RU2824154C1 - Method of processing aluminium production wastes - Google Patents

Abstract

FIELD: various technological processes.

SUBSTANCE: invention relates to processing of aluminium production wastes, in particular, to treatment of aluminium production wastes. Wastes in the form of spent lining are preliminarily crushed to fraction of not more than 5 mm, heated to temperature from 500 to 750 °C and held at this temperature for 10 to 40 minutes. Heated wastes are sprinkled with water, reducing material temperature to values of not more than 150 °C. Reaction gases obtained during irrigation are fed into a combustion chamber where they are burnt. Further, the irrigated material is supplied through a cooler into a storage bin.

EFFECT: method makes it possible to reduce toxicity of processing wastes of aluminium production, namely spent lining.

7 cl, 1 dwg, 3 ex

Description

The method for processing aluminum production waste relates to non-ferrous metallurgy, and in particular to methods for cleaning aluminum production waste [B01D53/02, C22B7/00, C22B21/00, C22B21/06, F27B7/00].

A METHOD FOR PRODUCING ALUMINUM FLUORIDE [RU 2462418-2011-06-07] is known from the prior art, which pertains to chemistry. Fluorine-containing material from the electrolytic production of aluminum is treated with aluminum sulfate in an amount no less than the stoichiometrically required amount for binding sodium into sodium sulfate and then treated at a temperature of 400-700°C. The resulting agglomerate is leached with water. The products are separated to obtain aluminum fluoride and a solution containing sodium sulfate. Technical result: the invention allows processing industrial fluorine-containing materials, which are of little demand in the electrolytic production of aluminum, into aluminum fluoride. A disadvantage of this method is the toxic emissions accompanying the technological process.

Also known from the prior art is a DEVICE FOR ELECTROLYTIC TREATMENT OF CARBONIC ALUMINUM RESIDUES [CN 216245494 (U) - 2022-04-08] intended for electrolytic treatment of aluminum carbon residue, which includes a process unit, a smelting part, a molding machine located on one side of the smelting part, a crushing part located on one side of the molding machine, a conveyor part located on one side of the smelting part. One side of the smelting part and a smoke supply element located at the top of the smelting part. And the cleaning unit is located on one side of the smelting part and contains a spray absorption tower, a bag-type dust collector located on one side of the spray absorption tower, and a smoke exhaust pipe located at one end of the bag-type dust collector, a collector type. According to the device disclosed in the utility model, carbon residues can be processed and converted by the processing unit, and harmful gases during recycling and conversion can be purified by the purification unit, so that the purpose of processing carbon residues is achieved, carbon residues can be processed, resource losses are reduced, and the cost price of the products is reduced. The disadvantage of this technical solution is the need for frequent maintenance of the purification unit with the removal of filtration products from it.

The closest in technical essence is the PROCESSING OF SMELTING BY-PRODUCTS [US 2006053973 (A1) - 2006-03-16], in which the spent refractory after use in the aluminum smelting process includes crushing and classifying the spent refractory, placing the sorted and crushed spent refractory in a furnace at a temperature above 450 °C, heating the spent refractory to a temperature above 450 °C, mixing the heated spent refractory with water to obtain reaction gases and a residue, burning the reaction gases, mixing the residue with water in a well-ventilated room for several weeks to solidify the residue. This method also includes mixing the solidified residue with other chemicals and minerals to obtain specific mineral products. The disadvantages of this treatment are:

1. High toxicity, since there is a high carryover of fine-grained crushed waste lining (up to 30%) due to the use of a rotary kiln with a burner for heating, this entails the installation of additional special filters (high temperature of the captured material) and the repeated return of toxic material to the recycling cycle. This also reduces the productivity and efficiency of heating the material.

2. Large amount of exhaust gases due to the use of a burner for heating, which requires a more powerful flue gas cleaning system.

