RU2426108C1 - Method of determining platinum in ores via stripping voltammetry - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of determining platinum in ores via stripping voltammetry involves converting platinum (IV or II) from a sample into a solution and performing voltammetric determination, for which platinum is accumulated on a soot or uglesitall electrode in a stirred solution in the presence of indium (III) ions for 50…100 s with subsequent recording of peaks of selective electro-oxidation of indium from the intermetallic compound Pt_xIn_y with potential sweep rate of 50…150 mV/s first at electrolysis potential -1.0 V, and then at -0.4 V on a background electrolyte of 1…3 M HCl. Concentration of platinum ions is determined from the height of the indium peak on the volt-ampere curve at potential ranging from -0.05 to 0.05 V relative a saturated silver chloride electrode by adding standard mixtures.

EFFECT: invention enables to lower the limit and lower boundary of determined content of platinum from the peak for electro-oxidation of indium from an intermetallic compound Pt_xIn_y, obtained after electro-concentration of a binary residue of platinum-indium on a soot electrode.

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Description

The invention relates to analytical chemistry, and in particular to methods for the determination of metal ions, and can be used in hydrometallurgy, in various geological explorations for prospecting and exploration in the case of ore analysis, to determine the content of platinum ions by inversion voltammetry (IV).

The method of film polarography with accumulation is used to determine platinum, which includes the electrochemical reduction of platinum on a graphite electrode against a background of 0.1 M NH ₄ F [Dominova IG, Kolpakova NA, Stromberg AG “Determination of platinum in the presence of mercury by the method of film polarography with accumulation” // Zh. anal chemistry. - 1977. - T. 32. - Issue 10. - S.1980-1983].

The possibility of voltammetric determination of noble metals on a carbon paste electrode modified with crown ethers was studied. The detection limit for platinum is 3 ... 8 · 10 ^-7 mol / l depending on the modifier [Shaydarova L.G., Al-Gahri M.A., Ulahovich N.A., Zabirov N.G., Budnikov G.K. . "Inversion-voltammetric determination of palladium, platinum and gold using a carbon paste electrode modified with crown ethers" // Zh. anal chemistry. - 1994. - T. 49. - Issue 5. - S.501-504].

A method for voltammetric determination of platinum on a mercury-graphite electrode has been developed. In the determination, the method of concentrating platinum in an alloy with mercury is used [Kolpakova N. A., Shifris B. S., Shvets L. A., Kropotkina S. V. “Determination of platinum metals and gold by inversion voltammetry” // Zh. anal chemistry. - 1991. - T. 46. - Issue 10. - S. 1910-1913].

The method of currentless inversion chronopotentiometry is suitable for determining up to 1 · 10 ^-8 mol / l of platinum, if KMnO ₄ and HCl are used at the dissolution stage. The technique was proposed using a mercury-graphite electrode and is based on the interaction of platinum chloride complexes with mercury [Toropova V.F., Polyakov Yu.N., Krut S.Kh. "Determination of gold and platinum metals by the method of inverse currentless chronopotentiometry" // Izv. universities. Chemistry and chemical. technol. - 1993. - T.36. - No. 2. - S.111-114].

A technique has been developed in which Pt (IV) is extracted from hydrochloric acid solutions into the volume of a carbon paste electrode containing piperidinethyl dodecyl sulfide or morpholinoethyl dodecyl sulfide as an organic binder. The detection limit of platinum is 2 · 10 ^-8 mol / l [Maistrenko V.N., Kuzina L.G., Amirkhanova F.A., Murinov Yu.I. "Voltammetric determination of platinum (IV) and iridium (IV) after extraction concentration on a carbon-paste electrode" // Zh. analyte. chemistry. - 1989, - T. 44. - No. 9. - S.1658-1661].

A method for voltammetric determination of platinum after decomposition of a sample in a Wickbold apparatus and UV irradiation of a solution in a variant of cathodic differential pulse inversion voltammetry using a static mercury electrode [Hoppstock K., Michulitz M. "Voltammetric determination of trace platinum in gasoline after Wiclbold combustion" / / Anal. chim. acta. - 1997 - 350 - No. 1-2. - P.135-140].

