Imagine a high-purity sheet of zinc metal “grown” directly from a seemingly ordinary ore solution
by the marvelous action of electrical energy. This is not magic, but the core of modern wet zinc
refining - zinc electrolysis, a silent but vital “electrical energy alchemy”. It has replaced the ancient
fire smelting process, and with its high efficiency and purity, it has become the mainstay of global
zinc metal production.
Why choose electrolysis? Dilemmas and new paths for traditional
pyrometallurgy
Historically, zinc extraction has long relied on pyrometallurgy. However, this process is like panning for gold in a
hot flame: the energy consumption is huge, the equipment wear and tear is severe, and what's more, the zinc
vapors are easily oxidized or contaminated by impurities, making it difficult to achieve a purity of 99.99% or
more in the final product. In the face of growing demand for pure zinc (e.g., high-quality galvanized steel,
precision alloys, pharmaceutical chemicals) and stringent environmental requirements, wet zinc refining, and
in particular its core electrolytic deposition process, has emerged as the industry's dominant process, thanks
to its mild operating conditions (ambient temperature and atmospheric pressure) and excellent purity.
Uncovering “Electricity Makes Gold”: The Core Principle of Zinc Electrolysis
The stage for zinc electrolysis is a huge electrolyzer filled with an acidic solution of zinc sulfate (ZnSO₄). Here,
a precise “charge transfer” takes place:
The cathode “grows” miraculously: An aluminum plate (cathode) submerged in the solution is connected to
the negative side of the current. Zinc ions (Zn²⁺) in the solution are attracted to the surface of the cathode as
if by a magnet, acquire electrons (2e-), are reduced to metal zinc atoms, and are densely and homogeneously
deposited, layer by layer, on the aluminum plate, forming a solid sheet of zinc. This is the core result of “gold refining”.
The “oxygen factory” of the anode: A special lead-based alloy anode is used for the other pole (connected to the
current positive pole). Here, water molecules (H₂O) are stripped of their electrons, an oxidation reaction occurs,
and a steady stream of oxygen (O₂) escapes, while hydrogen ions (H⁺) are generated to maintain the acidic
environment of the solution.
The whole process is like setting up a “zinc atom highway” in the microscopic world, where electrical energy drives
the zinc ions to migrate in a directional manner and reduce them precisely. Current efficiency (the percentage of
actual zinc deposited over the theoretical value) is a key indicator of the energy utilization of this “alchemy” and is
directly related to production costs.
Precise control of efficient “alchemy”.
Achieving stable, efficient and high-quality zinc deposition is no easy task. It is a delicate balancing act of multiple
process parameters:
Purity of the solution “bloodline”: The electrolyte is the “lifeline” of zinc electrolysis. The “acid-zinc ratio” between the
zinc ion concentration (usually ~55 g/L) and the sulfuric acid concentration (~150-180 g/L) is critical. An imbalance in
the ratio will either result in slow deposition and inefficiency, or contamination of the zinc flake by co-deposition of
impurities. More critically, cobalt (Co), nickel (Ni), germanium (Ge), antimony (Sb) and other trace “destructive molecules”
must be completely eliminated through in-depth purification, and even if they are present in very low levels (ppm), they
can seriously deteriorate the quality of zinc flakes, resulting in burnt plates, growths, or reduced current efficiency.
Current density of the “throttle” control: cathode unit area through the current intensity (current density) as the
production of the “throttle”. Too low, slow deposition, poor efficiency; too high, it may be “out of control”, resulting
in zinc flakes loose and porous, dendritic clusters, and even cause a large number of impurities precipitation. It must
be precisely regulated according to the solution composition, temperature and additive effect.
Temperature and flow “comfort zone”: The electrolyte temperature (usually 35-45°C) needs to be stabilized. If the
temperature is too low, the deposition rate will be slow and energy consumption will increase; if the temperature is too
high, it will increase the escape of acid mist, accelerate the decomposition of additives, and may reduce the density of
zinc flakes. At the same time, keeping the electrolyte flowing evenly and adequately in the tank (through the recirculation
system) ensures that the ions, heat and additives are evenly distributed, and avoids concentration polarization, which is
the basis for producing homogeneous zinc flakes.
Additives: the “invisible” masters of the process: Trace amounts of organic additives (e.g. animal glue, lignosulfonates)
and sodium silicate (water glass) play the role of “magicians”. They can:
Flatten zinc flakes: Inhibit the growth of dendrites and encourage the flat deposition of zinc atoms to form a smooth, dense surface.
Enhance purity: prevent the reduction of impurity ions at the cathode through a “shielding” effect.
Facilitates stripping: Helps to separate the zinc flake from the aluminum cathode plate smoothly. Additive types,
concentrations and replenishment strategies need to be continuously optimized.
Evolving: Zinc electrolysis for the future
Zinc electrolysis technology never stops moving forward. Researchers and engineers are working on it:
The battle for energy efficiency: development of new energy-saving electrodes (e.g., low oxygen precipitation
overpotential anodes), optimization of the electrolytic cell structure (lowering the cell voltage), and improvement
of the current efficiency, in order to significantly reduce the electricity consumption per tonne of zinc, which is
currently the main cost item.
Intelligent “brain”: Introducing advanced sensors, big data analysis and artificial intelligence (AI) to realize real-time
accurate monitoring and intelligent feedback control of key parameters such as electrolyte composition, temperature,
flow rate, tank voltage, etc., so as to make production more stable and efficient.
Extend the life of “tools”: develop more corrosion-resistant and longer-lasting anode materials to reduce the frequency
and cost of downtime replacement.
Green environmental protection upgrade: Strengthen the capture and treatment of acid mist, explore the comprehensive
recovery of valuable metals (such as manganese) in the electrolyte, reduce waste emissions and realize green production.
Conclusion
Zinc electrolysis, the silent “electric energy alchemy” in the electrolyzer, is the beating heart of the modern zinc industry. It
is not only the physical and chemical process of converting ions into metal, but also the ultimate pursuit of efficiency, purity,
cost and environmental protection. Understanding the principles, mastering the operational aspects and embracing
technological innovation are the keys to unlocking the full potential of this “alchemy” and moving the zinc industry towards
a more efficient, cleaner and smarter future. By mastering these core principles, your zinc production will continue to lead
the way in terms of efficiency and quality.