RU2599475C1 - Method of producing aluminium-silicon alloy in electrolyzer for aluminium production - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to a method of producing aluminium-silicon alloys in an electrolysis cell for aluminium production using amorphous silicon-containing oxide raw material. Method comprises periodic loading an electrolyte of fluoride salts, alumina, amorphous silicon-containing oxide raw material into the molten and further recovery of aluminium and silicon oxides, microsilica, produced during cleaning process gases when producing silicon and silicon-containing alloys, is used as an amorphous silicon-containing oxide raw material, which is loaded into the molten electrolyte using installations for automatic supply of the electrolysis cell. Quantity of electrolyte molten, increased by 5÷30 wt% is maintained in the electrolysis cell, together with microsilica, ground quartzite in an amount up to 40 % of the microsilica weight is added to the electrolyte molten. Microsilica is additionally preliminary mixed with alumina or fluoride salts and loaded into the electrolyte molten, mixing of microsilica with alumina is performed by their combined feed into the dry adsorption scrubbing of aluminium electrolysis housing, then the produced mixture is loaded in the electrolyte molten in the form of fluorinated alumina and fluorinated microsilica.

EFFECT: higher efficiency of the electrolysis cell for an aluminium-silicon alloy, higher current output, improved quality of the aluminium-silicon alloy.

5 cl, 4 tbl

Description

The invention relates to non-ferrous metallurgy and can be used to obtain aluminum-silicon alloys in an electrolytic cell for aluminum production.

Obtaining aluminum-silicon alloys by electrolytic reduction of alumina and silicon-containing oxide raw materials can reduce the cost of alloys through the use of inexpensive and non-deficient silicon oxides instead of technical silicon obtained by electrothermal reduction in ore-thermal furnaces.

A known method of producing aluminum-silicon alloys, comprising introducing into cryolite electrolyte as an oxide raw material of alumina obtained by processing aluminum silicates by sintering and containing sodium aluminum silicate, and electrolysis of the obtained melt. The proposed method allows to reduce energy consumption by 10 ÷ 12%, to simplify the process by abandoning special dispensers with continuous or periodic alternating input of components and to reduce the consumption of pure silicon-containing materials (AS No. 1502663, C22C 21/02, 1989 [ one]).

The main disadvantage of the known solution is associated with an increase in the cryolite ratio of the electrolyte (alkalization of the electrolyte) due to the introduction of an additional amount of sodium with sodium aluminosilicate. To adjust the cryolite ratio of the electrolyte, an additional consumption of aluminum fluoride will be required. As a result, excess electrolyte will be generated in the electrolyzer, which must be periodically drained.

A known method of producing aluminum-silicon alloys in serial aluminum electrolysis cells (patent RU 2030487, C25C 3/36, 1995 [2]). The method includes periodic loading of alumina and silicon-containing oxide raw materials onto the electrolyte crust, crust breaking, followed by immersion of the raw materials in a cryolite oxide melt, and loading of silicon-containing oxide raw materials during the day every 3 ÷ 6 hours, and the mass of the loaded portion of silicon-containing oxide raw materials is 0.2 ÷ 0.4% (calculated on SiO ₂ ) of the mass of the electrolyte.

The known solution allows you to maintain the optimum concentration of silicon in the electrolyte, which does not exceed the maximum allowable and prevents negative phenomena leading to an increase in process temperature and a decrease in current efficiency.

The disadvantages of the known solutions include in-line processing of the electrolyzer with the loading of alumina and silicon-containing oxide raw materials on the electrolyte crust with an interval of 3-6 hours, which leads to certain fluctuations in the concentration of alumina and silica in the electrolyte. It does not provide for the adjustment of the operational parameters of the technology, which remain the same as in a conventional electrolytic cell for producing aluminum. This reduces the efficiency of obtaining aluminum-silicon alloy in the cell.

