CEN/TR 15018:2005

SLOVENSKI STANDARD
01-maj-2006
Karakterizacija odpadkov – Alkalni razklop vzorca odpadka
Characterization of waste - Digestion of waste samples using alkali-fusion techniques
Aufschluss von Abfallproben mittels Alkalifusion
Caractérisation des déchets - Digestion d'échantillons de déchets par mise en solution
par fusion alcaline
Ta slovenski standard je istoveten z: CEN/TR 15018:2005
ICS:
13.030.01 Odpadki na splošno Wastes in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 15018
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
November 2005
ICS 13.030.01
English Version
Characterization of waste - Digestion of waste samples using
alkali-fusion techniques
Caractérisation des déchets - Digetsion d'échnatillon de Aufschluss von Abfallproben mittels Alkalifusion
déchets par Mise en solution par fusion alcaline - Guide de
bonnes pratiques pour la mise en solution par fusion - Les
différentes méthodes et protocoles existants
This Technical Report was approved by CEN on 6 December 2004. It has been drawn up by the Technical Committee CEN/TC 292.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15018:2005: E
worldwide for CEN national Members.

Contents
Introduction.4
1 Scope.5
2 General information.5
2.1 Digestion of samples.5
2.2 Digestion by fusion.5
3 Fluxes.6
3.1 Alkaline fluxes.7
3.2 Acid fluxes.10
3.3 Oxidising fluxes.11

3.4 Reducing fluxes (alkaline fluxes + reducing agents, sulphides).12
3.5 Digestion by sintering.12
4 The crucibles.12
4.1 Platinum.12
4.2 Silver.13
4.3 Nickel.13
4.4 Vitreous carbon.13
4.5 Iron.13
4.6 Porcelain.13
5 Protocols currently used within industry.13
5.1 Analysis of 16 metallic elements in crushing residues [11] .13
5.2 Determination of Si, Al, Fe, Mn, Mg, Cr, Ti, and F in slags [12] .15
5.3 Fusion with carbonate or borate mixture [15].16
5.4 Fusion with lithium borate [14] .17
5.5 Standards (non exhaustive list) .17
5.6 Fluxes and their applications.18
6 Comparison of different digestion techniques .21
7 Conclusion.23

