Entering a modern lead refinery is like stepping into a metallic kingdom of order and power. The air is
filled with the afterglow of heat waves, and in the huge containers, molten lead, silver-gray with a blue
sheen, flows slowly as it undergoes a metamorphosis from ruggedness to extremity. Here, is the lead
refinery - the fire smelting output of crude lead, or recycled lead material, purified to 99.99% or even
higher purity of the heart of the industry. Every removal of impurities and every casting concerns the
lifeblood of performance in key areas such as downstream batteries, protection and alloys.
Arrival of crude lead: the beginning of the journey
The arrival of transportation vehicles loaded with crude lead ingots or liquid crude lead marks the beginning
of the refining journey. This crude lead usually contains 1-5% impurities, which are:
Metal Partners: Copper (Cu), Arsenic (As), Antimony (Sb), Tin (Sn), Bismuth (Bi) - affecting hardness and workability.
Valuable guests: silver (Ag), gold (Au) and sometimes platinum group metals - treasures to be recovered.
Non-metallic “spoilers”: Sulphur (S), Oxygen (O) - form slag or affect purity.
The first stop in a refinery is the molten lead pot. Huge reflector furnaces or steel pots (lined with refractory)
melt the solid crude lead into liquid form. The heat usually comes from natural gas or fuel oil. The molten
crude lead is pumped or siphoned to the next stage - the arena of refining.
The music of refining: the art of removing impurities
At the heart of lead refining is a precise combination of physico-chemical methods, which, like a delicate dance,
invite away the unwelcome “guests” one by one:
Copper (Cu) Removal - The Duo Dance of Melting and Sulfiding:
Cu removal by melting: Molten crude lead is slowly cooled down (but still above the melting point of lead, 327°C).
Copper and its compounds (e.g., Cu₂S) have a higher melting point and are the first to crystallize and precipitate,
forming a hard, brittle “copper slag” that floats or adheres to the walls and bottom of the pot, and is mechanically
fished out. This is the initial removal of copper.
Add sulfur in addition to copper: for further depth in addition to copper, to the molten lead liquid added elemental
sulfur (S) powder. Sulfur and residual copper react violently to generate insoluble in lead liquid copper sulfide (Cu₂S)
slag, was carefully skimmed. The temperature of the lead liquid needs to be precisely controlled at this moment.
Removal of Arsenic, Antimony and Tin (As, Sb, Sn) - the oxidizing dance of alkaline refining:
The oxidizing agent makes its appearance: Caustic soda (NaOH) and an oxidizing agent (traditionally nitrate NaNO₃,
modern times more often compressed air or oxygen) are added to the molten lead. With vigorous stirring, the
oxidizing agent oxidizes arsenic, antimony, and tin.
Alkaline capture: The oxidized arsenic, antimony and tin (forming sodium arsenite Na₃AsO₃, sodium antimonite
Na₃SbO₃, sodium stannate Na₂SnO₃, etc.) combines with the caustic soda and forms the loose “alkali residue”
floating on the surface of the lead. The operator skims it out skillfully. This process may need to be repeated
several times to meet requirements. The slag is used as a raw material for the recovery of metals such as antimony.
Extraction of Silver and Precious Metals (Ag, Au) - The Dance of the Gold Catchers in the Zinc Shell Method (Parkes Method):
Zinc “bait”: This is one of the most dramatic aspects of the refinery. Zinc (Zn) ingots (usually 1-2% of the weight of the
lead) are added to the molten lead from which the copper, arsenic, antimony and tin have been removed. Zinc and
lead are partially miscible in the molten state.
The birth of “Treasure Island”: After intense stirring, zinc has a strong affinity for silver, gold and other precious metals,
preferentially forming silver-zinc alloys with a high melting point (Ag₂Zn₃, etc.). As the lead liquid slowly cools down,
these alloys crystallize and precipitate, forming a layer of silver-gray, precious metal-rich crust - “zinc shell”, floating
on the surface of the lead liquid.
Harvesting the treasure: The operator carefully extracts the entire zinc shell with special tools. This “shell” is a valuable
raw material for the subsequent extraction of high-purity silver and gold. The residual zinc in the lead is removed by
vacuum dezincification (volatilization of the zinc at high temperatures and under negative pressure) or by alkaline
refining again.
Bismuth (Bi) removal - the final threshold for high purity:
The “fine combination” of calcium and magnesium (Croll-Betherton method): Bismuth is a stubborn last impurity for
very demanding fine lead (e.g. 99.99%+). Calcium (Ca) and magnesium (Mg) metals (or alloys) are added to molten
lead. Calcium and magnesium form high melting point compounds with bismuth (e.g., CaMg₂Bi₂), which crystallize
and precipitate as a slag that is skimmed off.
Electrolytic Refining - Ultimate Purification: In some top refineries, the previously refined lead is cast into anode
plates and placed into electrolytic baths containing a solution of lead silicofluoride (PbSiF₆) and free silicofluoride
(H₂SiF₆). A direct current is applied and pure lead is deposited and precipitated on the cathode (usually a thin
sheet of pure lead), with residual traces of impurities (including bismuth) remaining in the anodic sludge or solution.
This is the most reliable method of obtaining fine lead of the highest purity (99.995% or more).
