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DEVICES AND METHODS OF EXTRACTING COLORFUL AND NOBLE METALS
INVENTION
Patent of the Russian Federation RU2115752

METHOD OF PYROMETALLURGICAL REFINING OF PLATINUM ALLOYS

METHOD OF PYROMETALLURGICAL REFINING OF PLATINUM ALLOYS

The name of the inventor: Mazaletsky AG; Ermakov AV; Sivkov M.N .; S. Nikiforov; Timofeev N.I .; Dmitriev VA; Khlebnikov A.I.
The name of the patent holder: Open Joint-Stock Company "Ekaterinburg Non-Ferrous Metals Processing Plant"
Address for correspondence:
Date of commencement of the patent: 1997.09.30

The method can be used for refining platinum alloys by vacuum electron beam zone melting in a crystallizer. Vacuum electron beam zone melting is carried out in the crystallizer by at least two electron beams, by exposing the first beam to the surface of the metal in the crystallizer and keeping it stationary until the metal melts in the zone of its focal spot, moving the beam along the extended water-cooled crystallizer and stopping the second beam , Setting it to the initial position of the first and then simultaneously moving both rays along the mold. The distance between the beams and the speed of their simultaneous movement are chosen from the conditions of ensuring between the focal spots the metal temperature between the liquidus points and the solidus of the platinum alloy. When creating and maintaining a solid-liquid phase state in the zone between beams, the valuable component is extracted more fully by evaporation from the melt, and impurities - by recrystallization of the alloy. Recycling of platinum alloys with deep recovery of this component at low irrecoverable losses of the base is carried out.

DESCRIPTION OF THE INVENTION

The invention relates to the field of non-ferrous metallurgy, namely to methods for producing noble metals, and can be used for pyrometallurgical refining of platinum-based alloys, preferably with a valuable component lowering the melting point of the base.

There are known methods for regenerating platinum group metals in which the recovery of platinoids is carried out in chlorides (eg, Japanese Nos. 1 to 132722, class C 22 B 9/00, 3/00, v. 3 of Japan No. 1-132723, cl. C 22 B 9/00, 3/00; E of Japan N 313532, Class C 22 C 11/02).

A method for purifying precious metal concentrate from impurities by distilling the latter in the form of halides is also known (GB No. 1502765, C1A).

A method for separating platinum and palladium is known in which palladium is isolated in the form of bromides (German pp. 4042031, class C 22/11/02).

However, despite the high degree of isolation of platinum metals as valuable components, the methods are directed to the additional formation of chemical compounds containing platinoids, which increases the duration of the refining process and increases the irretrievable loss of platinoids.

A method for purifying one of the metals of the platinum group, palladium, from impurities (NB Sandesara, JJ Vuillemin "Float Zone Purification in Palldium", met.Trans, 1977, v. 88, No. 12, pp. 693-695) In air due to the passage of the molten zone through the metal (cleaning only by recrystallization).

However, despite the shortening of the duration of the palladium refining process, the recovery of such a valuable component as, for example, platinum, in the process is only at the level of recovery of other low-value impurities.

A method for refining metal impurities from another metal of the platinum-iridium group is known, with induction oxidative melting (g. "High-purity substances", 1990, No. 1, pp. 143-146). The method includes not only induction oxidative smelting aimed at refining from palladium, but also electron-beam vacuum melting conducted for further refining from platinum and rhodium.

However, the possibility of using induction melting material as a charge for electron beam melting is noted without specifying specific temperature-time regimes for the implementation of the method.

A method for the production of pure metals of the platinum group, osmium and ruthenium, is also known, by electron-beam remelting of scrap or anode slurry (US No. 5142549, cl. H01J 37/305).

However, this method allows the extraction of only volatile metals such as osmium and ruthenium, which are sublimated and condensed in a remote refrigerator. This method does not allow to get rid of the whole complex of impurities present in the raw material.