The closest in technical essence, the presence of similar features to the claimed method is the "Method of producing aluminum-silicon alloy in an electrolyzer for aluminum production" (RF patent No. 2037569, C25C 3/36, 1995 [3]). According to the known method, amorphous silica cake obtained by treating silicon-fluorine-containing solutions with aluminum hydroxide is used as a silicon-containing raw material. The size of the silicon dioxide in the silica cake is 10 ÷ 40 microns. Before loading into the electrolyte, the cake is heated to 400 ÷ 600 ° C, and if necessary, before the heat treatment, the cake is mixed with a sodium-containing component with a mass ratio of sodium to aluminum contained in the cake equal to (1.20 ÷ 2.20): 1. The use of highly active amorphous SiO ₂ provides high technical and economic performance of the process. The raw material base for the production of aluminum-silicon alloys is expanding, and the cost of production is decreasing.

This solution is selected as the closest analogue.

The disadvantages of the method include the limited raw material base of amorphous silica cake, which can be produced only in factories producing cryolite and superphosphate fertilizers. Another disadvantage is the need for preliminary heat treatment of silica cake at 400 ÷ 600 ° C in order to remove crystallization moisture from aluminum fluoride trihydrate.

The objective of the invention is the expansion of the raw material base of amorphous silicon-containing oxide raw materials, increasing the productivity and efficiency of obtaining aluminum-silicon alloys in electrolytic cells for aluminum production.

The technical result when implementing the invention:

- increase the productivity of the cell for aluminum-silicon alloy;

- increase in current efficiency;

- improving the quality of aluminum-silicon alloy.

The technical result is achieved by the fact that in the method for producing an aluminum-silicon alloy in an electrolytic cell for aluminum production, comprising periodic loading of fluoride salts, alumina, amorphous silicon-containing oxide raw materials into the electrolyte melt and subsequent reduction of aluminum and silicon oxides, microsilica is used as an amorphous silicon-containing oxide raw material obtained in the process of purification of process gases in the production of silicon and silicon-containing alloys, which is loaded into electrolyte alloy using automatic electrolyzer power plants. At the same time, the amount of molten electrolyte increased by 5–30 wt.% Is supported in the electrolyzer. Also, crushed quartzite is introduced into the molten electrolyte together with silica fume in an amount of up to 40% by weight of silica fume. Additionally, silica fume is pre-mixed with alumina or fluoride salts and loaded into the molten electrolyte, moreover, silica fume can be mixed with alumina by their combined feeding into a dry adsorption gas purification of the aluminum electrolysis body, after which the resulting mixture is loaded into the molten electrolyte in the form of fluorinated alumina and fluorinated silica fume.

The technical nature of the proposed technical solution is as follows. In the proposed solution, as an amorphous silicon-containing oxide raw material, silica fume is used, which is formed during the purification of process gases in the production of silicon and silicon-containing alloys in ore-thermal furnaces.

Silica fume is an ultrafine material consisting of particles of predominantly spherical shape. The main component of silica fume is silica of amorphous modification. Table 1 shows the approximate chemical composition of silica fume.

The average particle size of silica fume is a fraction of a micron, which determines a large specific surface area of the particles, which is equal to an average of ~ 20 m ² / g. Table 2 shows the percentage of silica fume particles of various fractions.

The true density of silica fume in its natural state is 2.2 g / cm ³ . The bulk weight of silica fume depends on the degree of compaction and is:

- in an uncompressed state - 0.17 ÷ 0.20 t / m ³ ;

- in a compacted state - 0.35 ÷ 0.65 t / m ³ .

The angle of repose of silica fume is:

- in a loose state - 75 ÷ 80 degrees;

- in a sealed (pneumatic way) state - 25 ÷ 30 degrees.

The amorphous structure of silica fume and its finely divided composition contribute to the accelerated dissolution of silicon dioxide in the molten electrolyte and more efficient reduction to metal with the subsequent formation of an aluminum-silicon alloy. The loading of silica fume into the electrolyte melt with the help of automatic power units will ensure a uniform supply of raw materials into the electrolyzer in small portions, minimizing jumps in the concentrations of alumina and silica fume in the electrolyte. In particular, with bath days of the electrolyzer 1250 kg of Al, the daily consumption of alumina will be about 2410 kg. To maintain the silicon concentration in the produced metal at the level of 5%, the daily load of silica fume in the electrolyzer is ~ 150 kg. During the operation of automatic alumina feeding plants, its concentration in the electrolyte is 2.5–3.0%. In this case, the average SiO ₂ content in the electrolyte will be 0.15 ÷ 0.19%.

