RU1772219C - Method of aluminium production - Google Patents

Abstract

Usage: obtaining aluminum by electrolysis of cryolite-alumina melts. SUBSTANCE: aluminum production is carried out by electrolysis of cryolite-alumina melts. The method includes filling alumina onto an electrolyte crust, crust breaking, introducing a portion of alumina into the melt and periodically eliminating anode effects. The purpose of the invention is to increase productivity and reduce power consumption and anode mass. What is new is that during the first 10–20 anode effects they maintain a voltage of at least 40 V, raise the anode by 3-5 cm and introduce alumina and hold for 2–5 min., They support voltage in the following anode effects 60 V, three portions of alumina are introduced and aging is carried out for 5-6 minutes. further electrolysis is carried out at a voltage of 3.9-4.3 V. an interpolar distance of 13-18 cm and a cryolithm of the electrolyte ratio of 2.85-3.00. 1 s.p. f-ly. 2 ill.

Description

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The invention relates to the metallurgy of non-ferrous metals, in particular the production of aluminum by electrolysis of cryolite-alumina melts.

A known method for producing aluminum by electrolysis of a cryolite-alumina melt, including filling alumina () on the electrolyte cake and feeding alumina to the electrolyzer by destroying the cryolite-alumina crust, removing carbon foam as it accumulates, adjusting the composition of the electrolyte. In this method, the operating voltage at the electrolytic cell is maintained at a constant level of 4.1-4.3 V. Anode effects are considered harmful and try to reduce their number and duration. The main disadvantage of this method is the low current efficiency of 82-88%, the high physical cost of removing carbon foam.

Due to the uneven combustion of the sole of the anode, various protrusions, cracks and concave surfaces can be on it

In order to level the sole of the anode, a method is proposed that includes increasing the interelectrode distance and burning irregularities on the anode sole by increasing the interelectrode distance by the height of the unevenness, in the region of which an oxidizing gas is pulsed towards the bottom of the anode. The oxidizing gas is supplied at intervals of 1-3 s under a pressure of 1-2 atm.

A known method for the continuous electrolytic production of aluminum, including changing the operating voltage on the electrolysis cell per cycle, consisting of the operations of backfilling AfeOa, the actual electrolysis and destruction of the cryolite-alumina crust, In order to increase

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productivity, reducing specific energy consumption and reducing labor costs during crust breaking, the voltage on the cell is increased to a value of 0.15-0.25 V higher, and between crust breaking operations it is reduced to a value of 0.15-0.25 V lower than the average voltage per cycle.

The method reduces the frequency of anode effects by 3-5 times, specific energy consumption by 400-600 kWh / t. AND.

The disadvantage of this method is the low current efficiency (less than 90%), high physical labor costs, and insignificant energy savings (2-3%). In addition, the consumption of the anode mass is not reduced.

A method for producing aluminum is known in which aluminum oxides of variable valency, in particular aluminum suboxide, are used. Said suboxide is obtained in an electrothermal furnace by reduction of alumina with carbon, captured and loaded into an electrolysis cell, where the electrolytic reduction of AteO to A.

Since the electrochemical equivalent of Ai + is equal to 1.05 versus 0.335 dl, the electrolyzer productivity when passing the same current strength will be 3 times higher. The disadvantage of this method is the need to build an expensive electrothermal furnace and the complexity of the equipment for the capture of aluminum suboxide.

The closest in technical essence and the achieved result is a half-aluminum method by electrolysis of cryolite-alumina melts, characterized in that in order to increase current efficiency, reduce energy consumption by reducing the frequency of anode effects, 10-30 minutes after loading another portion of alumina periodically raise the anode to a height of 0.05-0.2 interpolar distance, maintain the anode for 5-8 minutes in this position, and then lower it to its original position, and the duration of the pause between rises The ode is between 0.15 and 0.5 times between the treatments of the cell.

The aim of the invention is to increase the productivity of the cell (1.4-2.7 times), reduce power consumption (by 7000 kW / h), reduce the consumption of the anode mass.

