Overview
ISO 5068-2:2025 specifies an indirect gravimetric method for the determination of moisture in the analysis sample of brown coals and lignites. The method measures moisture by drying a representative test portion and calculating the moisture mass fraction from the mass loss. It is intended for laboratory analysis where precise moisture values are needed for subsequent testing (volatile matter, calorific value, C/H analysis, etc.).
Key topics and technical requirements
- Test principle: Loss in mass of a test portion dried to constant mass at 105 °C to 110 °C in a nitrogen atmosphere.
- Sample size and preparation: Typical test portion is 1 g to 2 g, ground to pass a 0.212 mm sieve and prepared according to ISO 18283 or ISO 13909-4.
- Atmosphere and gas purity: Dry high‑purity nitrogen with a maximum oxygen content of 30 µl/l; nitrogen flow providing about 15 oven-volume changes per hour. Annex A describes a nitrogen purification train option.
- Apparatus: Minimum free-volume nitrogen oven, shallow silica/glass dish with fitted lid, balance sensitive to 0.0001 g, flow meter, drying tower (magnesium perchlorate or silica gel) and a cooling vessel/desiccator.
- Drying end point: Constant mass defined as successive mass losses of less than 0.001 g; use the higher loss for calculations.
- Calculation and reporting: Moisture mass fraction calculated from initial and final masses; report the arithmetic mean of duplicate determinations to the nearest 0.1%.
- Repeatability: Duplicate determinations by the same operator/apparatus should not differ by more than 0.3% (absolute).
- Safety/chemicals: Desiccants such as magnesium perchlorate and silica gel recommended; note safety warning for magnesium perchlorate (strong oxidizer).
Applications and users
- Laboratories performing routine coal and lignite analysis (QA/QC, research, energy content determination).
- Coal testing facilities and utilities calculating calorific value and composition where accurate moisture correction is required.
- Producers and trading organizations requiring consistent moisture measurement for specification, billing, and compliance.
- Environmental and materials testing labs where hygroscopic behavior of brown coals and lignites affects downstream analyses.
Related standards
- ISO 18283 - Manual sampling of coal (sample preparation referenced).
- ISO 13909-4 - Mechanical sampling and preparation of test samples.
- ISO 1213-2 - Vocabulary for sampling, testing and analysis (terms and definitions used).
Keywords: ISO 5068-2:2025, brown coals, lignites, moisture determination, indirect gravimetric method, nitrogen oven, sample preparation, coal analysis, repeatability limit.