Method for decontaminating and utilizing aluminium production waste sludges

Abstract

The invention relates to metallurgical methods for decontaminating and utilizing aluminium production waste sludges, and more particularly to obtaining aluminium and alloys thereof from oxidized forms in combination with alumina or alumina-containing products. The technical result of the invention is an increase in the efficiency of aluminium reduction. A method for decontaminating and utilizing aluminium production waste sludges entails the thermal reduction of oxidic forms of aluminium, silicon iron and copper, which are reduced from a molten charge during treatment with carbon monoxide. A prepared charge of metal oxides is treated in a gas lift furnace, with molten charge being continuously circulated through separated melting, gas lift and settling chambers at a temperature of 1000-1100ºС.

Description

[0001] Method of neutralization and utilization of sludge waste from aluminum production FIELD OF TECHNOLOGY

[0002] The invention relates to metallurgical methods for rendering harmless and utilizing sludge waste from aluminum production, in particular to the production of aluminum and its alloys from oxidized forms together with alumina or alumina-containing products.

[0003] LEVEL OF TECHNOLOGY

[0004] A method is known for producing aluminum from waste, which includes heat treatment of aluminum oxide in the presence of carbon, interaction of the obtained product containing aluminum carbide and aluminum trifluoride, upon heating to form aluminum subfluoride and decomposition of the subfluoride to aluminum and aluminum trifluoride, wherein before heat treatment, agglomeration of the initial material is carried out with a coating of the agglomeration particles with carbon, heating is carried out by a resistive method, and decomposition is carried out by condensation using a layer of aluminum trifluoride at 1100°C (SU 1253433 AZ, published 23.08.1986).

[0005] The disadvantages of the described method are the insufficiently high purity of the aluminum obtained.

[0006] A method is known for producing aluminum from alumina-containing materials, including reduction with a solid carbon-containing material (SLI 313374 A1, published 31.08.1971), wherein the starting materials are chlorinated with manganese chloride in the presence of a solid carbon-containing material at a temperature of 900-1400°C, and the resulting aluminum trichloride, purified from carbon monoxide, is reduced to metallic aluminum with metallic manganese formed during chlorination at a temperature higher than the melting point of manganese chloride, and in no less than one and a half times its excess against the theoretically necessary amount, with the production of manganese chloride, which is returned for chlorination.

[0007] The disadvantages are the complexity of the technological process of obtaining aluminum and the presence of harmful impurities that pollute the atmosphere.

[0008] A method for producing aluminum is known (SLI 193720 A1, 12.02.1969), the essence of which is that aluminum oxide is reduced with carbon to form mainly AlO3, which is captured in a known way and sent to electrolysis. The known method is difficult to implement and involves returning the reduced aluminum oxide to the electrochemical process, which increases the cost of the process.

[0009] A method for producing aluminum is known (RU 2157856 C2, published 20.10.2000), which includes the reduction of alumina with a carbon-containing material and the subsequent separation of aluminum at the cathode; graphite is used as the carbon-containing material; before reduction, alumina is mixed with graphite; reduction is carried out by heating using high-frequency inductors until the mixture sinters and melts, using the mixture as an anode.

[0010] The disadvantage of the known method is the initial production of aluminum carbide and its decomposition at very high temperatures, which reduces both the purification of aluminum and reduces the economic indicators of the process.

[0011] A method for producing aluminum is known, disclosed in the article by Plakhut V. V., Aluminum production, new technology, Voprosy naukm, 19.08.2017 August 2017, prototype (https: / / portalus.ru / modules / science / print.php?subaction=showfull&id=1503156694&archive=&st art from=&ucat=& ) The known method is based on the carbothermic reduction of aluminum according to the known method is an alternative process for producing aluminum using a chemical reduction reaction in a reactor. Carbothermic processes require much less physical space than the Hola-Heroult electrolytic reduction process. The process of producing aluminum by carbothermic reduction leads to a decrease in electricity consumption. The estimates obtained indicate that the carbothermic process reduces energy requirements by more than 30%. The carbothermic process for producing aluminum, in addition, significantly reduces emissions of perfluorocarbons into the atmosphere.

[0012] According to many authors, the electrothermal reduction method is more promising than the electrolysis method, since it is based on the processing of aluminosilicate raw materials, which are much more abundant than bauxites, and requires lower costs for raw material preparation. At the same time, the electrothermal reduction method has a number of disadvantages that hinder its widespread use. There is an increased formation of aluminum carbide, liquid slags, disruption of the dynamics of the charge and reduction products, In addition, the need to add silicon or iron oxides to prevent the formation of aluminum carbide in the standard technology of carbothermal reduction of aluminum from oxide requires additional technologies for separating aluminum from other components of the resulting alloy when it is necessary to obtain pure aluminum.

[0013] The article in question discloses a new method for producing aluminum, which consists of the following.

[0014] Aluminum is reduced not by carbon, but by carbon monoxide. It is known that carbon monoxide CO, unlike elemental carbon, is a more active reducing agent. Carbon monoxide is produced in a special external gas generator, which is then fed into the electrolyzer bottom. And to increase the contact time of carbon monoxide with the melt of the charge, a number of plates with a recess in the lower part are installed in the electrolyzer to delay the movement of CO gas. The plates are installed on supports fixed in the carbon bottom of the bath. The plates and supports are made of refractory, chemically resistant, non-conductive material, for example, silicon carbide. In this case, the height of the electrolyzer increases to 0.8 m. The process is carried out in the following way. Cryolite is loaded into the bath, lined with carbon mass or graphite blocks, it is melted in the arc mode and brought to a liquid state. Then a batch consisting of a mixture of aluminum and silicon oxides is loaded into the bath.Joint reduction of aluminum and silicon oxides is carried out at a temperature of 1000-1100°C, including the formation of a reaction volume of melt based on metal fluorides, the application of direct electric current to the melt. Graphite electrodes immersed in the melt reduce the cryolites of aluminum and silicon oxide dissolved in the melt at a direct current of 50-100 kA. In parallel, the reduction of aluminum and silicon oxides with carbon monoxide occurs.

