RU2418080C1 - Procedure for processing wastes of aluminium production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in heating wastes of aluminium production in reactor and in separation of their oxide and salt component parts by implementation of deduster and bag hose. There are used wastes not contacting moisture. Wastes are heated in the reactor to temperature as high, as 800°C and conditioned to the beginning and completion of alumo-thermal reactions at simultaneous mixing and supply of air into the reactor. Concentrate of metal aluminium is settled in the deduster. Salt component of wastes is settled in the successive bag hose. The procedure can be carried out both in cyclic or continuous modes.

EFFECT: processing slag sifting and gas purification slime containing salts and dispersed aluminium; extraction of dispersed aluminium; reduced power consumption and avoiding complex preparing operations.

2 cl, 3 tbl, 4 ex

Description

The invention relates to the field of secondary metallurgy of aluminum, namely to the processing of aluminum slag, depleted in the metallurgical method (for example, in rotary inclined furnaces), screenings of slag enrichment lines, sludge for gas treatment of aluminum remelting furnaces and other aluminum production wastes containing dispersed metal aluminum (small beads) and aluminum dust).

A known method of processing poor aluminum slag, which consists in grinding it, leaching in water, evaporating the brine or enriching the brine using ion-exchange or membrane technologies, followed by drying the released salts and drying the water-insoluble oxide component, from which a small amount of aluminum kings is isolated. The rest of the oxide component goes for further processing or disposal (Integrated processing of aluminum salt-containing slag [Text]: monograph / S.D. Kutsenko, L.N. Kurdyumova, N.V. Kubatkina. - Orel: Orel State Technical University, 2007. - 171 from.).

The disadvantages of this method are its high energy intensity, multi-stage process, negative profitability and the inability to extract dispersed aluminum, which is oxidized upon contact with water.

Closest to the technological essence of the claimed invention is a method of processing aluminum slag, in which the crushed slag after separation of aluminum metal in the form of kings is subjected to granulation with fuel, and then the oxide and salt parts of the slag are separated by evaporation of salts during sintering of the granular material at a temperature above boiling point of salts. In this case, the salt part of the slag condenses in a dust precipitation device and a bag filter (RF patent No. 2132398 from 06/27/1999, C22B 7/04, C22B 1/16). This method is adopted as a prototype.

The disadvantage of the prototype is the inability to extract dispersed aluminum, which is oxidized during the preparation of granules and pellets, carried out with the addition of water or aqueous solutions or as a result of a preliminary reaction with water. The latter is indicated by the absence of aluminum nitride in the feed and the presence of 6 to 12 percent water, which is given in the examples of the method. The prototype is also characterized by high energy intensity and complex preliminary preparation of slag.

The technical result of the proposed method is the ability to extract from aluminum slag and other aluminum waste production of dispersed aluminum contained in them, which is impossible to implement by known methods, including the prototype. This provides the possibility of processing slag, slag screenings and gas treatment sludge containing salts and dispersed aluminum, which are currently being disposed of. At the same time, the energy intensity decreases, complicated preparatory operations are excluded.

The specified technical result is achieved by the fact that in the known method of processing waste from aluminum production, comprising heating the waste in a reactor with separation of their oxide and salt components using a dust collecting device and a bag filter, according to the invention, non-contact waste is used, which is heated in the reactor to temperatures not lower than 800 ° C and maintained until the onset and complete passage of aluminothermic reactions with stirring and supplying air to the reactor, while in dust extraction itelnom device precipitated concentrate of metallic aluminum and in sequentially located baghouse precipitated salt component of the waste.

Waste processing can be carried out both in cyclic and continuous modes.

Limiting the contact of the waste with atmospheric moisture avoids the oxidation of small kings and dusty aluminum, which are a source of energy in aluminothermic reactions. In the reaction zone, metal aluminum is oxidized to oxides, aluminum nitride is oxidized to free nitrogen and aluminum oxides. The energy released in this process is used to support the reaction, the formation of complex oxides of aluminum and other metals with a spinel structure, the evaporation of the chloride salts that were part of the fluxes and volatile aluminum compounds, heating new portions of waste to the temperature of the onset of the reaction during continuous operation of the reactor. The oxide component discharged from the reactor is a mixture of spinel, aluminum oxide and magnesium oxide, the ratio of which depends on the composition of the waste loaded into the reactor.