To determine platinum in the ore material, the method of inversion voltammetry on a mercury-graphite electrode is used [Smyshlyaeva EA, Kolpakova NA, Kaminskaya OV “Voltammetric determination of platinum in gold ore raw materials” // Chemistry and Chemical Technology, 2002, T 45, Issue 3, S.94-96] (prototype). The determination of platinum is carried out according to the following procedure. As the background electrolyte, a solution of 1 M HCl is used. Electrodeposition is carried out at a potential limit current mercury of EE-1.0 V, an accumulation time of 180 s, a potential sweep speed of 60 mV / s. Determination of platinum (IV) by inversion voltammetry is recorded by the peak of the electrooxidation of mercury from an intermetallic compound (IMS) with platinum. The method has high sensitivity, the range of the determined contents with a constant mercury content of 1 · 10 ^-2 ... 10 mg / DM ³ .

The task was set in the work - to reduce the limit and lower boundary of the determined platinum (IV) contents by the peak of indium electrooxidation from the Pt _x Ih _y intermetallic compound obtained after electroconcentration of a binary platinum-indium precipitate on a carbon black electrode by the IV method.

This object is achieved in that platinum (IV or II) ions and indium (III) ions are electrochemically concentrated on the surface of various types of graphite electrode: carbon black composite electrode (SCE), carbon-metal electrode (SSE) in the form of an intermetallic compound Pt _x In _y , s subsequent dissolution of the precipitate and registration of the anode current-voltage curves. New in the method is that to obtain a useful signal, which depends on the concentration of platinum (IV or II), the process of electrooxidation of indium from IMS of platinum with indium is used.

In the proposed method for the first time established the ability of a precipitate of platinum with indium to oxidize from the surface of various types of graphite electrodes. SKE was used as an indicator electrode (a mercury-graphite electrode was used in the prototype). The use of such electrodes is due to the high chemical and electrochemical stability of graphite, a wide range of working potentials, as well as the simplicity of mechanical surface renewal and safety requirements. The analysis does not use mercury, as mercury is toxic. The lower limit of the determined contents by this method was 1 · 10 ^-4 mg / dm ³ (in the prototype 3 · 10 ^-2 mg / dm ³ ).

The results of the determination of platinum from IC with indium on SCE are shown in table 1 and table 2. As can be seen from table 2, the measurement error is about 7.6%. The calculation of the determined concentrations of platinum is carried out according to the method of "entered-found."

Against the background of 1 ... 3 M HCl, electroconcentration of platinum ions (IV or II) is carried out on the surface of the carbon black electrode in a mixed solution in the presence of indium ions for 50 ... 100 s, first at an electrolysis potential of -1.0 V, followed by oxidation from the electrode surface, and then, with an electrolysis potential of -0.4 V, followed by registration of anode peaks at a potential sweep speed of 50 ... 150 mV / s. The concentration of platinum ions (IV or II) is determined by the height of the anode peak in the potential range from -0.05 to 0.05 V relative to the saturated silver chloride electrode (chemical grade). The use of the concentration technique at different potentials improves the reproducibility and metrological characteristics of the determination of platinum ions (IV or II) in solution. Figure 1 presents the current-voltage curves of electrooxidation of the precipitate Pt _x In _y from the surface of the carbon black electrode. Background 1M HCl containing C _{In (III)} = 0.2 mg / L, curve 1 - C _{Pt (IV)} = 0.003 mg / dm ³ , curve 2 - C _{Pt (IV)} = 0.006 mg / dm ³ .

Thus, the established conditions made it possible for the first time to quantify the content of platinum ions (IV or II) based on the reaction of selective electrooxidation of indium from the intermetallic compound (IMC) Pt _x In _y obtained at the stage of preliminary electroconcentration (figure 2).

The proposed voltammetric method allowed to significantly improve the metrological characteristics of the analysis of platinum (IV or II), increase the sensitivity of the determination (1 · 10 ^-4 mg / kg), which is two orders of magnitude lower compared to the prototype.

