Overview - ISO 11258:2015 (Iron ores for shaft direct‑reduction feedstocks)
ISO 11258:2015 specifies a laboratory method to evaluate how readily oxygen can be removed from iron ores under conditions simulating shaft direct‑reduction processes. The standard defines procedures to determine the reducibility index, the final degree of reduction (R after 90 min) and the degree of metallization (M) for lump ores and hot‑bonded pellets. Results are intended for quality control, contract specification and research comparisons between feedstocks.
Key topics and technical requirements
- Test principle: isothermal reduction of a fixed bed at 800 °C ± 5 °C with continuous mass loss measurement (or at set intervals) up to 90 minutes.
- Reducing gas composition (volume fractions): CO 30% ±1%, CO2 15% ±1%, H2 45% ±1%, N2 10% ±1%. Impurities limited to O2 ≤ 0.1% and H2O ≤ 0.2%.
- Flow rates: reducing gas 50 L/min ± 0.5 L/min; nitrogen for heating/cooling 25 L/min, with 50 L/min during temperature equilibration (volumes referenced at 0 °C, 101.325 kPa).
- Sample and test portions: minimum test sample 2.5 kg (dry); prepare ≥5 test portions ≈ 500 g each; specified particle size ranges for pellets and lumps. Oven‑dry to constant mass at 105 °C ± 5 °C.
- Apparatus: reduction tube (internal diameter 75 mm ± 1 mm) with perforated support plate, furnace capable of uniform 800 °C, balance accurate to 1 g, gas‑supply and flow control ensuring frictionless weighing connection.
- Measured outputs:
- Reduction curve and reducibility indices (dR/dt at R = 40% and 90%)
- Final degree of reduction (R90) from oxygen mass loss after 90 minutes
- Degree of metallization (M) determined either by chemical analysis or via formula derived from R
- Quality assurance: procedures for repeatability, acceptance of test results and required test reporting are included.
Practical applications and users
Who uses ISO 11258:2015:
- Metallurgists and process engineers evaluating feedstock performance for shaft direct‑reduction (DR) plants.
- Iron‑ore producers and quality control laboratories for product specification and batch acceptance.
- Direct reduced iron (DRI) plant operators selecting or benchmarking lump ore and pellet feedstocks.
- Research institutions comparing reducibility and metallization behaviour for process development.
Practical uses:
- Feedstock selection and blending decisions for DR processes.
- Contractual specification and verification of ore shipments.
- R&D and laboratory comparison of ore beneficiation or pelletizing effects on reducibility.
Related standards
Keywords: ISO 11258:2015, reducibility index, degree of metallization, final degree of reduction, shaft direct‑reduction, iron ores, pellets, lump ores, reducibility testing.