Choosing the optimal method sample preparation ferrotungsten and

A. Belozerova, A. Mayorova, N. Pechishcheva, K. Shunyaev,
N. Nemytova
Institute of Metallurgy, Ural Branch of the Russian Academy of
Sciences, Yekaterinburg, Russian Federation
The quality of metal is largely determined by the presence and
amount of undesirable impurities, such as lead, tin, arsenic, which even
in small quantities cause cold cracking of the metal [1]. In some cases
the impurities content should not exceed 0.001 %. Strict analytical
control of the impurities at all stages of processing of raw materials to
the final product obtaining is necessary. The ferrous metallurgy uses
ferrotungsten, produced from the tungsten concentrate for alloyage of
steel and alloys in order to increase the hardness, wear resistance and to
improve mechanical properties at elevated temperatures [1]. The
normative documentation strictly limit the content of impurity elements
such as phosphorus, sulfur, bismuth, tin, copper, lead, antimony, and
arsenic in the tungsten concentrates and ferrotungsten [2-3]. A special
place among harmful impurities takes arsenic, even a small amount of it
in the raw material affects on the quality of metal products and the
environment. Currently, determination of arsenic in tungsten
concentrates in the Russian Federation is regulated by RF National
Standard 11884.6-78 [4], in ferrotungsten – by RF National Standard
14638.15-84 [5]. For arsenic determination they recommend photometry
(for the range of 0.08-0.5 % in [4], for 0.002-0.10 % in [5]) and
titrimetry (for the 0.005-0.5 % in [4]). These procedures are long and
complex; require the use of large amounts of reagents.
Currently, inductively coupled plasma atomic emission
spectrometry (ICP-AES) is widely used for chemical analysis of
metallurgical raw materials and products [6-9], due to its rapidity, high
reproducibility, wide range of determining concentrations and low
detection limits. However, ICP-AES determination of arsenic in
tungsten materials is difficult due to the low concentration of this
element, a small amount of available emission lines and its low
sensitivity [10]. Commonly used methods of the tungsten material
sample preparation (dissolving in acid mixture [11], in oxalic acid and
hydrogen peroxide mixture [12], alkaline fusion [6, 13], etc.) are not
suitable for the subsequent ICP-AES determination of arsenic. Matrix
components - tungsten and iron – completely pass into solution and have
a significant impact on the emission signal of arsenic [14], particularly
due to overlapping of the spectral lines (Table 1).
Table 1. Overlapping lines arsenic and tungsten in the emission
spectrum [14]
Interfering spectral lines of tungsten,
W I 289.825
W I 286.016
W I 278.028
W I 245.653
W I 237.088
W I 236.933
W II 234.982
W I 228.767
W I 193.680
W I 193.680
W I 189.181
The spectral lines of arsenic, nm
As I 289.871
As I 286.04
As I 278.02
As I 245.653
As I 237.077
As I 236.967
As I 234.98
As I 228.81
As I 193.759
As I 193.696
As I 189.042
For ICP-AES determination of arsenic in tungsten materials it is
necessary to separate arsenic from main part of the matrix, there are a
number of effective methods [10]. The choice of method depends on the
chemical composition of the analyzed material and on the content of
For example, in [16] for sample preparation of arsenic ore
sintering materials using sulphiding reagents have been proposed. As the
flux alkaline earth metal oxides (MgO, CaO), and alkali metal
carbonates (Na2CO3, K2CO3) are used. The separation of arsenic from
the matrix occurs at the stage of water leaching. Large part of the matrix
remains in the form of insoluble sulphides; arsenic forms soluble
In determining of trace level of the impurities interfering tungsten
matrix can be precipitated. Barium acetate is one of the most
commercially available and inexpensive precipitants of tungsten [11].
For the separation of small amounts of arsenic from the matrix its
co-precipitation, for example, with ferric hydroxide is widely used [10].
For example, for [15] ICP-AES determination of arsenic in the
technogenic raw materials (copper anodes, copper production waste)
sorption group concentrating on iron, lanthanum and magnesium
hydroxides have been proposed. In the process of sample preparation
matrix is separating, impurities (As, Se, Te) are concentrating. However,
it is known [10] that a number of other elements - tin, tungsten,
vanadium - fully or partially coprecipitated with ferric hydroxide as well
as arsenic. To study the degree of separation of matrix components
experimental testing of the above methods of sample preparation of
tungsten-containing materials is required.
The aim of the present study was selection of the optimal method
for sample preparation of tungsten-containing materials for further ICPAES determination of arsenic.
