ISO 23596:2023

INTERNATIONAL ISO
STANDARD 23596
First edition
2023-08
Rare earth — Determination of rare
earth content in individual rare
earth metals and their compounds —
Gravimetric method
Terres rares — Détermination de la teneur en terres rares dans les
différents métaux des terres rares et leurs composés — Méthode
gravimétrique
Reference number
ISO 23596:2023(E)
© ISO 2023

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ISO 23596:2023(E)
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© ISO 2023
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Published in Switzerland
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ISO 23596:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Reagents . 3
6 Apparatus . 4
7 Sample preparation .5
8 Procedure .5
8.1 Test portion . 5
8.2 Dissolution . . 6
8.2.1 General . 6
8.2.2 Dissolution of rare earth metal test portion . 6
8.2.3 Dissolution of rare earth oxide and rare earth oxalate test portion . 6
8.2.4 Dissolution of rare earth carbonate test portion . 6
8.2.5 Dissolution of rare earth hydroxide test portion . 7
8.2.6 Dissolution of rare earth chloride test portion . 7
8.2.7 Dissolution of rare earth fluoride test portion. 8
8.3 Precipitation . 8
8.4 Ignition and weighing. 8
9 Calculation and expression of results . 9
9.1 Calculation of result . 9
9.2 Precision . . . 10
10 Test report .10
Annex A (informative) Information on the precision test .11
Bibliography .12
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ISO 23596:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
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This document was prepared by Technical Committee ISO/TC 298, Rare earth.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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ISO 23596:2023(E)
Introduction
Individual rare earth metals and their compounds are both materials containing only one kind of
rare earth element. They are refined and separated rare earth products, which are widely used as the
feedstock for making downstream products in the rare earth industry. In the products, there exist
trace non-rare earth impurities including some carbonates, oxalates and moisture. Some of them (such
as Ca, Si, Fe) come from raw materials and others (such as Fe) come from industrial processes of rare
earth metal from the electrolytic process.
Rare earth content refers to the mass fraction of all rare earth elements in the material. It is an
important chemical composition index to determine the quality of the individual rare earth metals
and their oxides. A scientific and standardized method to determine the rare earth content, which is
used to price the product in trading, is helpful to reduce variability and to improve the consistency and
comparability of interlaboratory results, consequently facilitating the fair trade of rare earth products.
The document aims to supply a classic gravimetric method for the determination of rare earth content
for individual rare earth metals and their compounds, which can be adopted by rare earth producers,
consumers, traders and other stakeholders.
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INTERNATIONAL STANDARD ISO 23596:2023(E)
Rare earth — Determination of rare earth content in
individual rare earth metals and their compounds —
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 rare earth content in 11 kinds
of individual rare earth metals (lanthanum, cerium, praseodymium, neodymium, samarium, europium,
gadolinium, terbium, dysprosium, holmium and yttrium) and their compounds, such as oxides,
carbonates, hydroxides, oxalates, chlorides and fluorides.
The determination ranges for the rare earth content in mass fraction are as follows:
— rare earth metal: 98,0 % (mass fraction) to 99,5 % (mass fraction);
— rare earth oxide: 95,0 % (mass fraction) to 99,8 % (mass fraction);
— rare earth oxalate: 95,0 % (mass fraction) to 99,8 % (mass fraction);
— rare earth fluoride: 75,0 % (mass fraction) to 90,0 % (mass fraction);
— other compounds (i.e. rare earth hydroxide, rare earth chloride and rare earth carbonate): 40,0 %
(mass fraction) to 70,0 % (mass fraction).
It does not apply to individual rare earth metals and their compounds when:
a) the matrixes of the sample are erbium, thulium, ytterbium and lutetium;
b) the content of thorium or lead in the sample is greater than 0,1 % in mass fraction.
2 Normative references
There are no normative references in this document.
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/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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ISO 23596:2023(E)
3.1
rare earth content
total rare earth content
mass fraction of rare earths in the material
Note 1 to entry: For rare earth oxides and other compounds, the fraction is generally provided as a percentage of
rare earth oxide, i.e. % REO or % TREO. For metals and alloys, the content is generally provided as a percentage
of rare earth metal, i.e. % REM or % TREM.
Note 2 to entry: For rare earth oxides and other compounds, the formula of the rare earth content is RE O except
2 3
for CeO , Pr O and Tb O .
2 6 11 4 7
[SOURCE: ISO 22444-1:2020, 3.7, modified — Note 2 to entry added.]
3.2
rare earth content (original basis)
rare earth content (3.1) of a material as contained in the original as-received sample that has not
undergone any treatment
3.3
rare earth content (dry basis)
rare earth content (3.1) of a material as contained in the sample subjected to drying in air at 105 °C for
1 h
3.4
rare earth content (ignition basis)
rare earth content (3.1) of a material as contained in the sample subjected to ignition in air at 950 °C for
1 h
3.5
individual rare earth metal
metallic substance containing only one rare earth element, including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, Lu, Sc and Y
Note 1 to entry: It is assumed that the relative rare earth purity (3.7) of an individual rare earth metal is at least
99,5 %.
Note 2 to entry: Pm, Er, Tm, Yb, Lu and Sc are not within the scope of this document.
[SOURCE: ISO 22444-2:2020, 4.2, modified — Note 1 to entry deleted. New Notes 1 and 2 to entry
added.]
3.6
individual rare earth compound
chemical compound containing one rare earth element and the oxygen element or one acid radical
Note 1 to entry: The oxide, chloride, carbonate, hydroxide, fluoride and oxalate compounds of rare earth are in
the scope of this document.
