Imagine: a car battery runs out of life and is sent to a recycling plant. A few short weeks later, the lead
contained in it will be driving a brand new vehicle again. This is not magic, but a resource miracle created
by modern lead processing technology. From buried ore to used batteries, lead processing is a model of
the industrial circular economy.
Starting point: the double play of ore and recycled materials
The journey of lead starts from two main sources:
Primary Ore: Galena (PbS) is the most important lead-containing mineral. The mined ore is crushed, ground
and then flotation-separated to produce a high-grade lead concentrate.
Recycled raw materials (core protagonist): Used lead-acid batteries account for the absolute mainstay of recycled
lead raw materials (more than 85%). In addition, cable sheathing, lead plates, lead alloy scrap, etc. are also
important sources. Recycling is the cornerstone of the modern lead industry, with more than two-thirds of
global lead production originating from recycling.
Smelting: metamorphosis at high temperatures (pyrometallurgical
smelting predominates)
The core step in both concentrates and reclaimed material is smelting and reduction to extract lead from its
compounds. Modern mainstream processes include:
Primary Ore Smelting - Sinter Roasting - Blast Furnace Smelting (traditional mainstream):
Sintering: Lead concentrate is sintered with a flux to form lumps while removing most of the sulfur (SO₂ is
produced for acid production).
Blast furnace smelting: Sintered lumps, coke, etc. are added to the blast furnace. At high temperature, lead oxide is
reduced to liquid crude lead, and impurities form slag and matte (containing copper, precious metals, etc.). The
crude lead is discharged in layers with the slag.
Short process direct lead refining technologies (increasingly important): e.g. oxygen-enriched top-blown immersion
smelting (e.g. SKS method), oxygen bottom-blown smelting (e.g. QSL method), etc. These technologies are used in
one or fewer stages. These technologies complete the oxidation desulfurization and reduction in one or less
equipment, short process, good environmental protection, low energy consumption, high sulfur utilization rate.
Recycled Lead Smelting - Pretreatment is crucial:
Crushing and sorting: Waste batteries are crushed and separated from lead paste (containing lead oxides,
lead sulfate), lead grid (lead alloy), plastics and waste acid by hydraulic or mechanical methods.
Desulfurization conversion: Lead sulfate (PbSO₄) in the lead paste is the difficult part of treatment. It is usually
converted to lead carbonate (PbCO₃) or lead oxide (PbO) with soda ash (Na₂CO₃) or sodium hydroxide (NaOH),
and the sodium sulfate by-product is recovered. This step significantly reduces sulfur emissions from
subsequent smelting.
Smelting Reduction: The treated lead paste, lead grids, etc. are smelted in rotary kilns, short kilns, or furnaces
(e.g., converters, blast furnaces) designed for regeneration. The lead compounds are reduced to crude lead by
a reducing agent (coke, coal) and the impurities enter the slag. Regenerative melting temperatures are usually
lower than primary smelting.
Refining: the pursuit of ultimate purity
The purity of crude lead produced by smelting is about 94%-99%, containing impurities such as copper, antimony,
tin, arsenic, bismuth, silver and gold. The goal of refining is to efficiently separate these impurities and obtain
high-purity refined lead or lead alloys of specific compositions. Main Methods:
Fire refining (commonly used and highly efficient):
Removal of copper (fusion precipitation/sulfur addition): Crude lead is slowly cooled down, and copper and its
compounds are first crystallized due to its high melting point (fusion precipitation). Or add sulfur to generate
copper sulfide slag skimming.
In addition to arsenic, antimony, tin (alkaline refining): add sodium hydroxide and saltpeter (sodium nitrate)
to the molten lead, impurities oxidized to generate sodium salt slag (such as sodium arsenite, sodium
antimonate) is removed.
In addition to silver, gold (plus zinc silver - Parkes method): add zinc, silver, gold and zinc to form a higher melting
point of zinc-silver-gold alloy (silver-zinc shells) floated on the surface of the lead solution, fished out of the
distillation after the recovery of zinc and get the gold-silver alloy. This is a key step in the recovery of precious
metals in lead refining.