At temperatures of aluminothermic reactions, aluminum becomes bivalent and monovalent. In addition to this, instead of Al2O3 and AlCl3, volatile subcompounds AlO, Al2O, AlCl2, AlCl are formed, which are carried away by the exhaust gases to the gas treatment. Cooling when mixed with cold air, these compounds decompose according to the reactions:

3AlO → Al2O3 + Al

3Al2O → Al2O3 + 4Al

3AlСl2 → 2АlСl3 + Аl

3AlСl → АlСl3 + 2Аl

The resulting metallic aluminum and aluminum oxide condense in the form of particles larger than 100 microns and are well captured in dust collecting devices. The salt component of the waste (sublimation of salts) condenses in the form of smaller particles and is captured in a bag filter. Thus, the aluminum concentrate is separated from the salt component.

From 33 to 50% of the aluminum contained in the feed is used to maintain the reaction. From 50 to 67% of the aluminum through the described transport reactions are transferred to a dust collection system.

The reactor may be an axisymmetric vessel, rotating around its axis and lined internally with heat-resistant material.

In a cyclic mode, the waste is loaded into the reactor, heated to tanning, aluminum is burned until the reaction ceases or decays, and is discharged from the reactor, then the cycle is repeated. In continuous mode, after the onset of aluminothermic reactions, the waste is continuously or in portions fed into the reaction zone through the loading section of the reactor, and the annealed waste is continuously discharged from the opposite side of the reactor. The mixing of the waste is carried out by rotating the reactor. The flow of air into the reaction zone is carried out by gravity or by blowing a fan. The reaction temperature is controlled by changing the speed of the reactor, the feed rate of the processed waste and the air feed rate.

Example 1. As a reactor, a rotary inclined furnace with a capacity of 1 ton was used with an individual dust collection system consisting of a spark arrester as a dust precipitation device and a bag filter connected in series. As raw materials for processing, we used slag remaining in the same furnace after the scrap was remelted and the metal thus obtained was drained. According to the results of preliminary studies of the chemical composition of such slag, it contains 2-5% of kings of aluminum with dimensions less than 3 mm and up to 10% of dispersed dust-like aluminum, which cannot be extracted by the metallurgical method. By machining or leaching, only part of the kings can be extracted, which does not cover the cost of processing. The remainder of the slag consists of aluminum oxides and oxides of alloying metals and salts (40-50%), which are used as a flux in smelting to prevent aluminum oxidation. The presence of metallic aluminum and especially salts makes the further use of slag impossible. Therefore, such slag is usually disposed of in specially equipped dumps.

The remaining in the furnace aluminum-depleted slag with a temperature of 700-750 ° C (temperature measurements were carried out by a remote infrared pyrometer) was further heated by a gas burner with continuous rotation of the furnace to evaporate most of the salts and cause firing. At temperatures from 800 ° C and above, strong smoke was observed in the furnace, which indicates intense evaporation of salts. When the rotation of the furnace stopped, the smoke decreased and on the surface of the slag foci of fire (white glow) with a higher temperature than the bulk of the slag became noticeable, which indicates the onset of aluminothermic reactions. With continued heating and rotation, hot spots spread throughout the entire mass of slag. The volatile reaction products emitted in this case were sucked together with the surrounding air into an autonomous dust collection system, where they were condensed and precipitated.

After all the slag was ignited, the lid of the furnace on which the burner was installed was discharged and the burner was turned off. Opening the lid provided air to the combustion zone. The rotation of the furnace provided mixing of the slag and the passage of oxidative reactions throughout the volume of slag. The temperature of the slag rose to 1700 ° C and above. The combustion rate was controlled visually by changing the rotational speed of the furnace (from 0 to 6 revolutions per minute). After about 30 minutes of burning with the lid open, the temperature in the reaction zone decreases, smoke emission and white light are reduced. After waiting another 10 minutes, the annealed slag and other reaction products were unloaded.

As a result of the operations, bulk material was unloaded from the furnace reactor, consisting of aluminum oxides and spinel (the oxide component of the waste), where metal aluminum was completely absent. An aluminum concentrate with an aluminum content of about 50% suitable for the separation of aluminum by metallurgical method was unloaded from a dust precipitation device (spark arrestor), and a mixture of sodium and potassium chlorides in an amount of about 85% (salt component of the waste) was unloaded from a bag filter.

