ISO 24548:2025
(Main)Rare earth — Determination of moisture content in rare earth products — Gravimetric method
Rare earth — Determination of moisture content in rare earth products — Gravimetric method
This document specifies a gravimetric method for the determination of the moisture content in rare earth solid concentrate, rare earth oxides and rare earth fluorides. The specified measurement ranges for moisture are shown in Table 1. This document is not applicable to: a) lanthanum oxide and neodymium oxide; b) rare earth oxides containing lanthanum oxide or neodymium oxide, such as lanthanum-cerium oxide, praseodymium-neodymium oxide, etc. This document does not involve sampling. NOTE Since the lanthanum oxide and neodymium oxide will react with water and carbon dioxide in the air, moisture cannot be accurately determined. However, this method can also be a guidance for the determination of the moisture in these materials.
Terres rares — Détermination de la teneur en humidité des produits à base de terres rares — Méthode gravimétrique
General Information
Standards Content (Sample)
International
Standard
ISO 24548
First edition
Rare earth — Determination of
2025-10
moisture content in rare earth
products — Gravimetric method
Terres rares — Détermination de la teneur en humidité des
produits à base de terres rares — Méthode gravimétrique
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Apparatus . 2
6 Samples . 2
6.1 Sample storage .2
6.2 Sample preparation .2
7 Procedure . 3
7.1 Preparation of the weighing vessel .3
7.2 Test portion .3
7.3 Determination .3
8 Calculation and expression of results . 4
8.1 Calculation of moisture content .4
8.2 Precision . . .4
9 Test report . 4
Annex A (informative) Information on the precision test . 5
Annex B (informative) Regression formulae of precision . 6
Bibliography . 7
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 298, Rare earth.
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iv
Introduction
Determination of moisture content is one of the most basic detection requirements for the trade of rare
earth (RE) mineral products, including rare earth oxides and rare earth fluorides. It is also the preliminary
step in chemical composition analysis or physical performance inspection of the sample. A standardized
moisture content determination method is helpful to improve the consistency and comparability of data
when collected from a number of laboratories and to reduce trade disputes due to inconsistency of test
results, thereby facilitating the fair trade of rare earth products.
The RE solid concentrate refers to enriched material obtained from rare earth containing minerals, including
mineral concentrate of bastnaesite, mineral concentrate of monazite, and mixed mineral concentrate of
bastnaesite and monazite.
Rare earth oxides include those that contain one rare earth element and mixed rare earth oxides that
contain more than one rare earth element. Lanthanum oxide and neodymium oxide are not included because
they can easily absorb moisture and carbon dioxide from the air. Also mixed rare earth oxides containing
lanthanum oxide or neodymium oxide, such as praseodymium-neodymium oxide, lanthanum-cerium oxide
and lanthanum-cerium-praseodymium-neodymium oxide, are not included in the scope of this document.
The rare earth fluorides include individual rare earth fluorides and mixed rare earth fluorides.
The Loss on Ignition (LOI) test is determined for this rare earth oxides in accordance with ISO 5976.
v
International Standard ISO 24548:2025(en)
Rare earth — Determination of moisture content in rare earth
products — Gravimetric method
WARNING — The use of this document can involve hazardous materials, operations and equipment.
This document does not purport to address any safety problems associated with its use. It is the
responsibility of the user of this document to establish appropriate safety and health practices and
determine the applicability of regulatory limitations prior to use.
1 Scope
This document specifies a gravimetric method for the determination of the moisture content in rare earth
solid concentrate, rare earth oxides and rare earth fluorides.
The specified measurement ranges for moisture are shown in Table 1. An instrument capable of achieving
the below ranges is used for this determination.
Table 1 — Measurement range — Gravimetric method
Validated measurement range Applicable measurement range
in the inter-laboratory test by this determination method
Sample types
(mass fraction %) (mass fraction %)
Rare earth solid concentrates
Rare earth oxides 0,16 to 6,65 0,10 to 10,0
Rare earth fluorides
This document is not applicable to:
a) lanthanum oxide and neodymium oxide;
b) rare earth oxides containing lanthanum oxide or neodymium oxide, such as lanthanum-cerium oxide,
praseodymium-neodymium oxide, etc.
This document does not involve sampling.
NOTE Since the lanthanum oxide and neodymium oxide will react with water and carbon dioxide in the air,
moisture cannot be accurately determined. However, this method can also be a guidance for the determination of the
moisture in these materials.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles
and definitions
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for
the determination of repeatability and reproducibility of a standard measurement method
ISO 5725-3, Accuracy (trueness and precision) of measurement methods and results — Part 3: Intermediate
precision and alternative designs for collaborative studies
ISO 22927, Rare earth — Packaging and labelling
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obpt
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
constant mass
the state at which a mass does not change more than 0,04 % of the mass after additional drying at 105 °C for 1 h
4 Principle
The percentage of moisture content in a sample is determined by the loss in mass of a sample subjected to
thermal treatment in a laboratory oven maintained at 105 °C.
5 Apparatus
5.1 Weighing vessels, shallow weighing vessels of approximately 50 mm diameter and 30 mm height
should be used. These vessels can be comprised of borosilicate (pyrex) glass, silica, mullite or of corrosion-
resistant metal (such as platinum), with covers. Rare earth fluorides should be contained in corrosion-
resistant metallic weighing vessels (such as platinum).
5.2 Analytical balance, with tare compensation, and accurate to the nearest 0,1 mg.
5.3 Laboratory oven, should be able to work continuously for more than four hours at a temperature of
105 °C (±5 °C).
5.4 Desiccator, should be used that contains a desiccant silica gel. If the desiccant fails, it should be
replaced in time.
NOTE If the laboratory uses a silica gel desiccant, when it turns pink, then it needs to be replaced with the dried
silica gel desiccant.
6 Samples
6.1 Sample storage
Packing for the samples should prevent them from being accidentally dispersed or otherwise discharged
into the environment and from absorbing moisture or gases. The samples shall be sealed in double-layer
polymer film bags according to ISO 22927. The samples should be weighed immediately after unsealing the
polymer film bags to prevent the samples from absorbing or losing moisture.
The laboratory should measure the moisture content immediately after receiving the sample. If the
laboratory cannot measure immediately, seal sample with a double-layered polymer film bags and place the
bagged sample in a desiccator (the desiccant should not be added to the desiccator). The laboratory should
complete measurement of the moisture content of the
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