RU2401312C1 - Method of electrochemical treatment of heatproof nickel alloy metal wastes that contain rhenium - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: proposed method comprises dissolving wastes in acid electrolyte by applying AC electric field thereto. Dissolving is performed in nitrate or sulphate electrolyte on applying half-wave asymmetric AC industrial-frequency current and on using second electrode made from tantalum or niobium plates. Note here that anodic dissolution is carried at acidity of nitrate electrolyte at the level of 200-250 g/l HNO3, while that of sulphate electrolyte making 150-200 g/l H2SO4 at 20-40C and current of at least 1 kA. ^ EFFECT: increased process rate, better ecology. ^ 3 cl, 3 tbl, 3 ex

Description

The invention relates to the regeneration of secondary metal raw materials, in particular to the processing of metal waste from heat-resistant nickel alloys containing rhenium.

After the collapse of the USSR, Russia was left without developed and reliable raw materials for rhenium, which is widely used in a number of modern fields of technology (aviation, space, petrochemicals, etc.). In this regard, the industrial production of this rare and scattered element in the Russian Federation has practically stopped. In this situation, the relevance of extracting rhenium from various types of secondary raw materials containing this metal has sharply increased. One of the most widespread type of such materials is metal waste of multicomponent aviation heat-resistant nickel alloys of ZhS-32 brand. Their average chemical composition is as follows (in%): Ni ~ 60; Co, W 5-10; Re, Ta 2.0-4.0; Mo, Cr, Al 0.5-5.0.

In industrial practice, nickel-cobalt alloy wastes are usually lined up during pyrometallurgical processing of ore and secondary nickel raw materials [Khudyakov I.F., Tikhonov A.I. et al. Metallurgy of copper, nickel and cobalt. M .: Metallurgy, 1976, 230 pp.]. In this case, rhenium and other valuable components (tungsten, tantalum, niobium, molybdenum) are lost with the total mass of the melt and are not returned to production.

Another way is to dissolve the waste of heat-resistant nickel alloy grade ZhS-32 in solutions of strong mineral acids (nitric or its mixture with sulfuric or hydrochloric acids) [Istrashkina MV, Peredereeva Z.A., Fomin S.S. Promising technologies for the extraction of rhenium from waste nickel alloys. In the anniversary collection of "Giredmet", Moscow: TsINAO, 2001, p.111-119] - analogue.

According to this method, in an optimal mode, rhenium is transferred to ~ 95% into an acidic solution, from which it is then extracted by known methods (for example, sorption on anion-exchange resins). The main disadvantages of the analogue are as follows:

1. Kinetic difficulties determining a high leaching time (up to 8-10 hours or more per operation).

2. The need for preliminary grinding of waste.

3. Environmental restrictions associated with the intensive release of environmentally harmful nitrous gases.

The closest technical solution is a method for the extraction of valuable metals from superalloys (patent RU 2313589 from 2002.11.13). According to this method, the oxidation (dissolution) of this alloy is carried out in solutions of mineral acids by applying alternating current, and recycled waste is directly used as electrodes (soluble). The disadvantage of this method is the relatively low rate of oxidation (dissolution) of the waste, even with a fairly high current output (~ 90%).

The problem to which the present invention is directed is to create a method for the electrochemical processing of heat-resistant nickel alloys containing rhenium by applying a half-wave alternating current of industrial frequency to intensify the process.

The technical result of the invention is to increase the speed of the oxidation process of metal waste of heat-resistant nickel alloy containing rhenium, while ensuring environmental cleanliness.

This technical result is achieved by the fact that in the method of electrochemical processing of metal waste of heat-resistant nickel alloys containing rhenium, including anodic dissolution of the alloy in acidic electrolytes when applying alternating electric current, according to the invention, the dissolution is carried out in nitric acid or sulfuric electrolyte when applying a half-wave asymmetric alternating electric current of industrial frequency when a tantalum or niobium plate is used as the second electrode. In this case, anodic dissolution is carried out while maintaining the acidity of the nitric acid electrolyte at a level of 200-250 g / l HNO ₃ and a sulfate electrolyte at a level of 150-200 g / l H ₂ SO ₄ , a temperature of 20-40 ° C and a current strength of at least 1 kA.

The essence of the invention lies in the fact that the oxidation (dissolution) of a heat-resistant nickel alloy containing rhenium is carried out in a nitrogen or sulfuric acid electrolyte when a half-wave asymmetric alternating current of industrial frequency is applied, which is achieved by using Ta or wafers as the second electrode Nb, which is associated with the semiconductor properties of tantalum and niobium oxides (for more details, see the book "The Institute of Metrology and Informatics of the Russian Academy of Sciences is 70 years old", Moscow: Kontakt, 2008, p.