Spent lining after use in the aluminum smelting process is classified as hazardous waste, contains metallic aluminum, metallic sodium, carbides, nitrides and cyanides. It easily absorbs atmospheric water (humidity), which reacts with a number of these components. The following typical chemical reactions of metals or chemical compounds with water are distinguished:

- Metallic aluminum in hydrogen 2Al + 3H2O → 3H2 + Al2O3

- Metallic sodium to hydrogen 2Na + 2H20 → H2 + 2NaOH

- Aluminum carbide is converted into methane Al4C3 + 6H2O → 3CH4 + 2Al(OH)3

- Ammonia from aluminum nitride 2AlN + 3H20 → 2NH3 + Al2O3.

The spent barrier layer is particularly dangerous due to:

- something that has a tendency to combine with water and release explosive gases;

- has leachable cyanide;

- contains leachable fluorides.

The technical result consists in reducing the toxicity of processing aluminum production waste, namely spent lining.

The claimed technical result is achieved due to the fact that the method of processing aluminum production waste is characterized by the fact that the spent lining, pre-crushed to a fraction of no more than 5 mm, is heated to a temperature of 500°C to 750°C, and maintained at this temperature for 10 to 40 minutes, then the heated waste is irrigated with water, reducing the temperature of the material to values not more than 150°C, the reaction gases obtained during the irrigation are fed into the combustion chamber, where they are burned, then the irrigated material is fed through a cooler into a storage bin.

In particular, heating is carried out in a screw-retort furnace.

In particular, heating is carried out by induction heaters.

In particular, irrigation is carried out using nozzles on a feed auger.

In particular, reaction gases are fed into the combustion chamber using an ejector.

In particular, combustion of gases in the combustion chamber is carried out using a burner.

In particular, cooling is carried out by means of a screw with a hydraulic jacket.

Brief description of the drawings

Fig. 1. Schematic representation of the installation

Figure 1 shows: 1 – storage bin, 2 – auger, 3 – dosing bin, 4 – auger-retort furnace, 5 – feed auger, 6 – hydro-jet chamber, 7 – nozzles, 8 – ejector, 9 – combustion chamber, 10 – burner, 11 – filter-smoke exhauster, 12 – smoke stack, 13 – cooling auger with hydro-jacket, 14 – storage bin.

Implementation of the invention

The line for processing aluminum production waste contains a storage bin 1 connected via a screw 2 to a dosing bin 3, which is connected to sections of a screw-retort furnace 4, which is connected via a feed screw 5 to a hydro-retort chamber 6, in which nozzles 7 are made. The hydro-retort chamber 6 and sections of the screw-retort furnace 4 are connected via an ejector 8 to a combustion chamber 9 with a burner 10. After the combustion chamber 9, a smoke exhaust filter 11 and a smoke stack 12 are mounted. In this case, the hydro-retort chamber 6 is connected via a cooling screw with a hydro-jacket 13 to the storage bin 14.

The method for cleaning aluminum production waste is characterized by heating the spent lining in the presence of air to destroy the cyanide present in the lining, and mixing the lining with water to ensure neutralization of reactive materials.

It is aimed at eliminating (significantly reducing) health hazards and explosive hazards of spent lining. The process includes the destruction of cyanide and the neutralization of reactive compounds that release acetylene, ammonia, methane, hydrogen and other gases in the process described below, some requirements such as heating temperature and holding time may vary depending on the type of material included in the spent lining.

The spent lining is loaded into the storage bin 1, from which it falls under its own weight onto the screw 2. Through the screw 2, the spent lining enters the dosing bin 3 and then into the tube-screw furnace 4 (consists of 4 sections) for heating and holding at a given temperature, additional air is supplied to the furnace to support the chemical decomposition of the cyanide. The temperature in the furnace is carefully monitored using temperature sensors, after which it passes through the feed screw 5 into the hydroactive chamber 6, where it is irrigated with water from nozzles 7. The reaction gases formed as a result of the irrigating, as well as gases from the sections of the tube-screw furnace, pass into the combustion chamber 9 using the ejector 8, where they burn under the action of the burner 10. Gaseous combustion products are removed through a smoke exhaust filter 11 and a smoke stack 12. In this case, from the hydroactive chamber 6, the processed barrier layer enters the storage bin 14 via a cooling screw with a hydraulic jacket 13.