Bibliography.24

Foreword
This Technical Report (CEN/TR 15018:2005) has been prepared by Technical Committee CEN/TC 292
“Characterization of waste”, the secretariat of which is held by NEN.
This Technical Report is the translation of the French guideline BP X 30-428 "Digestion by fusion – Good practice
guide for digestion by fusion: the different existing methods and protocols" and adoption as a CEN/TR. It gives
information about the digestion of the waste samples using alkali-fusion techniques.
Introduction
EU regulations (e.g. hazardous waste, waste incineration, European waste catalogue) ask in many cases for the
total content of certain elements. In the European landfill directive, knowledge of total composition is given as an
example of waste property-based criteria and is part of the basic characterization of waste.
In these special cases the total content of certain elements has to be determined. The standard based on acid
digestion of waste samples (EN 13656) is in almost all cases applicable. However for some elements or waste
composed of very refractory matrix (e.g. silicates, carbides, oxides), or when some residue is left after acid
digestion, alkali-fusion may be used to bring the waste sample completely into solution.
1 Scope
This Technical Report describes digestion methods for the determination of element contents of waste samples by
using different alkali-fusion techniques.
2 General information
2.1 Digestion of samples
The determination of the elemental chemical composition of waste material includes a pretreatment of the sample
comprising several stages:
 sampling for analysis (drying, crushing, homogenisation, sample reduction);
 digestion.
This last stage of digestion is essential because it allows to obtain a homogenous medium compatible with current
analytical methods (atomic absorption spectrometry AAS, inductively coupled plasma and atomic emission
spectrometry ICP/AES, inductively coupled plasma mass spectrometry ICP/MS, molecular absorption spectrometry
MAS, X-ray fluorescencespectometry XRF).
The diversity of the materials is such that this stage remains very complex and can give rise to major errors due
mainly to:
 contamination of the sample by digestion reagents;
 incomplete digestion;
 loss of elements by adsorption onto the mineralization residue, onto the filter, or onto the walls of the
mineralization reaction vessel;
 loss of elements by volatilisation (over and above those connected with drying and crushing);
 loss by reprecipitation in the form of hardly soluble salts.
Digestion is generally conducted in two stages. The attack, which consists in destroying the sample's organic
matter and in dissolving the mineral residue by possibly modifying the specification by a very aggressive medium,
followed by a dilution of the residue by a liquid allowing to obtain a homogeneous solution compatible with the
subsequently implemented analytical techniques. Specific methods have been developed for volatile elements.
While numerous digestion methods exist, none is universal. The choice depends, on the one hand, on the nature of
the sample (matrix type) and, on the other hand, on the sought after element(s) or on the targeted objective :
determination of the total content or search for exogenous contaminants. Digestion can be performed by a wet
(acid attack) or dry (fusion, calcination, combustion) technique.
The purpose of this code of good practices is to inventory those fusion methods which allow the mineralisation and
digestion of waste for which acid attacks do not give satisfactory results.
2.2 Digestion by fusion
Fusion is often employed for the digestion of mineral materials (silicates, alumino-silicates, .) and more particularly
of certain refractory oxides (zircon, chromite, .), but it is unsuitable for the digestion of volatile elements.
Digestion by fusion requires the use of a specific flux which determines the nature of the reaction involved:
 acid-alkaline reaction:
 alkaline fusion (carbonates, borates, hydroxides);
 acid fusion (disulphates and pyrosulphates, fluorides, boron oxides);
 redox reaction:
 oxidizing fusion (alkaline fluxes + oxidants, peroxides);
 reducing fusion (alkaline fluxes + reducing agents, sulphides).
Fusion is conducted in platinum, porcelain, silver, nickel, iron, vitreous carbon, zirconium, graphite or terracotta
crucibles. The choice of the crucible depends on the nature of the substance to be decomposed and on the type of
flux.
Heating can take place in muffle ovens, induction ovens, tunnel ovens, over flames (Mecker burner) or more
recently in microwave ovens. The time and temperature vary depending on the sample, crucible and flux being
used.
The dilution of the fusion product is generally carried out in water or acidified water (water acidified with
hydrochloric or nitric acid up to 5 % ml/l) which is heated in order to solubilise the solid formed at time of fusion.
3 Fluxes
Several types of salts or other chemicals are proposed for the fusion of rock samples: alkaline borates, sodium
carbonate (Na CO ), sodium hydroxide (NaOH), sodium peroxide (Na O ), equivalent potassium compounds,
2 3 2 2
potassium pyrosulphate (mixture of K S O and KHSO ), alkaline fluorides (e.g. : KHF ). These fluxes have
2 2 7 2
specific applications.