As can be seen from table 1, the process of acid decomposition of the nickel alloy is significantly accelerated by the anodic dissolution of the waste under these conditions. Moreover, the rate of electrochemical oxidation of the alloy is approximately 1.5 times higher than the theoretical value calculated from the corresponding electrochemical equivalent. This indicates the activation of the chemical process of oxidation of the alloy due to the application of the above mode.

Table 1
Electrochemical oxidation (dissolution) of heat-resistant nickel alloy grade ZhS-32 in solutions of mineral acids Mineral acid, acidity The mode of oxidation (dissolution) of the alloy The dissolution rate of the alloy, g / h · cm ² HNO ₃ , 250 g / l Symmetric sinusoidal alternating current of industrial frequency, working current 2 A, the area of the dissolved sample 16.5 cm ² , temperature ~ 30 ° C. 0.012 HNO ₃ , 250 g / l Asymmetric half-wave alternating current of industrial frequency, current strength 2 A, the area of the dissolved sample 16.5 cm ² , temperature ~ 30 ° C. 0,050 H ₂ SO ₄ , 200 g / l Symmetric sinusoidal alternating current of industrial frequency, current strength 1 A, area of the dissolved sample 49 cm ² , temperature ~ 25 ° С 0.010 H ₂ SO ₄ , 200 g / l Asymmetric half-wave alternating current of industrial frequency, current strength 1 A, area of the dissolved sample 49 cm ² , temperature ~ 25 ° С 0.056

From the physicochemical point of view, the dissolution of this alloy in solutions of strong mineral acids upon application of electric current can be considered as a summation of two approximately equivalent processes:

- anodic electrochemical oxidation (dissolution) of the alloy;

- purely chemical oxidation (dissolution) of the alloy.

In this case, the application of a half-wave alternating electric current significantly activates the process of chemical oxidation, as a result of which such increased performance in the rate of dissolution of the alloy is achieved.

It should be emphasized that although the concentration of nitric acid does not significantly affect the rate of oxidation of the alloy, with an increase in acidity of nitric acid electrolyte> 250 g / l HNO ₃ and temperature> 50 ° C, a sharp increase in the emission of harmful nitrous gases occurs. Therefore, an increase in the temperature of the electrochemical redistribution above 50 ° C is not desirable.

Therefore, the optimal parameters of the electrochemical processing of metal waste from heat-resistant nickel alloys in nitrogen and sulfuric acid electrolytes are as follows:

- temperature 20-40 ° C;

- the acidity of the electrolyte is 200-250 g / l HNO ₃ or 150-200 g / l H ₂ SO ₄ ;

- current strength of 1 kA and above;

- electric mode - a half-wave alternating current of industrial frequency, the material of the second electrode is tantalum or niobium.

This mode provides maximum performance for the dissolution rate of the alloy, which is up to 2 kg / h at a current strength> 1 kA and minimization of harmful gas emissions.

During the electrochemical processing of waste heat-resistant nickel alloy, the alloy components are separated into different phases at the first stage of the electrochemical redistribution. So, tungsten, molybdenum, tantalum and niobium oxides precipitate in the anode cake (precipitate), and the main non-ferrous metals (nickel, cobalt, aluminum and chromium) accumulate in the acidic electrolyte. The distribution of rhenium depends on the type of electrolyte. In the nitric acid version, rhenium mainly passes into an acidic electrolyte (~ 95%). In the case of a sulfate electrolyte, rhenium is 70% accumulated in the anode sludge, and 30% concentrated in a saturated electrolyte.

Rhenium and other valuable components are recovered from the saturated electrolyte and anode sludge by known methods of leaching, precipitation, ion exchange sorption or liquid extraction.

The balance distribution of metals during electrochemical oxidation (dissolution) of metal waste of heat-resistant nickel alloy in sulfuric and nitric acid electrolytes is shown in Tables 2 and 3.

table 2
Balanced distribution of metals during electrochemical oxidation (dissolution) of heat-resistant nickel alloy grade ZhS-32 in sulfuric acid electrolyte in optimal mode,% Processing product Re W Mo That Nb Ni Co Al Cr Saturated Electrolyte + Promotions 27.0 1,0 20,0 0.5 1,0 86.5 87.5 102 40,0 Kek (anode slurry) 70.0 94.0 75.0 95.5 95.0 13.0 9.0 2.0 55.0 Total 97.0 95.0 95.0 96.0 96.0 99.5 96.5 104 95.0 Imbalance 3.0 5,0 5,0 4.0 4.0 0.5 3,5 +4.0 5,0