In this way, the claimed method can be implemented, but a rapid increase in the temperature of the slag by 900 ° C for lining the furnace reactor is a thermal shock and contributes to its accelerated destruction. In this regard, it is better to carry out the process in a continuous mode.

Example 2. The proposed method was implemented in continuous mode on a pilot reactor made in the form of a rotating cylinder, lined with heat-resistant concrete and installed at an angle of 7 ° degrees to the horizontal. We used slag taken after the scrap was remelted on a rotary inclined furnace, which was stored in the absence of contact with moisture. Air was forced into the combustion zone by a burner fan installed on the discharge side of the annealed slag, cold slag was loaded from the opposite side using a vibratory feeder. The flame of the burner was used only at the initial moment of the process for heating the lining and bringing the first portion of slag to the beginning of aluminothermic reactions, which was visually assessed by the appearance of white light and intense smoke in the reactor. A new portion of slag was added to the reactor when signs of attenuation of combustion reactions appeared.

As a result of processing 10 tons of cold slag, the following was obtained:

oxide component - 5.8 tons;

aluminum concentrate - 1.2 tons;

salt component - 3.6 tons.

470 kg of aluminum metal was smelted from aluminum concentrate in a crucible furnace.

The composition of the obtained components in percent, determined by x-ray phase analysis, are presented in table 1.

Example 3. In a cylindrical reactor, the slag elimination fraction of 3 mm was processed, which remained after the slag was enriched by crushing it and sieving it into fractions (slag elimination was stored in the absence of contact with moisture). This fraction is usually not used for further processing and goes to landfill.

As a result of processing 10 tons of slag screening by the claimed method, the following was obtained:

oxide component - 5.3 tons;

aluminum concentrate - 3.2 tons;

salt component - 3.2 tons.

1520 kg of aluminum metal was smelted from aluminum concentrate in a crucible furnace. The composition of the obtained components in percent, determined by x-ray phase analysis, are presented in table 2.

The data obtained as a result of processing slag screenings are close to the results obtained when processing slag from a rotary inclined furnace.

Example 4. In a cylindrical reactor was processed dusty sludge gas treatment furnace for melting aluminum waste (storage of sludge was carried out in the absence of contact with moisture). Such a slurry is not used and is only for disposal.

To exclude dust formation and entrainment of unannealed dust into the dust collection system, the sludge was pre-packed in plastic bags, the reactor rotation speed was reduced to 0.5 rpm, and air was supplied by gravity due to natural draft.

As a result of processing 10 tons of sludge received:

oxide component - 5.8 tons;

aluminum concentrate - 1.8 tons;

salt component - 3.6 tons.

870 kg of aluminum metal were smelted from aluminum concentrate in a crucible furnace.

The composition of the obtained components in percent, determined by x-ray phase analysis, are presented in table 3.

The data in the tables on the composition of the components obtained from the processing of aluminum production waste by the proposed method show that this method allows the processing of aluminum waste containing salts and dispersed aluminum, which are currently being disposed of. In this case, the annealed slag does not contain aluminum metal, aluminum nitride and practically does not contain salts. This allows you to use it in the production of heat-resistant concrete, brick, other heat-resistant products and for the preparation of molding compounds in foundry.

Aluminum concentrate contains metallic aluminum, which can be isolated in pure form metallurgically. Moreover, its amount exceeds the number of kings, which can be obtained mechanically by processing slag by selecting kings.

The salt component contains more than 80% salts and can be used as a flux in the production of secondary aluminum.

Compared with well-known analogues in the implementation of the proposed method there is a decrease in energy intensity, excludes complex preparatory operations.

Claims (2)

1. A method of processing waste from aluminum production, including heating the waste in a reactor with separation of their oxide and salt components using a dust precipitation device and a bag filter, characterized in that they use waste that has no contact with moisture, which is heated in the reactor to temperatures not lower than 800 ° C and kept until complete aluminothermic reactions with stirring and supplying air to the reactor, while a concentrate of aluminum metal is precipitated in a dust precipitation device, and in An ice-located baghouse precipitates the salt component of the waste. 2. The method according to claim 1, characterized in that the waste treatment is carried out in cyclic or continuous modes.