When implementing the claimed method, the spent lining, in the form of waste from the electrolytic production of aluminum, pre-crushed to a fraction of no more than 5 mm, enters the storage bin 1, from where it is fed by auger 2 to the dosing bin 3, from which the spent lining enters the tube-auger furnace 4. In this case, the layer thickness and the dimensions of the trays are determined experimentally depending on the required productivity. In the tube-auger furnace 4, the material is heated to a temperature of 500 ° C to 750 ° C and maintained at this temperature for 10-40 minutes (depending on the original material, during this time the material passes all 4 sections of the tube-auger furnace, the speed is regulated by the revolutions of the augers). The material is heated in the tube-auger furnace by induction or other electric heaters. It is possible to use other types of heaters (for example, heating elements) or combined heating with different types of heaters. Additional air is supplied to the furnace to support the chemical decomposition of cyanide. The temperature in the furnace is carefully controlled using temperature sensors, gases from the sections of the tube-auger furnace are discharged into the combustion chamber 9 using an ejector. Then, the hot material is fed by the feed screw 5 into the hydro-reactive chamber 6, inside which the feed screw 5 has an open upper part, where the hot material is irrigated with water to a temperature of no more than 150°C using nozzles 7. The reaction gases are fed into the combustion chamber 9 using an ejector 8, where all harmful and explosive components are burned. If necessary, the gases are burned at the outlet with illumination using standard fuel. Combustion in the combustion chamber 9 is maintained by a burner on standard fuel 10. The exhaust gases are removed through a smoke exhaust filter 11 via a smoke stack 12. The neutralized material enters the storage bin 14 via a cooling auger with a hydraulic jacket 13, where the neutralized material is cooled to ambient temperature at the outlet.

The technical result is a reduction in the toxicity of processing aluminum production waste, namely spent lining, which is achieved, among other things, by eliminating the carryover of toxic material. This is achieved due to the fact that the spent lining, pre-crushed to a fraction of no more than 5 mm, enters the tube-screw furnace 4, is heated from 500 °C to 750 °C and is maintained (passes through 4 furnace sections) for 10-40 minutes (the time is determined depending on the minimum required to reduce the hazard of the material with different granulometric compositions of the incoming raw materials) while potentially hazardous cyanide is destroyed), air is supplied to the furnace sections, and the resulting gases are discharged into the combustion chamber 9 using an ejector 8, then the hot material is fed into the hydro-reactive chamber 6, where, using nozzles 7, the hot material is irrigated with water to a temperature of no more than 150 °C. Water reacts with the hot material from the furnace, releasing steam and reaction gases such as acetylene, ammonia, hydrogen and methane. Thermal shock, which occurs as a result of contact of hot solid mineral material with water, which has a much lower temperature, causes cracking of the surface of the material. As a result of surface cracking, the surface area of particles reacting with water increases, which accelerates the reaction process), after which the reaction gases are fed by ejector 8 into combustion chamber 9, where all harmful and explosive components (including acetylene, ammonia, methane, hydrogen and other gases) are burned. Thus, heating and holding at the specified temperature with rapid cooling allows to eliminate (significantly reduce) hazardous to health and explosive factors of the spent lining, which makes it possible to further use it both in various industries and for recycling purposes in the production of aluminum.

The use of a retort-type furnace eliminates the possibility of gases penetrating into the environment when heating the material, and eliminates the removal of material hazardous to human health (when using a rotary furnace, the removal of finely dispersed material reaches 30%).

The use of induction heating, in the implementation version, allows for the furnace to be brought to the required temperature parameters almost quickly and the required temperature to be maintained in each zone with high precision.

Justification of the boundaries of the ranges used in the declared method.

