When you build a house out of galvanized steel, drive a car with zinc-alloyed parts, or pick up an ordinary
battery, have you ever wondered how zinc, the element that silently protects metals from corrosion and is so
ubiquitous in industry and in life, transformed itself from an ore buried deep in the ground into the shiny
metal we hold in our hands?
The birth of zinc is a fascinating journey that combines geological wisdom, chemical magic and the power
of modern industry. Today, we will unravel the mysteries of zinc production and explore its critical transformation
from ore to finished product.
Step One: Treasure Hunting and Departure - Mining and Beneficiation
Zinc's journey begins deep within the earth in deposits rich in sphalerite (ZnS) or rhodochrosite (ZnCO₃). Miners
excavate the zinc-containing ores through open-pit or underground mining methods. However, the raw ore is like
a treasure mixed with sand and gravel. The zinc content is usually very low (1-15%) and has to be carefully washed
in a “beneficiation” process.
In a beneficiation plant, the ore is first crushed in a crusher and ground in a ball mill to a fine powder. Then, taking
advantage of the differences in physical or chemical properties between zinc minerals and other impurities (such as
veins), the most critical step - flotation - takes place. Specific chemicals are added to the ore slurry and air is introduced
into the flotation tanks, creating numerous air bubbles. These bubbles act as precise “magnets”, selectively attracting
only the zinc mineral particles and bringing them to the surface to form a froth layer that is scraped out, resulting in a
high-grade zinc concentrate (up to 50-60% zinc). The tailings are then properly disposed of or stockpiled.
Step 2: Baptism of fire and wind - roasting (wet mainstream process)
For zinc sulfide-based concentrates, the next stop in the modern mainstream (wet zinc refining) process is the boiling
roaster. Here, the concentrate particles are blown up and down by a strong stream of air, like boiling water. At temperatures
of around 900-950°C, the key reaction takes place:
2ZnS + 3O₂ → 2ZnO + 2SO₂
The zinc sulfide is oxidized and converted into zinc oxide (zinc roasting sand), which can be easily treated by subsequent
acid solubilization, while sulphur dioxide (SO₂)-rich gases are produced. This flue gas is a valuable resource, and after
efficient dust removal and purification, it is sent to the acid production system to be converted into sulfuric acid, an
important industrial raw material. The high efficiency, energy saving and environmentally friendly characteristics of the
boiling roaster make it a standard feature in modern zinc plants.
Step 3: Dissolution in acid - leaching
After getting the zinc roasted sand, the journey enters
Leaching, the heart of hydrometallurgy. The zinc roasting sand is fed into a huge leaching tank, where it is thoroughly
mixed and agitated with a dilute sulfuric acid solution (from the electrolysis process or purchased). Zinc oxide reacts
chemically with the sulfuric acid:
ZnO + H₂SO₄ → ZnSO₄ + H₂O
Elemental zinc is dissolved into the solution in the form of zinc sulfate (ZnSO₄), forming a zinc-containing leach solution.
However, impurities such as iron, copper, cadmium, arsenic, etc. accompanying the roasted sand are also dissolved into
the solution to a greater or lesser extent. Therefore, leaching is usually designed as a multi-stage process, in which the
zinc is dissolved as much as possible through precise control of acidity, temperature and addition of oxidizing agents
(e.g., manganese dioxide), while some of the impurities (e.g., iron) are inhibited or precipitated.
Step 4: The “purification” journey of the solution - purification and removal
of impurities
Although the leaching solution (neutral supernatant) is rich in zinc, it is also like a glass of mixed fruit juice, containing a variety
of “uninvited guests” (impurity ions). These impurities, especially trace amounts of copper, cadmium, cobalt, nickel, etc., if they
enter the subsequent electrolysis, will seriously affect the quality of zinc precipitation, increase energy consumption and even
cause explosions. Therefore, deep “purification” is necessary.
