Overview
ISO 16878:2016 - "Iron ores - Determination of metallic iron content - Iron(III) chloride titrimetric method" specifies a laboratory titrimetric procedure to measure the metallic iron content of reduced iron ores (direct reduced iron and metallized fines). The method applies to samples with metallic iron mass fractions from 57.5% to 90.5%. “Metallic iron” is defined as iron not bonded to oxygen or present as pyrite. The standard describes reagents, apparatus, sampling, step‑by‑step procedure, result expression and precision criteria.
Key topics and technical requirements
- Analytical principle: Metallic Fe(0) is oxidized by iron(III) chloride (FeCl3) to Fe(III); the resulting Fe(III) is titrated with potassium dichromate (K2Cr2O7) using sodium diphenylaminesulfonate as indicator.
- Scope and range: Valid for reduced iron ores containing 57.5–90.5% metallic iron.
- Reagents: Preparation of FeCl3 solution (250 g FeCl3·6H2O per litre), 0.01667 mol·L−1 potassium dichromate standard, sulfuric/phosphoric acid mixture, sodium diphenylaminesulfonate indicator, and inert gases (CO2, Ar or N2).
- Apparatus: A‑grade volumetric glassware, analytical balance (0.1 mg), 500 mL Erlenmeyer, magnetic stirrer, non‑magnetic spatula, burette and inert‑gas flushing arrangement.
- Sampling & sample prep: Use a laboratory sample ground to −160 µm in accordance with ISO 10835. Metallized fines must be dried and stored under an inert atmosphere to prevent re‑oxidation; test portions should be representative and exposed to air as briefly as possible.
- Procedure highlights: Typical test portion ~0.2000 g ±0.0050 g; pre‑flush flask with inert gas (~3 L/min for 5 min), add 35 mL FeCl3, stir under inert gas (~5 L/min) for ≥45 min, add acid mix and indicator, then titrate to permanent purple end point. Perform a blank for each new FeCl3 batch.
- Calculation: %Fe(met) = ((V − V0) × 0.0055847) / (m × 3) × 100 where V is sample titrant volume, V0 is blank and m is sample mass.
- Precision: Independent duplicate limit R = 0.349; independent duplicate standard deviation σ = 0.351; between‑laboratories σL ≈ 0.586; permissible inter‑laboratory tolerance ≈ 1.015.
Applications and users
- Quality control and acceptance testing for direct reduced iron (DRI), metallized iron ore fines and reduced pellets.
- Feedstock verification for steelmakers and iron producers ensuring correct metallization levels for blast furnace or electric steelmaking.
- Analytical and commercial laboratories performing routine chemical analysis of iron ore products.
- Research labs studying metallization, reduction processes and product specifications.
Related standards
- ISO 10835 - Sampling and sample preparation for reduced pellets and lump ores
- ISO 11323 - Iron ore and direct reduced iron vocabulary
- ISO 648, ISO 1042 - Laboratory glassware specifications
Safety note: The standard cautions about hazardous operations and requires appropriate lab safety and regulatory compliance when handling acids, dichromate and inert‑gas setups.
Keywords: ISO 16878:2016, iron ores, metallic iron content, iron(III) chloride titrimetric method, FeCl3 titration, potassium dichromate, reduced iron ores, direct reduced iron, metallized fines, laboratory analysis.
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