Overview
ISO 5931:2000 specifies a reference method for the determination of total sulfur in calcined coke and calcined carbon products used in the production of aluminium. The method is the classical Eschka method, intended for materials that contain at least 0.1% (mass) sulfur and preferably less than 4% (mass). ISO 5931:2000 is used as a benchmark for laboratory measurements and for validating faster instrumental methods.
Key topics and requirements
- Scope and sample: Applies to calcined coke and calcined carbon products for the aluminium industry. Test sample preparation follows ISO 6375 principles and results are reported on an air-dried basis.
- Eschka mixture: Prepared from 2 parts light calcined magnesium oxide to 1 part anhydrous sodium (or potassium) carbonate, passed through a 212 µm sieve.
- Test portion: Two duplicate portions of 1 g are analysed; results are reported as the mean to the nearest 0.1% by mass.
- Ignition and conversion: Test portion mixed with Eschka mixture, ignited in a muffle furnace at 800 ± 25 °C (at least 3 h) to convert sulfur to sulfate.
- Extraction and precipitation: Sulfate extracted with hydrochloric acid, then precipitated as barium sulfate using barium chloride; final determination is gravimetric (weighing BaSO4).
- Precision: Repeatability limit 0.05% (absolute); reproducibility limit 0.10% (absolute).
- Quality controls: Includes a blank run, use of duplicate determinations, and specified reagent and apparatus quality (e.g., platinum/silica/glazed porcelain crucibles, Gooch crucibles, specified glassware standards).
Applications and users
ISO 5931:2000 is primarily used by:
- Laboratory analysts and QC personnel in the aluminium smelting and carbon materials industry.
- Manufacturers of calcined coke and calcined carbon products for product certification and internal quality control.
- Testing laboratories that require a reference method to validate faster instrumental techniques (e.g., combustion analysers) for total sulfur determination.
- Regulatory and procurement teams needing reproducible, comparable sulfur measurements for process control, furnace feedstock specification, and material conformity.
Practical benefits include standardized sample handling, robust gravimetric endpoint (barium sulfate), and accepted precision limits that support traceable reporting and method comparison.
Related standards
- ISO 6375:1980 - Sampling of coke for aluminium electrodes (sample preparation)
- ISO 4787 / ISO 4788 - Laboratory volumetric glassware and measuring cylinders
- ISO 5725 - Precision of measurement methods
- ISO 1170 - Converting results to moisture bases
Keywords: ISO 5931:2000, Eschka method, calcined coke, calcined carbon products, total sulfur determination, aluminium industry, barium sulfate gravimetric.