Recycling and reusing iron-containing waste materials generated in industrial production can expand iron ore resources, reduce pig iron costs, and reduce solid waste emissions, making it a core aspect of the circular economy in the steel industry.
Currently, the main recyclable materials include: blast furnace dust, converter dust (steelmaking dust and sludge), rolling mill scale, iron filings, sulfuric acid slag, converter steel slag, and high-iron tailings of non-ferrous metals.
Ⅰ,Characteristics of Various Iron-Containing Materials and Their Application in Blast Furnaces
- Blast Furnace Dust (Gas Ash/Gas Sludge)
Source: By-product recovered from the blast furnace gas dust removal system, composed of ore and coke powder.
Production: 30-50 kg per ton of pig iron
Composition: TFe ≈ 40%, carbon 10%-20%, high CaO content
Characteristics: Fine particle size, poor hydrophilicity
Applications: Sintering feedstock; can replace some iron ore powder and fuel, reducing costs; addition amount 3%-5%
2,Converter Dust (Steelmaking Dust/OG Sludge)
Source: Iron-containing powder recovered from oxygen converter flue gas dust collectors
Production: 20-25 kg per ton of steel
Composition: TFe 50%-60% or more, mainly Fe₃O₄, containing 16%-30% metallic iron
Characteristics: Extremely fine particle size
Applications: Auxiliary raw material for sintering or pelletizing; a high-quality iron-containing resource
3,Steel Rolling Scale (Iron Oxide Scale)
Source: Iron oxide scale that peels off the surface of hot steel billets during the rolling process, accounting for 2%~3% of steel production.
Composition: 60%~70% TFe, mainly Fe₃O₄, containing a small amount of metallic iron, and very few SiO₂ and Al₂O₃ impurities.
Characteristics: Flake-like, extremely high iron content.
Application: Used in sintering batching to steadily improve the grade of sintered ore; large impurities must be screened out before use, and the particle size must be controlled <10mm.
- Iron Scrap
Source: Turning and forging waste from iron casting machines and machining.
Composition: Mainly iron and a small amount of carbon.
Characteristics: Exothermic during high-temperature oxidation, saving solid fuel.
Application: Added to sintering materials to increase the iron content of sintered ore and reduce fuel consumption.
- Sulfuric Acid Slag
Source: Residue from the roasting of pyrite to produce sulfuric acid in chemical plants
Composition: TFe≈50%, mainly Fe₂O₃; high sulfur content (1%~2%), and contains non-ferrous metals such as Cu, Pb, Zn, and Co, as well as precious metals such as Au and Ag.
Characteristics: Extremely fine particle size, <0.1mm is the majority.
Applications: – For slag with higher iron content: Agglomerated and fed into the blast furnace; added at 3%~5% in sintering batches (sulfur content must be strictly controlled).
Pelletizing process: Chlorinating agent is added, and valuable metals such as Cu, Pb, and Zn are recovered through high-temperature volatilization; the pellets are then fed back into the furnace.
For slag with lower iron content: Used as a raw material in cement production.
- Converter Slag
Source: Slag produced by oxygen converter steelmaking or open-hearth steelmaking
Composition: TFe≈16%, containing a large amount of alkaline oxides CaO and MgO, with low-melting-point minerals
Characteristics: Recoverable iron, can replace some limestone and dolomite as flux; disadvantage is high phosphorus content
Applications: Sintering batching, can reduce sintering temperature, increase sinter strength, and reduce costs; the amount added should not be too high to avoid excessive phosphorus content in pig iron
Ⅱ,Latest Industry Developments and Precautions in 2026
- Significantly Improved Utilization Rate: The comprehensive utilization rate of iron-containing dust and sludge in domestic steel enterprises has reached over 98%, and the proportion of secondary resources in sintering batching of some advanced enterprises exceeds 20%
- Technological Upgrade: The widespread adoption of dezincification processes such as rotary hearth furnaces and rotary kilns has solved the problem of zinc-containing dust and sludge circulating and eroding the furnace lining within the blast furnace
- Key control points for blast furnace operation:
Strictly control the sulfur content of sulfuric acid slag and the phosphorus content of steel slag to prevent excessive pig iron quality.
All materials must be mixed thoroughly in advance to avoid unstable blast furnace conditions caused by composition fluctuations.
Dust and sludge with a zinc content >0.5% must be dezincified first and are strictly prohibited from being directly fed into the furnace.