The birth of purity: casting and the mark of quality
The lead liquids that have been purified through heavy refining shine with a pure silver-gray luster. They are fed
into the casting machine at a precisely controlled temperature:
Ingot casting: The lead is injected into standard molds (e.g., 1-ton ingots or 25-kg ingots), cooled, and then demolded.
Large ingots are commonly used in battery manufacturing plants.
Pelletizing: Some of the lead passes through the pelletizing tower, dripping down from a high place, cooling and
solidifying into uniform lead pellets during the descent, which are convenient for subsequent alloy batching or
small batch use.
Surface treatment: Ingots or lead pellets may be cleaned with dilute acid, washed and dried to remove the surface
oxide film and present a perfect metallic luster.
Quality control: the guardian of purity
At the heart of the refinery is the laboratory. Each batch of refined lead product is subjected to rigorous inspection:
Fire assay: a classic method, especially accurate in determining gold and silver content.
Spectroscopic analysis (OES/ICP): rapid and precise determination of trace impurities (Cu, Bi, Ag, As, Sb, Sn, Zn, etc.) in lead.
Physical property tests: Hardness, tensile strength, etc. (for specific lead alloys).
Only products that meet or exceed the target purity (e.g. 99.994% Pb min) and customer specifications will be stamped
as qualified and ready to leave the factory.
The invisible lifeline: environmental protection and recycling
The core competence of a modern lead refinery is deeply rooted in its environmental performance and its ability to
recycle resources:
The “purification journey” of the flue gas: the lead-containing dust and trace SO₂ produced by the refining pot and
casting line are captured by the powerful ventilation system, and then processed by the high-efficiency bag filter and
wet scrubber tower to ensure that they meet the standard discharge.
Solid Waste: All slags (copper slag, alkali slag, calcium and magnesium slag) and soot generated from the refining
process are considered as resources:
Copper slag, alkali slag: returned to the upstream smelter or specialized treatment plant to recover valuable metals (Cu, Sb, Sn).
Precious metal-rich zinc shells: the main raw material for silver and gold refineries.
Calcium and magnesium slag: an important source for bismuth extraction.
Electrolytic anode sludge: rich in precious metals and other rare metals.
The pursuit of “zero” wastewater: production wastewater (cleaning water, cooling water, etc.) undergoes strict processes
such as neutralization, precipitation, filtration, deep treatment (e.g., ion exchange), etc., to maximize recycling, and a very
small amount of discharged wastewater is ensured to meet the strictest standards.
Occupational health “armor”: Strict work area division (clean area/potentially contaminated area), powerful ventilation,
high-efficiency air filtration system (HEPA), mandatory wearing of special respiratory protection equipment (PAPR) and
protective clothing by employees, strict hygiene management (after-shift showers, centralized washing of uniforms), and
regular blood-lead monitoring all work together to build a solid defense for workers' health. Together, they build a strong
defense for workers' health.
Integration of recycled lead: More and more refineries are processing recycled lead feedstock directly (e.g., lead paste,
lead grids from used batteries) or are working closely with recycled lead plants to apply refining capacity to the purification
of recycled lead, significantly reducing the environmental footprint.
The heavy lifting of lead: the value of refining
The high-purity lead ingots coming out of the refinery carry the trust of industry:
The cornerstone of lead-acid batteries: more than 80% of refined lead is used to make the grids and active materials
for batteries, the heart of car starting, electric vehicle, and energy storage systems.
Shield for radiation protection: its high density makes it an irreplaceable material for shielding X-rays and γ-rays,
guarding the safety of medical treatment, nuclear energy and scientific research.
Chemical corrosion-resistant barrier: made into pipelines, tank linings, against strong acids (especially sulfuric acid) erosion.
Bone and blood for special alloys: solder, bearing alloys, bullets, counterweights... Fine lead is the key component that
gives them their specific properties.
The furnace of the future: greener, smarter, tougher
The lead refining industry continues to evolve in the face of challenges:
Cleantech deepening: developing continuous refining processes with lower energy consumption and emissions;
optimizing bismuth removal technology; exploring the application of wet refining in specific scenarios.
Intelligent Upgrade: Apply sensor networks, automated control systems (PLC/DCS), big data analytics to optimize
refining parameters (temperature, stirring, dosing), predict equipment maintenance, and improve energy efficiency
and product consistency.
Closed Loop Circular Economy: Strengthen the integration with the recycling network of recycled lead, and enhance
the technical capability of handling complex recycled materials (e.g., leaded glass, e-waste), so as to make the lead
resources “unending”.
Safety and protection technology: Introducing more advanced real-time air monitoring, intelligent ventilation
control, and robot-assisted operation to continuously reduce the risk of occupational exposure.
Conclusion: Forging the future between purity and responsibility
A lead refinery is not a simple metal furnace. It is a sophisticated stage where chemistry and physics intertwine, a key
hub for resource recycling, and a practitioner of balancing environmental responsibility with industrial needs. Between
the hot lead and the condensed ingots, under efficient fans and tight security, the refinery uses the power of science
and technology to transform the impurity-laden crude lead into the pure bedrock that drives the security and energy
needs of modern society. Every refining process delivers not only a high-purity lead product, but also a strong commitment
to a sustainable future. It's a never-ending dance of purity that continues to infuse the world with the power of reliability
and security in the heart of the furnace.