In general, the efficiency of a flux for attacking silicate rocks increases from Na CO < NaOH < Na O . Table 1
2 3 2 2
gives a non exhaustive list of the fluxes together with their melting point and the generally used crucibles.
Table 1 — Fluxes used for the fusion of silicate rocks
Salt Melting point (°C) Fusion crucible
Lithium metaborate LiBO 845 Pt + 5 % Au
Lithium tetraborate Li B O 930 or graphite
2 4 7
Sodium carbonate Na CO 851 Pt or Ni
2 3
K CO
Potassium carbonate 891
2 3
a
Sodium hydroxide NaOH Zr (or Au, Ni, Ag)
318, 314
Potassium hydroxide KOH 360
Na B O
Sodium tetraborate (borax) 741
2 4 7
a
Sodium peroxide Na O Zr
480 d, 675
2 2
Potassium superoxide KO 380
a
Potassium fluoride KF
846, 856
a
Potassium hydrogen fluoride KHF
225 d, 239
a
K S O
Potassium pyrosulphate
300, 414
2 2 7
a
Sodium pyrosulphate Na S O
2 2 7
a
Lithium carbonate LiCO
a
Cesium carbonate CsCO
a
NaKCO
Sodium Potassium carbonate 500
a
Ammonium hydrogen sulphate NH HSO
4 4
a
Sodium hydrogen sulphate NaHSO
a
KHSO
Potassium hydrogen sulphate
a
Ammonium hydrogen fluoride NH HF
4 2
a
Sodium nitrate NaNO
a
Potassium nitrate KNO
a
d : decomposes.
3.1 Alkaline fluxes
3.1.1 Carbonates
Fusion using sodium carbonate is the most generally employed method of attack for the digestion of silicates (rocks
and glasses). One can use either sodium carbonate which melts at 850 °C, or a mixture of potassium carbonate
and sodium carbonate in equal parts, an eutectic mixture which melts at 700 °C. Sodium and potassium carbonate
(NaKCO ) has a melting point of 500 °C.
Potassium carbonate is rarely used alone. Mixed with sodium carbonate, it is used for analysing silicates because
the fusion temperature is lower than that of the sodium carbonate alone. This mixture can therefore be used for the
determination of volatile elements such as chlorine, fluorine.
Sometimes a little nitrate is added in order to stimulate the oxidation of chromium for example.
Fusions using carbonates generally take place in platinum crucibles at 900 °C. These fusions shall be performed
preferably in an inert atmosphere in order to limit the formation of soluble sodium platinate.
Conversely, when the sample under analysis contains iron, the fusion shall be conducted maintaining an oxidising
atmosphere inside the crucible in order to prevent the reduction of the iron and the attack of the platinum crucible.
During fusion using carbonates, Hg and Tl volatilise completely, As and Se partially.
After attack, the majority of the anions are dissolved in the water; metals which do not produce any anions remain
in the state of oxides, but these oxides are generally able to be attacked by acids. Fe (III), Ti (IV), Zr (IV), Be (II),
rare earths remain insoluble in the water in the state of oxides. Al (III), V (V), P (V) are dissolved in the state of
2-
anions, as well as chromium in the state CrO after oxidation by the air during fusion. U divides into parts; likewise
2- 2+ 2-
for Zn which is in the state of ZnO and of ZnCO . Mn changes partially to the state of MnO ; post-dilution
2 3 4
boiling or the addition of a drop of alcohol produces MnO which precipitates.
In presence of SiO and Al O , sodium silicoaluminates form that are hardly soluble and very difficult to filter when
2 2 3
diluted by the water. Where anion separation is not required, it is preferable to directly dilute the attack product by
an acid, and to insolubilise the silicium oxide [3] and [8].
1)
Procedure : 0,8 g to 1 g of finely crushed sample is mixed in a platinum crucible with 4 g to 5 g of the equal parts
mixture of anhydrous sodium and potassium carbonates. First of all heat gently for 5 min, then to fusion for 30 min.
When there is no longer formation of CO bubbles, heat as high as possible during 10 min. Allow to cool, solidifying
the content in a film on the walls of crucible. Fill up to a third with water; heat gently. Remove the solid. If unable to
do so, place the crucible in a beaker in presence of water. Heat up until disintegration [3].
Fusion with sodium carbonate mixed with SiO has been used for the determination of the fluorine and chlorine
present in geological materials [10]. Fusion takes place in a platinum crucible at 900 °C for 30 min.
It shall also be noted that alkaline carbonates can be used mixed with:
 a compound of boron for the analysis of highly refractory products (natural oxides or calcined aluminium or
silicium, corundums, zircons, cassiterites, chromites, .);
 a MgO or ZnO oxide in order to increase the fusion temperature (use of a porcelain crucible);
 sulphur for the analysis of tin oxide and materials forming soluble sulphurs compounds in an alkaline medium;
 an oxidant (alkaline peroxide or nitrate) for the determination of the chromium and sulphur in silicates and
chromites containing lead;
 ammonium chloride.
3.1.2 Molten borates
Lithium metaborate and tetraborate
These are widely used fluxes. Metaborate is more alkaline than tetraborate. It is used for dissolving acid materials:
silicate materials, siliceous sands, acid oxides [13]. Lithium metaborate is used preferably in view of analyses by
AAS or ICP after dilution.
Tetraborate, more acidic, is used for the attack of alkaline materials such as alkaline oxides, highly aluminic
materials, alumino-silicates, bauxites.[13].

