RU2796566C1 - Method for aluminium recycling by scrap melt electrolysis and a device for implementing this method - Google Patents

Abstract

FIELD: aluminium recycling.

SUBSTANCE: invention relates to a method for recycling aluminium by electrolysis of its scrap melt and a device for its implementation. The method is based on loading solid aluminium or aluminium-containing scrap into a bath for electrolysis and separation of aluminium purified from metal impurities. By heating the bath, the specified scrap is transferred into a melt with a temperature of 660-750C° and this conductive melt with impurities dissolved in it is used as an electrolyte. A voltage of 2 to 5 V is applied to the electrodes partially or completely immersed in the melt, in the mode of changing the current strength from 10 to 1000 A, to obtain a cathode and anode current density equal to 0.9-1.0 A/cm². To maintain the level of ionic processes in electrolysis on the electrodes, a periodic change in the alternating voltage to a constant voltage and a change in polarity on the electrodes are carried out when they are connected to a constant voltage source. During electrolysis, process gas may be supplied to the melt to bubble the melt. The device contains a stainless steel bath with a heater of its side or side walls, two replaceable low-consumption electrodes, a regulated DC source, a regulated AC source, a first two-position switching unit and a second two-position switching unit. In the bottom part of the bath, holes can be made for supplying gas to the bath for bubbling the melt. In the bottom part of the bath, the electrodes can be equipped with removable trough-shaped platforms for the deposition of impurities during electrolysis. The heater can be connected to an alternating voltage source.

EFFECT: simplification of the aluminium recycling method by electrolysis of its scrap melt, purification of aluminium recovered from scrap from impurities and bringing them to values that are less than those established for recycled aluminium.

6 cl, 1 tbl, 1 dwg

Description

The invention relates to the field of non-ferrous metallurgy, and in particular to methods for recycling aluminum by remelting its scrap, followed by separating impurities dissolved in aluminum and depositing them on electrodes during the electrolytic process.

The task of recycling aluminum and its alloys is a very urgent task of the day due to the ever increasing accumulation of unclaimed products from aluminum-containing metal materials, on the one hand, and the continuously growing demand for commercially pure aluminum in the market of metal raw materials, on the other hand. Existing technologies are mainly reduced to the elementary remelting of aluminum scrap in furnaces with the correction of the charge process and the processes inside the furnace processing of the melt. Such approaches make it difficult to standardize the product, lead to unacceptable scatter in both the parameters and the chemical composition of the final product. Naturally, the price of such an aluminum product on the market is significantly lower compared to the price of standardized aluminum from aluminum smelters. The service properties of such materials due to the scatter of the composition of impurities prevent their use in critical technology. The problem of recycling can be considered solved only when the service properties of "recovered" aluminum approach the service properties of primary aluminum from aluminum smelters.

The aluminum and/or aluminum-containing scrap supplied for processing has a diverse composition in terms of chemical structure. It may include fragments of high-purity aluminum, fragments of technical aluminum or duralumin, cast aluminum or aluminum-containing alloys (AMg - aluminum-magnesium alloy, AMts - aluminum-manganese alloy, SAP - sintered aluminum powders and CAC - sintered aluminum alloys). Each type of such material has its own chemical composition and features for the inclusion of impurities. So, even in aluminum alloys with a purity of 99.8 and 99.7, iron can be from 0.15 to 0.25%, zinc - from 0.04 to 0.07%, silicon - from 0.1 to 0.2% . Thus, scrap with an exactly unspecified percentage of impurities is sent for processing in the recycling mode. It makes no sense to carry out a chemical analysis of scrap fragments; it is required to establish the total content of impurities, and this can only be done in the melt of this scrap.

The separation of impurities from aluminum is an important factor. The separation of impurities is also understood as their reduction in the melt. In addition to the determined impurities (Fe, Si, Cu, Zn, Ti), primary aluminum contains more than a dozen other metallic impurities, in quantities of several thousandths or decimals of a percent (G.F. Shemetev "Aluminum alloys: compositions, properties, applications", educational manual on the course "Production of castings from non-ferrous alloys", St. Petersburg State Polytechnic University, St. Petersburg, 2012).

