RU2498289C1 - METHOD OF DETERMINING PLATINUM IN ORES FROM PEAK OF SELECTIVE ELECTROOXIDATION OF Cu FROM INTERMETALLIC COMPOUND PtXCuY BY STRIPPING VOLTAMMETRY - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of determining platinum in ores from the peak of selective electrooxidation of Cu from the intermetallic compound Pt_xCu_y by stripping voltammetry involves transferring platinum (IV or II) from a sample into a solution, accumulating platinum on a soot or carbositall electrode in a stirred solution in the presence of copper (II) ions for 50-100 s at electrolysis potential of -0.62 V, followed by detection of peaks of selective electrooxidation of copper from the intermetallic compound Pt_xCu_y at potential sweep rate of 50-150 mV/s on a background electrolyte of 0.1-1M HCl; concentration of platinum ions is determined from the height of the copper peak on the current versus voltage curve in the potential range of -0.3 to -0.1 V relative a saturated silver chloride electrode by standard addition method.

EFFECT: lowering the maximum and minimum levels of the determined content of platinum.

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Description

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

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 disadvantage of this method is the low sensitivity of 1 · 10 ^-5 mol / l and the use of toxic mercury.

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 the method of inverse voltammetry” // Zh. anal chemistry. - 1991. - T. 46. - Issue 10. - From 1910-1913]. The disadvantage of this method is the use of toxic mercury. The detection limit is 1 · 10 ^-7 mol / L.

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. [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]. The disadvantage of this method is the use of additional equipment (Wickbold apparatus), which uses the combustion and complete thermal decomposition of the sample at a high temperature of a hydrogen-oxygen flame.

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 by this method 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]. The main disadvantage of this method is the complexity of the structural manufacturing and one-time use of a carbon-paste electrode for determining platinum in solution.

To determine platinum in the ore material, the method of inversion voltammetry on 1 M HCl 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 a background electrolyte, a solution of 1 M HCl is used. The electrodeposition was carried out at the potential limit current of mercury E _e = -1.0 V, the accumulation time of 180 seconds, the potential sweep speed of 60 mV / s. Determination of platinum (IV) by inversion voltammetry is possible 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 to reduce the limit and lower limit of the determined platinum (IV) contents by the peak of copper electrooxidation from the Pt _x Cu _y intermetallic compound obtained after electroconcentration of a binary platinum-copper precipitate on a carbon black electrode by the IV method.

The problem is achieved in that platinum (IV or II) is transferred from the sample to the solution and voltammetric determination is carried out. Platinum is accumulated on a carbon black or carbon-metal electrode in a mixed solution in the presence of copper (II) ions for 50-100 s at electrolysis potentials of 0.62 V, followed by registration of peaks of selective electrooxidation of copper from the Pt _x Cu _y intermetallic compound at a potential sweep speed 50-150 mV / s on a background electrolyte of 0.1-1 M HCl. The concentration of platinum ions is determined by the height of the copper peak on the current-voltage curve in the potential range from -0.3 to -0.1 V relative to the saturated silver chloride electrode by the method of additives of certified mixtures.

New in the method is that to obtain a useful signal, depending on the concentration of platinum (IV or II), the process of electrooxidation of copper from the IC of platinum with copper is used.

In the proposed method for the first time established the ability of a precipitate of platinum with copper to oxidize from the surface of various types of graphite electrodes. A carbon black composite electrode (SKE) was used as an indicator, (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 copper on SCE are shown in table 1 and table 2. As can be seen from table 2, the measurement error is about 9%. The calculation of the determined concentrations of platinum is carried out according to the method of "entered-found."

An electroconcentration of platinum (IV or II) ions is carried out on the surface of a carbon black or carbon-metal electrode in a mixed solution in the presence of copper ions for 50-100 s at an electrolysis potential of -0.62 V. At a potential of -0.62 V, the anode peak approaches its limiting value. A further increase in the electrolysis potential causes a discharge of copper and distorts the peak shape of the IC of copper with platinum, therefore, the electrolysis potential was chosen equal to -0.62 V. The measurements were carried out against 0.1-1 M HCl, followed by registration of peaks of selective electrooxidation of copper from the Pt intermetallic compound _x Cu _y at a scan rate of 50-150 mV / s. The concentration of platinum ions (IV or II) is determined by the height of the peak of copper on the current-voltage curve in the potential range from -0.3 to -0.1 V relative to the saturated silver chloride electrode (v.h.s.). Figure 1 presents the current-voltage curves of electrooxidation of the precipitate Pt _x Cu _y from the surface of the carbon black electrode. Curve 1 — background 0.1 M HCl containing C _{cu (II)} is 1 mg / L, curve 2 — C _{Pt (IV)} is 0.002 mg / L, curve 3 — C _{Pt (IV)} is 0.005 mg / L.