This goal is achieved by using the energy of the anode effect to carry out the reaction

A120s + C AI20 + CO.

which can be carried out at a temperature not lower than 2500 ° C.

The aluminum sub-acid-AteO obtained by this reaction is dissolved in the electrolyte

In the future, its electrochemical decomposition into aluminum and oxygen occurs.

During AlaO electrolysis, the amount of aluminum produced will be 3 times higher at

0 passage of the same current through the cell.

In addition, the decomposition stress of AteO in a cryolite with a carbon anode is 0.7–0.8 V, which is less than that of alumina by

5 0.8-0.9 V.

Our studies have found that the dependence of electrical conductivity on the cryolite ratio for melts containing a mixture with suboxys

0 has a complex character, with a cryolithic relation in natural cryolite (NaaAlFr, it is much higher than the specific electric hydroperiod of cryolite, both pure and containing alumina (2.8-3),

5 and with a cryolite ratio of 2.7 and 2.5, on the contrary, 2-3 times lower than the corresponding values for pure cryolite and cryolite-alumina melts (1.5-1.6 for coalescing 2.7 and 5 % suboxide and 0.7-0.8

0 dl to, about. 2.5).

With a cryolite ratio of 2.85, the electrical conductivity is 2.5 Ohm-cm 1, Therefore, it is necessary to maintain a cryolite ratio above 2.85,

With an aluminum suboxide or monovalent aluminum electrolyzer, the energy savings will be due to 3 factors: due to the electrochemical coefficient AlaO, which is 3 times higher than that of

0 due to increased electrical conductivity; due to the lower decomposition voltage,

At the same time, a certain amount of electricity needs to be spent on

5 production of AlaO in an electrolyzer due to the above reaction.

The total energy savings will be 7000 kW / h per 1 ton of aluminum.

To obtain AI20 in the electrolyzer for

0 energy of the anode effect, it is necessary to perform the following technological operations.

I. The operation of preparing the anode and electrolyte,

5 Once a day without processing electrolyzers, i.e. without immersing alumina in the electrolyte, wait for the anode effect, which should be 40 0, at the moment of the anode effect raise the anode 3-5 cm, punch the crust on one side, immerse

alumina into the electrolyte, warm the cell for 2-2.5 min and eliminate the anode effect by conventional methods. The above sequence of operations should be carried out 10-20 times gradually increasing the duration of the anode effect to 4-5 minutes. With an anode effect of 40 V and a duration of 4-5 minutes, the anode sole is fired and its surface becomes strictly horizontal, in addition, the electrical conductivity changes due to the appearance of more conductive Al + ions, and the interelectrode distance gradually increases.

I. The reaction of reducing alumina with carbon to a suboxide occurs at the time of the anode effect with the following parameters. At the time of the anode effect, raise the anode by a value that provides a voltage of 60 V, punch one of the sides and load alumina 1.5-3 times more than usual, with the anode effect, warm the bath for 5-6 minutes and extinguish the anode effect (using pole). Set the working voltage of 3.9-4.3 and the interelectrode distance of 13-18 cm,

After quenching the anode effect, make a full load of alumina on the crust of the electrolyzer, spud the anode and collect alumina from the work sites.

The implementation of the reaction

AI203 + 2C-

AI20 + 2CO

is due to the consumption of the anode and the dispersed carbon in the electrolyte, i.e. carbon foam, therefore, the electrolyte is cleaned of carbon particles, which significantly increases the electrical conductivity of the electrolyte.

Thus, the use of the anode effect to undergo the partial reduction reaction of alumina to suboxide provides an increase in productivity from 1.3 to 3 times, depending on the number of anode effects per day, reduces the consumption of electricity and anode mass, reduces labor costs by eliminating the operation of removing coal foam .

If we do not carry out the sequence of operations that we propose, then without preparing the anode and electrolyte (alignment of the anode, reducing the amount of carbon in the electrolyte, increasing the electrical conductivity), holding the cell at the anode effect will lead to overheating of the electrolyte to enter a hot run, i.e. to a gross violation of technology. In turn, the preparation of the anode and electrolyte, i.e. alignment of the anode sole and increase in electrical conductivity due to the cleaning of the electrolyte from the foam without the operation of restoring A120z to AteQ due to the anode effect will lead to a slight increase in current efficiency as a result of an increase in the interpolar distance.

