When you feel the breeze on a galvanized steel bridge or twist open a bottle of vitamin supplements, the journey
of a silver-blue metal is complete. The birth of zinc, the "metallic moonlight" that guards human civilization, is a
sophisticated ritual that combines geological mysteries, chemical magic and engineering ingenuity. Let's go into
a modern zinc smelter and unravel the mystery of how zinc metal is born from the sleeping ore.
Chapter 1: The Beginning of the Earth's Gift (Ore and Beneficiation)
The source of zinc is deep in the earth's crust, mainly found in sphalerite (ZnS), often symbiotic with galena. The
raw ore is mined as an uncut diamond:
Crushing and milling: A giant crusher crushes the ore to gravel size, then a ball mill grinds it to a fine powder (as
fine as flour), releasing the zinc mineral particles.
FLOTATION MAGIC: This is the critical step. Ore powder is mixed with water and special chemicals in a flotation tank:
The trapping agent "kisses" the surface of the sphalerite, making it hydrophobic.
Foaming agents create a rich froth.
When air is introduced, the hydrophobic zinc mineral particles float to the surface with the bubbles forming a frothy
layer, which is scraped out as zinc concentrate (Zn 50%-60%).
The veinstone sinks to the bottom of the tank and becomes tailings. Flotation accurately separates co-occurring
minerals (e.g., lead and zinc in lead-zinc ore).
Chapter 2: Baptism of Fire - Roasting Conversion (Prologue to
Wet Zinc Refining)
Once the zinc concentrate is obtained, 90% of the zinc is extracted by hydrometallurgy (electrolysis), which
begins with a high-temperature transformation in a roaster:
Boiling roasting: The zinc concentrate is injected into a high-temperature (900-1000°C) boiling furnace, where
it is violently "boiled" and burned in oxygen-enriched air.
Sulfur conversion: The core reaction takes place: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
PRODUCTS AND VALUES:
Produces porous solid roasted sand (containing mainly ZnO) ready for subsequent leaching.
High concentration of SO₂ flue gas is produced, which is immediately sent to the acid production system to
be converted into industrial sulfuric acid, an important by-product. Environmental protection and economic
benefits are a win-win situation here.
Chapter 3: Liquid Purification - The Chemical Dance of Leaching
and Purification (Wet Core)
Roasted sand enters the “water world” of wet smelting, and zinc undergoes layers of purification in the solution:
Neutral leaching:
Roasted sand is mixed with dilute sulfuric acid (from the electrolysis process) or spent electrolyte in a large leach tank.
Zinc dissolution: ZnO + H₂SO₄ → ZnSO₄ + H₂O.
Control the endpoint pH (~5.2), so that iron, arsenic, antimony and other impurities hydrolyzed and precipitated,
forming impurity-containing neutral leaching slag (sent to the lead system or further processing).
Get zinc-containing solution (neutral supernatant), but there are still trace impurities.
Acid leaching (treatment of slag):
The medium leach slag is re-leached with more concentrated sulphuric acid at high temperature to maximize zinc recovery.
Final leach slag rich in iron, silicon and other impurities is produced (harmless treatment or comprehensive utilization).
Solution depth purification - molecular level snip of impurity removal:
Zinc powder displacement removal: Add zinc powder to the solution, like a magnet to accurately remove:
Cadmium (Cd): Zn + Cd² ⁺ → Zn² ⁺ + Cd↓ (formation of sponge cadmium recycling)
Cobalt, nickel (need to be activator): add antimony or arsenic salts to activate the zinc powder displacement to remove: Zn + Co² ⁺ → Zn²⁺ + Co↓
Copper: Zn + Cu²⁺ → Zn²⁺ + Cu↓
Multi-stage precision control: Temperature, zinc powder particle size, add the order of strict optimization, to ensure the
removal of impurities in depth, and the output of pure zinc sulfate (ZnSO ₄) electrolyte.
Chapter 4: Rebirth of Electricity - Electrolytic Deposition (ED)
The pure electrolyte flows into the electrolysis plant to witness the “electrochemical crystallization” of zinc metal:
Array of electrolysis tanks: huge concrete tanks with lead-silver alloy anodes alternating with aluminum cathodes,
submerged in zinc sulfate solution.