So, for example, iron is present in technical grades of aluminum in the amount of several tenths of a percent. At the same time, it is slightly soluble in solid aluminum. At temperatures below the eutectic temperature (655°C), the solubility is 0.052% or less, and at 400-450°C it is practically zero. The second phase in the eutectic in the Al-Fe system is the FeAl ₃ intermetallic compound, which precipitates in the form of needles or plates. The FeAl ₃ phase consists of 40.83% Fe and 59.17% Al. Its crystal lattice belongs to orthorhombic with periods a=47.7 Å, b=15.52 Å, and c=8.11 Å. The density of FeAl ₃ is 3.811 kg/m ³ , melting point 1158°C. Due to the heterogenization of the structure, the tensile strength and hardness of the alloys increase, while the plastic properties sharply decrease. In addition, when the iron content is from 0.1 to 0.5%, the rate of aluminum corrosion in an acidic environment increases. An increase in the iron content also has a similar effect on the properties of alloys, with the ductility and impact toughness of the alloys being most strongly reduced. In this regard, iron is one of the most harmful impurities for aluminum alloys.

Silicon is an inevitable impurity in aluminum and has a negative impact on operational and technological properties. Despite the high equilibrium solubility of silicon in aluminum at the eutectic temperature, under nonequilibrium crystallization conditions, the appearance of a eutectic is already observed at silicon contents greater than 0.05%. Heating the metal for subsequent plastic deformation leads to the transfer of the eutectic into a liquid state, which makes it difficult or eliminates plastic deformation, since cracks appear on the deformed products.

Entering into a solid solution in significant quantities, copper impurity does not have any noticeable effect on the mechanical properties of aluminum, but plays a significant role in corrosion processes, especially for high-purity aluminum. It has been established that with a copper content above 20⋅10 ^-4 %, an aluminum sheet 1.5 mm thick corroded through and through during a week when held in 20% hydrochloric acid; under the same conditions, an aluminum sheet containing from 0.9 to 3x10 ^-4 % copper collapsed only after 2 weeks.

Gallium destroys the layer of aluminum oxide, penetrates into aluminum and dissolves it. The result is a gallium-aluminum amalgam that can react with water to form hydrogen and aluminum hydroxide. During refining, gallium is concentrated in the residual anode alloy, in which its content is 0.1-0.3%.

Known methods of purification and refining of aluminum and its alloys, the leading of which is the method of three-layer electrolysis, protected by patent RU 2092591, C22B 7/00, C25C 3/24, publ. October 10, 1997 /D1/

This method includes loading an anode alloy into a bath, electrolysis, separation of aluminum on the cathode, its withdrawal and removal of an anode alloy enriched with impurities, while aluminum-copper-tin alloy waste in solid and/or molten form is loaded as an anode alloy. , and the removal of pure cathode aluminum is carried out periodically.

This method is adopted as a prototype.

According to this method, aluminum of technical purity is obtained directly after electrolysis. Since the purity of technical aluminum for some purposes is insufficient, the most pure grades of technical aluminum (A85, A80) are subjected to electrolytic refining using a 3-layer technology. The essence of the known method is as follows. There are three molten layers in the electrolytic cell. The lower layer - aluminum, in which up to 30-40% of copper is dissolved - is the heaviest (density is more than 3000 kg/m ³ ) and serves as an anode. The second layer is formed by an electrolyte consisting of pure fluorides or a mixture of barium chloride with aluminum and sodium fluorides. The density of the electrolyte is about 2700 kg/m ³ . Aluminum, dissolving from the anode layer in the electrolyte, is released above the electrolyte, since its density is -2300 kg/m ³ . The pure metal is the cathode. The current is supplied to the cathode layer by a graphite electrode. The bath operates at 750-800°C, the power consumption is about 20 thousand kWh/ton, i.e. higher than in the electrolysis of aluminum from alumina. During anodic dissolution, all impurities that are more electropositive than aluminum (Fe, Si, Cu, Zn, Ti, etc.) remain in the anode layer without passing into the electrolyte. Anodically, only Al dissolves in the electrolyte, which passes into the electrolyte in the form of Al ₃ + ions. The latter are then discharged at the cathode: Al ₃ ++3e → Al. As a result, a layer of liquid refined aluminum accumulates on the cathode, and the anode layer becomes enriched with impurities. In the Al-Fe-Si-Cu quaternary system, a eutectic is formed with a melting point of 520°C. Gradual accumulation of impurities Fe, Si, Cu leads to hypereutectic concentrations in the anode layer. Lowering the temperature of the anode layer leads to precipitation of FeSiAl ₅ and Cu ₃ FeAl ₇ intermetallic compounds. In the refining cell there are pockets in which the temperature of the anode layer is 30-40°C lower than in the main bath. Therefore, first of all and in the largest amount, intermetallic compounds are released in pockets. Periodic cleaning of the pockets to remove intermetallic deposits allows the anode alloy to be cleaned without its renewal. Using the method of electrolytic refining according to 3-layer technology, high purity aluminum is obtained. The purity of such aluminum reaches A995.