A method for purifying impurities, including those from palladium, platinum and platinum metals, is also known, electron-beam melting or joint application of electron-beam and beige zone melting ("Non-ferrous metallurgy processes at low pressures", Moscow: Nauka, , 1983, pp. 195-200).

In electron-beam melting, the content of a number of non-ferrous metals is reduced by an order of magnitude in the known manner. The successive carrying out of electron-beam and beige zone melting makes it possible to perform separate purification by evaporation of impurities and zone recrystallization.

However, these methods provide an insignificant degree of purification from impurities and for the production of high purity platinum, it is necessary to improve the melting methods, for example, the heating of alloys.

A method for pyrometallurgical refining of platinum is also known (GG Devyatykh, "High-purity refractory and rare metals", Moscow: Nauka, 1993, p. 57). In the known method, electron-beam zone melting of platinum makes it possible to reduce by one or two orders the content of many impurities.

Refining from impurities of other platinoids - ruthenium and osmium, in two stages: the first - by electron-beam remelting of powders, the second - by zone recrystallization of the obtained polycrystalline ingots, leads to a decrease in the impurity concentration, however, the content, for example, of palladium varies insignificantly, i.e. The allocation of such a valuable component is small.

The closest analogue is also known - the method of pyrometallurgical refining of platinum alloys ("Noble Metals", a reference book edited by VM Savitsky, Moscow: Metallurgiya, 1984, pp. 32-33).

The known method includes electron-beam zone melting in a crystallizer in a vacuum of at least 10 -3 mm Hg. Art.

However, the known method is aimed at refining all platinum metals and their alloys, and because of the uncertainty of the regimes it does not allow to purify specific platinoids from a certain group of impurities. Therefore, it is necessary to select the appropriate set of purification methods for refining each particular platinum alloy.

In the case of realizing this pyrometallurgical refining of a platinum alloy, for example, with a valuable component that lowers the melting point of the alloy base, it is necessary to recognize the insufficiently high degree of purification from impurities and the recovery of the valuable component, and significant losses of platinoids.

Indeed, it is known ("Technology": "Applied Physics", No. 1, 1994, pp. 3Z) that the effect of electron beams on metals and alloys leads to heating, melting, evaporation in a small time interval in a space comparable to With the radius of the energy flow. The size of the zone of action on the metal can be quite small.

The difference from other metal processing processes, namely, the electron beam, is due to the high input energy rates of the source and, as a result, high heating rates of the impact zone (up to 10 10 fps) and its subsequent cooling (up to 10 8 fps). High processing speeds noticeably reduce the size of the zone of thermal influence, reduce the volume of the impurity element being removed, both by pushing it through the molten zone, and by volatilization. Because of the high supercooling of the melt, its crystallization occurs very rapidly, all the impurities, both valuable and not having time to evaporate, are of little value, which did not have time to redistribute and move to the edge of the liquid zone, undergo joint recrystallization. To remove them, a new metal melting is required. And even repeated operations of zone melting, in which, as noted (V. Pfann, "Zone melting", Mir, M., 1970, p. 16), the purification rate is higher the greater the number of passes - single zones passed through the sample , Do not allow to achieve a high degree of purification, especially from evaporating impurities. The joint finding of valuable impurities with other fusible impurities in a small zone of the thermal effect of the beam does not make it possible to create a sufficiently high concentration in some local area of ​​the melt zone for complete and deep refining. The metal base of the alloy as a result of repeated melts and recrystallizations (in the case of conventional electron-beam zone melting by a single beam with a large number of passes) is partially lost irrecoverably due to evaporation in the zone of thermal influence of the beam, and the duration of the method is rather large.

With multiple crystallizations (as a result of multiple separate zone meltings), the composition of the alloy with respect to its base remains approximately the same as the composition of the initial melt.

Thus, during secondary melting, the composition of the melt repeatedly has a concentration of the refractory base, as in the crystallized after crystallization of the ingot.