The purification plant is like a sophisticated chemical laboratory. A multi-stage purification process is used, usually utilizing zinc
powder as the “cleaning agent”. Under specific temperature and stirring conditions, zinc powder and the necessary activators
(such as antimony or arsenic salts) are added to the solution. Zinc powder has a stronger reducing properties, through the
replacement reaction or co-precipitation, the solution of copper, cadmium, cobalt, nickel and other harmful impurities ions
one by one “capture” out of the formation of solid dregs precipitation (purification slag). After repeated filtration, and
finally get pure as water zinc sulfate solution, for electrolysis to make perfect preparation.
Step 5: The Magic of Electricity - Electrolytic Deposition
This is the magic moment to witness the birth of zinc metal! The pure zinc sulfate solution is pumped into the bright and
spacious electrolysis workshop and injected into the huge electrolysis tank. Inside the tank, cathodes (aluminum plates) and
anodes (lead-silver alloy plates) are arranged in parallel. When a powerful direct current flows through, magic happens:
At the cathode (aluminum): Zn²⁺ + 2e- → Zn The zinc ions gain electrons and are reduced to metallic zinc, and layers of
dense, shiny zinc flakes are deposited and grow on the aluminum.
At the anode: 2H₂O → O₂ + 4H⁺ + 4e- Water molecules lose electrons and are oxidized and decomposed, generating
oxygen and hydrogen ions (to maintain solution acidity).
After 24-48 hours of continuous deposition, the zinc flakes on the cathode plate reach a sufficient thickness (a few millimeters).
They are automatically lifted out and stripped, and those shiny silver zinc flakes are our final product - the cathode zinc plate!
The stripped aluminum cathode plates are cleaned and reused. The poor liquid after electrolysis (with lower zinc content
and higher acidity) is returned to the leaching process for recycling.
Step 6: Molding and new life - melting and casting
The freshly stripped zinc cathode sheets are in thin sheets and need a final “shaping” for transportation and use. They are melted
into liquid zinc in a reflector or induction furnace. In the molten state, the composition can be adjusted again (e.g., by adding a
small amount of aluminum to improve the properties) or poured directly into a mold. As it cools and solidifies, a zinc ingot
(usually weighing about one ton) or zinc alloy ingot is produced, bearing a brand name and marking in accordance with
international standards. These ingots are the basic raw materials that flow into various industrial sectors and play a key
role in corrosion protection, casting, battery manufacturing, and more.
The Ancient Wisdom of Pyrolysis - Closed Blast Furnace Zinc Refining (ISP)
Although the wet electrolysis process accounts for more than 80% of global zinc production, another ancient and unique
pyro-process, the closed blast furnace zinc smelting (ISP), is still used in specific regions. It treats lead-zinc syngenetic ores
or complex materials together to produce both crude lead and zinc-containing vapors in a huge blast furnace using high
temperatures and a reducing atmosphere generated by the burning of coke. The zinc-containing vapors are rapidly cooled
and absorbed by the incoming lead rain outside the furnace to form zinc-containing crude lead, which is then separated
from the zinc by a vacuum dezincing unit.The ISP process is capable of efficiently processing complex raw materials and
achieving lead-zinc co-production.
Green and efficient: the pursuit of the modern zinc industry
Modern zinc production is not only about technology, but also about responsibility and innovation:
Resource recycling: leaching slag, purification slag, soot, etc. are rich in valuable metals such as lead, silver, gold, indium,
germanium, etc., which are comprehensively recycled through advanced technology, turning waste into treasure.
Energy saving: Utilizing the roasting waste heat to generate electricity, utilizing the waste heat of electrolytic lean liquor, and
popularizing energy efficient equipment to continuously reduce the unit energy consumption.
Environmental protection: Strict flue gas desulphurization (SO₂ recovery for acid production), in-depth treatment and recycling
of wastewater, harmless disposal of solid wastes and resource utilization to minimize the impact on the environment. Wet
smelting is especially known for its environmental friendliness.
From dark ore to silver ingot, the birth of zinc unites the wisdom of geological explorers, the precision design of engineers,
the rigor and meticulousness of operators, as well as the relentless pursuit of high efficiency and environmental protection
in modern industry. This wonderful journey of metal transformation not only provides indispensable material protection for
modern life, but also highlights mankind's extraordinary ability to utilize and transform nature and its responsibility. The next
time you come into contact with a zinc product, imagine the magnificent journey of science and industry behind it.