1) Gradings not exceeding 200 µm - 300 µm are recommended.
The metaborate/tetraborate mixture in a 4/1 ratio constitutes a practically universal flux. The eutectic point of this
mixture is one of the lowest; it is efficient in 95 % of cases, just as much for the fusion of siliceous rocks as for
aluminic rocks or siliceous limestones, hence its superiority compared with meta- or tetraborates alone.
Furthermore, the rapidity of the dissolution of the bead of this flux mixture in 3 % or 4 % nitric acid is in the region of
10 min to 15 min versus 40 min to 60 min for meta- and tetraborates alone [2]. The combined attack is therefore
recommended for the majority of silicates, except for extra-aluminic materials which must be attacked by
tetraborate and extra-siliceous materials by lithium metaborate.
Procedure: These fusions using alkaline borates are conducted most often in vitrified graphite crucibles, placed in
graphite jackets fitted with lids, if the operation is carried out in muffle ovens in an uncontrolled atmosphere. Fusion
lasts 15 min to 30 min and the temperature borders on 900 °C – 1 000 °C. But the use of induction ovens in
presence of an inert gas (Ar or N ) allows to reduce the fusion time by 3 min to 4 min, at a temperature of 1100 °C,
and to extend the lifetime of the crucibles 40 to 50 fold.
At lower temperatures, the obtained attack bead is often too viscous, the silicium oxide can be incompletely
attacked and the dissolutions, even by 4 % nitric acid, can exceed 60 min.
2)
The attack is generally performed on test portions of 0,1 g to 0,2 g with a flux/sample ratio between 8 and 1
depending on the refractory properties and the granularity of the products under attack [2].
Crucibles made of platinum iridium (5 %), gold or gold-platinum-rhodium (GPR) alloy are also used at 1 000 °C
during 15 min in a muffle oven. Boron nitride crucibles are to be used in order to prevent contamination by traces of
silicates.
Lithium metaborate alone
A 5 to 1 flux/sample ratio can be applied to the majority of the samples [1]. It can be lowered to 3 where it is wished
to minimise the influence of the matrix at time of analysis. The purity of reasonably priced lithium metaborate and
the low interferences generated by this reagent make it the best flux able to be used in ICP-MS [1]. Fusion takes
place from 900 °C to 1 050 °C in Pt-Au or graphite crucibles in a muffle oven and the fusion product is recovered in
nitric acid.
It has been demonstrated by Totland et al. [20] that fusion using lithium metaborate allowed a better solubilisation
of the elements Si, Cr, Hf and Zr, and of the elements of rare earths than acid mineralisation in an open vessel.
2)
Procedure: For rock and soil samples , it is possible to use lithium metaborate alone in a graphite crucible. The
obtained bead is solubilised by shaking in a hydrochloric medium [8]. The major sample-solution dilution (factor
10 000) reduces the field of application to the principal elements: Al, Si, Fe, Ca, Mg, Na, and K [9]. Fusion is
conducted preferably in platinum crucibles; those made of graphite have a shorter lifetime. The sample is mixed
with excess lithium metaborate and fusion is performed from 900 °C to 1 050 °C during 15 min to 30 min in a muffle
oven [7]. Certain authors limit the fusion temperature to 900 °C in order to prevent the low loss of alkaline
compounds by volatilisation [7].
Borax (Na B O , 10 H O)
2 4 7 2
This flux has been much used. Its fusion point is 878 °C. It shall firstly be dehydrated. It allows to solubilise certain
natural oxides which are not easily attackable by other processes, e.g. ZrO , calcined Al O , corundum.
2 2 3
2)
Procedure: Place 0,3 g of powder together with 4 g of anhydrous borax in a platinum crucible. Melt and heat
around 1000 °C – 1200 °C until it becomes transparent (30 min to 1 h). Dilute with 2 Mol/l hydrochloric acid
(150 ml) in a water bath.
For highly aluminic products: two parts of anhydrous borax and 10 parts of anhydrous sodium carbonate are
heated until a clear liquid is obtained. The sample is added to this liquid. Fusion is performed as previously [3].

