ISO 23597:2023

INTERNATIONAL ISO
STANDARD 23597
First edition
2023-08
Rare earth — Determination of rare
earth content in individual rare earth
metals and their oxides — Titration
method
Terres rares — Détermination de la teneur en terres rares dans les
métaux des terres rares individuels et leurs oxydes — Méthode de
titrage
Reference number
© ISO 2023
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ii
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 . 5
7 Sample preparation .5
8 Procedure .5
8.1 Test portion . 5
8.2 Dissolution . . 5
8.3 Titration. 6
9 Calculation and expression of results . 6
9.1 Calculation of results . 6
9.2 Precision . . . 7
10 Test report . 8
Annex A (informative) Information on the precision test . 9
Bibliography .10
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 298, Rare earth.
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iv
Introduction
Individual rare earth metals and their oxides 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 titration method for the determination of rare earth content
for individual rare earth metals and their oxides, which can be adopted by rare earth producers,
consumers, traders and other stakeholders.
v
INTERNATIONAL STANDARD ISO 23597:2023(E)
Rare earth — Determination of rare earth content in
individual rare earth metals and their oxides — Titration
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 titration method for the determination of rare earth content in 15 kinds of
individual rare earth metals (lanthanum, cerium, praseodymium, neodymium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium) and
their oxides.
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 99,5 % (mass fraction).
It does not apply to individual rare earth metals and their oxides when:
a) the relative rare earth purity is less than 99,5 % in mass fraction;
b) the total content of various (non-rare earth) metallic elements is greater than 0,5 % in mass
fraction;
c) the content of thorium, scandium or zinc 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/
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 purity of an individual rare earth metal is at least 99,5 %.
Note 2 to entry: Pm 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 oxide
chemical compound containing one rare earth element and the oxygen element
Note 1 to entry: It is assumed that the relative rare earth purity (3.7) of an individual rare earth oxide 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]
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 the 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
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. Rare earth ions are titrated and complexed quantitatively
at pH 5,5 with a standard EDTA solution and xylenol orange as an indicator after masking coexisting
non-rare earth ions such as iron, etc. with sulfosalicylic acid.
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 alkalis shall be carried out in a fume hood.
...