[0015] AL2O3 + 3 CO = 2 AL + 3 CO2

[0016] Si 02 + 2 CO = Si + 2CO2 The resulting metal alloy descends to the furnace bottom. Since there is no free carbon in the melt, aluminum carbide does not form.

[0017] The method disclosed above does not provide sufficient completeness of recovery due to the bubbling process and the complex design of increasing the contact time of the charge with the blast gas.

[0018] DISCLOSURE OF INVENTION

[0019] The objective of the claimed invention is to develop a method for recycling sludge waste from aluminum production that is simpler in the implementation of the technological process of obtaining aluminum, it does not contain harmful impurities that pollute the atmosphere, which improves the environment, the absence of additives in the recovery process increases the purity of aluminum, in addition, due to the continuity of the process, the productivity of aluminum production will be quite high.

[0020] The technical result of the invention is to increase the efficiency of aluminum recovery.

[0021] The specified technical result is achieved due to the fact that the method for rendering harmless and utilizing sludge waste from aluminum production includes thermal reduction of oxide forms of aluminum, silicon, iron, copper, which are reduced during treatment with carbon oxide from the melt of the charge. In this case, the prepared charge of metal oxides is processed in a gas-lift furnace with constant circulation of the melt of the charge through fenced off melting, gas-lift and settling chambers at a temperature of 1000-1100 °C. In addition, the specified technical effect is achieved due to the fact that in order to maintain the temperature regime of the furnace, direct current electrodes with the function of additional reduction of metals by electrochemical processes are installed in the settling chamber.The specified technical effect is also achieved by the fact that the process gases leaving the furnace are cooled to a temperature of 600 - 800°C, cleaned of foreign impurities and sent to generate carbon monoxide in the gas generator and then to the gas lift furnace as blast gases, eliminating the emission of process gases into the atmosphere.

[0022] IMPLEMENTATION OF THE INVENTION

[0023] The claimed method is implemented in the following way. The calculated amount of a mixture containing an alloy of aluminum and cryolite (or spent electrolyte from electrolysis baths) is loaded into the furnace, the said mixture is melted to a liquid state using carbon-containing DC electrodes installed in the furnace settling zone and maintaining a temperature in the furnace of 1000-1100°C. Then, gases containing CO are fed from a CO generator through tuyeres installed in the furnace gas lift chamber into the said molten mixture as a blast, as a result of which a foam-liquid phase of the said molten mixture is formed in the melt of the said mixture, which circulates between the gas lift chamber and the melting chambers of the furnace due to the formed flow of the said blast gases. Then, a charge containing sludge waste from aluminum production (for example, spent melt from electrolyzers) together with other oxides and cryolite is loaded into the furnace.When the said blast gases are supplied by tuyeres, a foam-liquid phase containing sludge waste from aluminum production and cryolite is formed in the melt layer, which, due to the formed flow of said blast gases, enters the gas-separating chamber located above the gas-lift and melting chambers, where the foam-liquid phase is stratified into gaseous and liquid phases. The gaseous phase is removed from the furnace through a gas duct for removing gases from the gas-separating chamber for cooling to 600-800°C, gas cleaning and then into the gas generator and the technological process, and the liquid phase enters the slag melt layer in the melting chamber.As a result of processing the circulating melt containing aluminum production sludge waste and cryolite with the said blast gases, a joint reduction of aluminum and silicon oxides occurs at a temperature of 1000-1100°C, the formation of a reaction volume of the melt based on metal fluorides by applying direct electric current to the melt using the electrodes specified above. The reduced aluminum and silicon oxides peel off from the melt and settle on the bottom of the furnace and are then removed from the furnace. Excess melt is also removed from the furnace.

[0024] Processing of the melt of the charge in a gas-lift furnace with the organization of the reaction process in the gas-lift with the formation of the "melt-gas" system in the form of a foam-liquid layer removes diffusion restrictions, which ensures a faster and more complete process of metal reduction. In addition, the specified technical effect is achieved by the fact that the processing time with a fresh portion of the reducing agent increases due to the circulation of the melt of the charge through the fenced melting, gas-lift and settling chambers.

[0025] The invention has been disclosed above with reference to a specific embodiment thereof. Other embodiments of the invention may be obvious to specialists, without changing its essence as disclosed in the present description. Accordingly, the invention should be considered limited in scope only by the following claims.

Claims

CLAUSE OF THE INVENTION 1. A method for rendering harmless and utilizing sludge waste from aluminum production, including thermal reduction of oxide forms of aluminum, silicon, iron, and copper, which are reduced during treatment with carbon oxide from a molten batch, characterized in that the prepared batch of metal oxides is treated in a gas-lift furnace with constant circulation of the molten batch through enclosed melting, gas-lift, and settling chambers at a temperature of 1000-1100°C.

2. The method according to item 1, characterized in that the furnace is heated using carbon-containing direct current electrodes installed in the settling zone of the furnace, wherein the bottom metal phase serves as the cathode, and the carbon-containing electrode serves as the anode.

3. The method according to paragraph 1, characterized in that the exhaust gases are cooled to a temperature of 600-800°C and sent to a CO generator to increase the concentration of CO in them and are then used in hot form as blast gases.