Grinding to a fraction of no more than 5 mm allows achieving the stated technical result, since when using a fraction of more than 5 mm, there is no complete thermal destruction and release of all environmentally harmful gases from their waste at the temperature conditions specified in the application materials, and the time of the detoxification process is significantly increased.

Using a temperature for heating from 500°C to 750°C allows achieving the stated technical result, since using a lower temperature does not result in complete thermal destruction and release of all environmentally harmful gases, using a temperature higher than 750°C is not advisable since it is important that the fluorides in the lining do not pass into the gaseous phase. (Usually, such a transition occurs at temperatures of about 850°C.) Using a temperature after irrigation higher than 150°C will not allow achieving the stated technical result, due to the fact that the release of material at a temperature higher than 150°C can lead to a decrease in the quality of waste processing (the possibility of residues of environmentally harmful substances and gases in the waste is not excluded).

Using a holding time of less than 10 minutes does not guarantee complete thermal destruction and release of all environmentally harmful gases, more than 40 minutes is not advisable due to the fact that increasing the value does not affect the declared technical result. Also, the time can be selected depending on the fraction size (smaller fraction size - less time is required, larger fraction - more time) as well as on the specific composition of the spent lining. The values were determined experimentally.

Example of implementation

Example 1

The waste was fed into the hydroactive chamber crushed to a fraction of 1-5 mm heated to a temperature of 700°C (heating was carried out by induction heaters). The holding process - the total time of passage through all 4 sections of the furnace was 40 minutes. The irrigation process to a temperature of 100°C. At the outlet, it was found that the content of released residual cyanides does not exceed the maximum permissible dose (does not have a negative impact on human health and the environment), thus 89% of all harmful and explosive components were processed (and for cyanides, the reduction is up to 500 times) of waste from the electrolytic production of aluminum.

Example 2

The waste was fed into the hydroactive chamber crushed to a fraction of 1-5 mm heated to a temperature of 750°C (heating was carried out by induction heaters). The holding process - the total time of passage through all 4 sections of the furnace was 30 minutes. The irrigation process to a temperature of 100°C. At the outlet, it was found that the content of released residual cyanides does not exceed the maximum permissible dose (does not have a negative impact on human health and the environment), thus 91% of all harmful and explosive components were processed (and for cyanides, the reduction is up to 500 times) of waste from the electrolytic production of aluminum.

Example 3

The waste was fed into the hydroactive chamber crushed to a fraction of 1-5 mm heated to a temperature of 750°C (heating was carried out by induction heaters). The holding process - the total time of passage through all 4 sections of the furnace was 40 minutes. The irrigation process to a temperature of 150°C. At the outlet, it was found that the content of released residual cyanides does not exceed the maximum permissible dose (does not have a negative impact on human health and the environment), thus 93% of all harmful and explosive components were processed (and for cyanides, the reduction is up to 500 times) from the waste of electrolytic aluminum production.

Claims (7)

1. A method for processing aluminum production waste, characterized in that aluminum production waste in the form of spent lining is pre-crushed to a fraction of no more than 5 mm, heated to a temperature of 500 to 750 °C and maintained at this temperature for 10 to 40 minutes, then the heated waste is irrigated with water, reducing the temperature of the material to values of no more than 150 °C, the reaction gases obtained during the irrigation are fed into a combustion chamber, where they are burned, then the irrigated material is fed through a cooler into a storage bin. 2. The method according to item 1, characterized in that the heating is carried out in a screw-retort furnace. 3. The method according to item 1, characterized in that heating is carried out by induction heaters. 4. The method according to item 1, characterized in that irrigation is carried out using nozzles on a feed auger. 5. The method according to item 1, characterized in that the reaction gases are fed into the combustion chamber using an ejector. 6. The method according to item 1, characterized in that the combustion of gases in the combustion chamber is carried out using a burner. 7. The method according to item 1, characterized in that cooling is carried out by means of a screw with a hydraulic jacket.