The task for solving the claimed invention is to create a technology for complex processing of platinum alloys with a high degree of recovery of the valuable component and purification from impurities at low irrecoverable losses and a short duration of the process.

The objective is achieved by a technical result that can be obtained by carrying out the invention: deeper and full recovery of the valuable component by evaporation from the liquid phase with its increased concentration and increasing the degree of purification from impurities by carrying out a double or more, depending on the number of beams, Cleaning in one pass due to additional recrystallization of the alloy, which is caused by the creation between the solid-liquid rays of the refined alloy.

The object of the invention is achieved in that in the method for pyrometallurgical refining of a platinum alloy, advantageously with a valuable component reducing the melting point of the substrate, by vacuum electron beam melting in a crystallizer, the invention uses an extended water-cooled crystallizer and melts are carried out by at least two electron beams in the following The first beam is placed on the surface of the metal in the crystallizer and held steady until the metal melts in the area of ​​its focal spot, then the beam is moved along the crystalliser, then the second beam is turned on and set to the initial position of the first one, then simultaneously moving both beams simultaneously Along the crystallizer, the melting being carried out under conditions characterized by the distance between the spots of the rays and the speed of their simultaneous movement, ensuring the maintenance of the metal temperature in the zone between their focal spots in the liquidus and solidus temperature range of the platinum alloy.

In addition, in particular cases of the invention:

- simultaneous movement of the rays is conducted at a speed of 6-8 mm / min;

- the first beam is moved along the mold to a distance greater than the zone of its focal spot, which is 90-100 mm;

The focal spot of the second ray is not less than that of the first;

- melting is carried out by rays with focal spots equal to the width of the crystallizer;

- the first beam is held stationary, and the second beam is set to the initial position of the first beam power of 30 kW;

We specify that under the focal spot of the electron beam we mean the convergence of all the rays of this electron beam. Due to this focusing of the rays on the recrystallized ingot, a molten zone is formed in it.

In the claimed method, the molten zone moves through the refiner metal from the beginning to the end of the extended water-cooled crystallizer, thereby redistributing the impurities.

The molten zone of each of the rays moving along the platinum alloy has two interfaces between the liquid and solid phases - melting and solidifying. The ability of the zone to redistribute impurities is due, mainly to what happens on the solidifying surface. On the melting surface, the alloy simply melts and mixes with the content of the zone, the fusible impurities are pushed away by the moving zone in the direction of metal melting along the length of the mold to one end. Refractory impurities are pushed into the melt to the other end of the crystallizer. A valuable component of the alloy, lowering the melting point of its base - platinum, is concentrated in the liquid phase.

Conducting electron beam zone melting with at least two beams and heating the metal with a second beam in a regime ensuring the maintenance of the metal temperature in the zone between the focal spots of the rays in the interval between the liquidus point and the solidus point of the platinum alloy makes it possible to create a special zone between the zones of thermal radiation, Maintaining in it a solid-liquid state of the melt.

It should be noted that the solid-liquid state is a special state of the melt, in which the following processes occur simultaneously:

- due to more than just a solid state of diffusion in the solid-liquid state of the melt, there is a constant equalization of its chemical composition along the length of the solid-liquid zone, and hence a constant increase in the constantly evaporating valuable component in the liquid component of the solid-liquid phase, It has low-melting impurities;

- due to the movement of the crystallization front - the displacement into the liquid zone of the fugitive component evaporating more easily from it;

- due to the presence of a solid component in the solid-liquid phase - sublimation of the valuable component;

- an abrupt increase in the refractory basis of the alloy in the solid phase of each subsequent solid-liquid state upon recrystallization of the alloy.

The presence of a solid-liquid state of the melt increases the size of the zone of thermal influence, increases the volume of the valuable component being removed. Because of the sufficient time for the passage of these processes, the valuable admixture has time to evaporate, and low-value impurities have time to be redistributed.

