RU2479837C1 - METHOD OF DETERMINING PLATINUM IN ORE AND ORE CONCENTRATES BY STRIPPING VOLTAMMETRY ON SELECTIVE ELECTROOXIDATION PEAKS OF BISMUTH FROM INTERMETALLIC COMPOUND PtxBiy - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method of determining platinum in ore and ore concentrates by stripping voltammetry according to the invention involves transferring platinum (IV or II) from a sample into a solution and conducting voltammetric determination, wherein platinum is accumulated on glass-carbon or graphite electrodes impregnated with polyethylene and paraffin in a stirred solution in the presence of bismuth ions for 60-120 s, followed by recording of anode peaks for selective electrooxidation of bismuth (III) from intermetallic compound PtBiwith potential sweep rate of 60-100 mV/s, electrolysis potential from -0.30 to -1.1V on the following backgrounds: 1-0.5 M HNOor 1-0.5 M HCl. Concentration of platinum (IV or II) ions is determined from the value of area under the voltage versus current curves at potential ranging from 0.15 V to 0.45 V relative a saturated silver chloride electrode using a certified mixture addition technique, in order to reduce the lower limit of the determined content and widen the range of determined content of platinum (IV or II) by determining platinum from selective electrooxidation peaks of bismuth from an intermetallic compound (IMC) PtBi.EFFECT: reducing the lower limit of the determined content and widening the range of determined content of platinum when determining platinum from selective electrooxidation peaks of bismuth from an intermetallic compound PtBi.1 dwg, 2 tbl

Description

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

Platinum (IV) is extracted from hydrochloric acid solutions into the volume of a coal-bed electrode containing piperidinethyl dodecyl sulfide or morpholinoethyl dodecyl sulfide as an organic binder. The detection limit of platinum by this VA method is 4 · 10 ^-3 mg / dm ³ [Maystrenko VP, Kuzina LG, Amirkhanova FA, Murinov Yu.I. “Voltammetric determination of platinum (IV) and iridium (IV) after extraction concentration on a coal-bed electrode” // Zh. analyte. chemistry. - 1989, - T. 44. - No. 9. C.1658-1661].

Voltammetric determination of platinum ions after its extraction concentration with N-thiophosphorylated thiobenzamide from aqueous media into a melt of a low-melting organic solvent allows platinum to be determined up to 5 · 10 ^-3 mg / dm ³ [Pestova N.Yu., Ulakhovich N.A., Mashkina S. V., Zabirov N.G. "The use of thiophosphorylated thiobenzamide in the extraction-voltammetric determination of platinum metals using fusible compounds" // Izv. universities. Chemistry and chemical. technology. -1998. - T.41. - No. 4. - C.3-7].

A method for voltammetric determination of platinum after decomposition of a sample in a Wickbold apparatus and UV irradiation of a solution in the variant of cathodic differential pulse inversion voltammetry using a static mercury electrode was developed. To determine platinum (II) aryl mercaptoquinolinates by alternating current voltammetry, aromatic amines are used as extractants [K. Hoppstock, Michulitz M. Anal. chim. acta. -1997 - 350 - No. 1-2. - P.135-140].

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 6 · 10 ^-2 -0.2 mg / dm ³ 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]. All of the above methods are distinguished by a limited range of determined concentrations of platinum, the detection limit is insufficient.

To determine platinum in ore objects, an inversion voltammetric method is used to determine platinum on 1 M HCl on a mercury-graphite electrode [Smyshlyaeva EA, Kolpakova NA, Kamenskaya OV "Voltammetric determination of platinum in gold ore" // Izv. universities. Chemistry and Chem. technology., 2002, pp. 94-96] (prototype). The determination of platinum is carried out according to the following procedure. As a background electrolyte, a 1M HCl solution is used. Electrodeposition was carried out with a potential limit current mercury E _e -1.0 V, an accumulation time of 180 seconds, a potential sweep speed of 60 mV / s. A standard solution of mercury (II) with a concentration of 1.3 mg / L was prepared from a salt of mercury (II) nitrate. Determination of platinum (IV) by the method of inverse voltammetry is possible by the peak of the electrooxidation of mercury from IMS with platinum. The method is characterized by high sensitivity, the range of the determined contents with a constant mercury content of 1 · 10 ^-2 -10 mg / DM ³ . A prerequisite for the process is that mercury is used to determine platinum. This condition is a disadvantage of this method.

