When galvanized steel shines in the wind and rain for decades, when zinc flakes quietly release energy
in batteries, behind is a sophisticated electrochemical nirvana - zinc electrolysis, a process that dominates
the global production of zinc, is being silently staged in the electrolysis tanks of a giant workshop.
There is no scorching flame, only the whisper of electric current and the flow of solution, but the
insignificant ore is transformed into a guardian of the metal with amazing purity.
Prologue: The Road to Ore Metamorphosis
The saga of zinc electrolysis began with sphalerite (ZnS) buried deep in the earth. Its journey has been one
of industrial ingenuity:
Crushing and flotation: The ore is crushed and ground, and dances with chemicals in flotation cells. Air
bubbles lift the hydrophobic zinc minerals to produce a zinc concentrate containing 50-60% zinc.
Boiling roasting: The concentrate is rejuvenated in a 950°C boiling furnace:
2ZnS + 3O₂ → 2ZnO + 2SO₂↑
The product is loose, porous roasted sand (ZnO), while the pungent SO₂ gas is immediately captured and
converted into industrial sulphuric acid - a double win for the environment and the economy.
Core Stage: Liquid Purification in Wet Smelting
The essence of zinc electrolysis lies in hydrometallurgy - zinc undergoes molecular-level purification in solution:
Step 1: Embrace of Acid (Leaching)
Neutral Leaching: Roasted sand meets with dilute sulfuric acid (from the electrolysis cycle) in a giant stirring tank:
ZnO + H₂SO₄ → ZnSO₄ + H₂O
Precise control of pH ≈ 5.2, iron, arsenic, antimony, and other impurities hydrolyze into colloidal precipitate, forming
a neutral leaching slag. The supernatant is zinc-containing solution.
Acid leaching: neutral leaching residue by concentrated sulfuric acid second "extraction", maximum recovery of zinc,
the residual leaching final residue (containing iron, silicon) by harmless treatment or resource utilization.
Step 2: Purification snip (the chemical art of removing impurities)
The leach solution still contains trace amounts of cadmium, cobalt, copper and other "destructive elements".
Purification workshop is like a precision laboratory:
Zinc replacement in addition to copper and cadmium:
Zn + Cu²⁺ → Zn²⁺ + Cu↓
Zn + Cd²⁺ → Zn²⁺ + Cd↓
Zinc powder such as magnets adsorption of impurity ions, spongy copper and cadmium slag is extracted and recycled.
Activation in addition to cobalt-nickel: add antimony or arsenic salts to activate cobalt-nickel, zinc powder again:
Zn + Co²⁺ → Zn²⁺ + Co↓
cobalt dregs can be enriched to extract strategic metals.
Deep purification: Multi-stage counter-current operation and precise temperature control ensure that the solution
reaches ppb-level (parts per billion) purity - a key lifeline for successful electrolysis.
Sacred Moment: Electrolytic Deposition (ED) - Rebirth in Current
The purified liquid flows into the electrolysis plant, where the concrete electrolysis tanks, arranged like a
hall of mirrors, await:
Plate configuration:
Anode: lead-silver alloy plate (corrosion-resistant and conductive)
Cathode: polished aluminum plate (hotbed of zinc crystallization)
Electrochemical miracle (DC-driven):
Cathode (reduction): Zn² ⁺ + 2e- → Zn↓
Zinc ions crystallize and grow on the aluminum plate, forming a 3-5 mm dense zinc layer in 24-48 hours
Anode (oxidation): 2H ₂O → O₂↑ + 4H⁺ + 4e-
Oxygen bubbles continue to escape and the acidity of the electrolyte rises
Precise control:
Current density: 500-600 A/m² (e.g. intensity of daylight)
Voltage of the tank: 3.3-3.5 volts
Temperature: 35-40°C (constant spring temperature)
Pole spacing: 30 mm (millimetre precision)
Time of discharge: crane The cathode plate covered with silver-blue zinc layer is slowly lifted up, washed
and sent to the automatic stripping machine - with a "click", the shiny zinc sheet is uncovered like the
pages of a book, with a purity of 99.995%. Waste electrolyte (rich in H₂SO₄) is pumped back to the
leaching process, completing the closed loop of resources.
Final Chapter: Melting and Casting and New Life
Stripped zinc flakes are melted in a low-frequency induction furnace:
Air-isolated melting prevents oxidative losses
Aluminum, copper and other elements are added as needed to blend into die-casting alloys
(e.g., ZA8, ZAMAK)
Liquid zinc is injected into the casting mold to form a 25-kg ingot, or atomized to form zinc powder,
which is silvery and fluid, ready to go.
The glorious frontiers of electrolytic zinc
Steel armor (55%): hot-dip galvanizing and zinc plating protect bridges, cars and buildings from
corrosion for 100 years
Precision casting (20%): zinc alloy die-casting for cell phone cases, door handles, gears
Chemical cornerstone: zinc oxide for rubber, ceramics, sunscreen
Energy future: zinc-air batteries to power drones and storage power stations
Element of life: zinc gluconate guards the Great Wall of human immunity
Green current: The sustainable evolution of zinc electrolysis.
Modern zinc electrolysis plants are an example of the circular economy:
Energy revolution: green electricity (hydro/wind) reduces carbon footprint, electricity consumption
per tonne of zinc down to 2900-3300 kWh
Elemental recycling: cadmium, cobalt, copper, indium, germanium and other associated metals are
efficiently extracted from purification slag
Zero wastewater discharge: in-plant recycling of water resources with in-depth treatment technology
Scrap regeneration: galvanized scrap recycled from the electric arc furnace, zinc extracted from fumes
and reused in the electrolysis line
Intelligent optimization: dynamic control with big data Intelligent optimization: Big data dynamic
regulation and control Current efficiency, approaching the theoretical limit (90%+)
Conclusion:
There is no ear-splitting roar in the zinc electrolysis workshop, only the buzzing of the electric current
and the rattle of the stripping machine play an industrial symphony. From the dark ore to the shining ingot,
after a long journey of flotation, roasting, leaching and purification, the sacred transformation is finally
completed between the cathode and the yang in the electrolyzer. Each zinc ingot is embedded with the
profound wisdom of geochemistry and electrochemistry, and they are the silent guardians of modern
civilization - guarding our world of steel and iron with a silver-blue light that resists rusting and transmits
energy. The next time you touch the cool texture of galvanized railings, it is the poetry of metal written
by millions of amperes of current.