Overview
ISO 6129:1981 specifies a gravimetric method for determining the hygroscopic moisture content of analytical samples of chromium ores. The method is intended to be performed together with other chemical determinations on the same analytical sample so that results for other constituents can be reported on an absolutely dry basis. ISO 6129 is intended to be read in conjunction with ISO 6629 (general instructions for chemical analysis of chromium ores).
Key topics and requirements
- Scope: Determination of hygroscopic (surface) moisture in analytical samples of chromium ores using oven drying and gravimetric weighing.
- Sample preparation: Use a test sample crushed to a particle size not exceeding 0.10 mm and air‑dried under laboratory conditions.
- Test portion: 5 g of the prepared sample is weighed into a pre‑dried weighing bottle with stopper (bottle diameter not less than 5 cm).
- Drying conditions: Place the open weighing bottle in an oven controlled at 105–110 °C. Initial drying is 1 hour, followed by cooling in a desiccator for 20–30 minutes, then weighing.
- Repeat drying cycles: Continue drying (typically 30 min cycles), cooling and weighing until the difference between two successive masses is ≤ 0.0005 g. If mass increases after repeated drying, accept the preceding mass.
- Calculation: Hygroscopic moisture content (%) is calculated gravimetrically by comparing bottle+sample masses before and after drying. Using the standard notation:
- ml = mass of weighing bottle + sample + stopper before drying
- m2 = mass of weighing bottle + sample + stopper after drying
- m1 = mass of the test portion
- Hygroscopic moisture (%) = (ml − m2) / m1 × 100
- Quality control: The standard provides permissible tolerances for duplicate determinations depending on the moisture content range.
Applications and who uses it
ISO 6129 is used by:
- Laboratory analysts and assayers conducting chemical analysis of chromium ores and concentrates
- Mining companies and QA/QC teams verifying ore moisture for reporting and process control
- Metallurgical laboratories and buyers/sellers requiring moisture-corrected compositional data
Practical uses include converting analytical results to an absolutely dry basis, ensuring consistency in chemical assays, and establishing moisture figures for contract and process specifications.
Related standards
- ISO 6629 - Chromium ores and concentrates - Methods of chemical analysis: General instructions (read in conjunction with ISO 6129)
Keywords: ISO 6129, chromium ores, hygroscopic moisture, gravimetric method, moisture determination, oven drying, analytical samples, ISO 6629.