The heat balance of the melting with two beams is selected in such a way that in the region between the zones of thermal radiation, two processes can be simultaneously performed: directional crystallization with recrystallization of the alloy forming the solid phase and active evaporation of the valuable component from the liquid phase in equilibrium with it. The mobile balance of these processes, created by the operation of the modes of the claimed method, allows the separation of platinum and the valuable component to be stably performed.

The principal difference between the proposed method of joint processing of a platinum alloy by two or more electron beams from the methods of influencing an alloy with a single beam, even with multiple passes, is that along with the existence of the first melting phase interface due to the thermal action of the first beam on solid raw materials and The last solidifying phase interface after the last beam has been disconnected, additional melting and solidifying surfaces are created in the material to be refined, which facilitates deeper cleaning of impurities and a high degree of recovery of the valuable component. If the solid-liquid state of the alloy is maintained between the first and second beam, the second and each subsequent beam melts the previously recrystallized solid phase with a sharply increased content of the refractory component and the refinement process continues. Thus, even with one pass (from complete melting to complete crystallization of the alloy), the melting process is carried out twice: both the initial solid feedstock and the recrystallized solid phase from the solid-phase alloy composition, i.e. Zone cleaning from fusible and refractory impurities occurs also twice.

We specify that in the solid phase of the solid-liquid state, which is subjected to melting by the second beam, there is an increased content of the more refractory component (for example, platinum in the palladium alloy) and further melting and final crystallization in the ingot, the latter and has an increased content of this component .

As the number of rays increases, the solid phase of each subsequent solid-liquid state is more and more enriched by a more refractory component (for example, platinum in a palladium alloy), which, when it is further melted by an electron beam and finally crystallizes, forms the most platinum alloy as enriched and purified from impurities.

The use of an extended water-cooled crystallizer makes it possible to provide a sufficient temperature gradient for directional crystallization of the alloy and a necessary extended zone for distilling off the fusible and refractory impurities at different ends of the ingot of the refined alloy.

The exposure of the first ray to the surface of the metal in the crystallizer and its holding in the stationary state until the metal melts in the zone of its focal spot, the subsequent movement along the crystallizer and the stop make it possible to create an actively stirred metal melt, the diffusion processes in which are easily realized and ensure the distribution of impurities and evaporation of the valuable component .

The further inclusion of the second ray and its installation in the initial position of the first one makes it possible to create between the zones of thermal action of the rays-the zones of the melt, the colder zone and, therefore, the conditions for its crystallization.

The melting is carried out under conditions characterized by the distance between the focal spots of the rays, which is chosen so as to provide a temperature in the zone between these spots corresponding to the interval of the liquidus points and the solidus of the platinum alloy. This makes it possible to create a region of gradual cooling between the metal melting zones and favorable conditions for the formation of primary solid particles of highly enriched platinum and impurities evenly distributed in the liquid phase with an increased content of the valuable component. The temperature of the first hot zone during the heat of the first beam is sufficient to melt the metal, the temperature of the intermediate zone between the stains of the melt and the cold zone ensures the coexistence of the liquid and solid phases, and the metal temperature in the zone of thermal action of the second electron beam is sufficient for Melting.

The simultaneous simultaneous movement of both beams along the mold at a certain rate allows the refined alloy to withstand a liquid and solid-liquid state for a time that is necessary and sufficient to completely volatilize the valuable component from the platinum-based alloys, and also improves the degree of purification from impurities.

Reduction of the speed of joint movement of the rays below the selected value leads to the evaporation of other components of the alloy, including its platinum base, to a decrease in the degree of purification of the fusible impurities due to their possible reverse transition to the liquid phase due to an increase in the diffusion time by Boundary of their solid and liquid phases, as well as to an increase in irrecoverable metal losses. An increase in the rate of simultaneous successive movement of the rays by a more selected value means that the valuable component does not have time to evaporate during the process and the purity of the platinum metal decreases.

