RU2506580C1 - Method to detect rhenium by kinetic inversion-voltammetric method in rocks and ores - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention is aimed at detection of rhenium in rocks and ores by kinetic inversion-voltammetric method and may be used in different industries to detect content of concentrations of various metal ions in solutions. The method according to the invention includes detection of rhenium on the background of 0.1 M H₂SO₄ with addition of 0.03 ml of 30% H₂O₂ by the method of kinetic inversion voltamperometry, when electric concentration of rhenium is carried out in a mercury film electrode with subsequent registration of cathode peaks, taking voltamperegrams at the speed of potential deployment of 100 mV/s, at the same time the concentration is determined by the height of the cathode peak in the range of potentials from 0.0 to 0.20 V by the method of addition of certified mixtures.

EFFECT: invention makes it possible to exclude using highly toxic materials when detecting ions of rhenium (VII), and also provides for higher accuracy, resolution and express nature of determination.

1 ex, 2 tbl, 2 dwg

Description

The invention relates to analytical chemistry, and in particular to methods for determining metal ions in rocks and ores, and can be used in geology, surveys in the case of analysis of geological objects of rhenium ion concentrations by the method of kinetic inversion voltammetry (KinIV).

The known method of polarographic determination of rhenium, first studied in solutions of acids (HCl, HClO ₄ , H ₂ SO ₄ ) and neutral solutions (KCl, phosphate buffer). The determined concentration of rhenium (VII) used in the studies was 1 · 10 ^-3 M [Lingan JJ / J. Am. Chem. Soc. 64, 1001 (1942); Lingan JJ // J. Am. Chem. Soc. 64, 2182 (1942)]. The disadvantage of this method is the low sensitivity and the use of large quantities of metallic mercury during polarographic determinations of rhenium in solution.

A known method for the determination of rhenium in sulfate and hydroxy sodium solutions. It was shown that the number of recovery waves and their nature vary with the concentration of H ₂ SO ₄ . The half-wave potential of E _1/2 for rhenium (VII) in 3.5 M H ₂ SO ₄ is from 0.2 to -0.45 V, in a 2 M alkaline solution of E _1/2 for rhenium (VII) is -1, 4 B. The determined concentration was 1 · 10 ^-4 M [Geyer R. // Z. anorg. u. allgem. Chem., 263, 47 (1950)]. The disadvantage of this technique is the low sensitivity of the determined rhenium content, the use of metallic mercury, the vapors of which are toxic. When determining rhenium, the anions Cl ^- , NO ₃ ^- , PO ₄ ^3- , and also the metal ions Mo, Fe, and Ti interfere.

A known method of restoring perrhenate ion at a mercury-drop cathode. The diffusion current in a 4 M HClO ₄ solution is directly proportional to the ReO ₄ concentration ^- in the solution in the range from 1 · 10 ^-4 to 1 · 10 ^-3 M. In 2 M and 4.2 M HCl E _1/2 solutions are equal respectively - 0.45 V and -0.31 V (relative to N.E.C.) [Rulfs CL, Elving PJ // J. Am. Chem. Soc. 73, 3284 (1951)]. The disadvantage of this method is the low sensitivity of the determined content of rhenium and the use of metallic mercury, the vapors of which are toxic.

A known method for determining small concentrations of rhenium in neutral, alkaline and buffer solutions. The rate of catalytic hydrogen evolution is significantly affected by the pH of the solution and the buffer capacity of the solution. A mercury-drop electrode was used in the studies, and saturated calomel served as the auxiliary and reference electrodes. The maximum current reaches a maximum value in the range of pH 7-9. The concentration of perrhenate ion used in the studies was 8 · 10 ^-5 mol / l [Rubinskaya T.Ya., Mairanovsky S.G. On the restoration of perrhenate ion on a mercury dropping electrode in alkaline and neutral environments // Electrochemistry, 1971, V.7, No. 10, S.1403-1408]. The disadvantage of the method is the significant effect of the pH of the solution and its buffer capacity, low sensitivity, catalytic waves suitable for analytical purposes, are in the very negative region of -1.6 V, as well as the use of toxic mercury.

A known method for the determination of rhenium, carried out on the background of a NaCl solution with Na ₂ SO ₃ (pH 11.3-11.5) E _1/2 = -0.45 V. The open minimum is 1 · 10 ^-5 M. The determination is also carried out after sample preparation, during which molybdenum, tungsten and other related elements are separated from rhenium [Duca A., Stanescu D., Puscasu M. Studii si cercetari chim. Acad. RPR Fil. Cluj, 6, 123 (1955); 13, 197 (1962)]. The disadvantage of this method is the use of mercury. When dissolving samples containing rhenium, nitric acid is used, and nitrate ions interfere with the determination, so nitrogen oxides must be removed.