The selection of the sample preparation method
Standard reference materials of ferrotungsten and mixtures of two
standard reference materials of ferrotungsten were tested following the
Procedure 1. Sintering. (0.5 ± 0.001) g of the ferrotungsten
sample was weighed into the porcelain crucible with a flux: Na2CO3:
K2CO3: S (1.8 g: 2.2 g: 4 g) and was mixed thoroughly. The crucible
was placed in a muffle furnace at 500 °C for 5 min. Then the crucible
with flux was cooled and placed in a heat-resistant glass beaker of 250
cm3, 40 cm3 of distilled water was added and heated. The precipitate was
filtered through "blue ribbon" filter, then washed with hot distilled water
and discarded. The filtrate was transferred to a 200 cm3 flask, diluted to
the mark with water and stirred.
Procedure 2. Sintering is followed by the deposition of tungsten.
According to procedure 1 ferrotungsten sample was sintered. Then, after
leaching to flux 60 cm3 of hot freshly prepared 10 wt. % barium acetate
solution was added portionwise. The resulting precipitate of barium
tungstate (BaWO4) was filtered using "blue ribbon" filter, washed with
hot distilled water and discarded. The filtrate was transferred to a
200 cm3 flask, diluted to the mark with water and stirred.
Procedure 3. Preconcentration on ferric hydroxide.
(0.5 ± 0.001) g of ferrotungsten sample was placed in Teflon beaker, a
mixture of hydrochloric acid, nitric acid, hydrofluoric acid (15:15:5 cm3)
was added and heated on an electric stove until complete decomposition
of the material. 0.2 g of iron nitrate (III) was added to the solution and
heated to dissolve. Small portions of ammonium hydroxide were added
to form ferric hydroxide. The resulting precipitate was filtered using
"blue ribbon" filter and washed with an aqueous solution of ammonium
hydroxide (1:20). The filtrate was discarded. The precipitate was
dissolved in hydrochloric acid solution (1:1), transferred into a 200 cm3
volumetric flask, diluted with water to the mark and stirred.
ISP-AES spectrometer and operating conditions
Emission measurement of solutions after sample preparation was
carried out using ICP-AES spectrometer «Optima 2100» (Perkin Elmer)
with argon plasma as emission source. Operating parameters: Rf power 1300 W; carrier gaz flow rate – 0.8 dm3/min; auxiliary argon flow rate0.2 dm3/min; plasma gaz flow – 15.0 dm3/min; method of plasma
observation- axial (in the case of arsenic), radial (in the case of
tungsten); nebulizer flow rate – 1.5 cm3/min; spraying time – 30 c,
number of replicas – 2, analytical spectral lines: W II 207.912 nm, As I
189.042 nm, As I 193.759 nm.
Results and discussion
Procedures 1-3 was carried out with the samples of certified
reference materials of ferrotungsten. Arsenic and tungsten content were
determined by ICP-AES in the resulting solutions. The results are shown
in Tables 2 and 3. It is shown that significant amount of tungsten,
350 mg/cm3, remains in the sample solution obtained by Procedure 1.
Spectral lines W I 189.181 nm and W I 193.680 nm overlap the
analytical lines of arsenic and the determination of arsenic is impossible.
In the samples prepared by Procedure 2 and Procedure 3 the tungsten
contents were less significant, 150 mg/cm3 and 100 mg/cm3 respectively
(Table 2).
Table 2. The results of ICP-AES determination of tungsten in the
solution sample after sample preparation
tungsten content,
wt.% (mg/dm3)
(1850 mg/dm3
after complete
dissolution of 0.5
g in 200 cm3)
The tungsten content
in the sample solution, mg/dm3
Procedure 1
Procedure 2 Procedure 3
Table 3. The results of ICP-AES determination of arsenic in the solution
sample after sample preparation (mean results obtaining using two lines:
As I 189.042 nm and As I 193.759 nm)
(500 mg)
Mix of RF CRM
765-92P and RF
CRM 2853-84
(250 mg:250 mg)
Procedure 2
Found, wt.%
Procedure 3
The Tables 3 shows that the Procedure 2 is not suitable for ICPAES determination of arsenic content less than 0.02 wt. % due to the
effect of the overlapping of the above-described tungsten lines on the
arsenic lines. The tungsten content in the sample solution after
Procedure 3 have not disturbing influence on the determination of
arsenic at a concentration below of 0,01 wt %.
From the three tested procedures to further develop of the
techniques of ICP-AES arsenic determination in the tungsten materials
the most promising is that including dissolution in the acid mixture
followed by co-precipitation of arsenic on ferric hydroxide.
This work was financially supported by young scientists and
graduate students of Ural Branch of the Russian Academy of Sciences
project № 14-3-NP-4 and in the frame of the IMET UB RAS theme
“Developing of the analyze techniques of the oxide row materials,
wastes and products of its treatment”.
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