Note 2 to entry: It is assumed that the relative rare earth purity (3.7) of an individual rare earth compound is at
least 99,5 %.
3.7
relative rare earth purity
mass fraction of the specified rare earth element or rare earth oxide out of the rare earth content (3.1)
Note 1 to entry: It is expressed as a percentage with the basis (REM or REO) stated.
[SOURCE: ISO 22444-1:2020, 3.13]
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ISO 23596:2023(E)
3.8
permissible tolerance
α
alternative expressions for precision parameters, including r (repeatability limit), R (intralaboratory
w
reproducibility limit) and R (interlaboratory reproducibility limit)
Note 1 to entry: Permissible tolerances replace precision parameters only when precision parameters are
independent of the level.
Note 2 to entry: Permissible tolerances can be expressed as α(s ), α(s ) and α(s ) and calculated by using the
r Rw R
following formula from ISO/TR 21074:2016, 6.6.5:
n
1
2
αβ=×28,
∑ i
n
i=1
where
β is the statistical values of s , s and s for each level;
r Rw R
i is the identifier for each level;
n is the number of levels.
4 Principle
The samples are dissolved in acid solutions. The rare earth ions are precipitated with ammonia to
remove impurities of calcium, etc. The precipitate is dissolved with hydrochloric acid, followed by
quantitative precipitation with oxalic acid at pH 1,6 to 2,0 to remove impurities of iron, etc. After being
ignited at 950 °C, the rare earth oxalate precipitate is transformed into the rare earth oxide. The rare
earth oxide is weighed and the rare earth content is calculated.
5 Reagents
WARNING — Concentrated acids and alkalis are corrosive and their vapours irritate the mucous
membranes. Users should consult the safety data sheet and safety labelling for each reagent
before using. Care shall be taken to avoid any type of contact during use. Appropriate protective
equipment shall be worn when working with concentrated acids and alkalis. All the procedures
involving acids and alkali shall be carried out in a fume hood.
The following reagents and indicators may be used in the procedure. Where applicable, instructions are
provided for creating solutions. All reagents should be of known analytical grade, and only distilled or
demineralized water should be used.
5.1 Oxalic acid, H C O , powder.
2 2 4
5.2 Ammonium chloride, NH Cl, powder.
4
5.3 Sulfuric acid, H SO , ρ = 1,84 g/ml.
2 4
5.4 Perchloric acid, HClO , ρ = 1,67 g/ml.
4
5.5 Hydrogen peroxide, H O , 30 % (mass fraction), ρ = 1,11 g/ml.
2 2
5.6 Hydrochloric acid, HCl, ρ = 1,19 g/ml.
5.7 Nitric acid, HNO , ρ = 1,40 g/ml.
3
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ISO 23596:2023(E)
5.8 Ammonia, NH , ρ = 0,91 g/ml.
3
5.9 Hydrochloric acid, diluted 1 + 1.
Add 250 ml of hydrochloric acid (5.6) into 250 ml of water and mix.
5.10 Nitric acid, diluted 1 + 1.
Add 250 ml of nitric acid (5.7) into 250 ml of water and mix.
5.11 Sulfuric acid, diluted 1 + 1.
Add 250 ml of sulfuric acid (5.3) into 250 ml of water and mix.
5.12 Ammonia, diluted 1 + 1.
Add 250 ml of ammonia (5.8) into 250 ml of water and mix.
5.13 Oxalic acid solution, 50 g/l.
Weigh 25 g of oxalic acid (5.1) and place into a 500 ml beaker. Add 400 ml of water and heat to dissolve.
Make up the volume to 500 ml with water and mix.
5.14 Ammonium chloride-ammonia washing solution.
Weigh 10 g of ammonium chloride (5.2) and place into a 500 ml beaker. Add 300 ml of water and stir to
dissolve. Add 10 ml of ammonia (5.8). Make up the volume to 500 ml with water and mix.
5.15 Oxalic acid washing solution, 2 g/l.
Transfer 20 ml of oxalic acid solution (5.13) and place into a 500 ml beaker. Make up the volume to
500 ml with water and mix.
5.16 Hydrochloric acid washing solution, diluted 1 + 99.
Add 5 ml of hydrochloric acid (5.6) into 495 ml of water and mix.
6 Apparatus
6.1 Analytical balance, sensitive to 0,1 mg.
6.2 High temperature furnace (air), with a temperature upper limit ≥ 1 000 °C and a precision
of ±10 °C.
6.3 Drying oven, with a precision of ±5 °C.
6.4 Crucible (platinum or ceramic crucible).
6.5 Polytetrafluoroethylene (PTFE) beaker, resistant to acids (especially fluoric acid) and alkali.
6.6 Filter paper, medium quantitative filter paper and dense quantitative filter paper with post-
ignition residues less than 0,1 mg/g.
6.7 Cotton and filter pulp, absorbent cotton and ashless pulp with post-ignition residues less than
0,1 mg/g.
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ISO 23596:2023(E)
7 Sample preparation
7.1 For rare earth metals, the laboratory sample is normally prepared into the form of drillings
or fragments after removing the oxidized surface layer by filing. Weigh immediately after sample
preparation to minimize oxidation in air.
7.2 For rare earth oxides, weigh the sample in its as-received state to determine the rare earth
content (original basis).
7.3 For rare earth oxides, approximately 5 g of the sample is put into a shallow weighing vessel of
approximately 50 mm dia
...