There is a known technique where a mercury-dropping electrode was used, and nas.ke. - reference electrode. As the background electrolyte, a solution consisting of 3 M in NH ₃ , 3 M in KSCN, 3 M in EDTA and 0.16 M in Na ₂ SO _{3 was used} for the found new electrochemical reaction. The detection limit was 0.05 mg / L (2.5 · 10 ^-7 ), which makes it possible to determine from 2 · 10 ^-5 % rhenium with a 2 g sample and a final volume of 10 ml. The method is highly selective and does not interfere with most elements: Mo, W, Fe, Cd, Zn, Sb, Bi, Ag, Al. Polarography is carried out from -1.0 to -1.5 V [Vasilyeva L.I., Semenova I.A., Justus Z.L. Polarographic determination of rhenium in complex products of non-ferrous metallurgy // Journal of analytical chemistry. 1986, t. 41, No. 2, p. 293-297]. The disadvantage of this technique is the use of mercury. As the background electrolyte, a multicomponent background is used, which is prepared on the day of use. The method, having high selectivity, however, is inferior in sensitivity to the determination of rhenium.

A known method for the catalytic determination of rhenium [Gyorbiro K. // Acta Chim. Acad. Sci. Hung., 27, 120 (1961)] (prototype). It is proposed to use the system in the method: 5 M H ₂ SO ₄ + 2 · 10 ^-3 M H ₆ TeO ₆ + x · ReO ₄ ^- . Rhenium catalyzes the process of tellurium oxidation with the appearance of a catalytic wave on a mercury-dropping electrode, which makes it possible to determine it in the range from 4 · 10 ^-7 to 1 · 10 ^-5 M. The disadvantage of this method is the long exposure of the system to determination, the use of a sufficiently large amount of mercury, which relates to substances of the first hazard class.

The task was set to reduce the limit and lower limit of the determined rhenium (VII) contents by the peak of the electrocatalytic decomposition of hydrogen peroxide obtained after electroconcentration of rhenium in the form of ReO ₂ on a mercury-film electrode (RPE) by the KinIV method.

The task is achieved in that the rhenium (VII) ions are electrochemically concentrated on the surface of the RPE in the form of ReO ₂ in a stirred solution for 10-20 s with an electrolysis potential of E _e = -0.2 V against a background of 0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ followed by registration of the cathode peaks at a sweep speed of 100 mV / s. New in the method is that to obtain a useful signal, which depends on the concentration of rhenium (VII), hydrogen peroxide is used to carry out the catalytic reaction of its decomposition into ReO ₂ , obtained by electroconcentration of rhenium (VII) ions from a solution.

In the proposed method, the ability of the precipitate ReO _{2 to} decompose hydrogen peroxide on the surface of mercury-film electrodes is established. The concentration of rhenium (VII) ions is determined by the height of the cathode peak in the potential range from 0.0 to 0.20 V relative to the saturated silver chloride electrode (n.a.

As an indicator used RPE (in the prototype used a mercury-dropping electrode). The use of such electrodes is due to the ease of updating the surface, and the consumption of mercury is also significantly reduced. The lower limit of the determined contents by this method was 1 · 10 ^-8 M (in the prototype 4 · 10 ^-7 M).

The prototype describes the use of 5 M H ₂ SO ₄ and 2 · 10 ^-3 M H ₆ TeO ₆ as the background. When a higher concentration of tellurium salt is used on the current-voltage curve, a tellurium recovery wave appears, which interferes with the determination of rhenium (VII) ions, and at a lower content, rhenium (VII) ions do not catalyze the oxidation of tellurium compounds that give peaks on the current-voltage curve. The use of sulfuric acid with a high concentration of background electrolyte is dangerous and not preferred for inversion methods. Proposed in the claimed invention, the background of 0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ allows you to determine rhenium with good reproducibility. The use of a larger amount of 30% H ₂ O ₂ leads to the appearance of the wave of decomposition of hydrogen peroxide on the RPE.

Another distinguishing feature is the established conditions of electrochemical accumulation: the electrolysis potential E _e = -0.2 V. The experimental data showed the dependence of the rhenium oxidation current on the electrolysis potential (E _e ), presented in table 1, where C ReO ₄ ^- = 2 mg / l ; τ _e = 10 s; background 0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ ; E _p = 0.10 V. The value of the cathode current increased and reached a maximum value in the potential region (-0.2 ÷ -0.4) V. Using pre-electrolysis at potential values greater than -0.4 V does not increase the wave of electrocatalytic decomposition of peroxide hydrogen. The lower electrolysis potential increases the service life of the electrodes, which eliminates the need for additional cleaning and records reproduced voltammograms. This improves the accuracy and resolution of the proposed method.