The task was set to reduce the lower limit of the determined contents and increase the interval of the determined platinum (IV or II) contents by determining platinum from the peaks of selective bismuth electrooxidation from the Pt _x Bi _y intermetallic compound obtained after electroconcentration of a platinum-bismuth binary precipitate on glassy carbon graphite electrode by inversion voltammetry.

This object is achieved by the fact that platinum (IV or II) is transferred from the sample to the solution and voltametric determination is carried out, platinum is accumulated on glassy carbon or graphite electrodes impregnated with polyethylene and paraffin in a mixed solution in the presence of bismuth ions for 60-120, followed by registration of the anode peaks of the selective electrooxidation of bismuth (III) from the Pt _x Bi _y intermetallic compound at a potential sweep speed of 60-100 mV / s, with electrolysis potentials from -0.30 to -1.10 V on the background: 1- 0.5 M HNO ₃ or 1-0.5 M HCl, the concentration of platinum ions (IV or II) is determined by the area under the current-voltage curves in the potential range from 0.15 to 0.45 V relative to the saturated silver chloride electrode by the method of additives certified mixtures .

In the proposed method for the first time established the ability of a precipitate of platinum with bismuth to oxidize on various types of graphite electrodes. As indicator glassy carbon or impregnated with polyethylene with paraffin graphite electrodes were used (in the prototype a mercury-graphite electrode was used). The use of such electrodes is due to the maximum value of the detected current, 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.

Proposed in the claimed invention backgrounds 1-0.5 M HCl or 1-0.5 M HNO ₃ can determine the low content of platinum ions (IV or II) with good reproducibility. The highest sensitivity coefficient was observed on the backgrounds of 1 M HNO ₃ or 1 M HCl. The lower limit of the determined contents by this method was (1 · 10 ^-3 mg / dm ³ ) (in the prototype 3 · 10 ^-2 mg / dm ³ ).

The results of using different electrodes on different backgrounds are shown in Table 1. The table shows that the electrodes of glassy carbon or impregnated with graphite paraffin polyethylene have the highest sensitivity coefficients.

Figure 1 shows the current-voltage curves of electrooxidation of the Pt _x Bi _y precipitate from the surface of a graphite electrode against a background of 1 M HNO ₃ at a constant bismuth concentration of 2.00 mg / dm ³ (curve 1-background line). With an increase in the concentration of platinum (IV or II) ions in solution from 0.01 to 0.03 mg / dm ³ (curves 2-4) and a constant concentration of bismuth (III) on the anode current-voltage curve, the number of anode peaks of the Pt _x Bi _y precipitate increases . Using the area under the anode peaks, the quantitative content of platinum was evaluated.

Thus, the established conditions made it possible for the first time to quantitatively determine the content of platinum ions (IV or II) based on the reaction of selective electrooxidation of bismuth from the intermetallic compound (IMS) Pt _x Bi _y obtained at the stage of preliminary electroconcentration.

Table 2 presents the metrological characteristics of the results of voltammetric determination of platinum (IV or II) in artificial mixtures. The proposed method allowed to significantly improve the metrological characteristics of the analysis of platinum (IV or II) and increase the sensitivity of the determination (1 · 10 ^-3 mg / kg), which is an order of magnitude lower compared to the prototype.

Examples of specific performance:

Example 1. The measurements were carried out on artificial mixtures. 10 ml of 1 M HNO ₃ background electrolyte is placed in a quartz glass. Without stopping stirring, electrolysis of the solution is carried out on a glassy carbon graphite electrode under the condition: E _e -0.30 V, τ _e 100 s. The background volt-ampere curve of electrooxidation is taken at a sweep speed of 80 mV / s, starting from potential E _nach -0.20 V. The absence of peaks indicates the purity of the background. Then add 0.20 ml of a certified solution of bismuth (III) ions with a concentration of 100 mg / dm ³ and conduct the electrochemical concentration of the precipitate under similar conditions. The peak of bismuth of the indicated concentration of the substance is recorded in the potential range from -0.15 to 0.10 V relative to the saturated silver chloride electrode. The absence of other peaks indicates the purity of the background.

