Behind the zinc-coated steel bridges spanning rivers and the efficient operation of electronic device heat
sinks lies a metallurgical revolution that has spanned millennia. Zinc, a blue-gray metal with a melting point
of just 419.5°C, quietly underpins the backbone of modern industry with its unique corrosion-resistant and
alloy properties. Its manufacturing process is undergoing a profound transformation—from flame to
electricity, from high-energy consumption to green intelligence.
A Century-Long Rivalry in Smelting Technology: The Clash Between
Pyrometallurgy and Hydrometallurgy
Fire-based metallurgy once dominated history: zinc concentrate was mixed with coke and reduced in a blast
furnace at temperatures exceeding 1,000°C, with the resulting zinc vapor condensing into zinc ingots in a
condenser. However, this method demands high-grade raw materials, is energy-intensive, and struggles to
process complex ore types, leading to its gradual marginalization—its global market share now stands at
just 12%–13%³⁶.
The rise of hydrometallurgy is the contemporary mainstream: accounting for over 85% of global production.
Its core lies in electrolytic deposition:
Roasting: Zinc sulfide concentrate (ZnS) is oxidized into zinc oxide in a fluidized bed furnace, simultaneously
recovering sulfur dioxide to produce acid;
Leaching: Zinc oxide is dissolved in dilute sulfuric acid to form a zinc sulfate solution;
Deep purification: zinc powder is added in three stages to replace impurities such as copper, cadmium, and
cobalt, achieving a solution purity of 99.99%³⁶;
Electrolytic deposition: the purified solution is pumped into an electrolytic cell, and zinc flakes are deposited
at the cathode after applying direct current, with each ton of zinc consuming approximately 3,000
kilowatt-hours of electricity⁴.
Technical challenges in wet zinc smelting: Balancing efficiency
and environmental protection
Leaching residue treatment was once a major industry challenge: Traditional neutral leaching residues contained
up to 20%–30% zinc, and direct disposal was both wasteful and polluting. Two solutions addressed this issue:
High-temperature, high-acid leaching: Under conditions of 95°C and acidity of 60 g/L, secondary leaching
achieves a zinc recovery rate exceeding 98%;
Fuming volatilization method: Zinc is reduced from the residue using coke in a rotary kiln, recovering it as zinc oxide dust.
Iron removal processes determine water quality purity: Iron ion concentrations in the solution directly impact
electrolytic zinc quality. The potassium iron sulfate method and goethite method control pH and temperature
to precipitate iron as crystals for filtration, ensuring electrolyte impurities remain below 0.1 mg/L.
The “millimeter-level art” of the electrolysis workshop: Precision
control in the electrolysis process
Within the electrolytic cell, a transformation of metals occurs between the aluminum cathode and the
lead-silver alloy anode:
Precise control of current density: the optimal range is 450–600 A/m², with higher values causing a loose zinc
layer and lower values resulting in a sharp drop in efficiency;
Dual balance of temperature and acidity: The electrolyte is maintained at 35–45°C, with sulfuric acid concentration
at 150–180 g/L; fluctuations exceeding ±2% can cause dendrite short circuits⁴;
The mysterious role of additives: Animal glue and antimony ions synergistically optimize the crystalline structure
of the zinc layer, enhancing density and stripping efficiency.
A certain factory once experienced a short circuit due to zinc dendrites growing through the membrane because
the cathode edges were not coated with an insulating layer, resulting in the entire batch of products being scrapped.
This lesson led to the development of a rotating cathode design: rotating the electrode plates at a constant
speed of 5 r/min improves deposition uniformity by 40%.
The closed-loop revolution in resource regeneration: transforming
waste into high-purity zinc
Zinc recycling has become a focal point of the industry, particularly for zinc-containing waste materials such as
electroplating sludge and spent catalysts:
Ammonia leaching purification: Selectively leach [Zn(NH₃)₄]²⁺ from spent zinc catalysts using ammonia water,
avoiding iron and silicon impurities;
Deep copper removal: Adding (NH₄)₂S to precipitate copper ions, leveraging the solubility product difference
(Ksp(CuS) = 6.4 × 10⁻³⁶ << Ksp(ZnS) = 1.6 × 10⁻²⁴) to separate zinc and copper;
Electrolytic regeneration: The purified solution undergoes electrowinning to produce regenerated zinc with a purity
of 99.995%, with energy consumption only 1/325 of that for mined zinc.
Future manufacturing: Green technology and high-value transformation
Direct oxygen pressure leaching technology is revolutionizing traditional methods: zinc sulfide concentrate, oxygen,
and sulfuric acid are added to a high-pressure reactor, and at 150°C, zinc sulfate solution is directly produced,
eliminating the calcination step. Sulfur is recovered in its elemental form, reducing emissions by 90%⁶;
Breakthroughs in high-end zinc-based materials:
Nano-Zinc Oxide: Used in sunscreen agents and antimicrobial coatings, with an 8-fold increase in value-added;
Zinc-Air Battery Materials: High energy density characteristics support the energy storage industry, with a cycle
life exceeding 500 cycles.
Conclusion: Zinc Builds Everything, Smart Manufacturing Shapes the Future
From the “smelting of zinc from calamine” recorded in the ancient text *Tian Gong Kai Wu* to intelligent electrolysis
workshops, the history of zinc manufacturing mirrors the progression of human industrial civilization. When zinc liquid
coats vehicle bodies to prevent corrosion, and when zinc alloy castings bear loads in spacecraft, this silent metal
revolution continues—with lower energy consumption, higher purity, and a more closed-loop cycle, reshaping the
very essence of modern manufacturing. In the wave of green metallurgy, the story of zinc has only just begun to
unfold a new chapter.