In modern steelmaking, the presence of lead (Pb) and zinc (Zn)—both heavier than iron—can cause serious challenges to refining operations and final steel quality. Understanding their harmful effects and applying effective removal techniques are essential for optimizing the steelmaking process.
Hazards of Lead and Zinc in Steel
- Damage to steel structure
Lead and zinc disrupt the ferrite matrix and lattice structure, which negatively affects the mechanical properties of steel, reducing its strength and toughness. - Impact on furnace equipment
Due to their high density, lead and zinc tend to settle at the furnace bottom. This not only damages the bottom electrode but also accelerates the erosion of furnace refractory materials. - Difficulty in refining operations
Removing lead and zinc is not easy and requires dedicated refining techniques to achieve stable and effective results.
European Experience in De-lead and De-zinc Processes
In Europe, excess lead and zinc in scrap are quite common, pushing steelmakers to develop advanced removal technologies. Notably, the BSW steel plant in Germany and the 90-ton electric arc furnace (EAF) technology have matured and are successfully applied in production. Our own practice in DC EAFs has also proven that these methods can meet production requirements.
Lead Removal Methods
Lead is a low oxidation potential and relatively stable element, which tends to evaporate quickly under steelmaking conditions. The main steps for lead removal are:
- Oxidation stage: When sampling shows excess lead in molten steel, carbon injection is stopped. Oxygen blowing intensity and angle are increased to oxidize carbon in steel to below 0.10%. Strong stirring raises steel temperature, which promotes oxidation of lead at the furnace bottom and its capture by slag. This process usually lasts 2–6 minutes.
- Reduction and evaporation stage: Foaming carbon powder is then injected, rapidly reducing lead oxides back to metallic lead. The lead evaporates and escapes into the furnace gas, effectively removing a portion of it. Studies show that this method can eliminate more than 25% of lead, making it a practical industrial solution.
Zinc Removal Process
Because zinc shares similar chemical and physical properties with lead, the process for zinc removal is largely the same. However, in practice, zinc removal tends to be even more effective, making it a widely adopted method in electric arc furnace steelmaking.