However, this method has a number of disadvantages. The complexity of the process hardware is expressed in the need for constant correction of the composition of the layers, the use of expensive copper in the process, the need to develop original technological equipment due to the impossibility of using standard equipment used in the aluminum industry.

The present invention makes it possible to bring the amount of impurities in the resulting aluminum as close as possible to acceptable values.

The present invention is aimed at achieving a technical result, which consists in simplifying the method of recycling aluminum by electrolysis of the melt of its scrap, which makes it possible to maximally purify aluminum recovered from scrap from impurities, including gas-containing components, and bring them to values that are less than those established for recycled aluminum.

The specified technical result for the method is achieved by the fact that in the method of recycling aluminum by electrolysis of the melt of its scrap, which consists in loading solid aluminum or aluminum-containing scrap into a bath for electrolysis and separating aluminum purified from metal impurities, by heating the bath, the specified scrap is transferred into a melt with a temperature of 660 -750C ° and use this conductive melt with impurities dissolved in it as an electrolyte, a voltage from 2 volts to 5 V is sold to the electrodes partially or completely immersed in the melt in the mode of changing the current strength from 10 to 1000 A to obtain the density of the cathode and anode currents equal to 0.9-1.0 A/cm ² , while to maintain the level of ionic processes in electrolysis on the electrodes, periodic change of alternating voltage to direct voltage and polarity change on the electrodes are carried out when they are connected to a direct voltage source.

In the process of electrolysis, process gas is supplied to the solution for sparging the latter. You can do without bubbling.

The specified technical result for the device is achieved by the fact that the device for aluminum recycling by electrolysis of its scrap melt is characterized by the fact that it includes a stainless steel bath equipped with a heater of its side or side walls and used to load solid aluminum or aluminum-containing scrap into it, two oriented along the wall or walls of the bath of replaceable low-consumption electrodes, fixed on the bottom of the bath at a distance from each other and isolated from the bath, as well as connected to a centralized AC power supply network by an adjustable DC source that converts the AC voltage at the input into a DC output with the possibility of regulation current and an adjustable AC source with the ability to control the current, while the outputs of both sources are connected to the first two-position switching node, which allows the output contacts to have a constant voltage when the AC voltage is turned off or an alternating voltage when the DC voltage is turned off, and the outputs of the first two-position switching node connected to the input of the second on-off switching unit, configured to connect an AC source to the electrodes or connect a DC source to the electrodes and with the possibility of changing the polarity of the DC voltage on the electrodes from minus to plus and from plus to minus when connected to the DC voltage source.

At the same time, in this part of the bath, holes can be made for supplying gas to the bath for bubbling the melt. In the bottom part of the bath, the electrodes are equipped with removable trough-shaped platforms for the deposition of impurities during electrolysis. And the heater is connected to an alternating voltage source.

These features are essential and are interconnected with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The present invention is illustrated by a specific example of execution, which, however, is not the only possible one, but clearly demonstrates the possibility of achieving the desired technical result.

In FIG. 1 is a block diagram of a device that implements the claimed aluminum recycling method.

According to the present invention, a new method is considered for recycling aluminum by remelting its scrap, followed by separating the impurities dissolved in aluminum and depositing them on electrodes during the electrolytic process. Purified aluminum is drained for further use, and impurities docked on the electrodes are sent to technological waste. At the same time, the technologist has at his disposal hardware that makes it possible to actively influence the ionic processes in the melt by changing the polarity of the electrolysis voltage, changing the magnitude of the electrolysis voltage and current, replacing the constant electrolysis voltage with an alternating one, depending on the chemical composition of the material being processed. The method can be applied to purify other metals and alloys.

Usually draft aluminum (raw) from the electrolytic cell contains 3 groups of impurities:

- non-metallic (fluoride salts, α and γ - alumina, aluminum carbide and nitride, coal particles);

- metal (Fe, Si, Ti, Na, Ca, etc.) passing from raw materials;

- gaseous - mainly hydrogen, which is formed as a result of the electrochemical decomposition of water entering the cryolite-alumina melt together with the raw material.

