Chemistry and
chemical technologies / 7. Inorganic chemistry
PhD-doctoral Troeglazova A.V., associate professor Zlobina
E.V.
al-Farabi Kazakh National University
Development of the standard sample
of single-component solution of rhenium
Improving
the product quality and the technology of rhenium and its compounds production
are inseparably linked with the improvement of techniques for determination of
metal. High accuracy and rapidity of analysis are achieved by using the modern
analytical instrumentation. One of the main problems in the development of
measurement techniques is the lack of standard samples (SS) which are required
for the calibration of instruments, for obtaining calibration curves, for
evaluation of accuracy and precision of techniques.
The aim
of this paper is to develop the standard sample.
The most
stable in aqueous solutions are compounds of rhenium (VII) [1], so ammonium
perrhenate was used as a starting reagent for the preparation of SS of
single-component solution of rhenium. Study of the initial preparation on the
content of impurities was performed using an atomic absorption spectrometer
«Shimadzu» AA 6200 (Japan). Purification of ammonium perrhenate from impurity
metals – magnesium, sodium, potassium, calcium, copper, iron and nickel presented
in the solution in the form of cations, was carried out by recrystallization
and ion exchange methods (extraction with the solution of di-2-ethyllhexylphosphoric
acid (D2EHPA) in kerosene and ion exchange on strong basic cationite KU-2).
Recrystallization
is an effective method of cleaning up, but the use of large volumes and masses
of the ammonium perrhenate is unacceptable in the development of SS. Carrying
out the extraction can only partially reduce the content of magnesium, iron and
nickel. Concentrations of other metals remain practically invariable. Ion-exchange
treatment reduces the content of impurity metals. Results of the analysis
before and after cleaning of ammonium perrhenate are presented in Table
1.
Table 1. Contents of impurities in ammonium perrhenate before and after
treatment, %
|
Metal |
Extraction |
Ion-exchange |
|||
|
before cleaning |
after cleaning |
before cleaning |
after cleaning |
||
|
ðÍ=2 |
ðÍ=4 |
||||
|
Mg |
1.98·10-3 |
1.7·10-3 |
1.2·10-3 |
- |
- |
|
Na |
1.4·10-2 |
1.4·10-2 |
1.4·10-2 |
2∙10-3-1∙10-3 |
1.1∙10-2 |
|
K |
1.22·10-3 |
1.22·10-3 |
1.22·10-3 |
5∙10-3-5∙10-2 |
5.0∙10-4 |
|
Ca |
1.13·10-2 |
1.13·10-2 |
1.13·10-2 |
3∙10-3-1∙10-3 |
6.4∙10-3 |
|
Cu |
3.87·10-4 |
3.87·10-4 |
3.87·10-4 |
5∙10-5-5∙10-3 |
1.96∙10-4 |
|
Fe |
1.53·10-3 |
1.53·10-3 |
8.8·10-4 |
5∙10-4-1∙10-3 |
2.1∙10-3 |
|
Ni |
9.01·10-4 |
9.01·10-4 |
5.3·10-4 |
2∙10-4-2∙10-3 |
7.0∙10-4 |
Standardless methods of gravimetric and titrimetric analysis were used for
the determination of rhenium in SS.
Gravimetrically rhenium was determined as perrhenate nitron C20H16N4·HReO4
[1]. Residual content of rhenium in the mother liquor after precipitation of
rhenium nitron is determined by Agilent-7500 mass-spectrometer (Agilent
Technologies, Japan). The residual content of organic compounds (nitron) was
removed on a microwave mineralizer "Minotaur-1" (Lumex, Russia) before
determination. Titrimetric determination of rhenium is based on the recovery of
ions of rhenium (VII) by tin dichloride in hydrochloric acid medium [2]. The
results of gravimetric and titrimetric determinations of rhenium in the
prepared standard sample are given in Table 2.
Table 2. Results of the gravimetric and titrimetric
determinations of rhenium in SS
|
Method of
analysis |
n |
|
|
D, % |
Analysis duration |
|
Gravimetric |
13 |
66.79 |
7.03 |
3.94 |
7 hours |
|
Titrimetric |
14 |
71.03 |
4.12 |
2.27 |
30 min |
As follows from the above data, both
methods yield the satisfactory results of the determination of rhenium. It
should be noted that the advantage of titrimetric determination of rhenium in comparison
with gravimetric analysis is the reduction of the duration of the test and
getting the best metrological characteristics.
Thus, the content of impurities in ammonium perrhenate
was determined. It was established that the best method of cleaning is the ion
exchange on strong basic cationite KU-2. SS
of the solution of rhenium with metal concentration of 1 mg/mL was prepared. Standardless
methods of gravimetry and titrimetry were used for the determination of rhenium
in the SS. It was shown that titration of rhenium with standard solution of tin
chloride (II) has a smaller error compared with gravimetric precipitation of
rhenium in the form of perrhenate nitron. Prepared SS can be used to calibrate
the instrument for atomic-emission determination of rhenium.
References
1. Borisova L.V, Ermakov A.N. Analytical chemistry of
rhenium. – Moscow: Nauka, 1974. – 319 p.
2. SST 31411-2009.
"Ammonium perrhenate. Specifications". – Moscow: Standartinform,
2010.