Calculations show that using one anode effect per day allows increasing the productivity of the cell by 600-700 kg, which increases the productivity of the cell by 1.3 times.

AfeQ electrolysis requires a consumption of a carbon anode 3 times less than usual, therefore, the total consumption of the anode mass will be significantly reduced. In addition, depreciation, consumption of fluorine salts and other materials except alumina are sharply reduced.

For holding the electrolyzer on the anode effect for 5-6 minutes, at a voltage of 60 V, it will require an increase in the voltage margin on the series, i.e. installation of a smaller number of electrolyzers, by 5-10 units in a series. But the remaining electrolysers will have a productivity of 1.3-3.0 times higher than usual, therefore there will be an overall increase in the productivity of the series 1.2-2.5 times.

Example 1. A cryolite weighing 52.5 g (0.25 mol) was loaded into an alundum crucible with a diameter of 50 mm and a height of 80 mm, melted and kept at a temperature of 1035 ° C for 0.5 h, 2 molybdenum electrodes with an area of 2V56 cm were lowered, 20 mm between them. Conductivity measurements were carried out according to a bridge circuit with a built-in unit of model resistances of 1.0 Ohms and at a current strength of 0.5 A. For

to eliminate the influence of thermopower on the measurement results, the direction of the current in the network was changed with the switch and the measurement was repeated. Arithmetic mean of the results of 2 or 3 independent

The experiments were taken as the resistance of the electrolyte at a given temperature and melt composition. For pure cryolite with co. 3, the electrical conductivity was 3.6.

The calculated relative measurement error was 3.5%, (M.O. dpg) equal

3; 2.5.

cryolite alumina melts with 5% A $ 20z;

cryolite with additive, suboxide mixture.

The measurement results are given in figure 1.

Conductivity versus cryolite ratio dl.

floats containing a mixture with suboxide are complex.

With a cryolite ratio of 3, it is significantly higher than the electrical conductivity of cryolite, both pure and containing alumina, equal to 5 Ohm cm at 1030 ° C, and with a cryolite ratio of 2.7 and 2.5, on the contrary, is lower than the corresponding values for a conventional electrolyte.

The most preferred is a cryolite ratio of 2.85-3.

Example 2. An alundum cylinder with an inner diameter of 43 mm and a height of 100 mm was installed in a graphite crucible, 210 g of cryolite with the NaF AlFs ratio was deposited

The cathode in the cell was a graphite crucible, and the anode was a graphite rod inside which a chromel – alumel thermocouple was placed in an alundum sheath. The temperature in the furnace was maintained at 940-1000 ° C. After deposition of the electrolyte, 4 g of AI was lowered into it and held for 20 minutes, then a mixture containing aluminum suboxide was loaded into the electrolyte and a direct current of 12 A was passed for 20 minutes. Then the contents of the cell were poured into a graphite conical glass. From the solidified electrolyte, an aluminum bead was removed, washed from the electrolyte and weighed. The weight gain, minus dissolved aluminum, was 3.4 g and the total weight was 7.2.

The current efficiency for monovalent aluminum was 84%, and for 3-valent 252%, or a 2.5-fold increase in productivity.

In further experiments, the current strength varied from 3.5 to 18 A, which corresponded to a current density of 0.33-1.96 A / cm2.

The dependence of the current efficiency on the current density during the electrolysis of aluminum oxides in terms of 3-valent aluminum is shown in figure 2. Thus, the highest current efficiency is obtained in the range of current densities of 0.6-0.9 A / cm2.

EXAMPLE 3. On an industrial electrolyzer (C-8 B named after S8BM), the current strength of 157-160 KA was not processed (did not crack the electrolyser crust) until an anode effect, which should be at least 40 V, was obtained by lifting They lifted the anode per cm, pierced the crust on one side of the electrolyzer, immersed it together with alumina in the electrolyte, kept the electrolyzer on one 40 V effect for 4-5 min and eliminated the anode effect, for example, using a wooden slat. Specified

the sequence of work was carried out on the electrolyte from 10 to 20 times within 10-30 days.