In the proposed method, the melt of a refined alloy with impurities is used as an electrolyte, in which, under the action of a direct electric current, metal ions that are electropositive with respect to aluminum (Mn, Zn, Cr, Fe, Si, Co, Ni, Pb…) are concentrated in the region anode pole, and which are electronegative aluminum ions (Li, Cs, K, Ba, Ca, Na, Mg) are concentrated in the region of the cathode pole. In this case, complex processes of ionic interaction occur in the aluminum melt (it was established experimentally), leading to separation into the main component - aluminum and the amount of impurities deposited on the replaceable electrodes. A feature of the proposed technology is the need for a laboratory selection of the material of replaceable electrodes and the electrolysis mode in relation to an aluminum alloy with the amount of impurities to be purified.

To implement the method, a device is used, which is an electrolytic installation, the block diagram of which is shown in Fig. 1. The installation includes a stainless steel bath 1 for electrolyte 2 (electrolytic melt), into which aluminum or aluminum-containing scrap (raw material) is loaded from above. A heater 3 is mounted around the bath, powered by an alternating voltage supply system 4. Inside the bath, two rod electrodes 5 spaced relative to each other (one of which is the anode and the other is the cathode) are removable. The term "removable" means the possibility of replacing one used electrode with a new one, on which there are no deposits of impurities. Structurally, the attachment point, which allows the electrodes to be removed from the sockets inside the bath, is not presented.

Both electrodes are powered by a regulated supply of AC and DC voltage, which includes

- regulated source 6 of direct current, which converts the alternating voltage at the input into a constant at the output with the ability to change the current strength from 0 to 1000 A.

- adjustable source 7 alternating current.

Both of these sources 6 and 7 can be connected to an industrial AC power supply network. The output contact elements of both sources 6 and 7 are connected to the first two-position switching unit 8, which allows the output contacts 9 to have either a constant voltage (with the AC voltage supply lines turned off) or an alternating voltage (with the DC voltage supply lines turned off).

The output elements 9 are connected to the electrodes 5 through the second two-position switching unit 10, which allows:

- in the mode of communication with source 7 (AC supply), in any position of the contacts of the switching group of node 10, power the electrodes with an alternating voltage of the set power, this source is configured to change the voltage in the range up to 5 V, preferably from 2 to 5 V, if possible, vary current strength from 10 A to 1000 A;

- in the mode of communication with the source 6 (power supply with constant voltage), change the polarity on each electrode 5 from minus to plus (the first switching mode) and from plus to minus (the second switching mode). Thus, on each electrode periodically its polarity changes from minus to plus and vice versa. This source is configured to vary the voltage in the range up to 5 V, preferably from 2 to 5 V, with the possibility of varying the current from 10 A to 1000 A.

To test the claimed method, an installation was manufactured and launched according to the block diagram of Fig. 1, which involves processing 5 kg of aluminum scrap, for which a stainless steel bath 1 is used in the temperature zone of the resistance furnace (thermal heating circuit - heat heater 3), where aluminum scrap is melted and converted into aluminum melt with a temperature of 660-750C °. A low-consumable anode (neutral to the melt) is immersed in the aluminum melt, in the lower part of which there is an active structural part in the form of structure 11 with many holes for the gas outlet, which processes or sparges the melt (if technologically necessary) parallel to the bottom of the boiler at a distance of 20 mm.

In the molten metal - refining gas system, with an excess of dissolved hydrogen in the melt relative to its content in the gas phase, a redistribution of hydrogen should take place. This process of transition of hydrogen into the refining gas will proceed until equilibrium is established between the melt and the gas phase.

In practice, either standing the melt in a neutral gas environment or blowing (bubbling) it with neutral gas is used. But bubbling is a more profitable process compared to standing: at the same specific gas flow rate, it provides a higher degree of hydrogen removal or, with an equal degree of removal, savings in refining gas (Gokhshtein M.B., Morozov Ya.I. “Refining of primary aluminum from oxide inclusions”, M, “Metallurgy”, 1979 /D2/).

