Overview
ISO 24548:2025 - "Rare earth - Determination of moisture content in rare earth products - Gravimetric method" defines a standardized gravimetric procedure for measuring moisture content in rare earth solid concentrates, rare earth oxides and rare earth fluorides. The method is based on loss of mass after thermal drying and aims to improve comparability of moisture data across laboratories and trade partners. The standard does not cover lanthanum oxide or neodymium oxide, nor mixed oxides containing them, because these materials react with water and CO2 in air.
Key technical topics and requirements
- Principle: Moisture is quantified from mass loss after drying in a laboratory oven at 105 °C (±5 °C).
- Measurement ranges: Table 1 provides validated and applicable measurement ranges; for example, rare earth oxides show a validated range of 0.16–6.65% and an applicable range of 0.10–10.0% (mass fraction).
- Apparatus:
- Analytical balance accurate to 0.1 mg (0.0001 g).
- Weighing vessels (glass, silica, mullite or corrosion‑resistant metal); rare earth fluorides require corrosion‑resistant metallic vessels (e.g., platinum).
- Laboratory oven capable of 105 °C continuous operation and a desiccator with silica gel.
- Sample handling:
- Samples sealed in double-layer polymer film bags per ISO 22927.
- Measurement should be performed immediately or within 48 hours if stored in sealed bags.
- Test portion masses specified (e.g., 10.00 g for concentrates; 5.00 g for oxides/fluorides).
- Procedure:
- Dry empty vessel to constant mass (constant mass = mass change ≤ 0.04% after additional 1 h at 105 °C).
- Weigh test portion, dry at 105 °C for at least 1 h, cool in desiccator, and reweigh until constant mass achieved.
- Results and precision:
- Moisture % calculated from mass before and after drying.
- Precision (repeatability and reproducibility) requirements are specified and referenced to ISO 5725 series; r and R limits are provided via Annex B.
Applications and users
ISO 24548:2025 is intended for:
- Quality control laboratories at rare earth producers and processors
- Trading and inspection labs verifying moisture for commerce
- Regulatory and customs testing where moisture affects classification or pricing
- Research laboratories performing compositional or physical property analyses that require accurate moisture correction
Practical benefits include consistent moisture reporting, reduced trade disputes, and reliable input for downstream chemical analyses (e.g., LOI measured per ISO 5976).
Related standards
- ISO 5725‑1 / ‑2 / ‑3 (trueness, precision, repeatability/reproducibility)
- ISO 22927 (packaging and labelling of rare earths)
- ISO 5976 (Loss on Ignition for certain rare earth oxides)
Keywords: ISO 24548:2025, gravimetric method, moisture determination, rare earth oxides, rare earth fluorides, rare earth solid concentrate, laboratory oven, analytical balance, repeatability, reproducibility.