Mill Scale
Mill Scale
Mill scale, a byproduct of steel production, is a flaky layer of iron oxides (FeO, Fe₃O₄, Fe₂O₃) that forms on hot-rolled steel. With an iron content of 68–72%, it is recycled in steelmaking as a raw material in sinter or pellets and used in cement manufacturing to enhance clinker quality. Other applications include industrial coatings, chemical reducing agents, and the production of ferrous powders and ferroalloys, making mill scale a valuable material for waste reduction and resource reuse.
Chemical Composition and Properties for Mill Scale (Iron)
General Formula: Predominantly FeO (iron(II) oxide), with varying amounts of Fe₃O₄ (magnetite) and Fe₂O₃ (hematite)
-Primary Components: A mixture of iron oxides, primarily wüstite (FeO), magnetite (Fe₃O₄), and hematite (Fe₂O₃), along with trace impurities like silica, alumina, or carbon
– Iron Content: Typically around 68% to 72% iron by weight, depending on purity and composition
– Colour: Dark grey to black, often with a metallic or matte appearance
– Crystal System: Varied, with wüstite being isometric, magnetite isometric, and hematite trigonal
– Hardness: 5 – 6.5 on the Mohs scale
– Specific Gravity: 5.0 – 5.2
Chemical Information
– CAS Number: 65996-74-9 (commonly used to refer to mill scale)
– Chemical Composition: A mixture of iron oxides, primarily FeO, Fe₃O₄, and Fe₂O₃, with minor impurities
– Molecular Weight: Variable, due to the proportions of oxides and impurities
– HS Code: 2619.00.90.00 (for slag, dross, scaling, and other waste products of iron and steelmaking)
Specifications
Typical Properties
| Iron as Fe | 70% Basis Rejection Below 68% |
| Sulphur as S | 0.10% max. |
| Silica as SIO2 + Calcium as CAO | 3% max. |
| Phosphorus as P | 0.10% max. |
| Alumina as AL2O3 | 2.5% max. |