2) Gradings not exceeding 200 µm - 300 µm are recommended.

3.1.3 Hydroxides
Sodium hydroxide allows the disintegration of a large number of silicates (kaolins, clays, feldspars) and easily
fusible products (glass), of certain oxides (TiO , SnO ), phosphates (monazite) or sulphates and of various ores
2 2
(Cr, Sn, Zn, Zr). Sodium hydroxide melts at 318 °C.
Caustic potash, of which the fusion point is at 360 °C, has a more vigorous action than sodium hydroxide and
allows to solubilise chromites. On the other hand, its salts are less soluble which leads to a longer washing of the
precipitates and to a possible occlusion of these salts.
Fusion using hydroxides is performed in silver, iron, nickel or zirconium crucibles.
This mode of attack is far more vigorous than with carbonates and allows fusion at lower temperatures. During the
course of attacks by hydroxides, Sn, V, W, Mo, As, Sb, P, S, B and halogens produce sodium and potassium salts
which are water soluble in an alkaline medium, whereas Fe, Ti, Zr, Co remain insoluble in the form of hydroxides or
carbonates.
3)
Procedure: Melt 10 times to 20 times the mass of the sample to be attacked of sodium hydroxide in pellet form.
Heat gently in order to expel the water. Allow to cool. Introduce the sample in powder form. Heat to fusion with a
low flame. 400 °C – 450 °C shall not be exceeded. Under these conditions, the nickel crucible is not attacked.
Leave 10 min to 15 min.
For silicates, a flux/sample ratio of 10 to 12/1 is used.
For the analysis of soils and rocks by atomic absorption, silver crucibles are used.
3)
Procedure: Weigh in a 30 ml to 40 ml silver crucible 100 mg of crushed and dried rock. Add 1,5 g of sodium
hydroxide. Place on an electric hot plate for 15 min. Next progressively heat the crucible over a gas burner, shaking
during 1 min. Cool and place the crucible in a 250 ml beaker containing 100 ml of distilled water and 20 ml of 2,5 N
sulphuric acid. Heat the beaker until the residue has completely dissolved. Discard the crucible.
NOTE The method is used for the solubilisation of rocks, soils and sediments. The high quantities of iron
(10 – 20) % are sometimes difficult to solubilise. The solution lends itself to the determination of silicium and aluminium; calcium
and magnesium can be determined if their content is higher than 0,1 %. Nickel crucibles are sometimes used: the attack is more
delicate and difficult to control [8].
3.2 Acid fluxes
3.2.1 Pyrosulphates
Fusions by pyrosulphates of alkaline metals or NH HSO are very vigorous and are used for certain alkaline
4 4
refractories (chromium-magnesium oxide), complex alloys, Fe O , TiO , Nb O , aluminium oxide, a large number
2 3 2 2 5
of ores (Al, Sb, Cu, Cr, Co, Fe, Mn, Ni, Ta.), steels, phosphates and slags. These fusions are used whenever
alkaline borate fluxes are inefficient. In all cases, the silicium oxide remains insoluble. The operation can be
performed in platinum or quartz crucibles. After attack, one dilutes by diluted sulphuric acid.
K S O has a melting point of 415 °C and Na S O of 400 °C. The pyrosulphate behaves like a mixture of neutral
2 2 7 2 2 7
2-
sulphate and of SO : SO combines with the oxides to give SO .
3 3 4
Sulphate-based reagents are unfavourable for certain elements such as lead, barium and calcium on account of
the poor solubility of their sulphates.

3) Gradings not exceeding 200 µm - 300 µm are recommended.