Thus, the established conditions allowed for the first time to quantify the content of platinum ions (IV or II) based on the reaction of selective electrooxidation of copper from the intermetallic compound (IMC) Pt _x Cu _y obtained at the stage of preliminary electroconcentration (Fig. 2).

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

Case Studies

Example 1. The measurements were carried out on artificial mixtures. 10 ml of background electrolyte (0.1 M HCl) is placed in a quartz glass. Without stopping mixing, an electrolysis of the solution is carried out, at E _e equal to -0.62 V and at τ _e equal to 80 seconds, the current-voltage curve of the electrooxidation is removed at a sweep speed of 70 mV / s. Then, a certified Cu (II) solution of 0.1 ml of 10 mg / L was added and the precipitate was electrochemically concentrated 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 was added to the background and copper was electroconcentrated at a storage potential of 0.62 V. A standard platinum sample of 0.02 ml of 0.1 mg / L was added and the analytical signal of platinum was recorded under similar conditions. By the difference in the currents of the peaks of copper, the concentration of platinum in the solution was calculated. The peak current of copper was recorded in the potential range from -0.3 to -0.1 V (rel.

Example 2. Measurements were carried out in ore material.

1 g of ore material, placed in a corundum crucible, treated with a mixture of acids 37% HCl and 68% HNO ₃ (3: 1), to transfer metals into solution. The resulting mixture is filtered through a blue ribbon filter, and precipitation is carried out with a 3% solution of NaOH matrix elements. The resulting solution was evaporated to a dry residue at 170 ° C.

10 ml of background electrolyte 0.1 M HCl is placed in a quartz glass. The solution is electrolyzed with constant stirring at τ _e equal to 80 s. 0.1 ml of 10 mg / L Cu (II) is added to the background electrolyte, electrochemical concentration of the precipitate is carried out, and the current-voltage curve is taken at a potential sweep speed of 70 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, copper is accumulated at a potential of -0.62 V and the current-voltage curve of copper electrooxidation is measured. An addition of a standard sample of platinum of 0.02 ml from 0.1 mg / L was made and the analytical signal was again recorded under similar conditions. By the difference in the currents of the peaks of copper, the concentration of platinum in the solution was calculated. The peak current of copper was recorded in the potential range from -0.3 to -0.1 V (rel.

Thus, for the first time, the ability of quantitative analysis of platinum by the peaks of selective electrooxidation of copper from the intermetallic compound Pt _x Cu _{y was established} .

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.

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

Table 1 The result of the determination of platinum (IV) in ores of various compositions Object of study (ore) The content of Pt in ore, g / t Found Pt, g / t Sr, (t ₀ , ₉₅ ) n = 8 SHT-1 16.6 16.0 ± 0.20 0,07 SOP 108.1 2,5 2.1 ± 0.30 0,047 VP-2 2.64 2.3 ± 0.2 0.06 ST-2 2.5 · 10 ^-6 (2.3 ± 0.1) -10 ^-6 0.08

table 2 The result of the determination of platinum (IV) in the background electrolyte (0.1 M HCl) Introduced C _Pt , mg / L Found C _Pt , mg / L n Sr, (t _0.95 ) ε,% 0.2 0.18 ± 0.02 8 0,025 5 0.5 0.42 ± 0.01 8 0.05 9 one 0.91 ± 0.02 8 0.04 8

Claims (1)

A method for determining platinum in ores by the peak of selective electrooxidation of Cu from an intermetallic compound Pt _x Cu _y by inversion voltammetry, which means that platinum (IV or II) is transferred from a sample to a solution and voltammetric determination is carried out, characterized in that platinum is accumulated on carbon black or carbon-metal electrode in a mixed solution in the presence of copper (II) ions for 50-100 s with electrolysis potentials of 0.62 V followed by registration of peaks of selective electrooxidation of copper from Pt _x Cu _y intermetallic compound at a potential scan rate of 50-150 mV / s on a background electrolyte of 0.1-1 M HCl, the concentration of platinum ions is determined by the height of the copper peak on the current-voltage curve in the potential range from -0.3 to -0, 1 V relatively saturated silver chloride electrode by the method of additives of certified mixtures.

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