Usually, purge (bubbling) is carried out through graphite tubes equipped with nozzles. The gas is supplied at an excess pressure of 0.007-0.15 atm. Gas consumption 0.1-1.0% of the volume of metal being processed. The maximum effect during treatment with neutral gases is obtained by the use of porous nozzles, which are made from various refractories (corundum, graphite, etc.). The effect of refining in this case increases due to the grinding of gas bubbles, which provides an increase in the contact surface, refining gas - melt.

On the bottom under the anode 5 is a removable flat metal receiver 12 impurities. Process gas (argon, nitrogen, air, chlorine) is supplied from above through a stainless steel tube passing through the processed melt and taking the temperature of the melt to the active part of the anode, being distributed over the surface of the active part of the anode, it passes into the melt, carrying out the processing and bubbling process in accordance with the technological card. A “+” of a DC source was applied to the anode, and a “-” of a DC source with a power of 500 A was applied to the cathode. In this case, the density of the anode and cathode currents were equal and amounted to a value equal to 0.9 A/cm ² . The process of electrolytic treatment of the melt lasted 4 hours.

Nitrogen to some extent can be attributed to the group of neutral gases, and therefore it is often used for the treatment of aluminum melts. However, it should be noted that the reaction of its interaction with liquid aluminum (2Al + N ₂ \u003d 2AlN) is thermodynamically possible, but it develops noticeably only at temperatures above 1000 K (726.85 ° C) (Mondolfo L.F. Structure and properties of aluminum alloys, Moscow, Metallurgy, 1979 /D3/). The presence of Mg in the alloy significantly enhances the interaction of nitrogen with the melt with the formation of nitride phases even at 730°C. This negatively affects the plastic characteristics of the cast metal. In practice, purge of aluminum melts with nitrogen is carried out, as a rule, in cases where the magnesium content in them does not exceed 2% (Makarov G.S. Refining aluminum alloys with gases, Moscow, Metallurgy, 1983 /D4/).

In the bath, the anode and cathode replaceable, horizontally or vertically located mutually parallel electrodes (with an interpole distance of 20.0-40.0 mm with a horizontal or vertical, parallel arrangement of electrodes) with replaceable impurity receivers or without them are partially or completely immersed in the processed aluminum melt with impurities at a melt temperature of 660-750°C. After loading the aluminum scrap and melting, a coating flux is added to the furnace to reduce the "waste" of aluminum. Set the temperature of the melt 660-750°and set the specified mode of electrolysis. Aluminum samples are periodically taken for the degree of purification and the electrolysis mode is adjusted. Upon reaching the specified technological parameters, the electrolysis process is stopped and the purified aluminum melt is drained for further use. If necessary, the impurity receivers on the electrodes are removed to be sent to technological waste.

Electrolysis is a complex of specific processes in the system of electrodes and electrolyte when a direct electric current flows through it. Its mechanism is based on the occurrence of an ionic current. An electrolyte is a type 2 conductor (ionic conductivity) in which electrolytic dissociation occurs. It is associated with decomposition into ions with a positive (cation) and negative (anion) charge. The electrolysis system necessarily contains a positive (anode) and a negative (cathode) electrode. When a direct electric current is applied, cations begin to move towards the cathode, and anions - towards the anode. The cations are mainly metal ions and hydrogen, and the anions are oxygen, chlorine. At the cathode, cations attach excess electrons to themselves, which ensures the occurrence of a reduction reaction. At the anode, on the contrary, an electron is donated from the anion with an oxidative reaction taking place. One of the options for electrolysis is the use of a melt as an electrolyte. In this case, only melt ions participate in the electrolysis process. A classic example is the electrolysis of molten salt NaCl. Negative ions rush to the anode, which means that gas (Cl) is released. Metal reduction will occur at the cathode, i.e. deposition of pure Na formed from positive ions that have attracted excess electrons. Similarly, other metals (K, Ca, Li, etc.) can be obtained from the melt of the corresponding salts. During electrolysis in a melt, the electrodes do not undergo dissolution, but participate only as a current source. In their manufacture, you can use metal, graphite, copper, some semiconductors.

It is believed that during electrolysis, ionization of the electrolyte occurs when positive and negative charges move towards opposite electrodes. To do this, the electrodes must be maintained in opposite polarity as long as the process continues, which is possible with a DC current. But if we pass an alternating current, the polarity of the electrodes will constantly change and the ions will not be attracted to any particular electrode, which will not lead to ionization. Therefore, electrolysis cannot occur with alternating current.