During this time, the anode sole became strictly horizontal, and there was no foam in the electrolyte, the electrolyte conductivity increased.

After the preparatory

work on aligning the anode at the time of the next anode effect paused for one minute, then lifted (supported) the anode jacket until the crust completely collapsed into the electrolyte, which

dissolved within one to two minutes (approximately 600 kg), then kept on the anode effect for another 2-3 minutes and the anode effect was eliminated with a quenching pole. Thereafter, an interfield & nos distance of 13-18 cm was established, i.e. voltage of 3.9-4.3 V and 500-600 kg of alumina were poured on both longitudinal sides.

The productivity of the cell increased to 2100-2200 kg / day against

1170-1200, with conventional technology,

PRI me R 4. On an industrial electrolyzer according to example 3 after preparatory work to align the anode at the time of the next anode effect when

At a voltage of 60 V, a pause was made for one minute, then the anode jacket was lifted (supported) until the crust completely crumbled into the electrolyte, which was dissolved within one minute (approximately 600 kg), then it was held for another 3 minutes on the anode effect and eliminated the anode effect extinguishing pole. After that, an interpole distance of 18 cm was established, a voltage of 4.3 V, and 600 kg of alumina were poured onto both longitudinal sides. The productivity of the cell increased to 2200 kg / day.

Example 5. On the industrial electrolyzer according to example 3, after preparatory work was carried out to align the anode at the time of the next anode effect at a voltage of 60 V, a pause was made in

for one minute, then the anode jacket was lifted (supported) until the crust completely rolled into the electrolyte, which was dissolved for 2 minutes (approximately 600 kg), then kept for another 3 minutes

anode effect and eliminated the anode effect with a blanking pole. After that, an interpole distance of t3 cm was established, a voltage of 3.9 V, and 550-600 kg of alumina were poured on both longitudinal sides. The productivity of the cell increased to 2100 kg / day.

The application of the proposed technology will allow to obtain an economic effect by increasing the productivity of the electrolyzer to reduce the consumption of carbon and electricity.

Claims (2)

SUMMARY OF THE INVENTION 1. A method for producing aluminum, comprising electrolysis of cryolite-alumina melts, filling alumina onto an electrolyte cake, crust breaking, introducing a portion of alumina into the melt and periodically eliminating anode effects, characterized in that, in order to increase productivity and reduce consumption S.O- 40-5.02 .0Y .O. li-D 990 SJ / 030 1050 SO70 Temperature ° C Dependence of the electrical conductivity of cryolite melts of various compositions on temperature a - pure cryolite with co 3 c - pure cryolite with acting 2.5 1 cryolite + 5% AipOg; 2 - cryolite + 10% AlgO (sec); 4 - cryolite with co. 3 + 5% of the mixture 5- cryolite with c.o., 2.7 t 5% smsi, 6- cryolite with co 2.5 + 5% electricity and anode mass, during the first 10-20 anode effects maintain a voltage of at least 40 V, raise the anode by 3-5 cm and carry out the introduction alumina and holding for 2-5 minutes, the following anode effects maintain a voltage of 60 V, three portions of alumina are introduced and holding is carried out for 5-6 minutes, while further electrolysis is carried out at a voltage of 3.9-4.3 V, an interpolar distance of 13-18 cm and a cryolitic ratio of electrolyte of 2.85-3.00. 2. The method according to p. 1, characterized in that the electrolysis is carried out with 2-3 anode effects per day. 280 2W 200 f60 Y20 fifty 40 0 -40 -Y0 -/twenty 0.4 0.8 4.2 Yes, a / cm2 The dependence of the current efficiency on the current density during the electrolysis of aluminum oxides (in terms of 3-valence aluminum) 1 - during the electrolysis of alumina; Ј - during electrolysis of a mixture containing a suboxide; 3 - according to the literary source of work & 2, °