Overview
ISO 334:2020 - "Coal and coke - Determination of total sulfur - Eschka method" is an ISO reference method for measuring total sulfur in hard coal, brown coal (lignite) and coke. The standard specifies the classical Eschka method, a gravimetric procedure in which sulfur is converted to sulfate during ignition with an Eschka mixture and quantified by precipitation as barium sulfate. ISO 334:2020 is the fourth edition and updates referenced documents and definitions while retaining the Eschka procedure as a laboratory reference.
Key topics and requirements
- Scope: Reference method for total sulfur in coal and coke via the Eschka method.
- Principle: Ignite a prepared test portion intimately mixed with Eschka mixture in an oxidizing atmosphere (800 °C ± 25 °C) to convert sulfur to sulfate; extract with HCl and determine sulfates gravimetrically by barium chloride precipitation.
- Eschka mixture: Two parts light calcined magnesium oxide to one part anhydrous sodium (or potassium) carbonate; sieved to pass 212 μm.
- Test portions: Masses depend on expected sulfur (e.g., for coal: <5% → 1.0 g, 5–10% → 0.5 g, >10% → 0.25 g; coke typically 1 g).
- Apparatus & conditions: Electrically heated muffle furnace (800 °C ± 25 °C; ~5 air changes/min), platinum/silica/glazed porcelain crucibles, Gooch crucible, analytical balance (0.1 mg).
- Analytical steps: sample preparation to 212 μm; weigh and mix with Eschka mixture; ignition schedule; extraction with hydrochloric acid; filtration and washing; neutralization and controlled precipitation; gravimetric determination of BaSO4.
- Quality & validation: Clause 10 gives repeatability/reproducibility limits; instrumental alternatives must be validated against this reference to demonstrate absence of bias.
Applications and users
- Laboratories performing coal and coke chemical analysis and routine quality control.
- Coal producers, coke manufacturers and power plants monitoring fuel sulfur content for combustion performance and emissions compliance.
- Regulatory and environmental testing bodies requiring a reference gravimetric method for verification of faster instrumental techniques (e.g., XRF, combustion analyzers).
- Research institutions comparing analytical methods or studying sulfur behavior in fuels.
Related standards
Normative references include:
ISO 334:2020 remains a key reference for accurate, comparable measurement of total sulfur by the Eschka method in coal and coke testing.