Zinc removal (vacuum dezincification/alkaline refining): If zinc is used to extract silver, it is necessary to remove
the residual zinc by vacuum distillation or alkaline refining.
Bismuth Removal (Electrolysis or Calcium-Magnesium): Bismuth is the most difficult to remove. Traditionally, the
Betton-Kroll method is used (with the addition of calcium and magnesium to produce a bismuthized slag).
Electrolytic refining is often used for high purity lead requirements.
Electrolytic refining:
After the initial refining by fire, lead is cast into an anode plate, and pure lead sheets are used as cathodes, which
are energized by placing them into an electrolytic solution made of lead fluorosilicate and fluorosilicic acid.
Lead is dissolved at the anode and precipitated at the cathode with very high purity (>99.99%), with most impurities
remaining in the anode mud (rich in bismuth and precious metals). This method yields the highest purity of fine
lead, but at a higher cost.
The End: The Birth of Refined Lead and Alloys
The refined lead is cast into standard lead ingots (e.g. 99.97% or 99.99%), or directly melted and cast into various
lead alloys according to a strict recipe:
Lead-antimony alloys: to improve hardness and strength, used for battery grids and bearing alloys.
Lead-calcium alloy: Mainstream grating alloy for modern maintenance-free battery, less gas precipitation, low water consumption.
Lead-tin alloy: solder, bearing alloy.
Lead-copper alloy: corrosion-resistant, easy to process.
Closed loop: the core advantage of recycled lead
The brightest chapter in lead processing is its closed-loop recycling capability:
High Recycling Rate: Lead-acid battery lead recycling rate can reach more than 95%.
Infinite cycle: the performance of recycled lead is no different from that of virgin lead, and can be recycled again and again.
Energy saving and environmental protection: the energy consumption of recycled lead is only 25%-35% of that of virgin
lead, which greatly reduces the environmental pressure brought about by ore mining, long-distance transportation
and high-energy smelting, and reduces greenhouse gas and waste emissions.
Urban mine: Used batteries are a valuable resource that stably exists in the city.
Applications: The ubiquitous “heavy” role
Storage batteries (king status): About 80% of the world's lead is used in the manufacture of starter, lighting and
ignition (SLI) automotive batteries, industrial energy storage batteries.
Radiation protection: lead plates, lead clothing used in the medical and nuclear industries to shield X-rays and γ-rays.
Chemical corrosion protection: lead lining, lead pipes for acid-resistant environments.
Cable sheathing (historical applications, less and less): corrosion-resistant protective layer.
Alloying components: Enhance the performance of other metals (e.g. free-cutting steel).
Ammunition and counterweights.
Safety and the environment: a constant responsibility
Lead and its compounds are toxic. The modern lead industry prioritizes safety and the environment:
Enclosed operations and efficient dust removal: strict control of dust fugitive at all stages of production.
Deep purification of flue gas: High-efficiency desulfurization of sintering/smelting flue gas (acid production),
dust removal and heavy metal removal.
Wastewater “zero discharge” treatment: Strict treatment and recycling.
Solid Waste Resourcing: Slag and soot are treated to recover valuable metals or safely utilized.
Strict protection and health monitoring: Workers are equipped with professional protective equipment and
regular medical checkups.
Standardized recycling system: establish a perfect collection network for waste batteries to prevent environmental pollution.
Conclusion: A model for recycling industry
The history of lead processing, from ancient smelting to modern high-tech closed-loop recycling system, shows an
industrial revolution of resource regeneration. It is not only the transformation of physical form (ore/waste → refined
lead/alloy), but also the perfect sublimation of resource value under the concept of circular economy. When a piece
of shiny lead ingot or a brand-new battery comes off the production line, what they carry is not only the wisdom of
industry, but also the unremitting pursuit of human beings for the sustainable utilization of resources. Lead, the
densest common metal, is laying a solid foundation for the future of sustainable development with its unique
“heavy” way of life.