4)
Procedure : 0,5 g of powder is attacked by 5 g to 7 g of pyrosulphate. Heat for 20 min to 30 min, just to melting
with a low flame, avoiding the loss of SO3. Next bring the crucible up to 600 °C – 700 °C and heat until the liquid is
limpid (e.g. 1h). Cool down. Place in a beaker containing 250 ml to 750 ml of water and 25 ml of concentrated
sulphuric acid. Heat and filter the silicium oxide. Wash.
Platinum crucibles undergo very slight attack by the disulphate and the traces of Pt which are dissolved can
present difficulties for certain determinations. Consequently, operations will be performed in quartz crucibles [3].
3.2.2 Alkaline fluorides (KF, KHF , NH F)
2 4
The use of alkaline fluorides allows the disintegration of the resistant silicates and of Be, Nb, Ta, and Zr oxides.
These fluxes allow to have a higher digestion temperature than with HF. The KHF melting point is 240 °C, 857 °C
for KF. NH F looses NH at 145 °C to produce NH HF which melts at 124,6 °C. These are low temperature fluxes.
4 3 4 2
Operations are generally performed in platinum crucibles [3].
3.2.3 Boron oxide and others
Sands, aluminium silicates, tourmaline, corundum, enamels are attacked by boron oxide B O which melts at
2 3
580 °C. Difficulties are encountered for silicates having a high magnesium and calcium content and for chromium
ores which are not attacked [13].
3.2.4 Lithium tetraborate
(see subclause 3.1.2).
3.2.5 Other boron fluxes
A boric acid-potassium carbonate mixture has been used as a flux. This fusion shall be followed by an acid
dissolution and a separation of the cations on a resin ion exchanger. The cations are then eluted with hydrochloric
acid. On the eluate, it is possible to determine the major elements (Fe, Al, Ca, Mg, Na, K) and the trace elements
(Rb, Ba, Sr, Cu, Cr, V, Ni, Co.) insofar as their concentration is sufficient, namely approximately 50 mg/kg in the
sample. It is possible to determine the silicium in the initial effluent solution. This method offers the advantage of
separating the silicium oxide more rapidly than with the traditional methods [9].
3.3 Oxidising fluxes
3.3.1 Sodium peroxide
In many cases, the attack by sodium peroxide is more efficient than fusions with other fluxes. This attack is suitable
for a large number of Sb, As, Cr, Mo, Ni, V, U, Sn ores, for certain chromium alloys and steels and for chromium
oxide or refractory oxide-based products (ZrO , Al O ). Its oxidising action is used as a last resort when the other
2 2 3
fluxes have failed. By bringing up to a red heat, Na O decomposes, giving off oxygen. Its action is identical to that
2 2
of sodium hydroxide, but here all the elements are at their upper oxidation stable state.
Operations are performed in a nickel, iron or zirconium crucible. These crucibles are attacked as from 600 °C to
700 °C. One operates just to melting at 500 °C. The disadvantage of peroxide fusions resides in the production of a
violent reaction (also in presence of organic compounds) which results in the destruction of the bottom of vitreous
carbon, iron or nickel crucibles. In presence of Na CO or of magnesium oxide-based calcareous or refractory
2 3
ores, the reaction is much less violent.

4) Gradings not exceeding 200 µm - 300 µm are recommended.

5)
Procedure: Add to 1 g of powdered material 10 g of sodium peroxide. Heat gently to melting and leave 15 min to
20 min. Cool and dilute with water. Boil during 15 min in order to destroy the excess sodium peroxide and the
hydrogen peroxide which has formed. Highly reducing compounds are oxidised and cause an explosion [3].
Sometimes sodium peroxide is used mixed with sodium hydroxide. This allows the determination of the rare earth
elements. These two fluxes attack platinum; one therefore uses gold, silver, nickel or zirconium crucibles which are
subject to less attack. However, traces of the crucible constituent material are found in the analysed solutions. The
commonly used sample/flux ratio is 1/4 and the fusion is performed at around 800 °C for 15 min to 30 min [7].
3.3.2 Nitrates
Where it is wished to avoid the use of sodium peroxide and where the product is not too refractory, a mixture of
caustic alkali with an alkaline nitrate, which is the oxidising agent, can be used. The chromites can thus be
attacked. The attack of the crucibles is consequently less significant than in the case of sodium peroxide.
3.4 Reducing fluxes (alkaline fluxes + reducing agents, sulphides)
 Melted sulphur and sodium carbonate.
This method of attack is suitable in the case where one of the major constituents produces a soluble sulphide in an
alkaline medium (complex sulphides). Example: attack of SnO (cassiterite) [3].
3.5 Digestion by sint
...