Examples of specific performance:

Example 1. The measurements were carried out on artificial mixtures. 10 ml of background electrolyte (1M HCl) is placed in a quartz glass. Without stopping mixing, the solution is electrolyzed at Ee - 1.0 V and τ _e 100 s on SLE, the current-voltage curve of the electrooxidation is taken at a sweep speed of 100 mV / s. Then add 0.2 ml of a certified solution of In (III) with a concentration of 0.1 mg / DM ³ and conduct electrochemical concentration of the precipitate under similar conditions. The absence of peaks on the current-voltage curve indicates the purity of the background. An aliquot of 1 ... 2 ml of the test solution is added to the background and electroconcentration is carried out at an accumulation potential of -1.0 V, followed by oxidation from the electrode surface. Then, electroconcentration is carried out under the same conditions at an accumulation potential of -0.4 V, and the current-voltage curves of selective electrooxidation of indium from indium IC with platinum are recorded. An addition of 0.02 ml of a certified solution of platinum (IV) ions with a concentration of 0.01 mg / dm ^{3 is} introduced into the analyzed solution and again electrolysis is carried out first at an accumulation potential of -1.0 V, and then at -0.4 V followed by registration of voltammograms . From the difference in peak currents of selective indium electrooxidation from Pt _x In _y ICs, the concentration of platinum in a solution is calculated (the values of peak currents whose polarograms were obtained at a potential of -0.4 V are estimated). The anode peak current is recorded in the potential range from -0.05 to 0.05 V (rel. N.h.s.se.).

Example 2. Measurements were carried out in ore material.

1 g of ore material is placed in a corundum crucible, treated with a mixture of acids 37% HCl and 68% HNO ₃ (3: 1), to transfer the metals into solution. The resulting mixture was filtered through a blue ribbon filter and precipitated with a 3% NaOH solution. The resulting solution was evaporated to a dry residue at 180 ° C. The precipitate was dissolved in 5 ml of background electrolyte.

10 ml of background electrolyte 1M HCl is placed in a quartz glass. Electrolysis of the solution is carried out with constant stirring at Ee -1.0 V and τ _e 60 s on SSE. 0.2 ml of a certified In (III) solution with a concentration of 0.1 mg / dm is added to the background electrolyte and a current-voltage curve is taken at a potential sweep rate of 80 mV / s. The absence of additional peaks indicates the purity of the background. An aliquot of 1 ... 2 ml of the resulting solution is added and electroconcentration is carried out at an accumulation potential of -1.0 V, followed by oxidation from the electrode surface. Then, measurements and estimation of the height of peak currents are carried out at an accumulation potential of -0.4 V. An addition of 0.02 ml of a certified solution of platinum (IV) ions with a concentration of 0.01 mg / dm ^{3 is made} and measurements are carried out under similar conditions. The difference in the peak currents of the selective electrooxidation of indium from the Pt _x In _y ICs calculates the concentration of platinum in the test sample.

Thus, the ability to quantitatively analyze platinum by the peaks of selective electrooxidation of indium from the Pt _x In _y intermetallic compound was established for the first time.

The proposed method is simple, mercury is not used due to its toxic effect. The method can be applied in any chemical laboratory having computerized analyzers such as CTA, TA or a polarograph.

The proposed method can be used to determine platinum in ore material.

Table 1 The result of the determination of platinum (IV) in ores of various compositions Object of study (ore) Pt content, g / t Found Pt, g / t Sr, (t _0.95 ) n = 8. SHT-1 16.6 16.3 ± 0.30 0,07 SOP 108.1 2.5 2.1 ± 0.10 0.10 VP-2 2.64 2.23 ± 0.13 0.12 ST-2 2.5 · 10 ^-6 2.3-10 ^-6 ± 0.09 0.09

table 2 The result of the determination of platinum (IV) in the background electrolyte (1 M HCl) Introduced C _Pt , mg / L Found C _Pt mg / L n Sr, (t _0.95 ) ε,% 0.1 0.13 ± 0.013 9 0,033 7.6 0.5 0.47 ± 0.015 7 0.015 4.2 0.9 0.93 ± 0.043 8 0.024 5.5 1.3 1.29 ± 0.027 9 0,023 5,4

Claims (1)

The method for determining platinum in ores by the method of inverse voltammetry, namely, that platinum (IV or II) is transferred from the sample to the solution and voltammetric determination is carried out, characterized in that platinum is accumulated on the carbon black or carbon-metal electrode in a mixed solution in the presence of indium ions ( III) for 50 ... 100 s, followed by registration peaks selective electrooxidation of intermetallic compounds of indium Pt _x in _y at the potential scan rate of 50 ... 150 mV / s initially at potentials elec of rollerization - 1.0 V, and then at -0.4 V on a background electrolyte of 1 ... 3 M HCl, the concentration of platinum ions is determined by the height of the indium peak on the current-voltage curve in the potential range from -0.05 to 0.05 V relative to saturated silver chloride electrode by the method of additives of certified mixtures.

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