However, in the work (A.B. Kilimnik and E.E. Degtyareva "Electrochemical processes on alternating current", journal "Bulletin of the Tambov State Technical University", 2006), the use of non-stationary electrochemical processes for obtaining pure metals and their alloys, organometallic compounds is conclusively considered and organic substances using alternating voltage.

In the monograph B.A. Purina (Purin B.A. “Electrodeposition of metal from pyrophosphate electrolytes”, Riga, Zinatne, 1975” /D5/) describes the effect of asymmetric alternating current on the electrodeposition of metals from pyrophosphate electrolytes. Asymmetric alternating current was obtained by superimposing alternating current on direct current. If a cathodic current greater than the anode current was required, then the value of the anode current density component was controlled by superimposing an alternating current on the half-wave rectification current. An oscilloscope was used to record the current waveform and measure the potential of the electrodes.

The electrodeposition of tin on asymmetric alternating current at the beginning of electrolysis is characterized by the absence of a limiting current and a small difference in the maximum values of the cathode polarizations in the cathode and anode half-cycles of the current. A jump in the limiting current appears after 10 ... 12 minutes of electrolysis, if the maximum current density in the cathode half-cycle is more than 0.01 A/cm ² . During electrolysis by asymmetric alternating current, the near-cathode layer is enriched with divalent tin ions due to ionization in the anodic half-cycle. This leads to the fact that even at the maximum current density in the cathode half-cycle (0.04 ... 0.05 A / cm ² ), the first limiting current occurs only 2.5 minutes after the start of electrolysis, and the second limiting current does not appear, although when the DC is turned on current with a density greater than 0.03 A / cm ^2, the time for the appearance of the first limiting current is 5.10 s, after which the second limiting current appears.

A.B. Purin established that during the electrodeposition of cobalt by asymmetric alternating current from pyrophosphate electrolytes, the cobalt pyrophosphate complex decomposes in the near-electrode layer with the formation of the [Co(OH)] + complex, which is reduced to metallic cobalt. He also discovered the existence of hydrocomplexes of the xCo(OH)2 ⋅ g[Co(OH)]+ type, which form a highly dispersed sol in the reaction mixture.

Under the action of an alternating electric field, the hydration shells of ions are disturbed; this position was expressed in the work of A.I. Ionkin and others (Ionkin, A.I., V.M. Karavaev, A.I. Koshelev and others in the book “Research in the field of applied electrochemistry”, Tr. Novocherk. Polytechnic Institute, Institute named after S. Ordzhonikidze, 1970). Studying the polarization of platinum during electrolysis with alternating current, they found that the overvoltage of the discharge of metal ions in the series K+ ^ Na+ ^ Li+ decreases. At a constant current, the overvoltage in this series increases, since it is more difficult for a more hydrated lithium ion to approach the cathode surface.

The authors suggested that an alternating electric field “rips off” the hydration shell from the cations and promotes their discharge during the cathode half-cycle.

A.I. Didenko, V.A. Lebedev, S.V. Obraztsov with employees (A.I. Didenko, V.A. Lebedev, S.V. Obraztsov et al. “Intensification of electrochemical processes based on asymmetric alternating current.” Intensification of electrochemical processes: edited by A.P. Tomilov, M, “ Nauka, 1988) showed that the best physical and mechanical properties of coatings made of zinc, nickel, iron, copper, silver and lead are obtained using alternating current with a resonant frequency corresponding to each element.

In this case, as is known, during electrolysis with alternating current, in addition to dissolution and complex formation, metal, gases and other processes are released from the solution. Techniques such as interruption of the current, the imposition of an alternating current on a direct, reverse current, make it possible, under constant electrolysis conditions, to control the quality of the deposit according to its nature and structure due to the removal of diffusion restrictions. When an electric current is passed through the electrolyte, electrolysis and the associated polarization of the electrodes occur, which can be avoided by applying alternating current. P. Debye and X. Falkenhagen found that at an alternating current oscillation frequency above 5 MHz, the equivalent electrical conductivity increases.

In the claimed method, the electrolysis mode is used both at constant voltage and at alternating voltage. Each of the processes, depending on the type of voltage used, provides for special modes of separation of impurities. These regimes do not coincide in the nature of the processes occurring in the electrolyte. This is the feature of the claimed method of recycling aluminum from scrap. When melting scrap in the bath, a melt is obtained with an unspecified content of impurities, both metal and gas. With direct current, ionization of the electrolyte occurs when positive and negative charges move towards opposite electrodes. This leads to the direct precipitation of metal-containing impurities within the standard ion transport pattern. Due to the difference in electrolyte densities in the layers, these impurities settle in the lower layer and are placed on sites 12 prepared for collection. The process of transfer and deposition of metallized particles decreases with a decrease in their number and with an increase in the purity of the aluminum melt in the upper layer.