Given the finely divided composition of silica fume, in order to reduce its dust removal to the gas cleaning system of the aluminum electrolysis body, silica fume is pre-mixed with alumina or fluoride salts. Also, preliminary mixing of the raw materials will exclude the formation of microsilica agglomerates in the electrolyte melt, which will accelerate the dissolution of SiO ₂ and exclude the formation of a precipitate on the bottom of the cell. As one of the options for mixing alumina and silica fume, it is proposed that they be fed together into a dry adsorption gas treatment of an aluminum electrolysis body, after which the resulting mixture is loaded into the electrolyte melt in the form of fluorinated alumina and fluorinated silica fume. The large specific surface of silica fume will provide sufficient dry gas cleaning efficiency. The use of fluorinated alumina and fluorinated silica fume will increase the rate of their dissolution in the molten electrolyte.

The volume of electrolyte increased by 5–30 wt.% In the electrolytic cell, all other things being equal, increases the electrolytic cell productivity due to the increased amount of dissolved silicon-containing oxide raw materials, and ensures more stable operation of the electrolyzer. With an increase in electrolyte volume of less than 5 wt.%, The effect of increasing the productivity of the electrolyzer is minimal. When the electrolyte level rises by more than 30% of the electrolyte volume on an ordinary electrolyzer, difficulties arise with the operation of the electrolyzer in terms of retaining the electrolyte melt in the cell of the electrolysis cathode (operation of the electrolyzer with an increased skull).

The introduction of crushed quartzite together with silica fume into the melt is advisable, if necessary, to obtain aluminum-silicon alloys with a low content of impurities, in particular, iron impurities. The concentration of iron oxide in silica fume varies from 0.2 to 1.0 wt.%. When reducing oxides of silicon and iron per 1 kg of reduced silicon, an increase in the iron content in the alloy will be from 0.0043 kg of Fe to 0.0214 kg of Fe. For example, in the production of an alloy with 7% silicon in the electrolyzer according to the proposed solution, an increase in the concentration of iron in the metal can be from 0.03% to 0.10%, which in some cases is unacceptable. Therefore, it is proposed to add pure quartzite to silica fume with a minimum content of iron oxide (0.01–0.10% wt.) In an amount of up to 40% by weight of silica fume. Quartzite is less soluble in electrolyte, so its addition to silica fume is limited. With the addition of quartzite more than 40% by weight of silica fume, the productivity of the cell and the current efficiency noticeably decrease.

Comparison of the proposed solution with the closest analogue shows the following. The proposed solution and the closest analogue are characterized by similar features:

- both solutions are aimed at obtaining an aluminum-silicon alloy in an electrolytic cell for the production of aluminum by the joint reduction of alumina and silicon-containing oxide raw materials;

- to obtain an aluminum-silicon alloy using amorphous, finely dispersed, silicon-containing oxide raw materials.

The proposed solution differs from the closest analogue in the following features:

- as amorphous silicon-containing oxide raw materials use silica fume obtained in the process of purification of process gases in the production of silicon and silicon-containing alloys;

- amorphous silicon-containing oxide raw materials are loaded into the molten electrolyte using the automatic power supply of the electrolyzer;

- in the electrolyzer support the increased by 5 ÷ 30 wt.% the amount of molten electrolyte;

- silica fume before loading into the melt of the electrolyte is mixed with alumina or fluoride salts, including the combined supply of alumina and silica fume to dry adsorption gas purification of the aluminum electrolysis body;

- crushed quartzite is introduced into the molten electrolyte together with silica fume in an amount of up to 40 wt.%.

The proposed technical solution is characterized by features similar to those of the closest analogue, and distinctive features, which allows us to conclude that it meets the patentability condition of "novelty."