The miracle of electricity:
Cathode reaction (regeneration): Zn²⁺ + 2e- → Zn↓ (zinc ions crystallize on aluminum cathode)
Anode reaction (regeneration): 2H₂O → O₂↑ + 4H⁺ + 4e- (oxygen is released, acid is produced)
Elaborate carving:
Every 24-48 hours, a worker will remove the deposited zinc. Every 24-48 hours, workers lift out the aluminum cathode
with a dense zinc layer (2-3mm thick) deposited on it.
Automatic stripping machines strip off the shiny zinc cathode sheets.
The acid-containing waste liquid (containing H₂SO₄) from the anodes is returned to the leaching process for
recycling, closing the resource loop.
The purity of the precipitated zinc is as high as 99.995%.
Chapter 5: Melting and casting molding
Zinc cathode sheet enters the final melt molding:
Low-frequency induction melting: the cathode sheet is melted into liquid zinc in an oxygen-free
environment to prevent oxidation.
Alloy blending (optional): Trace amounts of aluminum, copper, magnesium, etc. are added as required to
melt-cast specific grades of zinc alloys (e.g., Zamak alloys for die casting).
Ingot/Pelletizing: Liquid zinc is injected into the casting mold to form a standard zinc ingot (25 kg), or
blown into pellets for easy transportation and use.
Chapter 6: The Other Path - Fire Distillation (ISP vs. Electrothermal)
About 10% of zinc is extracted by fire extraction, suitable for specific feedstock or co-production needs:
Imperial Smelting Process (ISP) - The king of co-production of lead and zinc co-products:
Lead and zinc concentrates are mixed and sintered and added to a blast furnace.
High temperature reduction in the furnace produces crude lead (sinking) and zinc vapor (rising).
The zinc vapor is dissolved in a lead rain condenser by a liquid lead "bath", and the zinc precipitates out
and separates after cooling to yield crude zinc (98.5%).
Electrothermal / Vertical Pot Distillation: Processing of low iron zinc ores or secondary raw materials, coke
reduction of zinc oxide produces zinc vapor, which is condensed to yield crude zinc.
FIRE REFINING - PURIFICATION IN REFINERY TOWERS:
Crude zinc is evaporated and condensed several times in refining towers (lead and cadmium towers).
Separation of zinc, lead and cadmium utilizing the difference in boiling points (907°C for zinc, 767°C for cadmium and 1749°C for lead).
Yields 99.99%+ high purity zinc.
The world of applications where zinc shines
Defender of steel: Zinc plating (55% usage) provides corrosion-resistant armor for steel bridges,
cars and household appliances.
Element of life: Zinc oxide is used in rubber, pharmaceuticals and skin care products.
Precision casting: zinc alloy die castings support automotive and electronic housings.
Chemical cornerstone: Zinc powder is used in chemical synthesis, zinc compounds are used in pigments and agriculture.
Energy carrier: Zinc-air batteries are a potential new star.
The Green Zinc Way: Recycling and Innovation
The modern zinc industry is a model for recycling:
Recycling of galvanized scrap: Zinc in electric arc furnaces is efficiently collected as soot (20%+ zinc content)
and returned to smelting.
Resourcefulness of smelting slag: Iron extraction from leaching slag, recovery of rare metals such as indium and germanium.
Energy Consumption Revolution: Continuous optimization of wet process, decreasing electricity consumption per ton of zinc.
Bio-metallurgical exploration: the use of microorganisms to leach low-grade ore, a promising prospect.
Conclusion:
From the flotation tank foam churning, to the electrolysis tank of the current whispers, and then to the melting furnace
of the silver flow, zinc's every form of transformation are condensed human deciphering the wisdom of the natural code.
It is not only a cold metal, but also an active link between mining and life, industry and environment. The next time a
raindrop slides across a galvanized roof, or a fingertip touches a zinc door handle, remember this extraordinary journey
through ore, fire and electricity - zinc, with its quiet resilience, continues to shape and protect our world.