In non-ferrous metal smelting, lead-acid battery recycling and lead-containing chemical production and
many other industrial processes, a complex shape, composition of the solid residue - lead slag - inevitably
produced. For a long time, its heavy metal lead and associated arsenic, cadmium and other toxic and harmful
substances, as if hanging over the head of the environment and health of the sword of Damocles. Traditional
landfill disposal not only takes up valuable land resources, but also has a huge risk of long-term slow release
of pollutants and leachate contamination of groundwater and soil. How to safely, efficiently and resourcefully
dispose of lead slag has become a key bottleneck restricting the green upgrading of related industries, and
is also a must-answer question for building a “waste-free city” and realizing a circular economy.
Lead dregs treatment: from simple landfill to technological attack
In the early days, lead slag was often regarded as useless waste, and simple stockpiling or landfilling was the
mainstream practice. However, with the awakening of environmental awareness and increasingly stringent
regulations, especially the “National Hazardous Waste List” clearly most of the lead slag into the scope of
hazardous waste management, the road of crude disposal was completely blocked. The industry has begun
to seek technological breakthroughs:
Solidification/stabilization technology: As a relatively basic means, the heavy metal ions in lead slag are fixed
or transformed into a stable form with low solubility and low migration through the addition of materials such
as cement, lime, and specific chemicals. This method can effectively reduce short-term environmental risks and
create conditions for subsequent safe landfilling. However, its limitations are clear: valuable metal resources
cannot be recovered, the products of the treatment still need to be finally disposed of, and the long-term
stability still needs to be continuously monitored and evaluated.
Safe landfill: For lead residue that has been adequately pre-treated (e.g., solidified and stabilized) to meet entry
standards, entering a dedicated hazardous waste safe landfill with a complete containment system, leachate
collection and treatment facilities, and stringent environmental monitoring is currently a compliant means of
disposal under the hood. But this is ultimately the problem “sealed” for future generations, not the ideal end
of the resource cycle.
Resource recycling: the core path of turning waste into treasure
Facing the double challenges of resource shortage and environmental protection pressure, the resourceful
regeneration of lead slag is the key to break the situation, and its core objective is to efficiently and environmentally
friendly recovery of valuable metals (mainly lead), and the rational use of secondary products.
Pyrometallurgical smelting technology: This is currently the most widely used and technologically mature
pathway for lead slag resource utilization.
Oxygen-enriched melting pool smelting (such as oxygen bottom-blowing, side-blowing smelting): this type of
advanced smelting technology mixes lead slag with flux and reductant (coke or coal), and carries out high-temperature
smelting in an oxygen-enriched environment. Lead and its compounds are reduced to crude lead, which is
effectively separated from the slag formed. This process has the advantages of large treatment capacity, high
metal recovery rate (lead recovery rate can reach more than 95%), easy centralized treatment of flue gas
(supporting acid production or tail gas desulfurization), etc. It is especially suitable for the treatment of large
quantities of lead slag with relatively stable composition.
Rotary kiln treatment: more applications in the treatment of lower lead content or more complex composition
of waste lead-acid batteries lead paste slag, lead-containing sludge and so on. Lead slag undergoes drying,
roasting desulfurization, reduction smelting and other processes in the rotary kiln, and eventually produces
crude lead or lead alloy. Its advantage lies in the strong adaptability to raw materials, but the energy consumption
is relatively high and fine control is needed to prevent ring formation.
Key advantages: high technological maturity, large processing scale, excellent lead recovery efficiency, and by-products
(slag, soot) that can be further resourced or harmlessly disposed of (e.g., slag can be used as raw material for building
materials or road base material after quenching by water).
Challenges and optimization direction: need to continue to reduce energy consumption, improve the level of
automation and intelligence, strengthen the complex components (such as arsenic, antimony) of the synergistic
recovery or open-circuit processing capabilities, and improve the efficiency of flue gas purification in order to
comply with more stringent emission standards.
Wet metallurgy technology: as an important supplement to pyrometallurgy, it is especially suitable for processing
lead-containing materials that are not suitable for direct high-temperature smelting (such as very fine particles,
low-grade slag, or materials with high chlorine and fluorine content).
Leaching-purification-electrolysis: lead is selectively dissolved from slag by using acidic (e.g., fluorosilicic acid, acetic
acid-hydrogen peroxide system) or alkaline (e.g., sodium hydroxide) leaching agents, and then the leaching solution
is purified by chemical precipitation, ion exchange, solvent extraction, etc., and finally electrolyzed to obtain
high-purity lead electrowinning.
Conversion-dissolution: Lead in the slag is first converted into compounds that are easily soluble in specific solvents
(e.g., lead carbonate), and then separated and extracted.
Key advantages: relatively mild reaction conditions (atmospheric pressure, medium-low temperature), high metal
selectivity, easier to realize automated control, suitable for small and medium scale or specific composition of
lead slag treatment, high product purity.
Challenges and optimization directions: the process is relatively complex, reagent consumption may be large, and
the cost of subsequent harmless treatment of leaching slag and waste liquid needs to be finely controlled. R&D of new
leaching system and purification technology with high efficiency, low cost and environmental friendliness is the focus.
Policy Driven and Future Prospects: Toward Green Cycle
The solid waste law, recycling economy promotion law, “no waste city” construction pilot program and other policies
and regulations continue to be issued at the national level, providing solid legal protection and guidance for the
standardized management and resource utilization of hazardous waste such as lead slag. Strict enforcement of
environmental protection inspections and market access standards also force enterprises to adopt advanced and
clean treatment technology.
The future development of lead slag treatment technology will be more focused:
Synergy and coupling: Explore the synergistic treatment process of lead slag and other lead-containing wastes or
metallurgical by-products to enhance the overall resource utilization efficiency and economic benefits.
Greening and low-carbonization: Continuously optimize the thermal process to reduce energy consumption and
carbon emissions; develop new wet process technologies that are more efficient and less polluting; and strengthen
waste heat recycling.
Intelligence and refinement: Utilize Internet of Things, big data and artificial intelligence technology to achieve
precise control and intelligent optimization of the treatment process.
Whole-chain management: the concept of whole-process management from source reduction, process control
to end-resource utilization will be more in-depth.
Conclusion
Lead slag, once regarded as a heavy environmental burden, is now under the dual drive of science and technology
and policy, undergoing a magnificent transformation from “hazardous waste” to “urban mine”. Resource recycling
technology innovation and application, not only significantly reduce the risk of environmental pollution, to protect
ecological safety and public health, but also to achieve the effective cycle of lead as a strategic metal resource for
the industry to inject green momentum. Promoting the continued progress and large-scale application of lead
residue resource utilization technology is a key step in cracking the lead pollution dilemma, practicing green
development and building a beautiful China. Only by transforming waste into resources can we truly realize the
win-win situation of economic development and environmental protection.