A comparative analysis of the proposed technical solutions with known solutions in this technical field, carried out according to the search results in the patent and scientific literature, revealed the following:

The article “Adding refractory materials from spent lining to electrolysis cells for the production of Al-Si alloys” (authors Björn Moxnes, Havard Gikling, Halvor Quande, Sverre Rolset and Kietil Straumsheim) presents the results of positive industrial tests on the production of an aluminum-silicon alloy in a self-calcining electrolytic cell 115 kA anode using refractory aluminosilicate lining from cathodes of disconnected electrolyzers. The experimental cell was operated continuously for five months with a mixture of conventional alumina and spent refractory lining being fed into the electrolyte. Operational results were generally positive. The silicon content in alumina exceeded 10 wt.% (Light metals, 2003. Edited by Paul N. Crepe TMS (Society for the Study of Minerals, Metals and Materials) [4]).

In the method for producing an aluminum-silicon alloy in an electrolyzer for aluminum production, sodium silicofluoride is used as a silicon-containing component, which is pre-sintered with alumina at 550 ÷ 650 ° C with a mass ratio of 1: (0.5 ÷ 1.5), and the silicon content in alloy support no more than 9 wt.%. Sintering of sodium silicofluoride with alumina results in the formation of amorphous, highly active silicon oxide, which dissolves well in the electrolyte and is reduced to metal. The method provides an alloy yield by current of 87 ÷ 88% and a silicon electrolyzer productivity of 74 ÷ 79 kg / day (patent RU 1826998 С25С 3/36. Publ. 1993 [5]).

A known method of producing an aluminum-silicon alloy in an electrolytic cell for aluminum production, comprising supplying fluoride salts, an oxygen-containing aluminum compound and sodium silicofluoride to the electrolyte, using alumina and / or aluminum hydroxide as an oxygen-containing aluminum compound, a mixture of sodium silicofluoride and oxygen-containing is used in the electrolyte aluminum compounds with a weight ratio of 1: (1.5 ÷ 5.0) in terms of alumina, and an automatic machine is used to supply materials to the electrolyte matic power cell. The method is characterized by high technical and economic performance due to the amorphous structure of silicon oxide formed during sintering of sodium silicofluoride and an oxygen-containing aluminum compound and the use of an automatic electrolysis unit (patent RU 2383662 C25C 3/06, C25C 3/36, C25C 3/00. Publ. 2010 g. [6]).

The analysis carried out by the authors showed that at the time of filing the application for the invention, technical solutions were not identified that are characterized by a combination of known and unknown features similar to the proposed solution, which indicates the compliance of the proposed technical solution with the condition of patentability of the invention “inventive step”.

Compliance with the patentability condition “industrial applicability” is proved by experimental data obtained during industrial tests.

Example 1

Industrial tests were carried out on three S-8BM electrolyzers with self-baking anodes, which at the time of the start of the tests were in the same technological state and had a close service life of ~ 30 months. The current strength at the electrolyzers was maintained at a level of 164 kA with an average cryolite ratio of electrolyte of 2.32.

Alumina and silica cake were charged into the first two electrolysers; alumina and silica fume were fed into the third electrolyzer. Silica cake contained 82 wt.% SiO ₂ and 18 wt.% AlF ₃ · 3H ₂ O. The concentration of SiO ₂ in silica fume was 94.8 wt.%.

The loading of alumina and silica cake into the electrolyte melt in the first electrolysis cell was carried out during the in-line treatment 12 times a day after preliminary heat treatment of the silica cake on the cryolite-alumina crust of the electrolyzer at 480 ÷ 520 ° C to remove crystallization moisture from AlF ₃ · 3H ₂ O. On In the second electrolyzer, the supply of alumina and pre-dehydrated silica cake to the electrolyte melt was carried out using four point-type automatic power plants (APGs). The loading of alumina and silica fume into the third electrolyzer was carried out using four point-type automatic power plants (APGs).

For 36 days, the electrolytic cells were treated with alumina and amorphous silicon-containing oxide raw materials with a gradual increase in the supply of silicon-containing raw materials in terms of SiO ₂ from 80 to 120 kg / day until the Si content in the aluminum-silicon alloy reached 6.5 ± 0.2%. During this period, the electrolysis cells were adapted to new raw materials, in particular, saturation of the crust and skull of electrolysis cells with silicon oxide. Throughout the test period, the electrolyte melt was corrected by the addition of aluminum fluoride and calcium fluoride. To maintain a stable concentration of silicon in the alloy at the level of 6.5 ± 0.2%, the loading of silicon-containing raw materials into the electrolyzer was stabilized within 170–175 kg / day in terms of SiO ₂ .