Then add 0.02 ml of a certified solution of platinum ions (IV or II) with a concentration of 10 mg / dm ³ , electrochemical concentration of the precipitate is carried out under similar conditions. The volt-ampere curve of selective bismuth electrooxidation is recorded from IC with platinum in the potential range from 0.15 to 0.45 V relative to the saturated silver chloride electrode.

An addition of 0.02 ml of a certified solution of platinum ions (IV or II) with a concentration of 10 mg / dm ³ is added to the analyzed solution and the analytical signal is recorded again. The concentration of platinum ions (IV or II) in solution is calculated from the difference in the areas under the anode peaks of the selective bismuth electrooxidation from the Pt _x Bi _y IC.

Example 2. Measurements were carried out in ore material. 1 g of ore material containing platinum is annealed in a muffle furnace at a temperature of 850 ° C, then dissolved in a mixture of concentrated HNO ₃ and HCl (acid ratio 1: 3) in a 30 ml crucible for 15-20 minutes. Then add 10 ml conc. HCl to convert platinum compounds to chloride complexes and heat for 10 minutes.

10 ml of 0.5 M HNO ₃ background electrolyte is placed in a quartz glass. Without stopping stirring, electrolysis of the solution is carried out on a glassy carbon graphite electrode under the condition: E _e -0.30 V, τ _e 100 s. The background volt-ampere curve of electrooxidation is taken at a sweep speed of 80 mV / s, starting from potential E _nach -0.20 V. The absence of peaks indicates the purity of the background. Then add 0.20 ml of a certified solution of bismuth (III) ions with a concentration of 100 mg / dm ³ and conduct the electrochemical concentration of the precipitate under similar conditions. The peak of bismuth of the indicated concentration of the substance is recorded in the potential range from -0.15 to 0.10 V relative to the saturated silver chloride electrode. The absence of other peaks indicates the purity of the background.

After that, an aliquot of the analyzed solution is taken and placed in a quartz glass, electrolysis of the solution is carried out with constant stirring under similar conditions.

Then add 0.02 ml of a certified solution of platinum ions (IV or II) with a concentration of 10 mg / dm ³ , electrochemical concentration of the precipitate is carried out under similar conditions. The volt-ampere curve of selective bismuth electrooxidation is recorded from IC with platinum in the potential range from 0.15 to 0.45 V relative to the saturated silver chloride electrode. The concentration of platinum ions (IV or II) in solution is calculated from the difference in the areas under the anode peaks of the selective bismuth electrooxidation from the Pt _x Bi _y IC.

Thus, for the first time, the ability of quantitative analysis of platinum by the peaks of selective electrooxidation of bismuth from the intermetallic compound Pt _x Bi _{y was established} . The proposed method is simple, mercury is not used due to its negative physiological 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 ores and ore concentrates.

Table 1 Graphite electrode Sensitivity factors of various 1M background electrolytes H ₂ SO ₄ HNO ₃ Hcl HClO ₄ Glassy carbon 0.02 0.30 0.31 0.20 Impregnated with paraffin polyethylene 0.09 0.37 0.32 0.27

table 2 Found platinum, mcg / kg Metrological characteristics of IV I · 10 ⁶ , A Standard deviation S _i · 10 ⁷ Relative error, Δ,% Relative standard deviation Sr 0.46 0.09 0.19 50.3 0.42 2.04 0.38 0.75 44.1 0.37 5.06 0.95 0.56 13.3 0.11 10.02 2.17 0.89 10.4 0.09 19.46 3.98 1.17 7.2 0.06 50.10 8.52 0.50 1.2 0.01

Claims (1)

The method for determining platinum in ores and ore concentrates by the method of inverse voltammetry, which consists in the fact that platinum (IV or II) is transferred from a sample to a solution and a voltametric determination is carried out, characterized in that platinum is accumulated on glassy carbon or impregnated with polyethylene and graphite electrodes paraffin in graphite electrodes in stirred solution in the presence of bismuth ions for 60-120 s followed by registration of the anode peaks of selective bismuth (III) electrooxidation from the intermetallic compound Pt _x Bi _y at a potential sweep speed of 60-100 mV / s at electrolysis potentials from -0.30 to -1.10 V on the background: 1-0.5 M HNO ₃ or 1-0.5 M Hcl, concentration platinum ions (IV or II) are determined by the area under the volt-ampere curves in the potential range from 0.15 to 0.45 V relative to the saturated silver chloride electrode by the method of additives of certified mixtures.

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