Table 3
Balanced distribution of metals during electrochemical oxidation (dissolution) of heat-resistant nickel alloy grade ZhS-32 in nitric acid electrolyte in optimal mode,% Processing product Re W Mo That Nb Ni Co Al Cr Saturated Electrolyte + Promotions 94.9 1,0 10.0 - 0.5 95.0 94.6 99.5 90.0 Kek (anode slurry) 1.9 90.0 83.0 103 96.0 0.5 4.0 1,0 2.0 Total 96.8 91.0 93.0 103 96.5 95.5 98.6 100.5 92.0 Imbalance 3.2 9.0 7.0 +3.0 3,5 4,5 1.4 +0.5 8.0

Example 1

ZhS-32 grade heat-resistant nickel alloy metal fragments and fragments of blades of gas turbines of geometric dimensions: length 2-7.5 cm, width up to 4.5 cm, chemical composition of the waste is as follows (in%): Co 7 0; W 8.5; Mo 1.15; Re 3.6; Si 0.75; Ta 3.2; Nb 1.35; Cr 4.75; Al 5.15; C 0.15, the rest is nickel.

The waste was subjected to electrochemical oxidation (dissolution) under the action of a symmetric sinusoidal alternating current of industrial frequency. Process mode: temperature 40 ° C, a solution of 200 g / l H ₂ SO ₄ , current density 0.1 A / cm ² , duration 1 hour. In this mode, the oxidation (dissolution) rate of the alloy was 0.450 g / h. The current efficiency is 90%.

Similar results were obtained when using a solution of HNO ₃ (250 g / l).

Example 2

ZhS-32 grade heat-resistant nickel alloy metal fragments and fragments of blades of gas turbines of geometric dimensions: length 2-7.5 cm, width up to 4.5 cm, chemical composition of the waste is as follows (in%): Co 7 0; W 8.5; Mo 1.15; Re 3.6; Si 0.75; Ta 3.2; Nb 1.35; Cr 4.75; Al 5.15; C 0.15, the rest is nickel.

Oxidation (dissolution) of the alloy was carried out by applying a half-wave asymmetric alternating current of industrial frequency in the storage mode. To do this, in this case, a plate of Ta (25 × 10 mm) was used as the 2nd electrode.

The conditions of the electrochemical anodic dissolution of the alloy: the acidity of the sulfate electrolyte is ~ 200 g / l H ₂ SO ₄ , the current density is ~ 0.1 A / cm ² , the temperature is 40 ° C, the duration of the electrochemical leaching is 100 hours. In total, 177.5 g of ZhS-32 alloy was dissolved in this mode, that is, the dissolution rate of the alloy was ~ 1.8 g / h. Thus, the rate of oxidation (dissolution) of the alloy increased ~ 4 times.

Example 3

ZhS-32 grade heat-resistant nickel alloy metal fragments and fragments of blades of gas turbines of geometric dimensions: length 2-7.5 cm, width up to 4.5 cm, chemical composition of the waste is as follows (in%): Co 7 0; W 8.5; Mo 1.15; Re 3.6; Si 0.75; Ta 3.2; Nb 1.35; Cr 4.75; Al 5.15; C 0.15, the rest is nickel.

Anodic oxidation (dissolution) of the alloy is carried out in a solution of 250 g / l HNO ₃ . Process mode: current density 0.1 A / cm ² , temperature 30 ° C, the duration of the electrochemical leaching was 72 hours. In total, 130 g of ZhS-32 alloy was dissolved in this mode, that is, the dissolution rate was 1.8 g / h, which is comparable to the process indicators when using sulfate electrolyte (example 2).

The given examples confirm the achievement of the positive effect of the application of the half-wave regime for intensifying the process of electrochemical oxidation (dissolution) of metal waste from a heat-resistant nickel alloy containing rhenium.

The advantages of the proposed technical solution compared to the base object include:

1. High dissolution rate of waste due to the activating effect of half-wave alternating current in these conditions.

2. The possibility of processing waste without prior grinding.

3. The complexity of the technology with the extraction of almost all valuable components (Ni, Co, Ta, Nb, W, Re).

4. Environmental cleanliness associated with minimizing harmful gas emissions by optimizing the process conditions.

Claims (3)

1. The method of electrochemical processing of metal waste from heat-resistant nickel alloys containing rhenium, including anodic dissolution in an acidic electrolyte when applying an alternating electric current, characterized in that the dissolution is carried out in a nitric acid or sulfuric acid electrolyte when applying a half-wave asymmetric alternating electric current of industrial frequency when used as the second electrode is a plate of tantalum or niobium. 2. The method according to claim 1, characterized in that the anodic dissolution is carried out while maintaining the acidity of the nitric acid electrolyte at a level of 200-250 g / l HNO ₃ , at a temperature of 20-40 ° C and a current strength of at least 1 kA. 3. The method according to claim 1, characterized in that the anodic dissolution is carried out while maintaining the acidity of the sulfate electrolyte at a level of 150-200 g / l H ₂ SO ₄ , at a temperature of 20-40 ° C and a current strength of at least 1 kA.