But if an alternating current is passed through the electrolyte, the polarity of the electrodes will constantly change, and the ions will not be attracted to any particular electrode in terms of deposition of metal impurities. But at the same time, it becomes possible to isolate gaseous impurities and preserve the transfer of metal ions in the half-cycle.

The essence of the claimed method is not to preserve the usual modes of impurity deposition during electrolysis, but that the deposition of impurities is an ion transfer process that takes place both at a constant voltage on the electrodes and at a variable one. What is important is not to maintain the stationarity of the transport regime, but to bring it to a flow that is not aligned in terms of laminarity, in which the direction of ion motion is constantly changing. This is ensured by switching from direct to alternating voltage and by changing the polarity of the electrodes at constant voltage. It is essential that with such a changing nature of the flow, a suspended arrangement of ions in the melt occurs, which makes it possible to separate impurities in the areas 12 of the electrodes in a shorter time.

The results of aluminum recycling according to the claimed method are shown in Table 1 as follows.

From tabular comparisons it follows that the ionic processes occurring with metal impurities in the melt correlate with the place of the metal in the electrical activity series of the metal relative to AL. It is not observed at the given parameters of the electrolytic process of purification of aluminum from manganese impurities, presumably due to K being close to 1, which requires a more thorough correction of the electrolysis mode of the process.

The present invention is industrially applicable and can be used in the non-ferrous metallurgical industry for the recovery of purified aluminum from aluminum-containing scrap with an unidentified chemical composition of impurities. The method allows to significantly reduce the cleaning time to 4 hours (in the prototype - 20 hours) and to obtain high-purity recovered aluminum with an impurity content below the established limits for this category of aluminum.

Claims (6)

1. A method for recycling aluminum by electrolysis of a melt of its scrap, which consists in loading solid aluminum or aluminum-containing scrap into a bath for electrolysis and separating aluminum purified from metal impurities, characterized in that by heating the bath, said scrap is transferred into a melt with a temperature of 660-750 ° C and use this conductive melt with impurities dissolved in it as an electrolyte during electrolysis, while voltage from 2 volts to 5 V is applied to the electrodes partially or completely immersed in the melt in the mode of changing the current strength from 10 to 1000 A to obtain the density of the cathode and anode current equal to 0.9-1.0 A/cm ² , while the electrodes carry out a periodic change of alternating voltage to a constant voltage and a change in polarity on the electrodes when they are connected to a constant voltage source. 2. The method according to p. 1, characterized in that during electrolysis, process gas is supplied to the melt for bubbling the melt. 3. A device for recycling aluminum by electrolysis of its scrap melt, characterized in that it contains a stainless steel bath equipped with a heat heater of its side or side walls and used to load solid aluminum or aluminum-containing scrap into it, two replaceable low-consumption electrodes oriented along the wall or walls of the bath , an adjustable DC source, an adjustable AC source, the first on-off switching unit and the second on-off switching unit, wherein the two electrodes are fixed at the bottom of the bath at a distance from each other and are configured to be connected to the centralized AC power supply network by means of an adjustable DC source , which converts the alternating voltage at the input to a constant at its output with the ability to regulate the current strength, while the adjustable AC source is made with the ability to regulate the current strength, the output contacts of both sources are connected to the first two-position switching unit, which allows the output contacts to have a constant voltage when turned off AC voltage or alternating voltage when the DC voltage is turned off, the outputs of the first on-off switching unit are connected to the input of the second on-off switching unit, configured to connect an AC source to the electrodes or connect a DC source to the electrodes and with the possibility of changing the polarity of the DC voltage on the electrodes from minus to plus and from plus to minus when connected to a DC voltage source. 4. The device according to claim 3, characterized in that holes are made in the bottom part of the bath for supplying gas to the bath for bubbling the melt. 5. The device according to claim 3, characterized in that in the bottom part of the bath, the electrodes are equipped with removable trough-shaped platforms for the deposition of impurities during electrolysis. 6. Device according to claim 3, characterized in that the heater is connected to an alternating voltage source.

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