Pouring from the electrolyzer of the accumulated aluminum-silicon alloy was carried out with a vacuum ladle once a day. The technical and economic indicators of the operation of electrolyzers were calculated by the number of loaded amorphous silicon-containing oxide raw materials, by the weight of the cast alloy and the silicon content in it. The averaged results of monthly operation of electrolyzers are given in table 3.

Example 2

Industrial tests were carried out in four S-8BM electrolyzers with self-baking anodes, which have similar operational characteristics. The test conditions, the electrolysis parameters and the gradual conversion of the electrolytic cells to a silicon-containing feed were maintained, basically, similarly to example 1. In all electrolytic cells, alumina and silica fume were used to produce an aluminum-silicon alloy, which were loaded into the electrolyte melt using automatic power plants (APG) point type, four on each cell.

At electrolyzers No. 1 and No. 2, three APG units were loaded with alumina into the electrolyte melt, and one silica fume. At electrolysis cell No. 2, an increase of ~ 20% in the amount of electrolyte was maintained. The weight of the additional electrolyte was ~ 1050 kg. Alumina was charged through electrolyzer No. 3 through two APG plants, and through a third, a mechanical mixture of alumina and silica fume, and through a fourth, a mechanical mixture of silica fume and aluminum fluoride. Alumina and a mixture of silica fume with finely ground quartzite were loaded into electrolyzer No. 4. The addition of quartzite in terms of SiO ₂ amounted to 30% by weight of silica fume.

Based on the results of a monthly operation, technical and economic indicators of the operation of electrolyzers are determined. The average test results are shown in table 4.

The industrial application of the proposed technical solution for the production of aluminum-silicon alloys by reduction of silica fume in electrolyzers equipped with APG plants provides an increase in the productivity of electrolyzers for aluminum-silicon alloy, an increase in current efficiency, and an improvement in the quality of aluminum-silicon alloys.

Information

1. Auth. St. No. 1502663, C22C 21/02, 1989 [1].

2. Patent RU 2030487, C25C 3/36, 1995 [2].

3. RF patent No. 2037569, C25C 3/36, 1995 [3].

4. Light Metals 2003. Bjørn Moxnes, Håvard Gikling, Halvor Kvande, Sverre Rolseth and Kjetil Straumsheim. ADDITION OF REFRACTORIES FROM SPENT POTLINING TO ALUMINA REDUCTION CELLS TO PRODUCE Al-Si ALLOYS [4].

5. Patent RU 1826998 C25C 3/36, 1993 [5].

6. Patent RU 2383662 C25C 3/06, C25C 3/36, C25C 3/00, 2010 [6].

Claims (5)

1. A method of producing an aluminum-silicon alloy in an electrolytic cell for aluminum production, comprising periodically loading fluoride salts, alumina, amorphous silicon-containing oxide raw materials into the electrolyte melt and subsequent reduction of aluminum and silicon oxides, characterized in that microsilica is used as amorphous silicon-containing oxide raw materials, obtained in the process of purifying process gases in the production of silicon and silicon-containing alloys, which are loaded into the electrolyte melt by setting the automatic power of the electrolyzer. 2. The method according to p. 1, characterized in that in the electrolyzer support increased by 5 ÷ 30 wt.% The amount of molten electrolyte. 3. The method according to p. 1, characterized in that crushed quartzite is introduced into the melt of the electrolyte together with silica fume in an amount of up to 40% by weight of silica fume. 4. The method according to p. 1, characterized in that silica fume is pre-mixed with alumina or fluoride salts and loaded into the molten electrolyte. 5. The method according to claim 4, characterized in that the mixing of silica fume with alumina is carried out by co-feeding them into a dry adsorption gas purification, followed by loading the resulting mixture into the molten electrolyte in the form of fluorinated alumina and fluorinated silica fume.