Simultaneous movement of the rays can lead at a speed of 6-8 mm / min, which maintains the solid-liquid state of the melt.

In this case, the first ray is moved along the mold to a distance greater than its focal spot, which makes it possible to create a solid-liquid state of the melt.

This distance can be 90-100 mm.

In addition, the focal spot of the second ray is not less than that of the first ray.

In this case, the focal spots of the rays can be equal to the width of the crystallizer. This allows completely refining the entire volume of the platinum alloy placed in the crystallizer.

In addition, the first beam is held stationary, and the second beam is placed in the initial position of the first one at the power of each of the rays of 30 kW. The power of the beams is selected depending on the heat sink and the composition of the refined metal, sufficient to melt it.

Comparative analysis of the proposed solution with the closest analogue shows that the claimed method differs from the known one in that it carried out a specific sequence of operations with refined values ​​of regimes, obtained a technical result, the possibility of achieving it does not follow from the disclosure of the content of the general known solution.

Thus, in the claimed method of pyrometallurgical refining of platinum alloys, zone purification occurs simultaneously with the extraction into the vapor phase of the valuable component under conditions of specific regimes and the refined composition of the alloy to which the method actions are directed. Execution of its evaporation not only from the initial melt, but also from the liquid phase of the special solid-liquid state of the metal makes it possible to extract it to an extent that is the closest analogue previously unavailable for the known general solution of this problem.

New types of features of the claimed method - operation modes, materials and devices involved in the process, lead to a more complete and selective recovery of the valuable component and increase the degree of purification from impurities, preservation of the metal - the basis, i.e. Contribute to the achievement of a technical result that was not inherent in the known pyrometallurgical treatment method. Therefore, if the general solution is known, the claimed particular solution of the technical problem can be recognized as new.

The invention is in accordance with the inventive step. Considering the totality of its essential features, it can be noted that they do not follow explicitly from the prior art. It should be noted that among the objects of the same purpose, there is no known technology with the same set of essential features.

In order to confirm the possibility of implementing the invention, we give an example of implementing the method.

They took 22500 g of a platinum alloy containing a valuable component, the palladium to be extracted. At the same time, the chemical composition of the alloy was presented in weight. %: Platinum - 89.624; Iridium - 0.028; Palladium 4.74; Rhodium - 5,534; Gold - 0.005; Copper - 0.003; Nickel - 0.041; Magnesium - 0.003; Iron - 0.002; Zirconium - 0.020.

The wrought-iron plate of the alloy was cut into pieces of the size 50x30x80 mm, which were evenly spread out in an extended water-cooled mold.

As a crystallizer, a copper water-cooled mold, a "boat", was used.

Electron beam melting was carried out in a vacuum. For this purpose, the vacuum chamber of the installation in which the crystallizer was located was closed and evacuated from it to a vacuum of not less than 10 -3 mm Hg, preferably up to 1 × 10 -5 mm Hg.

The fusion was carried out by two electron beams in the following order.

Initially, using the electron gun N 1 "UE-193", the first beam was switched on and at low power it was exposed to the surface of the metal in the crystallizer, namely the beginning of the "boat", then the gun power was adjusted to 30 kW. Thus, the first beam was held motionless until the metal melted in the zone of its focal spot with a diameter equal to the width of the crystallizer "boat". Then, switching on the beam, it was moved along the crystallizer to a distance greater than the zone of its focal spot - by 100 mm, and stopped.

Then, with the electron gun N 4 "UE-193", a second beam was included and with the size of the focal spot equal to its size at the first ray, it was set to the initial position of the first - and the beginning of the "boat", then the beam power was raised to 30 kW. The area of ​​the focal spot of the beam was equal to the width of the crystallizer. The heating of the metal was carried out in a regime ensuring the temperature of the metal in the zone between the focal spots of the rays in the interval between the liquidus points and the solidus of the platinum alloy.