The pre-electrolysis time (τ _e ) is 10-20 seconds, while the maximum value of the oxidation current of hydrogen peroxide is reached and the expressness of determination increases.

Thus, the established conditions made it possible for the first time to quantify the content of rhenium (VII) ions based on the catalytic decomposition of hydrogen peroxide with the release of oxygen on the surface of a mercury-film electrode.

The proposed voltammetric method has significantly improved the metrological characteristics of the analysis of rhenium ions (VII); to increase the sensitivity of the determination (1 · 10 ^-8 M = 2 · 10 ^-3 mg / DM ³ ), which is more than an order of magnitude lower compared to the prototype. Definition does not interfere with chromium, tungsten and copper, which are accompanying elements.

Case Studies

Example 1. The measurements were carried out on artificial mixtures (table 2). 10 ml of background electrolyte (0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ ) is placed in a quartz glass. Without stopping mixing, electrolysis of the solution is carried out, at E _e = -0.2 V and at τ _e = 10 s, the current-voltage curve of the electrooxidation is removed at a sweep speed of 100 mV / s. The absence of peaks on the current-voltage curve in the range from 0.0 to plus 0.2 V (relative to H.s.a.) indicates the purity of the background. Then added a certified solution of rhenium (VII) ions of 0.02 ml of 0.1 mg / DM ³ and the current-voltage curve of the electrooxidation was taken. A peak of electrocatalytic decomposition of hydrogen peroxide on ReO ₂ appears in the range from 0.0 to plus 0.2. A certified rhenium (VII) solution was added 0.02 ml of 0.1 mg / dm ³ and the volt-ampere curve of the electrocatalytic decomposition of peroxide on the rhenium oxide precipitate was taken in the range from 0.0 to plus 0.2 (relative to n.h.s. e.). The difference in peak currents was used to calculate the concentration of rhenium (VII) in solution (Fig. 1).

Example 2. The measurements were carried out in a sample of dolomite (table 2).

In a weighed portion of dolomite weighing 1 g was added a certified solution of rhenium (VII) ions of 0.02 ml of 10 mg / DM ³ . 2 ml of 1 M NaOH was added to a weighed portion of dolomite until the sample was completely wetted and 8 ml of 30% H ₂ O ₂ were added portionwise, each new portion was added after the termination of the intense reaction. After decomposition of the sample with hydrogen peroxide, the solution was filtered and quantitatively transferred to a distillation flask. Conc. Was added to the distillation flask to the solution. H ₂ SO ₄ with a volume equal to the sample filtrate volume. The open flask on the stove was heated to 200-230 ° C. Then the distillation plant was assembled and distilled off at 300 ° C for 30 min until the first H ₂ SO ₄ vapors appeared. To determine rhenium, 10 ml of the background electrolyte (0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ ) was placed in a quartz glass, an aliquot of 0.5-1 ml of the distilled solution was added. The current-voltage curve of the electrooxidation of hydrogen peroxide on the electrolytic precipitate ReO _{2 was} recorded. An addition of a standard rhenium (VII) solution of 0.02 ml of 0.1 mg / dm ^{3 was made} and an analytical signal was recorded. The difference in the currents of the rhenium peaks calculated the concentration in the solution (figure 2).

Thus, the ability to quantify rhenium (VII) ions by the peaks of electrocatalytic decomposition of hydrogen peroxide on a ReO ₂ precipitate was first established.

The proposed method is simple, a much smaller amount of mercury is used in comparison with a mercury-dropping electrode. The method can be applied in any chemical laboratory having computerized analyzers such as CTA or TA.

Table 1 E _e , B I · 10 ⁶ , A 0,000 2,088 -0,100 9,422 -0,200 11,031 -0,300 11,348 -0,400 12,379 -0,500 13,211

table 2 Object of study Introduced Found Sr (t _0.95 ), With ReO ₄ ^- , mg / dm ³ With ReO ₄ ^- , mg / dm ³ n = 5 Background solution (0.1 M H ₂ SO ₄ + 0.03 ml 30% H ₂ O ₂ ) 2 1.90 ± 0.05 0.018 Dolomite twenty 18.3 ± 0.26 0,093

Claims (1)

A method for determining rhenium by the kinetic inversion voltammetric method in rocks and ores, which consists in the accumulation of rhenium (VII) ions on a mercury-film electrode in a stirred solution for 10-20 s at an electrolysis potential of -0.2 V relative to saturated silver chloride an electrode on the background of 0.1 M H ₂ SO ₄ with the addition of 0.03 ml of 30% H ₂ O ₂ followed by registration cathodic peaks shooting voltammograms when potential scan rate of 100 mV / s, the concentration is determined by the height of the cathodic peak potential-in range als from 0.0 to 0.20 The method certified mixtures of additives.

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