Overview
ISO 4695:2021 - "Iron ores for blast furnace feedstocks - Determination of the reducibility by the rate of reduction index" defines a laboratory test method to provide a relative measure of reducibility for iron ores used as blast furnace feedstocks. The method simulates conditions in the blast furnace reduction zone and is applicable to lump ores, sinters and hot‑bonded pellets. The fifth edition (2021) is a minor revision of the previous edition.
Key topics and technical requirements
- Test principle: Isothermal reduction of a fixed bed at 950 °C ± 10 °C using a CO/N2 reducing gas; mass loss is recorded until degree of reduction reaches 65%. The rate of reduction index is calculated at an oxygen/iron ratio of 0.9.
- Sample & sizing: Material sized to −12.5 mm +10.0 mm; minimum dry test sample 2.5 kg. Prepare at least five test portions (~500 g each: four for testing, one for chemical analysis).
- Reducing gas: Composition CO 40.0% ±0.5% / N2 60.0% ±0.5%. Purity limits for impurities (H2, CO2, O2, H2O) are specified. Flow rate during reduction: 50 L/min ± 0.5 L/min.
- Heating/cooling gas: Nitrogen (N2) used for heating/cooling; flows vary (25 L/min during heat‑up, 50 L/min during temperature equilibration, 5 L/min during cooling).
- Apparatus: Reduction tube (internal diameter 75 mm ±1 mm) with perforated plate to ensure uniform gas flow, electrically heated furnace with a balance capable of 1 g accuracy, thermocouple positioned in the bed centre, and gas‑supply/mixing system.
- Analytical: One test portion used for chemical determinations (total iron and acid‑soluble Fe(II)) per referenced ISO methods.
- Safety: Carbon monoxide hazards - testing requires ventilation and appropriate safety procedures.
Applications and users
ISO 4695:2021 is used to:
- Support quality control in iron ore production and blast furnace feedstock management.
- Provide comparative data for purchasing contracts and material specifications.
- Inform blast furnace performance modelling, charge blend optimisation and R&D on ore behaviour.
Primary users include steelmakers, iron‑ore producers, independent testing laboratories, material procurement teams and researchers studying reducibility and sinter/pellet performance.
Related standards
- ISO 3082 - Sampling and sample preparation for iron ores
- ISO 2597‑1 / ISO 2597‑2 - Determination of total iron content
- ISO 9035 - Determination of acid‑soluble Fe(II) content
- ISO 11323 - Vocabulary for iron ore and direct reduced iron
Keywords: ISO 4695:2021, reducibility, rate of reduction index, iron ores, blast furnace feedstocks, lump ores, sinter, pellets, CO/N2 reducing gas, 950 °C, fixed bed, quality control.