From sleeping ores in the depths of the earth to glistening metallic zinc ingots, a modern “alchemy” is
taking place that combines chemical ingenuity with the power of electricity. Wet zinc refining, with its
advantages of high efficiency, purity and environmental protection, has become the dominant force in
the global production of zinc metal, completely revolutionizing the traditional fire smelting pattern.
The choice between fire and water: the rise of the wet process
Historically, the extraction of zinc has long relied on pyrometallurgical processes - dancing with coke in
high-temperature furnaces to reduce the zinc in the ore. However, this ‘road to fire’ was fraught with challenges:
huge energy consumption, rapid wear and tear of equipment at high temperatures, and the dilemma that zinc
vapors were difficult to capture, oxidized or contaminated with impurities. At a time when demand for high
purity zinc (>99.99%) is surging (for high grade galvanized steels, precision die casting alloys, pharmaceutical
chemicals, etc.) and environmental regulations are becoming increasingly stringent, wet zinc refining stands
out as the choice of the times with its mild operating conditions (ambient temperature and pressure),
excellent purity and relatively clean production process.
The wet zinc trilogy: from ore to metal
Modern wet zinc refining is an elaborate relay race of chemical reactions and electrical energy conversion:
Roasting: releasing soluble zinc
The zinc sulfide concentrate (ZnS) first enters the boiling roaster. At precisely controlled temperatures, sulfur
combines with oxygen to form sulfur dioxide (SO₂, used in the production of acids), while zinc is converted into
zinc oxide (ZnO), which is more soluble in dilute sulfuric acid. This step opens the door for the subsequent “dissolution”.
Leaching: the “zinc trap” in the acid solution
The roasted product (zinc baking sand) enters the leaching tank and reacts fully with dilute sulfuric acid (H₂SO₄).
Zinc oxide (ZnO) is dissolved and converted to zinc sulfate (ZnSO₄) solution. However, iron, arsenic, antimony, germanium,
copper, cadmium, cobalt, nickel and other impurities in the ore are also dissolved. The solution is “a mixture rich in zinc
but also full of impurities”.
Purification: the precise capture of chemical "hunters
The first stage (copper and cadmium removal): Zinc powder (Zn) is added, and the replacement reaction is utilized to
accurately capture copper (Cu²⁺) and cadmium (Cd²⁺) in the solution like a magnet, forming a sponge-like copper and
cadmium residue that is filtered out.
The second stage (removal of cobalt and nickel): special activators (such as antimony salts and arsenic salts) are added in
synergy with the zinc powder to remove stubborn cobalt (Co²⁺) and nickel (Ni²⁺) in depth under specific conditions. This
step is extremely delicate, with temperature, pH, and intensity of stirring all having a direct impact on the purification results.
This is the most important and technically advanced part of wet zinc refining. There is only one goal: to completely remove
the impurity ions from the solution with minimal loss of zinc.
Multi-stage deep purification is the core strategy:
After several layers of “filtration”, the result is a pure, transparent electrolytic solution of zinc sulfate (ZnSO₄), which lays the
perfect foundation for electrolytic deposition.
Electrolytic deposition: the “crystallization” of electrical energy
The pure ZnSO₄ electrolyte is pumped into the huge electrolyzer.
Cathode (aluminum plate): The negative electrode, which is charged with direct current, attracts zinc ions (Zn²⁺), which gain
electrons on its surface and are reduced to metallic zinc atoms, which are then deposited layer by layer to form dense
cathodic zinc sheets. This is the crystallization moment of “alchemy”.
Anode (lead alloy sheet): The positive electrode is energized with direct current, where water molecules (H₂O) are oxidized,
releasing oxygen (O₂) continuously and generating hydrogen ions (H⁺) to maintain the acidity of the solution.
After a certain number of cycles, the cathode zinc flakes are stripped and fused to become the final product, a high-purity
zinc ingot. The lean solution (high in sulfuric acid and low in zinc ions) after electrolysis is returned to the leaching process for recycling.
Treatment of leaching slag: the double challenge of resources and environment
The residual slag after leaching (containing iron, lead, silver, indium and other valuable elements and undissolved matter) is an
important by-product of wet zinc refining, and its treatment is not only a requirement for environmental protection, but also a key
to resource utilization:
Mainstream process: Hot acid leaching combined with iron precipitation technology (e.g. acicular iron ore method, hematite method
or yellow potash alum method) is usually adopted to maximize the recovery of valuable metals such as zinc and indium, and to
produce stable iron slag that can be safely stockpiled or utilized.
Continuous innovation: Research and development of more efficient, more environmentally friendly slag treatment and valuable
metal recovery technology is the industry hot spot.
Looking to the future: “Alchemy” for continuous optimization
Zinc extraction technology never stops innovating:
Green leaching: Explore new ways of atmospheric pressure oxygen enrichment or bioleaching to reduce energy consumption
and improve efficiency.
Intelligent purification: applying advanced sensors and process control models to realize accurate, stable and low-consumption
purification processes.
Energy-saving electrolysis: research and development of new low-energy anode materials (such as coated titanium anode),
optimize the design of electrolysis tanks and current distribution, and significantly reduce electricity consumption, which accounts
for the bulk of the cost.
Circular Economy: Strengthen the efficient recovery of valuable metals (indium, germanium, silver, etc.) from leaching slag to
maximize resource utilization and reduce environmental footprint.
Digital empowerment: Optimize the whole process operation by using big data and artificial intelligence to improve
overall efficiency and product quality stability.
Conclusion
Modern wet zinc refining, the “electric alchemy” from ore to high-purity zinc ingot, is a masterpiece of human wisdom
dancing with the elements of nature. It is not only an efficient metal extraction process, but also a relentless pursuit of clean
production, resource recycling and continuous innovation. By mastering the core principles of roasting, leaching, deep
purification, electrolytic deposition and slag treatment, and by embracing technological innovation, the zinc industry will
continue to break through on the road to efficiency and sustainability, and will provide solid “zinc” power for the development
of modern society. Grasp these key processes, and your zinc extraction technology will be even more competitive.