.99%.
The core unit: a huge electrolyzer filled with an electrolyte consisting mainly of sulfuric acid and copper sulfate. A
refined anode plate (containing about 99.5% copper) serves as the anode, and a thin sheet of pure copper starter
or stainless steel cathode master plate serves as the cathode.
Electrochemical purification: When direct current is applied, the copper in the anode plate as well as the more reactive
metal impurities (e.g. iron, nickel, zinc) undergo oxidation and dissolve into the electrolyte. At the cathode, only copper
ions (Cu2+) are preferentially reduced and precipitated, forming a dense, flat layer of pure copper deposits (copper
cathode). Precious metals (gold, silver, platinum group) and inert impurities (selenium, tellurium) fall into the anode
mud, which becomes an important raw material for the recovery of precious metals.
Precision control: The electrolysis process needs to be tightly controlled:
Current Density: Affects deposition rate and crystallization quality.
Electrolyte Composition: Maintain the appropriate concentration of copper ions, acidity, temperature and additives
(such as gum, thiourea, Cl- ions) to ensure that the surface of the copper cathode is bright and clean, and the
physical properties are excellent.
Circulation purification: impurity ions (e.g. nickel, arsenic, antimony) in the electrolyte will gradually accumulate, and
need to be removed through specialized purification systems (e.g. extraction, electrowinning decontamination) to
keep the electrolyte clean.
Hydrometallurgical refining: a green path for processing complex raw materials
Hydrometallurgical refining offers unique advantages for raw materials such as low-grade oxide ores, complex sulfide ores, or
electronic scrap that are not amenable to direct thermal processing:
Leaching: Copper is dissolved from the ore or concentrate using an acidic (sulfuric acid) or basic (ammonia) solution. Common
methods include heap leaching, tank leaching, agitated leaching or high pressure oxygen leaching.
Extraction: Utilizing the selectivity of organic extractants (e.g. hydroxamic oximes), the copper ions in the leach solution are
efficiently extracted into the organic phase to achieve a deep separation from the majority of impurities.
Electrowinning: The copper-loaded organic phase comes into contact with the reverse extraction solution (usually a highly acidic
solution) and the copper ions are reverse extracted into the aqueous phase. The copper-rich counter-extract enters the
electrolyzer and deposits high purity copper cathode (comparable to electrolytically refined copper cathode) directly on the
cathode by electrodeposition.
Environmental Advantages: The wet process typically operates at lower temperatures and atmospheric pressures, with
relatively low energy consumption, fixation of sulphur in the form of sulphate, and minimal SO2 emissions, making it a
cleaner method of production.
Continuous innovation: towards an efficient and green future
Copper refining technology is always striving for higher efficiency, lower energy consumption and better environmental
performance:
Pyro-enhancement: Oxyfuel combustion and flash melting/blowing technologies are widely used to significantly
increase melting efficiency and flue gas SO2 concentration (for acid production) and reduce energy consumption.
Continuous refining processes are also being explored.
Electrolysis optimization: Permanent cathode (stainless steel mother plate) technology replaces the production
of starting electrode sheets, improving automation and cathode quality. High current density electrolyzer design
improves unit capacity. Intelligent control system to optimize process parameters.
Wet upgrading: Development of efficient and low-toxic extractant, direct electrowinning technology, and
cooperative treatment technology for complex materials are hot spots in R&D.
Resource recycling and environmental protection: the comprehensive recovery technology of precious metals
in anode sludge is becoming more and more mature; the resource utilization of smelting slag and electrolysis
purification slag; the stabilization treatment of arsenic and other harmful elements; the whole process of energy
saving and carbon emission reduction technology is the core topic of the industry.
Conclusion
Copper refining, which combines high-temperature flames and micro-current “metal purification technology”,
is a key link to stabilize the cornerstone of modern industry. Whether it is the fire process, which is hardened at
high temperatures, or the wet process, which realizes purity through solution extraction and current drive, the
core of the process lies in the pursuit of the ultimate - removing every trace of impurity and forging copper
materials with excellent performance. With continuous technological innovation and evolution in the direction
of higher efficiency, smarter and greener, the copper refining industry will continue to inject a steady stream of
“pure energy” for the electrification, intelligentization and sustainable development of human society. The quality
of refined copper directly determines the smoothness and robustness of modern industrial “blood vessels”.