After the roar of metal smelting, a kind of “by-products” that have long been regarded as a
burden are quietly changing their identity - smelting residues. They used to be mountains of waste,
occupying land, polluting the environment and consuming management costs. However, with the
sharp increase in pressure on resources and environmental protection regulations, a profound cognitive
revolution is taking place: smelting residues are no longer simply industrial waste, but contain great
value of the “secondary resource treasure”. How to efficiently, cleanly, high-value use of these residues,
has become a key proposition for the sustainable development of the non-ferrous industry.
Heavy burden: the traditional pain of residue disposal
Smelting process is bound to produce a large number of residues, its composition is complex and variable,
often containing a variety of valuable metals, non-metallic minerals and harmful substances. Traditional
disposal methods face serious challenges:
Huge environmental hazards: open-air stockpiling occupies valuable land, the rain wash, weathering, heavy
metal ions in the residue (such as lead, cadmium, arsenic, etc.) and acidic substances are very easy to infiltrate
into the soil, contaminate the groundwater, or spread the formation of dust to pollute the atmosphere, posing
a long-term threat to the ecological environment and human health.
Serious waste of resources: The residue often contains considerable valuable metals (such as zinc, copper, tin,
indium, germanium and other precious metals or rare elements) and iron, silicon, calcium and other basic elements.
Simple landfilling or stockpiling means a permanent loss of these valuable resources.
High economic costs: The construction of compliant landfills, impermeable treatment, leachate collection and
treatment, long-term maintenance and monitoring, and eventual closure of the landfill constitute a heavy economic
burden for enterprises. The risk of environmental penalties for non-compliant disposal is unbearable.
The way out: resource utilization technology blossomed
Burden into wealth, the core lies in the resource utilization driven by technological innovation. At present, for
different composition characteristics of smelting residues, a variety of efficient utilization path has matured:
Valuable metal deep recovery:
Hydrometallurgy: For the slag containing zinc, copper, nickel, cobalt and other metals, acid leaching, alkaline leaching,
bioleaching and other technologies are used to selectively dissolve the target metals, and then efficiently recovered
through extraction, precipitation, electrowinning and other methods, with a recovery rate of more than 90%.
Pyrometallurgy: For the slag containing lead, tin and other metals, smelting can be enhanced by smelting technology
such as smelting furnace, Osmert furnace, etc., so that the valuable metal volatilization into the soot enrichment and
recovery, or extraction of metals through reduction smelting.
Combined process: often use “fire pretreatment + wet purification” or a variety of wet combination of processes to
deal with complex composition of the residue, to achieve a comprehensive recovery of a variety of metals.
High-value conversion of bulk materials:
Raw materials for building materials: Silicon, calcium, aluminum, iron rich slag (such as copper slag, lead slag, part of the
zinc leaching slag) can be used to replace natural sand and gravel aggregates for road construction and foundation backfill
after stabilization and granulation; it can also be made into micropowder through deep processing and be used as cement
mixing material or concrete admixture (slag micropowder), which can significantly enhance the performance and durability
of building materials, and reduce the energy consumption and carbon emission of cement production.
Functional material preparation: Using specific components in the residue (such as iron oxides, silicates, etc.), we can develop
and produce ceramic glaze, wear-resistant flooring materials, environmental remediation materials (e.g., heavy metal adsorbents),
and so on.
Agricultural mineral fertilizers: certain residues rich in silicon, calcium, magnesium and trace elements (need to be strictly
harmless treatment), can be processed into soil conditioners or slow-release mineral fertilizers.
Harmless and safe disposal:
For residues with low recycling value or immature technology, but containing hazardous substances, the first priority is to
achieve harmlessness and stabilization:
Solidification/stabilization: Add cement, lime, special agents, etc., to encapsulate and immobilize the hazardous substances,
reduce their leaching toxicity, and achieve safe landfill standards.
High-temperature melting and vitrification: The residue is melted to form glassy substances at very high temperature (>1300℃),
so that heavy metal ions are firmly bound in the glass network structure, achieving permanent stable sequestration and
extremely low leaching toxicity.
Benefit resonance: economic, environmental and social win-win situation
Promoting the resource utilization of smelting residues brings multi-dimensional and deep-level benefits:
Considerable economic benefits: direct recovery of metals to create profits; slag into building materials and other commodities,
opening up new revenue channels; significantly reduce the cost of storage, disposal, environmental fines and other costs.
Significant environmental benefits: minimize the land occupied by solid waste stockpiling; completely eliminate heavy metal
pollution and the risk of acidic wastewater; replace natural resources (e.g. sand, gravel, cement raw materials) to protect the
ecological environment; reduce energy consumption and carbon emissions per unit of product (e.g. use of slag micropowder to
produce low-carbon cement).
Demonstration of social responsibility: practicing the concept of circular economy to improve the efficiency of resource utilization;
meeting the increasingly stringent environmental protection regulations to reduce environmental risks; shaping a green and
responsible social image of the enterprise to enhance the competitiveness of the industry.
Facing the future: technological innovation and policy-driven
dual-wheeled progress
Although the resource utilization of smelting residues has made great progress, but the challenges remain: complex slag processing
efficiency, low-cost depth of impurity removal, high value-added product development, technical and economic balance. The
direction of future development is clear:
Iterative upgrading of technology: research and development of more efficient, cleaner, more adaptable sorting, extraction, conversion
technology; explore the application of artificial intelligence in process control and optimization; strengthen the coupling and integration
of a variety of technologies.
Improvement of the standard system: accelerate the development of various types of national standards for resource products,
industry standards, standardize the market, enhance user confidence, and open up the application bottleneck (especially in the
field of building materials).
Strong policy support: Strengthen the “extended producer responsibility system”, the main responsibility of enterprises; improve
the comprehensive utilization of resources, tax incentives, green credit and other incentives; increase the support for the research
and development of cutting-edge technologies and industrialization demonstration.
Synergistic industrial symbiosis: to build a multi-industry synergistic circular economy industry chain such as “metallurgy - building
materials - environmental protection”, to realize the optimal allocation of resources and efficient recycling of waste in the region.
Conclusion: Nuggets “slag” bottom, light up the green future!
Smelting residue, the former “environmental burden”, is through the empowerment of science and technology and conceptual
innovation, accelerating the transformation into a valuable “urban mine”. Deep excavation of its resource value and environmental
protection potential is not only a realistic requirement for enterprises to reduce costs and increase efficiency, compliance and survival,
but also a necessary way for the non-ferrous industry to crack the resource and environmental constraints and achieve high-quality
development. Embrace residue resource utilization, is to embrace a cleaner, more efficient, more resilient industrial future. In the
“waste to treasure” on the green journey, every technological breakthrough is a treasure of the earth's resources, a solid commitment
to sustainable development. Nuggets of gold in the “slag”, is really beneficial in the autumn and winter.