The choice of the power of the rays was carried out taking into account the heat removal and composition of the affinity metal, the presence of a solid-liquid state of the alloy was detected visually.

Having obtained two distinct molten zones and a zone of solid-liquid state, simultaneous sequential movement of both rays along the crystallizer - to the end of the "boat", at a speed of 6 mm / min. The velocity of the rays was selected from the condition for maintaining the solid-liquid state of the alloy between their focal spots. After passing through the rays of the whole crystallizer, they were sequentially switched off - first, and then the second ray.

Leave the metal in the chamber for cooling for 30 minutes. After that, air was opened into the chamber and opened.

The chamber and the mold were cleaned of sublimes and scraps, and the ingot was removed. From the ends of the ingot cut into 50 mm, which were the most contaminated parts of the ingot and required a second remelting. The remaining ingot was tested. A chemical analysis of the sublimates and the resulting ingot was carried out by chemical, spectral and X-ray spectral analysis. The results of the studies are listed in Table 1 (examples N 4-9 lie within the claimed method, N 1-3 and 10-13 beyond the declared limits). The degree of purification from impurities and the degree of extraction of the alloy components, incl. Valuable - palladium, were defined as the ratio of the content of the element in the final product as a result of the implementation of the method to its initial content in the initial alloy.

Table 2 presents the chemical composition of the feedstock and final refining products.

In order to obtain comparative data, a platinum alloy having the specified specific composition was exposed according to a known method - the closest analogue, pyrometallurgical refining in two versions: vacuum electron beam zone melting with one beam in one pass and under the same processing conditions of the platinum alloy, but For two passes. The results of a comparative analysis of one of the examples of the claimed method and the indicated variants of the known method are listed in Table 3.

As can be seen from the table, the degree of recovery of the valuable component - palladium, in the proposed method is much higher compared to the known technology, even with a double remelting by one beam. It should be noted that in the new method the base of the alloy is less vaporized. The degree of purification from impurities in the claimed technology rises over all impurity elements. In addition, the refining time is halved, which increases the productivity of the process.

The proposed method is a technological scheme of complex processing of platinum alloys with a selective extraction of a valuable component ready for industrial use. The declared decision can be put in a basis of the closed wasteless technology of ecologically pure manufacture.

CLAIM

1. A method for pyrometallurgical refining of a platinum alloy, advantageously with a valuable component reducing the melting point of the substrate, by vacuum-electron-beam zone melting in a crystallizer, characterized in that an extended water-cooled crystallizer is used and the melting is carried out by at least two electron beams in the following order: The first beam is exposed to the surface of the metal in the crystallizer and held steady until the metal melts in the area of ​​its focal spot, then the beam is moved along the crystallizer and stopped, followed by the second beam and placed in the initial position of the first, then simultaneously moving both beams along Crystallizer, the melting being carried out under conditions characterized by the distance between the focal spots of the rays and the speed of their simultaneous movement ensuring the metal temperature in the zone between these spots in the liquidus and solidus temperature range of the platinum alloy.

2. A method according to claim 1, characterized in that the simultaneous movement of the beams is conducted at a speed of 6-8 mm / min.

3. The method according to claims 1 and 2, characterized in that the first beam is moved along the mold at a distance greater than the zone of its focal spot.

4. Method according to claims 1 to 3, characterized in that the first beam is moved along the crystallizer by a distance of 90-100 mm.

5. Method according to claims 1 to 4, characterized in that the focal spot of the second ray is not less than the first.

6. Method according to claims 1-5, characterized in that the fusion is carried out by rays with focal spots equal to the width of the crystallizer.

7. The method according to claims 1-6, characterized in that the first beam is held stationary and the second beam is set to the initial position of the first beam at the power of each 30 kW beam.

print version
Date of publication 14.03.2007gg